Built-in flexibility at retrofitted power plants: What is it worth and can we afford to ignore it?

AbstractMaking best use of existing assets is a high priority for industry, particularly when significant capital expenditure would be required to construct replacement capacity to meet continued demand if they were taken out of service. In this context, the potential to retrofit carbon dioxide (CO2) capture to existing power plants so that they can continue to operate in plausible future scenarios where significant cuts in CO2 emissions are required from the electricity sector has become an increasingly ‘hot topic’. One potentially important characteristic of retrofitted plants that is typically over-looked in assessments of CO2 capture retrofit is that they are likely to have ‘built-in flexibility’. For example, for plants that retrofit post-combustion capture without any significant changes to the power cycle (i.e. that do not undertake a boiler/turbine retrofit at the time as adding capture), it should be technically feasible for the plant to avoid the majority of the efficiency penalty associated with operating CO2 capture by temporarily bypassing the capture unit. The low pressure steam turbine, condenser and generator will be sized so that they are able to use the steam that is diverted away from the CO2 capture unit for power generation without any additional expenditure, since this steam was included in the design flow before capture was fitted. This paper and a related PhD thesis contributes to developing understanding of the potential value of built-in flexibility of coal-fired power plants retrofitted with post-combustion capture and potential enhancements associated with temporary storage of rich solvent. This analysis is important to inform investment and policy decisions and brings together engineering and economic assessment. Thus, it is able to draw robust conclusions that are relevant in determining both priorities for future technical design work and decisions about which modes of operating flexibility may be sufficiently valuable to warrant further analysis within investment appraisal or policy-making related to retrofitting post-combustion capture to pulverised coal plants