Q: Why is Mirant installing scrubbers?
A: To improve the environmental friendliness of our plant. In particular, scrubber installation at our Mid-Atlantic facilities complies with the Maryland Healthy Air Act of 2006 (HAA).
For the coals our units are permitted and designed to burn, we cannot comply with the HAA using dry scrubbers. In addition, the wet scrubbers allow us to comply with more stringent requirements of the HAA that must be in place by the year 2013. By choosing this technology, we can meet 2013 standards three years earlier — and avoid a drawn-out, phased compliance program.
Q: Don't wet scrubbers require a lot more water than dry scrubbers?
A: No, in fact both wet and dry scrubbers use about the same amount of water daily. The difference in water consumption is only about 15 percent after application to plant-specific operations for our Mid-Atlantic fleet — and the “wet” process produces far less solid waste, making it better for the environment overall.
Q: How much water do the scrubbers use?
A: For each household that consumes electricity, approximately 2.5 gallons of water is used to “scrub” that amount of generation each day, assuming an average-sized home and consumption rate.
According to the Partnership for Advancing Technology in Housing (PATH), the average household uses about 350 gallons of water per day. So the water consumed by the scrubber is only 0.75% of a typical household's daily water usage.
Q: What happens to the “used” water after the scrubbing process?
A: The largest part of the water consumed by the scrubber is evaporated in the air. A small portion is discharged to the river after treatment. None of it is routed to the aquifer.
Q: If dry scrubbers use water, why is the process called “dry scrubbing?”
A: “Dry” refers to the waste product that comes out as dry ash, compared to a wet scrubber where the byproduct (gypsum) is extracted with water. The primary consumption of water in scrubbers relates to water evaporation in the SO2 removal process, which is similar for both wet and dry scrubbers.
Q: Don't wet and dry scrubbers produce the same type of byproduct?
A: No. As noted above, dry scrubbers produce large quantities of ash that is solid waste. It is not usable and must be landfilled. Wet scrubbers produce a recyclable material that can be used by the wallboard and cement industries, so there is no extra waste.
Q: What is the source of the water used by Mirant to operate these scrubbers?
A: Each power plant has undergone extensive water use studies to determine the best source of water. The analyses included reuse of industrial wastewater where appropriate, use of groundwater where quality and quantity is sufficient, and use of river water where quality and quantity of groundwater is not sufficient. A thorough environmental and economic impact of each option is being conducted by multiple state agencies. Mirant has applied for water appropriation permits for each of its Maryland plants as part of its application for approval to construct scrubbers.
Q: Is it true that wet scrubbers require a stack and dry scrubbers don't?
A: No. Both wet and dry scrubbers require the same type and height of stack.
Q: Do scrubbers reduce other types of emissions besides SO2?
A: Yes. Both wet and dry scrubbers remove a significant percentage of mercury from the flue gas.
Q: Is it true that wet scrubbers create a visible plume and dry scrubbers don't?
A: Actually, they both do. Both wet and dry scrubbers involve a visible water vapor plume.
Q: Which process — dry scrubbing or wet scrubbing — has more of an impact on the local environment and community?
A: Dry scrubbing poses the most significant adverse effect due to the massive amounts of solid waste created. For example, if dry scrubbers were implemented at our Morgantown plant, we would be disposing of 520,000 tons of waste per year — that’s about 17,000 18-wheel tractor-trailer loads and enough to require a new landfill! Not only that, dry scrubbing is less effective at SO2 removal than wet scrubbing, so the choice is clear for Mirant and the communities in which we operate.
Q: Is it true the wet scrubber is the least costly technology for Mirant?
A: No, actually, the wet scrubber technology is the more expensive capital investment for the company and its shareholders. For that investment, Mirant will achieve greater reductions in SO2 and mercury emissions and minimize the need for landfill of scrubber byproduct. From an environmental standpoint, this investment is superior.
Q: How will the power plants receive delivery of the limestone required for the scrubbers?
A: Mirant’s preferred and primary choice for limestone delivery is by barge. Rail is a secondary mode of delivery if barge shipments are not feasible due to economic or logistical reasons. Truck deliveries are used as back up.
Q: How will the gypsum created by these scrubbers be removed from the power plant site?
A: Mirant’s preferred and primary choice for gypsum export is rail. Under a full capacity operation of the power plants — that is running at maximum output — approximately 70 rail cars per week will be added to our rail deliveries. This should not increase the number of rail deliveries but rather add to the length of the trains.
Q: I've read that this is a multi-year construction project. Where will the workforce for the project come from?
A: Our contractor, Shaw Constructors, Inc. (Shaw), is responsible for the direct hire of needed workforce. As part of our contract with Shaw, local recruitment offices will be established near the generating stations and a comprehensive on-the-job training program will be available to potential hires.