H2 from seawater
H2 from seawater
(OP)
Why can't you place two electrodes in seawater, place a voltage source across the electrodes and produce hydrogen and oxygen?
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: H2 from seawater
You now have two large containers full of gas. What are you going to do with them?
Cheers
Greg Locock
RE: H2 from seawater
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)
RE: H2 from 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.
RE: H2 from seawater
RE: H2 from seawater
RE: H2 from seawater
Cheers
Greg Locock
RE: H2 from seawater
HAZOP at www.curryhydrocarbons.ca
RE: H2 from seawater
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?
RE: H2 from seawater
But you're on the right track- better to use the power locally than to try to distribute and/or store it.
RE: H2 from seawater
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.
RE: H2 from seawater
HAZOP at www.curryhydrocarbons.ca
RE: H2 from seawater
RE: H2 from seawater
RE: H2 from seawater
Photocatalytic materials ?
RE: H2 from seawater
I am not sure what you are asking.
RE: H2 from seawater
Thread804-80670
Maybe it is possible to avoid the noble metals etc in this process.
RE: H2 from seawater
How are photocatalytic materials involved in this hypothetical hydrogen production scheme?
RE: H2 from seawater
> 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
RE: H2 from seawater
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.
RE: H2 from seawater
I would further argue that transporting anything material or physical is another loser in the overall system efficiency. How is that more efficient than using power lines?
How many trucks does it take to transport "thousands of megawatt-hrs" of energy?
TTFN
RE: H2 from seawater
Trucking is not required (an option to remote areas), the natural gas pipeline infastructure is already in place. Utilities in Austraila are experimenting with mixing hydrogen and natural gas, and delivering that mixture, via pipelines to their customers, both residential and commercial.
RE: H2 from seawater
my words excatly, except 200 miles is not a long distance and power lines would be used to. The problem 9 times out of ten with useing renewable energy like tidal energy etc. is that the renewable energy energy source is no where near a in place grid system thus by the time you install the power lines etc and power systyem that can cope with major fluctuations with the power generated then, you find that most of the energy does not make it to it's useful point of end use. that is where hydrogen comes in it can be piped 1000kms with minimal loss and essential is storing 100'sMWhours as it runs down the pipe
RE: H2 from seawater
Hydrogen transportation in a pipeline isn't the main loss in hydrogen as a storage medium for energy. Rather, the main energy losses are in making the hydrogen, and then in compressing the hydrogen up to a pressure which makes pipeline transportation economical, and then in the fuelcell (provided you can afford it!). If the route is to make electricity from tidal energy, then make hydrogen from it to make it cheaper to transport to destination, I'd say you're off your tree. If the goal is the storage of off-peak generation energy, that's a different story, because there are so few alternatives for energy storage.
I'd wager that the capital cost differences between building an electrical transmission line and a high pressure hydrogen pipeline are not insignificant either, with electricity being the clear winner on that front.
The best use would be to generate some electricity-intensive product nearby- aluminum, say. That would permit you to "transport" the energy without so many losses, while displacing product which is made by more conventional means.
RE: H2 from seawater
RE: H2 from seawater
When hydrogen produced from electrolysis it is possible to have the hydrogen bubble off at high pressure by placing the electrodes at a water depth, using nat gas pipeline for example, often at 400kpa then this pressure can be acheived in lass than 10M of water. no need for loss of compresson if a long distance is necessary than a larger water depth to begin with can be used. I am unaware of a reduction in electrolysis efficency at depth.
If the hydrogen is to be then used to generate electricity it can be used as a fuel in a conventional Internal combustion engine at high efficency, if the engine's fuel/air mixture is leaned out to equivelence ratio 2.5 engine efficency often is above 40% (ford model U recently realised 38% brake eff). These in turn can turn a generator. At equivelence ratio of 2.5 and above then no NOx is produced, no need for a catalytic convertor
Hydrogen Internal combustion charistics are coming along now. With many benifits of hydrogen addition into even the highly polluting desiel and petrol engines with increases in brake efficency, lower HC , lower CO, lower Co2, lower N0x, thus reduces running cost and good for environment and this set to save the bus companies millions in fuel costs.
Have you heard of the air car? it runs of compressed air. www.theaircar.com . I meantion it because the compression of hydrogen is a major issue and it shows that the compression energy in hydrogen tank could also be utilised by a correctly designed engine! and hence drive further again.
cost of powerlines coming down because of bad weather hence snow storms or cyclones are a major issue and in countries where these occur regularly most residents don't depend on electricity gas is everywhere because of it realability in such a situation. Hydrogen well ahead there simply because of realiability.
Molten I don't understand this:
The best use would be to generate some electricity-intensive product nearby- aluminum, say. That would permit you to "transport" the energy without so many losses, while displacing product which is made by more conventional means.
Celebur
certainly does depend on the pipelines. pipes in aussie have shown 10% vol is safe while it might be possible to reach 20% by vol no need for upgrade etc.
RE: H2 from seawater
If using an acid - is one better then the other for such a combination - EC can create phosphoric acid, nitric acid, carbolic acid, etc. - so the solution may not be "hydrogen fuel cells" but an acid reaction fuel cell using sea water as the "crude" source.
The other point - sea water is not pure - you have heavy metals, phosphates, carbonates, and other "impurities" that may have to be removed or accounted for in the reaction.
Dave Orlebeke/Aquatic Technologies
RE: H2 from seawater
Transmission capital costs:
Given that the generators would be located off shore. I have been told by a colleague of mine, that the cost of installing undersea cable or pipe line is in the equipment to do the job, not the actual cable or pipeline. My colleague assures me that for the undersea segment of these "transmission facilities" the cost is approximatly the same. Once on shore, then I believe the electrical transmission line may be cheaper.
Assuming that capital cost are the same to get the energy commodity to shore, what are some thoughts about hydrogen production on shore at one larger facility versus hydrogen production equipment located at each tidal stream generator?
Generator voltages:
A typical AC generator produces electricity in the 13-15 KV range. (FYI, This is typically close to the voltage range selected for ditributing electrical power in suburban areas.) I suppose the generator could be manufactured to produce a voltage idealy suited for hydrogen electrolysis. What is the ideal voltage for hydrogen electrolysis?
RE: H2 from seawater
RE: H2 from seawater
Puget Sound, with its 10 foot or higher tides, could take advantage of this type of device. A float could be installed under any of the many fixed piers in Seattle, Tacoma or Olympia. The rising tide could wind a spring or raise a weight attached to a gear driven generator. The float itself could be of significant enough mass (concrete) allowing it's falling with the outgoing tide to add to the power output. The potential energy could be stored and used to provide electrical power at waterfront properties.
RE: H2 from seawater
Is there an upper limit (theoretical and/or practical) of the DC voltage for "splitting" the hydrogen-oxygen bond? What is the upper limit based on?
DubyaDee
Interesting patent, I looked up the patent on the US patent office web site. The pilings on the piers I can look at, appear to be spaced 1 to 2 meters apart in a grid pattern. I wonder if any studies have been done to determine an optimum size of the "float/barge" for the vertical tide range in a given area.
RE: H2 from seawater
Some firms uses both - the breakdown of the saltwater to create hydrochloric acid, plus evaporation, evenutally releasing sufficient chloride that sodium hydroxide is created - this i snot a new concept to desalination plants. Figure upper reach is 400vDC.
RE: H2 from seawater
What results is an energy efficiency loss to produce compressed hydrogen. It may be less than the loss required to compress the hydrogen using a multi-stage mechanical compressor, or not- but it's still a loss. The energy you put in to store it in higher density form is gone forever as heat.
When you let down a compressed gas through a piston engine (i.e. like the "air car"), you get only the PV energy back. If you want to get a little more than that back, you need to use a Stirling-type engine, or you need a big gas-to-gas exchanger so you can use the atmosphere to heat up your gas after expansion. Hydrogen's a little different because of its negative Joule-Thompson coefficient, but you're still certainly getting nowhere the energy you put in to compress the hydrogen in the first place, back out as work to drive the vehicle. I've run the numbers on the air car and can't understand why anyone would do it, unless
Face it, guys- hydrogen is hydrogen. One of its fundamental properties is that there are only weak Van Der Vaals forces attracting hydrogen molecules to one another- so weak in fact that the normal boiling point is ~ 20 Kelvin. This material would much rather be a gas...To overcome the repulsive forces of molecular collisions resulting from stuffing a lot of molecular hydrogen into a small space, you need to put in some energy- and you only get some of that back, if any. Doesn't matter if you use chemical adsorption by forming hydrides, or if you use physical adsorption using carbon nanotubes, or if you don't bother with adsorption at all and just use massive pressures and store it as a compressed gas or compressed refrigerated liquid. Hydrogen's inherently poor as a high-density energy storage medium.
RE: H2 from seawater
RE: H2 from seawater
With a heating value 3 times that of natural gas, one could argue that energy transport via hydrogen would be more economical than natural gas.
RE: H2 from seawater
Cheers
Greg Locock
RE: H2 from seawater
Hydrogen being about 6 times less dense than Methane. Power consumed in a compressor being directly proportional to density. Everything else being equal (and perhapse a little over simplified). Hydrogen (gas) transport via pipeline should be significantly cheaper!
The issue then become cost of production? Can hydrogen be produced in the range of $4.00 to $5.00 per MMBTU/FT^3?
RE: H2 from seawater
b) adding H2 to a natural gas pipeline has a lot disadvantages, including changing the combustion stability of any equipment that fires the gas ( Wobbe induex, flashback, etc)- one can kiss goodbye any warranties on gas turbines or large boilers that fire the mixed gas. This is a big issue ( in the opposite direction) now being considered in the USA by pipeline companies and users due to the expected change in natural gas composition associated with increased use of LNG and also reduced recovery of heavies from gas fields
c) H2 will leak through seals in valves and other joints much faster than methane, and may be incompatible with some metals and some sealants
d) H2 can be economically produced using bit coal or Pet coke gasification, but the reliability of individual components is an issue. Each gasification vessel may have a max continuous runnig life of about 6 months ( due to corrosion) prior to major maintenance, so spare vessels are needed .
RE: H2 from seawater
Fuelcells are a great part of a renewable energy infrastructure, but you need the renewable energy sources to replace existing fossil-fuel derived electrical generation capacity FIRST. Fossil-fuel derived hydrogen as a stop-gap measure on the way there is not sensible from an engineering perspective- everything I've seen tells me that the net environmental benefit is marginal at best, and indeed may not exist at all once you take everything into account. Fuelcell technology right now is not driven by hydrogen- it's driven by media hype, generated by people who profit from this technology and kept aloft by politicians looking for the magic "technological fix" to our energy woes.
RE: H2 from seawater
I just wanted to jump in and mention that even though I am very excited about energy storage systems, a tidal energy generator doesn't neccesarily need to store the energy at off peak times does it? And if it does, the storage location doesn't have to be the same as where the generation occurs. Tidal energy is very predictable and can therefore be sold on the electric power spot market pretty easily. The energy can be used to offset other fossil fuel plants.
This is a problem with wind and solar energy, because it is not predictable, and since the energy needs to be sold in advance in most deregulated spot markets, it does not work well within the current energy trading system. Storing the energy makes it much easier to integrate into the grid.
I'm currently working on a project looking at adding energy storage systems into large offshore wind farms. I was looking for info about ocean water electrolysis and found this forum. I am excited to join the community.
I also wanted to note that even though there are inefficiencies in storing energy, due to the variations in the market value of energy from peak to off peak hours, it can still make financial sense. The differences can be upwards of 500% in some markets. So even a 50 % loss can still make money. I even see the potential in the future for local (customer side) energy storage systems that would allow people to buy energy from the grid at night (when it's cheap) and sell it during peak periods..
I also wanted to throw in some of the storage systems that are out there that haven't been discussed:
CAES: compressed air energy storage. This is usually done in large underground caverns but can be done in vessels. As mentioned in this thread, there are some vehicles that use compressed air. This is heavily being looked at for wind power, an interesting variation is to couple the aerodynamic rotor directly to the compressor, skipping the mechanical->electrical->mechanical energy conversion process.
Reversible Fuel Cells. (still in infancy)
Flywheels
Pumped Water. (this is really the only utility scale energy storage system in use today, except for a couple of compressed air systems.) Pumped hydro storage could be used with a tidal energy generator and managed by the utility.
For my location, I will be looking at steam reforming of methane that happens to exist under our location. This will generate H2 that will be burned in a gas turbine or fuel cell. The heat from burning the H2 will drive the steam reformer...and... hey.. perhaps it will distill the seawater before it goes into the electrolyser.
(I just thought that.. awesome! )
I still haven't found solid info about salt water electrolysis. Does it really need to be purified? I am looking at a system in the Gigawatt range...I mean big big big.
(i hope i'm not to verbose...)
john
RE: H2 from seawater
Flow Batteries.
Like a reversible fuel cell but use a oxidation reduction process with Vanadium or other fluids.. actually have a lot of potential for the future. Sometimes called Vanadium Redox batteries. Very cool.
RE: H2 from seawater
Does anyone know specifics about splitting sea water?
Does it really need to be purified first in a seperate step?
Does anyone know specifics about what needs to be done or any references I can find? I NEED to design a system to store electric energy by electrolyzing sea water..
There don't seem to be any electrolysers that work on seawater...
I guess the choices are to distill the water, or use reverse osmosis...then electrolysis.. is this the simplest way to do it?
RE: H2 from seawater
RE: H2 from seawater
Does the statement: " If you want hydrogen and oxygen, you'll need a different electrolyte." mean that in order to split seawater for hydrogen, the salt in ocean water must be removed, and a different electrolyte must be added?
An electrolyte isn't added to water before it goes into an electrolyzer (as far as I know) so I'm not sure what that means....
are there any electrolysis units that directly extract hydrogen from seawater, or is it always a multi-step system? From what I have found, it always needs to be purified first. I guess this is because the electrodes will corrode or get poisoned if they are in direct contact with ocean water which is impure.. So even though electroloysis might be near 90 percent efficiency, once you inlude the energy required for water purification, this would potentially be much lower.
I am really thinking flow batteries are the energy storage system to watch. Because of the fact that you can scale them up by just adding more electrolyte, which is stored in tanks. They can be charged and discharged fully with no degradation, and especially with the Vanadium REDOX type, there is no crossover membrane crossover pollution problems, since the negative and positive side are both just different oxidation states of the same material. These systems can be cycled thousands of times and keep coming back for more. They are also up to 90 percent round trip effiency
RE: H2 from seawater
The nature of the ions in the electrolyte, and the electrochemical side reactions they undergo, determine to a large degree the efficiency of any electrolyzer you might want to build.
In theory, you don't need to add electrolyte to a continuous electrolyzer if you choose one which is stable. All you do is add fresh PURE water to an initial charge of electrolyte which remains in the cell. However, just like in distillation, any impurities in the water will accumulate in the electrolyzer, requiring ultimately a bleed stream and an electrolyte replenishment stream if you want to run a continuous electrolysis process.
RE: H2 from seawater
RE: H2 from seawater
http:/
Bruce Toski
Bruce Toski
ASE Master Certification
Automotive Instructor