ClearStack Combustion Corporation has developed a dry scrubber technique called
ClearGas™ that uses potassium hydroxide (KOH) to reduce sulfur oxides and nitrogen
oxides from flue gases by 70 to 90%. It will also remove sulfur trioxide ( SO3 ) that will
reduce flue gas opacity. The presence of potassium salts on a downstream electrostatic
precipitator (ESP) increases the “spark over” voltage and improves ESP performance
even though SO3, a fly ash conditioning agent, is removed in the process. A baghouse
may also be used. The process produces a byproduct of salable potassium nitratepotassium
sulfate-fly ash fertilizer. In 2001 a US patent was granted to ClearStack for
this technology. Economics show that this dry scrubber technology is a low cost
technique to bring coal-fired stokers into environmental compliance. It is less costly than
a stoker replacement with a natural gas-fired boiler system or a conversion to coal-fired
fluidized bed systems. It was also evaluated for niche market use as a trim technology
for large coal-fired electric utility boilers.
A 100 scfm ClearGas pilot unit was built and the technology will be tested in 2008.
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