http://web.ist.utl.pt/ist11061/leq-II/Documentos/OpUnitarias/BubbleColumnReactors(review).pdf

Bubble column reactors

The formation of gas bubbles and their subsequent rise due to buoyancy are very important fundamental phenomena that contribute significantly to the hydrodynamics in gas−liquid reactors. The rise o...

Bubble Formation and Bubble Rise Velocity in Gas−Liquid Systems: A Review

Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...

Multiphase catalytic reactors: a perspective on current knowledge and future trends

https://hal.archives-ouvertes.fr/hal-01394969/document

Measuring techniques in gas–liquid and gas–liquid–solid reactors

http://fs.teledos.gr:2206/%3ERESEARCH%20PUBLICATIONS/CHEMICAL%20ENGINEERING/Reactor/Multiphase%20reactors%20-%20revisited.pdf

Multiphase reactors – revisited

Experiments of pressure effects on gas holdup and bubble size in slurry bubble columns at 5.6 MPa and at gas velocities up to 45 cm/s indicate that the gas holdup increases with an increase in pressure, especially at high slurry concentration. At ambient pressure, a higher solids concentration significantly lowers gas holdup over the entire gas-velocity range, while at 5.6 MPa, the effect of solids concentration on gas holdup is relatively small at gas velocities above 25 cm/s. An empirical correlation was developed based on these data and those in the literature to predict gas holdup in bubble and slurry bubble columns over a wide range of operating conditions. An analysis of bubble flow characteristics during dynamic gas disengagement indicates that large bubbles play a key role in determining gas holdup due to the large bubble and wake volumes that induce the acceleration of small bubbles. Direct measurement of bubble size shows that elevated pressures lead to smaller bubble size and narrower bubble-size distributions. Bubble size increases significantly with increasing solids concentration at ambient pressure, while at high pressures this effect is less pronounced. A theoretical analysis of circulation of gas inside the bubble yields an analytical expression for maximum stable bubble size in high-pressure slurry bubble columns. Based on this internal circulation model, the maximum stable bubble size at high pressures is significantly smaller due to the high gas inertia and low gas-liquid surface tension. The smaller bubble size and its reduced bubble rise velocity account for the observed pressure effect on gas holdup.

Maximum stable bubble size and gas holdup in high-pressure slurry bubble columns

Some aspects of high-pressure phenomena of bubbles in liquids and liquid–solid suspensions

High-pressure operations are common in industrial applications of gas-liquid-solid fluidized-bed reactors for resid hydrotreating, Fischer-Tropsch synthesis, coal methanation, methanol synthesis, polymerization, and other reactions. The phase holdups and the heat-transfer behavior were studied experimentally in three-phase fluidized beds over a pressure range of 0.1--15.6 MPa. Bubble characteristics in the bed are examined by direct flow visualization. Pressure effects on the bubble coalescence and breakup are analyzed mechanistically. The study indicates that the pressure affects the hydrodynamics and heat-transfer properties of a three-phase fluidized bed significantly. The average bubble size decreases and the bubble-size distribution becomes narrower with an increase in pressure. The bubble-size reduction leads to an increase in the transition gas velocity from the dispersed bubble regime to the coalesced bubble regime, an increase in the gas holdup, and a decrease in the liquid and solids holdups. The pressure effect is insignificant above 6 MPa. The heat-transfer coefficient between an immersed surface and the bed increases to a maximum at pressure 6--8 MPa and then decreases with an increase in pressure at a given gas and liquid flow rate. This variation is attributed to the pressure effects on phase holdups and physical properties of the gas and liquid phases.more » A mechanistic analysis revealed that the major heat-transfer resistance in high-pressure three-phase fluidized beds resides in a liquid film surrounding the heat-0transfer surface. An empirical correlation is proposed to predict the heat-transfer coefficient under high-pressure conditions.« less

High-pressure three-phase fluidization: Hydrodynamics and heat transfer

On the rise velocity of bubbles in liquid-solid suspensions at elevated pressure and temperature.

The heat-transfer behavior between an immersed heating surface and the surrounding gas−liquid−solid medium in a slurry bubble column is studied experimentally and analytically. The operating pressures and temperatures vary up to 4.2 MPa and 81 °C, respectively. Nitrogen, Paratherm NF heat-transfer fluid, and 53-μm glass beads are used as the gas, liquid, and solid phases, respectively. The solids concentrations are varied up to 35 vol %, while the superficial gas velocities are varied up to 20 cm/s. The effects of gas velocity, solids concentration, pressure, and temperature on the heat-transfer coefficient are examined. It is found that pressure has a significant effect on heat-transfer characteristics. The heat-transfer coefficient in a slurry bubble column decreases appreciably with an increase in pressure. It is noted that the variation in the heat-transfer coefficient with pressure is attributed to the counteracting effects of the increased liquid viscosity, decreased bubble size, and increased gas h...

Xukun Luo

Papers

Maximum stable bubble size and gas holdup in high-pressure slurry bubble columns

Some aspects of high-pressure phenomena of bubbles in liquids and liquid–solid suspensions

High-pressure three-phase fluidization: Hydrodynamics and heat transfer

On the rise velocity of bubbles in liquid-solid suspensions at elevated pressure and temperature.

Heat-Transfer Characteristics in Slurry Bubble Columns at Elevated Pressures and Temperatures