Conventional and energy level based exergoeconomic analysis of biomass and natural gas fired polygeneration system integrated with ground source heat pump and PEM electrolyzer

Abstract

In this research, energy level based exergoeconomic evaluations are performed for a novel biomass and natural gas fired polygeneration system of electricity, hot water, chilled water and hydrogen production. The proposed system mainly consists of a biomass gasifier, a proton exchange membrane (PEM) electrolyzer, a gas turbine cycle (GT), an absorption chiller, and a ground source heat pump cycle. Conventional and energy level based exergoeconomic performances of the proposed system are compared; related exergy and economic analysis are also performed. In addition, the variations in unit exergy cost of products (electricity, hot water, chilled water and hydrogen) are studied under economic factors. The results show that energy and exergy efficiency of the electrolyzer and the proposed system decrease with the increasing current density of the PEM electrolyzer. The unit exergy cost of electricity and hydrogen are 5.24 $/GJ and 20.41 $/GJ under the energy level based exergoeconomic method, respectively, which are higher than that under the conventional exergoeconomic method (electricity: 4.38 $/GJ, hydrogen: 19.00 $/GJ), while the unit exergy cost of hot water and chilled water under the energy level based exergoeconomic method are lower than that under the conventional exergoeconomic method. Moreover, the exergoeconomic factor and relative cost difference of the system equipment also show distinctions under the conventional and energy level based exergoeconomic methods. The presented polygeneration system is a promising technology to utilize renewable energy and improve the flexibility of the integrated system; and the energy level based exergoeconomic method shows certain rationality and feasibility in the system analysis.