Other Tray Types

The discussions in this chapter emphasize sieve and valve trays, as these trays Eire most frequently encountered in industrial practice. Several of the considerations also apply to other tray types (e.g., bubble-cap trays). Considerations unique to bubble-cap trays were excluded from this chapter. The infrequent application of this type of tray in modern distillation practice argnes against a detailed discus-... 

The separation operation called distillation utihzes vapor and hquid phases at essentially the same temperature and pressure for the coexisting zones. Various lands of devices such as r andom or sti uctui ed packings and plates or tr ays are used to bring the two phases into intimate contact. Trays are stacked one above the other and enclosed in a cyhndrical shell to form a column. Pacldngs are also generally contained in a cyhndrical shell between hold-down and support plates. A typical tray-type distillation column plus major external accessories is shown schematically in Fig. 13-1. 

Compared more with tray type performance than other packing materials. Usually used in large diameter towers, above about 24-inch dia., but smaller to 10-inch dia. available. Metal only. 

Efficiency most data are for this type, as high as other tray designs. 

In conveyor and tray types of dryer, air is often recirculated inside the drying vessel in an attempt to save energy or to maintain a relatively high moisture content in the drying air. In other direct dryers such as flash, fluidised-bed, rotary and spray units, any recycle of exhaust air must be returned to the dryer using external ducting, the cost of which is offset by the net savings from the lower volumes of exhaust streams which have to be handled. 

Pyrocat-HD is a Pyrocatechin/Phenidone-based developer formula that can be used for development in tanks or trays. It is also recommended for JOBO and other rotary type processing in tubes and drums. Although originally meant for sheet film, subsequent use has shown that it is also an excellent developer for use with 35 mm and medium-format films because of its high acutance and tight grain pattern. 

Available in metal onl) , compared more vrith tray type performance than other packing materials. About same HETP as Spraypak for available data. Used in towers 24 in. and larger. Shows some performance advantage over bubble cap trays up to 75 psia in fracuonadon service, but reduced advantages above this pressure or in vacuum service. 

Multiple factors influence tray efficiency. These include the physical properties of the system, operating conditions, vapor and liquid loads, compositions, tray type, fabrication details of the tray, and many others. A range of experimental studies have examined tray efficiency under different conditions. These studies show often conflicting results for the influence of the mechanical and process conditions involved. Study results reveal few useful engineering guidelines for tray design and efficiency. 

As noted above, a number of equipment parameters must normally be specified so that the mass transfer coefficients can be estimated correctly. For example, the diameter of all columns must be known. For trayed columns, the tray type, weir height, liquid flow path length, and bubbling area must be known for packed columns, the packing type, size, and material must be known. It may also be necessary to allow for different diameters, tray or packing type, or other tray or packing parameters in different parts of the same column. 

Conventional dryers used in the mineral-processing industry are classified as hearth type, shaft type, and grate type. Other types of dryers used less commonly in current practice are the spray type, fluid-bed type, pneumatic or flash type, conveyor type, drum type, stationary- and rotating-tray type, infrared type, and others. Only the more commonly used dryers are discussed in this chapter. 

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