Heat exchangers are used to transfer heat from one medium to another. These media may be a gas, liquid, or a combination of both. The media may be separated by a solid wall to prevent mixing or may be in direct contact. Heat exchangers are required to provide heating and/or cooling to meet a process requirement. Typically, any direct heat input to the system comes from a furnace or steam. Therefore, any inefficiency in the heat transfer at exchangers will require a higher amount of duty from the furnace or steam.

Heat exchangers can also improve a system’s energy efficiency by transferring heat from systems where it is not needed to other systems where it can be usefully used. In general, the heat exchangers are used to exchange heat between two or more process streams or between process stream(s) and a utility stream, which can be either hot or cold utilities.

The selection between using a direct process-to-process heat exchanger versus using utilities to transfer heat depends on the temperature and pressure required by the process stream and whether there is an available process stream to provide that duty given the temperature approach required. When there is no process stream available, a utility stream is required to provide the heating or cooling duty required.