Air Power

Discussion in 'Homesteading Questions' started by zekell, Jun 1, 2004.

  1. zekell

    zekell Member

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    Has anyone tried storing energy in the form of compressed air ?

    Them danged air tools work awful hard, last forever, put out like 250 lbs of torque, and have very high rpm rates.

    Wouldn't be too hard to hook an air tool up to an alternator/generator and power away.

    Been thinking 'bout slapping together some ferro concrete air storage tanks, fill them from an air compressor running part time on surplus produced power.

    How much air could the tanks hold ?

    At what psi ?

    Before they blew up, and shot across the valley leaving tank sized holes in all asunder ?

    I dunno, depends on the depends.......

    Just 'bout anything would be better then wanking around with a bunch of batteries.
     
  2. VonWolfen

    VonWolfen Well-Known Member

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    Don't know how close you are to Ohio Amish country, but years ago many of the Amish/Plain farms ran households and farm with predominantly air power...on a huge scale. As I remember, some had used train tanker cars as storage tanks, which provided vast volumes under relatively high pressure. I think you are correct...this is a viable long-lived source of power...especially if you have wind or moving water.
     

  3. zekell

    zekell Member

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    --Amish ? I would never have guessed that. If I get this to work do I get to wear one of those cool Amish hats ?

    Yes a train tanker car would be handy to have, or a big steel store bought pressure tank.

    Price wise though, I'm afraid 'couple bags of cement, rebar, and chicken wire is closer to the reality of this exercise.

    BTW I just looked at the air tool specs again, some of those tools put out 12,000 rpms-----
     
  4. I think the problem with air power may be the volume of air required... air tools are certainly great and can achieve extremely high rpms (a die grinder for example), but they use a very large amount of air to power them. Air tools will list their cubic feet per minute air requirements.

    Volume of a cylindrical tank is piexRxRxH (pie radius squared height). Volume of a 'room' is LxWxH (length width height). How much pressure can a tank hold? Depends on the tank.

    My opinion, the best way to get electricity is from the grid... next best would be a diesel generator. Unless you live in a wind tunnel or next to a large waterfall... all the rest of the alternatives are either far too expensive, far too complicated, extremely inefficient or produce relatively tiny amounts of power. No free lunch when it comes to electricity... as it is extremely difficult and costly to produce the amount of energy that we have become accustomed to.

    cheers,
     
  5. timmcentire

    timmcentire Active Member

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    Here is an interesting article about a compressed air car. It came from MIT's Technology Review:

    Air-powered Autos

    By John Harney September 19, 2002

    Zero-emission driving may be more than hot air.

    Guy Negre, an engineer from the little town of Carros,
    France, discovered a breath of fresh air, both
    literally and figuratively. During his career
    designing formula one engines he became familiar with
    isotherm dynamics, a process that creates power by
    expanding air at an almost constant temperature. Negre
    theorized that by heating and expanding super-cooled
    compressed air he could power a nonpolluting car. Six
    years and four prototypes later, it would appear he?s
    done it.

    Negre?s company, Motor Development International
    (MDI), created what it calls the Compressed Air
    Technology (CAT) car by combining a lightweight
    automobile body with a new type of small rear-mounted
    engine. The 1,500-pound frame is made from aluminum
    and fiberglass with four very light, steel-reinforced
    thermoplastic air tanks attached to the undercarriage
    of the car. The engine measures only one- foot square
    and weighs just 70 pounds, but because it propels a
    relatively light vehicle, it can run at 55 mph.

    Negre, who was interviewed through an interpreter,
    explains that, in the tanks, the air is both cooled to
    minus 100 degrees Centigrade and compressed to 4,500
    pounds per square inch. Then it?s injected into a
    small chamber between the tanks and pistons, where
    it?s heated up by ambient outside air that forces it
    to expand into a larger chamber situated between the
    small chamber and the pistons. That heat exchange
    between the two chambers, he continues, creates the
    propulsion that drives the up-and-down strokes of the
    engine?s four pistons. Finally, the air is passed
    through carbon filters like those in scuba diving
    tanks and expelled as pollutant-free exhaust. The
    dynamic is not unlike that of a spring that takes in
    energy when it?s compressed and gives it back when it
    expands.

    The big plusses of the air-powered car, according to
    Negre, are super-efficient energy consumption as well
    as minimum pollution and maximum affordability. Though
    the car seats five, it will go from zero to 50 mph in
    seven seconds? certainly adequate acceleration for an
    urban vehicle like a taxi. What?s more, with fully
    loaded air tanks, it will take passengers about 120
    miles at an average of 30 mph?again, about the right
    capacity for urban drivers who don?t want to fill up
    too often.

    Charging the car with air is fairly easy?it takes four
    hours using a household electric outlet or three
    minutes using special compressed air stations that MDI
    sells for about $100,000. Obviously, the vehicle also
    drastically reduces pollution?it takes in polluted
    outside air, filters it, and expels cleaner air as
    exhaust. All that for a price tag of between $10,000
    and $14,000.

    According to Michael Baltierra, a reporter for ABC
    News, ?we tested the car and it ran quite well. The
    only major problem that we noticed,? he continues,
    ?was that it was quite noisy?[but Negre] said this was
    something that would be fixed in later models.?
    According to Shiva Vencat, vice president of the U.S.
    wholly owned subsidiary of MDI, Baltierra tested the
    car in June, 2000. At the time, Vencat explains, the
    car ?was not a finished product?our engine was
    attached to the car but did not have the body shell
    all the way around it to muffle the noise.? Since
    then, he says they have encased the engine to make it
    run more quietly.
     
  6. j.r. guerra in s. tx.

    j.r. guerra in s. tx. Well-Known Member

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    I'm not sure if a ferro-concrete tank makes a good air container. Concrete is good in compression, NOT TENSION and though would work, not as well as a steel tank. That tankcar is a great idea, as are utilizing those old gas tanks on stilts which are used to gas up rural farmsteads. Put a tank on wheeled trailer and your power goes whereever your vehicle goes.
     
  7. Zack

    Zack Well-Known Member

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    I would think the storage loss would be to great (Hp to drive compressor would be much more than you could get out )as well as the amperage to drive the compressor being to high to be met by most RE sources.
    Where would you be getting your energy from?
     
  8. Farmer Brown

    Farmer Brown Well-Known Member

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    Mennonite friend of mine uses air for everything--even pumping water from deep well. Has air powerd fans in house for cooling his family. Has a "skil saw" that looks normal but has a air hookup and really whizzes. Uses a tank off propane truck for storage and a gas motor to pump up. Has air lines everywhere. FB
     
  9. tkrabec

    tkrabec Well-Known Member

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    Compressed air is just a storage system like batteries are. 1 is chemical and the other is mechanical. You loose energy when you charge a battery and recover it, you also loose energy when you compress and decompress air. It depends on which method is more efficient, suitable, and safe enough for your project.

    I do not know how many cycles an air tank has but a battery can only handle about 1000 cycles below 80% before it really starts showing it.

    -- Tim
     
  10. Darren in TN

    Darren in TN Guest

    <Hanging my neck out on the block here>

    Large used propane tanks (like the unused one outside my house) might be a good way to store air, too. Of course, they better be in PERFECT condition structurally-- no rust or damage-- and you need to add a couple of drains to the bottom of the tank to get rid of collected water... Anyway, just a thought. Research carefully before attempting!

    Darren
     
  11. comfortablynumb

    comfortablynumb Well-Known Member

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    if you live on a windy ridge like I do, I can see where a few windmills continuously compressing air would be as good or better than electric. electric has electrical gremlins... whats air have? leaks. it cant short out when it gets wet or fry a control ciurcut and leave you powerless.
    This is a good thread its given me Ideas... windmills hooked to cast iron compressors... some of em dont even have to run that fast to work.

    I bet in the longrun it would be cheaper than electric generation also. An unmolested airline lasts practicly forever, the tools if kept oiled and clean last forever. Ive seen old cast iron air comressor heads from the stone age still being used daily.

    no real danger of explosion unless your air pump is super effecinet and goes haywire.

    thinking of the tools I have, fans would take very little cfm to keep them moving.

    a combo of electric windmills and air compressing windmills would be a pretty neato Idea!
     
  12. Farmer Brown

    Farmer Brown Well-Known Member

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    I doubt any worry about propane tanks--other that getting the smell out of them. If you ever cut open a 500 gallon you would be suprised at the thickness. About half an inch. I'd hate to see how thick a transport tank would be.

    Anyone with a copy of the "Budget" newspaper can find all kinds of air powered stuff advertised in it.

    FB
     
  13. zekell

    zekell Member

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    timmcentire- Huh, a compressed air car, I don't even know what to make of that. I found this on the web ;

    http://www.tecsoc.org/pubs/history/2002/dec13.htm

    j.r. guerra- Yes, in all my webcrawling research I didn't find one reference to storing anything in concrete under pressure, not even pressurizing water holding systems.

    Over pressurizing a concrete and steel container would make for a horrendous fragmentation device.

    Zack- The charging energy would come from any system that happened to be operating at a surplus, wind, sun, or the creek rising ?

    Farmer Brown- Am I becoming a Mennonite ? I've always thought air powered tools worked harder, faster, and less trouble free then 'bout anything else.

    tkrabec- A steel tank, as long as its properly maintained, not overstressed, and not rusted, will last longer then you and me. Batteries are only good for a 'coupla years.

    Darren- Ain't you a lucky guy, big old tank just sitting out there waiting for you to do something with it. Air systems, and air tanks usualy have water drain out petcocks built in to them. Usualy in line between the air tank/compressor and the air tool there are two containers, one to take the water out of the system, and the other to mist lubrication oil to the air tool.

    Unreg- Thanks for the volume formula, though you've kinda stepped on the urge a little there.

    Let's see if I can do the arithmetic, hokays, keep it simple, pi would equal 3, the diameter of the tank would be 6, radius squared would be 9, the heighth of the tank would be 10.

    That would come to 270 cubic feet, round up call it 300 cf.

    An air tool that runs on from 60-90 psi at 12,000 rpm consumes, 4 cubic feet per minute, (4 CFM).

    That would mean the air tool could run off the tanks stored compressed air for 75 minutes ?

    Naw, that can't be right, I must be doing this wrong.

    Even if I cut the air tools power back by 1/2, 'cause I think 12,000 rpm would be way too fast for an alternator to run, the tanks stored compressed air would only last for an hour and a half.

    Naw, can't be, I'm going to have to look back at this again later, right after I go throw myself into the air, and shoot myself........


    -PULL-
     
  14. VonWolfen

    VonWolfen Well-Known Member

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    If you want free or inexpensive power.....there are about 4 ways.....I mentioned wind and moving water. The third is biodiesel, the ability to get free or inexpensive veggie oil and burn it in a Listeroid or Pedder stationary diesel. See the "otherpower" and "udderpower" websites to view them that's doin. The fourth is the Stirling cycle engine, which will run on any heat source....there are some people working hard on this technology....so if you have anything free that burns...you got power to pump. If I had the brain power of some of the super posters on this site, I would take a serious look at the Stirling. I have experimented with it some, and it is for real....possibly revolutionary for home power production, air or electric.
     
  15. VonWolfen

    VonWolfen Well-Known Member

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    Second website is "utterpower", not "udder". Got my cows and dinosauers crossed...
     
  16. mightybooboo

    mightybooboo Well-Known Member

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    I met a guy in the desert doing the compressed air thing,using a windmill.He powers his whole house on it,but how I dont know,and he didnt want to talk to a stranger(me) much about it.But it can be done,Ive seen his lights going,if he told me truthfully about the compressed air business.
    BooBoo
     
  17. charles

    charles Well-Known Member

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  18. zekell

    zekell Member

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    Well, it was only a flesh wound, I guess I can look at this again.


    VonWolfen- thanks, found;

    http://www.otherpower.com/

    Interesting site, couldn't find "Utterpower.com", I think they're down.

    I been watching the Stirling engine for awhile, very elegant heat engine. They still haven't done much real work with it yet though. I'm surprized that nobody has hooked one up to solar heat and generated a significant amount of electricity. I think they're waiting on better component materials. Kinda like the fuel cell people are looking for a better permiable membrane, and the supercondutivity folks are looking for a room temperature superconductor.

    mightybooboo- Maybee he's running his windmill as a compressor ? Wonder if he converts his compressed air to electricity and stores it in batteries, or some other way ? Scince he's in the desert I wonder how much water he gets out of his air system ?

    charles- Well the volume calc was for a guesstament of 90 psi. Usual operating pressure for air tools is 60-90 psi. A tank with higher pressure would power longer, but even the large store bought manufactured steel tanks are not pressured much over 120-150 psi from what I saw.


    Well shucks, I was hoping somebody would tell me I just slipped a decimal point, (or was a brick shy,,,,). And there I was ready to start digging a bunch of 10 foot deep holes in the ground and setting up an array of comressed air storage containers.

    Further webcrawling found that comressed air energy storage can be a viable alternative, on a major high tech level ;

    http://www.eere.energy.gov/EE/power_energy_storage.html

    http://unisci.com/stories/20013/0802016.htm

    But unless you have a hard rock mine shaft, or a salt dome in your back yard, and are capable of compressing air to around 1,000 psi, I don't think this is going to pan out.
     
  19. River

    River Well-Known Member

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    zekell,

    Your idea is viable. Take a look at: http://airliftech.com/

    LP tanks are used a lot by the Amish for pressurized air storage. They are not expensive as a rule.

    You can convert gallons to cubic feet by multiplying by 0.13368. So a 1000 gal. LP tank should hold about 133.68 cubic feet.

    When you say a tool uses X "cubic feet per minute," at what pressure is this flow rate measured? If it is atmospheric, (at a known temperature), you will have to take that into account when you figure how long a tank will last. Also, your tank is never empty -- it always has at least atmospheric pressure in it.

    If you can find out what pressure and temperature at which the flow rate is specified for a tool, post it here. If you also state a range of pressures at which the tool will operate, we can estimate how long the tool may be used as the tank depressurizes from the upper limit to the lower limit.

    I hope this helps.

    River
     
  20. zekell

    zekell Member

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    River- Thanks for the site, I've been wondering 'bout bubbler well pumps for some time. 300 feet deep is quite a haul from just an air line. Though those are fairly serious windmills and compressors. They weigh in at 200 pounds and the compressors put out around 4CFM.

    Heres an example of an air tool with a high rpm rate ;

    http://www.sears.com/sr/javasr/prod...9976000&tab=description&bidsite=CRAFT#tablink

    (air sander)

    It uses around 4 CFM at from 60-90 psi, how much air it uses depends on how much you pull the trigger or its work load.

    Air/gas does expand and contract with ranges in elevation/barometric pressure, and heat/cold temperatures. But I think, unless those values are very extreme, say 1,000 psi and/or 400C, theres not much change in how much more time your going to get an air tool to work.

    I imagine the Amish were using something like a water turbine to run an air compressor, and the LP tanks for temporary storage. Kinda like the electric compressor and 5 gal tank system you buy at Sears.

    If a air tank holds 300 cf at 90 psi, then an air tool that uses 4 CFM at 90 psi will only run for 75 minutes. Now you could run the tool at half speed, say 2 CFM at 60 psi, then maybe you could run the tool for an hour and a half or two hours.




    (I want to believe.)