How Does a Waste Oil Centrifuge Work?

Waste oil centrifuge machines are used to filter out waste oil to derive the useful biofuel contained within. The design basis of these machines is primarily based on the different densities of the various components of waste oil. The machine uses centrifugal force to separate the various components of the oil.

Working principle of a waste oil centrifuge unit

Centrifugal force is a force in which objects moving along the circumference of a circle are pushed outwards. A common example of the basis of this force is observed in a slingshot. As you spin your hand in a ring motion, the sling gathers more force and becomes taut with time generating more force. This means the rock will be flung further and will pack a bigger punch. Another point to note is that bigger rocks will generate more force implying a direct correlation between the mass of the rock and the distance travelled. Oil centrifuges take advantage of this principle in combination with pressure.

The process begins by pumping oil into the centrifuge via an intake pipe. This oil then moves up the central shaft and starts to fill the centrifuge unit. The bypass valve is then closed as the centrifuge unit continues to fill up with the impure oil. The oil also begins to exit the centrifuge via two nozzles at the bottom of the unit. The nozzles are placed 180 degrees apart from each other at the cross-sectional centre of the circular unit. This causes the unit to begin spinning. What then happens is that pressure builds up within the unit, and it begins to spin around faster. Situated on the shaft is a series of slanting horizontal metallic slits. These slits perform the same function as the elastic band of the slingshot. As the central shaft pole begins to spin, the oil begins to spin away from the centre.

Impure oil

The impure oil that is pumped into the centrifuge unit is usually a composite of multiple types of oil. These different oils have different densities which mix to form one mix of oils. These differing densities influence the centrifugal force produced by the oil. As stated, the centrifugal force is directly correlated with the mass. Thus, for sets of oil with similar volume but differing densities, the denser liquid will contain more liquid particles per unit volume and so will have more mass. These means that for the same amount of spin, the denser liquid will exert more centrifugal force.

High pressure

What happens then is that as the central shaft begins to spin faster and faster, the pressure within the unit can go as high as 80psi. This generates a G – force well over 2000G which is about 200 times more the force generated by the acceleration of fighter jets. This easily removes the heavier solid objects which form a layer of solid on the sides of the unit. The cleaner oil is then pumped out, and then the layer of solid is removed.

The centrifuge is not self – regulating in terms of pressure and so this aspect must be manually configured. The unit comes with a secondary lever valve which regulates pressure by providing another outlet for the oil. Depending on the amount of leeway you allow for the oil to pass, you either build up pressure within the centrifuge or reduce the pressure within the unit. The natural conclusion is that the higher the pressure, the higher the level of filtration that will take place. However, too much pressure may be detrimental as this combination of high pressure and the force exerted through the centrifugal action can lead to the catastrophic breakdown of the entire centrifuge unit.

Heating units for collecting barrel

Some centrifuge units come with heating units for the collecting barrel. The reason behind this is that heating the oil makes it thinner and thus making it easier to filter out the oil. This also reduces the number of runs required for the oil to be purified since the heat makes it easier for the less dense components of the oil to be separated from the impurities. If this is the case, one should be careful to ensure that the system’s pump can withstand the heat that will emanate from the hot oil. By the end of a few runs, the oil centrifuge unit should have sufficiently filtered out the impurities from the oil.

The centrifuge is advantageous in that it is very simple to operate. The unit is purely mechanical without any need for digital parts and only requires one to maintain a well – balanced pressure level for the optimal functionality of the unit.