Bubble heat effects, slurry reactor

THE REACTIONS OF INDUSTRIAL IMPORTANCE WHICH ARE CARRIED OUT IN BUBBLE COLUMNS AND SLURRY REACTORS AND ARE ACCOMPANIED BY LARGE HEAT EFFECTS... 

Though the term "slurry refers to a suspension of fine solid particles in a liquid, the term slurry reactor is often used for a three-phase system, where both gas bubbles and solid particles are suspended in a liquid phase. For a solid/liquid/gas process, slurry reactors have two obvious advantages the possibilities for very large solid/liquid surface areas and for good heat transfer to the reactor wall. Therefore the volumetric capacity of slurry reactors can be relatively large. However, effective separation of the fine catalyst from the liquid phase may offer considerable technical problems. One possibility is an external separation, e.g. with centrifuges or hydrocyclones, and a transport of a concentrated catalyst slurry back into the reactor. More often internal filters are used, usually consisting of porous tubes (sintered stainless steel, or ceramics), that are cleaned every few minutes by a periodic reversal of the flow. 

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. 

In contrast to the fixed-bed reactor, the slurry-phase reactor (Figure lb) is relatively simple. Basically, a finely divided catalyst is suspended in a liquid. For F-T synthesis, this liquid is a waxy portion of the product. The reactant gases are bubbled through the catalyst slurry and react on the surface of the catalyst to produce the desired product. The use of finely divided catalysts ensures high rates of reaction that result in a large amount of product per unit of reactor volume per unit of time. The presence of the liquid and the turbulence caused by the gas flow allow the effective removal of heat from the surface of... 

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