NOx Development in Gas Fired Research Furnace

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Fig 11 demonstrates the change of N O as a function of air-factor if the temperature of furnace chamber is 1250 and 1350°C. In a chamber-type furnace the following formula can be proposed for calculating the No-content of dry flue gas at a characteristic flame-temperature of 1350°C: V N O = -171 n2 + 347.n-84. ppmv (8) 3.04 Effect of steam-content on NO-development The water content of air influences the reaction velocity and by this the length and temperature of flame as an inert gas The natural moisture content can be different in the different hours of the day (it can change between 20-100% on the different places). Owing to its great heat-capacity the water cools the flame intensively, therefore the N O x emission can be decreased by atomizing the water during industrial firing. This method cannot be used at furnaces operating in the steel industry owing to the oxide-active properties of water Our water-atomizing experiments were carried out by using both burners The mass flow of atomized water was 0-72.5 ml/min and the oxygen-content of flue gas was 1.5. .1.7% in the course of measurements A pipe placed in the burner-axis was used for introducing the water. Starting with 0 % water at the beginning of the experiment the flow mass of water was gradually increased. Fig. 12 shows the characteristic water-NO diagram. AxOr-bumer 70 _ 60 I 50 a 40 O 30 Z 20 10 0 m m - r = 1200 'c -•-NO -*-viz Vg as = 2.2 m3 02 = 2,5% T -•- 0.0 C02 • 0.3 C02 -*-0.6CO2 M 0.9 C02 -•-1,2 C02 Burner A j - * * * * " ^ i 1150 1200 1250 1: Temperature [*C] Fig. 13. NO emission of „A" burner time [s] 8SS P 1100 1130 1200 Tompcrature [ *C ] Fig 14 NO emission of ,JB" burner 28 34 45 49 54 61 water (m|/mjn) Fig. 12: NO-content as a function of water mass flow According to our experiences the N O emission significantly decreases by atomizing 720 ml/m gash water The water-atomizing is disadvantageous from the point of view of the efficiency of the furnace. 3.05 Influence of flue gas in combustion air The jet moving in a closed chamber always injects flue gas, what mixes with the fuel-air mix on the radiation-border. The rotation burners, especially the O R E and O R C type ones, if they have a great swirl parameter and operate with flat flame, inject a flue-gas mass exceeding their o w n mass, in axial direction. In the course of our experiments flue gas was mixed into the combustion air of "A" and "B" burners so, that the COr-content of the air changes from 0.3% to 1.2%. The firing parameters and the furnace-characteristics were kept at a constant value during the measurements. Owing to the decreasing flame-temperatures caused by the flue-gas mixing, the temperature of furnace-chamber was stabilized so, that the furnace was heated by means of pushed-in cooling probes, and then the protrusion of probes was decreased so, that the temperature of chamber be approximately constant. Fig. 13 shows the NO emission of "A" burner, while Fig. 14 - the NO emission of "B" burner as a function of the temperature of furnace chamber and the C 0 2 concentration. W e suggest to use the following polynomes for the approximating calculations at parallel flow (IP, O P ) burners: At a temperature of 1300°C: VN0= 18C02 2 -58C02 +76, ppmv (9) 1200°C: V N D = 9C02 2-39CO+62, ppmv (10) 1100°C:VN O=5CO2 2-29CO2+53, ppmv (11) The use of the following polynomes is proposed for burners of ORA type on the basis of the measurements made by the same parameters: At the flame temperatures below, if 0.0 <C02<1.2%: 1250°C 1150°C 1050°C V N 0 = 3.97 C 0 2 2 -37C02+79, VN 0 - 5.556C022 -36C02 +70, VN0=3.175C022 -33C02 +67, ppmv ppmv ppmv (12) (13) (14) The following conclusions can be drawn on the basis of the measurements: a,/ The flue gas forced recirculation proves to be an effective tool for decreasing the N O emission in the furnaces operating in the steel industry, b./ The NO-emission of burners having swirling flame at similar conditions is greater in each temperature range than that of the parallel jet burners, 0/ The flue gas mixing has a great effect even at low concentration. The efficiency of mixed flue gas decreases by increasing the concentration.