fuel gas system- candidate.pdf
TRANSCRIPT
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8/11/2019 FUEL GAS SYSTEM- CANDIDATE.pdf
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Training Services Petrofac
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Utility units fuel gas system
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REV 01: Process fuel gas system: April 2011 Page 2 of 11
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Training Services
REV 01: Process fuel gas syste
Introduction:
The function of a fuel
delivery to the variou
filtration, superheatin
.
Typical gas
turbine
m: April 2011
HANDOUT
gas system is to treat fuel gas to an accept
users. This treatment includes knockout of
g, and pressure control
Typic
comp
Petrofac
Page 3 of 11
ble Level for
liquids,
l gas
essor
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The system supplies fuel gas to the following users:
Power generation gas turbines
Gas compressor gas turbines
Water Injection Pump gas turbines
Flare pilots
HP/LP Flare header purges
Stripping gas for Glycol Regeneration Packages
There are typically two pressure systems on a fuel gas system
1- High pressure users:
Main power gas turbine
Gas compression or main oil pump gas turbine
Blanketing purpose (blanket gas for LPG and Odorant tank)
And it can also be used for purging purpose.
Supplies the Low pressure fuel gas system.
Typical HP gas
turbine
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2- Low pressure users:
Purge gas to flare headers and used as a pilot gas for the flare.
Stripping gas to the glycol regeneration or deoxygenating systems
Blanket gas to storage vessels (Methanol Condensate TEG storage tank)
Reboilers _ Fired heaters
Typical HP
fuel gas
system
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The fuel gas system incorporates the following process equipment:
Fuel Gas K.O. Drum
Fuel Gas Heaters
Fuel Gas Filters
Typical LP fuel gas
system
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Fuel Gas K.O. Drum
Pressure drop across the pressure control valveat the inlet to the Fuel Gas KO Drum leads to
Joule-Thompson cooling of the hydrocarbon
gas. Any condensed liquid is knocked out in
the Fuel Gas KO Drum.
The vessel contains a mesh pad, which ensures
that there is minimum liquid carryover in the
dry gas flow. The vessel is also fitted with a
vane type inlet device to improve separation
efficiency.
If the liquid level rises above the vessel tan
line, a high high level trip is activated which
closes a shutdown valve (XXV), that stops all
inflow to the Fuel Gas KO Drum.
Fuel gas flows out of the Fuel Gas KO Drum to the Fuel Gas Package. The piping between the drum
and the package is insulated to reduce the likelihood of condensation in the line.
Fuel Gas Heaters
The Fuel Gas Package consists of two heaters and two filters. The heaters are designed to superheat
the gas to prevent condensation in the downstream systems/equipment. Fuel gas from the Fuel Gas
KO Drum is heated in the Fuel Gas Heaters. The two electrically powered heaters, one heater is online whilst the other is on standby .Changeover from duty to standby heater is a manual activity.
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Heater operation is controlled by differential
temperature controllers, which compare the gas
inlet temperature and outlet temperature and this
will adjust heater output, via the Thyristor control
panel, to meet the duty requirement.
The Thyristor panel for each heater contains
over-temperature protection, which stops the heater
in the event of high temperature detection at the
elements or flange. Activation of a trip on both
heaters could happen if the gas outlet temperature
exceeds 90C, which would be a detection system
downstream of the filters.
Fuel Gas Filters
The superheated fuel gas flows from the Fuel Gas Heaters to the inlets of the Fuel Gas Filters.
There are two cartridge type filters, one operating whilst the other is on standby, each designed to
remove 99.9% of all particulate matter and to reduce the solids content. The filtration specification
is dictated by the requirements of the power generation gas turbines.
A differential pressure transmitter is fitted on the common inlet and outlet lines. This permits
monitoring of the state of the filter elements. When the pressure drop exceeds 0.5 bar, the filters
should be changed over and the dirty element cleaned or replaced.
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The heaters and filters are insulated for
heat conservation. The gas piping
downstream of the heaters is insulated
and electrically heat traced to maintain
gas temperature.
The filters are fitted with a Quick
Opening Closure to provide easy access
to the filters for maintenance. The
Quick Opening Closure is fitted with a
patented integral safety interlock to
prevent opening while the filter is
pressurised.
SYSTEM DESCRIPTION:
Dry or wet gas may be used as a fuel source. Wet gas is more corrosive.
The system shown uses a "wet gas "source.
The system treats the gas by first cooling, and knocking out heavier hydrocarbons in
the scrubbers or knockout drums.
The gas is then super heated by about 20c to ensure that it remains above its dew
point.
The fuel gas is now considered "dry"
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Typical fuel gas system description diagram
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Fuel gas sources
The source for fuel gas is often the first stage separator, or the LP gas
compressor.
Supply and distribution:
The fuel gas separated into two different headers, HP (25 barg) and LP (5 barg),
each with its own flow and pressure controllers.
On some generator systems, if the fuel gas supply stops, the engines turn
automatically to an alternative fuel (diesel), but this is much more costly.