WVO Centrifuge for Waste Vegetable (UCO) Purification

Synopsys

The food processing industry generates millions of gallons of contaminated Waste Vegetable Oil (WVO) annually. This used edible oil has commercial value, and an industrial WVO centrifuge is the most efficient way to separate the oil from water and solid impurities.

As compared to commercial (open bowl) centrifuges, a disc-stack type industrial centrifuge generates a very high centrifugal force and has an effective settling area, which is thousands of times larger. For large scale processing of WVO, an industrial centrifuge is a robust and durable solution for used cooking oil recovery.

Waste Vegetable Oil (WVO), Used Cooking Oil (UCO)

The terms mentioned above describe edible oil used in food processing and is no longer useful for cooking purposes due to degradation and contamination from cooking byproducts.

What is WVO?

WVO an abbreviation of Waste Vegetable Oil. Waste vegetable oil is a general term for all kinds of used edible oils. Used Cooking Oil (UCO) and Yellow Grease are other terms for waste vegetable oil.

Sources and Composition

Cooking oil, fryer oil, grease trap waste, yellow grease, etc. comprise UCO. Also, used edible oil, such as palm oil, canola oil, and peanut oil, is a primary WVO source. Other fats such as chicken fat, beef lard, fish oil, etc. are also present in waste vegetable oil.

Typical Contaminants

Water is the primary contaminant of WVO. It can come from the water in the fried food to wash water from food prep. Soapy wash water from cleaning activities also adds to the water content of used cooking oil.

In the presence of soap (detergent), water and oil combine to form an emulsified phase. This emulsion is also known as the ‘rag layer.’ We discuss this emulsion processing in detail further down in this article.

Solids or sludge is the other contaminant in WVO. Flour, crumbs, organic particles, bone fragments, sand, etc. turn to sludge.

Uses of purified WVO

Feedstock for biodiesel production is the primary use of purified WVO. Biodiesel processing requires clean WVO without any water or sludge. Biodiesel procedures prefer the least FFA (Free Fatty Acids) in their feedstock. In-fact, neutralizing FFA in the WVO is essential before making biodiesel.

Diesel engines use clean WVO as a fuel. Lubricant or feedstock for lubricant manufacturing is another use. Residential and commercial heating uses low quality (not purified) WVO fuel.

Other uses of WVO include the manufacturing of soap, cosmetics, clothing, elastomers, etc.

The sludge separated during WVO purification has nutritional value. It retains fat and other nutrients from processed foods. WVO sludge is a good animal feed additive.

WVO Centrifuge

A WVO Centrifuge is an industrial centrifuge designed to remove water and solid impurities (sludge) from Waste Vegetable Oil (WVO). It is a three-phase, industrial, disc-stack centrifuge which separates the used edible oil from free water and fine sediment down to a 1-micron level, continuously.

Operation

A WVO centrifuge exerts a high centrifugal force (up to 8,000 Gs) on the used oil. This force causes the sludge and water to separate from the WVO, and the separated water and clean oil exit the centrifuge through separate passages. The self-cleaning process of the centrifuge periodically discharges the separated sludge.

Emulsified WVO Separation

Emulsified oil is also broken down into oil and water by the centrifuge. The percentage of emulsion separated depends on the presence of soaps. Acid or other demulsifying chemicals help emulsion separation.

Emulsion breaking releases more oil for the producer. Read about waste oil emulsion breaking with an industrial centrifuge here.

How well does an industrial centrifuge purify the WVO?

A disc stack type industrial centrifuge can produce 99% or better clean oil from WVO. Processing temperature and centrifuge tuning are critical to high separation efficiency. The separated water phase contains trace amounts of oil. Further tuning of the centrifuge can reduce this oil in water to a minimum level for water disposal.

WVO solids separated by an industrial centrifuge comes out as a thick sludge. It is pumpable sludge but not runny. Oil content in this sludge varies from 10% to 50%, depending on the centrifuge settings and processing temperature.

Benefits of Disc Centrifuge versus Open Bowl (Disc-Less) Centrifuge and Filters

	Disc Centrifuge	Open Bowl Centrifuge	Filtration
Centrifugal Force (Gs)	8,000 ~ 10,000	500 ~ 1,500	N/A
Construction	Industrial Grade	Commercial Grade	Industrial Grade
Bowl Material	316L Stainless Steel	Aluminum or Carbon Steel	All Material (Housings)
Capacity (Gallon/Minute)	3 ~ 100+	0.1 ~ 7	1 ~ 500+
Separation Efficiency	0.5 Micron	100 Micron	0.1 Microns
Water Separation	Continuous (Any Proportion)	Not Capable	Not Capable
Sludge Removal	Automatic During Operation	Manual (Stop Centrifuge)	Manual
Operating Mode	Continuous	Batch	Batch
Equipment Cost	High	Low	Cheap
Labor Cost	None	Medium	Very High
Media Cost	None	Noce	Very High

Waste Vegetable Oil (WVO) Centrifuge Plant Setup

The diagram below shows a typical centrifuge based WVO/UCO/Brown-Grease recovery plant layout. A description of each step of the process follows the schematic.

WVO Collection Tank (Agitated)

The incoming collected WVO is dumped into the collection tank, as shown. This tank is typically agitated to keep the sludge from settling. It is advisable to keep this tank heated to reduce the thermal load on the system heater. Special consideration is given to the tank design to alleviate sludge blocking issues.

Slurry Feed Pump

The feed pump is a positive displacement pump with a high sludge handling capacity. It functions to transfer the raw WVO to the centrifuge or back to the tank when it in bypass mode. In this bypass mode, the pump also acts as an agitator to keep the tank from settling. It is critical to protect the pump from WVO specific issues, which we design into our system.

Duplex Strainer

The duplex strainers protect the downstream centrifuge from damage due to large solid contaminants such as rocks, debris, twigs, rags, bones, etc. We recommend specially designed strainers for a quick change and long-term durability of the equipment.

Heat Exchanger

For maximum centrifuge separation efficiency, the WVO needs to be hot! The ideal processing temperature is around 180 F. An inline heater (or heat exchanger) is perfect because it only heats the oil in the process instead of heating the entire tank of 1000s of gallons. We have specially designed heaters, which are gentle heating to avoid overheating and burning of the UCO.

3-Way Valve

This 3-way valve works as a diverter valve to recirculate the oil when the centrifuge is not ready for processing or is in cleaning mode. Our PLC automatically operates it with many process parameters influencing this valve’s operation and position.

Alfa Laval 3-Phase Disc Centrifuge

The centrifuge is the heart of the system where the separation takes place. A previous section describes the purpose of this device and its operation.

Sludge Tank

The ‘self-cleaning’ WVO centrifuge ejects the sludge through the bottom of the centrifuge frame. Therefore, a sludge receptacle is placed under the centrifuge to collect the separated sludge. Our system integrates this sludge tank into the centrifuge base skid as an option. This design feature allows the centrifuge package to mobile and is not fixed to a location.

Clean Oil Tank

Most self-cleaning Alfa Laval centrifuges discharge the clean oil under pressure. Therefore there is adequate pressure to transfer the pure oil to a local clean oil tank. We also offer an optional upgrade to our WVO centrifuge system wherein this clean oil tank is integrated into the skid.

Separated Water Tank

The water separated by the centrifuge is also discharged under pressure by most disc centrifuges. Depending on the WVO’s anticipated water contamination, the centrifuge may need to be modified to ensure maximum throughput efficiency.

It is often possible to discharge the separated water into the local drain, but we recommend storing the separated water before discharge to verify oil levels.

Auxiliary and Recommended Accessories

Our WVO centrifuge packages typically include sample ports, sight glasses, flow-meters, flow sensors, temperature monitors, and other process-enhancing features. However, we recommend customers procure some additional accessories to understand and draw the maximum benefits from the centrifuge skid. A detailed description and source of each of these accessories are available to our customers.

Waste Vegetable Oil (WVO) Centrifuge Sizing & Specifications

Industrial centrifuges come in a wide variety of sizes and capacities. The following table lists the sizing parameters for WVO centrifuge systems from the smallest, medium, and largest centrifuges. You can always call or contact us to get more information.

Waste Vegetable Oil Centrifuge Specifications
Centrifuge Type	Alfa Laval Self-Cleaning, Disc Stack
Centrifuge Efficiency	Solid Particles > 1 µ ; Free Water > 2 µ
Centrifuge Model	Alfa Laval WHPX 405	Alfa Laval WHPX 510
Bowl Speed (RPM)	8,500	5,180
Rated Capacity (GPM)	23	69
WVO Capacity @ 180 F (GPM)	15	45
Sludge Space (Gal)	0.36	1.55
Motor Power (HP)	5	15
Skid Dimensions (ft)	4′ x 5′	5′ x 6′
Skid Weight (Lbs)	1,500	3,500
* Specifications are for base skid without any options.

Summary

There are various ways and equipment available to clean WVO to recover good, sale oil. If it is a small scale operation (<100 Gallons/Day), a simple heat, settle, filter process will work. However, serious consideration needs to be given to our robust, durable, high-speed, high-G centrifuge for larger volumes. These centrifuges not only produce clean WVO continuously but also separate the water at high throughput capacities.

WVO Centrifuge Systems for Sale

Shown at the bottom are WVO / UCO centrifuge packages of different capacities featuring Alfa Laval centrifuges.