Koch-Glitsch

 

One method for retaining solvent in liquid-liquid columns is by adding a downstream horizontal accumulator/settler. However, this adds significant cost and complexity since the secondary vessel will require additional piping, controls, safety systems, and maintenance. As a cost savings measure, many times the job of solvent retention can be accomplished with a COALEX™ liquid-liquid coalescer placed above the interface level in the liquid-liquid column itself. 

 

The first hurdle in estimating performance requirements
for a vertical-flow coalescer is determining what size
“heavy-phase” droplets will actually be flowing to the top of column. The majority of droplets will be large enough that their terminal settling velocity is greater than the superficial velocity of the up-flowing “light-phase” bulk flow. When given proper settling distance (T-T space), this phenomenon allows these larger droplets to fight the up current – thus never reaching the top of the column. So the question is: at what size droplet is the terminal settling velocity not enough?

 

We can answer this by first determining the superficial velocity of the light-phase flow – above the liquid-liquid interface level. The velocity should be very low, less than
2 ft/min in most cases. Therefore, the low calculated Reynolds number for this stream allows us to reasonably predict dispersed phase droplet size cutoff using the equation for terminal velocity in “creeping flow”:

 

 

or

 

 

Where:

 

V_t = terminal velocity

 d = diameter of dispersed "heavy" phase droplets

μ_c = viscosity of continuous "light" phase
ρ_d = density of dispersed "heavy" phase
ρ_c = density of continuous "light" phase
 g = gravitational constant

 

The diameter of dispersed “heavy-phase” droplets with terminal velocity equal to up-flow continuous “light-phase” velocity is the maximum size droplet that will continue flowing up to the coalescer.   Using that maximum, a droplet size distribution can be generated and the coalescer designed for that range of droplets.  If you are running a liquid-liquid column without a COALEX™ coalescer you may be losing valuable solvent in the light phase outlet.

 

 

 

Contact your local Koch-Glitsch representative to discuss your needs for a coalescer solution.

 

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