Enhancing methane hydrate formation in bulk water using vertical reciprocating impact

Abstract

A new method to improve the methane hydrate formation rate and gas uptake was developed through continuous impact on hydrate block with high interstitial water cut. Experimental investigations were conducted at temperature and pressure ranges of 273.3–279.2 K and 3.4–6.0 MPa, respectively, for different water loads and impact frequencies. Hydrate formation in quiescent sodium dodecyl sulfate (SDS) solution and pure water with rotational stirring was investigated for comparison. The reciprocating impact intensification method significantly improved the formation rate in both slurry and hydrate block stages as well as the final gas uptake. The fastest formation was observed at 274.7 K and 6.0 MPa, where 90% of hydrate formation was completed within 4 h. The largest gas uptake (150.3 V/V) in the hydrate was observed at 279.2 K and 6.0 MPa, which was slightly higher than that obtained from SDS. The advantage of the proposed method is that the final hydrate block is compacted in a significantly smaller bulk volume than that of the fluffy hydrate formed from SDS. Multi-growth was observed in hydrate formation when the reciprocating impact method was adopted. Temperature and pressure affected the formation kinetics but not methane uptake. The optimal conditions for hydrate formation in bulk water included a water/inner reactor space volume ratio of 0.18 and an impact frequency of 30 times/min. Additionally, the lowest power consumption for reciprocating impact was calculated as 3.77 × 10−3 kW h/mol. These results indicate that it is feasible to store methane using clathrate hydrates without additives.