Coal consumption accounted for 36% of America’s $CO2$ emissions in 2005, yet because coal is a relatively inexpensive, widely available, and politically secure fuel, its use is projected to grow in the coming decades (USEIA, 2007, “World Carbon Dioxide Emissions From the Use of Fossil Fuels,” International Energy Annual 2005, http://www.eia.doe.gov/emeu/iea/carbon.html). In order for coal to contribute to the U.S. energy mix without detriment to an environmentally acceptable future, implementation of carbon capture and sequestration (CCS) technology is critical. Techno-economic studies establish the large expense of CCS due to substantial energy requirements and capital costs. However, such analyses typically ignore operating dynamics in response to diurnal and seasonal variations in electricity demand and pricing, and they assume that $CO2$ capture systems operate continuously at high $CO2$ removal and permanently consume a large portion of gross plant generation capacity. In contrast, this study uses an electric grid-level dynamic framework to consider the possibility of turning $CO2$ capture systems off during peak electricity demands to regain generation capacity lost to $CO2$ capture energy requirements. This practice eliminates the need to build additional generation capacity to make up for $CO2$ capture energy requirements, and it might allow plant operators to benefit from selling more electricity during high price time periods. Post-combustion $CO2$ absorption and stripping is a leading capture technology that, unlike many other capture methods, is particularly suited for flexible or on/off operation. This study presents a case study on the Electric Reliability Council of Texas (ERCOT) electric grid that estimates $CO2$ capture utilization, system-level costs, and $CO2$ emissions associated with different strategies of using on/off $CO2$ capture on all coal-fired plants in the ERCOT grid in order to satisfy peak electricity demand. It compares base cases of no $CO2$ capture and “always on” capture with scenarios where capture is turned off during: (1) peak demand hours every day of the year, (2) the entire season of peak system demand, and (3) system peak demand hours only on seasonal peak demand days. By eliminating the need for new capacity to replace output lost to $CO2$ capture energy requirements, flexible $CO2$ capture could save billions of dollars in capital costs. Since capture systems remain on for most of the year, flexible capture still achieves substantial $CO2$ emissions reductions.

1.
Metz
,
B.
,
Davidson
,
O.
,
de Coninck
,
H.
,
Loos
,
M.
, and
Meyer
,
L.
, 2005,
IPCC Special Report on Carbon Dioxide Capture and Storage
,
Cambridge University Press
,
New York
.
2.
USEIA
, 2007, “
World Carbon Dioxide Emissions From the Use of Fossil Fuels
,” International Energy Annual 2005, http://www.eia.doe.gov/emeu/iea/carbon.htmlhttp://www.eia.doe.gov/emeu/iea/carbon.html
3.
Davidson
,
R. M.
, 2007, “
Post-Combustion Carbon Capture From Coal Fired Plants—Solvent Scrubbing
,” Technical Report No. CCC/125, IEA Clean Coal Centre.
4.
Bergerson
,
J. A.
, and
Lave
,
L. B.
, 2007, “
Baseload Coal Investment Decisions Under Uncertain Carbon Legislation
,”
Environ. Sci. Technol.
0013-936X,
41
(
10
), pp.
3431
3436
.
5.
Rao
,
A. B.
, and
Rubin
,
E. S.
, 2002, “
A Technical, Economic, and Environmental Assessment of Amine-Based CO2 Capture Technology for Power Plant Greenhouse Gas Control
,”
Environ. Sci. Technol.
0013-936X,
36
(
20
), pp.
4467
4475
.
6.
Katzer
,
J.
,
Ansolabehere
,
S.
,
Beer
,
J.
,
Deutch
,
J.
,
Ellerman
,
A. D.
,
Friedmann
,
S. J.
,
Herzog
,
H.
,
Jacoby
,
H. D.
,
Joskow
,
P. L.
,
McRae
,
G.
,
Lester
,
R.
,
Moniz
,
E. J.
, and
Steinfeld
,
E.
, 2007,
The Future of Coal: Options for a Carbon Constrained World
,
Massachusetts Institute of Technology
,
Cambridge, MA
.
7.
Chalmers
,
H.
,
Chen
,
C.
,
Lucquiaud
,
M.
,
Gibbins
,
J.
, and
Strbac
,
G.
, 2006, “
Initial Evaluation of Carbon Capture Plant Flexibility
,”
Proceedings of the Eight International Conference on Greenhouse Gas Technologies
,
Elsevier
,
Oxford, UK
.
8.
Gibbins
,
J. R.
,
Crane
,
R. I.
,
Lambropoulos
,
D.
,
Booth
,
C.
,
Roberts
,
C. A.
, and
Lord
,
M.
, 2005, “
Maximizing the Effectiveness of Post Combustion CO2 Capture Systems
,”
Proceedings of the Seventh International Conference on Greenhouse Gas Technologies
,
Elsevier
,
Oxford, UK
.
9.
ERCOT
, 2006,
2006 Annual Report
,
ERCOT
,
Taylor, TX
.
10.
Jones
,
S.
, 2006,
Electric Reliability and Resource Adequacy Update
,
ERCOT
,
Taylor, TX
.
11.
Rubin
,
E. S.
,
Chen
,
C.
, and
Rao
,
A. B.
, 2007, “
Cost and Performance of Fossil Fuel Power Plants With CO2 Capture and Storage
,”
Energy Policy
0301-4215,
35
, pp.
4444
4454
.
12.
Rao
,
A. B.
, and
Rubin
,
E. S.
, 2006, “
Identifying Cost-Effective CO2 Control Levels for Amine-Based CO2 Capture Systems
,”
Ind. Eng. Chem. Res.
0888-5885,
45
(
8
), pp.
2421
2429
.
13.
USNETL
, 2007, “
Cost and Performance Baseline for Fossil Energy Plants
,” Technical Report No. DOE/NETL-2007/1281.
14.
ERCOT
, 2007,
Report on the Capacity, Demand, and Reserves in the ERCOT Region: Summer Assessment Update
,
ERCOT
,
Taylor, TX
.
15.
USEIA
, 2007,
Average Cost of Coal Delivered for Electricity Generation by State, Year-to-Date Through October 2007 and 2006
,
USDOE
,
Washington, DC
.
16.
USEIA
, 2008,
,
USDOE
,
Washington, DC
.
17.
USEPA
, 2007, Emissions and Generation Resource Integrated Database (eGRID) Ver. 2.1.
18.
2007,
U.S. Electricity Production Costs and Components
,
NEI
,
Washington, DC
.
19.
IEA
and
NEA
, 2005,
Projected Costs of Generating Electricity: 2005 Update
,
OECD
,
Paris, France
.
20.
ERCOT
, 2006,
,
ERCOT
,
Taylor, TX
.
21.
Pe-Ltd
, 2007,
2006 State of the Market Report for the ERCOT Wholesale Electricity Markets
,
Potomac Economics, Ltd.
,
Austin, TX
.