Process Economics Program Report 180B
Carbon Capture from Coal Fired Power Generation
Published: December 2008
The largest and most expensive part of the overall carbon capture and storage process is capturing CO2 from a power plant. Maintaining coal as a viable source of electric power thus depends critically upon improving plant efficiency in order to produce less CO2 for a given amount of power generation, and on finding more cost-effective ways to capture the CO2 produced – either before or after combustion.
Pre-combustion efforts have focused on integrated gasification-combined cycle (IGCC) systems, in which coal is processed with oxygen and steam under pressure to form a synthesis gas that can be fired directly in a gas turbine. The CO2 can be removed relatively efficiently from the synthesis gas, but CO cannot, so before firing, the gas is sent to a water gas shift reactor that converts the majority of CO to CO2 and hydrogen. Following water gas shift, other gas conditioning operations are required including gas cooling and mercury removal before CO2 is removed from the synthesis gas using absorption. The extent of CO2 removed by this means is about 90%.
Conventional coal plants are faced with a more difficult task of capturing post combustion CO2 from flue gas at atmospheric pressure. The CO2 concentration of the flue gas from a supercritical pulverized coal (SCPC) power plant is typically less than 15%, with most of the remaining gas composition being nitrogen from the air used to support combustion. Nevertheless about 90% of the CO2 can potentially be removed from the flue gas by a post combustion process.
In this report we describe and review the economic units involved in the production of power from coal without and with the baseline techniques for carbon capture from post and pre-combustion capture using high grade bituminous coal for which IGCC is well suited. Economics are then compared four ways (without and with CO2 capture) to ultimately discover the cost of CO2 removed from nominal 550 MW supercritical combustion and IGCC power plants.