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Show 4.3 EFFECf OF AIR VELOCITY Fig. 7 shows the effect of the air velocity on NOx emission with the type A burner configuration as shown in the Fig. 6(heat input 0.7MW air ratio 1.05 furnace temperature 1300t: preheated air 650t: ). The effect of air velocity on NOx level is clear. NOx level decreases when the air velocity is increased. It is believed that the NOx reduction is due to the increased entrainment of the combustion products by higher air velocity as indicated by the mathematical modeling. Further NOx reduction seems limited with the air velocity higher than 120m/s. For practical application of the burner, however, the air velocity could be restricted by a limited source pressure of the combustion air. Optimum air velocity for this combustion technique appears to be 120m/s, for which approx. 360mmH20 (preheated air temperature 650t) is necessary. -~ 0 or-or- II C\I 0- E 0. 0. X 0 Z 50 Heat Input : 700kW Air Ratio ; 1.05 Air Temp. : 650°C· 40 Furnace Temp. : 1,300°C Gas V~100m/s 30 --r--o---+--~ 20 10 40 60 80 100 120 Air Velocity m/s 140 Fig. 7 Effect of air velocity on NOx emission 4.4 EFFECf OF RADIAL GAS FLOW Further NOx reduction has been obtained when part of the gas is injected radially from the gas injector tip as shown in Fig 8. Fig 9 shows the effect of the ratio of the radially injected gas ratio on NOx level. When radial gas ratio is zero, i.e., baseline case, NOx emission level was 30 ppr (heat input 1.7MW, air ratio 1.05, preheated air temperature 550t, furnace temperature 13Cv t:, air velocity 120 m/s). The NOx emission level decreases by about 20% when the radial gas ratio is increased up to 30% or more. However, no further reduction of NOx is observed when the radial gas ratio exceeds 50%. 8 |