Salt water eletrolysis idea

[sonicj01]

(I don't know a lot about science so pls explain things simply

I had an idea and I want to know if it would work, and if so what kind of energy it would need to do it big scale.

My idea is to connect a reverse osmosis module to an electrolysis device to produce hydrogen and oxygen from brine.

If this works, would it be able to be used on a submarine/ship to extract hydrogen for fuel?

Thanks! 

[studiot]

What exactly would be the purpose of the reverse osmosis module?

What would it do?

And what do you mean by connect?

[Raider5678]

20 minutes ago, sonicj01 said:

(I don't know a lot about science so pls explain things simply

I had an idea and I want to know if it would work, and if so what kind of energy it would need to do it big scale.

My idea is to connect a reverse osmosis module to an electrolysis device to produce hydrogen and oxygen from brine.

If this works, would it be able to be used on a submarine/ship to extract hydrogen for fuel?

Thanks! 

Nuclear submarines already use electrolysis devices to extract oxygen from salt water. Massive ones.

They'd by default, also get hydrogen.

So I'm not sure why they'd want to bring brine along with them to use instead of the salt water around them.....

[Endy0816]

Hydrogen storage and safety would be the main concerns. You would also need to be snorkeling or surfaced to burn it to regain some of the energy that went into production.

[swansont]

6 hours ago, sonicj01 said:

(I don't know a lot about science so pls explain things simply

I had an idea and I want to know if it would work, and if so what kind of energy it would need to do it big scale.

My idea is to connect a reverse osmosis module to an electrolysis device to produce hydrogen and oxygen from brine.

If this works, would it be able to be used on a submarine/ship to extract hydrogen for fuel?

Thanks! 

It takes more energy to create the gases than the useful energy you will get from creating it.

It might have utility as a storage medium (electrolysis when you have the extra energy available, burn the gas when you don't) which might make sense if you had a diesel-electric boat and you ran on a fuel cell while submerged, instead of a battery.

But hydrogen is generally not an energy source, in the big picture.

[John Cuthber]

2 hours ago, Endy0816 said:

Hydrogen storage and safety would be the main concerns. You would also need to be snorkeling or surfaced to burn it to regain some of the energy that went into production.

Submarines (at least the nuclear ones) are not noted for energy efficiency.
I always assumed they  vented teh hydrogen.

It's not flammable under water, and by the time it gets to the surface, it is someone else's problem.

[swansont]

Plus, if you have a reactor, there is no need for this stored energy.

[Endy0816]

5 hours ago, John Cuthber said:

Submarines (at least the nuclear ones) are not noted for energy efficiency.
I always assumed they  vented teh hydrogen.

It's not flammable under water, and by the time it gets to the surface, it is someone else's problem.

They do vent actually. Goes out with the CO2. Can cause cavitation though depending.

 

1 hour ago, swansont said:

Plus, if you have a reactor, there is no need for this stored energy.

Could imagine a boat fitted out with a hydrogen fuel cell, instead of the Diesel as backup.

 

Lot of complex issues with Hydrogen as a fuel, but would definitely save us some tax dollars if they could be solved.

Actually we would talk about onboard the subs too. Heyday of talk about a hydrogen economy and there we were dumping it. Gotta laugh sometimes.

[swansont]

9 hours ago, Endy0816 said:

 Could imagine a boat fitted out with a hydrogen fuel cell, instead of the Diesel as backup.

Since they both require oxygen, it would probably be a matter of how much space it takes up. And I suspect diesel wins, because the energy density of the fuel is going to be much greater.

[Raider5678]

12 hours ago, Endy0816 said:

They do vent actually. Goes out with the CO2. Can cause cavitation though depending.

 

Really? Wouldn't that give away their position? Bubbles?

[swansont]

58 minutes ago, Raider5678 said:

Really? Wouldn't that give away their position? Bubbles?

You're probably not releasing a huge volume all at once.

"Sixteen electrolytic cells at about 1000 amps are required to produce 120 SCFH of O2 (sufficient for 120 men) "

http://web.mit.edu/12.000/www/mission2005websitefolder/a2/8/pdf1.pdf

2 SCF per minute. So twice as much hydrogen, but it's also venting under pressure, probably continuously. If you're 100 ft down, that's 3 atmospheres of compression. 3 cubic feet becomes 1. And that will tend to disperse as it rises. 

[Raider5678]

1 minute ago, swansont said:

You're probably not releasing a huge volume all at once.

"Sixteen electrolytic cells at about 1000 amps are required to produce 120 SCFH of O2 (sufficient for 120 men) "

http://web.mit.edu/12.000/www/mission2005websitefolder/a2/8/pdf1.pdf

2 SCF per minute. So twice as much hydrogen, but it's also venting under pressure, probably continuously. If you're 100 ft down, that's 3 atmospheres of compression. 3 cubic feet becomes 1. And that will tend to disperse as it rises. 

Alright.

I head that the propeller on the back had to be specially made because the water pressure it made caused the water to boil, resulting in bubbles that would pop and give their position away.

[swansont]

1 hour ago, Raider5678 said:

Alright.

I head that the propeller on the back had to be specially made because the water pressure it made caused the water to boil, resulting in bubbles that would pop and give their position away.

Cavitation from the propellers  — the low pressure allowing bubbles to form and then almost immediately collapse — makes noise (and causes damage to the propeller), and is something Endy mentioned as a possibility.  But propeller cavitation is a low pressure event, collapsing because the bubble moves to a region of higher pressure. A high-pressure bubble would not have the same instability.

[Raider5678]

2 minutes ago, swansont said:

Cavitation from the propellers  — the low pressure allowing bubbles to form and then almost immediately collapse — makes noise (and causes damage to the propeller), and is something Endy mentioned as a possibility.  But propeller cavitation is a low pressure event, collapsing because the bubble moves to a region of higher pressure. A high-pressure bubble would not have the same instability.

Huh alright.

 

 

Out of curiosity, would low pressure water require less electricity to use electrolysis? Does water pressure affect the efficiency of the process?

[Endy0816]

5 hours ago, swansont said:

Since they both require oxygen, it would probably be a matter of how much space it takes up. And I suspect diesel wins, because the energy density of the fuel is going to be much greater.

Yeah, hard to compact safely with present technology.

2 hours ago, Raider5678 said:

Really? Wouldn't that give away their position? Bubbles?

If memory serves there's a diffuser so the bubbles are smaller. Only thing I've ever heard mentioned was to try and avoid the collapse of said bubbles.

Not sure on what all happens to it once it is out. Physics meets Chemistry situation.

[John Cuthber]

If I could be bothered I would look up the solubility of hydrogen in water- under great pressure.

1 hour ago, Raider5678 said:

Does water pressure affect the efficiency of the process?

Marginally.

Producing hydrogen under pressure requires a slightly higher voltage than at 1 atmosphere. 

In principle, the increased energy use in the cell is (unsurprisingly) the same as the energy that would be needed to compress the hydrogen if it had been generated at atmospheric pressure...

 

[Raider5678]

57 minutes ago, John Cuthber said:

If I could be bothered I would look up the solubility of hydrogen in water- under great pressure.

Marginally.

Producing hydrogen under pressure requires a slightly higher voltage than at 1 atmosphere. 

In principle, the increased energy use in the cell is (unsurprisingly) the same as the energy that would be needed to compress the hydrogen if it had been generated at atmospheric pressure...

 

I was thinking more along the lines of doing it with water in space.