As the intro to a piece broadcast this week on KQED-FM, an NPR station in the SF Bay Area, says, cement is not something one thinks about too often. But a single limestone quarry and kiln in the hills on the Peninsula is one of the the Bay Area’s biggest CO2 emitters. When one leafs through IPCC reports and such on emission sources, cement is always there, front and center. But the instinct is likely to be cement? That gray powder in bags? All those sidewalks? How does one fix that? Let’s think about conservation, plug-in hybrid cars, and wind turbines (their feet set in concrete) etc. instead.
Producer Laura Sommer and reporter Amy Standen , who work for the station’s Quest science show, visited a big cement operation south of SF. It has a 1000-foot-deep limestone quarry and a monumental steel and brick kiln. They watch and listen as the kiln bakes the limestone, with the help of lots of coal, to 3000 degrees F. Out comes clinker, or quicklime – cement’s key ingredient. Mostly the story is about mercury pollution, serious but more easily solved than is the CO2.
It’s an enterprising and important piece on something of which most listeners know virtually nothing. But it includes at least one misleading passage. It strongly suggests that all that burnt coal explains the CO2. If only it were so. One could just bake the stuff in solar ovens or nuclear furnaces or something else and presto, green cement. But no. Limestone is mainly calcium carbonate. The heat transforms the carbonate into CO2 to get the desired clinker (basically calcium oxide). The byproduct CO2 from the chemistry itself accounts for maybe 80 percent of the greenhouse emissions from a coal-fired cement kiln. With or without coal it’ll take serious carbon capture and sequestration to clean this vital industry. Everywhere one looks, saving this planet is hard.
For another angle on cement, something of what’s coming worldwide is pretty clear at the Vancouver Sun. Its Scott Simpson reported on plans in British Columbia to impose a carbon tax on fretting cement makers. The manufacturers worry they won’t be able to compete with foreign suppliers. One wonders how hard it might be, even with fair trade agreements and all, to slap a carbon tax on imported cement as well.
Grist for the Mill: Something of the chemistry of cement production, and CO2 emissions, is in this report on how to do it with solar heat.
-CP
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