Hydrodynamic model for a biomass grate fired system

Sousa, Nelson; Azevedo, João L.T.

http://hdl.handle.net/10400.1/18207

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Authors

Sousa, Nelson

Azevedo, João L.T.

Abstract(s)

The present paper describes a hydrodynamic model for the solids motion in a grate fired combustion system. The overfed bed material is considered in a Lagrangian referential until the particles stop in a position over the bed or exit the domain. The solid material in the grate is then considered as an incompressible continuous media. The momentum balances are applied in an Eulerian referential to particle elements to calculate their velocity in the grate direction. For the conditions considered the calculated velocity of the elements increase always from the start of the grate towards the exit, so the motion in the vertical direction is always downward. This motion is calculated from continuity and the two components enable the definition of the solids flow within the bed. The application of the model for solids motion is shown to be representative of different situations that are analysed for a vibrating grate working with wood pellets. The distribution of solids in the bed is visually and computationally characterised for three situations: i) feeding particles above the bed over an inclined still grate, ii) vibrating an initial bed promoting the motion of particles and iii) vibrating the bed and feeding above the grate in order to achieve a continuous evolution. The comparison of the results show that the model provides a good representation of reality although it can be improved by adjusting model parameters. The model allows for the generation of solids flow patterns in the bed and is a base for the development of a model for grate fired combustion systems.