6 Applications of Throttling Valves
Throttling valves are specialized valves that facilities can use to regulate/control flow. They are typically globe-style designs, allowing for the control of flow through the valve sealing surfaces. Single seated, globe-type valves provide for uniform wear on the seat and disc. Throttling valves are used in various applications, including feedwater by-pass applications, blowdown applications, and more.
Throttling Valve Applications
Some of the most common applications for throttling valves include:
When generating steam to produce power, blowdown is an important step that involves modulating the flow rate of water flashing to steam. It is not uncommon for power plants to utilize standard globe valves for blowdown applications. However, the harsh conditions found in this type of setting, particularly in continuous blowdown and intermittent blowdown, generally exceed the capabilities of these valves.
Continuous blowdown valves remove dissolved solids from the boiler feedwater. The valve must be able to handle continuous flashing service 24/7 and then shut tight when required. Intermittent blowdown valves are used to rapidly blowdown the HP/IP drum to control swell during firing, in duct burners, and when ramping up. Traditionally this is a standard globe or metal seated ball valve.
Due to the flashing service, this is a great application for a Conval throttling valve. In regions where plants have frequent starts and stops, they could use their intermittent blowdowns 2-3 times per day 200+ days a year. Operators can use throttling valves to keep the facilities running cost-effectively and efficiently.
Total Dissolved Solids Steam Drum Applications
When suspended solids begin to build up within a boiler, it negatively impacts heat transfer. As these solids begin to dissolve, boiler water may start foaming and become incorporated into the steam. Throttling valves help prevent these issues by controlling the flow of water as it is periodically discharged from the boiler. These regular discharges ultimately reduce the overall levels of total dissolved solids within the boiler water.
Power Plant Quick Start/Warm Up Applications
When starting a cold Heat Recovery Steam Generator (HRSG), the drums will have no pressure. To fill the drums, the plant will use their HP/IP/LP level valves, which are normally cage-guided control valves. This application typically requires a full-ported valve with an equal percentage trim. This type of cage struggles to handle the high pressure drop of a cold start when there is no pressure on the outlet of the valve. An alternative is to install a parallel Conval throttling valve as a sacrificial valve to take the high pressure drop as the drum fills.
Feedwater By-Pass Applications
Throttling valves play an important role in extending the lifespan of the cage trim within feedwater regulator valves. Without the use of a throttling valve, feedwater impacts the cage trim at a high velocity whenever the regulator valve opens. Over time, this repeated exposure to high-velocity water can damage the cage trim. To avoid this, throttling valves can bypass the initial burst of feedwater until the regulator valve opens. After it has opened to approximately 20%, the regulator valve can take over without the risk of exposure to high-velocity water.
Boiler Feedpump Warm-Up
Prior to starting up the boiler feedpumps, throttling valves are utilized to flow hot water through the warming loop on the pump in order to maintain the case temperature. This reduces the thermal shock during start-up.
Hydro-Cracker Effluent Sampling Applications
Valves in this type of application have an SS316 yoke and are composed of SS347. These valves are often made from non-standard materials, including Ultimet, Nitronic 50, and Nitronic 60.
Throttling Valves From Conval, Inc.
Since 1967, Conval, Inc. has been manufacturing industry-leading forged steel valves. We are dedicated to creating durable, high-performance valves that can operate dependably even in high-pressure, high-temperature applications. Our throttling valves offer repeatable flow control, with the best shutoff in the industry. To find out how we can meet your throttling valve needs, contact us today.