Hydrogen sulphide oxidation under claus furnace conditions

The oxidation of hydrogen sulphide under Claus furnace conditions (800 to 1500°K and one atmosphere pressure) was studied theoretically and experimentally. Equilibrium compositions of mixtures resulting from reactions, between H₂S and air were calculated for temperatures and O₂/H₂S ratios ranging from 600 to 2000°K and 0.05 to 1, respectively. Forty-four compounds containing nitrogen, hydrogen, oxygen and sulphur were assumed to be present at equilibrium, but only 25 had concentrations exceeding 0.1 ppm. Eleven carbon compounds were later included, but only five of them had. concentrations greater than 0.1 ppm. Sulphur yields in the furnace were found to increase about 10% when O₂/H₂S ratios less than 0.5 (stoichiometric) are used. Feed impurities such as NH₃.(below 1600°K), H₂O and CO₂ diminish the sulphur yields. A computer model was developed to simulate a Claus plant consisting of a furnace and two catalytic converters operating adiabatically. The model showed that the maximum sulphur yields for the plant are obtainable when operating with stoichiometric air. Preheating the furnace feed or recycling part of the furnace products enhances the overall yield only slightly. Enriching the combustion air with pure oxygen causes the sulphur yield to drop since, with N₂ absent, the furnace temperature rises to over 2200°K. Above 1750°K, the sulphur yield falls with temperature. To determine equilibrium compositions experimentally, various mixtures of known H₂S/air ratios were introduced into a quartz vessel located in a furnace and operating between 800 and 1500°K. The contents of this vessel were sampled and analysed by gas chromatography. Experimental measurements for H₂S dissociation were in excellent agreement with Raymont's results and theoretical predictions. Results for H₂S oxidation showed the same trend as the theoretical predictions, but did not agree quantitatively; the experimental sulphur yields exceeded the predicted values by up to 15%. Reasons for these discrepancies are discussed.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat