Table of Contents
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) is another term for waste vegetable oil.
Sources and composition of WVO
Cooking oil, fryer oil, grease trap waste, yellow grease, etc. comprise WVO. Used commercial cooking oil such as palm oil, canola oil, peanut oil is a major source of WVO. Other fats such as chicken fat, beef lard, fish oil, etc. are also in WVO.
Contaminants in WVO
Water is the main 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 WVO.
In the presence of soap (detergent), water and oil combine to form an emulsified phase in WVO. 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 in the WVO.
Uses of purified WVO
Purified WVO is mainly used as feedstock for biodiesel production. 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.
Clean WVO is used as a fuel in diesel engines. It is also used as lubricant or feedstock for lubricant manufacturing. Low quality (not purified) WVO is sought as heating fuel for residential and commercial heating.
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.
How does an industrial centrifuge purify WVO?
WVO industrial centrifuges exert high centrifugal force on the WVO. This force causes the sludge and water to separate from the oil.
The internal design of the WVO industrial centrifuge allows the separated water and oil to exit the centrifuge bowl through separate passages. Clean oil exits the centrifuge and so does the separated water.
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.
The separated sludge accumulates inside the bowl cavity. This sludge is automatically ejected by the ‘self-cleaning’ centrifuge on a periodic basis.
How clean is the WVO purified by an industrial centrifuge?
A disc stack type industrial centrifuge can produce 99% or better clean oil from WVO. Processing temperature and centrifuge tuning are key to high separation efficiency. The separated water phase contains trace amounts of oil. Centrifuge tuning 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%. This depends on the centrifuge settings and processing temperature.
Case study of centrifuge on WVO processing.
WVO customer background
A large-scale, mid-west WVO collection company processed 6M gallons per year. They collect waste oil consisting of grease trap waste, UCO, yellow grease, restaurant slop oil, fryer oil, etc.
The company was using the age-old method of heating and settling to get good oil from their WVO. In this process, the processor heats the WVO and allows it to settle under gravity. They then decant the clean oil off the top leaving the ‘rag layer’ (emulsion), water, and sludge in the tank.
WVO processing challenges
There are many challenges with this method of purifying WVO. Some of these are listed below.
- Settling under gravity takes time – it is a slow process.
- Settling also requires storage volume – more investment in tanks.
- Heating large volumes of crude WVO is energy-intensive.
- Decanting clean oil leaves a lot of ‘good’ oil in the tank bottom.
- Cleaning tank bottoms are essential to reclaiming storage volume.
- Disposal costs associated with a large volume of tank bottom waste.
Centrifuge selection and validation process
The WVO company contacted Dolphin Centrifuge in mid-2018. They wanted to investigate using an industrial centrifuge to improve their process efficiency.
The customer provided a detailed process flow diagram (PFD) to Dolphin Centrifuge. The PFD provided details on their existing facility, equipment, and process.
Customer sample testing
Dolphin Centrifuge has extensive past experience with WVO processing. Based on our experience we suggested pilot-scale centrifuge testing the customer’s WVO sample.
As part of this process, we run a small sample of the process fluid through our small-scale disc stack centrifuge. This is a 3-phase centrifuge capable of separating water, oil, and sludge.
Phase separation, if confirmed by pilot-scale testing, assures the customer on the applicability of disc stack centrifuges for their process.
WVO sample testing results
The test results showed excellent separation at an optimum process temperature of 180F. The test simulated a flow-rate of about 40 GPM. This was the customer’s preferred throughput rate in production.
The customer compared the clean oil from the test centrifuge with their product. The disc-stack centrifuge produced a much better product. The centrifuged clean oil had no sludge and < 0.05% water!
Based on the test results, Dolphin offered a detailed technical proposal for a centrifuge system. Dolphin also provided an improved PFD for the customer’s existing plant. The intent was to repurpose some of the existing pre-straining equipment.
Quality of the purified WVO and centrifuge related cost savings convinced the customer to order the centrifuge system.
Installation, startup, and benefits of WVO centrifuge system
Dolphin Centrifuge designed and manufactured a complete, turn-key centrifuge system. It has the capacity to process 30,000 gallons of WVO per day. The customer installed the centrifuge system at their facility under our guidance. After installation, Dolphin engineers helped startup the centrifuge system at the customer’s site.
Labor (decanting, changing filters, etc.) and material cost savings (filter media, etc.) were soon realized. The customer was able to recoup the capital investment in less than 6 months of installation! The ~30% increased throughput was an extra benefit. Their annual throughput was on track to reach 8M gallons.
The centrifuge also eliminated some of the settling tanks.
WVO centrifuge specifications
Featured image (on top) shows the centrifuge supplied for WVO processing at 40 GPM.
Listed below are the components and accessories of this centrifuge system.
- Alfa Laval WHPX510 Self-Cleaning Disc Stack Centrifuge
- VFD Control PD Feed Pump
- Automatic PLC/Touch-Screen Control Panel
- Sludge Tank with Sludge Disposal System
WVO centrifuge capabilities
The centrifuge is capable of 3-Phase separation of WVO to remove all free-water and sediment down to 0.5µ. The system can process up to 40 GPM of WVO at 180 F to separate all free water and sludge.
In summary, an industrial centrifuge is an ideal solution for the purification of WVO. As detailed above, it is cost-efficient for large scale purification of WVO.
Contact Dolphin Centrifuge for more information or to discuss your particular application with our centrifuge experts!