ANS:B - dearation

Dearation, also known as deaeration, is the process of removing dissolved gases from a liquid or vapor, typically from water or steam. The presence of dissolved gases, such as oxygen and carbon dioxide, in liquids or vapors can have adverse effects on various industrial processes and equipment. Dearation is performed to reduce the concentration of these gases to acceptable levels, improving the quality and performance of the liquid or vapor. In the context of water treatment and steam systems, dearation is particularly important. Dissolved gases in water can lead to corrosion, scaling, and other issues in boilers, piping, and other equipment. In steam systems, the presence of non-condensable gases can reduce thermal efficiency and cause damage to turbine blades and other components. There are several methods used for dearation, including:

1. Mechanical Dearation: In this method, water is mechanically agitated to promote the release of dissolved gases. This can be achieved through various means, such as spraying water into a vessel or passing it through packed towers.
2. Chemical Dearation: Chemical agents, such as oxygen scavengers or reducing agents, can be added to the water to chemically react with dissolved gases and remove them from solution.
3. Vacuum Dearation: In vacuum dearation, water is heated under vacuum conditions, which lowers the partial pressure of dissolved gases and promotes their release from the water. The released gases are then removed using a vacuum pump.
4. Membrane Dearation: Membrane technologies, such as reverse osmosis or membrane contactors, can be used to selectively remove dissolved gases from water or steam.