CO2 Gasification Of Coal Char Research Articles

Recent Progress on Hydrogen-Rich Syngas Production from Coal Gasification

Coal gasification is recognized as the core technology of clean coal utilization that exhibits significant advantages in hydrogen-rich syngas production and CO2 emission reduction. This review briefly discusses the recent research progress on various coal gasification techniques, including conventional coal gasification (fixed bed, fluidized bed, and entrained bed gasification) and relatively new coal gasification (supercritical water gasification, plasma gasification, chemical-looping gasification, and decoupling gasification) in terms of their gasifiers, process parameters (such as coal type, temperature, pressure, gasification agents, catalysts, etc.), advantages, and challenges. The capacity and potential of hydrogen production through different coal gasification technologies are also systematically analyzed. In this regard, the decoupling gasification technology based on pyrolysis, coal char–CO2 gasification, and CO shift reaction shows remarkable features in improving comprehensive utilization of coal, low-energy capture and conversion of CO2, as well as efficient hydrogen production. As the key unit of decoupling gasification, this work also reviews recent research advances (2019–2023) in coal char–CO2 gasification, the influence of different factors such as coal type, gasification agent composition, temperature, pressure, particle size, and catalyst on the char–CO2 gasification performance are studied, and its reaction kinetics are also outlined. This review serves as guidance for further excavating the potential of gasification technology in promoting clean fuel production and mitigating greenhouse gas emissions.

Gasification behavior and kinetics of chars derived from coal pyrolysis in a CO-containing atmosphere

Char gasification enables clean and efficient utilization of low-rank coal resources. The CO2 gasification behavior and kinetics of char samples produced via low-rank coal pyrolysis under the N2 and CO-containing atmospheres (char-N2 and char-CO) were investigated based on a series of thermogravimetric experiments, and the physicochemical structure of chars were characterized via Raman diffraction, X-ray diffraction, and CO2 adsorption methods, respectively. The apparent activation energies (Ea) of char-N2 and char-CO were obtained using the Flynn–Wall–Ozawa method and the reaction mechanism was determined via the Malek method. The results indicate that the graphitization and order degrees of the carbon chemical structure of char-CO are higher than those of char-N2 below gasification temperature (approximately 850 °C), whereas the specific surface area of char-CO is higher than that of char-N2 before gasification. Char-CO gasifies faster than char-N2 owing to its developed pore structure, and the gasification activation energy is lower than that of char-N2 (from 450 °C to 650 °C, the activation energy of char-N2 is 186.3 kJ mol−1, 192.4 kJ mol−1, and 203.6 kJ mol−1, and that of char-CO is 175.8 kJ mol−1, 187.5 kJ mol−1, and 199.1 kJ mol−1, respectively). The CO2 gasification reaction process of char-N2 and char-CO can be explained using a three-dimensional diffusion model. Moreover, the ash content in coal char affects the diffusion of reaction carrier gas and gas products during the gasification process, indicating that diffusion is the primary limiting factor in coal char CO2 gasification.

Detailed kinetic analysis and modelling of the dry gasification reaction of olive kernel and lignite coal chars

The dry gasification process of solid fuels is a promising pathway to mitigate and utilize captured CO2 emissions toward syngas generation with tailored composition for several downstream energy conversion and chemical production processes. In the present work, comprehensive kinetic analysis and reaction modelling studies were carried out for olive kernel and lignite coal chars gasification reaction using pure CO2 as gasifying agent. Chars reactivity and kinetics of the gasification reactions were thoroughly examined by thermogravimetric analysis at three different heating rates and correlated with their physicochemical properties. The reactivity of olive kernel char, as determined by the mean gasification reactivity and the comprehensive gasification characteristic index, S, was almost three times higher compared to that of the lignite coal char. It was disclosed that the fixed carbon content and alkali index (AI) have a major impact on the reactivity of chars. The activation energy, Ea, estimated by three different model-free kinetic methods was ranged between 140 and 170 kJ/mol and 250–350 kJ/mol for the olive kernel and lignite coal chars, respectively. The activation energy values for the lignite coal char significantly varied with carbon conversion degree, whereas this was not the case for olive kernel char, where the activation energy remained essentially unmodified throughout the whole carbon conversion range. Finally, the combined Malek and Coats-Rendfrem method was applied to unravel the mechanism of chars-CO2 gasification reaction. It was found that the olive kernel char-CO2 gasification can be described with a 2D-diffusion mechanism function (D2) whereas the lignite coal char-CO2 gasification follows a second order chemical reaction mechanism function (F2).

Influence of Different Catalysts on Coal Char-CO2 Gasification

The influence of catalyst Fe(NO3)3, CaO and composite catalysts on the thermostatic gasification process of char-CO2 at atmospheric pressure were studied in this paper. The experimental conclusions Indicate that the catalytic effect of CaO is stronger than that of Fe(NO3)3 at relatively low gasification temperatures. As the gasification temperature increases, the catalytic gap between the two catalysts decreases. The catalytic effect of the composite catalyst at lower gasification temperatures is between the single component catalysts CaO and Fe(NO3)3. When the gasification temperature exceeds 850°C, the promoting effect of the composite catalyst is better than that of the to single-component catalysts. After adding composite catalyst, the time of the coal char is shorter by 103 minutes than the original char, which is shortened by 18 minutes compared with the two single-component catalysts, and the gasification temperature is lowered by 100°C, lower than 120°C of one-component CaO, and higher than 90°C of Fe(NO3)3.

CO2 gasification of Yangchangwan coal catalyzed by iron-based waste catalyst from indirect coal-liquefaction plant

Coal char-CO2 gasification is a strong endothermic reaction with high energy consumption, and a cheap catalyst use is one of the keys to save process costs. The iron-based waste catalyst (IWC) from indirect coal-liquefaction plant contains active component, but its effect on the gasification reactivity of coal char is seldom reported. Thus, CO2 gasification of Yangchangwan coal (YCW) was conducted in thermogravimetric analyzer (TGA) with IWC as the catalyst. The change of functional group on coal char surface was measured by a Fourier transform infrared (FT-IR) spectroscopy. The morphology of coal char was characterized by focused ion beam scanning electron microscope (FIB-SEM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze phases and valences of iron. The results indicate that IWC was effective for YCW gasification. In the range of 1000–1200 °C, the optimal temperature of catalytic gasification was 1000 °C. The FT-IR spectra of YCW gasified char showed the changes of small molecule active groups, such as –OH, C–O, –CH2, –CH3, C=C and Fe–O in the process of catalytic gasification. The surface structure of coal char was rough and there were lots of tiny pores. The metallic Fe formed by IWC at 0 min was finally oxidized by gasification agent CO2 to FeO and Fe3O4. The redox cycle between Fe0, Fe2+ and Fe3+ is the main reason for the catalytic YCW-CO2 gasification reactivity in the presence of IWC.

Kinetic and thermodynamic investigations of CO2 gasification of coal chars prepared via conventional and microwave pyrolysis

This study examined an isothermal CO2 gasification of four chars prepared via two different methods, i.e., conventional and microwave-assisted pyrolysis, by the approach of thermogravimetric analysis. Physical, chemical, and structural behaviours of chars were examined using ultimate analysis, X-ray diffraction, and scanning electronic microscopy. Kinetic parameters were calculated by applying the shrinking unreacted core (SCM) and random pore (RPM) models. Moreover, char-CO2 gasification was further simulated by using Aspen Plus to investigate thermodynamic performances in terms of syngas composition and cold gas efficiency (CGE). The microwave-induced char has the largest C/H mass ratio and most ordered carbon structure, but the smallest gasification reactivity. Kinetic analysis indicates that the RPM is better for describing both gasification conversion and reaction rates of the studied chars, and the activation energies and pre-exponential factors varied in the range of 78.45–194.72 kJ/mol and 3.15–102,231.99 s−1, respectively. In addition, a compensation effect was noted during gasification. Finally, the microwave-derived char exhibits better thermodynamic performances than the conventional chars, with the highest CGE and CO molar concentration of 1.30% and 86.18%, respectively. Increasing the pyrolysis temperature, gasification temperature, and CO2-to-carbon molar ratio improved the CGE.

Diffusion effect and evolution of kinetic parameters during coal char-CO2 gasification

Large coal char particle (LCC, 12 mm and 20 mm cube) and small coal char particle (SCC, less than 50 μm) were gasified under different temperatures in fixed bed reactor and thermogravimetric analyzer, respectively. The effectiveness factor and kinetic parameters (apparent activation energy and apparent pre-exponential factor) were also calculated to investigate the diffusion effect and the evolution of kinetic parameters during coal char-CO2 gasification. It was found that the internal effectiveness factor was not constant during the conversion process of coal char. In the intermediate and later stage of gasification reaction, there was a remarkable increase for the effectiveness factor. The effectiveness factor of LCC and SCC in the higher temperature range were all much less than 1, this indicated that the gasification of LCC and SCC at high temperature was limited by pore diffusion. Apparent activation energy and apparent pre-exponential factor evolved gradually during the whole conversion process, the existence of diffusion effect would lead to a certain change for the evolution law. A kinetic compensation effect was observed between the apparent activation energy and apparent pre-exponential factor during the conversion process of coal char. When the diffusion effect was very significant, it would have a certain weakening effect on the compensation effect.

Different catalytic action of ion-exchanged calcium in steam and CO2 gasification and its effects on the evolution of char structure and reactivity

The catalytic action of ion-exchanged calcium (Ca) in steam and CO2 gasification of coal char was examined. Its effects on pore structure and reactivity of char were also investigated. The char was prepared from a low rank coal that was first demineralized and then loaded with Ca by ion-exchanging. It was gasified at 900 °C in steam or CO2 on a specially designed thermogravimetric reactor (TGR). Partially-gasified chars were extracted at different time intervals and subject to analyses by X-ray diffraction (XRD), nitrogen adsorption measurement and scanning electron microscopy (SEM). The results show that, in steam gasification, the Ca evolves predominantly into CaO particles. They are highly dispersed on the char surface and seen to attack the char by a typical channeling mode. In contrast, the Ca is transformed into both CaO and CaCO3 in CO2 gasification. These Ca-containing compounds undergo significant sintering and form a mixture layer on the char surface. The catalytic action of Ca can be appropriately described by a surface recession mode. These differences are responsible for the evolution of char structure and reactivity. The channeling action of Ca in steam gasification results in a higher surface area and pore volume. The highly dispersed CaO particles more efficiently catalyze the reactions at the early stage of gasification. In CO2, the char possesses a less developed pore structure. The catalysts are in close contact with carbon at the later stage of CO2 gasification and the char remains a higher specific reactivity.

Development of LaFeO3 modified with potassium as catalyst for coal char CO2 gasification

Coal catalytic gasification is an effective way to realize clean coal utilization. The core of this technology is the preparation of highly efficient and stable catalysts. At present, perovskite-type oxides have attracted increasing attention as a promising catalyst because of its good thermal stability and redox activity. In this study, perovskite-type oxides were proposed to act as catalyst for coal char CO2 gasification, and K was further used for LaFeO3 catalyst modification to improve its catalytic activity. The catalytic performances of La1-xKxFeO3 (x=0-0.9) were tested by thermogravimetric analysis and fixed-bed tube reactor. The crystal structure was determined by X-ray diffraction (XRD), the percentage content and valence state of surface elements were examined by X-ray photoelectron spectroscopy (XPS), the surface morphology of perovskite samples was observed by scanning electron microscopy (SEM). Besides, the specific surface area and average particle diameter were analyzed by N2 absorption/desorption technology (BET) and laser particle size analyzer, respectively. Results suggested that the perovskite-type catalyst can effectively lowered the initial reaction temperature and exhibited improved catalytic activity after a part of La3+ at A-site was replaced by K+. The time required to achieve 50% carbon conversion in the initial reaction was reduced by 87.3% when the molar ratio of K+ increased from 0 to 0.7. The La0.3K0.7FeO3 perovskite also exhibited relatively stable catalytic activity during cyclic process, and its optimal temperature in coal char CO2 gasification was approximately 850 °C. The XRD patterns indicated that the perovskite structure of catalyst can remain unchanged when K+ doping ratio was lower than 0.8. Therefore, 0.7 is a suitable doping ratio. The perovskite La0.3K0.7FeO3 still exhibited perovskite crystal structure after 10 cycles of experiment. The XPS results indicated that additional oxygen vacancies and Fe4+ formed after K+ doping, which contributed to gas adsorption and electron transfer and improved oxidation performance. SEM and BET showed that the pore structure of catalyst was destroyed during cyclic gasification, resulted in the enlargement of particle size detected by laser particle size analyzer. Leading to the decrease in effective contact area and catalytic performance. Thus, K+-modified perovskite La1-xKxFeO3 is a kind of equipment-friendly, efficient and recyclable catalyst and can be used as a promising catalyst for coal char CO2 gasification.

Competitive or additive behavior for H2O and CO2 gasification of coal char? Exploration via simplistic atomistic simulation

Here, a large-scale char atomistic structure (41,438 carbon atoms) and simple simulation approaches explored char gasification behavior for H2O and CO2 — comparing their mixture with one gas being passive (non-reactive) and the dual reactive mixture. Reactivity was captured through simplistic atomistic simulations via an automated sequence of gas diffusion, close-contact determination for gas (es) to reactive edge sites, then “reaction” via atom deletion. The higher reactivity of H2O was captured by a reaction probability function. For the reactive mixture (where both gases are reactive), the char consumption rate was 14% higher than with H2O alone, but lower (∼80%) than the sum of the individual gases (where only one gas is reactive), demonstrating competitive behavior. The H2O out competed the CO2 molecules and contributed ∼83% to the char consumption — with the reaction rate being similar to that of H2O independently. The pore size development for individual gases also differed with H2O favoring development in the smaller pore sizes in comparison to CO2. With fewer gas molecules (using 10% to capture a lower pressure), the competitive behavior was muted and became much closer to additive behavior. These simple simulations are consistent with the emerging rationalization of contributing factors to char gasification.

Na2CO3 catalyzed CO2 gasification of coal char and its intermediate complexes

The catalytic effect of Na2CO3 on the CO2 gasification of Zhundong coal char was analyzed using the thermo-gravimetric analyzer. Besides, the structural characteristics of the sodium-added chars were examined using scanning electron microscopy (SEM), X-ray photoelectric spectroscopy (XPS), confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The results indicate that the Na2CO3 induces the remarkably promotional effect on the CO2 gasification of the Zhundong coal char. As the catalyst content increased from 2.5 to 10 wt%, the reactivity index increases by approximately eight times. Furthermore, the SEM, CLSM and Raman reveal that the addition of Na2CO3 contributes to the formation of disordered and amorphous carbon structure. The sodium-added chars exhibit relatively rough morphology with the multi-particles and large size of pores. In addition, the Na2CO3–carbon interactions occur at low temperature, together with the release of CO2. As the temperature increased, complex precursors containing O and Na start to generate. The existence of the complex –CONa is proven through the analysis of the XPS and FT-IR results. These complexes make it easy for CO2 to attack the char, thereby prompting the gasification reactivity of the Zhundong char.

Experimental estimate of CO2 concentration distribution in the stagnant gas layer inside the thermogravimetric analysis (TGA) crucible

The measurement of char gasification reactivity and kinetic parameters by TGA is generally complicated with mass transfer limitations. There is a reactant gas concentration gradient in the stagnant gas region between the mouth of the TGA crucible and the surface of the char bed because of gas consumption by the sample. The counter-diffusions between the reactant and product gases occur in this stagnant region. The Maxwell-Stefan equation has been used to estimate the distribution of gas concentration in the stagnant gas region. However, there is some uncertainty associated with semi-empirical gas diffusion coefficients used in the equation. In this study, we propose a new method to estimate the distribution of CO2 concentration in the stagnant gas region during CO2 gasification of coal char in TGA. The external effectiveness factors obtained in this way were in a reasonably good agreement with the value obtained by the traditional method widely used in literature.

Syngas production via coal char-CO2 fluidized bed gasification and the effect on the performance of LSCFN//LSGM//LSCFN solid oxide fuel cell

Fluidized bed reactor is widely used in coal char-CO2 gasification. In this work, the production of syngas by using a fluidized bed gasification technique was first investigated and then the effect of the produced syngas on the performance of the solid oxide fuel cell with a configuration of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ//La0.8Sr0.2Ga0.83Mg0.17O3-δ//La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ(LSCFN//LSGM//LSCFN) was studied. During the syngas production, we found that the volume fraction of CO increased with the increment of gasification temperature, and it reached a maximum value of 88.8%, corresponding to a composition of 0.76% H2, 88.8% CO, and 10.44% CO2, when the ratio of oxygen mass flow rate to that of coal char (MO2/Mchar) increased to 0.29. In the following utilization of the produced syngas in solid oxide fuel cells, it was found that the increasing CO volume fraction in the syngas results in a gradual increase of the peak power density of the LSCFN//LSGM//LSCFN cell. The maximum peak power density of 410mW/cm2 was achieved for the syngas produced at 0.29 of MO2/Mchar. In the stability test, the cell voltage decreased by 4% at a constant current density of 0.475A/cm2 after 54h when fueled with the syngas with the composition of 0.76% H2, 88.8% CO, and 10.44% CO2. It reveals that a carbon deposition with the content of 13.66% in the anode is attributed to the cell performance degradation.

Formation, fates and roles of catalytic precursors generated from the K2CO3-carbon interactions in the K2CO3-catalyzed CO2 gasification of coal char

A study was carried out in both inert and CO2 atmosphere to investigate the interaction mechanism of K2CO3 with graphite and coal char during the catalytic gasification of coal char. The formation of K2CO3 catalytic precursors was identified by using series of different techniques. The results obtained in an inert atmosphere show that the interaction between K2CO3 and carbon readily took place at low temperature. For the K2CO3 loaded graphite, the intermediate of CnK clusters formed by the interactions of K2CO3 with carbon prevented the evaporation of K at low temperature. At temperatures above 800°C, however, the CnK clusters were unstable, and decomposed to release K through vaporization. On the contrary, for the K2CO3 loaded demineralized coal char, due to the presence of oxygen groups, K was tightly bonded to carbon during heating, forming a complex precursor containing O and K with high thermal stability. The reaction pathway of carbon-K2CO3 interactions in an inert atmosphere are proposed for both char and graphite. The results of DRIFTs experiment suggest that CO2 is chemisorbed by the K- catalytic precursors during CO2 gasification to form potassium phenolate species and a covalently bound carbonate group (dimethyl carbonate). It is believed that these species act as active intermediates in the gasification process.

Brown coal char CO2-gasification kinetics with respect to the char structure. Part I: Char structure development

German lusatian brown coal was gasified in a laboratory scale fluidized-bed type reactor using CO2 as gasification agent. The experiments were carried out at temperatures of 800, 850, 900 and 950°C. The raw brown coal was first pyrolyzed in a way to minimize the volatile matter content in the resulting char. Then the char was used to study the Boudouard reaction (C+CO2=2CO) with respect to the char structure. Temperature range as well as char particle size fraction (200–315μm) were specifically chosen in order to approach the chemically controlled kinetic regime. Chars were gasified completely as well as partially up to certain carbon conversion degrees. Structure characteristics of partially gasified chars such as surface area and porosity were determined using the N2 adsorption technique and mercury porosimetry respectively. Surface area values were obtained from adsorption isotherms using several methods: Brunauer–Emmett–Teller (BET), Langmuir, t-plot and Barrett–Joyner–Halenda (BJH). The choice of the methods was discussed. The results show that the development of char surface area with char conversion at lower temperature (800°C) slightly differs from those at higher temperatures (850–950°C). It was found, that the heterogeneous char-CO2 reaction mostly takes place on mesopore surface area, which presumably is developed from micropore surface area in the beginning of char conversion. This was also confirmed by mercury porosimetry analysis. Total char porosity increases linearly during char conversion at all studied temperatures. The change of char particle size during carbon conversion showed no obvious change in char particle size until 50% of carbon conversion; however, the size decreased beyond this carbon conversion from particle fragmentation.

Effect of CO2 gasification reaction on char particle combustion in oxy-fuel conditions

CO2 gasification of coal char may play an important role in oxy-combustion environments with flue gas recirculation (FGR), but its effect on the overall reaction rate has not been clearly understood. To give clarity to the likely impact of CO2 gasification on the oxy-combustion of pulverized coal chars, burnout simulations of coal char particles were carried out, adopting apparent char reactivity and a single-film model that includes the Stefan flow effect on mass and energy transfer. Three oxygen concentrations (21%, 30%, and 5% O2), representing air, oxy-fuel, and oxygen-deficient combustion environments were simulated. A new experimental approach was used to directly measure the CO2 gasification rate of a subbituminous coal char at high temperatures and atmospheric pressure. The measured gasification rate is somewhat higher than previous measurements. The simulation results show that the endothermic gasification reaction reduces the char particle temperature and thereby reduces the oxidation rates. However, due to the contribution of the direct gasification reaction on carbon consumption, the char burnout time and the carbon consumption were improved. The gasification reaction has a greater influence on the char burnout time and the relative carbon consumption in an oxygen-deficient environment and on the drop of particle temperature in an oxygen-enriched environment (for a given gas temperature). In addition, the influence of the gasification reaction on char combustion increases as the gas temperature increases and as the particle size increases. Further, it was observed that the impact of the gasification reaction is dependent on the presumed kinetic rate, which highlights the importance of using reliable kinetic parameters in simulations. Based on the present results, it is important to include the gasification reaction by CO2 when simulating char combustion in oxy-fuel combustion environments.

Effects of CO2 Atmosphere and K2CO3 Addition on the Reduction Reactivity, Oxygen Transport Capacity, and Sintering of CuO and Fe2O3 Oxygen Carriers in Coal Direct Chemical Looping Combustion

Chemical looping combustion (CLC) of coal has received increasing interest in recent years. However, few attempts have been made to examine the effects of CO2 atmosphere and K2CO3 addition on the reduction rate, the oxygen transport capacity (OTC), and the sintering of the oxygen carrier when coal is used directly in CLC. In this work, these issues for Fe2O3 and the CuO oxygen carriers were investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and inductively coupled plasma–atomic emission spectrometry (ICP-AES). The TGA results indicate that the reduction rates can be increased by either the CO2 atmosphere or the K2CO3 additive due to the enhanced CO2 gasification of coal char. Detailed analyses demonstrate that the CO2 atmosphere affects the OTC and the sintering of the oxygen carrier by thermodynamic restrictions. The CO2 atmosphere has no effect on the OTC of the CuO oxygen carrier, and there are no significant differences in si...

The kinetics of CO2 gasification of coal chars

The gasification reactivities of three char samples derived from coals of varying ranks (“Turow” lignite, “Piast”, and “Wieczorek” sub-bituminous coals) toward CO2 were investigated isothermally using thermogravimetric analysis. Kinetic behavior was studied at temperatures of 900, 950, and 1,000 °C under atmospheric pressure. Conditions for the chemical-controlled regime were established at these temperatures and pressure. In this paper, four kinetic models were applied to describe the varying conversion rate: volumetric model, grain model, modified volumetric model, and random pore model. From these models, only the random pore and the volumetric models positively corresponded to nearly the entire range of experimental results. Calculated values of activation energy for study samples were in the range of 180–250 kJ mol−1, which is in accordance with other reported data. Moreover, the obtained results confirmed the significant impact of parent coal rank on its char reactivity, offering possibilities in the approximation of coal char kinetic behavior after further more detailed studies with a larger number of samples.

A quantitative evaluation of active site number for CO2 gasification of various coal chars by temperature-programmed desorption method.

A temperature-programmed desorption (TPD) method was applied to the characterization of CO2 gasification of coal chars obtained by pyrolysis of coals of various ranks ranging from brown to sub-bituminous coals. Gasification was carried out at temperatures of 1073 and 1273 K and pressures from 0.4 to 1.6 MPa, using a high-pressure TGA apparatus. For all chars employed, the rate constant based on the initial char weight, kv, decreased with the progress of gasification. This variation of kv was unexplained in terms of the change in the BET surface area of the chars obtained at different conversions; in general, the rate constant based upon the surface area, ks, decreased with char conversion lower than about 0.2 and then remained constant before decreasing again at the conversion of 0.8 towards the completion of the reaction. The active site number, NCO, was evaluated on the basis of the amount of CO desorbed in TPD runs after CO2 was adsorbed. Thus, the rate constant per unit number of active sites, ka, was estimated on the basis of the NCO and the Kv values for chars having different conversion levels. The values of ka obtained at 1073 and 1173 K were found to be invariable for conversions up to about 0.8 to 0.9 and to be of the same order of the magnitude for all chars at a given temperature. However, in all cases they decreased with conversion in the range higher than 0.9. This decrease in char reactivity was attributed to variation in the carbon structure of the char. X-ray diffraction spectra indicated an appreciable growth of the graphite peak at the final stage of gasification.