The composition of CO2 streams can vary due to the specific components in the feedstock, the type of process that is used to convert theinto usable energy, the capture process, and any post-capture processing. Furthermore, the amounts and proportions of various components removed from a raw flue gas stream before CO2 capture (e.g. through de-NOx and/or desulfurisation processes) will affect the relative concentrations of components remaining in the gas stream. Removal of air pollutants from a raw flue gas may already be required in order to comply with the Integrated Pollution Prevention and Control (IPPC), LCP and Industrial Emissions Directives. The concentration of incidental substances in most cases can be decreased by adding additional stages of purification (subject to process limits), albeit at higher costs.
The influence of the different kinds of CO2 capture processes on the composition of the CO2 stream is discussed in the following sections131.
131 Based on Implementation of Directive 2009/31/EC on the Geological Storage of Carbon Dioxide, Guidance Document 2, Characterisation of the Storage Complex, CO2 Stream Composition, Monitoring and Corrective Measures, European Communities, 2011.