Study on the effects of steam on the precipitation characteristics of sodium during coal thermal conversion
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摘要: 在不同水蒸气体积分数及温度条件下制备了相同焦产率的NaCl浸渍煤的煤焦样品，并利用电感耦合等离子体质谱仪分析了不同煤焦中钠的赋存形态及含量，研究了水蒸气及温度对煤热转化过程中钠迁徙转化的影响。结果表明，水蒸气体积分数的增加，一方面，增强了煤热转化过程中水溶态钠的释放；另一方面，也促进了水溶态钠向醋酸铵溶态、盐酸溶态以及不溶态钠的转化，使得钠的释放受到一定程度抑制。煤焦结构演化对碱金属钠释放具有重要影响。水蒸气的气化反应引起煤焦缩聚程度增加，小芳香环缩聚形成大芳香环结构时会对钠起到一定的包裹作用，使得钠的释放受到抑制；同时，气化反应产生的煤焦比表面积越大，越有利于钠直接释放。提高反应温度一方面会促进水溶态钠的释放；同时也会促进水溶态钠向其他溶态形式钠的转化，使得钠析出率随反应温度上升而增加的趋势逐渐变缓。Abstract: The char samples were prepared from the coal impregnated with NaCl under different steam concentrations and temperatures. The mode of occurrence of sodium and the contents of sodium in different chars with the same conversion ratio were analyzed by inductively coupled plasma mass spectrometry. The effects of steam and temperature on the migration and transformation of sodium in the coal during the thermal conversion processes were studied. The results showed that the increase of steam concentration enhanced the release of water-soluble sodium during the thermal conversion of coal and promoted the transformation of water-soluble sodium into ammonium acetate, hydrochloric acid and insoluble sodium. As a result, the release of sodium was suppressed to a certain extent. It was also observed that increasing the reaction temperature could promote the release of water-soluble sodium and promote the transformation of water-soluble sodium to the other soluble forms of sodium. The evolution of char structure was an important influence on the release of sodium. The results revealed that the degrees of char condensation increased with the steam gasification reaction. The formation of large aromatic ring structures from the condensation of the small aromatic rings played the important role in the encapsulation of sodium, which would inhibit the release of sodium.
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Key words:
- sodium /
- steam /
- temperature /
- migration transformation
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图 1 实验系统示意图
Figure 1 Experimental system
1: gas cylinder; 2: mass flowmeter; 3: steam generator; 4: reactor; 5: vertical tubular heater; 6: quartz basket; 7: thermostat; 8:U-shaped tar condenser
图 2 不同水蒸气体积分数对钠析出影响
Figure 2 Effect of different steam concentrations on sodium precipitation
图 3 不同水蒸气体积分数下煤焦中不同形态钠的含量分布
Figure 3 Content distribution of different forms of sodium in coal char under different steam concentrations
: water soluble sodium;
: ammonium acetate soluble sodium;
: hydrochloric acid soluble sodium;
: insoluble sodium
图 4 不同水蒸气体积分数下煤焦的拉曼特征参数
Figure 4 Raman characteristic parameters of coal char under different steam concentrations
图 6 不同温度下煤焦中不同形态钠的含量分布
Figure 6 Content distribution of different forms of sodium in coal char at different temperatures
: water soluble sodium;
: ammonium acetate soluble sodium;
: hydrochloric acid soluble sodium;
: insoluble sodium表 1 样品的元素分析和工业分析
Table 1 Proximate and ultimate analyses of samples
Sample Ultimate analysis wad/% Proximate analysis wad/% C H N S Oa Na Cl M A V FC Zhun dong coal 61.45 4.29 0.46 0.41 12.20 - - 14.34 6.85 24.91 53.90 Na-coalb 67.01 4.15 0.67 0.21 12.94 1.97 3.03 4.91 5.11 34.64 55.34 a: subtraction; b: 5%NaCl impregnated coal 
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表 2 实验工况及样品焦产率
Table 2 Experimental conditions and char yields of samples
NO. Temp. t/℃ Ar/% φH2O/% Reaction time/s η/% 1 700 90 10 200 74.07 2 800 100 0 150 73.83 3 800 90 10 145 73.84 4 800 80 20 140 73.75 5 800 60 40 130 74.01 6 900 90 10 130 73.82
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表 3 煤焦样品的钠含量及析出率
Table 3 Sodium content and precipitation rate of sample
NO. Temperature t/℃ Ar/% φH2O/% Sodium content/(μg·g-1) αg/% 1 700 90 10 12069 57.86 2 800 100 0 16309 43.26 3 800 90 10 8772 69.48 4 800 80 20 10573 63.25 5 800 60 40 12364 56.88 6 900 90 10 7904 72.50
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表 4 不同水蒸气体积分数下煤焦的BET比表面积
Table 4 BET specific surface area of coal char under different steam concentrations
Coal char sample Specific surface area A/(m2·g-1) Ar-char 9.685 10%H2O-char 10.259 20%H2O-char 9.942 40%H2O-char 9.605
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