| As an important energy recovery device for boiler equipment,rotary air preheater has many advantages such as small size,low steel consumption and convenient layout,but it also has fatal shortcomings with high air leakage rate.Contact-type flexible sealing is a new type of sealing technology that has recently emerged.In theory,a “zero” gap seal can be realized.However,the load formed by the pressure difference between the two sides of the sealing sheet is not considered in the existing design,and it is difficult to achieve the desired sealing effect.In addition,the inherent structure of the rotary air preheater determines that the contact type flexible sealing device is in a high cycle fatigue working environment at 400 ° C,and it is difficult to ensure a high service life.In view of the above problems,this paper studies a new type of composite flexible sealing device on the market.Through the research on the structure and working principle of the rotary air preheater,it is concluded that the air leakage is mainly caused by direct air leakage.The fundamental of reducing the air leakage rate is to minimize the sealing gap,and the thermal deformation of the rotor is the main cause of the increase in the leakage gap.Through theoretical analysis,the calculation relationship between the flow field pressure difference that the sealing device can withstand and the overall size is derived.The flow field model of the partial rotary air preheater with the sealing device under the most unfavorable working conditions,the fluid-solid coupling model of the flexible sealing device and the surrounding local flow field and the mechanical model of the flexible sealing device were established.Numerical simulation analysis was carried out separately.Through the numerical simulation of the flow field of the partial rotary air preheater,the relationship between the sealing gap and the flow field pressure and the air leakage rate,and the fluctuation curve of the flow field pressure and the air leakage rate during the rotor operation are obtained.The numerical simulation results show that:(1)The pressure distribution of the flow field from the cold end to the hot end,the inlet and outlet to the seal and the secondary seal to the first stage seal has a certain regularity;(2)In order to make the air leakage rate of the rotary air preheater less than 5%,the air leakage gap should be controlled within 3mm.(3)The internal flow field pressure,sealing pressure difference and air leakage rate of the air preheater in the rotor operation will cause certain fluctuations.Based on the calculation results of flow field numerical simulation,the fluid-solid coupling simulation of the sealing plates with different structural parameters was carried out,and the difference between the fluid-solid coupling calculation results and the direct application surface pressure calculation results was compared.The fluid-solid coupling calculation results show that the new sealing piece can withstand the flow field pressure difference of 7300 Pa,but due to the pressure difference of the flow field,the sealing compensation of the sealing piece can only reach about 4mm,which can meet the area of the hot end rotor within 4m.The deformation requirement requires that a hot bimetal self-compensation device be added to the area other than 4m to achieve the desired sealing effect.Finally,in order to objectively evaluate and test the fatigue life and reliability of the new flexible sealing device,the fatigue life test at 400 °C was carried out.According to the test results,the high-temperature fatigue cycle life of the new composite flexible sealing device reached more than 6 million times.The new composite flexible sealing device has good measured installation effect,the air leakage rate is only about 4%,and has a high service life and reliability.The new composite flexible sealing device is not only suitable for 1000 MW boiler units,but also has reference significance for other units of different sizes. |
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