Static Enhancement Technology Of Methane Hydrate Formation

Gas hydrates technology can be contributed to many fields, such as natural gas storage andtransportation, carbon dioxide capture and sequestration, seawater desalination, mixture gasseparation and cold storage in the form of hydrate. However, hydrate formation has beencritically challenged by its poor rate of mass and heat transfer. Mechanical methods andsimple-structure metal fills are often employed in experimental operations to enchancehydrate formation. However, the substantial cost of mechanical devices and energyrequirements may be an unwise payment in real gas storage application. The efficiency ofenhancing heat transfer by simple-strcuture metal fills is also very poor. Hence, in this paer,properties of methane storage in the form of hydrate in static systems were conducted tostudy.Dry water (DW) with high specific surface was prepared by mixing water, hydrophobicSiO2nanoparticles and air at high speeds. Hydrophobic SiO2particles can encapsulateisolated macroscopic water droplets. Dispersed DW can dramatically reduce the inductiontime and enhance the formation rate of methane hydrare by increasing gas-liquid contactsunder static conditions. However, the capsule-structure water droplets were destabilized byhydration-dissociation process. Most of destroyed DW droplets were connected together andformed continuous liquid phase. The rest DW droplets and continuous water has poorperproties of gas storage and little prospect of reversible storage.Gel-supporting dry water (GDW) with high specific surface was fomed by mixing water,SiO2nanoparticles, Gellan gun powder and air at high speeds. The modified dry water aremicro-hygrophanous gel particles encapsulated by hydrophobic SiO2particles and also owngood dispersion. GDW can accelerate methane hydrate formation by enhancing contacts ofmethane and hygrophanous gel particles. After hydrate dissociation, some GDW particlesalso connected together and became agglomerative gel particles; the others still kept gooddispersion and can store methane for4~6times due to the supporting action of gel. ThoughGDW primarily realized reversible methane storage, the storage capacity/rate was inferior tothat of DW and decay of storage capacity/rate existed in GDW system.Another modified dry water, dry solution (DS), was prepared by mixing0.03wt%sodium dodecyl sulfate (SDS) solution, hydrophobic SiO2nanoparticles and air in a high speedblender. SDS-DS combined the good dipersity of DW and the surface activity of SDSsolution. Each SDS-DS droplet can be considered as a micro system of surfactant solution.SDS-DS can enhance gas-liquid contacts and promote methane hyrate formation formmacroscopic and microscopic aspects. The dispersion effect of SDS-DS samples with variouscontents of SiO2was different, but no obvious kinetic differences of hydrate formation wereobserved among them. Rates of methane hydrate formation in these SDS-DS systems were allnearly equivalent to that of single SDS solution and all storage capacities were higher thanthat of SDS solution. The sample with7.5wt%SiO2exhibited about the same CH4storagecapacity as dry water (7.5wt%SiO2), but about twice faster rate than dry water. ThoughSDS-DS combined the advantages of dispersed liquid and surfactant solution, thecapsule-structure of droplets was still destabilized after hydrate dissociation.Aluminum foam (AF) can provide numerous natural micro vessels with excellent thermalconductivity wall. The addition of AF into SDS solution can promoted hydration heatremoval and accelerate methane hydrate formatioin. The acceleration effect of SDS-AF onhydrate formation is superior to that of SDS itself. Increment fractions of maximum hydrationrates in the presence of AF became smaller with the increasing pressure. Under low pressure,the addition of AF also can promote hydrate nucleation due to its rough metal surface. Areliable heat conduction model based on two-phase materials with spherical inclusions hasbeen applied to determine the effective thermal conductivity (ETC) of hydrate-AF―composites‖. The predicted ETC of composites was132times higher than the thermalconductivity of methane hydrate.The systems of copper foam (CF) filled with DW or GDW exhibited better storage ratecompared to single DW systems or GDW systems, respectively, because the addition of CFaccelerated hydration heat transfer. For each system, the increment fraction of maximumhydration rates in the presence of CF became greater with the increasing pressure. The metalframework of CF can not play a supporting action in DW or GDW systems and thecapsule-strcuture of droplets in the two systems was also destroyed after hydrate dissociation.The destruction degree was more serious than the systems without CF.Fast methane storage was achieved in above static systems by enhancing gas-liquid contacts and removing the hydration heat timely, which can provide significance informationon large-scale production of hydrate.