Designing Carbon Capture power plants to assist in meeting peak power demand

The designs of power plants fitted with carbon capture have been evaluated in many studies in order to establish the additional costs and efficiency reductions. Such studies generally focus on plants providing base load power with continuous capture of CO2. The energy efficiency and power output of such plants is significantly reduced because of the parasitic heat and power requirements of the capture process. Typically the efficiency reduction is 8–12% which means that if the capture process could be turned off roughly 20–30% more power could be delivered [J. E. Davison, Performance and costs of power plants with capture and storage of CO2, Energy 32 (2007) 1163–1176]. This paper examines options to extend the flexibility of power plants fitted with carbon dioxide capture to allow additional electrical demand to be met at times of peak capacity. One reason for designing and operating CCS plant in this way would be the high prices which usually prevail during periods of peak demand. Another reason of rising importance is to support the increasing amount of “variable” sources of power from renewables, particularly wind energy which are being connected to the electrical grid [H. Holttinen, Estimating the impacts of wind on power systems, Modern Power Systems, 28 (5) (2008) 49–52]. Options fall into two classes, those which result in cessation of some or all CO2 capture and those which maintain CO2 capture and hence revenues from emission certificates. The former option is shown to be economically unattractive unless peak prices are extremely high or carbon prices become extremely low. The abilities of each the three main capture technologies of pre, post and oxy combustion to modify their operation and design to provide some economic peak power capability are reviewed. There are two options to do this, one is to design the units so that they can operate at reduced capacity while retaining their normal CO2 capturing functionality. The other is to temporarily suspend energy consuming parts of the capture process. The technical operational and economic implications of doing the latter are discussed.