Steam Separation Increases Quality for Your Fluid System

Three different designs remove water from vapour for better performance

The Baffle-Type Separator, Centrifugal Separator, and Mechanical Coalescing Separator.

The efficiency of any steam system depends largely on the quality of the steam that's delivered to the process equipment. The goal is 100 percent vapour and no liquid, also known as saturated steam. Anything less can cause problems. In a steam turbine, for example, moisture will erode the internal parts. In heat-transfer units, entrained moisture will increase the condensate film on the heat-transfer surface, which can reduce heat-transfer performance efficiency by 14 percent or more.

If a steam system is properly designed, specified, installed, operated, and maintained, it should operate with steam at or close to 100 percent. Proper steam velocities will allow the moisture to drop out of the steam vapour to the bottom of the pipe, where a drip leg steam trap station can remove it. But not every system can always operate under ideal conditions. That's the time to use a steam separator, sometimes called a moisture separator. 

A steam separator takes advantage of the inertia difference between condensate (liquid) and steam (vapour). They do that by creating a pressure drop across the device. The design of the separator determines the amount of pressure drop.

Three types

There are three basic types of steam separators: baffle, centrifugal and mechanical coalescence. Often, a combination of two different types of separators is used to achieve higher efficiencies.

The baffle-type separator consists of one or more internal baffles that redirect the steam in one or more different directions. This allows the heavier condensate droplets to be removed by a control valve or steam trap station. This is the simplest separator to design and manufacture, but it also is the least efficient.

A centrifugal separator, as the name implies, uses centrifugal force to separate the condensate from the vapour. The steam is directed into a steam-flow pattern resembling a spinning cyclone. The heavier condensate is expelled to the wall of the separator then drained by gravity to the condensate collection point. The steam pressure drop across this type of separator tends to be larger than in the other types because the velocity required for operation is larger. Less centrifugal action will decrease its performance. It's especially important, therefore, to determine the effect a pressure drop might have on the rest of the system.

The mechanical coalescing steam separator uses a two-stage process. In the first stage, the steam is introduced to a stainless steel mesh that makes the steam flow change directions. Fine water particles combine (increasing their size and mass), fall by gravity to the bottom of the separator, and are removed through a drain device. Any droplets that are not removed are directed to a second, centrifugal stage. In the second stage, deflector blades separate all the condensate droplets from the steam flow and on to a drain. The mechanical coalescing separator is usually the preferred design because it is not flow dependent and has a high efficiency factor. Also, it has a relatively low pressure drop compared to the other two designs.

You can read more detailed information about steam separators online, courtesy of Swagelok Energy Advisors. Then give Edmonton Valve and Fitting a call to discuss how we can help you get the setup that's best for your system.