Gas Hydrate Storage Research Articles

Researches on Start Control Strategy of CNG Engine

With the discovery of abundant gas hydrate storage, the natural gas will become an important fuel for future vehicles. In order to improve the starting performance of the CNG engine, an electrical control system was developed and the starting control mode was set up according to the engine operating characteristics. The control parameters of injection quantity, injection timing, ignition energy and ignition timing were considered in the model. The tests of start and idle were conducted on a four stroke CNG engine. The results indicated that the CNG engine can start faster and more reliably by using the optimal start control strategy.

Research on cool storage and release characteristics of R134a gas hydrate with additive

Theoretically R134a gas hydrate is a good choice for practical cool storage application due to its excellent boiling and condensation properties, but earlier researches indicate that pure R134a alone is not suitable for practical cool storage application as it floats and occupies upper space in the storage tank, resulting in difficulty both in the storage and release processes. For this reason, this study tries to develop R134a hydrate's potential in cool storage by means of alcohol additives. The system has been performed to test the performance of both cool storage and release process and its industrial applicability. The results show that 1.34% n-butanol additive among three different concentrations exhibits the best result which substantially accelerates the cool storage rate. The lumped hydrate density increases apparently comparing with pure R134a hydrate running, which eliminates the hydrate floating during the hydration process under certain additive concentration. It indicates that the added alcohol in R134a hydrate-water solution is essential for a stable and smooth cool storage operation and a cool storage tank with indirect-contact configuration is industrially applicable.

Gas hydrates: past and future geohazard?

Gas hydrates are ice-like deposits containing a mixture of water and gas; the most common gas is methane. Gas hydrates are stable under high pressures and relatively low temperatures and are found underneath the oceans and in permafrost regions. Estimates range from 500 to 10,000 giga tonnes of carbon (best current estimate 1600-2000 GtC) stored in ocean sediments and 400 GtC in Arctic permafrost. Gas hydrates may pose a serious geohazard in the near future owing to the adverse effects of global warming on the stability of gas hydrate deposits both in ocean sediments and in permafrost. It is still unknown whether future ocean warming could lead to significant methane release, as thermal penetration of marine sediments to the clathrate-gas interface could be slow enough to allow a new equilibrium to occur without any gas escaping. Even if methane gas does escape, it is still unclear how much of this could be oxidized in the overlying ocean. Models of the global inventory of hydrates and trapped methane bubbles suggest that a global 3( degrees )C warming could release between 35 and 940 GtC, which could add up to an additional 0.5( degrees )C to global warming. The destabilization of gas hydrate reserves in permafrost areas is more certain as climate models predict that high-latitude regions will be disproportionately affected by global warming with temperature increases of over 12( degrees )C predicted for much of North America and Northern Asia. Our current estimates of gas hydrate storage in the Arctic region are, however, extremely poor and non-existent for Antarctica. The shrinking of both the Greenland and Antarctic ice sheets in response to regional warming may also lead to destabilization of gas hydrates. As ice sheets shrink, the weight removed allows the coastal region and adjacent continental slope to rise through isostacy. This removal of hydrostatic pressure could destabilize gas hydrates, leading to massive slope failure, and may increase the risk of tsunamis.

Evaluation and analysis method for natural gas hydrate storage and transportation processes

An evaluation and analysis method is presented to investigate an approach to scale-up a hydration reactor and to solve some economic problems by looking at the natural gas hydrate storage and transportation process as a whole. Experiments with the methane hydration process are used to evaluate the whole natural gas hydrate storage and transportation process. The specific contents and conclusions are as follows: first, batch stirring effects and load coefficients are studied in a semi-continuous stirred-tank reactor. Results indicate that batch stirring and appropriate load coefficients are effective in improving hydrate storage capacity. In the experiments, appropriate values for stirring velocity, stirring time and load coefficient were found to be 320 rpm, 30 min and 0.289, respectively. Second, throughput and energy consumption of the reactor for producing methane hydrates are calculated by mass and energy balance. Results show that throughput of this is 1.06 kg/d, with a product containing 12.4% methane gas. Energy consumption is 0.19 kJ, while methane hydrates containing 1 kJ heat are produced. Third, an energy consumption evaluation parameter is introduced to provide a single energy consumption evaluation rule for different hydration reactors. Parameter analyses indicate that process simplicity or process integration can decrease energy consumption. If experimental gas comes from a small-scale natural gas field and the energy consumption is 0.02 kJ when methane hydrates containing 1 kJ heat are produced, then the decrease is 87.9%. Moreover, the energy consumption evaluation parameter used as an economic criterion is converted into a process evaluation parameter. Analyses indicate that the process evaluation parameter is relevant to technology level and resource consumption for a system, which can make it applicable to economic analysis and venture forecasting for optimal capital utilization.

Structure and kinetics of gas hydrates from methane/ethane/propane mixtures relevant to the design of natural gas hydrate storage and transport facilities

AbstractThe kinetics of gas hydrate growth from binary CH4/C2H6 and CH4/C3H8 and ternary CH4/C2H6/C3H8 gas mixtures were obtained by the gas uptake method in a semibatch stirred vessel at constant pressure and a temperature of 273.7 K. These data are of interest for the design of facilities for natural gas storage and transportation in the solid (hydrate) state. During hydrate formation, samples from the gas phase were taken and analyzed by gas chromatography. It was found that the molar composition of CH4 in the vapor phase increased as hydrate crystallization progressed. The observed fractionation effect (enrichment of the hydrate phase with propane) complicates the natural gas storage process. The fractionation effect was also confirmed with molecular‐level studies where hydrate from the CH4/C2H6/C3H8 gas mixture was characterized by powder X‐ray diffraction (PXRD), NMR, and Raman spectroscopy. The hydrate phase composition and cage occupancy of each gas were calculated with the help of information obtained by Raman spectroscopy, gas chromatography, and PXRD. The results were consistent with those obtained by NMR. The composition of the gas phase and the hydrate are found to evolve over time, suggesting that kinetic and transport factors contribute in addition to thermodynamics. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Investigations into surfactant/gas hydrate relationship

Gas hydrates have unique physical properties portending useful industrial applications of gas storage, gas separation, or water desalination. When gas hydrates were found in the early 1990s to occur naturally and abundantly in seafloors, three other primary interests and concerns emerged: potential new energy source, climate threat from their greenhouse gases, and seafloor instabilities. This paper presents research showing how anionic synthetic surfactants helped develop an industrial gas hydrate storage process for natural gas and how naturally-occurring in-situ anionic biosurfactants influence the formation and placement of gas hydrates in ocean sediments. The catalytic effects, mechanisms, and surface specificities imparted by synthetic surfactants in the gas storage process and imparted by biosurfactants in porous media are discussed. The Bacillus subtilis bacterium that is indigenous to gas hydrate mounds in the Gulf of Mexico was cultured in the laboratory. Its biosurfactant was separated and found to catalyze gas hydrates in porous media. The experiments indicate that seafloor-biosurfactants can be produced rapidly in-situ to achieve threshold concentrations whereby hydrates are promoted. The biosurfactants accumulate and promote hydrate formation on specific mineral surfaces such as sodium montmorillonite.

The influence of additives and metal rods on the nucleation and growth of gas hydrates

A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH 3CCl 2F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal the influence of the additives and the iron rod on the nucleation and growth of the gas hydrate. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath at 274.15–280.15 K and under atmospheric pressure. The experimental results show that, compared to the pure water and the HCFC141b system, the properly placed iron rod combined with proper concentrations of lauryl sodium sulfonate, lauryl sodium sulfate, and sodium dodecylbenzenesulfonate-6 considerably reduces the hydrate nucleation time and promotes formation speed. The formation rate of HCFC141b gas hydrate increases with increasing concentration of sodium dodecylbenzenesulfonate-6 in the water solution, while the addition of potassium oxalate monohydrate in water has shown no effect on the nucleation and growth of HCFC141b gas hydrate. Under the experimental conditions, both the anion surfactants and the iron rod strongly induce the first nucleation of HCFC141b gas hydrate, while the following growth of the HCFC141b gas hydrate is primarily influenced by the anion surfactant. This experiment suggests a new way of fast formation of clathrate hydrate, which may be much easier for practical application of the gas hydrate for cold storage in air conditioning systems.

Cool Energy Storage of Gas Hydrate Using Natural Circulation of Refrigerant with Direct Contact Boiling and Condensation.

The method of cool energy storage using heat transfers of direct contact boiling and condensation between refrigerant as a working medium and water as a PCM in an enclosure was proposed in the previous report. It was also shown that the efficient storage and release of cool energy were achieved for small height of water up to 50mm. In this report, the effect of height of storage material, the rate of heat storage and release and the heat transfer characteristics using same method were investigated under large height of storage material up to 517mm. HCFC142b and water or 2% n-butanol-water solution were used as a working medium and a storage material, respectively. Heat of chemical reaction of gas hydrates of HCFC142b and water was utilized. As a result, an efficient cool energy storage and release was achieved for large height of storage material. In particular, high rate of heat storage was maintained for all heights of the storage material for n-butanol solution.