Introduction

To-date, capture technology developers have largely focused on designing plant for CO₂ capture rates of 85% to 90%, leaving 10-15% of the emissions uncaptured, which are usually referred to as residual emissions. In a “well below 2°C” scenario, it is projected that net zero carbon emissions would be required by early in the second half of this century. A review of the literature indicated that there were no technical barriers to increasing capture rates in the three classic CO₂ capture routes (post-, pre- and oxyfuel combustion) and with the broad suite of CO₂-capture technologies currently available or under development. A techno-economic analysis of a standard PCC process applied to both coal- and gas-fired power plants revealed that, with dedicated process design, the additional costs of achieving essentially zero CO₂ emissions were quite modest in comparison with the costs of achieving 90% CO₂ capture. For coal-fired power stations, the analysis found that using biomass co-combustion (10% biomass) combined with a standard PCC process (90% CO₂ capture) was the lowest cost option.

Key Messages

• Fossil fuel power plants equipped with carbon capture and storage (CCS) need to demonstrate a pathway to zero CO₂ emissions if they are to have the same greenhouse gas footprint as competing new power generation technologies, such as renewables, and particularly if the technology is to contribute cost-effectively to a ‘2°C’ or ‘well below 2°C’ scenario by the year 2100.

• Carbon dioxide (CO₂) capture rates from fossil fuel power plants applied in almost all integrated assessment models (IAMs), front-end engineering and design (FEED) studies, pilot plants, demonstration plants and technical analyses are currently based on a 90% capture rate cap, regardless of the technology type, the location or the fuel type.

• A literature review undertaken as part of this study exposes the 90% capture rate cap as an artificial limit. It is an historical benchmark, originally based on the economics of capture. The review indicated there were no technical barriers to increasing capture rates beyond 90% in the three classic capture routes (post-, pre- and oxyfuel combustion) and with the broad suite of CO₂ capture technologies currently available or under development.

• As CO₂ capture rates are increased, however, indirect emissions from fossil fuel use become significant, i.e. as the direct emissions tend to zero, the indirect emissions become proportionately greater. This is a factor to be managed in reducing overall CO₂ emissions, particularly in the fuel supply chains.

• This study provides a techno-economic analysis of a standard post-combustion capture (PCC) process applied to fossil fuel-fired power plants. It has revealed that, with dedicated process design, the additional costs of achieving essentially zero CO₂ emissions were quite modest in comparison with the costs of achieving 90% CO₂ capture. For 99.7%[1] CO₂ capture on an ultra-supercritical (USC) coal plant with CCS, the levelised cost of electricity (LCOE) increased by 7% and the CO₂ avoided cost by 3%. For 99%¹ CO₂ capture on an NGCC plant with CCS, the costs increased by 7% and 8%, respectively. It is essential that these findings are now demonstrated in practice.

• Where the achievement of high capture rates for a particular capture technology proves more challenging, either a hybrid capture approach or a combination with biomass co-combustion may offer more success.

• For coal-fired power stations, the option of using biomass co-combustion (10% biomass) combined with a standard PCC process (90% CO₂ capture) was the lowest cost option to achieve zero emissions, but is dependent on the region of deployment. The techno-economic study undertaken for this study indicated that, for a USC coal plant with CCS, the LCOE increased by 2% and the CO₂ avoided cost by 1.5%.

• Techno-economic analyses of other process routes and capture technologies need to be undertaken and, if warranted, validated by demonstration.