Extrusion International 4-2023

48 Extrusion International 4/2023 Insulation on melt adapter: a very effective method to cut heat loss EXTRUSION TECHNOLOGY Energy-Efficient Extrusion – How Can We Lower Energy Costs? Polymer extrusion is an energy-intensive process. In the last decades, many efforts have been directed towards improving the energy efficiency of SML extrusion lines. Especially in times of rising energy prices and a growing environmental awareness, the topic of saving energy is now attracting more attention than ever. Extruder configuration “A major contribution towards energy savings can be made when configuring an extrusion line. Most of the energy is consumed in the extrusion process when melt- ing the polymer and so the choice of the extruder size and the design is crucial”, Hans-Jürgen Luger, Head of Research & Development at SML, clarifies. Extruders are generally efficient when operating with ideal drive and screw configurations. This applies in particular to SML´s High Speed Extruders with diameters of 75 mm and 90 mm, which are designed to deliver up to 1,200 kg/h for PP, LDPE, LLDPE and PS. Compared to extruders with a larger diameter, a HSE requires up to 80 % less heating power with the same throughput. Another example is SML’s HO-LT extruder for sensitive polymers like EVOH or tie materials, which enables high output rates with lowmelt temperatures. By using a 35 mm HO-LT extrud- er instead of a 75 mm standard extruder for EVOH with the same maximum throughput, the specific energy in - put (SEI) is reduced from 250 Wh/kg to 200 Wh/kg. Factory: efficient cooling water treatment Apart from the heating and melting of the polymer, the cooling process is also something which deserves consideration. Firstly, the water quality in the cooling circuits is crucial to achieve a high cooling efficiency and process reliability. The heat transfer deteriorates as a re- sult of deposits and cooling circuit contamination and, thus, the cooling water temperature has to be lowered to achieve the same cooling capacity. In general, the temperature level required for the cooling water should not be lower as necessary. Secondly, the system for cooling water generation offers the opportunity to save energy. For example, SML uses an advanced system of water wells on the premises, geothermal pumps (which can also be solar-powered) and a rooftop chiller in the headquarters in Redlham. Additionally, heat dissipated from the extrusion lines in operation is used to heat the building in winter. Line configuration: efficient reduction of edge trims Another key-topic is the amount of edge trims ground, refed into the process and re-melted. In prin- ciple, the portion of refeeding decreases as the film width of an extrusion line increases. Thus, wide extru- sion lines with a larger filmwidth can be assumed to be more efficient. Comparing SML´s MiniCast stretch film line (1,500 mm net width) with SML’s PowerCast XL line (4,500 mm net width) as exhibited at K'2022, the por- tion of edge trim is decreased from 27 % to 17 %. This means, that the additional power consumption due to refeeding per kg/h net output of the line is 50 Wh/kg (iStock)