Aquatic Pollution and Coastal Zone Managememnt (2+1)

Unit 9 : Thermal pollution

9.2.Sources
The production of energy from a fuel source can be direct, such as the burning of wood in a fireplace to create heat, or by the conversion of heat energy into mechanical energy by the use of a heat engine. Examples of heat engines include steam engines, turbines, and internal combustion engines. Heat engines work on the principal of heating and pressuring a fluid, the performance of mechanical work, and the rejection of unused or waste heat to a sink. Heat engines can only convert 30 to 40 percent of the available input energy in the fuel source into mechanical energy, and the highest efficiencies are obtained when the input temperature is as high as possible and the sink temperature is as low as possible. Water is a very efficient and economical sink for heat engines and it is commonly used in electricity generating stations.
The waste heat from electricity generating stations is transferred to cooling water obtained from local water bodies such as a river, lake, or ocean. Large quantities of water are used to keep the sink temperature as low as possible to maintain a high thermal efficiency. The San Onofre Nuclear Generating Station between Los Angeles and San Diego, California, for example, has two main reactors that have a total operating capacity of 2,200 megawatts (MW). These reactors circulate a total of 2,400 million gallons per day (MGD) of ocean water at a flow rate of 830,000 gallons per minute for each unit. The cooling water enters the station from two intake structures located 3,000 feet offshore in water 32 feet deep. The water is heated to approximately 19°F above ambient as it flows through the condensers and is discharged back into the ocean through a series of diffuser-type discharges that have a series of sixty-three exit pipes spread over a distance of 2,450 feet. The discharge water is rapidly mixed with ambient seawater by the diffusers and the average rise in temperature after mixing is less than 2°F.

Sources of Thermal Pollution