CO2-gasification of a lignite coal in the presence of an iron-based oxygen carrier for chemical-looping combustion
CO2-gasification of a lignite coal in the presence of an iron-based oxygen carrier for chemical-looping combustion
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DOI：
10.1016/j.fuel.2013.07.045
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发表时间：
2014-07
期刊：
影响因子：
7.4
通讯作者：
Marco A. Saucedo;J. Lim;J. S. Dennis;S. Scott
中科院分区：
文献类型：
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作者：
Marco A. Saucedo;J. Lim;J. S. Dennis;S. Scott
化学链燃烧具有从烟气中分离产物CO2的固有特性。它不使用空气，而是使用氧载体，通常以金属氧化物的形式，为燃烧提供氧气。迄今为止提出的所有固体燃料化学循环技术最初都涉及固体燃料的气化，以便使气体产物与氧载体反应。在此，比较了当在流化床中进行气化时煤的气化速率，流化床为（i）用于化学循环的活性Fe基氧载体或（ii）惰性砂。这使得能够检查化学链材料提高固体燃料气化速率的能力。报道了德国褐煤及其半焦在1073 ~ 1223 K温度范围内的间歇气化和化学链燃烧实验。流化气体为氮气中的CO2。发现在氧载体的存在下，气化的动力学明显更快，特别是在高于1123 K的温度下。开发了一个数值模型来解释外部和内部的传质和成环剂的影响。该模型还包括在不同的转化率的孔结构的演变的影响。Fe 2 O3的存在下，由于快速氧化CO的氧载体CO2的气化速率的增加。这导致CO的去除，并保持较高的摩尔分数的CO2的气体混合物周围的焦炭颗粒，即在周围的颗粒的传质边界层。这种效果是最突出的转化率约20%时，（i）反应的表面积是在其最大值和（ii），因为伴随的孔隙率和孔径的增加，颗粒内的气体传质的炭颗粒内的阻力下降，与初始颗粒相比。数值模型预测的速率和实验观察到的速率之间观察到极好的一致性。
Chemical-looping combustion (CLC) has the inherent property of separating the product CO2from flue gases. Instead of air, it uses an oxygen carrier, usually in the form of a metal oxide, to provide oxygen for combustion. All techniques so far proposed for chemical looping with solid fuels involve initially the gasification of the solid fuel in order for the gaseous products to react with the oxygen carrier. Here, the rates of gasification of coal were compared when gasification was undertaken in a fluidised bed of either (i) an active Fe-based oxygen carrier used for chemical looping or (ii) inert sand. This enabled an examination of the ability of chemical looping materials to enhance the rate of gasification of solid fuels. Batch gasification and chemical-looping combustion experiments with a German lignite and its char are reported, using an electrically-heated fluidised bed reactor at temperatures from 1073 to 1223 K. The fluidising gas was CO2in nitrogen. The kinetics of the gasification were found to be significantly faster in the presence of the oxygen carrier, especially at temperatures above 1123 K. A numerical model was developed to account for external and internal mass transfer and for the effect of the looping agent. The model also included the effects of the evolution of the pore structure at different conversions. The presence of Fe2O3led to an increase in the rate of gasification because of the rapid oxidation of CO by the oxygen carrier to CO2. This resulted in the removal of CO and maintained a higher mole fraction of CO2in the mixture of gas around the particle of char, i.e. within the mass transfer boundary layer surrounding the particle. This effect was most prominent at about 20% conversion when (i) the surface area for reaction was at its maximum and (ii) because of the accompanying increase in porosity and pore size, intraparticle resistance to gas mass transfer within the particle of char had fallen, compared with that in the initial particle. Excellent agreement was observed between the rates predicted by the numerical model and those observed experimentally.