Author(s)

A. Zaryankin, N. Rogalev, A. Rogalev, E. Oleynikova, E. Grigoriev

Abstract

Control valves are immediate regulating devices in control systems of steam turbines. As of now, high aerodynamic drag and low dynamic reliability are the most notorious operational shortcomings of control valves. This paper surveys newly developed control valve designs ensuring high reliability and economy of steam turbine control components. Findings from simulation studies are presented. Our studies involved mathematical and physical simulation of new valve designs and were concerned with determining their flow-rate, force and vibration behavior. Several proposals for improving valve reliability and economy have been put forward. Among them, the greatest efficiency is promised by new layouts of steam-actuated valving and the use of finned wide-angle diffusers with cylindrical entry sections downstream of valve seats. Compared to known designs, nextgeneration balanced valves feature structural changes: shaped axially symmetrical confusor duct, enveloping surface of the spool and inlet section of the diffuser seat featuring perforation bands that open into a common dampening chamber offset toward the interior of the actuator (spool), an axial force balancing system that is disengaged automatically when the spool is lifted higher than 50% of its travel range, the use of longitudinally finned wide-angle valve diffusers, and a cylindrical section added downstream of the seat confusor section to improve flow uniformity upstream of the tapered diffuser. The designs make it possible to decrease almost 20% of hydraulic resistance inherent in control valves. The increase in efficiency of electric power production is followed by a decrease in specific fuel consumption in a power plant by about 0.2%. As a result, emission of carbon dioxide in the atmosphere decreases significantly.

Keywords

steam turbine, control valve, diffuser, pressure pulsations, vibration, throttling, steam-actuated valving