Diffusion Combustion in a Tube-Nested Combustor(<Special Issue>International Conferences on Power and Energy System)

An advanced-type compact water-tube boiler has been designed on the basis of the new concept of cooling flame by water-tube bank in the furnace, and is referred to as "tube-nested combustor". It realized drastic reduction in boiler size as well as in the NO_x emission. In this present study, aiming at further improvement of boiler efficiency and reduction of NO_x emission, the combustion characteristics in the furnace were investigated by using the test boiler of 0.5t/h steam output. Experimental results indicated that the NO_x formation was restricted in the narrow area close to the burner exit, and that the CO-concentration decreased drastically with the combustion gas stream through the tube-bank. These facts were closely related to the experimental evidence of the cross-sectional distribution of gas temperature being rather uniform owing to the agitation by the tube-bank. These experimental results verified the soundness of the boiler design and, in addition, gave relevant information on local combustion characteristics available for the R&D of the next generation tube-nested combustor.