Thermomechanical stress analysis and fatigue lifetime evaluation of coal-fired boiler components during peak shaving transient processes: Effects of load cycling rate

The operational flexibility of coal-fired power plants has become a critical concern, but it leads to heightened fatigue damage and reduced operational lifetime as the load cycling rate increases. This study mainly focuses on the fatigue lifetime evaluation of main components within the boiler. Based on the dynamic model of the coal-fired power plants via GSE software, the dynamic characteristics of main thermodynamic parameters within the boiler under different load cycling rates are obtained. Additionally, the equivalent thermomechanical stresses by using the finite difference method are calculated and the fatigue lifetimes in accordance with the ASME design fatigue evaluation code of main components within the boiler are evaluated. It turns out that the maximum load cycling rate is 3.0 % Pe min⁻¹ for the loading up and down processes between 50 % THA and 75 % THA. Moreover, during the loading up process, the panel superheater exhibits the highest equivalent thermomechanical stress, peaking at 171.22 MPa, and is the component with the lowest allowable number of cycles, merely reaching 19458 at a 3.0 % Pe min⁻¹ load cycling rate. Conversely, during the loading down process, the high temperature superheater exhibits the highest equivalent thermomechanical stress at 145.74 MPa and is also the component with the fewest allowable cycles, amounting to 20182 at a 3.0 % Pe min⁻¹ load cycling rate.