Circulating fluidized beds reactor applications

New applications and novel reactor configurations or operational modes for three-phase systems are continually being reported. These include the operation of a three-phase fluidized bed in a circulatory mode (Liang et al., 1995), similar to the commonly applied gas-solid circulating fluidized bed the application of a three-phase fluidized bed electrode that can be used as a fuel cell (Tanaka et al., 1990) magnetically stabilized three-phase fluidized beds centrifugal three-phase reactors and airlift reactors. 

Engstrom, Folke. Method and apparatus for separating solid particles from flue gases in a circulating fluidized bed reactor, PATENT PCT International WO 8603986 A1 DATE 860717, APPLICATION WO 86FI2 (860109) FI 85134 (850111), 11 pp. (1986). 

Substantial improvements in the performance of several processes of hydrocarbon selective oxidation can be achieved solely by developing new reactor configurations. An important step in this direction is exemplified by the circulating fluidized bed reactor, which over the years has been proposed for use in several selective oxidation reactions and has, finally, found application in w-butane selective oxidation to maleic anhydride. Although production at the plant (built in Spain) was later stopped, because it was uneconomic, it remains an interesting example that may find application in other reactions. 

We would also like to stress the importance of additional requirements related to the physical properties such as the mechanical strength of potential CO2 sorbents. The calcium looping process will most likely be operated in a circulating fluidized bed reactor set-up. This requires the development of attrition-resistant materials. However, the mechanical strength or attrition resistance of new developed CO2 sorbents is rarely assessed and, thus, requires more attention if the materials are to be relevant for practical applications. 

Bischi, A., Langdrgen, 0., Saanum, I., Bakken, J., Seljeskog, M., and Bysveen, M. (2011) Design study of a 150 kWth double loop circulating fluidized bed reactor system for chemical looping combustion with focus on industrial applicability and... 

Lambert, Joseph M. Jr., and Townsend, Eric J. Application of Various Design Criteria for Circulating Fluid Bed Reactors in Pilot Plants, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 502-508. Somerset, Pennsylvania (1993). 

In this study, it was concluded that although the operation of both CLC reactor configurations is different, the process efficiency is quite close. So, the process efficiency is not an important factor in the selection of the CLC reactor configuration. The reactor configuration of CLC will be selected based on either the application of efficient cyclones with circulated fluidized beds and the possibility to operate continuously at high pressure or high temperature valves in the packed bed configuration. 

The main drawback of kinetic models, based only on steady-state data, is associated with the fact, that start-up and transient regimes cannot be reliably modeled. Kinetic models for nonstationary conditions should be applied also for the processes in fluidized beds, reactions in riser (reactor) - regenerator units with catalyst circulation, as well as for various environmental applications of heterogeneous catalysis, when the composition of the treated gas changes continuously. 

Mixing can be provided by application of an agitator in a stirred tank reactor or a fluidized bed or forced circulation-type crystallizer. A variety of impellers of different geometry, for larger vessels also equipped with several turbines, are available. An extended discussion of mixing in crystallization is found in Chapter 13. 

A major application of fluidized bed technology is to be found in the catalytic-cracking reactor, or Cat Cracker , which lies at the heart of the petroleum refining process. Here, the catalyst particles (which promote the breakdown of the large crude petroleum molecules into the smaller constituents of gasoline, diesel, fuel oil, etc.) are fluidized by the vaporized crude oil. An unwanted by-product of the reactions is carbon, which deposits on the particle surfaces, thereby blocking their catalytic action. The properties of the fluidized state are further exploited to overcome this problem. The catalyst is reactivated continuously by circulating it to another bed, where it is fluidized with air in which the carbon burns... 

It seems that fluid-bed cracking reactor (thermal or catalytic) is the best solution for industrial scale. However, regeneration and circulation of so-called equilibrium cracking catalyst is possible for relatively pure feeds, for instance crude oil derived from vacuum gas oils. Municipal waste plastics contain different mineral impurities, trace of products and additives that can quickly deactivate the catalyst. In many cases regeneration of catalyst can be impossible. Therefore in waste plastics cracking cheap, disposable catalysts should be preferably applied. Expensive and sophisticated zeolite and other molecular sieves or noble-metal-based catalysts will find presumably limited application in this kind of process. The other solution is thermal process, with inert fluidization agent and a coke removal section or multi-tube reactor with internal mixers for smaller plants. 

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