Used Oil Centrifuge

Definition of Used Oil

Used oil is defined as any oil originating in crude oil or petroleum with physical or chemical impurities as contaminants from its use.

The United States produces over 2 Billion gallons of used oil annually. This oil has considerable value as a heating fuel and for reblending into lube oil after recycling.

See the real numbers from a U.S. military contractor's marine waste-oil installation ->

Difference Between Used Oil and Waste Oil

Used oil has mineral-based origins, as in crude oil or synthetic oil. Used engine oil, transformer oil, turbine lube oil, etc., are examples of used oil.

On the other hand, Waste oil is an oil with organic origin such as WVO (Waste Vegetable Oil), Used Cooking Oil, yellow grease, etc.

For waste-qualified systems, see our waste oil centrifuge for sale page.

Reclaiming Used Oil

Used oil reclamation is a thriving industry that collects and purifies used oil in large quantities. These industries use different types of separation techniques that are listed below in the methods section.

Benefits of Used Oil Reclamation

The commercial reclamation of used oil has multiple benefits from a commercial and environmental perspective. Some of these benefits are listed below.

Reduce Environmental Pollution

Used oil discarded in landfills is a significant source of environmental pollution. It contaminates groundwater and soil. Recovery of used oil prevents this pollution.

Feed Stock for Fresh Lube Oil

Refined used oil is a feedstock for the production of virgin lubricating oil. This process allows for the reuse of used oil as a low-cost and environmentally friendly alternative.

Re-refiners use the centrifuge as the front end of that process. Before vacuum distillation or hydrotreating, the collected oil has to be dewatered and de-ashed, and a three-phase disc stack centrifuge does both in one continuous pass. In a typical US re-refining plant the duty is split across capacities: an Alfa Laval MOPX 207 or WHPX 407 on a 20 to 25 GPM collection stream, an Alfa Laval MOPX 209 or WHPX 410 at 40 GPM, and an Alfa Laval WHPX 513 at 72 GPM on 13 cSt diesel on the main feed line, with an Alfa Laval NX-418 decanter ahead of them when the incoming oil carries bulk sludge. Dolphin supplies these machines remanufactured, skidded, heated, and test-run, which is how a re-refiner adds capacity for a fraction of new-equipment cost and lead time.

Heating Fuel

A considerable amount of used oil finds use in heating industrial buildings. Though contaminated, used oil has a high calorific value and is ideal for heating fuel.

Black Diesel (Diesel Blend for Engines)

Purified used oil is also known as black diesel. This name comes from the use of this oil as fuel for diesel engines. The blend of diesel and used oil is allowable by the manufacturers of large diesel engines.

Methods of Used Oil Recovery

Heating, Settling, and Filtration

A used oil filtration system includes tanks, heaters, multi-bank filters, pumps, etc. The typical process involves the following steps.

• Pre-straining the incoming oil: In this step, the freshly collected used oil passes through a coarse strainer (½") to remove large debris such as rocks, twigs, nuts, bolts, etc.
• Heating and settling: An air diaphragm or similar pump transfers the used oil to a storage tank with heating coils or a circulation heater. The increase in oil temperature causes the water and sludge to drop out.
• Draining water: The operator then drains the water out of the settling tank from a drain port above the sludge level.
• Clean oil recovery: The remaining oil layer is siphoned from the top and is the clean oil from this system.
• Filtering & Distilling: The 'clean oil' recovered from the siphoning carries entrained water and fine sludge particles from the used oil. This oil is passed through a bank of filters or progressively finer mesh size to remove the small particles. Vacuum distillation removes the entrained water.

Centrifugation

An industrial oil centrifuge combines most of the recovery mentioned above steps into one device that uses highly amplified centrifugal force to separate the oil from water and sediment. These centrifuges are continuous processing devices that offer high separation efficiency with a small footprint.

Used Oil Centrifuge

A used oil centrifuge is an industrial disc-stack centrifuge that exerts over 7,000 Gs of centrifugal force on the oil. This force is sufficient to separate all free water and sediment as small as 0.5 microns. The self-cleaning feature of the centrifuge allows it to eject the separated solids intermittently while the separated water exits the centrifuge continuously.

Every used oil centrifuge Dolphin supplies is a remanufactured Alfa Laval self-cleaning disc stack separator: the WHPX 405 and MOPX 205 in the DMPX-014 module, the MOPX 207 and WHPX 407 in the DMPX-028, the MOPX 209 and WHPX 410 in the DMPX-042, and the WHPX 513 and MOPX 213 in the DMPX-070. Dolphin Centrifuge is the independent specialist in Alfa Laval centrifuges, with remanufactured machines, turnkey systems, parts, and service built on 40+ years of Alfa Laval experience, and every used oil system is sized and engineered by Sanjay Prabhu, M.S.M.E. Apart from Alfa Laval itself, Dolphin is the reliable source for quality Alfa Laval used oil separators in the United States. Dolphin is an independent remanufacturer and is not affiliated with or authorized by Alfa Laval.

Read our new article: 6MGY Used Oil Centrifuge Plant Layout

Operation

A used oil centrifuge works on the principle of differential settling of the different phases in used oil based on their respective specific gravity. The contaminated oil enters the rotating centrifuge bowl through an inlet pipe and passes through the rotating stack of discs within the bowl. The rotating discs impart the rotational velocity to the oil and its contaminants.

The heavier sludge moves towards the bowl wall due to the high centrifugal force. This sludge displaces the lighter oil towards the center from where the separated oil enters an exit chamber before discharge from the bowl.

The sludge and water (if any) accumulate at the bowl wall, and the centrifuge automatically ejects the sludge periodically. The centrifuge bowl has a passage for the separated water, which allows the water to discharge through.

Separation Efficiency

One of the advantages of using an industrial centrifuge for waste oil separation is the separation efficiency of these centrifugal separators.

Particle Separation

A disc-stack centrifuge has a separation efficiency of 0.5 microns for metal particles and 2 microns for non-metal particles.

Water Removal

In addition to particle removal, a used oil centrifuge also simultaneously separates all free water from the oil. This centrifuge can also break oil-water emulsions and recover more oil under certain conditions as an added benefit.

Ash

Ash particles impart a black color to used oil. Though these particles are sub-micron level in size and light, the high centrifugal force in a disc-stack centrifuge can separate a considerable amount of ash from used oil. Flocculants enhance this ash separation ability further as they solidify some finer ash particles into larger particles that the centrifuge can separate.

Emulsion Breaking

Used oil often carries an emulsion phase that is difficult to separate by gravity settling without chemicals. Disc stack centrifuges can break oil emulsion to a certain extent based on the emulsion type.

Chemically bonded emulsions need acid treatment or demulsifiers to separate the oil from the water.

Industrial centrifuges with high centrifugal force can extract the microparticles that act as nucleoids, thus assisting in emulsion breakdown.

Benefits

There are several benefits to using centrifuges for used oil purification compared to gravity settling and filtration. The following is a list of the advantages.

Three Phase Separation

Disc stack centrifuges separate water and sludge simultaneously from used oil. This ability is referred to as three-phase separation and is unique to disc-stack centrifugal separation.

Filters and gravity separation are only helpful for separating sludge from used oil but not water.

Small Footprint

Disc stack centrifuges have a relatively smaller footprint than conventional devices for used oil purification. A used oil centrifuge has a fraction of the size of filters and settling tanks for similar capacity.

Operating Cost

Used oil centrifuges use gravitational force to affect oil-water separation. These centrifuges do not use media for separation, thus eliminating the media and related labor costs. Therefore, industrial centrifuges have very low operating costs as compared to filters and tanks.

Separation Efficiency

The particle separation efficiency in the case of settling and filtration depends on the filter media. Filter media with a tiny mesh size tends to need frequent replacement, and the related costs add up.

Oil centrifuges separate a range of particle sizes that would otherwise require multiple filters of different sizes. The smallest particle size rating for a centrifuge is 0.5 microns.

Emulsion Separation

In addition to microscopic particle size separation, disc stack centrifuges can often break oil-water emulsions by extracting the tiny particles that bind mechanical emulsions. The emulsion-breaking ability depends on the emulsions and may require chemical demulsifiers to assist in the separation.

Equipment Durability & Longevity

Industrial centrifuges incorporate heavy-duty construction that allows these centrifuges to last for decades of operation. In addition, with periodic maintenance, these centrifuges operate continuously over extended periods without needing a stoppage. In other words, it is not uncommon for industrial centrifuges to operate for months without the need for shutdown or operator involvement.

Disadvantages

The following list of the most prominent disadvantages of used oil centrifuges.

Capital Cost

The initial capital expenditure for centrifuges is relatively higher than for filters and tanks. However, the lower operating costs and labor cost savings quickly recover the additional expense.

Utilities Required

Used oil centrifuges are mechanically driven and therefore require utilities such as electricity and water for operation. Filters are primarily non-moving media that do not require utilities for operation.

Noise

The rotating components in an Alfa Laval used oil centrifuge create noise from the gears and drive motors as well as the air movement within the centrifuge also generates noise. Filters, on the other hand, are relatively quiet during operation.

Maintenance

All mechanical devices that operate at high rotational speeds require periodic maintenance. This upkeep ensures reliable operation of the equipment as well as equipment longevity.

Filters only need to be replaced with new media on an ongoing basis with little maintenance.

Design Considerations

Specific design considerations apply to used oil centrifuges. Some of the important considerations are as follows.

Acidic Material

Used oil processors use acids to dissolve and remove metals and break emulsions. The low pH value of the oil necessitates the use of corrosion-resistant material in the centrifuges and related piping. Centrifuges with all stainless steel wetted parts are available for such applications.

Chemical Injection

The provision of chemical injection ports upstream of the centrifuge allows adding chemicals such as demulsifiers or flocculants. Metering chemical pumps as an option are well suited for these applications.

Water Phase Proportion

The standard disc stack centrifuges design uses large volumes of oil with a small proportion of water. However, the water proportion can be relatively high in the case of used oil.

Some internal centrifuge modifications allow for the discharge of this larger volume of water to allow the centrifuge to process maximum volumes.

Special Elastomers

Adding chemicals or inherent used oil properties may not be compatible with ordinary elastomers. In such cases, the centrifuges have special elastomers with specific compatibility for the process fluid.

Specifications

The following are typical specifications for the used oil centrifuges Dolphin supplies, listed by the Dolphin module code and the Alfa Laval base machine inside it. The centrifuges themselves are self-cleaning, three-phase disc stack machines manufactured by Alfa Laval; Dolphin remanufactures them and builds the skid, heater, pumps, and controls around them.

Plant Layout

The following diagram shows a large-scale used-oil centrifuge processing plant layout using our three-phase centrifuges. This layout includes a decanter centrifuge that is a preprocessor to remove bulk sludge from the used oil if needed.