城市污泥热解特性及热解过程中Pb、Cd迁移特性
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摘要
以城市污泥为研究对象,考察了其在不同升温速率下的热解特性、热解反应动力学特征以及重金属Pb和Cd在热解过程中的迁移规律。通过热解失重曲线图得出,污泥的热解过程可分为水分析出阶段、挥发分析出阶段和半焦分解阶段。提高升温速率会导致污泥的失重量减少,挥发分最大失重速率增加。根据Coats-Redfern积分法计算结果得到,挥发分析出的第1阶段和第2阶段的反应级数分别为1和2,且不同升温速率下挥发分析出的第1阶段和第2阶段下的活化能总体上变化不大。通过管式炉热解实验可知,在热解温度为400、500、600和700℃范围内,重金属Pb和Cd的残留率随热解温度的升高均表现为先上升后下降的规律。Cd的残留率在热解温度为500和700℃时分别达到最高(41.64%)和最低(2.92%),而Pb的残留率随温度变化不大,均为93%以上。热解温度为400~500℃,Cd和Pb挥发较少。
The pyrolysis process and kinetics of sewage sludge under various heating rates and the migrations of Pb and Cd during the pyrolysis process were investigated. The results showed that the sewage sludge pyrolysis process can involve water evaporation,organics volatilization and char decomposition steps. Higher heating rate results in the higher volatile weight loss rate,while lower heating rate can increase the sludge loss weight. Based on Coats-Redfern integration method,the organics volatilization step can be divided into two stages,namely,the first stage and the second stage,with a first order reaction for the first stage and a second order reaction for the second stage. No significant changes in the activation energy of the first and the second stages under various heating rates are observed. The pyrolysis experiment by a tube furnace showed that the fixation rate of Pb and Cd increases first and then decreases as the pyrolysis temperature increases in the range of 400-700 ℃. Cd fixation rate reaches the maximum( 41. 64%)at 500 ℃ and the minimum( 2. 92%) at 700 ℃. However,the Pb fixation rate changes a little with the pyrolysis temperatures and remains above 93%. At pyrolysis temperature of 400 ℃ ~ 500 ℃,little Pb and Cd are released.
The pyrolysis process and kinetics of sewage sludge under various heating rates and the migrations of Pb and Cd during the pyrolysis process were investigated. The results showed that the sewage sludge pyrolysis process can involve water evaporation,organics volatilization and char decomposition steps. Higher heating rate results in the higher volatile weight loss rate,while lower heating rate can increase the sludge loss weight. Based on Coats-Redfern integration method,the organics volatilization step can be divided into two stages,namely,the first stage and the second stage,with a first order reaction for the first stage and a second order reaction for the second stage. No significant changes in the activation energy of the first and the second stages under various heating rates are observed. The pyrolysis experiment by a tube furnace showed that the fixation rate of Pb and Cd increases first and then decreases as the pyrolysis temperature increases in the range of 400-700 ℃. Cd fixation rate reaches the maximum( 41. 64%)at 500 ℃ and the minimum( 2. 92%) at 700 ℃. However,the Pb fixation rate changes a little with the pyrolysis temperatures and remains above 93%. At pyrolysis temperature of 400 ℃ ~ 500 ℃,little Pb and Cd are released.
引文
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[2]严建华,蒋旭光,池勇,等.污泥流化床焚烧技术研究和环境影响分析[J].热能动力工程,1996,11(1):25-29.YAN Jian-hua,JIANG Xu-guang,CHI Yong,et al.A study on fluidized bed sludge combustion technology and analysis of environmental impacts[J].Journal of Engineering for Thermal Energy and Power.1996,11(1):25-29.
[3]陈亚,陈建林,刘龙茂,等.城市污水污泥热解动力学研究[J].河南科学,2009,27(6):727-730.CHEN Ya,CHEN Jian-lin,LIU Long-mao,et al.Kinetics of municipal sewage sludge thermal pyrolysis[J].Henan Science,2009,27(6):727-730.
[4]WANG Zhi-qi,GUO Qing-jie,LIU Xin-min,et al.Low temperature pyrolysis characteristics of oil sludge under various heating conditions[J].Energy Fuels,2007,21(2):957-962.
[5]刘文铁,王淑彦,陆慧林,等.污泥的热解动力学及机理研究[J].热能动力工程,2006,21(5):529-531.LIU Wen-tie,WANG Shu-yan,LU Hui-ling,et al.The kinetics and mechanism research of sludge pyrolysis[J].Journal of Engineering for Thermal and Power,2006,21(5):529-531.
[6]高现文,单春贤,李海英,等.温度对污泥热解产物及特性的影响[J].生态环境,2007,16(4):1189-1192.GAO Xian-wen,SHAN Chun-xian,LI Hai-ying,et al.The effect of temperature on sludge pyrolysis products and the relevant characteristics[J].Ecology and Environment,2007,16(4):1189-1192.
[7]NOWICKIL,STOLAREK P,OLEWSKI T,et al.Mechanism and kinetics of sewage sludge pyrolysis by thermogravimetry and mass spectrometry analysis[J].Chemical and Engineering,2008,29(3):813-825.
[8]KISTLER RC,WIDMER F.Behavior of chromium,nickel,copper,zinc,cadmium,mercury,and lead during the pyrolysis of sewage sludge[J].Environmental Science and Technology,1987,21:704-708.
[9]CHEN Tao,YAN Bo.Fixation and partitioning of heavy metals in slag after incineration of sewage sludge[J].Waste Management,2012,32:957-964.
[10]何艳峰,卓建坤,李清水,等.污水污泥的燃烧特性及动力学研究[J].热能动力工程,2011,26(5):609-614.HE Yan-feng,ZHUO Jian-kun,LI Qing-shui,et al.Combustion characteristics and dynamic study of sewage water and sludge[J].Journal of Engineering for Thermal Energy and Power.2011,26(5):609-614.
[11]何品晶,邵立明,陈正夫.污水厂污泥低温热化学转化过程机理研究[J].中国环境科学,1998,4(1):40-42.HE Pin-jing,SHAO Li-ming,CHEN Zheng-fu.Study on the mechanism of a low-temperature thermo-chemical conversion process for sewage sludge[J].China Environmental Science,1998,4(1):40-42.
[12]金湓,李宝霞,金诚.不同温度区间内污泥热解气固相产物特征[J].化工学报,2014,65(6):2316-2322.JIN Pen,LI Bao-xia,JIN Cheng.Characteristics of products from sewage sludge pyrolysis at various temperature ranges[J].CIESC Journal,2014,65(6):2316-2322.
[13]李春雨,蒋旭光,费振伟,等.热重-红外联用分析制革污泥的燃烧特性[J].化工学报,2010,61(5):1301-1306.LI Chun-yu,JIANG Xu-guang,FEI Zhen-wei,et al.The combustion characteristics of the leather sludge by TG-FTIR analysis[J].CIESC Journal,2010,61(5):1301-1306.
[14]王俊琪,方梦祥,骆仲泱,等.煤的快速热解动力学研究[J].中国电机工程学报,2007,17:18-22.WANG Jun-qi,FANG Meng-xiang,LUO zhong-yang,et al.Study on fast pyrolysis kinetics of coal[J].Proceedings of the CSEE,2007,17:18-22.
[15]胡艳军,宁方勇,钟英杰.城市污水污泥热解特性及动力学规律研究[J].热能动力工程,2012,27(2):253-256.HU Yan-jun,NING fang-yong,ZHONG Ying-jie.Study on pyrolysis characteristics and kinetics of the sewage sludge[J].Journal of Engineering for Thermal and Power,2012,27(2):253-256.
[16]陆昌伟,奚同庚.热分析质谱法[M].上海:上海科学技术文献出版社,2002.LU Chang-wei,XI Tong-geng.Thermal analysis-mass spectrometry[M].Shanghai:Shanghai Scientific and Technical Literature Publishing House,2002.
[17]胡荣祖,史启祯.热分析动力学[M].北京:科学出版社,2001.HU Rong-zu,SHI Qi-zhen.Thermal analysis kinetics[M].Beijing:Science Press,2001.
[18]沈伯雄,郭彩霞,吴顺伟.焚烧污泥重金属迁移的研究进展[J].电站系统工程,2008,24(1):15-40.SHEN Bo-xiong,GUO Cai-xia,WU Shun-wei.Research progress of heavy trace metal migration during the incineration of sludge[J].Power System Engineering,2008,24(1):15-40.