PERFORMANCE-CHARACTERISTICS OF THE NOVEL LOW-NOX CGRI BURNER FOR USE WITH HIGH AIR PREHEAT

In the nonpremix furnace firing strategy FODI (Fuel/Oxidant Direct Inj ection), fuel and oxidant jets discharge directly into the furnace cav ity rather than into a burner quarl. The jets entrain substantial quan tities of product gases that have cooled by furnace heat transfer. Thu s fuel and oxidant enter the subsequent combustion zone much diluted b y cooled products, depressing reaction temperatures and reactant conce ntrations and so greatly reducing NOx emissions. In the present realiz ation, FODI is implemented in a patented unitary burner providing a pl urality of oxidant jets surrounded by a plurality of fuel jets, suitab le for retrofit as well as new installations and particularly advantag eous for applications with air preheat. We here present results of exp erimental investigation and theoretical analysis of the burner perform ance. Characteristic of FODI, NOx reduction is won at an expense to co mbustion stability, confining steady-state operation to furnace refrac tory temperatures above about 870 degrees C and exhaust gas temperatur es above about 1000 degrees C. The NOx emissions vary strongly with th e temperature of the recirculating furnace gases; when the furnace loa d is substantial, that temperature falls much below the adiabatic comb ustion level and NOx is very low. By appropriate choice of burner desi gn parameters, reasonably small combustion zones are obtained, avoidin g wall impingement and enhancing stability. The analysis given of burn er behavior, particularly in respect to combustion aerodynamics, is re vealing in respect to mechanisms and provides a basis for assessing ef fects of variations in design, including scaleup. The present is the f irst systematic investigation of a system employing FODI, and the gene ral analysis is pertinent to other FODI implementations. This is a new and challenging field for combustion research, involving complex mixi ng processes coupled with nonadiabatic reaction at unusually low tempe ratures and concentrations. Much work remains to be done on the detail ed mechanisms of mixing and reaction and on the development of appropr iate mathematical modeling. (C) 1998 by The Combustion Institute.