Liang Deqing

Gas hydrate fast nucleation from melting ice and quiescent growth along vertical heat transfer tube

During the observation of HCFC141b gas hydrate growth processes outside a vertical heat transfer tube, two exciting phenomena were found: fast nucleation of gas hydrate from melting ice, and the spontaneous permeation of water into the guest phases along the surface of heat transfer tube to form gas hydrate continuously. These two phenomena were explained with Zhou & Sloan’s hypothesis and the theory of surface free energy respectively, and a novel method of gas hydrate formation was presented—gas hydrate fast nucleation from melting ice and quiescent growth along heat transfer tube. There is no mechanic stirring in this method, the formed gas hydrates are compact, the ratio of unreacted interstitial water is little, which overcome the drawback of high energy cost and high ratio of unreacted interstitial water among the formed gas hydrates in the system with mechanic stirring. This finding will benefit the gas hydrate application technologies such as natural gas storage technology or cool storage technology with gas hydrate.

Gas hydrate formation in fine sand

Gas hydrate formation from two types of dissolved gas (methane and mixed gas) was studied under varying thermodynamic conditions in a novel apparatus containing two different natural media from the South China Sea. The testing media consisted of silica sand particles with diameters of 150–250 μm and 250–380 μm. Hydrate was formed (as in nature) in salt water that occupies the interstitial space of the partially water-saturated silica sand bed. The experiments demonstrate that the rate of hydrate formation is a function of particle diameter, gas source, water salinity, and thermodynamic conditions. The initiation time of hydrate formation was very short and pressure decreased rapidly in the initial stage. The process of mixed gas hydrate formation can be divided into three stages for each type of sediment. Sand particle diameter and water salinity also can influence the formation process of hydrate. The conversion rate of water to hydrate was different under varying thermodynamic conditions, although the formation processes were similar. The conversion rate of methane hydrate in the 250–380 μm sediment was greater than that in the 150–250 μm sediment. However, the sediment grain size has no significant influence on the conversion rate of mixed gas hydrate.

Decomposition Characteristics of Ethane Hydrate and Propane Hydrate by Microwave Heating

The decomposition of type I ethane hydrate and type II propane hydrate stimulated by 2.45 GHz microwave (MW) were experimentally investigated. The decomposition characteristics of the hydrates under MW heating were analyzed based on the two. step dissociation mechanism accompanied by heat and mass transfer at the crystal surface. Results show that the decomposition behavior of the gas hydrate during MW heating is coupled with the real. time electromagnetic field. Volumetric heating enhances the heat and mass transfer process at the surface layer of the hydrate particles. The time. accumulated thermal effect of MWheating promotes the destruction of the clathrate host lattice. The average decomposition rates of ethane hydrate and propane hydrate obtained in this work range from 0.109 to 0.400 mol . min(-1) . L-1 and from 0.090 to 0.222 mol . min(-1) . L-1, respectively, under incident MW power that ranges from 120 to 540 W. We conclude that the average decomposition rates of ethane hydrate and propane hydrate are faster as the MW power increases within a certain range. The decomposition rates of ethane hydrate are mainly controlled by the MW power. In contrast, the decomposition rates of propane hydrate are controlled by both the MW power and the kinetic mechanismunder relatively higher power.

Influence of 5A-Type Zeolite Powder on Tetrahydrofuran Hydrate Formation and Dissociation Process

Visual observations of tetrahydrofuran (THF) hydrate formation and dissociation processes with 5A-type zeolite powder were made at normal atmospheric conditions and below zero temperature by microscope. Results indicate that 5A-type zeolite powder can promote THF hydrate growth. At the same time, in the presence of 5A-type zeolite, agglomerated crystals and vein-like crystals of THF hydrate were also formed. SA-type zeolite powder increases the crystallization temperature and decreases the dissociation temperature. The particle size distribution of 5A-type zeolite powder influences THF hydrate formation and its dissociation characteristics significantly.