Biomass combustion behaviors based on online monitoring system: Morphological, thermodynamic and kinetic analysis

Abstract

Identifying the matching law between the morphology, thermodynamic and kinetic characteristics of single biomass can significantly achieve high-efficiency combustion. A visual combustion furnace with online monitoring system was designed and built to record in real-time the apparent volume shrinkage, particle heating process and gas releasing behaviors of single biomass briquette during the combustion process. Furthermore, this work aimed to present a new method to infer the effect of ambient temperature on the pore structure of volatile precipitation and char combustion, mainly through a comparative analysis of the changes in shrinkage ratio and activation energy with carbon conversion efficiency (CCE). The higher the ambient temperature, the faster the biomass heating rate, and the earlier it reached the peak heating rate and the ambient temperature, but the heating process of biomass in the water evaporation stage was almost the same at different ambient temperatures. Oxygen concentration had a significant effect on the volume shrinkage and gas product releasing characteristics, but less on the particle heat transfer. After deducting the experimental system errors, the biomass reaction mode, activation energy and pore structure changed significantly around 40–45% CCE. When the CCE was less than 40%, the biomass mainly underwent volatile precipitation and combustion, with smaller apparent volume shrinkage but larger pore volume at 700 °C compared to 900°C ambient temperature. With the CCE greater than 45% and less than 70%, the char combustion dominated the reaction process, the apparent volume shrinkage was smaller, but the pore structure was more developed at higher ambient temperatures compared to lower temperatures. When the CCE exceeded 70%, the apparent volume and carbon conversion remained almost constant at 700°C, but the volume shrinkage ratio continued to decrease at 900°C ambient temperature. This research and proposed method provide more accurate fundamental support for modeling particle combustion at the reactor scale and designing biomass combustion systems.