Diesel Engine Exhaust Gas Emissions And The Effects Of Alternate Fuels

Comparative Analysis
Studies were conducted in 1990 under the Marine Exhaust Emissions Research Program of Lloyd's Register Engineering Services in London, England, of exhaust gas emissions from some forty motor-ships operating under normal service conditions. The power range of the ships involved varied from 369 kW (494 bhp) to 7,700 kW (10,318 bhp) including slow-speed, direct-drive, and medium speed, geared-drive vessels in variable speed operation, plus Diesel-Electric drive at constant speed. The results of this research show that compared to medium-speed geared-drive Diesel engines operating in a variable speed mode, a significant reduction in nitrogen oxide emissions can be achieved by a Diesel-Electric powered ship operating for extended periods at partial loads, while the main propulsion Diesel generators are operating at constant speed. Charts of comparative curves of toxic emissions based on the findings of the Lloyd's Engineering Services study show two sets of curves plotted from quantitative analysis of toxic products of combustion from typical medium speed Diesel engines. The curves shown for variable speed operation (bold line) represent typical exhaust emissions of a medium speed geared Diesel with controllable pitch propeller. With a variable speed engine operating at approximately 30% of mcr (MAXIMUM CONTINUOUS RATING) such as may occur when entering or leaving port; maneuvering to lower or recover over-the-side scientific sensors or samplers; tracking satellites or missiles, the exhaust emission of nitrogen oxides peaks around 2,230 ppm, which is about 280% higher than NOx emissions at 100% of mcr. The curves shown for constant speed operation (broken line), are representative of typical Diesel-electric propulsion or power plant emissions wherein regardless of electrical load fluctuations the prime mover continues to operate at constant operating speed for maximum efficiency and optimum fuel economy. This research effort also determined that one metric ton of Diesel fuel generates approximately 60 kg of NOx; 8.0 kg of CO, 3 kg of HC; and up to 60 kg of S02, depending on the sulfur content of the fuel.

Exhaust Gas Composition
Prior to combustion the elemental constituents are air and fuel. Volumetric composition of air at sea level is approximately 78% nitrogen and 21% oxygen, at a ratio of: 78 divided by 21 = 3.714:1, meaning that combustion air includes 3.714 mols of nitrogen for each mol of oxygen. Since nitrogen is an inert gas it does not participate in the combustion process except for a small portion that reacts chemically to form oxides of nitrogen (N0x), the production of which increases in proportion to temperature rise. A typical grade of Diesel fuel may comprise 13.51% hydrogen and 84% carbon (by weight), plus minor amounts of sulfur, oxygen and ash. Given 1.0 lb. of fuel, nominal weight factors are 0.1351 lbs. of hydrogen plus 0.84 lbs. of carbon. During the combustion process a portion of the oxygen in the charge air reacts with the carbon, hydrogen and sulfur of the fuel to produce carbon dioxide (CO2), water vapor (H20) and sulfur dioxide (S02) which become the products of combustion. Approximately 3% of the sulfur dioxide oxidizes in the atmosphere to sulfur trioxide (S03).

In its original form nitric oxide (NO) is not considered hazardous. but as it cools upon discharge into the atmosphere much of it will convert to nitrogen dioxide which is toxic. While some people tend to fault marine Diesel engines for their exhaust emissions far more so than that of their highway or railroad counterparts, the truth is that for a riverine tugboat pushing a "Fleet" of twelve loaded barges upstream, the Diesel engine exhaust emissions are estimated to be approximately 0.470 grams per ton/mile; about 27.70% lower than that of railroad trains and 35.60% lower than that of highway trucks. Depending upon the feasibility of LNG bunker space requirements relative to contemporary Diesel fuel tankage aboard tugboats, conversion to LNG, if feasible, is expected to reduce their exhaust emissions even further.

Environmental Preservation
In keeping with world-wide concern for environmental preservation, the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO) has recommended quantitative limitations to restrict atmospheric pollution by harmful exhaust emissions from marine propulsion plants of all types. The objective was to reduce nitrogen oxide emissions to 70% of current levels and that of sulfur dioxide to 50% of current levels, with even more restrictive levels during the next few years. The importance of minimizing current levels of such toxic effluent and its adverse impact upon us should be evident from Table 1 (Above) which shows typical toxic exhaust gas emissions and their respective harmful effects.

Effective limitation of exhaust gas toxic emissions will require a concerted research effort to devise means that are capable of achieving significant reduction of harmful emissions while minimizing adverse impact upon fuel consumption economy. Effective technology is available and now in use albeit on a very small scale but it is still rather expensive. In addition to limitations of toxic Diesel exhaust gas emissions recommended by the Marine Environment Protection Committee of the International Maritime Organization, (IMO), the Air Resources Board of the State of California (CARB) has proposed its own rules. These limitations apply to all vessels, new and existing, operating within 100 miles off the coast of California, for more than 100 hours per year. Unlike the IMO recommendations, requiring a percentage reduction of harmful exhaust emissions relative to current levels, the proposed CARB rules specify limits of NOx concentration, in terms of parts per million, for main propulsion engines, and for generator engines, plus maximum allowable sulfur (SO) content of fuel to be used for all engines and a smoke opacity limit. The proposed date for such rules was January 1, 1995, subject to Federal approval by the EPA. However, despite the good intentions of the CARB, the Environmental Protection Agency has determined that the State of California does not have the authority to enforce such legislation beyond the coastline of California, that properly falls within the jurisdiction of the Federal Environmental Protection Administration. In this regard, the EPA has expressed concern over the adverse contribution of nitrogen-oxide (NOx) emissions from marine engines to atmospheric pollution. Elaborating upon existing rules applicable to railroad locomotives and off-highway heavy equipment engines, the EPA is seeking to extend its jurisdiction to include marine engines by publication of an Advance Notice of Rulemaking, in May 1998. Under this proposal, marine engines would be grouped into three categories, as follows:

Category I — Engines of 2,000 bhp or less.

Category II - Engines classed as "locomotive-derivative", meaning the typical medium-speed main propulsion engines found on coastal freighters, ferries and tugboats.

Category III - Heavy duty, slow-speed main propulsion engines found on ocean-going oil tankers, bulk carriers and container, ships.

A second Notice of Proposed Rulemaking was issued in December, 1998 with more specific details, and a final rule was expected to be published in November, 1999. Legislation was passed by the U.S. House and Senate in October 1998 to amend the Energy Policy Act of 1992 (EPACT) by allowing Federal and State Diesel-powered vehicle fleets to burn bio-diesel fuel, a soybean-derivative fuel as opposed to the conventional petroleum-based Diesel fuel. This legislation is a part of the Energy Conservation Reauthorization Act. (ECRA) of 1999 and as such allows Federal and State fleet managers to meet EPACT requirements to acquire alternative fuel vehicles (AFV), by blending twenty percent or more bio-diesel with conventional Diesel fuel. By means of this compromise, in lieu of outright replacement of existing Diesel-powered fleets with AFV's, credits would be allowed to Federal and State fleets of up to 50 percent each year of AFV acquisition requirements. International concern with exhaust emissions is evident in the recent Air Pollution Control Regulation of 1998 published by the Hong Kong Government, which imposes stringent emission standards for privately-owned Diesel cars and to strengthen such standards for light duty Diesel-powered trucks. These new standards are expected to be comparable to those of the European Union. Meanwhile, as of December 1998, several European Union countries have agreed upon more rigid air pollution standards intended to reduce Diesel truck emissions by 30 percent by the year 2000 and by 50 percent by 2005.The agreement specifically includes emissions of NOx, CO and HC and is also intended to cover heavy-duty vehicles fueled by LPG and natural gas. With Diesel-Electric propulsion plants this level of NOx reduction may be expected to be somewhat higher given the more stable temperature and flow rate of the exhaust gas. Both are conducive to effective catalytic reaction as shown during comparative tests of exhaust gas emissions from a Diesel-Electric ferry and a geared-Diesel ferry sailing at reduced speed close to destination ports, the results of which were published in October 1991 by ABB Marine. While operating in the reduced speed mode, such as navigating a narrow ship channel, maneuvering in or out of the terminal slip, power loading of the geared Diesel vessel ranged from 24% to 62%. In the case of the Diesel-Electric vessel power loading varied between 42% and 85%.

The difference in reduction of NOx emissions between the two vessels averaged approximately 20% higher for the Diesel-Electric vessel. On this basis is appears that as technology improves and usage of SCR becomes more widespread, the nitrogen oxide component of exhaust emissions could be considerably reduced. Successful attainment of such results however, is costly and there is still SOx and HC, etc., to contend with. A typical SCR system for either new construction or retrofit of an existing vessel involves initial cost plus installation of the catalytic conversion equipment plus re-routing of the exhaust uptakes. Additionally, there will be a continuing cost of ammonia and water, plus the inevitable expense of additional equipment maintenance. Estimated increase in fuel consumption is in the order of 3 to 4 percent.

SCR System for Slow-Speed Diesel Engines
In response to an enquiry from Hyundai Heavy Industries, regarding the feasibility of emission control system to MAN-B&amp;W slow speed engines, MAN-B&amp;W, and Haldor Topsoe (HTAS), a Danish chemical engineering company, conducted an in-depth analysis of both the primary pre-combustion and the secondary post-combustion approaches to determine the relative feasibility of each option. The intent was to have three new bulk carriers of 30,000 deadweight tons, built at the Hyundai Heavy Industries (HHI) shipyard in Ulsan, Korea, to transport steel products from the Korean steel mill POSCO in Pohang, Korea, to the United States Steel facility in Pittsburg, California. Given that the pre-combustion approach, involving permanent modification of fuel injection timing and water emulsification of the fuel, was found to be much less cost-effective due to expensive mechanical alteration, adverse impact upon fuel economy and lack of flexibility, it was discarded in favor of the post-combustion or secondary approach involving a selective catalytic reduction system. After selecting the engine to be tested, basic design parameters of the catalytic reactor involving the estimated volume of exhaust gas flow, in terms of cubic meters per hour, estimated concentration level of nitrogen oxide (NOx) therein, plus the resultant or target level of NOx concentration, in terms of parts per million, after catalytic reduction, were established.

Next factor to be determined was the required injection rate of ammonia (NH3) since the effectiveness of NOx removal is contingent upon the volume of ammonia injected into the gas stream, expressed as the NH3/NOx ratio. The importance of this factor is based on the need to avoid an excessively high ratio beyond what is normally required for catalytic reaction, such unused ammonia is termed NH3 slip. In the cooling process of the flue gas passing through the tubes of an exhaust boiler or heat exchanger such as found on many motor ships, reaction of the NH3 with sulfur trioxide (S03) in the exhaust gas, is conducive to the formation of ammonium sulfates that over a period of time would result in fouling of the tube surfaces.

A MAN-B&amp;W type 6S50MC slow speed Diesel engine of 10,680 bhp @ 127 rpm, was chosen as the prime mover for these vessels that in 1989 became the first three ships in the world equipped with Selective Catalytic Reduction Systems. Low Sulfur Fuel Compatibility - It has been established that the requirement for continued reduction in allowable sulfur content of fuel, such as Low Sulfur Fuel (LSF), and Ultra-Low Sulfur Fuel (ULSF), adversely affects cylinder liner lubrication, particularly of the large-bore, slow-speed, main propulsion Diesel engines. This is due to the use of a cylinder oil having a rather high Total Base Number (TBN), such as 70 TBN, that may result in excessive deposits on the pistons and scuffing of the cylinder liners. The severity of such adverse factors will vary in accordance with the degree of usage of LSF. For ships operating on trans-oceanic routes, wherein the majority of their running time is outside of the above-mentioned coastal areas, the use of conventional Diesel fuels with a relatively higher sulfur content will be permissible. However, upon approaching such regulated areas it will become mandatory to switch to LSF for the duration of passage and/or presence therein. Conversely, ships engaged mainly in coastal trade on a full-time basis, and burning LSF, will require the use of a cylinder oil of a correspondingly lower Total Base Number such as 40 TBN. Given that the acidity of Diesel fuel is proportional to the level of sulfur content, the Total Base number of the lubricant is relative to the oil's ability to neutralize the acid. This is why the Total Base Number of an oil is also considered to be its Neutralization Value, and can be expressed as a measure of the acidity or alkalinity of the oil, whichever characteristic it possesses, and is also called the Acidity Number. A significant advantage of these Mechanical Lubricators is that based on the known sulfur value of the fuel, the corresponding feed rate of the cylinder lubricant can be adjusted accordingly, for maximum effect. Should the need arise to change from the 70TBN cylinder oil, commonly used for high sulfur fuels, to the lower 40 TBN cylinder oil, for use with low sulfur fuel, it is advisable to contact the lubricant supplier to determine the recommended feed rate of the lubricant, in order to ensure that the appropriate degree of cylinder liner lubrication is maintained.

Cylinder Liner Lubrication
Currently, most large container ships, bulk carriers and super tankers are propelled by large slow speed large bore Diesel engines of the crosshead type. Many of them are now equipped with electronically controlled common rail fuel injection systems in addition to Selective Catalytic Reduction (SCR) systems of which there are several variations. Because of their immense size, these engines with cylinder bores ranging from 500 millimeters to 980 millimeters (19.68 inches to 38.58 inches) cannot rely on splash lubrication of the cylinder walls exclusively. For this purpose a separate cylinder liner lubrication method is employed using Mechanical Lubricators, independent of the main engine-driven lubrication system. The requirements for independently lubricating the cylinder liners of slow speed, large bore engines are to neutralize acids formed during combustion and thereby protect the cylinder liner from cold corrosion attack to establish a reasonably stable oleous film between the cylinder liner and the piston rings and to preserve a degree of cleanliness of the cylinder liner surface and piston ring pack.

Mechanical Lubricators
One of the most common mechanical lubricators is the Liquid-Filled Sight Glass Lubricator. In this type there may be six or eight pumping elements to an assembly, with a separate assembly for each cylinder. Each pumping element has its own suction and discharge ball type check valves and delivery of oil is metered by the plunger. The discharge nozzle of each pumping element is covered by a glass tube (sight glass), filled with either distilled water or a solution of distilled water and glycerin and capped with a delivery valve assembly. The liquid minimizes emulsification but occasionally, when clouding occurs, the liquid has to be changed. Oil globules discharged by the plunger are guided up through the center of the liquid column by a strand of fine wire extending the full length of the sight glass. After several plunger strokes the delivery valve is unseated and the oil flows into small bore tubing for delivery to the point of lubrication. Each delivery tube leading to the engine cylinder is connected to a quill penetrating the water jacket and cylinder wall and provided with a final check valve to prevent blowback of cylinder gas pressure. When cylinder pressure falls below that of the oil in the delivery tube, the final check valve opens and a small quantity of oil is discharged to lubricate the cylinder wall. Since the number of drops per stroke varies as the plunger stroke setting, the rate of feed for any pumping element can be increased or decreased by adjusting the plunger stroke. This engine-driven cylinder wall lubrication system is used on most large bore slow speed main propulsion Diesel engines. After several plunger strokes the delivery valve is unseated and the oil flows into small bore tubing for delivery to the point of lubrication. The delivery tube leading to the engine cylinder is connected to a quill that penetrates the water jacket and cylinder wall and provided with a final check valve to prevent blowback of cylinder gas pressure into the oil system.

Dual Fuel
Yet another possible alternative, lies in the feasibility of converting contemporary main propulsion Diesel engines, whereby they become capable of burning "Dual Fuel". This would involve retaining the conventional Marine Diesel Oil (MDO) capability and modifying the engines to be capable of also burning Liquefied Natural Gas (LNG). Several recently built European tankers, designed for the LNG trade with dual fuel (DF) capability plus a fleet of Norwegian ferries currently in operation are also burning LNG, from which the exhaust emissions are reportedly extremely low. While conventional wisdom appears to fault marine Diesel engines for their exhaust emissions far more so than that of their highway or railroad counterparts, the truth is that for a riverine tugboat pushing a "Fleet" of twelve of fifteen loaded barges upstream, the Diesel engine exhaust emissions are estimated to be approximately 0.470 grams per ton/mile; which is about 27.70% lower than that of railroad trains and 35.60% lower than that of highway trucks, and are expected to become even lower if and when they eventually switch to burning LNG, given the current trend toward the adoption of LNG as a preferred marine engine fuel,

Readiness
Since most ships are now powered by oil-burning Diesel engines, either direct-drive, geared-drive or Diesel-electric drive, the number of steam ships still in operation has diminished considerably. However, in the case of heavy oil tankers, such as VLCCs, (Very Large Crude Carriers), despite their large main propulsion Diesel engines, of 50,000 bhp or more, steam boilers play a prominent role in providing steam to sustain the cargo tank heating coils. This is due to the fact that in cold climates such as found in Northern European seaports, the relatively low sea water temperature has chilled the heavy black crude oil to such a high viscosity that the cargo can not be pumped out without being pre-heated by the steam-heated tank coils. In such instances, the critical factors become (a) the oil seals of the fuel oil transfer pumps and boiler service pumps and (b) the steam boiler burner tips. Are they all currently designed for use with ULSF? Or do they also need to be replaced with ULSF-compatible components? The inevitable conclusion to all this is that solutions to certain problems that in turn, create problems of their own, are unacceptable and must be carefully evaluated before allowing one problem to be replaced by another potentially worse. Hence, responsible ship-owners and ship-managers can not afford to ignore the above-mentioned factors and have a moral obligation to alert their crews to such potential problems and take appropriate instructive and/or corrective measures to ensure that the required level of "readiness" is capable of sustaining the appropriate level of sea-worthiness.

LNG
Likewise, in view of the growing trend towards Dual-Fuel Diesel engines, 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 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. In this regard, the eventual enforcement of ECA and SECA legislation is fast approaching, and the new Emission Control Area (E.C.A.) for North America takes 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 currently numerous LNG carriers equipped with DF (dual fuel) main propulsion Diesel engines, capable of burning cargo-boil-off gas, built by MAN-B&amp;W and by Wartsila. 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. However, 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. However, 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. Additionally, 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 contended with 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 and the Rules for LNG-fuelled ships that 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-fuelled 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, Ship-Owners of LNG-fueled vessels will be required to apply for permission of the Harbor Master or equivalent authority prior to entering port.

LNG-Related Research
Currently, 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, and partners. In addition to Germanischer Lloyd, this group includes TGE Marine Gas Engineering, MAN-B&amp;W, and NEPTUN Stahlkonstruktion. 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, etc., for the ultimate refinement of all phases involved in developing the most cost-effective LNG-burning marine propulsion plant possible. Additionally, a conceptual design for a conventional feeder container vessel, of approximately 1,200 TEU capacity, and equipped to burn LNG, provides the Group yet another life-size platform on which to develop and test innovative features, not only pertaining to cargo stowage, operating range, etc., but also the radical design of LNG-specific bunker tanks and ultimately, the operational cost/benefit analysis of such a vessel compared that of conventional vessels within the same size range. 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&amp;W; Wartsila and Rolls-Royce, as world-renowned experts in this field.

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. LNG is neither corrosive nor toxic. 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 above-ground storage tanks. Natural gas is the cleanest burning fossil fuel. It produces less 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. LNG carriers are 1000 feet long, and require a minimum of 40 feet 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; Lybia; 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. LNG peak-shaving facilities are used for storing surplus natural gas that is to be used to meet the requirements of peak consumption later during the winter or summer. Each peak-shaving facility has a re-gasification unit attached but may or may not have a liquefaction unit. These facilities without a liquefaction unit depend upon tank trucks to bring LNG from other nearby sources to them. Of the approximate 113 LNG facilities in the United States, 57 are peak-shaving facilities. The other LNG facilities include marine terminals, storage facilities and operations involved in niche markets such as LNG vehicular fuel.