High-capacity And Reversible Hydrate Technology For Methane Storage

Gas hydrate technology is a novel natural gas storage and transportation method. Butthere are still some problems such as low storage capacity and irreversible materials whichrestrict the industrial application of hydrate storage technology. This paper aimed toimprove these problems and a series of high-capacity and reversible hydrate storagemethods were proposed.Firstly,300mL stainless steel high pressure reaction cell was used to study the gasstorage capacity and rate based on hydration of anion surfactant solution such as sodiumlignin sulfonate and sodium dodecyl sulfate at different conditions. The hydration hadstarted before the inlet pressure reached the target pressure, the storage capacity was180.7VC H4/VH2Owithin30.0min, and the final storage capacity of second hydration was up to204.1in0.5wt%sodium lignin sulfonate solution at the initial pressure of8.3MPa and water bath temperature of273.2K. Metal packings, for example, copper foam andstainless steel Pall rings, were added to0.03wt%sodium dodecyl sulfate solution, theinduction time was shortened from5.7min to5.0min and the storage capacity reached176.4from156.9within30.0min when the mass ratio (R) ofstainless steel Pall rings and water was1:5. at the initial pressure of8.3MPa and water bathtemperature of273.2K. These anionic surfactants produced tiny bubbles, increased thesurface wetting activity and gas solubility, and reduced surface tension. When they wereadded into hydration system, the gas-water contact area increased, the mass transfer ratewas improved, the induction time was shortened and the storage capacity increased. Addingpackings promoted the remove of hydration heat, and the hydration rate increased.Secondly, the same experimental apparatus were used to examine the hydration storagereversibility of methane for poly(2-hydroxyethyl methacrylate)(pHEMA) hydrogel and drywater series. The storage capacity of pHEMA-20reached about110.0within11hydration-decomposition cycles at the initial pressure of7.5MPa and water bathtemperature of273.2K. The reversibility hydration storage of pHEMA-20was goodbecause the three-dimensional network structure was maintained and the channels were still open within11hydration-decomposition cycles. Afterwards, dry water was modified byadding pHEMA. At the initial pressure of7.5MPa and water bath temperature of273.2K,the gas storage capacity of dry water was178.0、78.2、20.5VC H4/VH2Ofor3hydration-decomposition cycles, while the gas storage capacity of hydrogel supported drywater was137.5,101.5,75.9and45.3for4hydration-decomposition cycles.Compared with dry water, the reversibility of hydrogel supported dry water was greatlyimproved, though the storage capacity of first hydration declined slightly. The pHEMA inhydrogel supported dry water played the role of fixing water and supporting the systemduring the hydration-decomposition process, and it delayed the destruction of the "water insilicon" structure of dry water to keep its good dispersibility.Finally, the gas storage of pHEMA-20and dry water series was tested in the cell ofconstant volume5.3L. The5-cycle storage capacity of pHEMA-20was86.9,73.1,58.1,55.8and48.1, and the storage capacity reduced slowly. The storage capacity ofdry water diminished from100.0to11.7, which indicated that drywater was very unstable for its large specific surface area was easily destroyed duringhydration-decomposition cycles. Hydrogel supported dry water showed a good reversibilityof gas storage for the8-cycle storage capacity was159.9,70.8,72.7,62.4,56.5,48.8,41.9and53.8, respectively.