Experimental Research On Pulverized Coal Supply Stability Of High Efficiency And Low NO_x Pulverized Coal Industrial Boiler And Discussion On The Adaptablity Of Coal Species

NO_x is a major air pollutant,and reducing its emissions is one of the important contents of China's environmental protection work.As one of the main sources of NO_x emissions whose limit has been gradually tightened by the government,the coal-fired industrial boilers are mostly facing the dilemma of being eliminated due to excessive NO_x emissions.In this context,a high-efficiency low-NO_x pulverized coal industrial boiler system is developed by the cooperation of the research team with a Shanghai company,including raw coal milling,pulverized coal transportation,boiler body,soot collection and flue gas treatment.As the core equipment,the high-efficiency low-NO_x liquid slagging pulverized coal burner adopts the low-excess air grading combustion technology to reduce the NO_x emission.As a prerequisite for reducing NO_x emissions,stable coal-air ratio is of great importance in low excess air staged combustion.However,due to the large fluctuation range of boiler load,and the wide range of pulverized coal transportation volume,powder supply stability is often difficult to control at high delivery rates,so that the wind-to-coal ratio often fluctuates and deviates from the optimal parameters,and then large fluctuations in the oxygen and NO_x emissions at the tail of the boiler.In view of the problem of unstable powder supply caused by high wind-to-volume ratio,the pulverized coal conveying system in the boiler system is taken as the research in object this topic.The factors affecting the stability of powder supply are tested by single factor control method,so as to obtain the intrinsic relationship between these factors and the stability of powder supply.The guidance is provided for the improvement of the powder supply system,which lays a good foundation for further improving the stability of powder supply and reducing NO_x emissions.Firstly,this paper studies the working principle of spray nozzle,and then analyzes the factors affecting the stability of powder feeding according to practical experience.The results show that venturi nozzle back pressure,blanking pressure and pulverized coal fluidity are the main influencing factors of powder stability.Thepowder stability can be improved by reducing venturi nozzle back pressure,increasing blanking pressure and improving pulverized coal fluidity.Secondly,For the influencing factors of Venturi back pressure: Single factor control method is used for the pulverized coal conveying capacity,the inner diameter of the conveying pipe and the outlet diameter of the venturi nozzle.The relationship between the three and venturi back pressure is studied experimentally to analyze the internal relationship between the three and the stability of powder supply.The results show that the venturi back pressure is reduced and the powder supply stability is improved with the decrease of pulverized coal conveying capacity,the increase of the inner diameter of the conveying pipe and the decrease of the outlet diameter of the venturi nozzle.Thirdly,for phenomenon that the self-weight of coal powder,the blanking pressure and the powder supply is reduced,and the oxygen content in the tail of the boiler is gradually increased.Taking the pressure of the powder bin as a variable,the test is carried out,and the results showed: Properly increasing the pressure of the powder supply bin can weaken the influence of the self-weight change of the coal powder on the stability of the powder supply and improve the stability of the powder supply.After,analyzing the large fluctuation of oxygen in the boiler tail before and after the feeding period,there are two main reasons for the discovery: the self-weight of the coal powder increases after the feeding,and the pressure of the powder silo increases during the feeding process.For the second reason,this paper increases the inner diameter of the balance pipe between the powder storage bin and the powder supply bin,and proves by the test that the reform effectively reduces the fluctuation range of the pulverized coal transport volume before and after feeding.Then,according to the verification by experiments that the larger the gap of the sealed rotary feeder,the worse the powder supply stability.From the specific wear condition of the sealed rotary feeder,the main reason for the increase in clearance is significant cutting,microplastic deformation and contact fatigue wear.In response to this phenomenon,PVD coating treatment and test are performed on the blade tip of the sealed rotary feeder.Compared with test results of the untreated high manganese steel ZGMn13 wear-resistant material,the results show that PVD coating on the blade can effectively reduce the increase rate of the gap and prolong the service life of the sealed rotary feederFinally,the relationship between coal quality and pulverized coal fluidity is analyzed.The applicable index of coal quality characteristics of high efficiency low NO_x pulverized coal industrial boiler is discussed according to the combustion characteristics of high efficiency low NO_x liquid slag pulverized coal industrial burner.