A way of a single biomass particle shape characterization in a CFD model

In this study, sieving, 2D imaging analysis (CAMSIZER/CAMSIZER XT) and optical microscopy were applied to the characterization of the size and shape of biomass particles. The 2D imaging technology was found to be the most convenient characterization method, providing information on the shape and external surface area of the particles.

Different biomass samples were measured with an optical microscope and the results were compared with those from 2D imaging analysis. The main result of this study is that the data on particle width, measured by these two techniques, is identical. However, for the particle length, measured by 2D imaging analysis, it is proposed to apply a correction factor equal to cos (45°).

Based on the analysis of different biomass types, it is recommended to set the particle’s thickness to 2/3 of its width. In this study, a way to quantify all three dimensions of biomass particles was established. For the shape representation of biomass particles in the combustion model, measurements on CAMSIZER/CAMSIZER XT were carried out to estimate geometrical parameters as sphericity, aspect ratio and symmetry of the total particle size distribution.

Additionally, a calculation of shape factors was conducted, in which shape factors were determined by relating irregular-shaped biomass particles to regular geometrical bodies such as a cylinder, parallelepiped, sphere and ellipsoid. Based on the calculated shape factors and the main principles of the combustion phenomena, it is recommended to represent a biomass particle in CFD models as an infinite cylinder with the ratio of volume to surface area (V/A) measured with CAMSIZER/CAMSIZER XT technology for the total particle size distribution and multiplied with the estimated correction factor 1.5.

Alternatively, the ratio of volume to surface area (V/A) can be implemented by using equations for the volume and surface area of different geometrical forms, correlated to three dimensions, measured either by 2D imaging technology with the main advantage to conduct measurements quickly with the reproducible results by using small amount of samples, or optical microscopy.