This work presents experimental results on droplet entrainment in two different geometries: a stratified liquid film, and a wire flooded by liquid. The experiments feature the system pressure ranging from 900 to 1600 kPa (130 to 220 psia) and surface tension of the system in the lower range of 24 mN/m.
The resulting droplet size distribution after a liquid entrainment event plays a major role in the modeling of the gas liquid scrubbers. When a mesh pad-based separator gets flooded, the high speed gas running throughout the mesh can reentrain the liquid and carry over liquid droplets into the dry gas processing facility.
Conventional correlations for liquid entrainment overestimate the resulting droplet size as they were derived from higher surface tension systems. In addition, a correlation for the entire droplet size distribution is presented.
A description of the interaction between the phases in multiphase flow is of major interest for the oil and gas industry as the presence of droplets in the gas phase can cause erosion and breakdown of equipment. The use of conventional separators at high pressure may not be sufficient since very small droplets may be entrained from liquid films at the walls. The droplet size plays a major role in choosing which separation technology is to be used, as smaller droplets are more difficult to separate than bigger drops, given the smaller ones have low inertia and will follow the gas stream lines.
The droplet separation process normally takes place inside a gas scrubber or separator. In a conventional vertical gas scrubber/separator the gas/liquid mixture typically enters the separator sideways through the inlet vane, then flows upward through a mesh pad or vane pack and finally through the cyclone deck. A schematic drawing of the separator is shown in Fig. 1. A detail description and characterization of a scrubber can be found in Austrheim et al. (2006).
When the gas/liquid mixture enters the separator the major portion of its liquid is removed in the inlet vane. The inlet vane is intended to redistribute and redirect the flow before reaching the mesh pad. The mesh pad is an arrangement of knitted wires that can be placed on top of each other or rolled into a cylindrical structure. The mesh pad is based on separation by droplet impactation to the wires. At low pressures, a mesh pad can give a very high separation efficiency, but when operating at high pressures the efficiency drops. Under high pressure conditions the mesh pad is in practice used as a coalescer and operates at, or above, the flooding point. At the flooding point, the liquid load is higher than the liquid drainage capacity and the gas re-entrains the liquid surrounding the wires (Helsør & Svendsen 2007).
