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Tags oxygen , hydrogen , electrolysis

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Old 22nd May 2007, 03:05 PM   #1
briandunning
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Home hydrogen production

I was reading an article that described the basic process of electrolysis, with an anode and a cathode in water - hydrogen bubbling off of one, oxygen bubbling off the other (in fact my son has a toy rocket that's hydrogen powered that works this way) - but the article concluded saying that this simple process does not practically scale up to home hydrogen production.

I'm wondering why not. I can easily envision a system with a solar panel and your home water supply, charging a battery to run a compressor, and constantly bubbling off hydrogen. A few valves and sensors and you've got what appears to me to be a complete package. What am I missing? Why wouldn't this work?
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Old 22nd May 2007, 03:10 PM   #2
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My (admittedly poor) understanding is that it takes more energy to extract the hydrogen from water then you'd get from recovering it.
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Old 22nd May 2007, 03:13 PM   #3
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That's fine, and it may well be, but it doesn't prevent such a machine from being a source of useful compressed hydrogen. Maybe the complete cycle is less efficient than using the solar electricity directly, but that's not the question. Unfortunately the author of the article did not say why the method does not scale up practically.
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Old 22nd May 2007, 04:00 PM   #4
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Originally Posted by briandunning View Post
That's fine, and it may well be, but it doesn't prevent such a machine from being a source of useful compressed hydrogen. Maybe the complete cycle is less efficient than using the solar electricity directly, but that's not the question. Unfortunately the author of the article did not say why the method does not scale up practically.
Certainly, if you store excess solar-derived electricity as hydrogen, it can be beneficial. I don't know how it compares, economically, to battery storage.

Moreover, I don't know how economic solar electricity is overall (it varies enormously- by location). People who go purely solar may lead a more spare lifestyle and/or wait a long time before their savings in electricity match their investment.

I suspect the problem doesn't scale because the demand for electricity, by itself, meets or exceeds the abilty to provide it by solar panels- in most places. Thus, there is little left to store, in any form.
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Old 22nd May 2007, 04:38 PM   #5
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Originally Posted by briandunning View Post
I was reading an article that described the basic process of electrolysis, with an anode and a cathode in water - hydrogen bubbling off of one, oxygen bubbling off the other (in fact my son has a toy rocket that's hydrogen powered that works this way) - but the article concluded saying that this simple process does not practically scale up to home hydrogen production.

I'm wondering why not. I can easily envision a system with a solar panel and your home water supply, charging a battery to run a compressor, and constantly bubbling off hydrogen. A few valves and sensors and you've got what appears to me to be a complete package. What am I missing? Why wouldn't this work?
A) waste B)cost per unit C)cost to get it stored and keep it stored D)Danger!!
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Old 22nd May 2007, 05:04 PM   #6
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I saw a prototype on This Old House where they used solar cells to produce hydrogen from water. The hydrogen powered a fuel cell at night and when the solar cells weren't enough to meet the energy demands in the home. They said they were about 20 years away from bringing it to market.

Also, on a news report where a guy was doing something similar on his own, his backyard looked like a chemical plant because of all the tanks he needed to store the hydrogen.
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Old 22nd May 2007, 10:18 PM   #7
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Beyond the thermodynamics, I wouldn't visit anyone who kept copious amounts of hydrogen around. I just don't need that much excitement in my life.
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Old 23rd May 2007, 12:27 AM   #8
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Originally Posted by briandunning View Post
That's fine, and it may well be, but it doesn't prevent such a machine from being a source of useful compressed hydrogen. Maybe the complete cycle is less efficient than using the solar electricity directly, but that's not the question. Unfortunately the author of the article did not say why the method does not scale up practically.
I think it may be "possible" but not "practical."

What sort of equipment would you need to compress the hydrogen? If you kept large amounts of it in balloons, that would be dangerous, I imagine, and also not particularly practical.

Like fuelair said, basically.
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Old 23rd May 2007, 01:24 AM   #9
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I asked this question before in this thread. It doesn't appear to be straightforward.
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Old 23rd May 2007, 04:10 AM   #10
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Originally Posted by briandunning View Post
I'm wondering why not. I can easily envision a system with a solar panel and your home water supply, charging a battery to run a compressor, and constantly bubbling off hydrogen. A few valves and sensors and you've got what appears to me to be a complete package. What am I missing? Why wouldn't this work?
It would. It's not quite that simple, but it is much easier than many people seem to think. The great thing about fuel cells is that they work just as well in both directions. When there is too much electricity you produce hydrogen, when there is not enough you send it the other way and get electricity.

The only problems at the moment are cost, since all this technology is still very much in the development stage, and risk, since hydrogen is just a little explosive. Unfortunately, the biggest factor is likely to be risk. The cost will come down as the technology matures and demand increases. However, there is something about having every home with it's own tanks of self-igniting explosive that just seems unlikely to happen. It seems quite likely that this sort of thing could happen on an industrial scale, but I can't see it happening in people's homes.
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Old 23rd May 2007, 02:56 PM   #11
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A few valves and sensors and you've got what appears to me to be a complete package.
You've got what actually appears to be a home-made bomb! As other's have addressed, one of the biggest deterrents is the inherent danger of large amounts of hydrogen, which in and of itself isn't all that dangerous. It's when it's mixed properly with oxygen it becomes a possible problem. Sticking a fork in an electrical outlet can be dangerous. Multiply that danger by some variable larger than one and you have hydrogen. Imagining a bunch of homes around the neighborhood with hydrogen tanks in their garages scares the hell out of me.

P.S.

I work with the stuff pretty much daily, but we have strict procedures to adhere to which the average home-brewed hydrogen farmer would either throw away once they put their 'kit' together, or simply loose in the garage with that damn lawn mower manual. "Where did I put that garage door opener manual again??"
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Old 24th May 2007, 05:36 AM   #12
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I used electrolysis to crack (is that the right term?) some water this weekend to demonstrate how oxygen and hydrogen can be made from water. I used two 6volt lantern batteries and it took about 1/2 an hour to fill a film can. It took about 1/10 of a second to make it go pop with a flame.

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Old 24th May 2007, 07:49 AM   #13
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Originally Posted by Orangutan View Post
I used electrolysis to crack (is that the right term?) some water this weekend to demonstrate how oxygen and hydrogen can be made from water. I used two 6volt lantern batteries and it took about 1/2 an hour to fill a film can. It took about 1/10 of a second to make it go pop with a flame.

How long it takes to generate a particular volume of hydrogen depends on the current flow. Current flow depends on voltage, the resistance of the water, and the surface area of the electrodes.

High voltage is not really where you want to go. Solar cells have a relatively low output voltage, so you'd either have to use them in series or use electronics to step up the voltage. Both methods cause losses - I'm not sure which would be worse.

You can lower the resistance of water by adding minerals or salts to it, but then you end up with the mineral fouling your electrodes. If you use a salt (like common table salt), you end up with the components of the salt fouling things up. NaCl (table salt) gets you sodium on your electrodes and chlorine in your gas. Nasty.

Easiest by far to have a larger surface area on your electrodes. A sheet of copper fanfolded so that it fits under your gas collector will have a far larger surface area than a simple rod that fits under you collector.
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Old 24th May 2007, 10:15 AM   #14
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Originally Posted by MortFurd View Post
If you use a salt (like common table salt), you end up with the components of the salt fouling things up. NaCl (table salt) gets you sodium on your electrodes and chlorine in your gas. Nasty.
Uh, you're not going to get sodium plating out from an aqueous solution. Not unless you're using a mercury electrode and some crazy current density.

The chlorine will be a problem, though, although it's sufficiently soluble that you simply won't get any gas given off.

Sodium sulphate, or sulphuric acid, will be a much better electrolyte.

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A sheet of copper fanfolded so that it fits under your gas collector will have a far larger surface area than a simple rod that fits under you collector.
Don't use copper for your anode (the electrode where you expect oxygen to be given off). Copper is more easily oxidized than water, so the electrode will simply dissolve without giving you any oxygen. Once you've got copper ions in solution, they'll migrate over to the cathode, where they'll plate out as copper, thus lowering the amount of hydrogen produced. A graphite rod will work fine as an anode (assuming you can't afford platinum or gold).
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Old 24th May 2007, 10:50 AM   #15
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I used magnesium sulphate as It's easy to get hold of. (Its Epsom Salts!).

Also I used the graphite from a carpenters pencil as its nice and flat and thick, As I wanted it fully submerged I wrapped the copper coils where I connected the graphite in electrical tape so only the graphite stuck out.



Edit:
Getting the graphite from the pencil without breaking it is the hardest part. careful if you use a box cutter to whittle it out!

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Old 24th May 2007, 11:00 AM   #16
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Originally Posted by Orangutan View Post
I used magnesium sulphate as It's easy to get hold of. (Its Epsom Salts!).
That works, too. Adding a small amount of battery acid will make sure that you don't get any magnesium plating out, regardless of what voltage you use.

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Getting the graphite from the pencil without breaking it is the hardest part. careful if you use a box cutter to whittle it out!
Even if you just get most of the wood off with the knife, you can get the rest off by holding the graphite in a candle flame for a short period of time. I found my electrodes broke less often when I did that.
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Old 24th May 2007, 12:39 PM   #17
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I do not think hydrogen in a tank all by itself is much more dangerous than other gases. When was the last time you heard of oxy-acetylene welding units blowing up?

I was reading in the book Skunk Works about Ben Rich's attempts to build a hydrogen fueling and handling station for a hydrogen powered jet. He also had the same concerns that are voiced here. He found that rupturing and igniting a pressurized hydrogen tank did not result in much of an explosion, he had to have a mix of oxygen and hydrogen to make it really nasty.

Diverting surplus solar electricity sounds like a good way to store hydrogen and oxygen in separate tanks. The US Navy makes oxygen (using DC power from the reactor plant) for their subs this way; they let the hydrogen vent overboard.

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Old 24th May 2007, 01:24 PM   #18
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Originally Posted by Ranb View Post
I do not think hydrogen in a tank all by itself is much more dangerous than other gases. When was the last time you heard of oxy-acetylene welding units blowing up?

I was reading in the book Skunk Works about Ben Rich's attempts to build a hydrogen fueling and handling station for a hydrogen powered jet. He also had the same concerns that are voiced here. He found that rupturing and igniting a pressurized hydrogen tank did not result in much of an explosion, he had to have a mix of oxygen and hydrogen to make it really nasty.

Diverting surplus solar electricity sounds like a good way to store hydrogen and oxygen in separate tanks. The US Navy makes oxygen (using DC power from the reactor plant) for their subs this way; they let the hydrogen vent overboard.

Ranb
People are quite happy to drive around in petrol powered cars, fill them up themselves and even keep them indoors. I wouldn't say hydrogen is any more dangerous than that. It may involve a different set of precautions, but my experience of working with hydrogen didn't exactly make me fear for my safety.

I have a gas cooker and central heating, I'm not particualy concerned about them springing a leak and going boom either.
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Old 24th May 2007, 05:57 PM   #19
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I do not think hydrogen in a tank all by itself is much more dangerous than other gases.
When it's in the tank all by itself it's fine! It's when a hose, connection or valve leaks in the system leaks and the H mixes with the O that it becomes a problem. Explosive gas meters could help a little.
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Old 24th May 2007, 05:59 PM   #20
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I wouldn't say hydrogen is any more dangerous than that.
You guys are underestimating the potential dangers of hydrogen. Hydrogen is the most explosive gas used in industry today. It's definitly not a gas that just any ole' civilian should have unchecked access to. Without proper precautions, working with hydrogen can be extremely dangerous. The general public is simply not trained to work with such gases.
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Old 24th May 2007, 06:01 PM   #21
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Remember that natural gas and propane, both, have an additive which smells which allows people to detect leaks before they become problems (usually). If this could be done with hydrogen without affecting it's usefulness, then that could lessen the danger.

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Old 24th May 2007, 06:05 PM   #22
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Originally Posted by Ranb View Post
I do not think hydrogen in a tank all by itself is much more dangerous than other gases. When was the last time you heard of oxy-acetylene welding units blowing up?

...He found that rupturing and igniting a pressurized hydrogen tank did not result in much of an explosion, he had to have a mix of oxygen and hydrogen to make it really nasty.
You don't think hydrogen is more dangerous than nitrogen? Helium? Argon? I would review my chemistry.

It's not that I disagree with your confidence so much as I think you've maybe gotten too comfortable with the basic engineering that makes hydrogen safe to handle in industrial settings. Acetylene welding units don't blow up precisely because they're hyper-engineered not to. If you review the schematics of the regulator, the tank, the valve, the torch and its tubing, you'll see that painstaking work has been done to keep the gas from leaking or contacting anything that would be reactive.

As far as the guy who busted the hydrogen tank, was it outside or inside a building? I agree that breaking a compressed gas tank of most gases will present only an asphyxiation hazard (unless the gas is itself toxic that is). However, if the tank had been in a building where the hydrogen could have mixed with air to get to the "nasty" stage, he might not have been able to write the book you are reading.

Consider what we are talking about that that is for each household to have a supply of pure hydrogen therein. Maybe you would be able to control it but do you have the same confidence in your neighbor? your in-laws?
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Old 24th May 2007, 08:03 PM   #23
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Originally Posted by cloudshipsrule View Post
You guys are underestimating the potential dangers of hydrogen. Hydrogen is the most explosive gas used in industry today. It's definitly not a gas that just any ole' civilian should have unchecked access to. Without proper precautions, working with hydrogen can be extremely dangerous. The general public is simply not trained to work with such gases.
Hydrogen gas is also the lightest, so as long as your H2 tank is outside not under cover, any leaks will dissapate very rapidly.

If a compressed gas tank ruptures explosively ("catasthrophic mechanical containment failure"?), that's bad regardless of the contents, but you might get a fireball if there is a igition source handy at the same time - the H2 will not have time to mix with atmospheric O2 to produce an explosion. Remember the Hindenburg? It suffer a containment failure due to a lightening strike that ruptured the "ballon" and ignited the gas - the H2 just burned.

So, have your H2 tank outside away from buildings, ensure that any enclosed area that has H2 lines running into (e.g. where the fuel cell is kept) it is well ventaliated and has a H2 alarm, has no spark sources, and has an abosolute minimum of combustibles (i.e. a concrete block shed). And regulaly check the tank for signs of failure. Btw, H2 will leak through the tank walls anyway...

There's an island *somewhere* in the US where someone has peiced together a H2-based fuel cell and storage system, use PV cells as the collector. The Fuel cell is used to convert excess electricity to H2 and store it, and provide power from the stored H2 when demand requires it. Unfortunately, I cannot find the link to the website describing it!
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Old 24th May 2007, 08:47 PM   #24
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So, have your H2 tank outside away from buildings, ensure that any enclosed area that has H2 lines running into (e.g. where the fuel cell is kept) it is well ventaliated and has a H2 alarm, has no spark sources, and has an abosolute minimum of combustibles (i.e. a concrete block shed). And regulaly check the tank for signs of failure. Btw, H2 will leak through the tank walls anyway...
This would help miminize headlines like "Home destroyed by hydrogen explosion", but it wouldn't eliminate them altogether!

The 'regularly check the tank for signs of failure' is the scary part. The average homeower won't do it.
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Old 24th May 2007, 08:49 PM   #25
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Apropos of this discussion, while hydrogen's chemistry does indeed prersent special problems, the risk inherent storing any compressed gas seems to be unappreciated. CO2, N2, or even air are all reasonably inert, but when a few atmospheres are compressed into a cylinder, both the cylinder itself and the cylinder head are potential projectiles, which have been known to go through concrete walls. This is why one should never move a compressed gas cylinder with a regulator in it (if it falls over and the regulator snaps off you have big problems - if you see a cylinder and regulator attached to a trolley complain!), and compressed gas cylinders are routinely chained or strapped to a wall. Industries where cylinder usage is a bit lax (for instance the hotel trade, which uses many compressed cylinders of beer gas) have very poor safety records.
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Old 25th May 2007, 12:17 AM   #26
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Originally Posted by Pidge View Post
There's an island *somewhere* in the US where someone has peiced together a H2-based fuel cell and storage system, use PV cells as the collector. The Fuel cell is used to convert excess electricity to H2 and store it, and provide power from the stored H2 when demand requires it. Unfortunately, I cannot find the link to the website describing it!
I wouldn't have thought that running a fuel cell backwards was very efficient. I always assumed that they were optimised to run best when making electricity. If they were as good backwards as forwards they would be being sold as such, because as far as I know the available electrolysis cells are not well suited to the intermittent use that a home system would require.
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Old 25th May 2007, 12:26 AM   #27
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Originally Posted by cloudshipsrule View Post
This would help miminize headlines like "Home destroyed by hydrogen explosion", but it wouldn't eliminate them altogether!

The 'regularly check the tank for signs of failure' is the scary part. The average homeower won't do it.

Sticking odorants in gas for homes hasn't completely eliminated "house destroyed by gas explosion" either.
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Old 25th May 2007, 12:33 AM   #28
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As has been discussed in the other solar/hydrogen thread, for most circumstances sealed lead-acid batteries are a far more practical and efficient way to store excess solar power.

As for home hydrogen production, you can easily produce heaps of the stuff using drain cleaner and another common household item. In my pyromaniac days I used to fill balloons with a mix of hydrogen and natural gas and let them float off with a fuse attached. Quite spectacular (although as a responsible adult I do not recommend trying it)
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Old 25th May 2007, 04:52 AM   #29
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Originally Posted by EHLO View Post
As has been discussed in the other solar/hydrogen thread, for most circumstances sealed lead-acid batteries are a far more practical and efficient way to store excess solar power.
This just isn't true, as I have pointed out in that thread. Some batteries are more efficient, but they are in no way practical at all. Which is why no-one has tried doing this with batteries.
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Old 25th May 2007, 10:21 AM   #30
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Originally Posted by Cuddles View Post
This just isn't true, as I have pointed out in that thread. Some batteries are more efficient, but they are in no way practical at all. Which is why no-one has tried doing this with batteries.

It is fairly common for people to use batteries for solar backup and storage as far as I am aware.

The issue with batteries vs hydrogen is really that batteries will discharge, if just left to sit, at a faster rate than a hydrogen bottle wil lose energy due to leaks. So batteries are better for short term storage and hydrogen would be better for longer term storage. It depends on what you want the system to do. Each method has pros and cons and you need to weigh them up with regards to how you want the system to operate.

And this only really matters if you don't want to be grid connected. If you are grid connected there isn't really any reason why you would need to have on site storage at all. The grid is your store.
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Old 25th May 2007, 10:42 AM   #31
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Originally Posted by Slimething View Post
You don't think hydrogen is more dangerous than nitrogen? Helium? Argon? I would review my chemistry.......?
If you read my post again, it says I did not think it was MUCH MORE dangerous, not just more dangerous, there is a difference.

If a company is going to sell a "home energy unit" that uses compressed hydrogen gas, I think they would be liability conscience enough to engineer into the system enough safe guards to keep the home from exploding and getting sued into non-existence.

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Old 25th May 2007, 11:17 AM   #32
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Originally Posted by MortFurd View Post
You can lower the resistance of water by adding minerals or salts to it, but then you end up with the mineral fouling your electrodes. If you use a salt (like common table salt), you end up with the components of the salt fouling things up. NaCl (table salt) gets you sodium on your electrodes and chlorine in your gas. Nasty.
I remember seeing a exploitation to see if some heavy water was sunk by resistance groups in Norway I believe. One test they used was ph as the heavy water was collected from electrolysis breakdown(it is just enough harder to break up than normal water to be able to be concentrated by this means) and so they tested the PH as the heavy water used NaOH as an electrolyte in its production.
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Old 25th May 2007, 11:20 AM   #33
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Originally Posted by cloudshipsrule View Post
When it's in the tank all by itself it's fine! It's when a hose, connection or valve leaks in the system leaks and the H mixes with the O that it becomes a problem. Explosive gas meters could help a little.
But is it more dangerous than having natural gas lines in your house? Or a tank of liquified propane out back?
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Old 25th May 2007, 11:22 AM   #34
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Originally Posted by Slimething View Post
You don't think hydrogen is more dangerous than nitrogen? Helium? Argon? I would review my chemistry.
Chlorine?
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Old 25th May 2007, 11:35 AM   #35
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Originally Posted by ponderingturtle View Post
... water used NaOH as an electrolyte in its production.
For home use, most people would prefer to use a solution that's less corrosive.

Like battery acid.
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Old 25th May 2007, 11:41 AM   #36
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Originally Posted by anor277 View Post
Apropos of this discussion, while hydrogen's chemistry does indeed prersent special problems, the risk inherent storing any compressed gas seems to be unappreciated. CO2, N2, or even air are all reasonably inert, but when a few atmospheres are compressed into a cylinder, both the cylinder itself and the cylinder head are potential projectiles, which have been known to go through concrete walls. This is why one should never move a compressed gas cylinder with a regulator in it (if it falls over and the regulator snaps off you have big problems - if you see a cylinder and regulator attached to a trolley complain!), and compressed gas cylinders are routinely chained or strapped to a wall. Industries where cylinder usage is a bit lax (for instance the hotel trade, which uses many compressed cylinders of beer gas) have very poor safety records.
You want to know one industry where cylinders are always transported with regulators attached? EMS, small cylinders of O2 up to 2000 PSI.
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Old 25th May 2007, 11:46 AM   #37
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Originally Posted by Madalch View Post
For home use, most people would prefer to use a solution that's less corrosive.

Like battery acid.
Well there is that.
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Old 25th May 2007, 11:52 AM   #38
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Look, the issue is not a hydrogen tanks at home, it's hydrogen tanks in cars going 85mph down 95 at night in a winter rainstorm. Not a bright idea.
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Old 25th May 2007, 12:20 PM   #39
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Originally Posted by Rob Lister View Post
Look, the issue is not a hydrogen tanks at home, it's hydrogen tanks in cars going 85mph down 95 at night in a winter rainstorm. Not a bright idea.
And gas tanks is a bright idea? Personaly I think you lose bright idea status when you get into those speeds at those conditions.
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Old 25th May 2007, 12:33 PM   #40
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Originally Posted by ponderingturtle View Post
And gas tanks is a bright idea? Personaly I think you lose bright idea status when you get into those speeds at those conditions.
Gasoline is not very explosive. Hydrogen is very, very explosive.
Gasoline is well behaved (most any container will contain it). Hydrogen is the polar opposite (liquefied hydrogen requires some pretty sturdy, thick, heavy containment that you most certainly do not want to fail) .

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