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Energy Efficiency and the Use of Waste Heat Energy in Plastics Processing

This thesis gives a holistic view on energy efficiency in plastics processing with a special attention to the processes of injection molding and extrusion. Because of challenges linked to large price increases for electric energy, different issues of this topic are of great importance for the whole industry sector. The threat to the international competitiveness for production facilities in Germany has also been a topic for some time. A production site with high energy efficiency is becoming a key success factor. The results of this work include solutions for common processes as well as for processspecific potentials to increase energy efficiency in plastics processing.

The thesis covers four issues. After an introduction into the overall energy situation of the sector an overview of processspecific and processindependent measures for increasing energy efficiency is given. This includes machine and process technology as well as opportunities to increase energy efficiency by using waste heat energy. After the presentation and interpretation of established study results and energy indicators, the topic is considered in the light of relevant political developments and the derived consequences for plastics processors. In many cases, a reduction of energy costs is possible by using tax concessions. The implementation of a sensible designed energy management system therefore has special significance.

The second part deals with the evaluation of energy indicators in the focussed processes. The components and performance indicators for a meaningful evaluation are developed. With that, the effects of different measures on energy efficiency can be examined. These measures consist of a variation of operating parameters and the use of several machine technologies with different drive concepts. The results show a clear ability of these activities to influence energy efficiency. After that, an analysis of data obtained from a survey of plastics processors in North Rhine-Westphalia takes place. This enables insights into their energy situation and the creation of a benchmarking database for the injection molding process.

After that, an extrusionspecific concept for using the waste heat flow of an internal pipe cooling system is designed and tested. The extracted heat flow is used directly for preheating of the processed plastic granulate. In addition to validating the technical feasibility, an evaluation of the economic efficiency of this approach is given. The processspecific interactions between the resulting temperature of the plastic granulate, the melt temperature and changes to throughput are examined in particular. The findings allow a complete balance for the resulting energetic effects caused by the use of waste heat energy. Furthermore, they lead to the conception of an alternative waste heat recovery system, which is more generalized and not only usable for pipe extrusion with waste heat coming from inner pipe cooling. As a result, it is also applicable to general extrusion processes without an additional internal product cooling system.

The final part of this thesis covers an alternative method for assessing changes in energy efficiency if there is a change in product or process design. In addition to changes of specific energy consumption a change of product value is also considered from the manufacturer`s as well as from the customer's point of view. It can be shown that an assessment of such changes using the established specific energy consumption can lead to misinterpretations. The formation of processspecific case studies and the evaluation of the resulting changes in energy consumption illustrate this fact.

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