An experimental, theoretical and kinetic-modeling study of hydrogen sulfide pyrolysis and oxidation

Abstract

Hydrogen sulfide chemistry has recently undergone a renewed interest due to the current energy transition, requiring a proper treatment of such impurities in the sources like shale gas or biogas. Moreover, the lower-temperature, diluted conditions considered nowadays for reducing pollutant emissions require a wider-range development and validation of the pyrolysis and oxidation mechanisms. In this work, this was addressed through an experimental campaign carried out in three reactor facilities, namely a jet-stirred reactor and two flow reactors. A wide range of operating conditions could thus be covered, in terms of equivalence ratios under lean conditions (0.018≤Φ≤0.5), temperatures (400K≤T≤2000K) and residence times (0.1s≤τ≤2s). The mole fractions of reactants (H2S, O2), products (SO2, H2O) and intermediates (H2) were measured. In parallel, a kinetic mechanism of H2S pyrolysis and oxidation was developed by including the latest available kinetic rates on sulfur pyrolysis and oxidation chemistry, which were added to a core H2/O2 module, previously validated. Such a mechanism included a re-evaluation of selected key reaction steps, identified via sensitivity analysis. Results showed a general agreement of the experimental measurements with predictions: in the case of pyrolysis, the thermal decomposition reaction (H2S + M = H2 + S + M) was identified as the sole controlling step: a critical choice of the kinetic rate had to be made, due to the significant disagreement among the literature rates. Concerning oxidation, the H-abstraction from H2S by O2 was found to be the major bottleneck at the lowest temperatures, with HO2 becoming a key abstractor, too, under very lean conditions. At higher temperatures, a key role was played instead by the H-abstraction of H2S with S (H2S + S = SH + SH), acting in the reverse direction and providing S radicals, boosting the oxidation process.

Topics & Concepts