WASTE / LOW QUALITY HEAT RECOVERY AND UTILIZATION WITH LOW TEMPERATURE ECONOMIZERS

摘要

Modern combustion steam-electric plants are designed to recover as much heat as economically feasible fromthe combustion products. As a part of the continuing effort by utilities to increase plant efficiency, extracting lowquality heat from the flue gas stream prior to discharge to through the stack to the environment has becomeeconomically attractive. “Economic feasibility” is strongly dependent on the cost of the fuel as well as quality of theheat recovered. The economic feasibility of deploying low-temperature economizers to cool flue gas from coal-firedsteam-electric plants to a temperature well below the sulfuric acid mist dew point is not commonly practiced butcould have a number of salutary effects on unit operations including reduction in fuel use, reduction in water,reduction in fly ash resistivity upstream of cold-side electrostatic precipitators and enhanced mercuryoxidation/capture.Using a theoretical 600 MW (nominal) coal fired facility an additional 30.8 MW of electrical output is availablewith the installation of a Low Temperature Economizer. This represents a 1% improvement in the plant heat ratewith an attractive payback period. The components required for this heat recovery sub-system are readily availableand the technology has matured to a point where uncertainties are minimized.In addition to improving the operation of the plant Low Temperature Economizer reduce emissions of SOx,NOx, Hg, PM and CO2. In a difficult regulatory environment reducing emissions while increasing plantperformance is extremely beneficial. Furthermore Low Temperature Economizer lowers the volume of scrubberwater required.Cooling the flue gas leaving the air heater below the acid mist dew point is not commonly practiced. Thecorrosion potential of the condensed sulfuric acid is a major materials selection/maintenance challenge as is thepotential for gas-side fouling of the heat exchange surface with fly ash.