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Environmental Profile

The Mesaba Energy Project will achieve significant emission reductions compared to other solid fuel, base load technologies.

By using Integrated Gasification Combined Cycle (IGCC) technology, the Mesaba Energy Project will have a superior environmental profile compared to conventional coal-fueled steam electric generating units, such as Super Critical Pulverized Coal (SCPC) units.  The emissions reductions will be due to the following operating characteristics:

  • Use of 95 percent pure oxygen instead of air as the oxidant for producing syngas
  • Operation of the gasifier at high pressure
  • Pre-combustion clean up of syngas
  • Marketable status of the by-products derived from IGCC process operations

The combination of the first three characteristics serves to reduce the volume and mass of syngas and allows its cleanup to be conducted more efficiently and with equipment greatly reduced in size.  The result is that criteria pollutant emissions from the Project will generally be 60% lower relative to comparably-sized, recently permitted state-of-the-art conventional coal-fueled power plants, which use post-combustion cleanup techniques.  These three characteristics also facilitate the capability of the equipment to remove significant quantities of carbon dioxide from syngas.  The final characteristic alleviates the need to landfill flue gas desulfurization wastes, which reduces carbon dioxide emissions associated with the Project.

Techniques exist that would allow virtually all of the potential carbon dioxide emissions from the combustion of syngas to be removed prior to combustion.  This process involves shifting the production of carbon monoxide normally produced during the gasification process to carbon dioxide via the reaction between carbon monoxide and water in the presence of a catalyst.  This reaction liberates hydrogen, the cleanest burning of all fuels.  Hydrogen has a wide range of future applications.  It can be used to fuel automobiles and trucks instead of gasoline, thereby reducing the nation's current dependence on foreign sources of oil.  It can also be used to power fuel cells.  The Mesaba Project is viewed by the U.S. Department of Energy as a major stepping-stone in its Clean Coal Power Initiative toward FutureGen, a coal-fired, IGCC power plant with near-zero environmental emissions. FutureGen would use a turbine powered by hydrogen, instead of syngas.

The Mesaba Energy Project Compared to Recently Permitted Coal Plants

The analysis below compares Mesaba Unit I to the following three recently permitted, utility-scale, SCPC plants:
  • NRG Cajun in Louisiana
  • Mid American in Iowa
  • Elm Road in Wisconsin

This group of plants typifies the emissions profile of a SCPC plant with a full suite of pollution control technology. The following figure compares the permitted criteria pollutant levels for each of these facilities with the maximum expected Mesaba Energy Project emission levels.

With respect to mercury as shown in the next figure, the Mesaba Project mercury emissions will be half of the mercury emissions from the Elm Road SCPC plant in Wisconsin, and will represent a two-thirds to seven-eighths reduction in the mercury emissions from the other recently permitted SCPC plants in Iowa and Louisiana.  This is a significant achievement by the IGCC technology.

Even when compared to the cleanest existing coal-fueled power plants in the nation, the Mesaba Energy Project achieves substantially lower emission results across the board.  In order to establish the comparison group of power plants, regulatory decision-making was reviewed on three levels to find the coal-fueled power plants that emit the least of each pollutant to compare to the Mesaba Project's emissions of that pollutant.  The comparisons illustrate that whenever a combustion facility achieves emission parity with IGCC for one pollutant, that same facility has significantly, and often dramatically, higher emissions of other pollutants than does IGCC.  The fact that the Mesaba Project's emissions of each category of pollutant are essentially equal to or lower than even those plants subjected to the maximum controls achievable with a combustion technology for that category of pollutant underscores IGCC's superior environmental profile.  The following figures illustrate the results of comparing the Mesaba Project to these "best in class" existing coal-fueled plants.