critique and commentary on world energy news…

Calera's CO2 capture systems would treat flue gas from power plants to create a cement.

As the largest source of CO2 emissions in the United States, scientists have long sought a process to clean up the coal-fired power industry. Unfortunately the solutions to capture and sequester carbon have yet to be economically feasible without the government placing a hefty price on carbon emissions. The new Silicon Valley start-up, Calera, claims to have developed a process that sequesters carbon dioxide emissions from flue gas (the gaseous product of coal or natural gas combustion in a power plant) in a cement product, as reported in a recent NYTimes article. Considering that in 2007 we produced 91 million tons of Portland cement and 4 million tons of masonry cement with a value of $9.7 billion, cement from a CO2 capture plant would be entering a large and profitable market. In addition, the US cement industry is one of the largest contributors to industrial process-related GHG emissions. Thus, capturing CO2 from power plants in a cement product could mitigate emissions from both the coal combustion and conventional cement production.

Generally when people talk about carbon capture and sequestration, they’re referring to the chemical absorption of CO2 in a liquid (usually ammonia based) solution. This solution is then passed through a stripper (funny name, I know!) where the liquid is heated to release the captured CO2. Finally, the CO2 is compressed and injected into geological formations underground. The exact details of the Calera process are unknown, but we do know that the process involves combining the flue gas (containing CO2) with sea water (containing calcium, magnesium, and oxygen). The process produces calcium carbonate and magnesium carbonate which are then used to make cement and aggregate. To make the resulting carbon capture cement compatible with Portland cement, Calera makes a 20% CO2 cement and 80% Portland cement blend.

A test plant in California has been found to capture 86% of CO2 in the flue gas (though it is unclear how much of the flue gas the Calera plant treats). Though Calera has had success in their pilot plant, questions remain as to the scalability of the process. Critics of the technology are concerned with an acid byproduct from the reaction that must be neutralized and disposed of. I also have questions about the water requirements of the process. To produce cement the Calera process must have a plentiful source of sea water or brine, so how will they implement their idea at inland and water starved power plants? And what are the energy requirements of the Calera process? One of the main downsides of ammonia based CO2 capture systems is that they require about 30% of the energy produced by the power plant to treat the plant’s flue gas. This means that to continue to produce the same amount of energy, the plant will have to increase its capacity (and emissions) by 30%. To be a winner in the CO2 capture race, Calera should also perform well on the energy front. I suppose we’ll have an answer to these questions soon, Calera has announced it will open its first commercial plant next year.

Bottom line: Calera’s CO2 capture technology has given us hope that CO2 capture can be economical, and produce useful byproducts, but they still have to prove that it’s actually viable at a large scale.