操作条件对双循环回路变径提升管压降的影响

Effects of Operating Conditions on Pressure Drops in a Dual-loop Circulating Fluidized Bed

针对生产清洁汽油组分的催化裂化新工艺,建立了具有双循环回路的变径提升管冷模实验装置.提升管由下部具有较小床径、较高气速的气力输送区和上部具有较大床径、较低气速的快速流化区组成,循环物料可在提升管的下部和中部分别加入,形成主、副两个循环回路.分析了系统主、副循环回路的压力平衡关系,研究了操作条件对提升管压降的影响.结果发现,主、副循环回路的提升管压降均随表观气速的增加而降低;增加2个循环回路中任意一个固体循环速率时,将使另一循环回路的固体循环速率降低,但总固体循环速率和2个循环回路的提升管压降均升高.2个循环回路相互影响并保持各自的压力平衡,在固体循环速率控制阀处,只有循环管端压力大于提升管端压力才能维持系统正常操作.增加系统藏料量、循环管直径、副循环供料床高度和直径均有利于维持循环系统的正常操作.

A riser with varying diameter and dual-loop is set up to study the fluid catalytic cracking （FCC） process of maximizing iso-paraffins （MIP）. The riser is composed of a bottom pneumatic transport region with smaller diameter and higher gas velocity and a top fast fluidization region with larger diameter and lower gas velocity. Particles are added to the riser at both the bottom and the middle positions, and two solids circulating loops named main-loop and sub-loop are formed, The pressure balance of the two solids circulating loops and the effects of operating conditions on pressure drops of the riser were investigated in experiment. The pressure drops of both main-loop and sub-loop of the riser decrease with increasing gas velocity. The total solids circulating rate and the pressure drop of the two solids circulating loops increase with increase in the either solids circulating rate, although the increase of one solids circulating rate leads to the decrease of the other. Two circulating loops are influenced by each other, and the prerequisite for normal operation is that pressure balances of both loops are maintained and the pressure of downcomer side is higher than that of riser side at each solids circulating rate control valve. The increase in inventory, downcomer diameter and downcomer height is helpful to maintain the normal operation of system.