Retrofitting CO₂ Capture to Existing Power Plants

Publication Overview

The main purpose of this report is to examine, at a generic level, the scope for cutting CO₂ emissions from suitable existing fossil fuel plants by retrofitting CCS to them, as an alternative to replacing them with new build fossil fuel plants with CCS.  In this context it should be seen as a discussion of preliminary screening assessment methods to address the general issue of ‘under what conditions might it be worth considering retrofitting CCS to an existing fossil power plant, instead of replacing it by a new plant with CCS’?  As a generic study though it cannot address either future costs for construction, fuel etc. or site- and region-specific questions that will govern the feasibility and cost of a specific retrofit project, although it does discuss some of the principles involved and examine sensitivities. Nor does it make comparisons with other options for emission reductions from a particular site, such as fuel switching from coal to gas.

Publication Summary

• The cost of abatement for different retrofit options is not directly affected by the efficiencies of the plants concerned (as noted above). Some factors are, however, affected by base power plant efficiency, e.g. retrofits to lower efficiency plants cost more per unit electricity produced but capture correspondingly more CO₂. 
• While retrofit abatement costs do not vary significantly with efficiency, replacement abatement costs do vary. Hence at existing plants with low base plant efficiency, replacement with new build plant will become a cheaper way of reducing existing plant CO₂  As noted above, a definite efficiency threshold below which replacement would be preferred cannot specified since the retrofit/replacement decision depends on a number of parameters.
• For a range of conditions that might be encountered in practice it appears that the reduced capture costs for new build CCS plants may be offset by the much higher capital cost of the base power plant itself compared to a retrofit, even if some level of refurbishment to the base power plant is required to achieve an adequate retrofit project life.
• A wide range of theoretical options appear to exist for effective integration of post-combustion (and oxyfuel[1]) capture equipment with the steam cycles of existing coal and gas power plants, which would allow electricity output penalties per tonne of CO₂ captured to be achieved that are close to those for new build plants using the same capture technology.
• If the electricity output of the plant is to be maintained on-site then additional fuel should be used in ways that deliver as much electricity as possible (i.e. natural gas turbine combined cycle or high-pressure steam coal CHP plants); unless a large increase in power output is required it is most effective to combine this 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 turbines to make up the power loss, and meet some of the heat requirements, of post-combustion capture retrofits to existing coal plants.