“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Monday, September 02, 2013

A home for CO2?

Photo credit: MIT
A hybrid group comprised of The University of Newcastle (through it's commercial entity, Newcastle Innovation), Orica (a chemical company), and GreenMag Group (appears to be an ecologically oriented innovation facilitator) has launched a pilot plant that converts carbon dioxide into bricks, pavers, aggregate, and other construction products. The idea is to capture CO2 from power plants and other large industrial emitters and turn it into such products. It's seemingly plausible. After all, cement is made, in large part, by cooking the CO2 out of limestone, which is CaCO3, i.e., calcium carbonate, to form CaO, lime. The Mineral Carbonation International facility, in a simplistic view, reverses this.

In the inhabitat.com article that alerted me to this concept, it's stated that "fifty carbon capture plants around the world could potentially sequester over a billion tons of CO2 annually." Now, our species emits on the order of 31.6 gigatonnes (Gt) annually, so this potential, if it's real, represents maybe 3.2% of our emissions (I'm assuming that metric tons or "tonnes" is the unit, if not, then it's 2.9%). I'm assuming that the sequestration plant would be collocated with the carbon dioxide emitter. I wouldn't think compressing and shipping the CO2 would be feasible. There are some 50,000 coal fired power plants worldwide. So, if they all had such capability, we could sequester some 1,000 billion tonnes of CO2, 32 times our actual total annual emissions! Woo hoo, let's get started!

But how do we reconcile these numbers? A "typical coal fired power plant," per the Union of Concerned Scientists, emits 3.5 million tons of carbon dioxide annually. If I assume they're utilizing short tons, it fits fairly well with an estimate calculated from Wikipedia that yields 2.4 megatonnes, using a one gigawatt power plant at 80% capacity factor. OK, so 50,000 plants times 3.5 million tons per plant yields 175 billion tonnes, or over five times worldwide emissions. Nothing sensible there either, clearly none of that makes sense unless the average coal fired plant is much smaller than a gigawatt plant. The Union of Concerned Scientists must be referring to a very large, gigawatt scale coal fired power plant.

OK, finally, looking through the EIA site, I can estimate that about 14 gigatonnes of COare emitted worldwide via coal combustion for energy. So the average annual emission of a plant would be 14 billion/50,000 or 280,000 tonnes per plant per year.  Does THIS make sense? The estimate in the previous paragraph of 2.4 megatonnes came from my plugging in a 1 gigawatt nameplate capacity plant at 80% capacity factor. That would mean that the "average" plant operates at (280,000/2,400,000)*800 megawatts or 93 megawatts. I don't find this to be unrealistic, there may very well be many thousands of relatively small coal fired power plants around the world.

But back to the claim that 50 pilot plants can sequester a gigatonne. That would be 20 megatonnes per plant, FAR more than the 2.4 megatonnes emitted by a large (gigawatt size) power plant. The only way for the claim to make sense is if, in contradiction to my speculation above, carbon dioxide is compressed and transported to a sequestration facility. Sorry, I doubt it. Next post: how much carbonate will be produced and what can be done with it? After that, energetics and economics.

1 comment:

GRLCowan said...

In general, CO2 does not require human assistance to find its way to an alkaline mineral surface, but does require our assistance in increasing the mineral's surface area and dispersing it, if tens of gigatonnes per year are to be garbage-collected.

Also see http://www.inference.phy.cam.ac.uk/withouthotair/c31/page_246.shtml, http://www.innovationconcepts.eu/res/literatuurSchuiling/olivineagainstclimatechange23.pdf