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If we ever end up converting surplus electrical energy into hydrogen by electrolysis, an important by-product of electrolytic hydrogen production is oxygen. If the demand for oxygen is insufficient to consume all that's produced, it could be use instead of air in conventional fossil fuel (or biofuel)
burning power stations. This would mean that the flue gases wouldn't be diluted with a large proportion of nitrogen, making sequestering the carbon dioxide a much more economical proposition (if a suitable place to sequester it can be found).
It would also probably increase the efficiency of the plant, and would certainly dramatically reduce the production of nitrogen oxides.
Ocean-going hydrogen economy
Ocean-going_20hydrogen_20economy
Floating offshore wind turbines power a hydrogen economy [Cosh i Pi, May 27 2007]
[link]
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I was researching a CO2 idea last month, and stumbled across the fact that some large power plants already [later: will someday] process the air so that they are using mostly oxygen. I'll see if I can find a link. |
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How are you going to use the hydrogen? All of the uses of hydrogen as an energy source that I know of rely on the fact that oxygen is also going to be available in situ when you use it. |
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In use, you use precisely the amount produced in the electrolysis. |
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If this excess oxygen production is going to rely on the sequestration of the hydrogen, I have a very acidic fishbone for you. |
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[lurch], almost all uses of hydrogen as a
fuel rely on ambient air to provide the
oxygen (not on the pure oxygen
produced
alongside the hydrogen). |
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I don't think this is a very practical idea,
but it is not silly. Break water into
hydrogen and oxygen; burn the
hydrogen in air (where it combusts
cleanly and efficiently in 20% oxygen),
and use the pure (electrolytic) oxygen
to improve the burning of carbon fuels
(which don't burn as efficiently in air
alone). |
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[baconbrain] I'd be surprised and
intrigued if power plants can oxygen-
enrich air at an adequate rate - did you
find the link? |
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No, I can't find it. I was looking at some proposal and not realizing it was speculative. (I was otherwise focussed, really.) |
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I have found references to "Air Separation for Power Generating Industries", and to "oxygen-blown, entrained-bed gasifiers", and to "oxy-fuel combustion". |
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From Wikipedia, on oxy-fuel combustion: "However, because of the energy and economic costs of producing oxygen, an oxy-fuel power plant is less efficient than a traditional air-fired plant. In the absence of any need to reduce CO2 emissions, oxy-fuel is not competitive. However, oxy-fuel is a viable alternative to removing CO2 from the flue gas from a conventional air-fired fossil fuel plant." |
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Yes, oxy-injection makes the fire hotter and cleaner, but our oxygen supply needs to be cheaper than dirt for it to work! |
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[thisispeterstanley] Exactly so - that's why the title is "By-product oxygen". It's a suggestion for a use for the oxygen created as a by-product when hydrogen is generated by electrolysis, if no other higher value use consumes all the oxygen. |
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For the record, I think massive scale production of hydrogen by electrolysis is spectacularly stupid - hydrogen would be a wonderful fuel if there was any sensible way to carry a significant quantity of it on a vehicle, but there isn't, and there isn't ever likely to be. |
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Incidentally, you're slightly exaggerating when you say "cheaper than dirt" - if carbon dioxide sequestration is going to be used, because using oxygen rather than air for combustion results in a substantial saving in the post combustion separation of carbon dioxide from nitrogen. |
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Again, for the record, I rather doubt whether CO2 sequestration is really sensible. I'm not as confident of this view as of my views on hydrogen as a fuel, but I'm concerned about the likelihood that "sequestered" CO2 will leak back out to atmosphere rather quicker than its proponents hope. |
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I could be wrong about this, but isn't oxygen bubbled off a carbon anode/cathode as CO2 during electrolysis? |
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Also, if it isn't, the most efficient use of oxygen and hydrogen would be to use them together instead of fossil fuels, but that of course would mean that you would get less out of the system than you put in. |
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[marklar] You are wrong about that. Electrolysis of water normally produces hydrogen at one electrode and oxygen at the other, even if the electrode is carbon (an unusual choice except in DIY set-ups). |
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As was mentioned further up, hydrogen is normally burnt in air, because there's no particular advantage in burning it in oxygen (unless you're trying to achieve the highest possible temperature - too high for an internal combustion engine or turbine). But in fact it's likely to be used in fuel cells, where there's no advantage at all in using pure oxygen. |
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On top of that, if the hydrogen is destined for use in vehicles you don't want to have to carry oxygen as well as hydrogen (adding 50% to the weight and volume of tanks required), or if it's for use in domestic CHP, you don't want to have to have an extra set of delivery pipes. |
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You're right that you get less out of the system, in all cases, than you put in. The issue is whether it enables you to use convenient sources of electricity (such as offshore wind) to produce useful fuels other than electricity. As I said, "I think massive scale production of hydrogen by electrolysis is spectacularly stupid" - but a lot of people are suggesting it, and it may happen regardless of what you or I think. See link for what prompted the whole proposal. |
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