Cement is a binder material that hardens independently and can bind other materials together. It is the most important construction ingredient around the world and hence cement production is a significant source of global CO2 emissions accounting for around 3% of the total emissions from industrial and energy sources. The most important use of cement is in the production of mortar and concrete. Due to its properties it is widely used in construction industry. Cement is made from limestone in a clinker in a process known as calcination, wherein the limestone is heated along with small quantities of other materials at a high temperature of 1450 0C. During this process the limestone (CaCO3) is converted into lime (CaO) and CO2 is emitted as the by-product in this chemical conversion process.
The global production of cement is 3.04 billion tonnes in 2009. China is the leading producer followed by India. These 2 countries alone account for over 50% of the global annual cement production. Researchers have found a way to convert the CO2 captured from power plants and other industrial sources to manufacture cement. Calera, a California based company has devised a method to capture CO2 before it enters atmosphere and use it as a feedstock for cement production. By traditional cement making process, for every one tone of cement produced, roughly one ton of CO2 is released into the atmosphere. But using the process developed by Calera, not only the chance of emission of CO2 from cement factory is eliminated and but also the CO2 released in combustion of fossil fuels is sequestered in useful products like cement.
The Calera process takes the calcium and magnesium in seawater and using it to form carbonates at normal temperature and pressure. They turn CO2 to carbonic acid and then form carbonates. It is believed that for every ton of cement produced, ½ a ton of CO2 is required in Calera process. Assuming that this process is proved to be commercially viable in large scale and all the traditional cement manufacturing process is substituted with those of Calera process, roughly around 1.5 billion tonnes of CO2 would be required for making cement (global cement production is approximately 3 billion tonnes in 2009).
Calera recently completed a demonstration project near Moss Landing, California that is capable of capturing 30,000 tons per year of a CO2, equivalent to a 10MW natural-gas power plant. In January, Calera began drawing 1 percent of the stack gas from a Dynegy power plant across the street through a massive pipe to its cement plant. Calera was hoping to capture 80 percent of the smokestack CO2, and sequester it in its patented cement mixture using the abundant stock of magnesium hydroxide (Mg (OH) 2) available on site. Calera is also the recipient of US Department of Energy (DOE) funding for CO2 reuse projects. The DOE is investing $106 million in 6 projects from the American Recovery and Reinvestment Act to find ways of converting captured CO2 emissions from industrial sources into useful products such as fuel, cement, plastics and fertilizers. Calera corporation cement production from CO2 is one among the 6 projects identified by DOE for funding purpose.