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Compressed air

 
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Let's pretend I have an energy source that is abundant, low cost, and environmentally friendly, but using it requires I stand over it as it is used, the entire time.

So, I want to use it at high output for a short time to store that energy, then bleed off that stored energy over a longer period of time, unsupervised. Compressed air is what I'm wondering about even if it is inefficient.

Assuming I want to run a small pneumatic motor/alternator long enough to charge a 2 day home battery bank, what size tank will I need to fill with compressed air. The pneumatic motor is ONLY meant to charge a battery bank and nothing else. It doesn't need to be overly powerful. It's output should match a battery bank's max charge rate and the compressed air needs to last until the bank is fully charged.

So, any guesses as to how big a tank of compressed air would be needed to run a pneumatic motor/alternator setup long enough to charge a 2-day home battery bank? Would a 500 gallon tank be big enough? And, what type motor would work best?

My preferred fuel is bio-briquettes made from waste material. The more I use, the less goes into some landfill.
 
Bill Bianchi
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My thought on this is to use the bio-briquettes to fuel either a steam engine or charcoal gasifier. Rather than spend 4-6 hours standing over a gasifier or steam engine as it slowly feeds my battery bank, I want to spend an hour compressing a large tank of air. After that, I want to put that compressed air to a pneumatic motor and walk away while the battery bank charges, then come back hours later and shut it down.

So, aside from the extra energy (waste products) used to do this, what is wrong with this system?
 
pollinator
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Bill Bianchi wrote:Let's pretend I have an energy source that is abundant, low cost, and environmentally friendly, but using it requires I stand over it as it is used, the entire time.

So, I want to use it at high output for a short time to store that energy, then bleed off that stored energy over a longer period of time, unsupervised. Compressed air is what I'm wondering about even if it is inefficient.

Assuming I want to run a small pneumatic motor/alternator long enough to charge a 2 day home battery bank, what size tank will I need to fill with compressed air. The pneumatic motor is ONLY meant to charge a battery bank and nothing else. It doesn't need to be overly powerful. It's output should match a battery bank's max charge rate and the compressed air needs to last until the bank is fully charged.

So, any guesses as to how big a tank of compressed air would be needed to run a pneumatic motor/alternator setup long enough to charge a 2-day home battery bank? Would a 500 gallon tank be big enough? And, what type motor would work best?

My preferred fuel is bio-briquettes made from waste material. The more I use, the less goes into some landfill.



Please be more specific about how much battery charging you would like from the compressed air system, and I will provide an estimate as to the tank size required. I will say that the tank is almost certainly going to be a lot larger than you expect. Most likely, a 500 gallon tank is not going to be nearly large enough... but this also depends on the pressure. So, what pressure is acceptable for you? Please note that I already believe this idea to be completely impractical, but I wish to provide some figures so you can arrive at the same conclusion. I used to maintain and operate large compressed air systems at 3000 psig (total tank volume of 10,000+ gallons per system - total of four systems). So, while I can do the physics, I also have first hand experience here.

BTW, a wood gas engine system or a small steam system can fairly easily be devised to operate unattended while at low power, and this seems an ideal solution. The gasifier cannot be allowed to run out of fuel as it will combust the charcoal directly and generate excessive temperatures. Also, there should be a means to shut down the furnace of a steam system should the engine stall for any reason, but there are many different ways to do this. Also, a small monotube steam generator does not present a danger of explosion, and this is the main reason why small steam systems have to be watched (to make sure the boiler doesn't overpressurize or run dry). It's also possible to shroud the steam supply line to the engine so that any leak or rupture directs steam to the furnace to protect anyone who might be standing nearby.
 
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