Design bubble slurry column reactors

In the third section an extensive writing on two types of slurry catalytic reactors is proposed Bubble Slurry Column Reactors (BSCR) and Mechanically Stirred Slurry Reactors (MSSR). All the variables relevant in the design and for the scale-up and the scale-down of slurry catalytic reactors are discussed particularly from the point of view of hydrodynamics and mass transfer. Two examples of application are included at the end of the section. 

Design of bubble slurry column reactors (BSCR)... 

In the design of upflow, three phase bubble column reactors, it is important that the catalyst remains well distributed throughout the bed, or reactor space time yields will suffer. The solid concentration profiles of 2.5, 50 and 100 ym silica and iron oxide particles in water and organic solutions were measured in a 12.7 cm ID bubble column to determine what conditions gave satisfactory solids suspension. These results were compared against the theoretical mean solid settling velocity and the sedimentation diffusion models. Discrepancies between the data and models are discussed. The implications for the design of the reactors for the slurry phase Fischer-Tropsch synthesis are reviewed. 

The general difficulties in design and scale-up of bubble column reactors concern reaction specific data, such as solubilities and kinetic parameters as well as hydrodynamic properties. The paper critically reviews correlations and new results which are applicable in estimation of hydrodynamic parameters of two-phase and three-phase (slurry) bubble column reactors. 

Although considerable advances have been made both in understanding the basic aspects of slurry bubble column reactors (SBCR) and in developing rational design procedures, computational fluid dynamics (CFD) - assisted design methodology for reactor optimization is sparse. 

The more advanced model of Wu and Gidapow 19) is used to explore novel reactor designs optimum catalyst size and reactor configuration. The model included the effect of the mass transfer coefficient between the liquid phase and the gas phase and the water-gas shift reaction. With reaction, diis model was used to predict slurry height, gas hold-up and the rate of methanol production of the Air Products/DOE LaPorte slurry bubble column reactor. 

Deckwer, W. D. Bubble Column Reactors, Wiley, New York, NY, 1992. Prakash, A. Bendale, P. G. Design of Slurry Reactor for Indirect Liquefaction Applications, Final Report to DOE/PETC Viking Systems International, 1991. 

Turner JR, Mills PL. Comparison of axial dispersion and mixing cell models for design and simulation of Fischer-Tropsch slurry bubble column reactors. Chem. Eng. Sd. 1990 45 2317-2324. 

The most difficult problem to solve in the design of FT reactors is the high exothermicity combined with a high sensitivity of product selectivity to temperature. Hence, the reactor must have provisions for efficient heat removal. Four reactor types are considered today, namely, multi-tubular fixed bed reactors, slurry bubble column reactors, circulating fluidized bed reactors, and bubbling fluid bed reactors. 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

An important aspect of the design of three phase bubble columns is the variation of catalyst distribution along the reactor height, and its effect on reactor performance. Many factors influence the degree of catalyst distribution, including gas velocity, liquid velocity, solid particle size, phase densities, slurry viscosity, and, to a lesser extent, column diameter, solid shape and chemical affinity between the solid and liquid phases. 

An SBC is a vertical, tubular column in which a three-phase (gas-solid-liquid) mixture is used. The slurry phase consists of FT catalysts and FT wax. The syngas flows though the slurry phase in the form of bubbles, as shown in Figure 12.12. The effective heat and mass transfer, low intraparticle diffusion, low pressure drop, and design simplicity are important advantages of this type of reactor. However, considerable problems arise in separating the liquid-phase synthesis products from the catalyst. With their attractive features, the SBC reactors are receiving extensive investment in both R D and commercialization. The concept of SBC is not new. 

Chapters 7 and 8 present models and data for mass transfer and reaction in gas-liquid and gas-liquid-solid systems. Many diagrams are used to illustrate the concentration profiles for gas absorption plus reaction and to explain the controlling steps for different cases. Published correlations for mass transfer in bubble columns and stirred tanks are reviewed, with recommendations for design or interpretation of laboratory results. The data for slurry reactors and trickle-bed reactors are also reviewed and shown to fit relatively simple models. However, scaleup can be a problem because of changes in gas velocity and uncertainty in the mass transfer coefficients. The advantages of a scaledown approach are discussed. 

Of the reactors listed in Table 17.1, the four most important are the mechanically agitated slurry reactor (MASR), the bubble-column slurry reactor (BCSR), the loop-recycle slurry reactor (LRSR), and the trickle-bed reactor (TBR). The first three, sketched in Figure 17.5, are slurry reactors, whereas the fourth is a fixed-bed reactor. The features most relevant to a preliminary design of these reactors in organic synthesis and technology are briefly described here. 

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