铁基载氧体的沼气化学链燃烧反应动力学研究

Study on kinetics of biogas chemical looping combustion reaction of iron-based oxygen carrier

化学链技术能够实现碳基燃料燃烧所释放的CO_(2)的全捕获,可为我国早日实现“双碳”目标提供一种全新的视角。首先理论推导得到铁基载氧体CH_(4)还原反应的改进动力学模型;对Fe_(2)O_(3)与CH_(4)之间的反应系统进行了热力学计算,为后续反应操作温度的选择提供理论指导;在固定床反应器中通过改变混合气流速,研究外扩散对反应过程的影响,当气体流速达到180 mL·min^(-1)以后,表观反应速率不再增加,表明外扩散影响消除;在消除外扩散及灰尘扩散影响的前提下进行表面反应动力学测定,回归获得反应活化能E=147.574 kJ·mol^(-1)和指前因子k0=6.3995×10^(7) s^(-1),并建立了表面反应动力学方程式;在温度为680℃时,延长反应时间至1 h,反应不再进行,据此确定对应于该温度下的反应的固体产物,该固体产物以Fe_(2)O_(3)·nFeO形式虚拟表示,进而获得虚拟反应计量系数;通过对反应时间与载氧体Fe_(2)O_(3)转化率之间关系的研究,对反应模型进行了筛选,获得最优反应动力学模型,其中包含3个模型参数:虚拟组成比n=8,灰层扩散系数De=1.0841×10^(-9)m^(2)·s^(-1),表面反应速率常数(680℃)ks=5.576×10^(3) m·s^(-1),由于温度对De的影响一般不大,该优化反应动力学模型适应于变温条件。

Chemical looping technology is a promising approach for China to achieve its dual carbon goal by effectively capturing CO_(2) emissions from carbon-based fuel combustion.Various modified kinetic models for the CH_(4) reduction reaction of iron-based oxygen carriers were obtained through rigorous theoretical derivation.Additionally,thermodynamic calculations were conducted to guide the selection of the subsequent reaction temperature for the Fe_(2)O_(3) and CH_(4) reaction system.The impact of external diffusion on the reaction process was investigated using a fixed-bed reactor,revealing that the apparent reaction rate reached a saturation point at a gas flow rate exceeding 180 mL·min^(-1),indicating the elimination of external diffusion effects.Kinetic experiments were then conducted,eliminating the influences of external and ash layer diffusion.The resulting surface reaction kinetics equation was established with an activation energy E of 147.574 kJ·mol^(-1) and an exponential factor k0 of 6.3995×10^(7) s^(-1).At a temperature of 680℃,the reaction was carried out for 1 hour,and the solid product was virtually represented as Fe_(2)O_(3).nFeO,determining the corresponding reaction stoichiometric coefficient.By examining the relationship between reaction time and the conversion of the oxygen carrier Fe_(2)O_(3),a reasonable kinetic model was obtained,incorporating model parameter values of n=8,ash layer diffusion coefficient De=1.0841×10^(-9)m^(2)·s^(-1),and rate constant ks of 5.576×10^(3) s^(-1) at 680℃.This optimized model is suitable for varying temperature conditions,as temperature has minimal impact on De.