Electicity and cell requirements to generate enough hydrogen to fill
a single person blimp
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Subject: Electrolysis to produce hydrogen
Date: Mon, 04 Mar 2002 22:23:48 +1100
From: Robin Whittle
To: Little Blimps mailing list
Some searching with Google did not lead immediately to how many kilowatt
hours of electricity is needed to make a cubic metre of hydrogen, so I
got out a calculator and Perry's Chemical Engineers Handbook from 1950.
I was going to work with coulombs and Avodadro's number, but this
1990+ page book already has a treatise on electrolysis of water.
It takes 2,171 amp hours to produce a cubic metre of hydrogen, at 20
degrees C and 760 mm of mercury pressure.
The cell voltage is in the range 1.8 to 2.6 volts. So lets pick
the
upper limit, to allow for inefficiencies in stepping down from grid
(110/240V) to a lower voltage for a number of cells in series.
That makes it 2.6 x 2171 = 5.6 kilowatt hours per cubic metre, or
0.158 kw hours per cubic foot.
Assuming we get ten amps from a 240V outlet, this means we can produce
hydrogen at half a cubic metre per hour. I weight 76 kg and so
would
need 100 to 150 cubic metres (at about 1kg lift per cubic metre - though
that was a rough figure for helium) so lets say that is 150 x 5.6
kilowatt hours:
840 kw hours
My electricity bill says a kilowatt hour costs AUD$0.12 a kw hour, so
this would cost AUD$100 - or USD$50.
Perry says that the electrolyte is 15% NaOH or KOH (Sodium or Potassium
Hydroxide). Iron electrodes are used with nickel and perhaps cobalt
plating for the oxygen and hydrogen ends respectively.
A "Type B Levin Cell" measures 43 x 37 x 8 1/2", weighs 325 pounds (147
kg), takes a current of 600 amps (sheessh!) and produces 9.6 cubic feet
of hydrogen an hour (and half this volume of oxygen). At 35.31
cubic
feet per cubic metre, this means 0.27 cubic metres an hour.
Plan A - Quick Fill in the Field:
With the aid of a truck mounted 100kVA (100 kilowatt) three
phase
transformer, arrive at the launch site in the wee-small hours
and
clip it gingerly to the 22 kV lines of Amalgamated Oligopolies
(Energy) Inc. The electrons have been patiently
awaiting this
liberation and 8 1/2 hours later are all fully part of the Movement,
reunited with their proton comrades-in-arms and are collectively
lifting the Blimp skywards.
Larceny seems the most likely way of obtaining such quantities
of electricity in any aesthetically pleasing launch site, but
only
if you plan a life of comic farce could a single person blimp
be considered a suitable getaway vehicle, since the tranny,
truck
and 65 325lb electrolysis cells must be left behind.
Plan B - Slow Fill from the Grid:
A substantial set of cells chewing 2.4 kilowatts could run for
about two weeks to fill the Blimp, and be used to top her up,
if
this is a way of maintaining the envelope's gas in ship-shape
form.
Plan C - Slower still - solar power:
This involves a substantial outlay on solar panels, but the
current
can probably be used directly to drive a few cells in series,
and
there are no costly transformers, rectifiers, regulators etc.
It could take months to fill her, but sunlight is free and this
will also keep her topped up indefinitely.
An excellent advantage of this is that the Blimp is powered
and
lifted by totally renewable energy with very little environmental
impact.
Plans B and C are for the Blimp located in a secure hanger of very large
proportions - probably costing a great deal more than the Blimp herself
and running costs for many years.
For occasional launches in remote locations, bottled hydrogen or helium
seem the only practical option - though I suppose there is is some way
of producing it with sulphuric acid and zinc . . . which I am sure
someone else has researched.
- Robin