System Level Implications of Flexible CO2 Capture OperationEPA Grant Number: F08A10194
Title: System Level Implications of Flexible CO2 Capture Operation
Investigators: Cohen, Stuart M
Institution: The University of Texas at Austin
EPA Project Officer: Klieforth, Barbara I
Project Period: January 1, 2008 through December 31, 2008
RFA: STAR Graduate Fellowships (2009) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Coal consumption for electricity generation produces over 30% of U.S. carbon dioxide (CO2) emissions, but coal is also an available, secure, and low cost fuel that is currently utilized to meet roughly half of America’s electricity demand. While the world transitions from the existing fossil fuel-based energy infrastructure to a sustainable energy system, carbon dioxide capture and sequestration (CCS) will be a critical technology that will allow continued use of coal in an environmentally acceptable manner. Post-combustion CO2 capture from power plant flue gas is one CO2 capture technology that is especially important for CO2 mitigation at facilities that are currently built or will be built prior to widespread CO2 capture deployment.
While post-combustion CO2 capture systems can be designed to remove 90% of the CO2 from flue gas, systems have high capital costs, and the energy requirement for CO2 capture can reduce power plant output by 30%. CO2 capture is typically assumed to operate continuously at a full-load operating point, meaning that any generation capacity lost to CO2 capture must be replaced. In contrast, this work will investigate the feasibility and implications of operating CO2 capture flexibly in response to variations in electric grid demand and pricing. With a flexible capture system, the energy intensive components in the CO2 capture process could temporarily turn down or off to allow for increased power plant output under favorable electricity market conditions. For a representative case study, a first-order electricity dispatch model of the Electric Reliability Council of Texas (ERCOT) electric grid compares scenarios with flexible CO2 capture to those with inflexible CO2 capture and without CO2 capture.
In ERCOT, turning flexible CO2 capture systems off during infrequent periods of peak electricity demand can avoid hundreds of millions to billions of dollars in capital costs to replace the power output lost to CO2 capture energy requirements. When CO2 prices are high enough to justify investment in a CO2 capture system, operating economics will likely justify continuous full-load CO2 capture. However, flexibility can still be a valuable tool to hedge against the risk of CO2 price volatility; if CO2 prices were to fall, flexibility could improve operating profits by tens to hundreds of millions of dollars annually, though CO2 emissions could increase. Coal and natural gas prices have a major effect on flexible CO2 capture operation. In ERCOT, where natural gas-fired power plants predominantly determine electricity prices, higher natural gas prices increase the CO2 price required to justify full-load CO2 capture. In addition, any operating profit improvement due to CO2 capture flexibility increases as the disparity between coal and natural gas prices increases.