Power Plant Water Management
Recovery of Water from Boiler Flue Gas – Lehigh University
Conducted by Lehigh University, this project is a combination of laboratory and pilot scale experiments and computer simulations that investigate the use of condensing heat exchangers to recover water from boiler flue gas at coal-fired power plants. Boiler flue gas moisture comes from three sources: fuel moisture, water vapor formed from the oxidation of fuel hydrogen, and water vapor carried into the boiler with the combustion air. The quantity of water vapor in flue gas varies depending on coal rank. Powder River Basin (PRB) and lignite coal-fired power plants, equipped with a means of extracting all flue gas moisture and using it for cooling tower makeup, would be able to supply from 25% (for PRB) to 37% (for lignite) of the makeup water using this approach.
Researchers are conducting computational fluid mechanics analyses to aid in the design of the compact fin tube heat exchanger to condense water vapor from flue gas. The extent to which removal of acid vapors from flue gas and condensation of water vapor can be achieved in separate stages of the heat exchanger system is determined via laboratory and pilot plant experiments. Additional experiments are conducted to measure the heat transfer effectiveness of the fin-tube bundle designed for condensing water vapor. Analyses of the boiler and turbine cycle are carried out to estimate potential reductions in heat rate due to recovering sensible and latent heat from the flue gas.
The technology developed could provide coal-fired utilities a method of producing water from flue gas that would otherwise be evaporated from the stack. This water would then be available for power plant operations such as cooling tower or flue gas desulfurization make-up water. An added benefit of cooling the flue gas to remove water is the potential to remove vapor phase sulfur trioxide/sulfuric acid (SO3 /H2SO4 ) and to utilize the rejected sensible and latent heat in the boiler or turbine cycle resulting in increased boiler efficiency.