NUMERICAL SIMULATION OF COAL GASIFICATION IN A CIRCULATING FLUIDIZED BED GASIFIER

Abstract This paper presents a 3D full-loop simulation of a circulating fluidized bed gasifier. The model is validated with experimental results from the literature. The validated model is thereupon used to compare Bubbling Fluidized Bed (BFB) and Circulating Fluidized Bed (CFB) gasifiers to highlight the effect of a change in fluidization regime from bubbling to fast fluidization on hydrodynamics, temperature and gas composition. Feed temperature as well as Air/Coal (A/C) and Steam/Coal (S/C) ratios are kept constant, whereas the velocity of the feed (Air-Steam) is increased so as to get into the fast fluidization regime. It was concluded that the flue gas from the CFB is richer in desired gases, i.e., CO and H2 than that from BFB. H2 remains approximately the same, CO2 and CH4 decreased to a negligible amount and CO approximately doubles when the regime is changed. In addition, tar content in the gas also decreases.

摘要 本文针对循环流化床气化炉（Circulating Fluidized Bed Gasifier, CFB）开展了三维全回路模拟研究。该模型通过公开文献中的实验数据完成验证。随后，借助验证后的模型对鼓泡流化床（Bubbling Fluidized Bed, BFB）与循环流化床气化炉进行对比分析，以明晰流化工况从鼓泡流化向快速流化转变对流体动力学特性、温度分布及气体组分的影响。实验过程中保持进料温度、空气/煤（Air/Coal, A/C）与蒸汽/煤（Steam/Coal, S/C）比值恒定，仅提升进料（空气-蒸汽）流速以切换至快速流化工况。研究结论显示：循环流化床烟气中的目标气体（即CO与H₂）含量高于鼓泡流化床；当流化工况改变后，H₂含量基本保持稳定，CO₂与CH₄含量降至可忽略水平，CO含量约提升一倍；此外，烟气中的焦油含量也随之降低。