PRODUCTION | ENERGY MANAGEMENT
Images show the difference between a traditional kneading block (left) and Feddem’s FME mixing elements Image: Feddem
Kneading blocks
making processes could change, Dreiblatt points out. “In today’s business environment, twin-screw extruders are favoured where initial capital cost is the primary criteria for evaluating new equipment. With the new green economy, we may see energy consumption become more important,” he says. “For resin producers operating twin-screw
extruders above five tonnes per hour, a small decrease in specific energy can represent signifi- cant cost savings over the life of the extruder. In such cases, a larger diameter extruder operating at a lower screw speed will result in lower specific energy as compared to smaller diameter machines operating at high screw speed. The motor size is the same for both machines, but the higher initial capital cost of the larger diameter machine is not favourable in today’s economy,” he explains.
New opportunities An increased focus on energy efficiency could also open up opportunities for alternative machinery solutions, such as the multiple screw Ring Extruder technology that CPM acquired with its 2017 purchase of German company Extricom. “CPM Extrusion Group has demonstrated use of the RE RingExtruder in significantly reducing specific energy via elongational mixing as compared to twin-screw extruders [Figure 3]. As energy costs becomes increasingly important, RingExtruder technology will be seen as lower cost over the lifecycle of the equipment,” Dreiblatt predicts. He claims that elongational mixing is the only way to achieve a significant reduction in specific energy. However, Dreiblattt also sees potential to further
improve the efficiency of twin screw compounding technology. “Twin-screw extruders are highly efficient friction-energy generating machines; the average efficiency in converting 1kWh of electricity into melting of polymers is approximately 97%. Electrical energy is applied to increase the tempera- ture of the solid polymer and then we use additional energy, for example from chillers or cooling towers, to remove the heat for pelletising,” he explains. “The electrical energy from the main drive motor
is dissipated as waste heat through the cooling water for gearbox lubrication and extruder barrel temperature control and the water used to quench
38 COMPOUNDING WORLD | February 2021
FME mixing elements
and solidify the molten polymer, for example in a water bath. All of this waste heat is currently diverted to the environment via cooling towers or chillers. In the future, this waste heat should be recoverable and presents tremendous opportuni- ties for innovation,” he says. German extruder manufacturer Feddem says
that screw configurations and barrel temperatures have a significant influence on compounding efficiency in terms of energy consumption. “With our kneading-block-free melting and mixing zones we can achieve energy savings of up to 10% in these sections of the compounding process compared to conventional screw configurations,” says Klaus Hojer, Business Development Manager. “Heat insulation of the processing section of the extruder is also vital - not only for protecting the operator against accidental contact with hot surfaces, but also for heat conservation purposes.” Other practical steps that a compounder should consider to manage energy use efficiently include optimising the process and plant operation itself, including sequencing of compounds with respect to barrel temperature changes and the like. “Production capacity should be planned with a weekly yield of the lines in mind and not on the basis of the highest throughput rate for an indi- vidual line, Hojer says. “It is also necessary to take into consideration on what line the job can be processed on, without requiring a change of processing screws.” Hojer says Feddem is currently working on optimising particular screw configurations that can process a wide range of compounds without requiring a screw change. “The developmental targets are optimised screw elements and screw configurations. In the future, Feddem also sees more focus on the optimisation of compounding line sizes, which are adapted to new formulations and lot sizes for future demands,” he says.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.tangram.co.uk �
www.busscorp.com �
www.farrel-pomini.com �
www.centuryextrusion.com �
www.feddem.com
www.compoundingworld.com
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