In the fall of 2015, the U.S. Environmental Protection Agency (EPA) promulgated revised effluent guidelines for steam electric power generating units (EGUs). The 2015 Effluent Limit Guidelines (ELGs) final ruling (1) is now in place. While there is now some uncertainties as to the effective start date for the new guidelines, the tightening discharge limits will certainly impact a number of electric power plants across the United States. Particularly challenging wastewaters in this context include flue gas desulfurization (FGD) purge water and coal combustion residual (CCR) pond waters.
The Electric Power Research Institute (EPRI) conducted a study using a different evaporation technology installed at the Water Research Center at Southern Co.’s Plant Bowen, located in Cartersville, GA. The purpose of this project (2) was to evaluate the efficacy of an adiabatic evaporator for FGD wastewater treatment/concentration at a 952-megawatt (MW) coal-fired power plant. The system used flue gas from the power station as the source of thermal energy for evaporation.
The study revealed that the adbiatic concentrator technology, which uses a direct contact evaporation process, can be a particularly appealing option for sites implementing a ZLD treatment train and without many of the disadvantages experienced by more traditional technologies. Furthermore, there is potential for producing a concentrated slurry that can be stabilized (or solidified) for disposal without the need to add a crystallizer stage to the process. The study validated that the adiatic concentrator offered an alternative to reducing plant wastewater volumes and facilitating efficient capture and disposal of water contaminants in an environmentally responsible manner.