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| CSG Well (source: http://www.glng.com.au/ ) |
Those in favour of expanding the coal seam gas industry promote it as a green alternative to coal for use in power stations. They argue that coal seam gas, which is mainly methane, results in 70% less carbon dioxide emissions for the same amount of energy.
The 70 per cent figure relates to greenhouse gas generation at the power plant and comes from a comparison between a modern combined cycle gas turbine (CCGT) power plant and a traditional power station burning brown coal, which is the lowest grade of coal. If we make the comparison with a traditional plant burning higher grade black coal the difference falls to about 50%. If we make the comparison with a modern ultra-super critical coal plant the difference drops even further, though it is still significant.
But what happens at the power station is only part of the story. If we really want to know if CSG is greener we need to do a ‘cradle to grave’ comparison, that is, we need to look at greenhouse gas contributions from the coal deposit to the smoke stack. Coal is relatively easy and cheap to dig up and put on a truck and send to the power station. The energy input needed to mine and process the coal is about 2-3% of the amount of energy released by burning it. Coal seam gas is trickier. It needs to be captured, processed, compressed and transported at an energy cost of 20-25% of the energy that is released by burning it.
But the real villain in this story is fugitive emission. If we drop a few lumps of coal between the mine and the power station it is no big deal. But if we leak a bit of methane it’s a very big deal because methane is 20-30 times more potent as a greenhouse gas than carbon dioxide (methane breaks down more rapidly in the atmosphere than carbon dioxide and is about 25 times more potent as a greenhouse gas over a 100 year period, but over a 20 year period methane is over 70 times more potent than carbon dioxide). These leaks are known in the industry as ‘fugitive emissions’ and while the CSG industry argues that they are negligible, the truth is that there doesn’t seem to be any good published data on fugitive emissions from CSG in Australia. The most similar data we have at present comes from a paper by Robert Howarth on fugitive emissions from shale gas production in the United States. Howarth estimated fugitive emissions of 4‑8%. But shale gas production is not the same as CSG production, and to be fair there is also some leakage of methane from coal mining operations (just ask the canaries), but if the rate of leakage for CSG was comparable to that reported by Howarth, then it would be more than enough to wipe out any greenhouse benefit from switching to coal.
To this complicated picture we need to add another very cruel irony. CSG is definitely cleaner than coal in the sense that it produces much lower amounts of sulphur dioxide and particulates which contribute to acid rain and smog. But sulphur dioxide and particulates reflect solar radiation and also help cool the planet. In other words, this pollution from coal may actually help fight global warming.
So you can see that the science is quite complicated. A recent article in the peer reviewed journal Climate Change by Tom Wigley from Adelaide University tried to put all these pieces together and found that a switch in power generation from coal to CSG would most likely result in an increased greenhouse effect out till about 2100 and only a negligible decrease after that.
So does this mean that CSGs future as a ‘green fuel’ is dead. Maybe not. There is a great deal of uncertainty about the level of fugitive emissions associated with CSG in Australia, and fugitive emissions are, in theory, controllable. What we really need is some comprehensive independent scientific studies to give us the information to determine whether CSG really is the green transitional fuel we would all like it to be.
