METHANE de-NOX? REBURN TECHNOLOGY FOR STOKER BOILERS

摘要

Historically, stokers have had problems with solid combustion performance, gaseous and particulate emissions, erosion, slagging, and fouling. Today, many units cofire with natural gas to stabilize grate combustion and a number are turning to ammonia/urea injection to control NOx emissions. Improved combustion from cofiring is limited however, and the potential of ammonia-slip is a serious concern. GTI has developed a natural gas-based reburn technology, METHANE de-NOX, which effectively reduces emissions of NO_x and improves grate combustion of solids in stoker boilers. Successful commercial technology demonstrations have included MSW-, coal-, and wood waste, sludge-fired stoker boilers. Presently, METHANE de-NOX is installed and in continuous operation on nine boilers. Results from field evaluations provided 50 to 70% reduction in NOx, reduced or controlled emissions of CO within regulated limits and reduced ash unburned carbon. In this process, natural gas equivalent to 5-20% of the boilers thermal input is mixed together with a portion of recirculated flue gas and injected into the primary combustion zone just above the grate. An oxygen-deficient zone is created and as a result, NO_x formation is limited and NOx precursors decompose. Overfire air is introduced higher in the furnace to burnout combustibles and to allow sufficient time to complete the NO_x reduction reactions. Recognition of the technology has included: an Environmental Prize in Japan, a GRI Pace Setters Award, a 1997 R&D 100 Award and a 1999 American Forest & Paper Association Environmental and Energy Achievement Award.