Gases doi: 10.3390/gases6020025

Authors: Monica Canepa

Maritime transport accounts for around 3% of global anthropogenic greenhouse gas (GHG) emissions, a share expected to grow without effective technological and regulatory intervention. Recent policy developments, including the IMO Revised GHG Strategy (2023), the extension of the EU Emissions Trading System to maritime transport, and the FuelEU Maritime Regulation, require ports and shipping stakeholders to evaluate multiple decarbonization technologies under complex and often conflicting constraints. These decisions involve trade-offs across economic, technical, environmental, social, and cyber–physical security dimensions, which are not adequately addressed by conventional decision-support tools. This paper introduces XAI–MCDA-HoDEM, an explainable multi-criteria decision framework integrating Analytic Hierarchy Process (AHP), Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), and SHAP-based explainability. The framework explicitly incorporates cyber–physical security as a core evaluation criterion and provides transparent, criterion-level explanations of decision outcomes. Using real-world data, the methodology is demonstrated through an illustrative case study and empirically validated at the Port of Rotterdam. Results show stable and robust rankings, alignment with observed port decarbonization strategies, and improved interpretability of decision drivers. The proposed framework supports transparent, policy-relevant decision-making for the maritime energy transition.

Gases doi: 10.3390/gases6020024

Authors: Xiao Luo Hirofumi Kanoh

Metal-organic frameworks (MOFs), particularly ELM-11, are promising sorbents for CO2 capture due to their gate-opening phenomenon and excellent reusability. Since actual exhaust gases contain impurities such as NO2, in this study, the effect of NO2 on the CO2 sorption performance of ELM-11 was investigated. ELM-11 was exposed to 1000 ppm NO2 for varying durations, ranging from short to long, and subsequent CO2 sorption was evaluated using several methods: gravimetric analysis (TG-DTA), volumetric analysis (sorption isotherms), FT-IR spectroscopy (to detect chemical bond changes), TG-MS (to analyze decomposition products), and PXRD (to observe structural changes). The TG-DTA results indicated that long-term NO2 exposure (e.g., 20 h) generally reduced CO2 sorption, whereas short-term exposure (3 h) could enhance it. This finding was supported by volumetric sorption isotherm measurements. FT-IR and TG-MS analyses revealed that NO2 underwent both physical and chemical sorption in small amounts, with chemical sorption occurring through reactions with Cu2+ ions. Consequently, 20 h of NO2 exposure resulted in approximately a 6 or 10% reduction in CO2 recovery capacity. However, since the degradation was only 6 or 10% despite exposure to a relatively high concentration of NO2 (1000 ppm), these results suggest that ELM-11 exhibits high resistance to NO2, making it suitable for practical applications.

Gases doi: 10.3390/gases6020023

Authors: Ahmed M. S. Soliman Yahia H. Ahmad Roman Tschentscher Duncan Akporiaye Ma’moun Al-Rawashdeh

The integration of catalytic methane decomposition (CMD) with CO2 gasification (Reverse Boudouard Reaction) offers a promising chemical looping route for carbon-negative hydrogen and syngas production. This work systematically investigates the gasification reactivity of six carbon morphologies, CNTs, CNFs, activated carbon, graphite, graphene, and CMD-derived carbon, with and without Ni addition. First, activity tests and characterization (XRD, XPS, Raman) revealed that CMD-derived carbon outperformed all other benchmarks due to its highly amorphous nature (sp3/sp2 = 0.98), which provides a high density of reactive sites. Second, kinetic analysis showed that the incorporation of 5 wt% Ni on CMD carbon reduced the activation energy (Ea) from 435.3 kJ mol−1 to 114.6 kJ/mol, the lowest among all samples. This 74% reduction confirms that structural defects in CMD carbon act as anchoring sites for Ni, facilitating a strong metal–support interaction (MSI) that promotes CO2 activation. Third, an investigation into structural synergy revealed that higher Ni loadings (>5 wt%) increased the activation energy (up to 171.2 kJ mol−1). This trend is attributed to Ni agglomeration and weakened MSI, which reduces the active catalytic interface. These findings demonstrate that the efficiency of CO2 valorization is highly sensitive to carbon morphology, providing a clear optimization strategy for integrated chemical looping methane-to-syngas energy cycles.

Gases doi: 10.3390/gases6020022

Authors: Yousef Alqaheem

Flaring is necessary to prevent pressure buildup in the unit. Due to hydrotreatment processes at the refinery, flare gas can contain significant amounts of hydrogen sulfide. Combusting this gas can result in environmental and health issues. One method to reduce hydrogen sulfide is to replace the water in the seal drum with an amine solution. Honeywell UniSIM® process simulation was used to calculate the hydrogen sulfide removal efficiency with 45 wt% MDEA solution. Results show that removal efficiency depends on amine loading and pool height. Removal efficiency of up to 72.5% was achieved with a hydrogen sulfide-to-amine molar loading of 0.2 (4:20 ratio) and a pool effective height of 2.5 m.

Gases doi: 10.3390/gases6020021

Authors: Marcus D. Palmer Adrian P. Crew Matt J. Bell

Electronic nose platforms based on metal-oxide (MOX) sensors offer potential for low-power gas classification under dynamic operating conditions. This study evaluates a BME688-based digital nose configured with a temperature-modulated heater profile (HP-354) and reduced duty cycle (RDC-5-10) for binary ethylene presence classification in fruit headspace. Seven climacteric fruit types were sealed in bags to allow natural ethylene accumulation and were sampled across multiple sessions over a two-week period. A structured alternating protocol between fruit headspace (Class A) and neutral air (Class B) generated 21 ethylene sessions and 23 neutral-air sessions, comprising 38,882 individual thermal scan cycles (~10 s per cycle). Each full heater cycle was treated as a training instance within BME AI-Studio. A supervised neural-network classifier trained on 70% of cycle-level data achieved 92.9% overall accuracy with a macro F1 score of 91.9% on validation data. Results demonstrate that temperature-modulated MOX signatures enable robust discrimination of biologically generated ethylene from baseline air under realistic headspace variability. This study demonstrated classification feasibility under naturally accumulated fruit emissions while highlighting the need for future concentration-resolved calibration studies.

Gases doi: 10.3390/gases6020020

Authors: Yingying Li Jin Xue Fathi Boukadi

During natural gas production and transportation, multi-stage pressure regulation is often required to meet downstream pressure demands, resulting in substantial waste of residual pressure energy at high-pressure wellheads. This study focuses on high-pressure natural gas at the wellhead of the XC gas well in western Sichuan. Based on thermodynamic and exergy analysis, Aspen HYSYS was employed to simulate residual pressure power generation processes, and a systematic comparison was conducted between single-stage and multi-stage expansion schemes. Under operating conditions of an inlet pressure of 20 MPa, an inlet temperature of 70 °C, and a flow rate of 50 × 104 m3/d, the influence of operating parameters on power generation performance was analyzed. The results indicate that power output increases with increasing natural gas flow rate and inlet temperature but decreases with increasing outlet pressure. Under large pressure differential conditions, single-stage expansion is unable to meet the requirements of high-pressure wellhead residual pressure power generation due to excessive temperature drop and limitations in existing expander performance. On this basis, two-stage, three-stage, and four-stage expansion power generation processes were further developed, and the effects of intermediate pressure selection on power output, heating demand, and pressure energy recovery efficiency were systematically examined. The results show that operating under equal expansion ratio conditions enhances pressure energy utilization. By comprehensively comparing power generation performance, heating power requirements, and economic feasibility, the two-stage expansion scheme was identified as the most favorable option under the investigated operating conditions, providing a practical reference for process design and engineering applications of high-pressure natural gas wellhead residual pressure power generation.

Gases doi: 10.3390/gases6020019

Authors: Haridian del Pilar León Carlos Morillas Sara Martinez Guillermo Armero Sergio Alvarez

Carbon dioxide (CO2) enrichment using fuel combustion is widely applied in greenhouse production. However, its implications for air quality and occupational safety under real operating conditions remain insufficiently characterized. This study evaluates a propane-based CO2 enrichment system in an advanced greenhouse. The analysis integrates CO2 dynamics, combustion-derived pollutants, and occupational exposure. High-resolution monitoring at 5 min intervals was conducted in an enriched module and a control module over a five-month period. Two operational modes were assessed: continuous and diurnal-only enrichment. The system maintained CO2 concentrations within agronomic targets. Mean values reached 1200 ppm and 940 ppm for continuous and diurnal operation, respectively. However, significant CO2 losses were observed due to ventilation. The maximum enrichment efficiency, expressed as the Combustion Efficiency Index (CEI), was 2.67 × 10−3. Combustion-related pollutants (CO, NO, NO2, SO2, and O3) showed transient peaks during burner activation. However, concentrations remained below occupational exposure limits when evaluated using time-weighted averages. The incomplete combustion ratio (ICR) remained stable at approximately 1.9 × 10−3. This indicates predominantly complete combustion. These results provide field-based evidence on the performance and safety of propane-based CO2 enrichment systems. They also highlight the importance of continuous monitoring and improved CO2 retention strategies in semi-confined greenhouse environments.

Gases doi: 10.3390/gases6020018

Authors: Tagwa Musa Razan Khawaja Luc Vechot Nimir Elbashir

As the global imperative for climate neutrality intensifies, hydrogen (H2) from fossil fuels remains central to decarbonizing hard-to-abate sectors. Conventional production via steam methane reforming (SMR), however, is carbon-intensive and, even with carbon capture and storage (CCS), incurs energy penalties and long-term storage constraints. This review develops a harmonized well-to-gate, market-oriented framework to evaluate methane pyrolysis (MP) relative to SMR and autothermal reforming (ATR), with or without CCS, moving beyond reactor-focused assessments toward system-level commercialization analysis. MP decomposes methane into hydrogen and solid carbon, avoiding direct CO2 formation and the need for CCS infrastructure. Integrating with the reverse water–gas shift (RWGS) reaction enables flexible syngas production with adjustable H2:CO ratios for methanol and chemical synthesis. A central finding is the dominant role of the “carbon lever”: MP generates approximately 3 kg of solid carbon per kg of H2, making the carbon market’s absorptive capacity the primary scalability constraint. While carbon monetization can reduce levelized hydrogen costs, large-scale deployment would rapidly saturate existing carbon black and specialty carbon markets. Techno-economic evidence indicates that carbon prices above $500/ton are required to achieve parity with gray hydrogen, whereas $150–200/ton enables competitiveness with blue hydrogen. Lifecycle assessments further show that climate superiority over SMR or ATR with CCS requires upstream methane leakage below 0.5% and very low-carbon electricity. Commercial readiness varies, with plasma MP at TRL 8–9 and thermal, catalytic, and molten-media pathways remaining at the pilot or demonstration stage. Parametric decision-space analysis under harmonized boundary assumptions shows that MP is not a universal substitute for reforming but a conditional pathway competitive only under aligned conditions of low-leakage gas supply, low-carbon electricity, credible carbon monetization, and supportive policy incentives. The review concludes with a roadmap that highlights standardized carbon certification, end-of-life accounting, and long-duration operational data as priorities for commercialization.

Gases doi: 10.3390/gases6020017

Authors: Julian Zenner Bryan Rainwater Daniel Zimmerle

Methane emissions from end-use installations in residential natural gas systems remain poorly quantified, despite their importance to both safety and climate policies worldwide. While distribution networks and appliances have received research attention, interior piping between the meter and appliances represents a critical knowledge gap. To address this gap, a systematic survey of 473 residential systems in Saarlouis, Germany, was conducted using standardized pressure decay tests (DVGW G 600). Measurements were performed during the installation of gas regulators necessitated by a grid pressure increase from 23 mbar to 55 mbar above ambient. This provided a unique opportunity to assess whole-system leakage under controlled conditions without installation modifications. Leak rates were standardized to reference pressure and converted to methane emissions using measured gas composition, using a linear pressure scaling as a provisional approximation valid for the small pressure differences in the applied test conditions. A total of 411 (86.9%) installations showed no detectable leak rate (LDL: 0.2 Lh−1). However, seven systems (1.5%) exceeded 1 Lh−1, and one surpassed the unacceptable threshold of 5 Lh−1. Mean emissions across all systems were 0.067 [0.041, 0.098] gh−1, with smaller installations showing higher volume-normalized rates. Critically, fewer than 1.48% of systems contributed more than 46% of total emissions, demonstrating a strongly skewed, heavy-tailed distribution. Scaled nationally using Monte Carlo methods accounting for sampling uncertainty and skewed distributions, residential interior piping contributes 12.30 [8.11, 18.55] Ggyear−1 to Germany’s methane emissions. These results emphasize the need to include residential leak rates in emission inventories and highlight the efficiency potential of targeted mitigation strategies focused on high-emitting installations under evolving EU methane regulations.

Gases doi: 10.3390/gases6010016

Authors: Princewill M. Ikpeka Ugochukwu I. Duru Stanley Onwukwe Nnaemeka P. Ohia Johnson Ugwu

Gas condensate banking can significantly reduce near-well gas productivity by as much as ~60% in tight gas reservoirs. Existing treatment techniques are resource demanding and could alter the reservoir structure permanently. This study investigates the effectiveness of enhanced electrokinetic oil recovery (EK-EOR) as a low-impact alternative for treating condensate banks. Using compositional reservoir simulation (CMG GEM), the influence of key reservoir and operational parameters—porosity, permeability, producer well location (i, j), injection rate, and injection pressure—on cumulative gas production (CGP) was examined. A Box–Behnken design of experiments was employed to generate 62 simulation runs, and a proxy model was developed to approximate full-field responses. Statistical validation showed strong model fidelity (R2 = 0.99, AAPE = 2.2%). The proxy was then optimized using a genetic algorithm (GA) to identify conditions that maximize gas recovery. Results indicate that lower injection rates and lower injection pressures maximize CGP through enhanced electro-osmotic flow and reduced water blocking, achieving a peak cumulative gas of 4.06 × 108 ft3. A secondary optimum at high injection pressure could be attributed to re-pressurization and partial re-vaporization of condensate near the wellbore. Reservoir quality also exerted a strong control: higher permeability and moderate porosity favoured gas yield, while optimal producer placement near the reservoir boundary increased drainage efficiency. This study demonstrates a systematic optimization framework combining design of experiments, proxy modelling, and evolutionary algorithms to evaluate EK-EOR performance.

Gases doi: 10.3390/gases6010015

Authors: Alberto Ballerini Tommaso Lucchini

This study numerically investigates the conversion of a Heavy-Duty (HD) Spark-Ignition (SI) Compressed Natural Gas (CNG) engine to operate with hydrogen-rich syngas produced from waste plastic pyrolysis. The engine was modeled with a one-dimensional simulation tool. Fuel-specific properties were included through a tabulated Laminar Flame Speed (LFS) approach, and knock occurrence was predicted with a Tabulated Kinetic of Ignition (TKI) model. Full-load simulations revealed that direct substitution of CNG with syngas leads to abnormal combustion. With adjusted values of Spark Advance (SA) to avoid knock, syngas operation resulted in average reductions of approximately 15% in brake torque and 6% in total efficiency compared to the CNG baseline. Parametric analyses showed that Late Intake Valve Closing (LIVC) provides no benefits, whereas increasing the Compression Ratio (CR) partially recovers performance and efficiency, with knock being a limiting factor. Lastly, a complete engine map of the converted configuration was generated, reporting Brake-Specific Fuel Consumption (BSFC) and emissions. Overall, the study demonstrates that HD SI engines can be operated on hydrogen-rich syngas at the cost of moderate performance penalties. Moreover, it provides a robust modeling framework to support system-level and well-to-wheel assessments of syngas-based powertrains.

Gases doi: 10.3390/gases6010014

Authors: Ana Buelvas Deibys Barreto Hermes Ramírez-León Juan Fajardo

Synthetic natural gas (SNG) production from biomass residues represents a promising strategy to reduce greenhouse gas emissions and enhance energy security in regions with abundant agricultural waste. This study evaluates the thermodynamic performance of SNG synthesis from rice husk (RH) and empty fruit bunches (EFB) bio-oils, major residues in the department of Bolívar, Colombia. The process was simulated in Aspen Plus®, integrating syngas data and methanation under equilibrium conditions at 320 °C and 30 bar, complemented by hydrogen injection via alkaline electrolysis to maintain an H2/CO ratio above 3. Energy and exergy analyses were performed to quantify efficiencies and irreversibilities. Results indicate carbon conversion rates of 48.3% for EFB and 47.4% for RH, producing SNG with 96% CH4 suitable for grid injection. Energy efficiencies reached 71.9% and 71.0%, while exergy efficiencies were 87.2% and 82.9%, respectively, aligning with or surpassing literature benchmarks. The main irreversibilities occurred in methanation and CO2 removal, highlighting thermal integration and gas recycling as key improvement strategies. These findings demonstrate the potential of leveraging local biomass for clean energy production and support the development of Power-to-Gas systems in Colombia.

Gases doi: 10.3390/gases6010013

Authors: Sushobhan Pradhan Prem Bikkina

This research investigates wettability-induced, preferential, pressure-driven bubble nucleation of gases from a multi-gas dissolved liquid system in hydrophilic and hydrophobic glass vials. The hydrophobic glass surfaces were prepared using (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (HT). Degassed deionized water in a vial, placed inside a pressure cell, was saturated with a precisely controlled mixture of CO2 and CH4 gases at either 6000 mbar or 3000 mbar for 24 h. To initiate the pressure-driven bubble nucleation process, a 500 mbar step-down pressure was applied to the pressure cell every 15 min until bubble nucleation was observed. CH4 and CO2 volume fractions were measured using micro-gas chromatography (Micro-GC), while a digital microscope was employed to observe the bubble nucleation process. No bubble nucleation was observed in the case of the hydrophilic vial even when the system pressure was brought to atmospheric pressure. In the case of the hydrophobic vial, the average onset bubble nucleation pressures were 4800 mbar and 2000 mbar for 6000 mbar and 3000 mbar saturation pressures, respectively. The average feed gas concentrations during saturation were 84.44 ± 0.14% and 15.44 ± 0.2% of CH4 and CO2, respectively, while at the onset pressure for bubble nucleation, the concentrations shifted to 85.24 ± 0.48% and 13.12 ± 0.52% of CH4 and CO2, respectively, when the saturation pressure was 6000 mbar. The average feed gas concentrations during saturation were 85.12 ± 0.28% and 14.67 ± 0.1% of CH4 and CO2, respectively, and the average concentrations of CH4 and CO2 gases at onset pressure for bubble nucleation were 86.06 ± 1.21% and 12.03 ± 1.03%, respectively, when the saturation pressure was 3000 mbar. The increase in CH4 concentration is attributed to its preferential separation during the bubble nucleation process.

Gases doi: 10.3390/gases6010012

Authors: Jabier Retegi Bart Kamp Juan Ignacio Igartua

This study examines how different sustainability assessment approaches influence climate-policy choices when evaluating greenhouse gas (GHG) emissions across industrial value chains. Using Spain as an empirical setting, we apply Environmentally Extended Input–Output Tables combined with Production Layer Decomposition to quantify Scope 1–2–3 emissions and assess economic and employment impacts. The results show that indirect emissions dominate most value chains, revealing structural dependencies that are not captured by sector-level inventories. Incorporating social and economic dimensions highlights the need for transition pathways that minimise employment disruption while maximising environmental gains. Although public procurement can enhance the uptake of emerging low-carbon and circular-economy technologies, it has limited quantitative influence on total value-chain emissions. The findings demonstrate that value-chain-based sustainability assessments provide a more comprehensive basis for designing coherent, equitable, and effective decarbonisation strategies.

Gases doi: 10.3390/gases6010011

Authors: Magzhan N. Orynbasar Vladimir E. Messerle Alexandr B. Ustimenko Sestager Kh. Aknazarov

An experiment was conducted to produce synthesis gas (main components CO and H2) via plasma–steam gasification of brown coal with an ash content of 9% and a volatile matter yield of 48%. Satisfactory agreement between the calculation results and experiments for various types of solid fuel allowed the TERRA thermodynamic calculation program to be verified. A thermodynamic analysis of plasma–steam gasification of shale, brown, and hard coals was performed over a wide range of their characteristics (ash content 3–88%, volatile yield 5–50%) at temperatures from 600 to 3000 K. The composition of the gas and condensed phases of the gasification products, the degree of carbon gasification, and the specific energy consumption for the process were calculated. Although solid fuels differ significantly in ash content and volatile matter yield, synthesis gas is the primary gaseous product of their gasification, with a higher hydrogen concentration than carbon monoxide, thereby improving the environmental performance of solid fuels. In all types of fuels, the maximum synthesis gas concentration occurs between 1200 and 1600 K, with low ballast impurities (H2O, CO2, N2) and zero harmful emissions (NOX, SOX). Synthesis gas combustion heat ranges from 10,475 to 11,570 kJ/m3. A 100% gasification rate occurs at temperatures between 1250 and 1300 K. Energy consumption varies between 0.7 and 2.7 kWh/kg. In solid fuel plasma–steam gasification, the volatile yield reduces specific energy consumption, but the ash content has a negligible effect. Plasma–steam gasification of solid fuels containing 9 and 88% ash and 48% and 50% volatile yield shows a 12% reduction in specific energy consumption. Plasma–steam gasification of solid fuels with volatile yields of 48 and 5% and ash contents of 9% and 3%, respectively, results in a 60% reduction in specific energy consumption.

Gases doi: 10.3390/gases6010010

Authors: Sadaf Zeeshan Muhammad Ali Ijaz Malik

In South Asia, smog has become a critical environmental concern that endangers public health, ecosystems, and the regional climate. To determine the primary causes of smog formation in Lahore during peak polluted months (October and November), the current study develops a dual analytical framework that combines cutting-edge machine learning with sector- and pollutant-specific emission analysis. To assess their relationship with Air Quality Index (AQI) and create a high-accuracy predictive model, meteorological factors and emission data from key sectors are used to build Random Forest and extreme gradient boosting (XGBoost) models. The current study evaluates the joint effects of weather and emission loads on AQI variability by integrating atmospheric dynamics with comprehensive emission profiles. The XGBoost model forecasts important pollutants from the transportation, industrial, and agricultural sectors, including carbon dioxide (CO2), oxides of nitrogen (NOx), Volatile Organic Compounds (VOCs), and particulate matter, in the second analytical tier. Particulate matter (PM), NOx, and transport-related pollutants are consistently identified by the models as the primary predictors of AQI, with high prediction performance. Furthermore, a 3-fold split is used for cross-validation, making sure that each fold maintained the data’s chronological order to avoid leakage. The model has modest root mean square error (RMSE) levels (4.32 and 8.14) and high coefficient of determination (R2) values (0.93–0.99). Approximately 90% of Lahore’s annual emissions resulted from the transportation sector. These results offer aid to policymakers to anticipate air quality, identify important emission sources, and execute targeted initiatives to minimize smog and promote a healthier urban environment. The current study also helps in analyzing the causes of atmospheric and sectoral pollution. While the study captures smog dynamics during peak pollution months, its temporal scope is limited, and finer spatial measurements could further improve the generalizability of the results.

Gases doi: 10.3390/gases6010009

Authors: Mustafa Hakan Ozyurtkan Coşkun Çetin Cenk Temizel

This review examines the emerging concepts of hydrogen production and storage directly within hydrocarbon reservoirs (in situ), evaluating their technical feasibility, infrastructure requirements, challenges, and potential role in net-zero strategies. The in situ hydrogen production involves injecting substances, like water or gases, into the reservoir where they react with the natural materials underground. Heat and catalysts can also help speed up chemical reactions. Techniques such as methane reforming, steam gasification, and aquathermolysis show promise for producing hydrogen efficiently while keeping carbon emissions low. There are several benefits when producing and storing hydrogen underground, including lower costs, less need for surface equipment, and reduced gas emissions. However, there are still certain challenges to this process, such as finding the optimal reaction conditions and keeping the reservoir stable over time. This review outlines key technological breakthroughs, real-world applications, and future research directions for in situ hydrogen generation and storage initiatives to help meet net-zero emission goals by 2050.

Gases doi: 10.3390/gases6010008

Authors: Campbell Oribelemam Omuboye Chigozie Nweke-Eze

This study presents a techno-economic assessment of a modular, solar-assisted methane pyrolysis pilot plant designed for sustainable hydrogen production in Nigeria using concentrated solar power (CSP). Driven by the need to convert flare gas into value and reduce emissions, the work evaluates a hypothetical 100 kg/day hydrogen system by integrating a methane pyrolysis reactor with a solar heliostat–receiver field. Process modelling was carried out in DWSIM, while solar concentration behavior was represented using Tonatiuh. The mass–energy balance results show a hydrogen output of 3.95 kg/h accompanied by 12.30 kg/h of carbon black, with the reactor demanding roughly 44 kW of high-temperature heat at 900 °C. The total capital cost of the ≈50 kW pilot plant is approximately USD 1.5 million, with heliostat and receiver technologies forming the bulk of the investment. Annual operating costs are estimated at USD 69,580, alongside feedstock expenses of USD 43,566. Using annualized cost and discounted cash flow approaches, the resulting levelized cost of hydrogen (LCOH) is USD 5.87/kg, which is competitive with off-grid electrolysis in the region, though still above blue and gray hydrogen benchmarks. The results indicate that hydrogen cost is primarily driven by solar field capital expenditure and carbon by-product valorization. Financial indicators reveal a positive NPV, a 13% IRR, and a 13-year discounted payback period, highlighting the promise of solar-assisted methane pyrolysis as a transitional hydrogen pathway for Nigeria.

Gases doi: 10.3390/gases6010007

Authors: Shan-Heng Fu

This study examines the determinants of U.S. CO2 emissions and provides evidence to inform more effective carbon-reduction policies. Using Autoregressive Distributed Lag (ARDL) and Nonlinear ARDL (NARDL) models, the analysis covers January 1997 to February 2022 across four end-use sectors: Residential, Commercial, Industrial, and Transportation. The models capture both long-run equilibria and short-run adjustments between emissions and key drivers, including industrial production, interest rates, climate policy uncertainty (CPU), and energy prices. Results indicate a long-run asymmetric relationship in which economic growth and interest rates differentially affect total emissions, while CPU exerts a significant negative influence only in the transportation sector. Methodologically, the combined ARDL–NARDL approach offers robust evidence of nonlinear and asymmetric effects of macroeconomic and policy variables on emissions. These findings underscore the need to integrate economic and financial conditions into climate policy design and suggest that sector-specific measures—particularly targeting transportation—may substantially improve the effectiveness of carbon-mitigation strategies.

Gases doi: 10.3390/gases6010006

Authors: Altea Pedullà Paolo S. Calabrò

Anaerobic digestion (AD) of ensiled orange peel waste (OPW) offers a promising pathway for the valorisation of citrus-processing residues and the generation of renewable energy. This study evaluated the impact of two carbon-based materials, biochar and granular activated carbon (GAC), on methane yield and process stability using Biochemical Methane Potential (BMP) tests. The experimental setup consisted of two consecutive cycles, the second of which was designed to examine microbial acclimation by reusing both the digestate (as the inoculum) and the previously added carbon materials. Ensiled OPW exhibited a methane yield of 578 ± 59 mLCH4/gVS during the initial cycle, confirming its high biodegradability. The addition of biochar and GAC resulted in comparable yields (approximately 520–560 mLCH4/gVS) and did not enhance the ultimate methane potential; however, both additives proved fully compatible with the process. In the subsequent cycle, a marked increase in methane production was observed, with OPW reaching approximately 730 mLCH4/gVS, primarily attributed to improved microbial adaptation. Kinetic analysis revealed moderate enhancements in degradation rates, which were more pronounced when higher biochar dosages were used. Overall, ensiled OPW emerges as a highly suitable substrate for AD. At the same time, biochar and GAC did not adversely affect the AD process under the tested conditions; however, their potential benefits have yet to be fully demonstrated and warrant further investigation, particularly under continuous reactor operating conditions.

Gases doi: 10.3390/gases6010005

Authors: Khaled Enab

Gas injection is a well-established method for enhancing oil recovery by improving oil mobility, primarily through viscosity reduction. While its application in heavy oil reservoirs is extensively studied, the specific impact of carbon dioxide (CO2) injection pressure on fluid viscosity reduction and the ultimate recovery factor from light oil reservoirs has not been fully investigated. To address this gap, this experimental study systematically explores the effects of CO2 injection pressure and reservoir permeability on light oil recovery. This study conducted miscible, near-miscible, and immiscible gas injection experiments on two core samples with distinct permeabilities (13.4 md and 28 md), each saturated with light oil. CO2 was injected at five different pressures, including conditions ranging from immiscible to initial reservoir pressure. The primary metrics for evaluation were the recovery factor (measured at gas breakthrough, end of injection, and abandonment pressure) and the viscosity reduction of the produced oil. The results conclusively demonstrate that CO2 injection significantly enhances light oil production. A direct proportional relationship was established between both the injection pressure and the recovery factor and between permeability and overall oil production at the gas breakthrough. However, a key finding was the inverse relationship observed between permeability and viscosity reduction: the lower-permeability sample (13.4 md) consistently exhibited a greater percentage of viscosity reduction across all injection pressures than the higher-permeability sample (28 md). This unexpected trend is aligned with the inverse relationship between the permeability and the recovery factor after the gas breakthrough. This outcome suggests that enhanced CO2 solubility, driven by higher confinement pressures within the nanopores of the lower-permeability rock, promotes a localized, near-miscible state. This effect was even evident during immiscible injection, where the low-permeability sample showed a noticeable viscosity reduction and superior long-term production. These findings highlight the critical role of pore-scale confinement in governing CO2 miscibility and its associated viscosity reduction, which should be incorporated into enhanced oil recovery design for unconventional reservoirs.

Gases doi: 10.3390/gases6010004

Authors: José Miguel Mahía-Prados Ignacio Arias-Fernández Manuel Romero Gómez

This study provides a comprehensive analysis of the impact of different marine fuels such as heavy fuel oil (HFO), methane, methanol, ammonia, or hydrogen, on energy efficiency and pollutant emissions in maritime transport, using a combined application of the Energy Efficiency Design Index (EEDI), Energy Efficiency Operational Indicator (EEOI), and Carbon Intensity Indicator (CII). The results show that methane offers the most balanced alternative, reducing CO2 by more than 30% and improving energy efficiency, while methanol provides an intermediate performance, eliminating sulfur and partially reducing emissions. Ammonia and hydrogen eliminate CO2 but generate NOx (nitrogen oxides) emissions that require mitigation, demonstrating that their environmental impact is not negligible. Unlike previous studies that focus on a single fuel or only on CO2, this work considers multiple pollutants, including SOx (sulfur oxides), H2O, and N2, and evaluates the economic cost of emissions under the European Union Emissions Trading System (EU ETS). Using a representative model ship, the study highlights regulatory gaps and limitations within current standards, emphasizing the need for a global system for monitoring and enforcing emissions rules to ensure a truly sustainable and decarbonized maritime sector. This integrated approach, combining energy efficiency, emissions, and economic evaluation, provides novel insights for the scientific community, regulators, and maritime operators, distinguishing itself from previous multicriteria studies by simultaneously addressing operational performance, environmental impact, and regulatory gaps such as unaccounted NOx emissions.

Gases doi: 10.3390/gases6010003

Authors: Mikhail Zhumagulov Aizhan Omirbayeva Davide Papurello

Solar energy enhances the energy and environmental performance of coal gasification by lowering carbon emissions and increasing the yield and quality of synthesis gas. This patent review surveys recent global advances in solar thermochemical reactors for coal gasification, focusing on key innovations disclosed in patent applications and grants, with particular attention to technologies that improve process efficiency and sustainability. The novelty of the review is that unlike most patent reviews that focus primarily on statistical indicators such as application counts, geography, and classification, this work integrates qualitative analysis of specific technical solutions alongside statistical evaluation. This combined approach enables a deeper assessment of technological maturity and practical applicability. Fifteen patents from different countries were reviewed. The largest number (8, 53%) belongs to the United States. China has the second place with 4 (27%). The remaining countries (the EU, Korea, and Russia) hold 1 patent (7% each). The present work emphasises the technological and engineering solutions associated with the integration of solar energy into gasification processes. The author’s design is free of the disadvantages of its counterparts and is a simplified design with a high degree of adaptability to various types of fuel, including brown coal, biomass, and other carbon-containing materials.

Gases doi: 10.3390/gases6010002

Authors: Bruce M. Prince Daniel Vrinceanu Mark C. Harvey Michael P. Jensen Maria Zawadowicz Chongai Kuang

Methoxy radicals (CH3O•), formed as intermediates during methane oxidation, may play an underexplored but locally significant role in the atmospheric oxidation of dimethyl sulfide (DMS), a key sulfur-containing compound emitted primarily by marine phytoplankton. This study presents a comprehensive computational investigation of the reaction mechanisms and kinetics of DMS oxidation initiated by CH3O•, using density functional theory B3LYP-D3(BJ)/6-311++G(3df,3pd), CCSD(T)/6-311++G(3df,3pd), and UCBS-QB3 methods. Our calculations show that DMS reacts with CH3O• via hydrogen atom abstraction to form the methyl-thiomethylene radical (CH3SCH2•), with a rate constant of 3.05 × 10−16 cm3/molecule/s and a Gibbs free energy barrier of 14.2 kcal/mol, which is higher than the corresponding barrier for reaction with hydroxyl radicals (9.1 kcal/mol). Although less favorable kinetically, the presence of CH3O• in localized, methane-rich environments may still allow it to contribute meaningfully to DMS oxidation under specific atmospheric conditions. While the short atmospheric lifetime of CH3O• limits its global impact on large-scale atmospheric sulfur cycling, in marine layers where methane and DMS emissions overlap, CH3O• may play a meaningful role in forming sulfur dioxide and downstream sulfate aerosols. These secondary organic aerosols lead to cloud condensation nuclei (CCN) formation, subsequent changes in cloud properties, and can thereby influence local radiative forcing. The study’s findings underscore the importance of incorporating CH3O• driven oxidation pathways into atmospheric models to enhance our understanding of regional sulfur cycling and its impacts on local air quality, cloud properties and radiative forcing. These findings provide mechanistic insights that improve data interpretation for atmospheric models and extend predictions of localized variations in sulfur oxidation, aerosol formation, and radiative forcing in methane-rich environments.

Gases doi: 10.3390/gases6010001

Authors: Stefania Moioli

Carbon Capture, Utilization and Storage (CCUS) is a critical area of research due to its potential to significantly reduce CO2 emissions from industrial processes and fossil fuel-based power generation. Aqueous amine solutions are commonly used as chemical solvents for CO2 capture. However, their application is disfavoured by the high energy requirements and related operational costs, toxicity, and corrosion issues. To address these limitations, research is in general focused on developing novel solvents that can overcome the drawbacks of traditional amines. This development needs the study of phase equilibria in systems for which detailed physicochemical data are often scarce in the literature. In particular, understanding the solubility of gases (CO2) in possible solvent mixtures is essential for evaluating their suitability for chemical or physical absorption processes. In this work, a dedicated setup was installed to generate the experimental data for these novel systems. This unit was designed to measure the solubility and diffusivity of gases in low-volatility liquids that could be alternative CO2 solvents. A detailed experimental procedure was established, and the unit was initially validated by measuring CO2 solubility in a 30 wt% monoethanolamine (MEA) solution, one of the most widely used industrial solvents. The experiments were conducted under conditions representing both the absorption and the regeneration sections of a CO2 removal plant. The resulting equilibrium data were analyzed by employing several thermodynamic models, and the model providing the best representation was selected.

Gases doi: 10.3390/gases5040029

Authors: We Lin Chan Arun Dev

Global carbon emissions are driving the maritime industry toward cleaner fuels, with LNG already established as a transitional option that reduces SOx, NOx, and particulate emissions relative to conventional marine fuels and in line with decarbonisation strategies. This research aimed to explore the transition of offshore and marine platforms from conventional marine fuels to cleaner alternatives, with liquefied natural gas (LNG) emerging as the principal transitional fuel. Subsequently, floating liquefied natural gas (FLNG) platforms are increasingly being deployed to harness offshore gas resources, yet they face critical challenges related to weight, space, and energy efficiency. The study proposes pathways for transitioning FLNG energy systems from LNG to zero-carbon fuels, such as hydrogen derived directly from LNG resources, to optimise fuel supply under the unique operational constraints of FLNG units. The work unifies the independent domains of pure-fuel and blending-fuel processes for LNG and hydrogen, viewed in the context of thermodynamic processes, to optimise hydrogen–LNG co-firing gas turbine performance and meet the base power line of 50 MW. Furthermore, the research article will contribute to the development of other floating production platforms, such as FPSOs and FSRUs. It will be committed to clean energy policies that mandate support for green alternatives to hydrocarbon fuels.

Gases doi: 10.3390/gases5040028

Authors: Mohammad Hassan Mahmoodi Pezhman Ahmadi Antonin Chapoy

The aim of this study is to generate density and viscosity data for carbon capture utilization and storage (CCUS) mixtures using equilibrium molecular dynamics (EMD) simulations. Binary CO2 mixtures with SO2 and H2S impurities at mole fractions of 0.05, 0.10, and 0.20 were constructed. Simulations were performed across a temperature range of 223–323.15 K and at pressures up to 27.5 MPa using ms2 software. The simulation results were compared with predictions from established models. These included the Multi-Fluid Helmholtz Energy Approximation (MFHEA) for density, and the Lennard-Jones (LJ), Residual Entropy Scaling (ES-NIST), and Extended Corresponding States (SUPERTRAPP) models for viscosity. Available experimental data from the literature were also used for validation. Density predictions showed excellent agreement with MFHEA, especially for CO2 + SO2 mixtures, with %AARD values below 1% for 0.05 and 0.10, and 1.60% for 0.20 mole fraction SO2. For CO2 + H2S mixtures, deviations also increased with impurity concentration, reaching a maximum %AARD of 4.72% at 0.20 mole fraction. Viscosity data were validated against experimental values from the literature for a CO2 + CH4 (xCH4 = 0.25) mixture, showing strong agreement with both models and experiments. This confirms the reliability of the MD approach and the thermodynamic models, even for systems lacking experimental data. However, viscosity estimates showed higher uncertainty at lower temperatures and higher densities, a known limitation of the Green–Kubo method. This highlights the importance of selecting an appropriate correlation time to ensure the pressure correlation functions reach a plateau, avoiding inaccurate or uncertain viscosity values.

Gases doi: 10.3390/gases5040027

Authors: Yousef Alqaheem Abdulaziz A. Alomair Mohammad Alobaid

The demand for heavy-duty 5% (HD5) propane is expected to increase in the future due to the use of the gas as a fuel for engines. A refinery produces HD10 propane, and it is looking to upgrade to HD5 propane using either the conventional process (distillation) or an energy-saving unit (membrane). This study compared the two technologies in terms of product quality and quantity using process simulation in UniSIM®. The software also provided the design parameters and power consumption for the two processes. The results show that the membrane was competitive with distillation and was capable of producing 96 mol% propane with a recovery of 99.3%. On the other hand, distillation achieved a maximum propane quality of 95 mol% with a recovery of 99.9%. Surprisingly, the energy consumption in the membrane was 669 kWh, which was higher than that of distillation (540 kWh) due to the requirement for a pre-heating step. Therefore, the technology should be selected based on either the quality or quantity of propane.

Gases doi: 10.3390/gases5040026

Authors: Emmanuel Appiah Kubi Hamid Rahnema Abdul-Muaizz Koray Babak Shabani

Large-scale underground hydrogen storage in saline aquifers requires an understanding of hydrogen–brine two-phase flow properties, particularly relative permeability, which influences reservoir injectivity and hydrogen recovery. However, such hydrogen–brine relative permeability data remain scarce, hindering the predictive modeling of hydrogen injection and withdrawal. In this study, steady-state hydrogen–brine co-injection coreflood experiments were conducted on an Austin Chalk core sample to measure the relative permeabilities. Klinkenberg slip corrections were applied to the gas flow measurements to determine the intrinsic (slip-free) hydrogen permeability. The core’s brine permeability was 13.2 mD, and the Klinkenberg-corrected hydrogen gas permeability was 13.8 mD (approximately a 4.5% difference). Both raw and slip-corrected hydrogen relative permeability curves were obtained, showing that the gas-phase conductivity increased as the water saturation decreased. Gas slippage caused higher apparent gas permeability in the raw data, and slip correction significantly reduced hydrogen relative permeability at lower hydrogen saturations. The core’s irreducible water saturation was 39%, at which point the hydrogen relative permeability reached 0.8 (dropping to 0.69 after slip correction), which is indicative of strongly water-wet behavior. These results demonstrate a measurable impact of gas slippage on hydrogen flow behavior and highlight the importance of accounting for slip effects when evaluating hydrogen mobility in brine-saturated formations.

Gases doi: 10.3390/gases5040025

Authors: Guido Satta Pierluigi Cau Davide Muroni Carlo Milesi Carlino Casari

Emerging technologies such as the Internet of Things (IoT), big data, mobile devices, high-performance computing, and advanced modeling are reshaping urban management. When integrated with conventional tools, these innovations enable smarter governance—particularly in air quality control—improving public health and quality of life. Yet, urban expansion driven by economic growth continues to worsen pollution and its health impacts. This study presents AERQ, a decision support system (DSS) designed to address urban air quality challenges through real-time sensor data and the AERMOD dispersion model. Applied to Cagliari (Italy), AERQ is used to evaluate key traffic-related pollutants (CO, PM, NO2) and simulate mitigation scenarios. Results are delivered via a user-friendly web-based platform for policymakers, technicians, and citizens. AERQ supports data-driven planning and near real-time responses, demonstrating the potential of integrated digital tools for sustainable urban governance. In the case study, it achieved 10 m spatial and 1 h temporal resolution, while reducing simulation time by 99%—delivering detailed five-year scenarios in just 15 h.

Gases doi: 10.3390/gases5040024

Authors: José Luis Pineda-Tapia Edwin Huayhua-Huamaní Milton Edward Humpiri-Flores Kevin Fidel Quispe-Monroy Deyna Lozano-Ccopa Robinson Chaiña-Sucasaca Milagros Lupe Salas-Huahuachampi Dennis Enrique Mamani-Vilca Cristian Abraham Cutipa-Flores

The aim of this study was to rigorously quantify and analyse the concentrations of atmospheric pollutants (PM10, PM2.5, SO2, NO2, CO, H2S, and O3) emitted by artisanal brick kilns in Juliaca City, Peru. The AERMOD dispersion model and a network of low-cost sensors (LCSs) were employed to characterise air quality at specific receptor sites. A georeferenced inventory of kiln operations was created to determine their parameters and operational intensity, providing a foundation for estimating emission factors and rates. Data were obtained from the United States Environmental Protection Agency (EPA) and supplemented with locally gathered meteorological records, which were processed for integration into the AERMOD model. The findings revealed that brick kilns are a principal source of atmospheric pollution in the region, with carbon monoxide (CO) emissions being especially pronounced. The LCSs facilitated the identification of pollutant concentrations at various locations and enabled the quantification of the specific contribution of brick production to ambient aerosol levels. Comparative assessments determined that these sources account for approximately 85% of CO emissions within the study area, underscoring a significant adverse impact on air quality and public health. Background pollutant levels, emission rates, spatial distributions, and concentration patterns were analysed within the assessment zones, resulting in solid model performance. These results provide a sound scientific basis for the formulation and implementation of targeted environmental mitigation policies in urban areas and the outskirts of Juliaca.

Gases doi: 10.3390/gases5040023

Authors: Nadieh Salehi Mohammad Kazemi Mohammad Amin Esmaeilbeig Abbas Helalizadeh Mehdi Bahari Moghaddam

Carbon dioxide (CO2), a major greenhouse gas, contributes significantly to global warming and environmental degradation. Carbon Capture, Utilization, and Storage (CCUS) is a promising strategy to mitigate atmospheric CO2 levels. One widely applied utilization approach involves injecting captured CO2 into depleted oil reservoirs to enhance oil recovery—a technique known as CO2-Enhanced Oil Recovery (CO2-EOR). The effectiveness of CO2-EOR largely depends on complex rock–fluid interactions, including mass transfer, wettability alteration, capillary pressure, and interfacial tension (IFT). Various factors, such as the presence of asphaltenes, salinity, pressure, temperature, and rock type, influence these interactions. This review explores the impact of these parameters on the IFT between CO2 and oil/water systems, drawing on findings from both experimental studies and molecular dynamics (MD) simulations. The literature indicates that increased temperature, reduced pressure, lower salinity, and the presence of asphaltenes tend to reduce IFT at the oil–water interface. Similarly, elevated temperature and pressure, along with asphaltene content, also lower the surface tension between CO2 and oil. Most MD simulations employ synthetic oil mixtures of various alkanes and use tools such as LAMMPS and GROMACS. Experimentally, the pendant drop method is most commonly used with crude oil and brine samples. Future research employing actual reservoir fluids and alternative measurement techniques may yield more accurate and representative IFT data, further advancing the application of CO2-EOR.

Gases doi: 10.3390/gases5040022

Authors: Julián Cardona-Giraldo Laura C. G. Velandia Daniel Marin Alejandro Argel Samira García-Freites Marco Sanjuan David Acosta Adriana Aristizabal Santiago Builes Maria L. Botero

Gasification of residual biomass has emerged as an efficient thermochemical conversion process, applicable to a wide range of uses, such as electricity generation; chemical manufacturing; and the production of liquid biofuels, BioSNG (biomass-based synthetic natural gas), and hydrogen. Thus, gasification of biomass residues not only constitutes an important contribution toward decarbonizing the economy but also promotes the efficient utilization of renewable resources. Although a variety of gasification technologies are available, there are no clear guidelines for selecting the type of gasifier appropriate depending on the feedstock and the desired downstream products. Herein, we propose a gasifier classification model based on an extensive literature review, combined with a multi-criteria decision-making approach. A comprehensive and up-to-date literature review was conducted to gain a thorough understanding of the current state of knowledge in biomass gasification. The different features of the different types of gasifiers, in the context of biomass gasification, are presented and compared. The gasifiers were reviewed and evaluated considering criteria such as processing capacity, syngas quality, process performance, feedstock flexibility, operational and capital costs, environmental impact, and specific equipment features. A multi-criteria classification methodology was evaluated for assessing biomass gasifiers. A case study of such methodology was a applied to determine the best gasifiers for BioSNG inclusion in the natural gas distribution system in a small-scale scenario. Validation was conducted by comparing the matrix findings with commercially implemented gasification projects worldwide.

Gases doi: 10.3390/gases5030021

Authors: Ananya Srivastava Rohan Sonar Achim Bittner Alfons Dehé

This work presents a proof of concept including simulation and experimental validations of acoustic gas sensor prototypes for trace CO2 detection up to 1 ppm. For the detection of lower gas concentrations especially, the dependency of acoustic resonances on the molecular weights and, consequently, the speed of sound of the gas mixture, is exploited. We explored two resonator types: a cylindrical acoustic resonator and a Helmholtz resonator intrinsic to the MEMS microphone’s geometry. Both systems utilized mass flow controllers (MFCs) for precise gas mixing and were also modeled in COMSOL Multiphysics 6.2 to simulate resonance shifts based on thermodynamic properties of binary gas mixtures, in this case, N2-CO2. We performed experimental tracking using Zurich Instruments MFIA, with high-resolution frequency shifts observed in µHz and mHz ranges in both setups. A compact and geometry-independent nature of MEMS-based Helmholtz tracking showed clear potential for scalable sensor designs. Multiple experimental trials confirmed the reproducibility and stability of both configurations, thus providing a robust basis for statistical validation and system reliability assessment. The good simulation experiment agreement, especially in frequency shift trends and gas density, supports the method’s viability for scalable environmental and industrial gas sensing applications. This resonance tracking system offers high sensitivity and flexibility, allowing selective detection of low CO2 concentrations down to 1 ppm. By further exploiting both external and intrinsic acoustic resonances, the system enables highly sensitive, multi-modal sensing with minimal hardware modifications. At microscopic scales, gas detection is influenced by ambient factors like temperature and humidity, which are monitored here in a laboratory setting via NDIR sensors. A key challenge is that different gas mixtures with similar sound speeds can cause indistinguishable frequency shifts. To address this, machine learning-based multivariate gas analysis can be employed. This would, in addition to the acoustic properties of the gases as one of the variables, also consider other gas-specific variables such as absorption, molecular properties, and spectroscopic signatures, reducing cross-sensitivity and improving selectivity. This multivariate sensing approach holds potential for future application and validation with more critical gas species.

Gases doi: 10.3390/gases5030020

Authors: Li Chen Yuan Tian Nana Zhang Ziyi Xu Zhisheng Li

To prevent toxic and harmful gas suffocation accidents in underground metal mine stopes, the Fluent numerical simulation method was employed to investigate the wind field distribution patterns and the diffusion laws of blasting fumes in stopes with and without middle–end roadways under varying effective ranges. The simulation accuracy was validated through laboratory experiments. The results demonstrate that over time, the CO concentration in the blasting area decreases, while in other regions of the stope, it initially increases before declining. The presence or absence of a middle roadway does not significantly alter the migration and diffusion behavior of blasting fumes in the stope. When the effective range is ER–1, the simulation error is only 8 s. As the effective range increases, the time required to reduce the CO concentration to 24 ppm on the respiratory plane, across the entire space, and at the monitoring point follows a linearly increasing trend. Meanwhile, the maximum wind speed at the working face exhibits a linearly decreasing trend, whereas the peak CO concentration shows a linearly increasing trend. Under the ER–1 effective range, the CO concentration can be reduced to a safe threshold more rapidly. The experimental and simulation results exhibit an error margin within 16.97%, confirming the accuracy of the numerical simulation.

Gases doi: 10.3390/gases5030019

Authors: Wai Ming To Billy T. W. Yu

The air transport industry has played a crucial role in Hong Kong’s economic growth. However, aircraft operations produce a considerable volume of greenhouse gases emissions. By analyzing aviation kerosene consumption data from the first quarter of 2011 to the fourth quarter of 2018, this study developed a seasonal autoregressive integrated moving average (ARIMA) model—ARIMA(1,1,0)(0,1,1)4—that accurately reflects the actual consumption patterns. This model was then utilized to forecast aviation kerosene consumption from the first quarter of 2019 to the fourth quarter of 2024, a period marked by Hong Kong’s social unrest, followed by the pandemic and post-pandemic effects of COVID-19. As COVID-19 transitioned to an endemic stage, the number of aircraft movements has steadily risen over the past three years, resulting in increased aviation kerosene consumption. This study assessed the reduction in aviation kerosene consumption and the corresponding greenhouse gases emissions during the first quarter of 2020 to the fourth quarter of 2024, primarily attributed to the impacts of the COVID-19 pandemic. It was determined that the reduction reached a peak of 15,973 kT of CO2 in 2022, subsequently falling to 7020 kT of CO2 in 2024. Utilizing both actual and forecasted consumption data, this study estimated greenhouse gases emissions from the Hong Kong air transport industry for the years 2011 to 2030.

Gases doi: 10.3390/gases5030018

Authors: Dimitrios-Aristotelis Koumpakis Savvas Petridis Apostolos Tsakirakis Ioannis Sourgias Alexandra V. Michailidou Christos Vlachokostas

The naturally occurring radioactive gas radon presents a major public health danger mainly affecting people who spend time in poorly ventilated buildings. The periodic table includes radon as a noble gas which forms through uranium decay processes in soil, rock, and water. The accumulation of radon indoors in sealed or poorly ventilated areas leads to dangerous concentrations that elevate human health risks of lung cancer. The research examines environmental variables affecting radon concentration indoors by studying geothermal installations and their drilling activities, which potentially increase radon emissions. The study was conducted in the basement of the plumbing educational building at the Aristotle University of Thessaloniki to assess the potential impact of geothermal activity on indoor radon levels, as the building is equipped with a geothermal heating system. The key findings based on 150 days of continuous data showed that radon levels peak during the cold days, where the concentration had a mean value of 41.5 Bq/m3 and reached a maximum at about 95 Bq/m3. The reason was first and foremost poor ventilation and pressure difference. The lowest concentrations were on days with increased human activity with measures that had a mean value of 14.8 Bq/m3, which is reduced by about 65%. The results that are presented confirm the hypotheses and the study is making clear that ventilation and human activity are crucial in radon mitigation, especially on geothermal and energy efficient structures.

Gases doi: 10.3390/gases5030017

Authors: Seckin Karagoz

Minimizing carbon dioxide emissions is crucial due to the generation of energy from fossil fuels. The significance of carbon capture and storage (CCS) technology, which is highly successful in mitigating carbon emissions, has increased. On the other hand, hydrogen is an important energy carrier for storing and transporting energy, and technologies that rely on hydrogen have become increasingly promising as the world moves toward a more environmentally friendly approach. Nevertheless, the integration of CCS technologies into power production processes is a significant challenge, requiring the enhancement of the combined power generation–CCS process. In recent years, there has been a growing interest in process intensification (PI), which aims to create smaller, cleaner, and more energy efficient processes. The goal of this research is to demonstrate the process intensification potential and to model and simulate a hybrid integrated–intensified adsorptive-membrane reactor process for simultaneous carbon capture and hydrogen production. A comprehensive, multi-scale, multi-phase, dynamic, computational fluid dynamics (CFD)-based process model is constructed, which quantifies the various underlying complex physicochemical phenomena occurring at the pellet and reactor levels. Model simulations are then performed to investigate the impact of dimensionless variables on overall system performance and gain a better understanding of this cyclic reaction/separation process. The results indicate that the hybrid system shows a steady-state cyclic behavior to ensure flexible operating time. A sustainability evaluation was conducted to illustrate the sustainability improvement in the proposed process compared to the traditional design. The results indicate that the integrated–intensified adsorptive-membrane reactor technology enhances sustainability by 35% to 138% for the chosen 21 indicators. The average enhancement in sustainability is almost 57%, signifying that the sustainability evaluation reveals significant benefits of the integrated–intensified adsorptive-membrane reactor process compared to HTSR + LTSR.

Gases doi: 10.3390/gases5030016

Authors: Mohammadsajjad Zeynolabedini Ashkan Jahanbani Ghahfarokhi

This work uses the MATLAB Reservoir Simulation Toolbox (MRST) to reduce the 3D reservoir model into a 2D version in order to investigate CO2 storage in the Aurora model using the vertical equilibrium (VE) model. For this purpose, we used an open-source reservoir simulator, MATLAB Reservoir Simulation Toolbox (MRST). MRST is an open-source reservoir simulator, with supplementary modules added to enhance its versatility in addition to a core set of procedures. A fully implicit discretization is used in the numerical formulation of MRST-co2lab enabling the integration of simulators with vertical equilibrium (VE) models to create hybrid models. This model is then compared with the Eclipse model in terms of properties and simulation results. The relative permeability of water and gas can be compared to verify that the model fits the original Eclipse model. Comparing the fluid viscosities used in MRST and Eclipse also reveals comparable tendencies. However, reservoir heterogeneity is the reason for variations in CO2 plume morphologies. The upper layers of the Eclipse model have lower permeability than the averaged MRST model, which has a substantial impact on CO2 transport. According to the study, after 530 years, about 17 MT of CO2 might be stored, whereas 28 MT might escape the reservoir, since after 530 years CO2 plume reaches completely the open northern boundary. Additionally, a sensitivity analysis study has been conducted on permeability, porosity, residual gas saturation, rock compressibility, and relative permeability curves which are the five uncertain factors in this model. Although plume migration is highly sensitive to permeability, porosity, and rock compressibility variation, it shows a slight change with residual gas saturation and relative permeability curve in this study.

Gases doi: 10.3390/gases5030015

Authors: Haval Kukha Hawez Hawkar Bakir Karwkh Jamal Matin Kakakhan Karzan Hussein Mohammed Omar

Carbon dioxide (CO2) geosequestration is a critical technology for reducing greenhouse gas emissions, with shale caprocks, such as Opalinus Clay (OPA), serving as essential seals to prevent CO2 leakage. This study employs computational fluid dynamics and finite element analysis to investigate the hydromechanical behavior of OPA during CO2 injection, integrating qualitative and quantitative insights. Validated numerical models indicate that capillary forces are the most critical factor in determining the material’s reaction, with an entry capillary pressure of 2–6 MPa serving as a significant threshold for CO2 breakthrough. The numbers show that increasing the stress loading from 5 to 30 MPa lowers permeability by 0.3–0.45% for every 5 MPa increase. Porosity, on the other hand, drops by 9.2–9.4% under the same conditions. The OPA is compacted, and axial displacements confirm numerical models with an error margin of less than 10%. Saturation analysis demonstrates that CO2 penetration becomes stronger at higher injection pressures (8–12 MPa), although capillary barriers slow migration until critical pressures are reached. These results demonstrate how OPA’s geomechanical stability and fluid dynamics interact, indicating that it may be utilized as a caprock for CO2 storage. The study provides valuable insights for enhancing injection techniques and assessing the safety of long-term storage.

Gases doi: 10.3390/gases5030014

Authors: Ahmad Abuhaiba

Micro gas turbines serve small-scale generation where swift response and low emissions are highly valued, and they are commonly fuelled by natural gas. True to their ‘micro’ designation, their size is indeed compact; however, a noteworthy portion of the enclosure is devoted to power electronics components. This article considers whether these components can be made even smaller by substituting their conventional silicon switches with switches fashioned from silicon carbide. The wider bandgap of silicon carbide permits stronger electric fields and reliable operation at higher temperatures, which together promise lower switching losses, less heat, and simpler cooling arrangements. This study rests on a simple volumetric model. Two data sets feed the model. First come the manufacturer specifications for a pair of converter modules (one silicon, the other silicon carbide) with identical operation ratings. Second are the operating data and dimensions of a commercial 100 kW micro gas turbine. The model splits the converter into two parts: the semiconductor package and its cooling hardware. It then applies scaling factors that capture the higher density of silicon carbide and its lower switching losses. Lower switching losses reduce generated heat, so heatsinks, fans, or coolant channels can be slimmer. Together these effects shrink the cooling section and, therefore, the entire converter. The findings show that a micro gas turbine inverter built with silicon carbide occupies about one fifth less space and delivers more than a quarter higher power density than its silicon counterpart.

Gases doi: 10.3390/gases5030013

Authors: Duraid Al-Bayati Doaa Saleh Mahdi Emad A. Al-Khdheeawi Matthew Myers Ali Saeedi

This work examines how multiphase flow behavior during CO2 and N2 displacement in a microfluidic chip under capillary-dominated circumstances is affected by interfacial tension (IFT) and the viscosity ratio. In order to simulate real pore-scale displacement operations, microfluidic tests were performed on a 2D rock chip at flow rates of 1, 10, and 100 μL/min (displacement of water by N2/supercritical CO2). Moreover, core flooding experiments were performed on various sandstone samples collected from three different geological basins in Australia. Although CO2 is notably denser and more viscous than N2, the findings show that its displacement efficiency is more influenced by the IFT values. Low water recovery in CO2 is the result of non-uniform displacement that results from a high mobility ratio and low IFT; this traps remaining water in smaller pores via snap-off mechanisms. However, due to the blebbing effect, N2 injection enhances the dissociation of water clots, resulting in a greater swept area and fewer remaining water clusters. The morphological investigation of the residual water indicates various displacement patterns; CO2 leaves more retained water in irregular shapes, while N2 enables more uniform displacement. These results confirm earlier studies and suggest that IFT has a crucial role in fluid displacement proficiency in capillary-dominated flows, particularly at low flow rates. This study emphasizes the crucial role of IFT in improving water recovery through optimizing the CO2 flooding process.

Gases doi: 10.3390/gases5030012

Authors: Everaldo Attard Jamie Buttigieg Kalliroi Simeonidis Grazia Pastorelli

This study evaluated the effects of feedstuffs and additives in dairy cow rations on rumen methane production and nitrate content in groundwater. Two basal rations and their supplements were analyzed in regard to proximate parameters, and an in vitro rumen fermentation system assessed methane release and nitrate levels over 72 h. Supplementing dairy cow rations with Brassica rapa (BR) boosted the ether extract content, while silage produced the highest amount of methane. Rapidly degrading substrates like BR and ground maize produced methane faster, but in smaller amounts, than straw and silage. BR, Opuntia ficus-indica (OFI), and Posidonia oceanica (PO)-supplemented rations had mixed effects; PO reduced the methane yield, while OFI increased methane production rates. BR-supplemented rations had the lowest nitrate levels, making it suitable for anaerobic digestion. The multivariate analysis showed strong correlations between crude protein, dry matter, and ash, while high-nitrate substrates inhibited methane production, supporting the literature on the role of nitrates in reducing methanogenesis. These results emphasize the need to balance nutrient composition and methane mitigation strategies in dairy cow ration formulations.

Gases doi: 10.3390/gases5020011

Authors: Dario Atzori Luca Debidda Claudia Bassano Simone Tiozzo Sandra Corasaniti Angelo Spena

Decarbonization has become a central policy and industrial priority across the European Union, driven by increasingly ambitious climate targets. The EU’s regulatory framework now mandates a 55% reduction in CO2 emissions by 2030 (compared to 1990 levels), with the overarching goal of achieving climate neutrality by 2050. This challenge is particularly critical for energy-intensive and hard-to-abate sectors, such as the glass industry. This paper begins with a brief overview of the relevant EU regulations and the structure of the Italian glass sector. It then identifies seven key decarbonization levers applicable to the industry. Drawing on literature data and expert consultations, these levers are integrated into two main decarbonization strategies tailored to the Italian context, both aligned with the 2050 net-zero target. This study further analyzes the estimated implementation costs, the barriers associated with each lever, and potential solutions to overcome them. Finally, Italian strategies are compared with decarbonization approaches adopted in other major European countries. The findings indicate that the transition to climate neutrality in the glass sector, while technically and economically plausible, remains highly contingent on the timely deployment of enabling technologies, the alignment of regulatory and financial frameworks, and the establishment of sustained, structured cooperation between industrial stakeholders and public authorities.

Gases doi: 10.3390/gases5020010

Authors: Ibrahim Yayaji Xiaoyi Mu Tong Zhu

This study examines the impact of flare tariff adjustments on gas-flaring volumes in Nigeria. Utilising a 52-year dataset, this analysis demonstrates that the effectiveness of flare tariffs in reducing gas flaring depends on the stringency of imposed charges. To isolate this effect, this study distinguishes between tariff regimes implemented before and after 2018, a pivotal year marked by the introduction of substantially higher tariffs under revised regulations. The findings indicate that the pre-2018 tariffs had no statistically significant effect on gas-flaring volumes, whereas the post-2018 tariffs led to a statistically significant reduction. Specifically, the pre-2018 tariffs were associated with a negligible reduction in flaring (0.05 percentage points), which was statistically insignificant. By contrast, the post-2018 tariff regime resulted in a 9.26 percentage-point decline in flaring volumes, significant at the 1% level. Additional factors contributing to the flaring reduction include oil production levels, oil prices, and the availability of gas infrastructure. These results highlight the critical role of sufficiently stringent tariff policies in achieving substantial reductions in global gas flaring.

Gases doi: 10.3390/gases5020009

Authors: Xuejia Du Shihui Gao Gang Yang

Hydrogen is increasingly recognized as a key contributor to a low-carbon energy future, and machine learning (ML) is emerging as a valuable tool to optimize hydrogen production processes. This review presents a comprehensive analysis of ML applications across various hydrogen production pathways, including gray, blue, and green hydrogen, with additional insights into pink, turquoise, white, and black/brown hydrogen. A total of 51 peer-reviewed studies published between 2012 and 2025 were systematically reviewed. Among these, green hydrogen—particularly via water electrolysis and biomass gasification—received the most attention, reflecting its central role in decarbonization strategies. ML algorithms such as artificial neural networks (ANNs), random forest (RF), and gradient boosting regression (GBR) have been widely applied to predict hydrogen yield, optimize operational conditions, reduce emissions, and improve process efficiency. Despite promising results, real-world deployment remains limited due to data sparsity, model integration challenges, and economic barriers. Nonetheless, this review identifies significant opportunities for ML to accelerate innovation across the hydrogen value chain. By highlighting trends, key methodologies, and current gaps, this study offers strategic guidance for future research and development in intelligent hydrogen systems aimed at achieving sustainable and cost-effective energy solutions.

Gases doi: 10.3390/gases5020008

Authors: We Lin Chan Ivan C. K. Tam Arun Dev

The LNG maritime industry started to anticipate offshore LNG production in tandem with increasing demand for FLNG platforms as offshore gas resources were developed further. The rapid expansion of FLNG deployment demands equipment and procedures that handle challenges associated with weight and space constraints. The chemical composition of LNG will result in slightly fewer CO2 emissions. While not significant, another crucial aspect is that LNG predominantly comprises methane, which is acknowledged as a greenhouse gas and is more harmful than CO2. This requires investigation into clean energy fuel supply for power generation systems, carbon emissions from the process, and thermodynamic analysis and optimisation. Focus on supplying fuel for FLNG power generation to reduce the essential management of boil-off fuel gas, which can be researched on the direct reforming method of hydrogen as a marine fuel gas to support the power generation system. The principal reason for choosing hydrogen over other energy sources is its exceptional energy-to-mass ratio (H/C ratio). The most effective method for hydrogen production is the methane reforming process, recognised for generating significant quantities of hydrogen. To optimise the small-scale plant with a carbon capture system (CCS) as integrated into the reforming process to produce blue hydrogen fuel with zero carbon emissions, this research selection focuses on two alternative processes: steam methane reforming (SMR) and autothermal reforming (ATR). Furthermore, the research article will contribute to other floating production platforms, such as FPSOs and FSRUs, and will be committed to clean energy policies that mandate the support of green alternatives in substitution of hydrocarbon fuel utilisation.

Gases doi: 10.3390/gases5020007

Authors: Adriaan M. H. van der Veen Kjetil Folgerø Federica Gugole

The total quantity and energy delivered through a gas grid is calculated using simple formulæ that sum the increments measured at regular time intervals. These calculations are described in international standards (e.g., ISO 15112 and EN 1776) and guidelines (e.g., OIML R140). These guidelines recommend that the associated measurement uncertainty is evaluated assuming the measurement results to be mutually independent. This assumption leads to the underestimation of the measurement uncertainty. To address the growing concern among transmission and distribution system operators, the underlying assumptions of these uncertainty evaluations are revisited and reworked to be more adequate. The dependence of measurement results coming from, e.g., the same flow meter and gas chromatograph will be assessed for correlations, as well as other effects, such as the effect of the chosen mathematical approximation of the totalisation integral and fluctuations in the flow rate and gas quality. In this paper, an outline is given for improvements that can be implemented in the measurement models to render them more responsive to the error structure of the measurement data, temporal effects in these data, and the fluctuations in the gas quality and gas quantity. By impact assessment using a simple scenario involving the injection of (renewable) hydrogen into a natural gas grid, it is shown that these improvements lead to a substantive difference. This preliminary work demonstrates that correlations occur both in the instrumental measurement uncertainty and due to temporal effects in the gas grid. To obtain a fit-for-purpose uncertainty budget for custody transfer and grid balancing, it is key to enhance the current models and standards accordingly.

Gases doi: 10.3390/gases5010006

Authors: Cagri Un

This study assesses the potential for biogas production from wastewater treatment plants (WWTPs) in Adana, Türkiye, and evaluates the feasibility of transitioning a fleet of 83 municipal buses (ranging from 15 to 24 years old) to operate exclusively on biogas generated from these WWTPs. Biogas production data from three distinct WWTPs in Adana were analyzed, revealing a total annual biogas production of 5,394,346 Nm3. Replacing the diesel fleet with biogas-powered buses was found to yield a significant reduction in environmental impacts. CO2 emissions were reduced by 84%, particulate matter emissions decreased by 84.4%, and nitrogen oxides (NOX) dropped by 80%. These findings highlight the substantial potential of wastewater-derived biogas as a renewable energy source in public transportation, not only reducing reliance on non-renewable fuels but also contributing to improved air quality and energy efficiency. Transitioning to biogas-powered buses presents a promising model for sustainable public transportation, with broader implications for reducing the environmental footprint of urban transit systems.

Gases doi: 10.3390/gases5010005

Authors: Francesco D’Amico Giorgia De Benedetto Luana Malacaria Salvatore Sinopoli Claudia Roberta Calidonna Daniel Gullì Ivano Ammoscato Teresa Lo Feudo

The central Mediterranean and nearby regions were affected by extreme wildfires during the summer of 2021. During the crisis, Türkiye, Greece, Italy, and other countries faced numerous challenges ranging from the near-complete destruction of landscapes to human losses. The crisis also resulted in reduced air quality levels due to increased emissions of pollutants linked to biomass-burning processes. In the Mediterranean Basin, observation sites perform continuous measurements of chemical and meteorological parameters meant to track and evaluate greenhouse gas and pollutant emissions in the area. In the case of wildfires, CO (carbon monoxide) and formaldehyde (HCHO) are effective tracers of this phenomenon, and the integration of satellite data on tropospheric column densities with surface measurements can provide additional insights on the transport of air masses originating from wildfires. At the Lamezia Terme (code: LMT) World Meteorological Organization–Global Atmosphere Watch (WMO/GAW) observation site in Calabria, Southern Italy, a new multiparameter approach combining different methodologies has been used to further evaluate the effects of the 2021 wildfires on atmospheric measurements. A previous study focused on wildfires that affected the Aspromonte Massif area in Calabria; in this study, the integration of surface data, tropospheric columns, and backtrajectories has allowed pinpointing additional contributions from other southern Italian regions, as well as North Africa and Greece. CO data were available for both surface and column assessments, while continuous HCHO data at the site were only available through satellite. In order to correlate the observed peaks with wildfires, surface BC (black carbon) was also analyzed. The analysis, which focused on July and August 2021, has allowed the definition of three case studies, each highlighting distinct sources of emission in the Mediterranean; the case studies were further evaluated using HYSPLIT backtrajectories and CAMS products. The LMT site and its peculiar local wind patterns have been demonstrated to play a significant role in the detection of wildfire outputs in the context of the Mediterranean Basin. The findings of this study further stress the importance of assessing the effects of wildfire emissions over wide areas.

Gases doi: 10.3390/gases5010004

Authors: Verónica Calva Nelson Játiva Marvin Ricaurte

The increase in atmospheric CO2 caused by human activities has driven the development of technologies to capture this gas before it reaches the atmosphere. This study analyzed CO2 sorption using amine-based solvents, such as methyldiethanolamine (MDEA), diethylenetriamine (DETA), triethanolamine (TEA), and monoethanolamine (MEA) in 40 wt.% aqueous solutions, under high-pressure conditions (initial pressure: 500 psia) and room temperature (30 °C), in both non-stirred and stirred systems. Piperazine (PZ), a heterocyclic compound, was tested as an additive to improve the kinetics of the CO2 sorption process. Kinetic and thermodynamic analyses were conducted to evaluate the efficiency of each amine-based solution in terms of reaction rate and CO2 loading capacity. MEA and TEA exhibited higher reaction rates, while DETA and MDEA were the most thermodynamically efficient due to the highest CO2 loading capacity. The PZ kinetic behavior depended on the equipment used; in the non-stirred system, no kinetic effect was observed, while in the stirred system, this effect was appreciable. Additionally, a corrosivity study revealed that MEA, a primary amine, was the most corrosive, whereas TEA, a tertiary amine, was the least corrosive.

Gases doi: 10.3390/gases5010003

Authors: Karine Arrhenius Sandra Hultmark

Biogas usually contains volatile organic compounds such as terpenes, siloxanes, halogenated hydrocarbons, ketones, alcohols, furans and esters whose presence in the biogas is highly dependent on the feedstock. These trace components can affect the integrity of the materials they come into contact with, e.g., equipment, pipelines and engines, and their presence in the gas may pose health, safety and environmental risks. Understanding the composition of gases is a prerequisite to ensure the correct function of gas infrastructure, appliances and vehicles. This study examined how volatile organic compound (VOC) content in biogas varies depending on the feedstock and evaluated the efficiency of different upgrading processes in removing VOCs. The data, primarily collected in Sweden, include biogases produced in digesters and landfills. The selection of VOCs included in this study was based on extensive analysis of samples collected from numerous biogas and biomethane industrial facilities over an extended period, providing a comprehensive overview of VOC composition. The conducted research is intended to serve as a basis for more systematic studies on the influence of process parameters and feedstock composition on the formation of VOCs. The data have multiple potential uses, including predicting which VOCs would be found in biomethane for a given feedstock and upgrading techniques. Additionally, these data can also be used in standardization discussions to assess the plausibility of the proposed limit values and the need to regulate additional compounds.

Gases doi: 10.3390/gases5010002

Authors: Maryam Shourideh Sirous Yasseri Hamid Bahai

This article investigates how safety culture impacts the safety performance of blue hydrogen projects. Blue hydrogen refers to decarbonized hydrogen, produced through natural gas reforming with carbon capture and storage (CCS) technology. It is crucial to decide on a suitable safety policy to avoid potential injuries, financial losses, and loss of public goodwill. The system dynamics approach is a suitable tool for studying the impact of factors controlling safety culture. This study examines the interactions between influencing factors and implications of various strategies using what-if analyses. The conventional risk and safety assessments fail to consider the interconnectedness between the technical system and its social envelope. After identifying the key factors influencing safety culture, a system dynamics model will be developed to evaluate the impact of those factors on the safety performance of the facility. The emphasis on safety culture is directed by the necessity to prevent major disasters that could threaten a company’s survival, as well as to prevent minor yet disruptive incidents that may occur during day-to-day operations. Enhanced focus on safety culture is essential for maintaining an organization’s long-term viability. H2-CCS is a complex socio-technical system comprising interconnected subsystems and sub-subsystems. This study focuses on the safety culture sub-subsystem, illustrating how human factors within the system contribute to the occurrence of incidents. The findings from this research study can assist in creating effective strategies to improve the sustainability of the operation. By doing so, strategies can be formulated that not only enhance the integrity and reliability of an installation, as well as its availability within the energy networks, but also contribute to earning a good reputation in the community that it serves.

Gases doi: 10.3390/gases5010001

Authors: Dung Bui Son Nguyen William Ampomah Samuel Appiah Acheampong Anthony Hama Adewale Amosu Abdul-Muaizz Koray Emmanuel Appiah Kubi

This study presents a comparative analysis of CO2-EOR and water flooding scenarios to optimize oil recovery in a geologically heterogeneous reservoir with a dome structure and partial aquifer support. Using production data from twelve production and three monitoring wells, a dynamic reservoir model was built and successfully history-matched with a 1% deviation from actual field data. Three main recovery methods were evaluated: water flooding, continuous CO2 injection, and water-alternating-gas (WAG) injection. Water flooding resulted in a four-fold increase from primary recovery, while continuous CO2 injection provided up to 40% additional oil recovery compared to water flooding. WAG injection further increased recovery by 20% following water flooding. The minimum miscibility pressure (MMP) was determined using a 1D slim-tube simulation to ensure effective CO2 performance. A sensitivity analysis on CO2/WAG ratios (1:1, 2:1, 3:1) revealed that continuous CO2 injection, particularly in high permeability zones, offered the most efficient recovery. An economic evaluation indicated that the optimal development strategy is 15 years of water flooding followed by 15 years of continuous CO2 injection, resulting in a net present value (NPV) of USD 1 billion. This study highlights the benefits of CO2-EOR for maximizing oil recovery and suggests further work on hybrid EOR techniques and carbon sequestration in depleted reservoirs.

Gases doi: 10.3390/gases4040024

Authors: Guihe Li Jia Yao

Excessive emissions of greenhouse gases, primarily carbon dioxide (CO2), have garnered worldwide attention due to their significant environmental impacts. Carbon capture, utilization, and storage (CCUS) techniques have emerged as effective solutions to address CO2 emissions. Recently, direct air capture (DAC) and bioenergy with carbon capture and storage (BECCS) have been advanced within the CCUS framework as negative emission technologies. BECCS, which involves cultivating biomass for energy production, then capturing and storing the resultant CO2 emissions, offers cost advantages over DAC. Algae-based CCUS is integral to the BECCS framework, leveraging algae’s biological processes to capture and sequester CO2 while simultaneously contributing to energy production and potentially achieving net negative carbon emissions. Algae’s high photosynthetic efficiency, rapid growth rates, and ability to grow in non-arable environments provide significant advantages over other BECCS methods. This comprehensive review explores recent innovations in algae-based CCUS technologies, focusing on the mechanisms of carbon capture, utilization, and storage through algae. It highlights advancements in algae cultivation for efficient carbon capture, algae-based biofuel production, and algae-based dual carbon storage materials, as well as key challenges that need to be addressed for further optimization. This review provides valuable insights into the potential of algae-based CCUS as a key component of global carbon reduction strategies.

Gases doi: 10.3390/gases4040023

Authors: Matthieu Vierling Maher Aboujaib Richard Denolle Jean-François Brilhac Michel Molière

This article reports on field tests devoted to the emissions of particles from gas turbines (GT) and more particularly to the formation of soot and its suppression by fuel additives. These field tests involved four heavy-duty gas turbines used as power generators and equipped with air atomization systems. These machines were running on natural gas, No. 2 distillate oil, heavy crude oil and heavy fuel oil, respectively. The GT running on natural gas produced no soot or ash and its upstream air filtration system in fact allowed lower concentrations of exhaust particles than those found in ambient air. Soot emitted when burning the three liquid fuels (No. 2 distillate; heavy crude oil; and heavy oil) was effectively reduced using fuel additives based on iron(III), cerium(III) and cerium(IV). Cerium was found to be very effective as a soot suppressant and gave rise to two surprising effects: cerium(III) performed better than cerium(IV) and a “memory effect” was observed in the presence of heat recovery boilers due to the deposition of active cerium species. All of the reported results, both regarding natural gas emissions and soot reduction, are original. A review of the soot formation mechanisms and a detailed interpretation of the test results are provided.

Gases doi: 10.3390/gases4040022

Authors: Manoela Dutra Canova Marcos Vitor Barbosa Machado Marcio da Silveira Carvalho

Hydrocarbon fields that contain non-associated gas, such as gas condensate, are highly valuable in terms of production. They yield significant amounts of condensate alongside the gas, but their unique behavior presents challenges. These reservoirs experience constant changes in composition and phases during production, which can lead to condensate blockage near wells. This blockage forms condensate bridges that hinder flow and potentially decrease gas production. To address these challenges, engineers rely on numerical simulation as a crucial tool to determine the most effective project management strategy for producing these reservoirs. In particular, relative permeability curves are used in these simulations to represent the physical phenomenon of interest. However, the representativeness of these curves in industry laboratory tests has limitations. To obtain more accurate inputs, simulations at the pore network level are performed. These simulations incorporate models that consider alterations in interfacial tension and flow velocity throughout the reservoir. The validation process involves reproducing a pore network flow simulation as close as possible to a commercial finite difference simulation. A scale-up methodology is then proposed, utilizing an optimization process to ensure fidelity to the original relative permeability curve at a microporous scale. This curve is obtained by simulating the condensation process in the reservoir phenomenologically, using a model that captures the dependence on velocity. To evaluate the effectiveness of the proposed methodology, three relative permeability curves are compared based on field-scale productivities and the evolution of condensate saturation near the wells. The results demonstrate that the methodology accurately captures the influence of condensation on well productivity compared to the relative permeability curve generated from laboratory tests, which assumes greater condensate mobility. This highlights the importance of incorporating more realistic inputs into numerical simulations to improve decision-making in project management strategies for reservoir development.

Gases doi: 10.3390/gases4040021

Authors: Hossein Asgharian Ali Yahyaee Chungen Yin Vincenzo Liso Mads Pagh Nielsen Florin Iov

Many governments around the world have taken action to utilise carbon capture (CC) technologies to reduce CO2 emissions. This technology is particularly important to reduce unavoidable emissions from industries like cement plants, oil refineries, etc. The available literature in the public domain explores this theme from two distinct perspectives. The first category of papers focuses only on modelling the CC plants by investigating the details of the processes to separate CO2 from other gas components without considering the industrial applications and synergies between sectors. On the other hand, the second category investigates the required infrastructure that must be put in place to allow a suitable integration without considering the specific particularities of each carbon capture technology. This review gives a comprehensive guideline for the implementation of CC technologies for any given application while also considering the coupling between different energy sectors such as heating, power generation, etc. It also identifies the research gaps within this field, based on the existing literature. Moreover, it delves into various aspects and characteristics of these technologies, while comparing their energy penalties with the minimum work required for CO2 separation. Additionally, this review investigates the main industrial sectors with CC potential, the necessary transportation infrastructure from the point sources to the end users, and the needs and characteristics of storage facilities, as well as the utilisation of CO2 as a feedstock. Finally, an overview of the computation tools for CC processes and guidelines for their utilisation is given. The guidelines presented in this paper are the first attempt to provide a comprehensive overview of the technologies, and their requirements, needed to achieve the cross-sector coupling of CC plants for a wide range of applications. It is strongly believed that these guidelines will benefit all stakeholders in the value chain while enabling an accelerated deployment of these technologies.

Gases doi: 10.3390/gases4040020

Authors: Victor Leonardo Acevedo Blanco Waldyr Luiz Ribeiro Gallo

This work presents a diagnosis of greenhouse gas (GHG) emissions for floating production storage and offloading (FPSO) platforms for oil and gas production offshore, using calculation methodologies from the American Petroleum Institute (API) and U.S. Environmental Protection Agency (EPA). To carry out this analysis, design data of an FPSO platform is used for the GHG emissions estimation, considering operations under steady conditions and oil and gas processing system simulations in the Aspen HYSYS® software. The main direct emission sources of GHG are identified, including the main combustion processes (gas turbines for electric generation and gas turbine-driven CO2 compressors), flaring and venting, as well as fugitive emissions. The study assesses a high CO2 content in molar composition of the associated gas, an important factor that is considered in estimating fugitive emissions during the processes of primary separation and main gas compression. The resulting information indicates that, on average, 95% of total emissions are produced by combustion sources. In the latest production stages of the oil and gas field, it consumes 2 times more energy and emits 2.3 times CO2 in terms of produced hydrocarbons. This diagnosis provides a baseline and starting point for the implementation of energy efficiency measures and/or carbon capture and storage (CCS) technologies on the FPSO in order to reduce CO2 and CH4 emissions, as well as identify the major sources of emissions in the production process.

Gases doi: 10.3390/gases4040019

Authors: Megghi Pengili Slawomir Raszewski

At the Group of Seven (G7) summit held on 13–15 June in 2024, the Group’s leaders committed to establishing a collective cyber security framework and reinforcing the work of the cyber security working group to manage the risks targeting energy systems. Likewise, oil and electricity, and natural gas rely on complex and interdependent technologies and communication networks from production to consumption. The preparedness to handle cyber security threats in the energy infrastructures among decision makers, planners, and the industry in a concerted manner signifies that cyber security is becoming more appreciated. Therefore, considering the ambition and achievement of the G7 countries towards energy and cyber sovereignty, this paper’s focus and research question aims to explore the potential existence of the cyber governance alliance in the gas subsector within the G7. The objective of this paper is twofold. First, it explores the potential of the G7, the world’s seven largest advanced economies, to lead on a nascent cyber governance for risk management in the gas sector. The qualitative analysis conducted through the institutional analysis and design method examines up-to-date data involving mainly state actors. Second, by drawing on LNG, one of the world’s fastest growing energy types in the coming decades, the paper points out the need for further research on the transnational governance operating through public–private engagement to address the cyber risks to gas systems. While the paper makes an empirical contribution to the field of security governance and a practical contribution to security consulting, its limitations rely on the necessity to also conduct a quantitative enquiry, which would necessitate, among others, a review of the literature in the G7 countries, and a group of researchers from academia and practitioners to obtain a sense of the cyberspace in the energy reality.

Gases doi: 10.3390/gases4030018

Authors: Denise Matos João Gabriel Lassio Katia Cristina Garcia Igor Raupp Alexandre Mollica Medeiros Juliano Lucas Souza Abreu

Since retrofitting existing natural gas-fired (NGF) power plants is an essential strategy for enhancing their efficiency and controlling greenhouse gas emissions, this paper compares the carbon footprint of natural gas-fired power generation from an NGF power plant in Brazil (BR-NGF) with and without retrofitting. The former scenario entails retrofitting the BR-NGF power plant with combined-cycle gas turbine (CCGT) technology. In contrast, the latter involves continuing the BR-NGF power plant operation with open-cycle gas turbine (OCGT) technology. Our analysis considers the BR-NGF power plant’s life cycle (construction, operation, and decommissioning) and the natural gas’ life cycle (natural gas extraction and processing, liquefaction, liquefied natural gas transportation, regasification, and combustion). Moreover, it is based on data from primary and secondary sources, mainly the Ecoinvent database and the ReCiPe 2016 method. For OCGT, the results showed that the BR-NGF power plant and the natural gas life cycles are responsible for 620.87 gCO2eq./kWh and 178.58 gCO2eq./kWh, respectively. For CCGT, these values are 450.04 gCO2eq./kWh and 129.30 gCO2eq./kWh. Our findings highlight the relevance of the natural gas’ life cycle, signaling additional opportunities for reducing the overall carbon footprint of natural gas-fired power generation.

Gases doi: 10.3390/gases4030017

Authors: Charise Cutajar Tonio Sant Luke Jurgen Briffa

This paper investigates the operating benefits and limitations of utilizing carbon dioxide in hydro-pneumatic energy storage systems, a form of compressed gas energy storage technology, when the systems are deployed offshore. Allowing the carbon dioxide to transition into a two-phase fluid will improve the storage density for long-duration energy storage. A preliminary comparative study between an air-based and a carbon dioxide-based subsea hydro-pneumatic energy storage system is first presented. The analysis is based on thermodynamic calculations assuming ideal isothermal conditions to quantify the potential augmentation in energy storage capacity for a given volume of pressure containment when operating with carbon dioxide in lieu of air. This is followed by a transient thermal analysis of the carbon dioxide-based hydro-pneumatic energy storage system, taking into account the real scenario of a finite thermal resistance for heat exchange between the gas and the surrounding seawater. Results from numerical modelling revealed that the energy storage capacity of a carbon dioxide-based subsea hydro-pneumatic energy storage system operating under ideal isothermal conditions can be theoretically increased by a factor of 2.17 compared to an identical air-based solution. The numerical modelling revealed that, under real conditions under which transient effects resulting from a finite thermal resistance are accounted for, the achievable factor is lower, depending on the charging and discharging time, the initial temperature, and whether a polyethene liner for corrosion prevention is considered or not.

Gases doi: 10.3390/gases4030016

Authors: Mohammad Gheibi Reza Moezzi

This paper presents an analysis of NO2 emissions in Mashhad City utilizing statistical evaluations and the Cisco Network Model. The present study begins by evaluating NO2 emissions through statistical analysis, followed by the application of histograms and radar statistical appraisals. Subsequently, a model execution logic is developed using the Cisco Network Model to further understand the distribution and sources of NO2 emissions in the city. Additionally, the research incorporates managerial insights by employing Petri Net modeling, which enables a deeper understanding of the dynamic interactions within the air quality management system. This approach aids in identifying critical control points and optimizing response strategies, thus enhancing the overall effectiveness of urban air pollution mitigation efforts. The findings of this study provide valuable insights into the levels of NO2 pollution in Mashhad City and offer a structured approach to modeling NO2 emissions for effective air quality management strategies which can be extended to the other megacities as well.

Gases doi: 10.3390/gases4030015

Authors: João Gabriel Souza Debossam Mayksoel Medeiros de Freitas Grazione de Souza Helio Pedro Amaral Souto Adolfo Puime Pires

In this work, we analyze non-Darcy two-component single-phase isothermal flow in naturally fractured tight gas reservoirs. The model is applied in a scenario of enhanced gas recovery (EGR) with the possibility of carbon dioxide storage. The properties of the gases are obtained via the Peng–Robinson equation of state. The finite volume method is used to solve the governing partial differential equations. This process leads to two subsystems of algebraic equations, which, after linearization and use of an operator splitting method, are solved by the conjugate gradient (CG) and biconjugate gradient stabilized (BiCGSTAB) methods for determining the pressure and fraction molar, respectively. We include inertial effects using the Barree and Conway model and gas slippage via a more recent model than Klinkenberg’s, and we use a simplified model for the effects of effective stress. We also utilize a mesh refinement technique to represent the discrete fractures. Finally, several simulations show the influence of inertial, slippage and stress effects on production in fractured tight gas reservoirs.

Gases doi: 10.3390/gases4030014

Authors: Stuart N. Riddick Mercy Mbua Abhinav Anand Elijah Kiplimo Arthur Santos Aashish Upreti Daniel J. Zimmerle

Methane is a powerful greenhouse gas with a 25 times higher 100-year warming potential than carbon dioxide and is a target for mitigation to achieve climate goals. To control and curb methane emissions, estimates are required from the sources and sectors which are typically generated using bottom-up methods. However, recent studies have shown that national and international bottom-up approaches can significantly underestimate emissions. In this study, we present three bottom-up approaches used to estimate methane emissions from all emission sectors in the Denver-Julesburg basin, CO, USA. Our data show emissions generated from all three methods are lower than historic measurements. A Tier 1/2 approach using IPCC emission factors estimated 2022 methane emissions of 358 Gg (0.8% of produced methane lost by the energy sector), while a Tier 3 EPA-based approach estimated emissions of 269 Gg (0.2%). Using emission factors informed by contemporary and region-specific measurement studies, emissions of 212 Gg (0.2%) were calculated. The largest difference in emissions estimates were a result of using the Mechanistic Air Emissions Simulator (MAES) for the production and transport of oil and gas in the DJ basin. The MAES accounts for changes to regulatory practice in the DJ basin, which include comprehensive requirements for compressors, pneumatics, equipment leaks, and fugitive emissions, which were implemented to reduce emissions starting in 2014. The measurement revealed that normalized gas loss is predicted to have been reduced by a factor of 20 when compared to 10-year-old normalization loss measurements and a factor of 10 less than a nearby oil and production area (Delaware basin, TX); however, we suggest that more measurements should be made to ensure that the long-tail emission distribution has been captured by the modeling. This study suggests that regulations implemented by the Colorado Department of Public Health and Environment could have reduced emissions by a factor of 20, but contemporary regional measurements should be made to ensure these bottom-up calculations are realistic.

Gases doi: 10.3390/gases4030013

Authors: Haoying Wang Ning Lin Mariam Arzumanyan

As carbon capture and storage (CCS) technologies mature, the concept of a low-carbon or net-zero-carbon economy becomes more and more feasible. While many chemical and energy products do not contain carbon in their compounds, the upstream production process does. An added CCS module allows the removal of carbon emissions from the production process, which expands the value chain. This paper focuses on one of such commodities—low-carbon-intensity ammonia (LCIA). Even though ammonia is carbon-free in its final product, it is commonly made from natural gas, and the production process could generate significant carbon emissions. The idea of LCIA is to reduce the carbon footprint of the ammonia production process (e.g., blue ammonia) or eliminate carbon from the production process (e.g., green ammonia via electrolysis) so that the entire supply chain is decarbonized. The goal of this paper is two-fold. We first explore the US domestic market and the international market for LCIA. We then discuss relevant federal and local policies that could help grow markets for LCIA. The agricultural sector will be the center of the discussion, which consumes an estimated 70–90% of the global ammonia supply as fertilizers. The paper also examines other potential uses of LCIA, such as alternative fuels for decarbonizing agricultural machinery and transportation sectors. Finally, we argue that developing a comprehensive LCIA value chain, supported by dedicated policy measures and broad stakeholder engagement, is critical for materializing the potential of LCIA in contributing to a climate-resilient and sustainable economy.

Gases doi: 10.3390/gases4030012

Authors: Yolanda Mapantsela Patrick Mukumba KeChrist Obileke Ndanduleni Lethole

To reduce and convert biodegradable waste into energy-rich biogas, anaerobic digestion technology is usually employed. Hence, this takes place inside the biogas digester. Studies have revealed that these digesters are designed and constructed using bricks, cement, and metal; often require a large footprint; and are bulky and expensive. The innovation of portable biogas digesters has come into the market to address these challenges. This present review provides an overview of the in-depth and comprehensive information on portable biogas digesters in the literature. Areas covered in the review include the modification of the biogas digester design, the need for a portable biogas digester, recent studies on the factors affecting the performance of portable biogas digesters, and specific assumptions taken into consideration for designing any portable biogas digester. Convincingly, portable biogas digesters appeal to small rural families because of their ease of operation, maintenance, and ability to save space. The material for the construction and comparison of the portable biogas digester with other designs and the economic feasibility of the system were also reviewed. Implications: The full-scale design, fabrication, and utilization of a portable biogas digester are viable but not widely employed compared to other designs. However, there is a lack of readily available information on the portable design of biogas digesters. This review presents various aspects relating to portable biogas digesters and the quality of biogas produced. Therefore, the review suits audiences in energy process design and engineers, energy researchers, academics, and economists.

Gases doi: 10.3390/gases4030011

Authors: Luigi De Simio Luca Marchitto Sabato Iannaccone Vincenzo Pennino Nunzio Altieri

Phased injection of natural gas into internal combustion marine engines is a promising solution for optimizing performance and reducing harmful emissions, particularly unburned methane, a potent greenhouse gas. This innovative practice distinguishes itself from continuous injection because it allows for more precise control of the combustion process with only a slight increase in system complexity. By synchronizing the injection of natural gas with the intake and exhaust valve opening and closing times while also considering the gas path in the manifolds, methane release into the atmosphere is significantly reduced, making a substantial contribution to efforts to address climate change. Moreover, phased injection improves the efficiency of marine engines, resulting in reduced overall fuel consumption, lower fuel costs, and increased ship autonomy. This technology was tested on a single-cylinder, large-bore, four-stroke research engine designed for marine applications, operating in dual-fuel mode with diesel and natural gas. Performance was compared with that of the conventional continuous feeding method. Evaluation of the effect on equivalent CO2 emissions indicates a potential reduction of up to approximately 20%. This reduction effectively brings greenhouse gas emissions below those of the diesel baseline case, especially when injection control is combined with supercharging control to optimize the air–fuel ratio. In this context, the boost pressure in DF was reduced from 3 to 1.5 bar compared with the FD case.

Gases doi: 10.3390/gases4030010

Authors: Sascha Krysmon Johannes Claßen Marc Düzgün Stefan Pischinger

The systematic analysis of measurement data allows a large amount of information to be obtained from existing measurements in a short period of time. Especially in vehicle development, many measurements are performed, and large amounts of data are collected in the process of emission calibration. With the introduction of Real Driving Emissions Tests, the need for targeted analysis for efficient and robust calibration of a vehicle has further increased. With countless possible test scenarios, test-by-test analysis is no longer possible with the current state-of-the-art in calibration, as it takes too much time and can disregard relevant data when analyzed manually. In this article, therefore, a methodology is presented that automatically analyzes exhaust measurement data in the context of emission calibration and identifies emission-related critical sequences. For this purpose, moving analyzing windows are used, which evaluate the exhaust emissions in each sample of the measurement. The detected events are stored in tabular form and are particularly suitable for condensing the collected measurement data to a required amount for optimization purposes. It is shown how different window settings influence the amount and duration of detected events. With the example used, a total amount of 454 events can be identified from 60 measurements, reducing 184,623 s of measurements to a relevant amount of 12,823 s.

Gases doi: 10.3390/gases4030009

Authors: Tatiana Nevzorova

Climate projects can become one of the key tools for decarbonization in Russia. They have powerful potential in terms of solving the problems of reducing emissions and increasing the absorption of greenhouse gases, as well as monetization potential for businesses. Despite the geopolitical crisis and sanctions imposed on Russia, certain opportunities for implementing climate projects have remained accessible. This study aims to provide a comprehensive analysis of the current status, including the regulations and approved methodologies, prospects, and challenges for climate projects in the carbon market in Russia. It also offers an overview of international carbon market mechanisms and analyses the advantages and disadvantages of the nature-based and technological solutions of climate projects for carbon sequestration. This, in turn, can facilitate the realization of future strategies for realizing the bigger potential of Russian climate projects in the domestic and international carbon markets. This research also provides up-to-date data on the current situation of the carbon market in Russia.

Gases doi: 10.3390/gases4030008

Authors: Steven Kluge Karla Hartenauer Murat Tutuş

In a previous study, we demonstrated a change in membrane morphology and gas separation performance by varying the recipe of a casting solution based on polysulfone in a certain solvent system. Although all results were reproducible, all used solvents were harmful and not sustainable. In this study, the solvents tetrahydrofuran (THF) and N,N-dimethylacetamide (DMAc) are replaced by the more sustainable solvents 2-methyl-tetrahydrofuran (2M-THF), N-butyl pyrrolidinone (NBP) and cyclopentyl methyl ether (CPME). The gas permeation performance and, for the first time, morphology of the membranes before and after solvent replacement were determined and compared by single gas permeation measurements and SEM microscopy. It is shown that THF can be replaced by 2M-THF and NBP without decreasing the gas permeation performance. With CPME replacing THF, no membranes were formed. Systems with 2M-THF as a THF alternative showed the best gas permeation results. Permeances for the tested gases oxygen (O2), nitrogen (N2), carbon dioxide (CO2) and methane (CH4) were 5.91 × 10−2, 8.84 × 10−3, 4.00 × 10−1 and 1.00 × 10−2 GPU, respectively. Permselectivities of those membranes for the gas pairs O2/N2, CO2/N2 and CO2/CH4 were 6.7, 38.3 and 34.0, respectively. When also replacing DMAc in the solvent system, no or only porous membranes were obtained, even if the precipitation procedure was adjusted. These findings indicate that a complete replacement of the solvent system without affecting the membrane morphology or gas permeation performance is not possible. By varying the temperature of the precipitation bath, the formation of mechanically stable PSU membranes is possible only if THF is replaced by 2M-THF.

Gases doi: 10.3390/gases4020007

Authors: Sherif Fakher Abdelaziz Khlaifat Abdullah Hassanien

Carbon-capture technologies are extremely abundant, yet they have not been applied extensively worldwide due to their high cost and technological complexities. This research studies the ability of polymerized fly ash to capture carbon dioxide (CO2) under low-pressure and low-temperature conditions via physical adsorption. The research also studies the ability to desorb CO2 due to the high demand for CO2 in different industries. The adsorption–desorption hysteresis was measured using infrared-sensor detection apparatus. The impact of the CO2 injection rate for adsorption, helium injection rate for desorption, temperature, and fly ash contact surface area on the adsorption–desorption hysteresis was investigated. The results showed that change in the CO2 injection rate had little impact on the variation in the adsorption capacity; for all CO2 rate experiments, the adsorption reached more than 90% of the total available adsorption sites. Increasing the temperature caused the polymerized fly ash to expand, thus increasing the available adsorption sites, thus increasing the overall adsorption volume. At low helium rates, desorption was extremely lengthy which resulted in a delayed hysteresis response. This is not favorable since it has a negative impact on the adsorption–desorption cyclic rate. Based on the results, the polymerized fly ash proved to have a high CO2 capture capability and thus can be applied for carbon-capture applications.

Gases doi: 10.3390/gases4020006

Authors: Santiago Martinez-Boggio Pedro Teixeira Lacava Felipe Solferini de Carvalho Pedro Curto-Risso

The gasification of residues into syngas offers a versatile gaseous fuel that can be used to produce heat and power in various applications. However, the application of syngas in engines presents several challenges due to the changes in its composition. Such variations can significantly alter the optimal operational conditions of the engines that are fueled with syngas, resulting in combustion instability, high engine variability, and misfires. In this context, this work presents an experimental investigation conducted on a port-fuel injection spark-ignition optical research engine using three different syngas mixtures, with a particular focus on the effects of CO/H2 and diluent ratios. A comparative analysis is made against methane, considered as the baseline fuel. The in-cylinder pressure and related parameters are examined as indicators of combustion behavior. Additionally, 2D cycle-resolved digital visualization is employed to trace flame front propagation. Custom image processing techniques are applied to estimate flame speed, displacement, and morphological parameters. The engine runs at a constant speed (900 rpm) and with full throttle like stationary engine applications. The excess air–fuel ratios vary from 1.0 to 1.4 by adjusting the injection time and the spark timing according to the maximum brake torque of the baseline fuel. A thermodynamic analysis revealed notable trends in in-cylinder pressure traces, indicative of differences in combustion evolution and peak pressures among the syngas mixtures and methane. Moreover, the study quantified parameters such as the mass fraction burned, combustion stability (COVIMEP), and fuel conversion efficiency. The analysis provided insights into flame morphology, propagation speed, and distortion under varying conditions, shedding light on the influence of fuel composition and air dilution. Overall, the results contribute to advancing the understanding of syngas combustion behavior in SI engines and hold implications for optimizing engine performance and developing numerical models.

Gases doi: 10.3390/gases4020005

Authors: Abubakar Jibrin Abbas Salisu Kwalami Haruna Martin Burby Idoko Job John Kabir Hassan Yar’Adua

The growing importance of hydrogen as an energy carrier in a future decarbonised energy system has led to a surge in its production plans. However, the development of infrastructure for hydrogen delivery, particularly in the hard-to-abate sectors, remains a significant challenge. While constructing new pipelines entails substantial investment, repurposing existing pipelines offers a cost-effective approach to jump-starting hydrogen networks. Many European countries and, more recently, other regions are exploring the possibility of utilising their current pipeline infrastructure for hydrogen transport. Despite the recent efforts to enhance the understanding of pipeline compatibility and integrity for hydrogen transportation, including issues such as embrittlement, blend ratios, safety concerns, compressor optimisation, and corrosion in distribution networks, there has been limited or no focus on pipeline expansion options to address the low-energy density of hydrogen blends and associated costs. This study, therefore, aims to explore expansion options for existing natural gas high-pressure pipelines through additional compression or looping. It seeks to analyse the corresponding cost implications to achieve an affordable and sustainable hydrogen economy by investigating the utilisation of existing natural gas pipeline infrastructure for hydrogen transportation as a cost-saving measure. It explores two expansion strategies, namely pipeline looping (also known as pipeline reinforcement) and compression, for repurposing a segment of a 342 km × 36 inch existing pipeline, from the Escravos–Lagos gas pipeline system (ELPS) in Nigeria, for hydrogen transport. Employing the Promax® process simulator tool, the study assesses compliance with the API RP 14E and ASME B31.12 standards for hydrogen and hydrogen–methane blends. Both expansion strategies demonstrate acceptable velocity and pressure drop characteristics for hydrogen blends of up to 40%. Additionally, the increase in hydrogen content leads to heightened compression power requirements until approximately 80% hydrogen in the blends for compression and a corresponding extension in looping length until around 80% hydrogen in the blend for looping. Moreover, the compression option is more economically viable for all investigated proportions of hydrogen blends for the PS1–PS5 segment of the Escravos–Lagos gas pipeline case study. The percentage price differentials between the two expansion strategies reach as high as 495% for a 20% hydrogen proportion in the blend. This study offers valuable insights into the technical and economic implications of repurposing existing natural gas infrastructure for hydrogen transportation.

Gases doi: 10.3390/gases4020004

Authors: Alfred Rufer

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system’s adiabatic and isothermal characteristics.

Gases doi: 10.3390/gases4020003

Authors: Alessandra de Carvalho Reis Ofélia de Queiroz Fernandes Araújo José Luiz de Medeiros

Despite the growth of renewable energy, fossil fuels dominate the global energy matrix. Due to expanding proved reserves and energy demand, an increase in natural gas power generation is predicted for future decades. Oil reserves from the Brazilian offshore Pre-Salt basin have a high gas-to-oil ratio of CO2-rich associated gas. To deliver this gas to market, high-depth long-distance subsea pipelines are required, making Gas-to-Pipe costly. Since it is easier to transport electricity through long subsea distances, Gas-to-Wire instead of Gas-to-Pipe is a more convenient alternative. Aiming at making offshore Gas-to-Wire thermodynamically efficient without impacting CO2 emissions, this work explores a new concept of an environmentally friendly and thermodynamically efficient Gas-to-Wire process firing CO2-rich natural gas (CO2 > 40%mol) from high-depth offshore oil and gas fields. The proposed process prescribes a natural gas combined cycle, exhaust gas recycling (lowering flue gas flowrate and increasing flue gas CO2 content), CO2 post-combustion capture with aqueous monoethanolamine, and CO2 dehydration with triethylene glycol for enhanced oil recovery. The two main separation processes (post-combustion carbon capture and CO2 dehydration) have peculiarities that were addressed at the light shed by thermodynamic analysis. The overall process provides 534.4 MW of low-emission net power. Second law analysis shows that the thermodynamic efficiency of Gas-to-Wire with carbon capture attains 33.35%. Lost-Work analysis reveals that the natural gas combined cycle sub-system is the main power destruction sink (80.7% Lost-Work), followed by the post-combustion capture sub-system (14% Lost-Work). These units are identified as the ones that deserve to be upgraded to rapidly raise the thermodynamic efficiency of the low-emission Gas-to-Wire process.

Gases doi: 10.3390/gases4010002

Authors: Cevat Yaman

Greenhouse gases trap heat in the atmosphere, causing the Earth’s surface temperature to rise. The main greenhouse gases are carbon dioxide, methane, nitrous oxide, perfluorocarbons, hydrofluorocarbons, and sulfur hexafluoride. Human activities are increasing greenhouse gas concentrations rapidly, which is causing global climate change. Global climate change is increasing environmental and public health problems. To reduce greenhouse gas emissions, it is necessary to identify where the emissions are coming from, develop a plan to reduce them, and then implement and monitor the plan to ensure that emissions are actually reduced. Anthropogenic global climate change has large and increasingly adverse economic effects. Cities emit the most greenhouse gas due to fossil fuel burning and power usage. The four major greenhouse gas emitters are energy, transportation, waste management, and urban land use sectors. Organizations should prepare action plans to lower their greenhouse gas emissions and stop the worst consequences of climate change. These action plans require companies and local authorities to submit their greenhouse gas emissions reports on a yearly basis. A greenhouse gas emissions management system includes several processes and tools created by organizations to understand, measure, monitor, report, and validate their greenhouse gas emissions. Two of the most widely adapted frameworks for greenhouse gases inventory reporting are ISO 14064 and the greenhouse gas protocol. This review paper aims to identify some of the key points of GHG inventory preparation and mitigation strategies.

Gases doi: 10.3390/gases4010001

Authors: Subhadip Ghosh Rajarshi Majumder Bidisha Chatterjee

India, the world’s most populous country, is the world’s third-largest emitter of greenhouse gases (GHGs). Despite employing several energy sources, it still relies heavily on coal, its primary energy source. Given India’s swiftly rising energy demand, this challenges meeting emission reduction targets. In recent years, India has significantly increased investments in renewables like solar and hydrogen. While commendable, these initiatives alone cannot meet the country’s expanding energy demands. In the short term, India must rely on both domestic and imported fossil fuels, with natural gas being the most environmentally friendly option. In this context, this paper attempts to forecast energy consumption, natural gas production, and consumption in India until 2050, using both univariate and multivariate forecasting methods. For multivariate forecasting, we have assumed two alternative possibilities for GDP growth: the business-as-usual and the high-growth scenarios. Each of our forecasts indicates a notable shortfall in the projected production of natural gas compared to the expected demand, implying our results are robust. Our model predicts that nearly 30–50 percent of India’s natural gas consumption will be met by imports, mainly in the form of LNG. Based on these findings, this paper recommends that Indian government policies emphasize increasing domestic natural gas production, importing LNG, and expanding renewable energy resources.

Gases doi: 10.3390/gases3040013

Authors: Juan Sebastian Serra Leal Jimena Incer-Valverde Tatiana Morosuk

Helium is an inert gas with no color or odor [...]

Gases doi: 10.3390/gases3040012

Authors: Oleg V. Golubev Dmitry E. Tsaplin Anton L. Maximov

Global warming occurs as a result of the build-up of greenhouse gases in the atmosphere, causing an increase in Earth’s average temperature. Two major greenhouse gases (CH4 and CO2) can be simultaneously converted into value-added chemicals and fuels thereby decreasing their negative impact on the climate. In the present work, we used a plasma-catalytic approach for the conversion of methane and carbon dioxide into syngas, hydrocarbons, and oxygenates. For this purpose, CuCe zeolite-containing catalysts were prepared and characterized (low-temperature N2 adsorption, XRF, XRD, CO2-TPD, NH3-TPD, TPR). The process of carbon dioxide methane reforming was conducted in a dielectric barrier discharge under atmospheric pressure and at low temperature (under 120 °C). It was found that under the studied conditions, the major byproducts of CH4 reforming are CO, H2, and C2H6 with the additional formation of methanol and acetone. The application of a ZSM-12 based catalyst was beneficial as the CH4 conversion increased and the total concentration of liquid products was the highest, which is related to the acidic properties of the catalyst.

Gases doi: 10.3390/gases3040011

Authors: Cherng-Yuan Lin Pei-Chi Wu Hsuan Yang

The maritime industry is recognized as a major pollution source to the environment. The use of low- or zero-carbon marine alternative fuel is a promising measure to reduce emissions of greenhouse gases and toxic pollutants, leading to net-zero carbon emissions by 2050. Hydrogen (H2), fuel cells particularly proton exchange membrane fuel cell (PEMFC), and ammonia (NH3) are screened out to be the feasible marine gaseous alternative fuels. Green hydrogen can reduce the highest carbon emission, which might amount to 100% among those 5 types of hydrogen. The main hurdles to the development of H2 as a marine alternative fuel include its robust and energy-consuming cryogenic storage system, highly explosive characteristics, economic transportation issues, etc. It is anticipated that fossil fuel used for 35% of vehicles such as marine vessels, automobiles, or airplanes will be replaced with hydrogen fuel in Europe by 2040. Combustible NH3 can be either burned directly or blended with H2 or CH4 to form fuel mixtures. In addition, ammonia is an excellent H2 carrier to facilitate its production, storage, transportation, and usage. The replacement of promising alternative fuels can move the marine industry toward decarbonization emissions by 2050.

Gases doi: 10.3390/gases3040010

Authors: Cheolwoong Park Yonghun Jang Seonyeob Kim Yongrae Kim Young Choi

Because ammonia is easier to store and transport over long distances than hydrogen, it is a promising research direction as a potential carrier for hydrogen. However, its low ignition and combustion rates pose challenges for running conventional ignition engines solely on ammonia fuel over the entire operational range. In this study, we attempted to identify a stable engine combustion zone using a high-pressure direct injection of ammonia fuel into a 2.5 L spark ignition engine and examined the potential for extending the operational range by adding hydrogen. As it is difficult to secure combustion stability in a low-temperature atmosphere, the experiment was conducted in a sufficiently-warmed atmosphere (90 ± 2.5 °C), and the combustion, emission, and efficiency results under each operating condition were experimentally compared. At 1500 rpm, the addition of 10% hydrogen resulted in a notable 20.26% surge in the maximum torque, reaching 263.5 Nm, in contrast with the case where only ammonia fuel was used. Furthermore, combustion stability was ensured at a torque of 140 Nm by reducing the fuel and air flow rates.

Gases doi: 10.3390/gases3040009

Authors: Danial Qadir Humbul Suleman Faizan Ahmad

Polymer blending has attracted considerable attention because of its ability to overcome the permeability–selectivity trade-off in gas separation applications. In this study, polysulfone (PSU)-modified cellulose acetate (CA) membranes were prepared using N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF) using a dry–wet phase inversion technique. The membranes were characterized using scanning electron microscopy (SEM) for morphological analysis, thermogravimetric analysis (TGA) for thermal stability, and Fourier transform infrared spectroscopy (FTIR) to identify the chemical changes on the surface of the membranes. Our analyses confirmed that the mixing method (the route chosen for preparing the casting solution for the blended membranes) significantly influences the morphological and thermal properties of the resultant membranes. The blended membranes exhibited a transition from a finger-like pore structure to a dense substructure in the presence of macrovoids. Similarly, thermal analysis confirmed the improved residual weight (up to 7%) and higher onset degradation temperature (up to 10 °C) of the synthesized membranes. Finally, spectral analysis confirmed that the blending of both polymers was physical only.

Gases doi: 10.3390/gases3030008

Authors: Olga V. Solovtsova Ilya E. Men’shchikov Andrey V. Shkolin Alexander E. Grinchenko Elena V. Khozina Anatoly A. Fomkin

Nutshells are regarded as cost-effective and abundant raw materials for producing activated carbons (ACs) for CO2 capture, storage, and utilization. The effects of carbonization temperature and thermochemical KOH activation conditions on the porous structure as a BET surface, micropore volume, micropore width, and pore size distribution of ACs prepared from walnut (WNS) and hazelnut (HNS) shells were investigated. As a result, one-step carbonization at 900/800 °C and thermochemical KOH activation with a char/KOH mass ratio of 1:2/1:3 were found to be optimal for preparing ACs from WNS/HNS: WNS-AC-3 and HNS-AC-2, respectively. The textural properties of the WNS/HNS chars and ACs were characterized by low-temperature nitrogen vapor adsorption, XRD, and SEM methods. Dubinin’s theory of volume filling of micropores was used to evaluate the microporosity parameters and to calculate the CO2 adsorption equilibrium over the sub- and supercritical temperatures from 216.4 to 393 K at a pressure up to 10 MPa. The CO2 capture capacities of WNS- and HNS-derived adsorbents reached 5.9/4.1 and 5.4/3.9 mmol/g at 273/293 K under 0.1 MPa pressure, respectively. A discrepancy between the total and delivery volumetric adsorption capacities of the adsorbents was attributed to the strong binding of CO2 molecules with the adsorption sites, which were mainly narrow micropores with a high adsorption potential. The high initial differential heats of CO2 adsorption onto ACs of ~32 kJ/mol confirmed this proposal. The behaviors of thermodynamic functions (enthalpy and entropy) of the adsorption systems were attributed to changes in the state of adsorbed CO2 molecules determined by a balance between attractive and repulsive CO2–CO2 and CO2–AC interactions during the adsorption process. Thus, the chosen route for preparing ACs from the nutshells made it possible to prepare efficient carbon adsorbents with a relatively high CO2 adsorption performance due to a substantial volume of micropores with a size in the range of 0.6–0.7 nm.

Gases doi: 10.3390/gases3030007

Authors: Stefan H. Spitzer Gerald Riesner Sabine Zakel Carola Schierding

Safety characteristics are used to keep processes, including flammable gases, vapors, and combustible dusts, safe. In the standards for the determination of safety characteristics of gases and vapors, the induction spark is commonly used. However, classic transformers are hard to obtain, and replacement with new electronic transformers is not explicitly allowed in the standards. This article presents the investigation of five gases that are normally used to calibrate devices for the determination of safety characteristics, the maximum experimental safe gap (MESG), with an electronic transformer, and the values are compared to the ones that are obtained with the standard transformer. Additionally, calorimetric measurements on the net energy of both ignition sources were performed as well as open-circuit voltage measurements. It is concluded that the classic type of transformer can be replaced by the new type obtaining the same results for the MESG and introducing the same amount of energy into the system.

Gases doi: 10.3390/gases3030006

Authors: Ahmad Naquash Amjad Riaz Fatma Yehia Yus Donald Chaniago Hankwon Lim Moonyong Lee

Hydrogen (H2) is known for its clean energy characteristics. Its separation and purification to produce high-purity H2 is becoming essential to promoting a H2 economy. There are several technologies, such as pressure swing adsorption, membrane, and cryogenic, which can be adopted to produce high-purity H2; however, each standalone technology has its own pros and cons. Unlike standalone technology, the integration of technologies has shown significant potential for achieving high purity with a high recovery. In this study, a membrane–cryogenic process was integrated to separate H2 via the desublimation of carbon dioxide. The proposed process was designed, simulated, and optimized in Aspen Hysys. The results showed that the H2 was separated with a 99.99% purity. The energy analysis revealed a net-specific energy consumption of 2.37 kWh/kg. The exergy analysis showed that the membranes and multi-stream heat exchangers were major contributors to the exergy destruction. Furthermore, the calculated total capital investment of the proposed process was 816.2 m$. This proposed process could be beneficial for the development of a H2 economy.

Gases doi: 10.3390/gases3020005

Authors: Salman Qadir Muhammad Ahsan Arshad Hussain

The membrane gas separation process has gained significant attention using the computational fluid dynamics (CFD) technique. This study considered the CFD method to find gas concentration profiles in a hollow fiber membrane (HFM) module to separate the binary gas mixture. The membrane was considered with a fiber thickness where each component’s mass fluxes could be obtained based on the local partial pressures, solubility, diffusion, and the membrane’s selectivity. COMSOL Multiphysics was used to solve the numerical solution at corresponding operating conditions and results were compared to experimental data. The two different mixtures, CO2/CH4 and N2/O2, were investigated to obtain concentration gradient and mass flux profiles of CO2 and O2 species in an axial direction. This study allows assessing the feed pressure’s impact on the HFM system’s overall performance. These results demonstrate that the increment in feed pressures decreased the membrane system’s separation performance. The impact of hollow fiber length indicates that increasing the active fiber length has a higher effective mass transfer region but dilutes the permeate-side purities of O2 (46% to 28%) and CO2 (93% to 73%). The results show that increasing inlet pressure and a higher concentration gradient resulted in higher flux through the membrane.

Gases doi: 10.3390/gases3020004

Authors: Harshita Singh Pallavi Singh Shashi Bhushan Agrawal Madhoolika Agrawal

Plant responses to air pollution have been extensively studied in urban environments. Nevertheless, detailed and holistic studies assessing their retaliation to air contaminants are still limited. The present study evaluates the effect of criteria pollutants (SO2, NO2, PM10 and O3) on the overall biochemistry and resource allocation strategy of plants in order to categorize the dominant roadside species (Mangifera indica, Psidium guajava, Ficus religiosa, Azadirachta indica, Dalbergia sissoo, Cascabela thevetia and Bougainvillea spectabilis) of the Indo-Gangetic Plains (IGP), with different morphologies and habits, into species that are tolerant and sensitive to the prevailing air pollutants. This study was performed at three different land-use sites (industrial, commercial and reference) in Varanasi for two seasons (summer and winter). It was inferred that NO2 and PM10 consistently violated the air quality standards at all the sites. The fifteen assessed parameters reflected significant variations depending upon the site, season and plant species whereupon the enzymatic antioxidants (superoxide dismutase and catalase) and resource utilization parameters (leaf area and leaf dry matter content) were remarkably affected. Based on the studied parameters, it was entrenched that deciduous tree species with compound leaves (D. sissoo > A. indica) were identified as the less sensitive, followed by a shrub (C. thevetia > B. spectabilis), while evergreen species with simple leaves were the most sensitive. It was also substantiated that the morphology of the foliage contributed more toward the differential response of the plants to air pollutants than its habit.

Gases doi: 10.3390/gases3010003

Authors: Konstantina Akamati George P. Laliotis Iosif Bizelis

The poultry sector is considered to be one of the most industrialized sectors of livestock production. Although the livestock sector contributes the 14.5% of total anthropogenic greenhouse gas (GHG) emissions, less attention has been paid in the respective emissions of the poultry sector compared to other farmed animals such as ruminants. The aim of the study was to estimate the carbon footprint of the poultry sector (layers, broilers, and backyards) in the Greek territory during the last 60 years as a means of exploring further mitigation strategies. Tier 2 methodology was used to estimate GHG emissions. Different mitigation scenarios related to changes in herd population, feeds, and manure management were examined. GHG emissions showed an increased trend over time. The different scenarios explored showed moderate to high mitigating potential depending on the parameters that were changed. Changes in manure management or diet revealed to have a higher potential to eliminate GHG emissions. Changes in population numbers showed a low mitigating potential. However, if mortality could be improved within industrialized farming systems, then it could be an indirect increase in product quantities with a slight increase in emissions. Therefore, depending on national priorities, the sector could improve its environmental impact by targeting aspects related to husbandry/management practices.

Gases doi: 10.3390/gases3010002

Authors: Jose M. Marín Arcos Diogo M. F. Santos

Hydrogen has become the most promising energy carrier for the future. The spotlight is now on green hydrogen, produced with water electrolysis powered exclusively by renewable energy sources. However, several other technologies and sources are available or under development to satisfy the current and future hydrogen demand. In fact, hydrogen production involves different resources and energy loads, depending on the production method used. Therefore, the industry has tried to set a classification code for this energy carrier. This is done by using colors that reflect the hydrogen production method, the resources consumed to produce the required energy, and the number of emissions generated during the process. Depending on the reviewed literature, some colors have slightly different definitions, thus making the classifications imprecise. Therefore, this techno-economic analysis clarifies the meaning of each hydrogen color by systematically reviewing their production methods, consumed energy sources, and generated emissions. Then, an economic assessment compares the costs of the various hydrogen colors and examines the most feasible ones and their potential evolution. The scientific community and industry’s clear understanding of the advantages and drawbacks of each element of the hydrogen color spectrum is an essential step toward reaching a sustainable hydrogen economy.

Gases doi: 10.3390/gases3010001

Authors: Robin Abu Kumar Patchigolla Nigel Simms

Natural gas flaring, with its harmful environmental, health, and economic effects, is common in the Nigerian oil and gas industry because of a lower tax regime for flared gases. Based on the adverse effects of flared gas, the Nigerian government has renewed and improved its efforts to reduce or eliminate gas flaring through the application of natural gas utilisation techniques. However, because the conventional approach to flare gas utilisation is heavily reliant on achieving scale, fuel, and end-product prices, not all technologies are technically and economically viable for typically capturing large and small quantities of associated gas from various flare sites or gas fields (located offshore or onshore). For these reasons, this paper reviews and compares various flare gas utilisation options to guide their proper selection for appropriate implementation in the eradication of routine gas flaring in Nigeria and to promote the Zero Routine Flaring initiative, which aims to reduce flaring levels dramatically by 2030. A qualitative assessment is used in this study to contrast the various flare gas utilisation options against key decision drivers. In this analysis, three natural gas utilisation processes—liquefied natural gas (LNG), gas to wire (GTW), and gas to methanol (GTM)—are recommended as options for Nigeria because of their economic significance, technological viability (both onshore and offshore), and environmental benefits. All these gas utilisation options have the potential to significantly reduce and prevent routine gas flaring in Nigeria and can be used separately or in combination to create synergies that could lower project costs and product market risk. This article clearly identifies the environmental benefits and the technical and economic viability of infrastructure investments to recover and repurpose flare gasses along with recommendation steps to select and optimise economies of scale for an associated natural gas utilisation option.

Gases doi: 10.3390/gases2040009

Authors: Alexander Khimenkov Julia Stanilovskaya

The relevance of studying explosive processes in permafrost lies in the prospect of gas production from small gas-saturated zones in the subsurface; the influx of significant amounts of greenhouse gases from frozen soils creates a threat to infrastructure. The purpose of this article is to reveal the general patterns of frozen soils’ transformation in local zones of natural explosions. The greatest volume of information about the processes preceding the formation of gas-emission craters can be obtained by studying the deformations of the cryogenic structure of soil. The typification of the elements of the cryogenic structures of frozen soils that form the walls of various gas-emission craters was carried out. Structural and morphological analyses were used as a methodological basis for studying gas-emission craters. This method involves a set of operations that establishes links between the cryogenic structure of the crater walls and the morphologies of their surfaces. In this study, it is concluded that gas-emission craters are the result of the self-development of local gas-dynamic geosystems that are in a non-equilibrium thermodynamic state with respect to the enclosing permafrost.

Gases doi: 10.3390/gases2040008

Authors: Tomasz Chrulski

The coronavirus pandemic caused a crisis in industrial economies, enforcing public concern. The first case of the infection in Europe occurred in Italy. Nowadays, in the field of European gas infrastructure, Italy stands as one of the leading countries transporting gaseous fuel to end users. This article provides an overview of the distribution of natural gas flows in the Italian gas infrastructure in the face of the coronavirus outspread in the country and GAZPROM’s natural gas supply restrictions for European countries. This article presents, using the ARIMA method, a forecast of natural gas consumption of Italian consumers measured up to 2024.

Gases doi: 10.3390/gases2030007

Authors: Guilherme da Cunha José de Medeiros Ofélia Araújo

Gas–liquid membrane contactor is a promising process intensification technology for offshore natural gas conditioning in which weight and footprint constraints impose severe limitations. Thanks to its potential for substituting conventional packed/trayed columns for acid-gas absorption and acid-gas solvent regeneration, gas-liquid membrane contactors have been investigated experimentally and theoretically in the past two decades, wherein aqueous-amine solvents and their blends are the most employed solvents for carbon dioxide removal from natural gas in gas-liquid membrane contactors. These efforts are extensively and critically reviewed in the present work. Experimentally, there are a remarkable lack of literature data in the context of gas–liquid membrane contactors regarding the following topics: water mass transfer; outlet stream temperatures; head-loss; and light hydrocarbons (e.g., ethane, propane, and heavier) mass transfer. Theoretically, there is a lack of complete models to predict gas-liquid membrane contactor operation, considering multicomponent mass balances, energy balances, and momentum balances, with an adequate thermodynamic framework for correct reactive vapor–liquid equilibrium calculation and thermodynamic and transport property prediction. Among the few works covering modeling of gas-liquid membrane contactors and implementation in professional process simulators, none of them implemented all the above aspects in a completely successful way.

Gases doi: 10.3390/gases2030006

Authors: Yaohui Li Zheng Liu Shuhui Yan Yaoxin Yang Yu Zhou Zheng Sun

Coalbed methane (CBM) shows tremendous in situ reserves, attracting a great deal of research interests around the world. The efficient development of CBM is closely related to the dynamic pressure distribution characteristics in the coal seam. As the dominant component of the geological reserve for CBM, the adsorption-state gas will not be exploited until the local coal pressure becomes less than the critical desorption pressure. Therefore, although the CBM reserve is fairly large, the production performance is generally limited, with a poor understanding of the dynamic pressure field during the CBM production. In this work, in order to address this issue properly, the coal’s inherent properties, the coal’s orthotropic features, as well as artificial hydraulic fracturing are considered, all of which affect pressure propagation in the coal seam. Notably, to the current knowledge, the impact of coal’s orthotropic features has received little attention, while the coal’s orthotropic features are formed during a fairly long geological evolution, changing the dynamic pressure field a lot. Numerical simulation is performed to shed light on the pressure propagation behavior. The results show that (a) coal’s orthotropic features mitigate the depressurization process of CBM development; (b) the increasing length of a hydraulic fracture is helpful for efficient decline in the average formation pressure; and (c) there exists an optimal layout mode for multi-well locations to minimize the average pressure. This article provides an in-depth analysis upon pressure distribution in CBM reservoirs under impacts of coal orthotropic feature and hydraulic fractures.

Gases doi: 10.3390/gases2030005

Authors: João Gomes Helder Esteves Luis Rente

This paper describes how an extreme Saharan dust event that took place in March 2022 affected the Iberian Peninsula and was noticed not only by the outdoor air quality monitoring stations measuring PM2.5 and PM10 but also by indoor air monitoring systems in Fatima, central Portugal. The observed particulate matter concentrations clearly show the influence that such an event has on the indoor air quality inside buildings and that the magnitude of that influence is also dependent on the specific characteristics of the buildings, mainly the ventilation conditions, as should be expected. Therefore, this study alerts us to the necessity of integrating indoor and outdoor air quality monitoring systems to achieve automated air conditioning systems capable of efficiently controlling both temperature and air cleanliness.

Gases doi: 10.3390/gases2020004

Authors: Sami Jarboui Achraf Ghorbel Ahmed Jeribi

The petroleum industry faces crucial environmental problems that exacerbate business instability, such as climate change and greenhouse gas emission regulations. Generally, governments focus on pricing, environmental protection, and supply security when developing energy policy. This article evaluates the technical efficiency of 53 oil and gas companies in the United States during the period 1998–2018 using the stochastic frontier analysis methods and investigates the degree to which energy policies influence the efficiency levels in these companies. Our empirical results show that the average technical efficiency of the 53 U.S. oil and gas companies is 0.75 and confirm that prices, production, consumption, and reserves of the U.S. petroleum and gas have a significant influence on technical efficiency levels. Specifically, our findings show that renewable energy and nuclear power contribute to explaining the distortion between the optimal and observed output of the U.S. oil and gas companies.

Gases doi: 10.3390/gases2020003

Authors: Mukhtar A. Kassem

Oil and gas construction projects are of great importance to support and facilitate the process of operation and production. However, these projects usually face chronic risks that lead to time overrun, cost overrun, and poor quality, affecting the projects’ success. Hence, this study focused on identifying, classifying, and modeling the risk factors that have negative effects on the success of construction projects in Yemen. The data were collected through a structured questionnaire. Statistical analysis, relative important index method, and probability impact matrix analysis were carried out to classify and rank the risk factors. The partial least squares path modeling or partial least squares structural equation modeling (PLS-PM, PLS-SEM) is a method for structural equation modeling that allows an estimation of complex cause–effect relationships in path models with latent variables. PLS-SEM was employed to analyze data collected from a questionnaire survey of 314 participants comprising the clients, contractors, and consultants working in oil and gas construction projects. The results showed that the goodness of fit index of the model is 0.638. The developed model was deemed to fit because the analysis result of the coefficient of determination test (R2) of the model was 0.720, which indicates the significant explanation of the developed model for the relationship between the causes of risks and their effects on the success of projects. The most impacted internal risk categories include project management, feasibility study design, and resource material availability. The main external risk elements include political, economic, and security considerations. The created risk factor model explained the influence of risk factors on the success of construction projects effectively, according to statistical and expert validation tests.

Gases doi: 10.3390/gases2020002

Authors: Sharmin Jahan Subrata Banik Nure Alam Chowdhury Abdul Mannan A A Mamun

A rigorous theoretical investigation has been made on the nonlinear propagation of dust-ion-acoustic shock waves in a multi-component magnetized pair-ion plasma (PIP) having inertial warm positive and negative ions, inertialess non-thermal electrons and positrons, and static negatively charged massive dust grains. The Burgers’ equation is derived by employing the reductive perturbation method. The plasma model supports both positive and negative shock structures in the presence of static negatively charged massive dust grains. It is found that the steepness of both positive and negative shock profiles declines with the increase of ion kinematic viscosity without affecting the height, and the increment of negative (positive) ion mass in the PIP system declines (enhances) the amplitude of the shock profile. It is also observed that the increase in oblique angle raises the height of the positive shock profile, and the height of the positive shock wave increases with the number density of positron. The applications of the findings from the present investigation are briefly discussed.

Gases doi: 10.3390/gases2010001

Authors: Theodora Noely Tambaria Yuichi Sugai Ronald Nguele

Enhanced coal bed methane recovery using gas injection can provide increased methane extraction depending on the characteristics of the coal and the gas that is used. Accurate prediction of the extent of gas adsorption by coal are therefore important. Both experimental methods and modeling have been used to assess gas adsorption and its effects, including volumetric and gravimetric techniques, as well as the Ono–Kondo model and other numerical simulations. Thermodynamic parameters may be used to model adsorption on coal surfaces while adsorption isotherms can be used to predict adsorption on coal pores. In addition, density functional theory and grand canonical Monte Carlo methods may be employed. Complementary analytical techniques include Fourier transform infrared, Raman spectroscopy, XR diffraction, and 13C nuclear magnetic resonance spectroscopy. This review summarizes the cutting-edge research concerning the adsorption of CO2, N2, or mixture gas onto coal surfaces and into coal pores based on both experimental studies and simulations.