Pressurized oxy-combustion is a promising new technology for coal-fired power production that can deliver high combustion efficiency with a concentrated CO_2 stream suitable for carbon sequestration or utilization. In this approach, the combustion takes place at elevated pressure, e.g. 15 bar, such that the dew point of the combustion flue gas is raised and the latent heat is recovered. Prior to final compression for storage or utilization, gaseous pollutants (primarily NO, NO_2 and SO_2) must also be removed from the combustion exhaust stream. If not carefully removed, harmful acid condensation and corrosion can occur in downstream equipment. Pressurized oxy-combustion provides an opportunity fora new method of pollutant removal, which uses direct water contact for flue gas cooling and latent heat recovery combined with simultaneous purification via pollutant adsorption and complex liquid phase chemistry. However, several important aspects require further research before large scale implementation is possible - primarily the determination of reaction kinetics and the effect of scaling up. We have investigated these aspects using two different reactors, a bench scale CSTR and a 100-kW prototype column. An ASPEN™ model was also developed in parallel to provide a numerical sub-model for integration into a full-scale process model of a Staged, Pressurized Oxy-Combustion power plant. The CSTR experiments investigate the interaction between nitrite and sulfite in the liquid phase, quantifying parallel reaction rates for the formation of nitrous oxide (N_2O) and hydroxylamine disulfonic acid (HADS). The results determine the effects of pH, nitrite and sulfite molar ratio, and temperature in the initial formation period of N_2O and HADS, determining the liquid species composition at each concentration, temperature and reaction time applicable for commercial scrubbing columns. A kinetic model was developed from these results, describing the dependencies experimentally measured. The larger prototype column utilizes the liquid phase kinetics and process model to scale up the liquid chemistry as function of gas pressures, temperatures, flowrates, and pollutant concentrations equivalent to a 100-kWth oxy-combustor output. The primary objective of the column is to optimize parameters to maximize flue gas purification while controlling liquid discharge temperature and heat recovery. The practical implications can lead to a reduction in costs and risk associated with flue gas purification and carbon capture, and can provide an additional efficiency gains for new, low CO_2 coal power plants.
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