Reduction of Particulate and NOx Emissions from Kraft Recovery Boilers Using Catalytic Filtration Technology, 2018 PEERS

This study examines the application of new technology for reduction of nitrogen oxides (NO_x) and particulate emissions from Kraft recovery boiler flue gases. The technology, developed by W.L. Gore and Associates, is based on catalytic filtration. The new technology has been successfully applied at five municipal solid waste (MSW) combustion sites in Europe. In this technology, two-layer filters are deployed using a bag house. The first layer of the filter comprises expanded PTFE (polytetrafluoroethylene) filtration for removal of particulate matter. The second layer comprises a second, coarser layer of expanded PTFE, filled with inorganic catalyst for promoting the reaction of NO_x with ammonia-based reactants. The technology has been deployed as a stand-alone Selective Catalytic Reduction (SCR) process or, as a polishing step after Selective Non-Catalytic Reduction (SNCR) treatment. The ammonia-based reactants may be supplied as anhydrous ammonia, as aqueous ammonia, or as urea. The requirements for the technology are an especially good fit with the modern Kraft recovery boiler – low sulfur dioxide (SO₂), moderate carbon monoxide (CO), low heavy metal content and a temperature in the range of 180-230°C. In some boilers today, high CO emissions are the result of operating strategies to reduce NOx. This technology could eliminate this divergence of control objectives. The technology may be employed i) for NO_x reduction alone if the electrostatic precipitator is fully compliant, ii) for removal of NO_x as well as further particulate following a marginally compliant electrostatic precipitator, or iii) to replace the electrostatic precipitator. The authors present assessments of the technology, applied to a modern Kraft recovery boiler under these three scenarios. The assessments are based on extrapolation from MSW experience. Plans for pilot and full scale demonstration with Kraft recovery boiler flue gas will be discussed. 

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