OCR Text |
Show 3) 7 This burner has stable firing on condition that the temperature is 500°C and the 0 2 concentration is 14% (dry ) that the exhaust gas temperature is 400°C or higher concentration is 15% (dry). exhaust or more, and the gas and °2 4) It can be to reduce remaining 0 2 concentration to less than 3% (dry) wi thout additional air at the maximum firing rate. Therefore, large amount stearn can be obtained. 5) NOx emission at 500°C of exhaust gas and 15% of 0 2 is such low as less than 50 ppm (02 = 0%) 6) the burner exhaust gas differential pressure is less than 100 mrnH20. This is sufficient for the allowable back pressure of gas turbine. When developing the burner, we learned the fol l owing facts. 1) Installation of the secondary swirler increases the stability of combustion. 2) To reduce the NOx emission, intensi ty, increase the gas gas nozzles. it is effective to reduce first swirler nozzle angle and decrease the number of 3) Turning down the burner in fixed amount of exhaust gas generats CO within low firing range. The control CO, it is effective to reduce the nozzle angle. At 500°C of exhaust gas and 15% (dry) of 0 2' complete combustion can be continued until T.D.R. becomes 1:3. According to the results of firing simulation analysis, it is assumed that generation of CO occurs because flame is cooled down by gas turbine exhaust. 4) NOx emission ha linear correlation to the theoretical flame temperature at maximum firing rate. Its rate is 20 ppm (02 = 0%) of NOx emission to 100°C of theoretical flame temperature. It is assumed that the burner has stable firing in the range of theoretical flame temperature higher than 1,750°C. 5) To reduce further NOx emission, steam injection and two-staged combustion are available. When stearn is added, NOx emission can be reduced by approx. 20% at stearn injection rate of W/Fb = 0.5 (kg/kg ) . In the two-staged combustion NOx emission is reduced by approx. 40% at a secondary exhaust gas ratio of 20%. The development of this burner will lead to a wide application of the repowering system to the existing and newly installed boilers in Japan. Reference s. Katsuki: Research of combustion and flame stability wi th low 0 2 concentration air, 1993. |