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.

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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.

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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

API Oil/Water Separators: Simple But Costly

Posted on Mon, Apr 02, 2012 @ 09:05 PM

The Origins

Simple gravity separation is where the marketplace began to deal with the removal of oil from water as well as spill containment.  Many older large holding tanks are commonly referred to as API oil/water separators, referring to the American Petroleum Institute who created the design parameters for certain flow rates. The American Petroleum Institute provides design criteria for oil/water separators. A design method is provided in the API Manual on Disposal of Refinery Wastes, Chapters 5 and 6- Oil-Water Separator Process Design and Construction Details (API publication 1630, 1979).  

 

API oil/water separators

The API oil/water separator is a simple gravity separation device designed by using Stokes Law to define the rise velocity of oil droplets based on their density and size. The design of the separator is based on the specific gravity difference between the oil and the wastewater because that difference is usually smaller than the specific gravity difference between the suspended solids and water. Based on that design criterion, most of the suspended solids will settle to the bottom of the separator as a sediment layer, the oil will rise to top of the separator, and the wastewater will be the middle layer between the oil on top and the solids on the bottom.

Advantages of the API separator are simplicity of design, low day-to-day maintenance, and resistance to plugging with solids. 

 

(Below is an excerpt from a presentation Mercer gave at an online Wastewater conference)

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Drawbacks:

API oil/water separators are designed to remove oil droplets down to 150 micron, which is not nearly enough removal necessary to stay compliant today.  Most API oil/water separators are not going to do any better than 50 parts per million as opposed to most state & federal regulations that today require below 20 ppm.

Most industries have abandoned building these large gravity settling vessels because they are simply too costly to justify. Most are built of concrete and with the high cost of labor and the need to reinforce these tanks with steel, new construction costs rise quickly. Plus API units have an excessively large footprint and are far too much of a real estate burden to consider this as a viable option.

Those who have API oil/water separators acknowledge they are easy to operate and maintain on a day-to-day basis, but when it is time to clean out the tank, the cost to pump out the sludge and clean this large space is just a nightmare. Some units have a chain and scrapper mechanism. This helps move the solids to one side to be pumped out, but the automation piece for these are usually as much as the construction of the pit itself—and require significant maintenance as well.

 The Mercer Advantage

 

 

Tags: Oil Water Separator, API oil/water separators