Electrolysis for oxygen supply for continuous blending

[bigchrisb]

Anyone considered or experimented with electrolysis for continuous blending?
Thinking that it couldnt be too hard to rig up an electrolysis bath with a couple of carbon electrodes, and run a reasonable current through them (DC). Collect the oygen and feed it into a blending stick.

Just have to figure out what to do with the hydrogen generated - vent it, flare it, make big hydrogen baloons, bank it for use in hydrox - well, maybe not just yet!

My cals suggest that ideal conversion will take approx 20 kJ of electricity to produce a litre of oxygen - working that through at Australian electricity supply rates suggests an electricity cost of approx 0.06 cents per litre of oxygen. I suspect that the inefficiencies woudl make a price of about three times that more realistic - so about 0.2c/litre. Converting to those silly non-metric units indicate about 0.15 kWh/cubic foot of oxygen. Dont know what your electricity rates are, but based on australian rates and the exchange rate, would be looking at a raw cost of approx 1.2 US cents/cubic foot. Multiple by three for a more realistic figure.

Guess the motivation for this is partly in a quest to be independant from frustrating gas suppliers, and partly because I can.

I'm going to have a crack at this, and run the output through a mass spec at work, and see what the output is like.

Anyone tried similar, or played with the concept?

 

[san diego diver]

havent tried it but if it works i'd pay for the info on you're system!!! good luck,let me know how it worked out!!! tired of being a slave to the dive shop myself!!

 

[bergersau]

How are you going to capture the O2 before compressing?
Are you planning to compress pure O2 into a bank then bleed it into a Nitrox stick? Why not just lease a cylinder of pure O2 blend from there?

How are you going to vent the Hydrogen into the atmosphere safely?

Have you considered the fire safety implications of a large balloon (Or somthing???) of O2 near electricity and Hydrogen gas (Off the other electrode.)

Great project in theory - I'd just like to know more.

 

[bigchrisb]

Hi bergersau,

I'm continuously blending, so I'll be feeding the oxygen in at ambient pressure. I'm using an oxyhacker style nitrox stick to do this. I currently do this using a If your not sure what continuous blending is, do a search on these forums, but basically it involves mixing air and oxygen at ambient pressure, and feeding the mix to the compressor intake. Only for mixes less than 40% O2 though!

I currently do this using compressed O2 purchased from a gas supplier here. However, where I'm from (Australia), oxygen is expensive (I pay approx $85 AUD for a G cylinder, which is 8100 litres (about 300 cf)). Welding and medical grade oxygen is similarly priced. Gas suppliers are always a pain to deal with, and make life hard for us divers. I'll still continue to buy HP compressed oxygen for decanting for deco mixes above 40% (PP fill with oxy, then top-fill with cont blended 40%, after hyperfilters).

The way I'm thinking, the O2 wont be banked prior to the compressor - I was thinking of plumbing a collection "funnel" directly above the electrode producing the oxygen to the continuious blending stick intake. Then vary the current to vary the quantity of oxygen supplied.

Its disposing of the large quantites of hydrogen that bother me - its a fire hazard! Its the biggest stumbling block in the plan at the moment. As it has a high risk of igniting, I'm almost tempted to set up up with a controlled burn, and deliberatley flare the hydrogen - not even any emissions in flaring it, because the only byproduct hydrogen burning is water. Its crude, but I suspect a controlled burn would be better than an unexpected ignition. For my small compressor, I need to supply about 20 litres a minute of oxy for a 40% fill, so would have about 40 litres a minute of hydrogen to deal with. Would be inerested to hear any other comments or suggestions on the hydrogen disposal!

 

[bergersau]

Chris,
I'm based in Melbourne's outer East (Mooroolbark) so I know about Gas prices from BOC etc in Australia (Helium prices don't bear thinking about).
Yes I've read enough on Nitrox stick blending to 40% to understand the theory. I've only heard of it being done by plumbing an O2 nozzel into the side of the stick and using a needle valve or similar to control the O2 % at the compressor intake though.

What do you do for a compressor and filters at the moment? <EDIT>: Don't worry I found your earlier thread. </END EDIT>

I'm not sure if you would be able to produce enough free gas to keep up with your compressor at your nominated 40%. (I've only seen a small reactor in a high school science lab - quite slow.)

Free O2 and Hydrogen gasses, electicity, and maybe a controlled Hydrogen flare sounds like an exciting combination - don't take any shortcuts in saftey on this one...

 

[pescador775]

Chris, I don't know beans about the practical engineering but the folks who play around with hydrogen generation do. They experiment and design devices for hydrogen generation for fuel cells. I've even heard talk of using solar to cause electrolysis. There should be a ton of info on the web. I don't believe it will be practical to funnel collected oxygen directly into the stick. You will need to collect and pressurize it. This will require a small compressor. There may be used compressors available for sale on the web. These are made by Invacare are ordinarily used by patients who generate and compress their own oxygen. (Yes, there are cheap, low volume commercial oxygen extracter/generators).They are very small electrical devices and should be ideal for setting and forgetting while slowly pressurizing a storage tank.

 

[Tom Winters]

You sure it wouldn't be easier to get gas from an industrial supplier instead of building your own industrial complex?

 

[pescador775]

Guess the motivation for this is partly in a quest to be independant from frustrating gas suppliers, and partly because I can.

That says it all and qualifies you to enter this room. O2 is cheap in the US, $30 for 280 cf but I can dig your problem and proposed solution. I own my own compressor, O2 booster, etc. Why? Independence. It costs, but the work involved is hardly a consideration, and I built my own compressor and Nitrox stick not to mention a lot of other stuff I yak about. Dive shops, ugh. Oxygen suppliers, *&*^%$#*&^(

 

[gunnutz]

it doesn't really relate and don't even ask..and yes, i know this is nuts, but somehow i remembered that a side benefit of electrolizing water is generation of Deuterium. Water in which most of the hydrogen is replaced by deuterium is called heavy water, or sometimes simply deuterium. Although deuterium is not radioactive, it is important in both military and civilian nuclear domains. Deuterium is a thermonuclear material. See http://www.francenuc.org/en_mat/deuterium_e.htm The most common method for producing deuterium or heavy water at the industrial level is the treatment of ordinary water, either by distillation, electrolysis or isotopic exchange to increase the percentage of deuterium.
Sorry for hijacking the thread..but my mind works in strange ways.

 

[oxyhacker]

You've seen www.stuartenergy.com/our_products/ hydrogen_generation.html I assume? Gives an idea of what a system might look like.

Looking at their costs, even a crude homebuilt system ends up costing in the same general range as a membrane separator, so if you don't need the hydrogen, the latter would seem to be a better choice, and much easier to operate/maintain.