Computational fluid dynamic simulation of a solid biomass combustor: modelling approaches

  • Martin Miltner
  • Aleksander Makaruk
  • Michael Harasek
  • Anton Friedl
Original Paper


The importance of biomass in combustion processes for the combined production of electrical power and district heat is still rising. In the presented work, CFD is used for the development and optimisation of an innovative combustion chamber for a solid stem-shaped biofuel in the form of compressed biomass bales. The main focus of this investigation is the maximisation of the thermal output of the combustor by an optimisation of the bale burnout and the minimisation of gaseous emissions such as VOCs, carbon monoxide and nitrogen oxide. For this purpose the functionality of a commercial CFD-solver has been extended in terms of the solid phase description and the solid–gas interactions. These sub-routines comprise the description of the solid biomass fuel as a porous bed, the biomass drying, the degradation during devolatilisation and char burnout, as well as the generation of gaseous species and the release/consumption of energy during these three steps. Moreover a simplified model for the prediction of NO x -emissions emanating from the fuel-bound nitrogen has been implemented. The results of this work show that the application of CFD enables a significant reduction of the development costs and the time-to-market of innovative chemical engineering concepts such as solid biomass combustion.


Biomass Combustion Emission reduction NOx Straw CFD 

List of symbols


Arrhenius pre-exp. Factor


specific surface (m2/m3)


molecular diffusion coefficient (m2/s)


particle diameter (m)


activation energy (J/mol)


heat transfer coefficient (W/(m2 K))


heat transfer coefficient for radiation at the contact surface (W/(m2 K))


effective radiation heat transfer coefficient of the voids (W/(m2 K))


Colburn factor


kinetic constant


effective reaction rate constant


film diffusion coefficient


equivalent thickness a layer of fluid should have to represent the same thermal resistance as the sphere (m)


equivalent thickness a layer of fluid should have to represent the same thermal resistance as the fluid film (m)


distance between char particles (m)


mass (kg)


molecular weight (g/mol)


Nusselt number

\( p_{{{\text{O}}_{{\text{2}}} }} \)

oxygen partial pressure (Pa)


universal gas constant (J/(mol K))


chemical reaction rate (kmol/(m3 s))


Reynolds number


Schmidt number


Sherwood number


temperature (K)


time (s)


cell volume (m3)


gas velocity (m/s)


species mass content (wt%)


char bed porosity


char combustion stoichiometric ratio


effective thermal conductivity of a packed bed (W/(m K))


thermal conductivity (W/(m K))


gas viscosity (kg/(m s))


gas density, (kg/m3)





We gratefully acknowledge the support from the European Union, Research Grant NNE5-2001-00517.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Martin Miltner
    • 1
  • Aleksander Makaruk
    • 1
  • Michael Harasek
    • 1
  • Anton Friedl
    • 1
  1. 1.Institute of Chemical EngineeringVienna University of TechnologyViennaAustria

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