Abstract
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 NOx emission. In this present study, aiming at further improvement of boiler efficiency and reduction of NOx 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 NOx 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.