Transient combustion of a methane-hydrate sphere

A solution is presented for the spherically symmetric, transient vaporization and combustion of methane-hydrate in a three-phase configuration with rate control by liquid-phase diffusion. The simulation has two moving boundaries due to a solid methane-hydrate core that melts, a transient water shell with small methane gas bubbles, and a quasi-steady gas phase with Stefan convection and advection, diffusion, and chemical reaction. First, a model for melting and vaporization without oxidation is considered. Then, the combustion process is considered at an infinite chemical reaction rate (i.e., a "thin flame" case).The characteristics of the methane-hydrate combustion are examined at different ambient temperatures, pressures and compositions and values of methane-to-water mass ratio. Different values of products in the environment are examined, considering individual particles burning in an environment which has been heated by the presence of other burning droplets, as in-situ production methods are currently developed. An appropriate characteristic time scaling is identified for particles of initial radius of 100 . μm or less, considering these will be relevant for combustion of grounded hydrates.