Pre-combustion capture refers to removing CO2 from fossil fuels before combustion is completed. For example, in gasification processes a feedstock (such as coal) is partially oxidized in steam and oxygen/air under high temperature and pressure to form synthesis gas. This synthesis gas, or syngas, is a mixture of hydrogen, carbon monoxide, CO2, and smaller amounts of other gaseous components, such as methane. The syngas can then undergo the water-gas shift reaction to convert CO and water (H2O) to H2 and CO2, producing a H2 and CO2-rich gas mixture. The concentration of CO2 in this mixture can range from 15-50%. The CO2 can then be captured and separated, transported, and ultimately sequestered, and the H2-rich fuel combusted.
Compared to post-combustion technology, which removes dilute CO2 (~5-15% CO2 concentration) from flue gas streams and is at low pressure, the shifted synthesis gas stream is rich in CO2 and at higher pressure, which allows for easier removal before the H2 is combusted. Due to the more concentrated CO2, pre-combustion capture typically is more efficient but the capital costs of the base gasification process are often more expensive than traditional pulverized coal power plants.
Today’s commercially available pre-combustion carbon capture technologies generally use physical or chemical adsorption processes, and will cost around $60/tonne to capture CO2 generated by an integrated gasification combined cycle (IGCC) power plant. The goal of DOE's research efforts is to reducethis cost to $40/tonne of CO2. Research focuses on three key separation technologies – advanced solvents, sorbents, and membranes – in order to meet this goal.
The pre-combustion capture research activities will coordinate closely with the gasification and hydrogen turbine programs to ensure that pre-combustion capture technologies can be successfully integrated into an IGCC facility. Advances in those programs will also help meet the goal of limiting the cost of pre-combustion capture to $40/tonne.