Rational Use of Cooling Water in Heat Exchanger Network on Industrial Site

Abstract

The parallel heat exchanger network (HEN) arrangement is typically used industrially for once-through cooling water systems of several hot streams. The studied systems are when the cooling water temperature increase is rather low and limited by environmental restrictions, e.g. temperature increase lower than 10 °C, and the cooling water is at a temperature much lower than the output temperature of the hot streams. In the parallel arrangement, the water is supplied to each exchanger at the lowest temperature available. The series HEN arrangement requires higher exchanger area because the increase of cooling water temperature in each exchanger is lower than the attainable for the parallel arrangement. Nevertheless, the present study shows using a MINLP optimisation that some configurations combining series and parallel arrangements of heat exchangers can be more advantageous than the parallel. The optimal arrangement is obtained when the heat exchangers with similar amount of heat exchanged are grouped in parallel in the same stage where the stages are in series.