Abstract:

Reaction characteristics and kinetics of biochar gasification with steam at temperature(T) of 1123—1223 K and steam partial pressure(SP) of 10%—40% were studied by a micro fluidized bed reaction analyzer (MFBRA). It shows that increasing T and SP was beneficial to shorten reaction time and increase the production of gaseous product (H₂, CO and CO₂) and total C conversion. At low temperature (1123 K), gasification reaction was greatly affected by SP, especially for H₂ with an increase of 1.97 times. At 1223 K and SP≥20%, due to the limitation of active sites, SP had little effect. With the increase of T, the volume yield ratio of CO/CO₂ showed a trend of first decreasing and then increasing; at 1123 and 1173 K, with the increase of SP, the ratio decreased; while at 1223 K, it basically maintained at 1.25. The generation active energy(E_a) of H₂, CO₂, and CO under different SP was calculated via shrinking core model, which were in the range of 95.44—101.82, 83.56—89.35 and 70.41—74.86 kJ/mol. The E_a of total C conversion was in the range of 71.29—76.78 kJ/mol. The test results make up for the limitations of existing analyzers that are difficult to determine the gas product generation characteristics and kinetics during the gasification process.

Key words: biochar, steam, isothermal gasification, micro fluidized bed, reaction kinetics

摘要：

利用微型流化床反应分析仪考察了1123~1223 K及10%~40%蒸汽分压(SP)条件下生物质半焦-水蒸气气化的反应特性并计算动力学。结果表明：升高温度和SP有利于缩短反应时间，提高产物(H₂、CO和CO₂)生成率及总C转化率。低温(1123 K)下，反应受SP影响较大，以H₂最为明显，增幅达1.97倍；在1223 K、SP≥20%条件下，因受活性位点制约，SP对反应影响较小。随温度升高，CO/CO₂体积产率比呈现出先减小后增大趋势；在1123 K和1173 K下，随SP升高，CO/CO₂的体积产率比值降低；在1223 K下，该值维持在1.25左右。采用缩核模型求取不同SP下总碳转化活化能(E_a)在71.29~76.78 kJ/mol范围内，H₂、CO₂和CO的生成活化能分别在95.44~101.82、83.56~89.35和70.41~74.86 kJ/mol之间。测试结果弥补了现有分析仪难以测定气化过程中气体产物生成特性和动力学的局限性。

关键词: 半焦, 水蒸气, 等温气化, 微型流化床, 反应动力学