The features of self-preservation for hydrate systems with methane

Abstract

Dissociation of hydrate systems is studied experimentally: gas hydrate of methane produced artificially in the reactor–crystallizer; natural gas hydrates of methane; water–methane–isopropanol systems in the air atmosphere. Artificial gas hydrate of methane and natural hydrates demonstrate the ranges of abnormally low dissociation rate. At that the boundaries of the temperature windows of self-preservation differ significantly for natural and artificial hydrate systems. Despite the similar structures of elementary hydrate cells of natural and artificial gas hydrates, the dissociation rate of natural samples was significantly lower than the dissociation rate of artificial powders. Moreover, natural hydrates had the expanded time period of the stable thermodynamic state. The mechanism of gas hydrate dissociations depends not only on the driving forces and structural characteristics, but also on the average initial diameter of the powder particles. The creep properties of gas hydrates and limits of their strength are associated with microstructural characteristics, and the dissociation rate depends on the size of the grains. The temperature fields of separate granule surface were obtained via many-times magnification of thermal images. Temperature distribution over the surface is significantly non-uniform, and this characterizes non-uniform hydrate dissociation within the granule volume. Dissociation kinetics for the natural and artificial samples was studied at different heat fluxes. The maximal heat flux and maximal dissociation rate were achieved at combustion of methane hydrate. Both instantaneous and average dissociation rates were measured.