Getting rid of CO2

Well, here's another post where I just go about educating myself, and you can follow along if you wish.

It would seem that the problem with "clean coal technology" is not likely to be the CO2 capture part. The CSIRO seems particularly optimistic about this, talking about retrofitting capture devices to existing power stations. The National Energy Technology Laboratory in the US seems fairly upbeat about it as well:

Carbon capture and sequestration begins with the separation and capture of CO₂ from power plant flue gas and other stationary CO₂ sources. At present, this process is costly and energy intensive, accounting for the majority of the cost of sequestration. However, analysis shows the potential for cost reductions of 30–45 percent for CO₂ capture. Post-combustion, pre-combustion, and oxy-combustion capture systems being developed are expected to be capable of capturing more than 90 percent of flue gas CO₂.

For a general background on how coal burning power plants work, the Australian Coal Association gives a good short explanation. There are clearly some efficiencies (and CO2 to be saved) just by using better ways of burning coal, and I suppose getting China and India to use the most efficient methods would at least be a start. But for dramatic reduction of CO2 release, it doesn't look like you can pin too much hope on that.

But back to what to do with the CO2. Geosequestration seems to be the only idea being given serious consideration.

There's a post at Treehugger which gives reasons for being sceptical. Mostly it quotes from tim Flannery, who (despite exaggerating about aspects of global warming) may be onto something here.

It's important to get an idea of the scale of the problem. In the Treehugger post there is an attempt to picture the volume, but as is clear from the comments, it makes a mistake here.

It seems Karl Kruszelnicki made the same mistake in the lead up to the election, but he corrected himself at his blog. As he explains, the correct figure for the volume of CO2 made in Australia by power stations can be roughly calculated as follows:

The daily amount of carbon dioxide emitted from burning coal, when you liquify it, would fill a box 100 metres on a side - not 1,000 metres. And this is from burning coal to supply electricity for all of Australia, not just one of the states or one of the capital cities.

Well, that's an appalling enough figure anyway, isn't it? Every day, even if you captured only half of the CO2, you would still be left (Australia wide) with a volume of liquid CO2 that is 100m square by 50 m high. Seems a hell of lot to be looking to put down a hole somewhere every single day.

The thing is, it's not only the issue of where to put it, but how to get it there. It would seem that both the liquidification process (itself using significant amounts of energy) and its transport would be the really expensive aspects of this; not so much the pumping into the ground. If you were using pipes to move it around as a gas, you have the issues of the years it seems to take to build pipes of any length, and how long the place it eventually gets to can keep taking the gas. I suspect in the United States this may be somewhat less of a problem, as the geography seems more varied over shorter distances than Australia, and as such there might on average be shorter distances to get to useful places to pump the gas into the ground.

Earlier this year, a former head of BHP was quoted as expressing scepticism about its viability from the point of view of public concern about its safety:

Paul Anderson, who ran BHP-Billiton in 2002 and still sits on its board, told the Herald: "People can't believe you're safe putting nuclear waste five miles under the ground when it's petrified in glass. How are they going to feel safe putting pressurised gas under the ground?

"I think it's as big as the issue of nuclear waste. What are you going to do with millions of tonnes of carbon dioxide that is not nearly as compact as nuclear waste?"

So...are there any alternatives to pumping liquid CO2 into the ground?

The comments in that Treehugger post listed above include one promoting Enpro, a Norwegian company which is promoting a process using salty water to convert CO2 into solid sodium carbonate (with clean water as a by-product.) The website is short on detail, and there is no mention of what can be done with the mountains of sodium carbonate this would produce. (There is also the added problem of the source of salty water if your power station is not near the ocean or adequate bore water.) The website claims these appealing features:

Unlike any other solution proposed thus far, EnPro technology:

• Provides a 95% reduction in CO₂ emissions from flue gases.
• Provides a 95% reduction of CO₂ in natural gas.
• Is effective in oil, gas or coal-powered plants.
• Can be retrofitted to existing plants at a reasonable cost.
• Produces commercially valuable by-products.
  (water suitable for industrial use and sodium carbonate etc.)

Given the very significant problems associated with geosequestration, surely anything leaving open the possibility of a solid that can be safely buried is worth looking into in detail.

(By the way, the Enpro site links to the Wikipedia entry on the similar Solvay process, which links to the abstract to a paper which sounds very significant on the issue. Unfortunately, you have to pay for it. But the abstract notes:

Long-term storage of a gaseous substance is fraught with uncertainty and hazards, but carbonate chemistry offers permanent solutions to the disposal problem. Carbonates can be formed from carbon dioxide and metal oxides in reactions that are thermodynamically favored and exothermic, which result in materials that can be safely and permanently kept out of the active carbon stocks in the environment. Carbonate sequestration methods require the development of an extractive minerals industry that provides the base ions for neutralizing carbonic acid.

The Wikipedia entry on carbon sequestration is not as detailed as one might expect.

I doubt that ocean dumping of liquid CO2 is a good idea, and would be seen as a big environmental unknown. (Iron fertilization would seem to me a much safer thing to try.) Pumping CO2 into areas where it is expected to be mineralised in the ground quickly gets mentioned in quite a few places on the Web, but again, you have transport and safety issues to consider.

A Google search shows up a fair few ideas for using carbonate reactions for CO2 sequestration.

Seems to me that, as with pebble reactors, it is an idea that is being pursued rather slowly, but in theory sounds very promising. At some stage, governments may have to start trying to pick winners if this is to be investigated as thoroughly and as quickly as possible.