Design of a gas distributor: three-dimensional CFD simulation of a coupled system consisting of a gas chamber and a bubble column

Abstract

CFD simulation for bubble column and a large number of chamber configurations have been carried out. The numerical simulations were based on a two-fluid k-ε model. An attempt has been made to simulate the flow pattern on the upstream and downstream of the distributor and its effect on performance of the bubble column. A procedure has been proposed for connecting the gas chamber to bubble column reactor. The extreme cases of uniform and mal-distribution were considered and the effect of mal-distribution was investigated on the flow pattern in the bubble column. The effects of opening area and hole diameter were investigated in the range of 0.64-4% and 2-4 mm, respectively. The effect of inlet nozzle size and its location with respect to the distributor were found to be very important. The flow pattern within the gas chamber has been comprehensively analyzed and the velocities through all the holes have been estimated for assessing the uniformity of the gas distribution. It was found that, the chamber configuration has an effect on the uniformity of gas distribution particularly in the sparger region of bubble column reactors. The uniformity of gas distribution was found to increase with an increase in the distributor pressure drop and a decrease in the inlet kinetic head of the gas. Recommendations have been made for the inlet nozzle size and its location, opening area and hole diameter. Further, the development of hold-up profile and its significance on design parameters have been explored. From the quantitative information reported in this paper, it may be possible to select the design parameters of distributor and gas chamber depending upon the desired level of uniformity of distribution and for a given bubble column in terms of diameter (D), height of dispersion (H_D), superficial gas (V_G) and liquid velocity (V_L).