Research On Optimization Of Cold End Heat Storage Element Of Rotary Air Preheater

As an important auxiliary device in large boiler thermal systems,rotary air preheaters are widely used because of their compact structure,corrosion resistance and low operating costs.The heat storage element is an important part of the rotary air preheater,which is used to store the heat in the flue gas and increase the inlet temperature.It is particularly critical to improve the surface heat transfer efficiency of the heat storage element.The study of rotary air preheater rotor temperature distribution,thermal deformation and heat transfer characteristics of the thermal storage element,and optimization of the corrugated structure of the thermal storage element,is of great significance to improve the heat transfer efficiency of rotary air preheaters.Through the empirical design formula and boiler flue gas parameters,a finite element model of the rotor of rotary air preheater is established and the rotor temperature distribution is obtained.Based on the thermo-fluid-solid coupling method,combined with multiple reference systems and porous media model,the rotor internal temperature distribution at different rotational speeds is analyzed to obtain the rotor thermal deformation law at different rotational speeds as well as the flue gas and air temperature distribution law at the rotor outlet.Combined with the temperature distribution in the low temperature section of the rotor,numerical simulations are carried out on a conventional NF plate type thermal storage element to obtain the air temperature,velocity and surface pressure distribution at the outlet of the thermal storage element.Based on different Reynolds number conditions in the air medium,the variation patterns of surface convective heat transfer coefficient,Nussle number and drag coefficient of the thermal storage element are calculated.In combination with the discrete phase model,numerical simulations are carried out for spherical soot particles with ash accumulation sizes from 1 to 100μm based on the Eulerian-La Grange bi-directional coupling method to obtain the variation patterns of ash accumulation concentration and particle mass flow rate of the ash accumulation particles in the channel of the thermal storage element.Based on the study of the heat transfer characteristics of conventional NF plate type thermal storage elements,a CU corrugated plate type thermal storage element with flow disturbance effect is proposed,and the heat transfer characteristics of the thermal storage element are analyzed for corrugation inclination angles of 10° to 65°.The heat transfer and resistance characteristics of the CU corrugated plate heat storage element under different working conditions are analyzed by combining the Nussle number,convective heat transfer coefficient and resistance coefficient,and the heat transfer and resistance characteristics of the element are obtained under the corrugation inclination angle of 20°,25° and 30°.The heat transfer and fluid resistance characteristics of three types of corrugated elements with a corrugation gap of 3.5 to 6mm were studied separately,and the optimal heat transfer and fluid resistance characteristics were obtained for a corrugation angle of 20° and a corrugation gap of 4.5mm.Numerical simulations of the particle characteristics of the optimized accumulation element were carried out to obtain the flow time and particle velocity distribution of the accumulated particles in the accumulation element,as well as the particle concentration and particle deposition characteristics of the accumulated particles under bi-directional coupling.The results of the study provide a theoretical basis for the optimization of the thermal storage element of rotary air preheaters.