Experimental Investigation On Enhanced Heat And Mass Transfer In Methane Hydration

Hydrate based natural gas storage allows the high density natural gas storage under the medium temperature section(~273 K)and relatively mild pressure(P=4~10 MPa).In order to solve the problem of slow methane hydrate formation kinetics and achieve the goal for high density natural gas storage under lower operation pressure,enhanced heat transfer and enhanced mass transfer were concentrated in this article.The dual enhanced effects of heat and mass transfer and dual mass transfer enhancements were systematically studied in this article.Two kinds of hydrophobic metal foams were applied into 0.03 wt% quiescent SDS solution system(aluminum/copper,with the corresponding porosities of 72.8% and 95.0% respectively).The experiment results of methane storage within 15 min from the nucleation point were shown as follows.(1)In the presence of hydrophobic coatings,38.7% maximum increase in gas storage capacity and 1 MPa reduction in operation pressure were observed by the comparisons between hydrophobic aluminum foam-0.03 wt% SDS solution system and aluminum foam-0.03 wt% SDS solution.It could be well illustrated that better enhanced mass transfer effect was observed in hydrophobic aluminum foam.(2)With the adding of hydrophobic aluminum foam and hydrophobic copper foam,87.1% and 26.2% maximum increases in gas storage capacity and the promotion effect of methane hydration under low operation pressure were observed in contrast with 0.03 wt% SDS solution alone,respectively.For one thing,the thermal conductivity of hydrophobic metal foam-air [hydrophobic aluminum foam-air: 4.716 W/(m·K);hydrophobic copper foam-air: 2.205 W/(m·K)] was larger than that of water [0.58 W/(m·K)],which could enhance the heat transfer during the methane hydrate formation in the aqueous solution system.For another,the surface of liquid phase would shrink on account of the existence of hydrophobic coating,which could provide extra channels for the diffusion of methane molecules inside the reaction system.Namely,the mass transfer process was enhanced.Hence,there were dual enhanced effects of heat and mass transfer in hydrophobic methal foams during methane hydrate formation.Dry water was filled into the highly porous hydrophobic copper foam for promotion of methane hydrate formation.The methane storage capacity almost kept constant between the first run and second run of methane hydrate formation.However,the reaction heat couldn’t be rapidly conducted in dry water on account of the highly dispersed structure.And 36% reduce in thermal conductivity was observed in dry water system,compared with the figure of aqueous solution.Therefore,the promotion effect of hydrophobic copper foam in dry water wasn’t as good as copper foam.Leucine dry solution(Leucine plus dry water)was investigated for its influence in methane hydration.On one hand,methane could be well dispersed into water phase by methane bubble in leucine solution(methane dispersion).On the other hand,the water in silica structure of dry water could disperse aqueous solution into gas phase(water dispersion).Both of them have impacts on the gas-liquid mass transfer during the methane hydrate formation,reaching the dual mass transfer enhancement in methane hydration.The research showed that the optimum leucine concentration of leucine dry solution was 0.5 wt%,with the gas storage capacity within 100min(Time zero at nucleation point)of 159.61 V/V.In comparison with dry water alone,the coresponding figure increased over 10%.From the analysis of dual enhanced effects of mass and heat transfer and dual mass transfer enhancements in the quiescent methane hydrate formation process,the performance of hydrate based methane storage could be further improved,which could provide guidance for the industrialization of hydrate based natural gas storage.