Energy, exergy and exergoeconomic analysis of a combined cooling, desalination and power system

Abstract

Ocean thermal energy has attracted much attention for its unique advantages. Multi-generation systems are emerging as an effective solution to further improve energy efficiency and economy of ocean thermal energy conversion (OTEC) system. In this paper, a novel hybrid OTEC system combing cooling, desalination and power (CCDP) is proposed facing the actual demands of remote islands at low latitudes. The cogeneration of cooling capacity, fresh water and power are achieved by the subsystems of ejector refrigeration cycle (ERC), multi-effect distillation (MED) desalination and organic Rankine cycle (ORC). A detailed mathematical model for the proposed system is developed based on the thermodynamics and exergoeconomics. The effects of key operating parameters on the system performances are investigated from the perspectives of energy, exergy and exergoeconomic. The results indicate that the highest primary energy saving ratio (PESR) and exergy efficiency of the proposed system are up to 33.72% and 29.33%, respectively. The main sources of exergy destruction are the MED unit, generator and ejector, accounting for about 80% of the total exergy destruction. The improvement of both thermodynamic and exergoeconomic performances can be achieved at a higher generation pressure and a larger distillate production. The rise of condensing pressure is conducive to cutting down the unit costs of products, but will result in lower exergy efficiency and PESR.