Dolphin Centrifuge

Used Oil Centrifuge | Applications, Benefits, Specifications & Commercial Plant Layout

Used Oil Centrifuge Alfa Laval MAPX-204
Used Oil Centrifuge Module

Definition of Used Oil

Used oil is defined as any oil that has its origin in crude oil or petroleum that has 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.

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.

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 to 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.

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 an ideal choice 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.

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 out the separated solids intermittently while the separated water exits the centrifuge continuously.


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 used 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 the 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 type of emulsion.

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 and thus assist 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 the water.

Small Footprint

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

Operating Cost

Used oil centrifuges use gravitational force to affect oil-water separation. These centrifuges do not use media for separation and thus eliminate 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 the need for a stoppage. In other words, it is not uncommon for industrial centrifuges to operate for months without the need for shut down or operator involvement.

Disadvantages

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

Capital Cost

Compared to filters and tanks, the initial capital expenditure for centrifuges is relatively higher. 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 as well as to break emulsions. The low pH value of the oil necessitates the use of corrosion resistance 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 is for large volumes of oil with a small proportion of water. However, in the case of used oil, the proportion of water can be relatively high.

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

Special Elastomers

The addition of 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 of used oil centrifuges manufactured by Alfa Laval. These are disc-stack-type centrifuges with self-cleaning ability.

Centrifuge Model >>>DMSC-042DMSC-075
40 GPM68 GPM
Capacity (Heavy Used Oil)25 GPM @ 180 F40 GPM @ 180 F
Motor Power10 HP15 HP
Bowl Speed5,200 RPM4,200 RPM
Weight3,200 Lbs5,100 Lbs
Dimensions4' x 5' x 7' (H)5' x 6' x 8' (H)
Sludge HandlingSelf Ejection (Automatic)Self Ejection (Automatic)
Liquid Phase DischargeLight & Heavy Phase - Pressurized Light & Heavy Phase - Pressurized
Bowl Wetted Parts316 Stainless Steel / Marine Grade Bronze (Nickel Plated)
Operating Voltage230 or 460 VAC - 3-Phase - 60 Hz (50 Hz Available)

FAQ

Why is a used oil centrifuge a three phase centrifuge?

A used oil centrifuge needs to be a three-phase centrifuge to separate the water and solid particles simultaneously. A two-phase centrifuge will only separate the solids from used oil but not the water.

Is a used oil centrifuge same as a waste oil centrifuge?

A used oil centrifuge is very similar to a waste oil centrifuge. Both are three-phase centrifuges capable of separating oil from water and sludge. A used oil centrifuge may require some modifications to accommodate chemicals such as acids in the process.

Can used oil centrifuges separate emulsified oil?

A used oil centrifuge can separate oil emulsions to a certain extent. Disc stack centrifuges cannot separate chemically bonded emulsions without the use of demulsifiers.

What is the smallest particle a used oil centrifuge can separate?

A used oil centrifuge (disc-stack) can separate metal particles down to 0.5-microns. Non-metal particle separation efficiency is typically around 2-microns.

Do used oil centrifuges use filters or replaceable media?

Disc stack centrifuges for used oil do not use any filters or media. These centrifuges use the amplified force of gravity (centrifugal force) to separate water and sludge from used oil.

Can used oil centrifuges separate ash from used motor oil?

Used oil centrifuges of the disc-stack type can remove some of the ash content from used motor oil. Ash particles are microscopic carbon particles, and the centrifuge's separation ability is limited to such tiny particles separation.

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.

Used Oil Centrifuge Plant Layout
Used Oil Centrifuge Plant Layout

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