GAS MANIFOLD &
KNOCKOUT DRUMS
Liquid-free gas distribution and pipeline protection -- the last line of defense before your compressors, meters, and burners.
Where Gas Manifolds and Knockout Drums Are Specified
These vessels are not primary separators -- they are protection and distribution equipment. Their job is to ensure the gas stream arriving at sensitive downstream equipment is dry, clean, and at stable pressure.
Compressor Suction Knockout Drum
Reciprocating and centrifugal compressors have near-zero tolerance for liquid ingestion. Even small quantities of liquid carry-over from upstream separation -- droplets in the 10-100 μm range -- can cause compressor valve damage, cylinder wash-out, and catastrophic mechanical failure. A knockout drum at the compressor suction flange is the final liquid protection device before the gas enters the compression cylinder. It is a mandatory element of any compressor installation handling wet or partially-separated gas.
Fuel Gas and Instrument Gas Knockout
Fired heaters, generators, and gas-powered equipment require dry, clean fuel gas. Liquid contamination in fuel gas causes unstable flame behavior, burner tip coking, and in severe cases flame-out or flashback. Instrument gas systems supplying pneumatic control valves and positioners require liquid-free gas to prevent valve seat damage and control loop failures. A knockout drum on the fuel gas or instrument gas supply header ensures these utilities receive gas at the required quality.
Flare Knockout Drum (KO Pot)
Before gas is routed to a flare stack, it must pass through a flare knockout drum. This vessel removes liquid that would otherwise reach the flare tip -- creating a liquid-rich fireball, potential burning liquid rain, and a fire safety hazard. Flare knockout drums are a process safety requirement on all production facilities and are designed per API 521 or equivalent standards for vessel sizing and liquid hold-up volume.
Multi-Well Gas Manifold & Distribution
A gas manifold collects production gas from multiple wells or processing trains into a common header, provides pressure equalization across connected streams, and distributes the combined stream to downstream processing, compression, or export. For multi-well pad operations and gathering stations, the gas manifold with integral knockout functionality is the central distribution node of the gas handling system.
Associated Gas Recovery and LNG System -- Congo (Brazzaville), Jiarou Oilfield
The multi-stage gas processing system for this international project included gas distribution and knockout stages handling up to 300×10⁴ Nm³/d in Phase II and III. Reliable gas-liquid separation at every stage was critical to protecting downstream LNG liquefaction equipment.
View Full Project DetailsOperating Principle: Knockout Drum and Gas Manifold Design
01 Knockout Drum -- Removing the Residual Liquid
A knockout drum (also called a KO drum, knock-out pot, or scrubber) operates on the same gas-liquid separation principle as a primary separator -- but for a gas stream that already contains very low liquid content. Because the liquid loading is low, the vessel can be relatively small, but the demister performance must be high: the gas entering a compressor or metering station must meet a strict carry-over specification, often expressed as a maximum droplet size or liquid content in mg/Nm³.
The gas enters the knockout drum through an inlet nozzle, typically with a simple half-pipe or diverter inlet device. Any bulk liquid falls to the vessel bottom by gravity. The gas then passes upward through a wire mesh demister pad rated at 5-10 μm, which captures fine mist. The liquid that coalesces on the mesh drains back to the vessel sump. Clean, dry gas exits the top outlet nozzle.
Liquid accumulated in the sump is discharged through a level-controlled outlet. For small knockout drums at unmanned sites, a dump valve with high-level shutdown is standard. For larger or continuously-operating drums, a continuous level controller feeds a modulating level control valve.
02 Gas Manifold -- Collection, Equalization, and Distribution
A gas manifold is a header vessel -- typically a horizontal cylindrical vessel or a large-bore pipe assembly -- that receives gas streams from multiple inlet connections and distributes the combined or selectively routed stream through outlet connections. The manifold provides:
03 Flare Knockout Drum -- Safety-Critical Design
The flare knockout drum is sized differently from a process knockout drum. Per API 521, the primary sizing criterion is liquid hold-up volume -- the vessel must retain the maximum credible liquid surge from emergency pressure relief without liquid reaching the flare tip. Gas velocity through the drum is also constrained to ensure droplets above the critical settling size are removed. LINSON OIL designs flare knockout drums to API 521 / GB equivalent requirements, with liquid level alarms and high-level shutdown interlocks included as standard.
Engineering Specifications
Detailed parameters for standard and custom fabricated units.
Knockout Drum Specification
| Parameter | Standard Range | Notes |
|---|---|---|
| Orientation | Vertical (standard) / Horizontal | Vertical preferred for low liquid loading; horizontal for high gas flow |
| Design Pressure | 0.1 - 10.0 MPa (g) | Full range from low-pressure flare to high-pressure sales gas |
| Design Temperature | -20°C to +200°C | Low-temperature grades for gas dehydration service |
| Shell Material | Q345R / 16MnDR / 316L SS | Per gas composition and temperature |
| Corrosion Allowance | 1.5-3 mm | Per gas composition (H₂S, CO₂, moisture content) |
| Inlet Device | Half-pipe / Diverter baffle / Tangential | Per gas velocity and liquid loading |
| Demister | Wire mesh, 5-10 μm | Vane pack for high-velocity / high-efficiency duty |
| Liquid Level Control | Float-ball / Displacer / Guided wave radar | Per operating conditions and automation level |
| Liquid Dump Valve | On/off dump valve or modulating LCV | Per liquid generation rate |
| High-Level Shutdown | Level switch + shutdown valve | Standard for compressor protection duty |
| Design Life | ≥ 10 years | Per GB 150 design basis |
| Design Code | GB 150 / ASME VIII Div.1 / API 521 | Application-dependent (API 521 for flare duty) |
| NDT | RT / UT / MT / PT | Per weld class and design code |
| Pressure Test | Hydrostatic at 1.25× DP | Pneumatic test available |
Gas Manifold Specification
| Parameter | Standard Range | Notes |
|---|---|---|
| Configuration | Vessel-type or large-bore pipe header | Per flow volume and inlet count |
| Number of Connections | 2 - 20+ | Per well count or stream count |
| Design Pressure | 0.6 - 10.0 MPa (g) | |
| Design Code | GB 150 / GB/T 20801 | Per configuration (vessel vs pipe header) |
| Knockout Function | Integral sump + demister | Available as standard or optional |
| Pressure Equalization | Via manifold volume | Vessel-type manifold provides inherent equalization |
| Valve Arrangement | Per client P&ID / routing requirements | All valves can be supplied and skid-integrated |
| Material | Q345R / 20# / 316L SS | Per gas composition |
Standard Supply & Customization Scope
From bare vessel fabrication to fully integrated skid packages.
Standard Factory Configuration -- Knockout Drum
- › Inlet distributor (half-pipe or diverter type)
- › Wire mesh demister, 5-10 μm, with support ring
- › Float-ball liquid level controller with 4-20 mA output
- › High-level liquid shutdown switch (for compressor protection)
- › Dump valve connection (on/off or modulating LCV)
- › Pressure relief valve (per code)
- › Pressure gauge and transmitter nozzles
- › Thermometer connection
- › Inspection manhole or handhole (per vessel size)
- › Drain and vent connections
- › Support legs or skirt with lifting lugs
- › Surface treatment: internal Sa2.5 + lining; external primer + topcoat
- › Factory hydrostatic pressure test & Nameplate per GB 150
Standard Factory Configuration -- Gas Manifold
- › Vessel or large-bore pipe header per design
- › Inlet and outlet nozzles per client well count and routing
- › Integral sump (if knockout function specified)
- › Demister (if knockout function specified)
- › Pressure gauge connections on each inlet/outlet
- › Isolation valve connections (valves supplied or client-furnished)
- › Support structure
- › Surface treatment per service
- › Factory pressure test
OEM / ODM Customization Options
| Option | Typical Requirement |
|---|---|
| Vane pack demister (high-efficiency) | Sales gas, fuel gas, instrument gas -- very low carryover tolerance |
| Two-stage demisting (mesh + vane in series) | Compressor or turbine inlet protection with tight carryover spec |
| Guided wave radar level transmitter | High-accuracy level measurement; foaming or condensing service |
| Flare knockout drum per API 521 | Safety-critical flare system design; liquid hold-up volume sizing |
| Thermal insulation and tracing | Cold climate; preventing condensate re-formation in cold sections |
| Sour service package | H₂S wet service; NACE MR0175 / ISO 15156 |
| ATEX / IECEx instrumentation | Zone 1 / Zone 2 classification |
| Full skid integration | KO drum, valves, piping, instrumentation, control panel -- factory pre-fabricated |
| Automated dump system with PLC control | Unmanned remote site; automated liquid management |
| ASME U-stamp / 3.1 material certificates | International / export project requirements / European standards |
Certified Pressure Vessel Manufacturing. In-House Testing. Documented at Every Step.
Material Traceability
All pressure-bearing materials arrive with mill certificates. Identification tracked from receipt through delivery. 3.1 material certificates available on request.
Welding Qualification
WPS and PQR maintained per GB/T 19869 or ASME IX. All welders qualified. Compliance verified for each joint type, including pipe-to-vessel nozzle welds.
NDT Inspection
CNAS-accredited in-house laboratory: RT, UT, MT, PT per design code weld class. All NDT results documented and mapped on as-built weld drawings.
Hydrostatic Pressure Test
Every pressure-retaining assembly hydrotested at ≥ 1.25× design pressure. Calibrated equipment with traceable test records. Third-party witness available.
Instrument & Safety Verification
High-level shutdown switches and dump valves are function-tested before shipment. Full instrument loop check conducted for skid-integrated packages.
Export Packing
Nozzles blinded, internals preserved, export crating applied. Full shipping and customs documentation prepared.
Note on Piping Component Certification
Gas manifold header assemblies, when fabricated as piping rather than pressure vessels, fall under LINSON OIL's Pressure Piping Components Manufacturing License (GC2) and are designed per GB/T 20801. This dual licensing (vessel + piping) means we supply fully integrated assemblies from a single certified manufacturer, simplifying your equipment procurement.
Delivered Across China and Internationally
Proven field performance in critical gas handling applications.
Congo (Brazzaville) -- Jiarou Oilfield, Phase I / II / III
The associated gas recovery and LNG liquefaction system across three project phases included gas distribution and knockout stages operating at up to 300×10⁴ Nm³/d. Knockout drum performance directly determined the protection level provided to downstream LNG liquefaction equipment -- which has near-zero tolerance for liquid carryover. Delivered and commissioned across all three project phases.
Sinopec Northwest Bureau -- Shunbei No. 5 Molecular Sieve Dehydration Skid
The inlet gas conditioning stages of the Shunbei molecular sieve dehydration system -- which included gas-liquid knockout upstream of the adsorption beds -- were supplied by LINSON OIL. Liquid carryover into molecular sieve beds is a primary cause of premature sieve degradation; inlet knockout performance is a critical protection function in this application.
Sinopec & CNPC -- HSE Certified Supplier
Gas manifolds, knockout drums, and wellhead gas handling equipment are among the most frequently procured items in upstream facility projects. LINSON OIL's certified supplier status in both the Sinopec and CNPC procurement systems reflects a sustained delivery record across wellhead and station gas handling applications.
Industry-Leading Warranty & Support
Standard 2-Year Warranty
2 years from commissioning or 26 months from shipment. Industry benchmark: 1 year. Gas knockout drums and manifolds are static equipment with few wear points -- our 2-year warranty reflects this inherent reliability and our confidence in fabrication quality.
Long-Term Partnership Coverage
Extended up to 2.5 years, with spare demister elements, level controllers, and dump valves pre-identified in the quality dossier for rapid replacement.
After-Sales Engineering Support
- Demister pad replacement guidance and spare element documentation included at delivery.
- Remote consultation available for carry-over troubleshooting during commissioning.
- Engineering support for capacity expansion or nozzle layout modifications.
Protecting a Compressor? Distributing Field Gas? Tell Us the Duty.
Knockout drums and gas manifolds are sized to the specific gas flow rate, liquid loading, and downstream equipment requirements. Send us your gas conditions and protection duty, and our engineering team will come back with a sized vessel recommendation and relevant reference within 24 hours.
Free Engineering Resource
Submit your process parameters and receive:
- Preliminary knockout drum sizing (vessel diameter, height, demister type recommendation)
- Carryover performance estimate at your specified flow rate
- Relevant project reference for your application type
*Reviewed directly by LINSON OIL process engineers. Response within 24 business hours.
Request a Quote / Sizing Recommendation
LINSON OIL -- 21+ Years | 5,000+ Projects | 87 Patents | Pressure Vessel (A2) + Piping (GC2) Licensed Manufacturer