Impacts of dense heat exchanging internals on gas holdup cross-sectional distributions and profiles of bubble column using gamma ray Computed Tomography (CT) for FT synthesis

Abstract

The effect of heat exchanging internals that represent Fischer–Tropsch (FT) synthesis in bubble column has been investigated for the first time using gamma ray Computed Tomography (CT) in a 5.5″ (0.14m) inner diameter Plexiglas bubble column operated at atmospheric condition with air water system. Thirty vertical Plexiglas rods of 0.5″ outer diameter were used which covered ∼25% of the total cross-sectional area and were arranged in a triangular pitch of 0.84″ (2.14cm). The superficial gas velocities applied were based on both total cross-sectional area as well as free cross-sectional area available for the flow and were in the range of 5–45cm/s covering the bubbly through churn-turbulent flow regimes.New knowledge and findings have been obtained which have not been reported in previous studies. In churn turbulent flow regime, the overall gas holdup and the profiles of gas holdup obtained in bubble columns without internals can be extrapolated to those with internals in the central region of the column if the superficial gas velocity is based on the free cross-sectional area (CSA) available for the flow of the phases provide that symmetric time averaged gas holdup cross-sectional distributions are achieved. The results show that a significant increment in overall and local gas holdup are obtained upon inserted of the internals when the velocity measured based on the total cross sectional area of the column. The gas holdup distribution over the cross-sectional area (CSA) of the column in the presence of internals has a symmetrical shape at low gas velocities and asymmetry at higher ones for the honeycomb configuration and its installation used in this study. At a high superficial gas velocity that is based on free CSA for the flow, the influence of dense internal becomes insignificant at the central region of the column. However, the profiles of the gas holdup in the column with internals become less steeper compared to those that are like parabolic shape at high gas velocity in the column without internals due to higher gas holdup was obtained in the region near the wall with internals.