The simultaneous effect of particle size and concentration on the total gas holdup of slurry bubble column reactors was investigated in this work. The total gas holdup was measured for air-water-glass beads systems. Three solid concentrations and three particle diameters were used. It was found that increasing particle size at high constant concentration decreases gas holdup. Moreover, increasing solid concentration decreases gas holdup and this decreasing effect is higher for larger particles. Also, solid particles have two effects on hydrodynamics, namely, changing the viscosity and density of the liquid phase as well as hindering the bubbles from rising within the column by the collision phenomenon. Therefore, a novel correcting factor was introduced to correct the gas holdup. The hindering factor considers both the collision efficiency affected by the particle size as well as the solid concentration. A novel correlation was developed to predict the experimental data of the three-phase gas holdup.

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In a pilot‐scale bubble column operating with low and moderate viscosity hydrocarbons, the effect of pressure on the total and axial gas holdup as well as the regime transition velocity was investigated. Experiments were performed for two air‐Ketrul D100 and air‐Hydroseal G250 HL gas‐liquid hydrocarbon systems. It was found that increasing pressure increased gas holdup at the heterogeneous regime, and this effect was more pronounced for the low‐viscosity liquid. Moreover, increasing pressure further stabilized the homogeneous regime, and again, this stabilizing effect was more significant for the low‐viscosity liquid. Also, as a response to the pressure increasing, the axial gas holdup became more uniform in the case of the low‐viscosity liquid and less uniform in the case of the moderate‐viscosity liquid.

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