The Research About The Air-Coal Ratio Influence On The NO_x Fluctuation In Variable Load Operation

It's a significant impact to combustion economics and low emission combustion that there is an excellent matching performance between air and coal in boiler.As the industry policy slant from thermal power generation to renewable energy generation,thermal power plants need to frequently change their load to adjust AGC.On a stable load,combustion control system can perfectly finish its job.However,the air-coal ratio would deviate from the optimal values while the load from AGC change.The higher NO_x and Oxygen would occur due to terrible matching performance between air and coal in boiler.The hysteretic of real air and coal fed into boiler has been considered as the important factor of fluctuant NO_x in a 330MW coal-fired power plant.The control process of air-coal ratio will been optimized to improve the matching performance between air and coal fed into boiler.The purpose of reducing the NO_x?low emission combustion will be finished.First,plenty data from DCS is applied to establish the statistical model.And 20 typical variable loads are selected out to analyze the boiler's parameters while the load from AGC is changing.The result shows that the air-coal ratio stability of the boiler and pulverizing system is terrible,which result together to a more drastic NO_x fluctuation in reducing load.Second,the air data and coal data are measure online in real-time to analyze the hysteretic of real air and coal fed into boiler.The measurement of boiler air-flow and monitoring system of pulverized coal concentration are designed and optimized to offer more accurate data(errors less than 3%)for the paper.Analysis results that the air fed into boiler shows no hysteretic,and the coal fed into boiler shows a more obvious hysteretic time ranging from 7 min to 9 min.The average change rate of hysteretic air and coal is obtained according to using mathematical analysis methods to study the time model in this paper and a improvement operation scheme is presented.The secondary air has 1 min lag time and increase at a rate of 7.5 t/min when up load;however the secondary air has lmin leading time and decrease at a rate of 9 t/min.This operation scheme has been identified according to the running condition data.Finally,the factors of coal rate?coal standard?fan's outlet pressure and damper characteristics for air-coal matching performance have been analyzed according to the result of the test.This could offer guidance and basis for operation optimization and adjustment.