Portable Fuel Tank - The Application of a New Method of Bunkering for Small Scale Gas Fuelled...

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Portable Fuel Tank - The Application of a New Method of Bunkering for Small Scale Gas Fuelled Vessels 79

Portable Fuel Tank - The Application of a New Method of Bunkering for Small Scale Gas Fuelled Vessels

XU Junwei Kelvin, B.Eng

Abul BASHAR, BSc Eng

Sreekala KUMAR, B.Tech

Nigel KOH, BEng, MSc, PhD

THIS PAPER PRESENTS THE APPLICATION OF A NEW METHOD OF BUNKERING FOR SMALL SCALE GAS FUELLED VESSELS in which a portable LNG tank is used as the ship’s fuel tanks. The bunkering could be a simple procedure as replacing the empty tanks with preloaded fuel tanks which are transported by truck, ship or rail. This can greatly reduce the overall bunkering duration and ship will be no longer required to travel to remote designed shore facilities for bunkering. This bunkering method has been adopted in the KOMtech Ocean-going/Harbour LNG Fuelled (Dual Fuel) Tug design. This is achieved through a carefully designed and well-utilised deck layout without reducing the accommodation spaces, maintaining the vessel within the 500GT cap to avoid more implementation from SOLAS regulation.

80 KOMtech Technology Review 2016

INTRODUCTIONAs many LNG terminals over the world are either still under-development or planning for development, the supply of LNG for use as marine fuel via shore based terminals can be an issue. Other bunkering methods such as ship-to-ship, LNG bunker vessels (carrying dangerous cargo) are restricted to entering non-Petroleum harbour areas lest with authorized. Additionally, the industry is hesitant to invest in such vessels due to its high investment costs and limited alternative operations when LNG bunker demand is limited.

Due to lack of fully developed LNG bunkering infrastructure, the most preferred method will be perhaps either the conventional truck-to-ship bunkering method or the portable fuel tank transfer which is adopted in the KOMtech LNG fuelled tug. Both methods are best suited for smaller-sized LNG-fuelled vessels with up to 90m3 tank capacity due to the limited capacity of trucks with 44.5 m3 and LNG is only to transfer at a low rate. Refer to Table 1.

PORTABLE FUEL TANKS – APPLICATION ON A LNG FUELLED (DF) HARBOUR TUGKOMtech has introduced the use of portable tanks as primary fuel tank on a 32m tugboat. The cryogenic

Table 1. Comparison of LNG bunkering method for inland vessel

Description Shore-to-ship Ship-to-ship Truck-to-ship Portable tank transfer

Operation Cost High Very High Average Average

Maintenance Cost High Very High Average Low

Personnel Training Yes Yes Yes Only Ship Crews

Affect Other Trade Yes Yes Yes Yes

Ship Shore Link (with ESD)

Yes Yes Yes No

Bunkering Time (for 40m3 filling at low rate)

Max. 55 min Max. 45 min Max. 80 min *Max. 30min

Bunkering Rate 60 ~ 1000m3/hr 80 ~ 500 m3/hr 35 ~ 60m3/hr NA

Capacity Up to 2000m3 Up to 1000m3 45m3 (each) 20m3 ~ 40m3 (each)

Suitable Ship Scale 500 GT and above 500 GT and above 250 ≤ 1500 GT 250 ≤ 1500 GT

*Esitmated Note: Ship to Ship bunkering process time is longer depend on sea state and weather condition. Refer to [1] & [6]

tank container (IMO - container) is arranged on the aft deck area to avoid obstructing either the towing operation or the visibility of the master at bridge. This arrangement of the portable tanks on deck does not sacrifice spaces below the main deck which could otherwise be used as accommodation space or engine room and also eliminates the risk of enclosed vapour cloud explosions.

This arrangement is best suited for dual fuel vessels, in which the diesel tanks can be arranged within the hull and the LNG tanks can be arranged on the deck. However, this makes the tank vulnerable to high saline seawater which might cause corrosion of the exposed metal over a period of time.

KOMtech – Ship & Marine Technology have developed the dual fuel Tug for worldwide application as well for harbour use. Both versions are integrated with the new hull form which is developed by MTD (Marine & Offshore Technology) for Diesel Escort Tug version in 2015.

The 32m tugboat is designed as dual fuelled vessel which can run on both marine diesel oil and natural gas. The hull tanks for the diesel oil storage has been maintained as with its parent diesel version. The fuel LNG is carried in two portable fuel tanks arranged on the aft deck of the vessel.

Table 2. Principal Particulars of LNG Fuelled (DF) Harbour Tug.

Length Overall 32.00 m

Moulded Breadth 12.48 m

Moulded Depth 5.30 m

Design Draft 4.00 m

Extreme Draft (With Skeg) 5.40 m

Service Speed 13 knots

Bollard Pull (Astern) 65 Tons

Main Propulsion Engine 2 x 1920kW @ 800 RPM

Thruster (ASD) 2.7 m diameter

LNG Tank Capacity 2 x 20 m3

LNG System LNG Vaporizer, Buffer tank

Classification ABS +A1, + AMS, E , Towing Vessel, Fire Fighting Vessel Class 1, BP ( ), GFS (DFD), UWLD.

Vent Mast

LNG Tanks

Bunkering Station

The main areas of interest while having a gas fuelled vessel are the following:

1) Bunkering2) Supply of LNG from tank to the prime mover3) Gas venting arrangement

BUNKERINGPortable Fuel Tanks - Description A cryogenic tank (e.g. IMO-container) comprises a vacuum insulated container that is designed with performance, ease of operation and safety in mind. The cryogenic tank can store LNG. The cryogenic tank is designed in accordance with ISO standards and its size and dimensions ensure that the tanks can be conveniently transported by trailers, ship and railway. These tanks are to be certified and should comply with International Maritime Organization (IMO) regulations, Classification Societies and ISO 1496-3:1995(E) [4].

Figure 1. 3D View of the 32m LNG Fuelled (DF) Harbour Tugboat.



Figure 3. Plan View of the 32m LNG Fuelled (DF) Harbour Tugboat.

Figure 2. Profile View of the 32m LNG Fuelled (DF) Harbour Tugboat.

The structural frame around the tank helps to protect against mechanical damage. The tank is secured on the deck of the vessel using a twist-lock securing mechanism that is commonly used in container ships as illustrated in Figure 4.

The main components of the portable tanks are mainly LNG transfer line and the pressure relief valves.

Figure 4. Typical Portable Fuel tank and the twist lock arrangement.

Type Portable, IMO independent type C tank container

Insulation type Vacuum insulation

Size 20’ IGF ISO container

Dimensions 6,058 x 2,438 x 2,591 mm (L xW x H)

Vacuum ≤0.1Pa (Warm)

Net evaporation rate 0.34%/d (LIN) (ambient conditions: 100kPa and 15ºC

Total geometric volume Abt 20m3

MARVS (inner vessel) 1.0 MPa gauge

MAWP (inner vessel) 0.9 MPa gauge

Design pressure (outer vessel) -0.1 MPa gauge

Design temperature -196ºC

Medium density 426~470 kg/m3

Baffles Two transverse baffles

Frame material Stainless steel 304

Main materials Low alloy steel

Tare Weight 8200kg

Load Weight 8460kg

Maximum gross weight 16600kg

Vacuum design life 5 years

Production design life Not less than 20 years

Connections Quick- Coupling cryogenic hoses

Table 3. Typical Portable Tank Specification

The nitrogen on-board is used for the purging of the pipeline to ensure gas-free before connecting/ disconnecting cryogenic hoses/ stainless steel pipe connection. The cryogenic tank is fitted with o the pressure relief valve when the tank pressure increased above safe level.



Portable Fuel Tank Transfer – A new bunkering methodPortable fuel tank transfer is not considered as a typical bunkering process. The process is treated as loading and unloading of dangerous materials. Such operation will have to follow the stowage and handling requirements for portable tanks containing hazardous materials. Under CG-OES Policy letter 02-15 [7][8]. LNG delivered in Portable Tanks fall under the definition of “Dangerous Cargo” in 33 CFR Part 126 and must be loaded from a designed Waterfront Facility inspected under 33 CFR Part 126.

The advantage of portable fuel tank transfer compared to truck-to ship are mainly lesser maintenance and operation cost (including training of personnel with LNG handling training) and lesser bunkering time. Additionally, there is no requirement for vessel which adopts a Portable Tank transfer to have the Ship Shore Link (SSL) installed on board. However, the shore facility will need a crane facility to transfer these tanks.

Figure 5. Truck-to-Ship LNG Bunkering.

SUPPLY OF LNG FROM TANK TO THE PRIME MOVERIn the regasification unit, liquefied natural gas is boiled off then to regasified to form natural gas, in a circulation of an intermediate fluid (freshwater/ glycol mixture) between a vaporizer and ambient air heater. The gas from the regasification unit is supplied to the engine room through double walled pipes. The annular space in double wall pipe is ventilated by air/insert gas supplied either from engine room or via pipeline outside the engine room (to keep away from hazardous zone). This is to ensure maximum safety in event of gas leakage. The fuel supply from the vaporizer passes through a buffer tank for maintaining a stable supply to the engine to reduce the risk of knocking phenomenon in case of not within the range of fuel quality and temperature as recommended by engine maker.

GAS VENTING ARRANGEMENTExcessive Pressure Build UpThe changes in temperature result in higher vapour pressure in the tank especially if the tank is nearly

Figure 6. Portable Fuel Tank Transfer.

full with reduce vapour space in tank. The cryogenic tank container is fitted with at least two lines exiting the tank top into the pressure relief valve. In case of excessive pressure build up, gas passes through the lines into a main vent mast where it is vented to atmosphere.

Maintaining a minimum safe distance of the venting outlet from openings such as accommodation entrances, engine exhaust outlets and others, is done to avoid the risk of flammable or toxic mixtures accumulating in little air movement condition and drawn into machinery spaces or accommodation. These vapours can be heavier than air when in cold condition and will accumulate in bilges and other low areas.

Commonly observed when flammable or toxic gases can eddy and cause pockets of gas present in most unexpected places such as the aft of the superstructure when wind blowing from forward. The operation profile of a tug demands frequent turning and manoeuvring the vessel during towing, helps to avoid the accumulation of vapors on those areas.

Vent Mast ArrangementHence, directing the vent mast outlet as high as the foremast allows the vapours to rapidly disperse to atmosphere vertically, especially in windy condition. The vent mast outlet is directed to the foremast for achieving a safe distance radius of 10m away from the opening to accommodation and others. The safe distance can be reduced to 4.5m radius as long as a gas dispersion analysis is made to justify the risk and in case of vapour cloud form beyond the 4.5m, a gas detector system is to be provided to acknowledge operator of the risk for precaution. Refer to Figure 7, hazardous zone are define as per description in IGF-code MSC 95/WP.7 [3] and ABS Guideline [2].

Protecting the areas affected by Hazard area on vessel Any equipment within the hazard area is to be explosive proof certified. For example, the walkie-talkie, navigation lights and other lights etc. The main challenge in a small vessel like this tugboat is how to restrict the hazard zone.

Vent Mast Exit

Figure 7. Illustration of the Hazard Area Plan.

Entrance/ exit

Zone 2

Engine room ventilation inlet/outlet

Tank connection pipelines

Engine exhaust outlet

Zone 1

3.0m

4.5m



Efficient deck and equipment layout restricting the hazard zone to a small central area on the aft deck is the method adopted in the design of this tugboat. The LNG related equipment, tanks and pipelines are carefully arranged to avoid hazard zone area for tanks on deck. This also allows the people to work at the wharf/berth while vessel is alongside.

CONCLUSIONThe purposes of this paper is to introduce the portable fuel tank as an efficient method of fuel storage in small scale gas fuelled vessels and highlighting the issues related to installation and handling of such

tanks on deck. Portable fuel tank transfer is best suited for small vessels and in countries where facility is far from vessel operation region or facilities still under development. The advantage over truck-to-ship bunkering method is the reduction in bunkering time with minimum equipment, in a safer manner and also eliminates the ship shore link.

The design concept have been filed for Singapore Provisional Patent (Application no. 10201508833W) – “AN ARRANGEMNT OF CYROGENIC CONTAINERS FOR LNG OR CNG ON A DECK OF A TUGBOAT”.

ACKNOWLEDGEMENTS• ABS Classification Society • Marine Technology and Development (MTD)

We also acknowledge the information input from one of the LNG system suppliers; SHANGAI HANSAIL MARINE & OFFSHORE DESIGN CO., LTD

AUTHOR’S CONTACT [email protected]

REFERENCES [1] American Bureau of Shipping (ABS), Bunkering of Liquefied Natural Gas-Fuel Marine Vessels in North America 2th Edition, USA, 2015.

[2] American Bureau of Shipping (ABS), Guide for Propulsion and Auxiliary System for Gas Fueled Ships, Houston, USA, May 2015.

[3] International Maritime Organization (IMO), IGF-Code MSC 95/WP.7 Adoption of the International Code of Safety for Ships using Gases or other Low-Flashing Point (IGF CODE), NORWAY, 10 June 2015.

[4] International Standardization Organization (ISO), ISO 1496-3:1995 (E) Series 1 freight containers –Specification and testing; Part 3: Tank containers for liquids, gases and pressurized dry bulk, Switzerland, 1995.

[5] John L. Woodard and Rohin M Pitblado, LNG Risk Based Safety – Modelling and Consequence Analysis, Hoboken, New Jersey, John Wiley & Son INC., 2010.

[6] Swedish Marine Technology Forum (SMTF), LNG Bunkering Ship to Ship Procedure, Uddevalla, 2013.

[7] United States Coast Guard (USCG), Guidance Related to Vessles and Waterfront Facilites Conductiong Liqefied Natural Gas (LNG) Marine Fuel Transfer (Bunkering) Operation, Washington, 19 Feb 2015

[8] United States Coast Guard (USCG), Guidelines for Liquified Natural Gas Fuel Transfer Operations and Training of Personnel on Vessel Using Natural Gas as Fuel, Washington, 19 Feb 2015

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