In-situ measurement and distribution of flue gas mercury for a utility PC boiler system

The in-situ instrumentation technique for measuring mercury and itsspeciation downstream a utility 100 MW pulverized coal (PC) fired boiler system was developed andconducted by the use of the Ontario hydro method (OHM) consistent with American standard test methodtogether with the semi-continuous emissions monitoring (SCEM) system as well as a mobile laboratoryfor mercury monitoring. The mercury and its speciation concentrations including participate mercuryat three locations of before air preheater, before electrostatic precipitator (ESP) and after ESPwere measured using the OHM and SCEM methods under normal operation conditions of the boiler systemas a result of firing a bituminous coal. The vapor-phase total mercury Hg(VT) concentration declinedwith the decrease of flue gas temperature because of mercury species transformation from oxidizedmercury to particulate mercury as the flue gas moved downstream from the air preheater to the ESPand after the ESP. A good agreement for Hg°, Hg^(2+) and Hg( VT) was obtained between the twomethods in the ash-free area. But in the dense particle-laden flue gas area, there appeared to be abig bias for mercury speciation owing to dust cake formed in the filter of OHM sampling probe. Theparticulateaffinity to the flue gas mercury and the impacts of sampling condition to accuracy ofmeasure were discussed.

Analysis of solid sorbents for control and removal processes for elemental mercury from gas streams:a review

Due to the restriction such as the Minamata Convention as well as the IED of the European Commission,mercury removal from flue gases of coal-fired power plants(CPP)is an increasingly important environmental issue.This makes this topic very crucial for both the energy industry and scientists.This paper shows how mercury arises from natural resources,i.e.,coals,through their combustion processes in CPP and considers the issue of mercury content in flue gases and solid-state coal combustion by-products.The main part of this paper presents a review of the solid sorbents available for elemental mercury control and removal processes,tested on a laboratory scale.The described solutions have a potential for wider usage in exhaust gas treatment processes in the energy production sector.These solutions represent the latest developments in the field of elemental mercury removal from gases.The authors present an overview of the wide range of solid sorbents and their modifications intended to increase affinity for Hg^(0).Among the presented sorbents are the wellknown activated carbon solutions but also novel modifications to these and other innovative sorbent proposals based on,e.g.,zeolites,biochars,other carbon-based materials,metal-organic frameworks.The paper presents a wide range of characteristics of the described sorbents,as well as the conditions for the Hg^(0) removal experiments summarizing the compendium of novel solid sorbent solutions dedicated to the removal of elemental mercury from gases.

Mercury Speciation of Flue Gas Desulphurization By-Products in Coal-Fired Power Plants in China

The aim of this study was to develop and examine the morphology and distribution of mercury (Hg) in flue gas desulfurization (FGD) by-product. Mercury in the coal of coal-fired power plants is concentrated in the by-products of desulfurization process, and it is widely used as an additive in cement, building materials and other industries. Due to the different stability of various forms of mercury in the environment, subsequent use of products containing desulfurization by-product additives will continue to be released into the environment, endangering human health. Therefore, it is very necessary to study the form and distribution of mercury in the by-products of desulfurization in coal-fired power plants to provide a theoretical basis for subsequent harmless treatment. For content and morphology of mercury analysis, 1 sample of dry FGD ash and 6 samples of wet FGD gypsum were analyzed. The total 7 samples were extracted using a modification of sequential chemical extractions (SCE) method, which was employed for the partitioning Hg into four fractions: water soluble, acid soluble, H2O2 soluble, and residual. The Hg analysis was done with United States Environmental Protection Agency (USEPA) method 7471B. Comparing with the wet FGD gypsums of coal-fired boilers, the total Hg content in the dry FGD by-product was as high as 1.22 mg/kg, while the total Hg content in the FGD gypsum is 0.23 - 0.74 mg/kg, which was 2 times over the wet FGD gypsum. The concentration of water soluble Hg in the dry FGD by-product was the highest amount (0.72 mg/kg), accounting for 59.02% of the total mercury. While residual Hg content was 0.16 mg/kg, only about 13.11% of the total mercury. Mercury content in FGD gypsum was expressed in the form of ρ (residual Hg) > ρ (H2O2 soluble Hg) > ρ (water soluble Hg) > ρ (acid soluble Hg). The morphology and distribution of mercury in FGD by-products is supposed to be analyzed before utilization, and the impact of mercury on the environment should be considered.

Study on the removal of Hg^0 from flue gas by coal dry powder gasification coarse slag

The prevention and treatment of mercury in coal-fired power plants has always been the focus and difficulty.How to control the pollution of mercury to human body and ecological environment quickly and effectively is a hot research topic nowadays.As a low cost and potential adsorbent,there is a huge space for the development of coal dry powder gasification coarse slag.In this paper,Mercury osmotic tubes are heated by water bath tank as mercury source,and the scavenging effect of adsorbent on Mercury monomer under different influence conditions is explored.The adsorbent plays an important role in adsorption of mercury monomer because of its special active sites on the surface.The reason is that the adsorbent surface is rich in carboxyl group,hydroxyl functional group,combined with mercury to form complexes.This shows that chemical adsorption facilitates the adsorption process.

A novel carbon trap sampling system for coal-fired flue gas mercury measurement

A novel carbon trap sampling system for gas-phase mercury measurement in flue gas is developed, including the high efficient sorbents made of modified biomass cokes and high precision sorbent traps for measuring particle-bound and total vapor-phase mercury in flue gas. A dedusting device is installed to collect fine fly ash for reducing the measurement errors. The thorough comparison test of mercury concentration in flue gas is conducted between the novel sampling system and the Ontario hydro method （OHM） in a 6 kW circulating fluidized bed combustor. Mercury mass balance rates of the OHM range from 95.47% to 104.72%. The mercury breakthrough rates for the second section of the sorbent trap are all below 2%. The relative deviations in the two test cases are in the range of 15. 96% to 17. 56% under different conditions. The verified data suggest that this novel carbon trap sampling system can meet the standards of quality assurance and quality control required by EPA Method 30B and can be applied to the coal-fired flue gas mercury sampling system.

Distribution and Accumulation of Major and Trace Elements in Gypsum Samples from Lignite Combustion Power Plant

Flue gas containing volatile elements, fine fly ash particulates not retained by particle control devices, and limestone are the most important sources of trace and major elements (TMEs) in wet flue gas desulphurization (WFGD) gypsum. In this study, samples of gypsum slurry were separated into fine and coarse fractions. Multi-elemental analysis of 45 elements in the different size fractions of gypsum, slurry waters and lignite were performed by k0-INAA (k0-instrumental neutron activation analyses). The study found that the volatile elements (Hg, Se and halogens) in the flue gas accumulate in the fine fractions of gypsum. Moreover, the concentrations of most TMEs are considerably higher in the fine fractions compared to the coarse fractions. The exceptions are Ca and Sr that primarily originate from the limestone. Variations of TMEs in the finer fractions are dependent on the presence of CaSO4·2H2O that is the main constituent of the coarse fraction. Consequently, the content of TMEs in the fine fraction is highly dependent on the efficiency of separating the fine fraction from the coarse fraction. Separation of the finer fraction, representing about 10% of the total gypsum, offers the possibility to remove effectively TMEs from WFGD slurry.

Hierarchical Ag-SiO_2@Fe_3O_4magnetic composites for elemental mercury removal from non-ferrous metal smelting flue gas

Hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites were selected for elemental mercury(Hg^0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites had favorable Hg^0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe_3O_4 and SiO_2@Fe_3O_4. The Hg^0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O_2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO_2@Fe_3O_4 support. The large surface area of SiO_2 supplied efficient reaction room for Hg and Ag atoms. Ag–Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.

Mercury transportation in soil via using gypsum from flue gas desulfurization unit in coal-fired power plant

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.

Mercury removal from coal combustion flue gas by modified fly ash

Fly ash is a potential alternative to activated carbon for mercury adsorption. The effects of physicochemical properties on the mercury adsorption performance of three fly ash samples were investigated. X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, and other methods were used to characterize the samples. Results indicate that mercury adsorption on fly ash is primarily physisorption and chemisorption. High specific surface areas and small pore diameters are beneficial to efficient mercury removal. Incompletely burned carbon is also an important factor for the improvement of mercury removal efficiency, in particular. The C-M bond, which is formed by the reaction of C and Ti, Si and other elements, may improve mercury oxidation. The samples modified with CuBr2 , CuCl 2 and FeCl3 showed excellent performance for Hg removal, because the chlorine in metal chlorides acts as an oxidant that promotes the conversion of elemental mercury （Hg0） into its oxidized form （Hg2＋）. Cu2＋ and Fe3＋ can also promote Hg 0 oxidation as catalysts. HCl and O2 promote the adsorption of Hg by modified fly ash, whereas SO2 inhibits the Hg adsorption because of competitive adsorption for active sites. Fly ash samples modified with CuBr2 , CuCl2 and FeCl3 are therefore promising materials for controlling mercury emissions.

An Experimental Study on Oxidized Mercury Adsorption by Bromide Blended Coal Combustion Fly Ash

The application of forced mercury oxidation technology would lead to an increase of Hg^(2+)concentration in the flue gas.Although Hg^(2+)can be easily removed in the WFGD,the mercury re-emission in the WFGD can decrease the total removal of mercury from coal-fired power plants.Hence,it is necessary to control Hg^(2+)concentration in the devices before the WFGD.Fly ash adsorbent is considered as a potential alternative for commercial activated carbon adsorbent.However,the adsorption efficiency of the original fly ash is low.Modification procedure is needed to enhance the adsorption performance.In this study,the adsorption of Hg^(2+)by brominated fly ash was studied.The fly ash was collected from the full-scale power plant utilizing bromide-blended coal combustion technology.The brominated fly ash exhibited excellent performance for Hg^(2+)removal.The flue gas component HBr and SO_(2)could improve adsorbent’s performance,while HCl would hinder its adsorption process.Also,it was demonstrated by Hg-TPD experiments that the adsorbed Hg^(2+)mainly existed on the fly ash surface in the form of HgBr_(2).In summary,the brominated fly ash has a broad application prospect for mercury control.

Mechanism Research of Hg^0 Oxidation by Pulse Corona Induced Plasma Chemical Process

The oxidation of Hg^0 by Pulse Corona Induced Plasma Chemical Process （PPCP） was investigated through changing discharge voltage, pulse frequency and gas compositions. Experimental results indicate that active radicals including O, O3 and OH can contribute to the oxidation of elemental mercury. 10 kV is the onset voltage, and the higher voltage the better removal efficiency. While with the increase of pulse frequency, the Hg^0 concentration falls rapidly at first but then rises rapidly. The best oxidation condition is at 12 kV and 600-800 PPS. Adding O2 can significantly promote oxidation. With NO and SO2 existed, there is an inhibition of mercury oxidation, and NO has a greater influence. Addition of HCl can promote oxidation slightly but affect the initial concentration of mercury significantly. Little moisture content can promote oxidation, while too much H2O can not only resist the oxidation, but also affect the initial concentration of mercury. The mercury oxidation rate can increase to 97.95% at 12 kV/800 PPS with the system of 10% 02/3% H2O/50 ppm HCI. However, mercury oxidation efficiency can reduce down to 20% with 100 ppm NO added.

Hg^0 removal from flue gas over different zeolites modified by Fe Cl_3

The elemental mercury removal abilities of three different zeolites（Na A, Na X, HZSM-5）impregnated with iron（Ⅲ） chloride were studied on a lab-scale fixed-bed reactor. X-ray diffraction, nitrogen adsorption porosimetry, Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy, and temperature programmed desorption（TPD） analyses were used to investigate the physicochemical properties. Results indicated that the pore structure and active chloride species on the surface of the samples are the key factors for physisorption and oxidation of Hg0, respectively. Relatively high surface area and micropore volume are beneficial to efficient mercury adsorption. The active Cl species generated on the surface of the samples were effective oxidants able to convert elemental mercury（Hg0）into oxidized mercury（Hg2＋）. The crystallization of Na Cl due to the ion exchange effect during the impregnation of Na A and Na X reduced the number of active Cl species on the surface, and restricted the physisorption of Hg0. Therefore, the Hg0 removal efficiencies of the samples were inhibited. The TPD analysis revealed that the species of mercury on the surface of Fe Cl3–HZSM-5 was mainly in the form of mercuric chloride（Hg Cl2）, while on Fe Cl3–Na X and Fe Cl3–Na A it was mainly mercuric oxide（HgO）.

有色金属冶炼烟气中单质汞脱除研究现状

由于汞具有剧毒性、易挥发性和长距离迁移性等特点,汞污染已经成为全球性的环境问题。目前,有色金属冶炼行业是我国大气汞排放的主要来源之一,占总排放量的30%左右。面对汞污染的压力,如何实现有色金属冶炼烟气中汞的高效脱除已经成为研究热点。针对有色冶炼烟气中汞排放的特征,阐述了烟气中汞形态转化和分布规律,综述了冶炼行业汞污染治理的研究现状,主要介绍冷凝法、吸附法、催化氧化法和液相吸收法等,对各种方法进行详细的描述,并对现有有色金属冶炼行业汞污染防治技术现状进行了总结和建议。

Mercury emissions and partitioning from Indian coal-fired power plants

In India coal combustion is the single largest source of emission of mercury which is a widespread persistent global toxicant,travelling across international borders through air and water.As a party to the Minamata convention,India aims to monitor and reduce Hg emissions and stricter norms are introduced for mercury emissions from power plants(30μg/Nm 3 for flue gas in stack).This paper presents the results obtained during the experimental studies performed on mercury emissions at four coal-fired and one lignite-fired power plants in India.The mercury concentration in the feed coal varied between 0.12-0.27 mg/Kg.In the mercury mass balance,significant proportion of feed coal mercury has been found to be associated with fly ash,whereas bottom ash contained very low mercury.80%-90%of mercury was released to air through stack gas.However,for circulating fluidised bed boiler burning lignite,about 64.8%of feed mercury was found to get captured in the fly ash and only 32.4%was released to air.The mercury emission factor was found to lie in the range of 4.7-15.7 mg/GJ.

Absorption characteristics of elemental mercury in mercury chloride solutions

Elemental mercury （Hg^0） in flue gases can be efficiently captured by mercury chloride （HgCl2） solution. However, the absorption behaviors and the influencing effects are still poorly understood. The mechanism of Hg^0 absorption by HgCl2 and the factors that control the removal were studied in this paper. It was found that when the mole ratio of Cl^- to HgCl2 is 10：1, the Hg^0 removal efficiency is the highest. Among the main mercury chloride species, HgCl3^- is the most efficient ion for Hg^0 removal in the HgCl2 absorption system when moderate concentrations of chloride ions exist. The Hg^0 absorption reactions in the aqueous phase were investigated computationaIIy using Moller-Plesset perturbation theory. The calculated Gibbs free energies and energy barriers are in excellent agreement with the results obtained from experiments. In the presence of SO3^2- and SO2, Hg^2＋ reduction occurred and Hg^0 removal efficiency decreased. The reduced Hg^0 removal can be controlled through increased chloride concentration to some degree. Low pH value in HgCla solution enhanced the Hg^0 removal efficiency, and the effect was more significant in dilute HgCl2 solutions. The presence of SO4^2- and NO3^- did not affect Hg^0 removal by HgCl2.

Removal of elemental mercury with Mn/Mo/Ru/Al2O3 membrane catalytic system

In this work, a catalytic membrane using Mn/ Mo/Ru/A12O3 as the catalyst was employed to remove elemental mercury （Hg^0） from flue gas at low temperature. Compared with traditional catalytic oxidation （TCO） mode, Mn/A12O3 membrane catalytic system had much higher removal efficiency of Hg^0. After the incorporation of Mo and Ru, the production of C12 from the Deacon reaction and the retainability for oxidants over Mn/A12O3 membrane were greatly enhanced. As a result, the oxidization of Hg^0 over Mn/A12O3 membrane was obviously promoted due to incorporation of Mo and Ru. In the presence of 8 ppmv HC1, the removal efficiency of Hg^0 by Mn/Mo/Ru/A12O3 membrane reached 95% at 423 K. The influence of NO and SO2 on Hg^0 removal were insignificant even if 200 ppmv NO and 1000 ppmv SO2 were used. Moreover, compared with the TCO mode, the Mn/Mo/Ru/A12O3 membrane catalytic system could remarkably reduce the demanded amount of oxidants for Hg^0 removal. Therefore, the Mn/Mo/Ru/A12O3 membrane catalytic system may be a promising technology for the control of Hg~ emission.

Role of NO and SO_(2)in mercury oxidation over a La_(2)O_(3)/Fe_(2)O_(3)catalyst with high thermal stability

In this study,the thermal stability of a ferric oxide catalyst for mercury oxidation was found to be considerably promoted by doping with La_(2)O_(3).The catalysts doped with La_(2)O_(3)maintained a higher surface area when subjected to high-temperature calcination,with lower average pore size and a narrower pore size distribution.X-ray diffraction(XRD)results revealed that La_(2)O_(3)doping hinders the growth of catalyst particles and crystallization of the material at high temperatures.Both NO and SO_(2)inhibited Hg^(0)oxidation over the La_(2)O_(3)/Fe_(2)O_(3)catalyst.Fourier transform infrared(FTIR)spectra revealed that SO_(2)reacts with O_(2)over the catalysts to form several species that are inert for mercury oxidation,such as S042^(-),HS04^(-),or other related species;these inert species cover the catalyst surface and consequently decrease Hg^(0)oxidation capacity.In addition,NO or SO_(2)competed with Hg^(0)for active sites on the La_(2)O_(3)/Fe_(2)O_(3)catalyst and hindered the adsorption of mercury,thereby inhibiting subsequent Hg^(0)oxidation.Hg^(0)oxidation on the La_(2)O_(3)/Fe_(2)O_(3)catalyst mainly followed the Eley-Rideal mechanism.Moreover,the inhibition effects of NO and SO_(2)were at least partially reversible,and the catalytic activity was temporarily restored after eliminating NO or S0_(2).

Metal chlorides loaded on activated carbon to capture elemental mercury

Activated carbon （AC） was considered to be an effective sorbent to control mercury in combustion systems. However, its capture capacity was low and it required a high carbon-to-mercury mass ratio. AC loaded with catalyst showed a high elemental mercury （Hg 0 ） capture capacity due to large surface area of AC and high oxidization ability of catalyst. In this study, several metal chlorides and metal oxides were used to promote the sorption capacity of AC. As a result, metal chlorides were better than metal oxides loaded on AC to remove gaseous mercury. X-ray diffractometer （XRD）, thermogravimetric analyzer （TGA） and specific surface area by Brunauer- Emmett-Teller method （BET） analysis showed the main mechanisms： first, AC had an enormous surface area for loading enough MClx; second, Cl and MxOy were generated during pyrogenation of MClx; finally, there were lots of active elements such as Cl and MxOy which could react with elemental mercury and convert it to mercury oxide and mercury chloride. The HgO and HgCl 2 might be released from AC’s porous structure by thermo regeneration. A catalytic chemisorption mechanism predominates the sorption process of elemental mercury. As Co and Mn were valence variable metal elements, their catalytic effect on Hg 0 oxidization may accelerate both oxidation and halogenation of Hg 0 . The sorbents loaded with metal chlorides possessed a synergistic function of catalytic effect of valence variable metal and chlorine oxidation.

Mercury removal performance over a Ce-doped V-W/TiO_(2) catalyst in an internally illuminated honeycomb photoreactor

A new type of internally illuminated honeycomb photoreactor was designed. The honeycomb catalyst prepared by using Cedoped TiO2 with 1%–2% vanadium and tungsten was employed for mercury removal from simulated industrial flue gas. The adsorption kinetics in the reaction process were studied. The results showed that the internally illuminated honeycomb photoreactor had good mercury removal performance. When the temperature was 25℃ and the ultraviolet(UV) light intensity reached 80 μW/cm2, the mercury removal efficiency reached 92.5%. The mercury removal efficiency increased significantly with the doping ratio of Ce. XPS analysis showed that the oxidation state of Ce changed from 4 to 3 in the mercury removal reaction and produced lattice oxygen, which acts as an oxidant. O2 can promote mercury removal by honeycomb catalysts;SO2 and HCl also had positive effects, while NO had an inhibitory effect on mercury removal. Kinetic research in the reaction process showed that the quasi-first-order dynamic model had good fitting results, and the correlation coefficients of the fitting results for multiple sets of experimental data were more than 0.999.