LAUSR

An innovative dual-loop heat recovery and power generation system is proposed here to increase heat recovery from the gas engine (GE) exhaust and jacket cooling water and to augment the system power output and thermal efficiency. As this proposed dual-loop heat recovery system is not studied in existing references, for comparison purpose, 18 existing single- and dual-loop systems in the literature as well as one proposed dual-loop system with six working fluids in topping and six working fluids in bottoming loop (36 cases) are investigated here (54 cases in sum). These systems are modeled in energy, exergy and economic aspects and are optimized by selecting ten design variables and two objective functions (payback period and exergy efficiency) by the use of genetic algorithm. Results show that with water as working fluid for topping loop (Rankine cycle or RC loop) and R141b for bottoming loop (organic Rankine cycle or ORC loop), which are selected in modeling and optimization procedures, the proposed above RC–ORC system has advantages among 53 other studied single- and dual-loop cases. These advantages are higher power output, thermal efficiency, exergy efficiency, annual profit as well as lower investment cost per unit of power output ($ kW−1) and payback period. It is observed that the proposed configuration of RC–ORC (with water–R141b as working fluids), which is integrated with 2 MW gas engine (as an example) generated 617 kW power output with 24% thermal efficiency, 55% exergy efficiency, 1280 $ kW−1 investment cost per unit of power output and about 3-year payback period. Furthermore, the overall thermal efficiency of integrated system (GE–RC–ORC) was about 67%. Finally, RC–ORC power output, exergy efficiency, thermal efficiency and payback period are also obtained for 1, 2 and 3 MW gas engines at various partial loads.