Methane good or bad

Natural Gas, More Polluting than Coal? Only According to the IPCC. A Note from Cementafriend

METHANE is the major component of natural gas (>94 percent) and coal seam gas, which are claimed to be good clean fuels on the basis they have a lower carbon content than coal or oil.

Is this the same methane from the backsides of farting cows (or to a greater extent from the mouth of ruminants) that is considered to be a bad greenhouse gas and 21 times more potent than carbon dioxide? And the same methane that when escaping as a fugitive (lost through leakage) gas from coal mining is considered bad?

This is contradictory.

In the following note I consider how potent methane actually is as a greenhouse gas and then compare energy equivalents per heat absorbed all in carbon dioxide equivalents.

Methane (CH4) only absorbs significant radiation from the earth’s surface at around 288K, in the small range of 7.4-7.8 micron. By eye the absorption is less than one tenth that of CO2, see the Diagram (double click on the image for a larger view).

Yet we are continually told that methane is 21 times more potent as a greenhouse gas than CO2.

This is what the IPCC tells us.

I have contacted various respected climate scientists (on both sides of the AGW debate). But no one has been able or wished to provide a definite answer.

So I have made my own assessment.

When one burns CH4 in air the chemical reaction is:

CH4 + 2O2 > CO2 + 2H2O.

That is, methane combusts to form carbon dioxide and water vapour.

Water vapour absorbs IR close to 100 percent in the range 4.5 to 8.0 micron (completely overlapping CH4), raising from zero at about 12.5 micron to close to 100 percent at about 16 micron and then 100 percent above 16 micron into the microwave range, see the Diagram.

CO2 is only a significant IR absorber in the range 14 to 15.5 micron (with a peak at 14.8 micron) but there is an overlap with water vapour.

From a visual inspection of the amount of radiation transmitted, Diagram 1, it can be justified that the e-m absorption of water vapour in the range 4 to 40 micron is at least 10 times that of CO2.

So, CH4 equivalent IR absorption = (1* CO2 + 2*10*CO2) =21*CO2

In other words, that figure of 21 times more potent is actually calculated in water vapour equivalent.

So we have established that methane, the major component of natural gas, when it is burnt produces quantities of greenhouse gases. But it is called a green fuel. Why?

It is common practice for energy supply companies to give the energy content on a gross basis but in reference texts such as Perry’s Chemical Engineering Handbook the heats of formation and combustion energies are given for net and gross energy.

The gross energy includes the heat of condensation of water (2.3 GJ/t H2O) which in combustion processes is not available for heat transfer. To compare fuels, only the net heat should be used.

Reference values from Perry’s Chemical Engineering Handbook for the net heat of combustion are Hydrogen (H2) =120 GJ/t, Methane (CH4) =50 GJ/t, Ethane (C2H6) = 47.5 GJ/t, Carbon (C) =32.8 GJ/t, Carbon monoxide (CO) = 10.1 GJ/t

For a typical black coal with an ash content by weight of 15 percent and a delivered moisture of 7 percent and a typical natural gas with 94 percent methane, 2 percent ethane equivalent, and 4 percent CO2 by volume the following applies:

So, if we apply the IPCC methodology for methane as a greenhouse gas, to methane as a fuel, you more than double the emissions for the same energy when natural gas is used instead of coal.

Now let’s go back to the fugitive methane. In Perry’s Chemical Engineering Handbook the following can be found:-
a) ignition temperature in air =650C
b) lower limit of flammability (% gas in mixture)= 5
c) higher limit of flammability (% gas in mixture)= 15

It should be very clear that methane released into the air does not burn but to summarize this point for methane in the atmosphere a) at 1,7ppm it is below the flammability limit and b) everywhere in the atmosphere is below the ignition point (this even applies at points of high emission such as a swamp, landfill vent etc)

The level of methane in the air has been measured since at least 1980 and data from ice-cores is also available showing increases in CH4 up to the year 2000 and then levelling and possibly declining at approximately 1730 ppb (1.73ppm) (see Tom Quirk in Energy and Environment).

The existence of CH4 in the atmosphere is proof that CH4 does not burn.

There is a natural cycle for methane with sources and sinks. It is slightly soluble in water (oceans) and is absorbed by some plants and algae and bacteria. It can be oxidised in lower atmosphere by ozone (produced by lightning, electrical arcing such as welding, and breakdown of NOx emission by sunlight) such as

CH4 + O3 > CH3OH (methanol) + O2.

The methanol and other –OH radical compounds are highly soluble in water. This is part of the natural cycle. The removal of ozone in the lower atmosphere has health benefits.

In summary, if one is concerned about greenhouse gases then the statement that natural gas or coal seam gas (methane CH4) is a friendlier fuel than coal (i.e. good), and the statement, that fugitive methane (CH4) from coal mining or animal emissions is bad, are both false.

References

1. Perry’s Chemical Engineering Handbook 4th Edition & 7Th Edition

2. Tom Quirk has an article in Energy & Environment July 2010 (abstract http://multiscience.metapress.com/content/m7337203x121g1hh/?p=42ddd03a121f46138f01ccf97183c9ff&pi=4)

3. The source of the diagram http://en.wikipedia.org/wiki/Absorption_band

Disclaimer

My superannuation fund has shares in Origin Energy which produces, distributes and burns (in power stations) natural gas and coal seam gas & shares in BHP-Billiton which produces oil, gas and coal – I am pragmatic.

Chart from comment 3 below- my thanks Sunsettommy

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5 thoughts on “Methane good or bad

  1. This post was originally placed at http://jennifermarohasy.com/2011/07/natural-gas-more-polluting-than-coal-only-according-to-the-ipcc-a-note-from-cementafriend/
    Willis Eschenbach made the following comment
    • Comment from: Willis Eschenbach August 13th, 2011 at 6:02 pm

    Cementafriend, I fear that it is much more complex than that. Methane reactions in the atmosphere are so-called “photochemical” reactions, meaning that they are driven by light.
    Rather than the two possible pathways you posit above for the breakdown of methane (water and CO2, or menthon and O2), there are literally dozens and dozens of reactions that are intimately involved, each with their own rate constant. See here for a list of these important reactions.
    As a result, the totality of them must be considered to figure out which pathways are occurring at what rates. As the paper says:
    Diffusion equations were solved simultaneously for 22 different species: 03, O, H20, OH, HO2, H202, H, O2, H2, CO2, CO, HCO, H2CO, CH4, C2H6, C3Hs, C4H,0, C2H2, C2H4, CH3, 3CH2 and C2H8. Another 12 species, including O(1D), 1CH2, excited C2H2 (C2H2*), C2H, C2H3, C3H6, C4H8, C3H7, C4H9, CH3CHO, C2H5CHO and C3H7CHO, were assumed to be in photochemical equilibrium.
    What that comes out as in terms of co2 equivalent I haven’t a clue, and I don’t know if it’s right … but it’s far from as simple as just methanol and oxygen as you say above.
    All the best,
    w.
    • Comment from: Willis Eschenbach August 13th, 2011 at 6:21 pm

    … “methanol and O2″, not “menthon and O2″ …
    w.
    I replied as follows
    Comment from: cementafriend August 15th, 2011 at 10:52 pm

    Willis, nice to have a response from you. It is strange that with the paper, by Kasting et al 1983, you refer to that your BS indicator was not working.
    Please note the first sentence of the abstract “A detailed model is presented of methane photochemistry in the primitive terrestrial atmosphere along with speculation about its interpretation” – model, primitive terrestrial atmosphere, speculation and interpretation.
    The article refers to modelled anaerobic conditions ie no oxygen present. The present conditions in the atmosphere are completely different.

    I quite agree that the physical and chemical reactions which occur it the atmosphere are very complex. That is why the majority of people around the world and especially those well qualified & experienced in technical disciplines (such as geology and engineering) have doubts about the simplistic assumptions held by the pseudo-scientists with climatology beliefs with respect to CO2 heating the atmosphere.

    In the post I have tried to express the most common reactions of methane so that hopefully everyone can understand that false information is being disseminated by “green” groups (including the IPCC) and oil & gas companies (some of whom have been shown to back “green” groups)

    Finally, note that all the authors are associated with government funded “climate” groups. I am not familiar with any of the authors but it appears (from a limited search on the internet) that none of them has professional engineering qualifications in fields such as reaction kinetics, thermodynamics and fluid dynamics which might lead one to surmise that they know what they are writing about.

    Willis, I try to read most of your interesting posts. Keep up the good work and keep strong – cementafriend
    PS Jennifer could you pass on to Willis my best wishes?
    Comment from: cementafriend August 16th, 2011 at 4:19 pm

    In the above a typing problem which I frequently do -leave out words. The end of the second last paragraph should read “which might lead one to surmise that they do not know what they are writing about.”
    A further point about the Kasting et al article is that of the 134 supposed chemical reactions only equations 47 to 52 (ie 6 potential equations) are relevent to methane CH4
    The first 28 equations concern H2O and O radicals. Many of the equations could occur in liquid H2O (ie the oceans) rather than the atmosphere.

  2. If we take 7.6 microns as methane’s ‘best’ emitting range, Wien’s Law tells us this will happen at a peak temperature of 108C. I don’t know where on this planet the atmosphere reaches that temperature thus any absorption/radiation from methane in the atmosphere must be statistical from inter molecular collisions. Where methanes gets it’s ’21 times more potent than CO2′ I don’t know. CO2 can radiate in the 15 micron band from within the whole troposphere. Mind you, any surface area must be colder than -80C before it will absorb 15 micron radiation.

  3. Nice post….however you are missing some details on the “Radiation Transmitted by Atmosphere” graph. There is some absorption by Oxygen and Ozone, three bands of CO2 absorption by CO2, but over 50,000 spectral bands absorbed by water vapor, cooling the Earth, see “Greenhouse Gas Ptolemaic Model” at the FauxScienceSlayer site for more info.

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