Using Rust in Oxy-fuel Combustion in Coal Power Plants
Oxy-combustion is one of the potential methods explored for carbon capture and storage. Within this, a number of materials are being explored to capture the oxygen from the air so that pure oxygen is supplied for combustion. The latest material being tried in this context is iron, which converts to iron oxide – rust – upon oxygen capture.
This experiment is being conducted by researchers at Ohio State University, and has the potential to reduce the costs of oxy-fuel combustion.
Most coal-fired power plants burn pulverized coal in air, and since air is mostly nitrogen, so is the exhaust emissions–only about 14 percent is carbon dioxide. This process called chemical looping produces a highly concentrated stream of carbon dioxide. Such a stream would be easier to capture than a stream that has CO2 in dilute amounts.
With chemical looping, coal isn’t exposed directly to air. Instead, it involves a series of chemical reactions in which a solid material first captures oxygen from the air and then transfers it to the fuel – without the nitrogen or other gases in air. Thus there is little or no nitrogen present in exhaust stream, making CO2 capture a far easier process.
In the experiment conducted, iron is used as the intermediate material that captures oxygen from the air, and forms iron oxide. When this iron oxide is reacted with syngas formed from coal gasification, oxygen is released and iron oxide is converted to metallic iron which is again used for capture of oxygen from air. The oxygen oxidizes the carbon monoxide and hydrogen, forming steam and CO2. The steam can easily be removed by condensing it, leaving behind highly concentrated carbon dioxide that can be captured and stored.