o Fuel Gas
System
The primary source of fuel gas will be downstream of the
expander compressor. For start-up purposes fuel gas will be taken from the two
feed gas lines upstream of plant isolating valves and will tie-in to the main
fuel-gas header upstream of the FG scrubber.
An orifice type meter shall be installed to measure overall
plant gas consumption, which covers but is not necessary limited to, the
following:
• Fuel gas
for gas turbine driven compressors and gas engine generators
• Fuel gas
for hot oil furnace heater
• Purge gas
• Pilot gas
for flare and burn-pit ignition system
The Fuel Gas Package will comprise of the following:
• Fuel Gas
Scrubber (1 x 100 %)
• Fuel Gas
Filters (2 x 100 %)
• Fuel Gas
Heater (1 x 100 %)
The fuel gas off take is at 285 psig before let down into
the fuel gas scrubber. The gas is totally dry for star-up, the gas taken from
the pipelines will be water-saturated, so a fuel-gas heater is provided to
elevate the gas temperatures.
o Seal Gas
System
The system will be designed and supplied by the selected
Compressor VENDOR.
The seal gas system shall be able to handle the primary seal
gas requirement of the selected gas compressors.
The Seal Gas Package might comprise of the following:
• Seal Gas
Scrubber (1 x 100 %)
• Seal Gas
Filter/Coalesces (2 x 100% )
• Seal Gas
Electrical Heaters (2 x 100%)
In addition, seal gas treatment and its control system shall
be provided on the compressor skids.
o Flare and
Vent Systems
All hydrocarbon pressure relieving devices, with the
exception of low temperature extraction section gases, will discharge to the
high pressure flare header. This includes PSVs, rupture disks if approved for
use, and emergency blowdown valves. To prevent any liquid entering the flare
stack, a flare K.O. drum, and liquid removal pumps will be required. Downstream
of the KO drum a water seal-drum shall be provided to prevent air from entering
the flare header system.
The Flare Capacity shall be based on a worst-case scenario.
The design shall be completed in detail engineering.
A flare header designed for the maximum plant throughput
will pass 250 MMscfd under blocked outlet condition. The emergency blowdown
rate will quickly reduce to below the normal maximum throughput of 250 MMscfd
and is not the controlling case. If adequate protection against blocked
discharge and failure of the protective systems cannot be economically achieved
relative to the cost of a larger capacity flare system the system shall be
sized for the maximum throughput. It is anticipated that an elevated flare system
will be used.
In order to reduce the header size a maximum Mach number of
0.7 may be used for emergency discharge assuming the use of a conventional pipe
flare. Consideration is also to be given to the use of a sonic flare tip
operating at an elevated back pressure (approximately 30-50 psig at the tip
inlet) which will considerably reduce radiation levels at and around the plant.
In addition to the HP flare a cold vent line shall be
installed, which will be elevated and suspended from the HP flare stack. Some
of the relief valve discharges and vents in the unit are at a very cold
temperature and cannot be sent to the wet carbon steel flare system. These cold
discharges would cause the formation of ice and hydrates with potential
blockage of the free path to the flare. The cold temperature of these
discharges are also too cold for the use of carbon steel material in the piping
and flare. Therefore a separate cold flare system consisting of a stainless
steel, (or other material suitable for the discharge condition), flare header
shall be provided. Simulation indicates that cold liquid will not condense out
during discharge, so a KO drum has not been indicated for the cold vent system.
Bidders to confirm this fact or advise the installation of a SS KO-drum. Use of
this separate line for the relatively low pressure De-C2 discharge allows a
higher back pressure in the CS HP flare header thus reducing header size.
The radiation levels for personnel and equipment at the
limit of the restriction zone resulting from the HP Flare shall not be more
than the following:
(ref: API 520 Part II - Sizing, Selection and Installation
of Pressure-Relieving Devices in Refineries):
• Equipment
Protection 5000 Btu / (hr.ft2)
• Personnel,
one minute exposure 1500 Btu / (hr.ft2)
• Personnel,
continuous exposure 500 Btu / (hr.ft2)
Liquids collecting in the Flare K.O. Drum are to be directed
via the Flare K.O. pump to the Closed Drain Drum. The requirement for sizing of
these pumps is removal of all liquid between LLH and LLL in 30 minutes.
The water seal drum will have a permanent water-line
connection, level controlled to maintain a position seal in the drum. A water
seal drum is not envisaged for the cold vent. This cold vent line will be
fuel-gas purged only from its extreme upstream point.
The flare system will comprise of:
• HP flare
header
• HP flare
stack
• Cold vent
header
• HP flare
tip
• Flare
ignition system
• HP flare KO
drum
• HP flare KO
drum pump
• HP water
seal drum
Individual atmospheric vents are to be used where possible
with crossovers minimized and air-cooled exchanger fans used to assist
dispersion. Flame arrestors shall be fitted at individual local atmospheric
vents.
o Instrument
and Utility Air System
The Instrument and Utility Air System will comprise the following
main components:
• Instrument
/ Utility Air Compressors (2 x 100 %)
• Instrument
Air Drier (2 x 100 %)
• Instrument
/ Air Receiver
• Utility Air
Receiver
• Instrument
and Utility Air Distribution Systems
Air Compressors and Air Dryers capacity is shown in Table-4.
The air receiver shall be sized for 30 minutes of air
capacity from low pressure alarm down to low low pressure shutdown initiation.
o Diesel Fuel
System
The diesel storage facility with filter coalesces; loading
facilities and transfer are to be provided. The storage tank shall be designed
to accommodate the diesel fuel demand of diesel generator for 8 days in base
load continuous operation condition, supply the diesel fire pumps and provide
fuel for vehicle use through a day tank and vehicle fill hose.
The Diesel Fuel system comprises of:
• Diesel Fuel
Storage Tank
• Diesel Fuel
Daily Tank with fill hose
• Diesel Fuel
Loading Pump
• Diesel Fuel
Transfer Pump
• Diesel Fuel
Transfer Filter
