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dt _ Oil Separators (Continued from Page 21) pollution will meet at Washington on June 8 (while this paper is in the printer’s hands), and it is anticipated that the necessity for prohibition of the discharge of all oily bilge water will be recognized by the conference. Since bilge and ballast waters must necessarily contain some oil, the ne- cessity for an efficient form of oil sep- arator to be used for the discharge of all such waters is imperative. Efficient separators are available, and there is no reason why they should MIXTURE INLET. WATER OUTLET. Fic. 11.—C. S. Lenz anv G. E. Juppr’s PATENT OF 1922. not come into general use, for the value of the oil recovered will pay for the cost of installation in a few months, and the expenditure involved means no hardship to the shipowner, but the reverse. What a Separator Should Do It should be noted as a further rec- ommendation for the use of an efficient separator that it removes any objec- tion to the use of the fuel tanks, when empty, for ballasting purposes— a practice which may make in some cases all the difference between profit and loss on the running of the ship, in view of the greater cargo-carrying capacity thus made available. Before considering the actual ques- tion of separator design, it is desirable to outline the requirements of a use- ful and efficient separator. Having Fig. 12.—Tun “H. anv H.”’ DenypRATOR. MARINE REVIEW regard to capacity, large vessels may carry two thousand or more tons of oil fuel, and if something like one- half of the fuel tanks are assumed to be ballasted, it is obviously desirable to be able to discharge those tanks at a rate of, say, one hundred tons per hour. Thus, for ship installations a separator should have a capacity to suit the ship, and should not be ex- cessively bulky for large capacities of the order mentioned. In default of sep- arators fitted in every ship, harbor service barges must be equipped, and for these a capacity of two hundred tons per hour, or more, is desirable. ; ALTERNATIVE MIXTURE INLBT P. P. HARVEY AND H. J. Hotrorp’s Parent or 1924. Even with such capacities there is like- ly to be delay at the ports if many vessels rely on the barge service, and the installation of a smaller separator on each ship is the more convenient arrangement. As to the quality of the water discharged, it is essential that a cer- tain standard of purity be reached and maintained. One part of oil in ten thousand of water means over twenty gallons of oil discharged per thousand tons of water—a very un- desirable quantity, capable of produc- ing an iridescent film over a large surface of water. A considerable body of opinion supports the enforcement of a standard to ensure only one part of oil in a two hundred thousand of water. To secure this standard a scientifically designed plant is neces- sary, but the standard can be and is September, 1926 attained by separators of moderate size and price, and may therefore be regarded as a reasonable one. The standard is not reached by the use of a gravity separator alone, but by the combination of such plant with a filter which will remove the last fine traces of oil. Reference will be made to the filtering process later, but for the moment attention will be given to the design of the preliminary separ- ator. Principles of Separator Design The separation of the bulk of the oil from bilge and ballast water can be effected by gravity, advantage be- ing taken of the difference in density between oil and water. With the heavier grades of oil this difference is small, which makes it essential that the apparatus should be care- fully designed, since otherwise the size necessary becomes so great as to be prohibitive. In view of the large volumes of oily water to be dealt with, an attempt to employ the meth- od of centrifugal separation in order to increase the effect of the difference in density of oil and water is hardly practicable, and the trend of develop- ment has been to retain the gravita- tional process while seeking to en- sure the best possible conditions in its application. The general principles involved in a sound method of construction ap- pear to be comprehended in the fol- lowing review. 1. The lesser specific gravity of the oil tends to carry it vertically through the water. The velocity at which it rises depends on density and viscosity, and on the size of the oil globules. Small globules rise slowly, so that if the flow of the water is arranged to be vertically downwards’ those particles of oil whose relative velocity due to buoyancy is less than the velocity of the water will necessarily be carried away to the water discharged, however long the passage. If, on the other hand, the water flow is arranged horizontally, all particles having any tendency to rise at all can be separated if the passage is made long enough. The most effi- cient separators will therefore be those in which the main flow is sub- stantially horizontal. 2. Oil naturally accumulates at the top of the separator, and to ensure that it does not remix it is essential that the oil-collecting chamber should be entirely free from the circulation of water. Thus the oil-collecting chamber must be remote from the water inlet and outlet, and must not