killing two birds with one stone

There are all kinds of mechanisms being investigated to reduce carbon in the atmosphere, but there are only two basic approaches: one is to reduce carbon emissions at source, and the other is to capture and store emissions. Right now, most viable strategies involve reduction at source, which can involve eliminating the processes that create emissions (like driving less), changing technologies (switching from coal-powered generation to solar), or improving efficiencies (using machines that make better use of their energy source).

Some carbon capture and storage mechanisms are also being used right now, like scrubbers that take carbon out of gas in smokestacks before it enters the atmosphere - but the holy grail for industries that don't really want to change business as usual is large-scale storage using underground cavities. That is an idea that is being promoted in some quarters, but it's not a thoroughly proven concept.

So here is an approach that stores carbon while also reducing the environmental impact of the building industry. A company called Calera is developing a process that uses the flue gas from power stations that run on natural gas or other fossil fuels, and creates a form of cement that uses the carbon in the gas. They bubble the gas through sea water:

The Calera process essentially mimics marine cement, which is produced by coral when making their shells and reefs, taking the calcium and magnesium in seawater and using it to form carbonates at normal temperatures and pressures. "We are turning CO₂ into carbonic acid and then making carbonate," Constantz says. "All we need is water and pollution."

The company employs spray dryers that utilize the heat in the flue gas to dry the slurry that results from mixing the water and pollution. "A gas-fired power plant is basically like attaching a jet engine to the ground," Constantz notes. "We use the waste heat of the flue gas. They're just shooting it up into the atmosphere anyway."

Normal Portland cement produces a ton of CO₂ emissions for every ton of cement produced, and this new process is efficient enough to sequester half a ton of carbon emissions for every ton of cement. Emissions from power generation would be reduced, and emissions from the creation of cement would also be reduced. Buildings, bridges and other structures made of concrete using this cement would essentially be storing carbon, reducing their environmental impact.