The project team demonstrates the use of regenerative heat exchange to reduce flue gas temperature and minimize evaporative water consumption in wet flue gas desulfurization (FGD) systems on coal-fired boilers.  Most water consumption in coal-fired power plants occurs due to evaporative water losses.  For example, a 500-megawatt (MW) power plant will loose approximately 5,000 – 6,000 gallons per minute (gpm) to evaporation and 500 gpm in the wet FGD system.  Installation of regenerative reheat on FGD systems is expected to reduce water consumption to one half of water consumption using conventional FGD technology.

Electrostatic Precipitator

Researchers are conducting pilot-scale tests of regenerative heat exchange to determine the reduction in FGD water consumption that can be achieved and assessing the resulting impact on air pollution control (APC) systems.  The project team consists of URS Group, Inc. as the prime contractor, the Electric Power Research Institute (EPRI), Southern Company, Tennessee Valley Authority (TVA), and Mitsubishi Heavy Industries (MHI).  The team is conducting an analysis of the improvement in the performance of the APC systems and the resulting reduction in capital and operating costs.  The tests are intended to determine the impact of operation at cooler flue gas temperatures on FGD water consumption, electrostatic precipitator (ESP) particulate removal (see Figure 1), SO3 removal, and Hg removal.  Additionally, tests are conducted to assess the potential negative impact of excessive corrosion rates in the regenerative heat exchanger.

This project demonstrates the ability to use regenerative heat exchange to cut evaporative consumption by cooling the flue gas entering the FGD system.  Additionally, the project demonstrates possible benefits due to the flue gas being cooled upstream of the ESP, such as: control of SO3 emissions by condensation on fly ash; improved particulate control by the ESP due to reduced gas volume and lower ash resistivity; avoided costs associated with flue gas reheat or wet stacks; and potential additional reduction in native Hg removal in the ESP due to operation at a cooler flue gas temperature.