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Show 1600 1400 ^ 1200 O $S 1000 ro @ 800 E Q. 6a" 600 400 200 0 1 4343 TwinBed II LNI NOx emissions # No. 2 oil conventional firing • No. 6 oil conventional firing x Nat. gas conventional firing A No. 6 oil LNI + Nat. gas LNI j ^^^^^^jtH^gj»f£* 200 1250 1300 1350 1400 1450 Temperature, K 1500 1550 Figure 6 1600 Recent regenerative burner development has focused on the application of the LNI technique to #2 and #6 fuel oils. A steam or compressed air atomizer is used as a remotely located fuel injector for introduction of a stream of atomized fuel into the furnace. Figure 6 shows the effectiveness of the LNI technique in reduction of N O x emissions for oil firing, and the favorable comparison with the high reductions obtained on gas firing. Alternative Arrangement of Air and Gas Injector In order to investigate the effect of the nozzle arrangement on N O x emissions, Tokyo G as compared the two burner configurations shown in Figure 7. One has 6 gas nozzles arranged in a circle around a central air nozzle, the other has 6 air nozzles around a central gas nozzle. Table 1 compares N O x emissions for the two arrangements. For the arrangements considered, the center gas type is even more effective than the center air one. The combustion air momentum at 900 K is 50 times larger than natural gas, allowing more efficient entrainment of products of combustion. As mentioned above, both the angle and distance between the air nozzle and gas nozzle are important factors in N O x emissions, and increasing offset distance results in reducing N O x emissions. However, the acceptable distance is limited by both combustion properties and burner dimensions. If the offset is too large, C O emissions are increased and the burner size becomes unwieldly. ARRANGEMENT 1 CENTER GAS NOZZLE, SIX OUTSIDE AIR NOZZLES ARRANGEMENT 2 CENTER AIR NOZZLE, SIX OUTSIDE GAS NOZZLES Figure 7 Nozzle Arrangement N O x Emissions for Different Injector Arrangements 1.7 M W Firing Rate Air velocity, m/s Gas velocity, m/s Furnace temperature, K Air temperature, K NOx, ppm @ 3 % 0 2 Arrangement 1: Center gas injector, 6 outside air injectors 120 100 1573 923 61 Arrangement 2: Center air injector, 6 outside gas injectors 120 100 1573 923 72 Table 1 For the injector angle, diverging, parallel, and converging configurations were compared (see Figure 8). The diverging arrangement produced remarkably low N O x emissions, but at the cost of poor combustion characteristics, including high C O emissions at some operating conditions. The converging arrangement had the highest N O x emissions, but produced the best combustion characteristics. Figure 8 Nozzle Angle 5 |
