Gaseous Hg0 Research Articles

Investigation on synergistic oxidation behavior of NO and Hg0 during the newly designed fast SCR process

In the present study, elemental mercury (Hg0) oxidation behavior in the NO oxidation step of fast SCR process was investigated. The Mn doped CeO2-ZrO2 (CZM0.3) was selected as the catalyst, due to its superior oxygen storage capacity. The results showed that NO could be oxidized efficiently over the catalyst at around 250 °C under the atmosphere of NO/O2/N2. In the Hg0/NO/O2/N2 reaction system, NO oxidation reaction remarkably improved Hg0 oxidation efficiency. Two domination reaction pathways were proposed to interpret the influence of NO oxidation reaction on Hg0 oxidation: one through a heterogeneous oxidation process, and the other through a homogeneous reaction. In the heterogeneous oxidation process, NO was adsorbed on the active sites and activated by the surface oxygen to form more active intermediates for Hg0 oxidation. Hg0 was probably oxidized in its gaseous state, since the affinity between NO and the catalyst was stronger than that between Hg0 and the catalyst. The other reaction pathway was a homogeneous route, during which the gaseous NO2 generated by NO oxidation could oxidize the gaseous Hg0 within the designed reaction conditions. According to the present research, synergistic oxidation of NO and Hg0 in the first step of fast SCR appears to be a promising way to remove Hg0 and NOx in coal-fired power plants.

Constructing interfacial contact for enhanced photocatalytic activity through BiOIO3/g-C3N4 nanoflake heterostructure

The highly efficient BiOIO3/g-C3N4 with unique nanoflake heterostructures were synthesized through hydrothermal method by simply depositing BiOIO3 flake on the surface of g-C3N4. Photocatalytic ability of nanoflakes was tested by oxidation of gaseous Hg0 under 18 W and 24 W LED light irradiation. The g-C3N4/BiOIO3 composite with the molar ratio of 10:1 exhibited that the Hg0 removal efficiency reached up to 93.7%. The remarkable photocatalytic performance of the as-prepared catalysts can be attributed to the interfacial contact heterostructure formed between BiOIO3 and g-C3N4, which constructs an intimate interfacial interaction between the two components. Moreover, well-matched band structure can efficiently lead to the separation of photogenerated charges.

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environmental Hg data were previously lacking; integration of these data into global and regional models is continually improving estimates of global Hg cycling. New analytical techniques, such as Hg stable isotope characterization, provide novel constraints of sources and transformation processes. The major global Hg reservoirs that are, and continue to be, affected by anthropogenic activities include the atmosphere (4.4–5.3 Gt), terrestrial environments (particularly soils: 250–1000 Gg), and aquatic ecosystems (e.g., oceans: 270–450 Gg). Declines in anthropogenic Hg emissions between 1990 and 2010 have led to declines in atmospheric Hg0 concentrations and HgII wet deposition in Europe and the US (− 1.5 to − 2.2% per year). Smaller atmospheric Hg0 declines (− 0.2% per year) have been reported in high northern latitudes, but not in the southern hemisphere, while increasing atmospheric Hg loads are still reported in East Asia. New observations and updated models now suggest high concentrations of oxidized HgII in the tropical and subtropical free troposphere where deep convection can scavenge these HgII reservoirs. As a result, up to 50% of total global wet HgII deposition has been predicted to occur to tropical oceans. Ocean Hg0 evasion is a large source of present-day atmospheric Hg (approximately 2900 Mg/year; range 1900–4200 Mg/year). Enhanced seawater Hg0 levels suggest enhanced Hg0 ocean evasion in the intertropical convergence zone, which may be linked to high HgII deposition. Estimates of gaseous Hg0 emissions to the atmosphere over land, long considered a critical Hg source, have been revised downward, and most terrestrial environments now are considered net sinks of atmospheric Hg due to substantial Hg uptake by plants. Litterfall deposition by plants is now estimated at 1020–1230 Mg/year globally. Stable isotope analysis and direct flux measurements provide evidence that in many ecosystems Hg0 deposition via plant inputs dominates, accounting for 57–94% of Hg in soils. Of global aquatic Hg releases, around 50% are estimated to occur in China and India, where Hg drains into the West Pacific and North Indian Oceans. A first inventory of global freshwater Hg suggests that inland freshwater Hg releases may be dominated by artisanal and small-scale gold mining (ASGM; approximately 880 Mg/year), industrial and wastewater releases (220 Mg/year), and terrestrial mobilization (170–300 Mg/year). For pelagic ocean regions, the dominant source of Hg is atmospheric deposition; an exception is the Arctic Ocean, where riverine and coastal erosion is likely the dominant source. Ocean water Hg concentrations in the North Atlantic appear to have declined during the last several decades but have increased since the mid-1980s in the Pacific due to enhanced atmospheric deposition from the Asian continent. Finally, we provide examples of ongoing and anticipated changes in Hg cycling due to emission, climate, and land use changes. It is anticipated that future emissions changes will be strongly dependent on ASGM, as well as energy use scenarios and technology requirements implemented under the Minamata Convention. We predict that land use and climate change impacts on Hg cycling will be large and inherently linked to changes in ecosystem function and global atmospheric and ocean circulations. Our ability to predict multiple and simultaneous changes in future Hg global cycling and human exposure is rapidly developing but requires further enhancement.

H2S-Modified Natural Ilmenite: A Recyclable Magnetic Sorbent for Recovering Gaseous Elemental Mercury from Flue Gas

H2S-modified natural ilmenite (i.e., ilmenite-C-S) was developed as a recyclable magnetic sorbent to recover Hg0 in the flue gas as a cobenefit of the wet electrostatic precipitators (WESPs). Ilmenite-C-S showed an excellent Hg0 capture performance at 40–100 °C, and the chemical adsorption of Hg0 on ilmenite-C-S was hardly inhibited by H2O and SO2. The chemical adsorption of Hg0 on ilmenite-C-S mainly followed the Mars–Maessen mechanism (i.e., gaseous Hg0 was first adsorbed, and it was then oxidized to HgS by S22– on ilmenite-C-S). As the formed Hg species was HgS, the leaching of Hg species during the wet dust collection of the WESP was negligible. Ilmenite-C-S after the five cycles of Hg0 capture, Hg0 recovery, and sorbent regeneration still had an excellent superparamagnetism with a saturation magnetization of 14.1 emu g–1 and a superior performance for Hg0 capture with Hg0 removal efficiency of approximately 100%. Meanwhile, the ultralow concentration of Hg0 in the flue gas was recovered as a high con...

Transport and transformation of mercury during wet flue gas cleaning process of nonferrous metal smelting.

Reducing mercury emission is hot topic for international society. The first step for controlling mercury in fuel gas is to investigate mercury distribution and during the flue gas treatment process. The mercury transport and transformation in wet flue gas cleaning process of nonferrous smelting industry was studied in the paper with critical important parameters, such as the solution temperature, Hg0 concentration, SO2 concentration, and Hg2+ concentration at the laboratory scale. The mass ratio of the mercury distribution in the solution, flue gas, sludge, and acid fog from the simulated flue gas containing Hg2+ and Hg0 was 49.12~65.54, 18.34~35.42, 11.89~14.47, and 1.74~3.54%, respectively. The primary mercury species in the flue gas and acid fog were gaseous Hg0 and dissolved Hg2+. The mercury species in the cleaning solution were dissolved Hg2+ and colloidal mercury, which accounted for 56.56 and 7.34% of the total mercury, respectively. Various mercury compounds, including Hg2Cl2, HgS, HgCl2, HgSO4, and HgO, existed in the sludge. These results for mercury distribution and speciation are highly useful in understanding mercury transport and transformation during the wet flue gas cleaning process. This research is conducive for controlling mercury emissions from nonferrous smelting flue gas and by-products.

Impact of HCl and O2 on removal of elemental mercury by heat-treated activated carbon: Integrated X-ray analysis

Treated activated carbons, prepared by heat treatment of activated carbon sorbents under the protection of argon (Ar), were subjected to synthetic flue gases to investigate its elemental mercury (Hg0) capture and the specific role of HCl and O2. To elucidate the adsorption mechanisms & binding properties, subsequent sorbents were characterized by X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. The results suggest that Hg0 capture on the heat treated activated carbon (TAC) under HCl atmosphere mainly follows Eley-Rideal reaction mechanism, where, HCl reacts with the basic active carbon sites on the TAC leading to the formation of Cl-containing active sites, subsequently gaseous Hg0 heterogeneously reacts with these Cl-containing active sites through electron-transfer and forms HgClx compounds. Both the 2.42Å and 2.39Å bonding distance of Hg-Cl shows that only one of the two valence electrons on mercury bond with Cl, while the other electron bonds with the basic active carbon site covalently. In presence of HCl and O2, the synergistic effect of O2 on Hg0 adsorption might attribute to the O2 adsorption and the subsequent formation of oxygen-containing functional groups (OFGs) on TAC, which increase the amount of effective activated sites for Hg0 adsorption and at the same time enhance the adsorbing kinetics of adjacent Cl-containing sites.

Fabrication of BiOIO3 with induced oxygen vacancies for efficient separation of the electron-hole pairs

Bismuth-based nanomaterials exhibiting unique structures, which endow them with fascinating physicochemical properties, have received more and more interests as promising photocatalysts. Fabrication of BiOIO3 photocatalysts by calcination method was investigated for the first time. XRD patterns showed that the crystallinity of BiOIO3 photocatalysts could be controlled by calcination temperature. TGA demonstrated that calcining the precursor at a specific temperature range was appropriate for preparing BiOIO3 photocatalysts. XPS and FT-IR characterization revealed that the BiOIO3 photocatalysts prepared by calcination method possessed oxygen vacancies, which acted as the positive charge centers to trap the electron easily, inhibiting the recombination of photo electron-hole pairs. Furthermore, PL spectra confirmed the oxygen vacancies can favor for the separation of the electron-hole pairs and in turn enhance the photocatalytic performance. From the above analysis, the mechanism of preparing BiOIO3 photocatalysts by calcination method was proposed. Meanwhile, the effect of oxygen vacancies on the photocatalytic activity of BiOIO3 photocatalysts was investigated. The BiOIO3 photocatalysts with oxygen vacancies were found to be efficiently photocatalytically remove gaseous Hg0 and the relative photocatalysis mechanism was investigated.

Effect of gaseous mercury on nitric oxide removal performance and microbial community of a hybrid catalytic membrane biofilm reactor

The effect of gaseous elemental mercury on nitric oxide removal performance, microbial community and microbial nitrogen metabolism of a hybrid catalytic membrane biofilm reactor (HCMBR) were evaluated. A gaseous Hg0 concentration of 25±5μg·m−3 reduced the NO removal efficiency of HCMBR from 86.4% to 41.9%. In 80days of operation, NO removal efficiency was up to 68.8%, and Hg0 removal efficiency achieved 81.7%, respectively. The addition of gaseous elemental mercury affected the microbial community structure and changed microbial nitrogen metabolism, as shown by metagenomics sequencing method. Some phyla, such as Azospirillum, and Delftia, increased in abundance, whereas others, such as Weeksella, decreased. Hg0 could combine with merP and be transported by merT, and then be oxidized into Hg2+ by KatG or KatE. The nitrogen metabolism related processes such as catalysis, nitrification and denitrification, ammoniation and biological nitrogen fixation processes, exists in HCMBR and HCMBRHg.

Elemental Mercury Oxidation over Fe–Ti–Mn Spinel: Performance, Mechanism, and Reaction Kinetics

The design of a high-performance catalyst for Hg0 oxidation and predicting the extent of Hg0 oxidation are both extremely limited due to the uncertainties of the reaction mechanism and the reaction kinetics. In this work, Fe-Ti-Mn spinel was developed as a high-performance catalyst for Hg0 oxidation, and the reaction mechanism and the reaction kinetics of Hg0 oxidation over Fe-Ti-Mn spinel were studied. The reaction orders of Hg0 oxidation over Fe-Ti-Mn spinel with respect to gaseous Hg0 concentration and gaseous HCl concentration were approximately 1 and 0, respectively. Therefore, Hg0 oxidation over Fe-Ti-Mn spinel mainly followed the Eley-Rideal mechanism (i.e., the reaction of gaseous Hg0 with adsorbed HCl), and the rate of Hg0 oxidation mainly depended on Cl• concentration on the surface. As H2O, SO2, and NO not only inhibited Cl• formation on the surface but also interfered with the interface reaction between gaseous Hg0 and Cl• on the surface, Hg0 oxidation over Fe-Ti-Mn spinel was obviously inhibited in the presence of H2O, SO2, and NO. Furthermore, the extent of Hg0 oxidation over Fe-Ti-Mn spinel can be predicted according to the kinetic parameter kE-R, and the predicted result was consistent with the experimental result.

Mechanisms of Elemental Mercury Transformation on α-Fe2O3(001) Surface from Experimental and Theoretical Study: Influences of HCl, O2, and SO2.

The reaction mechanisms of a mixture gas of HCl, O2, and SO2 in Hg0 adsorption on α-Fe2O3(001) surface are clarified by a group of adsorption experiments and theoretical calculations based on the density functional theory. The role of O2 in removing Hg0 is greatly influenced by the reaction temperature, meanwhile, the O atom coverage could affect the adsorption performance of Hg0. The dissociated O2 competes with the active sites of Cl species on Fe surface at low temperature, however, at medium temperature HCl and O2 could simultaneously facilitate the Hg0 transformation. Combined with the theoretical calculations, the role of SO2 and the probable pathways in removing Hg0 are discussed. Lower concentration of SO2 as well as HCl could dissociate on α-Fe2O3(001) surface, and the intermediates combine with gaseous Hg0, forming mercury-sulfur, mercury-chlorine compounds, and so forth. In addition, the different concentrations of SO2 are also discussed, and the corresponding X-ray photoelectron spectroscopy analysis on contrasted samples is conducted to research the morphological characterization, providing a reliable basis for judging the probable pathways of Hg0 transformation.

Recyclable Naturally Derived Magnetic Pyrrhotite for Elemental Mercury Recovery from Flue Gas.

Magnetic pyrrhotite, derived from the thermal treatment of natural pyrite, was developed as a recyclable sorbent to recover elemental mercury (Hg0) from the flue gas as a cobenefit of wet electrostatic precipitators (WESP). The performance of naturally derived pyrrhotite for Hg0 capture from the flue gas was much better than those of other reported magnetic sorbents, for example Mn-Fe spinel and Mn-Fe-Ti spinel. The rate of pyrrhotite for gaseous Hg0 capture at 60 °C was 0.28 μg g min-1 and its capacity was 0.22 mg g-1 with the breakthrough threshold of 4%. After the magnetic separation from the mixture collected by the WESP, the spent pyrrhotite can be thermally regenerated for recycle. The experiment of 5 cycles of Hg0 capture and regeneration demonstrated that both the adsorption efficiency and the magnetization were not notably degraded. Meanwhile, the ultralow concentration of gaseous Hg0 in the flue gas was concentrated to high concentrations of gaseous Hg0 and Hg2+ during the regeneration process, which facilitated the centralized control of mercury pollution. Therefore, the control of Hg0 emission from coal-fired plants by the recyclable pyrrhotite was cost-effective and did not have secondary pollution.

Elemental mercury removal from syngas at high-temperature using activated char pyrolyzed from biomass and lignite

Activated char obtained by the co-pyrolysis of a mixture of lignite and biomass impregnated with ZnCl2 solution was found to be effective for the high-temperature capture of mercury from syngas. The prepared samples were characterized by X-ray photoelectron spectroscopy, Hg-thermal programmed desorption as well as Brunauer- Emmett-Teller analysis. The results show that activated char exhibits a large surface area as well as abundant micropores and C-Cl, C=O, and COOH functional groups. During the chemisorption of mercury, gaseous Hg0 is first oxidized by C-Cl to HgCl2; HgCl2 which acts as the intermediate product then reacts with the C=O and COOH functional groups on the surface of activated char to generate Hg-OM. At high adsorption temperatures, Hg-OM on the adsorbent surface can further decompose and generate HgO. The C-Cl group is important for the first oxidation step of gaseous Hg0, and the formation of HgCl2 is the rate-determining step for the entire process of adsorption.

Hydrothermal synthesis of carbon spheres – BiOI/BiOIO3 heterojunctions for photocatalytic removal of gaseous Hg0 under visible light

The carbon modified BiOI/BiOIO3 (CSs-BiOI/BiOIO3) composites with heterostructures have been prepared via a facile hydrothermal method, using carbon spheres, bismuth nitrate and potassium iodate as precursors. Moreover, a new synthesis mechanism has been proposed. The photocatalytic activities of as-prepared catalysts are evaluated by oxidation of gaseous elemental mercury under visible light irradiation. It is found that the CSs-BiOI/BiOIO3 exhibits highly enhanced visible photocatalytic activity, compared with that of pure BiOIO3. The results show that the Hg0 removal efficiency of CSs-BiOI/BiOIO3 reach up to 92.9% and 83.0% under LED light irradiation and simulated sunlight irradiation respectively. The improved photocatalytic activity can be ascribed to the increased the absorption of visible light, enhanced charge separation and transfer and the surface properties. This work points to CSs-BiOI/BiOIO3 nanocomposites as new and efficient visible light photocatalysts for environmental remediation applications.

Experiment study on mercury migration across wet flue gas desulfurization slurry under oxy-coal combustion atmosphere

Mercury in oxy-coal combustion flue gas may cause liquid metal embrittlement and material failure to aluminum (Al) heat exchangers, which needs to be removed with high efficiency before CO2 compression. Oxidized Hg (Hg2+) is soluble thus can be co-removed with SO2 in WFGD (Wet Flue Gas Desulfurization). However, the dissolved Hg2+ in slurry may also transform to the insoluble elemental mercury (Hg0) form and re-emitted, resulting a reduction of total Hg capture efficiency in WFGD. This paper experimentally examined the Hg migration across WFGD under high CO2 concentration atmosphere with simulated typical desulfurization slurry. Influences of solids (CaSO4, CaSO3) and anions (Cl−, NO3−, SO32−) in slurry are considered. According to the results, solids of CaSO3 with higher BET surface area are more favored for Hg retention than CaSO4. Slurry pH under high concentration of CO2 was a little bit lower than air combustion atmosphere. The decreased pH in turn hindered Hg retention on both solids while the gaseous Hg0 emission increased. For anions, 6mM NO3− and 5mM SO32− both led to large amount of Hg transformed from CaSO4 solids and liquid into the gas phase. The existence of 20mM Cl− can retain more Hg in the liquid, especially when NO3− and SO32− coexisted. However, this effect was quite pH sensitive. As to CaSO3 slurry, most of the Hg remained in slurry regardless the existence of other anions and atmosphere.

Mercury capture from natural gas by carbon supported ionic liquids: Synthesis, evaluation and molecular mechanism

Superiority of silica supported ionic liquids over other adsorbents in capturing elemental mercury (Hg0) from flue gases has been recently reported. In this study, activated carbon, which is more economical than silica, was experimented as a solid support for ionic liquids (ILs) for gaseous Hg0 removal. Four ILs were successfully coated on activated carbon. The carbon supported ionic liquids (CSILs) were characterized by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller surface area analysis, field emission scanning electron microscopy, energy-dispersive X-ray, X ray-photoelectron spectroscopy and nuclear magnetic resonance. A continuous fixed bed flow reactor was used to examine the performance of CSILs in treating 20–35ppm Hg0 vapor at a gas flow rate of 60mL/min. 1-Butyl-3-methylimidazolium chloride [Bmim]Cl coated activated carbon was the most reactive among CSILs studied and a powdered form of [Bmim]Cl coated activated carbon was able to uptake Hg0 up to 23mg/g and 60mg/g with N2 and CH4 as carrier gas, respectively. A molecular simulation was performed to investigate the molecular level interaction between the Hg0 and the ILs to understand the effect of structural variations of the ILs on Hg0 adsorption. The simulation reveals that the anion part of IL plays a major role in Hg0 adsorption. Based on experimental results, a possible mechanism of Hg–IL interaction was elucidated; the imidazolium cation can form a complex with HgCl2 through the C2 hydrogen.

The centralized control of elemental mercury emission from the flue gas by a magnetic rengenerable Fe–Ti–Mn spinel

A magnetic Fe–Ti–Mn spinel was developed to adsorb gaseous Hg0 in our previous study. However, it is currently extremely restricted in the control of Hg0 emission from the flue gas for at least three reasons: sorbent recovery, sorbent regeneration and the interference of the chemical composition in the flue gas. Therefore, the effect of SO2 and H2O on the adsorption of gaseous Hg0 on the Fe–Ti–Mn spinel and the regeneration of spent Fe–Ti–Mn spinel were investigated in this study. Meanwhile, the procedure of the centralized control of Hg0 emission from the flue gas by the magnetic Fe–Ti–Mn spinel has been analyzed for industrial application. The spent Fe–Ti–Mn spinel can be regenerated by water washing followed by the thermal treatment at 450°C with no obvious decrease of its ability for Hg0 capture. Meanwhile, gaseous Hg0 in the flue gas can be remarkably concentrated during the regeneration, facilitating its safe disposal. Initial pilot test demonstrated that gaseous Hg0 in the real flue gas can be concentrated at least 100 times by the Fe–Ti–Mn spinel. Therefore, Fe–Ti–Mn spinel was a novel magnetic regenerable sorbent, which can be used for the centralized control of Hg0 emission from the flue gas.

Accumulation and oxidation of elemental mercury in tropical soils

The role of chemical and mineralogical soil properties in the retention and oxidation of atmospheric mercury in tropical soils is discussed based on thermal desorption analysis. The retention of gaseous mercury by tropical soils varied greatly both quantitatively and qualitatively with soil type. The average natural mercury content of soils was 0.08±0.06μgg−1 with a maximum of 0.215±0.009μgg−1. After gaseous Hg0 incubation experiments, mercury content of investigated soils ranged from 0.6±0.2 to 735±23μgg−1, with a mean value of 44±146μgg−1. Comparatively, A horizon of almost all soil types adsorbed more mercury than B horizon from the same soil, which demonstrates the key role of organic matter in mercury adsorption. In addition to organic matter, pH and CEC also appear to be important soil characteristics for the adsorption of mercury. All thermograms showed Hg2+ peaks, which were predominant in most of them, indicating that elemental mercury oxidized in tropical soils. After four months of incubation, the thermograms showed oxidation levels from 70% to 100%. As none of the samples presented only the Hg0 peak, and the soils retained varying amounts of mercury despite exposure under the same incubation conditions, it became clear that oxidation occurred on soil surface. Organic matter seemed to play a key role in mercury oxidation through complexation/stabilization of the oxidized forms. The lower percentages of available mercury (extracted with KNO3) in A horizons when compared to B horizons support this idea.

Effects of flue gas components on the oxidation of gaseous Hg0 by dielectric barrier discharge plasma

This study investigated the effects of gas components on the oxidation of Hg0 by dielectric barrier discharge (DBD) non-thermal plasma (NTP) technology. The findings indicated that reactive species such as O and Cl generated by ionization of O2 and HCl played dominant roles during oxidation processes. The presence of 50ppm of HCl in N2/O2 atmosphere enhanced the Hg0 oxidation, the complete oxidation of Hg0 was observed by 6kV of applied voltage. The presence of NO in the reactor decreased the Hg0 oxidation efficiency due to the interference by NO reaction with O and O3. The addition of 310ppm of NO into the flue gas remained in 55% of Hg0 oxidation efficiency. Water vapor inhibited Hg0 oxidation, which was attributed to the consumption of reactive species and decomposition of HgOH. SO2 had a slight promoting effect on Hg0 oxidation, compared with the absence of SO2, the oxidation efficiency increased by 2–8% with the addition of 100–200ppm of SO2. This study leads to starting the development of a novel promising environmental technology for Hg removal in the flue gas.

High pressure conversion of NOx and Hg and their capture as aqueous condensates in a laboratory piston-compressor simulating oxy-fuel CO2 compression

Oxy-fuel technology for CO2 capture has largely focused on combustion characteristics as a driver towards demonstration. Impurity removal studies typically centre on the how current environmental control units (FGD, SCR, activated carbon beds) operate in oxy-fuel firing. However, it is expected that some removal of NOx and SOx may occur during compression of flue gas through the lead chamber process. Some commercial systems link the capture of mercury to the formation of acid condensates (as a soluble mercury salt). Mercury in compressed flue gas represents a potential corrosion risk in the processing of CO2 from oxy-fuel combustion processes. Gas phase elemental mercury (Hg0) is difficult to remove from the flue gas and the level of cleaning required to prevent corrosion of cryogenic brazed aluminium heat exchangers is uncertain.This work has investigated the behaviour of gaseous Hg0 in pressurised oxy-fuel systems in terms of the potential capture in acidic condensates, interaction with NOx gases and liquid stability on de-pressurisation. The work was undertaken on an adapted laboratory scale three stage axial-piston compressor with gas and liquid sampling at pressures up to 30bar.The main finding was that gaseous Hg0 reacts readily with NO2 formed from NO oxidation at high pressure. This reaction occurred without the presence of water, either water vapour or liquid water, contrary to speculation in the literature. Without NO2, no capture of Hg0 was observed in the compression system.Overall, the capture of mercury during compression occurred as a consequence of high pressure, longer residence time and concentration of NO2. Capture rates of 100% Hg and 75–83% NOx were measured from the compressor exit at 30barg.

Characteristics and stability of mercury vapor adsorption over two kinds of modified semicoke.

In an attempt to produce effective and lower price gaseous Hg0 adsorbents, two methods of HCl and KMnO4/heat treatment were used respectively for the surface modification of liginite semicoke from inner Mongolia. The different effects of modification process on the surface physical and chemical properties were analyzed. The characteristics and stability of mercury vapor adsorption over two kinds of modified semicoke were investigated. The results indicated that modification process caused lower micropore quantity and volume capacity of semicoke; the C-Cl functional groups, C=O bond and delocalized electron π on the surface of Cl-SC, the amorphous higher valency Mnx+, and O=C–OH functional groups on the surface of Mn-H-SC were the active sites for oxidation and adsorption of gaseous Hg0. Modification process led to higher mercury removal efficiency of semicoke at 140°C and reduced the stability of adsorbed mercury of semicoke in simulated water circumstance simultaneously.