Cascading uses of geothermal energy for a sustainable energy supply for Meshkinshahr City, Northwest, Iran

While renewable energy has been considered as an unlimited energy resourcein recent years, increasing dependency on natural gas has created various economic and environmental problems in Iran. Among renewables, geothermal energy is a powerful source for producing electricity and heat, simultaneously. The Sabalan geothermal field in northwestern Iran has a great geothermal potential and 11 geothermal wells have been drilled there during the last decade. The present design of the Sabalan geothermal power plant does not utilize the potential of the waste hot water and this useful energy flow would be wasted by injecting it into the underground reservoir. In this study, four geothermal energy utilization scenarios are modelled, analyzed and compared. The first and second scenarios are focused on electricity production in single and double flash geothermal system, while the third and fourth ones consider direct uses besides electricity production. Direct applications considered in this paper are district heating, greenhouses, tourist centres, fish farming and heat supply for factories. Exergy analysis is conducted to find a reliable system design. Also, the efficiency analysis indicates that the double-flash condensing power plant designed can generate 27.5 MW electricity and 76.1 MW heat from existing wells with direct geothermal uses. Lastly in this paper, the environmental effect of producing electricity and heat in the proposed system shows 696,200 tons of CO2 emission reduced compared to the using fossil fuel power plants and heating system.