Dense gas–liquid–solid flow in a slurry bubble column: Measurements of dynamic characteristics, gas volume fraction and bubble size distribution

Abstract

Dense three-phase slurry flows are important in several industrial processes (e.g., Methanol/ DME synthesis, Fischer Tropsch synthesis). In the present work, gas–liquid–solid flow in a pseudo 3D slurry bubble column is characterized under dense flow conditions for superficial gas velocity (UG) of 5–30cms-1 and overall solid loading (αS) of 0–40vol.%. In-house developed voidage probes were used to measure local gas volume fraction fluctuations. The high frequency fluctuations (∼1–10Hz) caused by individual bubbles or swarms of bubbles were found to increase with increase in αS and UG. The low frequency oscillations (∼<1Hz) corresponding to column-scale recirculating flow were found to decrease with increase in αS. Importantly, time-averaged gas volume fraction and its internal composition (i.e. gas volume fraction contained in different bubble size groups) and bubble size distribution were measured at different locations in the slurry bubble column. With an increase in αS, local gas volume fraction was found to decrease, accompanied by an increase in bubble size. Based on the distribution of bubble chord lengths, the gas volume fraction contained in different bubble size groups was measured for different αS and UG. With increase in αS, the gas volume fraction for small bubbles was found to decrease while that for large bubbles was found to increase. Under the dense flow conditions (at high UG and αS), while small bubbles were found to accumulate near the column walls, as indicated by the wall peaking in α‾G profiles, large bubbles/gas slugs were found to flow predominantly through the column center. In addition to the new experimental data, the present work helps to improve the understanding of dense slurry flows that will aid the development and verification of Eulerian multiphase models.