Homogeneous ignition of H2/CO/O2/N2 mixtures over palladium at pressures up to 8 bar

Ran Sui, John Mantzaras, Chung K. Law, Rolf Bombach, Meysam Khatoonabadi

Research output: Contribution to journalConference articlepeer-review

Abstract

The catalytic and gas-phase combustion of fuel-lean H2/CO/O2/N2 mixtures over palladium was studied experimentally and numerically at a global equivalence ratio Φ = 0.285, H2/CO volumetric ratios of 1-4, pressures of 1-8 bar and catalyst surface temperatures of 950-1200 K. In situ planar laser induced fluorescence (PLIF) of the OH radical was used to monitor homogeneous combustion inside a channel-flow catalytic reactor, while 1-D Raman measurements of main gas-phase species concentrations across the channel boundary layer were conducted to evaluate the heterogeneous processes. Simulations were carried out with a 2-D numerical code using detailed heterogeneous and homogeneous chemical reaction mechanisms and realistic transport. The simulated and measured transverse species profiles attested to a transport-limited catalytic conversion of H2 and CO at all operating conditions. The OH-PLIF measurements and the simulations confirmed the establishment of appreciable homogeneous combustion only for p < 4 bar, with progressively diminishing gas-phase contribution as the pressure increased from 4 to 8 bar. This strong pressure dependence reflected the complex pressure/temperature dependence of the homogeneous ignition chemistry as well as the competition between the catalytic and gaseous reaction pathways for H2 and CO consumption. Over the gaseous induction zones, the wall temperatures were below the pressure-dependent upper temperature limit for the decomposition of PdO to metallic Pd. Although palladium catalysts exhibited a “self-regulating” temperature effect due to PdO decomposition, the attained temperatures were still sufficient to ignite homogeneous combustion of the H2/CO/O2/N2 mixtures. This was contrary to hydrocarbon fuels for which gas-phase combustion was largely suppressed over PdO in the pressure range of 1-8 bar. The results suggested that for the elevated pressures and preheats of syngas-fueled heterogeneous/homogeneous combustion power systems, gas-phase chemistry cannot be ignored during reactor design.

Original languageEnglish (US)
Pages (from-to)6583-6591
Number of pages9
JournalProceedings of the Combustion Institute
Volume38
Issue number4
DOIs
StatePublished - 2021
Event38th International Symposium on Combustion, 2021 - Adelaide, Australia
Duration: Jan 24 2021Jan 29 2021

All Science Journal Classification (ASJC) codes

  • Chemical Engineering(all)
  • Mechanical Engineering
  • Physical and Theoretical Chemistry

Keywords

  • Homogeneous ignition of syngas over palladium at elevated pressures
  • In situ Raman and OH-PLIF measurements
  • Self-regulating temperature of palladium
  • Syngas combustion over palladium

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