Thermodynamic and exergoeconomic analysis of a combined cooling, desalination and power system for low-grade waste heat utilization

Abstract

As a form of sustainable energy, low-grade waste heat has considerable amount to be recovered, but the energy utilization efficiency is still low. In this paper, a novel multi-generation system is proposed to utilize the low-grade waste heat efficiently and meet the needs for cooling, freshwater and power simultaneously, by integrating vapor compression refrigeration (VCR), humidification and dehumidification (HDH) desalination with transcritical organic Rankine cycle (TORC). Thermodynamic and exergoeconomic performances of the multi-generation system with five working fluids are evaluated. Parametric studies are conducted to identify the key operating parameters. Results show that the highest exergy efficiency ηex and the lowest average unit cost of products (AUCP) can be obtained by using R161, while the highest coefficient of performance (COPtot) belongs to R143a. The proportion of the vapor generator in the total exergy destruction is the largest, followed by the condenser. Higher net power output and freshwater production can be achieved by raising the vapor generation temperature and the ratio of mass flow rates of working fluid, and the corresponding ηex and AUCP are also improved. There is an optimal pressure for the lowest AUCP and the highest net power output and ηex. Performance comparison with systems from the literature is conducted as well.