Environmental Innovations for Fossil Energy Applications; Development of Technologies to Reduce Freshwater Use and Consumption in Coal-Fired Power Plants

Electricity generation by coal-fired power plants requires an abundant and predictable source of freshwater, about 38 gallons of water per kilowatt hour of electricity produced. The water is used primarily for steam cooling with a lesser quantity for pollution control. Although alternate sources of water (such as mine pool water, coal-bed methane produced water, municipal wastewater, and brackish or saline water) could be used to supply the water needs of a fossil fuel power plant, these sources often are too contaminated to use without expensive treatment. This project will develop a cost-effective method for converting these non-traditional water sources into freshwater for use in a power plant or other industrial processes. The approach involves the use of low grade waste heat from fuel combustion, which normally is discharged into the atmosphere, to clean the contaminated water with a humidification/dehumidification process carried out at atmospheric pressure. An important feature will be the use of stack gas waste heat, as access to this heat stream is relatively easy and does not require a major redesign of the plant or a major shutdown for installation. In a preliminary model, it was demonstrated that in a 1000 MW power plant, 132 MW of heat could be recovered without appreciably affecting stack performance, resulting in 3.5 million gallons of water per day ¿ nearly 20% of the water lost due to evaporation and aerosol production from the cooling towers. Commercial Applications and other Benefits as described by the awardee: Anticipated public benefits can be estimated by assuming that the technology becomes widely adapted and retrofitted to a large number of U.S. power plants. At 500 power plants, at an average size of 600 MW, the volume of water produced would be one billion gallons per day. This would not only reduce electricity costs, but also improve water quality in discharge areas of all power plants.