Skimming and Separating Oil

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For fleets that transport food grade oils, Oil Skimmers and Oil Water Separators are used to remove oil and knock out high oil concentrations from wash water during the tank cleaning process. PHOTO Oil Skimmers

For fleets that transport food-grade oils, the cleaning of the tank is arguably even more important than the transportation itself.

In the transportation industry, regulations often require tanker trucks that haul food-grade oils to be thoroughly washed out before any new product is introduced.

So, to comply with the various local, state and federal requirements, facilities that clean tank trucks must find cost-effective water treatment solutions to remove the residual oil in wash water before it is discharged into the sewer and sent to a municipal facility.

Failing such regulatory compliance can be costly.  After treatment, if the water contains too much residual oil, municipal water treatment centres can refuse to accept it and levy hefty surcharges and fines.

In addition, when recovered efficiently, hydrogenated vegetable oils can be sold at a profit to companies making biofuels.

However, every tank truck wash facility is unique and must accommodate a wide range of variables. These can include different local or state regulatory requirements, the number of trucks washed, truck sizes, types of oils hauled, oil/water ratios, peak periods of use, changing flow rates, environmental conditions, and facility size and layout.

Particularly difficult

Exacerbating matters, hydrogenated vegetable oils (i.e., palm, soy, canola, etc.) can be particularly difficult to remove from the wash water.

Not only does it begin to solidify at relatively high temperatures, but the percentage of oil in the water can be quite high in the initial stages of the wash—a condition that can strain and even overwhelm oil removal equipment not designed to accommodate such high concentrations of oil.

In such applications, several key factors virtually dictate the ultimate design of an efficient oil removal system.

According to Jim Petrucci, Vice President at Oil Skimmers, Inc., a Cleveland, Ohio based manufacturer specializing in separating and recovering all types of waste oils, greases and fats, these include temperature, flow rate, the specific gravity of the oil to be removed, and percent of oil solids in the total flow.

In order to accommodate all these variables and sufficiently remove oil from wash water to comply with regulations, each application should be analyzed by professionals and the oil removal solution essentially engineered to meet the specific requirements of the application.

Ideally, these oil removal systems would be cost-effective, continuous and actively remove food-grade oil no matter the levels of concentration, without costly maintenance or direct supervision. Fortunately, such systems exist today and are growing in popularity.

Oil Skimmers

When a tank truck wash facility has a pit or sump to collect oily wash water, and the oil in wash water naturally separates into a top layer, an oil skimmer can be utilized to remove the oil from the surface.

The most efficient type of oil skimmer uses a Free-Floating Collector Tube that actively and continuously removes the oil and grease as it rises to the surface of the water.

As the tube moves across the surface, oil adheres to the outside, then goes through a series of ceramic scrapers that constantly remove the oil, which then drains by gravity into a collection vessel. The skimmer is not affected by water level fluctuation or floating debris and solids, removes very little water in the process, and operates continuously with minimal attention or maintenance.

“The efficiency of an oil skimmer is not just about removing the oil continuously, but doing so without collecting a lot of water,” says Petrucci.

One successful example of oil skimmer use at a tank truck wash facility involves a Minnesota-based trucking company with a fleet of 250 tanker trucks—35 of which are used to haul soybean oil.  The trucking company cleans its fleet after transportation jobs. However, because the tankers each haul approximately 48,000 pounds of oil, a significant amount of residual oil mixes with the wash water.

Local regulations require the trucking company to remove all residual oil from the wastewater before discharging it to the sewer system. However, when the trucking company reassessed their existing oil removal process, they found glaring inefficiencies.

To clean out the tankers, the maintenance crew was spraying water mixed with a non-toxic cleaner into the trailers. The oil-infused water collected in holding tanks where the crew had to manually skim the oil from the surface of the wastewater.

This practice met local wastewater regulations but was inefficient and labour intensive.  As a result, the company’s head mechanic sought a more efficient, cost-effective method to remove oil from the wastewater before it was treated further in an existing dissolved air flotation (DAF) unit.

The company decided to install a Model 5H Brill tube-type oil skimmer, mounting it directly on the edge of the main wastewater holding tank. Since the installation of the tube-type oil skimmer from Oil Skimmers, Inc., the trucking company no longer needs to manually collect sludge from the wastewater, delivering substantial labour savings.

The company notes that the oil skimmer, which runs continuously, is so effective it enhances the performance of their DAF unit and reduces the amount of flocking agent required, further reducing costs.

According to the mechanic, the oil skimmer saved enough time and money to more than pay for its cost within a few weeks, while meeting the city’s wastewater requirements.

Oil Water Separators 

In applications where waste oil doesn’t naturally rise to the water’s surface, there is a need for equipment that will facilitate the separation of oil and water so the oil can be effectively removed.

These are the conditions that warrant the installation of an oil and water separator with coalescing media. Coalescing media encourages efficient separation by providing the surface area required for non-emulsified oil droplets to combine, or coalesce, forming larger, more buoyant droplets which rise to the surface more quickly and easily.

Traditionally designed separators successfully achieve separation of oil and water under ideal conditions, like consistent flow rate, high temperature, and low oil concentration. But an oily water separator can become overwhelmed when flow, temperature and levels of oil concentration fluctuate and/or exceed the often-narrow design specifications of the oil-water separator tank.

In all cases, proper oil removal following oil and water separation is crucial to keeping a separator running efficiently. Many common styles of oil water separators, though, utilize passive oil removal methods such as slotted pipes or overflow weirs.

Without regular monitoring and manual adjustment from maintenance personnel, these passive removal methods are easily overwhelmed and can allow an oil layer to form, which is one of the primary causes of performance issues in oil-water separators.

A more cost-effective, efficient option today is to install an oil-water separator tank that is combined with a more capable oil skimmer: one that provides continuous, active oil removal.

Integrating an oil skimmer into the oil-water separator design will do more to prevent oil build-up after separation and allow the coalescing media to remain clean. This increases efficiency and minimizes the need for labour, supervision, and maintenance.

An example of such a system involves a Midwest-based, food-grade transportation company, specializing in the bulk transport of edible oils, syrups, milk and other food products. After a merger with another trucking company expanded its customer base, the tank washing operation quickly became a constraint on growth.

“In our business, tank washing is just as important as the transport itself,” explains the company’s Chief of Operations. “Our challenges with the tank washing operations were a growing impediment to our plans.”

The company’s tank truck washing facilities served up to a hundred vehicles daily and involved a process in which a custom spray system was lowered into the tanks through the top hatch.

To treat the oily water that emerged from the cleaning, the company had relied for many years on an oily water separator and the effluent was discharged to a municipal water treatment plant.

As the separator became overburdened, however, the effluent contained too much residual oil and the treatment plant stopped accepting it.

Avoiding costly fees

Facing the prospect of incurring costly third-party disposal fees, the firm turned to Oil Skimmers, whose engineers determined the tank wash process generated a considerable spike in the percentage of oil at the beginning of the wash cycle, before dropping to a more moderate level as the wash continued.

The food-grade oil was also thick and viscous, and because it cooled as it drained, it re-solidified by the time it reached the oil separator tank, clogging the system, slowing treatment, and increasing maintenance requirements.

In response, Oil Skimmers engineers designed a system for these conditions, capable of efficiently handling peak oily wash water flows at the operation.

To address the initial high oil volume and variable flow rate, Oil Skimmers, Inc. customized its SAS Tank oil water separator with multiple stages and custom controls to separate, then actively removed the oil from the wash water with minimal supervision or maintenance.

The SAS Tank Oil Water Separator combined the effective separation of oil and water with a Brill tube-type oil skimmer to provide continuous, Active Oil Removal from the water’s surface.

Because certain types of vegetable oil and greases are thick and difficult to clean, hot water is used in the tank wash process to keep it liquified and flowing.

According to Petrucci, it is important that SAS Tanks are capable of featuring a range of heating options and control systems to maintain the necessary temperatures throughout the process.

High concentrations of oil

When tank truck washdowns show high initial concentrations of oil, traditional oil-water separators invariably require excessive maintenance to perform adequately and often fail to perform at all.

To address high concentrations of oil, Oil Skimmers created a unique, multi-stage oil water separator with process controls and capabilities to “knock out” excessive amounts of oil during the oil-water separation process.

Multi-stage oil separators like this one from Oil Skimmers, use process controls and capabilities to knock out excessive amounts of oil during the separation process. PHOTO Oil Skimmers

The separator effectively minimizes clogging and maintenance concerns, while ensuring optimal separator performance. This oil water separator design has been dubbed the Triple Action Knock-Out (TAKO) or TAKO Tank.

As the oil separation process in the TAKO Tank proceeds, and as oil reaches the surface, the onboard Brill tube-type oil skimmer provides continuous, Active Oil Removal from the water’s surface, completing the final “knock out” of oil.

While customizing the configuration and options to efficiently remove oil from tank truck wash water today is important, so is working with a partner that can easily make adjustments when circumstances change.

As volumes, oil-water ratios, and other factors continue to evolve, adapting and tailoring the oil-water separator design to both current and future needs will reliably minimize the cost of compliance as well as labour, operation, and maintenance.

“Whether the application involves just oil skimming, or separation of oil and water prior to skimming, it is important to consider all the factors that can be essential to productivity and profitability,” says Petrucci.


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