Methane hydrate combustion by using different granules composition

Abstract

Dissociations of methane gas hydrate during gas combustion were investigated. The anomalous behavior of a sample was revealed after termination of combustion and long stay of powder at the ice melting temperature (“secondary self-preservation of methane”). Increasing storage temperature and transport of natural gas hydrate are the important scientific and technical problems. The effect of combustion on decay of gas methane clathrate is considered using the important key parameters: powder layer height, external heat flux, granules composition. Existing methods of combustion modeling use a simplified one-dimensional case of kinetic combustion without taking into account the granule size and thickness of the hydrate layer. In the present research, the boundary dissociation conditions at non-stationary combustion were determined from the experiment data. The heat flux before combustion was constant and it was controlled by the ambient air temperature. During combustion, the heat flux increased by an order, and its value was determined experimentally. Currently, when simulating non-stationary combustion of СH4 gas hydrate, constant flows of combustible gasses were used. In reality, magnitudes of mass gas flows vary by several orders in time. As a result, CH4 combustion occurs under the non-stationary and non-isothermal regime in violation of stoichiometric ratio. The proposed model allowed us to connect the non-stationary gas flows with decomposition kinetics of gas clathrate. Thus, chemical reaction kinetics is controlled by means of the internal transfer processes. The existing predictions for describing the decomposition at negative temperatures did not take into account the structural parameters of particle surface as well. As a result, these simplified models incorrectly described the decomposition process. It is shown that non-uniform distribution of particle sizes and thick powder layer will result in unsteady dissociation and hydrate burning and this will lead to a decrease in combustion efficiency.