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.
