Fuel Gas Conditioning Systems
Key Takeaway
Fuel gas conditioning systems process plant fuel gas streams to meet the specification requirements of gas turbines, fired heaters and other combustion equipment. Conditioning typically includes knock-out of liquids, filtration, pressure regulation, superheating to prevent condensation, and in some applications heating or pressure boosting to meet turbine inlet requirements.
Why Fuel Gas Conditioning is Required
Gas turbines and other combustion equipment are sensitive to the quality of the fuel gas supplied. Liquid carryover, particulates and rapid pressure or temperature variations in the fuel gas can damage equipment, affect combustion performance and cause operational issues including flame instability and blade erosion.
Fuel gas conditioning systems are designed to ensure that the gas supplied to combustion equipment meets the manufacturer's specification for the fuel gas inlet conditions, including pressure, temperature, dew point and particulate content.
Knock-Out and Liquid Separation
The first stage of a fuel gas conditioning system typically involves separation of any entrained liquids from the gas stream. A knock-out drum or scrubber vessel is used to remove bulk liquid. For applications requiring high-quality dry gas, coalescent filters or another liquid removal stage may follow.
Liquid carryover in fuel gas can originate from condensation in pipework upstream of the conditioning system, slug flow, or process upsets. The knock-out system must be designed to handle the expected liquid loads including upset conditions.
Pressure Regulation and Heating
Fuel gas is commonly available at a higher pressure than required at the combustion equipment inlet. Pressure let-down across a control valve causes Joule-Thomson cooling, which can result in condensation of heavier components in the gas or cause the gas temperature to fall below the fuel gas dew point.
To prevent condensation downstream of the pressure let-down, a fuel gas heater is typically installed upstream of the pressure control valve to superheat the gas before let-down. The heater raises the gas temperature sufficiently that, after the pressure drop and associated cooling, the gas remains above its dew point at the turbine or burner inlet conditions.
Gas Turbine Fuel Gas Specification
Gas turbine manufacturers specify the required fuel gas inlet conditions including pressure range, temperature range, dew point margin, Wobbe Index and particulate limits. The fuel gas conditioning system is designed to supply gas within these limits throughout the operating envelope of the turbine.
The Wobbe Index — a measure of the energy delivered per unit volume of gas at constant pressure drop — is used to characterise the interchangeability of fuel gases and is a key parameter in fuel gas specification for gas turbines.
Fired Heater and Boiler Applications
Fuel gas conditioning for fired heaters and boilers is generally less demanding than for gas turbines, but still requires removal of liquids and control of pressure and flow. In some applications, fuel gas metering and calorific value measurement are included in the conditioning skid.
Howe Baker Fuel Gas Conditioning Systems
Howe Baker designs and supplies fuel gas conditioning systems as standalone skid-mounted packages and as part of broader hydrocarbon processing or power generation projects. Engineering scope covers process design, equipment selection, skid layout and control system design.
Common Questions
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