Selection of the optimum prime mover and the working fluid in a regenerative organic rankine cycle

Abstract

A regenerative organic Rankine cycle (RORC) is modeled and optimized for the use of waste heat recovery from a prime mover (PM). Three PMs including, a diesel engine, a gas engine, and a microturbine are selected in this study. Four refrigerants including isobutane, R123, R134a, and R245fa are selected. The nominal capacity of the PM, PM operating partial load, turbine inlet pressure, condenser pressure, refrigerant mass flow rate, pump efficiency, turbine efficiency, and regenerator effectiveness are considered as the decision variables. Then, the Genetic Algorithm is applied to maximize the thermal efficiency and minimize the total annual cost (TAC), simultaneously. The optimum results demonstrate that the best working fluid and the PM are, respectively, R123 and the diesel engine, which have a thermal efficiency of 0.50 and a TAC of $170,276/year. The optimum results are compared with each of the other studied cases. For example, the optimum result in the case of a diesel engine working with R123 shows a 2% and 2.52% improvement in the thermal efficiency and the TAC, respectively, in comparison to the case of a gas engine working with R123. Furthermore, a 26% and an 18.38% improvement in the thermal efficiency and the TAC are found when the best-studied cycle is compared with a microturbine and R123.