Optimal post-combustion conditions for the purification of CO2-rich exhaust streams from non-condensable reactive species

The presence of a significant amount of oxygen and/or other non-condensable 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 processes. More specifically, oxygen, as well as other non-condensable species, increases the compression work required for the liquefaction of CO2. Furthermore, residual oxygen in CO2 streams used for EOR (Enhanced Oil Recovery) operations reacts with hydrocarbons in oil field both causing an overheating at the injection point and a higher oil viscosity increasing 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 on the post-oxidation processes of a CO2 rich gas stream, with composition typical of a CO2-capture-ready system, aimed to outline operative 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. Attention was focused on output streams of oxy-combustion plants.High temperatures and elevated levels of dilution of inlet streams make such a post-combustion process work in conditions typical of MILD combustion. Characteristic kinetic 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 main variables that influence the post-oxidation process such as inlet temperature system, composition of feed mixture, fuel and nature of diluent species.

► We consider the oxygen reduction in CO2 stream to be sequestrated.
► MILD post-combustion process is feasible to reduce O2 in CO2 streams.
► Characteristic Kinetic times of the process are compatible with practical applications.
► We identify the conditions to achieve the target concentration of undesired species.