二维双支腿流化床内气体混合特性

Characteristic of gas mixing in two-dimensional dual-leg fluidized bed

引言循环流化床（CFB）大型化后因炉膛截面积增大,一方面将导致二次风穿透能力不足,另一方面截面积增大也会造成炉内空气分布均匀性受到影响,导致炉内燃烧不能有效组织,进而降低锅炉的燃烧效率。双支腿（dual leg,DL）结构的引入能够有效解决上述问题,这一技术成为实现CFB大型化的一种重要设计方案。目前,我国虽然已经有众多300MWe亚临界机组成功运行。

Experiments of gas mixing between two half-beds were performed in a dual-leg circulating fluidized bed（DL-CFB）240 mm in width,40 mm in depth and 2000 mm in height by using glass beads with diameter of 0.25—0.28 mm as bed material.SO2 and CO as the gas tracers entering the left and right distributors separately were used to simulate the gas mixing between the two legs.MSD（mean square displacement）model was adopted to calculate the gas dispersion coefficient（Dw）which was used to investigate the effect of fluidization velocity and bed material inventory on gas mixing in the DL-CFB.The experimental results showed that Dw was about 50—300 cm2·s-1 at different fluidization velocities and bed material inventories.A higher fluidization velocity benefited particles exchange between two half-beds,which intensified the gas-solids interactions at the region with higher solids volume fraction.The gas mixing in the lower region of the DL-CFB was stronger than that in the upper region of the bed.A higher bed inventory was helpful to gas mixing at a lower fluidization velocity,while a higher fluidization velocity weakened gas mixing because of higher solids concentration in the center of the bed that prevented gas mixing.