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For CO 2 capture and storage deployment, the impact of impurities in the gas or dense phase CO 2 stream arising from fossil fuel power plants, or large scale industrial emitters, is of fundamental importance to the safe and economic transportation and storage of the captured CO 2 . This paper reviews the range and level of impurities expected from the main capture technologies used with fossil-fuelled power plants in addition to other CO 2 emission-intensive industries. Analysis is presented with respect to the range of impurities present in CO 2 streams captured using pre-combustion, post-combustion and oxy-fuel technologies, in addition to an assessment of the different parameters affecting the CO 2 mixture composition. This includes modes of operation of the power plant, and different technologies for the reduction and removal of problematic components such as water and acid gases (SO x / NO x ). A literature review of data demonstrates that the purity of CO 2 product gases from carbon capture sources is highly dependent upon the type of technology used. This paper also addresses the CO 2 purification technologies available for the removal of CO 2 impurities from raw oxy-fuel flue gas, such as Hg and noncondensable compounds. CO 2 purities of over 99 % are achievable using post-combustion capture technologies with low levels of the main impurities of N 2 , Ar and O 2 . However, CO 2 capture from oxy-fuel combustion and integrated gasification combined cycle power plants will need to take into consideration the removal of non-condensables, acid gas species, and other contaminants. The actual level of CO 2 purity required will be dictated by a combination of transport and storage requirements, and process economics.

A technique that is an extension of an earlier approach for marine sediments is presented for determining the acoustic attenuation and backscattering coefficients of suspensions of particles of arbitrary materials of general engineering interest. It is necessary to know these coefficients (published values of which exist for quartz sand only) in order to implement an ultrasonic dual-frequency inversion method, in which the backscattered signals received by transducers operating at two frequencies in the megahertz range are used to determine the concentration profile in suspensions of solid particles in a carrier fluid. To demonstrate the application of this dual-frequency method to engineering flows, particle concentration profiles are calculated in turbulent, horizontal pipe flow. The observed trends in the measured attenuation and backscatter coefficients, which are compared to estimates based on the available quartz sand data, and the resulting concentration profiles, demonstrate that this method has potential for measuring the settling and segregation behavior of real suspensions and slurries in a range of applications, such as the nuclear and minerals processing industries, and is able to distinguish between homogeneous, heterogeneous, and bed-forming flow regimes.

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