Knock-Out Drums in Biogas Trains: Why Your Mill Needs One

In a biogas train, the gas leaving an anaerobic digester or covered lagoon is saturated with moisture and often carries entrained liquid droplets. Left in the gas stream, that liquid causes corrosion, disrupts combustion, damages instruments, and can extinguish a flare. A knock-out drum, sometimes called a condensate pot or moisture separator, is the vessel that removes it before the gas reaches downstream equipment.

What a Knock-Out Drum Does

A knock-out drum is a separation vessel that slows the gas flow and lets gravity and changes in direction drop entrained liquid out of the stream. As gas enters the larger vessel, its velocity falls sharply, and heavier liquid droplets fall to the bottom where they collect and drain away. The dried gas continues on to the burner or flare in far better condition.

Why Your Mill Needs One

• Protects burners and flares from liquid slugs that cause flame instability or blow-out
• Reduces corrosion in downstream pipework and equipment from condensed moisture and hydrogen sulphide
• Protects flow meters and instruments from fouling and damage
• Improves combustion efficiency by delivering drier, more consistent gas

Where It Sits in the Train

Knock-out drums are typically placed at low points in the gas line and immediately upstream of sensitive equipment such as burners, flares, and flow meters. Because biogas cools as it travels and moisture condenses along the way, more than one separation point may be needed on a longer run. Correct placement, with proper drainage, is as important as the vessel itself.

Sizing and Construction

A knock-out drum must be large enough to drop gas velocity below the point where droplets are carried through, which depends on gas flow, pressure, and the size of droplets to be removed. Because biogas is corrosive, stainless steel construction — commonly SS316 — is preferred for durability. A drum that is too small will let liquid carry over; one properly sized and drained will run reliably for years.

A Small Vessel with a Large Role

Knock-out drums are easy to overlook next to the burner and flare they protect, but they are quietly essential to a reliable biogas system. A modest investment in correctly sized separation prevents a long list of downstream problems that are far more expensive to fix once they start.

How THAGO Can Help

THAGO designs and fabricates knock-out drums and condensate separation vessels in SS316 as part of complete biogas trains for palm oil mills. Our team sizes each vessel to your gas flow and integrates it with your burner, flare, and pipework.