Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/934530
www . machinerylubrication.com | January - February 2018 | 23 viscosity. Generally, oils are heated to just below the boiling point of water. is thins the oil so particles and water separate quickly. At this temperature, much water flashes off as steam and is ventilated from the centrifuge. e remaining moisture is separated as a layer of water in the centrifuge bowl. Higher temperatures are avoided, as they can cause spurting and spitting of the oil as the water boils. Some applications may use a solvent to reduce the oil's viscosity. e solvent is removed by distillation or may remain in the oil if it will be used as a fuel. Steam and Vapor Ventilation A centrifuge may be self-ventilating or require a vacuum to remove steam. A self-ventilating centrifuge uses a "P-trap" on the clean oil output to block vapors. is forces steam and vapors to the sludge drain where they may be condensed or ventilated. Venting Vapors During centrifugal cleaning, vapors may be emitted. Depending on the composition of the oil, these vapors may contain water, methanol or other light hydrocar- bons. Larger amounts of vapor are emitted with higher feedstock temperatures. Some centrifuges are designed to ventilate these vapors using a fan formed between the rotor bolts and the grooved lid. e centrifuge typically can produce air flow of approximately 35 cubic feet per minute through the output ports before piping losses. Directing the flow to the waste port vents water vapor, hydrocarbons or alcohol vapors away from the cleaned oil. Flow is directed by installing a P-trap. e liquid in the P-trap blocks the flow of vapors. is prevents vapors from collecting in the clean oil tank and condensing. e P-trap may be built from pipe fittings or be as simple as a low place in a hose. e P-trap must also be lower than the centrifuge. However, a long line before the P-trap will allow vapors to condense in the piping before the P-trap. Secondary traps formed by a sagging hose block the flow of oil and cause the oil output to back up and flow into the sludge drain. erefore, hoses must not kink. Using a 45-degree elbow on the output minimizes kinking when the clean oil tank is not located directly under the P-trap. Residence Time All good things come in time, and clean oil is no exception. If oil is left in a tank for months or even years, eventually a layer of clean oil will form on top. A centri- fuge speeds up this process. However, the oil must stay in the centrifuge long enough for the dirt to come out. Oil that remains in a centrifuge for only a few seconds does not have sufficient time for good cleaning. e longer the oil remains in the centrifuge, the better the cleaning will be. Residence time is controlled by the feed rate. You may find that a particular oil is cleaned well at 40 gallons per hour, but another oil can only be cleaned at 15 gallons per hour. Trial-and-error testing of the initial installation will quickly determine the best flow rate. Centrifuge Bowl Cleaning Knowing what is in your oil before you begin will allow you to estimate the proper draining or cleaning intervals for your centrifuge bowl. Lab analysis can be beneficial but not essential. Tests show that waste motor oil (WMO) typically contains between 3 to 5 percent solids. When cleaning WMO, solid particles become concentrated next to the bowl wall, while clean oil floats to the center of the bowl, spilling over the top edge and Sludge Sludge A P-trap with a spot that is too low can block oil flow. Low spot blocks flow ML Centrifuge Centrifuge Clean Oil Clean Oil