A Critical Assessment Of Thermo-Economic Analyses Of Different Air Bottoming Cycles For Waste Heat Recovery

Steam turbine cycle's low operating temperature makes it suitable for waste heat recovery applications. Even though conventional combined cycles, ie, topping gas turbine and bottoming steam turbine cycles, are thermodynamically efficient, they are not the most economical alternatives for power generation with capacities less than 50 MWe. A recently proposed alternative is to utilize a bottoming gas turbine cycle in form of an air bottoming cycle. In this study, an overview of air bottoming cycle is presented. Based on the discussed studies, it is decided to further evaluate the merits of water injection in the bottoming cycle air stream by using either a humidifier or an air saturator. Thermo-economic analysis and optimization are performed to evaluate simple and water injected air bottoming cycles against steam bottoming cycles. Results indicate that conventional combined cycles can achieve the highest thermal efficiency of about 48%. While water injected air bottoming cycle with air saturator is the most cost effective combined cycle configuration and most efficient air bottoming cycle with levelized cost of electricity and energy efficiency of 64.41 US$/MWh and 39%-40%, respectively, followed by the water injected air bottoming cycle with humidifier and simple air bottoming cycle with reported levelized cost of electricity of 65.75 US$/MWh, 66.36 US$/MWh, respectively. Steam bottoming cycle has the highest levelized cost of electricity of 68.88 US$/MWh.