International Journal of Greenhouse Gas Control 8 (2012) 180–195 Contents lists available at SciVerse ScienceDirect International Journal of Greenhouse Gas Control j our na l ho me p age: www.elsevier.com/locate/ijggc Optimizing post-combustion CO 2 capture in response to volatile electricity prices Stuart M. Cohen a,∗ , Gary T. Rochelle b , Michael E. Webber a a Department of Mechanical Engineering, The University of Texas at Austin, 1 University Station C2200, Austin, TX 78712, USA b Department of Chemical Engineering, The University of Texas at Austin, 1 University Station C0400, Austin, TX 78712, USA a r t i c l e i n f o Article history: Received 11 August 2011 Received in revised form 15 February 2012 Accepted 17 February 2012 Available online 17 March 2012 Keywords: CO2 capture Flexibility Economics Electricity markets Optimization Amine scrubbing a b s t r a c t Flexibly operating CO 2 capture at power plants allows a temporary increase in electrical output, which could help maintain grid reliability, meet peak demand, or improve profitability when electricity prices are high. This article presents a versatile optimization model that maximizes profits at a fossil-based power plant with CO 2 capture by operating in response to volatile electricity prices. The model is demon- strated for a 500 MW coal-fired unit using 7 molal monoethanolamine for post-combustion CO 2 capture. The importance of modeling electricity price volatility when valuing flexible capture is demonstrated by comparing model results to those from a first-order electricity dispatch model that does not incorporate price volatility. CO 2 emissions and plant economics are then compared for operation under three 20- year CO 2 price paths and four facility configurations: no CO 2 capture, inflexible CO 2 capture, flexible CO 2 capture that vents CO 2 at partial load, and flexible capture that uses solvent storage to mitigate venting at partial load. Flexible capture improves investment value over inflexible capture while maintaining substantial CO 2 emissions reductions, but economic benefits are greatest at low CO 2 prices where CO 2 capture investment might still be unjustifiable. Flexibility provides the greatest economic advantage if CO 2 prices are $40–50 per metric ton of CO 2 for a substantial portion of plant economic life. Solvent storage permits greater operating profits and lower CO 2 emissions than a venting-only flexible capture facility, but benefits can be offset by increased capital costs. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Introduction to flexible CO 2 capture Carbon dioxide capture and sequestration (CCS) enables con- tinued fossil fuel use for electricity production and industrial processes with substantial reductions in emissions of carbon dioxide (CO 2 ), the greenhouse gas primarily contributing to anthro- pogenic climate change (Metz et al., 2005). The largest application for CO 2 capture is electricity production, but while leading CO 2 capture technologies can remove 90% or more CO 2 from power plant flue gas, the energy requirements for leading CO 2 capture and compression technologies can reduce net electrical output by 20–30% (7–11% efficiency points) below that of facilities without CO 2 capture (Chalmers et al., 2010; Rochelle et al., 2011). Most studies assume that CO 2 capture and compression systems oper- ate continuously whenever the base plant operates, so any energy required for CO 2 capture and compression permanently reduces output and increases electricity production costs (Davison, 2007; Rubin et al., 2007). However, there is a growing attention to the ∗ Corresponding author. Tel.: +1 512 232 2754; fax: +1 512 471 1045. E-mail addresses: stuart.cohen@utexas.edu (S.M. Cohen), gtr@che.utexas.edu (G.T. Rochelle), webber@mail.utexas.edu (M.E. Webber). value of operating some or all CO 2 capture systems at partial or zero load and utilizing this flexibility to operate CO 2 capture in response to variable electricity market conditions (Chalmers et al., 2009, 2010; Husebye et al., 2010; Ludig et al., 2010). If the base plant must ever operate variably, some degree of CO 2 capture flexibility is needed to ensure stable operation across the base plant power output range (Davison, 2010). However, this work defines flexible CO 2 capture as operating CO 2 capture sys- tems at a different, typically lower, fractional load than the base power plant. With sufficient turbine-generator capacity and a cap- ture system conducive to flexible operation, reduced load on energy intensive CO 2 capture systems during full-load base plant opera- tion could allow net power output to approach non-capture levels. Alternately, operating the base plant at minimum load while all flue gas is treated by CO 2 capture reduces the net minimum power output, which could be desirable if electricity prices fall below oper- ating costs for too short a time to justify the costs of base plant shutdown and startup (Chalmers et al., 2009). Using flexible CO 2 capture to temporarily increase power output is valuable during periods of peak electricity demand. In a retrofit application, doing so eliminates the need to invest in new gen- erating capacity to replace the output lost to CO 2 capture energy requirements, and peak demand infrequency prevents any signifi- cant CO 2 emissions increase (Cohen et al., 2010b; Wiley et al., 2010). In electricity systems with deregulated markets, partial or zero load 1750-5836/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijggc.2012.02.011