CFD evaluation of premixed and non-premixed models as suitable representatives of fixed-bed biomass combustor freeboard

This paper presents a comparison of the performance of two numerical (CFD) models with experimental data obtained for a fixed-bed biomass domestic cooking stove. The two numerical models are two different representations of the possible behavior of the gas region of the combustor under consideration. The one model considers the pyrolysis products emanating from the fuel bed to be premixed with the oxidant (air), while the other model supposes that the pyrolysis products combusting in the freeboard enter this region through a stream that is separate from that of the oxidant. The geometry of the combustion chamber of the stove from which the experimental data was obtained is cylindrical with 11cm diameter and 25 cm depth. The study particularly monitors the exit flame temperature of the cylindrical combustor through the use of k-type thermocouples in the experimental case. The fuel used in the experiment is peanut shells. The premixed model achieved an exit temperature of 435K while the non-premixed model achieved an exit temperature of 747.9K. On the other hand, the highest experimentally obtained temperature is 778.15K whereas the average experimentally obtained temperature is 641.15K. Consequently the non-premixed model is chosen as the better representative of the freeboard.