Effect of temperature and water vapor on the form and evolution characteristics of nitrogen in coal char
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摘要: 研究水蒸气对不同赋存形态氮在热解过程中析出及转化规律有利于精细化调控氮氧化物的生成。利用X射线光电子能谱（XPS）仪分析了典型烟煤及其煤焦中氮的赋存形态，研究了温度、水蒸气浓度等因素对煤焦炭氮析出及转化特性的影响。结果表明，温度的升高以及一定范围内水蒸气浓度的增加有利于焦炭氮的析出，水蒸气浓度达到30%时，焦炭氮析出达到峰值；水蒸气的存在有利于煤焦中N-5和N-6等含氮结构物质从煤焦中析出，同时抑制N-Q和N-X等含氮结构物质的裂解。这是由于水蒸气的气化作用有利于芳香结构的分解，但同时高水蒸气浓度带来的H基团会与N-6结合从而形成N-Q，而由高水蒸气浓度带来的OH基团会促进N-6的氧化而生成N-X。Abstract: Studying the evolution and transformation of different forms of nitrogen in pyrolysis under water vapor atmosphere is conducive to control formation of nitrogen oxides. X-ray photoelectron spectroscopy (XPS) was used to examine forms of nitrogen in typical bituminous coal and its char, and effects of temperature, water vapor on evolution and conversion characteristics of coal nitrogen were investigated. The results indicate that raising temperature and concentration of water vapor are conducive to evolution of char nitrogen. When concentration of water vapor reaches 30%, the char nitrogen evolution reaches a peak. The presence of water vapor facilitates the evolution of N-5 and N-6 from coal char and suppresses that of N-Q and N-X, because the gasification effect of water vapor is beneficial to breaking aromatic structure, but the conversion of N-6 to N-Q and N-X is promoted as a result of H and OH groups brought by the high concentration of water vapor.
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Key words:
- char /
- nitrogen content /
- vapor /
- nitrogen forms /
- XPS
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图 1 实验系统示意图
Figure 1 Experimental system
1: syringe pump; 2: mass flowmeter; 3: gas cylinder; 4: steam generator; 5: insulation cable tie; 6: vertical tubular heater; 7: pulverized coal; 8: quartz basket
图 3 温度对惰性气氛焦炭氮形态转化的影响
Figure 3 Effect of temperature on nitrogen form of char in inert atmosphere
图 6 温度对气化煤焦氮形态转的化影响
Figure 6 Effect of temperature on nitrogen form of gasified coal char
图 8 1000 ℃下水蒸气浓度对气化煤焦氮形态转化的影响
Figure 8 Effect of vapor concentration at 1000 ℃ on nitrogen form of gasified coal char
表 1 原煤的元素分析与工业分析
Table 1 Proximate and ultimate analyses of raw coal
Proximate analysis wad/% Ultimate analysis wad/% M A V FC C H O* N S 1.75 41.09 13.37 44.21 40.94 2.56 11.94 0.72 1.00 *: calculated by difference 
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表 2 实验工况表
Table 2 Experimental condition
No. Temperature t/℃ Ar φ/% H2O φ/% 1 800 100 0 2 1000 100 0 3 800 85 15 5 1000 70 30 6 1000 60 40
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表 3 各形态氮N 1s结合能
Table 3 N 1s binding energy of various forms of nitrogen
Nitrogen forms Symbol Binding energy E/eV Pyridine N-6 398.7 ±0.4 Pyrrole N-5 400.5 ±0.3 Protonated pyridine，quaternary nitrogen N-Q 401.4 ±0.1 Nitrogen oxide N-X 403.5 ±0.5
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表 4 样品焦产率及各形态氮的相对含量
Table 4 Sample char yield and relative content of various forms of nitrogen
No. Char yield w/% Total nitrogen content w/% Relative content w/% N-6 N-5 N-Q N-X Raw coal - 1.42 14.96 31.46 27.57 26.01 1 90.3 1.00 26.70 56.11 6.79 10.40 2 84.1 0.88 23.45 70.85 0.01 5.70 3 87.4 0.98 31.94 36.91 15.34 15.81 4 82.3 0.66 19.69 28.52 27.62 24.18 5 81.0 0.54 25.85 28.25 30.05 15.85 6 80.9 0.54 30.96 28.45 25.46 15.13
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