Cost: The root cause of oil/water separator fouling

Posted on Fri, Apr 06, 2012 @ 09:00 AM

On Jan 25th, 2012 Mercer International's lead process engineer David Goding was asked to give a comparative review of oil/water separator coalescing media for Globalspec's Water Quality and Water Reclamation virtual conference. Below is an excerpt covering the emergence of the parallel plate pack in traditional API oil/water separators.

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Background:

Somewhere in the mid twentieth century the "plate pack" was designed and constituted what was the first coalescer to be introduced into the oil/water separation process.  Essentially a series of horizontal plates were stacked up one on top of another and placed inside API oil/water separators. This allowed capture of smaller micron sized oil droplets from the separator in the same sized tank (usually a concrete pit). The surface area of these thick ¼” steel plates would catch smaller oil droplets at the top of each plate and allow them to collide or coalesce into bigger droplets. So instead of only being able to remove oil droplets of 150 micron size, the oil and water separator was now able to hit the 100 micron removal range.

 

Parallel Plate Oil/Water Separator

Industry began to need more efficiency as government regulations ratcheted down the allowable oil concentrations in effluent (See Federal Water Pollution Control Act Amendments of 1972). Seeing how these parallel plate pack inserts were achieving higher removal capabilities, the design no longer required a large tank to achieve the desired removal.  The first packs started with very wide plate gaps, and companies began to tighten up these gaps in the attempt to obtain (claim) higher removal capabilities.

 

The Problems:

 

The first problem with this design was that these large parallel packs fouled very quickly. The presence of solids, and the accumulation of them on these parallel plates, led to very short process runs before shut down and cleaning was necessary. 

 

The second problem was in the material costs required to make such long parallel plates out of steel.  The higher the flow rate, the longer these plates needed to be to theoretically guarantee the desired removal rate. The costs began to climb signifigantly as manufactures began tightening the plate gaps in these horizontal parallel packs. The benefits of the pack were being outweighed by the high costs of construction and the growing maintenance pains of having to clean the oil/water separator very frequently. These problem areas eventually led to manufactures introducing corrugations into their designs to save on material costs, while still maintaining the structural integrity of the packs. This in turn paved the way for the plastic corrugated media that would go on to dominate the oil/water separator market for the next 25 years.

 

What Mercer has learned:

 

Maybe "plague" is the better word choice instead of "dominate" for what the end user community has been forced to endure since the first plate pack was introduced. The manufacturing community truly only addressed one of the two problems in the original design, and that was the cost. The introduction of corrugations into the design of coalescers did nothing to go to the root cause of industry's frustration, which was the fouling and clogging created by solids mixing with oils creating sludge.

 

The Mercer design took root after years of polling end users about what frustrates them most in the oily wastewater treatment process. Overwhelmingly, the problem has been with fouling coalescers that eat up maintenance dollars and compromise allowable effluent levels. 

 

How Mercer manufactures the highest performance oil/water separator 


comparing coalescers

 

 

 

 

Tags: API oil/water separators, flat plate coalescers, plastic corrugated coalescers, oil/water separators