Deviation exited between the four CEMS's measurement for NOx concentration in flue gas denitrification and desulfurization systems in a power plant

analysis showed that the reason was that due to the low NOx concentration in flue gas

the online instruments had large instrument error when measuring NOx with too low concentration.Moreover

NOx at the outlet of the denitrification system was not evenly distributed

causing the test points of the online instruments have no representativeness

which was another important reason.Thus

some suggestions were given

such as reasonably arranging the baffle

adjusting the ammonia injection grid

installing flue gas disturbance device and calibrating the analyzer with standard gas having concentration that is close to the actual gas's.