FUEL GAS SYSTEM- CANDIDATE.pdf

8/11/2019 FUEL GAS SYSTEM- CANDIDATE.pdf

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Training Services Petrofac

REV 01: Workshop Machine Tools: October 2010 Page 1 of 11

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

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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.

Documents

FUEL GAS SYSTEM- CANDIDATE.pdf