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Show arrows. By maintaining sufficient distance between the oxygen nozzles and fuel supply tube, enough of the furnace gases can be aspirated into the oxygen jet prior to mixing with the fuel so that the resulting flame temperature can be reduced to a value substantially below the theoretical flame temperature. At the point of combustion, both conventional air burners and the "A" Burner using 100~ oxygen have an oxidant with a low concentration of oxygen. For the air burner, the diluent is nitrogen while for the "A" Burner using oxygen, the furnaces gases make up the diluent. A simplified schematic representation of the process steps for a conventional burner and the "A" Burner in a furnace is given in Figure 3. OXYGEN (LOW VELOCITY) --FUEl-l HIGH FLAME TEMPERATURE ASPIRATION OF , • FURNACE GASES REDUCED GAS TEMPERATURE RADIATION TO CHARGE FLUE GAS OXYGEN (HIGH VELOCITY) ASPIRATION OF FURNACE GASES OXYGEN - FURNACE GAS MIXTURE '~FUEL--LOW FLAME TEMPERATURE RADIATION TO CHARGE FLUE GAS Fig. 3 - Schematic representation of the process steps for a conventional burner (left) and the "A" burner (right) in a furnace. An estimate of the flame temperature can be made using a simplified model of a jet. It is assumed that a given amount of furnace gas is mixed uniformly with the oxidant jet. Then the oxidant-furnace gas mixture is blended with the fuel and burned. Obviously, the actual operation is much more complex in practice considering the concentration gradients and fluctuations within a jet as well as the interaction between adjacent jets. However, for the purpose of explaining the essential features of the "A" Burner, the simplified model is justified. For this simple case, the flame temperature would depend upon 1) the amount of furnace gas aspirated into the oxidant prior to mixing with the fuel jet, 2) the furnace gas temperature, and 3) the oxygen concentration in the oxidant. The amount of furnace gas aspirated into the oxidant jet 331 can be designated by the recirculation ratio, R, as defined below: mole of furnace gas aspirated into the oxidant jet H2 moles of oxidant In Figure 4, the calculated flame temperature with methane as the fuel is plotted versus the oxygen concentration in the oxidant for an average furnace gas temperature of 2400°F and for recirculation ratios of 0 to 6. When the recirculation ratio is zero (no aspiration of furnace gas into the oxidant jet prior to mixing with the fuel), the flame temperature is the theoretical adiabatic flame temperature. As furnace gas is aspirated into the jet (increasing values of R) the flame temperature decreases. As an example, when using 100~ oxygen as the oxidant with an average furnace gas temperature of 2400°F, the flame temperature decreases from 5040 to 3530°F as the recirculation ratio increases from 0 to 6. ~ w ~ ~ ~ w Il. ~ W .... W ~ j u.. RECIRCULATION RATIO 5000 FUEL· METHANE 4500 4000 3500 3000 20 40 60 80 100 VOLUME % OXYGEN IN OXIDANT Fig. 4 - Flame temperature as a function of oxygen concentration in the oxidant and recirculation ratio. An essential feature of the "A" Burner is that furnace gases composed of hot combustion products are aspirated into the |
