Nitric oxide emissions and combustion performance of nontraditional ring-fired boilers with furnace geometries

The flow, combustion and emission characteristics of nontraditional ring-fired-type furnaces were investigated numerically to evaluate the effects of incorporating additional inner water walls on the heat transfer, carbon burnout and emissions of nitrogen oxides. Both tangentially and ring-fired-type furnaces were considered and the ring-fired-type furnaces were divided into four inner-water-wall cases: without, normal type, radiant expended type and both radiant and convective expended type. The presence of the inner water wall led to an improvement of approximately 50% in the heat flux. In particular, the reduction in nitrogen oxide emissions was approximately 30%, whereas the carbon burnout was kept constant.