Experimental Study On Assessment And Reconstruction Of A 600MW Boiler Combustion With Low NO_x Burners

In this paper,two 600 MW supercritical boilers in a thermal power plant are chosen as the research object.Based on the literature review,a,this paper discusses the technical methods related to the burnout and low NO_x production of the coal burners.A new low NO_x burner design scheme was proposed based on the numerical simulation results and practical experience in this field.The burners were installed on the boiler and it was carried out the industrial commission.The operation results of the boiler shows that the level of NO_x emission of the newly developed burners is very low,achieving the expected goals.The literature shows that,to achieve the low NO_x burning,it is important to design the the separation method of the pulverized coal in the primary air,to design the way of separating the secondary air with the primary air,and to design the burner nozzle.The actual flow velocity and the location of the over fire air(OFA)will affect the formation of NO_x and the combustion process to a large extent.Therefore,in the process of designing the burner and carrying out the numerical simulation,the above problems are discussed and studied extensively.The author designed a new burner for the # 4 boiler in the power plant.The specific features are as follows: The air distribution covers four air ducts,namely primary air,central air,external secondary air,secondary wind.The primary air to take the DC way,the secondary air to take swirl mode,in the primary air duct,the pulverized coal shade separation components are added.At the burner's outlet,a device to produce a new type of pulverized coal airflow which shows the characteristics of the outer dense coal concentration is designed..Also,the use of the corresponding outlet centre cone to strengthen its central inverse flow area step by step.Numerical simulations on the flow,heat transfer and coal combustion inside the boiler were carried out.In this process,the author found that the center of the burner produced obvious inverse flow area,and the coal powder could get a good enrichment effect.The new designed burner was installed on the # 4 boiler.The cold aerodynamics experiment is carried inside the furnace as the burner retrofit completed.The experimental results show that the swirl characteristics of this burner are excellent.After the completion of the technical retrofit,the boiler performance test shows that the boiler improve a lot from both point view of Economic and environment operation,Also,the boiler operation is very stable,But it also increased the carbon content of fly ash and risk of high temperature corrosion.Based on the experience of # 4 boiler retrofit,the burner design for # 3 boiler was improved and optimized.The relevant device of pulverized coal separation was improved to enrich the pulverized coal at the burner outlet.And the angles of the swirl vanesin the outer secondary air and the inner secondary air ducts are optimized.The corresponding numerical simulations were carried out,and the operating parameters were optimized.For example,with the help of different levels of over fire air,the the oxygen distribution inside the furnace was optimized and the corresponding thermal simulation activities were carried out.the # 3 boiler furnace retrofit including:(1)the new low NO_x burner installation;(2)two layers of over fire air duct installation.The boiler performance test data show that emission of nitrogen oxides is reduce to a large extent.In the case of ensuring stable and safe operation of the boiler,when boiler running at MCR load,the actual content of NO_x in the flue gas of the boiler back pass can be controlled to not more than 280 mg per cubic meter which is one of the objective of the present retrofit.