• 关键词：汞  褐煤  煤炭地下气化

• 基金项目：国家自然科学基金(编号:20207014);“863计划”经费资助项目(编号:20001AA529030)

• 刘淑琴
• 中国矿业大学北京校区化环学院煤炭地下气化研究中心, 北京 100083

• 冯银辉
• 中国矿业大学北京校区化环学院煤炭地下气化研究中心, 北京 100083

• 梁杰
• 中国矿业大学北京校区化环学院煤炭地下气化研究中心, 北京 100083

• 余力
• 中国矿业大学北京校区化环学院煤炭地下气化研究中心, 北京 100083

• 摘要：在褐煤地下气化模型试验的基础上, 研究了褐煤中汞的赋存形态, 褐煤地下气化煤气中汞含量的变化及存在形态, 以及气化工艺的影响;分析了地下气化过程中汞的析出及反应机理.实验结果表明, 汞在试验褐煤中主要以硫化物结合态和残渣态形式存在;褐煤地下气化煤气中汞含量随气化时间的变化而变化, 且主要以Hg₀(g)的形态存在;水蒸汽的存在会降低Hg₀(g)被其它气体氧化为Hg₂₊(g)的趋势;与地面气化及燃煤过程不同, 煤地下气化产物中, 气态汞占总汞比例低于20%, 明显低于地面气化及燃煤.

• Abstract：underground coal gasification (UCG) is a process in which underground coal, without mining and transportation, is directly converted into combustible gas. The regularity of mercury emission during UCG of lignite was studied with aims of prevention and control of mercury emission released from UCG. Mercury form in lignite is analyzed by sequential chemical extraction. It was found that the average mercury content of the test lignite is 0.3986μμg·g^-1 and mercury in lignite mainly occurs in bound-sulfide and residue, taking up 77.8% and 19.1%, respectively. Based on UCG simulation test of lignite, the change of mercury content in UCG gas varying with time and temperature and the influence of gasification technology were investigated. Elemental mercury, Hg⁰(g), and divalent mercury, Hg²⁺(g), in UCG gas was captured by Ontario Hydro Method (recommended by EPA in USA) and detected by atomic fluorescence spectrometer. In addition, the mechanism of mercury transformation and emission during UCG process was analyzed. Mercury exists mainly in the form of Hg⁰(g) in UCG gas. Small amount of Hg²⁺(g) is produced through chemical reaction of Hg⁰(g) and the product gas in the gasification tunnel, and it easily decomposes into Hg⁰(g) when the temperature is above 700K. The content of mercury in UCG gas changes with gasification time. At the initial stage of UCG, the content of Hg⁰(g) is lower and Hg²⁺(g) can not be detected. The content of both Hg⁰(g) and Hg²⁺(g) increases in the stable gasification process and decreases at the end of UCG due to different amounts of gasified coal in the different periods of UCG. The average content of Hg⁰(g) is 50～60μg·m^-3 and that of Hg²⁺(g) is 0.30～0.35μμg·m^-3. The highest content of Hg⁰(g) is found to be 160 times as much as that of Hg²⁺(g). Changes of Hg⁰(g) and Hg²⁺(g) content in UCG gas with temperature of gasification zone was obtained based on the results of temperature field. The content of Hg⁰(g) and Hg²⁺(g) increases with elevated temperature of gasification zone. The content of Hg⁰(g) reaches saturation when the temperature is higher than 600K, similar to the results of surface gasification. Gaseous mercury contents in UCG gas under different technologies were compared. It indicates that UCG gas contains more Hg²⁺(g) under oxygen gasification and less Hg²⁺(g) under oxygen-steam gasification since steam slows down the oxidation tendency of Hg⁰(g) to Hg²⁺(g). Analysis of mercury balance in UCG process shows that gaseous mercury takes up less than 20% of the total mercury in UCG products, lower than that from surface gasification and coal burning, and solid mercury takes up more than 60%. Since mercury content in UCG ash is lower, the majority of solid mercury is particulate mercury absorbed by char and ash when UCG gas flows through the long air stream tunnel. UCG gas from simulation test contains higher percentage of Hg⁰(g) than that from field test, since the tunnel length is shorter in simulation gasification.

• Key words：mercury  lignite  underground coal gasification

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