Search Results (228)

To elucidate the combustion behavior and molecular-scale reaction mechanisms of Fushun oil shale kerogen under oxy-fuel atmospheres, ReaxFF molecular dynamics simulations were performed based on a previously constructed kerogen model. Five reaction systems were established: 21% O₂/79% N₂, 21% O₂/79% CO₂, 35% O₂/65% CO₂, 55% O₂/45% CO₂, and 75% O₂/25% CO₂. Under programmed heating, the evolution of chemical bonds, gaseous products, char, tar and gas transformation, and system potential energy was systematically analyzed. The results show that, at the same O₂ concentration, CO₂ delays low-temperature oxidation, shifting C–C and C–H bond cleavage and O₂ consumption to higher temperatures. At elevated temperatures, however, CO₂-related pathways promote carbon skeleton fragmentation and CO formation. Increasing O₂ concentration from 21% to 75% advances O₂ participation and H₂O formation, suppresses low-temperature CO accumulation, accelerates char consumption, and drives the system toward complete oxidation dominated by small-molecule gases. Potential energy analysis further indicates that higher O₂ concentrations advance the intense exothermic oxidation stage. A four-stage oxy-fuel combustion mechanism is proposed, providing molecular-level insight into the coupled effects of CO₂ and O₂ concentration. Full article

Understanding the atomic-scale mechanisms of coal pyrolysis is essential for efficient coal utilization and carbon-neutral energy strategies, yet conventional computational approaches often struggle to balance between the high accuracy of quantum-chemical calculations and the efficiency of reactive force fields. To overcome this limitation, we proposed a multiscale computational framework integrating high-throughput density functional theory (DFT) calculations, ReaxFF-based configuration sampling, YARP reaction enumeration, and DPA3-based machine learning potentials (MLPs). Two coal-specific MLPs, DPA3-coal and DPA3-coal@dftb, were constructed and systematically benchmarked on both small molecular systems and larger C20–30 coal fragments extracted from MD simulations. DPA3-coal@dftb model demonstrated significantly improved accuracy over ReaxFF in predicting energies and atomic forces while maintaining good transferability. To balance computational efficiency and accuracy in large-scale simulations, the DPA3-coal model was employed to perform accelerated reactive molecular dynamics simulations of a Solomon-type bituminous coal molecule from 1600 to 2600 K. The simulations revealed temperature-dependent evolution of coke, tar, and gas products, including secondary condensation and deep-cracking processes at elevated temperatures. Higher-level DFT calculations further confirmed the thermodynamic consistency of key reaction pathways involving radical formation, H-transfer, recombination, and CO generation, indicating that coal-specific MLPs provide an effective atomistic tool for investigating mechanistic trends in coal pyrolysis. Full article

Flue gas torrefaction is an emerging biomass pretreatment technology that utilizes industrial flue gas as a reactive medium to replace inert atmospheres. However, the intrinsic complexity of biomass and the catalytic interference of ash hinder mechanistic elucidation. This study investigated the torrefaction behavior of demineralized poplar wood under N₂, CO₂, dry flue gas (DFG), and wet flue gas (WFG) at 300 °C for 5–20 min. Thermogravimetric analysis combined with kinetic modeling (FWO, KAS, and CR methods) revealed that the apparent activation energy (E_α) varied non-monotonically with atmosphere oxidizability. Under N₂, the average E_α was 177 kJ/mol following the three-dimensional diffusion model (D5). CO₂ gave the highest average E_α (314 kJ/mol) with the Avrami–Erofeev nucleation model (A₁/₄). DFG and WFG significantly reduced the average E_α to 133 and 128 kJ/mol, respectively, both following the A₁/₃ model. Consistently, WFG yields the lowest char and the highest gas yield. XPS and FTIR analyses indicated that flue gas atmospheres, especially WFG, promoted deeper deoxygenation and aromatization of biochar. Tar composition underwent a noticeable transition from ketones to aldehydes and saccharides under flue gas conditions, with the most remarkable variation observed under WFG. Gaseous products were dominated by CO₂ under N₂ and by CO under CO₂, while DFG and WFG produced moderate and stable gas compositions. These findings demonstrate that flue gas torrefaction, particularly under WFG, effectively enhances biomass effectively upgrades biomass quality by regulating pyrolysis kinetics and product distribution, and demineralized biomass is a suitable intermediate model for mechanistic investigation. Full article

The transition toward low-carbon energy systems and circular economy frameworks has intensified interest in biomass and waste valorization technologies that deliver reliable energy carriers while mitigating greenhouse gas emissions. Among the thermo-chemical pathways, gasification has emerged as a particularly flexible and robust option for transforming biomass resources into synthesis gas suitable for power generation, hydrogen production, and synthetic fuels. This review critically examines biomass gasification as a feasible alternative for valorizing waste and producing syngas. The manuscript discusses the physicochemical characteristics of biomass, highlights its influence on syngas quality, tar formation, and cold gas efficiency. The fundamental stages of the gasification process and the effects of different operating parameters were systematically reviewed. Special attention was given to the challenges posed by low-quality biomass, such as sewage sludge, digestates, and manures, which are characterized by high-ash content and high moisture levels. Syngas energy content reported across different experiences was usually around 4–5 MJ/m³ when operating with low-quality biomass, resulting in lower efficiencies than those reported for lignocellulosic biomass (around 30–70%, expressed as cold gas efficiency (CGE)). Current small-scale commercial gasification technologies were also reviewed, with emphasis on operational constraints. This review provides an integrated perspective on the operational challenges associated with low-quality biomass gasification and discusses technological pathways to enhance process efficiency and salability. Although biomass gasification cannot yet be regarded as a fully mature technology across all feedstocks, it nonetheless constitutes a technically significant pathway for strengthening energy system resilience and advancing the production of sustainable fuels within a net zero carbon framework. Full article

Pyrolysis of refuse-derived fuel (RDF) is a promising waste-to-energy route, but its use in higher-value applications remains limited by tar carryover, benzene, toluene, ethylbenzene, and xylenes (BTEX), heteroatom-containing compounds, and pollutant accumulation in recirculated scrubber water. This study evaluated operating windows for RDF pyrolysis coupled with direct wet scrubbing and closed-loop water reuse, with the aim of identifying regimes suitable for different end-use tiers. A Taguchi L27 design of experiments (DOE), i.e., an orthogonal array comprising 27 experimental runs, was applied to evaluate the effects of pyrolysis temperature, residence time, scrubber liquid-to-gas ratio, and scrubber-water temperature, while sequential reuse of the same scrubber-water inventory was evaluated at 5, 10, and 15 cycles. Cleaned-gas pollutants were quantified by compound-resolved gas chromatography–mass spectrometry (GC–MS) after solid-phase adsorption (SPA) sampling, while phenolics and polycyclic aromatic hydrocarbons (PAHs) in scrubber water were determined by extraction followed by GC–MS. Feasibility within each end-use tier was defined as simultaneous satisfaction of tier-specific cleaned-gas thresholds (C_tar, C_BTEX, I_N, and I_S) and the corresponding water-loop hazard limit (I_tox), using literature-informed engineering screening criteria. The results showed that stronger scrubbing reduced gas-phase tar and BTEX burdens, whereas extended water reuse caused systematic accumulation of phenolics and PAHs and increased the composite water-loop hazard index. Boiler-grade operation remained feasible across a broad operating range, with 23 of the 27 tested conditions remaining robust, whereas internal combustion engine combined heat and power (ICE-CHP) feasibility was restricted to a narrow robust regime, and no robust microturbine-grade condition was identified. These findings show that operating windows for RDF pyrolysis must be defined jointly by gas cleanliness and water-loop management constraints. Full article

Energy transformation requires the development of distributed renewable energy, in which heat and electricity are produced by small units or production facilities for local needs. One favorable development direction is the thermal conversion of biomass, which is classified as a renewable energy source. Due to the variability of its physicochemical properties, gasification technology offers a flexible and competitive alternative to combustion processes. One of the key challenges associated with biomass gasification is the relatively high concentration of contaminants in the raw producer gas. This article presents the results of pilot studies on producer gas purification using activated carbon fixed-bed adsorption. The pilot studies focused on assessing the effectiveness of this technology in the context of purifying producer gas from biomass gasification installations. During the conducted experimental study, approximately 2.2 kg of contaminants were adsorbed. The calculated unit mass of adsorbed contaminants per unit volume of producer gas was 11.7 g/Nm³. The removal efficiency of contaminants was 61.5% for tar compounds and 83.6% for volatile organic compounds. A 100% removal efficiency was achieved for the analyzed sulfur compounds (H₂S, COS, and CH₃SH). The research showed positive effects of adsorption for final producer gas purification, supporting further experimental research. Full article

The valorization of agro-industrial byproducts through pyrolysis represents a sustainable route for generating multifunctional raw materials within the framework of a circular bioeconomy. In this study, rice husk (RH) and sugarcane bagasse (SCB) were pyrolyzed in a semi-continuous reactor at 500 °C in order to compare product yields and to characterize resulting gas, aqueous and tar fractions. SCB produced the highest bio-oil yield (44.2 wt%), whereas RH generated the highest char yield (42.9 wt%), consistent with its higher ash and lignin contents. In both cases, tar represented about 12 wt% of the bio-oil. Detailed characterization revealed that the liquid products contained oxygenated compounds of interest, mainly carboxylic acids, ketones, and phenols. Acetic acid was the predominant compound in the aqueous phases, while tars were composed mainly of phenols, ketones, furans, and acids. Particularly, phenols accounted for 52.6% and 37.8% of the total chromatographic area in RH and SCB tars, respectively, whereas ketones represented about 10% in both cases. These results show that pyrolysis of agro-industrial residues not only enables energy recovery but also provides liquid fractions enriched in value-added chemicals. Full article

Coke, as an essential metallurgical raw material, is widely used in iron and steel production. To investigate the pyrolysis behavior and cross-linking reactions during the pyrolysis of coking coal, pyrolysis experiments were conducted in a quartz-tube fixed-bed reactor placed in an electric furnace. The yields and compositions of the pyrolysis products were systematically analyzed. Gaseous and tar components generated at different pyrolysis stages were characterized using gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The semi-coke was examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results indicated that the yields of tar from coking coal pyrolysis have a notable impact on the cross-linking reactions occurring during the coal pyrolysis process. The structural differences between Malan coal (ML) and Tunlan coal (TL) coals underlie their distinct behaviors in cross-linking intensity, tar evolution profiles, and coke-forming properties. For high-volatile, highly fluid ML coal, the release of the aliphatic compounds in tar volatiles remains relatively low at the temperature of maximum fluidity, which is beneficial to the cross-linking reactions. In contrast, for TL coal with lower volatility and fluidity, substantial H₂ emission during the early pyrolysis stage promotes cross-linking reactions. This study provides new insights into the temperature-dependent evolution of cross-linking reactions during coking coal pyrolysis. Full article

Catalytic biomass gasification is considered a promising route for the production of hydrogen-rich syngas. However, the impact of catalytic enhancement on gas composition is a complex phenomenon, as experimental outcomes are often strongly dependent on reactor configurations and kinetic effects. To address these challenges, a thermodynamic equilibrium-based modeling approach was developed to theoretically investigate the influence of catalytic enhancement in biomass steam gasification. The gasification process was modeled using Gibbs free energy minimization, focusing on the elemental composition of biomass and the equilibrium distribution among the major gaseous species, namely H₂, CO, CO₂, CH₄, and H₂O. The effects of the different catalyst types, including dolomite, Ni/olivine, and iron-based catalysts, were examined through catalyst-dependent activity coefficients. Simulations were carried out under steam gasification conditions at atmospheric pressure, with particular emphasis on the influence of temperature, steam-to-biomass ratio, and catalyst activity on syngas composition. The results showed that increasing catalyst activity enhanced hydrogen production while suppressing methane formation, primarily through intensified tar reforming and water–gas shift reactions. The model successfully reproduced widely accepted thermodynamic trends reported in the literature. Overall, the proposed framework can provide a flexible and computationally efficient screening-level tool for the theoretical assessment of catalytic effects in biomass gasification, offering valuable insights for preliminary catalyst selection and conceptual process design. Full article

Rising global municipal solid waste (MSW) generation poses severe environmental and resource challenges, necessitating sustainable management strategies beyond landfilling. This review critically synthesizes thermochemical waste-to-energy (WtE) technologies, including incineration, pyrolysis, gasification, and hydrothermal carbonization, as viable pathways for converting heterogeneous MSW into energy (electricity, heat, syngas, bio-oil) and valuable materials (biochar, ash for construction). Drawing on recent literature, it highlights their superior greenhouse gas reductions, energy recovery efficiencies, and residue valorization potential compared to traditional disposal, while addressing persistent limitations such as feedstock variability, tar formation, high capital costs, and stringent emission controls. Advanced variants and integration with circular economy principles enhance feasibility, particularly in diverse regional contexts. Despite technical and economic barriers, thermochemical WtE offers a transformative approach to resource-efficient waste management, supporting zero-waste goals and renewable energy transitions when combined with optimized pre-treatment, policy incentives, and ongoing innovation in process efficiency and pollutant mitigation. Full article

Waste biomass represents both an environmental pollutant and a potential renewable energy source. This study examines the feasibility of hydrogen production from tea residue biomass and solid waste, focusing on pyrolysis-based hydrogen generation. Compared to atmospheric pyrolysis, vacuum conditions reduce the saturated vapor pressure of biomass volatiles, thereby promoting char gasification, gas-phase interactions, and secondary tar cracking. Utilizing a self-designed vacuum-pyrolysis-catalysis system, we investigated the effects of key parameters—vacuum level, temperature, catalyst-to-feedstock ratio, and retention time on pyrolysis product distribution and formation mechanisms. Results indicate that Ni was successfully and uniformly loaded onto waste calcium oxide desiccant (DC) support via impregnation, thereby significantly increasing the specific surface area of the catalyst. Optimization using response surface methodology identified the following optimal conditions: pressure of 5 kPa, temperature of 835.89 °C, catalyst/feedstock ratio of 110.02%, and retention time of 2.35 h. Under these conditions, a hydrogen yield of 256.39 mL·g⁻¹ was achieved, corresponding to 95.3% of the simulated value. The process not only enabled efficient hydrogen production but also simultaneously yielded bio-oil and biochar, thereby facilitating carbon capture and recycling. These findings provide valuable insights into the resource-oriented application of vacuum pyrolysis-catalysis technology to waste biomass. Full article

As an important type of power and domestic coal, long-flame coal plays a significant role in China’s energy structure. In this study, long-flame coal from Dongsheng, Inner Mongolia (DS) and its vitrinite-enriched fraction (DSV) prepared by organic solvent flotation separation method were selected as research objects. Simultaneous thermal analyzer (TGA), thermogravimetry-gas chromatography-mass spectrometry (TG-GC/MS), and Gray-King assay of coal were mainly employed to investigate their pyrolysis characteristics and differences in pyrolysis products. Results indicate that at the same final pyrolysis temperature, the CO₂ content in the pyrolysis gas of DS is higher than that of DSV, while CO, CH₄, and C_mH_n follow the order of DSV > DS. At 400−600 °C, pyrolysis tar mainly comprises monocyclic aromatic hydrocarbons (MAHs), polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, phenols and other oxygen heteroatom-containing organics (OHCs). Except for aliphatic hydrocarbons and OHCs, the contents of other components reach their maximum values at 500 °C, with peak area intensities of 3.192 × 10⁸, 5.841 × 10⁸, and 8.562 × 10⁸, respectively. In summary, when compared with DS, DSV exhibits more pronounced volatile release and higher reactivity. Full article

Potassium (K⁺) is essential for plant growth and development, influencing numerous physiological processes and stress responses. While the importance of K⁺ in overall plant performance is well-established, its specific effects on root system architecture and the underlying molecular mechanisms in woody perennials remain poorly understood. This knowledge gap is particularly significant for citrus rootstocks like trifoliate orange (Poncirus trifoliata L.), where root system optimization directly impacts drought resistance, nutrient acquisition, and overall orchard productivity. Here, we investigated how varying K⁺ concentrations (K₀, K₂, K₆, and K₁₂) affect trifoliate orange seedling development by comprehensively analyzing root architecture parameters, root hair morphology, endogenous hormone levels, and expression patterns of cell-wall-modifying and auxin-related genes. We found that moderate K⁺ levels (K₆) optimized root architectural development while both deficiency (K₀, K₂) and excess (K₁₂) inhibited overall growth and root architecture but enhanced root hair development. This morphological dichotomy corresponded to distinct hormonal profiles, showing reduced auxin (IAA), gibberellins (GAs), and zeatin riboside (ZR) levels under K⁺ stress conditions. Gene expression analysis revealed significant upregulation of expansins (PtEXPA4, PtEXPA5, PtEXPA7) and reconfiguration of auxin biosynthesis (TAA/TAR/YUC) and transport (AUX/LAX/ABCB/PIN) machinery under non-optimal K⁺ conditions. Our findings suggest that K⁺ availability modulates trifoliate orange root development through coordinated regulation of hormone homeostasis and gene expression, particularly within the auxin signaling network. These findings elucidate K⁺-responsive root developmental plasticity as a potential adaptive strategy, providing valuable insights for optimizing fertilization strategies in citrus cultivation and identifying potential molecular targets for enhancing potassium use efficiency in woody perennials. Full article

The present study investigates the potential of poplar (Populus spp.) biomass from phytoremediation plantations as a feedstock for downdraft fixed bed gasification. The biomass was characterized in terms of moisture, ash content, elemental composition (C, H, N, O), and calorific values (HHV and LHV), confirming its suitability for thermochemical conversion. Gasification tests yielded a volumetric syngas production of 1.79 Nm³ kg⁻¹ biomass with an average composition of H₂ 14.58 vol%, CO 16.68 vol%, and CH₄ 4.74 vol%, demonstrating energy content appropriate for both thermal and chemical applications. Alkali and alkaline earth metals (AAEM), particularly Ca (273 mg kg⁻¹) and Mg (731 mg kg⁻¹), naturally present enhanced tar reforming and promoted reactive gas formation, whereas heavy metals such as Cd (0.27 mg kg⁻¹), Pb (0.02 mg kg⁻¹), and Bi (0.01 mg kg⁻¹) were detected only in trace amounts, posing minimal environmental risk. The results indicate that poplar pruning residues from phytoremediation sites can be a renewable and sustainable energy resource, transforming a waste stream into a process input. In this perspective, the integration of soil remediation with syngas production constitutes a tangible model of circular economy, based on the efficient use of resources through the synergy between environmental remediation and the valorization and sustainable management of marginal biomass—i.e., pruning residues—generating environmental, energetic, and economic benefits along the entire value chain. Full article

Biomass gasification serves as a key carbon-neutral technology. To effectively address the challenge of tar treatment during biomass gasification, the National Institute of Clean and low-carbon Energy developed a fluidized bed coupled with an entrained-flow bed. A steady-state Aspen Plus V12 model was designed to assess the compatibility between the two beds and optimize operating parameters. The model divides the process into three main zones: fluidized bed gasification, entrained-flow bed gasification, and bottom slag treatment, employing a reaction-restricted equilibrium assumption. Simulation results indicate that an increase in pressure leads to a reduction in the concentration of syngas components (CO and H₂), an insignificant rise in gas low heating value (LHV), and a notable decline in cold gas efficiency (η). A higher equivalence ratio (ER) results in decreased syngas components, along with a significant reduction in both LHV and η. The introduction of carbon dioxide reduces syngas components and lowers LHV. Similarly, the addition of steam reduces the CO content of the syngas and decreases its LHV. When the fluidized bed temperature exceeds 900 °C, changes in LHV and gas yield become negligible, while variations remain minimal when the entrained-flow bed temperature exceeds 1200 °C. Full article