淤浆聚合釜中三种桨型固液分散性能的比较

Comparison of Solid-Liquid Dispersion Performance with Three Types of Impellers in Slurry Polymerization Reactor

为考察淤浆聚合釜桨叶形式及转速对釜内液固分散性能的影响,建立了锥形釜体内锚式桨、螺带桨和斜叶桨的固液分散计算流体力学(CFD)模型和冷模实验.3种桨型的模拟扭矩与实验值平均误差在10%以内,模拟所得浓度场与摄像实验所得的固含率分布规律一致,模拟结果较为可靠.研究结果表明:搅拌功率随转速增大而增加,相同转速下三者功耗从大到小的顺序为锚式桨、螺带桨和斜叶桨;相同雷诺数(Re)下三者固液功率准数从大到小的顺序为斜叶桨、螺带桨和锚式桨;达到相同的浓度场方差的功耗从大到小的顺序为锚式桨、螺带桨和斜叶桨.以特征线上浓度分布行为判定,3种桨型均存在混合程度的临界转速;以浓度场方差为量化指标,3种桨型均存在最优固液分散转速.结合两者,锚式桨的实际操作转速推荐范围为120~480 r/min,螺带桨为240~600 r/min,斜叶桨为120~600 r/min.

A solid-liquid dispersion CFD model and cold model experiments of the anchor impeller(AI),double helical ribbon impeller(DHRI)and four pitched blade impeller(FPBI)in a conical reactor were established in order to investigate the influence of blade form and rotating speed of blade on the liquid-solid dispersion performance in the slurry polymerizer.The average error between the simulated torque and the experimental value for the three types of impellers was less than 10%.The simulated concentration field was consistent with the solid holdup distribution obtained from the photography experiment,and the simulated results were reliable.The results showed that the stirring power increases with the increase of agitation speed,and the power consumption relationship of the three impellers was AI>DHRI>FPBI at the same agitation speed,the power number relationship of the three impellers was FPBI>DHRI>AI at the same Reynolds number(Re),and the power consumption relationship for achieving the same concentration variance was AI>DHRI>FPBI.According to the concentration distribution on the characteristic line,the critical speed of full mixing existed for all three impellers.Taking the variance of concentration field as the quantitative index,the optimal solid-liquid dispersion speed existed for all three impellers.Combining the above conclusions,the recommended range of actual operating speed was 120-480 r/min for the anchor impeller,240-600 r/min for the helical ribbon impeller and 120-600 r/min for the pitched blade impeller.