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Six individual coals and one blended metallurgical coal were used in this investigation, and two additives, Fe2O3 (up to 1%) and K2CO3 (0.5%), were added to each coal before carbonization. Results showed that the additives strongly increase CRI (coke reactivity index) and decrease CSR (coke strength after reaction) of each coke, but there are no significant changes in coke microstructure. 相似文献
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基于整体煤气化联合循环和燃料电池发电技术,利用固体氧化物燃料电池产生的高温、高纯度CO2与H2O作为煤焦气化的气化剂,运用Aspen Plus模拟软件平台基于Gibbs自由能最小化方法对煤焦的H2O-CO2共气化反应进行了模拟计算。考察了O2流量、H2O流量、CO2流量、预热温度、操作压力、反应温度对气化反应合成气组成和煤气低位发热量的影响。结果显示:通过调节O2流量,得出O2的最佳流量为20 kg/h,此时反应温度和合成气低位热值处于最高值;分别增加水蒸气流量和CO2流量都使反应温度降低,且使反应活性降低导致合成气低位热值降低,所以合理控制水蒸气和CO2流量至关重要;降低操作压力会降低合成气的低位热值,但相对于物料流量改变,影响较小;CO2预热对煤气低位发热量的影响要小于O2的预热效果。 相似文献
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钾、钙对煤焦气化反应性具有重要影响,秸秆灰中含有丰富的钾、钙。以神木煤为制焦原料,通过STA409PC同步热分析仪研究了秸秆灰对煤焦气化反应性的影响,并通过测定煤焦的碘吸附值对其比表面积及孔隙结构进行了分析。结果表明:煤与玉米秸秆共焦化所得煤焦的气化反应性明显优于单独煤焦,且与玉米秸秆的添加比例有关;采用脱灰玉米秸秆与煤共焦化所得煤焦的气化反应性与单纯煤焦相近;将与玉米秸秆等效的秸秆灰添加到煤焦中,煤焦的气化效果明显优于等效玉米秸秆与煤共焦化所得煤焦。煤焦碘吸附值测定结果表明,脱灰秸秆与煤共焦化所得煤焦的碘吸附值最大,单纯煤焦的碘吸附值最小,说明玉米秸秆及秸秆灰对煤焦的比表面积及孔隙结构具有重要的影响,与煤焦的气化反应性评价结果基本一致。 相似文献
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Conventional gasification processes use coal not only as feedstock to be gasified but also for supply of energy for reaction heat, steam production, and other purposes. With a nuclear high temperature reactor (HTR) as a source for process heat, it is possible to transform the whole of the coal feed into gas. This concept offers advantages over existing gasification processes: saving of coal, as more gas can be produced from coal; less emission of pollutants, as the HTR is used for the production of steam and electricity instead of a coal-fired boiler; and a lower production cost for the gas. However, the process has the disadvantage that the temperature is limited to the outlet temperature (950 °C max) of the helium cooling gas of the HTR. Therefore the possibility of catalytic steam gasification was examined. Model calculations based on experimental results show that use of 3–4 wt% relative to coal of K2CO3 catalyst increases the throughput of a large scale nuclear gasification plant by ≈65%, while gas production costs decrease by ≈15%. Corrosion by catalysts is not significant at low concentration (< 5 wt%) and low temperature (< 900 °C). 相似文献
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Supaporn Sawettaporn Kunchana Bunyakiat Boonyarach Kitiyanan 《Korean Journal of Chemical Engineering》2009,26(4):1009-1015
Two sized fractions (<75 μm and 150–250 μm) of Ban Pu lignite A and Lampang subbituminous B coals were pyrolyzed in a drop
tube fixed bed reactor under nitrogen atmosphere at 500–900 °C. Gasification of coal chars with excess carbon dioxide was
then performed at 900–1,100 °C. The result was analyzed in terms of reactivity index, reaction rate and activation energy.
It was found that chars at lower pyrolysis temperature had highest carbon conversion, and for chars of the same sized fraction
and at the same pyrolysis temperature, reactivity indices increased with gasification temperature. The lower rank Ban Pu lignite
A had higher R
s
values than higher rank Lampang subbituminous B coals. Smaller chars from both coals had higher R
s
values, due to the higher ash content. At present, it can be concluded that, within the gasification temperature range studied,
gasification rates of chars obtained at various pyrolysis temperatures showed a linear correlation with temperature. However,
additional experiment is needed to verify the correlation. 相似文献
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A study was carried out to ascertain the effects of coal preoxidation and carbonization conditions on the structure and relative gasification potential of a series of bituminous coal chars. Chars were prepared from two freshly mined bituminous coals and preoxidized samples derived from them. Carbonization conditions included a wide range of heating rate (0.2–10000K s?1), temperature (1073–1273 K) and time (0.25–3600 s). Char properties were characterized in terms of analysis of char morphology, surface area, elemental composition, and gasification reactivity in air. Over the range of conditions used, preoxidation substantially reduced coal fluid behaviour and influenced macroscopic char properties (char morphology). Following slow heating (0.2 K s?1), preoxidized coals yielded chars having higher total surface areas and higher reactivities toward gasification in air than did similar chars prepared from fresh coal. Following rapid heating (10000 K s?1) and short residence times (0.25 s), chars prepared from preoxidized and fresh coals exhibited similar microstructural and chemical properties (surface area, ratios, gasification rates). Carbonization time and temperature were found to be the critical parameters influencing char structure and gasification potential. 相似文献
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Mingmin Wang Jiansheng Zhang Shouyu Zhang Jinhu Wu Guangxi Yue 《Korean Journal of Chemical Engineering》2008,25(6):1322-1325
The gasification rates of Shenmu coal chars with CO2 were experimentally studied with a pressurized thermo- gravimetric analyzer (PTGA). Shenmu coal is a typical Chinese coal,
and the coal char was prepared by a fixed-bed reactor in nitrogen at 900 °C. The experiments were carried out in the dynamic
heating segments from 750 °C to 1,000 °C, and the reaction pressure increased from 0.1MPa to 3.1MPa with pure CO2. The external diffusion resistances were minimized by increasing the flow rates and decreasing the thickness of sample layer
before the test, to ensure the reactions were under kinetic control. The results show that the gasification rates increase
proportionally to the 0.1 power of the CO2 partial pressure. The unreacted-core shrinking model was applied to predict the reaction rate by changing the molar fraction
of CO2 at 0.6Mpa and 1.6Mpa total pressures, which showed a good match with experimental data.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
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Zhongjie Shen Jianliang Xu Haifeng Liu Qinfeng Liang 《American Institute of Chemical Engineers》2017,63(2):716-724
A high temperature stage microscope to investigate the temperature effect caused by particle size on char gasification is applied in this study. Experiments were carried out with different particle sizes for raw chars and chars on molten slag surface, respectively. Heat transfer models were built for the raw char of two temperature distributions and char particle on molten slag, respectively. Results showed that reaction layer temperature of raw char decreased in the reaction dominant while char on molten slag had higher temperature. Temperature difference between two distributions increased with the initial particle size, indicating the temperature effect on large particles was obvious. Shrinking core model was applied and modified herein coupled with the modification of reaction layer temperature and reaction area. Model prediction and experimental data showed good agreements of carbon conversion and reactivity index for raw char and char on molten slag, respectively. © 2016 American Institute of Chemical Engineers AIChE J, 63: 716–724, 2017 相似文献
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《Fuel》2003,82(15-17):2057-2064
Six coals with different ranks and different ash contents have been used to study the effect of demineralization on N2 formation during coal pyrolysis. Chars obtained after pyrolysis have been also gasified with carbon dioxide at 1000 °C to investigate the influence of the demineralization on char gasification reactivity. The pyrolysis results show that the demineralization by acid washing drastically changes N2 formation profiles and decreases nitrogen conversion to N2 for low rank coals; on the other hand, the demineralization has little effect on N2 formation for high rank coals. Addition of 0.5 wt% Fe promotes N2 formation from the demineralized coals, but the catalytic effect depends on the coal type. It is found that the Fe remarkably promotes N2 formation from the demineralized low rank coals, but the effect is much smaller for high rank demineralized coals. These observations suggest that the existing state of Fe-containing minerals and added Fe catalyst is important for catalytic N2 formation during coal pyrolysis. Gasification results show that the demineralization lowers char gasification reactivity not only for low rank coals but also for high rank coals. 相似文献
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Keiichirou MitsuokaShigeya Hayashi Hiroshi AmanoKenji Kayahara Eiji SasaoakaMd. Azhar Uddin 《Fuel Processing Technology》2011,92(1):26-31
The effects of alkali and alkaline earth metals such as potassium (K) and calcium (Ca) on CO2 gasification reactivity of Japanese cypress (hinoki) char under various temperatures (1123-1223 K) and CO2 concentration (20-80 vol.%) were studied using thermal gravimetric analysis. The presence of K and Ca compounds in char improved the reactivity of hinoki char for CO2 gasification catalytically. It was also confirmed that K and Ca compounds can be supported on char to exhibit an enhanced catalytic effect during CO2 gasification of K-char and Ca-char. The char gasification rate increased with the increase of CO2 concentration at higher temperatures (1173-1223 K), however at lower temperature (1123 K) the gasification rate decreased at 80% CO2. The retardation of char gasification rate at higher CO2 concentration is caused by the inhibition effect of CO: CO is disproportionated on alkali metal catalysts to CO2 and carbon, and affected the CO2 gasification rate. The dependence of char gasification rate on reaction temperature yielded a straight line in an Arrhenius-type plot which indicated that there was no significant change in the gasification mechanism in the temperature range of 1123-1223 K. 相似文献
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Based on results from a variety of experimental measurements, a detailed mechanism is postulated for the action of the inorganic catalyst in char gasification. In this mechanism, a catalyst such as potassium carbonate in contact with char undergoes a chemical and physical transformation to form a molten potassium oxide film that covers the char surface. This film serves as an oxygen transfer medium between the gaseous reactant (H2O or CO2) and the char. At the catalyst/char interface, an oxidation-reduction reaction occurs and the anions in the catalyst react with the oxidized char to form a phenolate-type functional group that subsequently splits out CO. The anions are replenished by reaction between the oxidizing gas (H2O or CO2) and the oxide at the gas/catalyst interface. Net transport of oxygen from gas to char occurs by diffusion of the species in the molten catalyst film. 相似文献
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《Fuel》2005,84(2-3):127-134
Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573–1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy (E=146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal. 相似文献
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利用热重分析仪研究恒温煤气化是实验室常用的气化活性评价流程,但该实验中气体切换过程的影响却较少报道。本文以一种煤焦CO2气化反应为例,通过切换气体与全部采用CO2气体气化实验对比,分析气体切换步骤对恒温气化实验的影响,并结合在线质谱检测了切换过程中气体逸出规律。研究发现,存在切气步骤时,尽管CO2可快速扩散至反应区,但由于气体的置换过程并非简单的平推流,导致部分碳的气化是发生在变化着的反应性气体和惰性气体的混合气氛中。这极大地影响了煤焦样品的气化反应速率大小和趋势,进一步影响反应动力学模型的判断和选择,并将导致由此计算所得的活化能受扩散影响而偏低。因此,建议在应用热重分析仪采用气体切换流程研究恒温气固相反应时,应首先对其气体逸出规律进行检测,评估气体切换步骤对整个反应过程的影响,以减小实验误差。 相似文献
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Reactivities of peat char have been measured in CO2–N2 gas mixtures at temperatures ranging from 600°C and 900°C and pressures of up to 9.1 MPa using a fixed bed placed in a flow reactor. A semi-empirical kinetic expression is presented which includes the temperature, CO2 pressure and variation in the specific area of the substrate. An Arrhenius equation is used to obtain an activation energy of 99.1 kJ/mol for the gasification process. 相似文献