Blowdown vessel / Drum

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First some terminology. The term "Blowdown Vessel (or Drum)" is a function. The term "Knock-Out Drum" could also be used for the same vessel and same function.

The Purpose, The purpose of this type of vessel normally is to separate or remove a fluid from a gas or vapor stream.

The name, The name depends on what it is connected to and what the commodity is for "that" function. The commodity could be Steam therefore a Steam Blowdown Drum/Vessel (it could also be called a Condensate Blowdown Drum). If it is connected to a Relief system then it might be called a Flare Blowdown Drum or a Flare Knock-Out Drum. There are also Fuel Gas Blowdown Drums and many other functional needs where there is a wet gas or vapor. The actual name depends on the service and the training and experience of the Process Engineer doing the process design.

The design, The design of these vessels/drums may be any size and configuration. The flow is not always a constant rate. They will be small for a service with a low rate of flow. They will be large (even very large) for services where there is a very high rate of flow. The large versions tend to be horizontal configuration and the small versions tend to be vertical configuration. Flare rates will fluctuate from very low to very high. Steam Blowdown will tend to be any size depending on the needs of the process but will be constant. Fuel Gas will be a medium to low rate and will be constant. The inlet will often have some kind of defuser or baffle to break up the flow and knock out the liquids. The outlet on some (Fuel Gas) will often have a "Demister Pad" to prevent carry-over. All Blowdown and Knock-out Drums need a way to get rid of the fluid and impurities. For some safe commodities (Condensate) it may be a simple drain funnel to the Oily Water Sewer. Some (Flare Drum) may need a Boot (to catch the drips) and a pump (operated on level control) to get rid of the Slops.


The location, The location depends on the service.
- Steam Service Drum - Locate close to the Steam source
- Fuel Gas Service Drum - Locate not closer than 50 feet from the Heater/Boiler
- Unit Flare Knock-Out Drum - Locate at the Battery Limits of the Unit being served
- Main Flare Knock-Out Drum - Locate on the main Flare Line 200 to 300 feet before the Flare
- Other Blowdown/Knock-Out Drum - Location depends on service