EFPRO CEPI - Early Stage Researchers Workshop Dry defibration a waterless preparation process for difficult to recycle paper products

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1 Faculty of Mechanical Science and Engineering, Professorship of Paper Technology EFPRO CEPI - Early Stage Researchers Workshop 2014 Dry defibration a waterless preparation process for difficult to recycle paper products Thomas Schrinner Brussels,

2 Initial Situation Recent studies have shown that the specific energy consumption of quite some state-of-the-art technologies e. g. de-inking or pulping - is far higher than the theoretical minimum. Having been developed over decades it is highly unlikely that simply further developing such technologies will provide the energy savings required to achieve the objectives of CEPI s roadmap What is needed instead are entirely new processes of a superior energy efficiency. One of the main reasons for the inadequate energy efficiency of many stock preparation processes are low consistencies. Against this background the objective of the research work presented here was to examine in how far and for which qualities waterless processes are able to defibre recovered paper in a more energy efficient way. EFPRO-CEPI ESR Workshop 2014 Slide No. 2 of 12

3 Alternative Approach: Dry Defibration The search for solutions potentially transferable from other industries suggested a technology which originally had been developed for the treatment of difficult to grind and temperaturesensitive products. The corresponding devices are generally classified as mechanical airflow impact mills with a peripheral grinding track. The material to be ground is comminuted due to high-impact collisions with the walls or special installations of the grinding chamber induced by a highly turbulent air flow as well as by the shear forces acting in the grinding gap. Based on this principle a specialized aggregate for the dry defibration of paper products was developed and continuously optimized. EFPRO-CEPI ESR Workshop 2014 Slide No. 3 of 12

4 Technology of Dry Defibration screening zone grinding zone material inlet Acting forces Impact load between particles within a rotating turbulent flow, Impact load between particles and grinding elements, Compression and shear stresses in the gap between the grinding elements and the inner surface of the stator, Stresses within the turbulent air flow. EFPRO-CEPI ESR Workshop 2014 Slide No. 4 of 12

5 Preparation of Difficult to Recycle Paper Products Numerous corresponding trials showed that common grades of recovered paper can be defibred sufficiently though with limited advantages in terms of energy efficiency. It, however and even more importantly turned out, that this process has the potential to convert used paper and board products hitherto regarded difficult to recycle or non-recyclable like e. g. board cores, release papers, composite materials or wet-strength products - into valuable secondary fibre pulp at a reasonable energy consumption. In view of increasing scarcity of and rising costs for fibre resources for papermaking, this process might have the potential to become an attractive technology for the industry not only improving their economics but also increasing the security of raw materials supply. EFPRO-CEPI ESR Workshop 2014 Slide No. 5 of 12

6 Process of Dry Defibration 1 Shredder 6 All-Metal Separator Outlet Air 2 Paper Product 7 Material Inlet Feeding Paper Product 3 Paper Scraps 4 Material Bunker 5 Screw Conveyor 8 Dry Defibration Aggregate 9 Cyclone 10 Ventilator Product Baling Press 4 The technology has already been tested successfully at pilot scale. A recently developed test method allows to verify the fitness of the process for the treatment of a broad range of conceivable paper products and to provide a comprehensive and reliable paper technological and energetic assessment. EFPRO-CEPI ESR Workshop 2014 Slide No. 6 of 12

7 Results Different wet-strength products and specialty papers after dry defibration 5 cm 5 cm 5 cm 1 cm 1 cm 1 cm EFPRO-CEPI ESR Workshop 2014 Slide No. 7 of 12

8 Results As compared to dry defibrated pulps of ordinary recovered paper grades pulps those of wet-strength products and specialty papers exhibit higher shives contents. Increasing the revolution speed and extending the dwell time in the aggregate would serve to counteract this deficiency. The remaining shives content could also be reduced directly after the dry defibration process, for instance by air classification with subsequent re-introduction of the reject to the process chain. EFPRO-CEPI ESR Workshop 2014 Slide No. 8 of 12

9 Results A post-treatment of the dry fiber stock with a suitable wet process also leads to a significant reduction of the flake content at a comparable low specific energy input. A dry defibration stage should - whenever possible be implemented as early as possible in an existing process chain. Flakes that can not be disintegrated in the dry pulper could then be discharged by standard sorting processes and separately treated before. EFPRO-CEPI ESR Workshop 2014 Slide No. 9 of 12

10 Results The energy demand for the dry defibration highly depends upon - the properties of the product, - the acceptable shives content for the specific product, - the capacity of the dry defibrator and - the desired throughput. As a lower limit, a specific energy demand for the dry defibration of 75 kwh/t can be specified. This energy consumption results from the defibration resistance which is a. o. a function of the dry content of the paper product - which thus directly translates into the energy demand. EFPRO-CEPI ESR Workshop 2014 Slide No. 10 of 12

11 Summary The dry defibration process concept presented here has the capability to recycle difficult to recycle paper products at a far higher energy-efficiency than standard wet processes. Due to the lack of suitable recycling paths for wet-strength products or specialty papers the dry defibration process would allow to make such material part of the paper cycle and to use them as a source of raw material. In terms of quality and energy, however, the dry defibration of ordinary recovered paper grades represents only a limited alternative to the established wet processes. EFPRO-CEPI ESR Workshop 2014 Slide No. 11 of 12

12 Questions and Discussion Thank you for your attention! Contact: Dipl.-Ing. Thomas Schrinner Prof. Dr.-Ing. Harald Großmann EFPRO-CEPI ESR Workshop 2014 Slide No. 12 of 12