Air pollution control devices(APCDs) are installed at coal-fired power plants for air pollutant regulation.Selective catalytic reduction(SCR) and wet flue gas desulfurization(FGD) systems have the co-benefits of air p...Air pollution control devices(APCDs) are installed at coal-fired power plants for air pollutant regulation.Selective catalytic reduction(SCR) and wet flue gas desulfurization(FGD) systems have the co-benefits of air pollutant and mercury removal.Configuration and operational conditions of APCDs and mercury speciation affect mercury removal efficiently at coal-fired utilities.The Ontario Hydro Method(OHM) recommended by the U.S.Environmental Protection Agency(EPA) was used to determine mercury speciation simultaneously at five sampling locations through SCR-ESP-FGD at a 190 MW unit.Chlorine in coal had been suggested as a factor affecting the mercury speciation in flue gas;and low-chlorine coal was purported to produce less oxidized mercury(Hg2+) and more elemental mercury(Hg0 ) at the SCR inlet compared to higher chlorine coal.SCR could oxidize elemental mercury into oxidized mercury when SCR was in service,and oxidation efficiency reached 71.0%.Therefore,oxidized mercury removal efficiency was enhanced through a wet FGD system.In the non-ozone season,about 89.5%-96.8% of oxidized mercury was controlled,but only 54.9%-68.8% of the total mercury was captured through wet FGD.Oxidized mercury removal efficiency was 95.9%-98.0%,and there was a big difference in the total mercury removal efficiencies from 78.0% to 90.2% in the ozone season.Mercury mass balance was evaluated to validate reliability of OHM testing data,and the ratio of mercury input in the coal to mercury output at the stack was from 0.84 to 1.08.展开更多
The Ontario Hydro Method (OHM) recommended by the United States EnvironmentalProtection Agency (EPA) was used to determine mercury speciation in the combustionflue gas across wet FGD systems.Four coal-fired units with...The Ontario Hydro Method (OHM) recommended by the United States EnvironmentalProtection Agency (EPA) was used to determine mercury speciation in the combustionflue gas across wet FGD systems.Four coal-fired units with wet FGD systemswere chosen to evaluate mercury speciation and mercury removal efficiencies throughthese wet FGD systems.Chlorine content in coal had been suggested as a main factorthat affects mercury speciation in flue gas.It is shown that the higher the chlorine concentrationin coal is, the higher the percentage of oxidized mercury (Hg^(2+)) is removed in wetFGD systems, which can increase overall mercury removal efficiencies through wet FGDsystems.The selective catalyst reduction (SCR) system has a function of oxidizing elementalmercury (Hg^0) to oxidized mercury.A higher percentage of oxidized mercury in thetotal vapor mercury at the FGD inlet is observed when SCR is in service.Therefore, higheroverall mercury removal efficiencies through wet FGD are attained.Because of differentwet FGD operating conditions, there are different mercury removal efficiencies in differentunits.Elemental mercury reemission took place when a fraction of oxidized mercury absorbedin the slurry is reduced to elemental mercury, and Hg^0 is reemitted from stack,which results in decreases in mercury removal efficiencies through wet FGD systems.展开更多
Elemental mercury(Hg0)re-emissions from slurries and solutions were evaluated in a lab-scale simulated scrubber.Oxidized mercury(Hg2 +)standard solution was injected into the simulated scrubber at a desired rate to si...Elemental mercury(Hg0)re-emissions from slurries and solutions were evaluated in a lab-scale simulated scrubber.Oxidized mercury(Hg2 +)standard solution was injected into the simulated scrubber at a desired rate to simulate absorbing and dissolving of Hg2 +in the flue gas across wet flue gas desulfurization(WFGD)systems. PS analytical mercury analyzer was used to continuously determine Hg0re-emission concentrations in the carrier gas from the scrubber.Sulfite ion in the slurry of CaSO3 was validated to reduce Hg 2+to Hg 0,while no Hg 0 re-emission occurred from slurries of CaSO4 and CaO.Transitional metal ions with low chemical valence such as Fe2 +,Pb 2+,Ni 2+, 2 AsO-and Cu +were used to prepare solutions with concentration levels of mmol·L-1.Reduction reaction of Hg2 +to Hg 0was observed from these solutions.Reduction capabilities for the different transitional metal ions in the solutions were:Pb2 +>Cu +>Fe 2+> 2 AsO->Ni 2+.展开更多
Coke powder is expected to be an excellent raw material to produce activated carbon because of its high carbon content. Potassium hydroxide(KOH), as an effective activation agent, was reported to be effective in activ...Coke powder is expected to be an excellent raw material to produce activated carbon because of its high carbon content. Potassium hydroxide(KOH), as an effective activation agent, was reported to be effective in activating coke powder. However, the microstructures development in the coke powder and its mechanisms when KOH was applied were still unclear. In this study, effects of KOH on the microstructure activation of coke powder were investigated using the surface area and pore structure analyzer, scanning electron microscope(SEM) and thermogravimetry-differential scanning calorimetry-mass spectrometry(TG-DSC-MS), etc. Results revealed that the addition KOH at its lower ratio(mass ratios of KOH and coke powder in a range of 0.5 and 1) decreased the specific surface area and average lateral sizes, but sharply increased of the specific surface area to 132 m^2·g^-1 and 355 m^2·g^-1 and decreased of the space size of aromatic crystallites upon the further increase of the KOH addition amounts(ratios of KOH and coke powder in a range of 3 and 7), generating a number of new micropores and mesopores. The mechanisms study implied surface reactions between KOH and aliphatic hydrocarbon side chain and other carbon functional groups of the coke powder to destruct aromatic crystallites in one dimension and broaden pores at lower KOH addition. In the activation process, KOH was decomposed to be more active components, which can be rapidly destruct the aromatic layers in spatial scope to form developed porous carbon structures within coke powder at higher KOH addition.展开更多
In this study, the mercury adsorption characteristics of HBr-modified fly ash in an entrained-flow reactor were investigated through thermal decomposition methods. The results show that the mercury adsorption performa...In this study, the mercury adsorption characteristics of HBr-modified fly ash in an entrained-flow reactor were investigated through thermal decomposition methods. The results show that the mercury adsorption performance of the HBr-modified fly ash was enhanced significantly. The mercury species adsorbed by unmodified fly ash were Hg Cl2,Hg S and Hg O. The mercury adsorbed by HBr-modified fly ash, in the entrained-flow reactor,existed in two forms, Hg Br2 and Hg O, and the HBr was the dominant factor promoting oxidation of elemental mercury in the entrained-flow reactor. In the current study, the concentration of Hg Br2 and Hg O in ash from the fine ash vessel was 4.6 times greater than for ash from the coarse ash vessel. The fine ash had better mercury adsorption performance than coarse ash, which is most likely due to the higher specific surface area and longer residence time.展开更多
The mercury flux in soils was investigated, which were amended by gypsums from flue gas desulphurization (FGD) units of coal- fired power plants. Studies have been carried out in confined greenhouses using FGD gypsum ...The mercury flux in soils was investigated, which were amended by gypsums from flue gas desulphurization (FGD) units of coal- fired power plants. Studies have been carried out in confined greenhouses using FGD gypsum treated soils. Major research focus is uptakes of mercury by plants, and emission of mercury into the atmosphere under varying application rates of FGD gypsum, simulating rainfall irrigations, soils, and plants types. Higher FGD gypsum application rates generally led to higher mercury concentrations in the soils, the increased mercury emissions into the atmosphere, and the increased mercury contents in plants (especially in roots and leaves). Soil properties and plant species can play important roles in mercury transports. Some plants, such as tall fescue, were able to prevent mercury from atmospheric emission and infiltration in the soil. Mercury concentration in the stem of plants was found to be increased and then leveled off upon increasing FGD gypsum application. However, mercury in roots and leaves was generally increased upon increasing FGD gypsum application rates. Some mercury was likely absorbed by leaves of plants from emitted mercury in the atmosphere.展开更多
Flue gas from coal combustion contains significant amounts of volatile selenium(Se).The capture of Se in the flue gas desulfurization(FGD) scrubber unit has resulted in a generation of metal-laden residues.It is impor...Flue gas from coal combustion contains significant amounts of volatile selenium(Se).The capture of Se in the flue gas desulfurization(FGD) scrubber unit has resulted in a generation of metal-laden residues.It is important to determine Se speciation to understand the environmental impact of its disposal.A simple method has been developed for selective inorganic Se(IV),Se(VI) and organic Se determination in the liquid-phase FGD residues by hydride generation atomic fluorescence spectrometry(AFS).It has been determined that Se(IV),Se(VI) and organic Se can be accurately determined with detection limits(DL) of 0.05,0.06 and 0.06 μg/L,respectively.The accuracy of the proposed method was evaluated by analyzing the certified reference material,NIST CRM 1632c,and also by analyzing spiked tap-water samples.Analysis indicates that the concentration of Se is high in FGD liquid residues and primarily exists in a reduced state as selenite(Se(IV)).The toxicity of Se(IV) is the strongest of all Se species.Flue gas desulfurization residues pose a serious environmental risk.展开更多
基金Project supported by the National Basic Research Program (973) of China (No. 2006CB2003)the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Personnel Ministry.
基金supported by the U.S.Agency for International Development (USAID) cooperation agreement(No.486-A-00-06-000140-00)
文摘Air pollution control devices(APCDs) are installed at coal-fired power plants for air pollutant regulation.Selective catalytic reduction(SCR) and wet flue gas desulfurization(FGD) systems have the co-benefits of air pollutant and mercury removal.Configuration and operational conditions of APCDs and mercury speciation affect mercury removal efficiently at coal-fired utilities.The Ontario Hydro Method(OHM) recommended by the U.S.Environmental Protection Agency(EPA) was used to determine mercury speciation simultaneously at five sampling locations through SCR-ESP-FGD at a 190 MW unit.Chlorine in coal had been suggested as a factor affecting the mercury speciation in flue gas;and low-chlorine coal was purported to produce less oxidized mercury(Hg2+) and more elemental mercury(Hg0 ) at the SCR inlet compared to higher chlorine coal.SCR could oxidize elemental mercury into oxidized mercury when SCR was in service,and oxidation efficiency reached 71.0%.Therefore,oxidized mercury removal efficiency was enhanced through a wet FGD system.In the non-ozone season,about 89.5%-96.8% of oxidized mercury was controlled,but only 54.9%-68.8% of the total mercury was captured through wet FGD.Oxidized mercury removal efficiency was 95.9%-98.0%,and there was a big difference in the total mercury removal efficiencies from 78.0% to 90.2% in the ozone season.Mercury mass balance was evaluated to validate reliability of OHM testing data,and the ratio of mercury input in the coal to mercury output at the stack was from 0.84 to 1.08.
文摘The Ontario Hydro Method (OHM) recommended by the United States EnvironmentalProtection Agency (EPA) was used to determine mercury speciation in the combustionflue gas across wet FGD systems.Four coal-fired units with wet FGD systemswere chosen to evaluate mercury speciation and mercury removal efficiencies throughthese wet FGD systems.Chlorine content in coal had been suggested as a main factorthat affects mercury speciation in flue gas.It is shown that the higher the chlorine concentrationin coal is, the higher the percentage of oxidized mercury (Hg^(2+)) is removed in wetFGD systems, which can increase overall mercury removal efficiencies through wet FGDsystems.The selective catalyst reduction (SCR) system has a function of oxidizing elementalmercury (Hg^0) to oxidized mercury.A higher percentage of oxidized mercury in thetotal vapor mercury at the FGD inlet is observed when SCR is in service.Therefore, higheroverall mercury removal efficiencies through wet FGD are attained.Because of differentwet FGD operating conditions, there are different mercury removal efficiencies in differentunits.Elemental mercury reemission took place when a fraction of oxidized mercury absorbedin the slurry is reduced to elemental mercury, and Hg^0 is reemitted from stack,which results in decreases in mercury removal efficiencies through wet FGD systems.
基金Supported by the US Agency for International Development(USAID)cooperation agreement(486-A-00-06-000140-00)
文摘Elemental mercury(Hg0)re-emissions from slurries and solutions were evaluated in a lab-scale simulated scrubber.Oxidized mercury(Hg2 +)standard solution was injected into the simulated scrubber at a desired rate to simulate absorbing and dissolving of Hg2 +in the flue gas across wet flue gas desulfurization(WFGD)systems. PS analytical mercury analyzer was used to continuously determine Hg0re-emission concentrations in the carrier gas from the scrubber.Sulfite ion in the slurry of CaSO3 was validated to reduce Hg 2+to Hg 0,while no Hg 0 re-emission occurred from slurries of CaSO4 and CaO.Transitional metal ions with low chemical valence such as Fe2 +,Pb 2+,Ni 2+, 2 AsO-and Cu +were used to prepare solutions with concentration levels of mmol·L-1.Reduction reaction of Hg2 +to Hg 0was observed from these solutions.Reduction capabilities for the different transitional metal ions in the solutions were:Pb2 +>Cu +>Fe 2+> 2 AsO->Ni 2+.
基金Supported by the National Key R&D Plan(2016YFE0131100,2017YFB0603101)the Program for Sanjin Scholars of Shanxi Provincethe Talent Training Program of Shanxi Joint Postgraduate Training Base(2016JD07).
文摘Coke powder is expected to be an excellent raw material to produce activated carbon because of its high carbon content. Potassium hydroxide(KOH), as an effective activation agent, was reported to be effective in activating coke powder. However, the microstructures development in the coke powder and its mechanisms when KOH was applied were still unclear. In this study, effects of KOH on the microstructure activation of coke powder were investigated using the surface area and pore structure analyzer, scanning electron microscope(SEM) and thermogravimetry-differential scanning calorimetry-mass spectrometry(TG-DSC-MS), etc. Results revealed that the addition KOH at its lower ratio(mass ratios of KOH and coke powder in a range of 0.5 and 1) decreased the specific surface area and average lateral sizes, but sharply increased of the specific surface area to 132 m^2·g^-1 and 355 m^2·g^-1 and decreased of the space size of aromatic crystallites upon the further increase of the KOH addition amounts(ratios of KOH and coke powder in a range of 3 and 7), generating a number of new micropores and mesopores. The mechanisms study implied surface reactions between KOH and aliphatic hydrocarbon side chain and other carbon functional groups of the coke powder to destruct aromatic crystallites in one dimension and broaden pores at lower KOH addition. In the activation process, KOH was decomposed to be more active components, which can be rapidly destruct the aromatic layers in spatial scope to form developed porous carbon structures within coke powder at higher KOH addition.
基金Financial support from the National High Technology Research and Development Program of China (No. 2013AA065404)Program of Introducing Talents of Discipline to Universities of China (111 Project, B12034)Fundamental Research Funds for the Central Universities (13ZD04) is gratefully acknowledged
文摘In this study, the mercury adsorption characteristics of HBr-modified fly ash in an entrained-flow reactor were investigated through thermal decomposition methods. The results show that the mercury adsorption performance of the HBr-modified fly ash was enhanced significantly. The mercury species adsorbed by unmodified fly ash were Hg Cl2,Hg S and Hg O. The mercury adsorbed by HBr-modified fly ash, in the entrained-flow reactor,existed in two forms, Hg Br2 and Hg O, and the HBr was the dominant factor promoting oxidation of elemental mercury in the entrained-flow reactor. In the current study, the concentration of Hg Br2 and Hg O in ash from the fine ash vessel was 4.6 times greater than for ash from the coarse ash vessel. The fine ash had better mercury adsorption performance than coarse ash, which is most likely due to the higher specific surface area and longer residence time.
基金Financial support for this project was provided by the U.S.Department of Agriculture (No. 6445-12630-003-00D)
文摘The mercury flux in soils was investigated, which were amended by gypsums from flue gas desulphurization (FGD) units of coal- fired power plants. Studies have been carried out in confined greenhouses using FGD gypsum treated soils. Major research focus is uptakes of mercury by plants, and emission of mercury into the atmosphere under varying application rates of FGD gypsum, simulating rainfall irrigations, soils, and plants types. Higher FGD gypsum application rates generally led to higher mercury concentrations in the soils, the increased mercury emissions into the atmosphere, and the increased mercury contents in plants (especially in roots and leaves). Soil properties and plant species can play important roles in mercury transports. Some plants, such as tall fescue, were able to prevent mercury from atmospheric emission and infiltration in the soil. Mercury concentration in the stem of plants was found to be increased and then leveled off upon increasing FGD gypsum application. However, mercury in roots and leaves was generally increased upon increasing FGD gypsum application rates. Some mercury was likely absorbed by leaves of plants from emitted mercury in the atmosphere.
基金supported by the National Natural Science Foundation of China (No.90410018)the Shanxi Nature Science Foundation (No.20051017)+1 种基金the Shanxi Returned Scholar Research Project (No.2005-21)the Programfor Changjiang Scholars and Innovative Research Team at University in MOE,China (No.IRT0517)
文摘Flue gas from coal combustion contains significant amounts of volatile selenium(Se).The capture of Se in the flue gas desulfurization(FGD) scrubber unit has resulted in a generation of metal-laden residues.It is important to determine Se speciation to understand the environmental impact of its disposal.A simple method has been developed for selective inorganic Se(IV),Se(VI) and organic Se determination in the liquid-phase FGD residues by hydride generation atomic fluorescence spectrometry(AFS).It has been determined that Se(IV),Se(VI) and organic Se can be accurately determined with detection limits(DL) of 0.05,0.06 and 0.06 μg/L,respectively.The accuracy of the proposed method was evaluated by analyzing the certified reference material,NIST CRM 1632c,and also by analyzing spiked tap-water samples.Analysis indicates that the concentration of Se is high in FGD liquid residues and primarily exists in a reduced state as selenite(Se(IV)).The toxicity of Se(IV) is the strongest of all Se species.Flue gas desulfurization residues pose a serious environmental risk.
