PRODUCTION | ENERGY MANAGEMENT
Right: Buss claims its Compeo co-kneaders, shown here in an 88m 25LD version, avoid energy-con- suming shear peaks
ance. This means more electrical power is dissipated as heat, which in turn pushes the winding temperature even higher.
Motor management A motor management programme also needs a motor management policy (MMP). This can be used to define motor maintenance and inform the replace/repair decision – replace and not rewind. Kent suggests creating a motor register, which is a simple spreadsheet that lists: n The motor application; n The nameplate details; n The frame size; n The approximate running hours; n The repair history; n The spares held for the motor; n And the action to be taken in the event of failure – replace or repair. Dino Kudrass, Head of Design and Develop-
ment at Buss, agrees with Kent that the dominant contributor to the energy consumption of a plastics compounding plant is the machine’s main drive motor. “Here, electric energy is converted into kinetic energy, which is then used to melt, mix, convey and pressurise the polymer through shear forces present in the process chamber,” he says. “A large proportion of this energy input exits the compounder’s control volume through the elevated thermal heat energy of the polymer melt.” He explains that considerable energy is required to melt the polymer due to the high specific heat capacity of polymeric materials. “To put this into perspective, a typical polyolefin compounding machine with a throughput of approximately 1000
kg/h features a main drive motor power of 355kW, which is an order of magnitude more than the machine’s heating system. Therefore, even small improve- ments to the energy efficiency of the main drive and mixing process can yield comparatively significant savings,” Kudrass says. “One core issue in good energy management is including related considerations as early as possible. Too often new plants are planned and commis- sioned before the first serious considerations towards a suitable energy management strategy are made. Reducing overall energy consumption should be an important constraint from the early concept design, right through to the final implementation and operator training phase,” he says. Kudrass also agrees with Kent that one impor-
tant practical step towards using compounding energy efficiently is the correct drive line specifica- tion. “Electric motors are often operated far below their nominal speeds during production, which greatly increases thermal losses and decreases efficiency,” he says. “In this case, machines are specified with a reduction ratio and nominal speed to match the maximum required compounding speeds, although these are relative outliers and do not match the intended operating speeds. Another practical step that can be taken is to
recycle thermal energy, according to Kudrass. “In many cases waste heat from pellet conveying, H/C units or other cooling circuits can be easily used to pre-heat the polymer before entering the com- pounder. This in turn reduces the energy require- ment for melting the polymer inside the com- pounder,” he says. Compounding energy inputs for PVC material fed at room temperature and pre- heated are compared in Figure 2. Buss believes that the operating principle of its
Figure 2: Specific energy due to different inlet temperatures of PVC Rigid Dryblend
32 COMPOUNDING WORLD | February 2021 Source: Buss
Co-Kneader machines allows for an energy efficient mixing process due to the inherently homogenous shear rate distribution. Avoiding unnecessary shear peaks and stagnation zones not only reduces compound degradation, but also avoids the ineffec- tive use of kinetic energy, according to Kudrass. “Our recently developed machine series
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IMAGE: BUSS
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