Nitrogen, Sulfur, and Chlorine Transformations during the Pyrolysis of Straw

Transformation of nitrogen, sulfur, and chlorine during straw pyrolysis at temperatures from 35 to 1450 degrees C was investigated by using the coupled thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) techniques and compared with that of coal. The characteristics of the residual solid char from the straw were analyzed using x-ray diffraction (XRD). Results show that all the nitrogen species (HCN, NH3, H NCO, and CH3CN), chloric species (HCl and Cl-2), and sulfur species (SO2, H2S and COS) began to release from straw from 200 degrees C, compared with 350 degrees C for the case of coal. Most of the gaseous species from the straw were released in the form of a sharp peak, compared with the coal which has a much wider peak. NH3 and H NCO were the primary nitrogen species for both straw and coal; however for the straw the amount of NH3 released was much higher than that of HNCO. Sulfur species from the straw pyrolysis are sparse, and there was only a little COS released. During coal pyrolysis no COS was detected at all and H2S was mainly formed at 500 degrees C similar to 600 degrees C. SO2 was released in three stages (300-500 degrees C, 500-600 degrees C and 1200-1450 degrees C), and the largest SO2 emission was found at high temperatures due to the decomposition of sulfate. The major chloric species from the pyrolysis of both straw and coal was HCl, and the ion current intensity of Cl-2 was very low. There was a critical temperature of around 800 degrees C, beyond which most of the chlorine would be released.