Table of Contents
Synopsis
Industrial Centrifuges exert a very high centrifugal force on emulsified oils. This force can break waste oil emulsions by mechanical separation. Thus, industrial centrifuges recover clean oil from waste oil emulsion on a large scale.
What is an emulsion?
When two immiscible liquids mix to form one liquid phase – that combined liquid phase is an emulsion. In other words, it is the dispersion of microdroplets of one fluid in another non-dissolving fluid.
Types of Oil-Water Emulsions
Oil-water emulsions fall into 2 categories – Oil in Water (O/W) and Water in Oil (W/O) type. The following diagram illustrates the 2 types of emulsions.
Oil in Water (O/W) emulsion
When a small amount of oil is dispersed in a large volume of water, it is known as oil in water emulsion (O/W). Water-based machining coolant is an example of O/W emulsion. In this case, oil droplets are dispersed in a water medium. This is a desirable emulsion because this emulsion provides lubrication from the oil and cooling from the water phase.
Water in Oil (W/O) emulsion
When a small amount of water is dispersed in a large quantity of oil, it is known as water in oil emulsion (W/O). Waste oil emulsion is an example of W/O emulsion. W/O has water as the dispersed medium in the oil. This emulsion is not desirable because it has reduced value as fuel or lubricant feedstock.
What causes emulsion in waste oil?
Water in mineral oil emulsion is caused due to many causes. These reasons are broadly classified into mechanical and chemical causes.
Vigorous agitation of the oil-water mix can cause emulsions. Pumps and valve orifices, for example, can cause water droplets to get dispersed in the oil.
The presence of detergents, soaps, and other surface acting agents also cause emulsions. Such chemically bonded emulsions are particularly difficult to separate under the gravity settling method.
Methods of splitting water in oil emulsions.
Waste oil emulsions can be separated by mechanical or chemical means.
Separation of colloidal solids is the most effective mechanical way to split waste oil emulsions.
Chemical demulsifiers break the chemical bonds to help split emulsions. However, on a larger scale, the cost of chemicals adds up.
What are coalescence and flocculation?
The process of combining small water droplets into larger, separable droplets is coalescence. Aggregation of micro suspended solid particles is flocculation.
Flocculation and Coalescence Illustration
The diagram below shows a magnified section of an industrial centrifuge bowl. The following section describes the separation process in detail.
How does a disc stack centrifuge separate emulsified water from oil?
A centrifuge, by exerting high centrifugal forces, accelerates the flocculation and coalescence process.
As illustrated above, a disc stack centrifuge causes the combination of small, suspended water droplets. In other words, it coalesces the water particles. It also concurrently forces the flocculation of colloidal particles. These larger particles are easier to separate under the high centrifugal force.
Case study of centrifuge on emulsified waste oil.
Dolphin Centrifuge supplied an Alfa Laval disc stack centrifuge for waste oil recovery is Guam. The customer collects fuel and oil from naval ships and cruise ships tanks.
The collected oil often contains a high proportion of emulsified oil. Before using our centrifuge, the customer used chemicals to separate the oil emulsion with limited success.
We carried out a set of experiments at the customer site to check the performance of our centrifuge. The experiments were designed to optimize centrifuge efficiency on emulsion breaking.
From experience, we knew the centrifuge settings and fluid properties which are key for emulsion separation.
These are flow-rate, back pressure, temperature, and gravity disc selection. The main fluid property affecting emulsion separation is temperature.
To simplify the experiment, we changed the flow and temperature settings while keeping pressure and gravity disc unchanged. The following table summarizes the results of the experiment.
Results of centrifuge treatment of emulsified oil
The following table shows the results of the emulsion breaking experiment using an industrial centrifuge.
The benefit of the industrial centrifuge is tabulated in monetary terms below.
| Heating & Settling | Centrifuge Processing | Extra Oil Produced by Centrifuge | ||||
| After 24 hrs Settling | 12 GPM @ 180F | Daily | Monthly | Yearly | ||
| % Oil Recovered | Gal (15hr/Day) | % Oil Recovered | Gal (15hr/Day) | Gallons | Gallons | Gallons |
| 78% | 8,400 | 92% | 9,900 | 1,500 | 37,500 | 450,000 |
At the prevailing price of clean waste oil at $1.72/Gal in Guam, the annual additional revenue was estimated at $650,000!
Conclusion
In summary, an Alfa Laval industrial, disc stack centrifuge is capable of breaking water in oil emulsions. Specifically, as demonstrated above, it can break the oil from waste oil emulsion to produce clean sale oil.
Subjecting an emulsion to high centrifugal in a centrifuge, forces causes the separation of the dispersed phase from the carrier phase. This process is referred to as ‘breaking’ an emulsion.
The actual separation efficiency depends on the type of emulsion. It also depends on the type and amount of chemical emulsifiers, if present.
Contact Dolphin Centrifuge for more information or to discuss your particular application with our centrifuge experts!