Abstract:

The fluidized bed two-stage gasification (FBTSG) decouples the reaction process into fuel pyrolysis in a downer and char gasification in a riser or transport bed. By sending all pyrolysis products into the bottom section of the gasifier, the tars containing in the pyrolysis volatile can be thermally and catalytically cracked in the gasifier via its high-temperature circumstance and catalysis of conveyed char, respectively. Thus, low-tar producer gas is possible for the FBTSG. Taking Yulin bituminous coal as raw material and using steam-oxygen as gasification reagent, the FBTSG was tested in a laboratory facility treating about 10 kg/h fuel to produce low-tar syngas under varied excessive oxygen ratio ER, steam to carbon ratio S/C, and temperature of pyrolysis and/or gasification reaction. The results showed that the continuous steady operation of FBTSG is fully feasible, and for a continuous test lasting for more than 3 h at ER = 0.36 and S/C = 0.15, its characteristic temperatures of pyrolysis and gasifier were stable at 735℃ and 877℃, respectively. The produced syngas contained 14.33% CO, 10.07% CO₂, 18.39% H₂, 9.89% CH₄, 1.82% C _n H _m and 45.50% N₂, giving an LHV of 8.99 MJ/m³. The gas yield was 1.8 m³/kg, and tar content in the gas reached its lower value of 0.437 g/m³, showing the technical characteristics of preparing low-tar syngas. For practical long-term continuous operation, higher gasification temperature will result in better low-tar characteristics of two-stage fluidized bed gasification.

Key words: two-stage low-tar gasification, circulating fluidized bed, gasification, reaction decoupling, coal, syngas

摘要：

由下行床热解和提升管（或输送床）气化组合形成的流化床两段气化将煤气化反应过程解耦为煤热解和半焦气化两个反应阶段，热解产物完全进入气化反应器，利用其中的高温环境和输送的半焦催化作用分别实现焦油的热裂解与催化裂解，完成低焦油气化。利用该流化床两段气化的10 kg/h级实验室工艺实验装置，以榆林烟煤为原料、水蒸气/氧气作为气化剂，变化过量氧气系数ER、蒸汽炭比S/C、热解及气化温度等参数，研究水蒸气/氧流化床两段煤气化制备低焦油合成气的特性。结果表明，流化床两段气化系统可实现稳定运行（实验3 h以上），在ER=0.36和S/C=0.15时，热解和气化的代表温度分别稳定在735℃和877℃，合成气的CO、CO₂、H₂、CH₄、C _n H _m 和N₂含量分别为14.33%、10.07%、18.39%、9.89%、1.82%和45.50%，相应的合成气产量达到1.8 m³/kg，低位热值8.99 MJ/m³，焦油含量0.437 g/m³，展示了制备低焦油合成气的技术特征。对于实际的长时间连续运行，更高的气化温度将使流化床两段气化具有更好的低焦油特性。

关键词: 两段低焦油气化, 循环流化床, 气化, 反应解耦, 煤, 合成气