Fluidization systems three-phase

Special consideration needs to be given to heterogeneous reactors, in which interaction of the phases is required for the reactions to proceed. In these situations, the rate of reaction may not be the deciding factor in the reactor design. The rate of transport of reactants and products from one phase to another can limit the rate at which products are obtained. For example, if reactants cannot get to the surface of a soHd catalyst faster than they would react at the surface, then the overall (observed) rate of the process is controlled by this mass transfer step. To improve the rate, the mass transfer must be increased. It would be useless to make changes that would affect only the surface reaction rate. Furthermore, if products do not leave the surface rapidly, they may block reaction sites and thus limit the overall rate. Efficient contacting patterns need to be utilized. Hence, fluidized bed reactors (two-phase backmixed emulator), trickle-bed systems (three-phase packed bed emulator), and slurry reactors (three-phase backmixed emulator) have... 

The use of a fluidized-bed reactor is possible only when the reactants are essentiaUy in the gaseous phase. Eluidized-beds are not suitable for middle distiUate synthesis, where a heavy wax is formed. Eor gasoline synthesis processes like the MobU MTG process and the Synthol process, such reactors are especiaUy suitable when frequent or continuous regeneration of the catalyst is required. Slurry reactors and ebuUiating-bed reactors comprising a three-phase system with very fine catalyst are, in principle, suitable for middle distiUate and wax synthesis, but have not been appHed on a commercial scale. 

Very limited data on the heat and mass transfer in three-phase inverse fluidization systems is available up to now. For the wastewater treatment, the reactor temperature should be controlled and maintained within a certain level to optimize the reactor performance, since the temperature of reactor or process can provide the microorganisms with favorable circumances. 

Fig.3. Decomposition of acetic acid and ammonia over Ti02 and AI-Ti02 in three-phase fluidized photocatalytic system, a) For acetic acid decomposition and b) For ammonia decomposition...

Industrial Applications of Three-Phase Fluidization Systems... 

The term three-phase fluidization, in this chapter, is taken as a system consisting of a gas, liquid, and solid phase, wherein the solid phase is in a non-stationary state, and includes three-phase slurry bubble columns, three-phase fluidized beds, and three-phase flotation columns, but excludes three-phase fixed bed systems. The individual phases in three-phase fluidization systems can be reactants, products, catalysts, or inert. For example, in the hydrotreating of light gas oils, the solid phase is catalyst, and the liquid and gas phases are either reactants or products in the bleaching of paper pulp, the solid phase is both reactant and product, and the gas phase is a reactant while the liquid phase is inert in anaerobic fermentation, the gas phase results from the biological activity, the liquid phase is product, and the solid is either a biological carrier or the microorganism itself. 

Fan (1989) provided a detailed historical development of three-phase fluidization systems in reactor applications. Only a brief review of the significant accomplishments and the economic factors affecting the development of three-phase reactors will be provided here. Table 1 provides the important contributions in the application of three-phase fluidization systems for the past several decades. The direct liquefaction of coal to produce liquid fuels was the first commercial reactor application of three-phase fluidization systems, with development having occurred from the mid-1920 s throughout the 1940 s. A large effort was put forth at this time in Europe for the production of liquid fuels from coal as a direct... 

The 1970 s also brought about increased use of three-phase systems in environmental applications. A three-phase fluidized bed system, known as the Turbulent Bed Contactor, was commercially used in the 1970 s to remove sulfur dioxide and particulates from flue gas generated by coal combustion processes. This wet scrubbing process experienced several... 

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. 

This section covers recent advances in the application of three-phase fluidization systems in the petroleum and chemical process industries. These areas encompass many of the important commercial applications of three-phase fluidized beds. The technology for such applications as petroleum resid processing and Fischer-Tropsch synthesis have been successfully demonstrated in plants throughout the world. Overviews and operational considerations for recent improvements in the hydrotreating of petroleum resids, applications in the hydrotreating of light gas-oil, and improvements and new applications in hydrocarbon synthesis will be discussed. 

Table 13. System and Biological Parameters that Affect Three-Phase Fluidized Bed Bioreactor Performance...

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