Stress And Life Analysis Of Key Pressure Parts Of Boller Under Flexible Operation

With the increasing proportion of new energy installed capacity,such as wind energy and solar energy,the peak-to-valley difference of electric power load is increasing,which brings great pressure to the peak shaving of power grids.It is inevitable that thermal power units will participate in flexible operation.However,during the flexible peaking process of the thermal power unit,the unit is operating at the lowest load for a long time and requires a fast lifting load,which will inevitably increase the stress and life loss of the relevant pressure-bearing components.In this paper,a 600MW supercritical boiler with flexible peaking is taken as the reference boiler.According to the real-time operational data provided by the power plant,the finite element software ANSYS is used to analyze the data and thermal stress of the vertical tube water wall running under the minimum load(180MW)for a long time.The temperature field,thermal stress,mechanical stress and total stress of the final superheater outlet collection header during peak shaving operation with variable load are calculated,and the life loss of the header during peak shaving operation with variable load is analyzed according to the linear cumulative calculation method in ASME Boiler and Pressure Vessel Code.The results showed that the thermal deviation at the outlet of the vertical water wall tube increased with the decrease of the unit load,especially in the front wall and left side wall of the boiler.When the unit operated at 180MW,the thermal deviation could reach 160?.When the unit operated under the minimum load for a long time,the thermal stress at the maximum temperature difference could reach 228 MPa,which exceeded the yield limit of the material and was higher than the allowable stress of the material at the operating temperature for a long time,which was not safe and stable to the water wall.When the boiler peak shaving operation with variable load,the maximum thermal stress,mechanical stress and total stress of the header appeared on the intersecting line between the connecting pipe and the inner wall of the cylinder.According to the stress evaluation,the results of each stress classification did not exceed the limit value,which could ensure the safe operation of the boiler.In the fatigue-creep life analysis,the fatigue life loss of the header in the peak-shaving process was small,and the life loss was mainly derived from the high temperature creep of the material.