Comparison of high temperature chars of wheat straw and rice husk with respect to chemistry, morphology and reactivity

Fast pyrolysis of wheat straw and rice husk was carried out in an entrained flow reactor at high-temperatures (1000–1500) °C. The collected char was analyzed using X-ray diffractometry, N2-adsorption, scanning electron microscopy, particle size analysis with CAMSIZER XT, 29Si and 13C solid-state nuclear magnetic resonance spectroscopy and thermogravimetric analysis to investigate the effect of inorganic matter on the char morphology and oxygen reactivity. The silicon compounds were dispersed throughout the turbostratic structure of rice husk char in an amorphous phase with a low melting temperature (≈730 °C), which led to the formation of a glassy char shell, resulting in a preserved particle size and shape of chars. The high alkali content in the wheat straw resulted in higher char reactivity, whereas the lower silicon content caused variations in the char shape from cylindrical to near-spherical char particles. The reactivities of pinewood and rice husk chars were similar with respect to oxidation, indicating less influence of silicon oxides on the char reactivity.The authors would like to acknowledge the financial support that they received for this project from Danish Strategic Research Council (Grant DSF-10-093956), DONG Energy and Vattenfall. We also thank Gert Beckmann (Retsch Company) for assisting with the reproducibility tests on CAMSIZER XT, Professor Kenny Ståhl (DTU Chemistry) and Sunday Chukwudi Okoro (DTU, Chemical Engineering) for support with the XRD measurements and data processing, Dr. Martin Høj (DTU, Chemical Engineering) for assisting with N2-adsorption analysis and Andrea Hartung (TU Munich) for the careful ash compositional analysis. We emphasize special thank you to Andreas Geißler, Simon Schatzmann and Benedikt Schels for their support during measurements on the entrained flow reactor.peer-reviewe