NATURAL GAS VERSUS COAL: DUELING REPORTS
September 28, 2011 § 1 Comment
Until recently, natural gas was seen indisputably as a cleaner alternative to coal. Robert Howarth at Cornell University changed all that, at first abortively in 2009, when his study was demonstrably flawed. His revised report, which now includes the contribution of fugitive methane in coal mining, has been published. A hailstorm of criticism notwithstanding, some of the issues beg debate. A more recent study appears to be in support as well. In contrast is the report by the Worldwatch Institute, conducted in collaboration with Deutsche Bank which unequivocally concludes the superiority of natural gas, nevertheless recommends attention to fugitive emissions.
So what is the public to make of all of this? They are right to assume that science is deterministic at least in the broad swaths of the argument in question. So there is no dispute that when combusted, natural gas produces about 50% less carbon dioxide than coal in producing the same amount of electricity. Where the dueling reports diverge is in the area of fugitive emissions: these are releases of methane during the operations involved in producing and transporting the fuels. There is also no dispute that methane is about 25 times more potent than carbon dioxide in its global warming proclivity.
The bulk of the debate surrounding the Howarth work has been around the time scale for the analysis. This is because, although methane is much more potent, it turns out that this potency dissipates much faster than in the case of carbon dioxide. So, one gets a different result when the effects are studied for twenty years as for a hundred years. The latter has been the accepted standard. But Howarth and others make an argument for using the shorter time span, which turns out to disfavor methane. Of note is the fact that when carbon sequestration in deep saline aquifers is considered, the yardstick they are held to is well in excess of a hundred years. In other words the sequestered gas has to be guaranteed to not leak over that period.
In the case of coal, the emissions comprise methane found in association with the coal. For centuries this has been a known hazard of coal mining, both from the standpoint of poisonous atmosphere for miners and from the possibility of explosions in confined areas of the mines. In the past, canaries were famously used as indicators of methane. If they died you got out in a hurry; a sort of go no-go device. Some of those still awake through this discourse no doubt are skeptical in that you know you can smell a gas leak in your kitchen. Well, it turns out methane has no odor, but the producers deliberately introduce one for precisely the intended purpose of olfactory detection of leaks.
Natural gas production and distribution can leak in two principal areas. One is in transportation. The system of pipelines and associated valve assemblies at various points can leak after aging induced malfunctions. But this can be addressed through maintenance mechanisms. The main source of fugitive emissions is the natural gas produced prior to the existence of a pipeline to move it. This is in the early days of the prospect. Even in areas riddled with pipelines, a spur line to the new rig in question does not exist at the outset. Current custom is to not invest in that until the reservoir is proven commercially viable. The initial gas produced during the discovery process has nowhere to go. It is often released. Hence the problem. Now, it could be flared, which is the process of simply burning it on the end of a pipe. This would dramatically reduce the problem since the released pollutant would be carbon dioxide, not methane. But one imagines this approach is not taken probably because flaring draws singular attention to the enterprise. This gas produced in the very early days of the well is the problem.
The public may well ask why something useful is not done with the gas. The answer lies in part in the short duration of the production. It cannot economically warrant any sort of capture and use. But if such a technology were to be developed, the potential would be significant.
A final note: fugitive methane emissions from livestock exceed that from oil and gas operations. This results from the fact that ruminants such as cows produce methane as a normal consequence of their digestive process: they belch methane. An outbreak of vegetarianism would help the environment!