Numerical Analysis of the Coupling between Heat Transfer and Deformation in Rotary Air Preheater

Abstract

The rotary air preheater is one of the leading heat exchangers to be employed in steam power plants. However, thermal stress induced deformation of the rotor significantly decreases the efficiency of preheating system. The countercurrent arrangement of hot flue gas and cold air is the direct cause of greater temperature difference across the rotor, which leads to a mushroom deformation, and then serious problems of air leakage and mechanical friction. In this study, a numerical investigation was newly performed by the analysis modules of Fluid Flow (FLUENT) and Static Structural through ANSYS Workbench to couple heat transfer and thermal stress deformation in the rotary air preheater. Porous media method along with the local non-equilibrium thermal model was adopted to accurately obtain the temperature distributions of both matrix and gas. Good agreements were yielded by comparing the simulation results and experimental data. The effects of operational and structural parameters, i.e., the temperature difference between the hot and the cold ends, the rotation angle, the height, and the radius on thermal deformation behavior of the entire rotor were investigated in detail. The droopy deformation at the hot and the cold ends increases with the temperature difference and radius, whereas increasing the height of rotor has the opposite influence. With the rotation of matrix, the maximum droopy deformation is located at the entrance of flue gas section and the minimum occurs when reaching the air section. Furthermore, a series of formulas were presented with nonlinear curve fitting to evaluate the deformation amount, which were proved to be of excellent accuracy and can be a better guidance for the seal system of the preheater.