"Eeyore" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
>
> Karl wrote:
>
>> I was wondering about hydrogen gas used as the fuel for a gas stove?
>
> I'm sure it could but better be aware of the near invible flame scorching
> you.
> How would you judge the heat if you can't see the flame ?
>
>
>> Has it ever been done?
>
> Not by anyone sane I would imagine.
>
>
>> Gas is a better cooking fuel but if solar power ever got
>> cheap and it looks like it could happen
>
> And how did you come to that conclusion ?
>
>
>> I for one would prefer to use gas for cooking. So one should be able to
>> use
>> solar electricity and make hyrdogen for a gas stove.
>
> KooK alert !
>
> Graham
>
Here's something more from Home Power Magazine:
http://www.ibiblio.org/ecolandtech/a.../32/32p42a.txt
Hydrogen Basics
Amanda Potter
Mark Newell
c. Mark Newell and Amanda Potter
Home Power is gearing up to use hydrogen fuel for cooking. We've been
hoping to eliminate or at least reduce our propane use for a long time now
and have been encouraged by the interest and enthusiasm in hydrogen
that we've seen in our readers.
Hydrogen does not produce energy; rather, it is a non-toxic means of
storing and transporting energy. Any energy source can be stored in the
form of hydrogen. Solar, wind and hydro power can be used to break
down the molecular bonds which bind hydrogen in hydrocarbons and
water. Hydrogen, unlike electricity, is efficiently transported over long
distances (through pipelines, for example). It enables energy produced in
areas where renewable energy resources are abundant to be safely
transported to areas with high energy use. Part of hydrogen's virtue as an
energy storage medium is the fact that energy stored in the form of
hydrogen can be converted into different forms of usable energy without
producing pollutants; heat or electricity can be produced with water as the
primary by-product.
Catalytic Combustion
Hydrogen can be recombined with oxygen to produce heat in the normal
combustion process or it can be recombined in a fuel cell to produce
electricity. In both cases the primary by-product is water. Burning
hydrogen produces some nitrous oxides because of the high burning
temperature. However, using a catalyst (such platinum or nickel) lowers
the temperature and decreases the surface area of the reaction, which
increases efficiency and reduces the nitrous oxides to a negligible
amount. Pure catalytic combustion uses a catalyst to cause the hydrogen-
oxygen recombination to occur without the input energy of a flame. There
is a 100% efficient conversion of hydrogen to heat when temperatures are
kept below 100 degrees Celsius or 212 degrees Fahrenheit.
Converting a propane stove to run on hydrogen is a fairly simple process.
Low tech, inexpensive catalysts such as stainless steel wool (3% - 22 %
nickel) work well and are easy to use However, stainless steel wool is not
as effective in eliminating nitrous oxides as more expensive catalysts. For
more information on these operations see Fuel from Water by Michael
Peavey. Also look in your local library under hydrogen.
The Electrolyzer
An electrolyzer is a device that uses electric current to lyse or split
water
(H2O) into hydrogen and oxygen. (See Electrolyzer sidebar.) Electrolysis
is currently the cheapest, simplest, and most efficient method of home
scale hydrogen generation. Well-made and relatively inexpensive
electrolyzer cells from Hydrogen Wind in Iowa are available. Each
electrolyzer cell requires 2 Volts; the current determines how much
hydrogen they produce. (See HP #22 and 26.)
How Much Hydrogen Would We Use?
We plan to use electrolyzers to produce hydrogen, but how much
hydrogen do we need? Ideally we would like to supply the gas needs for
the eight of us that live here on Agate Flat. That, however, is no small
feat!
In order to determine how much hydrogen we need to produce and store,
we calculated how much hydrogen we would use on a daily basis. Here's
how much hydrogen we would need to run the cookstove, our only gas
appliance:
There are 82,000 British thermal units (BTU) per gallon of liquid propane.
We go through our 5 gallon tank of propane approximately every twenty
days. We therefore use:
82,000 BTU/gal x 5 gal = 410,000 BTU every 20 days,
or 410,000 BTU/20 days = 20,500 BTU every day.
How much electricity do we need to run through electrolyzers to produce
20,500 BTU of hydrogen? We have a number for converting BTU into
kilowatt-hours (kW-hr) of electricity but it assumes 100% efficiency. With
the kind of electrolyzers we are looking at, we expect the efficiency to be
about 50%.
1 BTU = 2.9287 x 10-4 kW-hr
20,500 BTU x (2.9287 x 10-4kW-hr/BTU) / .50 eff. = 12.0 kW-hr
This means we would need 12 kW-hr input to the electrolyzers each day
to produce hydrogen for our daily cooking needs. This is a lot of
electricity!
There are a lot of us up here now, but we are going to need to find more
efficient ways of our cooking and heating hot water if we hope to power
our entire stove with hydrogen. We are planning on installing a solar hot
water heater. We presently use our solar oven almost every sunny day
and we are planning on building a larger one to further cut down on our
propane use.
A Realistic Approach
We can begin by supplementing our propane use with hydrogen. The
next question is how much hydrogen we can produce. Home Power will
soon be adding two trackers to test. With our additional loads, this will
add about 1.5 kw-hr surplus power per day. We use the following
conversion factors to determine how many cubic feet of hydrogen (at
atmospheric pressure) 1.5 kW-hr will produce and how much energy in
BTU this amount of hydrogen will give us.
1cu. ft. H2=0.791 kW-hr or 1 kW-hr=12.6cu. ft. H2
1 cu. ft.=270 BTU
Electrolyzer efficiency = 50%
Using the above conversion factors,
1.5kW-hr/day x 12.6 cu. ft./kW-hr x .5 eff.=9.45 cu. ft. H2/day.
9.45 cu. ft. H2.x 270 BTU/cu. ft. H2=2551.5 BTU/day.
We will be able to produce 9.45 cubic feet of hydrogen at atmospheric
pressure (or 2550 BTU hydrogen) each day from our 1.5 kW-hr/day
surplus energy. This will only run our cookstove burner (assuming 10,000
BTU/hour) for a little more than 15 minutes.
Storage
Now that we have the hydrogen, how do we save it until we need it?
Hydrogen storage can be complicated and costly. Hydrogen can be
stored as a liquid, in a metal hydride or as a pressurized gas. Liquid
hydrogen at -253øC requires costly and complex storage containers and
the energy required to liquify hydrogen is 20-40% of the energy being
stored. Certain metals like magnesium, titanium, and iron absorb
hydrogen when cooled and release it when heated. In these metals,
hydrogen remains a gas but is confined in the spaces between molecules
in the metal. When the metal is "charged" with hydrogen, it is called a
metal hydride. Metal hydrides are the safest way to store hydrogen,
especially in transportation applications, but are also more costly and
complex than pressurized gas. Pressurized storage of hydrogen is the
most straight forward. The advantage of this method of storage is that
larger quantities of the voluminous can be stored in smaller tanks, saving
on space and tank cost.. However, compressing hydrogen to any sort of
high pressure ( pressures greater than 100 pounds per square inch)
would require an expensive gas compressor. We have chosen low
pressure storage because we would like to keep our storage system as
simple as possible.
To determine the size of our storage container, we've converted cubic feet
into gallons.
gal H2 =9.45 cu. ft. H2 x 7.5 gal/cu. ft.= 70.88 gallons
The Ideal Gas Law
When we talk about storage, we also need to talk about the pressure. The
above equation assumes we are storing the hydrogen at just above
atmospheric pressure. Hydrogen, stored as a gas, follows the ideal gas
law, PiVi=PfVf. The law states that the initial pressure times the initial
volume of a gas is equal to the final pressure times the final volume of the
gas.
Pressure in the ideal gas law must include atmospheric pressure. When
we inflate a tire to 35 pounds per square inch (psi), we are actually
inflating it to 35 psi above atmospheric pressure. Atmospheric pressure is
the pressure per square inch exerted on us by the atmosphere above us.
It varies according to elevation and temperature but is about 14.5 psi.
Anything less than that is a vacuum; anything more is pressurized. So, the
tire we inflated would actually be at 35 + 14.5 psi or 49.5 psi. The tires
walls only "feel" 35 psi because atmospheric pressure presses on it.
We have 70 gallons of hydrogen at just above atmospheric pressure, at
say 0.25 psi above atmospheric, or 14.75 psi. If we choose to store the
hydrogen at 50 psi above atmospheric pressure or, 64.5 psi we can
determine the resulting volume by applying the ideal gas law:
P1V1=P2V2
V2=P1V1/P2=14.75 psi x 70.88 gal H2/64.5 psi= 16.2 gal H2
The 70 gallons of hydrogen we produce can be stored in a 16 gallon
storage tank at 64.5 psi. The advantage of the higher pressure tank is the
low volume storage tank. Hydrogen at 64.5 psi could be stored in a
propane tank. Propane tanks, however, are expensive and a compressor
might be necessary to increase the pressure of the hydrogen. Since
hydrogen storage becomes more expensive and complicated as we
increase the amount of hydrogen stored, we decided to start our system
with only one day's worth of storage. Our options are to either store 16
gallons of hydrogen in an empty 10-20 gallon propane tank at 64.5 psi or
store the 70 gallons of hydrogen in two 55 gallon drums at slightly greater
than atmospheric pressure (See HP#26).
Hydrogen For Home Power Users
Hydrogen offers many possibilities for home power users. Indefinite, long
term storage becomes possible with hydrogen. Many home power
systems produce more power than can be used during only one season.
PV's produce surplus power in the summer; micro-hydro systems
produce surplus power in the winter. Hydrogen allows for the storage of
the surplus energy produced during one season to be used in another.
Hydrogen can be combusted to produce heat for cooking or space
heating with no pollutants; it gives home power producers the option of
eliminating the last of their fossil fuels. Because hydrogen and propane
are compatible, hydrogen can be mixed directly into an existing propane
tank and can be used in a propane appliances year-round, without any
modifications. (See HP#22).
In the foreseeable future, we may see fuel cells become a cost effective
method of producing electricity with stored hydrogen. Hydrogen could
then be used as an alternative to batteries which require proper
maintenance and employ toxic heavy metals which eventually need to be
disposed of or recycled.
This exercise has given us a good idea of the what it will take to replace
all of our propane use with hydrogen. It's brought home the importance of
conservation; our solar oven and solar hot water heater will determine if
our transition will be possible. There is little information on "home scale,
home budget" hydrogen systems. We welcome any advice or experience.
Access: Mark Newell and Amanda Potter, c/o Home Power, POB 520,
Ashland, OR 97520 ù 916-475-3179
Fuel From Water by Michael A. Peavey, (ISBN 0-945516), Merit Products,
Inc., Box 694, Louisville, KT 40201. Also available from Alternative Energy
Engineering (see ad on page 5 of this issue).
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