不同反应器中氧化反应与水蒸气气化反应协同作用差异性

在?80mm×3000mm气流床和?40mm×200mm流化床中进行了O₂、H₂O、H₂O+O₂气氛下800℃胜利褐煤气化实验,同时在流化床中进行了O₂、H₂O、H₂O+O₂气氛下半焦原位气化实验和H₂O气氛下半焦完全气化实验。比较了2种反应器中氧化反应与水蒸气气化反应协同作用的大小（强弱）;结合实验条件利用缩核模型分别推导了2种反应器中协同作用影响下水蒸气气化反应速率方程;同时,从传质（扩散）速率、动力学、半焦-挥发分相互作用3方面探讨了2种反应器中协同作用存在显著差异的原因。结果发现,气流床中H₂O+O₂气氛下褐煤转化率明显大于H₂O和O₂单独气氛下褐煤转化率之和,其差值稳定在2.11%～4.01%,而在流化床中差值仅为0～0.75%,相对流化床,气流床中协同作用更明显。这是由于,在流化床中水蒸气向炭粒表面扩散的传质速率约为气流床的11%～25%,水蒸气气化过程受气膜扩散控制,炭粒表面水蒸气全部参与气化反应,炭粒表面无“多余”水分子,氧气开孔/扩孔作用提供的活性位“闲置”,而气流床中气化反应为速控步,炭粒表面有“富裕”水分子,可充分利用氧气开孔/扩孔作用提供的活性位,促进作用显著;挥发分-半焦相互作用不是流化床反应器中协同作用不显著的原因。

Synergistic effect of oxidation reaction and steam gasification reaction in different reactors

Shengli brown coal was gasified at 800℃ under O₂, H₂O, H₂O+O₂ atmospheres comparatively by using a entrained-flow reactor with ?80× 3000 mm and a fluidized-bed reactor with ?40mm×200mm. Besides, in the fluidized-bed reactor, situ char gasification experiments under O₂, H₂O, H₂O+O₂ atmospheres and complete gasification experiments (coal conversion is close to 100%) under H₂O atmospheres were carried out to investigate the promoting effect of oxidation reaction on steam gasification reaction in different reactors. The rate equations of steam gasification reaction in two reactors were deduced based on unreacted shrinking core model. The results showed that the lignite conversion under H₂O+O₂ atmospheres was greater than the sum of those under H₂O atmosphere and O₂ atmosphere with a difference of 2.11%—4.01% in the entrained-flow reactor. In contrast, only 0—0.75% difference was observed in fluidized-bed reactor. The obtained difference can be explained that in the fluidized-bed reactor the mass transfer rate of steam to the carbon particles surface was 11%—25% of that in entrained-flow reactor and the steam gasification reaction occurred in the membrane diffusion controlled regime. This poor mass transfer led to a low steam concentration on carbon particles surface and some idle micro-/mesopores created by O₂. However, in entrained-flow reactor the steam gasification reaction happened in chemical kinetic controlled regime, and the rich steam can be absorbed by pores (created by O₂) on carbon particles surface to promote steam gasification. Moreover, it was verified that the volatile-char interaction was not main reason of the weak promotion of oxidation reaction to steam gasification reaction in the fluidized-bed reactor.