Extracting nucleation rates from ramped temperature measurements of gas hydrate formation

Abstract

The formation of solids in the energy industry poses a threat to safety and reliability of operational facilities across numerous process stages. Experimental studies of gas hydrate formation probability are conducted under both fixed-temperature and ramped-temperature conditions. Although a method to extract nucleation rates from constant temperature measurements of induction time probability distributions is well established, extracting such rates from constant cooling data is complicated by the time-dependent driving force for hydrate formation. Here, we present and use a method for extracting the stationary nucleation rate as a function of temperature from constant cooling experiments based on the hazard function, which accounts for the system’s history and the instantaneous formation probability. This method yields nucleation rates consistent with those measured using more time-consuming constant temperature experiments, while providing far more information about the underlying nucleation phenomena by sampling a wider range of temperatures. Measurements of methane hydrate formation probability obtained in well-mixed systems at 12 MPa with temperature ramp rates (1–3) K·min−1 were analysed using a framework based on Classical Nucleation Theory. The results suggest that the heterogeneous nucleation sites primarily responsible for the observed nucleation rate become more numerous and have higher average energy barriers as subcooling increases. This hypothesis is also consistent with recent experimental studies of systems containing kinetic hydrate inhibitors and provides a pathway to more reliable predictions of hydrate formation probability in production systems that experience a wide range of subcoolings.