Emission Characteristics Of Heavy Metal,SO_x And Cl From Circulating Fluidized Bed Boilers Co-firing Petroleum Coke And Coal

Coal-fired power plant is considered to be the main anthropogenic emission source of air pollutant such as heavy metals,SO_x and HCl.It has caused serious environment pollution problems and attracted highly concerns of whole society.Petroleum coke has been classified as an inferior and high polluting fuel because it has high content of compounds such as sulfur,nitrogen,vanadium,and heavy metals.The research on the emission characteristics of heavy metal and SO_x and Cl in CFB boilers co-firing petroleum coke and coal has a guiding significance for solving the environmental pollution problems of coal-fired power plants.Three 410 t/h CFB boilers co-firing petroleum coke and coal were selected as research subjects.Ontario Hydro Method?OHM?as well as EPA Method 30B,EPA Method 29,EPA Method 8 and EPA Method 26A were employed in this study to determine the migration and emission characteristics of mercury,other heavy metals,SO_x and Cl in tested boilers,respectively.The removal effects of air pollution control devices on mercury,other heavy metals and SO_x and Cl were also investigated.The result of mercury emission test shows that the mass balance rate of mercury is in the range of 83.9¹22.7%.The total Hg concentration measured by OHM is comparable with that determined by EPA Method 30B.The vast majority of mercury emitted was distributed in the fly ash and stack gas,the proportional values are in the range of 61.36⁶7.71%and22.22³3.35%,respectively.The removal efficiencies of ESP and FF on Hg^p are more than92%.The FF has better Hg⁰ and Hg²⁺removal efficiencies than ESP.Most of water-soluble Hg²⁺can be removed by WFGD,but the emission of Hg⁰ in the WFGD resulted in the comparatively lower mercury removal efficiency by WFGD.The Hg concentration in the stack gas is below the limit value?30?g/m³?specified by GB 13223-2011.The results of As,Cr,Cd,Ba,Mn,Pb and Cu emission test show that the mass balance rates of these heavy metals are in the range of 78.57¹21.08%.The vast majority of As,Cr,Cd,Ba,Mn,Pb and Cu was distributed in the fly ash and bottom ash,the proportional values are in the range of 57.34⁹2.12%and 6.29³5.78%,respectively.Particulate bound heavy metals are the dominant species in the flue gas at the inlet of dedust devices,whose proportional values are more than 96%.The removal efficiencies of heavy metals by dedust devices are more than 98%.The heavy metals can be further removed by WFGD by washing and removing them.The removal efficiencies of heavy metals by WFGD is in the range of 34.54⁷0.07%.Pb,Cu and Ba showed more enrichment in fine particulate matter such as fly ash,while Mn,Cd and Cr showed equal enrichment in bottom ash and fly ash.The result of SO_x emission test shows that the proportional value of SO₃/sulfuric acid mist is in the range of 0.83¹.99%at the outlet of air preheater,which is remarkably low.It is also positively correlated with the oxygen content in the flue gas.ESP and FF have no obvious removal effect on SO₃/sulfuric acid mist.Besides,the removal efficiency of particulate bound sulfur by ESP or FF is more than 95%.Part of SO₃/sulfuric acid mist can be removed by WFGD,the removal efficiency of which is in the range of 62.66⁶7.82%.The vast majority of sulfur in fuel was finally distributed in the bottom ash and fly ash,gypsum and wastewater,the proportional values are in the range of 56.79⁷0.12%and 29.25⁴1.70%,respectively.The result of Cl emission test shows that over 86.1%of total chlorine in the fuel was emitted into the flue gas in gaseous form.The HCl was the dominant species in the flue gas at the outlet of boilers,whose proportional values are in the range of 85.14⁸7.96%.The chlorine synergistic removal rates of dust removal equipment and WFGD were in the range of15.6¹9.68%and 91.2⁹6.1%,respectively.The majority of total Cl was migrated into wastewater and gypsum,accounting for 76.1⁸0.2%and 11.3¹2.8%,respectively.About1.4⁴.3%of total Cl was finally emitted into the atmosphere.The existing air pollution control devices installed in power plants all have a certain degree of removal effect on the air pollutant such as heavy metals,SO_x and HCl.As a result,great emphasize should be put on the reutilization of fly ash and gypsum as well as the discharge of wastewater.