Fuel Gas Conditioning Skids: How to Size Filtration, Superheat and Pressure Control

At a glance. A fuel gas conditioning skid removes liquids and solids, heats the gas so it stays well above its hydrocarbon dew point after pressure letdown, and regulates it to the pressure the consumer needs. Ask for coalescing filtration to about 0.3 µm, superheat of typically 28 °C (50 °F) above the hydrocarbon dew point at the consumer, and heating sized for the coldest gas and the largest pressure drop.

Why does fuel gas need conditioning?

Liquid droplets in fuel gas cause flame instability, hot spots and damage to combustion hardware, and solids erode fuel nozzles and control valves. Gas that is only just above its dew point can condense when its pressure is reduced, so a turbine that looks well protected at the pipeline can still receive liquid at the burner. Most turbine makers therefore specify a filtration level and a minimum superheat above the hydrocarbon dew point in their fuel gas specifications.

What goes on the skid?

Stage	Purpose
Inlet knock-out or scrubber	Removes slugs and bulk liquid
Filter separator or coalescer	Removes fine aerosols and solids, typically to 0.3 µm
Heater	Raises the gas temperature to give the required superheat
Pressure regulation	Reduces pressure to the consumer's supply pressure, with slam-shut and relief protection
Final filter (optional)	Protects the fuel system downstream of the heater
Metering (optional)	Measures fuel consumption or custody flow

Duplex filters, or a spare filter separator, let elements be changed without stopping the consumer.

Why must heating come before letdown?

Natural gas cools as its pressure drops, through the Joule–Thomson effect, by roughly half a degree Celsius for every bar of pressure reduction, depending on composition. A letdown of 40 bar can therefore cool the gas by around 20 °C. The heater must add enough heat to cover that cooling and still leave the required superheat at the consumer, at the coldest inlet temperature and the highest flow.

Electric or shell-and-tube heating?

Electric heaters are compact, simple to control and suit smaller flows or sites with spare power. Shell-and-tube or water-bath heaters using hot water, steam or another heat source suit larger flows where waste heat is available. The choice usually follows the site's utilities and the heat duty.

Specification checklist

• Gas composition, including heavy hydrocarbons and water

• Inlet pressure and temperature range

• Flow at minimum, normal and maximum demand

• Consumer's fuel gas specification: pressure, filtration and superheat

• Heater type and available utilities

• Design code: ASME VIII vessels and ASME B31.3 piping

• Hazardous-area zone and ambient range

• Instrumentation, metering and control interface

Tech Inc. fuel gas conditioning

Tech Inc. builds fuel gas conditioning skids, filter separator and coalescer skids, pressure reducing and metering stations and gas metering skids, and supplies replacement gas coalescer elements. Send your gas data and the consumer's fuel specification to mail@techincresearch.com.

Frequently asked questions

How much superheat does a gas turbine need?

Turbine makers commonly ask for about 28 °C (50 °F) above the hydrocarbon dew point at the turbine inlet. Always follow the turbine's own fuel gas specification.

What filtration level is usual?

Coalescing filtration removing liquids and solids down to about 0.3 µm is typical for turbine fuel gas.

Why not simply heat the gas downstream of the regulator?

The cooling happens across the regulator itself, so liquid can form there and in the pipework before a downstream heater. Heating upstream keeps the gas dry through the letdown.

Can one skid feed several turbines?

Yes, if it is sized for their combined demand and the pressure control suits their load changes. Spare filtration keeps all units running during element changes.