Research On The Windage Condition And Cooling Safety Of The Flow Passage Of The Low-Pressure Cylinder Of Zero-Output Operation Steam Turbine

In the context of "carbon peaking and carbon neutrality",new energy is being massively connected to the grid.However,due to the intermittency,randomness,and instability of new energy,the operation mode of the traditional thermal power generation industry must undergo adaptive changes,and its role in the power system must shift from carrying basic loads to deep peak shaving.Therefore,improving the flexibility of coal-fired power units is the trend.The zero-output operation of the low-pressure cylinder is to cut off all the inlet steam of the lowpressure cylinder for heating,and at the same time,introduce a small amount of cooling steam to take away the heat of the windage and reduce the temperature of the flow passage.The zerooutput operation of the low-pressure cylinder can not only increase the heating load of the unit,but also enhance the peak shaving capacity of the unit.However,it seriously deviates from the design operating conditions,leading to a series of safety issues in the flow passage of the lowpressure cylinder.This paper adopts research methods such as numerical calculation,field testing,and theoretical analysis to systematically study the windage conditions and cooling safety of the low-pressure cylinder flow passage at extremely low flow rates for a 300MW low pressure cylinder zero-output operating unit.The numerical calculation model for the flow passage of the low-pressure cylinder and the flutter calculation model for the final stage blade and the thermal coupling unsteady calculation model for the low-pressure cylinder rotor are constructed.Based on the physical model of the blades and channels in the flow passage of the low-pressure cylinder of a steam turbine,a numerical calculation model for the flow passage of the lowpressure cylinder and a thermal coupling unsteady calculation model for the low-pressure cylinder rotor were constructed.The windage condition and the cooling safety during the entering and exiting process of the zero-output operation of the low-pressure cylinder unit.The main content is as follows:(1)Based on numerical calculation of flow,the development process of the windage state in the low-pressure cylinder was studied based on the changes in steam flow distribution,pressure distribution,and temperature distribution under different operating conditions.It was concluded that the windage state first appears at the top of the final stage and gradually developed forward.(2)The sensitivity of steam thermodynamic parameters to changes in windage state is analyzed,the calculation results showed that among the three parameters of pressure,temperature,and total enthalpy at the top of the rotor blades,the total enthalpy has the earliest response to the change in flow rate.The paper proposed a method to determine the windage state using the total enthalpy ratio.(3)The last stage rotor blades of low-pressure cylinder zero-output units face two types of water erosion risks:wet-steam water erosion and last stage spray water erosion.Two indicators,wet steam water erosion risk index Fers and last stage spray water erosion risk index Iers,are defined to evaluate the water erosion of the last stage rotor blades.The Fers gradually increases with the decrease of steam flow rate,but sharply decreases when the steam mass flow rate reaches 20%;Iers is mainly affected by the spray flow rate and particle diameter,and when the spray flow rate is fixed,it first decreases and then rapidly increases with the increase of the spray particle diameter.(4)This paper conducted a study on the amplitude and flutter of the last stage blades of the low-pressure cylinder.The results show that during the reduction of steam flow rate,the amplitude of the last stage rotor blades first increases and then decreases,reaching the maximum value of 4.49mm at 10%steam flow rate.However,the amplitude under zero-output operating conditions of the low-pressure cylinder is 2.19mm,and the amplitude increases with the increase of cooling steam temperature.(5)This paper established a thermodynamic coupled unsteady model of the low-pressure cylinder rotor,and conducted transient calculations on the temperature and thermal stress fields of the rotor starting from different flow rates when cutting the cylinder.At the same time node,the highest temperature and maximum thermal stress of the rotor during cylinder cutting from high flow rate are smaller,and the highest temperature and maximum thermal stress during cylinder cutting with water spraying are smaller than those during cylinder cutting without water spraying.