两种循环流化床预提升结构的对比分析

COMPARATIVE STUDY OF TWO PRE-LIFTING STRUCTURES IN CIRCULATING FLUIDIZED BED

在循环流化床上考察了两种不同预提升结构对系统循环量的影响,并且从宏观和微观两方面对提升管内气固流动行为进行了比较分析。结果表明:立管结构提升管和莲蓬头结构提升管颗粒循环量存在明显的差别,立管结构提升管中颗粒流通截面积增加,进口阻力减少,系统循环量整体上高于莲蓬头结构,而且这种循环量差异在伴床高供料强度下更加明显;由于莲蓬头进口结构的强约束作用,相同操作条件下其底部颗粒浓度高于立管结构;在提升管底部区域,莲蓬头结构提升管中径向不均匀指数以及间歇性指数均高于立管结构,说明采用莲蓬头式分布器导致局部颗粒湍动剧烈的同时,气体与颗粒以及颗粒之间的作用力分布也更不均匀;瞬时颗粒浓度信号分析及概率密度分布结果表明,虽然底部采用莲蓬头式分布器可在一定程度上缓解过渡区气固分离现象,但整体不均匀流动结构并未发生根本的变化。

Effects of two different pre-lifting structures on solid circulation rate in an experimental irculating fluidized bed with a riser of 10. 6 m high and inner diameter of 0. 1 m and the gas-solid flow behavior were compared macroscopically and microscopically. The results showed that there is a remark-able difference in solids circulation rate between standpipe-type riser and showerhead-type riser. Due to he increased particles flow areas and the reduced entrance resistance, solid circulation rate in standpipe- ype riser as a whole is higher than showerhead-type riser, especially in high particle feed rate from stor-age vessel. Under the same operating conditions, the solid concentration at the bottom in showerhead- ype riser is higher than standpipe-type riser because of the strong restraining effect from the shower- head structure. The higher radial non-uniformity index and intermittency index in showerhead-type riser ndicates that while showerhead distributor causes a local intense particle turbulence, the interaction dis-ributions between gas and particle as well as particles are even more uneven. The instantaneous solid oncentration and probability density distribution reflect that although showerhead distributor at the bottom can partly relieve gas-solid segregations in transition region, no fundamental changes occur in general non-uniform flow structure as a whole.