Comparative GHG Emissions of Coal, Domestic Natural Gas, LNG, and SNG

joelupchurch

You might be interested in this paper:
Jaramillo, P., W. M. Griffin, and H.S. Matthews. 2007. Comparative life-cycle air emissions
of coal, domestic natural gas, LNG, and SNG for electricity generation. Environmental Science & Technology, Vol. 41, No. 17, 6290-6296

You can download it here:
http://www.desertrockenergyproject.c...s%20(2006).pdf

It analyzes the total GHG life cycle emissions for power from natural gas and coal. The numbers they come with are that NG isn't that much better than coal and LNG is actually much worse than coal. This set off my BS detector, but when I checked it, the paper is actually pretty good. They account for things like the release of NG during the production process. Since NG is 96% methane and methane is 20 times worse than CO2 as a GHG, that is a big difference right there.

I'd always assumed that natural gas emitted about half the CO₂ as coal, which is true, but incomplete.

Xnn

I've never seen an analysis like this before, but agree that it makes sense.

The point being that production, processing and transportation of natural gas results in greater carbon emissions than from the actual end use combustion.

Likewise, in the case of liquified natural gas, liquefaction, tanker transport and regasification result in additional emissions which push to total to more than than of coal.

But now consider the politics... Who is going to be responsible for the offshore carbon emission? The exporter or importer?

joelupchurch

I'm still trying to wrap my mind around the domestic implications. I would think that either a cap and trade or carbon tax needs to properly account for total lifecycle costs to work properly. For example, how do you figure out how much natural gas is actually released into the atmosphere as methane versus burned off as CO₂?

dwx

I think comments posted here are misleading the truth. First of all, mining activities from coal incur a much higher emission through machinery usages and heavy equipment. Secondly, there is a much higher cost associated with transporting coal while natural gas can use pipelines.

In terms of natural gas processing, carbon can be captured during pre-combustion. The technology for pre-combustion is widely applied in fertilizer, chemical, gaseous fuel (H2, CH4). In these cases, the fossil fuel is partially oxidized, for instance in a gasifier. The resulting syngas (CO and H2) is shifted into CO2 and more H2. The resulting CO2 can be captured from a relatively pure exhaust stream. The H2 can now be used as fuel; the carbon dioxide is removed before combustion takes place.

I only wish people speak the truth instead of always serving their self-interests.

mheslep

Eh? The paper shows NG equivalent CO2 emissions (1100 lbs/MWh) still has nearly half that of coal (2100 lbs/MWh) considering life cycles, and is vastly better than coal in SOx and NOx emissions. Even liquefied gas is not 'much worse' than coal per this paper and even if it was, so what? LNG is less than 2% of the mix and falling (~27TCF gas total US, 0.5 TCF liquefied ). Also, I see methane concentration in the atmosphere has been flat in the atmosphere for the last ~10 years.
http://www.epa.gov/methane/images/methane.gif

joelupchurch

The coal production GHG is accounted for in section 3.3 of the report. I suggest you read the paper before writing a review. It hardly seems relevant if the Natural Gas production could be using doing a better job. I'm sure the actual numbers on coal could be improved also.

I far as I can tell the paper was peer-reviewed and and uses standard DOE and EPA references. Is "Environmental Science & Technology" not a respectable journal?

I would like to point out that I have no axe to grind against NG. I've supported the use of CNG for automobiles, so this report dismayed me also. My position on coal varies from James Hansen only in that I think it should be more practical if it phased out a little slower, say 2050.

I came across this paper when I read the Russians were developing new jets to run on LNG, which sounded like a cool idea to me. I started doing some research on LNG and came across this paper.

mheslep

Again, why? CNG, even counting life cycle emissions, is far better than coal. And it leaves the atmosphere in ~10 years.

joelupchurch

The numbers are already in pounds of CO₂ not Carbon. You don't need to multiply by 3.67.

I also calculated how many pounds of CO₂ would be consumed by a NG gas turbine only plant. A lot of NG gets used for peaking power where a combined cycle plant is too expensive. Based on the GE brochure I read, you only get about 2/3 the power for the same amount of NG, so a gas turbine only plant would be about 45 pounds of CO₂ more per MWh versus a CC plant.

I'm interested in such things, because I have been fiddling with the idea of extending the range of electric cars by electrifying our freeways. It turns out that would require a lot of peaking power and NG gas turbines are by far the cheapest in terms of capitol costs. They are working on such a project in South Korea and they claim they could convert half their cars to electric power with only 2 additional nuclear power plants.

I should also point out that with the 2.8% in CO₂ emissions in 2008 CO2 since 2000 have been essentially flat also in the United States. Here is a chart of US methane emissions by energy source.



Of course, in terms of all sources of methane , natural gas is only #3 after Enteric Fermentation and Landfills.

http://www.epa.gov/methane/sources.html

joelupchurch

Cars don't burn coal, but now that you mention it, It would be nice to see a lifecycle analysis comparing CNG with gasoline and diesel.

For the long term I want an electric vehicle that gets it electricity from nuclear power, but I thought CNG might be a good intermediate term solution.

mheslep

I think there's some confusion here?NG power plants emit CO₂, they don't consume it. What do you mean you calculated it? The life cycle figures of CO₂ per MWh using NG are provided in the paper.

Yes there are NG plants with no integrated combined cycle. Meaning what?
Well yes, kind of. I think you ( and the GE brochure) mean here that a combined cycle gas turbine plant is more efficient than a GT plant alone, in that the heat rejected from the high temperature electric generation part of a CCGT plant is put to a useful purpose. However, if we take a 100MW GT only plant and a 100MW CCGT plant, they emit exactly the same amount of CO₂. To see the savings in CO₂ emissions, one has to look outside the plant in the case of the CCGT where it displaces what would be additional steam heating energy.

The plan generally for EV's is to charge most of them at night when there is plenty of spare generation capacity already. If its done that way no peaking is required.

NG is certainly not the cheapest to operate. Coal is (for fossil plants).

Many companies and countries have electric vehicle projects.

I also see there methane emissions dropped 20% over 15 yrs (US).

Bob S

Here is the EIA table on CO2 emissions per million BTU (in last column) for 3 types of natural gas and 4 types of coal:
http://www.eia.doe.gov/oiaf/1605/coefficients.html
I usually use 115 pounds of CO2 per MMBtu of natural gas, and 205 pounds for coal.
Bob S

joelupchurch

205 is pretty good. I usually use 212 pounds, since most electricity generation is done with subbituminous coal. subbituminous has been overtaking bituminous for quite awhile.
http://www.eia.doe.gov/emeu/aer/pdf/pages/sec7_7.pdf

I think that is because most low sulphur coal is subbituminous, but I'm not sure of that. Most coal power plants don't have SO₂ scrubbers, so they have to use low sulphur coal.
http://www.eia.doe.gov/cneaf/electri...a/epat5p2.html

jcwr

"It analyzes the total GHG life cycle emissions for power from natural gas and coal. The numbers they come with are that NG isn't that much better than coal and LNG is actually much worse than coal."

"Eh? The paper shows NG equivalent CO2 emissions (1100 lbs/MWh) still has nearly half that of coal (2100 lbs/MWh) considering life cycles, and is vastly better than coal in SOx and NOx emissions."

The way I read the article, NG isn't much better than coal (and LNG is worse) *only* for the CCS scenario (table 3). This is because of the greater contribution of upstream processes to overall GHG emissions, which of course isn't helped by CCS. Tables 1 and 2 support the conclusion that NG life-cycle emissions are roughly 40-50% lower, even in the "advanced technologies" case.

Thanks for posting the article - interesting data.

mheslep

Yes, that's my read as well - for CCS only, which has not been widely deployed anywhere yet. However, I don't buy even the CCS comparison in this paper as useful. Carbon Capture technology for coal essentially means taking extraordinary methods to remove CO2 from the traditional coal cycle. But if one accepts 'extraordinary' methods, meaning more expensive methods, then nearly all of the NG emissions upstream from the power plant can also be stopped - the well head flare offs, pipeline leaks - all of these can also be eliminated by throwing money at NG delivery.

joelupchurch

I'm sorry, I overlooked the part about the CCS. I wouldn't have posted the chart If I realized it was for CCS.