At 12:45 AM 8/18/2010, Karl Wolz wrote:
>LPG can be either propane or butane or a mixture of the two.  Difference is

To add a bit: Natural gas by the time it gets to you is almost pure
methane, CH4.  There's a good article on it here:
http://en.wikipedia.org/wiki/Natural_gas.  Methane is the beginning
of the series of "alkanes" that goes methane CH4, ethane C2H6,
propane C3H8, butane C4H10, pentane C5H12, hexane C6H14, septane
C7H16, octane C8H18, nonane C9H20 and decane C10H22.

Of these only the first four are gases at room temperature and are
used as fuel gases except for ethane which is too valuable as a
chemical feedstock.

Of the three fuel gases, methane is the only one which is lighter than air.

Butane boils at about 31F and propane at about -45F.  Each of these
can be held as a liquid at moderate (<300 psi) pressures at room temperature.

Methane, however, boils at about -260F and can only be liquefied at
cryogenic temperatures.  It's transported in this form (LNG) in
specially-built ships. For vehicle and other non-pipeline end uses
it's stored in gaseous form (CNG) at 3000-4000 psi, using tanks
comparable to overbuilt welding or SCUBA tanks.  If you see a city
bus with skinny cylinders (probably under a cover) on the roof,
that's CNG. I doubt that it's practical in ordinary terms to use CNG
for a vehicle unless there is a local infrastructure for filling the
cylinders on the vehicle.  Such infrastructure exists in various
places in South America and Asia; also on a limited scale in any city
that uses CNG for buses.

Methane can be aDsorbed at about 500 psi onto substrates like
activated charcoal -- this isn't commercial yet but will give better
density than CNG as well as less demanding requirements for
containment.  It will also make infrastructure easier, as natural-gas
pipelines already run at this pressure.

Yours,
David