Optimization of waste heat based organic Rankine cycle powered cascaded vapor compression-absorption refrigeration system

In this paper, the thermo-economic optimization of the waste heat based organic Rankine cycle powered cascaded vapor compression-absorption refrigeration system is presented. Organic Rankine cycle with dry organic working fluid is used as a power generating cycle to provide input to the vapor compression refrigeration system. Moreover, the high temperature organic working fluid at the expander outlet is used to supply thermal need of the vapor absorption refrigeration system. The present system achieves low temperature cooling efficiently. However, initial capital cost and complexity are the practical limitations for the present system. The energetic efficiency of the present system for only cooling mode and cogeneration mode (cooling and heating) are calculated to be 22.3% and 79%, respectively. It may be noted that the extra heat available, apart from the thermal energy requirement of the vapor absorption system, is taken as process heat in the cogeneration mode. The simple payback period and break-even point are calculated (for the base case) to be 5.26 years and 4.22 years, respectively. The system size and annualized cost are optimized, using nonlinear programming based on conjugated directions method, to make the system potentially attractive for the industrial sector. Optimization results reveal that the annualized cost of the present system is decreased by about 12% compared to the base case. Moreover, the simple payback period and break-even point are reduced to 4.50 years and 3.48 years, respectively. The results of comparative economic study, between the present and stand-alone vapor compression refrigeration systems, show that the higher value of electricity price and the lower value of discount rate are favorable for the selection of the present system.