Combustion mechanism and ash-to-gas products of star anise residues: Atmosphere and temperature dependencies and joint optimization

Abstract

The efficient energy utilization of biomass is still being explored to lessen the heavy dependence on fossil fuels. This study aimed at characterizing the combustion behaviors, performances, ash-to-gas products, reaction mechanisms, and joint optimization of star anise (Illicium verum Hook. f. (SA)) residues in response to temperature, heating rate, and atmosphere type (N2/O2 versus CO2/O2). The main combustion stage of SA was between 150 and 580 °C. The combustion performance indices were higher in N2/O2 than CO2/O2. The estimated activation energy varied between 168.26 and 241.77 kJ/mol. F1, F1.5, A1.5, and A2 well described the most likely reaction mechanisms. The energetically and environmentally multiple objectives were simultaneously optimized using artificial neural networks with the operational inputs of temperature and atmosphere type. The relative importance of the atmosphere type to the gaseous products were thus: aromatics < CO < CO < CO < CO2 < H2O < CH4. The combustion gaseous products were the same in both atmospheres. The SA ash was of K type with a high deposition risk in both atmospheres. Changing N2 to CO2 reduced the tendency of ash scaling and slagging.