Black diesel is an alternative fuel for diesel engines made from used motor oil, transmission fluid, or any mineral oil with calorific value. Often, a diesel fuel mixture with any used oils is also known as black diesel.
The fluids comprising black diesel are primarily used and often contaminated with sludge and water from their prior application. Removing these impurities from the black diesel before using them as engines is crucial.
There are multiple ways to clean black diesel. The actual method depends on a few parameters, such as the desired level of purification, the cost of purification equipment, and the volume of black diesel to be processed.
Two of the most common and popular methods of separating black diesel from its contaminants are the following.
The settling and filtration of black diesel is a standard method for small volumes or DIY applications. In contrast, black diesel is for individual use in personal vehicles or small diesel generators.
Heating and settling the black diesel allows the water to settle out. This step is followed by decanting the fuel to separate it from the settled water.
In the next stage, the black diesel passes through micron-level filters to remove sediment and particle contamination.
It is important to note that the filters cannot remove the black color of the fuel because the black color is due to the presence of sub-micron carbon particles that are hard to separate.
A black diesel centrifuge continuously separates the water and fine solids from black diesel. This disc stack centrifuge exerts over 7,000 Gs to simultaneously separate all free water and small particles down to 0.5-micron.
The self-ejecting feature of the centrifuge allows it to eject out the separated sludge automatically. The separated water exits the centrifuge through a discrete port.
Black diesel is a relatively inexpensive fuel for diesel engines compared to regular diesel fuel. Therefore, diesel vehicle owners prefer black diesel to save fuel costs.
On a larger scale, mining companies produce large quantities of used engine oil that is perfect for diesel engines as an alternative fuel.
However, it is essential to remove the water and solids contamination from the black diesel before use.
Also, it is critical to remove metal particles (from used engine oil) before using black diesel in commercial diesel generators. The presence of metals can void the manufacturer’s warranty on the generators.
In cold climates, used oil producers also use black diesel as heating fuel to heat industrial buildings and shops. Black diesel serves as fuel to heat fluids in cold climate industrial applications such as oil and gas drilling.
Waste oil burners require the use of clean fuel to perform efficiently and to ensure long-term durability. That makes it all the more important to purify black diesel before its use for heating.
Disc stack centrifuges offer several advantages over filters to purify black diesel. Some of these benefits are listed below.
A high-speed black diesel centrifuge has enough centrifugal (7,000 G-force) to separate particles to the 0.5-micron level. This separation capability is a distinct advantage over conventional filters and gravity settling.
A disc stack centrifuge can process up to 80 GPM of black diesel. The smallest centrifuges can process about 5 GPM of black diesel at 180 F.
Unlike filters, disc centrifuges can separate free water and sediment simultaneously from black diesel. This water separation ability is a considerable benefit over conventional filters that only separate solids.
Centrifuges do not use filter media or require media replated labor. They separate the black diesel from the impurities using mechanical separation, and the only operating cost is that of electricity.
A centrifuge capable of processing up to 5 GPM of black diesel has a 3’ x 4’ footprint, compact enough to be placed in space-limited facilities. In general, centrifuges have small footprints relative to their processing capacities.
Ash particles in black diesel are sub-micron size carbon that is a product of fuel combustion. It is not practical to remove these particles with filters due to the size and cost of replacing filters frequently.
A disc centrifuge can remove some of these ash particles (not all) and considerably reduce the ash content in black diesel.
Disc stack centrifuges can separate some of the oil in water emulsion present in black diesel. If the emulsion is chemically bonded, the user may need the addition of some demulsifier.
Emulsion breaking leads to the recovery of black diesel, usually lost.
Black diesel centrifuges have certain disadvantages, which are listed below.
Centrifuges are industrial machines that are capital intensive compared to filters that have low capital costs. But the centrifuge pays for itself quickly, given the considerable operating cost savings.
Like any machine, disc centrifuges require periodic maintenance for reliable operation. This maintenance needs to be performed by trained operators.
A black diesel centrifuge is a sophisticated machinery that requires a skilled operator to oversee the operation. Filters are static devices that do not need operators.
Self-cleaning disc centrifuges require water in addition to electricity to operate. That is an additional provision that is essential for centrifuges cleaning black diesel.
The following table lists the specifications of black diesel centrifuges manufactured by Alfa Laval.
| Centrifuge Model >>> | Alfa Laval MAB 104 | Alfa Laval WHPX 405 | Alfa Laval MOPX 207 | Alfa Laval WHPX 513 |
| Capacity on Black Diesel | 2 GPM | 10 GPM | 20 GPM | 40 GPM |
| Motor | 2 HP | 4 HP | 7.5 HP | 15 HP |
| Size (Skid) | 2' x 3' x 4' (H) | 4' x 5' x 5' (H) | 4' x 5' x'6' (H) | 5' x 6' x 6' (H) |
| Weight (Skid) | 600 Lbs | 1,200 Lbs | 2,000 Lbs | 3,500 Lbs |
| Bowl RPM | 7,800 | 7,600 | 7,200 | 4,140 |
| Particle Efficiency | Metal Particles < 0.5 Microns; Other Particles < 1.0 Microns | |||
| Sludge Discharge | Manual Clean | Self-Clean | ||