Post-Combustion CO₂ Capture Add-on for Power Plants – solid fuels

There are different requirements for flue gas cleaning and preparation for CO₂ capture (dust filters, NOx removal, sulphur scrubbers, etc.) which will influence performance and costs. The performance and cost ranges are considered to be sufficiently close for the variety of solid fuels to group them together in a single factsheet.

Post-combustion capture can be attached to an existing power plant or incorporated in the design of a new plant, the latter with potential for increased efficiency and lower total costs. The focus of this factsheet is add-on capture for a stand-alone plant, regardless of age or type of solid fuel, and therefore does not take into account potential efficiency gains or cost reductions from integrated design of new plants.

Post-combustion CCS generally entails capture from flue gases with low CO₂ concentrations. In the case of solid fuels CO₂ concentrations are generally below 15% (IPCC, 2005; IEAGHG 2013). There are a variety of techniques that can be used to separate CO₂ from the flue gas, including using sorbents/solvents, membranes and distillation machinery. Chemical solvents, such as Mono-Ethanolamine (MEA), are the most commonplace technique for post-combustion capture for power plants (IPCC 2005), therefore they are considered the default for this factsheet. After CO₂ capture, a regeneration step is required to release the CO₂ and clean the solvent so it can be reused.

By adopting amine technology, 85-95% of CO₂ can be captured from the flue gas (IPCC, 2005). Energy requirements for capture and compression of CO₂ lead to higher fuel consumption, hence net CO₂ reductions achieved are lower than the capture rate. CO₂ emission reduction rates for coal power plant retrofits range from 63%-94%, depending on whether emissions from auxilliary energy supply are captured or not (IPCC, 2005; Rubin et al., 2015a, Mantripragada, 2019).

Compression and dehydration of CO₂ is part of the capture process. CO₂ pressure after capture varies from 8 MPa to 20 MPa in the studies cited here. At these pressure levels it is possible to transport the CO₂ through low-pressure pipelines (maximum pressure of 4.8 MPa) or high-pressure pipelines (minimum of 9.6 MPa) (IPCC 2005) with minimal additional (de)compression required. It is therefore assumed that no additional compression step is required after capture to prepare the CO₂ for pipeline transport. If CO₂ is transported in liquid state, then additional compression will be required.