Wednesday, June 6, 2007


Some people think cement is boring and just soldier on anyway. They consider the considerable amount of ghost energy that is used in making cement and try to figure out ways to reduce it. The proposed solution, geopolymeric cement actually has historic, folkloric and even quasi-automotive aspects so it is puzzling why it would be considered dull. Monbiot is single minded in his effort to find ways to reduce carbon dioxide emission while preserving a civilized life. In converting from temperamental Portland cement to more durable geopolymeric cement he finds an 80% reduction in emission.

Owing to natural gas supplies from Russia, Monbiot tends to support the the idea of pumping carbon dioxide into deep saline aquifers to store it in a relatively stable liquid form while still using ghost energy. He runs into difficulty though when considering home heating because he needs two sets of pipes, one to bring in the gas and one to return the carbon dioxide to a central location for liquification. He feels that the timescale for reducing emissions is so short that a complete transition to real energy may not be possible before a 90% reduction in emissions is required. There are actually three sets of pipes connecting a typical British home and it seems to me that Monbiot has overlooked this. One set brings in natural gas, one set brings in water and one set carries water away. If Monbiot is looking for an extra pipe, it seems to me that the last set would work just fine for his purposes. A slight negative pressure would draw flue gas from his boilers and an application of this technology at the egress would condense the carbon dioxide in the manner he desires. With a high carbon dioxide partial pressure in the pipe a couple of other benefits occur. Anoxic bioprocessing of the sewage on the trip through the pipe will produce methane which can be mixed back with the natural gas while the carbonated water is just about perfect for biofuel production using algae and light. In gloomy England, he may want to use wind powered artificial light, but it does get around the land use issues that worry him. Deficiencies in the third set of pipes for this purpose would really be a matter of maintenance to correct rather than new infrastructure so that his timescale could be met.

But, let's not deal further with such spirits and turn to real sequestration using real energy (note to George: Klaus has cost estimates here, drop me a line if you don't have a subscription). In order to counter-act our interference in the geological carbon cycle we need to return carbon to the ground. But, as Lackner points out, there is not really enough room in the ground whence we have summoned the carbon to put it all back. Thus, he considers harvesting metal ions from silicate rocks in order to produce carbonates which can be left exposed on the surface of the Earth for very long periods without risk of the carbon returning to the atmosphere. He would have coal burned at rock quarries (it takes about five or six times the mass of rock to convert the carbon dioxide to carbonates so you bring the carbon to the rock) to produce power without releasing carbon dioxide. Like Monbiot, he still flirts with ghosts. But it seems a little silly to do for ourselves what real energy does for us, and surely the weathering of rock on the continents produces an abundant supply of the metal ions Lackner requires throughout our oceans and estuaries. Calcium ions, together with carbon dioxide are the raw material our of which corals and shellfish form their exoskeletons. Weathering of rock is a real energy process and the growth of these creatures is a real energy process and both are the real geological carbon cycle. Ghost energy is largely an accident that is only significant because it has had such a long time to accumulate. Most carbon sits in carbonates.

How can we participate in this real energy process while also reducing our reliance on Portland cement? This also turns out to be interesting in historic, folkloric and quasi-automotive ways. The only puzzle is: how did we killed our oysters? The answer is that we have overfed them. Historically, the Chesapeake Bay produced about 700,000 tons of oysters each year and since the wet flesh weight is less that 10% of the total weight, most of this was a harvest of calcium carbonate. Folklorically, you could walk across the bay on oyster reefs. And, in a quasi-automotive manner, crushed oyster shells once made permeable driveways near the Bay though now they are used for chicken feed and oyster restoration.

How does the carbon in 700,000 tons of oyster shells compare with the carbon in the 7 million tons of carbon dioxide emitted from home heating in Maryland in 1990? Well carbon is about 12% of the weight of the shells and about 27% of the weight of the gas so
a historic oyster harvest can sequester about 4.4% of a year's worth carbon from home heating. Or, 23 years of harvest can make up for each year we continue to use oil and gas for heating. This is not planting trees! This is permanent sequestration!

What could we do with all those shells? Tabby is a building material made from oyster shells that hearkens back to a day when we didn't use ghost energy. Returning to it's use may make some sense. But to do that, we've got to reduce the amount of nitrogen and phosphorus flowing into the Bay (and the Gulf on Mexico) because the anoxic conditions they produce, which might be useful in a sewer pipe (above), kill the oysters, crabs and other sea life that can help us in cleaning up our carbon mess. It is not enough to reduce the amount of carbon used to make nitrogen fertilizer, we also need to manage much more carefully where it ends up when we are done with it.

1 comment:

DaveMart said...

Chris, I think this needs a re-write - your ideas are fizzing too fast for clarity!

In particular, you have not adequately explained your ideas of 'ghost energy' and 'real energy'.

It is also too densely written - a number of different ideas fly past, without enough detail for them to make sense - it needs several separate blogs, taken at a slower pace.

For instance, you throw out the idea of using the sewage system - how would this interact with the sewage systems' primary use?

Would methane leak from pipes which weren't designed to carry this sort of content?

Obviously it would be too much to ask for a full development of everything here, but more detail and a slower pace is needed for your dimmer readers - I provide a perfect test-bed for this!