Pulverized straw combustion in a low-NOx multifuel burner: Modeling the transition from coal to straw

A CFD simulation of pulverized coal and straw combustion using a commercial multifuel burner have been undertaken to examine the difference in combustion characteristics. Focus has also been directed to development of the modeling technique to deal with larger non-spherical straw particles and to determine the relative importance of different modeling choices for straw combustion. Investigated modeling choices encompass the particle size and shape distribution, the modification of particle motion and heating due to the departure from the spherical ideal, the devolatilization rate of straw, the influence of inlet boundary conditions and the effect of particles on the carrier phase turbulence. It is concluded that straw combustion is associated with a significantly longer flame and smaller recirculation zones compared to coal combustion for the present air flow specifications. The particle size and shape distribution is the most influential parameter for the correct prediction of straw combustion. The inlet boundary conditions and the application of a turbulence modulation model can significantly affect the predicted combustion efficiency whereas the choice of devolatilization parameters was found to be of minor importance.