User:Milton Beychok/Sandbox

Reducing carbon dioxide emissions from coal-fired power plants

The leading technology for significantly reducing the CO₂ emissions from coal-fired power plants is known as Carbon capture and sequestration (CCS). It is currently (2008) regarded as the technology which could significantly reduce coal-fired power plant CO₂ emissions while also allowing the use of the Earth's aboundant coal resources to provide the increasing global need for energy. However, CCS technology is still in development and it is not expected to be ready for widespread commercial implementation on a large scale until about 2020.

It involves capturing the CO₂ produced by the combustion of coal and storing it in deep ocean areas or in underground geological structures deep within the Earth's upper crust. The capture of the CO₂ from the coal combustion flue gases can be accomplished by using absorbents such as amines (see Amine gas treating). The CO₂ is then compressed into a supercritical fluid at about 150 atmospheres (15 MPA), dehydrated and transported to the storage sites for injection into the underground or undersea reservoirs. Compressing the CO₂ into a supercritical fluid greatly increases its density which greatly reduces its volume as compared to transporting and storing the CO₂ as a gas.

Since the current global emissions of carbon dioxide from all energy supply sources is 28 Gt per year, the scale of CO₂ storage required to make a major difference in those emissions is massive. For example, based on a CO₂ emission factor of 1 kg per kWh, 570 coal-fired plants, each producing 1000 MW of electricity, would emit about 5 Gt per year of CO₂ into the atmosphere. Storing 5 Gt per year of CO₂ requires injection of about 65 million barrels per day (about 10 x 10⁶ cubic meters per day) of supercritical CO₂.

The worldwide capacity for storing CO₂ in depleted natural gas and crude oil production fields and in unmineable deep coal seams has been estimated as about 1000 Gt which is equivalent to 140 years of the 7 Gt emissions (in 2005) from the worldwide total coal-fired power generation. In addition, the worldwide capacity in deep saline formations has been estimated to range from 1000 to 10,000 Gt.

No matter what governmental regulations are eventually adopted to mitigate the emissions of CO₂ from coal-powered power plants (or other processes involving the combustion of substances containing carbon), there must be successful, integrated large-scale demonstration of the technical, environmental and economic aspects of the major components of a CCS sytem, namely CO₂ capture, transportation and storage. Such an integrated demonstration must also provide a definition of regulatory protocols for sequestration projects including site selection, injection operation, and eventual transfer of custody to public authorities after a period of successful operation.