Enhancing dynamic response of power plant with post combustion capture using “Stripper stop”

• A fast primary response of post combustion CCS power plants to frequency drops is proposed.
• Temporary reduction of capture solvent stripping steam is the method proposed.
• The dynamic response of the method has been explored in a simple model.
• The modelling results indicate that a significant additional fast primary response is possible.
• Practical tests on demonstration units and development of advanced controls will be required.

Fitting a power plant with carbon dioxide capture and storage (CCS) will modify its dynamic behaviour. It may impact on the flexibility to turn the plant capacity up and down and operate efficiently at reduced load. Post combustion capture is likely to be fitted to supercritical steam power plants which are less able to respond to rapid changes in output demanded by grid connection codes. Throttling of the steam prior to entering the HP turbine allows some energy to be stored for rapid release but is likely to be insufficient and also impacts on plant efficiency. Special measures such as “condensate stop” in which steam normally extracted from the steam turbines of the power plant for feedwater heating is temporarily diverted to the turbines to generate more power is one proposed method of providing fast primary response. This paper explores another possibility applicable to post combustion capture systems in which the LP steam normally extracted to supply the solvent regenerator reboiler is temporarily reduced or stopped. By allowing the pressure in the regenerator to fall stripping can continue during the period of primary response. Thus capture of CO2 is not interrupted. It is shown that sufficient hold up of hot solvent in the bottom of the solvent regenerator could be provided to provide a significant portion of the required primary response to frequency drop events which typically can call for 10% rated power increase in 30 s. A simple simulation of the dynamic process has been made and the extent of pressure and temperature drops required in the stripper evaluated. A number of control and process issues are identified on which further theoretical and practical experimental work would be needed.