ClearStack considers this technology as a "break-through" coal oxidation technique. The Ashworth Gasification - Combustion System™ uses gasification followed by two stages of oxidation to completely combust coal in a much more environmentally friendly manner than ever before. The innovation of this technique is that the four major air emission pollutants (SO2, NOX, Hg and particulate) associated with coal combustion are significantly reduced using only simple techniques. Limestone is added with the coal to capture sulfur, mercury, and other heavy metal air toxics in the slag produced. Further, up to 20% biomass can be fired with coal to reduce carbon dioxide emissions.

The environmental advantages of the technology are as follows:

• Reduces Sulfur Dioxide (SO2) emissions by 70+% ( 85% limestone utilization )
• Reduces Nitrogen Oxides (NOX) emissions down to < 0.095 lb/million Btu
• Reduces Mercury (Hg) emissions by 90+% ( captured mercury does not leach )
• Reduces Sb, As, Ba, Be, Cd, Cr, Co, Cu, Hg, Pb, Mo, Ni, Se, Ag, Tl, V, Zn and Mn by 80+%
• Slag and fly ash leachate tests (TCLP) showed Ag, As, Ba, Cd, Hg, Pb, and Se all well below the EPA regulatory limit
• Reduces chlorine by 13% and fluorine by 26%
• Co-firing of up to 20% biomass with coal to reduce CO2 emissions

The economic advantages of the technology are as follows:

• Lowest cost multi-pollutant retrofit control technology
• Requires minimal space compared to other pollution control techniques
• Combined with supercritical boilers will yield lower heat rate than current IGCC units
• No chemical plants required on back-end of boiler

Further, the Ashworth Gasifier removes a high percentage of the coal ash in the gasifier proper, reducing the rate of particulate entry into the boiler. Consequentially, there is less particulate in the flue gas entering the downstream electrostatic precipitators (constant efficiency removal devices) and less particulate will enter the atmosphere.

The following papers on the technology are provided in pdf form:

1. Demonstration of Ashworth Combustor
   Powergen (2000)
2. Demonstration of 3-Stage Coal Combustion at the Lincoln Developmental Center
   28th International Technical Conference Coal Utilization
   and Fuel Systems (2003)
3. Ashworth Combustor Demonstration
   Coal-Gen (2003)
4. Multi-Pollutant Emissions Control - AG-CS Retrofit
   to AEG Hutsonville Unit #4
   Coal-Gen (2005)

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