METHANOL AND HYDROGEN OXIDATION-KINETICS IN WATER AT SUPERCRITICAL STATES

The oxidation kinetics of methanol and hydrogen in a supercritical wat er medium were investigated. Numerical analyses were performed using a n isobaric, plug-flow reactor model coupled with the Chemkin Real-Gas software package to handle real-gas thermodynamic effects and elementa ry kinetics. In the present work, select unimolecular reactions that i nvolve thermal decomposition have been corrected for the high-pressure conditions found in supercritical reactors. Predictions of fuel destr uction rates obtained using an elementary reaction mechanism for hydro gen oxidation under isobaric, isothermal supercritical conditions (P > 22.1 MPa, and T > 374 C) were verified by comparison with previous ex perimental results obtained in a laboratory-scale supercritical water reactor. The H-2-O-2 model is a subset of a proposed elementary reacti on mechanism for methanol oxidation which was also verified by compari ng the present model predictions of the kinetic rate calculations with previous measurements. The mechanism was validated over a temperature range of 726 to 873 K, a fuel concentration range of 0.001 to 0.004 m ole/L, and at a pressure of 246 bar. To facilitate future computationa l fluid dynamic (CFD) modeling efforts in SCWO, a two-step reduced rea ction mechanism was constructed to simulate the oxidation process of m ethanol in supercritical water and H2O. The reduced model reflects the sequential oxidation of methanol into carbon monoxide, and eventually into final products consisting primarily of carbon dioxide and H2O. T he calculations of the two-step reduced mechanism matched the elementa ry reaction model well with respect to major species concentration pro files.