Method and system for reheating flue gas using waste heat to maintain dry chimney stack operation

Abstract

Flue gas is a by-product of many energy and industrial plants and is typically emitted through a chimney stack. If the flue gas temperature in the chimney stack drops below the flue gas dew point, condensation of water vapor and acid gases ensues. These gases are very corrosive for chimney stacks designed to operate in a dry condition. The Flue Gas Reheat System of the present invention continuously and proactively manages flue gas chimney stack temperatures above the dew point in order to optimize emission control and effectuate energy efficiency improvements in industrial plants. Waste heat is harvested from the exterior surfaces of existing steam and pollution control equipment through conduction, convection and radiation. This heat is transferred to a working fluid. The working fluid is then directly mixed with the flue gas prior to the flue gas entering the chimney stack to raise the temperature of (or re-heat) the flue gas above its dew point to maintain a dry chimney stack condition. The use of residual or waste heat from throughout the plant and the minimal equipment required to harvest the waste heat reduces the operating cost and improves the overall reliability of the system. This method is useful in many industries, including electric power generation plants and other energy intensive process industries that seek emission control and various boiler and fuel energy efficiency improvements, many of which improvements result in a reduction in normal chimney stack temperature.