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53 comments on Storing Energy Using Graphite
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Heating hot carbon hotter is an interesting way to store energy. Magnesium oxide, the principal component of some varieties of firebrick, is an alternative with a little less heat capacity per kilogram-kelvin (but about the same per litre-kelvin) that might be preferable because it cannot burn. Getting concentrated sunlight onto the bottom of a C block would seem to require the sunlight to go through some kind of window.
Ammonia cracking has the difficulty that the cracked material is largely hydrogen, very bulky.
H2 + (1/3) N2 <--> (2/3) NH3(l)
H2 + (1/2) O2 ---> H2O(l)
Looks as if these processes have deltas 'H' -41 kJ/mol and -286 kJ/mol: to get an erg of heat from the reaction of hydrogen with nitrogen, you must react seven times more of it than if you had reacted it with oxygen.
Let the baby play with matches in the fuel storage room
Since ammonia is of such enormous industrial importance(explosives and N-fertilizer in particular) and both electricity and ammonia are fungibles, why not just make ammonia from excess power and sell it? Then you can take the equivalent amount of natural gas(typically) that would otherwise have gone into ammonia production and use that for power production when it is nescessary. As long as people are using natural gas for power generation the end result will be the same; you saved some other source, typically coal or natural gas, that didn't have to go into either power or ammonia production.
ETA: Other sinks may be sodium/potassium hydroxide + chlorine gas or desalination of water. In essence find lucrative industrial end uses of power and integrate them as a variable load into your power generation scheme. Balance load instead of storing energy.
ammonia is a renewable, clean, combustible liquid fuel.
If you burn it you get back exactly what you had, only much less of it. If you keep it you have a valuable industrial and agricultural input.
you had at place you can't use it. in place you can't use it you can have it in over abundance and at much lower cost. you gain more in the first place and lose some later on, you can still be ahead.
ammonia as agriculture input degrades soil organicity, causes erosions and run-offs, generates strong GHG through soil interaction.
"you had at place you can't use it."
A frequent problem for cheap renewable power is that it's stranded out in the middle of a desert or up in the mountains somewhere.
Ammonia is actually fairly easy to transport and store; even more so if you produce end products like nitric acid or ammonium nitrate. If there are no transmission lines or the transmission lines are being used close to capacity it's certainly much easier to make ammonia or its derivates and transport them instead of transporting power.
"ammonia as agriculture input degrades soil organicity, causes erosions and run-offs, generates strong GHG through soil interaction."
And even so yields keep going up, farming still manages to be a carbon-sink according to every study I've seen on the subject and demand for "non-organic" food is still going strong.
As long as there's a market for explosives used in construction and mining and artificial N-fertilizer I don't see ammonia-derivatives being replaced anytime soon; you might as well make it with renewable energy rather than natural gas if it makes more economical sense than renewables for power.
even more so if you produce end products like nitric acid or ammonium nitrate.
one of the most cost effective way for transport is pipeline. ammonia can be transported via pipeline. can nitric acid or ammonium nitrate be transported in that way?
And even so yields keep going up, farming still manages to be a carbon-sink according to every study I've seen on the subject and demand for "non-organic" food is still going strong.
the question is for how long? performance enhance drug can do wonders for a short while but can kill the taker in the long run. farming sinks carbon but ammonia interacting with soil produces N2O which is a few hundred times stronger a GHG than CO2.
the point is that there is nothing in higher and more critical demand than renewable, clean and easily transportable liquid fuel. ammonia can play a much bigger role in this way than anything else.
no need to tell me the usefulness of NH3, since i am NH3 ;)
Building pipelines or storage is a huge barrier to entry. I believe just shipping it via boat/train/truck(in that order of preference) is good enough to get things started while still making environmental sense.
Yes, you could ship ammonium nitrate via pipeline in solution if you wanted to, but it probably makes more sense to ship the ammonia without excess water if you have access to a pipeline.
I don't see this debate being settled in the near future. In the mean time, is it better to fix nitrogen using renewable energy sources instead of natural gas when and where it is practical?
N20 is also produced by nitrogen-fixing bacteria, urine, manure etc. Most if not all sources of N-fertilizer share this problem. Are you sure it does not just come down to how much N-fertilizer you use and how timely the application is?(fertilizer application should be scheduled according to the specific needs of the plant and in the nescessary amounts for best effect)?
All the more reason you should take the ammonia and use it instead of converting it back to electricity.
the sooner to stop using hydrocarbons for fuel or fertilizer feedstock the better.
ammonia as agriculture input degrades soil organicity, causes erosions and run-offs, generates strong GHG through soil interaction.
One could always apply it as a folar feed.
Without doing more reading, I suspect that the attraction of the ammonia system is that it is also easier to crack, over cheaper catalysts than the splitting of water.
And although you might have to react seven times as much material (in the forward direction) the central issue is the rate of the reverse step.
IE, if you can produce the N2 and H2 from NH3 faster than you can produce the H2 and O2 from H2O for a given energy input, this is the important rate limiting step for a storage system. I suspect that reacting them is not the problem.
As far as I'm aware, the catalysts for water splitting generally involve expensive precious metals (Au, Pt) (anyone know better?) that are easily poisoned.
Also, the splitting of NH3 uses heat directly, does such a system exist for water?
Storing split water will also have the bulky H2, but at least we dont also have the problem of having to separate and store reactive O2 as well. In fact from what I understand, for the NH3 system, the cracked reagents are all stored in the same bottle along with uncracked NH3.
(I think I've got that right...)
Apparently an ammonia based system also got a Greenhouse Office grant (Wizard Power in Whyalla) - I'll do some digging and write a post on them...
I wonder if this is a 'political' statement since that is also a potential site for the desal plant for the Olympic Dam expansion. One is talking perhaps 50MW peak power and the other maybe 500 MW continuous. If I'm right the purpose could be to say we don't need nukular look at the green energy. Or maybe it will be like the solar steam plant at Liddell coal station in NSW which no-one notices.
Pic from anti-Baxter prison site is of the pipeline to Whyalla carrying precious river water.
Maybe - Malcolm Turnbull has a page claiming credit for it on his web site.
I like to think these things are being trialled for purposes beyond simple PR - lets face it - 99% of the population neither knows nor cares about this stuff.
BTW - try and keep the image size down - people on dialup complain about that sort of thing...
Yes, pressurized liquid NH3 under a gaseous mixture of NH3, H2, and N2.
Reactive O2 can be stored in the atmosphere. I'm reacting some right now.
At only a few hundred degrees Celsius, ammonia is less stable than
a mixture of hydrogen and nitrogen, and catalysts can accelerate
its breakdown, which would inevitably occur eventually anyway.
There are no "catalysts for water splitting" because water is stabler
than a mixture of its elements. At a few hundred degrees Celsius,
unlike ammonia, it would not spontaneously dissociate, ever.
No heat that any solid material can endure will split water.
There are multi-step processes that split it a little at a time,
and can occur at temperatures that containers can contain.
Let the baby play with matches in the fuel storage room
Apparently there are catalysts for water splitting 1, 2, 3... but thru photo catalytic processes, not using heat.
RE the storage of oxygen... I guess this depends on whether you are going to burn the hydrogen in a fuel cell, in which case pure oxygen is preferred... and if it is a byproduct of any water splitting process you would probably store it.
(EDIT)
And by chance Nature has an article on this very topic.
NB O2 in the atmosphere due to photosynthesis comes from water... not CO2 (as many seem to believe)
The electrodes of commercial alkaline electrolysis cells do have catalytic properties with respect to water splitting, although they obviously need the aid of an electric potential in order function efficiently. Nickel seems to be the preferred material rather than precious metals. Nevertheless electrolyzers are expensive, and the round trip efficiency of electricity==>chemical fuel==>electricity is low. I am skeptical that that fuel produced from electrolysis can support high levels of economic activity.
Other means of splitting water with sunlight are being pursued, including photo-catalytic splitting (as you mentioned) and thermochemical splitting. Also some people are now pursuing carbon dioxide splitting. If CO2 is split into CO and ½O2, then CO can be used to produce hydrogen via the water gas shift reaction CO + H2O ==> CO2 + H2. It is not immediately obvious that splitting CO2 is any easier than splitting H2O, but a number of people are pursing this option using photo catalytic methods, thermochemical splitting, and direct thermal splitting.
Los Alamos are doing some interesting work on using carbon dioxide for fuel, combined with more hydrogen:
http://www.greencarcongress.com/2008/02/los-alamos-deve.html
Green Car Congress: Los Alamos Developing Process for CO2 Capture and Stripping from Air for Synthetic Fuels Production
http://bioage.typepad.com/greencarcongress/docs/GreenFreedom.pdf
GreenFreedom.pdf
If they could really produce fuel at the cost they estimate, that is a game-changer - but of course the question is, can they?
It's not a game-changer. The same reactor can produce somewhere between 4x and 6x the vehicle-miles via electric vehicles and PHEVs than the synthetic fuel process, and at far lower capital cost (no chemical plant required). This is a diversion (see my comments in the GGC thread; this is a dead end just like H2CAR).
I, too, am extremely skeptical about the idea of using electricity to produce chemical fuel. Nevertheless we should not for get the "H" in PHEV. These vehicles need hydrocarbon fuels to operate, especially for long distance trips. If 8 billion people want high levels of personal mobility then figuring out how to decarbonize passenger miles is a worthwhile endeavor.
We don't need hydrocarbons for PHEVs; alcohols will do. If we can get sufficient carbon from wastes, non-food crop matter and so forth, it makes no sense to spend a couple billion to pull carbon from nuke plant cooling towers.
I regard alcohols as hydrocarbons even though they do have a bit of oxygen in them. If using plants to pull CO2 out of the atmoshere and H out of water is the cheapest option then naturally the market will choose that option. However, there is the small matter of the energy balance of biofuels and the opportunity cost associated with using land and water to produce fuel rather than food or ecological services.
If the materials involved are byproducts of things already being grown, the energy balance question is moot or nearly so; you're not going to reduce the energy input to a cornfield if you fail to make use of the corncobs.
I'm sceptical myself, but I don't rule it out.