| Slagging is one of the main reasons that affect the safe and efficient operation of pulverized coal boilers in power plants.Most power stations in my country use complex and diverse coals.Under the original operation plan,the slagging in the furnace deteriorates,resulting in a decrease in the heat transfer efficiency of the heating surface and an increase in flue gas temperature.The uneven heating of the local area accelerates the aging and damage of the tube wall,which seriously endangers the safety of boiler operation.Using the numerical test method to analyze the slagging characteristics of the boiler is an effective method to optimize the coal blending technology and realize the operation optimization.At present,most of the researches judge the slagging situation in the furnace by analyzing the gas phase field or the composition of the fly ash in the furnace,but the main process of slagging caused by the deposition of fly ash particles on the wall surface is not considered in depth.The deterioration of the operation of the water wall under the slag layer coverage is unclear.The above reasons lead to the lack of effective anti-slagging and safe operation strategies.In view of these problems,this paper takes a 350 MW front and rear wall hedging boiler as the research object,and deeply analyzes the influence of the air and coal blending scheme on the combustion dynamic field and slagging characteristics,and explores the influence of the slag layer on the temperature distribution of the water wall.Prediction of operating parameters and optimization of safe operation were carried out.Firstly,a 350 MW swirl hedging pulverized coal boiler in a power plant is mathematically modeled,and a three-dimensional model of the boiler half field is established,including the complete modeling of the swirl burner,and then the mathematical model involved in the combustion process in the furnace is carried out.A complete elaboration is presented,and a slagging model suitable for industrial-scale calculations is constructed based on the particle adhesion properties.On this basis,the calculation results of the reference conditions and accident conditions are verified and analyzed,and numerical tests are carried out for the air distribution and coal mixing schemes.The results show that the main areas where slagging occurs are the jet end area of the sidewall burner,the sidewall area from the top of the burnout air to the flue inlet sidewall and the bottom of the screen superheater.The air distribution scheme has a great influence on the combustion structure in the furnace,and the slagging situation in the furnace is affected by adjusting the flame position in the furnace.When the three types of coal are used alone,the slagging of coal type I is more serious;while the co-firing of coal type II and coal type III can alleviate the slagging in the furnace caused by coal type I,and the proportion of coal types and the location of the furnace will be affected.It affects the slagging level and slagging position in the furnace.Based on the numerical calculation results of combustion and slagging in the furnace,a one-dimensional tube heat transfer model and a wall temperature calculation model are constructed.The influence of the operation time and operation scheme on the heat transfer characteristics of the water-cooled wall of the side wall was explored,and the following conclusions were drawn: when there is no slag layer on the water-cooled wall surface,the high temperature area of the side wall and the high heat load distribution have a greater coincidence;The thickness of the slag on the tube wall gradually increases,and the surface temperature of the slag layer gradually increases,but the growth rate of the outer surface temperature of the slag layer gradually decreases with the increase of the wall thickness;adjusting the air distribution scheme in the furnace can effectively adjust the combustion structure in the furnace,and then Improve the uneven distribution of heat load in the furnace and alleviate the deterioration of wall heat transfer caused by slagging and slagging on the water-cooled wall surface;coal types with large differences in co-firing combustion performance can adjust the combustion structure in the furnace and reduce the area with severe slagging and the highest heat load.In case of regional overlap,the temperature of the outer surface of the slag layer can be reduced,thereby alleviating the effect of slagging on the deterioration of heat transfer in the water wall.Finally,based on Gaussian process regression and combined with the sample database obtained from the previous numerical simulation,a prediction model for parameters such as the total amount of coking in the furnace and the carbon content in fly ash was constructed,and a multi-objective combustion optimization strategy for global search of the wind coal sample database was proposed.The optimal design of the optimal coal-blending air-distribution scheme under a given coal-type ratio is realized.On this basis,the common coal blending schemes in the plant are analyzed,and the proposed combustion optimization strategy is verified by using the boiler combustion numerical model and side wall temperature calculation model constructed above.The results show that the constructed Gaussian process prediction model can achieve The accurate prediction of the carbon content of fly ash,the total amount of slagging in the furnace and the temperature difference between the side wall slag layer and the tube wall can meet the needs of actual boiler operation optimization.The level of slagging can realize efficient and safe combustion under the mixed combustion of three coal types in the furnace. |
