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Purifying Oil – The Centrifuge Way

written by: Ricky • edited by: Lamar Stonecypher • updated: 9/9/2008

What do you do when you want to filter some impurities from the oil in your can which, over the course of time, may be caused by soil, dust, water or other immiscible materials? You may over-simplify by using a sieve filter but see how large quantities of oil are purified.

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    What Oil is referred to here?

    Oil can refer to various liquids including (but not limited to) fuel oil, heavy oil, lubricating oil.  Fuel oils are used in engines for combustions while lubricating oils serve the dual purpose of lubrication as well as cooling under various conditions such as running machinery and absorbing heat from cutting tools to name a few.

    How are impurities added to Oil?

    Impurities can include a variety of foreign materials such as dust, soil, water, etc which can get into any stage or oil production, storage, or transfer. Before such oils are used for their intended purposes whether it is lubrication, burning, or whatever; the oil needs to be free from such impurities to the maximum possible extent. There are several ways of purifying oil and we will learn about one such way here in the subsequent section.

    Centrifugal Separation

    You must have noted that when you leave a liquid in a container undisturbed for a long time it settles into various layers (provided it is a mixture and not a compound). The heaviest layers come to the bottom follow by lighter layers above it. Gravel, sand etc would certainly settle at the bottom of the container. This could be used to separate these ingredients but it may not be possible due to various reasons such as lack of time and the separation may not be good enough if the specific gravity of the mixture elements isn’t large enough to produce well defined boundaries.

    This process can be accelerated if the same fluid is rotated at a high RPM inside the container and now the separation will be along vertical planes rather than horizontal planes. This is exactly the principle of centrifugal separation and machines known as purifiers or centrifuges are used for this purpose.

    Centrifuges come in a variety of flavours.  Disc type centrifuges are commonly used to purify heavy fuel oil, diesel oil and lubricating oil in industries. They basically consist of several cone shaped discs placed one over the other. The dirty oil is fed at one end and it gets separated into sludge, purified oil, and water when the container rotates at a high RPM. The purified oil is taken into a clean tank whereas the water and sludge are waste materials. Water is drained continuously whilst sludge is cleaned from the purifier at regular running hour intervals.

    The container and disc housing is placed over a spindle which is driven by an electric motor using appropriate gear arrangements to give a high rotational speed while maintaining balance. During the operation balance is critical since at such high RPM any imbalance could literally ruin the overall machinery causing loss of property and possible human injury as well.

    Hence we see that by rotating the force exerted by gravity by right angles into force along the vertical plane, the natural process of gravitational separation is quickened to a great extent.