Process Description of Dissolved Air Flotation
May 15,2023Read More
Steam generated by water boilers is used in a wide range of industrial applications. Unlike most other industrial fluids, steam has special characteristics that make it difficult to control with valves. If you are using valves as a process control tool, there are several considerations when dealing with steam.
1. Forgetting about steam condensation
Everyone knows that steam condenses, but this obvious feature is often forgotten when discussing process control of steam lines.
However, steam lines do not always run continuously, so cooling and condensation can occur. And the presence of condensate can result in a significant reduction in volume. While steam traps can effectively handle condensing steam, valve operation on steam lines must be designed to handle liquid water, often in a mixture of liquid and gaseous forms.
2. Operation beyond the valve's design
Valves designed for steam applications must be operated under design conditions of pressure and temperature. Steam can expand rapidly to very large volumes. A 20K rise in temperature can double the pressure of a valve that may not be designed for that pressure. The design of the valve must take into account the worst-case scenario (maximum pressure and temperature) in the system.
3. Using the wrong type of valve
A common mistake in the specification and selection of valves is the use of the wrong type of valve for steam applications. Most types of valves can be used in steam systems. However, they offer different functions and controls. A ball valve or a gate valve can provide precise flow control, which is more likely than a butterfly valve. This difference is critical in steam applications due to the high flow rates. Other common types of valves used in steam applications are gate valves and diaphragm valves.
4. Failure to estimate the pressure drop
Before you select a valve for a steam application, take some time to estimate the expected pressure drop across the valve.
5. Ignoring noise levels
Although it is cost-effective and tempting to use smaller valves, especially if they are adequate, they are unfortunately prone to noise. They are also associated with vibration, which can reduce the life of valves and pipe fittings. Consider using larger valves than required to manage noise and vibration.
The design of steam valves and their processes can be tricky. Specifications for dealing with volume differences between water and steam, condensate, water hammer, and noise can be confusing. Many people make these common mistakes when designing steam systems, especially on the first attempt. After all, making mistakes is a natural part of learning.
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