An Experimental Study of Combustion of a Methane Hydrate Layer Using Thermal Imaging and Particle Tracking Velocimetry Methods

Abstract

In this paper, the combustion of methane hydrate over a powder layer is experimentally studied using thermal imaging and Particle Tracking Velocimetry (PTV) methods. The experiments are carried out at different velocities of the external laminar air-flow from zero to 0.6 m/s. Usually, simulation of methane hydrate combustion is carried out without taking into account free convection. A standard laminar boundary layer is often considered for simplification, and the temperature measurements are carried out only on the axis of the powder tank. Measurements of the powder temperature field have shown that there is a highly uneven temperature field on the layer surface, and inside the layer the transverse temperature profiles are nonlinear. The maximum temperature always corresponds to the powder near the side-walls, which is more than 10 • C higher than the average volumetric temperature in the layer. Thermal imager measurements have shown the inhomogeneous nature of combustion over the powder surface and the highly variable velocity of methane above the surface layer. The novelty of the research follows from the measurement of the velocity field using the PTV method and the measurement of methane velocity, which show that the nature of velocity at combustion is determined by the gas buoyancy rather than by the forced convection. The maximum gas velocity in the combustion region exceeds 3 m/s, and the excess of the oxidizer over the fuel leads to more than tenfold violation of the stoichiometric ratio. Despite that, the velocity profile in the combustion region is formed mainly due to free convection, it is also necessary to take into account the external flow of the forced gas U 0 . Even at low velocities U 0 , the velocity direction lines significantly deviate under the forced air-flow. combustion is associated with the presence of three interrelated processes: The dissociation of solid particles of methane hydrate; gas filtration through a multicomponent medium (methane-water-water vapor); and diffusion combustion of methane in the mixing layer (methane-air-water vapor), which is usually implemented over the powder layer. Therefore, it is necessary to consider the features of these processes.The gas hydrate dissociation rate is determined by the following driving forces: Deviation of temperature and pressure from the equilibrium states, size of particles, and structural characteristics of ice crust [4,5]. Dissociation at positive temperatures has a thin film of water formed on the surface of solid particles. The dissociation rate is quasi-constant for most of the dissociation time. The case of negative temperatures is significantly more difficult to describe due to the emergence of the phenomenon of self-preservation [6]. In the temperature range of 230-268 K, the dissociation rate of methane hydrate decreases by several orders of magnitude and strongly depends on temperature. This annealing temperature region was called the self-preservation region. The lowest dissociation rate of methane hydrate is achieved at th...

A Review of Laboratory and Numerical Techniques to Simulate Turbulent Flows

“…Traditionally, this technique is widely used to study small-scale flows (Azadi and Nobes [149]) and to low-particle density flows (Cornic et al [150]) but recently its use has also been expanded to large-scale indoor airflows (Fu et al [151]) and to the investigation of the near-wall regions (Fu et al [152]). Further recent studies used PTV to study the combustion of methane hydrate over a powder layer (Misyura et al [153]), the activation of the low reactivity industrial fuel (Egorov et al [154]), the effect of highspeed jets in highly abrasive environments (Riha et al [155]), and velocity measurements in porous media (Sabbagh et al [156]). In recent years, the evolution of PTV has mainly concerned technological and algorithmic development, leading to the definition of 3DPTV and 4DPTV.…”

Effect of Lithological Parameters on Combustion Characteristics of Methane Hydrate Sediments

“…However, existing processes still require the external transportation of fuel and oxidizers into the combustion heat exchanger, involving on-site fuel storage and injection, which increases technical complexity and costs. By conducting combustion experiments on methane hydrates, scholars [18][19][20][21] have found that the energy transfer between the combustion flame and the hydrate decomposition products is uneven and unstable. Direct combustion of natural gas hydrates leads to lower flame temperatures and lower combustion efficiency [22,23].…”