Equipment in which vaporization of all or part of a liquid takes place may be described as Evaporators, Vaporizers, Concentrators, Evaporative Crystallisers, Boilers, or Reboilers. The differentiation between these is in some cases somewhat arbitrary, and similar equipment may be used for different functions. The differences lie more in the primary objective of the operation; in vaporizers or boilers, and reboilers for distillation columns, it is the generation of the vapour. Shell-and-tube reboilers are dealt with in Section 46. Waste heat boiler systems are covered in Section 56. Section 320 discusses fired process heaters and boilers, including power generation boilers.

The primary function of an evaporator or concentrator, on the other hand, is to concentrate a solution by evaporation of the more volatile solvent and the required end product is the concentrated liquid. In an evaporative crystalliser the process is carried to the point at which crystallization occurs, with the crystallized solid being the primary required product. In may cases, particularly those with high throughputs, the evaporated solvent is water. However, evaporators are not confined to aqueous duties.

This section is concerned with equipment for process vaporizers, evaporators and evaporative crystallisers. The various types of equipment which may be used for these duties are described in Section 270. The arrangements whereby these pieces of equipment may be combined with each other or with other types of equipment are described in Section 271. Section 272 discusses some of the design details of evaporators and their ancillary equipment. The choice of the best type and arrangement for the duties of vaporization, concentration and evaporative crystallization is considered in Section 273. Section 274, Section 275 and Section 276 deal with the thermal/hydraulic design of evaporators, including the estimation of heat transfer coefficients, critical heat flux and pressure drop.

Some of the opinions expressed in this section are based on advice given by the staff of the former Agricultural and Mond Divisions of Imperial Chemical Industries Limited and on information published by Chilton and Perry (1999). The authors express their gratitude for this help and for permission to publish.

Many types of evaporators are in use, including shallow ponds heated by solar radiation, direct fired open pans, coil-in-vessel evaporators and jacketed vessels with internal agitators. Section 270, however, deals with only twelve major types: