TYPES OF MOISTURE SEPARATOR

1. Baffle Type

Baffle type also called plate type or vane type separator and is made up of a series of plates arranged at various intervals in the flow path. When steam enters the baffle type separator it strikes the baffles and as a result, there is a change in momentum (Momentum = mass X velocity). Both steam and entrained water particles have the same velocity but different mass. The change in momentum for water particles is higher than for steam particles. This difference in the momentum of water particles results in the separation. 

Typical separation efficiency is 98% for steam with a dryness fraction of 90% plus. This is assuming a maximum 30% fluctuation in steam flow rate.

 

2. Cyclonic type

This type uses centrifugal force to separate the water droplets. The cyclonic type consists of guide vanes at the entry which creates high-velocity swirls or spins the steam around the separator and separates the water from steam. The efficiency of the separator is very sensitive to change in steam flow rates. The sizing of the separator is also very critical. Oversizing results in poor separation efficiency and under-sizing results in high-pressure drop. The pressure drop across the cyclone separator is higher than the baffle type by about 50 to 40%. Erosion problems are common with cyclonic separators hence not recommended for very wet steam (Dryness< 80%).

 

3. Coalescence Type

This type of separator is equipped with a demister pad. This is typically a wire mesh pad that traps the water molecules. The molecules of water combine to form large droplets, which are collected at the bottom of the separator. Separators with coalescence type combined with cyclone type are also used. These have greater efficiency as compared to both baffle and cyclone types. Coalescence separators are expensive and need frequent maintenance for the demister pad. Also have considerably high-pressure drop. Insulation on the separator is important, if the surface of the separator is not insulated, water droplets will be formed as a greater area is exposed to ambient temperature. Insulation jackets reduce heat loss thus saving energy. It is, therefore, necessary to use jackets that are designed for a particular type of separator. Improper design of the jacket reduces the insulation efficiency.