Research On The Technology And Optimal Design Of Advanced Steam Seals

Turbine seals are the key elements to reduce steam leakage loss and improve theefficiency of enery conservation. The development of steam turbine brings forward high request of the reliability and economics of modern thermal power plants. Therefore, developing advanced turbine seals, reducing leakage loss and improving thermal efficiency has become the focus of modern thermal plants.Reducing seal clearance can cut down steam leakage loss to a great extent. However, the clearance was limited by quite a few factors during unit startup and shut down, for example, thermal deformation due to temperature difference between stationary and rotating elements of the turbine, the increase of vibration amplitude around critical speed and inaccurate alignment. All these factors leads to the rubbing of seal teeth and the rotor, damaging both stationary and rotational elements, thus reducing seal clearance is limited in engineering application.This article concentrates on reducing the flow coefficient and increasing the service life of turbine seals. After summarizing and analyzing present turbine seal technology, this paper focuses on two aspects. Firstly, under the condition of fixed axial seal length, the structural parameters are optimized by FLUENT including increasing the density of seal teeth, optimizing the shape of teeth and adjusting the height-width ratio of seal grooves. The results of numerical simulation are analyzed combined with the internal flow field of turbine seal. Secondly, in order to deal with the incline of seals and unreliability of springs in the use of variable clearance seal, a mechanical model was established to study the forces on packing segment and the influence of unit load and tilt angle on the force of variable clearance seal were also studied by Fluent. At last, a few suggestions were given in this article.The numerical simulation of labyrinth seal shows some meaningful conclusions. Firstly, both the high-low packing and plain packing can reduce steam leakage loss through increasing the density of seal teeth. Secondly, steam leakage loss can also be reduced by slicing plain teeth tip thin if the slicing direction is right. Thirdly, it's necessary to select the ratio of height and width of seal grooves properly, or the amount of steam leakage will increase. The force analysis and simulation results indicate that the spring used in high pressure cylinder has great stiffness and endures severe forces, thus the spring should be manufactured with high-performance material and the diameter of spring wire should be increased as far as possible. Symmetrical packing segmentents would tilt under the pressure of steam, the moment can be reduced to zero if structural parameters are properly designed. It isn't right that current variable-clearance seal close under low load condition, which can be improved by opening pore in seal body to make turbine seal close under middle and high load condition. Lastly, quite a few suggestions were made to apply variable-clearance seal in low pressure cylinder.The results of this article provide suggestions for turbine seal modification and have some practical value.