A Throttle Control Valve for Steam Turbines Operating with Large Volumetric Flowrates of Working Fluids

Abstract

A new design of a throttle control valve for steam turbines with throttle steam admission and large volumetric steam flowrates is considered. The difficulty associated with using these valves is that increasing the seat dimensions of spools entails a drastic decrease in the relative valve chest free volume for steam passage. This, in turn, results not only in higher hydraulic losses in the steam admission system but also in a higher nonuniformity of steam flow in the flow paths of such valves. Both these factors facilitate generation of very high pulsations of pressure in the valve’s entire flow path, which gives rise to high levels of acoustic emission and dynamic loads acting on all components of the valve, thus degrading its vibration reliability. Along with the proposed valve design, the article considers the design version of standard balanced control valves installed in large-capacity Russian steam turbines. It is shown that the passage of large volumetric steam flowrates through standard valves entails a significant reduction in the free valve chest volume for passing steam. This results in a growth of local steam velocities inside the chest and in a more pronounced negative influence of the chest shape on the valve flowrate and vibration performance. This situation can be improved by using one of the following two ways: to make the chamber with a significantly larger structural volume (which entails a larger cost of making the chamber) or to radically change the valve design. The article considers the second approach to solving the problem. In the proposed design version, the entire valve balancing system is shifted to the valve chest upper part, and the guide bonnet is made with large lateral ports ensuring free passage of steam to the diffuser seat. To achieve a more uniform circumferential field of velocities in the valve flow path, its cup is made with two perforation belts, the holes of which are connected to a common damping chamber, and the chamber itself is connected via a hollow cylinder with the axial force relief system.