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1.
Char gasification by CO2 may play an important role in oxy-fuel applications and affect particle temperature histories and overall reaction rates during combustion. This paper presents the results of a complete set of experiments of char gasification in CO2 performed with a pulverized Indonesian sub-bituminous coal in an entrained flow reactor under realistic conditions; series of burnout curves at different reactor temperatures (1040–1300 °C) and CO2 concentrations (0.7–100%) reveal consistent trends in the gasification rates. The study included also devolatilization and oxidation tests with this coal in the same experimental facility. The data are used to derive apparent kinetics for the three processes, in a manner similar to that followed in a previous work for the oxidation of a pulverized coal. The gasification kinetic parameters and reaction rates measured are then compared with values taken or derived from previous works by others, obtained by thermogravimetric analysis or experiments in entrained flow reactors. Finally, the relevance of char gasification in the overall reaction rate under conditions representative of those in an industrial boiler is explored, in particular for the case of oxy-coal combustion. 相似文献
2.
Dongdong Feng Dawei Guo Yijun Zhao Heping Tan Guozhang Chang Tianpeng Zhang Shaozeng Sun 《能源学会志》2019,92(6):1670-1682
Oxygen-fuel combustion is a promising technology for CO2 emission reduction. The high-temperature entrained flow reactor and high-temperature drop tube furnace were used to analyses the formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions. It proposed “inflection point standard” of high-temperature flame method for the preparation of real-environmental oxy-fuel coal char according to the flame method. The results show that the ratios of C=O/C-O and C=O/Car increase in the coal char compared with the raw coals. The trend of C=O/Car in oxy-fuel condition is opposite to that in the inert atmosphere, due to the effect of high-concentration CO2. To achieve the burnout rate similar to air combustion for coal char, with the increase of coal rank, the O2 concentration should be enhanced. The optimal O2 concentration for the oxy-fuel combustion of JC anthracite is 30%, while that of other low-rank coals could be lower than 30%. The combustion characteristic of JC anthracite is with the highest sensitivity to temperature and O2 concentration. 相似文献
3.
《能源学会志》2020,93(1):1-14
The difference in combustion performance between brown coal and black coal blended with Eucalyptus woodchip and woodchar in varying blending ratios were examined in the air and oxy firing conditions. On top of the experimental investigation using a drop tube furnace (DTF), a computational fluid dynamics (CFD) model was further developed to interpret these results, validated using the experimental data. The CFD model incorporates a comprehensive reaction for devolatilisation reaction to predict the gas release utilising predictions based on chemical percolation devolatilisation (CPD) model. The heterogeneous reactions are defined based on the intrinsic reaction model that accounts for the influence of char properties in chemical and pore diffusion reactions using a user-defined function (UDF). Moreover, the C–CO2 gasification reaction rate which is critical in an oxy-firing mode was further studied using the CFD tool to determine how the role of gasification varied for various fuel blends. Based on carbon burnout and average particle temperature profiles, the blending of woodchips is highly beneficial to the overall combustion performance in particular for low reactive black coal while its effect on brown coal is marginal. Woodchar and black coal are comparable with similar temperature plots and relatively constant burnout but it behaves relatively inert with a highly reactive brown coal. During oxy firing, increasing the woodchip content enhanced the effect of C–CO2 gasification due to its extremely large pre-exponential factor for the CO2 gasification reactivity which explains the improved burnout. The blending of woodchar caused a gradual reduction in the gasification extent for both coals explained by the low heating rates under which woodchar was pyrolysed and also due to the decrease in the peak particle temperature. However, the observed gasification was found to be less than the expected value based on the linear addition of the two single fuels for both biomass blends. 相似文献
4.
Supplementary firing is adopted in combined‐cycle power plants to reheat low‐temperature gas turbine exhaust before entering into the heat recovery steam generator. In an effort to identify suitable supplementary firing options in an integrated gasification combined‐cycle (IGCC) power plant configuration, so as to use coal effectively, the performance is compared for three different supplementary firing options. The comparison identifies the better of the supplementary firing options based on higher efficiency and work output per unit mass of coal and lower CO2 emissions. The three supplementary firing options with the corresponding fuel used for the supplementary firing are: (i) partial gasification with char, (ii) full gasification with coal and (iii) full gasification with syngas. The performance of the IGCC system with these three options is compared with an option of the IGCC system without supplementary firing. Each supplementary firing option also involves pre‐heating of the air entering the gas turbine combustion chamber in the gas cycle and reheating of the low‐pressure steam in the steam cycle. The effects on coal consumption and CO2 emissions are analysed by varying the operating conditions such as pressure ratio, gas turbine inlet temperature, air pre‐heat and supplementary firing temperature. The results indicate that more work output is produced per unit mass of coal when there is no supplementary firing. Among the supplementary firing options, the full gasification with syngas option produces the highest work output per unit mass of coal, and the partial gasification with char option emits the lowest amount of CO2 per unit mass of coal. Based on the analysis, the most advantageous option for low specific coal consumption and CO2 emissions is the supplementary firing case having full gasification with syngas as the fuel. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
Oxy-fuel combustion has generated significant interest since it was proposed as a carbon capture technology for newly built and retrofitted coal-fired power plants. Research, development and demonstration of oxy-fuel combustion technologies has been advancing in recent years; however, there are still fundamental issues and technological challenges that must be addressed before this technology can reach its full potential, especially in the areas of combustion in oxygen-carbon dioxide environments and potentially at elevated pressures. This paper presents a technical review of oxy-coal combustion covering the most recent experimental and simulation studies, and numerical models for sub-processes are also used to examine the differences between combustion in an oxidizing stream diluted by nitrogen and carbon dioxide. The evolution of this technology from its original inception for high temperature processes to its current form for carbon capture is introduced, followed by a discussion of various oxy-fuel systems proposed for carbon capture. Of all these oxy-fuel systems, recent research has primarily focused on atmospheric air-like oxy-fuel combustion in a CO2-rich environment. Distinct heat and mass transfer, as well as reaction kinetics, have been reported in this environment because of the difference between the physical and chemical properties of CO2 and N2, which in turn changes the flame characteristics. By tracing the physical and chemical processes that coal particles experience during combustion, the characteristics of oxy-fuel combustion are reviewed in the context of heat and mass transfer, fuel delivery and injection, coal particle heating and moisture evaporation, devolatilization and ignition, char oxidation and gasification, as well as pollutants formation. Operation under elevated pressures has also been proposed for oxy-coal combustion systems in order to improve the overall energy efficiency. The potential impact of elevated pressures on oxy-fuel combustion is discussed when applicable. Narrower flammable regimes and lower laminar burning velocity under oxy-fuel combustion conditions may lead to new stability challenges in operating oxy-coal burners. Recent research on stabilization of oxy-fuel combustion is reviewed, and some guiding principles for retrofit are summarized. Distinct characteristics in oxy-coal combustion necessitate modifications of CFD sub-models because the approximations and assumptions for air-fuel combustion may no longer be valid. Advances in sub-models for turbulent flow, heat transfer and reactions in oxy-coal combustion simulations, and the results obtained using CFD are reviewed. Based on the review, research needs in this combustion technology are suggested. 相似文献
6.
Flameless combustion is a well known measure to reduce NOx emissions in gas combustion but has not yet been fully adapted to pulverised coal combustion. Numerical predictions can provide detailed information on the combustion process thus playing a significant role in understanding the basic mechanisms for pollutant formation. In simulations of conventional pulverised coal combustion the gasification by CO2 or H2O is usually omitted since its overall contribution to char oxidation is negligible compared to the oxidation with O2. In flameless combustion, however, due to the strong recirculation of hot combustion products, primarily CO2 and H2O, and the thereby reduced concentration of O2 in the reaction zone the local partial pressures of CO2 and H2O become significantly higher than that for O2. Therefore, the char reaction with CO2 and H2O is being reconsidered. This paper presents a numerical study on the importance of these reactions on pollutant formation in flameless combustion. The numerical models used have been validated against experimental data. By varying the wall temperature and the burner excess air ratio, different cases have been investigated and the impact of considering gasification on the prediction of NO formation has been assessed. It was found that within the investigated ranges of these parameters the fraction of char being gasified increases up to 35%. This leads to changes in the local gas composition, primarily CO distribution, which in turn influences NO formation predictions. Considering gasification the prediction of NO emission is up to 40% lower than the predicted emissions without gasification reactions being taken into account. 相似文献
7.
Jeffrey J. Murphy 《Combustion and Flame》2006,144(4):710-729
Oxygen-enhanced and oxygen-fired pulverized coal combustion is actively being investigated to achieve emission reductions and reductions in flue gas cleanup costs, as well as for coal-bed methane and enhanced oil recovery applications. To fully understand the results of pilot scale tests and to accurately predict scale-up performance through CFD modeling, accurate rate expressions are needed to describe coal char combustion under these unconventional combustion conditions. In the work reported here, the combustion rates of two pulverized coal chars have been measured in both conventional and oxygen-enriched atmospheres. A combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometry diagnostic and a rapid-quench sampling probe has been used for this investigation. Highvale subbituminous coal and a high-volatile eastern United States bituminous coal have been investigated, over oxygen concentrations ranging from 6 to 36 mol% and gas temperatures of 1320-1800 K. The results from these experiments demonstrate that pulverized coal char particles burn under increasing kinetic control in elevated oxygen environments, despite their higher burning rates in these environments. Empirical fits to the data have been successfully performed over the entire range of oxygen concentrations using a single-film oxidation model. Both a simple nth-order Arrhenius expression and an nth-order Langmuir-Hinshelwood kinetic equation provide good fits to the data. Local fits of the nth-order Arrhenius expression to the oxygen-enriched and oxygen-depleted data produce lower residuals in comparison to fits of the entire dataset. These fits demonstrate that the apparent reaction order varies from 0.1 under near-diffusion-limit oxygen-depleted conditions to 0.5 under oxygen-enriched conditions. Burnout predictions show good agreement with measurements. Predicted char particle temperatures tend to be low for combustion in oxygen-depleted environments. 相似文献
8.
《能源学会志》2020,93(4):1713-1725
As an emerging clean coal combustion technology, Moderate or Intense Low-Oxygen Dilution (MILD) combustion or oxy-fuel combustion, compared with traditional coal combustion, has many advantages. However, compared with MILD combustion and oxy-fuel combustion, MILD-oxy combustion is believed more attractive. In this work, MILD-oxy combustion characteristics with oxygen concentrations from 10% to 50% are studied numerically. The results show that within a certain range, increasing the oxygen concentration is in favor of MILD-oxy combustion performance close to that of MILD-air combustion. When the oxygen concentration is higher enough, the momentum reduced by the increase of oxygen concentration has a great influence on the furnace temperature. With the increase of oxygen concentration, the radiation heat transfer is enhanced and the convective heat transfer is weakened. The increase of oxygen concentration can promote the occurrence of char gasification reaction with CO2. In addition, MILD-oxy combustion has a large impact on CO emission. 相似文献
9.
10.
F.J. Higuera 《Combustion and Flame》2008,152(1-2):230-244
The burning rate, surface temperature, drag, and extinction conditions of a single char particle moving in a gas are computed numerically. The effects of the size and velocity of the particle and of the temperature and composition of the gas are examined in the framework of a simple model that includes O2 and CO2 heterogeneous reactions and, in some cases, a diffusion-controlled CO oxidation flame in the gas around the particle. In agreement with known results, the burning rate is found to increase with the velocity of the particle when the Reynolds number of the gas flow ceases to be small. The temperature of the particle increases with the temperature and oxygen mass fraction of the gas and is little affected by the size and velocity of the particle, except in the vicinity of extinction. The drag coefficient is a decreasing function of the particle size and velocity in the range of Reynolds numbers that has been analyzed. The presence of CO2 in the gas may have an important effect on the gasification of small particles. 相似文献
11.
Numerous coal gasification studies have been found in the literature those employed various kinds of gasifying agents such as steam and carbon dioxide. These studies are featured with wide variations in the parametric conditions and the usage of equipments. Steam is frequently employed as a gasifying agent, however, in several studies carbon dioxide has also been used as a gasifying agent either pure or in combination with other gasifying agents (H2O, O2, CO, H2). This paper is a brief review of the coal gasification with CO2 as a diluent. Different factors were studied over the coal gasification with CO2 such as coal rank, pressure, temperature, gas composition, catalyst and the minerals present inside the coal, heating rate, particle size, and diverse reactor types. It also deals with the application of the gas-solid models developed in the literature and the combustion and gasification mechanisms for O2/CO2 streams. Moreover, it reviews the kinetics and the reaction rate equations (Arrhenius and Langmuir-Hinshelwood types) for coal-char gasification both in the reaction kinetic control region (low temperature) and the diffusion control region (high temperature) and at both low and high pressures. 相似文献
12.
《International Journal of Hydrogen Energy》2020,45(35):18032-18041
This work examined the effects of CO2 gasification in the reduction layer on NO emissions during subsequent char combustion in the oxidation layer during a grate-fired process. In experimental trials, the pyrolysis char of Shenhua bituminous coal was initially gasified in CO2, employing different conversion rates so as to vary the residence time of the char in the reduction layer. The pore structure and degree of graphitization of the char were monitored and the effects of CO2 gasification on NO emissions were ascertained. In this manner, the relationship between the transformation of char nitrogen and the physicochemical characteristics of the char was clarified. The effects of CO2 gasification on the properties of the char and NO emissions in the subsequent oxidation layer were determined. The results show that CO2 gasification can improve the pore structure and degree of graphitization of the char, such that NO emissions are reduced in an inert atmosphere. However, the conversion rate of char nitrogen will increase in conjunction with oxidative combustion. 相似文献
13.
The ignition temperature and burnout of a semi-anthracite and a high-volatile bituminous coal were studied under oxy-fuel combustion conditions in an entrained flow reactor (EFR). The results obtained under oxy-fuel atmospheres (21%O2-79%CO2, 30%O2-70% O2 and 35%O2-65%CO2) were compared with those attained in air. The replacement of CO2 by 5, 10 and 20% of steam in the oxy-fuel combustion atmospheres was also evaluated in order to study the wet recirculation of flue gas. For the 21%O2-79%CO2 atmosphere, the results indicated that the ignition temperature was higher and the coal burnout was lower than in air. However, when the O2 concentration was increased to 30 and 35% in the oxy-fuel combustion atmosphere, the ignition temperature was lower and coal burnout was improved in comparison with air conditions. On the other hand, an increase in ignition temperature and a worsening of the coal burnout was observed when steam was added to the oxy-fuel combustion atmospheres though no relevant differences between the different steam concentrations were detected. 相似文献
14.
Juan Riaza Reza Khatami Yiannis A. Levendis Lucía Álvarez María V. Gil Covadonga Pevida Fernando Rubiera José J. Pis 《Combustion and Flame》2014
A fundamental investigation has been conducted on the combustion behavior of single particles (75–150 μm) of four coals of different ranks: anthracite, semi-anthracite, medium-volatile bituminous and high-volatile bituminous. A laboratory-scale transparent laminar-flow drop-tube furnace, electrically-heated to 1400 K, was used to burn the coals. The experiments were performed in different combustion atmospheres: air (21%O2/79%N2) and four simulated dry oxy-fuel conditions: 21%O2/79%CO2, 30%O2/70%CO2, 35%O2/65%CO2 and 50%O2/50%CO2. The ignition and combustion of single particles was observed by means of three-color pyrometry and high-speed high-resolution cinematography to obtain temperature–time histories and record combustion behaviors. On the basis of the observations made with these techniques, a comprehensive examination of the ignition and combustion behaviors of these fuels was achieved. Higher rank coals (anthracite and semi-anthracite) ignited heterogeneously on the particle surface, whereas the bituminous coal particles ignited homogeneously in the gas phase. Moreover, deduced ignition temperatures increased with increasing coal rank and decreased with increasing oxygen concentrations. Strikingly disparate combustion behaviors were observed depending on the coal rank. The combustion of bituminous coal particles took place in two phases. First, volatiles evolved, ignited and burned in luminous enveloping flames. Upon extinction of these flames, the char residues ignited and burned. In contrast, the higher rank coal particles ignited and burned heterogeneously. The replacement of the background N2 gas of air with CO2 (i.e., changing from air to an oxy-fuel atmosphere) at the same oxygen mole fraction impaired the intensity of combustion. It reduced the combustion temperatures and lengthened the burnout times of the particles. Increasing the oxygen mole fraction in CO2 to 30–35% restored the intensity of combustion to that of air for all the coals studied. Volatile flame burnout times increased linearly with the volatile matter content in the coal in both air and all oxygen mole fractions in CO2. On the other hand, char burnout times increased linearly or quadratically versus carbon content in the coal, depending on the oxygen mole fraction in the background gas. 相似文献
15.
Nitrogen oxides (NOx) as the principal air pollutants are mainly from the combustion of fossil fuels. Oxy-fuel combustion is a promising clean coal technology, by which carbon dioxide (CO2) can be captured in large-scale and NOx emission can be reduced significantly. The formation of nitrogen dioxide (NO2) in oxy-fuel combustion exceeds that under traditional air condition. However, the specific studies on NO2 chemistry under oxy-fuel condition are still insufficient and the functional mechanisms of minerals and combustion atmosphere on NO2 reduction have yet to be fully understood. The objective of present study is to experimentally clarify the effects of combustion atmosphere and coal char on NO2 reduction in oxy-fuel combustion using a fixed-bed reactor. Experimental results showed that the decomposition of NO2 had a strong temperature dependence and the NO2 reduction rate showed a positive variation with temperature. The strength of catalytic activity in NO2 reduction to nitric oxide (NO) was Fe2O3 > MgO > CaO > Al2O3 > Na2CO3 > K2CO3 > SiO2. In addition, the increased concentrations of carbon monoxide (CO) and CO2 could promote the reduction of NO2, while the low content of CO2 only established a slight impact on NO2 reduction. However, the increase of oxygen (O2) concentration displayed an inhibition effect on NO2 reduction to a certain extent. The variation of atmosphere in oxy-fuel combustion generated a substantial influence on the creation and reduction of NO2. The char prepared in lower temperature exhibited a higher promotion effect on the consumption of NO2. Higher contents of fixed carbon and basic oxides had more obvious stimulation effects on NO2 reduction. Fixed carbon had a superior activity in NO2 reduction than ash. The kinetic analysis indicated that high content of CO and the presence of char could reduce the apparent activation energy of NO2 reduction. The present study can be helpful to improve the understanding of NO2 chemistry in oxy-fuel combustion. 相似文献
16.
《International Journal of Hydrogen Energy》2023,48(19):6975-6985
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. 相似文献
17.
Reza Khatami Chris Stivers Kulbhushan Joshi Yiannis A. Levendis Adel F. Sarofim 《Combustion and Flame》2012,159(3):1253-1271
The combustion behavior of single fuel particles was assessed in O2/N2 and O2/CO2 background gases, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized coals from different ranks (a high-volatile bituminous, a sub-bituminous and two lignites) as well as pulverized sugarcane-bagasse, a biomass residue. Particles of 75–90 μm were injected under laminar flow in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400 K where, upon experiencing high heating rates, they ignited and burned. The combustion of individual particles was observed with three-color optical pyrometry and high-speed high-resolution cinematography to obtain temperature and burnout time histories. Based on combined observations from these techniques, a comprehensive understanding of the behaviors of these fuels was developed under a variety of conditions, including simulated oxy-fuel combustion. The fuels exhibited distinct combustion behaviors. In air, the bituminous coal particles burned in two distinctive modes; the volatiles burned in bright envelope flames surrounding the devolatilizing char particles followed by heterogeneous char combustion. The volatile matter of sub-bituminous coal particles burned either in subdued envelope flames, surrounding devolatilizing and occasionally fragmenting chars, or heterogeneously at the char surface. Lignite particles typically burned with extensive fragmentation, and their volatiles burned simultaneously with the char fragments. The volatiles of bagasse particles burned in spherical and transparent envelope flames. Increasing the oxygen mole fraction in N2, increased flame and char surface temperatures, and decreased burnout times; particles of all fuels burned more intensely with an increasing tendency of the volatiles to burn closer to the char surface. When the background gas N2 was substituted with CO2, the combustion of all fuels was distinctly less intense; at moderate O2 mole fractions (<30%) most particles did not ignite under active flow conditions in the furnace (they did ignite under quiescent gas flow conditions in the DTF). Increasing the oxygen mole fraction in CO2 increased the likelihood of combustion and its intensity. Combustion of volatiles in envelope flames was suppressed in the presence of CO2, particularly under active gas flow in the DTF. 相似文献
18.
Yijun Zhao Wenda Zhang Pengxiang Wang Peng Liu Guang Zeng Shaozeng Sun Shu Zhang 《International Journal of Hydrogen Energy》2018,43(24):10991-11001
This study aims to examine the char-steam reactions in-situ, following the pyrolysis process of a demineralized coal in a micro fluidized bed reactor, with particular focuses on gas release and its kinetics characteristics. The main experimental variables were temperatures (925 °C?1075 °C) and steam concentrations (15%–35% H2O), and the combination of pyrolysis and subsequent gasification in one experiment was achieved switching the atmosphere from pure argon to steam and argon mixture. The results indicate that when temperature was higher than 975 °C, the absolute carbon conversion rate during the char gasification could easily reach 100%. When temperature was 1025 °C and 1075 °C, the carbon conversion rate changed little with steam concentration increasing from 25% to 35%. The activation energy calculated from shrinking core model and random pore model was all between 186 and 194 kJ/mol, and the fitting accuracy of shrinking core model was higher than that of the random pore model in this study. The char reactivity from demineralized coal pyrolysis gradually worsened with decreasing temperature and steam partial pressure. The range of reaction order of steam gasification was 0.49–0.61. Compared to raw coal, the progress of water gas shift reaction (CO + H2O ? CO2 + H2) was hindered during the steam gasification of char obtained from the demineralized coal pyrolysis. Meanwhile, the gas content from the char gasification after the demineralized coal pyrolysis showed a low sensitivity to the change in temperature. 相似文献
19.
Cao Kuang Shuzhong Wang Song Lv Jianjun Cai Ming Luo Jun Zhao 《International Journal of Hydrogen Energy》2021,46(34):18032-18041
As one of clean coal combustion ways, chemical looping combustion (CLC) showed high CO2 capture efficiency with lower energy penalty. But these processes were limited by the low reaction rate between oxygen carriers (OCs) with coal char. This study evaluated the performances of Cu-based OCs with coal in in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) process. CuO modified by iron ore and chrysotile were employed as OCs which the addition of chrysolite improved the char gasification and iron ore enhanced the stability of CuO at high temperature. Results showed that CuO supported by ores (chrysolite and iron ore) had better H2 and CO conversion under H2O atmosphere than CuO and iron ore. Chrysolite decorated CuO can convert almost all H2 to H2O at 850 °C. Synthetic OCs showed better stability and high temperature tolerance during 10 redox cycles. 相似文献
20.
The present paper focuses on the gasification of thin wood particles in pure CO2 at 850 °C under high heating rate conditions (similar to fluidized bed gasifiers). The aim is to assess the potential use of CO2 as gasifying medium and to learn more about its effects on the pyrolysis as well as on the char gasification stages. Experimental and numerical modelling results provide answers on the unfolding of the whole CO2 biomass pyro-gasification process. It was found that despite the CO2 is present inside the particle during the pyrolysis stage, it has no noticeable impacts neither on the reaction rate nor on the char yield due to the relatively low temperature inside the particle. The CO2 char gasification is the rate limiting step of the global pyro-gasification reaction as its duration is near to 95% of the entire biomass conversion time. 相似文献