Showing papers by "Xiao-Sen Li published in 2011"

Experimental Investigation into the Production Behavior of Methane Hydrate in Porous Sediment by Depressurization with a Novel Three-Dimensional Cubic Hydrate Simulator

Abstract: The gas production behavior from methane hydrate in a porous sediment by depressurization was investigated in a three-dimensional (3D) cubic hydrate simulator (CHS) at 281.15 K, hydrate saturation of 33.1%, and a production pressure range of 4.5–5.6 MPa. The results show that the gas production process consists of three periods: free gas production, mixed gas (free gas and gas dissociated from the hydrate) production, and gas production from the hydrate dissociation. The temperature in the near-well region in the 3D hydrate reservoir changes during gas production in five stages. In the first period, the free gas in the system is released and the temperature change is not significant. In the second period, the temperature increases because of the reformation of the hydrate. In the third period, the temperature at each measuring point decreases quickly to the lowest value because of the considerable dissociation of the hydrate. The fourth period is the thermostatic hydrate dissociation period. During this p...

Precombustion Capture of Carbon Dioxide and Hydrogen with a One-Stage Hydrate/Membrane Process in the Presence of Tetra-n- butylammonium Bromide (TBAB)

Abstract: Trapping CO 2 in hydrates is a promising approach to reduce the greenhouse gas emissions. This work presents the efficient separation process of CO 2 from the simulated fuel gas (39.2 mol % CO 2 /H 2 binary mixture) based on the hydrate crystallization in the presence of tetra-n-butylammonium bromide (TBAB). The experiments were carried out in the TBAB concentration range of 0.14―1.00 mol %, the temperature range of 275.15―285.15 K, the driving force range of 1.00―4.50 MPa, the gas/liquid phase ratio range of 0.86―6.47, and the hydrate growth time from 15 to 120 min. The results indicate that the increase of the TBAB concentration or the driving force can enhance the separation efficiency, except when the TBAB concentration is above 0.29 mol % or the driving force is above 2.50 MPa. The lower gas/liquid phase volume ratio and the hydrate growth time can also promote gas consumption. However, H 2 more competitively encages into the hydrate phase with time. In addition, the temperature change has little effect on the CO 2 separation efficiency with the fixed driving force. It is worth noting that the one-stage hydrate formation/ decomposition process for the fuel gas in the presence of 0.29 mol % TBAB at 278.15 K and 2.50 MPa driving force could obtain a 96.85 CO 2 -rich gas and a 81.57 mol % H 2 -rich gas. The split fraction (SFr) and separation factor (SF) of CO 2 are 67.16% and 136.08, respectively. On the basis of the data of the separation efficiency, a hybrid conceptual process for precombustion capture based on only one hydrate formation/decomposition stage coupled with membrane separation is presented.

Equilibrium Hydrate Formation Conditions for the Mixtures of Methane + Ionic Liquids + Water

Abstract: The equilibrium hydrate formation conditions for methane in the presence of the aqueous solutions of the five ionic liquids with the mass fraction of 0.1 have been investigated. The data were measured using an isochoric method in the pressure range of (3 to 17) MPa and the temperature range of (276.15 to 289.15) K. It is found that the additions of the ionic liquids shift the methane hydrate equilibrium phase boundary to the temperature and pressure conditions that are unfavorable for the hydrate formation. The dialkylimidazolium-based ionic liquids with the hydroxylated cations exhibit an enhanced effectiveness in inhibiting hydrate formation. For the tetraalkylammonium-based ionic liquids, ones with the shorter alkyl substituents of the cations perform better thermodynamic inhibition effects than ones with the hydroxylated longer alkyl substituents of the cations. Among all of the ionic liquids studied, tetramethyl-ammonium chloride is the most effective one, which is comparable with ethylene glycol.

Study on Dissociation Behaviors of Methane Hydrate in Porous Media Based on Experiments and Fractional Dimension Shrinking-Core Model

Abstract: The dissociation kinetics of methane hydrate in the silica gels as the porous media are studied when the temperatures are above the quadruple-phase (hydrate(H)–water(LW)–ice(I)–vapor(V)) point temperatures. The dissociation experiments were carried out by depressurization in the temperature range of 269.15–278.15 K and the initial formation pressure range of 4.1–11.0 MPa. Four silica gels, with pore sizes of 9.03, 12.95, 17.96, and 33.2 nm (the particle size distribution is 0.105–0.15 mm) were used. The experimental results shows that the rate of methane released from the hydrate dissociation increases with the increase of the initial formation pressure, the decrease of the environmental temperature, and the increase of the pore size. The temperature in the hydrate crystallizer first immediately has an obvious drop in the process of the hydrate dissociation and then rises gradually to the environmental temperature after it reaches the lowest temperature point. Based on the fractal theory and the shrinking...

Method and device for exploiting natural gas hydrate in permafrost region

Abstract: The invention discloses a method and a device for exploiting natural gas hydrate in a permafrost region. The device comprises a water-pumping depressurization system, an underground in-situ combustion heating system, a gas collection system and a control system. The water pumping depressurization system comprises a water delivery pipe, a deep-well pump and a gas-liquid separator, wherein the deep-well pump is arranged at the bottom of a vertical well; and the gas-liquid separator is connected with the deep-well pump by the water delivery pipe. The underground in-situ combustion heating system comprises an electronic ignition device and an oxygen-containing gas conveying pipe, wherein the electronic ignition device is connected with a ground power supply by a power switch; and the oxygen-containing gas conveying pipe is connected with an external gas supply system and paved from the ground to the electronic ignition device through the vertical well. The gas collection system comprises a gas collection pipe which is arranged at a well head of the vertical well. The control system comprises a pressure sensor, the power switch and a regulation valve, wherein the regulation valve is arranged on the oxygen-containing gas conveying pipe; and the control system controls the aperture of the regulation valve and the on and off of the power switch according to a pressure, which is measured by the pressure sensor, of the vertical well. By the invention, the synchronous continuous exploitation of depressurization and underground in-situ combustion heating can be realized.