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

Bubble column reactors

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

https://ris.utwente.nl/ws/files/6739600/Beenackers93mass.pdf

Mass transfer in gas-liquid slurry reactors

With the dramatic increase in the international oil price, gas-to-liquid processes of Fischer -Tropsch (FT) synthesis, methanol synthesis, and dimethyl ether (DME) synthesis have become increasingly important and received much attention from both academic and industrial interests. The slurry reactor has the advantages of simple construction, excellent heat transfer performance, online catalyst addition and withdrawal, and a reasonable interphase mass transfer rate with low energy input, which make it very suitable for gas-to-liquid processes. However, its multiphase flow behaviors are very complex and the multiphase reactor has some remarkable scale-up effects; therefore, extensive studies are still needed for the development and design of a high-performance slurry reactor. This article gives a state-of-the-art review of the recent studies on the slurry reactor for gas-to-liquid processes. The influences of the superficial gas velocity, operating pressure and temperature, solid concentration, column dimensions, and gas distributor are discussed. Some recent developments in the liquid-solid separation in a slurry reactor are also summarized. The concept of using internals to intensify the mass transfer and improve the hydrodynamics is discussed based on both experimental results and theoretical analysis. Modeling and simulations of the gas -liquid and gas-liquid-solid flows are briefly reviewed, with focus on the new trend of coupling the population balance model (PBM) into the computational fluid dynamics (CFD) framework to describe the complex bubble behaviors and gas-liquid interphase interactions. The results of a 3000 ton/year pilot plant for DME synthesis are given, showing that the slurry reactor has promising applications in gas-to-liquid processes. Fast development of the world economy and increase of the international oil price have made the global energy and environmental problems increasingly serious. The supply of coal is much more abundant than that of oil; therefore, the development of coal-based technologies for producing clean fuel is very important for the sustainable development of the economy and of the energy supply for the world. Gas-to-liquid processes of Fischer-Tropsch (FT) synthesis, methanol synthesis, and dimethyl ether (DME) synthesis have become increasingly important and received much attention from both academic and industrial interests. 1-9 Besides providing clean fuel, the products of gasto-liquid processes can be further produced to many other chemical products. 10

Slurry Reactors for Gas-to-Liquid Processes: A Review

Size, structure and dynamics of “large” bubbles in a two-dimensional slurry bubble column

The effects of column dimensions, gas velocity and the properties of liquid and solid particles on the gas holdup eG and the volumetric liquid-phase mass transfer coefficient kLa in the solid-suspended bubble column of liquid-solid batch operation were studied experimentally. The presence of suspended solid particles in the bubble column reduces values of eG and kLa, and their reduction by an addition of solid particles to the column is high in the transition regime and low in the heterogeneous flow regime. Based on these observations, empirical equations for eG in transition flow and in heterogeneous flow, and an empirical equation for kLa a applicable to the above two flow regimes are proposed.

Akihiro Takazawa

Papers

Gas holdup and volumetric liquid-phase mass transfer coefficient in solid-suspended bubble columns

Distribution of total pressure within a bed of porous powders accompanied by adsorption and desorption of gases