Fluidized with draft tube

S.K. Jeon, Coal Gasification Characteristics in a Circulating Fluidized Bed with Draft Tube, MS Thesis, KAIST, Korea, 1994. 

Figure 6. The relationship between mean circulation time and variance of the circulation time distribution for a 150-mm diameter fluidized bed with draft tube insert (from Cheng, 1993).

Table 2. Typical Capacities of Fluidized Bed Coaters with Draft Tubes used in the Pharmaceutical Industry (Mehta, 1988)...

R.K. Stoecker, A. Rastogi, L.A. Behie, W.Y. Svreck, M.A. Bergougnou, A computer simulation of propane cracking in a spout-fluid bed reactor with draft tube, in K. Ostergaard, A Sorensen (Eds.), Fluidization V, Engineering Foundation, New York, 1986, pp. 465 172. 

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

Gasification of tire scrap and sewage sludge in a circulating fluidized bed with a draft tube... 

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... 

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. 

Ishida, M., and Shirai, T., Circulation of Solid Particles within the Fluidized Bed with a Draft Tube, J. Chem. Eng. (Japan), 8 477 (1975)... 

Judd, M. R., Masson, H., and Meihack, W., Solid Circulation and Gasification Experiments in a Fluidized Bed with a Draft Tube, Fluidization, (D. Kunii, and R. Toei, eds.), Engineering Foundation, New York, pp. 663 (1984)... 

However, for small scale equipment, Cheng (1993) and Xu (1993) measured the circulation times of a single tagged particle in a 150 mm diameter fluidized bed coater with a draft tube and found that typical circulation times were between 2-10 seconds. Robinson and Waldie (1978) made similar measurements in a 6" diameter conventional spouted bed and found mean circulation times in the range of 3-6 seconds. 

There are a wide variety of three-phase fluidized bioreactor designs possible. The conventional reactor, shown in Fig. 9, is fluidized by both gas and liquid entering at the bottom of the reactor and leaving at the top and is the most common type of three-phase fluidized bed bioreactor. This reactor may be configured to operate with little axial liquid mixing or in a well-mixed mode by adding a recycle stream. The airlift reactor or draft tube fluidized bed reactor, Fig. 10, is also frequently used. In this reactor, gas is injected at the bottom of a draft tube placed in the center of the... 

Understanding the effect of reactor diameter on the volumetric mass transfer coefficient is critical to successful scale up. In studies of a three-phase fluidized bed bioreactor using soft polyurethane particles, Karamanev et al. (1992) found that for a classical fluidized bed bioreactor, kxa could either increase or decrease with a change in reactor diameter, depending on solids holdup, but for a draft tube fluidized bed bioreactor, kxa always increased with increased reactor diameter. 

Fan, L. S., Fujie, K., Long, T. R., and Tang, W. T., Characteristics of Draft Tube Gas-Liquid-Solid Fluidized-Bed Bioreactor with Immobilized Living Cells for Phenol Degradation, Biotechnol. Bioeng., 30 498 (1987b)... 

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