二次氧量对分级气化炉气化特性的影响

分级给氧气流床气化炉具有碳转化率高、炉内混合过程强烈、喷嘴附近温度较低等优点。本文采用CFD数值模拟的方法研究了二次氧量变化对气化炉运行特性的影响，分析比较了不同二次给氧量下相交射流火焰特性的变化，及相交射流对煤气化炉炉内整体混合过程、煤气化特性的影响。发现当二次给氧量下降时，受炉内回流流场的影响，二次火焰明显随回流发生偏斜，壁面温度升高。当二次给氧量小于总给氧量的8%时，其射流动量不足以影响主射流产生的宏观流场。

Numerical investigation of effects of secondary oxygen ratio on performance of staged-entrained flow coal gasifier

The staged oxygen entrained flow coal-slurry gasifier has such advantages as higher carbon conversion rate,stronger turbulent mixing inside gasifier and lower temperature near coal slurry nozzle.In this paper,the effects of secondary oxygen mass flow rate(SOMFR)on gasification performance were numerically investigated through CFD simulation.The CFD model was based on the Euler-Lagrangian method.Realizable k-ε model was used to acquire the turbulent information in the gasifier.Presumed PDF method was adopted to consider interactions between turbulence and homogeneous reactions.The characteristics of the gasification flames were analyzed as well as the flow field under different SOMFR in the staged gasifier.As SOMFR decreased,the secondary gasification flame curved up with backflow near the wall.At the same time,dome wall temperature increased as well.When SOMFR was less than 8% of the total oxygen mass flow rate,the momentum flux of the secondary oxidizer is too low to change the macro flow field.When SOMFR was larger than 8% of the total oxygen mass flow rate,the recirculation region shrank due to the entrainment of secondary flow.However,particle residence time increased,since the velocity in back-flow region increased.Particle gasification process would be benefited from this change.As SOMFR increased,the down-flow flame length decreased as well as the average temperature in the top furnace region.The result showed that the average temperature decreased by 20℃ when SOMFR increased from 2% to 16% of the total oxygen mass flow rate.At the height where secondary oxygen was introduced,the average temperature increased by 300℃ as well.In all cases,the temperature flow field at the down-section of the gasifier did not change,since the oxygen-coal mass ratio was kept constant.