CONTROL OF CONCENTRATION IN HEAT SEPARATING PROCESS

PURPOSE: To provide a simple controller which is not limited to a pressure range or a temperature range by using a correction temperature being the function of an actual temperature and an actual pressure at the time of controlling the concentration of a multicomponent mixture at the exit of a thermal separation device. CONSTITUTION: A ternary mixture 2 constituted of water, dimethyl formamide, and formic acid is separated by a distillation column 1. A pressure compensated temperature T* decided from a pressure P and a temperature value T measured at a measurement point 5 at that time is used as a substituted variable. The temperature T* is decided as T*=f(T, P) by an expression I. An actual value T* and a theoretical value T* calculated by a computer 9 according to this expression are supplied to a PID controller 6. Then, the volume of steam is controlled, and the column is acted on by a heat exchanger 8. Thus, the water concentration of a column bottom product can be held in an extremely narrow range, and the column can be operated close to a specification limit.