A simulation study on the enhancement of the shift reaction by water injection into a gasifier

Although coal gasification is a clean and efficient use of coal, a reduction of CO₂ emissions is needed to mitigate global warming. The aim of this study was to improve the thermal efficiency of fuel production and electricity generation by dry coal feed gasification. The primary cause of thermal efficiency loss is steam use in a water-gas shift reactor. The shift reactor, installed downstream from the gasifier, uses a catalyst to adjust the H₂/CO ratio of the syngas. We have proposed a new process in which water is injected at the outlet of the gasifier and is vaporized to enhance the extent of the shift reaction. This process utilizes the high temperature of the syngas, which is sufficient for the shift reaction to occur without a catalyst. We have developed a model that incorporates the shift reaction velocity to evaluate our proposed process. In an optimized 5-stage water supply case, we found that the CO conversion reaches 9.9% at a water/syngas ratio of 0.14 mol/mol (water/CO = 0.25 mol/mol); the CO conversion needed for dimethyl ether production is 31%. This new process can improve the efficiency and reduce the cost of coal gasification.     

Experimental study on hydrogen-rich syngas production via gasification of pine cone particles and wood pellets in a fixed bed downdraft gasifier

The main objective of this research is to investigate gasification of pine cones particles and wood pellets in a pilot scale 10 kWth downdraft fixed bed gasifier using air as an oxidizing agent. In this work, it was found that syngas produced by gasification of pinecones particles is rich in environmentally friendly hydrogen and that would be a clean alternative energy carrier for the production of clean energy. In addition, the effect of gasification temperature and equivalence ratio on the composition of syngas and gasification performance for pine cones and wood pellet were analysed comparatively. During the experimental works gasification took place with air, in a temperature range of 701–1046 °C, for various air equivalence ratios (0.14–0.37) and under atmospheric pressure. It is found that H₂ and CO production increased by increasing reactor temperature. Another finding is that the mean cold gas efficiency was 65% for pinecone particles and 80% for wood pellet gasification.     

Steam and supercritical water gasification of densified canola meal fuel pellets

In this research, canola meal was densified using bio-additives including alkali lignin, glycerol, and l-proline. The fuel pellet's formulation was optimized. The best fuel pellet demonstrated relaxed density and mechanical durability of 1015 kg/m³ and 99.0%, respectively. Synchrotron-based computer tomography technique indicated that lack of water in pellet formulation resulted in a twofold increase in pellet porosity. Thermogravimetric analysis showed that ignition temperature (240 °C) and burn-out temperature (640 °C) for fuel pellet were smaller than those for coal. Impacts of process parameters were evaluated on the quality of the gas product obtained from pellet's steam gasification and hydrothermal gasification. The gasification experiments showed production of untreated syngas with a suitable range of H₂/CO molar ratio (1.3–1.6) using steam gasification. Hydro-thermal gasification produced a larger molar ratio of H₂/CO (1.8–51.2) for the gas product. Modeling of pellet's steam gasification showed an excellent agreement with experimental results of steam gasification.     

Characteristics of cardboard and paper gasification with CO2

Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000 °C using CO₂ as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO₂ gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800 °C while at elevated temperatures of 900 and 1000 °C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H₂ to exhibit after few minutes into the gasification that changed with gasification temperature. At 800 °C gasification temperature peak in H₂ was displayed at 3 min into gasification while it decreased to only 2 min, approximately, at gasification temperatures of 900 and 1000 °C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (C+CO₂2CO). The results show important role of CO₂ gas for the gasification of wastes and low grade fuels to clean syngas.     

Experimental analysis of air-steam gasification of biomass with coal-bottom ash

Biomass gasification is an attractive option for producing high-quality syngas (H₂+CO) due to its environmental advantages and economic benefits. However, due to some technical problems such as tar formation, biomass gasification has not yet been able to achieve its purpose. The purpose of this work was to study the catalytic activity of coal-bottom ash for fuel gas production and tar elimination. Effect of gasification parameters including reaction temperature (700–900 °C), equivalence ratio, EQR (0.15–0.3) and steam-to-biomass ratio, SBR (0.34–1.02) and catalyst loading (5.0–13 wt %) on gas distribution, lower heating value (LHV) of gas steam, tar content, gas yield and H₂/CO ratio was studied. The tar content remarkably decreased from 3.81 g/Nm³ to 0.97 g/Nm³ by increasing char-bottom ash from 5.0 wt% to 13.0 wt%. H₂/CO significantly increased from 1.12 to 1.54 as the char-bottom ash content in the fuel increased from 5.0 wt% to 13.0 wt%.     

Syngas production by chemical looping gasification of rice husk using Fe-based oxygen carrier

The chemical looping gasification (CLG) of rice husk was conducted in a fixed bed reactor to analyze the effects of the ratio of oxygen carrier to rice husk (O/C), temperature, residence time and preparation methods of Fe-based oxygen carriers. The yield of gas, H₂/CO, lower heating value of syngas (LHV), conversion efficiency and performance parameters were analyzed to obtain CLG reaction characterization and optimal reaction conditions. Results showed that when O/C increased from 0.5 to 3.0, the gas production, H₂/CO, CO₂ yield and carbon conversion efficiency gradually increased, while the yield of H₂, CO and CH₄ and LHV gradually decreased. At the same time, a highest gasification efficiency was obtained when O/C was 1.5. As increasing temperature, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, while the yield of H₂, CH₄ and CO₂, H₂/CO and LHV gradually decreased. Sintering and agglomeration was obvious when the temperature was higher than 850 °C. When the reaction time increased from 10 min to 60 min, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, but the yield of H₂, H₂/CO and LHV decreased, among which 30 min was the best reaction residence time. In addition, coprecipitation was the best preparation method among several preparation methods of oxygen carrier. Finally, O/C of 1.5, 800 °C, 30 min and coprecipitation preparation method of oxygen carrier were the optimal parameters to obtain a gasification efficiency of 26.88%, H₂ content of 35.64%, syngas content of 56.40%, H₂/CO ratio of 1.72 and LHV of 12.25 MJ/Nm³.     

Evaluation of biomass gasification in a ternary diagram

The present paper addresses the development of an alternative approach to illustrate biomass gasification in a ternary diagram which is constructed using data from thermodynamic equilibrium modeling of air-blown atmospheric wood gasification. It allows the location of operation domains of slagging entrained-flow, fluidized-bed/dry-ash entrained-flow and fixed/moving-bed gasification systems depending on technical limitations mainly due to ash melting behavior. Performance parameters, e.g. cold gas efficiency or specific syngas production, and process parameters such as temperature and carbon conversion are displayed in the diagram depending on the three independent mass flows representing (1) the gasifying agent, (2) the dry biomass and (3) the moisture content of the biomass. The graphical approach indicates the existence of maxima for cold gas efficiency (84.9%), syngas yield (1.35 m³ (H₂ + CO STP)/kg (waf)) and conversion of carbon to CO (81.1%) under dry air-blown conditions. The fluidized-bed/dry-ash entrained-flow processes have the potential to reach these global maxima since they can operate in the identified temperature range from 700 to 950 °C. Although using air as a gasifying agent, the same temperature range posses a potential of H₂/CO ratios up to 2.0 at specific syngas productions of 1.15 m³ (H₂ + CO STP)/kg (waf). Fixed/moving-bed and fluidized-bed systems can approach a dry product gas LHV from 3.0 to 5.5 MJ/m³ (dry STP). The ternary diagram was also used to study the increase of gasifying agent oxygen fraction from 21 to 99 vol.%. While the dry gas LHV can be increased significantly, the maxima of cold gas efficiency (+6.5%) and syngas yield (+7.4%) are elevated only slightly.     

Experimental assessment of woody biomass gasification in a hybridized solar powered reactor featuring direct and indirect heating modes

Solar thermochemical gasification is an opportunity for the production of sustainable fuels from carbonaceous resources including biomass. Substituting conventional gasification processes by solar-driven technologies may enable cleaner production of H₂-rich syngas while saving feedstock resources and alleviating CO₂ emissions. This work addresses hybrid solar-autothermal gasification of mm-sized beech wood particles in a lab-scale 1.5 kW_th spouted-bed reactor. Hybridization under reduced solar power input was performed by injecting oxygen and additional biomass inside the gasifier for complementary heat supply. Increasing O₂:C molar ratios (in the range 0.14–0.58) allowed to heat the reactor cavity and walls progressively, while gradually impairing the reactor performance with an increase of the syngas CO₂ content and a decrease of the reactor cold gas efficiency (CGE). Gasification with mixed H₂O and O₂ was then assessed at thermodynamic equilibrium and global trends were validated experimentally, showing that control of H₂:CO ratio was compatible with in-situ combustion. The impact of reaction temperature (1200–1300 °C) and heating mode (direct or indirect) was experimentally studied during both allothermal and hybrid gasification. Higher H₂ and CO yields were achieved at high temperatures (1300 °C) under direct reactor heating. Hybridization was able to counterbalance a 40% drop of the nominal solar power input, and the measured CGE reached 0.82, versus values higher than 1 during allothermal gasification.     

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H₂ from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m³/kg, the hydrogen output is 0.3–0.43 m³/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.     

Syngas production from algae biomass gasification: the case of China

A kinetic model of algae gasification for hydrogen production with air and steam as gasification agent and was developed. The developed model was based on kinetic parameters available in the literature. The objective was to study the effect of critical parameters such as reaction temperature, stoichiometric ratio (SR) and steam flow rate (SFR) on H₂/CO ratio in the syngas, hydrogen yield, and lower heating value (LHV) of the produced syngas. Model formulation was validated with experimental results on air-steam gasification of biomass conducted in an atmospheric fluidized bed gasifier. The results showed that higher temperature contributed to lower H₂/CO, while higher SFR resulted in higher H₂/CO. The LHV of producer gas increased with SFR and gasification temperature.     

Co-gasification between coal/sawdust and coal/wood pellet: A parametric study using response surface methodology

This study had compared raw biomass and pre-treated biomass co-gasified with coal with the aim of investigating the reliability of pre-treated biomass for enhancing gasification performance. Sawdust (SD) and wood pellet (palletisation form of sawdust - WP) and blends of these two feedstocks with sub-bituminous coal (CL), were gasified in an air atmosphere using an external heated fixed-bed downdraft gasifier system. Response surface methodology (RSM) incorporating the central composite design (CCD) was applied to assist the comparison of all operating variables. The three independent variables were investigated within a specific range of coal blending ratios from 25% to 75%, gasification temperature from 650 °C to 850 °C and equivalence ratio from 0.20 to 0.30 against the dependent variables, namely the H₂/CO ratio and higher heating value of the syngas (HHVsyngas). The results revealed the H₂/CO ratio and a higher heating value of the syngas of more than 1.585 and 6.072 MJ/Nm³, respectively. Findings also showed that the H₂/CO ratio in the syngas from CL/WP possessed a higher value than the CL/SD. In contrast, CL/SD possessed a higher heating value for syngas with about 1% difference compared to the CL/WP. Therefore, co-gasified coal with wood pellets could potentially be a substitute for sawdust.     

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen,CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H₂/CO ratio, the steam-O₂ reactant favours the most compared to those of the pure oxygen and oxygen-CO₂ reactants. Under comparable operating conditions, the highest H₂/CO ratio of 0.74 was determined using steam-O₂ reactant compared to that of 0.31 and 0.33 using steam-CO₂ and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H₂ with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO₂ and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.     

Comparison between isothermal and microwave gasification of lignite char for high syngas production

Using the water of lignite as gasification agent, this paper mainly studies the influence of microwave and isothermal gasification on the syngas production and H₂/CO ratio to obtain the maximum possible amount of high-quality syngas. The results show that microwave heating produced syngas had an immensely superior performance over conventional heating. The total gas yields of 1,000 W microwave gasification is 1.75 times more than that of the 1,000°C isothermal gasification. Moreover, the values of H₂/CO ratio obtained from microwave gasification was higher than 1,000°C isothermal gasification.     

Comprehensive experimental study on supercritical water gasification of oilfield sludge: Effect of operation parameters,and catalysts on the products

Supercritical water gasification (SCWG) was adopted to treat oilfield sludge and produce syngas. The effect of temperature (400–450 °C), reaction time (30–90 min) and catalyst addition on syngas production and residual products during SCWG of oilfield sludge was studied. When increasing SCWG temperature from 400 to 450 °C with reaction time of 60 min, the H₂ yield and the selectivity of H₂ increased significantly from 0.53 mol/kg and 75.53% to 0.98 mol/kg and 78.09%, respectively. It is noteworthy that when the reaction time was too long, CO₂ and CO were converted to CH₄ with the consumption of H₂ via methanation reaction. The addition of Ni/Al₂O₃ catalyst can substantially promote the production of high-quality syngas from SCWG of oilfield sludge. The H₂ yield and its selectivity at 450 °C and 60 min were as high as 1.37 mol/kg and 84.05% with 10Ni/Al catalyst. Moreover, the catalysts with bimetal loading (Fe–Ni, Rb–Ni or Ce–Ni) were found to be beneficial for improving gasification efficiency, H₂ yield, and the degradation of organic compounds. Among them, 5 wt% Rb on 10Ni/Al catalyst performed the best catalytic activity for SCWG at 450 °C and 60 min, which had the highest H₂ yield of 1.67 mol/kg and selectivity of 86.09%. More than 90% of total organic carbon in sludge was decomposed after the SCWG with all the catalysts. These findings indicated that catalytic SCWG is a promising alternative for efficiently dealing with oilfield sludge.     

Steam gasification of Greek lignite and its chars by co-feeding CO2 toward syngas production with an adjustable H2/CO ratio

Low-rank lignite is among the most abundant and cheap fossil fuels, linked, however, to serious environmental implications when employed as feedstock in conventional thermoelectric power plants. Hence, toward a low-carbon energy transition, the role of coal in world's energy mix should be reconsidered. In this regard, coal gasification for synthesis gas generation and consequently through its upgrade to a variety of value-added chemicals and fuels constitutes a promising alternative. Herein, we thoroughly explored for a first time the steam gasification reactivity of Greek Lignite (LG) and its derived chars obtained by raw LG thermal treatment at 300, 500 and 800 °C. Moreover, the impact of CO₂ addition on H₂O gasifying agent mixtures was also investigated. Both the pristine and char samples were fully characterized by various physicochemical techniques to gain insight into possible structure-gasification relationships. The highest syngas yield was obtained for chars derived after LG thermal treatment at 800 °C, due mainly to their high content in fixed carbon, improved textural properties and high alkali index. Steam gasification of lignite and char samples led to H₂-rich syngas mixtures with a H₂/CO ratio of approximately 3.8. However, upon co-feeding CO₂ and H₂O, the H₂/CO ratio can be suitably adjusted for several potential downstream processes.     

Effect of the type of gasifying agent on gas composition in a bubbling fluidized bed reactor

It is commonly accepted that gasification of coal has a high potential for a more sustainable and clean way of coal utilization. In recent years, research and development in coal gasification areas are mainly focused on the synthetic raw gas production, raw gas cleaning and, utilization of synthesis gas for different areas such as electricity, liquid fuels and chemicals productions within the concept of poly-generation applications. The most important parameter in the design phase of the gasification process is the quality of the synthetic raw gas that depends on various parameters such as gasifier reactor itself, type of gasification agent and operational conditions. In this work, coal gasification has been investigated in a laboratory scale atmospheric pressure bubbling fluidized bed reactor, with a focus on the influence of the gasification agents on the gas composition in the synthesis raw gas. Several tests were performed at continuous coal feeding of several kg/h. Gas quality (contents in H₂, CO, CO₂, CH₄, O₂) was analyzed by using online gas analyzer through experiments. Coal was crushed to a size below 1 mm. It was found that the gas produced through experiments had a maximum energy content of 5.28 MJ/Nm³ at a bed temperature of approximately 800 °C, with the equivalence ratio at 0.23 based on air as a gasification agent for the coal feedstock. Furthermore, with the addition of steam, the yield of hydrogen increases in the synthesis gas with respect to the water–gas shift reaction. It was also found that the gas produced through experiments had a maximum energy content of 9.21 MJ/Nm³ at a bed temperature range of approximately 800–950 °C, with the equivalence ratio at 0.21 based on steam and oxygen mixtures as gasification agents for the coal feedstock. The influence of gasification agents, operational conditions of gasifier, etc. on the quality of synthetic raw gas, gas production efficiency of gasifier and coal conversion ratio are discussed in details.     

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H₂ production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H₂ production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H₂ production. The H₂/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H₂ production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.     

Syngas production by integrating CO2 partial gasification of pine sawdust and methane pyrolysis over the gasification residue

The aim of this work was to study syngas production by integrating CO₂ partial gasification (for CO production) of pine sawdust (PS) and methane pyrolysis (for H₂ production) over the gasification residue. Effect of the gasification conditions (including CO₂ flow rate, reaction temperature, mass ratio of PS:Ni and reaction time) was investigated on properties of the gasification residue. Besides CO-rich gas released from the gasification process with CO₂ conversion up to about 92%, the gasification residue could serve as robust catalyst for H₂ production by methane pyrolysis. Thanks to the nickel crystallites formed with high reduction degree and high dispersion on the surface after the gasification process, the gasification residue was competent for high and stable methane conversion (about 91%) at 850 °C. In addition to the flexible syngas output (in theory, with an arbitrary ratio of H₂/CO), valuable filamentous carbons can be achieved by regulating the process parameters.     

Partial slagging coal gasifier operational performance and product characteristics for energy sustainability in an integrated gasification combined cycle system

Operational performance of two ton/day coal partial slagging entrained-bed gasifier has been investigated. Coal to syngas conversion under operating temperature (1100–1300 °C), pressure (19.7–20.4 bar) and oxygen to coal ratio of 0.70 produced syngas at a flow rate of 177.5 Nm³/h. Composition of produced syngas was; CO 38–40 vol%, H₂ 22–23 vol%, CO₂ 7–8 vol%, and CH₄ 1.0–1.5 vol%. Carbon conversion and cold gas efficiency after one pass through operation were found to be 92.81% and 73.83% respectively. Fly ash fines produced were high in carbon content and acidic oxides than the bottom slag. Non-metal leaching nature of bottom slag was confirmed with ICP analysis. Based on the results, an industrial symbiosis can be established by recycling and reusing high carbon content fly ash fines in the gasifier. The same can be sold to other industries as a quality energy fuel. Slag produced can be used for the construction of roads and pavements.     

Transient gasification and syngas formation from coal particles in a fixed‐bed reactor

An experimental investigation on gasification and syngas formation from coal particles in a fixed‐bed reactor is conducted; particular attention is paid to the transient reaction dynamics. Three different coals, including two high‐volatile coals and a low‐volatile coal, are taken into consideration. In the initial reaction period, a two‐stage reaction is clearly observed; specifically, an exothermic reaction followed by an endothermic reaction is exhibited. Meanwhile, seeing that the devolatilization and pyrolysis reactions are pronounced, the initial concentrations of H₂ and CH₄ are relatively high, especially for the former. With increasing time, the interaction between coal and char particles is dominated by the latter, the concentrations of CO and CO₂ thus become higher. From the observation of syngas combustion, the entire gasification intensity proceeds from intensified growth, rapid decay, and then to progressive decay with increasing reaction time. For the two high‐volatile coals, the mass depletion is enhanced markedly once the reaction temperature is as high as 1000°C, whereas it is insensitive to the temperature for the low‐volatile coal. Nevertheless, it is found that, based on the weights of moisture and volatile matter, their relative release ratio from the low‐volatile coal is better than that from the high‐volatile coals. This implies that the final devolatilization and pyrolysis extent is not determined by coal grade. Copyright © 2006 John Wiley & Sons, Ltd.