Model And Simulation Of Water Wall System For600MW Supercritical Once-through Boiler

Nowadays,600MW,1000MW of supercritical power unit or ultra-supercriticalpower unit are the main form of electricity generation used in our country. Theefficiency of them can reach42%and45%, respectively, which is much higher thansubcritical power unit at the same unit capacity. Although the supercritical power unithas many advantages, due to the lack of knowledge about it and some problems in thedesign and actual operation lead to the less understanding of the dynamic features ofsupercritical power unit well. Therefore, it is very important for us to learn and masterthe technology and operation characteristic of supercritical power unit in order to takeover dynamic features study, running analysis and accident forecast.This thesis takes DG1950/25.4-Ⅱ8supercritical once-through boiler as the studyobject which is designed by Dongfang Boiler Group.The nonlinear lumped parametermoving boundary mathematical method used to build the water-steam system modelwhich is suitable for large disturbance and whole working condition.Under the supercritical condition, water in the pipe directly converts into steamwithout evaporation process and there are no obvious bounds between the water andsteam. After analyzing the character of the working medium under the supercriticalcondition in the pipe, the maximal specific heat at the same pressure is used as thetransition point to divide the whole system into two parts which are similar toundercooling and superheating sections at the subcritical condition.In this thesis, simulation experiments are carried out under the subcritical conditionand supercritical condition respectively with the same external disturbances, andsimulation of the transcritical process from50%to100%load is enforced. The resultshowed that the method proposed in this paper can switch effectively betweensubcritical and supercritical condition, and simplify mathematical model and thecomputation of dynamic nature. Furthermore, the thesis presents the criterion for themethod of distinguishing the water and steam under supercritical condition, which canbe used to solve the problem of phase transition.