Carbon Capture Conundrum: Can Coal be Cleaned?
Many of us concerned about global warming would like to see the electricity coming down our mains line to be squeaky clean and green. And the breathless commentary from the US government, and renewable energy enthusiasts, on wind power may give us hope that green electricity will be at a neighborhood near you soon. A 33% rise in wind power generation in 2009 is certainly headline grabbing – but that takes the total slice of wind-powered electricity to a measly 1.9%. Compare that to coal’s whopping 45% chunk , and it’s obvious that our homes are going to be powered by electricity that is a shade of brown for a while yet.
But the coal industry has seen the light of the oncoming train – and it’s green. They know that they need to scrub their carbon-black product clean, if coal is to remain a part of the nation’s energy plans. And there is, in fact, a technology coming onto line that is being heralded as, not only the savior of coal, but possibly of the planet as well. It’s called carbon captures and storage (CCS), and its adherents say it will make coal power a near-zero CO2 emitter. Pilot schemes for this idea are already on the cards in Canada and Germany – but is it really going to be able to deliver on its promise?
Carbon captures and storage is a two-stage technology that aims, first, to capture CO2 at the point of emission, and second, to pipe it to locations where it can be safely stored. For coal-fired power stations, the basic idea is to strip the CO2 from the flue gases after combustion. This uses a well-known industrial process, that has been in use for many years. Although wide-scale trials, on real power stations, have yet to be tried, it seems that the technology is mature enough to trial. And the IPCC reckons up to 90% of coal-power plant emissions could be removed in this way.
Once the CO2 is captured, it is compressed and transported to a location that is safe for its storage. Many ideas have been put forward, but the most feasible is to store CO2 in underground reservoirs. Finding such vast structures, that can contain CO2 under pressure, and not leak, may sound like something of a challenge. But there is an ingenious solution to this – pumping CO2 into underground oil reservoirs, as they are emptied of oil. And most oil fields already have all the properties needed for holding gas under pressure.
However, the ‘everyone’s a winner’ credentials of CCS are possibly not all that they seem. All along the chain, in turns out that there are serious concerns – starting with when the coal is mined out of the ground. Not only does mining use energy (and so emit CO2), but much of the refuse from coal mining is carbon rich- and prone to emitting CO2. And worse – methane is a major greenhouse gas that positively leaks out of coal. Then there is the energy to transport the coal to the power station. Add up all of these ‘total lifetime’ emissions for coal, and it turns out that at least 5% of them occur away from the point of combustion in the power station. These can’t be captured.
Then there is the effect of CCS on the efficiency of the power plant. It has been shown that this drops precipitously – by about 25% – because of the lower throughputs from combustion, and the energy needed to compress the CO2. Add these into the equation, and the 90% emissions reduction becomes closer to 60%. Once the CO2 is stored in the reservoir, of course, it may leak out slowly, too– but the IPCC believes this will be less than 1% over 100 to 1000 years.
There is, however, another twist to this greener-than-green technology – which turns out not to be so verdant after all. The initial projects being slated for CCS include a project in Alberta. It will take CO2 from the terribly inefficient tars-sands extractions process (where huge amounts of energy are expended just to extract something useful from the stuff). It is then being piped straight to oilfields, in order to enhance oil recovery. In other words, CCS is actually planned to be used to increase oil production. Somewhat disappointingly, for eco-energy enthusiasts, it could be that CCS will only provide the thinnest of green washes to coal-powered electricity, after all.
[This article is a guest post from Woz, a blogger who writes on the topic of fitness at BuildMuscle.net]
[Image: eutrophication&hypoxia at Flickr]