Fuel Gas Hydrate Formation Probability Distributions on Quasi-free Water Droplets

Abstract

We systematically studied the formation probability distributions of methane–propane (C1/C3) mixed gas hydrates on a quasi-free water droplet as a function of the mixed gas pressure of up to 14 MPa. It was found that the maximum achievable subcooling temperature (ΔT) distributions of C1/C3 mixed gas hydrates on a quasi-free water droplet were significantly greater than those on a water sample contained in a glass sample cell, for all of the mixed gas pressures studied. The most probable subcooling was on average around 31 K on quasi-free water droplets, which was significantly greater than that on the water sample in a glass sample cell of around 14 K. The minimum subcooling was around 18 K on a quasi-free water droplet, which was significantly greater than that on a water sample in a glass sample cell of 4 K. The width of the Tf distribution showed a wide variation, from 6 to 22 K. This range of variation was similar to that of a water sample contained in a glass sample cell. We also carried out a series of control experiments using nitrogen gas at elevated gas pressures to decouple the C1/C3 mixed gas hydrate formation events from the ice formation events. Finally, the effect of ethanol vapor, a thermodynamic hydrate inhibitor (THI), which had been reported to enhance the rate of methane hydrate growth when seeded with ice, was also studied. The results showed that ethanol vapor reliably inhibited nucleation of C1/C3 mixed gas hydrate at all gas pressures studied.