Bubble column design

Tramper J, Smit D, Straatman J, Vlak JM (1988), Bubble-column design for growth of fragile insect cells, Bioproc. Biosyst. Eng. 3 37-41. 

Hydrodynamic parameters that are required for bubble column design and analysis include phase holdups (gas, liquid, and solid for... 

Many different bubble column designs have been used over the years, all adapted to particular practical needs [133]. Figure 8.6 depicts a few of the modifications frequently used. A special case is the down-flow bubble column. In the column part of this reactor flow of the two phases is co-current from top to bottom as shown in Fig 8.6. The advantages of this type of reactor is that the relatively short gas residence times obtained in up-flow reactors, can be increased since the residence time is determined by the bubble rise velocity [28]. Furthermore, incorporation of additional perforated plates transforms the simple column, sketched in Fig 8.1, into a multistage cascade version, Fig 8.6. This redistribution of gas over the perforated plates intensifies mass transfer,... 

For more details on general bubble column design, refer to [31-34]. 

In his text book, W-D Deckwer begins with a description of the simple bubble coliunn and then proceeds to describe various modified bubble column designs and bubble colurrms with directional liquid circulation, both internal and external (22). This modified bubble columns included ... 

Pilhofer, Th., H. F. Bach, and K. H. Mamgartz. Determination of Fluid Dynamic Parameters in Bubble Column Design. ACS Symp. Series 65 (1978) 372. 

Bubble caps were used almost exclusively as cross-flow-plate dispersers until about 1950, when they were largely displaced by simple or valve-type perforations. Many varieties of bubble-cap design were used (and therefore are extant in many operating columns), but in most cases bell caps of 75- to 150-mm (3- to 6-in) diameter were utilized. 

An extensive treaunent of gas-liquid flows encountered in industry applications, along with numerous design correlations can be found in Volume 3 of the Encyclopedia of Fluid Mechanics - Gas-Liquid Flows (N. P. Cheremisinoff, editor. Gulf Publishing Co, Houston, TX, 1986). Further discussions in this volume can be found in Chapter 4 with regard to flow regimes typically encountered in bubble columns and similar devices. 

Sada, E., Kumazawa, H., Lee, C. and Fujiwara, N., 1985. Gas-liquid mass transfer characteristics in a bubble column with suspended sparingly soluble fine particles. Industrial and Engineering Chemistry Process Design and Development, 24, 255-261. 

Shah, Y.T., Kelkar, B.G., Godbole, S.P. and Deckwer, W.D., 1982. Design parameter estimations for bubble column reactors. American Institute of Chemical Engineers Journal, 28, 353. 

Bubble-column slurries have much in common with two-phase bubble columns containing no solid particles, which have also been studied in great detail. Reference will be made in the following to a number of those studies considered to be of relevance with respect to the analysis and design of corresponding three-phase systems containing suspended solids. 

Bubble-column slurry operations are usually characterized by zero net liquid flow, and the particles are held suspended by momentum transferred from the gas phase to the solid phase via the liquid medium. The relationships between solids holdup and gas flow rate is of importance for design of bubble-column slurries, and some studies of this aspect will be reviewed prior to the discussion of transport phenomena. 

The aim of this report is to examine the principles of shear stress on particles that would allow the design of bioreactors for technical use, mainly stirred tanks, bubble columns and loop reactors. 

Special reactors are required to conduct biochemical reactions for the transformation and production of chemical and biological substances involving the use of biocatalysts (enzymes, immobilised enzymes, microorganisms, plant and animal cells). These bioreactors have to be designed so that the enzymes or living organisms can be used under defined, optimal conditions. The bioreactors which are mainly used on laboratory scale and industrially are roller bottles, shake flasks, stirred tanks and bubble columns (see Table 1). 

Airlift loop reactor (ALR), basically a specially structured bubble column, has been widely used in chemical industry, biotechnology and environmental protection, due to its high efficiency in mixing, mass transfer, heat transfer etc [1]. In these processes, multiple reactions are commonly involved, in addition to their complicated aspects of mixing, mass transfer, and heat transfer. The interaction of all these obviously affects selectivity of the desired products [2]. It is, therefore, essential to develop efficient computational flow models to reveal more about such a complicated process and to facilitate design and scale up tasks of the reactor. However, in the past decades, most involved studies were usually carried out in air-water system and the assumed reactor constructions were oversimplified which kept itself far away from the real industrial conditions [3] [4]. 

Many industrial processes which employ bubble column reactors (BCRs) operate on a continuous liquid flow basis. As a result these BCR s are a substantially more complicated than stationary flow systems. The design and operation of these systems is largely proprietary and there is, indeed a strong reliance upon scale up strategies [1]. With the implementation of Computational Fluid Dynamics (CFD), the associated complex flow phenomena may be anal)rzed to obtain a more comprehensive basis for reactor analysis and optimization. This study has examined the hydrodynamic characteristics of an annular 2-phase (liquid-gas) bubble column reactor operating co-and coimter-current (with respect to the gas flow) continuous modes. 

The slow water removal is obvious within the synthesis of, for example, myristyl myristate determining the total reaction time. In a stirred-tank reactor it takes 24 h to reach a conversion of 99.6% and in a fixed-bed reactor 14 h. Therefore, a new synthesis platform (Figure 4.11) which also enables conversion of highly viscous polyols and fatty acids from renewable resources to ester-based surfactants was designed. It is used by Evonik on a pilot scale, outperforming conventional methods, such as stirred-tank or fixed-bed reactors. In contrast to the setups introduced before, conversion of >99.6% is already obtained after 5.5 h in the bubble column reactor [44-47]. 

The most difficult problem to solve in the design of a Fischer-Tropsch reactor is its very high exothermicity combined with a high sensitivity of product selectivity to temperature. On an industrial scale, multitubular and bubble column reactors have been widely accepted for this highly exothermic reaction.6 In case of a fixed bed reactor, it is desirable that the catalyst particles are in the millimeter size range to avoid excessive pressure drops. During Fischer-Tropsch synthesis the catalyst pores are filled with liquid FT products (mainly waxes) that may result in a fundamental decrease of the reaction rate caused by pore diffusion processes. Post et al. showed that for catalyst particle diameters in excess of only about 1 mm, the catalyst activity is seriously limited by intraparticle diffusion in both iron and cobalt catalysts.1... 

In order to verify the simulation results, experiments on bubble behavior in bubble columns are carried out under conditions similar to the simulations. A 3-D rectangular bubble column with the dimension of 8 x 8 x 20 cm3 is used for the experiments. Four nozzles with 0.4 cm I.D. and a displacement of 2.4 cm are designed in the experiments. For single-nozzle experiments, air is injected into the liquid bed through one of the orifices while the others are shut off. The outlet air velocity from the nozzle is approximated using the measured bubbling... 

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