LNG Fact Sheet 

WHAT IS IT? When natural gas is cooled to a temperature of approximately
-260 F at atmospheric pressure it condenses to a liquid called liquefied
natural gas (LNG). One volume of this liquid takes up about 1/600th the
volume of natural gas at a stove burner tip. LNG weighs less than one-half
that of water, actually about 45% as much. LNG is odorless, colorless,
non-corrosive, and non-toxic. When vaporized it burns only in
concentrations of 5% to 15% when mixed with air. Neither LNG, nor its
vapor, can explode in an unconfined environment. 

COMPOSITION Natural gas is composed primarily of methane (typically, at
least 90%), but may also contain ethane, propane and heavier hydrocarbons.
Small quantities of nitrogen, oxygen, carbon dioxide, sulfur compounds, and
water may also be found in "pipeline" natural gas. The
liquefaction process removes the oxygen, carbon dioxide, sulfur compounds,
and water. The process can also be designed to purify the LNG to almost
100% methane. 

HOW IS IT STORED? LNG tanks are always of double-wall construction with
extremely efficient insulation between the walls. Large tanks are low
aspect ratio (height to width) and cylindrical in design with a domed roof.
Storage pressures in these tanks are very low, less than 5 psig. Smaller
quantities, 70,000 gallons and less, are stored in horizontal or vertical,
vacuum-jacketed, pressure vessels. These tanks may be at pressures any
where from less than 5 psig to over 250 psig. LNG must be maintained cold
(at least below -117 F) to remain a liquid, independent of pressure. 

HOW IS IT KEPT COLD? The insulation, as efficient as it is, will not keep
the temperature of LNG cold by itself. LNG is stored as a "boiling
cryogen," that is, it is a very cold liquid at its boiling point for
the pressure it is being stored. Stored LNG is analogous to boiling water,
only 470  colder. The temperature of boiling water (212 F) does not change,
even with increased heat, as it is cooled by evaporation (steam
generation). In much the same way, LNG will stay at near constant
temperature if kept at constant pressure. This phenomenon is called
"autorefrigeration". As long as the steam (LNG vapor boil off) is
allowed to leave the tea kettle (tank), the temperature will remain
constant. If the vapor is not drawn off, then the pressure and temperature
inside the vessel will rise. However, even at 100 psig, the LNG temperature
will still be only about -200 F. 

HAVE THERE BEEN ANY SERIOUS LNG ACCIDENTS? [See also A Brief History of
U.S. LNG Incidents.] First, one must remember that LNG is a form of energy
and must be respected as such. Today LNG is transported and stored as
safely as any other liquid fuel. Before the storage of cryogenic liquids
was fully understood, however, there was a serious incident involving LNG
in Cleveland, Ohio in 1944. This incident virtually stopped all development
of the LNG industry for 20 years. The race to the Moon led to a much better
understanding of cryogenics and cryogenic storage with the expanded use of
liquid hydrogen (-423 F) and liquid oxygen (-296 F). LNG technology grew
from NASA's advancement. In addition to Cleveland, there have two other
U.S. incidents sometimes attributed to LNG. A construction accident on
Staten Island in 1973 has been cited by some parties as an "LNG
accident" because the construction crew was work inside an (empty,
warm) LNG tank. In another case, the failure of an electrical seal on an
LNG pump in 1979 permitted gas (not LNG) to enter an enclosed building. A
spark of indeterminate origin caused the building to exploded. As a result
of this incident, the electrical code has been revised for the design of
electrical seals used with all flammable fluids under pressure. 

WHAT IS CNG? Compressed natural gas (CNG) is natural gas pressurized and
stored in welding bottle-like tanks at pressures up to 3,600 psig.
Typically, it is same composition of the local "pipeline" gas,
with some of the water removed. CNG and LNG are both delivered to the
engines as low pressure vapor (ounces to 300 psig). CNG is often
misrepresented as the only form natural gas can be used as vehicle fuel.
LNG can be used to make CNG. This process requires much less capital
intensive equipment and about 15% of the operating and maintenance costs. 

WHAT IS LPG? Liquid petroleum gas (LPG, and sometimes called propane) is
often confused with LNG and vice versa. They are not the same and the
differences are significant. LPG is composed primarily of propane (upwards
to 95%) and smaller quantities of butane. LPG can be stored as a liquid in
tanks by applying pressure alone. LPG is the "bottled gas" often
found under BBQ grills. LPG has been used as fuel in light duty vehicles
for many years. Many petrol stations in Europe have LPG pumps as well. 

Contact us for more information: info{at}ch-iv.com 

     Good luck...  M.

--- Msged/386 TE 06 (pre)