复旦大学：《能源与环境 Energy and the Environment》教学课件_6_Energy and the environment VI

Energy and the Environment CHEN HONG E-mail:chong@fudan.edu.cn Phone:021-65642526 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Energy and the Environment CHEN HONG E-mail: chong@fudan.edu.cn Phone: 021-65642526

Ocean Thermal energy conversion ceans Vast natural reservoir: Receiving and Storing Solar energy The oceans take in solar energy in proportion to their sur face area, where is nearly three times that of land O cean Land 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Ocean Thermal Energy Conversion Oceans Vast natural reservoir: Receiving and Storing Solar Energy The oceans take in solar energy in proportion to their surface area, where is nearly three times that of land. Ocean Land

Ocean Thermal Energy Conversion Water near the surface of tropical and subtropical seas is maintained by this solar radiation a higher temperatures than the water at greater depth or at higher latitudes Ocean Current The warm surface water From the equatorial regions either to the north or to the south Gulf Stream or Japanese Current 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Ocean Thermal Energy Conversion Water near the surface of tropical and subtropical seas is maintained by this solar radiation a higher temperatures than the water at greater depth or at higher latitudes. Ocean Current: The warm surface water From the equatorial regions either to the north or to the south. Gulf Stream or Japanese Current

Tapping the energy in the ocean currents Gigantic underwater turbines/like windmill Relatively steady velocity/intermittent of wind, solar radiations No need for energy storage The energy available is enormous Serious proposals have put forth to construct ocean current turbines with electricity produced then cabled to shore Economically? Competing with conventional power plant Have not been advanced beyond the discussion stage 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Tapping the energy in the ocean currents Gigantic underwater turbines/like windmill Relatively steady velocity/intermittent of wind,solar radiations No need for energy storage The energy available is enormous Serious proposals have put forth to construct ocean current turbines with electricity produced then cabled to shore. Economically? Competing with conventional power plant. Have not been advanced beyond the discussion stage

Through the use of heat engines Warm tropical surface 22oC Heat source,I hot t Electricity Cold water at depths of Heat sink, Tcold about 1000 m. 2C T difference is steady, different time different season So no need for energy storage system 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Through the use of heat engines Warm tropical surface 22 o C Cold water at depths of about 1000 m, 2 o C Heat source, Thot Heat sink, Tcold Electricity T difference is steady, different time, different season. So no need for energy storage system

Florida. Puerto rico Hawaii and other islands Electric e is no 级级 obtained primarily from imported fossil fuels E40E50E60E70c80E9oE10C110c120E130E140E150E160E170E180E170w160w150 60w 150w 140W 130w 120W 110W 100W 90w 80W 7OW 60w 50w 40 30w 20W 10W Ow 10E 60w150w140w130W12ow11ow100W90W80w70w6oW50W40w3ow2w10wow10E20E Figure 5.8 Globe distribution of the OtEC resource. The temperature difference(degrees Celsius )is shown between the surface and 1000 meter depth(Figure supplied by the National Renewable Energy Laboratory. 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Figure 5.8 Globe distribution of the OTEC resource. The temperature difference (degrees Celsius ) is shown between the surface and 1000 meter depth. (Figure supplied by the National Renewable Energy Laboratory.) Florida, Puerto Rico, Hawaii and other islands. Electric E is now obtained primarily from imported fossil fuels

Two types of heat engines have been considered, and demonstrated for ocean thermal energy conversion(OTEC) Closed-cycle system a working fluid such as ammonia to evaporate into gas by energy from warmer water Similar to the ordinary steam-powered electric generating plant in which water as working fluid Open cycle system where the working fluid is seawater Warm Vacuum Drive Condensed Cold Vapor turbine water water 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Two types of heat engines have been considered, and demonstrated, for ocean thermal energy conversion(OTEC) Closed-cycle system. A working fluid such as ammonia to evaporate into gas by energy from warmer water Similar to the ordinary steam-powered electric generating plant, in which water as working fluid. Open cycle system where the working fluid is seawater Warm water Vacuum Vapor turbine Cold water Drive Condensed by

Electric power generator Closed-cycle system Ammonia vapor. Turbi Warm water Evaporator outlet Condenser a water water outlet 25℃ mp Ammonia liquid Cold intake 5'C Figure 5.9 An OTEC heat engine using ammonia as a working fluid. The turbine is driven by the ammonia vapor and is connected to a generator to produce electricity The warm water is drawn from the ocean surface the cold water from a depth of 1000 meters.(Source: Figure supplied by the National Renewable Energy Laboratory) 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Figure 5.9 An OTEC heat engine using ammonia as a working fluid. The turbine is driven by the ammonia vapor and is connected to a generator to produce electricity. The warm water is drawn from the ocean surface; the cold water from a depth of 1000 meters. (Source: Figure supplied by the National Renewable Energy Laboratory.) Closed-cycle system

eg. Calculate the thermodynamic efficiency, n, for an ideal heat engine operating between surface waters and water at 1000 m depth if the surface water temperature is 25C and the deeper is 5°C. Solution T=5C=278K T,=25C=298K 7=(1-T2/7n)=(1-278/298)=0.067=67% Of course the efficiency of an actual heat engine will be less than that 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

eg. Calculate the thermodynamic efficiency, η, for an ideal heat engine operating between surface waters and water at 1000 m depth if the surface water temperature is 25 o C and the deeper is 5 o C. (1 / ) (1 278 / 298) 0.067 6.7% 25 298 5 278 = − = − = = = = = = c h h c T T T C K T C K η   Solution: Of course, the efficiency of an actual heat engine will be less than that

Efficiency The Carnot efficiency is only 7%, and the net efficiency to be expected in practice, about 2.5% Very large volumes of both warm and cold water must be circulated past the heat exchangers to produce useful amounts of power Estimated: 25X 106 liters/sec of both warm and cold water would be needed for 100MW of the electric output For 40MW plant, 10 meters diameter pipe needed Open cycle system to generate 22kW of electric power, 1930 Cuba However. more power was required to operate it than it produced 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan University

Efficiency The Carnot efficiency is only 7%, and the net efficiency to be expected in practice, about 2.5% Very large volumes of both warm and cold water must be circulated past the heat exchangers to produce useful amounts of power. Estimated: 25×106 liters/sec of both warm and cold water would be needed for 100MW of the electric output. For 40MW plant, 10 meters diameter pipe needed. However, more power was required to operate it than it produced. Open cycle system to generate 22kW of electric power, 1930 Cuba