CLEANTECH: CO2 to Carbonate

By Published On: July 31, 2009

A little-known pilot project facility next to the Moss Landing power plant on Monterey Bay is turning carbon dioxide emissions from a small coal power unit into construction material. It’s also attempting to keep global warming gases out of the atmosphere. The technology does “more than carbon dioxide sequestration,” according to Brent Constanz, Calera chief executive officer. “It represents permanent carbon dioxide conversion from gas to solid mineral.” Power plants emit about 39 percent of the nation’s greenhouse gases and cement plants about 1 percent, according to the U.S. Environmental Protection Agency. Calera’s technology holds the potential to cut emissions from cement-making indirectly because it provides an emission-free substitute product. The company’s facility--which includes a small coal plant it built to test its technology--captures carbon dioxide from flue gas produced by burning coal and turns it into about a ton a day of carbonate, Constanz told the House Select Committee for Energy Independence and Global Warming July 28. Carbonate is a chalky salt that is a key constituent of limestone, which is used in making cement. Backed by funding from Khosla Ventures, Calera next plans to construct a 20 MW plant at the site by 2010, according to Constanz--a professor at Stanford University. “The precipitation of carbonate minerals by consuming carbon dioxide in aqueous solution is one of the oldest extraordinarily well-proven industrial processes,” said Constanz. “Products from this process are used in everything from paper to plastic, from milkshakes to wallboard.” The way it works is that the flue gas is routed into a tank along with water containing magnesium and calcium. There, the technology applies a low voltage current that precipitates both calcium carbonate and magnesium carbonate. Water is left over. The carbonate slurry is dried and used to make cement and aggregate. U.S. demand for cement and aggregate is about 3 billion tons a year, according to Constanz. Worldwide demand is about 30 billion tons. This means there is a potentially large market for carbonate. Calera’s process also can capture 95 percent of the sulfur dioxide in the flue gas, eliminating the need to install scrubbers, according to the company. The company is working to incorporate a process to capture nitrogen oxides too. Both sulfur dioxide and nitrogen oxides are major air pollutants. Ultimately, Constanz thinks that the patented Calera process can operate by using just 20 percent of a coal plant’s power output, less than the 35 percent parasitic use now experienced at pilot projects that capture carbon dioxide for geologic sequestration. It also eliminates concerns and expenses related to pumping carbon dioxide into the ground, where it could contaminate drinking water. Calera envisions using its technology to control carbon dioxide emissions from other facilities too, such as oil refineries and industrial smelters.

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