Development and characterization of a lab-scale entrained flow reactor for testing biomass fuels E. Biagini a , M. Cioni b , L. Tognotti a, * a Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali, Universita ` di Pisa, via Diotisalvi, 2-Pisa 56100, Italy b Enel Produzione Ricerca, Pisa, Italy Received 22 October 2004; received in revised form 2 February 2005; accepted 3 February 2005 Available online 17 March 2005 Abstract Alternative fuels exhibit different features respect to traditional fuels and require an experimental characterization in conditions similar to those of practical applications (high temperature, high heating rate, low residence time). In this work, a lab-scale drop tube reactor is characterized and an experimental procedure is developed to test a bituminous coal and a biomass fuel at high heating rate in oxidative conditions. Thermogravimetric, size and SEM analyses are used to determine the conversion degree, the reactivity and the morphological variations (swelling, fragmentation, agglomeration) of solid residues in different operating conditions. Furthermore, a model is developed in order to simulate the fluidynamics, the energy balance and the mass transfer during the partial oxidation of fuel particles. The application of this model allows the residence time and the thermal history of the particle inside the drop tube to be estimated. The experimental and model results are in agreement, considering both configurations, namely, constant diameter and density models. q 2005 Elsevier Ltd. All rights reserved. Keywords: Solid; Fuel; Combustion 1. Introduction Biomass fuels cause problems from both economical and technological points of view during the preparation (seasonal availability, transport, drying, milling) or during the combustion process (ignition, slagging, emissions) because of specific characteristics: low calorific value, high moisture content, presence of alkali compounds, high ash content. Despite these drawbacks, the advantages are of current interest: biomasses represent a renewable energy source, are CO 2 neutral fuels and give lower emissions of SO 2 , NO x and heavy metals respect to coals, residues can be used as an energy source (instead of a more and more problematic disposal), big quantities of biomasses on a geographic local scale can be exploited. As a matter of fact, they do not satisfy the requirements for a safe and optimum performance in existing boilers. So, the use of these fuels requires a high flexibility of the boiler. Otherwise, alternative processes (co-combustion, pyrolysis, gasifica- tion) can be taken into account [1–4]. Peculiar features of these fuels during the thermal treatments should be investigated in detail in order to obtain an exhaustive characterization and provide important information on their behaviour during the different steps of the process. The reactivity of these fuels during the devolatilization is generally higher respect to traditional coals, with a release of a large amount of volatile compounds at relatively low temperature. Also, volatiles released by biomasses contain more oxygen respect to coals and this can be of interest for pyrolysis processes with the aim of chemical recovery [5,6]. In combustion units, ignition is favoured by the release of volatiles at low temperature, making biomass fuels attractive for cofiring with low volatile coals. However, the flame stability can be compromised [7]. Chars obtained after the devolatilization of biomass fuels are more reactive than those obtained from coals [8]. Even, the direct oxidation of the parent material can be a competitive mechanism respect to the classical Fuel 84 (2005) 1524–1534 www.fuelfirst.com 0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2005.02.001 * Corresponding author. Tel.: C39 050511240; fax: C39 050511266. E-mail address: tognotti@ing.unipi.it (L. Tognotti).