Fiery ice: An overview of methane hydrate combustion

Abstract

This article describes the combustion behavior of combustible gases as they are released from the clathrate cages of a hydrate. Gas hydrates (clathrates) are ice-like crystalline solids that encapsulate guest gas molecules. It has become known that a significant methane storehouse is in the form of methane hydrates on the sea floor and in the arctic permafrost. There is great interest in this large fuel storehouse, particularly how to extract the methane from the clathrates. One of the unique features of methane clathrate is that it is flammable, despite being 85% water – fiery ice. While methane clathrates are the most prevalent in nature, other combustible gas hydrates (notably, propane and hydrogen) also have potential energy technology implications. In addition, carbon-dioxide hydrates have been proposed as a potential post-combustion greenhouse gas sequestration strategy, and there is a wide range of separation technologies and thermal management that take advantage of the unique thermodynamic and kinetic features of hydrate formation. To better understand the important implications of direct utilization of fuel clathrates and the related potential environmental consequences of CO₂ hydrates, we describe the state-of-the-art knowledge regarding the formation and structure of gas hydrates, and the combustion behavior of flammable gas hydrates. The combustion studies involve determining the rate of ice melt and water evaporation during the hydrate burn, as well as the interesting phenomenon of self-healing, where the hydrates stop burning by forming an ice sheet on their surface. Experimental results are used to estimate the heat transfer from the flame into the hydrate and to calculate the amount of energy released to sustain the flame. This article provides the reader with a comprehensive understanding of the basics and the subtleties of hydrates and their combustion, thereby explaining the true meaning of fiery ice.