Ice Powder Research Articles

Synthesis of Methane Hydrate from Ice Powder Accelerated by Doping Ethanol into Methane Gas

Clathrate hydrate is considered to be a potential medium for gas storage and transportation. Slow kinetics of hydrate formation is a hindrance to the commercialized process development of such applications. The kinetics of methane hydrate formation from the reaction of ice powder and methane gas doped with/without saturated ethanol vapor at constant pressure of 16.55 ± 0.20 MPa and constant temperature ranging from −15 to −1.0 °C were investigated. The methane hydrate formation can be dramatically accelerated by simply doping ethanol into methane gas with ultralow ethanol concentration (<94 ppm by mole fraction) in the gas phase. For ethanol-doped system 80.1% of ice powder were converted into methane hydrate after a reaction time of 4 h, while only 26.6% of ice powder was converted into methane hydrate after a reaction time of 24 h when pure methane gas was used. Furthermore, this trace amount of ethanol could also substantially suppress the self-preservation effect to enhance the dissociation rate of methane hydrate (operated at 1 atm and temperatures below the ice melting point). In other words, a trace amount of ethanol doped in methane gas can act as a kinetic promoter for both the methane hydrate formation and dissociation.

Encapsulation of Powder Mixtures with Frozen Fluids by Pressing

A composite consisting of ice and a mixture of iron powder and zinc stearate that was prepared by freezing at –(6–8)°C has been pressed in a steel die for the first time. The porosity and extrusion pressure of the composite pellets are close to those in dry pressing at room temperature. The frozen cores consisting of ice and various powders have been encapsulated for the first time by joint pressing with a fully encapsulating mixture of iron powder and zinc stearate in dry state. The average porosity of the encapsulated core compacts subjected to drying and sintering is determined by the core properties, i.e., by the material being encapsulated. The use of direct and reverse water–ice transformations has been found to be promising in compaction processes.

Modeling Gas Hydrate Formation from Ice Powders Based on Diffusion Theory

Based on the diffusion theory, a gas–solid reaction model for gas hydrate formation from monosize ice powders was constructed and an effective diffusion coefficient through the gas hydrate shell was obtained by solving the diffusion equation. This model can be applied for a gas–solid reaction process with gas pressure drop during hydrate formation. Two cases termed as M1 and M2 were discussed and compared with each other. In the M1 case, the spherical particle geometry was assumed to be squeezed by adjacent particles. In the M2 case, the effect of adjacent particles on the object particle geometry was neglected. The results showed that the gas effective diffusion coefficient was a critical parameter for accurately simulating the reaction process, and it was found to vary during hydrate formation. In this model, the time-dependent gas effective diffusion coefficient was calculated by means of the measured gas pressure during hydrate formation, and the degrees of hydrate formation were obtained. In addition, the geometrical changes of the hydrate shell and ice powders were obtained during hydrate formation.

The effective thermal conductivity of methane hydrate-bearing seasand

The thermal properties of hydrate-bearing sediments can help to evaluate the stability of hydrate reservoir and improve the safety of natural gas hydrate exploitation. In this work, the thermal conductivities of methane hydrate and methane hydrate-bearing seasand were investigated by the transient plane source (TPS) technique. The high-quality samples of hydrate were prepared by synergistic uses of a variety of methods, i.e., the “seeding” ice, simultaneous slowly heating and slowly supplying gas, temperature oscillation and aging method. The measured thermal conductivity of methane hydrate is 0.4877–0.5467 W·m−1·K−1 with the temperature 263.2–283.1 K and the pressure 4.0–9.5 MPa. The effective thermal conductivities of the saturated seasand sample, supersaturated seasand sample and unsaturated seasand sample (Here, the “saturated”, “unsaturated” and “supersaturated” refers to the three relationships between the pore volume of seasand and the volume of ice powder, respectively) are 1.1310–1.2703 W·m−1·K−1, 1.0070–1.1490 W·m−1·K−1, 0.9221–1.1980 W·m−1·K−1 with the pressure 8.0 MPa and the temperature 253.8–281.2 K, respectively. The effective thermal conductivities of the saturated sample, supersaturated sample and unsaturated sample are 1.1280–1.1402 W·m−1·K−1 (1.1331–1.5974 W·m−1·K−1), 1.0172–1.0252 W·m−1·K−1 (1.0181–1.2032 W·m−1·K−1), 0.9154–0.9388 W·m−1·K−1 (0.9401–1.1543 W·m−1·K−1) with the pressure 4.0–10.0 MPa and the temperature 263.2 K (275.2 K), respectively. The relationship between the effective thermal conductivity and methane hydrate saturation in the sample are λe,saturated > λe,supersaturated > λe,unsaturated. The results suggest that the thermal conductivities of methane hydrate and methane hydrate-bearing seasand are positively correlated with the temperature and the influence of the gas phase pressure is negligible. Besides, the effective thermal conductivity shows a sudden increase near to the phase equilibrium temperature. Due to the complex of actual samples, the same classic theory model cannot accurately predict three samples simultaneously.

Strength Behaviors of Remolded Hydrate-Bearing Marine Sediments in Different Drilling Depths of the South China Sea

The mechanical behaviors of hydrate-bearing marine sediments (HBMS) drilled from the seafloor need to be understood in order to safely exploit natural gas from marine hydrate reservoirs. In this study, hydrates were prepared using ice powder and CH4 gas, and HBMS from the Shenhu area in the South China Sea were remolded using a mixed sample preparation method. A series of triaxial tests were conducted on the remolded HBMS to investigate the effects of soil particle gradation and the existence of hydrate on the mechanical properties of hydrate reservoirs. The results show that the stiffness and failure strength of HBMS decrease along with the decrease of mean particle size and soil aggregate morphology change at different drilling depths, and the reduction of failure strength is more than 20% when the drilling depth drops by 30 m. A better particle gradation of marine sediments may boost the stiffness and failure strength of HBMS. In addition, the existence of hydrate plays an important role in the strength behaviors of HBMS. The reduction of failure strength of HBMS with 30% initial hydrate saturation is more than 35% after complete hydrate dissociation.

Kinetics of sII and Mixed sI/sII, Gas Hydrate Growth for a Methane/Propane Mixture Using Neutron Diffraction

Gas hydrates are solid solutions formed from water and enclathrated gas molecules. The hydrate types sI and sII are formed from pure methane or propane, while mixtures of these gases can form either type. In this study, eight experiments are presented of gas hydrates grown under semibatch conditions using D2O ice powder and a feed gas of methane (90%)–propane (10%). In situ neutron scattering was used to measure the phase fractions of sI and sII hydrates, ice, and liquid–water components during hydrate growth and dissociation. The composition of the free gas and the methane/propane cage occupancies were derived from the observed phase fractions using mass-balance equations and Gibbs energy calculations. In all cases, the sII hydrate was formed before, or concurrent with, the sI phase. After an initial period of hydrate growth from ice, the temperature was increased to release liquid water by melting the ice particles. Different reaction mechanisms were observed; two occurred while the ice was melting and ...

Inhibition of Grain Boundary Sliding in Fine‐Grained Ice by Intergranular Particles: Implications for Planetary Ice Masses

AbstractIce in both terrestrial and planetary settings often contains rock particles. Here we present an experimental investigation of the influence of intergranular particles on the rheological behavior of ice. Experiments were performed on samples fabricated from 10‐μm ice powders +1‐μm graphite or 0.8‐μm alumina particles and subjected to elevated confining pressures. A critical particle fraction, ∼6%, was observed, below which samples behave like pure ice and deform by both grain boundary sliding (GBS) and dislocation creep, and above which GBS creep is impeded. Above this critical fraction, ice grains occur in particle‐free clusters surrounded by bands of particles mixed with fine‐grained ice, resulting in the impedance of GBS in the bands as well as sliding between the ice clusters. Our results imply that South Polar Layered Deposits and midlatitude lobate debris aprons on Mars must contain &gt;94% ice and that the shallow subsurface of Ceres could contain &gt;90% ice.

Influence factors of methane hydrate formation from ice: Temperature, pressure and SDS surfactant

Abstract A series of experiments of forming hydrate from ice powders in different conditions have been carried out with constant volume method to evaluate the influence factors such as pressure, temperature, and SDS surfactant. The change of temperature and pressure were collected as a function of elapsed time, which were used to calculate the gas consumption and hydrate saturation during hydrate formation (pVT method). Based on the experimental results and the analysis, it is concluded that: (1) Both initial pressure and temperature have effect on the hydrate formation and temperature plays a more important role in the process; (2) heating and secondary pressurization will promote the gas hydrate formation and enhance the hydrate saturation as a result. Meanwhile, the promotion of heating seems to be more obvious than that of secondary pressurization; (3) different concentrations of SDS surfactant have clearly influence on the saturation of gas hydrate and there is an optimal concentration to promote the hydrate formation.

INFLUENCE OF THE TIME STORAGE OF ICE POWDER ON KINETICS OF FORMATION AND GROWTH OF FREON-12 GAS HYDRATE

The article explores the influence a storage time on the samples of pure ice powder and mod-ified ice powder with polyvinylpyrrolidone on process formation and growth of the gas hydrate by used P-V-T measurements. It has been established that increased storage time of the pure ice powder leads to a decrease the rate of growth of gas hydrate. Fresh modified ice powder has induction time of hydrate formation which increased in a polyvinylpyrrolidone concentration. At long-term storage of modified ice powder with a polyvinylpyrrolidone concentration less 0,3 % the induction time don’t registrate and growth rate of gas hydrate likes zero. In the samples of modified ice powder with a polyvinylpyrrolidone concentration more 0,75 % after 10 days a storage were retained growth rate of gas hydrate likes fresh modified ice powder. There is no induction effect.

Experimental Study on the Effect of Pressure on the Replacement Process of CO2–CH4 Hydrate below the Freezing Point

The recovery of natural gas from CH4-hydrate deposits in permafrost environments through injection of CO2 is considered to be a suitable strategy for CH4 production and CO2 storage. In order to study the replacement characteristics of CO2-CH4 hydrate below the freezing point, the experiment was conducted in ice powder with particle size of 800 μm at different injection pressure (3.6 MPa, 4.0 MPa and 4.5 MPa) of CO2. The experimental results showed that, the average replacement rate and efficiency increased with the increasing of injected pressure of CO2 gas. And the average replacement rate and efficiency reached up to 0.403 mmol/h and 13.20% when the injected pressure of CO2 was at 4.5 MPa. The results also indicated that, compared with the temperature conditions above the freezing point, the replacement rate of CO2-CH4 hydrate was slow below the freezing point. It provided a theoretical guidance for gas production from methane hydrate using CO2-CH4 replacement method in permafrost region in the future.

Influence of Porous Media on Methane Hydrate Formation from Ice Powders

Abstract Methane hydrate formation from ice powders is a complicated process, and is affected easily by many factors. In this paper, a series of experiments were conducted to study the influence of porous media's particle size and volume proportion on the hydrate formation process. An experimental system based on PVT method was used to measure the gas consumption and the pressure change through the whole process of reaction. The pressure drop and hydrate saturation were analyzed to show the effects of porous media. The results indicated that porous media not only can improve the discrete degree of ice particles, but also increase the contact area of quasi liquid layer and methane gas. The specific effects of particle size and volume proportion were based on the two effects above.

Ice-Bentonite Powder Mixing Method to Improve the Homogeneity of Compacted Bentonite in An Initial Sample Preparation Stage

AbstractBentonite is considered as an ideal buffer/backfill material for preparing an engineering barrier for high-level radioactive waste (HLW) disposal. During initial sample preparation, the tendency of wet bentonite powder to gather into large agglomerates and the water to be spread unevenly in the traditional water content adjustment process decreases the homogeneity of compacted bentonite. The main purpose of this study was to solve this problem by applying a new wetting method, which mixes ice powder with bentonite powder (the ice-bentonite mixing method). This new method was used to adjust the water distribution in Gaomiaozi County, China (GMZ) bentonite powder and was compared to the traditional spray method. The screening method was used to separate macro-agglomerates (≥ 0.25 mm) from the water and bentonite mixture. The properties, the content of the various size agglomerates in loose mixtures, and the heterogeneity defects observed in compacted bentonite were compared. An index (P) was defined to quantitatively evaluate the water distribution in a loose bentonite/water mixture. Macro-agglomerates in loose mixtures produced heterogeneities in water content, density, and shrinkage. By using the ice-bentonite mixing method, fewer macro-agglomerates were formed and a homogeneous distribution of water was produced in the compacted bentonite. A homogeneous water distribution had the tendency to decrease the number of shrinkage cracks after the drying process and to maintain high mechanical strength in the compacted bentonite. Although the production of ice powder was laborious, the ice-bentonite mixing method has workability advantages: (i) a high mixing efficiency, (ii) a low mass loss rate, and (iii) a small deviation between measured water content and target water content. The low thawing efficiency of ice-bentonite mixtures can be solved by using a microwave-assisted thawing method. This research can improve the sample preparation method used to produce compacted buffer/backfill materials for HLW disposal.

CO2 Hydrate Conversion from Microscopic Ice Powder Under Low Pressure and Low Temperature

CO2 Hydrate Conversion from Microscopic Ice Powder Under Low Pressure and Low Temperature

Influence of production parameters on gas hydrate and ice powder pelletizing

A lab scale twin roll press machine was developed for pelletizing natural gas hydrate powder. Ice and hydrate powder were used for the pellet extrusion system. The effects of feeding pressure, pressure ratio, and rotating speed of the twin roll were investigated for producing high strength and stiffness hydrate pellets. The compressive strength and stiffness of pellet increased with increasing feeding pressure and rotation speed. In particular, there was a relatively large increase in the stiffness with an increase in rotating speed, and a relatively large increase in strength with increasing feeding pressure. The production ratio of pellets largely depended on the rotating speed of the twin roll. The results indicate the promising future of solid transportation of natural gas.

Experimental Study on the Methane Hydrate Formation from Ice Powders

An experiment with methane hydrate formation from ice powders was conducted through the gas consumption method (PVT system) to corroborate the existing phenomenological multistage kinetic model. The influence of temperature, pressure and ice grain size on hydrate formation was experimented and analyzed. Lower temperature can enhance the hydrate formation. At the temperature up to nearly the melting point of ice, the excess pressure dominatly influenced the rate of methane hydrate formation. The smaller grain size of the ice powder can promote the methane hydrate formation. The lower rate of pressurization has good effect on the pressure drop process.

Diffusion Theory of Formation of Gas Hydrate from Ice Powder without Melting

Based on the single ice particles shrinking core model, the authors simulated the kinetic of gas hydrates formation from ice powders by the improved rate of volume ice-to-hydrate transformation that considered the volume expansion and consolidation of the sample during hydrate formation. The comparsion of the degree of hydrate formation between the calculated and the measured was conducted. Gas hydrates grown at gas-ice interfaces were a submicron porous structure. The pore structure provides the diffusion for gas molecules through the hydrate shell in reactions. And the diffusion plays an important role in this process of the reaction. In comparison with the experimental data, the reasonability of the model is verified. The curve of the reaction degree with time in different temperatures and initial pressures calculated in this paper by our programs has a good agreement with measured value.

J0320504 マイクロ波焼結によるバイモーダル多孔質SiCの作製([J032-05]ポリマー・セラミックス・メタル多孔質材料の開発と応用(5),材料力学部門)

A bi-modal porous SiC with cylindrical pores and communicated pores were fabricated through unidirectional solidification of water slurry containing CO_2 gas and microwave sintering. The cylindrical pores were formed during the unidirectional solidification under reduced pressure and a composite of ice and SiC powder was obtained. Since the composite was formed by segregation of ice during the solidification, a communicated structure of ice was obtained. The ice was removed by vacuum freeze drying method. The porous bulk with cylindrical pores and communicated pores was sintered using microwave sintering for 5 minutes. Since the dielectric loss factor for SiC is larger than that of the other ceramics, a rapid heating of SiC bulk can be achieved by microwave sintering. The porosity and pore size was well controlled by the pressure during the solidification and sintering time. The degree of shrinkage can be controlled by adding a sintering agent.

Kinetics of CO2-Hydrate Formation from Ice Powders: Data Summary and Modeling Extended to Low Temperatures

The shrinking-core model of the formation of gas hydrates from ice spheres with a well-defined geometry gives experimental access to the gas permeation in bulk hydrates. Here we report on results obtained for CO2 clathration experiments in the temperature range from 185 to 272 K, extending earlier work to much lower temperature conditions. The activation energy deduced from the permeation coefficients changes its value from ∼46 kJ/mol at higher temperatures to ∼19 kJ/mol below 225 K. We compare our results with published molecular dynamics simulation as well as nuclear magnetic resonance studies and provide arguments that the rate limiting process at lower temperatures is the cage-to-cage jumping of CO2 molecules via a “hole-in-the-cage” mechanism involving extrinsic water vacancies in cage walls. The rate-limiting process at higher temperatures can be explained by the temperature-dependent creation of intrinsic water-vacancy-interstitial pairs. The results obtained for CO2-hydrate are compared to earlier...

A centrifugal ice microtome for measurements of atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on air trapped in polar ice cores

Abstract. For atmospheric CO2 reconstructions using ice cores, the technique to release the trapped air from the ice samples is essential for the precision and accuracy of the measurements. We present here a new dry extraction technique in combination with a new gas analytical system that together show significant improvements with respect to current systems. Ice samples (3–15 g) are pulverised using a novel centrifugal ice microtome (CIM) by shaving the ice in a cooled vacuum chamber (−27 °C) in which no friction occurs due to the use of magnetic bearings. Both, the shaving principle of the CIM and the use of magnetic bearings have not been applied so far in this field. Shaving the ice samples produces finer ice powder and releases a minimum of 90% of the trapped air compared to 50%–70% when needle crushing is employed. In addition, the friction-free motion with an optimized design to reduce contaminations of the inner surfaces of the device result in a reduced system offset of about 2.0 ppmv compared to 4.9 ppmv. The gas analytical part shows a higher precision than the corresponding part of our previous system by a factor of two, and all processes except the loading and cleaning of the CIM now run automatically. Compared to our previous system, the complete system shows a 3 times better measurement reproducibility of about 1.1 ppmv (1 σ) which is similar to the best reproducibility of other systems applied in this field. With this high reproducibility, no replicate measurements are required anymore for most future measurement campaigns resulting in a possible output of 12–20 measurements per day compared to a maximum of 6 with other systems.

Phenomenological diffusion theory of formation of gas hydrate from ice powder

The diffusion theory of the formation of gas hydrate from ice powder is stated. The theory takes into account that a gas hydrate has a pore structure that can change during formation of gas hydrate. The parameters of the theoretical model that are responsible for the kinetics of methane hydrate formation are estimated using a comparison between experimental and calculated data.