Fluidized bed combustion of a diesel fuel: A modeling interpretation for micro-explosions Francesco Miccio a,b, * , Lorenzo Ferrante c a Istituto di Ricerche sulla Combustione—CNR, Napoli I, Italy b European Commission, Joint Research Center, Institute for Energy JRC/IE, Petten NL, The Netherlands c Dipartimento di Ingegneria Chimica ed Alimentare, Universita ` di Salerno, Fisciano, Italy Abstract The present paper deals with the combustion of liquid fuels in bubbling fluidized bed. The focus is on micro-explosions that were experimentally observed when burning a commercial bio-diesel in the interme- diate temperature range 873–1023 K. The measured micro-explosions frequency fell in the range 2.4– 3.8 Hz. A simplified model for the combustion of a rising fuel-bubble was purposely developed. It applies to a single non-premixed bubble that can undergo coalescence with other bed bubbles. A mechanistic approach is also included in the model in order to relate the frequency of micro explosions to the frequency by which relatively well-premixed bubbles approach the bed surface. The number of coalescences experi- enced by the endogenous bubble during its residence time is less than one, as predicted by the model with reference to the experimental conditions reported in the paper. Even with large simplifications, the model is able to explain the temperature dependence of the micro-explosive behavior. The accordance between the experimental frequency of micro-explosions and the predicted frequency of coalescence-free bubbles reach- ing the bed surface is rather good. Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Fluidized bed; Liquid fuel; Segregation; Coalescence 1. Introduction The use of liquid fuels for fluidized bed (FB) combustion represents a small but not marginal niche for application during start-up, co-firing and waste incineration. Furthermore, increasing interest in bio and waste derived fuels, as a conse- quence of both the application of the Kyoto pro- tocol and the rising oil price, calls for innovative combustion solutions. The fluidized bed can be considered a suitable technology for burning liquid wastes with medium heating value and raw vegetable oils without any preventive chemi- cal treatment, required for enhancing the atomisa- tion behaviour in traditional burners. These fuels can be reliably processed using fluidized bed com- bustion thanks to its robustness, flexibility and effectiveness [1]. The literature on FB combustion of liquid fuels is sparse compared with solid fuels. A few authors [2–4] reported the difficulties experienced during operation, namely fuel cracking, bed agglomera- tion, injector blocking, post-burning in freeboard, non-uniform temperature distribution, unaccept- able combustion and desulphurisation efficiencies. Nevertheless, encouraging experiences on liquid 1540-7489/$ - see front matter Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2006.07.129 * Corresponding author. Fax: +39 081 5936936. E-mail address: miccio@irc.cnr.it (F. Miccio). Proceedings of the Combustion Institute 31 (2007) 2821–2828 www.elsevier.com/locate/proci Proceedings of the Combustion Institute