Oil/Water Separator Design:Beware of the Honeycomb

Posted on Sun, Apr 15, 2012 @ 07:30 PM

You get what you pay for, and most times much less. Below is an excerpt from a virtual trade show where lead design engineer Dave Goding discusses the fouling problems that are guaranteed to occur when using honeycomb/egg-carton plastic coalescer designs:

 

view-full-length-presentation

Once inexpensive corrugated plastic media took over as the “standard” in oil/water separator design, it became a race by manufactures to produce separators with low price as their selling feature. Now the oil/water separator industry was selling their equipment on price instead of features & benefits. Once price became the main selling function, many long-standing internal components and sound design standards began to be cheapened or eliminated. By designing down the coalescer, the inlet and outlet baffles, solids handling capacities, etc., manufactures began sacrificing functionality and efficiency. This drastically reduced the end user’s ability to stay in compliance.

Manufactures tightly pack these plastic bundles in separator units, selling promises of higher surface area and (theoretically) better oil removal capabilities.

corrugated coalescers

The “nooks and crannies” within these coalescers are the problem with this design. The various nooks, crannies, ridges and flat spots cause solids to lodge in and on the plates, building up and fouling the packs prematurely. Further, there is no clear path for solids particles to make their way out of the coalescer. The settling solids have nowhere to go and “dead end” within the coalescer causing even more rapid fouling.

clogged oil/water separator

To further complicate the problem with this design, these style coalescers are nearly impossible to clean. Because of their design, high-pressure washers can only penetrate from 6”-12” into the packs before the velocity is dissipated.

The cleaning becomes very labor intensive. Many times the packs cannot be cleaned all the way through, therefore the end user is forced to throw away these packs after a few cleanings and replace them with new ones. In certain more high-solids applications or applications with “sticky” oils and solids, this could entail a full coalescer replacement every time maintenance is performed.

plugged oil/water separator

Tags: Oil Water Separator, plastic corrugated coalescers, oil/water separators

The Emergence of the CPI Oil/Water Separator

Posted on Tue, Apr 10, 2012 @ 07:38 AM

Why Oil/Water Separator Manufactures Went The Way Of Plastic Corrugated Coalescing Media Decades Ago

Once those treating oily wastewater realized they no longer needed to take on the large treatment footprint of installing API oil/water separation pits or tanks, they were greeted by several new companies entering the oil/water separation marketplace. They also were faced with the difficulty of weighing one manufacturer's removal promises against another.

In response to this, the American Petroleum Institute (API) released a new set of sizing criteria in Feb of 1990 that dealt with the emergence of "plate pack style" or "Coalescing" oil water separators. This document, API Publication 421, went about laying out several calculations that would assist end users in determining how much surface area was needed to achieve an acceptable removal rate at a given flow. 

At that time, the growing fad within the Oil/Water separator industry was to make the coalescing plates corrugated to give the bundles more structural integrity (much in the way a corrugated cardboard box is able to maintain its shape). Originally this allowed a once flat 1/4" piece of steel to go to an 1/8" thickness or less and save on material costs. The manufacturing process went through an even more drastic cost reduction when these sinusoidal shaped plates began to be fabricated out of different types of plastic. The reason for the corrugation was basically cost reductions, as manufactures all went to battle against each other claiming higher removal rates at bargain pricing. 

 

Steel CPI oil/water separatorDownflow CPI oil water separatorplastic CPI oily water separators 

Corrugated Plate Interceptorcpi oil and water separator

 

The standard practice became to position these progressively slanted/tilted S shaped plates in an upflow or downflow position, so gravity could help in one of the two important aspects of the treatment process--downflow for solids and upflow for oil. The problem with the sinusoidal design, or the CPI (corrugated plate interceptor), was that solids would all concentrate in the  trough areas where they would quickly accumulate. The trade off for producing the required surface areas to keep up with higher removal mandates was a design that fouled very quickly.  

fouled oil/water separators 

The unequal distribution of solids loading combined with oils or solids having to work against a given flow, gave way to a new set of problems that would become commonplace in oil/water separation. The frustration with the new coalescing variety of oil/water separators back then, is still a problem today.  Oil/water separators that present themselves as low cost options have serious design flaws that foul prematurely and compromise efficiency. 

 

See Why Mercer Uses A Cross Flow Designed Oil/Water Separator With A Flat Plate 

In January of this year lead process designer Dave Goding had the opportunity to review several of the mainstream coalescing technologies during a keynote at Globalspec's water quality and reclamation virtual conference. Below is an excerpt from his portion that covered CPI oil/water separators.

Click me

 

Tags: Oil Water Separator, API oil/water separators, plastic corrugated coalescers, oil/water separators, cpi oil water separators

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.

 Click me

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