Question

Explain how each of the following conditions contributes to the satisfactory performance of oil centrifuges. (16)

(a) Correct bowl speed.

(b) Cleanliness of bowl.

(c) Low rate of feed to the bowl.

(d) Contaminated oil preheated prior to centrifuging.

(e) Contaminated oil allowed standing for an appreciable time prior to centrifuging.

Answer 1

Part (a)

If the purifier has not achieved full RPM (revolutions per minute), then the centrifugal force will not be sufficient enough to aid the separation.
The opening and closing of the bowl also depends upon the bowl speed; water alone can not open or close the valve.

Part (b)

Sediment will accumulate on the inside periphery of the bowl. When the sludge space is filled up, the flow inside the bowl is influenced by the sediment and thereby reducing the separating efficiency. In such cases, the time between cleaning should be reduced to suit these conditions.

Part (c)

Throughput means the quantity of oil pumped into the purifier/hr. To optimize the purification, the throughput must be minimal.
A lower feed rate results in a lower output of the purifier. The minimum feed rate of the purifier has to be greater than the feed rate at which the oil is being consumed by the machinery, failing which can lead to an empty service tank, which can further lead to main engine stoppage and black out situation.

Part (d)

Part (e)

Consider gravity separation, as occurs in a settling tank, over a gradual period, solids such as sludge, dirt, etc. will settle out at the bottom of the tank. The heavy liquids, such as water, will settle out above the solids, and the lighter liquids, such as oil, will be at the top of the tank. Thus, removing the major impurities before centrifuging helps in better purification.

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