I don't know what the limits are on diesel engine compression ratios. I think it probably has to do with the durability of the components. There is no basis for saying that a 40:1 compression ratio is doable, if in fact that were enough. To answer this question, you would need to consult a diesel engineer. The reference to a 500:1 compression ratio was to getting the methane concentrated enough for the catalytic system to break it down.
I think it is important also to look at the feasibility of processing the quantities of ambient air to achieve meaningful methane destruction. Methane increased in the atmosphere by about 27 million metric tonnes in 2007 and is now around 1800 ppmv or about 1.271g/m3. It has been stable since 1998 and the increase for 2007 is not necessarily an annual trend. There are around 5.6 billion tonnes of methane in the atmosphere. To remove 27 million tonnes of methane using a diesel engine's air compression would require that 2.7 x 10exp13 g methane be destroyed. This would require passing 2.1 x 10exp13 m3 of air through the system. Assuming a diesel system capable of processing 200L/min 24 hours per day would mean that the system could process 288 m3 per day. To remove the volume of air containing 27 million tonnes of methane using this system would require 190 million years or put another way, almost 200 million of these engines to do it in one year. Assuming flow rates can be increased even by several orders of magnitude does no good. We are not going to build millions or billions of diesel engines for this purpose whether it is to remove 27 million tonnes or 200X that amount, the total methane burden in 2009. The wind capacity to be dedicated to such a project would be better allocated to producing electricity that otherwise would be generated using coal or natural gas. ----- Original Message ----- From: "Andrew Lockley" <[email protected]> To: "Alvia Gaskill" <[email protected]> Cc: "David Schnare" <[email protected]>; <[email protected]>; "geoengineering" <[email protected]> Sent: Wednesday, January 28, 2009 8:10 PM Subject: [geo] Re: methane air capture > > 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. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
