Experimental investigation on the kinetics of biomass combustion in vertical tube reactor

Abstract

The paper presents results of experimental investigation performed in order to examine kinetics of loose biomass combustion in vertical tube reactor. The investigation conducted included continuous measurement of the fuel mass loss rate, with two biomass combustion models (piston and batch model) proposed, each relying on appropriate theoretical postulates. Results obtained indicated that piston combustion model had shown better agreement between theoretical and experimental data and was therefore used to further analyse effects of excess-air on the combustion kinetics, as well as associated effects of flue gas recirculation. Recirculation of cold flue gases is used to lower peak temperature inside the furnace, as well as to reduce a zone where ash melting problems may potentially occur. During the investigation performed, effects of flue gas recirculation on the combustion process were simulated by simultaneously injecting nitrogen and air flows into the furnace. This was deemed appropriate to simulate real-life conditions prevailing in the furnace with gas recirculation. Experiments were conducted on specially designed and constructed apparatus that enabled kinetic parameters to be determined for the combustion of different types of biomass. Results obtained have indicated that quantity of air affects kinetics of biomass combustion and that increased recirculation leads to reduced biomass reaction rate. The same conclusion was reached based on the results of experiments conducted with two different types of agro-biomass, namely wheat straw and corn stalks, which are most commonly used for energy generation. Results achieved are deemed particularly important when it comes to design of new plants that utilize cigarette type combustion system, but also for development of numerical models used to simulate combustion of biomass bales, with special emphasis placed on the impact of recirculation gases on the combustion kinetics.