Development of an air staging technology to reduce NOx emissions in grate fired boilers

Experiments with a newly designed controlled multiple air staging technology (CMAST) in grate firings show a considerable reduction in NOx emissions. The applicability of the CMAST depends on fuel parameters. Fuels with high moisture content cause a drop in the heat output during full load operation due to the reduced fuel conversion. Due to reduced temperatures in the furnace, the emissions of products of incomplete combustion rise during part-load operation. More primary air is necessary to decrease incomplete combustion products, thus preventing the successful implementation of the multi-air-staging technique. Experiments in the laboratory, and test and commercial firings assist in understanding the influence of different fuel characteristics on the combustion system, and detect practical potentials and limits of air staging. On this basis, concepts have been developed for an optimised operation of grate firings dependent on the fuel characteristics. These results promise a further improvement of combustion technology using wood fuels.