Abstract
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 NOx and N2O precursors. The concentrations of gaseous nitrogen components were monitored online. NH3, HCN, HNCO, as well as NO were identified components. A high dependency between the gaseous products and temperature was found. NH3 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. NH3, 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 NOx and N2O precursors during rice straw pyrolysis was concluded based on the experimental results.
Highlights
Biomass is considered as one of the most promising alternative energy because of its renewability and carbon-neutrality [1,2,3,4,5,6,7,8]
It is well known that pyrolysis is the first step of combustion, during which, part of the nitrogen in biomass is converted into NOx and N2 O precursors
NO was a major product during rice straw pyrolysis, it was not detected during the was a major product during rice straw pyrolysis, it was not detected during the was aamajor product during rice straw pyrolysis, ititglycine
Summary
Biomass is considered as one of the most promising alternative energy because of its renewability and carbon-neutrality [1,2,3,4,5,6,7,8]. Rice straw is a typical agricultural residue and contains a higher nitrogen content, it was employed to investigate the release of fuel-N into NOx and N2 O precursors during pyrolysis. The conversion of fuel-N into gaseous components during rice straw pyrolysis was researched in a few previous studies [17,28]. Ren et al [28] researched the formation of NOx precursors during rice straw pyrolysis using TG-FTIR They found that HCN and HNCO were the main nitrogen products. Pyrolysis experiments of rice straw were conducted in a horizontal tube furnace in this study, and the concentrations of NH3 , HCN, HNCO, and NO were accurately and dynamically monitored by a FTIR gas analyzer (Gasmet DX4000, Gasmet Technologies Inc., Helsinki, Finland) during the whole reaction process at temperatures ranging from 500 to 900 ◦ C. In order to further understand the fuel-N release mechanism during pyrolysis, XPS was performed to analyze the occurrence form in rice straw, and the appropriate nitrogen modeling compounds were selected according to the XPS result
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