IMPACT ANALYSIS OF WORKING FLUID ON THE PERFORMANCE OF GEOTHERMAL POWER PLANT

Abstract

Fossil fuels are the main source of energy supply today as they produce coal, oil and natural gas for fulfilling world’s energy demand. The next two decades might see energy demand grow by almost half as it is today. The quality of life and economy of globe will face problems and situations might arise to start run out of the energy resource. The renewable energy source with unlimited energy supply potential can solve the energy crisis problem. Geothermal energy is one of the renewable energy source and can be utilized in all the seasons. The low temperature geothermal energy sources are available worldwide. The low temperature geothermal energy sources can be utilized to generate electricity by using organic Rankine cycles which are promising systems. In present work investigation has been carried on eight working fluids using Organic Rankine Cycle consisting of water based cooling system with geothermal water inlet temperatures of 125°C and 150°C and reinjection temperature of 75°C. The investigated working fluids are pentane (R601), isopentane (R601a), butane (R600), isobutene (R600a), hexane, isohexane, R227ea, and R236ea. The various parameters of the ORC have been investigated. It is found that for all working fluids with increase in turbine inlet temperature the net power output shows increment and then decreases. For maximum power output the parameters at inlet of turbine have been optimized. With decrease in condensation temperature the net power output increases but at same time consumption of power by circulating pump increases, especially for higher mass flow rate of cooling water at low temperature of condensation. For geothermal source temperature of 150°C the optimum temperature of condensation is found to be in range 30-35°C with cooling water temperature at inlet 20°C and 5°C as condenser pinch point temperature difference. The maximum power is produced by R236ea at geothermal source temperature of 125°C it has maximum overall plant efficiency of 15.47% followed by R227ea, isohexane, isopentane, hexane, pentane, isobutene, and butane. At geothermal source of 150°C maximum overall plant efficiency is 18.77% followed by R227ea, R601a, hexane, pentane, isobutene and butane. At geothermal source temperature of 150°C optimum turbine inlet temperature range lies between 90 to 100°C for maximum overall plant efficiency.