Method of controlling heat exchangers using enthalpy flow as the correcting variable

A method for controlling a heat exchanger, wherein a process controller maintains a process parameter on a process side of the heat exchanger at a set point, the heat exchanger is operated by a heating medium flowing therethrough from a feed line including a valve controlled by an enthalpy controller which is controlled by the process controller, comprising the steps of:

• a) measuring mass flow, pressure and temperature of the heating medium input in the feed line to the heat exchanger and temperature of the heating medium output of the heat exchanger;
• b) determining from the measurements in step a) and a time response of the heat exchanger, the enthalpy of the heating medium input into the heat exchanger and the enthalpy of the heating medium output from the heat exchanger and forming a difference between the enthalpies to determine the enthalpy flow into the heat exchanger;
• and
• c) controlling the enthalpy flow into the heat exchanger by controlling the valve in the feed line such that the enthalpy flow is maintained at a set point, whereby the enthalpy flow into the heat exchanger is changed in response to the process controller.