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Energies 2019, 12(3), 565;

Torrefaction of Sewage Sludge: Kinetics and Fuel Properties of Biochars

Faculty of Agronomy and Bioengineering, Poznan University of Life Sciences, 60-637 Poznanń, Poland
Faculty of Life Sciences and Technology, Wrocław University of Environmental and Life Sciences, 50-375 Wrocław, Poland
Department of Environmental Engineering, Faculty of Building Services, Hydro and Environmental Engineering, Warsaw University of Technology, 00-653 Warsaw, Poland
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA
Author to whom correspondence should be addressed.
Received: 22 January 2019 / Revised: 3 February 2019 / Accepted: 9 February 2019 / Published: 12 February 2019
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We propose a ‘Waste to Carbon’ thermal transformation of sewage sludge (SS) via torrefaction to a valuable product (fuel) with a high content of carbon. One important, technological aspect to develop this concept is the determination of activation energy needed for torrefaction. Thus, this research aimed to evaluate the kinetics of SS torrefaction and determine the effects of process temperature on fuel properties of torrefied products (biochars). Torrefaction was performed using high ash content SS at six (200~300 °C) temperatures and 60 min residence (process) time. Mass loss during torrefaction ranged from 10~20%. The resulting activation energy for SS torrefaction was ~12.007 kJ·mol−1. Initial (unprocessed) SS higher heating value (HHV) was 13.5 MJ·kg−1. However, the increase of torrefaction temperature decreased HHV from 13.4 to 3.8 MJ·kg−1. Elemental analysis showed a significant decrease of the H/C ratio that occurred during torrefaction, while the O/C ratio fluctuated with much smaller differences. Although the activation energy was significantly lower compared with lignocellulosic materials, low-temperature SS torrefaction technology could be explored for further SS stabilization and utilization (e.g., dewatering and hygienization). View Full-Text
Keywords: waste to carbon; sewage sludge; kinetics; torrefaction; biochar; activation energy; fuel properties waste to carbon; sewage sludge; kinetics; torrefaction; biochar; activation energy; fuel properties
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Pulka, J.; Manczarski, P.; Koziel, J.A.; Białowiec, A. Torrefaction of Sewage Sludge: Kinetics and Fuel Properties of Biochars. Energies 2019, 12, 565.

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