Enhancement of char gasification in CO2 during chemical looping combustion
Enhancement of char gasification in CO2 during chemical looping combustion
复制标题
DOI：
10.1016/j.cej.2018.07.215
复制
发表时间：
2018-12
影响因子：
15.1
通讯作者：
Ewa J. Marek;Yaoyao Zheng;S. Scott
中科院分区：
文献类型：
--
作者：
Ewa J. Marek;Yaoyao Zheng;S. Scott
在惰性砂或fe2o3作为氧载体（从矿石中提取或在实验室中制备）的流化床中，将三个炭在co2中气化。发现气化速率随温度和活性氧载体的存在而增加。观察到的变化随炭素和载体的反应性而变化。建立了模拟炭气化过程的数值模型。它解释了：气化的内在动力学，焦炭的颗粒内传质，流化床颗粒相的外部传质以及Fe2O3床中的CO燃烧。在1223 K时，CO被氧载体氧化，从焦炭附近被除去；这伴随着二氧化碳浓度的同时增加，减少了传质带来的限制。结论是，只有当气化首先受到传质限制时，氧载体的气化加速才有意义。此外，还提出了一种解析解，将所有过程合并为一个简化表达式来估计表观气化速率。引入了有效因子对颗粒内阻力的影响；气化速率用泰勒级数线性化；最后以哈达数为基础，用增强因子描述了颗粒相的过程。这个简单的分析模型允许人们预测在化学环燃烧过程中氧载体对炭气化的影响。提出的效率表达式用于构建氧载体的各种动力学特性的期望增强图。
Three chars were gasified in CO2in a fluidised bed of inert sand or Fe2O3as an oxygen carrier (either derived from an ore or prepared in the laboratory). Rates of gasification were found to increase with temperature and the presence of active oxygen carriers. The observed change varied both with the chars’ and carriers’ reactivity. A numerical model was developed to simulate char gasification. It accounts for: intrinsic kinetics of gasification, intraparticle mass transfer in the char, external mass transfer in the particulate phase of the fluidised bed and CO combustion in the bed of Fe2O3. At 1223 K, CO was removed from the vicinity of the char on being oxidised by an oxygen carrier; this was accompanied by a simultaneous increase in CO2concentration, reducing the limitation imposed by mass transfer. It was concluded that the acceleration of gasification by oxygen carriers is significant only if gasification is limited by mass transfer in the first place. In addition, an analytical solution has been proposed, to combine all the processes into one simplified expression for estimating the apparent gasification rate. The influence of the intraparticle resistance was introduced with the effectiveness factor; the gasification rate was linearized with a Taylor series; finally the processes in the particulate phase were described with an enhancement factor, based on the Hatta number. This simple analytical model allows one to predict the influence of an oxygen carrier on the gasification of char during chemical looping combustion. The proposed expression for the effective rate was used to construct a map of the enhancement expected for various kinetic characteristics of an oxygen carrier.