Effect of hydrothermal treatment on Na and Ca migration behavior during pyrolysis of Baishihu coal
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摘要: 采用高压釜对富镜质组白石湖煤进行了水热处理，通过傅里叶红外光谱（FT-IR）分峰拟合方法分析了煤中含氧官能团变化。在固定床中开展分离废液和未分离废液水热处理煤样的热解实验，利用原子吸收分光光度计（AAS）测定了热解产物中钠钙含量。结果表明，白石湖煤经水热处理后水分、挥发分、氧含量以及Cl、Na和Ca等无机元素含量明显降低。水热处理过程中芳香醚水解和羧酸盐发生离子交换反应使得氢含量和H/C原子比增加，促进固定床热解焦油产率升高。300℃下水热处理脱除了部分有机形式Ca后随水废液被分离；废液中钠钙等无机元素的催化作用导致未分离废液较分离废液的样品具有更高热解气产率和更低焦油产率。白石湖原煤及其水热处理样品热解产物中Na含量和分布由高到低顺序均为：热解焦>热解水>焦油>热解气，Ca含量和分布顺序为：热解焦>焦油>热解水>热解气。水热处理温度越高，热解过程钠和钙释放率越低，释放的Na主要进入热解水，其次焦油；而释放的Ca则主要分布于焦油中，其次热解水。Abstract: Vitrinite-rich Baishihu coal (BSR) was hydrothermally treated in an autoclave. FT-IR spectra peak fitting was used to investigate change of oxygen functional groups. Fixed bed was applied to pyrolysis of hydrothermal treated samples with and without separation of liquid waste, then contents of Na and Ca in these pyrolysis products were determined by atomic absorption spectrophotometer (AAS).The results show that moisture and chlorine content in Baishihu coal and Na2O content in ash decrease significantly after hydrothermal treatment. The hydrolysis of aryl ethers of Baishihu coal and the ion exchange reaction of carboxylate lead to increase of hydrogen content and H/C atomic ratio, promoting increase of tar yield during pyrolysis. The organic Ca can be removed by hydrothermal treatment at 300℃ and is separated with the hydrothermal liquid waste. Because of catalysis of inorganic elements such as sodium and calcium in hydrothermal liquid on coal pyrolysis, the hydrothermal treated samples without separation of liquid waste has higher gas yield and lower tar yield than those with separation of liquid waste. Na content and distribution in pyrolysis products of BSR and treated samples decease as:char > water > tar > gas, while the order of Ca is:char > tar > water > gas. As the hydrothermally treated temperature increases, the released content of sodium and calcium during pyrolysis process decreases. The released Na during pyrolysis mainly distributes in water, followed by tar, while Ca is just opposite.
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图 1 间歇式搅拌高压釜反应器示意图
Figure 1 Schematic diagram of batch agitating autoclave
1: heating furnace; 2: stirring paddles; 3: thermocouple; 4: water cooled tube; 5: safety valve; 6: pressure gauge; 7: blender
图 2 热解实验装置示意图
Figure 2 Schematic diagram of the pyrolysis apparatus
1: mass flowmeter; 2: heating furnace; 3: reactor; 4: thermocouple; 5: conical flask; 6: ice bath; 7: washing bottle; 8: flowmeter; 9: dry pipe; 10: air bags
图 3 白石湖原煤及水热处理样品的红外光谱谱图
Figure 3 FT-IR spectra of BSR and hydrothermally treated samples
图 4 白石湖原煤及水热处理样品中Na、Ca含量和分布
Figure 4 Content and distribution of Na and Ca in BSR and hydrothermally treated samples
图 5 白石湖原煤及水热处理样品热解产物分布
Figure 5 Pyrolysis products of BSR and hydrothermally treated samples
图 6 白石湖原煤及水热处理样品热解产物中Na含量和分布
Figure 6 Content and percentage of Na in pyrolysis products of coal samples
图 7 白石湖原煤及水热处理样品热解产物中Ca含量和分布
Figure 7 Content and percentage of Ca in pyrolysis products of coal samples
图 8 白石湖原煤及水热处理样品固定床热解过程Na、Ca释放率
Figure 8 Release rate of Na and Ca during pyrolysis of coal samples
图 9 白石湖原煤及水热处理样品热解释放的Na、Ca在气液相产物中的分布
Figure 9 Distributionofreleased Na and Ca in pyrolysisproducts of coal samples
表 1 白石湖煤水热处理前后工业分析和元素分析
Table 1 Proximate and ultimate analyses of coal samples before and after hydrothermal treatment
Sample Proximate analysis w/% Ultimate analysis wdaf/% St, d
w/%Cld
w/%H/Cb O/Cb Mad Ad Vdaf FCda C H N Oa BSR 13.42 15.07 52.97 39.94 72.81 4.82 0.82 21.13 0.34 0.412 0.79 0.22 BS260w 5.33 16.15 50.78 41.27 74.44 5.25 0.88 19.02 0.34 0.026 0.85 0.19 BS300w 5.20 16.84 48.41 42.90 77.14 5.23 0.95 16.28 0.34 0.023 0.81 0.16 BS260 5.42 17.21 50.63 42.35 74.35 5.17 0.83 19.21 0.37 0.353 0.83 0.19 BS300 5.18 17.66 48.77 43.83 77.39 5.10 0.89 16.25 0.36 0.319 0.79 0.16 note: a: by difference; b: atomic molar ratio 
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表 2 白石湖煤水热处理前后煤灰成分分析
Table 2 Ash composition of coal samples
Sample Ash composition w/% SiO2 Al2O3 Fe2O3 TiO2 CaO MgO K2O Na2O MnO2 SO3 P2O5 BSR 46.42 21.99 7.91 0.75 14.34 0.63 0.34 3.10 0.17 3.87 0.05 BS260w 45.77 22.38 9.02 0.72 13.80 0.74 0.29 0.39 0.23 5.27 0.03 BS300w 46.54 22.40 8.45 0.72 13.52 0.70 0.30 0.49 0.23 4.80 0.03 BS260 42.75 21.10 8.06 0.66 14.04 0.72 0.32 2.84 0.22 5.59 0.03 BS300 43.69 21.96 8.16 0.68 14.92 0.70 0.31 2.54 0.22 5.00 0.03
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表 3 白石湖煤中不同形态钠钙的含量
Table 3 Contents of different kinds of sodium and calcium in BSR
Element Content w/(mg·g-1) water soluble ammonium acetate soluble hydrochloric acid soluble insoluble total Na 3.82(85.4) 0.36(8.1) 0.07(1.5) 0.22(5.0) 4.47 Ca 1.03(5.7) 8.45(46.8) 6.49(36.0) 2.07(11.5) 18.04 amount in the bracket is the percentage of each corresponding element
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表 4 含氧官能团位置及分峰拟合的峰面积百分比
Table 4 Main assignment of oxygen functionally groups and area percentage of fitted curves
Position/cm-1 Assignment BSR w/% BS260 w/% BS300 w/% 1005 clay minerals 6.34 13.91 6.83 1035 alkyl ethers 7.03 14.47 18.21 1100 aryl ethers 5.85 4.91 3.91 1167 C-O phenol 2.43 8.63 4.01 1207 C-O phenol 1.37 0.81 4.19 1269 C-O phenol 1.45 0.49 1.36 1310 C-O phenol 0.88 0.45 1.04 1376 CH3-Ar 2.56 1.77 2.47 1442 -CH3, -CH2 6.82 4.02 5.28 1556 aromatic C=C 8.02 7.70 8.63 1588 aromatic C=C 13.92 10.67 12.23 1620 conjugated C=O 18.39 13.88 15.95 1656 conjugated C=O 14.55 10.71 10.64 1696 carboxyl acids 10.39 7.56 5.23
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