Using LNG as Fuel
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 email@example.com.