Calera: Converting CO2 Into Calcium Carbonate For Concrete

Calera has developed a process to combine CO2 with seawater, or any kind of briny water, to produce calcium carbonate (CaCO3), which can be used as a building material. Specifically, it takes CO2 emissions from a coal or gas-fired power plant and sprays seawater into it and naturally converts most of the CO2 into calcium carbonate. It is then spray-dried into cement or shaped into little pellets that can be used as concrete aggregates for building walls or highways — instead of letting the CO2 emissions go into the atmosphere and produce climate change. Calera is demonstrating the process at a plant near Santa Cruz, California. In essence, the company is making chalk. The Calera cement can be used as a replacement for the Portland cement that is typically blended with rock and other material to make the concrete in everything from roads to buildings.

If the process can be made cost effective, it would eliminate the need for expensive carbon-sequestration and could make “clean coal” a possibility. A major challenge for most CO2 capturing technologies is to overcome the high costs of capture. The Department Of Energy (DOE) has reported that capturing a ton of CO2 from an existing coal fired power plant could cost $58. That means that until the price of carbon remains below $58 per ton, the emitter will suffer an important economic loss. This loss will have a direct impact on electricity rates, the price of cement and the price of all services that are energy intensive. Bechtel Renewables and New Technology has formed an alliance to build more Calera plants. Peabody coal company also intends to invest in Calera. (Calera-Economic Viability)

Cement, which is mostly commonly composed of calcium silicates, requires heating limestone and other ingredients to 2,640 degrees F (1,450 degrees C) by burning hydrocarbon fuels and is the third largest source of greenhouse gas pollution in the U.S., according to the U.S. Environmental Protection Agency. Making one ton of cement results in the emission of roughly one ton of CO2—and in some cases much more. While Calera's process of making calcium carbonate cement wouldn't eliminate all CO2 emissions, it would reverse that equation. For every ton of cement we make, we are sequestering half a ton of CO2. The Calera process could be applied to cement production, reducing CO2 emissions even more. The U.S. used more than 122 million metric tons of Portland cement in 2006, according to the Portland Cement Association (PCA), an industry group, and China used at least 800 million metric tons.

FROM THE CALERA WEBSITE (Carbonate Formation Science):

The heart of the Calera process is the technology associated with carbon capture and conversion to stable solid minerals. We refer to this new process as Carbon Mineralization via Aqueous Precipitation or CMAP for short. In its simplest form CMAP involves contacting gas from the power plant with water (aqueous) containing hardness and a base buffer (alkalinity). The water chemistry is controlled such that the carbon dioxide in the power plant gas is absorbed into the water and reacts with the water hardness to form solid mineral carbonates, which are very similar to fine limestone particles. These solid mineral carbonates now contain carbon dioxide that would have been emitted into the air. After removal from the water and appropriate processing the solids have value in a number of construction applications. The versatility of CMAP also allows the generation of bicarbonates using half the amount of input materials but still mineralizing carbon dioxide that can be pumped into any underground saline zone for storage without the possibility of leakage of carbon dioxide.

(NYT, 3/6/10, Scientific American, Calera)