Wednesday, February 21, 2018

Matching Methane Combustion to Carbon Capture

An idle thought that probably has occurred to a lot of people.  There is a lot of talk about clean coal with carbon (dioxide) capture. There is a lot of discussion about a hydrogen economy driven by catalytic electrolysis of water.

2H2(g)+ O2(g)--> 2H2O(g)    ΔH = 2(-241) kJ/mol = -482 kJ/mol

Eli's idle mind thought about comparing this to natural gas combustion

CH4(g) + 2O2(g) --> 2H2O(g)  + CO2(g)   ΔH = -801 kJ/mol 

Now methane, or natural gas, whether it is in the gas form or liquefied is easier to handle than hydrogen, if for no other reason that it can be liquefied. What interested Eli in this simple calculation is that methane and hydrogen have the same number of hydrogen atoms.  Eli knows that this is a very Rabett way of thinking, but if you twist your mind that way it means that there are 319 kJ/mol available for carbon capture.  True you might have to invest some of that to sweep out the water vapor, but even there there are possibilities for recapturing the heat generated in the condensation step

 2H2O(g)  --> 2H2O(l)    ΔH = 2(-44) kJ/mol = -88 kJ/mol

The interesting chemical question is can a bunny find a carbon dioxide capture system which can simultaneously capture CO2 and absorb the water vapor into solution as a liquid.  Eli is a clever bunny, it's easy to be clever and find the answer when you figure out what the question is.  Amines are obviously not going to do the job, ionic fluids might and there are some systems already known which may point the way

Setting this up as a process means that natural gas can be combined with carbon capture to yield an emission free system that can easily be combined with wind, solar, hydro and yep, nuclear to provide inexpensive (a friend taught Eli never to use the word cheap) and reliable electrical energy.  There is lots of energy to be used for the carbon capture process.  Given the right chemical system, it might even work for trucks and buses.  Autos, well leave them to Toyota, Tesla and GM.

The future will be clean natural gas and renewables.


bjchip said...

Yes, methane is almost the ideal carrier for H2... but only if you can put a high enough price on the fugitive emissions.

David B. Benson said...

Well, clever bunny, PNNL recently demonstrated that injecting supercritical carbon dioxide and "a little bit of water" into basalt resulted in carbonates within 2 years. So what does it take to remove the N2 from the air input or the exhaust? What does it take to supercriticalize? While I doubt that extra water is harmful to the basalt reaction, I doubt the energetics are good enough. But then, I am not a clever bunny.

Barton Paul Levenson said...

In what way does CH4 have "the same amount of hydrogen" as H2? The court finds itself unable to follow the alleged reasoning.

Fernando Leanme said...

Miscellaneous comments:

LNG isnt that practical for overland transport because the gas is already at high pressure so it's cheaper to put it in 2000 psi cylinders. I've done studies for enriched air methane gasifiers, but running enriched air in a turbine makes it run hotter, which means we have to develop viable turbine technology.

There isn't enough natural gas to replace gasoline in internal combustion engines, so the focus should be on heating and electricity generation.

So let's say we have a turbine running at 60% efficiency, to capture and liquefy the co2 we use X % of the energy, and then we got to put it away. And this requires a lot of energy for underground disposal. Plus here's the kicker many scientists forget: putting a liquid in an underground formation can eventually lead to pressures and stresses which cause earthquakes. So the obvious answer is to inject CO2 in large leaky acquifers. This may allow some CO2 to escape, but my models show that sealing the co2 forever isn't required. The carbon cycle handles small amounts leaking over hundreds and thousands of years.

I spent years looking at this issue, so if you have questions feel free to ask. But do grab the CO2 PVT chart and study it. Also focus on the liquid density at say 1400 psi (that's 100 atmospheres more or less)


Once you stipulate carbon capture, teh inorganic chemists get to play the game.

Energy density is so important in long distance transportation that one might consider turning coal into coke and coke and limestone into calcium carbide, which can provide a transportation fuel cycle that captures half its own CO2 on the road with the aid of a self sufficient limewater muffler:

CaCO3 -> CaO + CO2

CaO + C = CaC2 + CO2

2 H20 + CaC2 -> C2H2 + Ca (OH)2

C2H2 + O2 = H2O + CO2

CO2 + Ca(OH)2 -> CaCO3 ....

on't tell Watts, lest Pruitt's Oklahoma & Heartland Mafiosi declare the cycle the best thing since unpasturized armadillo chili.

Beakers said...

An alternative transport fuel for a long distance bus, HGV and shipping is Ammonia. The Dutch ran road transport on it, converting vehicles during the war when they could not get diesel.
The key thing for ammonia is that for fertiliser, we have to make it anyway. At present the huge global production is dominated by gulf gas where the gas is cheapest.
Once we start having 'excess' renewable and/or nuclear generation, displacing fossil fuel powered ammonia synthesis is a candidate for absorbing that excess.
It has already been used for an energy store on a small grid in Alaska. Siemens are progressing their tech and Yara (formerly Hydro, the Norwegian fertiliser giant) is working on a solar N plant in Western Australia. Uni of Minnesota have their wind powered Ammonia pilot plant project.
Its an interesting prospect of a viable transport fuel, grid power storage media and product that we have to transition back to renewable (and nuclear) powered synthesis anyway.

John ONeill said...

'methane and hydrogen have the same number of hydrogen atoms.'
Hydrogen gas has two hydrogen atoms per molecule, methane has four. Methane has about three and a half times the energy per litre of hydrogen gas, and doesn't embrittle metals like H2 does.Both need to be stored at very high pressure, or cooled to way below zero ( H2 about minus 250 C, CH4 about minus 180 C.) A better synthetic fuel would be dimethyl ether, CH3-O-CH3, which can be used in the same low-pressure tanks as LPG, and unlike methane, is not itself a greenhouse gas. It doesn't make soot either, and can be burnt in diesels with very low emissions of nitrogen oxides, without a catalytic converter.

Unknown said...

Yes and if the methane is from a renewable source instead of a fossil fuel, then sequestering the carbon is a carbon-negative outcome.

Jan Galkowski said...

@Brian Schmidt,

Yeah, like anaerobic digestion.


Mark said...

An item in Science (26 May 2017) claims greater turbine efficiency by using supercritical CO2 rather than steam, in a Brayton cycle. This would produce a water and carbon dioxide exhaust; CO2 would be recycled to run the turbines, and some of it would be easily captured. Perhaps its biggest drawback is the need for large refrigerators to separate O2, used for combustion, from air. However, the smaller overall facility size may make it an economic alternative to coal or natural gas combined cycle.

David B. Benson said...

This appears to be a description, almost, of the Allam cycle. A demonstration plant was supposedly completed in La Porte, TX, according to the Wikipedia article on the Allam cycle. However, nothing more seems to have been written about it; there is no guarantee that the generator actually works.

Jan Galkowski said...

@David B Benson,

Apparently, yes. Thanks.

However, there is an update by Alam, et al, and the project is nearing completion.

John Farley said...

I have read the first edition* of Burton RIchter's book, Beyond Smoke and Mirrors: Climate Change and Energy in the 21st Century. Richter gave his considered opinion about the feasibility of carbon captured storage. If you don't care what it costs, you can capture the carbon from fossil fuels. BUT then you have to sequester the carbon essentially forever. If the carbon leaks out in a few centuries, that's just not good enough.

Richter is a Nobel laureate in high energy particle physics, a field having little or no overlap with practical combustion engineering. Richter thinks Germany made a mistake in shutting down nuclear power, by the way.

* There is a second edition out also (2014 printing).

Jan Galkowski said...

@John Farley,

I can see reasons for not wanting to build new nuclear power (primarily because it is too expensive, and has a negative learning curve, even controlling for additional environmental and safety regulations over time), but I agree that keeping existing plants online would be wise. Unfortunately, a lot of fellow environmentalists don't agree with me, which is one of the reasons I'm trying to coin the phrase wishful environmentalism. It also applies to those who chant ``Green Power Now!'' and don't want natural gas (I don't want the latter either, except maybe for Allam cycle), but, then, don't want solar farms built near residential communities or any new growth forests cut or oppose hydropower or dislike wind turbines on land near the coats.

That said, large power plants, like nuclear, do not offer the consistency and reliability they seem to offer. Generally speaking, because they can go offline in less than two minutes, they need to be paired with incredibly dirty gas peaking plants which can jump on the grid in that timescale to offset their taking 640 MW off when they do go down.

I don't know what Richter addressed in his book. I have looked at Carbon capture and removal techniques, and priced clear air capture, and, I agree, they are horrifically expensive, unless someone can figure out how to do capture and sequestration for US$1/tonne CO2 However, the Allam power cycle, discussed here, and introduced by Eli, is a closed cycle for burning natural gas and automatically capturing the stuff. That said, it is attractive, even if we probably don't have enough natural gas in the states to power, say, our transport infrastructure for a long time.

Sequestration can be a problem, unless the CO2 is pumped into molten basalt in Iceland or some such place. It doesn't have to be perfect sequestration, but it can't leak more than 1% per century or something like that.

David B. Benson said...

There are many errors in this comment. The South Korean nuclear power plants demonstrate the appropriate learning curve. Nuclear power plants do not require a dedicated backup; the typical almost 15% utility generation reserve suffices. Sequestration of carbon dioxide in basalt does not require that the basalt be hot, in particular molten. Sequestration in basalt has recently been demonstrated by PNNL.

Jan Galkowski said...

@David B Benson,

1) Technical reference, please, on South Korea learning curve.

2) ISO-NE claims they need backup for Pilgrim Nuclear and others in the region, hence the claimed need for additional natural gas pipelines? Inconsistency? Things different here? Or are they misrepresenting because they want more pipelines?

3) Thanks for the PNNL reference. I stand corrected on the molten basalt. My familiarity with the process is the CarbFix project in Iceland, begun in 2007. They expect groundwater at 30 degrees C to 50 degrees C. They remark: ``However, in-situ mineral carbonation is not without challenges. CO2 dissolution into groundwater is slow and limits the mineral dissolution and precipitation reactions. Slow reactions require an impermeable cap rock above the injection reservoir to keep the dissolved CO2 in contact with the reactive rocks and to prevent leakage. Furthermore, mobilization of toxic metals as a result of CO2-water-rock interaction may lead to their migration within the reservoir. The chemical reactivity of these metals within the reservoir has to be addressed.''

Jan Galkowski said...
This comment has been removed by the author.
Jan Galkowski said...

Evidence for the negative nuclear learning curve, from Lovering, Yip, and Nordhaus, 2016:
Negative learning curve for nuclear power.

South Korea:
Learning curve for South Korea

If one squints, you can imagine seeing a negative learning curve there, but the dataset is not robust against a counter-hypothesis that the costs are flat.

(Deleted and reposted the comment finding I did not know how to put up images here.)

David B. Benson said...

Actually the cost per unit electricity generated by the South Korean line of nuclear power plants has declined slightly over time as most recently demonstrated by the build ongoing in the UAE.

The difference is that the South Koreans keep up building essentiallythe same design repeatedly.

David B. Benson said...

PNNL forced supercritical carbon dioxide and a "little bit of water" into basalt to obtain solid carbonate inclusions within 2 years; conventional geochemical wisdom is wrong.

David B. Benson said...

Yes, the New England grid does not have adequate reserves. I view that is a result of the incompetence of the politicians in that region. As I make it the rest of the USA has adequate reserves.

EliRabett said...

The needed storage time for CO2 is an interesting issue. The response to a pulse is a decline of 40% in ~20 years followed by a slower decline to about 33% in a century and 20% in 300 years. The rest takes pretty much forever, but if we ever got in the situation which it made a difference open air capture could help, so no, the CO2 does not have to stay captured forever.

Hank Roberts said...

> Allam cycle
Article is from mid-2017, and says ""first fire" scheduled for late November or early December."

Did it happen? Why no banner headlines??

Hank Roberts said...

OK, this is newer:

"02 October 2017. Posted in Meetings and conferences

"... TD 2As part of the Mission Innovation CCUS workshop in Houston, we visited the Net Power project at La Porte. ... The pilot project is at an advanced stage of construction. The expectation is testing of the combustion chamber in Q4 2017, and full operation in Q1 2018 with grid connection. ...."

Still needs an update.

Jan Galkowski said...

@Hank Roberts,

"Why no banner headlines?"

Possibly because completion is delayed, possibly because to make it work, some compromises needed to be made, or possibly, my personal favorite, none of the.parties who one would think care about this option actually do not.