How+Clean+Coal+Works

= Clean Coal Technologies - How They Work = = =

//**Pre-Combustion **//
With the pre-combustion method, the goal is to take all of the carbon dioxide out //before// the fuel is combusted. First, the fuel is reacted with steam and pure oxygen. Regular air can be used in place of pure oxygen. This reaction yields carbon monoxide and hydrogen gas, known as synthesis gas.

The synthesis gas is subjected to steam in a water-gas-shift reactor, transforming the carbon monoxide into carbon dioxide. The synthesis gas, now composed of carbon dioxide and hydrogen, is separated. The carbon dioxide is stored with methods that are discussed elsewhere, and the hydrogen becomes the energy carrier to run a turbine. This method removes 90% to 95% of the carbon dioxide.

**//Post-Combustion //**
Post-combustion involves removing carbon dioxide from the flue gas, which is the air full of waste product after the combustion to make steam. A typically organic solvent, such as monoethanolamine, is used to extract 85-95% of the carbon dioxide, according to the IPCC. The National Mining Association says that while post-combustion is more difficult, due to the "diluted nature of the post-combustion gases", it can be retrofitted to existing systems. This means that it could be cheaper for some companies, and is said to remove 80%-90% of the carbon dioxide.

**//Oxyfuel Combustion //**
Also known as Oxy-Coal Combustion, Oxyfuel Combustion sequesters the carbon dioxide by transforming the air involved in the actual combustion into almost pure oxygen (about 95-99% oxygen, according to the IPCC), so the flue gas is composed of water vapor and carbon dioxide.

The flue gas is then separated by compression (the water vapor compresses into liquid form, and the carbon dioxide remains in gas form), and the carbon dioxide is stored usually somewhere off-site. The NMA cautions that while oxyfuel combustion can remove 90% of the carbon dioxide, the process requires up to 15% of a power plant's annual output.

Back to Home Page