H2 from seawater 7

[thorangle]

Why can't you place two electrodes in seawater, place a voltage source across the electrodes and produce hydrogen and oxygen?

 

[GregLocock]

You can. You are using rather expensive electricity, probably got by burning fossil fuels to do so.

You now have two large containers full of gas. What are you going to do with them?



Cheers

Greg Locock

 

[HydroScope]

not sure if it is that easy, I know statements like electrolysis of water is 70% efficent are made but I think that is when they add efficent electrolyte(Ionic matter of some sort aka salt). Not sure what the ratings are for our ocean salt?? it maybe that if you don't make any changes to the compisition of ocean water the electrolysis process ain't very efficent. but really don't know?? I might found out tomorrow at hydrogen symposium ;O) as for what to do with it it does seem some poeple have found applications.

Australia is going to use relaibale tidal energy of the kimberly region to produce hydrogen via electrolysis of sea water for use into natural gas supply. apparently adding up to 10% hydrogen by Vol% will have no effect on the pipes etc currently used to supply hydrogen. And will emite a hell of a lot less emissions.

It is futher suggested that this hydrogen maybe removed from the piping system at point of end use for collection. giving the fuel cell vechiles and other hydrogen technologies an efficent infrustructure to begin with.
here is a link.

http://www.hydrogen.org.au/hydrogen-news-ed.5.htm

Mark ;O)

 

[moltenmetal]

The issue with water electrolysis is not generally the source of the water- it's the source of the energy to drive the electrolysis. The electrolyte is not consumed, so you choose its composition and concentration to maximize the efficiency of the electrolysis process. I guess if all you've got is seawater...but there are easier electrolytes to work with than the mixed bag that's in seawater.

There are plans of the sort Mark is describing to use remote or off-peak electrical generation capacity to electrolyze water to generate hydrogen to power fuelcells. In areas where power transmission lines don't exist but natural gas pipelines do, perhaps this "hythane" blending into an existing natural gas grid is an option. Neither long transmission lines nor hydrogen generation/reconversion to electricity by fuelcells are as efficient as local use of the electricity, but if the power source is renewable (like tidal), it's all good.

 

[thorangle]

Thanks everyone great responces. I live in the Puget Sound area of Washington state. There are lots of tide flow opportunities here. My thoughts are to use some form of tidal generator(s) to produce electricity when peak tide flow corrisponds with peak electricity demands. Use the tidal generators for hydrogen production when the peak tide flow is not in-line with peak electricity demands. The hydrogen is stored for generating electricity during peak electrical demand. Does anyone know of this type of application in use today?

 

[moltenmetal]

Electrolysis w/hydrogen storage and a fuelcell are definitely being considered for load-balancing applications like the sort you're describing- IMHO they have much more of a chance to be used in this type of application than in transporation. Each step (electrolysis, H2 storage and the fuelcell) loses some of the power you generated in the first place, so it's not perfect, and the capital costs of all three steps are far from negligible- but these applications can maximize our use of off-peak renewable power. Other means such as flywheels and even pumping water back up-hill at hydroelectric dams are also used to "store" off-peak power.

 

[GregLocock]

Why on earth would you not use a barrage to even out the water flow, rather than incurring two rather lossy chemical conversions?

Cheers

Greg Locock

 

[owg]

My chemistry book says that when you electrolyse fairly concentrated aqueous solutions of chlorides, chlorine is discharged at the anode rather than oxygen. For brine the liquid tends to change into caustic soda.

HAZOP at

http://www.curryhydrocarbons.ca

 

[thorangle]

Greglocock: My thougts behind the use of a tidal stream generator is to minimize the "foot print" of the generation equipment.

owg: Two questions on caustic soda. Is there a commercial market for caustic soda? If the hydrogern production equipment is located such that the two electrodes were emersed in the ocean with a "jar" to collect the hydrogen, would the amount of caustic soda produced be environmentaly significant?

 

[moltenmetal]

Electrolyze seawater in an "open" cell, and you'll get chlorine/hypochlorite/chlorate. If you want caustic and chlorine, you have to keep the two from mixing using a membrane cell. But sea salt isn't pure sodium chloride, and that will impair the value of the product caustic. If you want hydrogen and oxygen, you'll need a different electrolyte.

But you're on the right track- better to use the power locally than to try to distribute and/or store it.

 

[thorangle]

moltenmetal: If I understand you, to get hydrogen & oxygen from seawater I would first need to purify the sea water and then add an electrolyte. How pure would the seawater need to be and what kind of electrolyte would be added?

In addition to using the power locally (at the generator to produce H2 & O2), I am looking at the cost per foot of undersea electrical cable vs pipe.

 

[owg]

thorangle - Sorry I don't know the answers to your questions. I suppose the environmental assessment will look into that.

HAZOP at

http://www.curryhydrocarbons.ca

 

[moltenmetal]

The electrolyte won't be consumed. So- solar 'still the water and add it to the electrolyzer on a continuous basis as you produce oxygen and hydrogen. Purity will be good enough. Pretty ungainly, though. Or use some of your product electricity to run an RO system- not as environmentally elegant, but since you can return the brine to the sea, probably not too expensive to run either.

 

[thorangle]

moltenmetal: Too many cloudy days in the Puget Sound area for a solar still to be effective. However, the RO system sounds interesting. I wonder how sensitive the RO equipment would be to the cyclical nature of a tidal stream generator? How much "care and feeding" do RO systems require?

 

[k4lan]

how to increase the rates of Hydrogen Evolution from Water?
Photocatalytic materials ?

 

[thorangle]

k4lan,
I am not sure what you are asking.

 

[HydroScope]

I think it is a rhetorical question. He might be thinking like I do?? the refining of noble metals etc to be made into photocatalytic materials might not be the right way to go about a hydrogen economy. As first we must dig a dirty big hole in the ground (expenditure of energy) and then refine the metal shape it etc. Are you aware it takes 7 tonnes of ore to yeild 32gms of platinum and it takes 6 months to refine!! hence Why I started the thread "Sodium from ocean salt for generation of hydrogen"
thread804-80670

Maybe it is possible to avoid the noble metals etc in this process.

 

[thorangle]

OK,I will admit my ignorance of photocatalytic materials, and platinum production. I was/am interested in the possibilities of using ocean tide streams to generate electricity. Since tide flows are cyclical and often do not corrispond to peak electricity demands, I was also interested in using the off-peak electricity to produce a "storable" form of energy. Hydrogen from the electrolysis of sea water appeared to be a reasonably mature technological possibility.

How are photocatalytic materials involved in this hypothetical hydrogen production scheme?

 

[IRstuff]

Your concept of using tidal energy to generate hydrogen to generate power results in two large inefficiencies:

> when youconvert to hydrogen
> when you convert back

whereas, a direct storage of the electrical energy in super caps or the like would result in a minor inefficiency.

TTFN

 

[thorangle]

I agree that the production of hydrogen and the subsequent use of hydrogen to produce electricity are inefficent. However, all thermal power cycles share the same/similare ineffciencies. If one then compares the effcientcies associated with the production, transport, and storage of the hydrogen versus other forms of energy storage, I believe that hydrogen production from tidal stream generators (free energy source) compares rather favarably. The inductrial technology to acomplish this is in existance and use today.

Question: Can super caps be manufactured and configured to store thousands of mega-watt-hours worth of electrical energy? Assuming that super caps can be manufactured and configured to store that much electrical energy, an economic evaluation would be interesting.