Exergoeconomic and exergoenvironmental analysis of a combined heating and power system driven by geothermal source

Abstract

This paper develops a geothermal driven combined heating and power system to obtain multi-generation, in which power is generated by Organic Rankine Cycle and heating is supplied by radiant floor heating system. Comprehensive thermodynamic, exergoeconomic and exergoenvironmental models of the system are performed and the capital cost and environmental impacts of the system components are analyzed. Superheat degree of the organic working fluid and inlet pressure of the Organic Rankine Cycle turbine are selected as variables to assess the system performance. Multi-objective optimization is employed to obtain the maximum system net power output, minimum levelized cost per exergy unit and minimum levelized environmental impact per exergy unit of the system. Results show that the increase of the working fluid superheat degree and the Organic Rankine Cycle turbine inlet pressure would cause the decrease of the Organic Rankine Cycle turbine power output and the increase of the heat supplying. Cooling water holds the highest levelized exergy cost and geothermal water heat exchanger has the highest environmental impact reducing potential. Under the condition of 11 °C superheat degree and 833 kPa Organic Rankine Cycle turbine inlet pressure, the system obtains a better performance with system net power output 1.19 MW, levelized cost per exergy unit 4.80 $/GJ and environmental impact per exergy unit 16.0 mpts/GJ.