INTRODUCTION
:
BANAGAS operates LPG plant facilities to recover Propane, Butane and
Naphtha from oil wells associated gas, Arab gas and refinery gas.
Liquefied Propane and Butane are transferred to refrigerated storage
for ship loading at the Sitra Wharf. Naphtha is sent to the Bahrain
Petroleum Refinery (Bapco) for storage and subsequent export.
The tail or residue gas is used as fuel for Banagas furnaces and gas
turbines, and the rest is supplied to Aluminum
Bahrain (Alba) Power
Stations and the Bapco Refinery. This residue gas, 245 million standard
cubic feet per day (MMSCFD), represents 25% of Bahrain's daily fuel
gas consumption.
The original plant was commissioned in 1980 with capacity of 110 MMSCFD
of Associated Gas.
At present BANAGAS operates two gas-processing trains with a total
feed gas through put of 280 MMSCFD.
BAHRAIN OIL FIELD :
The low pressure associated gas is collected from 16 well
manifolds in the Bahrain Oil Field. The gas is separated in gas oil
separators (GOSPS) at a controlled pressure of about 35 psig. This
collected gas will later be sent to compressor stations 1-7. Additionally,
low pressure non dehydrated refinery gas is also supplied from Bapco
refinery to CS-7, whereby it is compressed along with the associated
gas and delivered to the central gas plant for LPG recovery.
COMPRESSOR STATIONS :
At each compressor station, gas from several GOSPS is gathered into
an inlet header and compressed by a two-stage centrifugal compressor
driven by gas turbines to about 420 psig. The gas is then cooled by
air fans to 110 ºF, and dehydrated.
During the process some of the gas is condensed and sent to Banagas's
Central Gas Plant (CGP). The compressed gas however contains some
water vapour and acidic gases like carbon dioxide and hydrogen sulphide.
The water vapour may condense in the pipe line due to natural cooling
and the free water, together with hydrogen sulfide
and carbon dioxide present in the associated gas stream, will form
corrosive acid. To avoid this the compressed gas is
dried in a glycol dehydration unit before being pumped through gas
pipelines to the CGP.
CENTRAL GAS PLANT :
The original plant was commissioned in 1980 with a capacity of 110
MMSCFD of Associated Gas.
After a series of plant expansions, BANAGAS now operates two process
trains with a total gas throughput of 280 MMSCFD,
of which 25MMSCFD is high pressure Arab Gas. The two process trains
are identical and use refrigerated lean oil-heavy
Naphtha to recover LPG from the feed gas. Each train consists of condensate,
absorption, fractionation, treating and intermediate storage sections:
Condense from the compressor stations including existing ones from
gas absorption system enters the condense system where fluctuation
in condense feed flow is absorbed and any solids and water are separated.
The condense draw off from the condense system is fed to the Depropanizer
for fractionation. The gas from the condense system is combined with
the feed gas for the absorption system.
| CONDENSATE
SYSTEM : |
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Stabilizer
:
Condensate from the compressor stations and from the
gas separation system is distilled in a stabilizer column to
remove light gas components such as methane and ethane. The
stabilized condensate is fed to the Depropanizer, while the
light gases join the inlet associated gas.
Separation Section :
Associated gas, at 420 psia and a dew point of 40 ºF, enter
the separation section where liquids are removed. Any solid
residue is separated and removed from the process.
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| GAS
ABSORPTION SYSTEM : |
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Dehydration :
The gas leaving the separation section is dehydrated to a dew
point of -45 ºF to prevent the formation of hydrates
in the subzero absorption section. Triethylene glycol is used
to absorb any water from the gas.
Absorber :
In the absorber column the refrigerated feed gas and lean oil
are intermingled at a temperature of minus 35ºF to allow the
lean oil to absorb the LPG products of Propane and heavier components
from the gas and become a rich oil. The residue gas leaves the
absorber to be used as fuel gas by Banagas as well as neighboring
industries.
The absorption of LPG is accelerated by high pressure and low
temperature. Refrigeration of the feed gas and product streams
is provided via a closed loop circulation of refrigerant Propane
using two gas turbines driven centrifugal
compressors at each train.
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FRACTIONATION SECTION :
The purpose of the fractionation system is to separate the stabilized
condense and the rich oil still overhead liquid into three marketable
products, Propane, Butane and Naphtha. |
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Deethanizer :
The purpose of the Deethanizer is to remove ethane and lighter
components from the rich oil in order to maintain a
maximum of 2% ethane in Propane. The overhead vapour is recycled
to the absorber section to recover any escaped Propane and heavier
components. The Deethanizer bottoms are fed to the rich oil
still column.
Rich Oil Still Column / Hot Oil System
:
In the Rich Oil still, lean oil is separated by distillation
from the absorbed LPG products. These LPG products go overhead
and are condensed by the Rich Oil still reflux condenser and
then routed to the fractionation columns. The liquid from the
bottom of these stills is circulated through the hot oil system
as a source of heat for all the plant reboilers and part of
it is used as absorbent Lean Oil. The hot oil temperature is
maintained by a gas fired heater.
Depropanizer And Debutanizer System :
The purpose of the columns is to separate the stabilized condensate
and the absorbed LPG products into three marketable products,
Propane, Butane and Naphtha.
Depropanizer :
The condensed LPG Product and the stabilized condensate are
fed to the depropanizer column. A distillation process
takes place where the light components of Propane are separated
and condensed in a reflux condenser prior to sending
to the treating section.
Debutanizer :
The lighter components of Butane vapour are separated and condensed
in a reflux condenser prior to sending to the
treating section. |
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TREATING
SECTION :
Propane and Butane contain contaminants such as hydrogen sulphide,
carbonyl sulphide and mercaptans.
For the removal of carbonyl sulphide and mercaptans both Propane
and Butane are treated in a fluidized bed of solid potassium hydroxide
(KOH). Prior to this, Propane is treated by Diethanol Amine solution
to remove hydrogen sulfide.
INTERMEDIATE STORAGE SECTION :
Treated Propane and Butane products are routed to horizontal tanks
(bullets). After the product is circulated and analyzed for purity
and water content it is routed to spherical tanks. If any product
fails to meet the required specification it is returned to the Gas
Plant to be reprocessed. Only " On-spec-products" are pumped from
their respective spheres to the refrigerated storage at Sitra.
A very small
quantity of Propane product is sold in the local market, after being
loaded in pressurized trucks. Naphtha product is stored in floating
roof tanks. "On-spec" Naphtha is pumped directly to the Bapco Refinery
for storage and subsequent export.
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REFRIGERATED STORAGE & SHIPPING :
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Refrigerated
Storage :
At Sitra, liquid Propane from the Gas Plant is received into
the surge drum at 356 psig and 120ºF. Some of the Propane
is used as refrigerant, first in the Butane chillers and then
in the Butane sub-coolers. During this process Butane is
cooled to +25ºF and the liquid Propane is flashed into vapour.
The balance of the Propane is flashed to its boiling point
of -45ºF into the Propane Storage tank.
The Propane vapours from the storage tank, Butane chillers
and sub-coolers are compressed by reciprocating
Compressors. The compressed vapours are condensed and used
as refrigerated Propane to cool down both Propane and Butane
products to their atmospheric boiling point of -45ºF and +23ºF
respectively. Each product is stored at its boiling point
in separate refrigerated tanks of 200,000 barrels capacity.
A 100,000 barrel dual purpose storage tank is
also available.
Product
Shipping :
The LPG shipping facilities consist of two loading pumps each
with a rated capacity of 5,000 bbls/hour, a 16" loading
line and a 10" vapour return line, each of which is fitted
with fully articulated arms.
Just before a ship's arrival the loading line is cooled down
with the product to be loaded. The vapour generated is
returned to its respective tank. The loading and vapour return
arms are then connected to the ship and loading
commences at a low rate. As conditions in the loading system
allow, the loading rate is increased up to a maximum
of approximately 10,000 bbls/hour.
Most vessels take a dual cargo of Propane and Butane. With
only one loading line, great care is taken to avoid contamination
of the ships tanks when switching from Propane to Butane or
vice versa. The method of detecting the
arrival of the second product at the ships rail is by closely
monitoring the temperature difference, or 'break', between
Propane (-45ºF) and Butane (+25ºF).
BANAGAS produces approximately 3000 bbls of Propane, 2700
bbls of Butane and 4500 bbls of Naphtha per day and these
products are exported to various parts of world where they
are used as industrial and domestic fuel. Some also finds
its way into petrochemical feed stock.
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