New IEAGHG report: 2022-08 Start-Up and Shutdown Protocol for Power Stations with CO₂ Capture

In modern power grids, a power plant with CO₂ capture will be required to operate as a low-carbon, flexible, dispatchable power generator. With increased penetration of intermittent renewables, greater load-following is likely and a rise in the frequency of start-up/shutdown cycles would be expected. If it transpired that frequent start-up/shutdown cycles resulted in appreciable CO₂ emissions, it could undermine the value proposition of including modern, flexible, dispatchable fossil fuel power generation assets in the grid even though CCUS applied to them could enhance energy security and grid resilience.

As limited work to-date has focused on the impact of start-up and shutdown of CO₂ capture plants, this study serves to broaden understanding of the dynamics of these processes, identifying key factors that impact CO₂ capture performance and operability. Factors shown to be important include the solvent inventory volume, the initial start-up temperature (cold vs hot) and the timing of steam availability.

Using a larger solvent inventory can be beneficial in terms of maximising the cumulative CO₂ capture rate from start-up, through steady state operation and shutdown, particularly in the case of cold start-ups. Overall, hot start-ups showed a significantly higher cumulative CO₂ capture rate and lower specific reboiler duty compared to cold start-ups. The ability to sustain high CO₂ capture rates depends on the volume of the solvent inventory, the amine concentration, the starting solvent CO₂ loading, and the timing of steam supply to the reboiler.

Results demonstrated that, during start-up, any delay in steam supply to the capture plant significantly reduces the cumulative CO₂ capture rate, thereby greatly increasing the residual CO₂ emissions. Start-up with preheating was shown to be a potentially valuable approach. During hot start-up, measures such as high preheating and lower solvent loading, were shown to markedly improve capture performance.

In the context of a net-zero energy system, the need for operational flexibility will rise. Hence, the ability to maximise the CO₂ capture rate during start-up and shutdown will be highly valuable as it reduces residual CO₂ emissions from power plants, thus easing the need for carbon offsets from CO₂ removal technologies, e.g., bioenergy with CCS, or direct air capture.