Efficiency of methane hydrate combustion for different types of oxidizer flow

Dissociation of natural methane hydrate was studied experimentally. Natural hydrate was mined from deep deposits. The granules of different sizes were obtained through crushing. Stable combustion is achieved at uniform diameter-distribution of granules and their average size of 0.5-0.8 mm, and at low height of the powder layer of 6 mm. At the layer height of 18 mm, an ice crust preventing gas hydrate decomposition was formed inside the granule layer. For the first time, the efficiency of gas hydrate combustion was studied experimentally for eight ways of the oxidizer flow, and a simple method to compare the efficiency of the dissociation rate was proposed. Kinetics of combustion is correlated with the methane hydrate dissociation kinetics. Experimental data show that the most stable combustion with the maximal reaction rate occurs for uniform composition of small granules, low layer height, and at the joint flow of the oxidant in the outer flow and inside the powder layer. An oxidizer flow inside the powder layer led to methane combustion inside this layer and excluded partial self-preservation. The maximal dissociation rate was achieved in the presence of the external incident airflow (velocity is 1.0 -1.5 m/s) and with the oxidizer flow inside the powder layer. At that, combustion inside the granule layer allows a significant increase in the layer height. The extreme of combustion rate is observed in a wide range of velocities. The extreme position depends on the injection parameter, length of dissociation region, ratio of velocities, and prehistory of the external incident airflow. To model the combustion, it is necessary to take into account the repulsion of the dynamic boundary layer from the wall and velocity and temperature distribution above the powder surface. (C) 2016 Elsevier Ltd. All rights reserved.