Numerical Analysis of Hydrogen Sulphide Conversion to Hydrogen during Its Pyrolysis and Partial Oxidation

Abstract

Production of hydrogen during pyrolysis and partial oxidation of hydrogen sulphide is analyzed on the basis of a detailed kinetic model of H₂S oxidation. It is shown that the H₂ yield in the case of H₂S pyrolysis in an adiabatic flow reactor with a residence time of ≈1 s is rather small. Even for the initial temperature of the mixture T₀ = 1400 K, the molar fraction of H₂ is only 12%, though the equilibrium value is reached within the reactor in this case. At T₀< 1200 K, there is no enough time for the chemical equilibrium inside the reactor to be established, and the H₂ concentration is lower than the equilibrium value. At T₀ < 1000 K, the pyrolysis reaction in the reactor practically does not occur. Addition of a small amount of air to H₂S leads to energy release, to an increase in temperature, and, as a consequence, to acceleration of H₂S conversion. The relative yield of H₂ can be increased by several times. For each value of T₀, there exists an optimal value of the fuel-to-air equivalence ratio φ that ensures the maximum H₂ yield in the H₂S–air mixture. The process of partial oxidation at high values of φ > φb and low values of T₀ is essentially nonequilibrium; as a result, the H₂ concentration at the exit from a finite-length reactor can be higher than its equilibrium value, e.g., the relative yield of H₂ can exceed the equilibrium value by 30–40% at T₀ = 800 K and φ = 6–10. The reasons responsible for reaching a “superequilibrium” concentration of H₂ at the flow reactor exit are determined.