Thermal Stress Analysis Of The Water Wall In A Supercritical "W" Flame Boiler

Since it is difficult to change the central character coal plays in the field of energy,and solve such problems as the waste of resources and environment pollutions caused byconsuming coal in next coming years in China, the coal-fired power generation needs tobe significantly reduced in coal and water consumption. Supercritical units are a realisticand feasible option for its advantage of energy-saving and environmental protection. Thelack of a constant temperature zone, formed by boiling heat transfer, may easily intrigueproblems as heat transfer deterioration, hydrodynamic instability, overlarge thermaldeviation etc., which will cause the stress damage or fatigue damage. Therefore theresearch is indispensable for common problems issued before.In this paper, a numerical analysis of the tensile failure on the water wall of theupper-furnace front wall in a W-type supercritical boiler in a power plant was investigatedby using Finite Element Method(FEM). Heat transfer and elastic mechanics system of thewater wall is developed, and the fixed solution conditions of the equations are analyzed,determining that the heat transfer boundary conditions are intra-pipe convection andextra-pipe heat flux and the elastic mechanics boundary conditions are intra-pipe pressureand corresponding displacement constraints. Numerical simulation of temperaturedistribution and thermal stress of the water wall is performed using ANSYS, and results ofdifferent models are obtained. The2-D temperature distribution and thermal stressdistribution on the cross-sections of the finned tubes under supercritical and near-criticalconditions are calculated, thus proving that the thermal stress of the tube is under theallowable stress of the tube material when the intra-pipe working medium is undersupercritical condition, while it does not exceed failure limit under near-critical condition.The results of3-D calculation in the2×2m domain demonstrate that the boundaryconstraint plays a decisive role in the determination of the maxima and distribution ofstress. The results of3-D computation on the whole water wall show that the denser thecomputational grids are, the better the agreement of the results and the practical thermalstress caused by temperature difference during will be, and that when fewer constraintsexist, the stress centers on the constraints while in other areas the thermal stress is much smaller. Moreover, the impact of different parameters is analyzed, thus generating severalmethods of optimizing the tube panel stress. And lastly, suggestions for future work aboutthe problems that appear in simulation are given.