Nitrogen Conversion of Pig Compost during Pyrolysis

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This study aims to understand the effect of pyrolysis temperature on the conversion of nitrogen species of pig compost containing a large amount of nitrogen. Various analysis techniques involving thermogravimetry, X-ray photoelectron spectroscopy, nuclear magnetic resonance, gas chromatography, total nitrogen analysis, ion chromatography were performed to characterize the nitrogen conversion of pig compost. Pyrolysis of the sample was carried out in a fixed bed reactor by varying temperature from 300 to 900°C. Nitrogen content of the residue was found to be decreased with increasing pyrolysis temperature. In contrast, the conversion of organic-nitrogen species into N2 and NOx-precursors (HCN and NH3) increased with increasing temperature. The significant release of NH3 below 500°C can be related to the high protein content in the pig compost. The nitrogen yield as HCN was lower than 2% during pyrolysis below 500°C, and sharply increased to 4% at 900°C due to thermal cracking of pyrrole and pyridine in the residual char at high temperature. Majority of the nitrogen species in residual char is converted into N2 during pyrolysis above 700°C.