Since the SCR device of a 2×300 MW unit was put into service in 2013

there has been serious problems such as ash deposition in the location of ammonia injection grid

horizontal flue gas duct and deflector. Meanwhile

the ammonia slip concentration obviously exceeded the standard value

resulting in a high differential pressure of the air preheater. To solve these problems

the flow field was checked through computational fluid dynamics(CFD) to find out the reason. The final optimization scheme is: replacing the original ammonia injection grid(AIG) by the petal type one better anti-fouling ability and mixing characteristics

optimizing the deflectors

and increasing the velocity near the guide plate and flue duct wall to alleviate ash accumulation. After the modification

the adjustable performance of the ammonia-spraying grille zoning was improved obviously

the distribution of nitrogen oxide concentration at outlet of the SCR denitrification system was more uniform

and the ammonia escape amount was significantly reduced. The abnormal ash blockage in the ammonia-spraying grille

flue and guide plate was solve when the furnace was shut down after 8 months' operation.