Abstract
The influence of O2 concentration on a premixed swirling flame was investigated for changes in discrete levels of CO2 and N2 dilution, with application to carbon capture in gas turbine systems. Chemical kinetic models were utilised to support and analyse generic burner experiments at 37.5kW. O2 mole fraction in the oxygen-diluent stream was varied between 0.21 and 0.70 and careful measurement of velocity field data using particle image velocimetry, representative heat release (OH* chemiluminescence) and flame location (OH planar laser-induced fluorescence) was undertaken. Results show that under lean N2-diluted operating conditions there is a minor change in burner operation for all O2 concentrations considered. CO2 dilution has a far more substantial impact than N2 on flame location, heat release and operational response, which is attributed to the fundamental differences in thermodynamic and transport properties between the two gases. This also resulted in increased CO concentrations sampled from the exhaust stream with a rise in diluent CO2, which is attributed to lower flame temperatures as opposed to thermal dissociation, whilst increased N2 dilution resulted in increasing NOX emissions.
Highlights
Other work demonstrated stability limits of tubular burners with various O2 and CO2 concentrations, proving O2–CH4 flames can be balanced with CO2 as a combustion moderator [13]
Such reaction kinetics have been studied with CHEMKIN to show differences in laminar burning velocity of O2–CH4 mixtures with N2 and CO2 diluents; it should be noted that CO2 contributes to soot oxidization and affects the rate of many chemical reactions compared with N2
There is an increase in CO production as CO2 concentrations rise to β = 0.21 in the CO2diluted flame, whilst a corresponding change in N2 leads to increased NOX formation
Summary
When comparing diluents, limited studies show that at constant mass flux, CO2 diluted flames are stabilised at higher O2 concentrations compared to N2 Such reaction kinetics have been studied with CHEMKIN to show differences in laminar burning velocity of O2–CH4 mixtures with N2 and CO2 diluents; it should be noted that CO2 contributes to soot oxidization and affects the rate of many chemical reactions compared with N2. Premixed O2–CH4 swirl stabilised burners, diluted with N2 and CO2, demonstrated dependence of strain rate through chemical kinetics and flow residence times on flame blowoff [15]. A rapidly mixed tubular burner has shown how oxygen concentration with CO2 and N2 diluents affected stability limits, utilising Damköhler number to describe the flow field in relation to mixing and chemical residence times [16]. This work demonstrated that CO2 dissociation in oxygen– methane flames is not significant at temperatures below 2400 K
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