Transformation of nitrogen during pyrolysis of Na-loaded Shengli brown coal
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摘要: 采用具有流化床/固定床特征的石英反应器进行不同Na负载量的胜利褐煤热解实验,考察不同Na负载量对煤热解过程中氮迁移的影响。用紫外可见分光光度计分析气相的NH3和HCN,用X光电子能谱仪(XPS)表征固体半焦中有机氮的存在形式。结果表明,低温热解时,增加Na的含量对煤中氮转化为NH3起促进作用;高温热解时,Na抑制煤中氮转化为NH3。Na对煤中氮转化为HCN表现为抑制作用,这种影响规律不随温度而变化。载Na量增加降低半焦氮含量,促进半焦中季氮的生成,但这种影响在低温时不明显。Abstract: The impact of Na content on nitrogen transformation during the pyrolysis of Shengli raw coal and the Na-loaded coal in a fixed-bed/fluidized-bed quartz reactor was investigated. The quantification of NH3 and HCN in gas product was carried out using an ultraviolet-visible spectrophotometer while the occurrence modes of nitrogen in the solid chars were detected by X-ray photoelectron spectroscopy (XPS). The results indicate that the transformation of coal-N to NH3 can be catalytically enhanced by certain amount of Na at low temperature. When the final pyrolysis temperature is relatively high, the presence of Na appears to inhibit the formation of NH3. Meanwhile, for any given pyrolysis temperature, the production of HCN will be suppressed by Na. When the pyrolysis temperature is high, the increase of Na content in coal causes the reduction of nitrogen remaining in char and promotes quaternary nitrogen formation, whereas, the effect is negligible at low temperature.
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Key words:
- brown coal /
- pyrolysis /
- Na /
- nitrogen
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图 1 流化床/固定床反应器热解实验装置流程示意图[18]
Figure 1 Schematic diagram of coal pyrolysis reaction system
1: argon; 2: flow rate controller; 3: coal feeder; 4: coal; 5: electrical furnace; 6: fluidized-bed/fixed-bed reactor; 7: NaOH or H2SO4 solution in absorption bottles
表 1 煤样的工业分析和元素分析
Table 1 Proximate and ultimate analysis of coal samples
Coal sample Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf FCdaf C H O* N S Na0 6.44 8.54 45.93 54.07 60.55 4.66 33.28 0.95 0.56 Na1 6.08 9.73 40.57 59.43 60.38 5.11 32.74 1.18 0.59 Na2 6.30 10.91 41.09 58.91 60.37 4.97 33.04 1.15 0.47 Na3 6.76 11.7 41.39 58.61 59.60 5.01 33.92 1.15 0.44 Na6 13.07 17.77 35.90 64.10 50.64 5.12 42.72 1.10 0.42 *: by difference;Na0, Na1, Na2, Na3 and Na6 represent coal loaded with 1%Na, 2%Na, 3%Na and 6%Na respectively 表 2 煤样的碱金属及碱土金属分析
Table 2 Alkali and alkaline earth metal analysis of coal samples
Coal sample Content w/% Na Ca Mg Na0 1.51 0.563 0.137 Na1 1.99 0.555 0.280 Na2 3.07 0.660 0.173 Na3 3.85 0.728 0.334 Na6 6.37 0.761 0.347 表 3 不同氮形态的结合能
Table 3 Binding energy of different nitrogen morphologies
Nitrogen morphology Binding energy E/eV Pyridine-N 398.7±0.4 Pyrrole-N 400.5±0.3 Quaternary-N 401.1±0.3 表 4 不同Na含量煤1 073 K热解半焦中氮官能团的相对含量
Table 4 Distribution (relative percentage) of nitrogen functional groups in chars from pyrolysis of coal with different sodium contents at 1 073 K
Char Content w/% N-6 N-5 N-Q Na0 char 33.43 55.69 10.87 Na1 char 33.59 53.14 13.27 Na2 char 32.84 52.83 14.33 Na3 char 24.82 42.77 32.41 -
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