Finite Element Calculation On Cold Start-up Fatigue Life Of 1025t/h Boiler Drum

With the rapid development of power industry, the peak-valley difference is growing, the task that large-capacity units participates peak shaving is also more and more urgent day by day. During the process of units starting and stopping, boiler drum works under alternating mechanical stress and thermal stress, the varying of the stress will result in low cycle fatigue damage to boiler drum, shorting the service life of boiler drum. Accordingly, cold start-up of different temperature rise rate is studied, transient temperature field and mechanical stress field and total stress field are calculated, studying the life of boiler drum and fuel loss is very significant to boiler in safety and economy running during the process of cold start-up.The thesis takes 1025t/h boiler drum of one power plant as object, in the first place, structure of boiler drum is simplified by applying the finite element theory and the practice experience. 3D solid model of the boiler drum is established in finite element analysis ANSYS software preprocessor and finite element model of boiler drum is established by using mapped grid partition,in addition, the key position vertical section inner corner is refined. In the second place, the transient temperature field, transient thermal stress, transient mechanical stress and transient total stress of the boiler drum are calculated to the cold start-up of different temperature rise rate by exerting constraint condition, thermal and pressure border condition and initial condition, the location of maximum thermal stress is determined, which shows that mechanical stress and pressure is proportional. After cycle stress amplitude of the most dangerous point is determined by using some theory formulas, cycle number can be obtained by using BS5500 design fatigue curve, which shows the key factor of affecting life. At last, the theory formula of the fuel loss is established during the cold start-up, the fuel loss of different temperature rise rate is calculated by using the theory formula, optimal temperature rise of cold start-up is determined by comparing the loss, after calculating life loss of different temperature rise rate. Temperature rise rate-temperature difference, stress-life, temperature rise rate-life and temperature rise rate-loss are obtained, meanwhile, life loss and fuel loss are calculated during the process of cold start-up, then the rational advice is advanced for one cold start-up, which provides valid basis for 1025t/h boiler in safety and economy running, the reference of life damage to boiler drum in other condition is provided, too.