A Study On Leakage And Sealing Of Rotary Air Preheater

The rotary air preheater has been widely used in large boiler units because of its characteristic of high heat exchange efficiency,compact structure and low metal consumption.The rotary air preheater,as an important heat exchange equipment of large thermal power unit's boiler heating surface,can adequately absorb the residual heat of flue gas at the end of the boiler,reduce the exhaust gas temperature,raise the temperature of primary air and secondary air,strengthen the combustion in the furnace,and improve the overall efficiency of the boiler unit.But the gap of rotary preheater's running structure,the pressure difference between the air side and the gas side,the thermal deformation of rotor and other factors caused the problem of large volume of leakage in the preheater.The air leakage will directly affect the safe operation of the preheater and reduce the economic benefit of the boiler unit.The main method to solve the air leakage problem of preheater is adopting a certain sealing device to the preheater.Therefore,it has been an attractive subject concerned by engineers and scholars that the research on the principle of air leakage and the the sealing method and sealing efficiency of rotary air preheater.Under the support of the national key special project “660MW high efficiency ultra supercritical circulating fluidized bed boiler unit's efficiency promotion research”,the air leakage and seal problem of rotary air preheater was studied in this paper.The main contents are as follows.In this thesis,the structure and operation principle of tube air preheater and rotary air preheater are firstly introduced.Also,the causes of air leakage in rotary air preheater was analyzed,and two kinds of air leakage types,carried air leakage and direct air leakage were summarized.It was pointed out that the pressure difference between the air side and the gas side and the radial air gap is the main causes of the leakage.This study also introduced the evaluation index of the air leakage in rotary preheater,and put forward main measures to reduce the leakage rate of the rotary preheater.Secondly,aiming at the problem of large radial clearance in preheater's rotor,this paper simulated and calculated the thermal deformation of segmental plate in rotary air preheater's rotor by using ANSYS finite element analysis method,and proved the reliability of finite element analysis method in calculating rotor's thermal deformation.The influence of the preheater's inlet temperature,the height of the segmental plate and the length of the segmental plate on the horizontal and vertical displacement of the hot end,cold end and outer edge of the preheater rotor is investigated.It was found that the leak gap increases with the height and decreases with the radius of rotor.Based on the influence of flue gas temperature and segmental plate size on rotor deformation,the empirical formula of the clearance size of rotor's cold end and hot end was presented.Finally,aiming at the technological characteristics of multiple seal structure which generally used in rotary air preheater,this study simulated the gas flow process of multiple seal by using CFD software.According to the velocity and pressure distribution of the seal cavity,the sealing principle of multiple seals was investigated,and the existence of “air leakage effect” was discovered.The influence of sealing pressure,seal gap size,sealing numbers and other factors on leakage flow and leakage coefficient was investigated.The results showed that reconstructing seal gap is of great benefit in the area with large sealing pressure difference;The more the sealing number,the lower the reform income;The sealing number suitable for large circulating fluidized bed units are Z=2 or Z=3.Then proposed a new seal method,fork seal combined with multiple seal.The numerical calculation results showed that the sealing mode of triple seal plus triple fork seal can reduce at least 40% of air leakage,which provided standard for the sealing modification in engineering,and would have certain practical value for the improvement of the efficiency of the preheater and boiler unit.