What is the primary purpose of a knockout drum in a natural gas processing plant?

The primary purpose of a knockout drum in a natural gas processing plant is to remove free liquids, such as water and condensate, from a gas stream to protect downstream equipment and prevent operational problems. A knockout drum is a vessel designed to separate liquids from gases using gravity separation. Gas streams often contain entrained liquids, which can cause damage to compressors, pumps, and other equipment. These liquids can also interfere with downstream processes, such as gas dehydration or NGL recovery. The knockout drum is typically located upstream of these sensitive equipment to remove the liquids before they can cause problems. The gas stream enters the knockout drum, where the velocity is reduced, allowing the heavier liquids to settle to the bottom of the vessel due to gravity. The separated liquids are then drained from the bottom of the drum, while the dried gas exits from the top. Knockout drums are designed with sufficient residence time to allow for effective separation of the liquids. They may also include internals, such as baffles or demisters, to enhance the separation process. Regular draining of the liquids from the knockout drum is essential to prevent liquid carryover and ensure effective operation. The size and design of the knockout drum depend on the gas flow rate, the liquid loading, and the desired separation efficiency.