| Gas hydrate cold storage is a newly-developing and efficient energy storage technology,which can solve the problems of low density,low efficiency and easy aging of equipment in traditional cold storage field.Gas hydrate formation,a gas solidification technology,is a phase change process,which enables gas hydrate to play an important role in gas storage and separation,seawater desalination and sewage treatment and other energy problems.However,gas hydrates are facing with such problems as strong randomness of formation,unstable cyclic formation process and slow nucleation and growth of gas hydrates.etc,which restrict the application of gas hydrates cold storage technology.Based on this,the cyclic formation stability of gas hydrate was discussed,the influencing factors of gas hydrate cycle formation and the efficient promoting method of hydrate formation was researched in this paper.The main research contents are as follows.(1)Based on the problem of unclear gas hydrate cycle formation mechanism,the application concept of gas hydrate cycle formation stability in cold storage was proposed in this paper.The cyclic formation stability in pure water system,SDS solution system and SDS+porous media system was compared and discussion.In addition,the hydrate dissociation was promoted by depressirization combined with thermal stimulation.The results showed that the induction time and full time of hydrate cycle formation were more stable and maintained at 40 min and 150 min in the presence of porous media,respectively,which also reduced the time cost and energy consumption cost.In addition,it was concluded that the hydrate decomposition can be completed faster and the decomposition time can be shortened to 150 min the combined dissociation at 0.1MPa.Finally,the mechanism of promoting the hydrate dissociation was summarized.(2)The influence of gas-liquid-solid migration in porous media on the formation of gas hydrate cycle under different working conditions was visually observed and experimentally analyzed by adopting the widely used depressurization dissociation method.The influence mechanism of gas hydrate cycle formation stability in porous media was analyzed systematically.The experimental results showed that the expansion rate of porous media layer was 176% due to gas-liquid-solid migration.At the same time,it was concluded that gas-liquid-solid migration was caused by pore evolution through model establishment and image analysis.The pore evolution was the result of the interaction of effective stress,pore pressure,back pressure and compensation pressure in the porous media.In addition,the abnormal phenomenon in the hydrate cyclic formation of induction time was found due to gas-liquid-solid migration,revealing the influence mechanism of gas-liquid-solid migration on the hydrate cyclic formation.(3)Combined with the problems of nucleation and growth of gas hydrates,the promoted hydrate formation was studied based on the process of boiling-condensation in this paper.A rapid hydrate formation system based on the boiling-condensation cycle was innovatively developed and built,which increased the gas-liquid contact area by an order of orders.The hydrate formation process was shortened from 6.5 days to 35 minutes,and the formation rate increased nearly 4,000 times.The experimental results showed that the boiling-condensation cycle could complete a large amount of hydrate accumulate within 35 min.The boiling-condensation changes the traditional hydrate formation,and increased the original two-interface of the hydrate nucleation interface to four-interface,and updated each interface at all times to achieve the purpose of effectively strengthening the hydrate formation.The effect of the boiling-condensation on the hydrate formation was enhanced efficiently,and the mechanism of the hydrate formation was summarized.Meanwhile,it was found that the hydrate reformation with more production and lower time cost was obviously better than the first formation.It was concluded that the best conditions for the hydrate formation were the experimental temperature of 4℃ and the thermal stimulation temperature of 60℃ during the boiling and condensation process,which could not only realize the rapid formation of hydrate,but also reduced the energy consumption,and providing important technical support for the application of gas hydrate cold storage technology. |
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