| Chlorine has an important role in promoting the morphological transformation of mercury and improving the efficiency of mercury removal.There are a large number of chloride ions in the desulfurization wastewater of coal-fired power plants.Combining flue gas demercuration and desulfurization wastewater treatment to minimize the emissions of coal-fired power plants has become a research hotspot.This article starts from the actual mercury migration and emission characteristics of power plants,uses tube furnace combustion experiments and fluidized bed combustion experiments to determine the characteristics of mercury emissions after coal combustion and chlorine addition,and uses quantum chemical simulations to explain the process and reaction of mercury-chlorine primitives.mechanism.This article explores the rules of mercury migration and emissions from coal-fired units in actual power plants.The mercury emissions from a power plant unit are mainly gas-phase.The gaseous mercury accounted for 71.2%of the mercury emissions,the fly ash accounted for 22.4%,and the rest was coal-fired.The bottom slag and desulfurized gypsum have a mercury mass balance of 94.3%.After the flue gas passes through a pollutant removal system consisting of denitration(SCR)+electrostatic precipitator(ESP)+wet desulfurization(WFGD)+wet electrostatic precipitator(WESP),most of the mercury in the flue gas is removed.There are a large number of chloride and sulfate ions in the desulfurization wastewater of the power plant.The CODcr value is high and many heavy metals can be detected in the wastewater,but their concentrations are very low.Combined with the actual measured data of the power plant,the tube furnace was used to investigate the mercury emissions from coal after coal combustion and coal chlorination.With the rise of the tube furnace temperature,the precipitation rate of mercury in coal samples gradually increased.When chlorine was added to the coal,the release of mercury in the coal was further promoted.When the temperature reached 1100℃,the precipitation rates of mercury in the three coal types were 86.8%,87.1%and 86.6%,respectively.After adding 0.015%Cl,0.030%Cl,and0.045%Cl to coal,the mercury precipitation rate in coal type A increased to 93.3%,94.7%,and96.5%,and the mercury precipitation rate in coal type B increased to 90%,92%,and 96%.%,The mercury release rate of coal type C increased to 87.1%,90.1%,and 92.8%.The slow-programming and fixed-temperature experiments were conducted to investigate the mercury occurrence forms in various coal types.After coal combustion and chlorine addition,the precipitation of Hg SO4 in coal type A was promoted,and the mercury in the Hg S-occurring state in coal type B was easier to precipitate.For coal type C,the addition of chlorine promoted the precipitation of Hg S and Hg O in the coal.The proportion of zero-valent mercury in the flue gas of raw coal combustion is much larger than that of oxidized mercury,and the addition of chlorine greatly increases the proportion of oxidized mercury in the flue gas.Adding chlorine to coal combustion will also promote the migration of Pb,Zn,Cu and Cr in the bottom slag to the gas phase or fly ash to a certain extent.A fluidized bed coal-fired furnace was built and used in conjunction with denitrification,dedusting,and desulfurization devices to study mercury emissions and migration along the way.The combustion temperature also has a significant effect on the precipitation of mercury in coal.After the coal is added with chlorine,the concentration of nitrogen oxides in the flue gas at the outlet of the burner decreases,and the concentration of sulfur oxides gradually increases.With the increase of the amount of chlorine,the smoke The proportion of oxidized mercury in the gas has also increased.After adding 0.015%Cl,0.030%Cl,and 0.045%Cl at 800°C,the proportion of oxidized mercury in the flue gas increased from 32.54%to 37.79%,40.91%,and 44.26.%.After the flue gas passes through the SCR denitration device,the chlorine-containing substance in the flue gas is combined with the denitration catalyst,and the catalyst shows that a chlorine-containing active site is formed,so that Hg~0 in the flue gas is oxidized to form oxidized mercury.Therefore,after passing through the SCR denitration system,the proportion of oxidized mercury in flue gas has been greatly improved.Most of the particulate mercury is removed after the dust collector,and the oxidized mercury is absorbed by the desulfurization slurry in the desulfurization device.Because the oxidized mercury is water-soluble,the desulfurization system has a high removal efficiency for the oxidized mercury.Mercury emissions from the entire system are dominated by gaseous zero-valent mercury,and the emission concentration is better than the requirements of emission standards.As for the mercury content in the solid product,the mercury content in the cyclone fly ash>the mercury content in the bag fly ash>the mercury content in the bottom slag.Finally,the quantum chemical calculation software was used to explore the reaction mechanism of the five mercury-chlorine elementary reactions,and the energy barriers between the reactants,transition states,and products of each elementary reaction were obtained.Based on this,five elements were identified.The reaction process of the reaction is to calculate the chemical reaction rate of each reaction at 5 temperature points,fit the mathematical expressions of ln K and1000/T,and use the Arrhenius formula to calculate the reaction rate in the temperature range of298K-1500K.Constant expression. |
PDF Full Text Request