Improving energy effi ciency | processing feature
Making extrusion more energy effi cient
Robin Kent, the author of
Energy Management in Plastics Processing, provides useful tips for reducing the energy consumption of extrusion lines
Plastics processing is one of the most energy intensive of the ‘light’ manufacturing industries and most processors now realise that energy is a signifi cant and increasing cost. Extrusion is one of the most energy effi cient methods of processing plastics in terms of the actual process load, but there are still many areas where it is possible to reduce energy use in the process. Before a company can start to reduce its energy costs, it needs to know where the money is being spent. The best, and most accurate, way to do this is to use ‘energy mapping’ to build a model of the energy use at the site (related to production activity) and then to use sub-metering or other energy use data to validate the energy map. This provides both a visual and mathemati- cal model of energy use and allows efforts to be targeted to have the most effect. At the global (site) level, most extrusion companies will fi nd that their energy use is distributed as shown in Figure 1a. This shows that, for a typical profi le extrusion site,
the extruders will use the most energy. For other types of extrusion, such as the production of sheet and fi lm (both blown and BOPP/BOPET), the downstream energy use can also be signifi cant, but will rarely be as much as the energy used by the extruders. For most sites, the ‘visible’ extruder loads will be
equalled by the ‘invisible’ services loads such as chillers, compressed air and pumps. These will generally be hidden away in services areas and whilst
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the extruders are the largest energy users, the other areas may provide easier savings. It is possible, using sub-metering or portable
monitoring equipment, to look at the energy use of the extruder itself and this can again be sub-divided to show where the most energy is used. At the machine level, most extrusion companies will fi nd that their energy use is distributed as shown in Figure 1b. At this level, the major energy user is the main
extruder motor and in most cases this will use around 66% of the total energy (depending on the process, screw, machine settings and other variables). These simple pie-charts give good guidance to
Lighting 5% Water pumps 5%
Heating 2% Offices 1%
Others (material
Vacuum 5% Heating
(barrel and other 25%)
Compressed air 11%
Extruders 50%
Chillers 26%
Main motor 65%
feed, ejection, etc.) 5%
Figure 1a (left) shows energy distribution across a typical site. Figure 1b (right) shows energy use at the machine level
March 2014 | COMPOUNDING WORLD 67
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