合成气旋流预混燃烧的大涡模拟

Large Eddy Simulation of Premixed Swirling Combustion with Synthesis Gases

关键词:  合成气  旋流预混燃烧室  大涡模拟  涡破碎 

Key words:  Syngas  Swirling premixed combustor  Large eddy simulation  Vortex breakdown

摘要:

如何高效洁净地燃烧合成气是整体煤气化联合循环(IGCC)系统中面临的主要问题。利用旋流贫燃预混燃烧可以达到强化传热传质,提高燃烧反应效率,降低NO_x等目的,但由于合成气中所含有的H₂成分, 同样面临燃烧不稳定问题。为了对合成气旋流预混燃烧室的燃烧不稳定性及污染物排放提供理论和数值上的指导,采用大涡模拟方法,对典型的旋流预混燃烧室中的合成气燃烧进行了模拟。结果显示,随着H₂含量的增加,火焰缩短向上游发展,燃烧室下游涡破碎更加集中。较高的入口雷诺数,加剧了涡团破碎的程度和速度,同时影响中心回流区和几何回流区的大小及分布。随着当量比的减小,火焰褶皱程度加大,燃烧趋向不稳定。增大压力火焰长度会明显缩短,NO_x排放量也会随之增大,但NO_x的反应速率只有在较低压力下才会对压力变化比较敏感。 

Abstract:

Combustion of synthesis gases in a clean and efficient way is the main problem in IGCC (Integrated Gasification Combined Cycle) system. Lean-premixed swirling combustion is an effective method to reduce NO_x, enhance heat and mass transfer, which improves the combustion efficiency, while still facing inherent combustion instability problem due to hydrogen composition in syngas. Large Eddy Simulation was adopted in this work, to simulate syngas combustion in a typical premixed swirling combustor. Results show that with increasing H_2content, flame is shortened and the downstream vortex breakdown becomes more focused. Higher inlet Reynolds number intensifies the extent and speed of vortex breakdown, while affecting both the size and distribution of central and geometrical recirculation zone. As the equivalence ratio decreases, the degree of flame wrinkling increases and combustion tends to be unstable. Higher pressure generates shorter flame and more NO_x emission, but the reaction rate of NO_x is only sensitive to pressure at lower value. 