No abstract

This project dealt with use of condensing heat exchangers to recover water vapor from flue gas at coal-fired power plants. Pilot-scale heat transfer tests were performed to determine the relationship between flue gas moisture concentration, heat exchanger design and operating conditions, and water vapor condensation rate. The tests also determined the extent to which the condensation processes for water and acid vapors in flue gas can be made to occur separately in different heat transfer sections. The results showed flue gas water vapor condensed in the low temperature region of the heat exchanger system, with water capture efficiencies depending strongly on flue gas moisture content, cooling water inlet temperature, heat exchanger design and flue gas and cooling water flow rates. Sulfuric acid vapor condensed in both the high temperature and low temperature regions of the heat transfer apparatus, while hydrochloric and nitric acid vapors condensed with the water vapor in the low temperature region. Measurements made of flue gas mercury concentrations upstream and downstream of the heat exchangers showed a significant reduction in flue gas mercury concentration within the heat exchangers. A theoretical heat and mass transfer model was developed for predicting rates of heat transfer and water vapor condensation and comparisons were made with pilot scale measurements. Analyses were also carried out to estimate how much flue gas moisture it would be practical to recover from boiler flue gas and the magnitude of the heat rate improvements which could be made by recovering sensible and latent heat from flue gas.v

Coal-fired power plants have traditionally operated with stack temperatures in the 300°F range to minimize fouling and corrosion problems due to sulfuric acid condensation and to provide a buoyancy force to assist in the transport of flue gas up the stack. However, as an alternative, there would be benefits to cooling the flue gas to temperatures below the water vapor and acid dew points, while capturing the condensed water vapor. This paper describes experimental results from a DOE and industry-funded project to develop condensing heat exchangers for application to coal-fired power plants. A system of condensing heat exchangers was designed, fabricated and tested using slip streams of boiler flue gas and experiments were performed to measure the effects of process parameters on rates of heat transfer and water vapor condensation. In addition, measurements were made to characterize the acid concentrations in the condensed water which collected on the heat exchanger tubes and to quantify the effects of the heat exchangers on flue gas mercury concentrations.