Distributor baffle-type

Conveying-screen dryers are fabricated with conveyor widths from 0.3- to 4.4-m sections 1.6 to 2.5 m long. Each section consists of a sheet-metal enclosure, insulated sidewalls and roof, heating coils, a circulating fan, inlet air distributor baffles, a fines catch pan under the conveyor, and a conveyor screen (Fig. 12-51). Table 12-23 gives approximate purchase costs for equipment with type 304 staimess-steel hinged conveyor screens and includes steam-coil heaters, fans, motors, and a variable-speed conveyor drive. Cabinet and auxiliary equipment fabrication is of aluminized steel or stainless-steel materials. Prices do not include temperature controllers, motor starters, preform equipment, or auxiliary feed and discharge conveyors. These may add 75,000 to 160,000 to the dryer purchase cost (2005 costs). 

The common types of flashing feed and vapor distributors are the baffle type (Fig. 3.9a), the vapor-liquid separator type (Fig. 3.96), the gallery type (Fig. 3.9c), and the tangential entrance tjrpe (Fig. 2.2j). Some of the vapor distributors discussed in Sec. 3.12 are also sometimes used for flashing feeds, especially when liquid distribution to the section below is not critical (e.g., when it contains trays). 

Figure 3.9 Flashing feed distributors, (a) Baffle-type distributor, (b) vapor-liquid separator-type distributor (c) gallety-type distributor. (Parts a, c Gilbert K. Chen, excerpted by special permission from Chemical Engineering, March 5,1984, copyright by McGraw-HiU, Inc., New York, NY 10020 part b reprinted courtesy of Norton Company.)...

These parts are used in fluidized beds for various purposes. For example, gas distributors and various types of baffles are installed to decrease the size of the bubbles. Moreover, draft tubes are used to enhance gas or solid circulation. Other devices such as horizontal baffles limit circulation and backmixing of solids and gas. Horizontal or vertical tubes are used for heat management. Devices used to control or improve fluidization behavior, to improve fluidization of cohesive particles or to achieve solids recovery are within the various internals met in fluidized bed reactors (Kelkar and Ng, 2002). Immersed tubes in small diameter beds may lead to slugging. Furthermore, attrition of particle breakage may change the size distribution and possibly change the fluidization behavior. 

For designing a reactor on a larger scale, one merely needs to take into account gas dispersion (see sections 4.6.1 and 4.7.22) and heat transfer. Heat can be transferred via the reactor wall, but heat removal via an evaporating solvent is generally to be preferred (sections 8.3.2 and 8.3.3). Both effects can be controll simultaneously in a bubble column type reactor, by adjusting the gas flow rate. This reactor type has the advantage that there are no internals save the gas distributor. In a stirred reactor, the baffles and the impeller shaft are often liable to fouling. 

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