The Shaw Group, Inc., has selected Siemens Water Technologies to provide a system to treat wastewater from flue gas desulfurization (FGD) scrubbers being constructed at Mirant Mid-Atlantic, LLC’s Dickerson and Morgantown Power Plants and Mirant Chalk Point, LLC’s Chalk Point Power Plant, all located in Maryland. The system will remove suspended solids, heavy metals and organics from the scrubber waste stream so that the water can be safely discharged. The wastewater projects are scheduled to begin operation in 2010.
New regulatory programs call for further reduction of sulfur dioxide emissions from coal-burning power plants. Flue gas systems frequently use limestone-forced-oxidation scrubbers to convert sulfur dioxide in the flue gas to gypsum, which can be sold for wallboard manufacturing, cement additive or agricultural applications, turning a waste stream into a usable resource.
The proper design of wastewater treatment systems and the selection of materials for construction are critical. Both of these key items can have a major impact on the treatment plant's operation and reliability. Siemens Water Technologies will provide the new physical/chemical and biological wastewater treatment system on an equipment design-supply basis and provide startup, training and commissioning services. The Shaw Group, Inc. will be responsible for installing the equipment. Each wastewater system will include storage tanks, reaction tanks, chemical feed systems, a clarifier, biological reactors, gravity sand filters and filter presses. The system flow rates are 200 gal per minute (gpm) for the Morgantown plant and 110 gpm each for the Dickerson and Chalk Point plants.
An equalization tank receives the waste stream and equalizes the flow to eliminate spikes in flow rates and concentration. Next, two reaction tanks in series continue the treatment process to de-saturate the wastewater, reduce heavy metals and prepare the wastewater for clarification. The treated wastewater then enters the clarifier, where suspended solids are coagulated and settled. Solids from the clarifier are dewatered in the filter presses. The treated water is sent from the clarifier to sequencing batch biological reactors for nitrogen reduction. The remaining treated water is sent to gravity sand filters for final treatment before discharge.
The largest power plant in Maryland, Chalk Point Generating Station is located on the Patuxent River. The plant serves over 2 million homes in Prince George’s County. The Morgantown Generating Station, located on the Potomac River in Charles County, serves almost 1.5 million homes in the area. Dickerson Generating Station is also located on the Potomac, in Montgomery County. Dickerson serves over 800,000 homes in the area.
To date, Siemens has supplied 13 FGD wastewater treatment systems at U.S. power plants.
