1. ZENITH ASIA COMPANY LIMITED
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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.
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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.
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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.
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Storage facilities
Storage
Crude 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.
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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.
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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.
8. 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.
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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.
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Storage facilities
Crude Storage
By the end of 1990 ， the 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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. 23
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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.
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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 8 一 to 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.
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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.
27. Tank Plan
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
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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.
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Storage facilities
Tank Bottoms
Flat. 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 Bottoms
Cone 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.
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Storage facilities
Tank Bottoms
Single-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.
39. GAS PIPELINE DESIGN SUMMARY(1)
1. Pipeline diameter vs. compressor horsepower
2. Reservoir pressure prediction
3. Pipeline design pressure limitation, i.e. valve
and flange pressure ratings
4. Optimum compression ration (1.25-1.35)
5. Future drilling (looping)
40. GAS PIPELINE DESIGN SUMMARY(2)
6. Pressure drop 20 to 65 kPa/km
7. Compressor station spacing
a) Reciprocating 130-160 km apart
b) centrifugal 65-80 km apart
8. Geographical, environmental, socio-
economic considerations
9. Gas storage capabilities/ requirements of
system
