Pyrolysis of wheat straw pellets in a pilot-scale reactor: Effect of temperature and residence time

Abstract

Pyrolysis of two types of pellets (T₁: 100% wheat straw, and T₂: 70% wheat straw; 10% sawdust, 10% biochar, and 10% bentonite clay) was performed in a pilot-scale reactor under a nitrogen environment at 20°C to 700°C. This was to investigate slow pyrolysis yields and gas composition as a function of temperature and residence time. The experimental data were obtained between 300°C and 600°C, with a residence time of 90 min, a nitrogen flow rate of 50 cm³/min, and a heating rate of 20°C/min. The results indicated that the maximum pyrolysis temperature is 605°C with a residence time of 55 min. The product analysis showed that the proportion of gas was higher than that of biochar and bio-oil. The conversion efficiency increased with higher temperatures and varied between 66% and 76%. The results showed that carbon dioxide was the main component in the produced gas, and the maximum gas concentration was 63.6% at 300°C for T₁. The higher temperature and longer residence time increased the syngas (CO + H₂) composition for both T₁ and T₂ treatments. Nevertheless, the produced biochar had a high carbon content and retained a high calorific value, indicating slow pyrolysis is the ideal utilization route of wheat straw pellet biomass for biochar.