Optimisation of Cooling-Water Systems Considering Temperature-Rise and Pressure-Drop

Abstract

Cooling-water systems (CWS) are widely used in process industries as a cold utility. In re-circulating CWS, cooling water from the cooling tower (CT) is transported only by pumps on the main supply pipeline and supplied to a coolers network that usually has a parallel configuration. However, series-parallel configuration of coolers can obviously reduce the cooling water flow-rate and increase its return temperature as well as the effectiveness of the CT, but the pressure drop along pipelines will increase accordingly. To save energy and cost, a mathematical model is established to optimise the cooling water system. A two-step solution strategy is proposed to obtain the optimal cooling-water network (CWN) with minimal total cost. Firstly the optimal heat exchanger network (HEN) is obtained, and then the optimal pump network with auxiliary pumps is synthesized. The proposed optimisation model can identify the optimal distribution of cooling water within the network and the optimal installation location and capacity of pumps required for CWS. An example has been provided to demonstrate the effectiveness of the method.