Background

Retrofitting CCS to existing power plants is one of the many ways of substantially reducing CO2 emissions from power generation; others include replacing existing fossil fuel power plants by new power plants with CCS or the use of renewable or nuclear energy. Partial reductions of emissions can be achieved by efficiency improvements and switching to lower carbon fuels.

Global rollout of proven CCS technologies on power plants is not expected to commence until 2020 at the earliest but deep reductions in emissions from electricity generation are expected to be required by as early as 2030 in some developed countries and by 2050 globally, well within the lifetimes of some existing power plants and plants that will be built between now and the time when CCS becomes widely available. It is therefore likely that some of these plants will have to either close prematurely to be replaced by new low-CO2 sources of electricity or they will have to be retrofitted with CCS. A programme of CCS retrofits would require less construction activity than replacement by new power plants. This could allow CO2 capture to be deployed more quickly than would be possible if new plants must be built before any CO2 capture can be implemented.

This study assesses at a generic level the relative merits of retrofitting CCS to existing power plants and building new plants with CCS. As such it focuses mainly on the question “is CCS retrofit worth doing” rather than “can it be done”. The latter would need to be addressed by detailed site specific studies for individual plants, examples of which are being undertaken by other organisations. However, the study also reports on high-level assessments of the potential for CCS retrofits in various countries: the USA, UK and China.

IEAGHG commissioned IC Consultants Ltd to carry out this study and the work was undertaken by staff of the University of Edinburgh, Imperial College London and the University of Cambridge.

Conclusions

• The decisions that face power generators when they have to reduce greenhouse gas emissions are complex. There are many options other than retrofit or new build CCS and many location-specific criteria will affect decisions about whether or not to retrofit CCS.

• For a range of conditions that might be encountered in practice it appears that the costs of electricity from power plants retrofitted with CCS may be lower than from new build power plants with CCS. Lower costs of CO2 capture at new build power plants compared to retrofits may be offset by the higher capital cost of the base power plant itself, even if some level of refurbishment to the base power plant is required to achieve an adequate retrofit project life.

• For new power plants that are being built now, which will be the existing plants of the future, concerns about plant life after retrofit are reduced. Additionally, concerns about unduly high retrofit costs should be avoided if current new power plants are built capture ready.

• CCS retrofits to plants with lower efficiencies will tend to have higher generation costs and so are generally less likely to be competitive with new build CCS replacements, but the strong effect of other site-specific factors on retrofit generation costs makes a definite minimum efficiency threshold for retrofitting inappropriate. Costs of abatement ($/t CO2) for retrofits are essentially independent of the original plant efficiency, since changes in generation costs with efficiency are balanced by changes in carbon emission reduction.

• A wide range of theoretical options exist for effective integration of post-combustion and oxyfuel capture equipment with the steam cycles of existing coal and gas power plants, which would result in electricity output penalties per tonne of CO2 captured that are close to those for new build plants using the same capture technology.

• If the electricity output of the plant site is to be maintained after retrofit then additional fuel should be used in ways that deliver as much electricity as possible consistent with the need also to provide heat for the capture plant (i.e. natural gas turbine combined cycle CHP (combined heat and power) or coal-fired high-pressure steam CHP plants). Unless a large increase in power output is required, for post combustion capture it is most effective to combine a CHP plant with some steam extraction from the main steam turbine. As a specific example of the above, while natural gas prices remain attractive it may be advantageous to use relatively small natural gas combined cycle units to make up the power loss and then to meet any heat requirements for a post-combustion capture unit partly by using heat from the new combined cycle plant and partly by extracting steam from the existing steam turbine.

• Surveys of existing plants using Google Earth/Map images in the USA, China and the UK suggest significant numbers of sites exist with space to add capture equipment and likely access to storage, although a number of uncertainties remain to be resolved and further work is required in this area.

• The overall conclusion arising from this work is that retrofitting CCS to existing power plants is worth examining objectively as an alternative to closing down existing plants and replacing them with new build plants, when a reduction in CO2 emissions from an existing fossil power plant fleet is required. A general rejection of retrofitting on grounds such as the age or lower efficiency of existing plants is not justified.
   

Recommendations

• The initial national surveys of retrofit-related characteristics of existing power plants reported in this study could be extended as ongoing reference databases covering more countries. These could be upgraded on an on-going basis by detailed data from site-specific engineering studies that might be carried out and by the addition of further data on other relevant factors such as location and capacity of CO2 storage.