Against such problems occurred in selective catalytic reduction(SCR)systems

such as large delay of ammonia injection control and not easy to realize automatic control

the NOxformation at entrance of the SCR denitration system was associated with variations of the unit main parameters.The principal component analysis method was applied to determine the main factors affecting the NOxformation.On this basis

a dynamic model for NOxformation prediction at entrance of the SCR denitration system was established

using the nonlinear fitting method.The NOxformation prediction value was compared with the actual data.The results show that this model achieved a good prediction in the unit's steady state.While for unsteady state

there is a certain deviation between the model prediction value and the actual data

the predicted value was about 100 second ahead.Therefore

this established model can be used as the feedforward of ammonia spraying control for the SCR system to overcome the large delay and control the secondary air flow.