The generation of electric power from ocean thermal energy conversion (OTEC) is based on the utilization of the natural temperature difference between the warm sea water at the surface and the cold sea water at some depth.The temperature of water at the surface of sea is about 28°C and the temperature of the cold deep sea water is about 5°C to 7°C at the depths of about 800 m to 1000 m in tropical seas. Thus,in tropical waters there are two infinite heat reservoirs.One is the heat source at the surface at about 28°C and the other is the depth of about 1000 m. OTEC systems are economically attractive where temperature difference of about 20°C exists between top and bottom sea water.
There are two OTEC systems. The open-cycle system uses the sea water as the working fluid. The warm surface water is "flash evaporated"in a chamber maintained under high vacuum and the generated vapour drives a low pressure turbine connected with the generator.The exhaust steam is condensed using sea water.
In the closed-cycle system,low boiling liquid such as Freon or ammonia is the working fluid.The fluid is evaporated using the warm surface sea water.After the vapour drives the turbine,it is condensed by cold sea water.This condensate is pumped back to the evaporator.
While the open-cycle system eliminates the need for a surface heat exchanger; its disadvantage is that steam is generated at very low pressure.This requires,a large volume of steam.Hence the diameter of the steam turbine is about 12 m for 1 MW plant. The maintenance of vacuum in the pumps need very large vacuum pumps.
In a closed-cycle system expensive fluids like Freon and ammonia are needed.But it would not require vacuum pumps as the fluids evaporate at around 25°C and the diameter of the ammonia turbine will be much smaller,not more than 0.6 m.Technically,fabrication of such a turbine is easier than that of large steam turbine used in the open-cycle system.
The efficiency of an OTEC system is about 3% because of the small temperature difference between warm and cold sea waters.The major advantage of the OTEC for power generation is that ocaen energy is a renewable source.since no fuel is used,the OTEC system may become more economical in future.
There are two OTEC systems. The open-cycle system uses the sea water as the working fluid. The warm surface water is "flash evaporated"in a chamber maintained under high vacuum and the generated vapour drives a low pressure turbine connected with the generator.The exhaust steam is condensed using sea water.
In the closed-cycle system,low boiling liquid such as Freon or ammonia is the working fluid.The fluid is evaporated using the warm surface sea water.After the vapour drives the turbine,it is condensed by cold sea water.This condensate is pumped back to the evaporator.
While the open-cycle system eliminates the need for a surface heat exchanger; its disadvantage is that steam is generated at very low pressure.This requires,a large volume of steam.Hence the diameter of the steam turbine is about 12 m for 1 MW plant. The maintenance of vacuum in the pumps need very large vacuum pumps.
In a closed-cycle system expensive fluids like Freon and ammonia are needed.But it would not require vacuum pumps as the fluids evaporate at around 25°C and the diameter of the ammonia turbine will be much smaller,not more than 0.6 m.Technically,fabrication of such a turbine is easier than that of large steam turbine used in the open-cycle system.
The efficiency of an OTEC system is about 3% because of the small temperature difference between warm and cold sea waters.The major advantage of the OTEC for power generation is that ocaen energy is a renewable source.since no fuel is used,the OTEC system may become more economical in future.
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