Directing against the problems occurred on No.5CFB boiler of Hangzhou United Thermoelectric Co.

Ltd.

such as high NO_xemissions which does not meet the requirements of ultra-low emission

low main steam temperature

high bed temperature and furnace outlet temperature

a low-NO_xcombustion retrofitting which includes adjusting the secondary air system

increasing the heating surface

adding the flue gas recirculation system and improving the SNCR system

has been carried out.It achieves the desired results successfully.At rated load

the final concentration of NO_xemissions decreased from 100mg/m~3 to less than 50mg/m~3

the main steam temperature increased by 20℃and reached the design temperature

the bed temperature and furnace outlet temperature dropped by 50 ℃

the amount of ammonia slip which can be controlled within 8mg/m~3 had a slight increase

the boiler efficiency was almost invariant.Moreover

further optimization test was conducted to solve the problem of high CO concentration after the air pre-heater.The results show that

in order to optimize the boiler operation

different amounts of flue gas recirculation should be chosen at different loads

simultaneously the upper secondary air damper opening degree should be 100%

the lower secondary air damper opening degree should be distributed like that the middle is large and the both sides are small.