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Effect of Mechanical Stress from the Grinding Device on the Biomass Powder Properties and Energy Consumption

Rajaonarivony K., Rouau X., Mayer-Laigle C.. 2018. In : Persson M. (ed.), Scarlat N. (ed.), Grassi A. (ed.), Helm P. (ed.). Proceedings of the 26th European Biomass Conference (EUCBE). Florence : ETA, p. 567-571. European Biomass Conference and Exhibition. 26, 2018-05-14/2018-05-17, Copenhagen (Danemark).

The use of biomass as a source of energy has increased in recent years. Whatever the application, the potential of the raw materials, such as cereal or wood by-products (CBP/WBP), needs to be enhanced by grinding processes to ensure the best conversion into energy vectors. However, the energy consumption by the grinding step could vary significantly according to the mechanical properties of the biomass, the process parameters and the targeted size. In this work, we study the influence of the mechanical stress generated by the grinder on the properties of the ground powder (size distribution, particle shape), and on the required energy. The materials were ground in a laboratory ball mill in impact and attrition modes with the same input of energy. Results showed that grinding kinetics were faster with impact than attrition, initial particle sizes being reduced by 98% in 10 and 40 minutes, respectively. An agglomeration index was defined as the ratio between specific surface areas determined with and without ultrasonic treatment. Powder obtained by impact displayed an agglomeration index of 0.5 (CBP) and 0.4 (WBP) after 60 minutes of grinding whereas in attrition this index was lower around 0.4 and 0.2 after 200 minutes of grinding. Moreover, in terms of energy, impact mode seemed to be more energy efficient than attrition.

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