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Experiments Related to the Performance of Gas Hydrate Kinetic Inhibitors
Author(s) -
SVARTAAS T. M.,
KELLAND M. A.,
DYBVIK L.
Publication year - 2000
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.2000.tb06830.x
Subject(s) - subcooling , hydrate , clathrate hydrate , nucleation , induction period , chemistry , kinetic energy , flow assurance , thermodynamics , chemical engineering , boiling , organic chemistry , quantum mechanics , engineering , catalysis , physics
A bstract : (1) The hydrate formation process and growth is described through three different stages: (a) an induction period (nucleation), (b) a slow growth period prior to (c) a final stage described by a catastrophic, fast growth rate. In this paper the effect of kinetic hydrate inhibitors (KI) is characterized by the total delay of the catastrophic growth process at given subcooling ratios at given pressures. (2) The effects of a 20,000 M w PVCap on a structure I (sI) ethane hydrate and a sII synthetic natural gas (SNG) hydrate have been examined in sapphire cells. A baseline was first established for each of two hydrate forming systems to describe the respective induction periods, slow growth periods, and initial growth rates. Without inhibitor, at similar subcoolings, and at similar pressures a longer induction period and a slower growth rate were observed prior to the catastrophic stage for the sII hydrate system as compared to the sI hydrate system. By the addition of 5,000 ppm PVCap to the aqueous phase the total delay of the catastrophic growth stage increased by a factor 12 for the sII SNG‐hydrate system and by a factor 5 for the sI ethane‐hydrate system. (3) The effect of different kinetic hydrate inhibitors (KI) at various pressures ranging from about 65 bar and up to about 200 bar has been examined in high pressure sapphire cells using a sII hydrate forming condensate‐SNG‐synthetic sea water system (SSW, 3.6% salt). For all the experiments reported the degree of subcooling (Δ T ) with respect to the hydrate equilibrium properties of the fluid system used was kept at a similar magnitude. This was done to examine KI effects at similar degrees of subcooling within the different pressure regions. The experiments at constant Δ T showed that the KI effect (i.e., total delay of the catastrophic growth stage) decreased with increasing pressure and that a dramatic decrease was observed for increasing pressures above 90 bar. The true driving force of a hydrate forming system is described through a chemical potential, Δμ, which is a function of pressure (i.e., fugacity) and absolute temperature (K). At a given Δ T the chemical potential is greater in the high‐pressure region than in the low‐pressure region.