Study On Optimization Of Valve Control Scheme For Supercritical Steam Turbine

With the increasing capacity of power grid and the change of power structure,the frequency and depth of thermal power units participating in peak shaving of power grid are increasing.When the unit participates in the peak shaving of the power grid,the change of its load will aggravate the erosion of(SPE)by solid particles of the regulating stage blade.When the constant pressure operation nozzle is used to adjust the unit,the unbalanced steam flow force will be produced due to the uneven intake of steam in the partial load reduction stage.As the main unit of thermal power generation,the erosion and unbalanced steam flow force of solid particles will be more serious because of its higher steam parameters.For the Supercritical Unit,the steam distribution mode of the regulating stage will directly affect the unbalanced steam flow force.And the flow state of steam is different under different steam distribution modes,which will lead to the erosion of solid particles in the blade.Therefore,it is of great engineering practical significance to explore an optimal valve control scheme to reduce the erosion rate and unbalanced steam flow force of the regulating stage blades.In this paper,a 660 MW supercritical steam turbine in Guizhou area is taken as the research object,and the unit is studied under two modes of compound sliding pressure operation and constant pressure operation.According to the regulation stage valve control mode recommended by the manufacturer,11 kinds of valve control schemes are combined.Eight operating points of 100%,95%,90%,75%,50%,30%,25% and 20% load were taken to calculate the regulating stage loss of each operating point under different valve control schemes.Numerical simulation method is used to study the reduction of node erosion characteristics and unbalanced steam flow force at different valve control schemes.Then considering the effects of erosion rate,unbalanced steam flow force and regulating stage loss,a valve optimization scheme based on these three aspects is proposed.According to the regulating stage blade material of a specific unit and its working environment,some undetermined coefficients and indices in the erosion model are modified.Through the simulation results,it is found that the erosion of solid particles in the regulating stage of steam turbine mainly occurs in the moving blade part.The valve control scheme has a great influence on the erosion rate when the load is between 75%—90% and 20%—25%,but has little effect on the erosion rate at 50% load stage.In the high load stage,the unbalanced steam flow force is small under the diagonal distribution scheme,and different diagonal steam distribution schemes have a great influence on the unbalanced steam flow force,while the adjacent steam distribution valve control scheme has little effect on the unbalanced steam flow force,but the opposite in the low load stage.Finally,considering the effects of solid particle erosion,unbalanced vapor flow force and regulating stage loss,a collaborative optimization scheme is proposed.