Dissociation of natural and artificial gas hydrate

• Storage and combustion methane hydrate is simulated.
• Natural methane hydrate from the bottom of Lake Baikal was investigated.
• There is much longer area of self-conservation for natural hydrate.
• Dissociation was modeled taking into account the granules size distribution, size and pore density.

Dissociation kinetics of natural and artificial methane hydrate were studied experimentally and theoretically. The artificial methane hydrate was produced in the reactor, and the natural clathrate was extracted from the bottom of Lake Baikal. The behavior of the natural gas hydrate decay is markedly different from the artificial one under non-isothermal conditions. For natural methane hydrates there is a much longer self-conservation area and a lower rate of dissociation caused by different initial defectiveness of samples. The proposed model takes into account the area of self-conservation and structural characteristics of the granules that allows qualitatively and quantitatively describing the dissociation. The non-isothermal dissociation was numerically simulated, taking into account heat and mass transfer, kinetics of phase transformation, gas filtering inside the granules and porous characteristics (size and density of pores). Different requirements are applied to technologies for efficient storage and combustion of gas hydrates. A more stable region of self-conservation of natural gas hydrate increases the efficiency of its storage and transportation. In this case, a durable crust of ice with a low concentration of pores is achieved for higher temperatures than for the artificially synthesized hydrate. In the course of dissociation of gas hydrate at negative temperatures of annealing, the density of the pores distribution in the formed ice crust decreases by eight orders that significantly changes the rate of decay during the dissociation. The simulation of dissociation of natural and artificial methane hydrates was implemented with a maximum density of pores and well agreed with the experimental data. Thus, it has been experimentally and theoretically shown that the density and size of pores dramatically affect the kinetics of dissociation. During storage, transportation and combustion of combustible gases solid hydrates it is necessary to determine the heat transfer coefficient and the temperature difference ∆T both for the outer medium (external boundary conditions) and the internal one (a layer of powder or pressed pellets). The dissociation rate of gas hydrates at negative temperatures T<0 °С is much more complex than for T>0 °С and currently there are no reliable calculation methods. The use of filtration model and structural parameters can effectively predict the behavior of gas hydrates at negative temperatures.