Application of entransy method in heat exchanger networkoptimization for low-grade waste heat utilization

Abstract

<p indent="0mm">Efficient utilization of low-grade industrial waste heat is of great significance to improve the efficiency of energy utilization and to reduce CO₂ emission. Energy system integration and corresponding heat exchanger network optimization are effective solutions. The entransy method is suitable for quantifying the irreversibility of the heat exchange process and guiding and evaluating heat exchanger network optimization. However, there are relatively few cases in which the entransy method is applied to the heat exchanger network optimization for waste heat utilization. In this study, the waste heat utilization of steam condensate in an industrial park through a heat exchanger network was analyzed based on the entransy method. By reducing the entransy dissipation of the heat exchange process of the condensate, the existing heat exchanger network was optimized, and the high-grade waste heat was utilized by an absorption chiller for local air conditioning demands. As a result, the discharge of high-grade waste heat was converted to the discharge of low-grade waste heat. The optimized heat exchanger network guided the redesign of the actual heat exchanger network. The testing results showed that the cooling effect of the developed seawater cooled absorption chiller reached <sc>3430 kW</sc>, with a coefficient of performance of 0.76. The entransy dissipation of the heat exchange process of the condensate was reduced by 57.3%. The thermal efficiency and exergy efficiency of the heat exchanger network were increased by 55.8% and 81.1%, respectively. These results demonstrate that the entransy method is valid in the application of low-grade waste heat utilization through heat exchanger network optimization.