Forum Archive Index - June 2003

[Mills <mills@chem.canterbury.ac.nz>]

Macdunk, might be getting the wrong idea with your 80T truck and
reference to existing technologies - are you saying to run trucks on
fuel cells or run them on hydrogen gas (H2) as the fuel source in an
internal combustion (IC) engine.

The big problem as I see it is the storage of the hydrogen gas in a
moving vehicle esp. a heavy truck  If you think about the fuel for an IC
engine, if a truck's tank holds 200kg (say 300L) of fuel, the rough
equivilent amount in energy terms would be about 80kg of H2.  In
conventional compressed gas cylinders, a large one weighs about 90kg and
would hold 0.8kg H2 (~50L internal volume at 200 atmosphere/ 2900psi). 
So instead of a 60kg conventional tank (guessing), you need a high
pressure tank that will need to be over 3500L in internal volume to hold
700 cubic metres of H2 at room pressure (storage won't be light say 9T
in conventional cylinders).  I'm sure that long haul trucks would hold
alot more than 300L of diesel fuel.  Shudder to think what would happen
if there was an accident with explosive gas instead of relatively safe
diesel.

They say that alot of the energy in an IC engine is lost as heat, so
fuel cells would be more feasible but how big and efficient can you make
a fuel cell for an 80T truck and you would still need alot of H2 carted
around as well for fuel.

If I remember how to use thermodynamic tables correctly, 1g of hydrogen
converted to water vapour will give you about 121kJ (143kJ for liquid
water).  If the highest power output of an IC motor was 300kW/400hp
(alot of trucks would blitz this), this would be the equivilent 2.1-2.5g
per second of H2 at peak consumption (7.5kg/hr) .  It comes down to how
much gas tank you can carry and how often you need to refill (eg not so
major in NZ but how far apart are the gas stations across the heart of
Oz?)

Whose that saying to use liquid H2? 1Kg of liquid H2 would still occupy
over 14L at -250C (very light liquid weighing only 70g per L), much much
larger by the time you include any cyrogenic cooling and insulation. 
You'll need a large school of extremely skill labour just to handle the
stuff.  Technology is never perfect or foolproof and if things go wrong,
they still go bang.  Think of a space shuttle disaster but smaller.

IMO fuel cell tech would translate to short journey and small vehicles
like the GM car production or city buses but I don't think it translates
as well into existing trucks/trucking and certainly not things like
planes, and unless people won't fly when we run out of oil, there will
have to another way such as synthesizing fuel from these abundant energy
sources that are going to be used to create and store the hydrogen from
water.

On a side note don't fancy atomic as people can make mistakes or cut
corners in too many areas in refining, generation or disposal.  Nuclear
fusion would be a different story - that would be the real hydrogen
power
Clint (lurker and investment diminisher)


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