Investigation of pyrolysis and combustion characteristics of chili straw waste with different O2/N2 ratios and heating rates

To utilize chili straw waste (CSW) for energy production and generate higher-quality fuel, the pyrolysis characteristics of CSW under varying particle sizes and heating rates, as well as the effects of different O₂/N₂ ratios on its combustion characteristics, were investigated using Thermogravimetry-Mass Spectrometry (TG-MS). The gas production performance under three different conditions was also analyzed. Results indicated that the solid yield decreased as particle size increased, with the maximum weight loss rate of 77.79 % occurring at a particle size of 1.25∼1.60 mm. The highest relative pyrolysis rate was 0.77 %/K at a heating rate of 10 K/min, corresponding to a weight loss rate of 74.46 %. Increasing the proportion of oxygen in the atmosphere reduced both the ignition and burnout temperatures of CSW by 9.34 K and 51.89 K, respectively, shifting the Derivative Thermogravimetry (DTG) curve to a lower temperature range. Furthermore, an increase in the heating rate enhanced hydrogen production intensity during CSW pyrolysis, with the peak particle current of H₂ rising from 8.7 × 10⁻¹⁰ A to 1.2 × 10⁻⁹ A, representing a 0.38-fold increase when the heating rate was raised from 5 K/min to 40 K/min. A kinetic analysis of CSW pyrolysis using the Coats-Redfern (CR) and Achar methods revealed that activation energy (E_a) increases with particle size, indicating higher energy requirements due to heat transfer resistance. The Friedman, Kissinger-Akahira-Sunose (KAS), and Ozawa-Flynn-Wall (OFW) methods showed rising E_a with increasing conversion rates, corresponding to the decomposition of hemicellulose, cellulose, and lignin. In combustion, oxygen concentration significantly influences E_a, raising it for volatile matter and fixed carbon, and also increasing it for lignin at high temperatures. The CR and Achar models provided strong fits, confirming their reliability in describing CSW pyrolysis and combustion.