Thanks. Is there any technical reason why a diesel engine couldn't be developed that would reach the compression ratios needed? I don't quite see why it needs to be 500:1 when you only need to get it to c1800C to burn methane. That suggests 40:1 approx, which is doable I think. I also don't see why compression adjusts the ppm - surely it stays the same and is squished. Is that to do with supercritical fluids?
I don't think we can just throw our hands up an admit defeat if methane outgasses on a large scale. We have to solve the problem! What about enhancing ozone levels to promote photchemical degradation, or using CSP for atmospheric-pressure oxidation? A 2009/1/29 Alvia Gaskill <[email protected]>: > I don't think methane at ambient levels (2 ppm) can be combusted in a diesel > engine. A typical diesel engine has a compression ratio of around 20, > meaning that the air drawn in is compressed by a factor of 20. > http://en.wikipedia.org/wiki/Diesel_engine#How_diesel_engines_work As a > result, the temperature of the compressed air is raised to around 1000 > degrees F, high enough for the diesel fuel to autoignite. Thus, no need for > spark plugs for a diesel engine. Unfortunately, the ambient concentration > for autoignition of methane is about 5% or around 50,000 ppm and at 1000 > degrees F. In the diesel combustion chamber, it will be around 40 ppm, > ambient nominally 2 ppm. So while a 5% methane in air fuel would probably > burn in a diesel engine, lower levels would not. > > This issue has been addressed in studies conducted for the USEPA as part of > the Coalbed Methane Outreach Program, run out of EPA's Climate Protection > Division. > > http://www.irgltd.com/Resources/Publications/US/Technical%20and%20Economic%20Assessment%20-%20Mitigation%20of%20Methane%20Emissions%20Coal%20Mine%20Ventilation%20Air.pdf > > The goal of this study was to determine ways to use methane from coal mine > ventilation air as fuel at levels above 3000 ppm. One of the units tested > was able to combust methane at levels as low as 800 ppm. As noted on page > 3, "Below 4.5%, methane will not ignite or sustain combustion on its own > without a constant ignition source, unless it can remain in an environment > where temperatures exceed 1832 degrees F. Therefore, any conventional > method proposed to use ventilation air as a fuel or even to destroy it, > would require a net energy input in addition to the fuel value of the > methane contained in the ventilation air." > > Internal combustion engines and solar gas turbines can burn low levels of > methane as ancillary fuel, but won't operate on ventilation gas alone as the > temperatures don't get high enough to combust the methane. To burn > ventilation air containing methane as a primary fuel, a thermal flow and a > catalytic reactor were evaluated. Both require an external source of > electricity to provide the initial heat for combustion, with the catalytic > system operating at lower temperatures of around 700-1500 degrees F vs. 1832 > for the other one (page 19). > > So, it doesn't appear that it is possible to combust ambient levels of > methane using a diesel engine or any other source using the methane as the > primary fuel. Compressing the low levels of methane in ambient air to 1000 > ppm, about the lower limit of the catalytic system, would require a > compression ratio of 500. Even if this could be overcome, in my opinion, > the extremely large volumes of air required would preclude the use of such a > system to mitigate ambient methane. The better approach would be to limit > the sources of methane emissions including feedbacks to prevent a runaway > outcome for which there is also no mitigation technology. > > > > ----- Original Message ----- From: "Andrew Lockley" > <[email protected]> > To: "David Schnare" <[email protected]> > Cc: <[email protected]>; "geoengineering" <[email protected]> > Sent: Wednesday, January 28, 2009 9:56 AM > Subject: [geo] Re: methane air capture > > >> >> You don't need a licence to squash air. I'm not proposing a fuel - >> I'm proposing to drive the diesel engine with windpower. >> >> A >> >> 2009/1/28 David Schnare <[email protected]>: >>> >>> In the U.S., use of a compresion ignition engine requires certification >>> of >>> both the fuel and the engine (by EPA), and limits the amounts of priority >>> pollutants that may be emitted from such an engine. These include NOx, >>> SOx >>> and particulates, all of which will emerge from the scheme you are >>> discussing. >>> >>> In a regulatory state, nothing is as easy as it seems. >>> >>> David Schnare >>> >>> >>> On Tue, Jan 27, 2009 at 8:33 PM, Andrew Lockley >>> <[email protected]> >>> wrote: >>>> >>>> You don't need a combustible fuel-air ratio provided that the >>>> combustion doesn't need to be self-sustaining. Once the correct >>>> temperature is reached, any methane present will oxidise. The >>>> advantage of using a diesel engine is that it runs with minimal energy >>>> input as the temperature can be changed without irrecoverable energy >>>> input - the mix cools as it expands. I thought about using a jet >>>> engine - essentially an adapted turboprop or high-bypass turbofan, but >>>> I think it would be more lossy. >>>> >>>> I don't agree that you'd be processing 'a few hundred cc'. I envisage >>>> building vast arrays of wind turbines, all connected to huge marine >>>> diesel engines. >>>> >>>> Why would you need a catalytic convertor? The CH4 just oxidises to >>>> H20 and Co2. I can see the benefit of a heat exchanger, and I already >>>> thought of that. >>>> >>>> I covered the issue of hydroxl radical - it's created by ozone >>>> photochemistry, so the best way to manipulate it seems to be by >>>> delivering ozone to the stratosphere. >>>> >>>> A >>>> >>>> 2009/1/28 dsw_s <[email protected]>: >>>> > >>>> > Compression ignition requires a suitable ratio of fuel to air. Even >>>> > if compression in a diesel engine perfectly removed methane from the >>>> > air, you're not going to process the atmosphere a few hundred cc at a >>>> > time. To remove methane from the air, I see two options: increase the >>>> > amount of hydroxyl radical if there's enough methane to deplete it, or >>>> > as you say build air-cooled CSP plants. For the CSP option you would >>>> > want a counter-flow heat exchanger and a catalytic converter on the >>>> > outgoing air. >>>> > >>>> > On Jan 27, 2:03 pm, Andrew Lockley <[email protected]> wrote: >>>> >> If you fixed up diesel engine to a wind turbine, you'd get >> >>>> >> compression >>>> >> ignition of any methane residue in the atmosphere, even without >>>> >> injecting any fuel. This would be expensive, but I think it would >>>> >> work. >>>> >> >>>> >> An alternative would be to pump air through concentrated solar power >>>> >> plants >>>> >> >>>> >> Any thoughts? We appear to need some bright ideas on methane >>>> >> remediation pretty soon. >>>> >> >>>> >> A >>>> > > >>>> > >>>> >>>> >> >>> >>> >>> >>> -- >>> David W. Schnare >>> Center for Environmental Stewardship >>> >> >> >> > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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