Effect of char powder on gaseous tar reaction during low-rank coal pyrolysis
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摘要: 热解焦油气在输送管路或除尘设备中会发生一定程度的反应，进而影响热解产物的分布和组成，而其中夹带的焦粉粉尘会对焦油气反应产生影响。本研究利用两段流化床热解反应器，考察了不同反应温度下（400−500 ℃），焦粉对淖毛湖长焰煤热解焦油气反应的影响。结果表明，添加焦粉后，焦油气不仅发生热裂解和热缩聚反应，还会被焦粉作用发生催化裂解反应，焦油产率和沥青含量减小，热解气和积炭产率增加；随着反应温度的升高，焦油气热裂解和热缩聚反应加剧，反应后焦油气较为稳定，不易被焦粉催化，因此，焦粉对焦油产率、沥青含量及热解气产率的影响随温度升高逐渐减弱；而反应温度升高，焦油气催化裂解生成的自由基更容易发生缩聚反应，焦粉对积炭产率的影响变强。此外，焦粉的催化裂解作用使不同反应温度下焦油中杂环化合物含量下降；同时焦粉促进了热解水与焦油气反应，导致不同反应温度下焦油中脂肪烃、芳香烃含量下降，酚类和含氧化合物含量上升。Abstract: The char powder entrained in gaseous tar influences the reaction of gaseous tar that exists in the transportation pipeline or dust removal equipment, which further affects the distribution and composition of pyrolysis products. This study investigated the effect of char powder on the reaction of gaseous tar during Naomaohu long-flame coal pyrolysis from 400 to 500 ℃ in a two-stage fluidized bed reactor. Results indicated that in addition to its thermal cracking and polycondensation reactions, catalytic cracking reaction of gaseous tar also occurred when char powder was added, resulting in the decrease of tar yield and pitch content, and the increase of pyrolysis gases and coke yield at different reaction temperatures. The thermal cracking and polycondensation reactions of gaseous tar intensified with increasing reaction temperature, which stabilized the gaseous tar and made it difficult to be catalyzed by char powder. Therefore, with the increase of reaction temperature, the influences of char powder on tar yield, tar pitch content and pyrolysis gases yield were reduced. The polycondensation reaction of free radicals from catalytic cracking of gaseous tar was prone to occur with increasing reaction temperature, which enhanced the effect of char powder on coke yield. Also, the catalytic cracking action of char powder reduced the content of heterocyclic compounds in tar at different reaction temperatures, and the reaction between gaseous tar and water was promoted by char powder, resulting in the decrease of aliphatics and aromatics contents in tar, and the increase of phenols and oxygenated compounds contents in tar at different reaction temperatures.
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Key words:
- char powder /
- low-rank coal /
- pyrolysis /
- gaseous tar /
- cracking reaction
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图 1 实验装置示意图
Figure 1 Diagram of the two-stage fluidized bed reactor
1：Nitrogen cylinder; 2: Mass flow controller; 3: Gas preheater; 4: Feeder; 5: Fluidized bed reactor; 6: Electric furnace; 7: Collection bottle; 8: Filter; 9: Gas analyzer
图 3 不同反应温度下焦粉对热解产物产率的影响
Figure 3 Effect of char powder on yields of pyrolysis products at different reaction temperatures
图 4 不同反应温度下焦粉对热解焦油馏分分布的影响
Figure 4 Effect of char powder on the distribution of tar fraction at different reaction temperatures
图 5 不同反应温度下焦粉对热解焦油组成的影响
Figure 5 Effect of char powder on tar composition at different reaction temperatures
表 1 煤样的工业分析和元素分析
Table 1 Proximate and ultimate analyses of Naomaohu coal
Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf C H N S O* 19.5 5.8 50.12 74.35 5.13 0.72 0.31 19.49 note: ad: air-dried basis; d: dry basis; daf: dry and ash-free basis; *: by difference 
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表 2 焦粉的工业分析和元素分析
Table 2 Proximate and ultimate analyses of char powder
Proximate analysis w/% Ultimate analysis wdaf/% Ad Vdaf FCdaf C H N S O* 9.35 26.69 73.31 82.69 3.98 0.83 0.42 12.08 note: dry basis; daf: dry and ash-free basis; *: by difference
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表 3 焦粉的灰成分分析
Table 3 Ash composition of char powder
Content w/% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 SO3 K2O Na2O P2O 13.68 9.83 14.37 43.64 1.52 0.24 2.67 0.14 1.26 0.01
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