Stress Analysis Of Supercharged Boiler Drum By Finite Element Method

Marine supercharged boiler uses the compressor of turbocharger unit instead of blower of turbine to transport air with a certain temperature and pressure to the furnace of boiler. Drum is the important pressure component in the boiler, which connects the rise and fall pipes and composes a natural loop, at the same time, accepts the supply water from the economizer, also transports saturated steam to the super heater, which is the connection point of heating, evaporation and overheating. Drum operating conditions are very complicated, not only have to bear a higher internal pressure, but also endure start-stop when it is cold and warm, and endure mechanical stress and thermal stress when load changes, which often leads to fatigue failure. Therefore, develop the analysis of boiler drum, get the change law when drum starts and runs steadily, which can supply some theoretical support for the optimal start plan, theoretical and practical significance are great.Found a three-dimensional model for a supercharged boiler drum hole using ANSYS, make the three-dimensional finite element simulating and analyzing of the pressure stress, thermal stress and the total stress distribution of drum. Get the steady-state pressure when it is 6.5 MPa, as well as the transient stress when the pressure changes from atmospheric pressure to 6.5 MPa, the steady-state thermal stress when the temperature difference between the upper and lower wall of drum is 52℃and 78℃, the transient thermal stress when the temperature varying from room temperature to the two conditions. Finally, calculate the pressure and the total steady-state of different temperature and the total transient stress of different conditions. Drum stress concentration situation is gained, and according to stress values and material properties make a strength assessment for drum, which provides evidence for safe operation and design of drum.Simulation results show that the greatest stress of this kind boiler is the interior point along the axial section of drum hole (which is commonly known as A), which is proportional to the pressure value. The thermal stress distribution is relatively complex, and in the vapor interface is relatively larger, which is proportional to the temperature difference between the upper and lower drum. The total stress is the vector sum of internal pressure stress and thermal stress, at the point A the total stress is smaller than the mechanical stress, which shows that the proper thermal stress can weaken the internal pressure stress in the supercharged boiler, but the stress around the hole becomes big, which demonstrates that the thermal stress has a strengthen effect on the inner pressure. When the temperature difference is larger than 300℃, because of the growing of thermal stress, the role of weakening is small, but the role of superposition becomes obvious, there will be dangerous. Especially, the shorter the boiler start time is, the larger the stress value is.