下吸式秸秆气化炉流场分析

Flow Field Analysis of Down Draft Straw Gasifier

为研究下吸式固定床气化炉内多相反应流场的详细信息及工艺参数对气化过程的影响,采用Fluent软件对其进行二维数值模拟,在Lagrangian坐标系下采用随机轨道模型追踪秸秆颗粒运动,基于P1模型模拟气化过程的辐射传热过程。结果表明:空气当量比在0.28~0.30之间时气化效果最佳;空气当量比小于0.28时,由于O 2含量少,会出现挥发分燃烧不完全、炉内温度较低的现象;空气当量比大于0.30时,挥发分与焦炭燃烧完全,但过多的O 2会稀释可燃气体;S/B(水蒸汽/秸秆质量比)小于0.25时,处于水煤气反应速率的增加阶段,CO随S/B值的增加而增加;S/B大于0.25时,由于温度过低,使得水煤气反应的反应速率开始下降,气化炉内CO含量随S/B值的增加呈下降趋势。

In order to study the detailed information of the multi-phase reaction flow field and the influence of process parameters on the gasification process in the downdraft fixed bed gasifier,two-dimensional numerical simulation was carried out with Fluent software.In the Lagrangian coordinate system,the random track model tracks the movement of the powder straw particles,and the P1 model is used to simulate the radiation and heat transfer process of the gasification process.The results show that when the air equivalence ratio is between 0.28-0.30,the gasification effect is the best.When the air equivalence ratio is less than 0.28,due to the low content of O 2,the phenomenon of incomplete volatile combustion and low temperature in the furnace will occur.When the air equivalence ratio is greater than 0.30,the volatiles and coke burn completely,but too much O 2 will dilute the combustible gas.When S/B(water vapor/straw quality ratio)is less than 0.25,it is in the increasing stage of water gas reaction rate.CO increases with the increase of S/B value.When S/B is greater than 0.25,the reaction rate of water gas reaction begins to decline because of the low temperature.The CO content in gasifier decreases with the increase of S/B value.