Evaporating equipment classification

Additional operations essential to commercial bauxite processing are steam and power generation, heat recovery to minimise energy consumption, process liquor evaporation to maintain a water balance, impurity removal from process liquor streams, classification and washing of ttihydrate, lime caustication of sodium carbonate [497-19-8] to sodium hydroxide [1310-73-2] repair and maintenance of equipment, rehabiUtation of mine and residue disposal sites, and quaUty and process control. Each operation in the process can be carried out in a variety of ways depending upon bauxite properties and optimum economic tradeoffs. 

Another useful classification is whether or not a dryer is a direct or indirect dryer. A direct contact dryer is one in which the material is dried by exposure to a hot gas, whereas in an indirect contact dryer, the heat required for evaporation is transferred from a heating medium through a metal wall to the material. Generally, direct heat dryers are more efficient. Dryer efficiency is defined by the fraction of energy supplied to the drying equipment which actually causes the evaporation of the liquid. As we shall see later in the chapter, heating is not always necessary to achieve drying. 

Crystallization cannot occur without supersaturation. A main function of any crystallizer is to cause a supersaturated solution to form. A classification of crystallizing equipment can be made based on the methods used to bring about supersaturation as follows (1) supersaturation produced by cooling the solution with negligible evaporation—tank and batch-type crystallizers (2) supersaturation produced by evaporation of the solvent with little or no cooling—evaporator-crystallizers and crystallizing... 

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