| A promising alternative to compressed natural gas (CNG) is adsorbed natural gas (ANG). Inthe ANG system, natural gas is stored in an adsorbed state within the microporous adsorbents atroom temperature and a moderate pressure3MPa-6MPa. However one of the problems whichare the main restraining of the ANG storage on the car is the thermal effect of ANG tanks in theprocess of charge and discharge, and this problem is still not solved. In allusion to the influenceof thermal effect, the main factor which caused the temperature gradient of the adsorption bedwas analyzed, the measures which alleviated the thermal effects was put forward. The results areas follows.It was simulation for the charging process of ANG tank. The temperature fields ofcylindrical tank’s adsorption bed was an object of study, which was obtained in the flow rate10L/min for charge process, and the charging process of ANG tank was used to develop themathematical modelling by ANSYS transient thermal analysis module. Some measures werecompared, such as charging thermal conductivity of the adsorption bed, built-in thermallyconductive sheet for adsorption bed and setting U-tube in the center of the tank and theflat-shaped structure,those measures had the influence on the temperature of adsorption bed. Theresults, it’s best to weaken the temperature gradient and the average temperature of the adsorbentbed, when the thermal conductivity of adsorbent bed was0.5W/(m。 C)to1.5W/(m。 C)andthe number of built-in thermally conductive sheet for adsorption bed was3to5. The localtemperature and averaging temperature of the adsorbent bed could be significantly reduced bythe U-tube with circulating water, but the effect of improving was weak for the temperaturegradient of the adsorbent bed. It was less about the temperature gradient of flat tank’s adsorbentbed, and the flat tank did not require additional supplementary equipment, the sorbents was filledconveniently.Synthesis of composite adsorbent for ANG. A new composite carbon monolith which wassynthesised activated cathon with expanded graphite was prepared by compression. A optimumscheme for the synthesis of composite adsorbent was obtained by adopting the orthogonalexperimental design method, and the experimental result showed that expansible graphiteexpanded at the temperature of600℃for about30second, mixing ratio of activated carbon withexpanded graphite was1:1by mass, the pressure of composite was9MPa; According to the different mixing ratio of activated carbon with expanded graphite, the composite adsorbent wassynthesized. And sorption capacities of the composite adsorbent were studied. The result wasthat when the mass ratio of activated carbon increased in the composite adsorbent, the amount ofnatural gas adsorption enhanced on the composite adsorbent. At4MPa and40℃, the proportionwhich was the adsorption quantity of methane on the composite adsorbent(1:4) and on activatedcarbon was0.696.Charging and discharging tests for ANG tank. According to the results of simulation, thebasic structure of the tank was determined, and a small flat-shaped tank whose volume was1385mL was manufactured. There were three situations to fill the adsorption beds, that wereactivated carbon, composite adsorbent and combination of activated carbon with thermallyconductive sheet. At ambient temperature, the charging and discharging of natural gas was testedon the three situations respectively. The results showed that when the charging and discharginggas of rate and the amount of filled activated carbon were same, the maximum temperature offlat tank was25℃lower than the cylindrical tank; The heat of effect which was the adsorbentbed with the composite adsorbent could be weakened, but the mass transfer of methane was notconducive in the adsorbent bed, and the process of adsorption was delayed; For the effectivelyrate of discharge, with the increasing discharge ratio, the amount of residual gas increased in theadsorption tank, and discharge efficiency reduced. |
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