Fluidized systems

When a stationary vessel is employed for fluidization, all sohds being treated must be fluidized nontluidizable fractions fall to the bottom of the bed and may eventually block the gas distributor. The addition of mechanical vibration to a fluidized system offers the following advantages ... 

Fluidizing systems generally convey prefluidized, finely divided, non-free-flowing materials over short distances, such as from storage bins or transportation vehicles to the entrance of a main conveying... 

FIG. 21-12 Types of air-conveying systems, a) Pressure, (h) Vacuum, (c) Pressure-vacuum, (d) Pressure vacuum unloading and transfer. (Whitlock, Inc.) (e) Fluidizing system. (Fuller Co.) (/) Blowtank. 

There is approximately a 22% deviation between the experimental and the distribution mean residenee time. However, the main purpose was to use the information from the RTD eurve to improve the reaetor operation. The results of the RTD provided vital information eoneern-ing the effeets of operating eonditions and struetural designs on solid-mixing patterns in fluidized systems. The perfeet mixing funetion was generated by e , where 6 = t/f. Figure 8-19 shows plots of these funetions against dimensionless residenee time 6. 

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. 

Most investigations of fluidization parameters take place at ambient temperature and pressure. Yet, nearly all processes operate at elevated temperature, and many at elevated pressure. Therefore, it is necessary to know how increasing temperature and pressure affect the operation of fluidized systems. However, the operation of fluidized test facilities at temperature and pressure is much more difficult and costly than operating them at ambient conditions. It is not surprising then that information on how temperature and pressure affect the operation of fluidized beds is not as prevalent as would be desired. However, many researchers have undertaken the difficult task of building and operating units to obtain these badly needed data. The purpose of this chapter is to present what is known about operating fluidized beds at elevated temperature and pressure. 

The early 1970 s saw the development of many new coal-based, synthetic-fuel, fluidized-bed processes which operated at high pressures. The scientists and engineers charged with designing these processes realized that there was a severe lack of information on how pressure (and also temperature) affected the operation of fluidized beds. Therefore, several studies to determine the effect of pressure on the operation of fluidized beds were commissioned. During the same period, other researchers in Japan, Europe, and the U.S. were also starting to conduct research to determine the effects that temperature and pressure have on fluidized systems. 

Leva, M., and Grummer, M., Correlation of Solids Turnovers in Fluidized Systems, Chem. Eng. Progr., 48(6) 307-313 (1952)... 

The pressure balance for the dense phase in the downcomer in the circulating fluidized system shown in Fig. 2 can be expressed as ... 

Qin, S., and Liu, G., Application of Optical Fibers to Measurement and Display of Fluidized Systems, Proc. China-Jpn. Fluidization Symp., p. 258-266, Hangzhou, China (1982)... 

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... 

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. 

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