Search Results (325)

Using waste biomass as a raw material for the combined production of electricity and heat offers corresponding energy, economic, environmental and resource efficiency benefits. The study examines both the performance of a system for combined energy production based on the Organic Rankine Cycle (ORC) utilizing wood biomass and the market interest in its deployment within Bulgaria. Its objective is to propose a technically and economically viable solution for the recovery of waste biomass through the combined production of electricity and heat while simultaneously assessing the readiness of industrial and municipal sectors to adopt such systems. The cogeneration plant incorporates an ORC module enhanced with three additional economizers that capture residual heat from flue gases. Operating on 2 t/h of biomass, the system delivers 1156 kW of electric power and 3660 kW of thermal energy, recovering an additional 2664 kW of heat. The overall energy efficiency reaches 85%, with projected annual revenues exceeding EUR 600,000 and a reduction in carbon dioxide emissions of over 5800 t/yr. These indicators can be achieved through optimal installation and operation. When operating at a reduced load, however, the specific fuel consumption increases and the overall efficiency of the installation decreases. The marketing survey results indicate that 75% of respondents express interest in adopting such technologies, contingent upon the availability of financial incentives. The strongest demand is observed for systems with capacities up to 1000 kW. However, significant barriers remain, including high initial investment costs and uneven access to raw materials. The findings confirm that the developed system offers a technologically robust, environmentally efficient and market-relevant solution, aligned with the goals of energy independence, sustainability and the transition to a low-carbon economy. Full article

A computational fluid dynamics (CFD) numerical simulation methodology was implemented to model transient heating processes in steel industry reheating furnaces, targeting combustion efficiency optimization and carbon emission reduction. The effects of oxygen concentration (O₂%) and different fuel types on the flow and heat transfer characteristics were investigated under both oxygen-enriched combustion and MILD oxy-fuel combustion. The results indicate that MILD oxy-fuel combustion promotes flue gas entrainment via high-velocity oxygen jets, leading to a substantial improvement in the uniformity of the furnace temperature field. The effect is most obvious at O₂% = 31%. MILD oxy-fuel combustion significantly reduces NOx emissions, achieving levels that are one to two orders of magnitude lower than those under oxygen-enriched combustion. Under MILD conditions, the oxygen mass fraction in flue gas remains below 0.001 when O₂% ≤ 81%, indicating effective dilution. In contrast, oxygen-enriched combustion leads to a sharp rise in flame temperature with an increasing oxygen concentration, resulting in a significant increase in NOx emissions. Elevating the oxygen concentration enhances both thermal efficiency and the energy-saving rate for both combustion modes; however, the rate of improvement diminishes when O₂% exceeds 51%. Based on these findings, MILD oxy-fuel combustion using mixed gas or natural gas is recommended for reheating furnaces operating at O₂% = 51–71%, while coke oven gas is not. Full article

In order to reduce gas consumption and increase the renewable energy proportion, this paper proposes a poly-generation system that couples geothermal, solar, and liquid natural gas (LNG) cold energy to produce steam, gaseous natural gas, and low-temperature nitrogen. The high-temperature flue gas is used to heat LNG; low-temperature flue gas, mainly nitrogen, can be used for cold storage cooling, enabling the staged utilization of the energy. Solar shortwave is used for power generation, and longwave is used to heat the working medium, which realizes the full spectrum utilization of solar energy. The influence of different equipment and operating parameters on the performance of a steam generation system is studied, and the multi-objective model of the multi-generation system is established and optimized. The results show that for every 100 W/m² increase in solar radiation, the renewable energy ratio of the system increases by 1.5%. For every 10% increase in partial load rate of gas boiler, the proportion of renewable energy decreases by 1.27%. The system’s energy efficiency, cooling output, and the LNG vaporization flow rate are negatively correlated with the scale of solar energy utilization equipment. The decision variables determined by the TOPSIS (technique for order of preference by similarity to ideal solution) method have better economic performance. Its investment cost is 18.14 × 10 CNY, which is 7.83% lower than that of the LINMAP (linear programming technique for multidimensional analysis of preference). Meanwhile, the proportion of renewable energy is only 0.29% lower than that of LINMAP. Full article

To compensate for the instability of renewable energy sources during China’s energy transition, large thermal power plants must provide critical operational flexibility, primarily through deep peaking. To investigate the combustion performance and wear and tear of a 600 MW pulverized coal boiler under deep peaking, the gas–solid flow characteristics and distributions of flue gas temperature, wall heat flux, and wall wear rate in a 600 MW tangentially fired pulverized coal boiler under variable loads (353 MW, 431 MW, 519 MW, and 600 MW) are investigated in this study employing computational fluid dynamics numerical simulation method. Results demonstrate that increasing the boiler load significantly amplifies gas velocity, wall heat flux, and wall wear rate. The maximum gas velocity in the furnace rises from 20.9 m·s⁻¹ (353 MW) to 37.6 m·s⁻¹ (600 MW), with tangential airflow forming a low-velocity central zone and high-velocity peripheral regions. Meanwhile, the tangential circle diameter expands by ~15% as the load increases. The flue gas temperature distribution exhibits a “low-high-low” profile along the furnace height. As the load increases from 353 MW to 600 MW, the primary combustion zone’s peak temperature rises from 1750 K to 1980 K, accompanied by a ~30% expansion in the coverage area of the high-temperature zone. Wall heat flux correlates strongly with temperature distribution, peaking at 2.29 × 10⁵ W·m⁻² (353 MW) and 2.75 × 10⁵ W·m⁻² (600 MW) in the primary combustion zone. Wear analysis highlights severe erosion in the economizer due to elevated flue gas velocities, with wall wear rates escalating from 3.29 × 10⁻⁷ kg·m⁻²·s⁻¹ (353 MW) to 1.23 × 10⁻⁵ kg·m⁻²·s⁻¹ (600 MW), representing a 40-fold increase under full-load conditions. Mitigation strategies, including ash removal optimization, anti-wear covers, and thermal spray coatings, are proposed to enhance operational safety. This work provides critical insights into flow field optimization and wear management for large-scale coal-fired boilers under flexible load operation. Full article

Most industrial processes depend on heat, electricity, demineralized water, and chemical inputs, which themselves are produced through energy- and resource-intensive industrial activities. In this work, acetic acid (AA) production from syngas (CO, CO₂, and H₂) fermentation is explored and compared against a thermochemical fossil benchmark and other thermochemical/biological processes across four main Key Performance Indicators (KPI)—electricity use, heat use, water consumption, and carbon footprint (CF)—for the years 2023 and 2050 in Portugal and France. CF was evaluated through transparent and public inventories for all the processes involved in chemical production and utilities. Spreadsheet-traceable matrices for hotspot identification were also developed. The fossil benchmark, with all the necessary cascade processes, was 0.64 kg CO_2-eq/kg AA, 1.53 kWh/kg AA, 22.02 MJ/kg AA, and 1.62 L water/kg AA for the Portuguese 2023 energy mix, with a reduction of 162% of the CO₂-eq in the 2050 energy transition context. The results demonstrated that industrial practices would benefit greatly from the transition from fossil to renewable energy and from more sustainable chemical sources. For carbon-intensive sectors like steel or cement, the acetogenic syngas fermentation appears as a scalable bridge technology, converting the flue gas waste stream into marketable products and accelerating the transition towards a circular economy. Full article

Circulating fluidized bed fly ash (CFBFA) stockpiles release alkaline dust, high-pH leachate, and secondary CO₂/SO₂—an environmental burden that exceeds 240 Mt yr⁻¹ in China alone. Yet, barely 25% is recycled, because the high f-CaO/SO₃ contents destabilize conventional cementitious products. Here, we presents a pressurized flue gas heat curing (FHC) route to bridge this scientific deficit, converting up to 85 wt% CFBFA into structural lightweight gravel. The gypsum dosage was optimized, and a 1:16 (gypsum/CFBFA) ratio delivered the best compromise between early ettringite nucleation and CO₂-uptake capacity, yielding the highest overall quality. The optimal mix reaches 9.13 MPa 28-day crushing strength, 4.27% in situ CO₂ uptake, 1.75 g cm⁻³ bulk density, and 3.59% water absorption. Multi-technique analyses (SEM, XRD, FTIR, TG-DTG, and MIP) show that FHC rapidly consumes expansive phases, suppresses undesirable granular-ettringite formation, and produces a dense calcite/needle-AFt skeleton. The FHC-treated CFBFA composite gravel demonstrates 30.43% higher crushing strength than JTG/TF20-2015 standards, accompanied by a water absorption rate 28.2% lower than recent studies. Its superior strength and durability highlight its potential as a low-carbon lightweight aggregate for structural engineering. A life-cycle inventory gives a cradle-to-gate energy demand of 1128 MJ t⁻¹ and a process GWP of 226 kg CO₂-eq t⁻¹. Consequently, higher point-source emissions paired with immediate mineral sequestration translate into a low overall climate footprint and eliminate the need for CFBFA landfilling. Full article

Understanding the adsorption mechanism is essential for developing efficient technologies to capture carbon dioxide from industrial flue gases. In this work, laboratory measurements, density functional theory calculations, and molecular dynamics simulations were employed to study CO₂ adsorption and diffusion behavior in LTA-type zeolites. The CO₂ adsorption isotherms measured in zeolite 5A are best described by the Toth model. Thermodynamic analysis indicates that the adsorption process is spontaneous and exothermic, with an enthalpy change of −44.04 kJ/mol, an entropy change of −115.23 J/(mol·K), and Gibbs free energy values ranging from −9.68 to −1.03 kJ/mol over the temperature range of 298–373 K. The isosteric heat of CO₂ adsorption decreases from 40.35 to 21.75 kJ/mol with increasing coverage, reflecting heterogeneous interactions at Ca²⁺ and Na⁺ sites. The adsorption kinetics follow a pseudo-first-order model, with an activation energy of 2.24 kJ/mol, confirming a physisorption mechanism. The intraparticle diffusion model indicates that internal diffusion is the rate-limiting step, supported by a significant reduction in the diffusion rate. The DFT calculations demonstrated that CO₂ exhibited a −35 kJ/mol more negative adsorption energy in zeolite 5A than in zeolite ITQ-29, attributable to strong interactions with Ca²⁺/Na⁺ cations in 5A that were absent in the pure silica ITQ-29 framework. The molecular dynamics simulations based on molecular force fields indicate that CO₂ diffuses more rapidly in ITQ-29, with a diffusion coefficient measuring 2.54 × 10⁻⁹ m²/s at 298 K, whereas it was 1.02 × 10⁻⁹ m²/s in zeolite 5A under identical conditions. The activation energy for molecular diffusion reaches 5.54 kJ/mol in zeolite 5A, exceeding the 4.12 kJ/mol value in ITQ-29 by 33%, which accounts for the slower diffusion kinetics in zeolite 5A. There is good agreement between experimental measurements and molecular simulation results for zeolite 5A across the studied temperature and pressure ranges. This confirms the accuracy and reliability of the selected simulation parameters and allows for the study of zeolite ITQ under similar simulation conditions. This research provides insights into CO₂ adsorption energetics and diffusion within LTA-type zeolite frameworks, supporting the rational design of high-performance adsorbents for industrial gas separation. Full article

The purpose of this study was to evaluate the energy and environmental potential of waste biomass in the form of hazelnut shells from selected Turkish varieties of Corylus avellana L. Eight commercial varieties (Çakıldak, Foşa, İnce Kara, Kalın Kara, Palaz, Tombul, Yassı Badem and Yuvarlak Badem) grown in different regions of the Black Sea coast of Turkey were analyzed. The scope of this study included whole nut and shell weight determination, technical and elemental analysis, higher heating value (HHV) and lower net heating value (LHV), as well as emission factors (CO, CO₂, NO_x, SO₂, dust) and flue gas composition based on stoichiometric calculations. The results showed a significant effect of varietal characteristics on all analyzed parameters. The share of shell in the total weight of the nut ranged from 43.5% (Tombul) to 55.3% (İnce Kara). HHV values ranged from 18.37 to 19.20 MJ·kg⁻¹, and LHV from 17.05 to 17.90 MJ·kg⁻¹. The İnce Kara and Yassı Badem varieties showed the most favorable energy properties. Elemental analysis confirmed a low nitrogen and sulfur content, which translated into low NO_x and SO₂ emissions. NO_x emissions were lowest for the Tombul variety (1.43 kg·Mg⁻¹), and SO₂ emissions were close to zero in each variety. The results confirm that Turkish hazelnut shells are a valuable energy resource and can be used as solid fuel or supplementary biomass. In particular, the İnce Kara variety was identified as the most promising due to its high shell weight, very good fuel properties, and high yield potential. This study underscores the importance of selecting the right variety to optimize agricultural waste utilization strategies within a circular economy. Full article

Despite the availability of various materials for chimney applications, ongoing research seeks alternatives with improved thermal and chemical resistance. Geopolymers are a promising solution, exhibiting exceptional resistance to high temperatures, fire, and aggressive chemicals. This study investigates fly ash-based lightweight geopolymer concretes that incorporate expanded clay aggregate (E.C.A.), perlite (P), and foamed geopolymer aggregate (F.G.A.). The composites were designed to ensure a density below 1200 kg/m³, reducing overall weight while maintaining necessary performance. Aggregate content ranged from 60 to 75 wt.%. Physical (density, thickness, water absorption), mechanical (flexural and compressive strength), and thermal (conductivity, resistance) properties were evaluated. F.G.A. 60 achieved a 76.8% reduction in thermal conductivity (0.1708 vs. 0.7366 W/(m·K)) and a 140.4% increase in thermal resistance (0.1642 vs. 0.0683). The F.G.A./E.C.A./P 60 mixture showed the highest compressive strength (18.069 MPa), reaching 52.7% of the reference concrete’s strength, with a 32.3% lower density (1173.3 vs. 1735.0 kg/m³). Water absorption ranged from 4.9% (REF.) to 7.3% (F.G.A. 60). All samples, except F.G.A. 70 and F.G.A. 75, endured heating up to 800 °C. The F.G.A./E.C.A./P 60 composite demonstrated well-balanced performance: low thermal conductivity (0.2052 W/(m·K)), thermal resistance up to 1000 °C, flexural strength of 4.386 MPa, and compressive strength of 18.069 MPa. The results confirm that well-designed geopolymer lightweight concretes are suitable for chimney and flue pipe linings operating between 500 and 1000 °C and exposed to acidic condensates and aggressive chemicals. This study marks the initial phase of a broader project on geopolymer-based prefabricated chimney systems. Full article

The goal of this paper consists in the experimental evaluation of the possibility to separate industrial gases using magnesium combustion in carbon dioxide–nitrogen mixtures of various concentrations. The choice was made primarily due to the chemical inertness of these two gases. The study investigates how the Mg combustion changes the concentration of the initial gas mixture and the possibility to apply this process to separate this gas mixture. On the other hand, due to its greenhouse effect, CO₂ separation is a process of high interest in itself. Mg reacts exothermically with CO₂, so a potential use for this purpose will also benefit from a significant amount of recovered thermal energy. N₂ has a particular importance due to its potential to be purified using Mg combustion, and this application might be an economical alternative to air distillation, which is widely used for N₂ production at industrial scale. In practice, the CO₂-N₂ mixtures are commonly used as flue gases resulting from various combustion systems. Mg combustion residue is analyzed by means of energy-dispersive X-ray spectroscopy. It is found that Mg can substantially reduce the concentration of CO₂, even more than the stoichiometric reaction for the formation of MgO would suggest. The percentage decrease in CO₂ concentration reaches values over 10 vol.%. A secondary yet notable effect is the heat generated by the Mg and CO₂ reaction, which is currently being studied as an energy source alternative. Full article

A significant portion of energy losses in industrial systems arises from the inefficient use of high-temperature exhaust gases, emphasizing the need for enhanced heat recovery strategies. This study aims to improve energy efficiency by examining the effects of radiation-intensifying inserts on combined radiative and convective heat transfer in flue-gas heated channels. A systematic literature review revealed a research gap in understanding the interaction between these mechanisms in flue-gas heat exchangers. To address this, analytical calculations were conducted for two geometries: a radiation-intensifying plate between parallel plates and the same insert in a circular pipe. The analysis covered a range of gas-flue and wall temperatures (560–1460 K and 303–393 K, respectively), flow velocities, and spectral emissivity values. Key performance metrics included Reynolds and Nusselt numbers to assess flow resistance and heat transfer. Results indicated that flue-gas temperature has the most significant effect on total rate of heat transfer, and the insert significantly enhanced radiative heat transfer by over 60%, increasing flow resistance. A local Nusselt number minimum at a length-to-diameter ratio of approximately 26 suggested transitional flow behavior. These results provide valuable insights for the design of high-temperature heat exchangers, with future work planned to validate the findings experimentally. Full article

District heating systems in northern China predominantly rely on coal-fired heat sources, necessitating sustainable alternatives to reduce carbon emissions. This study investigates a biomass combined heat and power (CHP) system integrated with cascaded absorption heat pump (AHP) technology to recover waste heat from semi-dry flue gas desulfurization exhaust and turbine condenser cooling water. A multi-source operational framework is developed, coordinating biomass CHP units with coal-fired boilers for peak-load regulation. The proposed system employs a two-stage heat recovery methodology: preliminary sensible heat extraction from non-saturated flue gas (elevating primary heating loop (PHL) return water from 50 °C to 55 °C), followed by serial AHPs utilizing turbine extraction steam to upgrade waste heat from circulating cooling water (further heating PHL water to 85 °C). Parametric analyses demonstrate that the cascaded AHP system reduces turbine steam extraction by 4.4 to 8.8 t/h compared to conventional steam-driven heating, enabling 3235 MWh of annual additional power generation. Environmental benefits include an annual CO₂ reduction of 1821 tonnes, calculated using regional grid emission factors. The integration of waste heat recovery and multi-source coordination achieves synergistic improvements in energy efficiency and operational flexibility, advancing low-carbon transitions in district heating systems. Full article

This paper deals with combustion air humidification for application with a biomass boiler and a spray flue gas condenser. The use of a combustion air humidifier increases the dew point temperature of the flue gas, thereby increasing the potential for heat recovery in the flue gas condenser and increasing the amount of heat supplied to the thermal system. The air humidification process in a counter current spray humidifier was experimentally analysed under conditions corresponding to the use before a biomass boiler with a flue gas condenser. For air heating and humidification, temperature factor values of up to 0.90 can be obtained; this value is mainly influenced by the ratio of the spray water and humidified air flow rates. The volumetric heat transfer coefficient is significantly affected by the humidified air velocity, although this velocity is negligible compared to the counter current spray water velocity. The volumetric heat transfer coefficient reaches higher values at higher spray water temperatures and therefore higher air heating. The whole process is also affected by the saturation of the incoming air, where the dew point temperature of the air drawn in from the surroundings is lower than its temperature. These results can be used as basic information for the design of combustion air humidifiers, for the selection of their operating parameters, and for a basic balancing of the energy contribution of the combustion air humidifier before a more detailed design of the whole system. Full article

Recognizing the growing importance of natural gas as a transition fuel in Poland’s energy mix and the necessity of reducing CO₂ emissions, this article aims to assess the use of carbon capture and storage (CCS) technology to effectively reduce CO₂ emissions from combined cycle gas turbine (CCGT). The research employs the pressure–temperature swing adsorption (PTSA) to capture CO₂ from flue gases. Computer simulations, using IPSEpro (SimTech), are used to calculate the heat and mass balances for CCGT and PTSA units and assess their performance. In the first part of the research, the effect of sorbent type (Na-A and 5A) and flue gas share directed to the PTSA unit on the performance of the CCGT was investigated. Secondly, the parametric analysis regarding the adsorption and desorption pressures in the PTSA was carried out. The results showed that CO₂ emissions from CCGT can be reduced by 1.1 Mt (megatons) per year, but the use of PTSA was associated with a reduction in net electrical power and efficiency of the CCGT by up to 14.7% for Na-A and 11.1% for 5A sorbent. It was also found that the heat and electricity demand of the PTSA depends on the adsorption and desorption pressures. Full article

The combustion of gaseous fuels in condensing boilers contributes to the greenhouse gas and toxic compound emissions in exhaust gases. Hydrogen, as a clean energy carrier, could play a key role in decarbonizing the residential heating sector. However, its significantly different combustion behavior compared to hydrocarbon fuels requires thorough investigation prior to implementation in heating systems. This study presents experimental and theoretical analyses of the co-combustion of natural gas with hydrogen in low-power-output condensing boilers (second and third generation), with hydrogen content of up to 50% by volume. The results show that mixtures of hydrogen and natural gas contribute to increasing heat transfer in boilers through convection and flue gas radiation. They also highlight the benefits of using the heat from the condensation of vapors in the flue gases. Other studies have observed an increase in efficiency of up to 1.6 percentage points compared to natural gas at 50% hydrogen content. Up to a 6% increase in the amount of energy recovered by water vapor condensation was also recorded, while exhaust gas losses did not change significantly. Notably, the addition of hydrogen resulted in a substantial decrease in the emission of nitrogen oxides (NOx) and carbon monoxide (CO). At 50% hydrogen content, NO_x emissions decreased several-fold to 2.7 mg/m³, while CO emissions were reduced by a factor of six, reaching 9.9 mg/m³. All measured NO_x values remained well below the current regulatory limit for condensing gas boilers, which is 33.5 mg/m³. These results highlight the potential of hydrogen blending as a transitional solution on the path toward cleaner residential heating systems. Full article