On the retrofitting and repowering of coal power plants with post-combustion carbon capture: An advanced integration option with a gas turbine windbox

Retrofitting a significant fraction of existing coal-fired power plants is likely to be an important part of a global rollout of carbon capture and storage. For plants suited for a retrofit, the energy penalty for post-combustion carbon capture can be minimised by effective integration of the capture system with the power cycle. Previous work on effective integration options has typically been focused on either steam extraction from the power cycle with a reduction of the site power output, or the supply of heat and electricity to the capture system via the combustion of natural gas, with little consideration for the associated carbon emissions.

This article proposes an advanced integration concept between the gas turbine, the existing coal plant and post-combustion capture processes with capture of carbon emissions from both fuels. The exhaust gas of the gas turbine enters the existing coal boiler via the windbox for sequential combustion to allow capture in a single dedicated capture plant, with a lower flow rate and a higher CO2 concentration of the resulting flue gas. With effective integration of the heat recovery steam generator with the boiler, the existing steam cycle and the carbon capture process, the reference subcritical unit used in this study can be repowered with an electricity output penalty of 295 kWh/tCO2 – 5% lower than a conventional steam extraction retrofit of the same unit – and marginal thermal efficiency of natural gas combustion of 50% LHV – 5% point higher than in a configuration where the gas turbine has a dedicated capture unit.