Study On Mechanical Characteristics Of Steam Seal Of Ultra Supercritical Steam Turbine High Pressure Cylinder

With the increase of environmental protection pressure in China,energy efficiency requirements have been continuously improved.The supercritical and supercritical steam parameters are used to improve the heat cycle efficiency of the coal-fired units,advanced steam seals are adopted and steam seal gap is reduced to improve the relative internal efficiency of steam turbines.The problems of high pressure rotor vibration and bearing bush temperature deteriorating with the increase of load occurred in many units after the reformation of the flow passage section of new and existing supercritical and ultra supercritical steam turbines,which endanger the operation safety of units and cause huge economic losses.The force exerted by steam seal on rotor is the main factor causing the problem.It is of great significance to study the relevant influencing factors for solving the above problems.In this paper,the blade top seal of a small diameter,multi-stage and dense-teeth type of N660-25/600/600 ultra-supercritical steam turbine is studied.Based on the Fluent,the Computational Fluid Dynamics simulation platform,a three-dimensional flow field calculation model was established to study the mechanical characteristics of high-pressure rotor.The results show that the eccentricity of the rotor in the seal is the main factor for the steam to exert force on the rotor.The pressure circumferential asymmetry of the rotor in the seal is caused by the rotation of the rotor,and the steam force is also produced on the rotor.In the coordinate system with the minimum clearance pointing to the maximum clearance,the steam force produced by the rotor eccentricity is mainly longitudinal component,and changes little with the rotational speed.The circumferential pressure distribution of the steam seal produced by the rotor rotation is asymmetrical,and the steam force is mainly transverse,which varies greatly with the rotational speed.The force of the steam on the rotor increases with the increase of eccentricity and speed.Under the same eccentricity,the force of the steam on the rotor increases with the decrease of the gap between the seals.The force of the steam on the rotor increases with the increase of the pressure difference between the front and behind of the steam seal.The high pressure cylinder has high steam pressure and large pressure difference before and after the steam seal,so the high pressure rotor suffers much more steam sealing force than the middle and low pressure rotor.With the reduction of unit load,the pressure in the flow passage part and the pressure difference before and after the steam seal decreases,so the steam pressure on the rotor decreases with the reduction of unit load.Reducing the gap of the steam seal can effectively improve the efficiency of the flow passage of the turbine.In addition to the risk of dynamic and static friction of the rotor,there is also a risk that the seal steam will increase the force of the rotor.When the bearing is not strong enough to restrain the rotor,it may cause the rotor vibration and bearing block temperature problems.Therefore,reducing the eccentricity of the rotor in the seal and rationally allocating the seal clearance are the main measures to reduce and control the seal force.