استراتژی های عملیاتی انعطاف پذیر برای نیروگاه های زغال سنگ و گاز CCS Flexible operation strategies for coal- and gas-CCS power stations under the UK and USA markets

1. Introduction and scope Carbon capture and storage (CCS) has been proposed as a means to enable a least-cost transition to a low carbon energy system and is also important for decarbonizing the industrial sector [1]. Given the increasing penetration of intermittent renewable electricity generation and the inflexible nature of traditional nuclear power generation, decarbonised power plants need to be designed for flexible operation in order to be able to promptly respond to variation in electricity demand [2] and to exploit the associated variation of electricity prices, while maintaining the carbon intensity of the plant at low levels [3]. Flexible capture can be achieved in a range of ways. At the level of an individual power plant, flexible operation can be achieved using measures such as adding a solvent storage tank, bypassing the capture facility for certain time periods or operating the capture facility at different capture rates according to electricity output requirements (time varying solvent regeneration). To the best of our knowledge, the concept of flexible operation, was first introduced by Gibbins and Crane [4] in 2004, noting that this study makes reference to private communication with Prof Rochelle1 on this subject in 2002. In the 2004 study, the concepts of solvent storage and exhaust gas venting (or capture bypass) were first introduced. Subsequently, several contributions focused on flexible operation of the capture process as a way to improve the economics of CCS power plants either by reducing the capture level through exhaust gas venting, by storing the solvent using rich and lean amine storage tanks or by varying the degree of solvent regeneration [3, 5-12]. In the solvent storage strategy, two solvent storage tanks are added between the absorber and the stripper. If solvent storage is available then a portion of the rich solvent can temporarily be stored, rather than being sent to the desorber for immediate regeneration. This stored rich solvent can then be subsequently regenerated by adding it to rich solvent generated by ongoing operations during a period of relatively low electricity prices. Previously-stored lean solvent from another tank is used to allow capture to continue. With the exhaust gas venting option, the power plant operates at times with partial or no capture of the CO2. Under this strategy, the energy required for solvent regeneration is anticipated to be reduced or eliminated by venting a portion of the exhaust gas directly to atmosphere. Thus, the steam that would have been used for solvent regeneration is instead not extracted, resulting in increased net power output. In the time varying solvent regeneration strategy, we use the working solvent as means to provide flexibility to the power plant. This is achieved by allowing CO2 to accumulate in the solvent during hours of peak electricity prices and regenerating the solvent during off-peak periods.