Pyrolysis magnetization of low-rank coal and distribution characteristics of sulfur and heavy metals in char products
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摘要: 用热解和磁选相结合的方法，研究了不同热解温度下甘肃褐煤和山西次烟煤热解磁化及其半焦产物中硫和重金属的分布特性。通过ICP-OES和ICP-MS分别对半焦中的硫和重金属元素含量进行分析测定，利用XRD和SEM-EDS对半焦的矿物组成和表观形貌进行了表征。结果表明，甘肃褐煤和山西次烟煤在最佳条件下的磁选脱硫率最高可以分别达到52.37%和17.54%；这与黄铁矿在热解过程中的相变行为有关。山西次烟煤半焦的磁选脱硫率低于甘肃褐煤半焦主要是由于其伴生矿物质的赋存包裹和有机质对黄铁矿在热解过程中的转化产生了影响。Ni和Cr与Fe-S矿物的亲和性较强，其随硫更多地富集到磁性半焦中；在800 ℃时，甘肃煤和山西煤磁性半焦中Cr含量分别比非磁性半焦中多8698.25和32327.47 µg/g。低阶煤热解磁化及其半焦产物中硫和重金属的分布特性为脱除煤中硫和重金属元素提供了数据支撑和新思路。Abstract: The distribution of sulfur and heavy metals in char of Gansu lignite and Shanxi subbituminous coal was studied by means of pyrolysis and magnetic separation at different pyrolysis temperatures. The contents of sulfur and heavy metal elements in char were analyzed and determined by ICP-OES and ICP-MS, and the mineral composition and apparent morphology of char were characterized by XRD and SEM-EDS. The results show that the highest desulfurization rates of Gansu lignite and Shanxi Subbituminous coal can reach 52.37% and 17.54% respectively under optimal conditions. This is related to the phase transition behavior of pyrite during pyrolysis. The desulphurization rate of Shanxi subbituminous char is lower than that of Gansu lignite char mainly because the occurrence and inclusion of associated minerals and the organic matter influence the transformation of pyrite during pyrolysis. Ni and Cr have a strong affinity with Fe–S minerals, which are enriched into magnetic char with sulfur. At 800 ℃, Cr content in magnetic char of Gansu coal and Shanxi coal is 8698.25 µg/g and 32327.47 µg/g higher than that in non-magnetic char, respectively. The pyrolytic magnetization of low-rank coal and the distribution of sulfur and heavy metals in its char products provide data support and a new idea for removal of sulfur and heavy metals from coal.
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Key words:
- low-rank coal pyrolysis /
- char /
- magnetization /
- sulfur /
- heavy metals
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图 3 煤热解半焦中重金属元素逐级化学提取法流程示意图
Figure 3 Flow diagram of stepwise chemical extraction of heavy metal elements in coal pyrolysis char
图 4 热解温度与磁性半焦产率的变化
Figure 4 Relationship between pyrolysis temperature and magnetic char yield
图 5 不同热解温度下半焦的XRD谱图
Figure 5 XRD spectra of char at different pyrolysis temperatures A：Pyrrhotite；P：Pyrite；Q：SiO2；T：Troilite
图 6 GS 500 ℃半焦的SEM照片和EDS谱图
Figure 6 SEM and EDS images of GX 500 ℃ char
(a): Magnetic char; (b): Non-magnetic char
图 8 不同热解温度下半焦的全硫含量
Figure 8 Total sulfur content of char at different pyrolysis temperatures
图 7 SX500 ℃半焦的SEM照片和EDS谱图
Figure 7 SEM and EDS images of SX 500 ℃ char
(a): Magnetic char; (b): Non-magnetic char
图 9 不同热解温度下的磁选脱硫率
Figure 9 Desulfurization rate of magnetic separation at different pyrolysis temperatures
图 10 不同热解温度下非磁性及磁性半焦的形态硫分析。
Figure 10 Morphological sulfur analysis of non-magnetic and magnetic chars at different pyrolysis temperatures So: Organic sulfur；Sp: Pyrite sulfur；Ss: Sulfate sulfur
图 11 不同热解温度下磁性半焦和非磁性半焦重金属元素的含量分布
Figure 11 Content distribution of heavy metal elements in magnetic and non-magnetic chars at different pyrolysis temperatures
图 12 GS不同热解温度半焦中重金属元素的提取率
Figure 12 Extraction rate of heavy metal elements in char at different pyrolysis temperatures of GS
图 13 SX不同热解温度半焦中重金属元素的提取率
Figure 13 Extraction rate of heavy metal elements in char at different pyrolysis temperatures of SX
图 14 GS 500 ℃磁性半焦SEM-EDS照片（面扫描）
Figure 14 SEM-EDS diagram of magnetic char at 500 °C of GS (area scan)
图 15 SX 500 ℃磁性半焦SEM-EDS照片（面扫描）
Figure 15 SEM-EDS diagram of magnetic char at 500 °C of SX (area scan)
表 1 GS和SX的工业分析、元素分析和硫形态分析
Table 1 Industrial analysis, elemental analysis and sulfur form analysis of GS and SX
Coal Industrial analysis w/% Elemental analysis w/% Sulfur form wad/% Mad Aad Vdaf FCdaf a Cdaf Hdaf Odaf a Ndaf St,ad Ss Sp Soa GS 9.69 22.96 46.68 53.32 70.02 5.78 19.68 2.01 1.69 0.45 0.23 1.01 SX 3.09 44.49 39.76 60.24 69.27 5.76 8.85 1.07 7.89 0.06 4.28 3.55 note: ad: air drying base; daf: dry without ash-based; Ss: Sulphate sulfur; Sp: Pyrite sulfur; So: Organic sulfur 
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表 2 煤样的灰分分析
Table 2 Ash analysis of coal samples
Coal Content/% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 SO3 K2O Na2O P2O5 Other GS 47.75 19.91 8.50 7.24 1.38 1.39 9.71 2.15 0.92 0.35 0.70 SX 41.42 35.24 18.92 0.23 0.08 3.40 0.14 0.21 0 0.22 0.13
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表 3 不同热解温度下磁性和非磁性半焦中重金属元素含量的差值
Table 3 Difference between the content of heavy metal elements in magnetic and non-magnetic chars at different pyrolysis temperatures
Types of heavy metal AC /(µg·g−1) GS SX 400 ℃ 600 ℃ 800 ℃ 600 ℃ 800 ℃ Co 19.33 12.53 57.99 32.18 106.23 Mo 12.55 4.22 31.13 84.79 114.57 Cd 0.06 1.79 0.45 0.31 0.05 Sn 3.51 −12.42 3.53 6.52 4.13 V 17.23 0.28 30.50 74.78 104.11 Pb 20.76 65.18 3.76 58.09 18.68 Cu 33.34 28.53 82.67 105.73 170.16 As 210.42 159.01 139.64 54.05 59.16 Zn 24.81 60.05 −97.29 50.98 −66.68 Ni 1791.29 854.21 8459.47 2526.26 11608.49 Mn 1990.32 1784.11 1002.25 6472.12 −1105.22 Cr 3516.63 1282.53 8698.25 6728.40 32327.47
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