Improving the Energy Efficiency of a Midsize Power Plant by Increased Recovery and Reuse of Waste Heat

An older, midsized coal-fired power plant was studied to improve overall plant efficiency. The power plant consists of a circulating fluidized bed (CFB) boiler and three turbines that produce up to 120 MW of electricity. Lake water provides cooling to the cycle through the condenser. The study examined increasing the heat recovery from the exhaust gases to increase the overall efficiency. Flue gas from the CFB is regularly near 160 degrees C (320 degrees F), allowing for a large amount of potential heat recovery. One realistic scenario was a 66.7 degrees C (120 degrees F) reduction of flue gas temperature, being partially condensed in a separate coated heat exchanger. If the recovered energy is completely used, the cycle efficiency would increase by 0.83%. The study examines possible uses for the heat, such as selling it to an industry if one was nearby, drying incoming coal, preheating air, or running an organic Rankine cycle (ORC). Selling the energy to an industry, if one was nearby, was the best economic option because there was a fairly low initial cost, and much of the heat could be used with the appropriate industry.