喷射环流反应器的放大效应

Study on scale-up effects of jet-loop reactors

实验测量了两种塔径( 200 和 500 mm)和两种操作模式(气体单独喷射和气液同轴喷射)下喷射环流反应器内的全塔平均气含率、局部气含率及轴向液速径向分布、循环液速,归纳出全塔平均气含率的关联式。实验发现,喷射环流反应器具有十分显著的放大效应。小塔( 200)与大塔( 500)中的全塔平均气含率存在很大差异:小塔的全塔平均气含率~气速关系曲线比大塔陡峭,低气速下小塔气含率低于大塔、较高气速下高于大塔。根据漂移通量法分析得到小塔中流型转变点在表观气速 0.1 m s 1左右,在实验气速范围内只存在拟均匀鼓泡流;大塔中流型转变点在表观气速 0.04 m s 1左右,随气速增大从拟均匀鼓泡流转变为湍动鼓泡流。喷射环流反应器比气升式环流反应器、一般鼓泡塔全塔平均气含率略低,但循环液速更大,适用于强化固体悬浮与混合的气液固三相反应过程。

Effects of column diameter ( 200 and 500 mm) and operating mode (gas jet and gas-liquid co-injection) on flow dynamics including overall gas holdup, radial distributions of local gas holdup, axial liquid velocity and liquid circulation velocity were experimentally studied in a gas-liquid jet-loop reactor (JLR). A modified drift-flux model was developed to predict the overall gas holdup at various superficial gas velocities. The results show that the scale-up effect in the JLR is significant. The overall gas holdups in the small column ( 200 mm) and large column ( 500 mm) are different. The curve of “overall gas holdup - gas velocity” in the small column is steeper than that in the large column, which indicates that the overall gas holdup in the small column at low superficial gas velocities is smaller than that in the large column, while the opposite is true at high gas velocities. According to the drift-flux method, the flow regime transition point in the small column is at superficial gas velocity of 0.1 m s 1, which means that a pseudo-homogeneous flow regime prevails under the present superficial gas velocity range. However, this value is 0.04 m s 1 in the large column, and the flow regime is transferred from the pseudo-homogeneous flow to turbulent flow with the increase of gas velocity. Comparing to airlift reactors and bubble columns, JLRs have slightly lower overall gas holdup, while its liquid circulation velocity is distinctly higher, which indicates that JLR is more suitable for gas-liquid-solid three phase reactions for intensification of solid suspension and mixture.