Despite their several years of experience with various grades of Diesel fuel,
an appropriate level of readiness will be required of all those crew members
newly involved with bunkering and monitoring of LNG fuel aboard ship. While
traditional bunkering procedures are required to be followed to ensure maximum
security and safety, the requirements for LNG bunkering are even more rigid.
For instance, given that each flange or coupling connection is a potential
spillage hazard, requiring absolute caution in connecting/disconnecting, the
number of such connections should be held to a minimum. Furthermore, the LNG
Bunkering Rules and Procedures shall include a mandatory “Emergency Shut-Down
Procedure” (ESD), drill to be practiced periodically.
The eventual enforcement of ECA and SECA legislation is fast
approaching, and the new Emission Control Area (ECA) for North America took
effect August 1, 2012, requiring ships to burn fuel oil with a maximum of 1.0%
sulfur content. This in turn will be reduced to 0.1% as of January 1, 2015,
hence, conversion to LNG appears to be the most logical solution, and in this
light, Ship-Owners are advised to consult with the major fuel refineries and
Classification Societies for training programs that cover formal LNG bunkering
procedures.
Meanwhile, it is reasonable to assume that as the demand for
LNG as a marine fuel increases, and that suppliers develop the capability for
economic mass production of same, comparable to that of conventional liquid
fuels, that the price of such fuel will gradually decrease to a more
competitive level and that bunkering stations for LNG will become established
all around the world. There are already numerous LNG carriers equipped with DF
(dual fuel) main propulsion diesel engines, capable of burning cargo-boil-off
gas, built by Rolls-Royce, MAN-B&W and by Wartsila, and their numbers
are gradually increasing.
The choice of LNG is evidently encouraged by proven claims
of lower exhaust emissions resulting from higher efficiency, cleaner burning
characteristics, reduction in NOx and particulate levels averaging 75 percent,
with almost zero levels of SOx.
LNG is not without its limitations, one of which is that LNG
storage tanks have to be heavily insulated to maintain a constant temperature
of minus 165 degrees Celsius. The insulation is required not only to preserve
the ultra-low temperature of the LNG tanks, but also to protect the ship
structures from the effects of the cryogenic temperatures of the LNG.
Aboard ship the required storage space for such tanks is
estimated to be as much as 250 percent larger than that required for
conventional diesel fuel tanks of corresponding fuel capacity.
Another cost factor to be addressed is in the design and
construction of LNG bunker tanks, since unlike conventional marine fuel storage
tanks that are not pressurized, LNG Bunker Tanks are designed, built and
classed as “Pressure Vessels”, and therefore subject to design and construction
rules similar to those of steam boilers and compressed air storage tanks for
use aboard ship. Accordingly, the International Maritime Organization (IMO) has
published IMO Interim Guideline MSC 285(86) adopted in 2009, as a preliminary
version of the IGF-Code. Rules for LNG-fuelled ships have been published by the
various classification societies based on several years of experience with LNG
as a marine fuel.
This document specifies approved criteria for the
arrangement and installation of LNG-fueled engines and related systems and
fixtures, intended to ensure a level of technical integrity regarding the
safety and reliability of same comparable to that of conventional oil-burning
machinery. Meanwhile, the International Maritime Organization is in the process
of compiling a new code that is expected to be incorporated into the SOLAS in
time for the next revision due in 2014. Accordingly, owners of LNG-fueled
vessels will be required to apply for permission of the Harbor Master or
equivalent authority prior to entering port.
Conversely, considerable funds are being expended in the
research of technical solutions and cost-effective methods of improving the
safety and efficiency of LNG-powered main propulsion machinery in an on-going
research and development program pioneered by Germanischer Lloyd, in
partnership with TGE Marine Gas Engineering, MAN-B&W and NEPTUN
Stahlkonstruktion among others.
This effort includes the conversion of an existing oil
tanker from conventional diesel fuel to LNG, to serve as a full-scale model to
provide engineers with a life-size platform on which to install, test and/or
modify their technical concepts to determine feasibility, efficiency and cost
effectiveness, for the ultimate refinement of all phases involved in developing
the most cost-effective LNG-burning marine propulsion plant possible.
While there is still much to be learned about LNG by
operating engineers, there is also much information available from the
manufacturers of LNG-burning marine Diesel engines such as MAN-B&W;
Wartsila and Rolls-Royce, as world-renowned experts in this field, staffed by
highly qualified Service Engineers, on-call, ready to fly out to wherever their
expertise may be needed.
Liquefied Natural Gas, otherwise known as LNG, is natural
gas in its liquid form. When natural gas is cooled to minus 259 degrees
Fahrenheit (-161 degrees Celsius), it becomes a clear, colorless, odorless
liquid and is not corrosive. Natural gas is primarily methane, with low
concentrations of other hydrocarbons, water, carbon dioxide, nitrogen, oxygen
and some sulfur compounds. During the process known as liquefaction, natural
gas is cooled below its boiling point, removing most of these compounds. The
remaining natural gas is primarily methane with only small amounts of other
hydrocarbons.
LNG weighs less than half the weight of water so it will
float if spilled on water. Natural gas may be stored in a number of different
ways. It is most commonly stored underground under pressure in three types of
facilities. The most commonly used in California are depleted reservoirs in oil
and/or gas fields because they are more available. Aquifers and salt cavern
formations are also used under certain conditions. The characteristics and
economics of each type of storage site will dictate its suitability for use.
Two of the most important characteristics of an underground
storage reservoir are its capability to hold natural gas for future use and its
deliverability rate. The deliverability rate is determined by the withdrawal
capacity of the associated valves and compressors and the total amount of gas
in the reservoir. In other states, natural gas is also stored as LNG after the
natural gas has been liquefied and placed in aboveground storage tanks. Natural
gas is the cleanest burning fossil fuel. It produces fewer emissions and
pollutants than either coal or oil.
The North American supply basins are maturing, and as demand
for natural gas increases in California and throughout the United States,
alternative sources of natural gas are being investigated. Natural gas is
available outside of North America, but this gas is not accessible by
pipelines. Natural gas can be imported to the United States from distant
sources in the form of LNG. Since LNG occupies only a fraction (1/600) of the
volume of natural gas, and takes up less space, it is more economical to
transport across long distances and can be stored in larger quantities.
LNG is transported in double-hulled ships specifically
designed to handle the low temperature of the LNG. These carriers are insulated
to limit the amount of LNG that boils-off or that evaporates. This boil-off gas
is sometimes used to supplement fuel for the carriers. Most LNG carriers
average about 1,000 feet in length, and require a minimum of 40 feet draft when
fully loaded.
There are currently 136 ships that transport more than 120
million metric tons of LNG every year, from sources such as Algeria; Australia;
Brunei; Indonesia; Libya; Malaysia; Nigeria; Oman; Qatar; Trinidad and Tobago.
Within the United States, LNG marine terminals are located in Everett,
Massachusetts; Cove Point, Maryland; Elba Island, Georgia; and Lake Charles,
Louisiana, plus Offshore Boston; Gulf of Mexico; Freeport, Texas; Sabine,
Louisiana and Penuelas, Puerto Rico.
It was recently announced that Guidelines for Using Gas as a
Ship Fuel, in line with I.M.O. regulations, have been issued by the German
Classification Society, Germanischer Lloyd. These provisions are applicable to
all ships powered by single-fuel such as natural gas, or dual fuel such as gas
and fuel oil, in conjunction with the relevant provisions established by the
SOLAS, and the natural gas may be stored in either a gaseous or liquid state,
according to Dr. Herman J. Klein, Executive Board Member of GL. However, they
do not apply to liquefied gas tankers.
In addition to several years’ service as engineering
officer, British Merchant Navy and as Chief Engineer, US Merchant Marine, Louis
Lemos is a US Navy certified Ship Superintendent (MINS); former Marine
Engineering Advisor to the South Vietnamese Navy, (US Defense Attaché Office, Saigon);
a licensed Stationary Engineer (Tampa, Florida); Commissioned Inspector of
Boilers and Pressure Vessels (National Board); former Port Engineer with
Military Sealift Command, (MSCPAC and MSCFE). Now retired, he has more time to
pursue his writing. Mr. Lemos can be reached at 415-897-9056 or
louislemos@comcast.net.
