层式下吸式气化炉中单颗粒生物质的热解模型

摘要

In the present study,a mathematical model to describe pyrolysis of single biomass particle in flaming pyrolysis zone of downdraft gasifier was developed by heat transfer equation coupled with the chemical kinetics equations. A tridiagonal matrix algorithm(TDMA) method was used for solving the heat transfer equation, and the Runge-Kutta 4th order method for the chemical kinetics equations. The simulated results, which calculated by the present model in oxygen-free atmosphere and flaming pyrolysing zone, were in good agreement with published experimental results. The pyrolysis of biomass particle in the flaming pyrolysing zone was investigated by the model. The results show that in the flaming pyrolysis zone of stratified downdraft gasifier, convective heat transfer coefficient(hs) and emissivity coefficient(ε) are 80. 4 W/(m2·K) and 0. 792, respectively. The trend of temperature change inside particls is contrary to that of the particle surface. The average flaming pyrolysis time is 16. 52%, which is shorter than that in oxygen-free atmosphere. The heating rate in the particle of the flaming pyrolysis zone was 182. 5 K/min, which was close to fast pyrolysis reaction. With the increaseing of flaming temperature, flaming pyrolysis time reduced, residue gradually reduced from 16. 92% to 13. 97%. With the increasing of particle diameter, pyrolysis time and char yield also increased. The depth of flaming pyrolysis zone was 6. 59-44. 1 mm,which equals to 1. 1-2. 2 diameters.%建立了层式下吸式气化炉中有焰热解区单个生物质颗粒的热解模型,耦合了传热方程和热解化学动力学方程,并利用三对角矩阵算法( TDMA)和四阶龙格库塔法进行了求解；分别针对普通无氧热解环境和层式下吸式气化炉中的有焰热解环境,运用文献中的试验结果对模型进行了验证,表明该模型能够较好地预测2种环境下颗粒内部不同位置的温度和热解速率；利用该模型对有焰热解区的生物质颗粒的热解过程进行了模拟分析。结果表明,层式下吸式气化炉有焰热解环境的传热参数为：对流换热系数(hs)为80.4 W/(m2·K)、炭的发射率(ε)为0.792。有焰热解过程中,颗粒内部的温度变化趋势与外部相反；颗粒的平均热解时间比普通无氧热解环境下缩短了16.52%；颗粒的升温速率为182.5 K/min,属于快速热解；随着有焰热解区火焰温度的升高,完全热解所需要的时间逐渐缩短,炭产量从16.92%逐渐降低到13.97%；随着颗粒直径的增加,热解时间逐渐增大,炭产量增加；有焰热解区的高度在6.59~44.1 mm范围内,相当于1.1~2.2个颗粒直径。