Recirculating fluidized bed

RECIRCULATING FLUIDIZED BEDS WITH A DRAFT TUBE... 

This concept was first called a recirculating fluidized bed by Yang and Kearins (1974). Several other names have also been used to describe the same concept the fluid-lift solids recirculator (Buchanan and Wilson, 1965), the spouted fluid bed with a draft tube (Y ang and Keaims, 1983 Hadzismajlovic et al., 1992), the internally circulating fluidized bed (Milne et al., 1992 Lee and Kim, 1992) or simply a circulating fluidized... 

Figure 1. Recirculating fluidized bed concept—draft tube operated as a dilute phase pneumatic transport tube.

The important design parameters for a recirculating fluidized bed with a draft tube were identified by Yang and Keaims (1978a) as the gas bypassing characteristics of the distributor plate, the area ratio between the downcomer and the draft tube, the diameter ratio between the draft tube and the draft tube gas supply, the distance between the distributor plate and the draft tube inlet, and the area ratio of the draft tube gas supply and the concentric solids feeder. The design and operation of a recirculating fluidized bed with a draft tube are discussed below. 

Most of the applications for the recirculating fluidized bed with a draft tube operate the draft tube as a dilute phase pneumatic transport tube. Hence we will discussed this system in more details. 

Downcomer and Draft Tube Pressure Drop. Typical experimental pressure drops across the downcomer, AP, 4, and the draft tube, AP2 3, show that they are essentially similar. Successful design of a recirculating fluidized bed with a draft tube requires development of mathematical models for both downcomer and draft tube. 

The results of an example calculation for a recirculating fluidized bed coal devolatilizer of 0.51 m in diameter handling coal of average size 1200 pm at 870°C and 1550 kPa are presented in Fig. 11. The calculation is based on operating the fluidized bed above the draft tube at 4 times the minimum fluidization velocity. It is also based on the selection of a distributor plate to maintain the downcomer at the minimum fluidization condition. If the two-phase theory applies, this means that the slip velocity between the gas and the particles in the downcomer must equal to the interstitial minimum fluidizing velocity as shown below. 

Alappat, B. J., and Rane, V. C., Studies on the Effects of Various Design and Operational Parameters on Solid Circulation Rate in a Recirculating Fluidized Bed, Can. J. Chem. Eng., 73 248 (1995)... 

Ohoka, I., and Conway, H. L., Progress in the Gasification of Heavy Hydrocarbon Oils in a Recirculating Fluidized Bed Hydrogenator, paper presented at the 5th Synthetic Pipeline Gas Symposium, Chicago, (1973)... 

Yang, W. C., and Keaims, D. L., Recirculating Fluidized Bed Reactor Data Utilizing a Two-dimensional Cold Model, AIChE Symp. Series, 70(141) 27 (1974)... 

Fig. 2. Frontal and single stage recirculating fluidized bed adsorption...

Arpalahti, Olli, Recirculating fluidized-bed reactor for the removal of particulate material from flue gases," Finland FI 77165 B, 881031, FI 86244 (860120), 11 pp. (1988). 

Engstrom, Folke, Henricson, Kaj, and Lundqvist, Ragnar. Solids removal from waste gases using a recirculating fluidized bed reactor, Germany (East), DD 253945. 

Fitting, Arno, and Hirsch, Martin. Sulfur recovery from sulfldic materials in a recirculating fluidized bed, PATENT Germany Often. DE 3926723 A1 DATE 910214, APPLICATION DE 3926723 (890812), 6 pp. (1991). 

Minet, Ronald G., and Tsotsis, Theodore T. Recirculating fluidized-bed process and apparatus for the recovery of chlorine from hydrogen chloride, ES 2010473 (1989). 

Rhodes, M. J., and Geldart, D. The hydrodynamics of recirculating fluidized beds, to Circulating Fluidized Bed Technology (P. Basu,ed.), pp. 193-200. Pergamon Press, 1986. 

Alappat BJ, Rane VC (2001) Solids Circulation Rate in Recirculating Fluidized Bed. J Energy Eng 127(2) 51-68... 

Chandel MK, Alappat BJ (2006) Pressure drop and gas bypassing in recirculating fluidized beds. Chem Eng Sci 61 1489-1499... 

Figure 7. Schematic diagram of the recirculating column reactor. Reactor has advantages of both the soil column and recirculating fluidized-bed reactor.

Since there is more flexibility in operating recirculating fluidized bed, it is applicable to handle all groups of powders and particles. Its application in drying has been reported in coating of tablets in pharmaceutical industries and in drying... 

Effect of H20 CH4 on effluent gas composition with NiO-yAlaOs carrier in a recirculating fluidized bed reactor. T = 900°C. 

Bierl TW, Gajdos LJ, Mclver AE, McGovern JJ. Studies in support of recirculating fluidized bed reactors for the processing of coal. DOE Rept. Ex-C-78-01-2449, 1980. 

Figure 4 Recirculating fluidized bed with draft tube operated as a pneumatic transport tube.

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