OCR Text |
Show Fig.16 Example of exhaust gas recirculation combustion of 35T/h water tube boiler Boiler type: E-350 Combustion chamber load :40.4x10** Burner:NFK-COEN % ' Lomoustion air temp.:156°C Combustion & JL exhaust 160°C Boilerc, 33"05C_:: Air preh 260°C ear! / •3^" er Flowchart «n o 200 150 4* 100 !T3 ' QJ ' J-i ' U 0) g o o D. X o z 50 25% 4 40 39 20 10 NOx ppm / (converted into y' 02- 5%)^ O^crfculation -*--^""""M circulation . \ „ N.18% circula- **««0\ tion NOx irculati 0O2 "•< 18% circulation 0 25% circulation NOx '8 7 6 5 4 3 2 J. .' ,ii The problems for the practice of exhaust gas recirculation combustion can be itemized as follows: (1) Installation of fan duct for combustion and others. (2) Expansion of combustion chamber or reduction of load (rate down) due to the problem in furnace pressure or enlarged flame. (3) Balance between exhaust gas recirculation rate and NOx reduction effect from the view point of flame stability. (4) Low sulfur energy such as city gas is more suitable from the point of corrosion of fan and duct. 3.8. Ejection and addition of water or steam The ejection or addition is to reduce NOx while lowering the combustion gas temperature by adding non-active substance to combustion air or fuel. By adding water or steam, the thermal capacity is increased by means of the sensible heat (or latent heat) to lower the 8 - 21- |