Committed to environmentally friendly ways to meet growing energy demands
Big Stone II is designed to help the five participating utilities meet customers' energy needs in an environmentally responsible manner—by investing in clean technology, reducing pollution, and building the infrastructure needed for renewable energy. On the transmission side, every effort is being made to minimize the environmental impact by optimizing the use of existing corridors.
Air emissions
While Big Stone II will more than double the combined plants' generation capacity, the emissions of sulfur dioxide, nitrogen oxides and mercury from the two plants will actually be less than or equal to historical emissions from the existing plant.
In part, this is because Big Stone II participants will voluntarily install a single, highly advanced wet scrubber large enough to remove sulfur dioxide emissions from both plants.
CO2 emissions
Big Stone II will use super-critical pulverized coal technology because it is the most efficient, commercially-available baseload generating technology—producing 20% less CO2 per megawatt hour than existing regional coal-fired plants.In addition, the plant is designed to produce fly ash suitable for use as a replacement of Portland Cement in concrete mixtures; this could lead to a reduction of 100,000 tons of CO2 per year that would otherwise be emitted during cement manufacture. More than a ton of CO2 is emitted in the production of a ton of Portland Cement.
At the same time, Big Stone II participants continue to be heavily involved in ongoing research on CO2.
Water use
The water plan for Big Stone I and II is designed to protect Big Stone Lake and serve the needs of our customers.Both Big Stone I and II will use water from the lake in accordance with conditions set forth in their permits. When the lake surface elevation falls below 967 feet, only limited pumping will occur from the lake, as has been the case for more than 30 years.
Currently, Big Stone I is permitted by the South Dakota Department of Environment and Natural Resources (SDDENR) to take 8,000 acre-feet from Big Stone Lake each year. That water is stored in a pond at the site. Big Stone II would use the same intake, treatment and storage facilities as Big Stone I. On July 12, 2006, the SDDENR issued a water appropriation permit, allowing the project to take 10,000 additional acre-feet from Big Stone Lake each year.
Original Big Stone II plans called for construction of a 450-acre holding pond on the Big Stone site. However, an evaluation of an aquifer near the Big Stone site indicated that the aquifer had sufficient water to supply the plant's supplemental water needs. The hydrological study also revealed that withdrawing water from the aquifer would not adversely impact existing water rights.
In March 2007, project participants applied for a permit to use up to 10,000 acre-feet per year from the adjacent aquifer. This would allow us to maintain an adequate water supply during those times when pumping from Big Stone Lake is prohibited—whenever the lake's levels fall below 967 feet elevation.
The availability of groundwater as a supplement to Big Stone Lake also adds a measure of drought protection and ensures the plant can continue operations under most drought conditions. Approximately 3,700 acre-feet of groundwater is expected to be used during the average year.
Technology selection
Easy access to the sub-bituminous supplies of Wyoming and Montana make coal the logical choice of generation fuel for regional energy suppliers. Big Stone II will use supercritical pulverized coal technology because it has a proven track record with all grades of coal and is the most efficient baseload generating technology commercially available today. To mitigate environmental impact, the seven utilities are spending an extra $59 million to not only clean emissions from the new plant, but also to reduce emissions from the existing plant.
Why not use IGCC at Big Stone II?
The Integrated Gasification Combined Cycle (IGCC) is a coal-conversion technology that has promise, but it is simply not an option for Big Stone II. It is a developing technology, not yet ready for commercial application.
IGCC applications to date have used higher-grade bituminous coals, rather than the sub-bituminous coal or lignite used in our part of the country. Several Big Stone participants are in the very early stages of funding a lower-grade coal demonstration project, but there is no known completion date.
While there is an IGCC demonstration plant that will use sub-bituminous coal being built in Florida expected to be in operation in 2010, project results will not be available in time for the Big Stone plant design, nor will the results demonstrate the feasibility of a project as large as Big Stone II.
Mercury emissions
In August 2007, the Big Stone II participants announced they will meet the requirements of the 2006 Minnesota Mercury Emissions Reduction Act, which applies to large existing power plants.In complying with the Act, the participants will use technology most likely to achieve a 90 percent mercury reduction goal by 2015. The Minnesota Mercury Emissions Reduction Act is considered to be one of the most stringent of its kind in the nation.
Potential for fewer emissions overall
The potential for fewer overall emissions exists because the plant's highly efficient design would make it a low-cost generating station. This means that the electricity it would generate would be dispatched before that from older, less environmentally friendly plants.
Energy dependence requires diverse resources
While we staunchly support investment in clean coal technology, such as coal gasification, as well as renewable sources of energy, the fact is, one source alone cannot produce sufficient electricity to meet the growing electrical demand. A diversity of energy sources is currently needed to supply a reliable energy mix for our customers. This diversity is absolutely critical as our nation works toward achieving energy independence.
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