Optimal design of industrial cooling water systems considering economic performance and water savings

Abstract

As large water-using systems in chemical industries, cooling water systems (CWSs) consume a large amount of water and power. Up to now, most research on the cooling water system mainly focuses on energy-saving aspects by using the series-parallel structure of the cooler network. In this work, to consider the water-saving aspects of the cooling water system, air coolers and closed cooling towers are applied. Considering the best implementation of air coolers and closed cooling towers, the trade-offs between energy consumption, water consumption, and capital cost should be considered. In this work, a multiperiod optimization of the cooling water system in a chemical plant is carried out. To achieve the above-mentioned trade-off, heat duty distribution between air cooling and water cooling is optimized. Meanwhile, a comparison of cooling performance between the open cooling system and closed cooling system is involved. The problem is formulated as a mixed-integer nonlinear programming (MINLP) model and solved by GAMS (The General Algebraic Modelling System) software to obtain the best cooling water system configuration. In a case study, the new method is used to guide the energy saving and water saving of the cooling water system in a refinery, which can reduce the total cost by at least 4%.