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