Coal char gasification with steam and H2:
I The |gasification reaction characteristics
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摘要: 分别以水蒸气/惰性气混合气、水蒸气/氢气混合气作为气化剂，在常压和875℃~950℃下，采用热天平对1200℃快速热解神府煤焦的气化反应特性进行了研究，并考察了气化过程中煤焦结构的变化及其对气化反应的影响。实验发现，煤焦在水蒸气/氢气作为气化剂条件下的气化反应过程可分为两个阶段，首先是反应急剧进行的阶段，然后是反应速率趋于稳定的阶段，且反应速率接近于石墨的反应速率。该现象与煤的化学结构有关，第一阶段气化剂与活泼性物质碳氢支链、含氧官能团的反应，第二阶段气化剂与芳香碳的反应；煤焦在水蒸气/氢气气氛下，气化过程中的碳难以转化完全。神府煤焦的SEM表明，煤焦表面有大量的裂缝、孔隙、褶皱、及碎块。碎块表面光滑，这些物质覆盖了内部裂缝与孔隙。煤焦和水蒸气/氢气气化残焦（碳转化率68%）由于气化反应，其碎块减少，表面的大孔暴露出来。比较两种气化剂条件下的气化反应过程发现，水蒸气/惰性气气化反应速率随碳转化率的增加而缓慢均匀地下降；水蒸气/氢气气化反应速率随碳转化率增加先迅速降低，而后较缓慢降低。Abstract: The reaction characteristics of gasification with H2O or H2O/H2 and the structure of Shenfu coal char pyrolyzed at 1200℃ were studied at 875℃~950℃ and at ambient pressure by TGA. There are two stages during the char gasification with H2O/H2: At first stage, the gasification rate is higher because of steam reaction with hydrocarbon side chains and oxygen containing function groups; at second stage, the gasification rate becomes lower because of steam reaction with residual aromatic carbon structure. When the gasification is performed with H2O/H2 , the carbon conversion is lower. It can be seen from the SEM photos of coal char that there are a large number of slots, pores and fragments, and lots of slots and pores are covered by those fragments. The fragments are reduced and diminished and the slots are exposed on the surface of residual coal char with the char gasification. Moreover, the carbon conversion curves of the gasification with H2O and H2O/H2 are remarkably different.
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Key words:
- coal gasification /
- coal structure /
- gasification mechanism
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