The Ergun equation with new values

3. Results and discussion
3.1. Particle sphericity
Sphericity of coal, char and the ash particles as a function of particle size is shown in Fig. 3. Sphericity of coal particles is in the range 0.73–0.83 and it increases with increasing particle size. Char particles are more angular with sphericity below 0.8. Smaller char particles are slightly more spherical than larger ones. In PH797804 to the trend observed for coal particles, sphericity of ash particles decreases with increasing particle size. This may be associated with the heat treatment (partial melting) in the combustion zone and particle agglomeration (clinker formation). Sphericity of small ash particles (below 5 mm) is slightly above 0.8. It drops to values close to 0.65 for 45 mm particles.
Fig. 3. Sphericity as a function of particle size for (a) coal, (b) char, (c) ash particles.Figure optionsDownload full-size imageDownload as PowerPoint slide
3.2. Bed voidage
Experimental data on packed-bed voidage have been used to derive a linear correlation hydrophobic describes voidage as a function of the average particle diameter and PSD width as shown in Eq. (7):equation(7)ε=a+bdpSM+cΔdpε=a+bdpSM+cΔdp