Comparison of mixing characteristic of bubble column and airlift reactors using tracer injection technique

The liquid mixing time in a bubble column reactor and in an internal loop airlift reactor were investigated. The total volume and diameter of two reactors as well as the type of gas sparger were the same. The riser to downcomer cross sectional area ratio (Ar/Ad) was 0.64 in the airlift reactor. The tracer injection method and impulse response was used to find the mixing time. The experimental results showed that the lower values of mixing time were related to internal loop airlift reactor compared to the bubble column reactor at the identical gas flow rate. The mixing time decreases with increasing the superficial gas velocity, with a power correlation. The exponent values were determined -0.86 for bubble column reactor and -0.48 for airlift reactor. The dimensionless mixing time depends only on the reactor geometry. Its dependence to the superficial gas velocity was negligible. Using airlift reactor instead of bubble column reactor shows that mixing time reduced about 50% at low gas flow rates.

Keywords:

Bubble column reactor , Internal loop airlift reactor , Mixing time , Tracer technique