Gas Processing Equipment

Gas Processing Equipment covers packages that condition raw gas for use or export: inlet scrubbers, filter coalescers, triethylene glycol (TEG) dehydration units, fuel gas conditioning skids and H2S removal vessels. On a drilling unit they appear mainly in extended well tests and early production. Each package is designed for one gas composition, pressure and flow, so a used unit is bought on its process data sheet.

How gas conditioning works

Raw gas carries liquid droplets, water vapour, solids and sometimes H2S and CO2. Each step removes one of them.

An inlet scrubber knocks out liquid droplets by gravity and a mist eliminator.
A filter coalescer catches fine aerosols and solids that would foul glycol or burners.
A glycol contactor absorbs water vapour so the gas will not form hydrates or corrode pipework downstream.
A fuel gas skid filters the gas, heats it to offset cooling across the pressure regulator, and drops it to the pressure an engine, turbine or heater needs.
A scavenger tower removes H2S with a liquid or solid scavenger.

In a TEG unit, wet gas rises through a tray or packed contactor against lean glycol. Rich glycol flows to a flash drum and filters, then to a reboiler that boils off the water. The reboiler must stay below the temperature at which TEG degrades, about 204 C (400 F).

Configurations

Skid-mounted TEG units with a fired or electric reboiler
Fuel gas packages with scrubber, filters, heater and duty and standby regulators
Contact towers for liquid H2S scavengers, or fixed-bed vessels for solid ones
Combined well test and early production packages with metering

Key specifications

Parameter	Why it matters	Typical classes or units
Gas throughput	Sets vessel diameters and glycol rate	MMscfd or Sm3 per day
Design pressure and temperature	Must cover the well's flowing conditions	psi or barg, F or C
Inlet composition	Sets materials and treatment steps	Mol percent CO2, ppm H2S
Outlet water dew point	Decides whether hydrates form downstream	F or C at pressure, or lb per MMscf
Glycol circulation rate	Sets dehydration performance	US gallons or litres of TEG per pound or kg of water
Utilities	Must exist on your unit	Power, instrument air, heating medium

Standards and certification

API 12GDU covers glycol-type gas dehydration units, and API 12J covers the separators and scrubbers. Vessels are normally built to ASME Section VIII. API RP 14C sets the safety devices each component needs. Sour gas calls for materials to NACE MR0175/ISO 15156. Motors, heaters and instruments need ATEX or IECEx certification for the zone.

Failure modes and inspection

Contactor fouling and foaming from hydrocarbon liquids and solids. Inspect trays or packing and the mist eliminator.
Reboiler fire tube scaling or burn-through. Inspect it visually and with ultrasonic thickness readings.
Glycol degradation, low pH and high salt content in units laid up full. Have the glycol analysed.
Corrosion in the still column and rich glycol piping, where acid gases concentrate.
Pressure regulator wear and heater faults on fuel gas skids.
Out-of-date relief valve tests and drifted instruments.

Documentation

Process data sheet and heat and material balance for the design case
Pressure vessel data books and hydrotest reports
Piping and instrumentation diagrams and cause and effect charts
Relief valve certificates and set pressures
PLC software backup, licences and instrument calibration records
Hazardous area certificates for each electrical item

Integration and compatibility

Have a process engineer run your gas through the original design. A unit sized for lean, dry gas may miss its dew point on a richer or warmer stream. Check that your unit can supply the power, instrument air and heating medium the package needs, and that its vents and drains connect to your flare and closed drain system. Liquids upstream come out in gas separators, and test packages usually sit behind the well test equipment spread.

Refurbishment and recertification

A typical overhaul replaces glycol, filters, packing or trays where needed, and the reboiler fire tube if thin. It also recalibrates instruments, retests relief valves and hydrotests or re-surveys the vessels. Used packages make sense for short or uncertain projects such as an extended well test. Many are built by regional fabricators to an operator's specification, so the data book matters more than the brand.

FAQ

Frequently asked questions

What does a glycol dehydration unit do?

A glycol dehydration unit removes water vapour from natural gas so it will not form hydrates or corrode pipework. Gas rises through a contactor against lean triethylene glycol, which absorbs the water. A reboiler then boils the water off below about 204 C (400 F) so the glycol can circulate again.

Can a used gas dehydration package handle a different gas stream?

Sometimes, but only after a process check. Each package is designed for one flow, pressure, temperature and composition. Have a process engineer run your gas through the original design to confirm the contactor, glycol rate and reboiler duty still reach the water dew point you need.

What should I inspect on a used fuel gas skid?

On a used fuel gas skid, inspect the scrubber and filter elements, the heater and the pressure regulators, and retest the relief valves. Confirm that the motors, heater and instruments carry hazardous area certification for the zone, and that the outlet pressure suits your engines or turbines.

Why does glycol degrade in a laid-up dehydration unit?

Glycol left in a laid-up unit absorbs oxygen and water and picks up salts and hydrocarbons, which lower its pH and form sludge. Degraded glycol foams, corrodes the still and fouls the contactor. Drain and analyse it before restart, and plan to replace it on any used package.

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