Retrofits for improved heat rate and availability: Low-level heat recovery economizer retrofits

The subject of this report, involves the recovery of heat from the flue gas to preheat combustion air and protect the air heater. Flue gas is a large potential source of heat, but this mode of heat recovery has seen limited application due to the corrosive environment created in plant tail-end systems by condensation in sulfur-laden flue gases. Several installations of low-level economizers'' (LLEs) have experienced varied degrees of success using cast iron-type heat exchangers. Alternate materials that may be suitable for this application were investigated in this project. The cost of various types of installations with regard to equipment arrangement, remaining plant life, plant capacity factor, plant operating modes, ambient temperature characteristics, fuel costs, utility cost evaluation methods, and external economic factors were investigated.