Excess air ratio effects on flow and combustion caracteristics of pulverized biomass (olive cake)

The aim of this paper is to study effect of excess air ratio (λ) on combustion dynamics of pulverized olive cake (OC) in a vertical furnace. Four cases namely (a), (b), (c) and (d) for the air inlet conditions with different excess air ratio (EAR) (λ = 1.3, 1.7, 2.3 and 2.7 respectively) are studied. The numerical approach is based on Reynolds Average Navier-Stokes (RANS) equations. The chosen turbulence closure model is the k–ε model. For turbulence-chemistry interactions of the non-premixed combustion, a mixture fraction/PDF approach is used. The particles of OC are injected perpendicularly to the central axe of furnace near the lower base. This injection mode increases the particle residence time in the furnace. The mean size particles diameter is 70 µm. The OC thermal characteristics are determined from thermogravimetric analysis (TGA). A comparison is done between (a), (b), (c) and (d) cases for, flow topology, velocity contours, temperature distribution and species concentration profiles in several locations along the furnace. Results show that increasing excess air ratio dilutes the emission of CO and CO2 inside to the furnace, lowered the temperature in the furnace exit and reduced the visible flames lengths Lvisible.