Modeling biomass particle drying, devolatilization and combustion in a grate fired combustor

Sousa, Nelson; Azevedo, João L.T.

http://hdl.handle.net/10400.1/18206

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Authors

Sousa, Nelson

Azevedo, João L.T.

Abstract(s)

The paper presents the application of a numerical model to describe the evolution of a particle in a grate fired combustion system. Due to the particle dimensions, important temperature gradients exist inside the particles and reactions occur within the particles. A model using layers is used to describe the processes inside the particles. The biomass composition is expressed as fractions of moisture, unreacted biomass, char and ash. Biomass conversion is described by a competitive reaction model leading to the formation of light volatiles, tars and char. Tar is subject of secondary reactions inside the particles forming either light gases or char. Transport equations are solved for the gases within the particle including oxygen from the environment that reacts with gases or char. The model is applied to different heating rates leading to different amounts of tars and char in accordance with data from the literature. The model is also applied to simulate the combustion of a single trunk standing in a heated gas stream and comparisons are done for the temperature and mass loss.