Saturated steam is typically moving through a steam system at 20-30 metres / second. Any water or particulate matter entrained in it is incompressible, which can lead to steam hammer and a reduction in the efficiency of heat transfer.
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Steam Separators Explained
Moisture particles can occur from carry over of water from the boiler, as well as when the steam gives up its useful heat in flowing through a pipe system. The steam generating plant may also be subject to overloading, which can contribute to carryover and priming. Poor water treatment can also lead to a stable foam layer building up on the boiler water surface, which may then be carried over into the steam distribution system. Additionally, where a steam main passes outside a building, additional moisture may be formed by being in a cooler ambient temperature. This can affect valves, heat exchangers and other plant in the system.
Steam separators are used to remove these entrained particles and moisture from the system to maintain the dry saturated quality required, minimise erosion and reduce the risk of steam hammer.
What are Steam Separators?
These are generally line sized pieces of equipment, which cause a change in velocity allowing the heavier moisture particles to drop out of suspension. The moisture can be in the form of water droplets, a mist, or small solid particles. Depending on the efficiency of the separator the aim is to create steam with a dryness fraction of 1.
There are several different types of steam separators, but all in some way cause the moisture particles to come out of suspension and then to be removed by a steam trap. It is important to consider, that a percentage of the steam mass flow will be lost from the system as condensate and that a pressure drop will occur through the body. This can be significant on long steam runs.
Different Types of Steam Separator
Baffle Type Separators
Baffle type separators use several plates to cause the wet steam to change direction. The water droplets being heavier and settle on the plates and fall to the bottom of the separator, where they are removed by a steam trap.
Baffle type separators tend to have a large volume and the velocity of the steam in the chamber is lower than that in the supply pipe. This makes them efficient at a wide rage of velocities and best suited to steam systems.
Coalescing separators use a de-mister section, such as a wire wool pad. The wet steam passes through this with the heavier water particles getting trapped in this pad and dry steam passing through to the outlet. The moisture falls to the bottom of the chamber and is removed by a steam trap.
Centrifugal separators use a series of plates to cause the steam to increase velocity. This results in the heavier moisture particles being flung to the outer wall of the velocity, where they run down the wall and are removed by a steam trap.
Steam Separator Maintenance
Steam Separators are generally installed vertically in line and can be either horizontal long units or vertical tall units. When installing steam separators, you must consider the space available above and below. The units must be installed with a steam trap to remove the high temperature water condensate. The most suitable type of trap is generally the ball float type trap, which removes condensate as it forms. Sizing this trap requires some deliberation and it is best to seek the guidance of a steam system specialist.
The separators are generally large vessels and should be insulated, to ensure moisture does not form in the vessel.
Large steam separators can have a sizeable volume to make them inspectable under a Written Scheme of Examination. Therefore, they may need to be included in the list of inspectable plant and you should consider access to them for this purpose.
If you have problems with steam quality or would like to discuss the use of steam separators on your plant in more detail, please call Valveforce on 0121 711 1908, where our team of steam system specialists will be pleased to help.
Steam Separator Benefits
The major benefits of fitting steam separators is:
- They removed water particles in suspension that a filter does not remove.
- Water particles moving at high velocities can cause erosion on pipe bends and lead to steam- hammer, which can be very dangerous.
- A water film inside pipework and on heat transfer surfaces, reduces overall heat transfer efficiency, and leads to greater energy consumption and higher fuel bills.