The potential for a single system to remove multiple pollutants using a simple staged-combustor design was identified by Bob Ashworth in 1980. Ashworth was involved with the development of a two-stage combustor at Florida Power Corporation (FPC) that reduced both sulfur and nitrogen oxide emissions. FPC demonstrated a two-stage 12 million Btu/hr combustor in 1984 at the Foster Wheeler Development Center in Livingston, New Jersey. At the time of testing the 2-stage technique, it met the emission limits of SO2 and NOX under the Clean Air Act Amendments (CAAA).
ClearStack Combustion Corporation was formed and incorporated in Illinois in June 1998. It is a privately held C-Corporation developed to demonstrate and commercialize clean coal Staged-Combustion (front-end of the plant) air pollution control technologies. ClearStack Power, LLC, was formed in March, 2013 to take charge of the commercialization of these low-cost, patented air pollution reduction systems. ClearStack currently has three technologies that are ready for commercialization; two 3-stage combustors and one dry scrubber.
However, in 1999, as preparations for the ClearStack Lincoln Developmental Center Demonstration project were underway, the U.S. EPA announced it would further limit nitrogen oxide (NOX) emissions to levels much lower than the current regulations. After the announcement, the 2-stage technique looked less attractive, since it couldn’t reduce NOX to the new EPA requirements. A post-combustion technology such as Selective Non-Catalytic Reduction (SNCR) or Selective Catalytic Reduction (SCR) would have to be added that would increase capital and operating costs for utilities seeking to reduce pollutants to meet air quality standards.
Based on ClearStack’s knowledge of NOX control techniques, a 3-stage combustion technique was conceived. Known as the Ashworth Combustor™, it retains the FPC gasifier but added techniques to reduce NOX emissions to meet the lower U.S. EPA limits. It achieves ultra-low NOx emissions and improved sulfur capture. Both of these goals were achieved and as a bonus mercury and other air metal toxics were also captured in the slag during testing of the three-stage technique on a 40 million Btu/hr gasifier-combustor at the Lincoln Developmental Center in 2003.
FPC sold the rights to the technology to Ashworth Technologies, LLC in 2008 and ClearStack has worldwide licensing rights to develop and commercialize the technology. It is used in combination with the ClearStack technology. ClearStack also developed a 3-stage technique that can be applied to coal cyclone-fired boilers to reduce NOX emissions to very low levels.