Fluidization three phase

Three-phase fluidization refers to operation in which an upward flow of gas and cocurrent or countercurrent flow of liquid supports a bed of 

Bed expansion and contraction are important phenomena in three-phase fluidization, since these affect the bed volume and the residence time(s) of all the phase(s). The phenomenon of bed contraction/expansion is also very closely linked to the problem of transition. The relationship between the expansion/contraction behavior and the transition will be clearly brought out later. 

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Three-phase fluidized bed reactors are used for the treatment of heavy petroleum fractions at 350 to 600°C (662 to 1,112°F) and 200 atm (2,940 psi). A biological treatment process (Dorr-Oliver Hy-Flo) employs a vertical column filled with sand on which bacderial growth takes place while waste liquid and air are charged. A large interfacial area for reaction is provided, about 33 cmVcm (84 inVirr), so that an 85 to 90 percent BOD removal in 15 min is claimed compared with 6 to 8 h in conventional units. 

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

Cocurrent three-phase fluidization is commonly referred to as gas-liquid fluidization. Bubble flow, whether coeurrent or countereurrent, is eonveniently subdivided into two modes mainly liquid-supported solids, in which the liquid exeeeds the minimum liquid-fluidization veloeity, and bubble-supported solids, in whieh the liquid is below its minimum fluidization velocity or even stationary and serves mainly to transmit to the solids the momentum and potential energy of the gas bubbles, thus suspending the solids. 

Countereurrent bubble flow with liquid-supported solids, whieh ean be affeeted by downward liquid fluidization of partieles having a density lower than that of the liquid, has been referred to as inverse three-phase fluidization. The mass transfer potential of sueh a eountercurrent operation is worthy of study, especially for cases in whieh dispersion of the gas rather than the liquid is ealled for and the required gas-liquid ratio and throughput ean be effected without flooding. In contrast, the eorresponding eoeurrent mode has reeeived more attention than all other eases and eonstitutes the majority of the literature on three-phase fluidization. 

Several other processes that are aimed at the manufacture of gasoline from coal have been applied over the years. The main reactor in these processes uses three phase fluidization in which solid coal particles, gases, and liquids are all contacted at very high temperatures and pressures. Fluid bed dryers and fluid cokers are also used in synthetic fuels manufacmre. 

Findings with PDU. Work with the PDU largely paralleled the bench-scale reactor tests there was one important addition—extensive three-phase fluidization studies. As was mentioned, the PDU is equipped with a traversing gamma-ray density detector that is capable of measuring bed density to within dbO.Ol specific gravity units. Thus, we could measure and correlate fluidized bed expansion as a function of liquid and gas velocities and physical properties, and could also determine the... 

Thermogravimetric analysis (TGA) 97 Three-phase fluidization studies. . 156... 

Hydrodynamics, Heat and Mass Transfer in Inverse and Circulating Three-Phase Fluidized-Bed Reactors for WasteWater Treatment... 

Recent research development of hydrodynamics and heat and mass transfer in inverse and circulating three-phase fluidized beds for waste water treatment is summarized. The three-phase (gas-liquid-solid) fluidized bed can be utilized for catalytic and photo-catalytic gas-liquid reactions such as chemical, biochemical, biofilm and electrode reactions. For the more effective treatment of wastewater, recently, new processing modes such as the inverse and circulation fluidization have been developed and adopted to circumvent the conventional three-phase fluidized bed reactors [1-6]. 

To provide the pr equisite knowledge for designing the three-phase fluidized-bed reactors with new modes, the hydrodynamics such as phase holdup, mixing and bubble properties and heat and mass transfer characteristics in the reactors have to be determined. Thus, in this study, the hydrodynamics and heat and mass transfer characteristics in the inverse and circulating three-phase fluidized-bed reactors for wastewater treatment in the present and previous studies have been summarized. Correlations for the hydrod3aiamics as well as mass and heat transfer coefficients are proposed. The areas wherein future research should be undertaken to improve... 

Bavarian and Fan [3, 4] reported a similar phenomenon occurring in a three-phase fluidized bed. In their case, the hydraulic transport of a packed bed occurred at the start-up of a gas-liquid-solid fluidized bed. Although the cause was different from the case reported in the present study, similar phenomena were observed in both cases. 

Fig. 3 gives the conversions for acetic acid and ammonia decomposition over Ti02 and Al-Ti02 in a three-phase fluidized photoreactor. In the case of acetic acid decomposition (Inlet condition of 300 ppm), the conversion increased with alununum addition. In particular, the conversion to CO2 reached about 90% and then it was kept until 600 mins on Al-TiOa catalyst. On the other hand, in b), the anunonia removal (Inlet condition of 80ppm) also enhanced on Al-Ti02 compared to that conventional Ti02 catalyst the conversion to N2 reached above 95% in Al-Ti02. We have also observed that the ammonia conversion in a conventional batch type steady photoreactor could be obtained up to 70%. From this result, we could confirmed that... 

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 development of three-phase reactor technologies in the 1970 s saw renewed interest in the synthetic fuel area due to the energy crisis of 1973. Several processes were developed for direct coal liquefaction using both slurry bubble column reactors (Exxon Donor Solvent process and Solvent Refined Coal process) and three-phase fluidized bed reactors (H-Coal process). These processes were again shelved in the early 1980 s due to the low price of petroleum crudes. 

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... 

The 1980 s and the early 1990 s have seen the blossoming development of the biotechnology field. Three-phase fluidized bed bioreactors have become an essential element in the commercialization of processes to yield products and treat wastewater via biological mechanisms. Fluidized bed bioreactors have been applied in the areas of wastewater treatment, discussed previously, fermentation, and cell culture. The large scale application of three-phase fluidized bed or slurry bubble column fermen-tors are represented by ethanol production in a 10,000 liter fermentor (Samejima et al., 1984), penicillin production in a 200 liter fermentor (Endo et al., 1986), and the production of monoclonal antibodies in a 1,000 liter slurry bubble column bioreactor (Birch et al., 1985). Fan (1989) provides a complete review of biological applications of three-phase fluidized beds up to 1989. Part II of this chapter covers the recent developments in three-phase fluidized bed bioreactor technology. 

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. 

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