removing methane from the atmosphere

[Andrew Lockley]

A while ago I raised the idea on geo of using compression ignition to clean methane out of the atmosphere.  The auto-ignition temperature of methane is about 600C.  This makes it conceivably possible to burn it out of the air by compression heating.

I've run some calculatons on the idea (attached), and it comes out with some not-completely mad numbers.  It will take about 14million large cylinders, completing a 4-stroke cycle every 10s, to process the atmosphere every 10 years.  By large, I mean a 10m radius and a 30m stroke. I'm guessing you'd make them pretty crudely out of concrete cores, with steel liners.  I reckon a 10m diameter cylinder would just about survive with a single conrod to the flywheel.

You can obviously reduce the number needed by building them near methane sources, so they're handling more concentrated methane/air mix.  You could run them faster, but the forces are a lot larger and you also end up with speed-of-sound issues in extreme cases.

I can't work out the energy costs of running these machines, as I paid scant attention to such matters at university.  The main losses would be pumping losses, heat transfer from the hot gas to the cylinder walls, and frictional losses - probably in that order.

If anyone's got some ideas about how such a large engine could be designed and constructed, and what the maths of energy, operation, wear, etc. might be, then please pipe up.  

I hope that's of interest to peeps on this list, but if you'd prefer me to develop further before presenting, let me know.

Thanks!

A

[Alvia Gaskill]

1. Methane is constantly being generated from natural sources and oxidized in the atmosphere, so you are not going to "clean it out of the atmosphere."

 

2. We discussed the feasibility of such systems more than a year ago and it was established that is was impossible, both due to scale and to the energy costs and likely due to the impossibility of such cylinders even functioning at all.

 

3. "Building them near methane sources" ignores the fact that methane is rapidly diffused into the atmosphere near the surface whether emitted by natural sources such as swamps or estuaries or from animal feedlots or rice paddies.  So there would be no advantage to this.

 

4. A small amount of methane is combusted along with fuel in internal combustion and diesel engines, so if you want to increase the amount of methane oxidized, build more cars.  Just make sure they don't run on natural gas.

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[Andrew Lockley]

Methane is being continually generated and destroyed, but adding an additional removal process would be very beneficial.  The proposed scheme as calculated would process the entire atmosphere every 10 years (although it doesn't take account recycling).  Compression ignition can work - it just has to use sufficiently high compression ratios to reach the low-concentration auto-ignition temperature for methane.

All combustion processes will tend to destroy methane, not just car engines.  These raise the gas temperature sufficiently to oxidise methane.  The problem with this approach is that combustion processes can't be scaled up sustainably.  Compression ignition, with large enough cylinders, should avoid the fuel requirements and frictional/heat transfer losses which will prevent sustainable scaling.

Methane does diffuse through the atmosphere, but ducting air into engines from swamps, thermokarst lake margins, etc., would indeed aid the treatment of slightly higher concentrations in air.

There are many alternative ideas for removing methane, but this is one of the easiest to calculate.

A

[Alvia Gaskill]

Where did the methane go?  Answer this and we may know a lot more about what would happen from a "catastrophic" release due to global warming.  For once, BP is probably correct.  Most of it made it to the surface and is now in the atmosphere.  Releases from decomposing hydrates would occur over a much larger area, not from a single two foot in diameter pipe and wouldn't be blasted out at 8000psi.  So the comparisons are not really there, but given how little we know about such releases, man-made or natural, the information gained may be very valuable in predicting future risk.  One way to tell what's going on is to measure the level of methane just above the surface and in the first few meters below it.   This will tell how much of it survived the trip up from 5000 ft.

Other work suggests that most of the methane should dissolve in seawater, with only 0.1% reaching the surface.  In  the pdf link, a mud volcano eruption was modeled.  Atmospheric levels were greatly enhanced for a short time, even with 99.9% never reaching the air.  In the figures below, you can see that the methane will be expected to dissolve in the seawater at 5000ft (~1500m) at concentrations of less than 0.1% (mole fraction of 0.001). 

 

That the hydrates are not appearing at the surface indicates that either the gas is making it all the way up or it is dissolved.  Small pieces of hydrates can be seen forming in the riser pipe video, but these represent a tiny fraction of the gas released.  The conditions in the upper left part of figure A probably best model the Deepwater Horizon conditions.  The figure isn't properly labeled and should say water + dissolved CH4. 

 

As the CH4 gets closer to the surface, however, it will primarily exist as a gas.  At 1500m, the pressure is 152 bar, whereas at 100m it is only 11 bar and at 500m, 50 bar.  So the methane has to survive as a gas to about 1500 ft in order to stay a gas and make it all the way to the surface.  Given the direct injection of dispersant into the riser pipe outflow and the likely rapid separation of the gas from the oil, the fate of it in the 3500 ft from there to the 1500m depth will likely determine how much dissolves. 

 

The fact that it took 8 weeks for any confirmable flow rates to be produced does not, however, bode well for the methane determinations.  Too much FRTTing around with the stinky oil, to combine a plethora of unpleasant metaphors in a single sentence.  Incidentally, Chris Matthews makes an effort to Chu bash every night, even when not prompted by a guest.  He ridiculed Carol Browner when she said Chu was personally responsible for the flow rate measurements and the idea to run the blowout preventer lines in reverse to capture more oil.  He did stop short of saying "you're doing a heck of a PR job, Browner," however.  The media has already made up its mind about the response and recorded the Administration's grade in its book: F.  Let's hope the actual one at least makes it to a C before SE Louisiana turns into the La Brea tar pits.

 

 

 

 

 

 

 

 

http://www.atmos-chem-phys-discuss.net/6/3611/2006/acpd-6-3611-2006-print.pdf

 

http://geology.geoscienceworld.org/content/vol32/issue1/images/large/i0091-7613-32-1-e42-f01.jpeg

 

http://news.yahoo.com/s/ap/20100618/ap_on_bi_ge/us_gulf_oil_spill

Gulf oil full of methane, adding new concerns

By MATTHEW BROWN and RAMIT PLUSHNICK-MASTI, Associated Press Writers Matthew Brown And Ramit Plushnick-masti, Associated Press Writers 26 mins ago

 

NEW ORLEANS – It is an overlooked danger in the oil spill crisis: The crude gushing from the well contains vast amounts of natural gas that could pose a serious threat to the Gulf of Mexico's fragile ecosystem.

The oil emanating from the seafloor contains about 40 percent methane, compared with about 5 percent found in typical oil deposits, said John Kessler, a Texas A&M University oceanographer who is studying the impact of methane from the spill.

That means huge quantities of methane have entered the Gulf, scientists say, potentially suffocating marine life and creating "dead zones" where oxygen is so depleted that nothing lives.

"This is the most vigorous methane eruption in modern human history," Kessler said.

Methane is a colorless, odorless and flammable substance that is a major component in the natural gas used to heat people's homes. Petroleum engineers typically burn off excess gas attached to crude before the oil is shipped off to the refinery. That's exactly what BP has done as it has captured more than 7.5 million gallons of crude from the breached well.

A BP spokesman said the company was burning about 30 million cubic feet of natural gas daily from the source of the leak, adding up to about 450 million cubic feet since the containment effort started 15 days ago. That's enough gas to heat about 450,000 homes for four days.

But that figure does not account for gas that eluded containment efforts and wound up in the water, leaving behind huge amounts of methane. Scientists are still trying to measure how much has escaped into the water and how it may damage the Gulf and it creatures.

The dangerous gas has played an important role throughout the disaster and response. A bubble of methane is believed to have burst up from the seafloor and ignited the rig explosion. Methane crystals also clogged a four-story containment box that engineers earlier tried to place on top of the breached well.

Now it is being looked at as an environmental concern.

The small microbes that live in the sea have been feeding on the oil and natural gas in the water and are consuming larger quantities of oxygen, which they need to digest food. As they draw more oxygen from the water, it creates two problems. When oxygen levels drop low enough, the breakdown of oil grinds to a halt; and as it is depleted in the water, most life can't be sustained.

The National Science Foundation funded research on methane in the Gulf amid concerns about the depths of the oil plume and questions what role natural gas was playing in keeping the oil below the surface, said David Garrison, a program director in the federal agency who specializes in biological oceanography.

"This has the potential to harm the ecosystem in ways that we don't know," Garrison said. "It's a complex problem."

BP CEO Tony Hayward on Thursday told Congress members that he was "so devastated with this accident," "deeply sorry" and "so distraught."

But he also testified that he was out of the loop on decisions at the well and disclaimed knowledge of any of the myriad problems on and under the Deepwater Horizon rig before the deadly explosion. BP was leasing the rig the Deepwater Horizon that exploded April 20, killing 11 workers and triggering the environmental disaster.

"BP blew it," said Rep. Bart Stupak, D-Mich., chairman of the House investigations panel that held the hearing. "You cut corners to save money and time."

In early June, a research team led by Samantha Joye of the Institute of Undersea Research and Technology at the University of Georgia investigated a 15-mile-long plume drifting southwest from the leak site. They said they found methane concentrations up to 10,000 times higher than normal, and oxygen levels depleted by 40 percent or more.

The scientists found that some parts of the plume had oxygen concentrations just shy of the level that tips ocean waters into the category of "dead zone" — a region uninhabitable to fish, crabs, shrimp and other marine creatures.

Kessler has encountered similar findings. Since he began his on-site research on Saturday, he said he has already found oxygen depletions of between 2 percent and 30 percent in waters 1,000 feet deep.

Shallow waters are normally more susceptible to oxygen depletion. Because it is being found in such deep waters, both Kessler and Joye do not know what is causing the depletion and what the impact could be in the long- or short-term.

In an e-mail, Joye called her findings "the most bizarre looking oxygen profiles I have ever seen anywhere."

Representatives of the National Oceanic and Atmospheric Administration acknowledged that so much methane in the water could draw down oxygen levels and slow the breakdown of oil in the Gulf, but cautioned that research was still under way to understand the ramifications.

"We haven't seen any long-term changes or trends at this point," said Robert Haddad, chief of the agency's assessment and restoration division.

Haddad said early efforts to monitor the spill had focused largely on the more toxic components of oil. However, as new data comes in, he said NOAA and other federal agencies will get a more accurate read on methane concentrations and the effects.

"The question is what's going on in the deeper, colder parts of the ocean," he said. "Are the (methane) concentrations going to overcome the amount of available oxygen? We want to make sure we're not overloading the system."

BP spokesman Mark Proegler disputed Joye's suggestion that the Gulf's deep waters contain large amounts of methane, noting that water samples taken by BP and federal agencies have shown minimal underwater oil outside the spill's vicinity.

"The gas that escapes, what we don't flare, goes up to the surface and is gone," he said.

Steven DiMarco, an oceanographer at Texas A&M University who has studied a long-known "dead zone" in the Gulf, said one example of marine life that could be affected by low oxygen levels in deeper waters would be giant squid — the food of choice for the endangered sperm whale population. Squid live primarily in deep water, and would be disrupted by lower oxygen levels, DiMarco said.

Meanwhile, the Coast Guard signaled a shift in strategy Friday to fight the oil, saying it was ramping up efforts to capture the crude closer to shore.

Coast Guard Adm. Thad Allen said an estimated 2,000 private boats in the so-called "vessels of opportunity" program will be more closely linked through a tighter command and control structure to direct them to locations less than 50 miles offshore to skim the oil. Allen, the point man for the federal response to the spill, previously had said surface containment efforts would be concentrated much farther offshore.

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