Abstract
Research on hydrate dissociation mechanisms is critical to solving the issue of hydrate blockage and developing hydrate slurry transportation technology. Thus, in this paper, natural gas hydrate slurry decomposition experiments were investigated on a high-pressure hydrate experimental loop, which was equipped with two on-line particle analyzers: focused beam reflectance measurement (FBRM) and particle video microscope (PVM). First, it was observed from the PVM that different hydrate particles did not dissociate at the same time in the system, which indicated that the probability of hydrate particle dissociation depended on the particle’s shape and size. Meanwhile, data from FBRM presented a periodic oscillating trend of the particle/droplet numbers and chord length during the hydrate slurry dissociation, which further demonstrated these micro hydrate particles/droplets were in a dynamic coupling process of breakage and agglomeration under the action of flow shear during the hydrate slurry dissociation. Then, the influences of flow rate, pressure, water-cut, and additive dosage on the particles chord length distribution during the hydrate decomposition were summarized. Moreover, two kinds of particle chord length treatment methods (the average un-weighted and squared-weighted) were utilized to analyze these data onto hydrate particles’ chord length distribution. Finally, based on the above experimental data analysis, some important conclusions were obtained. The agglomeration of particles/droplets was easier under low flow rate during hydrate slurry dissociation, while high flow rate could restrain agglomeration effectively. The particle/droplet agglomerating trend and plug probability went up with the water-cut in the process of hydrate slurry decomposition. In addition, anti-agglomerates (AA) greatly prohibited those micro-particles/droplets from agglomeration during decomposition, resulting in relatively stable mean and square weighting chord length curves.
Highlights
Non-stoichiometric, and clathrate solid consisting of water molecules and small gas molecules, wherein water molecules form hydrogen bonds in cages, gas molecules as guest molecules are wrapped in them [1]
Natural gas hydrate slurry decomposition experiments were investigated on a high-pressure hydrate experimental loop
A focused beam reflectance measurement (FBRM) probe and a particle video microscope probe were installed at the inlet of the test section, which allowed monitoring the evolution of (PVM) probe were installed at the inlet of the test section, which allowed monitoring the evolution of objects—droplets, bubbles, and solid particles—carried inside the flow
Summary
Non-stoichiometric, and clathrate solid consisting of water molecules and small gas molecules, wherein water molecules form hydrogen bonds in cages, gas molecules as guest molecules are wrapped in them [1]. The hydrate dissociation in a flowing system would be far more complicated, compared to these above morphological studies [24,25,26,27,28,29,30] of a single hydrate particle under static conditions Both decomposed and original particles coexist in a flowing system, increasing the probability of particle collision, agglomeration, and breakage under the shear effect. The FBRM and PVM were used to in situ to observe and record particle chord length and morphology, tracking the change degree of particles/droplets, and measuring the particle chord length, shape, and number during the hydrate decomposition process. These experiments explored the effects of pressure, flow rate, water-cut, and the polymerization inhibitor on the hydrate decomposition. This paper used two kinds of particle chord length treatment methods (the average un-weighted and squared-weighted) to treat the data of hydrate particle chord length distribution (CLD), in order to characterize the overall particle properties and the large-particle chord length trends during hydrate decomposition processes
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