Grantee Research Project Results

System Level Implications of Flexible CO₂ Capture Operation

EPA 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: Lee, Sonja
Project Period: January 1, 2008 through December 31, 2008
RFA: STAR Graduate Fellowships (2009) RFA Text |  Recipients Lists
Research Category: Academic Fellowships

Objective:

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. 

Approach:

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.

Expected Results:

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.

Progress and Final Reports:

Final