24-07-2012, 09:54 AM
OCEAN THERMAL ENERGY CONVERSION
OCEAN THERMAL ENERGY CONVERSION.docx (Size: 271.72 KB / Downloads: 66)
INTRODUCTION:
Oceans which occupy large areas of earth surface are origin of variety of energy sources such as ocean currents, waves, tides, hydrates, and temperature and salinity gradients at varying depth. OTEC is based on tapping energy potential created by temperature difference between sun-warmed surface water and deep polar fed bottom currents to generate electricity. Assuming that about 1.5 percent of the total incident solar energy could be converted into electricity by using OTEC plants, the power output would be 500 million megawatts. This is equal to 6000 million barrels of oil per day in terms of energy equivalent. According to MNES estimates, India has a potential of exploiting 80,000 MW of OTEC based power.
WORKING PRINCIPLE
• This plant works on the principle of a closed Rankine cycle.
• The operating cycle is essentially the same as the one used in Steam Power Plants fired by coal, oil or uranium. But the working fluid used here is either warm sea water or Ammonia or preferably a halocarbon refrigerant.
• The OTEC plant utilizes the temperature difference between the solar warmed ocean surface waters and the cold deep waters to produce electricity.
• Warm seawater is used in evaporators to evaporate the working fluid.
• This evaporated fluid expands in a low pressure turbine, which is coupled with a turbo alternator to produce electricity.
• Then the vapour from the turbine is condensed by the cold seawater taken from the deep sea.
VARIOUS PARTS
TURBINES:
Steam flows through large, low-pressure turbines, entering at a pressure of about 2.4 kPa. These turbines must be able to handle the large steam flows necessary to produce a significant amount of electric power. The most reliable and cost-effective turbine for a 100-megawatt (electric) (MW) (net) plant would be a low-speed (200 rpm) unit measuring 43.6 meters in diameter, which requires more development. Multistage turbines used in nuclear or coal-fired power plants are already available. The low-pressure stages of these turbines typically operate at conditions close to those needed in an open-cycle OTEC plant. The rotor that makes up the last stage (which is typically about 5 meters in diameter) together with a modified stator can produce about 2.5 MW of electricity (gross). Larger plants will require either several turbines operating in parallel or major advances in turbine technology that will lead to larger rotors.
HEAT EXCHANGERS:
Heat exchangers are a big part of the major performance and cost issues relating to closed-cycle systems. Open-cycle flash-evaporators include those with open-channel flow, falling films, and falling jets. These conventional evaporators typically perform to within 70% to 80% of the maximum thermodynamic performance at acceptable hydraulic losses. Research at the Solar Energy Research Institute (SERI), now the National Renewable Energy Laboratory (NREL), led to the development of a vertical-spout evaporator that can perform to within 90% of the thermodynamic limit. In this evaporator, water is drawn upward through a vertical pipe (a spout) and violently sprayed outward by escaping steam. To enhance performance, the spray may fall on screens that further break up the droplets and increase the evaporation rate.
CONDENSERS:
After steam passes through the turbines, it can be condensed in direct-contact condensers or surface condensers. The surface condensers considered for use in OTEC systems are similar to those used in conventional power plants; however, these surface condensers must operate under lower pressures and with higher amounts of noncondensable gases in the steam. Surface con-densers keep the cooling seawater separate from the spent steam during condensation. By using indirect contact, the condensers produce desalinated water that is relatively free of seawater impurities. Steam in the open-cycle system contains non condensable gases that can interfere with power production. These gases oxygen, nitrogen, and carbon dioxide are released from the seawater when it is exposed to low pressures under vacuum. Air also enters the open-cycle vacuum vessel through leaks, although good construction techniques can reduce the rate of air leakage to very low levels. Unless these gases are removed from the vacuum chamber, they can interfere with condensation, particularly with surface condensers, by blanketing the condensing surfaces; they can even build up enough pressure to stop evaporation. An exhaust compressor can remove these non condensable gases.
OCEAN THERMAL ENERGY CONVERSION.docx (Size: 271.72 KB / Downloads: 66)
INTRODUCTION:
Oceans which occupy large areas of earth surface are origin of variety of energy sources such as ocean currents, waves, tides, hydrates, and temperature and salinity gradients at varying depth. OTEC is based on tapping energy potential created by temperature difference between sun-warmed surface water and deep polar fed bottom currents to generate electricity. Assuming that about 1.5 percent of the total incident solar energy could be converted into electricity by using OTEC plants, the power output would be 500 million megawatts. This is equal to 6000 million barrels of oil per day in terms of energy equivalent. According to MNES estimates, India has a potential of exploiting 80,000 MW of OTEC based power.
WORKING PRINCIPLE
• This plant works on the principle of a closed Rankine cycle.
• The operating cycle is essentially the same as the one used in Steam Power Plants fired by coal, oil or uranium. But the working fluid used here is either warm sea water or Ammonia or preferably a halocarbon refrigerant.
• The OTEC plant utilizes the temperature difference between the solar warmed ocean surface waters and the cold deep waters to produce electricity.
• Warm seawater is used in evaporators to evaporate the working fluid.
• This evaporated fluid expands in a low pressure turbine, which is coupled with a turbo alternator to produce electricity.
• Then the vapour from the turbine is condensed by the cold seawater taken from the deep sea.
VARIOUS PARTS
TURBINES:
Steam flows through large, low-pressure turbines, entering at a pressure of about 2.4 kPa. These turbines must be able to handle the large steam flows necessary to produce a significant amount of electric power. The most reliable and cost-effective turbine for a 100-megawatt (electric) (MW) (net) plant would be a low-speed (200 rpm) unit measuring 43.6 meters in diameter, which requires more development. Multistage turbines used in nuclear or coal-fired power plants are already available. The low-pressure stages of these turbines typically operate at conditions close to those needed in an open-cycle OTEC plant. The rotor that makes up the last stage (which is typically about 5 meters in diameter) together with a modified stator can produce about 2.5 MW of electricity (gross). Larger plants will require either several turbines operating in parallel or major advances in turbine technology that will lead to larger rotors.
HEAT EXCHANGERS:
Heat exchangers are a big part of the major performance and cost issues relating to closed-cycle systems. Open-cycle flash-evaporators include those with open-channel flow, falling films, and falling jets. These conventional evaporators typically perform to within 70% to 80% of the maximum thermodynamic performance at acceptable hydraulic losses. Research at the Solar Energy Research Institute (SERI), now the National Renewable Energy Laboratory (NREL), led to the development of a vertical-spout evaporator that can perform to within 90% of the thermodynamic limit. In this evaporator, water is drawn upward through a vertical pipe (a spout) and violently sprayed outward by escaping steam. To enhance performance, the spray may fall on screens that further break up the droplets and increase the evaporation rate.
CONDENSERS:
After steam passes through the turbines, it can be condensed in direct-contact condensers or surface condensers. The surface condensers considered for use in OTEC systems are similar to those used in conventional power plants; however, these surface condensers must operate under lower pressures and with higher amounts of noncondensable gases in the steam. Surface con-densers keep the cooling seawater separate from the spent steam during condensation. By using indirect contact, the condensers produce desalinated water that is relatively free of seawater impurities. Steam in the open-cycle system contains non condensable gases that can interfere with power production. These gases oxygen, nitrogen, and carbon dioxide are released from the seawater when it is exposed to low pressures under vacuum. Air also enters the open-cycle vacuum vessel through leaks, although good construction techniques can reduce the rate of air leakage to very low levels. Unless these gases are removed from the vacuum chamber, they can interfere with condensation, particularly with surface condensers, by blanketing the condensing surfaces; they can even build up enough pressure to stop evaporation. An exhaust compressor can remove these non condensable gases.