Current Emission Regulations and Prospects of Liquefied Petroleum Gas (LPG) as Marine Fuel
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| Marine Fuel Oil Sulphur Content Requirements |
Marine Industry is undergoing a
transformation set forward by the coming into force of emissions regulations by
the International Maritime Organization (IMO). From 1 January 2020, the content
of Sulphur in Fuel Oil, for shipboard use, is limited to 0.5%. Ships which have
been burning low cost Heavy Fuel Oil with Sulphur content of 3.5% are now
required to use fuel with 0.5% Sulphur content resulting in huge financial
implications. Several alternatives are being explored for complying with the
regulations including the application of Liquefied Natural Gas (LNG), Methanol,
use of SOx scrubbers for exhaust gas treatment, Biodiesel, Hydrogen, Ammonia,
Synthetic gas, Nuclear power etc.
Liquefied Petroleum Gas
(LPG) is another fuel for consideration. With negligible Sulphur content, the SOx
emissions are eliminated from the exhaust (The World LPG Association, 2017) allowing compliance
with the global Sulphur cap as well as regional Sulphur cap of 0.1% in Sulphur
Emission Control Ares (SECAs). There is also a 13-18% reduction in Carbon
emissions (Solutions, n.d.) when compared with
equivalent HFO powered engines.
Using alternate fuels
poses several challenges in terms of managing the safety hazards, bunkering and
storage onboard, installation of additional machinery to process the fuel for
use in engines, training and familiarisation of crew for safe handling etc. Several
of these challenges would be easily managed if a vessel can safely use its
cargo as fuel, as in the case of LNG ships using boil-off gas as fuel. Considering
the above, using LPG as fuel would be an economical option for large ships
carrying LPG, provided the associated risks can be safely managed.
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Very Large Gas Carrier (VLGC) Source: http://www.helioslpg.com/fleet
Very Large Gas Carriers (VLGCs) are ships
that carry more than 75,000 cbm of liquified gases in fully refrigerated
condition. Mostly these vessels are designed to carry propane, butane or
mixtures of both. For these vessels it would make sense to power the vessel using the Sulphur
free LPG already being carried onboard as cargo. It doesn’t require additional
storage or bunkering facilities, crew are already familiar with LPG, saves valuable time – which would otherwise be
spent taking bunkers. The challenge remains now to
ensure its safe usage as a fuel.
Liquefied Petroleum Gas (LPG) – Properties &
Safety Hazards
Liquefied Petroleum
Gases are mainly mixtures of Propane and Butane in liquid form. In the context of LPG as fuel, the following discussions are based
on Propane.
Appearance
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Colourless gas/liquid
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Odour
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Odourless
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Flashpoint
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-105℃
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Auto-Ignition temperature
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450℃
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Flammable limit
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2-10% by vol.
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Boiling point (atmospheric pressure)
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-42℃
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Relative vapour Density
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1.55
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Table 1 LPG (Propane) Properties (International Chamber of
Shipping , 1995)
There are safety
hazards associated with LPG and safe handling of these hazards are imperative
in ensuring its usage onboard as fuel. Following are to be considered,
Flammability – It is the major hazard. Vapour has a
flammability range of 2-10% by volume. If ignited, the air-vapour mixture could
release explosive force causing structural damage.
Low Temperature Hazards – Direct contact with the cold liquid or
uninsulated section of piping/fuel processing equipment could cause cold burns
or frostbite. Inhalation of cold vapour is harmful to internal organs (International Chamber of
Shipping , 1995) .
Relative Vapor Density – Propane vapour is heavier than air, with a
relative vapour density of 1.55. Proper safety measures
to “heavier than air” must be considered for ventilation, gas detection and
venting system designs.
What then are the Challenges with using LPG as Marine fuel
Although compliant with the Sulphur content
requirement and readily available onboard the VLGC, application of LPG as a
marine fuel is not without its challenges. In addition to the safety hazards
associated with its usage, some of the key considerations are as follows.
Fuel Type
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Energy
Density MJ/L
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Req. Tank
Volume
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CO2
Emission Reduction Compared to HFO Tier II
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HFO
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35
|
1000
|
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LNG
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22
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1590
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24%
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LPG
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26
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1346
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13-18%
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Methanol
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15
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2333
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5%
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Ammonia
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12.7
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2755
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N/A
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Table 2 Alternative Fuels Energy Density Comparison (Solutions, n.d.)
Lower energy content in
comparison with other fuel types - The energy density of LPG is lower than Heavy Fuel
Oil, however it is still higher than LNG or other fuels. The lower energy
density would necessitate carriage of 30% more fuel as compared to HFO for
achieving the same endurance.
Requirement for additional auxiliary machinery - When compared with other traditional fuels,
storage and processing of LPG requires several additional machineries including
fuel processing equipment, safety systems, pressure relief systems etc. incurring
additional capital costs.
Regulatory Considerations for Application of
LPG as Marine fuel
Currently there are no prescriptive
statutory requirements for the use of LPG as fuel. LPG carriers complies with
IGC Code and Chapter 16 of the code contains detailed requirements for the use
of methane as
fuel, other gases are excluded. Use of LPG would require acceptance from the
vessel’s flag administration. It should be demonstrated to the Administration
that the proposed arrangements would provide equivalent level of safety,
reliability and dependability provided by oil fuelled marine machinery. This can
be considered in via SOLAS Reg. II-1/55 Alternate Design & Arrangements.
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