Effects of volatile–char interactions on char during pyrolysis of rice husk at mild temperatures

•Volatile–char interactions of in-situ char at mild temperatures were investigated.•Uniformity of the collected char was made sure by the pulse feeding method.•Volatile–char interactions inhibited char reactivity only above 650°C.•Inhibition intensified with temperature rise, but kept almost unchanged at 700–800°C.•Volatile–char interactions enhanced volatilization of K even at 600°C. In order to understand the sensitivity of volatile–char interactions to mild temperatures (600–800°C), in-situ rice husk char was prepared from fast pyrolysis (>103Ks−1) on a fixed-bed reactor. Retention of K in char, changes in char structure and char reactivity were determined. The results showed that volatile–char interactions did not cause obvious effect on the char yield but showed an inhibitory effect on char reactivity. The inhibition began only above 650°C and intensified with temperature rise, but kept almost unchanged at 700–800°C. Char structure and retention of K have a combined effect on char reactivity. The decreased reactivity was caused by additional volatilization of K from char matrix and transformation of relatively smaller aromatic ring systems to large ring systems (>6 benzene rings) above 650°C.