Effects of temperature and particle size on the compositions, energy conversions and structural characteristics of pyrolysis products from different crop residues

Abstract In order to explore the important influence of pyrolysis conditions on the pyrolysis mechanism and product formation, the compositions, energy conversions and structural characteristics of pyrolysis products from crop residues with various particle sizes at different temperatures were investigated. The results showed that increasing temperature (300–600 °C) resulted in decreases in the yields (75–35%), O (40–6%) and energy conversion rate (88–50%) of biochars, and increases in EC (2.3–6 ms/cm), pH (6.3–10), fixed carbon (16–60%), C (45–70%) and HHV (18–26 MJ/kg) of biochars as well as the percentages of CH4, CnHm, H2, HHV (2.5–13 MJ/kg) and energy conversion rate (1–14%) of gases. Besides, higher temperature also led to increases in specific surface area (1–12 m2/g) and pore volume (0.004–0.028 cm3/g) and decreases in pore diameter (28–8 nm) and functional group intensity of biochars. Among different particle sizes, coarse grinding sample had the highest yield, H, O and carbon conversion rate of biochars, while fine grinding sample had the highest percentages of CO, CH4 and HHV and energy conversion rate of gases. However, ultrafine grinding sample had the lowest biochar and gas yields and the highest pH, C, specific surface area, pore volume and functional group strengths while the smallest pore size.