Effect of coal layer thickness on secondary reaction during its infrared rapid pyrolysis

doi:10.11949/0438-1157.20191264

Abstract

Abstract:

Aiming at the problems of small sample addition amount (mg level) and difficult tar collection in the rapid pyrolysis of coal, this study uses the tablet method to prepare coal seams with a thin thickness (mm level) and uses an infrared heating device to investigate the large addition amount (g level), fast pyrolysis characteristics of thin coal seams. Compared to the stacking method of coals sample, in the experiment of thin coal layer, the effect of coal layer thickness on the secondary reaction was significantly inhibited, and the tar yield increased sharply, reaching 9.96% at 1000°C and 1.5 times of the Gray-King analysis. Furthermore, a synchronous increase in pyrolysis gas and tar was realized. The simulated distillation analysis shows that asphaltene was the main compound in the tar sample produced from the coal pyrolysis in the stacked state, while for the tar from the pyrolysis of tableting coal layer, it contained a large amount of light oil, phenol oil, naphthalene oil, washing oil and anthracene oil. From the GC-MS and FTIR analysis, it can be seen that with the decrease of thickness and number of the tableting layer, the kind of tar compounds and their corresponding contents increased, and the absorption of aromatic hydrocarbons and oxygen-containing functional groups was strengthened. All of these further verified the influence of coal layer on tar yield and quality in coal fast pyrolysis, and also revealed the primary reaction characteristics of high-temperature coal pyrolysis under the full suppression of secondary reaction.

Key words: low rank coal, pyrolysis, infrared heating, secondary reaction, tar, fuel, fixed-bed

摘要：

针对煤快速热解研究中样品添加量少(mg级)、焦油收集难等问题，本研究利用压片法制备微薄厚度(mm级)的煤层，并采用红外加热装置考察大添加量(g级)、微薄煤层的快速热解特性。对比堆积煤样和不同煤压片厚度(1.5~3 mm)与个数(1~2)的压片煤样热解特性发现，压片煤层热解过程的二次反应受到明显抑制，焦油产率急剧增加，在1000℃时达9.96%，为格金分析的1.5倍，实现油气产量的同步增长。模拟蒸馏分析发现，堆积状态下焦油以沥青质为主，而微薄煤层制焦油含大量轻油、酚油、萘油、洗油和蒽油。GC-MS和FTIR分析表明，随煤层厚度和个数的减少，焦油组分和含量提高，芳香烃类和含氧官能团吸收增加，进一步验证煤快速热解过程中煤层厚度对焦油产率和品质的影响，揭示在二次反应充分抑制下煤高温热解的初级反应特性。

关键词: 低阶煤, 热解, 红外加热, 二次反应, 焦油, 燃料, 固定床

CLC Number:

TQ 530.2

Jinfeng MA, Xi ZENG, Fang WANG, Guojun KANG, Rongcheng WU, Guangwen XU. Effect of coal layer thickness on secondary reaction during its infrared rapid pyrolysis[J]. CIESC Journal, 2020, 71(2): 736-745.

马金凤, 曾玺, 王芳, 康国俊, 武荣成, 许光文. 煤红外快速热解过程中床层对二次反应的影响[J]. 化工学报, 2020, 71(2): 736-745.

Figures/Tables 13

Fig.1 Common pyrolysis process and interaction between volatiles and char bed

Table 1 Result of proximate, ultimate and G-K analyses of Datong coal

Proximate analysis /

%(mass)

Ultimate analysis/%(mass)

G-K/

%(mass)

M_ad

A_ad

V_ad

O_daf^①

Fig.2 Schematics of adopted IR heating system for coal pyrolysis

Table 2 Detailed experiment conditions in this study

序号	样品质量/g	煤样			温度/℃	目的
序号	样品质量/g	样品状态	煤层厚度/ mm	放置压片数量	温度/℃	目的
1	3	堆积	13	—	600~1000	文献常见方法
2	3	压片	3	1	600~1000	验证压片法抑制二次反应可行性
3	3	压片	1.5	2	600~1000	验证临近煤层对二次反应的影响
4	1.5	压片	1.5	1	600~1000	二次反应最小化研究

Fig.3 Thermogravimetric analysis of adopted Datong coal

Fig.4 Effect of temperature on product yield and gas composition for stacking pyrolysis of coal particles

Fig.5 Effect of temperature on product yield and gas composition for pyrolysis of tableting coal layer

Fig.6 Effect of thickness on product yield and gas composition for pyrolysis of tableting coal layer

Fig.7 Product yield and gas composition of single tableting coal layer pyrolysis at different pyrolysis temperature

Fig.8 Tar yield and ratio between experiment and theory yield at 1000℃ for different experiments

Fig.9 Comparison of distilling fractions in tar from pyrolysis experiments at 1000℃

Fig.10 GC-MS analysis of tar samples prepared at 1000℃

Fig.11 FTIR analysis of tar samples from pyrolysis experiment at 1000℃

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