Safety Calculation and Analysis of Water Wall for a 700 MW Ultra-Supercritical Circulating Fluidized Bed Boiler Without External Bed After Power Failure

By analyzing the change laws of flue gas temperature, steam temperature and working fluid mass flow during a power failure accident in a 660 MW power plant, the change laws of heat load in dense phase zone, transition zone and dilute phase zone over time were obtained. On this basis, a 700 MW ultra-supercritical circulating fluidized bed (CFB) boiler was taken as the research object, the calculation model of flow and heat transfer in water wall after power failure accident was established, and a calculation program for the transient characteristics of the water wall was developed based on the Fortran language. The dense phase zone, transition zone and dilute phase zone were analyzed, respectively. Through calculation, the change laws of the thermal parameters such as water wall metal temperature and working fluid temperature after power failure accident were obtained. The calculation results show that, after the power failure accident, the maximum water wall metal temperature at the outlet of dense phase zone is 558.6 ℃, and the maximum water wall metal temperature at the outlet of dilute phase zone is 579.6 ℃. Therefore, there is no need to equip emergency water supply pump to ensure the safety of the water wall after power failure. The research results can provide guidance for power plants to deal with power failure accidents of ultra-supercritical CFB boilers.