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Old 07-18-2017, 04:09 AM   #11 (permalink)
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Old 07-18-2017, 08:22 AM   #12 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
You are not considering compressing HHO I hope?
Now there is a problem...
https://en.wikipedia.org/wiki/Hydrogen
Quote:
Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%...
And I would think 33.3% is optimal (a mixture of 2H2 + O2, e.g. Brown's gas or 'HHO'.
Optimal as in easiest to detonate on compression.

If you compress hydrogen like generated with your own electrolyser and you cannot guarantee that no oxygen will seep in along with it then you run a very high risk.
If you compress straight Brown's gas (yes 'HHO') then it goes beyond being a risk. Lethal detonation is a certainty.

Be safe and refrain from going this way.
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Old 07-18-2017, 08:26 AM   #13 (permalink)
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A few years ago some self proclaimed HHO scientist was trying to compress HHO with a compressor.
When the experiment reached its only logical outcome the guy was killed and 2 of his helpers were seriously injured.

Achievement unlocked: Darwin award.
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Old 07-18-2017, 01:56 PM   #14 (permalink)
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Quote:
Originally Posted by RedDevil View Post
If you compress straight Brown's gas (yes 'HHO') then it goes beyond being a risk. Lethal detonation is a certainty.
Thanks RedDevil, I haven't considered this.
Best way seems to be to filter out the O2 and then compress the H2 (so hydrogen, with no air). I don't really need to compress HHO, I just considered it as those HHO electrolysers are way cheaper and able to generate more gas than hydrogen electrolysers (well that's what I found, if someone found an H2 electrolyser generating 10-15 lpm and costing 3000$ or less, let me know). So if I'm able to filter out the 02 and store the hydrogen, I'll still be able to use these cheaper electrolysers. Any thoughts on the best way to do this ?

Last edited by smallscaleH2; 07-19-2017 at 02:34 AM..
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Old 07-18-2017, 02:50 PM   #15 (permalink)
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Old 07-18-2017, 11:51 PM   #16 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
I know precisely how to do it but it ain't cheap
If you're electrolizing with DC, then H2 and O2 should come off different electrodes, making separation fairly simple.
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Old 07-19-2017, 01:01 AM   #17 (permalink)
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The hho people use interlocking plates like a lead acid battery to get a lot of opposing plate surface are really close to each other. The H and the O come out pretty much on top of each other.
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Old 07-19-2017, 02:08 AM   #18 (permalink)
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I was referring to bad rentability, although my assumption was based on quick back of the envelope estimate.

Quote:
Originally Posted by smallscaleH2 View Post
You are comparing the price the owner of the refill station would pay to the price of the electricity from the grid ? If so, that's a wrong comparison; you should be comparing it to the price of fuel (say gasoline).
When you compare this, it should be way cheaper.
Now I had little time to search on:

According to this source: https://en.wikipedia.org/wiki/Electrolysis_of_water which cites this source You need approximately 65 kWh to produce 1 kg of hydrogen, which in turn can produce 23.3 kWh in a (fuel cell) car. So the exchange would be 65 kWh of electricity versus 3 liters of petrol, as 3 liters of petrol have about same energy content (24 kWh). Assuming price of ten cents per kWh you basically pay $6.50 in electricity to "manufacture" hydrogen equivalent of three liters of gas worth of how much? two-fifty? It makes sense only under specific circumstances, like you need to run tractors and farming equipment under large glasshouses and cannot risk any pollution etc, but otherwise it do not see it as viable bussiness modell. (And in glasshouses, I would go for loong extension cords or overhead wires)

Of course, you still haven't acconted the equipment price...

Sorry to be a spoilfun, but I hope we collectively saved you huge money and disappointment. There is a reason 95% of hydrogen is made from natural gas.

Last edited by seifrob; 07-19-2017 at 02:48 AM.. Reason: clarified one sentence
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Old 07-19-2017, 03:19 AM   #19 (permalink)
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Quote:
Originally Posted by seifrob View Post
The exchange would be 65 kWh of electricity versus 3 liters of petrol, as 3 liters has the same energy content.
Both estimates are incorrect (1 kg H2 isn't 65 kWh, it's 33,41 kWh as it's the same energy as in 1 gallon of gasoline; 65 kWh isn't the same as 3 liter of petrol, it's 7,36 liter of petrol;
1 liter petrol = 8,83 kWh/liter -33,41/3,78-)

I'm not sure why you start the calculation from 1 kg of H2 ?

Quote:
Originally Posted by seifrob View Post
Assuming price of ten cents per kWh for grid power
That's pretty high, where did you get that figure from ? I think it's going to be more like 5 cents per kWh (and even that's high, if you would be using say nuclear power). Even solar power is expected to drop to 5 cents per kWh or even below, see here

But let's say it's 10 cents per kWh:
then you'll pay 88,3 cents (= 0,883 euro) for 8,83 kWh
1 liter of gasoline costs about 1,3 euro ?

Obviously you'll have a lot of energy losses with hydrogen, so if you were to have say just 50% efficiency, you'd still have 1,766 euro, thus a bit more costly (assuming prices of 10 cents/kWh, whereas I think it's going to be say 5 cents/kWh, in which case it would still be cheaper than gasoline). I think it's worth it in either case as it's cleaner, and besides you won't be driving huge distances with it anyway due to amount of space needed for the tanks. So it will only be reserved for city use, and you'll not use that much of it anyway.

Last edited by smallscaleH2; 07-19-2017 at 03:25 AM..
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Old 07-19-2017, 04:13 AM   #20 (permalink)
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- as you have not filled in your location, I assumed you live in the U.S. Therefore I used Oregon average prices for fuel and kilowatt-hours : here and here. If you were so kind and let us know you live in the E.U., situation would be different.

- have you read provided sources? Have you read my post properly? You need about 65 kWh to produce 1 kg of compressed hydrogen by electrolysis, and that amount of hydrogen equals roughly to 3 liters of petrol in contained energy.

I did not start with kilograms, I cited this from abovementioned sources, but I can imagine why it is convenient to use mass instead of volume when talking about gases. Mass is a mass regardless pressure, and energy content is function of mass, not volume. Never mind, lets go on.

Even if you do not trust me, read please the second provided link. You can read that Norsk Hydro plans to sell 1 kg of compressed hydrogen for 90 NOK to be profitable. And they have a lot of cheap electricity. 1 kg of compressed hydrogens will move your car for 10 miles (same source, use google translate if you cannot read norwegian).

So - all physics set aside - this does not make sense for small scale manufacturer.

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