胜利褐煤外热式气流床温和气化建模研究:模型的建立

Modeling study on the external heated entrained flow reactor in Shengli lignite mild gasification process: Model development and description

以胜利褐煤为原料,在80 mm×3 000 mm下行气流床中进行了800℃/900℃气化实验,研究了炉内气固相流动特点、炉内反应分区、主要反应的动力学,进而建立了气化炉模型。结果发现,气相流动存在射流区、回流区、平流区,其中平流区占95%;实验条件下炉内依次发生热解、燃烧、气化反应;结合实验条件,利用缩合模型推导了H_2O-O_2协同作用影响下半焦氧化和气化反应的速率方程,发现它们分别受气膜扩散、化学反应控制,而且受协同作用影响,气化反应速率在添加氧气前后差异较大,故建模时采用推导的速率方程更切合实验条件和煤种特性;考虑H_2,CO,CH_4燃烧、半焦-CO_2/H_2气化,CO变换、CO-H_2甲烷化反应,忽略速率较小的焦油燃烧、半焦-H_2O甲烷化,CO_2-H_2甲烷化等反应;由于半焦微观结构的差异,不同温度和气氛下单位反应体积内气固相有效接触(碰撞)面积差异较大,建模时应分别考虑;通过以上研究建立了气化模型,模型预测值误差较小,92%预测值误差小于20%,75%预测值误差小于10%。

Shengli brown coal in 150-180 μm was gasified at 800 ℃/900 ℃ in a simulated entrained-flow reactor,80 mm× 3 000 mm. Kinetics of main reactions and flow characteristics of gas/solid were discussed to build a coal mild gasification model.The results show that,firstly,the gas phase flow was divided into 3 zones,including jet zone,recirculation zone and downstream zone.The height of downstream zone was 95% of that of reactor.Secondly,pyrolysis,combustion and gasification could be considered running in order as a result of different reaction rates.Thirdly,the rate equations of oxidation reaction（ OR） and steam gasification reaction（ SGR） derived were in good agreement with the experimental data.The OR rate was in membrane diffusion controlled regime,and SGR rate was in chemical controlled regime.Moreover,the apparent rate constant of SGR increased obviously after adding O2 to steam.Therefore,the kinetic equation derived was suitable with the experimental conditions. Fourthly,the reactions of H2,CO,CH4 combustion,char-CO2/H2 gasification,CO-H2 methanation,and water-gas shift reaction were considered,while the reactions of tar combustion,char-H2O methanation,CO2-H2 methanation were ignored. Fifthly,due to the difference of char microstructure,the effective contact（ collision） area between gas and solid in different temperatures and atmospheres is different significantly. Based on those,a numerical model of en-trained-flow reactor was built,and its predicted values were in good agreement with the experimental values,with the error of less than 20% for 92% predicted values and less than 10% for 75% predicted values.