Application Of Steam Mode Of Sequential Valve In 880MW Steam Turbine Unit Made In Russia

In North and northwest of China,a large number of steam turbine generator were running.Among them,880 MW steam turbines,because of their high operating parameters,imbalanced regulating gradation and large steam flow force,often have problems such as high tile temperature and severe vibration,which lead to the damage of steam turbines and even safety accidents.Therefore,in actual production practice,considering the safety and economy of the unit operation,the steam turbine unit usually operates under the sequential valve mode.This operation mode(throttle regulation mode)will cause greater throttle loss of the control valve,and seriously affect the economy and safety of the unit while regulating load.Because of the difference between the steam turbine unit in the manufacturing process and the field installation process,this deviation will lead to a large deviation between the actual valve flow characteristic curve and the valve flow characteristic curve set in DEH system.This kind of deviation may cause the difficulty of unit regulation and control when the unit changes load and primary frequency regulation,and affect the variable load capacity and safety of the unit.Therefore,whether from the point of view of improving the safety and economy of unit operation,or from the point of view of easy control of unit,it is necessary to optimize the valve management system and steam distribution law of unit.In this paper,the valve management technology and steam distribution law are optimized to solve the problem of excessive temperature during the operation of sequential valves in 880 MW units.Firstly,the extreme load conditions of half cylinder intake are analyzed,and the main factors affecting the safety and economy of steam turbine operation are obtained.Then,the steam distribution transformation of the valve management system is carried out,and the theoretical basis of valve management optimization is obtained by calculating the variable operating conditions of the regulating stage.The overall optimization of the valve opening sequence and nozzle group is carried out,and the appropriate overlap degree of the valve opening is set.The valve flow is identified by the flow characteristic identification software of the valve,and the optimization goal is achieved by modifying the DEH program online.After that,the valve sequential switch test and the new rule sequential valve load test are carried out respectively.Through comparative analysis and the test data before and after the transformation,the following three essential conclusions are drawn in this paper:(1)The analysis of the extreme stress of the steam turbine unit shows that the excess of the temperature is an important problem affecting the safe operation of the steam turbine unit.(2)Through comprehensive analysis of steam distribution scheme of steam turbine unit,it is concluded that the double diagonal intake scheme is the best one,which shows that the main steam pressure and temperature are relatively constant,and the temperature does not fluctuate greatly.Therefore,the double diagonal intake scheme is chosen to continue the research.(3)Valve management system is used to optimize the dual-diagonal intake scheme.After the optimization of steam distribution,the efficiency of high-pressure cylinder is obviously improved,and the temperature is equivalent to that of single valve,which improves the variable load performance of the unit as a whole.