Chemical kinetic evaluation of optimal post-combustion condition for non-condensable species reduction from CO2-rich exhaust streams

The presence of a significant amount of oxygen and/or other incondensable species in flue gases of CO2-capture-ready combustion systems is a relevant issue to be solved to avoid problems in CO2 sequestration and storage process. As matter of facts, oxygen as well as other non-condensable species, increases the compression work required for the liquefaction of CO2. Furthermore it was highlighted that residual oxygen in the CO2 streams used for EOR (Enhanced Oil Recovery) operations reacts with hydrocarbons in oil field causing an overheating at the injection point, a higher oil viscosity and increased extraction cost. Post-oxidation process is a feasible and economical possibility to reduce oxygen and non- condensable/oxidizable species (such as H2 and CH4) concentration to one digit ppm (or ppb) levels and obtain high purity CO2 streams that can be used for sequestration or EOR. This paper presents a numerical study of oxidation processes of a CO2 rich gas stream, reproducing those typical at the exit of a CO2-capture-ready combustion system, aimed to outline reaction conditions useful to achieve a significant reduction of the gas contaminants below the minimum required level allowing for a useful use of the resulting CO2 stream for storage or EOR purposes. High temperatures and elevated level of dilution of inlet streams put this post-combustion process in conditions typical of MILD combustion. For these reasons it appeared natural to face the problem with the approach usually followed by this research group in studying this class of combustion processes. Characteristic kinetics times and key species concentrations at steady state were evaluated in order to study the evolution and the completion of the oxidation process. Such parameters were correlated to the main variables that influence post-oxidation process such as inlet temperature system, composition of feed mixture, fuel and nature of diluent species.