Thermal Stress Analysis Of Boiler Drum

With the increasing of the power system scale and capacity of our country, the interval between the peak value and the valley value of the electricity net increases. In the meantime, because hydropower, wind power and solar power belong to renewable energy, they should not be abandoned in the process of load regulation. So thermal power units should play a significant role in the process of load regulation. Peak load units change load, start and stop frequently to meet load requirements, so boiler drum will endure alternate stresses. Therefore, to research into the stresses state of boiler drum is of great significance.Firstly, pre-processor of ANSYS builds a complete finite element model of the boiler drum, which is based on the actual boiler drum structure size. The problems about the length of downcomer and grid precision have many effects on calculation results by finite element method is discussed.Secondly, an analytical method for calculating the temperature distribution and stresses of boiler drum in the steady state and a method to load the circumferential temperature difference of boiler drum are described. It compared the results of analytical method and the results of ANSYS. For mechanical stress, and the thermal stress that is caused by radial temperature difference, the results obtained with both methods are approximate. For the thermal stress that is caused by circumferential temperature difference, the result obtained with the analytical method is much larger, and stress characters of the boiler drum obtained with the analytical method is wrong. The thermal stress value that is caused by circumferential temperature difference is one-seventh its value of the thermal stress value that is caused by circumferential temperature difference and one over thirty-four as much as mechanical stress. The influences of heat transfer coefficient on the circumferential and radial temperature difference are analyzed.Meanwhile, it introduces solutions of the temperature field and the stresses field in ANSYS. A hot start-up curve that gets from operation rules and some hot start-up and stop curves are used as the boundary conditions in calculating the transient temperature field and the stresses field of boiler drum. The distributions of stresses field in boiler drum are analyzed, and maximum stress positions of stresses are presented. Suggest that it should be comprehensive to consider the pressure, circumferential and radial temperature difference to limit the hot start-up and stop speeds of boiler. If this this theory can be utilized in practical production, will vastly improve the operating flexibility of boiler and influence greatly the safe and economic operation performance of peak load units.Finally, based on the ANSYS transient analysis calculation results and the design fatigue curve in UK BS5500, the calculation of the low circle fatigue life of the drum is conducted.