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Show A LOW NOx, LOW TEMPERATURE OXYGEN-FUEL BURNER John E. Anderson Union Carbide Corporation Tarrytown, New York, USA ABSTRACT The maximum fuel savings via oxygen enrichment is often achieved using up to lOO~ oxygen. High oxygen concentrations in a conventional burner, however, pose problems. The flame temperature is high (above SOOO°F) leading to local overheating and high thermal NOx ' In addition, the substantial reduction in gas flow rate through the furnace when converting from air to oxygen reduces the internal gas recirculation resulting in large temperature gradients and less uniform heating of the charge. These problems are overcome in a new burner in which oxygen is fed through a number of nozzles surrounding a central fuel jet. The oxygen jets are at a sufficient distance from the central fuel jet so that furnace gases are aspirated into the oxygen jets before mixing with the fuel. By proper design, the concentration of oxygen mixed with furnace gases can be 20~ or less before interacting with the fuel. The final flame temperature is substantially below that for conventional burners and NOx levels are one to two orders of magnitude below that for federal codes for fuel gas. Gas mixing and recirculation within the furnace is accomplished with oxygen jets at very high velocity, of the order of 1000 ft/sec. BACKGROUND The use of oxygen or oxygen enriched air in place of air for combustion can improve the overall performance and efficiency of industrial furnaces. As oxygen replaces 329 part or all of the air for combustion, the nitrogen portion is reduced accordingly in both the oxidant and the flue gas. The volume of the oxidant and flue gas are then reduced per unit of fuel burned. In addition, the concentration of oxygen in the fuel-oxidant mixture is increased. The main advantages accrued from these changes are 1) the fuel consumption is lowered primarily due to the reduced sensible heat loss to the flue; 2) the production rate of the furnace which is often limited by the burner ' capacity and the size of the flue and air ducts when using air, can be increased; and 3) gas cleaning of the reduced flue gas volume is less costly and more effective. Unfortunately, the use of oxygen in conventional burners for industrial furnaces suffer from the following disadvantages: 1. The flame temperature increases markedly as the oxygen concentration in the oxidant increases. The high flame temperature can be undesirable in two respects: a) The heat transfer rate by radiation and conduction can be unusually high in the localized region around the flame. This can lead to hot spots causing damage to the furnace refractory and to uneven temperature distribution in the charge being heated. b) Nitrogen oxide emissions can increase. Reaction kinetics and equilibria for the formation of nitrogen oxides are favored by high temperatures . This is a problem even when using pure oxygen since there is usually sufficient nitrogen in the fuel and through air leakage into the furnace to form the nitrogen oxides . |