ZENITH ASIA COMPANY LIMITED
Storage facilities
Storage facilities for crude, natural gas, and light hydrocarbon
products are an important element in all pipeline and tanker
transportation systems. Storage allows flexibility in pipeline and
refinery operations and minimizes unwanted fluctuations in pipeline
throughput and product delivery. The capacity of individual storage
tanks or facilities varies widely. Small crude storage tanks are
common on producing leases, while export tanker loading terminals
can have several million bbl of crude storage capacity in a few
giant tanks. Both aboveground storage and belowground storage are
used for both natural gas and hydrocarbon liquids.
Storage facilities
Storage : Crude Storage On the producing lease, oil from
individual wells is accumulated in tanks, then pumped into the
crude oil gathering pipeline. Typically, one or more 500 bbl or
1000 bbl tanks are located on an individual lease, depending on the
volume of crude produced. Crude may not be pumped continuously from
the lease tanks if produced volumes are small. If a LACT system is
used, the tank will fill to a prescribed level and the pump will
automatically start. When the fluid in the tank is lowered to
another preset level, pumping into the gathering pipeline will
.stop automatically. If the crude is run manually, an operator will
start the pump when the tank is full and will stop it when the tank
is nearly empty.
Storage facilities
Storage :Crude Storage At each step in the pipeline gathering
and delivery system, varying storage requirement exist. The point
at which a gathering pipeline system enters a main crude trunk
line, for example, often contains storage facilities. At the
terminus of the crude trunk line-either a refinery or an export
terminal-storage capacity is typically much larger. A refinery must
operate continuously to be efficient, though its throughput can be
reduced if necessary; enough crude to feed the refinery must be
available. A crude trunk line is seldom shut down, but variations
in throughput caused by conditions in the gathering system or in
the producing fields are not unusual. Refinery storage minimizes
the effect of these fluctuations and allows the refinery to operate
at a relatively constant throughput.
Storage facilities
StorageCrude Storage A refinery located near oil production or
at the end of a pipeline serving a major field may need less
storage than a refinery that receives crude by tanker. Storage must
be provided for periods between tanker deliveries. A refinery must
also have storage for the products it manufactures.
Storage facilities
Crude Storage Other factors that help determine the amount of
storage a refinery needs for both feedstock and products include:
Product delivery. If products are delivered continuously to a
pipeline, storage needs will be reduced. Small refineries may
accumulate products before delivery to the pipeline or to a tanker.
Refinery complexity. The more products a refinery produces, the
more storage will be needed for intermediate feedstocks. Seasonal
demand. One product may be produced in greater quantities during a
part of the year, another during another season. In the United
States, gasoline sales are greater in the summer, for instance, and
distillate fuel sales are greater in the winter Turnarounds.
Refineries are periodically shut down for inspection, repair, and
maintenance (a turnaround).Storage must be available for feedstock
and products during these periods.
Storage facilities
Crude Storage According to one source, a refinery that is
supplied by pipeline should have 6 days of crude feedstock storage;
if supplied by tanker, 32-35 days of storage is recommended. At
tanker terminals, the amount of storage depends on the amount and
type of product handled; the number, capacity, and type of tanker
berths in the terminal; expected periods of downtime; and the
number and size of ships using the terminal.
Storage facilities
Crude Storage Crude storage tanks are cylindrical and are
operated at near atmospheric pressure Small lease storage tanks are
typically shop-fabricated and are delivered to the site where they
are connected to pumps and other facilities. Large crude storage
tanks may be capable of storing up to several hundred thousand
barrels each and must be built on the site. Large crude storage
tanks often have a floating roof that moves up and down with liquid
level in the tank to minimize vapor losses. Smaller storage tanks,
including those on the producing lease, have fixed roofs.
Storage facilities
Crude Storage Many crude storage tanks are equipped with vapor
recovery systems that capture light hydrocarbons that evaporate
from the crude and would otherwise he lost to the atmosphere.
Economics, air-pollution regulations, or both may dictate the use
of vapor recovery systems, depending on the area and the amount of
vapor losses. Considerations involved in designing large crude
storage tanks include the integrity of the foundation, safety,
maintenance requirements and ease of maintenance, and operating
efficiency.
Storage facilities
Crude Storage Underground caverns mined from salt domes or other
formations are used for long term crude storage. This type of
storage is usually for strategic or emergency purposes. The United
States stores crude in its Strategic Petroleum Reserve in Texas and
Louisiana, for instance, in order to be prepared for interruptions
in the supply of imported oil. Crude is stored in five salt dome
caverns; pipelines connect the caverns to crude terminals. Crude
imported by tanker is pumped into the caverns through wells and
will be withdrawn through wells when needed.
Storage facilities
Crude Storage By the end of 1990the Strategic Petroleum Reserve
caverns held almost 600 million bbl, representing about 100 days of
oil imports at the then-current United States import rate. Plans
are to store a total of 1 billion bbl in the Reserve. Other
countries that are heavily dependent on imported oil have also
developed underground long-term crude storage facilities.
Storage facilities
Natural Gas Liquids Natural gas liquids(NGL)storage is provided
at natural gas processing plants where products are delivered into
the NGL gathering pipeline. Additional storage is required
throughout a natural gas liquids transportation system for the same
reasons crude storage is required in the crude transportation
system. Most natural gas liquids, however, must be stored in
pressurized tanks or vessels. Their vapor pressure is such that
they will evaporate if stored at atmospheric pressure. Typically,
storage tanks for propane, butane, and similar products are
horizontal, cylindrical tanks with hemi-spherical ends, often
called bullet tanks. Liquefied petroleum gases(LP-gas) are also
stored in underground caverns by injecting the fluid into the
cavern through wells. Withdrawal of product is also through wells
extending into the cavern.
Storage facilities
Natural Gas Natural gas is stored underground, or as LNG in both
aboveground and below ground tanks. Natural gas storage is needed
to meet peak demands that may be much higher than the pipeline's
average throughput. It would not be possible to vary production
from gas wells feeding into the transmission line as widely and as
frequently as demand varies. Natural gas demand is highly dependent
on weather, for instance, and a method to handle these fluctuations
is required.
Storage facilities
Natural Gas Natural gas can be stored underground in rock or
sand reservoirs that have suitable permeability and porosity. The
gas is injected through wells under pressure; then pressure in the
reservoir is used to force the gas out when it is needed. When
demand is high, gas is withdrawn from the reservoir and is combined
with gas being delivered by the transmission pipeline. Natural gas
can also be stored in depleted oil or gas fields. When demand is
low, natural gas is diverted from the transmission pipeline into
storage. Some of the natural gas in the reservoir must be used as
"cushion" gas to allow withdrawal and injection of usable gas.
Storage facilities
Natural Gas Storage reservoirs are ideally located near
consuming centers and near the transmission pipeline and its
compression facilities. To be suitable for gas storage, a reservoir
should have the following: An impermeable reservoir cap rock to
prevent leakage and pressure loss. High porosity and permeability
in the reservoir rock. A depth sufficient to allow a safe pressure
in the reservoir}'}. Either no water or a controllable water
condition. A thick vertical formation rather than a thin,
horizontal formation. An oil-free environment, although depleted
oil-producing formations have been used.
Storage facilities
LNG Natural gas is also stored as a liquid. LNG storage is a way
to compactly. When liquefied at about-260 its volume is reduced to
gaseous volume.LNG storage is required at base-load plants,
complete plants that include purification, liquefaction, storage,
and regasification; terminal plants where LNG is received from
tankers and regasified as needed; and peak-shaving plants used to
store natural gas 1/600 of the gas as liquid to meet peak
demands.
Storage facilities
LNG Underground storage tanks, aboveground storage tanks, and
frozen earth storage are all used to store LNG. Because it must be
stored at very low temperatures to maintain it in a liquid state,
insulation is one of the most important elements of LNG storage
design. In frozen earth storage, a cavity is excavated in the
ground. Pipes are installed around the cavity through which
refrigerant is circulated to freeze the earth and form an
impermeable barrier. The cavity is topped with an insulated cover
to contain the LNG. Aboveground LNG storage tanks are double
walled; insulation is contained between the inner and outer
walls.
Storage facilities
LNG Underground concrete storage tanks also used for LNG
storage, are considered applicable for large storage quantities of
1 million or more. These tanks must also be heavy insulated to
prevent vaporization of the LNG while it is in storage. Aboveground
storage is used in the majority of LNG peak-shaving and base-load
plants. There are many of both types of plants around the world.
Countries with no natural gas production, such as Japan, have been
very aggressive in increasing imports of LNG in recent years to
protect against high crude oil prices and crude supply
interruptions. From storage, LNG is pumped to a vaporizer that
regasifies the natural gas for delivery to customers.
Storage facilities
Tank Classification There are many ways to classify a tank, but
there is no universal method. However, a classification commonly
employed by codes, standards, and regulations is based on the
internal pressure of a tank. This method is useful in that it
depends on a fundamental physical property to which all tanks are
subjected--internal or external-pressure.
Storage facilities
Atmospheric Tanks There are many ways to classify a tank, but
there is no universal method. However, a classification commonly
employed by codes, standards, and regulations is based on the
internal pressure of a tank. This method is useful in that it
depends on a fundamental physical property to which all tanks are
subjected--internal or external-pressure.Low-pressure Tanks
Ironically, low pressure in the context of tanks means tanks
designed for a higher pressure than atmospheric tanks. In other
words, these are relatively high-pressure tanks. These tanks are
designed to operate from atmospheric pressure up to l5 psig.
Storage facilities
Pressure Vessels ( High-pressure Tanks) Since high-pressure
tanks (vessels operating above 15 prig) are really pressure
vessels, the term high-pressure tank is not used by those working
with tanks. Because pressure vessels are a specialized form of
container and are treated separately from tanks by all codes,
standards, and regulations, they are not covered in detail in this
section.
Storage facilities
Pressure Vessels ( High-pressure Tanks) However, a few words are
in order to clarify the relationship between pressure vessels and
tanks. When the internal design pressure of a container exceeds 15
psig, it is called a pressure vessel. The ASME Boiler and Pressure
Vessel Code is one of the primary standards that has been used
throughout the world to ensure safe storage vessels. Various
substances such as ammonia and hydrocarbons are frequently stored
in spherically shaped vessels which are often referred to as tanks.
Most often the design pressure is 15psig or above, and they are
really spherical pressure vessels and their design and construction
fall under the rules of the ASME Boiler and Pressure Vessel
Code.
Storage facilities
Major Tank Components There is no clear way of classifying tanks
based upon a single criterion such shape or roof type; however, the
vapor pressure of the substance stored or internal design pressure
is the broadest and most widely used method adopted by codes,
standard, and regulations, as explained above. To a large extent,
the vapor pressure determine the shape and, consequently, type of
tank used. Some of the key components that determine tank type are
described below (see Tables 3-1 to 3-3 and Fig.3-1)
Storage facilities
Fixed-roof Tanks The roof shape of a tank may be used to
classify the type of tank and is instantly self-explanatory to tank
fabricators and erectors. To understand why, it is helpful to have
a brief understanding of the effect of internal pressure on plate
structures including tanks and pressure vessels. If a flat plate is
subjected to a pressure on one side, it must be made quite thick to
resist visible bending or deformation. A shallow cone roof deck on
a tanks approximates a flat surface and is typically built of
3/16-in-thick steel. It is therefore, unable to withstand more than
a few inches of water column. The larger the tank, the more severe
the effect of pressure on the structure, As pressure increases, the
practicality of fabrication practice and costs force the tank
builder to use shapes which are more suitable for internal
pressure.
Storage facilities
Fixed-roof Tanks The cylinder is an economical, easily
fabricated shape for pressure containment. Indeed, almost all tanks
are cylindrical on the shell portion. The problem with cylinders is
that the ends must be closed. As discussed, the relatively flat
roofs and bottoms or closures of tanks do not lend themselves to
much internal pressure. As internal pressure increases, the tank
builders use domes or spheres. The sphere is the most economical
shape for internal pressure storage in terms of required thickness,
but it is more difficult to fabricate generally than dome- or
umbrella roof tanks.
Storage facilities
Floating-roof Tanks All floating-roof tanks have vertical shells
just as a fixed-cone-roof tank does. These common tanks have a
cover that floats on the surface of the liquid. The floating cover
or roof is a disk structure that has sufficient buoyancy to ensure
that the roof will float under all expected conditions, even if
leaks develop in the roof. It i} built with approximately an 8to
12-in gap between the roof and the shell, so it does not bind as
the roof moves up and down with the liquid level. The clearance
between the floating roof and the shell is sealed by a device
called a rim seal.The shell and bottom are similar to those of an
ordinary vertical cylindrical fixed-roof tank.
Storage facilities
Floating-roof Tanks The two categories of floating-roof tanks
are external floating roof (EFR) and internal floating roof
(IFR).If the tank is open on top of the tank, it is called an EFR
tank. If the floating roof is covered by a fixed roof on top of the
tank, it is called an internal floating-roof tank. The function of
the cover is to reduce evaporation losses and air pollution by
reducing the surface area of liquid that is exposed to the
atmosphere. Note that fixed-roof tanks can easily be converted to
internal floating-roof tanks by simply installing a floating roof
inside the fixed roof tank. Conversely, external floating-roof
tanks can be easily converted to internal floating-roof tanks
simply by covering the tank with a fixed roof or a geodesic
dome.
Tank Plan
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Storage facilities
Floating-roof Tanks The two categories of floating-roof tanks
are external floating roof (EFR) and internal floating roof
(IFR).If the tank is open on top of the tank, it is called an EFR
tank. If the floating roof is covered by a fixed roof on top of the
tank, it is called an internal floating-roof tank. The function of
the cover is to reduce evaporation losses and air pollution by
reducing the surface area of liquid that is exposed to the
atmosphere. Note that fixed-roof tanks can easily be converted to
internal floating-roof tanks by simply installing a floating roof
inside the fixed roof tank. Conversely, external floating-roof
tanks can be easily converted to internal floating-roof tanks
simply by covering the tank with a fixed roof or a geodesic
dome.
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Storage facilities
Floating-roof Tanks EFR tanks have no vapor space pressure
associated with them and operate strictly at atmospheric pressure.
IFR tanks, like fixed-roof tanks, can operate at or above
atmospheric pressure in the space between the floating roof and the
fixed roof. The fundamental requirement for floating roofs is
dependent upon whether the roof is for an internal or external
application. The design conditions of the external floating roof
are more severe since they must handle rainfall, wind, dead-load,
and live-load conditions comparable to and at least as severe as
those for building roofs.
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Storage facilities
Tank Bottoms As mentioned earlier, the shapes of cylindrical
tank closures(e, g., top and bottom) are a strong function of the
internal pressure. Because of the varying conditions to which a
tank bottom may be subjected, several types of tank bottoms have
evolved. Tank bottom classifications may be broadly classified by
shapes as flat-bottom, conical and domed or spheroid. Because
flat-bottom tanks only appear flat but usually have a small
designed slope and shape, they are subclassified according to the
following categories: flat, cone up cone down, single-slope.
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Storage facilities
Tank Bottoms Tank bottom design is important because sediment,
water, or heavy phases settle at the bottom. Corrosion is usually
the most severe at the bottom can have a significant effect on the
life of the tank. In addition, if the stock is changed, it is
usually desirable to remove as much of the previous stock as
possible. Therefore, designs that allow for the removal of water or
stock and the ease of tank cleaning have evolved. In addition,
specialized tank bottoms have resulted from the need to monitor and
detect leaks since tank bottoms in contact with the soil or
foundation are one of the primary sources of leaks from aboveground
tanks.
Storage facilities
Tank BottomsFlat. For tanks less than 20 to 30 ft in diameter,
the flat-bottom tank is used. The inclusion of a small slope as
described above does not provide any substantial benefit, so they
are fabricated as close to flat as practical.Cone up. These bottoms
are built with a high point in the center of the tank(Fig.3-1).
This is accomplished by crowning the foundation and constructing
the tank on the crown. The slope is limited to about 1 to 2 in per
10-ft run. Therefore, the bottom may appear flat, but heavy stock
or water will tend to drain to the edge, where it can be removed
almost completely from the tank.
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Storage facilities
Tank BottomsCone down. The cone-down design slopes toward the
center of the tank. Usually, there is a collection sump at the
center. Piping under the tank is then drained to a well or sump at
the periphery of the tank. Although very effective for water
removal from tanks, this design is inherently more complex because
it requires a sump, underground piping, and an external sump
outside the tank. It is also particularly prone to corrosion
problems unless very meticulous attention is paid to design and
construction details such as corrosion allowance and coating or
cathodic protection.
Storage facilities
Tank BottomsSingle-slope. This design uses a planar bottom but
it is tilted slightly to one side. This allows for drainage to be
directed to the point on the perimeter, where it may be effectively
collected. Since there is a constant rise across the diameter of
the tank, the difference in elevation from one side to the other
can be quite large. Therefore, this design is usually limited to
about 100 ft.Conical bottoms. Tanks often use a conical bottom
which provides for complete drainage or even solids removal. Since
these types of tanks are more costly, they are limited to the
smaller sized and often found in the chemical industry or in
processing plants.
OG Map
Tank Structure Unit
Plan A & B
PIPELINE MECHNICAL DESIGN
Professor Wangyuan
Department of Petroleum EngineeringSouthwest Petroleum
University
Design considerations (1)
Codes and standards
- ANSI
- ASME
- API
GAS PIPELINE DESIGN SUMMARY(1)
1. Pipeline diameter vs. compressor horsepower2. Reservoir
pressure prediction3. Pipeline design pressure limitation, i.e.
valve and flange pressure ratings4. Optimum compression ration
(1.25-1.35)5. Future drilling (looping)
GAS PIPELINE DESIGN SUMMARY(2)
6. Pressure drop 20 to 65 kPa/km7. Compressor station spacing a)
Reciprocating 130-160 km apart b) centrifugal 65-80 km apart8.
Geographical, environmental, socio-economic considerations9. Gas
storage capabilities/ requirements of system
ZAW MIN OO
THANK
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