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Multi-Stage Oil Water Separator at Tank Truck Wash Facility

Food-grade transportation company tackles tank truck wash water while growing their business

SAS Tank Oil Water Separator with Active Oil Removal

A food-grade transportation company specializing in the bulk transport of edible oils, syrups, milks and other food products was facing a classic good news / bad news challenge. The good news was that their Midwest based business was growing nicely and a recent merger with another trucking firm promised even more future growth. But while their trucking capacity and utilization grew, the bad news was the increasing constraint on their growth potential posed by the other side of their business, their tank washing operations. Bulk transport of food grade products is subject to federal and state regulation; in-between loads, trucks must be washed out and sanitized properly and in compliance with food safety guidelines. Oily wash water is a challenge to handle properly; the company was encountering capability limitations and capacity constraints on the truck washing side of the business that threated to choke their growth plans. The boss knew something had to change.

“In our business, tank washing is just as important as the transport itself,” explains the company's Chief of Operations. “Our growth opportunities seemed clear enough, but challenges with the tank

The company's truck washing facilities throughout the region serve up to a hundred trucks daily. They wash the trucks with hot water by lowering a custom spray system in through the top hatch of the tank. Certain types of vegetable oil are extremely sticky and difficult to clean and require wash water hot enough to liquify the residual oil and keep it flowing. Some oils and greases can require heating up to 180 degrees F to flow freely. Wash water thick with grease and oil must be treated properly before it’s sent to the city sewer. If it is not treated properly the company could be subject to fines and effectively shut down.

As the company’s customer base grew and expanded, their water treatment requirements grew as well. They experienced growth in regard to the range of products and volumes they transported, leading to increasingly unique challenges with the treatment of their oily wash water involving temperature, peak flow, and viscosity. At one of their main wash facilities, the wastewater treatment system, consisting solely of an oil/water separator, was designed for lower volumes and less challenging conditions. Now it was becoming a major bottle neck in their process flow and their growth potential.

As the company’s customer base grew and expanded, their water treatment requirements grew as well. They experienced growth in regard to the range of products and volumes they transported, leading to increasingly unique challenges with the treatment of their oily wash water involving temperature, peak flow, and viscosity. At one of their main wash facilities, the wastewater treatment system, consisting solely of an oil/water separator, was designed for lower volumes and less challenging conditions. Now it was becoming a major bottle neck in their process flow and their growth potential.

Local treatment plant rejects company's wash water and disposal fees loom

For many years the company relied on an oil water separator to treat their oily water and the separator’s effluent was discharged to the municipality’s water treatment plant. As the system became overburdened, the effluent contained too much residual oil. Finally, when the treatment plant stopped accepting the wash facility’s oily water, it was a wakeup call for management. Without a better option available, the company faced the prospect of costly third-party disposal fees. The situation motivated the team to look closer at their existing treatment system in the hope of making significant improvements.

In other wash applications at their other facilities, the company had successfully employed oil skimmers and oil skimming systems designed and manufactured in the USA by Oil Skimmers, Inc. to remove oil from the surface of wastewater. Confronted with these new oil separation and removal challenges, the company turned to their trusted partners at Oil Skimmers, Inc. for a solution. They were confident the engineering team at Oil Skimmers, Inc’s could evaluate their situation and develop the right plan to address the challenges they faced separating and removing oil from their wash water, get them back in good graces with the city, and eliminate expensive third-party disposal fees.

Tank wash water treatment system gets an Oil Skimmers, Inc. revamp

Designing for peek flow rate and high oil content ensures efficient separation

The Oil Skimmers, Inc. engineering team reviewed the company’s tank washing operation in detail. The nature of their wash process involved heavy surges of very oily washwater at the beginning of the process, eventually slowing to a more steady flow of moderately oily water later in the process. The oil could be very thick and viscous requiring high temperatures to flow properly.

These wash conditions present two challenges for typical oil water separators. The first is oil content. When oil content in wastewater exceeds 10% it spells trouble for most oil/water separators. Beyond 10%, waste oil can flow right through typical separation media in the separator and end up in the “clean” water effluent. The second is when the flow rate of the oily water is very inconsistent. In this compnay’s process, the initial washing procedures produced a surge of very oily washwater early in the process. Later on in the process, a lighter but still inconsistent flow.

The Oil Skimmers, Inc team got to work designing a system that would be effective in these application conditions. They determined that the system should be capacitized to a peak flow of approximately 20 gallons/min, to be able to handle the total flow of 15 to 20 trucks to be cleaned per day, with a single truck wash cycle taking around 45 minutes. The team confirmed that in the first first few minutes of a wash cycle the oil content in the wash-water spiked far above 10% and that percentage gradually decreased during the remainder of the wash process.

SAS Tank Oil Water SeparatorTo address the initial surge of oil and the subsequent variations in the flow rate which are difficult for typical oil water separators, the Oil Skimmers, Inc. engineering team developed a custom, multi-stage oil water separation and oil removal system called a “SAS Tank” to separate and remove the oil from the wash water. SAS is an acronym for Separate And Skim. A SAS tank can be customized to properly manage the often unique challenges of oil / water flow conditions. In addition, it combines the effective separation of oil and water with a tube type oil skimmer that provides continuous, Active Oil Removal™ once the oil reaches the surface of the water.

The importance of Active Oil Removal™

Oil Water Separators with Active Oil Removal“Active oil removal” is a key feature of Oil Skimmers, Inc. SAS Tanks and allows them to excel where many oil water separators fall short – waste oil removal after oil water separation. Traditionally, separators feature passive oil removal methods such as slotted pipes or overflow weirs that are intended to allow surface oil to overflow and drain to a collection vessel. These methods require monitoring and manual adjustment, demanding time and labor from maintenance personnel. If left unmonitored which most seem to be, a weir or slotted pipe set too high can cause a layer of oil to build up on the surface, causing a host of other maintenance and performance problems, including:


  • Buildup of oil on the surface… which prevents oxygen from reaching the water’s surface, resulting in formation and growth of anaerobic bacteria that can cause skin irritation, clog coalescing media and emit foul odors

  • Dirt and debris collecting on the oil layer… which combine to form a heavy sludge. Eventually the surface sludge tends to sink, effecting the performance of coalescing media and disrupting the operation of the separator. Risk of oil “flush out” … where any sudden or heavy inflow of water (for example, from an increase in production or from stormwater) can exceed the separator’s capacity, washing out the oil layer that has gathered on top and causing it to mix with the clean effluent.

  • “Crowding” … where the oil layer takes up an increasing space in the separation chamber, reducing the overall separation area and thus reducing the functionality and efficiency of the separation process.

Conversely, if a slotted pipe is set too low, too much water escapes with the oil, defeating the purpose of the separation system, allowing too much water in the oil waste stream and thus driving up the cost of haul away and recycling. It’s expensive enough to have “pure” waste oil hauled away, and even costlier to have water hauled away with it.

“Active oil removal” with a tube type oil skimmer is a 24/7 sentry guarding the performance of an oil water separator, eliminating these concerns, minimizing costs, and maintenance requirements and in general keeps the oil water separator performing at its peak efficiency.

Clogging prevention calls for temperature maintenance and durable materials

Many of the materials transported by this company’s tanker trucks have high viscosity and high melting points. In order to effectively remove them from the inner surface of the tank, the wash water needs to be hot enough to melt them. One of the company’s challenges with their previous system was that as the wash water drained it tended to cool off. By the time the oil reached their oil/water separator it began to re-solidify, clogging the system, slowing down the treatment process and increasing maintenance requirements.

When designing a SAS Tank for this application, the Oil Skimmers, Inc. team concluded that in order to reduce clogging, the tank itself must maintain the high temperature of the wash-water throughout the separation and oil removal process. So heating capabilities were added to the system controlled by an integrated thermostats set to maintain the overall liquid temperature at a minimum of 180 degrees F. The high heat of the system drove the selection of materials for the system that would function well in oily water at these temperatures.

Regulating variable flow with load-sensing pump system

To transfer wash water from the tank to the new SAS Tank oil water separator, the Oil Skimmers, Inc. engineering team developed and integrated a unique pumping system to take water directly from the outlet of the tank truck and deliver it to the SAS Tank at a controlled rate. When water levels in the tanker are low, the the pump waits until more water is available. The system was designed to regulate the flow rate of oily wash water entering the SAS Tank thus ensuring that a steady flow of water will optimize the performance of the media enhanced oil water separation process.

Once inside the separator, the multi-stage oil / water separation process manages the initial flows that contain large amounts of oil relative to the total flow, while still managing the more normal oil / water mixture that flows later in the process. This design protects the separation media and allows the separation process to work properly and effectively, under a wide range of operating conditions that would be difficult for traditional oil water separators. As with all the other equipment that Oil Skimmers, Inc. has been making for 50 years, the system was designed to be rugged, long lasting and maintenance friendly under the toughest industrial conditions.

One year later, the food-grade transportation company looks to Oil Skimmers, Inc. for future tank truck washing sites

The food-grade transportation company has had a busy couple of years. After a successful merger with a fellow transportation company, with the help of Oil Skimmers’ Inc they revamped their approach to managing wash water. By championing the innovative solution intregrated into the SAS Tank oil water separation and skimming system, they were able to conquer their previous challenges and avoid costly disposal fees.

“It's been a perfect long-term solution,” concludes the company's president. “We never would have thought we could get all the features and performance we have received in one system. It’s tailor made to handle our tough operating conditions and has the upside capacity to support our upside growth plans.”

As they embark on expanding their business, the transportation and tank wash operation has deemed Oil Skimmers, Inc. a valued solutions partner, and the two will team up again to address the separation and removal oil from water at another truck washing site, which recently went into operation.

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