Ensuring Safety and Efficiency in Vertical Liquid-Gas Separators with Analysis

Ensuring Safety and efficiency in vertical liquid-gas separators with analysis

Key words: flow regime, multiphase flows, computational fluid dynamics, mist eliminator, re-entrainment

 Abstract:  Liquid-gas separators or Knock-out drums are used to eliminate liquid droplets from upstream multiphase flows from being carried to downstream compressor and rotating equipment.  Liquid in any quantity is a safety concern since droplets may cause erosion damage in blades and corrosion in other downstream equipment if there is water present. Some common liquid gas separators in LNG are Dryer inlet separators, filter coalescers, Molecular sieve dehydrators, regeneration gas knock out drum and propane suction drums.  Most of these devices use mist eliminators, vane pack and use gravity, droplet coalescing and shear and momentum of the two streams for separating liquid.   GPSA standards place stringent Souder Brown coefficient (k-factor) to ensure that the velocities at the mist eliminator are sufficiently low to ensure no flooding of mesh.  However the incoming flow regime is unknown and high gas velocity may cause liquid re-entrainment from the free surface and also droplet shearing at the inlet device.  Localized flooding due to non-uniform incoming vapor distribution may lead to reduced carry over efficiency and may be verified using CFD.  This work deals with using several analysis tools and empirical correlations to study and reduce liquid entrainment into the outlet stream. Conclusions so drawn may be useful in future enhancements to the design of vertical liquid-gas separators.