Methane and methanol oxidation in supercritical water: Chemical kinetics and hydrothermal flame studies

Technical Report · Mon Jan 01 04:00:00 EST 1996

DOI:https://doi.org/10.2172/176803· OSTI ID:176803

Steeper, R R

Supercritical water oxidation (SCWO) is an emerging technology for the treatment of wastes in the presence of a large concentration of water at conditions above water`s thermodynamic critical point. A high-pressure, optically accessible reaction cell was constructed to investigate the oxidation of methane and methanol in this environment. Experiments were conducted to examine both flame and non-flame oxidation regimes. Optical access enabled the use of normal and shadowgraphy video systems for visualization, and Raman spectroscopy for in situ measurement of species concentrations. Flame experiments were performed by steadily injecting pure oxygen into supercritical mixtures of water and methane or methanol at 270 bar and at temperatures from 390 to 510{degrees}C. The experiments mapped conditions leading to the spontaneous ignition of diffusion flames in supercritical water. Above 470{degrees}C, flames spontaneously ignite in mixtures containing only 6 mole% methane or methanol. This data is relevant to the design and operation of commercial SCWO processes that may be susceptible to inadvertent flame formation. Non-flame oxidation kinetics experiments measured rates of methane oxidation in supercritical water at 270 bar and at temperatures from 390 to 442{degrees}C. The initial methane concentration was nominally 0.15 gmol/L, a level representative of commercial SCWO processes. The observed methane concentration histories were fit to a one-step reaction rate expression indicating a reaction order close to two for methane and zero for oxygen. Experiments were also conducted with varying water concentrations (0 to 8 gmol/L) while temperature and initial reactant concentrations were held constant. The rate of methane oxidation rises steadily with water concentration up to about 5 gmol/L and then abruptly falls off at higher concentrations.

• Research Organization: Sandia Labs., Livermore, CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 176803
• Report Number(s): SAND--96-8208; ON: DE96003923
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
40 CHEMISTRY
CHEMICAL REACTION KINETICS
DIFFUSION
FLAMES
IGNITION
METHANE
METHANOL
ORGANIC WASTES
OXIDATION
RAMAN SPECTROSCOPY
SUPERCRITICAL STATE
TEMPERATURE DEPENDENCE
TEMPERATURE MEASUREMENT
WASTE PROCESSING
WATER