层式下吸式气化炉中生物质热解的热力学模型

Thermodynamic Equilibrium Model of Biomass Pyrolysis in Stratified Downdraft Gasifier

基于物质平衡、能量平衡和化学反应平衡为层式下吸式气化炉有焰热解区建立了热动力学平衡模型,把灰分作为出口成分进行了考虑,并通过牛顿法对模型进行了求解。模型的预测结果与现有文献中的试验数据很好的吻合,与其他研究者的预测结果基本一致。利用该模型对有焰热解区进行了分析预测。结果表明,ER、原料的含水量、散热损失对有焰热解区出口的气体温度和成分都有比较明显的影响;空气预热温度和灰分含量对出口气体温度有一定的影响,而对气体成分的影响不明显;当ER较高而生物质含水量较低时,气化炉内发生结渣的可能性增加;在ER〈0.392时,提高空气的预热温度,对整个气化炉的气化是有利的;热损失超过14%,ER〈0.32时,可能出现生物质无法完全热解的情况;对于典型的玉米秸秆气化,有焰热解区出口气体成分中,对还原区反应有重要影响的H2O范围在20%～25%之间,CO2范围在10%～15%之间。本模型的预测结果还为还原区的模型提供了初始参数。

On the basis of mass balance,energy balance and chemical reaction equilibrium,the thermodynamic equilibrium model in flaming pyrolysis zone of stratified downdraft gasifier was developed including the consideration of ash as part of the exit products. Then it was solved by Newton method in Matlab. The calculated values were in good agreement with the experimental results and other models＇ results reported in literature. The model was used to analyze and calculate the flaming behavior in prolysis zone. The results showed that ER,moisture content and heat loss had obvious effect on the temperature and compositions of the product gas. The air preheated temperature and ash content also had obvious impact on the gas temperature,but no obvious impact on the gas compositions. With increment of ER and decreasing of moisture content,the possibility of slagging increased.As the ER value was lower than 0. 392,the increasing of air preheated temperature had positive effect on gasification. However,for heat loss 14% and ER 0. 32,the biomass cannot be pyrolyzed completely. The contents of H2O and CO2 in the product gas of flaming prolysis zone,which had important effect on the reaction of reduction zone,were 20%-25% and 10%-15% for corn stalk gasification. The model provided the initial parameters for development of reduction zone model.