| OCR Text |
Show Excess Air i One way to control flame temperatures in a premixed combustion system is to add more combustion air than required to burn the fuel. Above the threshold limit for thermal N O x formation (2700°F), increases in excess air levels suppress thermal N Ox formation. In diffusion burners the N O x concentration will rise, in most cases, with increasing excess air within the normal 1-3% 0 2 boiler conditions. Data obtained for the EV burner at full load with 20 % FGR for 190°F and 400°F preheated air (Figure 4) shows the decrease in N O x emission as excess air levels increase. CM O ^5 co X O •o 0) 120 100 80 60 40 20 n Full Load Data: - JlbJV I I EV Burner, LNV Burner EV Premixed f / m / LNV f /Diffusion L /• J^/i I I I 1600 1700 1800 1900 2000 Adiabatic Flame Temperature, K 2100 Figure 4: NOx Emissions as a Function of Calculated Adiabatic Temperature In contrast to the EV premixed burner, data obtained for the L N V ™ diffusion burner without FGR, showed a slight increase (~ 5 ppm) in N O x with increasing excess air over nominal boiler operating ranges. With FGR, changes in excess air did not have a significant effect on further reducing the flame temperature and the N O x concentration. Preheat Air Temperatures Two series of tests were conducted to evaluate the effect of combustion air temperature on the performance and emissions. In the first series, ambient combustion air was used 8 IV-24 |
