Numerical Analysis of Hydrogen Sulphide Conversion to Hydrogen during Its Pyrolysis and Partial Oxidation
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.
Keywordshydrogen production hydrogen sulphide pyrolysis partial oxidation kinetic mechanism simulation
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