Abstract: Thermogravimetric apparatus (TGA) and HBR are widely employed for determining the gasification kinetics. However,the limiting external mass transfer could not be avoided in these types of apparatus because the reacting gas is usually not allowed to flow through the sample bed. Consequently,the kinetics determined in TGA and HBR may not be intrinsic. To investigate this problem,a VBR and a HBR were used to study the kinetics of K₂CO₃ -catalysed steam gasification of pinewood char. The gasification experiments were conducted isothermally in the temperature range of 690-750℃ and at atmospheric pressure with 10% and 15% K₂CO₃ loadings. A characteristic difference of VBR from HBR was that the steam passed through the sample grain bed with a high flow velocity in the former reactor,resulting in an accelerated external mass transfer. It was found that the mean gasification rate obtained in VBR was 2.0-2.8 times that from HBR at a comparable condition. The activation energies obtained in VBR decreased with increasing carbon conversion,while those obtained in HBR showed an increase trend. These results were attributed to the different effects of external diffusion limitations in two types of reactor. A modified random pore model (MRPM) was found to be fit to the profiles of rate versus carbon conversion obtained from both reactors,but with distinct differences in the kinetic parameters.

Key words: biomass char, steam gasification, catalyst, kinetics, reactors, external mass transfer

摘要： 热重分析仪和横置式反应器（横管）是研究气化动力学的两种常用反应器，其共同特点是气化剂不能穿过原料床层，以致难以消除外扩散影响，由此测定的动力学未必是本征动力学。为探究此问题，本文采用竖直管反应器（竖管）和横管，在常压和690～750℃的温度范围内，以水蒸气为气化剂，对两种不同K₂CO₃添加量（质量比各为10%和15%）的松木炭进行等温催化气化实验，研究了不同反应装置所得的催化气化动力学特征。竖管区别于横管在于气化剂能以较高的流速穿过样品颗粒层，加速外扩散。结果表明，在可比工况下，竖管中得到的平均气化反应速率是横管的2.0～2.8倍；且随着碳转化率的增加，竖管对应的反应活化能逐渐减小，而横管对应的反应活化能呈相反趋势，反映了外扩散存在与否对反应速率和动力学参数的影响。修正随机孔模型可良好拟合两种反应器中反应速率随碳转化率变化的曲线，但模型参数存在明显差异。

关键词: 生物质炭, 水蒸气气化, 催化剂, 动力学, 反应器, 外扩散