Thursday, December 8, 2011

The Clean Coal Myth

Alex Lenferna reports that “clean coal” is being touted among other crazy options at COP17.

Coal is an inherently dirty fuel, releasing many pollutants besides CO2 when it burns, including heavy metals and radioactive elements. Part of the mythology around “clean coal” is that more modern power stations are better. They are slightly less bad. It is possible to wash the coal to remove some of the pollutants, but that requires a lot of water, and the pollutants don’t vanish. But let’s focus on the CO2. A low efficiency coal power plant has an efficiency of about 30%; the best designs in current use may improve this to up to 40%. In other words, 60-70% of the energy released burning coal in a power station disappears up the chimney. You can achieve higher efficiencies with gas, and there is research into increasing the efficiency of coal power stations to up to 50%, but all of this of course does not eliminate the problem of CO2 emissions.

Then there is the “dream” goal of really clean coal, carbon capture and storage (CCS, also sometimes called “sequestration”): burying the emitted CO2 underground. The problem with this idea is that you need to store vast quantities of CO2 underground indefinitely. Even compressed down to a liquid, the volumes amount to cubic kilometres if you want to make a significant difference to worldwide emissions. 27 billion tonnes of CO2 are emitted by industry annually. That quantity if I did my arithmetic right amounts to 35 cubic km per year (CO2 compressed to a liquid weighs 770kg per m3). If we aim for a rather modest 10% of this total, we will have to find space underground to store 3.5 km3 of CO2 every year. Every year until when? Until we run out of coal, or find a cleaner energy source. It strikes me that the proposed solution is a whole lot less practical than the more obvious alternative: a gradual, measured slowdown in coal usage, while increasingly investing in really clean energy alternatives.

Storing and in general handling CO2 in high volumes is extremely hazardous because it is heavier than air. The hot gases out of a high smokestack are mixed into the atmosphere by turbulence. A slow leak at ground level takes time to dissipate. A natural leak of CO2 from an underground source can be fatal, and the quantities that would have to be stored for a coal power station are big enough to be a serious safety hazard. Naturally proponents of the technology claim it’s totally safe, but they said that of nuclear power too, and after the Japan tsunami, the story became “no one could predict that”.

Another big problem with the CCS  “dream” is that it significantly cuts into the efficiency of coal power generation because of the high energy cost of carbon capture, compression and storage.

Several projects around the world have been abandoned, when it is so clearly in the industry’s interest to show it works.

Why then are billions of dollars worldwide being poured into this failed technology? Delay. If the promise of “clean coal” can be held out as an alternative, investment in alternatives can be stalled. Who gains? Only the fossil fuel industry. And even they consist of individuals who need a planet on which to live. The rest of us stand to lose big time not only because of the threat of climate change but because of the much higher cost of a very rapid transition to clean energy, which will be the only option left to us if we wait too long.

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