Separator's Digest 2004/1 - GEA Westfalia Separator Group

The disc stack in the separator bowl breaks down the product to be separated into a large number of thin layers. It thusincreases the effective clarifying area and reduces the sedimentation distance to be covered by a particle to be separated.these channels depends on the liquidcomponent to be recovered to thehighest degree of purity. For instance,if the heavy component (water) is tobe obtained from an oil-water mixture,the rising channels will be locatedtowards the centre of the disc stack. Ifthe light component (oil) is to be recovered,the rising channels are locatedtowards the edge of the bowl. If bothcomponents have to be separated withequal purity, the rising channels arelocated in the centre of the disc stack.Solid sediments settle in the solids-holdingspace making three-componentseparation possible.Battle against timeIn a clarifier bowl, the particle to beseparated has to reach the bottom ofthe disc before it leaves the gap. Thefactors of flow, centrifugal force andgap geometry result in a particle sizewhich just meets this requirement. Thisdiameter represents the separatinglimit. In theory, the separator removes100 percent of particles with a diameterwhich is equal to or greater thanthe separating limit. The separationrate is lower for smaller particles.“In such cases, smallerparticles have to dischargeinto the channel near thedisc bottom to win thebattle against time.“Acceleration and clarifyingarea – the tools of the designerTo optimize clarification and separation,the design engineer is able toincrease the rate of acceleration. However,the bowl material imposes limitson the maximum speed and externaldiameter of the bowl as the forcesgenerated are not permitted to imposeexcessive strain on the material.The second method is to increasethe number of discs. This can be achievedwith thinner discs and narrower spacesbetween the discs. However, the minimumdisc thickness is defined by thenecessary mechanical stability. Thereare also restrictions applicable forreducing the space between the discsas otherwise these spaces would becomeclogged up. In theory, the designengineer is able to choose which of thetwo parameters he wishes to change.A large area with a low speed is equivalentto a small area and a highspeed.Vibration-free operationNowadays, high-alloy special steelspermit bowl speeds of more than 750km/h.These high speeds generate strongforces that can have an effect on themachine components and the foundation.If the separator has an optimumdesign, the two systems that vibrate,namely the frame and the rotor, actagainst each other. The forces neutralizeeach other to a large extent internally.Only small foundation forcesoccur.Optimum machine momentumaccordingly guarantees maximum operatingreliable and minimum wear andtear. ■Separator´s World13Separator´s Digest 1/2004