Release Mechanism of Fuel-N into NOx and N2O Precursors during Pyrolysis of Rice Straw

Xiaorui Liu, Zhongyang Luo, Chunjiang Yu, Bitao Jin, Hanchao Tu
2018 Energies  
Rice straw, which is a typical agricultural residue in China, was pyrolyzed in a horizontal tube reactor connected with a Fourier transform infrared (FTIR) analyzer at temperatures ranging from 500 to 900 • C to research the release mechanism of fuel-N into NO x and N 2 O precursors. The concentrations of gaseous nitrogen components were monitored online. NH 3 , HCN, HNCO, as well as NO were identified components. A high dependency between the gaseous products and temperature was found. NH 3
more » ... was found. NH 3 and HNCO preferred to be formed at lower temperatures and HCN tended to form at higher temperatures. It is worth noting that NO was also an important product. X-ray photoelectron spectroscopy (XPS) was performed to analyze the nitrogen species in rice straw. The result showed that amino-N (N-A) was the main form of nitrogen which accounted for 88.85%. Pyrrolic-N (N-5) was also identified and occupied the rest. Then nitrogen modeling compounds, glycine and pyrrole, were appropriately selected based on the results of XPS to well understand the nitrogen release mechanism during pyrolysis of rice straw. The formation routes of all the nitrogen gaseous components were confirmed. NH 3 , HNCO and NO were originated from the decomposition of amino-N. While both amino-N and pyrrolic-N produced HCN. NO was not detected during the pyrolysis of pyrrole and a little NO was found during the pyrolysis of glycine. Hence, it can be deduced that the large amount of NO formed during the pyrolysis of rice straw was due to the direct oxidization reaction of -NH and -OH, the latter is abundant in the raw material. In order to provide evidence for this deduction, cellulose was added to increase the amount of -OH and co-pyrolysis of cellulose and glycine was conducted. The effect of -OH on the formation of NO was confirmed. Then, the release mechanism of fuel-N into NO x and N 2 O precursors during rice straw pyrolysis was concluded based on the experimental results. Energies 2018, 11, 520 2 of 13 biomass is released into gaseous precursors during pyrolysis at temperatures above 850-900 K [12] . It means that most of NO x and N 2 O originate from the combustion of volatile-N. Hence, it is necessary to understand the release mechanism of nitrogen during pyrolysis well, so that the emission of NO x can be reduced by appropriate in-furnace low-nitrogen combustion measures. Researches have been conducted to investigate the nitrogen release during biomass pyrolysis. It was reported that the gaseous components generally contain NH 3 , HCN, HNCO, [13] [14] [15] . Two approaches, chemical method and thermogravimetry infrared spectrum (TG-FTIR) method, were frequently used to research the conversion of fuel-N into gaseous nitrogen components. Chemical method was carried out by many researches [13, 14, [16] [17] [18] [19] [20] [21] [22] . In those studies, NH 3 and HCN were absorbed by acid and alkaline solutions to form NH 4 + and CN − , respectively. The total yields of NH 3 and HCN could be confirmed based on the ion concentrations of NH 4 + and CN − in the
doi:10.3390/en11030520 fatcat:ttdh5iu4eralpfnsjo6rlrejhe