Improving Methane Hydrate Formation Kinetics and Gas Storage Capacity with a Promoter
Liang Mu, Huixing Zhao, Ziqi Zhou, Jiguang Zeng, Qingyan Cui
Abstract
Solidified natural gas (SNG) has been viewed as a promising method for the storage and transportation of natural gas, while a primary challenge for this technology remains how to effectively enhance the hydrate formation kinetics as well as its storage capacity. In this study, a natural soil organic matter fulvic acid (FA) was used as the hydrate promoter, and the effect of the FA concentration and experimental pressure and temperature on CH 4 hydrate formation kinetics and gas uptake was systematically investigated. The findings revealed that the presence of FA significantly reduced the CH 4 hydrate induction time and accelerated its gas uptake rate. The CH 4 storage capacity in the 0.25 wt % FA solution reached 105.8 ± 1.1 V/V H at 274.15 K and 5.5 MPa, which was much higher than that of pure water (19.8 ± 0.9 V/V H ) and increased by 18% compared to that of the 500 ppm sodium dodecyl sulfate (SDS) solution (89.8 ± 0.7 V/V H ) under the same conditions. A high initial pressure and low temperature were favorable to obtain a high gas uptake, and the CH 4 storage capacity reached 158.5 ± 0.6 V/V H (volume ratio of gas to hydrate, with the theoretical value being 172 V/V H ) in the 0.5 wt % FA solution at 274.15 K and 8.5 MPa. Morphological observations showed that the CH 4 hydrate formed in the FA solutions was in a small-grained form, suggesting that FA presented the anti-agglomerant effect in the pure water system. No foam was generated during CH 4 hydrate formation in the FA solutions. In comparison to the SDS system, much less foam was observed during the CH 4 hydrate decomposition in the FA solutions, and the foam completely disappeared after hydrate decomposition.