Effect of oxygen enrichment in air on acid gas combustion under Claus conditions

The effect of oxygen enrichment (using a mixture of oxygen and nitrogen) in the oxidant on the combustion of acid gas (H₂S and CO₂) in hydrogen fuelled flames is examined under Claus condition (at equivalence ratio of Φ=3). The acid gas composition examined was 50% H₂S/50% CO₂ at different percentages of oxygen enrichment (0%, 19.5% and 69.3%) in the oxygen/nitrogen mixtures. Combustion of acid gas formed SO₂ with increase in 0₂ mole fraction. The results showed that an increase in oxygen enrichment to combustion air results in reduced formation of elemental sulfur while simultaneously increasing the amounts of SO₂ that is less favorable. This is attributed to the release of oxygen from CO₂ at high temperatures into the reaction pool. Moreover, the mole fraction of carbon monoxide increased at increased oxygen enrichment which is an indicator of increased release of oxygen into the reaction pool. Other sulfurous-carbonaceous compounds formed (primarily COS and CS₂) are due to the presence of carbon monoxide. The results showed mitigation of CS₂ formation with oxygen enrichment in the combustion process and increased rate of COS formation from the increased availability of CO due to the dissociation CO₂ at higher temperatures. The reduction in CS₂ formation helps to improve efficiency of sulfur capture in Claus thermal reactor.