Study On Adaptability Of CFB Boiler To Lignite-burning

At present,CFB boilers are generally adopted in China’s industry.Due to the unreasonable distribution of coal resources and insufficient capacity coal market in our country,the 130t/h CFB boilers of a certain enterprise in Hunan must be converted to lignite.The coal-fired boilers are designed according to a specific coal type.Once the coal quality is changed,the safety and economy of boiler operation will be affected.Therefore,in order to ensure the safety and stability of the boiler-burning lignite,the study on the adaptability of the CFB boiler to lignite-burning was carried out,reducing the cost of power generation and providing a reference for other CFB boilers to burn lignite.The 130t/h CFB boiler was taken as the research object.Firstly,in order to understand the boiler reform,three typical loads(100%,75%,50%)were selected to calculate the thermal characteristics of the coal by burning the designed coal and changing the coal.The changes of the relevant operating parameters of the lignite-burning under different loads were analyzed and diagnosed for the adaptability of the boiler to lignite.Secondly,the solid model of the boiler was modeled by Gambit,and the Fluent calculation software was used to numerically simulate the combustion process in the design of the coal and changing the coal.The flow field,temperature field,O2 concentration distribution,and CO concentration distribution in the two kinds of coal stoves were simulated.The distribution of particle concentration was compared to analyze the adaptability of burning in lignite-fired furnace.Finally,based on the problems existing in burning the lignite,a reform plan was proposed by combining with the actual layout of boilers.After the reform program was determined,the thermal characteristics of the boiler under different loads were studied through thermal calculation.The designed coal and the boiler before the transformation of the lignite were carried out.The thermal characternstics were contrasted and the boiler’s adaptability after burning the lignite was analyzed.The research results showed that the change of burning lignite has a big impact on the safe operation of the boiler.The flue gas temperature at the furnace exit becomes lower,only 850℃ under 100%load,and the local maximum temperature of the bed exceeds 1000℃,which easily leads to the boiler coking;The coefficient of export excess air is 1.31 and the concentration of CO reaches 0.75%.The combustion in the furnace is incomplete;The temperature of the main steam at the outlet of the boiler is low so that the boiler output is insufficient.It is 9.8℃,14.5℃,and 19.1℃ less than that of main steam of the designed coal respectively under the load of 100%,75%,and 50%.Therefore,the adaptability of the boiler to low-load lignite has a poorer adaptability.When the temperature of the exhausting gas increases,it is about 10℃ higher than that of the designed coal under these three loads,which reduces the efficiency of the boiler.In terms of the problems existing in the boiler-burning of lignite,the heating surface of the boiler was adjusted and reconstructed.In the furnace,a refractory castable was added to reduce the heated area of the water wall by about 60m2;The high temperature superheater of three pipe rings was adopted to improve the heated area by 13 6.2 m2.When the air preheater was kept unmoved,its upper and lower area was added by 371 m2 and 689m2 respectively.Through the verificaton of the boiler reform,the adaptability of the boiler after the lignite is burned has been improved.