Thermodynamics analysis of solar-ejector pump OTEC (SEP-OTEC) rankine cycle using ammonia as refrigerant

Abstract

Organic Rankine Cycle (ORC) applications include ocean thermal energy conversion (OTEC), in which mechanical work is generated from heat energy to rotate generators and generate electricity. The OTEC system heated and cooled its refrigerant by taking advantage of the relatively small temperature difference between the warmer surface seawater and the colder deep seawater. The low-temperature difference between seawater and the rest of the system meant that the thermal efficiency of the system was relatively low; to address this problem, the OTEC cycles needed to be revised. To increase the basic OTEC cycle's thermal efficiency by 3.3–4.0%, various modifications have been developed. Two such cycles are the Solar Boosted OTEC (SOTEC) cycle and the Ejector Pump cycle (EP-OTEC). While the two improvements alter the rotating turbine parameters in different ways, they can be combined to create an improved OTEC cycle through the use of thermodynamics. In this study, an algorithm for revised OTEC was developed using MATLAB, and the performance of the system after the modifications was further quantified. This SEP-OTEC cycle thermal efficiency gives a 1.2-fold improvement when compared to the previous OTEC cycle thermal efficiency, which was 3.1%.