Modeling of multiphase combustion and deposit formation in a biomass-fed furnace P. Venturini * , D. Borello, C. Iossa, D. Lentini, F. Rispoli Dipartimento di Meccanica e Aeronautica, Sapienza Università di Roma, Via Eudossiana 18, I 00184 Rome, Italy article info Article history: Received 14 October 2009 Received in revised form 17 February 2010 Accepted 21 March 2010 Keywords: Biomass Packed bed combustion Particle deposition Particle cloud tracking model Multiphase flows Stretched laminar flamelets abstract A comprehensive computational model for biomass combustion is presented, featuring a solid phase combustion model, a fluid dynamic model for the gas phase, and a solid particle transport and deposit formation model. The submodel developed to track particle trajectories is briefly outlined. The model is implemented on the Finite Element code XENIOSþþ, and a test case is considered of a furnace burning wooden biomass chips added with water and inert material; a dedicated flamelet library is worked out to model combustion. Results underline the capability of the code to predict combustion conditions and, in particular, the growth rates of deposits of different particle size over the furnace walls, as well as the most critical locations for particle deposition. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recent years have witnessed a rapid growth of the use of biomass as a fuel in combustion devices, especially in small- medium size power and/or heat plants. This growth can be ascribed to the steadily increasing cost of fossil fuels, and the individual countries’ energy policy guidelines, together with the fact that the efficiency of small power plants up to 1 MW e (the characteristic size of biomass applications) has significantly improved in recent years. In order to foster the widespread use of biomass as a renewable energy source, several technical problems must be addressed. Biomass fuel is often a waste material produced by industrial processes, or forest and agricultural residues, and the peculiar characteristics of such a fuel may cause problems to the burner. One of these is related to deposit formation, as biomass combustion produces ash which may have a low softening/melting temperature due to its relatively high alkali content. Accordingly, the ash particles entrained in the gas flow may be sticky even at relatively low temperatures, with an ensuing high chance of formation of deposits over the furnace walls [1e4], which reduce the furnace efficiency and require frequent stops for overhauling. Such circumstances underline the need for prediction models for the whole combustion process, aimed at locating the zones of deposit formation, identifying the most suitable kind of biomass fuel, and assisting the furnace optimal design and the management of its maintenance. In the last decade, several models of this kind have appeared, though mostly focused on particular aspects of the problem, rather than on the whole process. For example, Peters and Bruch [5] simulate the drying and pyrolysis of wood particles; Shin and Choi [6] and Goh et al. [7] develop a model for packed bed combustion, and similarly Yang and co-workers [8e12] model the burning behaviour of a wood or waste packed bed. Recently Costa et al. [13], studied the thermo-fluid-dynamic field in an incinerator plant by using a commercial software. Comprehensive studies are not frequent: Huttunen et al. [14] simulate wood combustion in a grate furnace, but they do not consider deposit formation. Kaer and co-workers [15e18] simulate the whole process using the deposition velocity approach for deposit formation. In the present paper a comprehensive model is presented, comprising three main submodels 1. 1D solid-phase combustion; 2. Gas-phase turbulent combustion; 3. Solid particle transport and deposit formation. Submodel 1 is aimed at describing packed bed combustion, based on a 1D model handling thermal decomposition and volume shrinkage of the solid phase in the bed, as well as gas-solid heat and mass transfer. Submodel 2 describes fluid dynamics and turbulent * Corresponding author. Fax: þ39 064881759. E-mail address: venturini@dma.ing.uniroma1.it (P. Venturini). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.03.038 Energy 35 (2010) 3008e3021