碎煤熔渣加压气化过程数值模拟分析

Numerical simulation of crushed coal pressurized slagging gasification

碎煤熔渣加压气化技术(British Gas-Lurgi,BGL)取缔了炉篦,干法排渣改液态排渣,气化性能显著改善。为揭示BGL煤气化本质结构特征,支撑企业气化装置性能再提升,论文采用数值模拟方法构建了热力学平衡模型、煤气化动力学模型和欧拉多相流模型,并验证了模型合理性。模拟研究表明:与鲁奇煤气化相比,气化平衡温度由795℃(鲁奇炉)提高到1029℃,水蒸气分解率由32.66%提高到93.12%;床层最高温度由1110℃提高至1837℃,远高于煤灰流动温度1210℃,提高了气化强度,保证了液态排渣;BGL煤气化反应在炉膛下部基本完成,仅有少量水蒸气参与变换反应,粗煤气中的CH_(4)基本来自煤热解;气化炉床层腾涌波动,增强了传热传质;喷嘴射流冲击煤焦颗粒,形成向中心区延伸的椭球形燃烧回旋区,成为BGL煤气化的重要功能单元,实现一次布气,为气化层和熔渣池提供热量;熔渣池中液渣上下回旋流动,有利于降低熔渣残碳,保障顺畅排渣。

The Crushed Coal Pressurized Slagging Gasification(British Gas-Lurgi,BGL)renders the use of gates obsolete and changes from dry slag discharge to liquid slag discharge,significantly improving the gasification performance.This study aims to reveal the essential structural characteristics of BGL coal gasification to further improve the performance of gasification equipment.We established the thermodynamic equilibrium model,coal gasification dynamics model and Euler multiphase flow model via numerical simulation,and validated these models.The simulation results show that 1)compared with Lurgi coal gasification,the gasification equilibrium temperature increases from 795℃(Lurgi gasifier)to 1029℃,and the decomposition rate of water vapor increases from 32.66%to 93.12%.The maximum bed temperature increases from 1110℃to 1837℃,much higher than the coal ash flow temperature(1210℃).This improves the gasification intensity and ensures liquid slag discharge.2)BGL coal gasification reaction is mainly completed in the lower part of the furnace,with only a small amount of water vapor participating in the shift reaction.CH_(4)in the crude gas mainly comes from coal pyrolysis.3)The fluctuation of bed surge in gasifier enhances heat and mass transfer.4)Nozzle Jet impacts and squeezes coal char particles,forming an ellipsoidal combustion raceway extending to the central area.This becomes an important functional unit of BGL gasification,realizing primary gas distribution and providing heat for gasification layer and slag pool.5)The liquid slag in the slag pool whirls up and down,which is beneficial to reduce carbon residue in slag and ensure smooth slag discharge.