Torrefaction of Biomass Pellets: Modeling of the Process in a Fixed Bed Reactor

Authors: Ekaterina Artiukhina, Panagiotis Grammelis

Abstract:

Torrefaction of biomass pellets is considered as a useful pretreatment technology in order to convert them into a high quality solid biofuel that is more suitable for pyrolysis, gasification, combustion, and co-firing applications. In the course of torrefaction, the temperature varies across the pellet, and therefore chemical reactions proceed unevenly within the pellet. However, the uniformity of the thermal distribution along the pellet is generally assumed. The torrefaction process of a single cylindrical pellet is modeled here, accounting for heat transfer coupled with chemical kinetics. The drying sub-model was also introduced. The nonstationary process of wood pellet decomposition is described by the system of non-linear partial differential equations over the temperature and mass. The model captures well the main features of the experimental data.

Keywords: Torrefaction, biomass pellets, model, heat and mass transfer.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1110952

References:

[1] P. C. A. Bergman, A. R. Boersma, R. W. R Zwart, J. H. A. Kiel. Torrefaction for biomass co-firing in existing coal-fired power stations. “Biocoal”. Technical Report ECN-C-05-013. Petten, The Netherlands: ECN; 2005.
[2] J. J. Chew, V. Doshi. Recent advances in biomass pretreatment — torrefaction fundamentals and technology. Renew SustEnerg Rev, 15 (2011), pp. 4212–4222.
[3] A. Uslu, A.P.C. Faaij, P.C.A. Bergman. Pre-treatment technologies, and their effect on international bioenergy supply chain logistics. Technoeconomic evaluation of torrefaction, fast pyrolysis and pelletisation. Energy 33 (2008), pp. 1206–1223.
[4] P. C. A. Bergman Combined torrefaction and pelletisation: the TOP process, Report No.: ECN-C-05-073, Energy Research Centre of the Netherlands (ECN), Petten, The Netherlands, 2005, pp. 29.
[5] R B. Bates, A.F. Ghoniem. Modeling kinetics-transport interactions during biomass torrefaction: The effects of temperature, particle size, and moisture content. / Fuel 2014; 137: pp. 216–229.
[6] R B. Bates. Modeling the coupled effects of heat transfer, thermochemistry, and kinetics during biomass torrefaction. MSc thesis, Massachusetts institute of technology, 2010.
[7] M. J. C. Van der Shtelt. Chemistry and reaction kinetics of biowaste torrefaction. PhD thesis, Eindhoven University of Technology; 2011.
[8] W-C. R. Chan, M. Kelbon, B. B. Krieger. Modelling and experimental verification of physical and chemical processes during pyrolysis of a large biomass particle. Fuel 1985;64: pp. 1505–1513.
[9] C. Di Blasi, S. Branc, Sparano, LaB Mantia. Drying characteristics of wood cylinders for conditions pertinent to fixed-bed countercurrent gasification. Biomass Bioenergy 2003;25: pp. 45–58.
[10] W. J. Parker Development of a model for the heat release rate of wood: a status report. Gaithersburg, MD: US National Bureau of Standards; 1985.
[11] B. Krieger-Brockett, D. Glaister. Wood devolatilization – sensitivity to feed properties and process variables. In: Bridgwater AV, Kuester JL, editors. Res. Thermochem. Biomass Convers.. Netherlands: Springer; 1988. p. 127–42.
[12] S. Shrestha, Cramer S, White R. Time temperature profiles across a lumber section exposed to pyrolytic temperatures. Fire Mater 1994;18:211–20.
[13] K. M. Bryden, K.W. Ragland, C. J. Rutland. Modeling thermally thick pyrolysis of wood. Biomass Bioenergy 2002;22:41–53.
[14] M. G. Grønli A theoretical and experimental study of the thermal degradation of biomass. PhD thesis, Norwegian University of Science and Technology; 1996.
[15] J. C. Wurzenberger, S. Wallner, H. Raupenstrauch, J. G. Khinast. Thermal conversion of biomass: comprehensive reactor and particle modeling. AIChE J 2002;48: pp. 2398–2411.
[16] H. Lu, W. Robert, G. Peirce, B. Ripa, L. L. Baxter. Comprehensive study of biomass particle combustion. Energy Fuels 2008; 22: pp. 2826– 2839.
[17] N. Ouelhazi, G. Arnaud, J.P. Fohr. A two-dimensional study of wood plank drying. The effect of gaseous pressure below boiling point. Transp Porous Media 1992; 7: pp. 39–61.
[18] S. S. Alves, J. L. Figueiredo. A model for pyrolysis of wet wood. ChemEngSci 1989; 44: pp. 2861–2869.
[19] A. Galgano, C Di Blasi. Modeling the propagation of drying and decomposition fronts in wood. Combust Flame 2004; 139: pp. 16–27.
[20] J. Porteiro, J. L. Míguez, E. Granada, J. C. Moran. Mathematical modelling of the combustion of a single wood particle. Fuel Process Technol 2006; 87: pp. 169–75.
[21] B. Peters, E. Schröder, C. Bruch, T. Nussbaumer. Measurements and particle resolved modelling of heat-up and drying of a packed bed. Biomass Bioenergy 2002; 23: pp. 291–306.
[22] R. Bilbao, J. F. Mastral, J. Ceamanos, M. E. Aldea. Modelling of the pyrolysis of wet wood. J Anal Appl Pyrolysis 1996; 36: pp. 81–97.
[23] J. Saastamoinen, J-R. Richard. Simultaneous drying and pyrolysis of solid fuel particles. Combust Flame 1996; 106: pp. 288–300.
[24] P. D. Aerts, K. W. Ragland. Pressurized downdraft combustion of woodchips. Twenty-Third Symp Int Combust 1991; 23: pp. 1025–32.
[25] M. Bellais. Modelling of the pyrolysis of large wood particles. PhD thesis, KTH Royal Institute of Technology; 2007.
[26] B. Peters, C. Bruch. A flexible and stable numerical method for simulating the thermal decomposition of wood particles. Chemosphere 2001; 42: pp. 481–90.
[27] Е. Artiukhina, P. Grammelis, G. Sin. Biomass pellet torrefaction: 2D model development, reliability assessment by sensitivity and uncertainty analyses, to be published.
[28] H. A. Noves, J. I. S. Fernandez-Golfin. Practical evaluation and operation of superheated steam drying process with different softwoods and hardwoods. Eur J Wood Wood Prod 1994; 52: pp. 135–138.