混燃石油焦循环流化床锅炉Pb排放特性
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摘要
燃煤电厂释放的Pb具有长距离迁移性、生物累积性和持久危害性等特点,尽管Pb在煤中含量较低,但由于我国煤炭消耗量巨大,每年因燃煤发电排放到环境中的Pb十分巨大,其造成的环境污染问题不容小觑。由于现场取样的复杂性,目前关于燃煤电厂Pb迁移排放特性的研究较少。选取某额定蒸发量为410 t/h的混燃石油焦循环流化床(CFB)锅炉为研究对象,采用EPA Method 29法对电厂布袋除尘器(FF)和石灰石-石膏湿法脱硫塔(WFGD)前后烟气中不同形态的Pb进行了平行取样,同时对入炉燃料、石灰石、底渣、飞灰、脱硫石膏和脱硫废水等物流进行取样分析,通过Pb的质量平衡核算得到Pb在燃煤副产物中的分配比例以及Pb的迁移排放特性。结果表明:Pb的质量平衡率为105. 1%～106. 4%,说明本次Pb排放测试结果的准确性和可信度较高。燃烧过程中,燃料中Pb元素主要以气态单质铅Pb~0或PbO形式释放到烟气中,少量残留在底渣中,本次测试底渣中Pb占总入炉Pb量的13. 7%。随着烟气流动和温度的降低,烟气中大部分Pb化合物会发生均相成核、异相凝结和颗粒表面沉积吸附等过程,形成颗粒态Pb,因此本次测试在空预器出口(布袋除尘器前)烟气中Pb主要以颗粒态形式存在,占比超过99%,而最终排放到大气中的Pb仅为0. 4%。布袋除尘器对烟气中Pb的脱除效率高达99%,主要是体现在对颗粒态Pb的脱除上。而湿法脱硫塔对水溶性较好的气态Pb和颗粒态Pb均有一定的脱除作用,脱除效率可达67%。经污染物控制装置脱除,最终排放到大气中的Pb浓度较低,仅为2. 99μg/m~3,Pb的大气排放因子为0. 90×10~(-12)g/J。
Pb released from coal-fired power plants is characterized by long-distance migration,bioaccumulation and persistent hazards.Although the content of Pb in coal is quite low,the amount of released Pb from the coal-fired power plant could cause serious environmental pollution due to the tremendous coal consumption.Due to the complexity of on-site sampling,the studies on the migration and emission characteristics of Pb in coal-fired power plants are very scarce. In this study,a 410 t/h circulating fluidized bed( CFB) boiler burning mixed fuel of coal and petroleum was selected as the research object,and the EPA Method 29 was used to simultaneously sample flue gas before and after fabric filter( FF) and wet flue gas desulfurization( WFGD).Meanwhile,the flue gas sampling,feed fuel,limestone,bottom ash,fly ash,gypsum,effluent water,limestone slurry and flush water were also sampled and analyzed.The distribution of Pb in combustion byproducts and the migration and emission characteristic of Pb were obtained based on Pb balance calculation. The results show that the mass balance ratio of Pb is in the range of 105.1%-106.4%,which indicates the high accuracy and reliability of the test.During the combustion process,the Pb released into the gas phase is mainly in the gaseous forms,such as Pb~0 and PbO,only a small part remains in the bottom ash.In this study,Pb in bottom ash accounts for 13.7% of the total Pb in the whole system.With the flue gas flow and temperature decrease,most of the Pb compounds in the flue gas will undergo the processes of homogeneous nucleation,heterogeneous condensation,deposition and adsorption on the particle surface to form particulate Pb.Therefore,at the outlet of air-preheater,particulate-bound Pb is the dominant species in the flue gas,accounting for over 99%; while the content of Pb released into the atmosphere is only 0.4%.The removal efficiency of Pb in the flue gas by the fabric filter is as high as 99%,which is mainly reflected in the removal of particulate Pb.The wet desulfurization tower has a certain removal effect on the water-soluble gaseous Pb and particulate Pb,and the removal efficiency can reach to 67%.After the removal by these pollutant control devices,the final concentration of Pb emitted into the atmosphere is extremely low( about 2.99 μg/m~3); and the emission factor of Pb is 0.90×10~(-12) g/J.
Pb released from coal-fired power plants is characterized by long-distance migration,bioaccumulation and persistent hazards.Although the content of Pb in coal is quite low,the amount of released Pb from the coal-fired power plant could cause serious environmental pollution due to the tremendous coal consumption.Due to the complexity of on-site sampling,the studies on the migration and emission characteristics of Pb in coal-fired power plants are very scarce. In this study,a 410 t/h circulating fluidized bed( CFB) boiler burning mixed fuel of coal and petroleum was selected as the research object,and the EPA Method 29 was used to simultaneously sample flue gas before and after fabric filter( FF) and wet flue gas desulfurization( WFGD).Meanwhile,the flue gas sampling,feed fuel,limestone,bottom ash,fly ash,gypsum,effluent water,limestone slurry and flush water were also sampled and analyzed.The distribution of Pb in combustion byproducts and the migration and emission characteristic of Pb were obtained based on Pb balance calculation. The results show that the mass balance ratio of Pb is in the range of 105.1%-106.4%,which indicates the high accuracy and reliability of the test.During the combustion process,the Pb released into the gas phase is mainly in the gaseous forms,such as Pb~0 and PbO,only a small part remains in the bottom ash.In this study,Pb in bottom ash accounts for 13.7% of the total Pb in the whole system.With the flue gas flow and temperature decrease,most of the Pb compounds in the flue gas will undergo the processes of homogeneous nucleation,heterogeneous condensation,deposition and adsorption on the particle surface to form particulate Pb.Therefore,at the outlet of air-preheater,particulate-bound Pb is the dominant species in the flue gas,accounting for over 99%; while the content of Pb released into the atmosphere is only 0.4%.The removal efficiency of Pb in the flue gas by the fabric filter is as high as 99%,which is mainly reflected in the removal of particulate Pb.The wet desulfurization tower has a certain removal effect on the water-soluble gaseous Pb and particulate Pb,and the removal efficiency can reach to 67%.After the removal by these pollutant control devices,the final concentration of Pb emitted into the atmosphere is extremely low( about 2.99 μg/m~3); and the emission factor of Pb is 0.90×10~(-12) g/J.
引文
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[13]FANG T,LIU G,ZHOU C,et al.Lead in Chinese coals:Distribution,modes of occurrence,and environmental effects[J].Environmental Geochemistry and Health,2014,36(3):563-581.
[14]Determination of metals emissions from stationary sources:EPAMethod 29[S].U.S.:Environmental Protection Agency,2017.
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[16]YI H,HAO J,DUAN L,et al.Fine particle and trace element emissions from an anthracite coal-fired power plant equipped with a bag-house in China[J].Fuel,2008,87(10/11):2050-2057.
[17]SANDELIN K,BACKMAN R.Trace elements in two pulverized coal-fired power stations[J].Environmental Science&Technology,2001,35(5):826-834.
[18]徐杰英.煤燃烧过程中痕量元素铅的反应机理研究[D].武汉:华中科技大学,2004.
[19]史燕红,吴华成.燃煤电厂重金属铅排放特性研究进展[J].热力发电,2016,45(1):1-8.SHI Yanhong,WU Huacheng.Emission characteristics of Pb in coal-fired power plant:Research development[J].Thermal Power Generation,2016,45(1):1-8.
[20]FURIMSKY E.Characterization of trace element emissions from coal combustion by equilibrium calculations[J].Fuel Processing Technology,2000,63(1):29-44.
[21]SONG W,JIAO F,YAMADA N,et al.Condensation behavior of heavy metals during oxy-fuel combustion:Deposition,species distribution,and their particle characteristics[J].Energy&Fuels,2013,27(10):5640-5652.
[22]LINAK W P,WENDT J O L.Trace metal transformation mechanisms during coal combustion[J].Fuel Processing Technology,1994,39(1/2/3):173-198.
[23]ZHAO S,DUAN Y,LI Y,et al.Emission characteristic and transformation mechanism of hazardous trace elements in a coal-fired power plant[J].Fuel,2018,214:597-606.
[2]ZHENG J,TAN M,SHIBATA Y,et al.Characteristics of lead isotope ratios and elemental concentrations in PM10 fraction of airborne particulate matter in Shanghai after the phase-out of leaded gasoline[J].Atmospheric Environment,2004,38(8):1191-1200.
[3]OTERO-REY J R,LPEZ-VILARIO J M,MOREDA-PIEIROJ,et al.As,Hg,and Se flue gas sampling in a coal-fired power plant and their fate during coal combustion[J].Environmental Science&Technology,2003,37(22):5262-5267.
[4]郭欣.煤燃烧过程中汞,砷,硒的排放与控制研究[D].武汉:华中科技大学,2005.
[5]任德贻.煤的微量元素地球化学[M].北京:科学出版社,2006.
[6]WANG X,SATO T,XING B,et al.Health risks of heavy metals to the general public in Tianjin,China via consumption of vegetables and fish[J].Science of the total environment,2005,350(1/2/3):28-37.
[7]中华人民共和国统计局.中国统计年鉴[M].北京:中国统计出版社,2018.
[8]吴正舜,张春林,陈汉平,等.石油焦的燃烧特性[J].化工学报,2001,52(9):834-837.WU Zhengshun,ZHANG Chunlin,CHEN Hanping,et al.Combustion characteristic of petroleum coke[J].Journal of Chemical Industry and Engineering(China),2001,52(9):834-837.
[9]WANG J,ANTHONY E J,ABANADES J C.Clean and efficient use of petroleum coke for combustion and power generation[J].Fuel,2004,83(10):1341-1348.
[10]ANTHONY E J.Fluidized bed combustion of alternative solid fuels,status,successes and problems of the technology[J].Progress in Energy and Combustion Science,1995,21(3):239-268.
[11]邓双,张凡,刘宇,等.燃煤电厂铅的迁移转化研究[J].中国环境科学,2013,33(7):1199-1206.DENG Shuang,ZHANG Fan,LIU Yu,et al.Lead emission and speciation of coal-fired power plants in China[J].China Environmental Science,2013,33(7):1199-1206.
[12]李兵,王宏亮,许月阳,等.燃煤电厂湿法脱硫设施对烟气中微量元素的减排特性[J].煤炭学报,2015,40(10):2479-2483.LI Bing,WANG Hongliang,XU Yueyang,et al.Reduction of trace elements in flue gas by wet desulphurization facilities in coalfired power Plants[J].Journal of China Coal Society,2015,40(10):2479-2483.
[13]FANG T,LIU G,ZHOU C,et al.Lead in Chinese coals:Distribution,modes of occurrence,and environmental effects[J].Environmental Geochemistry and Health,2014,36(3):563-581.
[14]Determination of metals emissions from stationary sources:EPAMethod 29[S].U.S.:Environmental Protection Agency,2017.
[15]XU M,YAN R,ZHENG C,et al.Status of trace element emission in a coal combustion process:A review[J].Fuel Processing Technology,2004,85(2/3):215-237.
[16]YI H,HAO J,DUAN L,et al.Fine particle and trace element emissions from an anthracite coal-fired power plant equipped with a bag-house in China[J].Fuel,2008,87(10/11):2050-2057.
[17]SANDELIN K,BACKMAN R.Trace elements in two pulverized coal-fired power stations[J].Environmental Science&Technology,2001,35(5):826-834.
[18]徐杰英.煤燃烧过程中痕量元素铅的反应机理研究[D].武汉:华中科技大学,2004.
[19]史燕红,吴华成.燃煤电厂重金属铅排放特性研究进展[J].热力发电,2016,45(1):1-8.SHI Yanhong,WU Huacheng.Emission characteristics of Pb in coal-fired power plant:Research development[J].Thermal Power Generation,2016,45(1):1-8.
[20]FURIMSKY E.Characterization of trace element emissions from coal combustion by equilibrium calculations[J].Fuel Processing Technology,2000,63(1):29-44.
[21]SONG W,JIAO F,YAMADA N,et al.Condensation behavior of heavy metals during oxy-fuel combustion:Deposition,species distribution,and their particle characteristics[J].Energy&Fuels,2013,27(10):5640-5652.
[22]LINAK W P,WENDT J O L.Trace metal transformation mechanisms during coal combustion[J].Fuel Processing Technology,1994,39(1/2/3):173-198.
[23]ZHAO S,DUAN Y,LI Y,et al.Emission characteristic and transformation mechanism of hazardous trace elements in a coal-fired power plant[J].Fuel,2018,214:597-606.
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