A water droplet size distribution dependent modeling of hydrate formation in water/oil emulsion

Abstract

Experimental data on chord length distributions and growth rate during methane hydrate formation in water‐in‐oil emulsions were obtained in a high pressure stirring reactor using focused beam reflectance measurement and particle video microscope. The experiments were carried out at 274.2 K for 10–30% water cuts and agitation rates ranging from 200 to 500 rpm initially at 7.72 MPa. Rapid growth was accompanied by gradually decrease in rate. Free water was observed to become depleted during rapid growth while some water remained encapsulated inside hydrate layers constituting a mass transfer barrier. The apparent kinetic constants of methane hydrate formation and free‐water fractions were determined using a newly developed kinetic model independent of the dissolution rate at the gas–oil interface. It was illustrated that continued growth depends on distribution and transfer of water in oil‐dominated systems. This perception accords with observations of hydrate film growth on suspended water droplet in oil and clarifies transfer limits in kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1010–1023, 2017

Effects of Combined Sorbitan Monolaurate Anti-Agglomerants on Viscosity of Water-in-Oil Emulsion and Natural Gas Hydrate Slurry

“…The viscosity probe was located in the middle of the high-pressure reactor to ensure that reliable trends of viscosity are obtained by representative sample deflected into the probe. The ability of adopted anti-agglomerants to disperse particles evenly was confirmed through sapphire-cell experiments [11] and observations by particle video microscope (PVM) and focused beam reflectance measurement (FBRM) probes with small flow shear rate [21]. The experiments were maintained at stirring condition during the whole process and, thus, the fluid should be fully dispersed owing to the addition of anti-agglomerant as emulsifier [3,31] in the water/oil systems and continuous shear.…”

“…The depletion of free water would lead to a smaller capillary bridge force between particles [13,14]. With continuous flow shear, particle size distribution tends to stabilize [21]. Thus viscosity would drop slightly and remain constant.…”

“…Upon nucleation, as shown in Figure 7 at time zero, system viscosity usually rises gradually and fluctuates with increasing conversion ratio of water. After conversion for 6 h, conversion ratio of water reaches approximately 56% and stabilizes when formation ceases due to the depletion of free water [21] and mass transfer resistance [1]. With the notably decreased formation rate, viscosity tends to level off.…”

“…After conversion for 12 h, the constant temperature and pressure conditions correspond to the natural gas hydrate stability field, while formation ceases and water is far from full conversion, as indicated in Table 2. This implies that remaining water is encapsulated in hydrate layers hindering the contact and reaction of host and guest molecules [1,21]. After formation stops, the volume fraction of particles, distribution of different phase, particle size distribution and relevant viscosity tend to stabilize.…”

“…The collision and agglomeration of particles and droplets would also cause the formation of water film around hydrate particles [21]. The location and amount of water could be an important variable in determining overall cohesive force [22].…”