Heat Transfer Related to Gas Hydrate Formation/Dissociation

Abstract

Gas hydrates are ice-like crystalline compounds comprised of small guest molecules, such as methane or other light hydrocarbons, which are trapped in cages of a hydrogen-bonded water framework. It has drawn attention in the gas and oil industry since 1930s because it was found that the formation of gas hydrates may block oil/gas pipelines (Sloan and Koh, 2007). However, with the gradual discovery of huge reserve of natural gas hydrates in the earth as well as the understanding of the peculiar properties of gas hydrates, more and more studies have focused on how to benefit from gas hydrates in recent decades. The most important aspect of gas hydrates research is attributed to the exploration and exploitation of natural gas hydrates. Additionally, people also try a lot in the development of novel technologies based on hydrates, such as separation of gas mixture via forming hydrates, storage of natural gas or hydrogen in the form of solid hydrates, and sequestration of CO2, etc. As the formation of gas hydrates is an exothermic process, heat transfer always accompanies hydrate formation or dissociation. The understanding of heat transfer mechanism is critical to the modeling of formation/dissociation kinetic process of gas hydrates, which favors the best exploitation of natural gas hydrates and the best design of reactor for hydrate production or decomposer for hydrate dissociation with respect to different kinds of hydrate application objects. In recent years, a variety of experimental and theoretical works focused on heat transfer involved in formation/dissociation of gas hydrates have been reported. They are summarized in this chapter accompanying presentation of our new work relevant to this topic. This chapter is organized as follows. In section 2, we present progresses in experimental measurement of the thermal conductivities of different kinds of gas hydrates, including pure gas hydrates and hydrate-bearing sediments. The achievements on mechanism and modeling of heat transfer occurring in the growth of hydrate film at the guest/water interface, as well as its influence upon the hydrate film growth rate are summarized in section 3. Our new experimental study on heat transfer in stirring or flowing hydrate system is given in section 4. Section 5 presents our recent work on the experimental and modeling studies on heat transfer in quiescent reactors for producing or decomposing big blocks of hydrates, and the formulation of the influence of heat transfer upon the hydrate formation/dissociation rate. In section 6, the mechanism of heat transfer in hydrate