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Tankers
Manuel Ventura
Ship Design I
MSc in Marine Engineering and Naval Architecture
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Main Types of Tankers (1)
- Oil Tanker – tanker for the carriage of crude-oil
• Shuttle Tanker- tanker ship for the carriage of crude-oil
directly from the offshore oil fields to terminals or
refineries.
- Product Tanker - tanker for the carriage of refined
products derived from crude oil (gasoline, Diesel oil, jet
fuel) from the refineries.
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Main Types of Tankers (2)
• Chemical (Parcel Tanker) - tanker for the carriage of
chemical products in bulk.
- Simultaneous carriage of different types of cargo
- More recent ships are equipped with clad tanks (steel coated with stainless steel) or completely built in stainless steel.
- Can carry a large number of different types of cargo
- Each tank has its own load/discharge system with separate pumps and piping systems.
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Main Types of Tankers (3)
- Liquefied Gases – tanker for the carriage of condensed
gases
- The gases are kept in the liquid state due to high pressures or to very low temperatures, in tanks with highly efficient insulation.
- More relevant cargo types:
- LNG (Liquefied Natural Gas) - mainly methane, with temperatures that can reach the –163 ºC.
- LPG (Liquefied Petroleum Gas) - This gases have a low boiling point (-44 to 0°C) and high vapor pressure. They are carried at environment temperature in pressurized tanks independent from the ship’s hull, or at reduced temperatures, at atmospheric pressure. Examples: propane, butane, propylene, butylene
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Ships on Order (2010)
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Shuttle Tankers
- Generally they are conventional tankers equipped to be
moored to a discharge buoy at deep sea
- Load their cargo directly from the oil field, where it is
stored in reservoirs, where generally the sulphur is
removed.
- Require a great maneuvering capability in comparison with
the traditional tankers, and generally are equipped with
dynamic positioning systems.
- Can be easily identified by the raised compartment at the
bow and ramp to handle the cargo hose.
- Typically, a shuttle tanker as DW ~ 120,000 t and a service
speed of abt. 16 knots, higher that conventional tankers.
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Shuttle Tankers
“Viktor Titov”, an Aframax tanker prepared for bow loading.
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Product Tankers
- Carry refined oil products that can be classified into 2 main groups:
- White products (Diesel oil, gasoline, jet fuels, kerosene, lube oils, etc.)
- Black products (fuel oils, residual products)
- Clean cargo tanks characterized by:
- No structural elements inside the cargo space (double skin)
- Corrugated bulkheads (transverse and longitudinal)
- Cargo tanks painted or internally coated
- Each cargo tank is provided with a segregated cargo system including a submersible pump and its own cargo line to the manifold, on deck
- The number of possible cargo segregations on board is equal to the number of cargo tanks
- Typically these tankers are smaller than the crude oil tankers, with DW < 70,000 t
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Heavy Grade Oil
- In MARPOL Convention the designation of Heavy Grade Oil
(HGO) is assigned to the following products:
- Heavy fuels with density at 15ºC > 900 kg/m
- Fuel Oils with
- Density at 15ºC > 900 kg/ m3, or
- Kinematic viscosity at 50ºC > 180 mm2/s
- Bitumen, tar and its emulsions.
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Crude Oil – Classification According to
the Origin
- Europe/North Sea – light product, reduced viscosity, black.
- West Africa - more viscous than the one from North
Europe, becomes more viscous at temperatures < 19 ºC and
volatizes quickly at temperatures > 27 ºC.
- South America – heavy product, viscous
- Persian Gulf
- Asia/China – very heavy product.
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Oil Products
- A large variety of products is obtained from the refined oil
- The oil products can be classified as:
- White Products
- Gasoline
- Petroleum
- Jet-fuel
- Gas oil
- Aromatics
- Black Products
- Diesel Oils
- Fuel Oils
- Asphalts
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Some Definitions and Units
- Barrel (bbl) - Measure of capacity commonly used for crude and refined products. Its historical origin were the wooden barrels that were used to transport the first crudes extracted for commercial purposes. 1 barrel = 35 imperial gallons = 42 US gallons = 159 liters.
- Specific Weight - the standard temperature used by ASTM
(American Society for Testing Materials) for the determination of
the specific weight is 15.5º C (60º F).
- API Grade - scale adopted by theAmerican Petroleum Institute to measure the oil density. The oils with a lower specific weight have higher API Grade. Calculated by the expression: API Grade = (141.5/Specific weight at 60° F) – 131.
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Cargo Systems
- Pump Room
- 1 pump for each cargo segregation (typically 3 or 4)
- Centrifugal pumps of large capacity
- The electrical driving engines are located in the Engine Room - Submersible Pumps − 1 pump for each cargo tank − 1 portable pump − Piping system entirely above the main deck
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Arrangement of the Cross-Over
- Refer to “Recommendations for Oil Tanker Manifolds and
Associated Equipment”, OCIMF.
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Other Cargo Systems (1)
Bow Loading System ( BLS )
• Used inshuttle-tankers to receive the crude oil from cargo
terminals, from cargo buoys and from FPSO's and FSU's.
The shape of the
bow of these ships
must be adapted to
the installation of
these systems.
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Other Cargo Systems (2)
Stern Discharge System ( SDS )
- Installed aft in FSU's and FPSO's to discharge the cargo to
shuttle-tankers.
- The system is supplied with a storage drum for the
discharge hose or, in alternative, with horizontal storage of
the hose in a conveyor
Stern Loading and Discharge System ( SLDS )
- Results from the development of BLS and SDS which allow a
ship to load/discharge cargo through the bow extremity.
- It is an attractive alternative from the economical point of
view for the multi-purpose ships.
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Ballast Systems
The ballast system can also be based on submerged pumps.
SOLAS
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Protection of the Fuel Oil Tanks
Void space or ballast water tank protecting fuel oil tank as shown in Figure, need not be considered as "cargo area" defined in Reg. II-2/3.6 even though they have a cruciform contact with the cargo oil tank or slop tank.
The void space protecting fuel oil tank is not considered as a cofferdam specified in Reg. II-2/4.5.1.1. There is no objection to the locations of the void space shown in the Figure, even though they have a cruciform contact with the slop tank.
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Inert Gas System (IGS)
- The system can be fed by the exhaust gases, by an inert gas
generator or by nitrogen.
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Cargo Tank Venting System
- SOLAS Chap.II-2 Regulations 59 e 62
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Cargo Tank Venting System
- On 1st July of 1998 it became a SOLAS requirement that
the tankers are equipped with a secondary mean to avoid
over/under pressure in the tanks in the eventuality of the
failure of the main pressure/vacuum (p/v) system.
devices that guarantee
that the valves are
opened before any
loading or ballasting
operation.
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Crude Oil Washing System (COW )
- Rotative washing machines
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Cargo Heating System (1)
• The cargo tanks and theslop tanks are equipped with a cargo
heating system
- The purpose of the system is to heat the crude up to a
temperature at which the viscosity will allow it to handled by
the cargo pumping system
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Comparison of Maintenance Costs of
Types Heating Systems
Fonte: Aalborg
The systems based on thermal fluid present higher efficiency values in comparison with the traditional steam ones
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Cargo Heating System (3)
- In alternative the heating
can be obtained by a system
without heating coils, based
on the recirculation of the
cargo by submerged pumps
through heat exchangers
mounted on deck
- Advantages:
- The absence of heating coils facilitates the tank washing
- The heat exchangers are not exposed to the cargo when the cargo is not beeing heated (less corrosion)
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Foam System for Fire Extinguishing (1)
Foam Monitors
- The foam supply rate shall be not less than the larger of the following values: - 0.6 liter/min./m2 of the protected area of the cargo tank, computed as the product of the maximum breadth by the length of the cargo zone - 6 liter/min./m2 of the maximum horizontal section of an individual tank - 3 liter/min./m2 of the area protected by the largest monitor, entirely forward of it, but not less than 1250 l/min.
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Foam System for Fire Extinguishing (2)
- The distance from the foam monitor to the extreme point of
the protected area shall not be > 75% of the monitor ranger
- Forward of the poop deck or of the superstructure, 2 foam
monitors shall be installed, one at each side, oriented to the
cargo area.
