Mercury emissions from six coal-fired power plants in China

Mercury emission field measurements based on the Ontario Hydro Method (OHM) were conducted for six coal-fired power plants in China. The mercury mass balances for the six power plants varied from 100.3% to 139.5% of the input coal mercury for the whole system. About 0.02%–1.2% of the mercury remained in the bottom ash. In the first five power plants equipped with pulverized coal boiler, most of the mercury was emitted from the stack to the atmosphere. The plants with Electrostatic Precipitator (ESP) system emitted more Hg⁰ than Hg²⁺, while the plants with the Fabric Filter (FF) emitted less Hg⁰ than Hg²⁺. Virtually all of the Hg^P enter the ESP or the FF was removed. The FF systems had better Hg⁰ and Hg²⁺ removal efficiencies than the ESP systems. The flue gas desulfurization (FGD) system removed up to 78.0% of Hg²⁺ and only 3.14% of Hg⁰ in the flue gas, while 8.94% of the original mercury in the coal was removed by the FGD system. The average mercury removal efficiencies of the ESP systems was 11.5%, that of the FF systems was 52.3% and that of the combined ESP + FGD system was 13.7%, much lower than the average removal efficiencies of pollution control device systems in US plants which have been used in previous studies of Chinese mercury emission inventory. Hg⁰, rather than Hg²⁺ as assumed in previous estimates, has been found to be the dominant species emitted in the atmosphere. The average emission factor was found to be 4.70 g/TJ (10.92 bl/Tbtu), which is much higher than for US plants burning bituminous coals due to the high mercury content in the Chinese coal and the low mercury removal efficiency of air pollution control devices of power plants.     

Mercury speciation and its emissions from a 220 MW pulverized coal-fired boiler power plant in flue gas

Distributions of mercury speciation of Hg⁰, Hg²⁺ and Hg ^P in flue gas and fly ash were sampled by using the Ontario Hydro Method in a 220 MW pulverized coal-fired boiler power plant in China. The mercury speciation was varied greatly when flue gas going through the electrostatic precipitator (ESP). The mercury adsorbed on fly ashes was found strongly dependent on unburnt carbon content in fly ash and slightly on the particle sizes, which implies that the physical and chemical features of some elemental substances enriched to fly ash surface also have a non-ignored effect on the mercury adsorption. The concentration of chlorine in coal, oxyge nand NO _x in flue gas has a positive correlation with the formation of the oxidized mercury, but the sulfur in coal has a positive influence on the formation of elemental mercury. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Cobenefit of SO3 reduction on mercury capture with activated carbon in coal flue gas

Parametric experiments were carried out to study the interactions of mercury, SO₃, and injected activated carbon (AC) in a coal flue gas stream. The levels of SO₃ vapor in flue gas were altered by individually varying flue gas temperature, moisture, or sodium fume injection in the flue gas. Meanwhile, mercury emissions with AC injection (ACI) upstream of an electrostatic precipitator (ESP) were evaluated under varied SO₃ concentrations. SO₃ measurements using a condensation method indicated that low temperature, high moisture content, and sodium fume injection in flue gas shifted SO₃ partitioning from the vapor to particulate phase, subsequently improving mercury capture with ACI. 0.08 g/m³ of DARCO^® Hg-LH injection only provided approximately 20% mercury reduction across the ESP in a bituminous coal flue gas containing 28 ppm SO₃, but mercury capture was increased to 80% when the SO₃ vapor concentration was lowered less than 2 ppm. Experimental data clearly demonstrate that elevated SO₃ vapor is the key factor that impedes mercury adsorption on AC, mainly because SO₃ directly competes against mercury for the same binding sites and overwhelmingly consumes all binding sites.     

Kinetic modeling of H2O2-enhanced oxidation of flue gas elemental mercury

Mercury emissions from coal-fired power plants account for 40% of the anthropogenic mercury emissions in the U.S. The speciation of mercury largely determines the amount of mercury capture in control equipments. Conversion of insoluble Hg⁰ into more soluble Hg²⁺ facilitates its removal in scrubbers. Past studies suggest that an added supply of OH radicals possibly enhance the mercury oxidation process. This study demonstrates that the application of H₂O₂, as source of OH radicals, accelerates the oxidation of Hg⁰ into Hg²⁺. A detailed kinetic reaction mechanism was compiled and the reaction pathways were established to analyze the effect of H₂O₂ addition. The optimum temperature range for the oxidation was 480–490 °C. The sensitivity analysis of the reaction mechanism indicates that the supply OH radicals increase the formation of atomic Cl, which accelerates the formation of HgCl₂ enhancing the oxidation process. Also, the pathway through HOCl radical, generated by the interactions between chlorine and H₂O₂ was prominent in the oxidation of Hg⁰. The flue gas NO was found to be inhibiting the Hg⁰ oxidation, since it competed for the supplied H₂O₂. Studying the interactions with the other flue gas components and the surface chemistry with particles in the flue gas could be important and may improve the insight into the post combustion transformation of mercury in a comprehensive way.     

Analysis of mercury species present during coal combustion by thermal desorption

Mercury in coal and its emissions from coal-fired boilers is a topic of primary environmental concern in the United States and Europe. The predominant forms of mercury in coal-fired flue gas are elemental (Hg⁰) and oxidized (Hg²⁺, primarily as HgCl₂). Because Hg²⁺ is more condensable and far more water soluble than Hg⁰, the wide variability in mercury speciation in coal-fired flue gases undermines the total mercury removal efficiency of most mercury emission control technologies. It is important therefore to have an understanding of the behaviour of mercury during coal combustion and the mechanisms of mercury oxidation along the flue gas path. In this study, a temperature programmed decomposition technique was applied in order to acquire an understanding of the mode of decomposition of mercury species during coal combustion. A series of mercury model compounds were used for qualitative calibration. The temperature appearance range of the main mercury species can be arranged in increasing order as HgCl₂ < HgS < HgO < HgSO₄. Different fly ashes with certified and reference values for mercury concentration were used to evaluate the method. This study has shown that the thermal decomposition test is a newly developed efficient method for identifying and quantifying mercury species from coal combustion products.     

Mercury speciation and emission from the coal‐fired power plant filled with flue gas desulfurization equipment

Mercury speciation and emission from two Chinese coal‐fired power stations equipped with flue gas desulfurization device were investigated. Research results reveal that Hg⁰ is the main form in the flue gas in Plant 1; Hg²⁺ is the main form in the flue gas in Plant 2. Most of mercury was emitted to the atmosphere, which was about 77–98%, and the elemental mercury released to atmosphere ranged 73–94% approximately. A pot of mercury is adsorbed by bottom ash, electrostatic precipitator (ESP) ash, and gypsum in Plant 1. However, most mercury, the scale of which is 75–83.2%, is collected by ESP ash, and only 7.0–12.2% mercury is emitted to the atmosphere in Plant 2. The mercury removal by NID semi‐desulfurization system is higher than wet flue gas desulfurization (WFGD) desulfurization system.     

Mercury control testing in a pulverized lignite-fired system

The Energy & Environmental Research Center (EERC) is evaluating and developing advanced and innovative concepts for controlling Hg emissions from North Dakota lignite-fired power plants with the goal of achieving 50%–90% Hg removal at one-half to three-fourths the current estimated costs. Pilot-scale tests were performed to evaluate potential sorbents and fuel additives for removing Hg from North Dakota lignite (Freedom and Center Mines) combustion flue gases. The Hg sorbents and Hg⁰ oxidation and sorbent enhancement additives were evaluated separately, and most were also tested in combination. A 580 MJ/h (550,000 Btu/h) pulverized coal combustion system was used to conduct sorbent injections and/or lignite additive additions upstream of three particulate control devices (PCDs): 1) an electrostatic precipitator (ESP), 2) a spray dryer and fabric filter, and 3) a retrofit advanced hybrid particulate collector (AHPC) filter (an ESP followed by an AHPC filter). ASTM International Method D6784-02 (Ontario Hydro method) and continuous Hg monitors were used to measure Hg species concentrations across the control devices. The effects of sorbent injection and coal additive addition rates on Hg removal were evaluated for each PCD option. The effects of continuous injection and batch addition of sorbents on the Hg removal performance of the ESP/AHPC filter system were also investigated. Increasing injection and additive rates and improving contact between the sorbents and flue gases generally promoted Hg capture. Most of the coal additives tested significantly enhanced PCD Hg removal, especially in the presence of a sorbent.     

Removal of elemental mercury from simulated coal-combustion flue gas using a SiO2–TiO2 nanocomposite

A novel silica–titania (SiO₂–TiO₂) nanocomposite has been developed to effectively capture elemental mercury (Hg⁰) under UV irradiation. Previous studies under room conditions showed over 99% Hg⁰ removal efficiency using this nanocomposite. In this work, the performance of the nanocomposite on Hg⁰ removal was tested in simulated coal-fired power plant flue gas, where water vapor concentration is much higher and various acid gases, such as HCl, SO₂, and NO_x, are present. Experiments were carried out in a fix-bed reactor operated at 135 °C with a baseline gas mixture containing 4% O₂, 12% CO₂, and 8% H₂O balanced with N₂. Results of Hg speciation data at the reactor outlet demonstrated that Hg⁰ was photocatalytically oxidized and captured on the nanocomposite. The removal efficiency of Hg⁰ was found to be significantly affected by the flue gas components. Increased water vapor concentration inhibited Hg⁰ capture, due to the competitive adsorption of water vapor. Both HCl and SO₂ promoted the oxidation of Hg⁰ to Hg(II), resulting in higher removal efficiencies. NO was found to have a dramatic inhibitory effect on Hg⁰ removal, very likely due to the scavenging of hydroxyl radicals by NO. The effect of NO₂ was found to be insignificant. Hg removal in flue gases simulating low rank coal combustion products was found to be less than that from high rank coals, possibly due to the higher H₂O concentration and lower HCl and SO₂ concentrations of the low rank coals. It is essential, however, to minimize the adverse effect of NO to improve the overall performance of the SiO₂–TiO₂ nanocomposite.     

Mercury species, mass flows and processes in a cement plant

The aim of the study was to evaluate the behaviour of mercury in the cement clinker production process. Simultaneous measurements of mercury in all important materials and gas streams were performed in three sampling periods on about 300 solid samples and about 80 samples taken from gas streams. Mercury species in flue gases at characteristic parts of the process were measured as total Hg(t), particulate Hg(p), elemental Hg⁰(g) and reactive Hg²⁺(g) mercury. Based on the results of measurements, mercury mass flows and mass balances of the whole and in certain parts of the process were evaluated. It was shown that the process comprises many mercury cycles which are strongly dependent on the operating conditions and technological specifics. Cycling of mercury causes a significant enrichment of mercury inside the process. In the annual mercury input of about 27 kg, raw materials accounted near by 60% and fuels about 40% (i.e. petrol coke 31%, waste tyres 10% and waste oil 0.4%). The annual emission of mercury represented 40-70% of the inputs, while cement clinker only contained about 10%. The difference between inputs and outputs (11-45%) obtained in the annual mass balance could be assigned to mercury recycling and significant enrichment inside the process, as well as variability between spot measurements. The parts of the process with the highest mercury mass flows and the lowest material/gas flows were identified. Such points represent an opportunity to remove a significant amount of mercury from the process at low material flows and to improve mercury control. Mercury was mainly emitted in gaseous form with 92% (direct mode) or 89% (combined mode) as Hg(g) on average, of which about 2/3 was as Hg²⁺(g), and about 1/3 as Hg⁰(g). Only a small part (the rest) was emitted as particulate Hg(p). Shares of individual mercury species in the last sampling period were 65.7% Hg²⁺(g), 34.0% Hg⁰(g) and 0.3% Hg(p) on average. Ratios between individual mercury forms were found to be related to operating modes. The quantities of Hg(t), Hg(g) and Hg²⁺(g) emitted were higher when operating with the raw mills off (direct mode). It was seen that the efficiency of Hg removal was strongly related to the dust removal efficiency. Bag filters very efficiently removed all mercury species.     

Novel sorbents for mercury emissions control from coal-fired power plants

The authors have successfully developed novel efficient and cost-effective sorbents for mercury removal from coal combustion flue gases. These sorbents were evaluated in a fixed-bed system with a typical PRB subbituminous/lignite simulated flue gas, and in an entrained-flow system with air simulating in-flight mercury capture by sorbent injection in the ductwork of coal-fired utility plants. In both systems, one of the novel sorbents showed promising results for Hg⁰ removal. In particular, this sorbent demonstrated slightly higher efficiencies in Hg⁰ removal than Darco Hg-LH (commercially available brominated activated carbon) at the similar injection rates in the entrained-flow system. The other novel sorbent showed excellent Hg⁰ oxidation capability, and may enable coal-fired power plants equipped with wet scrubbers to simultaneously control their mercury and sulfur oxides emissions. In addition, fixed-bed results for this sorbent showed that co-injection of a very small amount (∼10%) of raw activated carbon could eliminate almost all of the mercury generated by reactions of Hg⁰ with the sorbent.     

Removal of Elemental Mercury by Sodium Chlorite Solution

The important step for increasing gaseous elemental mercury (Hg⁰) removal in wet scrubber systems is altering the chemical form of the Hg⁰ to a water‐soluble oxidized species. This work focuses on the removal of elemental mercury from simulated flue gas by aqueous sodium chlorite in a bubble reactor. The effects of initial oxidizing solution concentration, reaction temperature, pH and mercury concentration in the inlet of the reactor on mercury oxidative absorption in sodium chlorite were investigated. The results indicate that higher concentrations of sodium chlorite favor Hg⁰ removal, with a greater efficiency observed in acidic than in alkaline solution. High temperature inhibits Hg⁰ absorption in aqueous sorbent when the reaction temperature is lower than ca. 40 °C, and the removal efficiency increases when the temperature is higher than that value. In conclusion, the major influencing factors on the levels of Hg⁰ removal are pH and chlorite concentration in solution.     

Effects of NOx, α-Fe2O3, γ-Fe2O3, and HCl on mercury transformations in a 7-kW coal combustion system

Bench-scale investigations indicate that NO, NO₂, hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃), and HCl promote the conversion of gaseous elemental mercury (Hg⁰) to gaseous oxidized mercury (Hg²⁺) and/or particle-associated mercury (Hg[p]) in simulated coal combustion flue gases. In this investigation, the effects of NO_x, α-Fe₂O₃, γ-Fe₂O₃, and HCl on Hg transformations were evaluated by injecting them into actual coal combustion flue gases produced from burning subbituminous Absaloka and lignitic Falkirk coals in a 7-kW down-fired cylindrical furnace. A bituminous Blacksville coal known to produce an Hg²⁺-rich combustion flue gas was also burned in the system. The American Society for Testing and Materials Method D6784-02 (Ontario Hydro method) or an online Hg analyzer equipped to measure Hg⁰ and total gaseous mercury (Hg[tot]) was used to monitor Hg speciation at the baghouse inlet (160–195 °C) and outlet (110–140 °C) locations of the system. As expected, the baseline Blacksville flue gas was composed predominantly of Hg²⁺ (Hg²⁺/Hg[tot]=0.77), whereas Absaloka and Falkirk flue gases contained primarily Hg⁰ (Hg⁰/Hg[tot]=0.84 and 0.78, respectively). Injections of NO₂ (80–190 ppmv) at 440–880 °C and α-Fe₂O₃ (15 and 6 wt.%) at 450 °C into Absaloka and Falkirk coal combustion flue gases did not significantly affect Hg speciation. The lack of Hg⁰ to Hg²⁺ conversion suggests that components of Absaloka and Falkirk combustion flue gases and/or fly ashes inhibit heterogeneous Hg⁰–NO_x–α-Fe₂O₃ reactions or that the flue gas quench rate in the 7-kW system is much different in relation to bench-scale flue gas simulators.An abundance of Hg²⁺, HCl, and γ-Fe₂O₃ in Blacksville flue gas and the inertness of injected α-Fe₂O₃ with respect to heterogeneous Hg⁰ oxidation in Absaloka and Falkirk flue gases suggested that γ-Fe₂O₃ catalyzes Hg²⁺ formation and that HCl is an important Hg⁰ reactant. The filtration of Absaloka and Falkirk combustion flue gases at 150 °C through fabric filters with ≈60 g/m² γ-Fe₂O₃ indicated that about 30% of the Hg⁰ in Absaloka and Falkirk flue gases was converted to Hg²⁺ and/or Hg(p). HCl injection (100 ppmv) into the Absaloka combustion flue gas converted most of the Hg⁰ to Hg²⁺, whereas HCl injection into the Falkirk flue gas converted most of the Hg⁰ and Hg²⁺ to Hg(p). Additions of γ-Fe₂O₃ and HCl did not have a synergistic effect on Hg⁰ oxidation. The filtration of Absaloka and Falkirk flue gases through much greater fabric filter loadings of 475 g/m² γ-Fe₂O₃ essentially doubled the baghouse Hg[tot] removal efficiency to about 50%. Results from this investigation demonstrate the importance of evaluating potential Hg⁰ reactants and oxidation catalysts in actual coal combustion flue gases.     

An investigation of mercury distribution and speciation during coal combustion

A multi-field electrostatic precipitator (ESP) and a two-stage condensing heat exchanger (CHX^®) have been added to the pilot scale Vertical Combustion Research Facility (VCRF) in CETC-O to further research into integrated emissions control for coal fired power plants. A series of combustion trials were conducted on the VCRF with three different coals (bituminous, sub-bituminous and lignite) to study mercury distribution and speciation at various VCRF locations. Results showed that, with the bituminous coal, as the flue gas cools down from 700 to 200 °C, 80% of total mercury in the gas phase existed in oxidized form and 20% in elemental form. For sub-bituminous and lignite coals, elemental mercury was the dominant form throughout the system. Analysis of deposited ash samples showed that oxidized mercury can be absorbed on carbon-rich ash deposits, although overall only a very small percentage of total mercury was absorbed on the ash. The potential of the CHX^® at removing mercury from the flue gas was also explored. Results indicated that, using wet scrubbing, the CHX^® was able to remove 98% of oxidized mercury. Though elemental mercury went through the system unabated, it is suggested that, with appropriate agent to oxidize elemental mercury in the CHX^®, it is conceivable to use CHX^® to remove both oxidized and elemental mercury. Finally, mercury balance was performed and good mercury balance was obtained across the VCRF, validating our sampling procedures and analysis methods.     

Effect of selective catalytic reactor on oxidation and enhanced removal of mercury in coal-fired power plants

The present study investigated the variation of mercury (Hg) speciation within the air pollution control devices (APCDs) in bituminous coal-fired power plants. The effect of selective catalytic reduction (SCR) system, which is mainly installed for NOx removal, on elemental Hg (Hg⁰) oxidation and enhancement of Hg removal within APCDs, was studied. Hg speciations in flue gas at the inlet and outlet of each APCDs, such as SCR, cold-side electrostatic precipitator (CS-ESP) and flue gas desulphurization (FGD), were analyzed. Sampling and analysis were carried out according to Ontario Hydro Method (OHM). Overall Hg removal efficiency of APCDs, on average, was about 61% and 47% with and without SCR system, respectively. In the flue gas, Hg was mainly distributed in gaseous (elemental and oxidized) form. The oxidized to elemental Hg partitioning coefficient increased due to oxidation of Hg⁰ across the SCR system and decreased due to the removal of oxidized Hg (Hg²⁺) across a wet FGD system. Hg⁰ oxidation across the SCR system varied from 74% to 7% in tested coal-fired power plants. The comparative study shows that the installation of an SCR system increased Hg removal efficiency and suppressed the reemission of captured Hg⁰ within a wet FGD system.     

Effect of porous structure and surface functionality on the mercury capacity of a fly ash carbon and its activated sample

The effect of porous structure and surface functionality on the mercury capacity of a fly ash carbon and its activated sample has been investigated. The samples were tested for mercury adsorption using a fixed‐bed with a simulated flue gas. The activated fly ash carbon sample has lower mercury capacity than its precursor fly ash carbon (0.23 vs. 1.85 mg/g), although its surface area is around 15 times larger, 863 vs. 53 m²/g. It was found that oxygen functionality and the presence of halogen species on the surface of fly ash carbons may promote mercury adsorption, while the surface area does not seem to have a significant effect on their mercury capacity.     

Impact of calcium chloride addition on mercury transformations and control in coal flue gas

Pilot-scale experiments were conducted to investigate mercury transformations in coal flue gas when firing subbituminous coal with a CaCl₂ additive. Cofiring the CaCl₂ additive with the subbituminous coal resulted in approximately 50% oxidized mercury, as a result of reactive chlorine species formed in coal flue gas, compared to the dominance of elemental mercury in the baseline flue gas. The mercury data indicate that mercury-flue gas chemistry reactions may occur at fairly high temperatures (>400 °C) in chlorine-enriched flue gas. Field tests were conducted to further demonstrate the impact of cofiring CaCl₂ on the eventual fate of mercury. These tests were completed on a 650-MW subbituminous coal-fired power plant equipped with selective catalytic reduction (SCR), a fabric filter (FF), and a wet scrubber. Overall mercury removals across the SCR-FF-wet scrubber system ranged from 75% to 96% with 200-800 ppm (coal basis) chlorine addition compared to 18-32% during baseline operations. Field data indicate that the SCR enhanced mercury oxidation, possibly as a result of the supplemental formation of reactive chlorine species and the aid of the SCR catalyst. As a result, most of the mercury in the flue gas was in an oxidized state and was removed in the downstream wet scrubber, indicating that cofiring CaCl₂ is an effective mercury control approach for a subbituminous coal-fired plant equipped with an SCR and wet scrubber.     

Abatement of Gas-Phase Mercury—Recent Developments

Among various pollutants, mercury has a significant impact on the environment, human beings, and wildlife with its different forms, namely, elemental mercury (Hg⁰), oxidized mercury (Hg²⁺), and particle-bound mercury (Hg_p). Mercury dispersions mainly occur from coal burning, which is the world's major energy source. Among the three forms, Hg²⁺ and Hg_p are relatively easy to remove from the flue gas by employing typical air pollution control devices; on the other hand, Hg⁰ is difficult to remove. Various methods are available to detain elemental mercury. Recent developments in mercury removal options, especially during the last years, are reviewed. Main concentration has been focused on the removal methods of elemental mercury by novel sorbents and catalytic systems. A current challenge is to develop novel nanomaterials meeting rigorous requirements (easy separation, recyclability, and cost-effectiveness) for eventual exploitation.     

Investigation on elemental mercury oxidation mechanism by non-thermal plasma treatment

Converting elemental mercury into divalent compound is one of the most important steps for mercury abatement from coal fired flue gas. The oxidation of elemental mercury was investigated in this paper using dielectric barrier discharge (DBD) non-thermal plasma (NTP) technology at room temperature. Effects of different flue gas components like oxygen, moisture, HCl, NO and SO₂ were investigated. Results indicate that active radicals including O, O₃ and OH all contribute to the oxidation of elemental mercury. Under the conditions of 5% O₂ in the simulated flue gas, about 90.2% of Hg⁰ was observed to be oxidized at 3.68 kV discharge voltage. The increase of discharge voltage, O₂ level and H₂O content can all improve the oxidation rate, individually. With O₂ and H₂O both existed, there is an optimal moisture level for the mercury oxidation during the NTP treatment. In this test, the observed optimal moisture level was around 0.74% by volume. Hydrogen chloride can promote the oxidation of mercury due to chlorine atoms produced in the plasma process. Both NO and SO₂ have inhibitory effects on mercury oxidation, which can be attributed to their competitive consumption of O₃ and O.     

Impacts of acid gases on mercury oxidation across SCR catalyst

A series of bench-scale experiments were completed to evaluate acid gases of HCl, SO₂, and SO₃ on mercury oxidation across a commercial selective catalytic reduction (SCR) catalyst. The SCR catalyst was placed in a simulated flue gas stream containing O₂, CO₂, H₂O, NO, NO₂, and NH₃, and N₂. HCl, SO₂, and SO₃ were added to the gas stream either separately or in combination to investigate their interactions with mercury over the SCR catalyst. The compositions of the simulated flue gas represent a medium-sulfur and low- to medium-chlorine coal that could represent either bituminous or subbituminous. The experimental data indicated that 5–50 ppm HCl in flue gas enhanced mercury oxidation within the SCR catalyst, possibly because of the reactive chlorine species formed through catalytic reactions. An addition of 5 ppm HCl in the simulated flue gas resulted in mercury oxidation of 45% across the SCR compared to only 4% mercury oxidation when 1 ppm HCl is in the flue gas. As HCl concentration increased to 50 ppm, 63% of Hg oxidation was reached. SO₂ and SO₃ showed a mitigating effect on mercury chlorination to some degree, depending on the concentrations of SO₂ and SO₃, by competing against HCl for SCR adsorption sites. High levels of acid gases of HCl (50 ppm), SO₂ (2000 ppm), and SO₃ (50 ppm) in the flue gas deteriorate mercury adsorption on the SCR catalyst.     

Mercury transformation across particulate control devices in six power plants of China: The co-effect of chlorine and ash composition

This paper presents the results of field measurements on mercury speciation in six power plants of China by applying the Ontario hydro method. During the tests, flue gas was sampled simultaneously before and after particulate control devices (electrostatic precipitator and fabric filter baghouse) along with the pulverized coal, bottom ash and fly ash sampling. The amount of oxidized mercury in gas phase before and after ESP/FF suggests that mercury oxidation after combustion is a kinetically controlled process. The comparison of mercury speciation in different power plant indicates a clear relationship with coal type, especially the chlorine concentration and the basic ash compositions in coal. Both of the factors are analyzed quantitatively in this study. A new parameter C (ratio of chlorine in coal to base/acid ratio) has been introduced to evaluate the co-effect of the two factors above on mercury speciation.