Effect of Oxygen enrichment on Acid Gas Combustion under Claus Conditions

Abstract

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 O2 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.