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Engineers are developing new ways to convert greenhouse gases to fuel

uc.edu

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Re: Engineers are developing new ways to convert greenhouse gases to fuel

#111

Post by fho »

gpm wrote: post #85
rolleiflex wrote: post #82

Earlier quoted context omitted.

If they’re not recycling CO2 into O2 and instead venting CO2 to space, does that mean ISS is constantly losing gas and it needs an ongoing resupply of oxygen all the time? I thought oxygen was used fast enough to make resupply impractical, but perhaps there are in fact gigantic tanks of O2 under immense pressure somewhere aboard the ISS.

Yes, and sort of. The ISS is constantly losing gas, I believe that the primary source of new O2 is actually electrolysis of water, not pressurized tanks, but that they do also have pressurized tanks as a backup. A person breathes out roughly 1kg of CO2/day, and it follows you breathe in about the same amount of O2, not an impossible amount of mass to resupply.

> 1kg of CO2/day

which is crazy low if you put it in perspective and see that (gas powered) cars release about 0.2 kg of CO2 ... per kilometer.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#112

Post by missedthecue »

yholio wrote: post #15

No, enough with this nonsense. Capturing, liquefying and transforming CO2 into fuel requires energy - due to thermodynamic limits, much more energy than what the fuel can give back. You then take that fuel, and... burn it into 25% efficient engines that spew the very same CO2 back into the air, along with some new carcinogenic fumes and acid-rain inducing nitrogen oxides? No, just no, full stop. They way forward is e…

You are correct that they can't break the laws of thermodynamics, but they don't need to in order to have a workable business model. The reason is because you don't need it to result in more energy than you put in. You just need it to result in more revenue than input costs. This is practically possible because different energy forms have different costs and they're not all substitutable for each other. For instance, electricity may become a lot cheaper than liquid fuel, but you can't electrify a long range airliner, or most military equipment. So in a world where a watt of electricity can be bought for 1/3 the price of a watt of kerosene, using 2 units of electricity energy to make 1 unit of liquid fuel energy would be economical. (made up numbers, you get the point)

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#113

Post by diarrhea »

lmilcin wrote: post #99

Don't get your hopes too high if you think this can be used to scrub significant amount of CO2 from atmosphere. Don't get me wrong, producing fuel from atmospheric CO2 is still wonderful news. But you know what they produce? Methane. And methane is what? It is A FUEL . And what we do with fuel? We BURN it. Once you burn methane you get the CO2 back, for net ZERO effect on the atmosphere. The only way this works to he…

It's even worse than zero net effect, it's negative, owed to all the auxiliary inefficiencies. Add to that methane slip and it's infeasible by a long shot.

The solution can never be to remedy surface-level GHG. The sources need to remain buried and replaced by true renewables. Anything else is just an afterthought, patching what's already too little too late. Almost all fossil-based material that made it to the surface will end up contributing to GHG.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#114

Post by eightysixfour »

yholio wrote: post #101
eightysixfour wrote: post #34

Earlier quoted context omitted.

I was with you until no hydrogen. While it is inefficient in compared to batteries, as long as it is being produced with carbon-neutral energy then there are areas where its kWh/kg ratio and comparatively rapid refilling are extremely beneficial.

You should take that kWh/kg figure with a kg of salt. You need a heavy COPV tank to store hydrogen under pressure, a 100 kg tank might store only a few kg of fuel, take 400 liter to do so, and be comparable with a 30l conventional fuel tank: https://www.fsec.ucf.edu/en/consumer/hydrogen/basics/documen...

Sure, and using it for small vehicles seems like the worst place to use them. I'm thinking more about vehicles that need significantly more fuel - diesel electric trains, container ships, airplanes, etc.

It won't work in all of those situations since hydrogen is so hard to manage, but there are a number of applications where batteries are not the right answer yet. Battery weight is going to scale close to linearly with capacity, hydrogen tank weight should not.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#115

Post by generalizations »

The problem, in general, is obtaining the CO2. Ironically, in industries where massive amounts of CO2 is needed (including biodiesel production from algae), one of the cheapest ways to get it is to just make it. Pulling it out of the air isn't feasible.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#116

Post by ncmncm »

_Microft wrote: post #27
yholio wrote: post #15

No, enough with this nonsense. Capturing, liquefying and transforming CO2 into fuel requires energy - due to thermodynamic limits, much more energy than what the fuel can give back. You then take that fuel, and... burn it into 25% efficient engines that spew the very same CO2 back into the air, along with some new carcinogenic fumes and acid-rain inducing nitrogen oxides? No, just no, full stop. They way forward is e…

It can make sort of sense for applications for which the energy density of the fuel (like for airplanes or rockets) matters a lot. The energy density of current generation lithium ion batteries is insufficient to allow for long-range flights. Synthetic fuels could allow planes to still travel around the world while being effectively net zero emitters because the CO_2 was harvested from the atmosphere (or another, una…

Liquid hydrogen LH2 electrically synthesized on-site at airports from excess peak production will be important in aviation after maybe 2035 (provided civilization doesn't collapse first). Aside from LH2's usefully extreme energy density, pumping less CO2 directly into the stratosphere would be good.

We may reasonably expect production of the needed aerogel-insulated LH2 tankage to be mature by then.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#117

Post by makeitrain »

fnord77 wrote: post #110
robbrown451 wrote: post #108

Title on HN should probably read "University of Cincinnati" rather than UC. Even I, a graduate of University of Cincinnati now first thought "University of California." (Admittedly I live in California now)

I'm impressed that University of Cincinnati snagged uc.edu

When you invent the internet but forget to register your own domain... oops.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#118

Post by CodeGlitch »

mlindner wrote: post #80

Converting CO2 into fuell isn't the hard part. The hard part is getting the CO2 out of the atmosphere in the first place. We've known how to convert CO2 into fuel since the end of the 19th century. https://en.wikipedia.org/wiki/Sabatier_reaction

This I do not understand... why do we not build a nuclear reactor out in the middle of no-where - easily accessible via shipping - that has the job of taking CO2 out of the atmosphere, and converting into liquid methane?

It can run 24/7.

Little running costs?

No one complaining about NIMBYISM.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#119

Post by ncmncm »

eightysixfour wrote: post #114
yholio wrote: post #101

Earlier quoted context omitted.

You should take that kWh/kg figure with a kg of salt. You need a heavy COPV tank to store hydrogen under pressure, a 100 kg tank might store only a few kg of fuel, take 400 liter to do so, and be comparable with a 30l conventional fuel tank: https://www.fsec.ucf.edu/en/consumer/hydrogen/basics/documen...

Sure, and using it for small vehicles seems like the worst place to use them. I'm thinking more about vehicles that need significantly more fuel - diesel electric trains, container ships, airplanes, etc. It won't work in all of those situations since hydrogen is so hard to manage, but there are a number of applications where batteries are not the right answer yet. Battery weight is going to scale close to linearly wi…

LH2 tanks on aircraft, insulated with aerogel, can be very light. But the extra volume will mean a need for new airframes.

Trains and ships, and maybe trucks, will do better with ammonia. The tanks are bigger, but those have room, and existing engines can burn ammonia with just changes to plumbing.

Re: Engineers are developing new ways to convert greenhouse gases to fuel

#120

Post by anamax »

makeitrain wrote: post #117
fnord77 wrote: post #110

Earlier quoted context omitted.

I'm impressed that University of Cincinnati snagged uc.edu

When you invent the internet but forget to register your own domain... oops.

The University of California schools think of themselves as independent entities, independent entities that just happened to all pick the same school colors.

berkeley.edu (where "University of CA" is a subtitle), ucla.edu, ucdavis.edu, etc.

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