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Comment by nanomonkey | Hacker News Reader

While everyone likes to mention that it's inefficient to split water to produce hydrogen (~60% efficiency round trip to produce electricity, if memory serves me), no one seems to take into account that you now also have a source of pure oxygen. Oxygen is great for producing syngas from carbonaceous materials like biomass (left over dry plant material). If used in tandem one could produce two carbon neutral or carbon negative fuel sources.

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See http://www.thermalhydrogen.com/ for a suggested carbon neutral energy economy with syngas, O2, and CO2 (for sequestration) pipelined around continents.

> it's inefficient to split water to produce hydrogen

You also have significant losses when you convert it back electricity/heat with fuel cells, or burning it.

> Oxygen is great for producing syngas

This is really interesting. I wonder how much this helps offset the losses mentioned above?

Syngas (a.k.a producer gas) is normally made from atmospheric oxygen, and is a conversion process of the stored fuel in biomass through pyrolysis to produce tar gas, which is then reduced by the hot charcoal left over. You are essentially producing fuel from garbage and is worthwhile on it's own. By using pure oxygen you can produce a more pure gaseous fuel, as the final product isn't diluted by the mostly inert nitrogen that is in air.

Thats not a round trip. That is just ONE WAY energy conversion. Imagen doing an actual round trip.....

And then think about gravity energy storage which has an actual back and forward efficiency of 85%.

Oxygen produced by air separation is extremely cheap, so the oxygen stream from electrolysis would have little value.

Pure oxygen is not actually that cheap, enriched oxygen like you would get from a pressure swing absorption concentrator is relatively cheap (although it still consumes energy), but it is still mixed with other gases that will dilute your syngas.

Most industrial oxygen comes from cryogenic separation, not PSA, and has a purity above 99%. Liquid oxygen is the second cheapest industrial liquid, after water.

Storing and shipping liquid oxygen is not that energy efficient. The point I'm making is that the oxygen can be used at the source of production (splitting water) to produce more fuel. Liquid oxygen storage is not something that one would do in most facilities while almost anyone could split water and utilize the oxygen to gasify their waste streams to produce syngas for heat and electricity production.

Liquid oxygen is trucked and stored all over the place. Most hospitals get their oxygen by warming LOX (you can see the frosted-over serpentine warming systems by the tanks if you look carefully.) It's easy to ship and does not suffer large losses when doing so.

You keep bringing up this point, but the idea isn't to sell the oxygen on this market, but to utilize it at the source to upcycle carbonaceous matter into usable fuel (Hydrogen, methane and carbon monoxide...i.e. syngas) for use alongside the hydrogen gas that is produced via electrolysis.

This is useful in remote locations (cell towers, villages, etc.) where a liquid oxygen tank would not be viable.

Just to clarify, when I say, "not cheap" I'm more or less referring to the energy costs and not the actual monetary costs. It's energy intensive to bring air down below −183 °C to liquify the oxygen out. When contemplating future energy sources, it's these round trip energy expenditures that are most important. Not to mention the infrastructure costs (liquid oxygen tanks, roads that can safely handle shipping, etc. aren't cheap either).

The market value of oxygen tells you how much your own production of oxygen is worth, even if you don't sell it on the market. If you could replace that O2 by buying it, its value to you is no higher than that replacement cost.

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