Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/934530
22 | January - February 2018 | www . machinerylubrication.com opening next to the bowl wall. Plate centrifuges are also a little more work to clean and operate. Bowl centrifuges must be cycled to dump water and sludge. The upper limit for these types of centri- fuges is 5 percent water. Higher percentages of water will require excessive cycling. More than one pass may be necessary if the cycle is not well-timed before the bowl overflows with water. A tube centrifuge has contin- uous discharge of both light and heavy fluids. It also separates partic- ulate but will quickly fill up with solid matter when the percentage is much more than 0.5 percent. is type of centrifuge must be disas - sembled to remove particulate and is more labor- intensive when the fluid contains a high percentage of particulate. Often called oil-water sepa- rators, tube centrifuges operate around 15,000 to 20,000 Gs and can break difficult emulsions. e separation factor is controlled by both the flow rate and annular rings that distribute flow over light and heavy output ports. To ensure the fluid is spinning the entire length of the tube, removable vanes are added to the tube bowl. This bowl contains many parts that must be assembled in the exact location where the bowl is balanced. Keep in mind that a 1-gram imbalance becomes 20 kilograms when spinning at 20,000 Gs, so do not operate an imbalanced centrifuge. Factors in Centrifugal Cleaning The main factors governing centrifugal cleaning are the size of the particles, the particles' specific gravity, the f luid's viscosity, the centrifuge's power or G-force and the residence time in the centrifuge. Of course, you have little control over the specific gravity of the particles. Some applications may utilize a flocking agent to make the particles larger, but generally this is avoided. e three factors you can control are the oil's viscosity, the centrifuge's G-force and the residence time in the centrifuge. e centrifuge's power relates to its relative centrifugal force (RCF), which is the amount of acceleration applied. is will depend on the revo- lutions per minute (RPM) and radius of the rotor. However, the centrifuge's RPM will tell you nothing of value regarding the device's cleaning power. Variable- speed centrifuges allow you to adjust the G-force as required for the application. Fine, light particles may require a high G-force to sepa- rate, but heavy particles can separate at a lower G-force. Test runs should be made during the design of a new cleaning process to ensure particles are not packing so tightly that they are difficult to remove. Also, don't forget that material weighs several thousand times more in a spinning centrifuge bowl. e oil's viscosity determines how easily particles will separate from the fluid. Consider that a handful of dry sand will quickly sink to the bottom of a bucket of water, but the same sand will move very slowly to the bottom of a bucket of molasses. Likewise, thin fluids clean more easily than thick fluids. Gasoline and diesel clean quickly and easily, while heavy oils require thinning. Heat and solvents are t wo commonly used methods to reduce OIL RECLAMATION Iron piping is preferred for P-traps. A P-trap is used to block vapors. Sludge Clean oil 2 inches minimum If the P-trap is too high, oil flow will be forced to the sludge port. From centrifuge To cleaned oil tank Oil Centrifuge Centrifuge Sludge