Abstract

Evaporation is used most often in the chemical industry for concentrating a solution or crystallizing a solid from solution. The high latent heat of the solvent (usually water) generally makes heat transfer the most important element of evaporator design and capital cost. Heat-transfer surfaces usually are metal tubes and many configurations are available to improve performance, the choice depending primarily on the characteristics of the material being processed and the scale of the operation. The high heat demand of evaporators makes energy consumption the most important element of operating cost. Means available for reducing energy demand include multiple-effect or multistage flash operation and vapor recompression, where the vapor given off by an evaporator is compressed so that it can serve as part or all of its own heating medium. Other important factors in evaporator selection and design are the separation of vapor from the residual liquid to the degree necessary in each case and the provision of a heat sink for the large amount of energy utilized.