Influence of H2O on Hg0 Oxidation in the Simulated Flue Gas in

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Influence of H2O on Hg0 oxidation in the simulated flue gas of oxygen-enriched combustion Changxing Hu, Deqiang Hang, Ruitang Guo, Zhiyan Guo, and Xiaoyi Yu Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 08 Jun 2017 Downloaded from http://pubs.acs.org on June 9, 2017

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Influence of H2O on Hg0 oxidation in the simulated flue gas in oxygen-enriched combustion Changxing Hu1*, Deqiang Hang1,2, Ruitang Guo2*, Zhiyan Guo1, Xiaoyi Yu1 1 Ningbo Institute of Technology, Zhejiang University, Ningbo, Zhejiang315100, the People’s Republic of China 2 College of Energy and Mechanical Engineering, Shanghai University of Electric Power, Shanghai200090, the People’s Republic of China

Corresponding author1： Chang-xing Hu E-mail:

[email protected]

Corresponding author2： Rui-tang Guo E-mail:

[email protected]

1

ACS Paragon Plus Environment

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ABSTRACT：The catalytic oxidation on elemental mercury (Hg0) to water soluble oxidized mercury (Hg2+) is a good mercury (Hg) control approach for coal-fired power plants, and Hg2+ can be removed by the existing wet flue gas desulfurization (FGD) device. Oxygen-enriched combustion (OEC) is considered as an optimal option for the post CO2 capture among the clean coal combustion technologies. Based on the established bench-scale experimental apparatus, this paper studied the influence mechanism of high H2O concentration on Hg0 oxidation in the simulated flue gas in OEC. The results showed that both the high HCl concentration and the high temperature could improve the Hg0 oxidation in the simulated flue gas above 500℃ and with as high as 30% of H2O content in OEC. A key intermediate reaction step was needed to complete the reaction between Hg0 and HCl. HCl was firstly oxidized to oxidative Cl by O2. Then Hg0 was further oxidized by oxidative Cl. The high H2O concentration could inhibit this process of Hg0 oxidation and the reason was that the high H2O concentration could inhibit the conversion from HCl to oxidative Cl. The inhibitory efficiency of oxidative Cl was affected by both HCl concentration and H2O concentration. The added SO2 consumed oxidative Cl in the simulated flue gas with high H2O content in OEC, which inhibited the oxidation of Hg0. Hg0 oxidation efficiency increased obviously in the heterogeneous flue gas with ash in OEC. The inhibitory effect of H2O on Hg0 oxidation could be weakened in the heterogeneous flue gas in OEC. Key words: H2O, Hg0 oxidation, oxygen-enriched combustion, oxidative Cl, SO2, heterogeneous

1．INTRODUCTION Mercury (Hg) is a kind of heavy metal pollution source with extremely strong biological toxicity

[1-2]

. Especially, it not only seems difficult to be metabolized out of the human body but

also brings a serious threat to the human health [3]. In recent decades, Hg content rises continually in the global atmosphere. Coal-fired utility boiler presents an important source of anthropogenic Hg emissions. Species of Hg emitting from coal combustion mainly consist of elemental mercury (Hg0), oxidized mercury (Hg2+) and particulate-bound mercury (Hgp). Because Hg0 is insoluble in aqueous solution and cannot be removed directly by currently available emission control devices in coal-fired plants, the capture of Hg0 is generally more difficult than that of Hg2+ and Hgp in coal-fired flue gas. Currently, the control on Hg0 emission from coal-fired plants mainly focuses 2


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on the conversion from gaseous Hg0 to Hgp by sorbent and to water soluble Hg2+ by catalyst. Hence, Hgp and Hg2+ can be effectively removed by particulate control devices and wet flue gas desulfurization (WFGD), respectively. Carbon dioxide (CO2) is considered as the most prevalent greenhouse gas resulting in global climate change. The CO2 capture and storage (CCS) is an integrated process, including carbon capture, transport and storage, which is to reduce the emission of CO2 into the atmosphere and mitigate global climate change

[4]

. Oxygen-enriched combustion (OEC) is considered as an

optimal approach for the post CO2 capture among clean coal combustion technologies. In OEC (often called O2/CO2 recycle combustion), fuel is combusted with high concentration or near pure oxygen rather than air and generally70% or 80% of the flue gas are recycled. Therefore, the CO2 concentration in the flue gas in OEC system is high enough to guarantee the CCS be more possible. [5] Compared to the conventional combustion, OEC can greatly reduce the generation of nitrogen oxide (NOX) during combustion without N2 gas [6-8]. Sulfides, such as SO2, and halogen compounds, such as HCl, would be the man acid gases. Based on the previous researches, chlorine (Cl) in coal could promote the transformation from Hg0 to Hg2+. It

[9]

indicated that Cl was the

important intermediate of oxidation reactions between Hg and hydrogen chloride (HCl) in flue gas. Cl could rapidly oxidize Hg0 in the coal-fired flue gas in a wide range of temperature. Coal mainly consists of five elements including carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and organic sulfur (S), in which C, H and O account for more than 95%. The high concentration O and H can react and generate large amounts of water during OEC. Previous researches [10] showed that H2O concentration was about 13% in the conventional coal-fired flue gas, whereas it was above 30% in the oxygen-enriched coal-fired flue gas. More H2O concentration during OEC can inhibit the generation of oxidative Cl in flue gas, which probably can inhibit Hg0 oxidation. Most Hg emission control researches focused on the conventional combustion

[11-15]

. Some

researchers have noticed the importance of the Hg emission control in OEC, such as Andrew Fry et al.

[16,17]

who have carried out prior research on Hg oxidation for OEC applications. However,

these work needs to be strengthened now. In this paper, we aimed to investigate the influence of H2O on Hg0 oxidation in the simulated flue gas in OEC on a fixed bed test bench. This work will help to reveal the mechanism of high H2O concentration on the inhibition of Hg0 oxidation. 3


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2．EXPERIMENT 2.1. Introduction of experimental system A schematic diagram of the simulated experimental system was shown in Figure 1. The system consisted of four subsystems: 1) simulated flue gas in OEC subsystem including flow controller, temperature controller, simulated gases, mixed gas box, electric heating tape, water injector and mercury vapor generator; 2) reaction furnace subsystem; 3) data analyzer record subsystem including data record computer，mercury and oxidizing Cl analyzer；and 4) tail gas treatment equipment including activated carbon fixed adsorption. In order to ensure safety and accuracy, the air impermeability of experimental system was inspected closely before starting each experiment. During the experiment, the concentrations of each component of the simulated flue gas was adjusted to the design values respectively. The concentration ranges of each component o were shown in table 1 and the total simulated flue gas flow 2L/min was balanced by CO2. Each component of gases entered firstly the mixed gas box through mass flowmeter, and then the reaction furnace. The Hg0 concentration could be adjusted by changing the flow of carrying gas N2 and the temperature of electric water-bath, in which the penetration tube of Hg0 was placed. The temperatures of reaction furnace were set at 150℃, 300℃, 500℃, 600℃, 650℃, 700℃, 900℃, and 1150℃, respectively. In order to eliminate the influence of Hg adsorption, all pipelines were heated to 130℃ by electric heating tapes.The Hg0 concentration in the simulated OEC gases was monitored online by Hg analyzer RA-915M LUMEX. The measuring of oxidative Cl followed the Chinese standard method

“Determination of Chlorine in Emission from Stationary Source——Methyl Orange

Spectrophotometric Method”(HJ/T30-1999).

2.2. Definition of analysis parameter and method. Four thermodynamic parameters were used to analyze the influence of H2O on Hg0 oxidation in the simulated flue gas during oxygen-enriched combustion. The definition of each parameter was as follows. 4


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2.2.1 Hg0 oxidation efficiency Hg0 oxidation efficiency was used to evaluate the extent of Hg oxidation from Hg0 to Hg2+ in different simulated flue gas in OEC. The Hg0 oxidation efficiency was defined as follow:

Hg 0 oxidation efficiency§, % =

∗ 100%

（1）

Where C1 represented the Hg0 concentration at the inlet of reaction furnace with the unit of µg/m3 and indicated the initial Hg0 content. The C1 kept stable in the experiment and controlled by the Hg0 vapour generator. C2 represented Hg0 concentration at the outlet of reaction furnace with the unit of µg/m3, and indicated the unreacted Hg0 content after the reaction furnace. The difference between the C1 and C2 indicated the Hg2+ concentration. In this paper, the chosen C2 was stable without and change, which meant that the Hg0 reaction was complete. Usually, it would take about 30 minutes to reach the stable condition. 2.2.2 Conversion efficiency of oxidizing Cl The conversion efficiency of oxidative Cl (∮ )was used to evaluate the extent of Cl conversion from initial non-oxidative Cl (HCl) to oxidative Cl (Cl2 etc.) in the different simulated flue gases in OEC. The concentration of oxidative Cl was detected by wet chemical method using adsorption liquid of (CH3)2NC6H4N+KBr based on the Chinese standard method HJ/T30-1999. Each sampling gas flow was fixed at 0.5L/min through the adsorption liquid and the sampling lasted for 20 minutes. The conversion efficiency of oxidative Cl was defined as follow:

Conversion efficiency of oxidative Cl"∮, %# = β &% ∗ 100% '

（2）

Where C3 represented the oxidative Cl concentration in the adsorption liquid of (CH3)2NC6H4N+KBr with the unit of µg/l(liquid), which was detected by the HACH - DR5000 spectrophotometer. C3 represented the average oxidative Cl concentration in each sampling tail gas. C4 was the initial non-oxidative Cl concentration of HCl in the simulated flue gas in OEC with the unit of ppm, and was determined by the mass flow meter and the standard HCl gas. βrepresented the unit conversion factor from µg/l (oxidative Cl concentration in the adsorption liquid) to ppm (non-oxidative Cl concentration of HCl in simulated flue gas in OEC) based on the 5


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experimental parameters during the adsorption process. 2.2.3 Inhibitory efficiency of oxidative Cl The inhibitory efficiency of oxidative Cl was used to evaluate the influence of H2O on Cl conversion from initial non-oxidative Cl (HCl) to oxidative Cl (Cl2 etc.) in the different simulated flue gases in OEC. The inhibitory efficiency of oxidative Cl was defined as follow: ∮ ∮

Inhibitory efficiency of oxidative Cl (Y ,%) =

∮

*100%

（3）

Where ∮( represented the conversion efficiency of oxidative Cl in the simulated flue gas without water in OEC；∮) represented the conversion efficiency of oxidative Cl in the simulated flue gas with water in OEC. 2.2.4 Consumption efficiency of oxidative Cl Consumption efficiency of oxidative Cl was used to evaluate the influence of SO2 and H2O on consuming the existing oxidative Cl simulated by Cl2 in the flue gas in OEC. The consumption efficiency of oxidative Cl was defined as:

Consumption efficiency of oxidative Cl(γ,%)=μ

+

)∗+

*100%

(4)

Where α( represented oxidative Cl concentration in the adsorption liquid of (CH3)2NC6H4N+KBr with the unit of µg/l (liquid), and indicated the average oxidative Cl concentration in each sampling tail gas from reaction furnace. α) represented the initial oxidative Cl concentration in the simulated flue gas in OEC with the unit of ppm, and was determined by the mass flow meter and the standard Cl2 gas. µ represented the unit conversion factor from µg/l (oxidative Cl concentration in the adsorption liquid) to ppm (the initial oxidative Cl concentration of Cl2 in the simulated flue gas in OEC) based on the experimental parameters during adsorption process.

3．RESULTS AND DISCUSSIONS 3.1. Influence of H2O on Hg0 oxidation in the simulated homogeneous flue gas in OEC 3.1.1. Influence of HCl and H2O on Hg0 oxidation in the simulated homogeneous flue gas in OEC Previous research showed that [10,18-20] halogen in flue gases (in which the dominant form was HCl) played a significant role on Hg0 oxidation. The reaction between Hg and Cl might occur 6


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through this pathway below: 2Hg+4HCl+O2⇆2HgCl2+2H2O

(5)

Based on our previous experimental results, it found that the reaction (5) proceeded depending on the temperature. Below 500℃, it was very difficult to form Hg2+ based on the reaction (5) in the simulated homogeneous flue gas in OEC, while, above 500℃, the reaction (5) easily proceeded to form Hg2+. As shown in Figure 2, the higher temperature has remarkably favourable influence on Hg0 oxidation efficiency. The Hg0 oxidation efficiency was higher at 900℃ and above than that at 600℃ and 700℃. For example, Hg0 oxidation efficiency was 28 % at 600℃and 74% at 1150℃ in terms of 60 ppm HCl. As shown in Figure 2, the concentration of HCl also had greatly impacted the Hg0 oxidation efficiency. It was apparent that the Hg0 oxidation efficiency increased with the increase of HCl concentration at different reaction temperature. For example, Hg0 oxidation efficiency increased sharply from the initial 29% to 79% when HCl concentration increased from 15ppm to 120ppm at 1150℃. Based on above experimental results, it could be concluded that the reaction temperature above 500℃ was necessary for reaction (5) proceeding in the simulated homogeneous flue gas in OEC as shown in Figure 2. In terms of the Hg0 oxidation efficiency, temperature and HCl concentration during the experiment, it appears that oxidative Cl, temperature and HCl concentration were interconnected. Cl and Cl2 only existed in high temperature regime, and HCl became the dominant form once the temperature decreased to 500℃ and below in flue gas. Based on the comprehensive analysis of the experimental above, a key intermediate reaction step was quite probable to proceed to complete the reaction (5). This intermediate was postulated to be the following reaction： 4HCl+O2⇆Cl2+2H2O

(6)

In the reaction (6), HCl was firstly oxidized to oxidative Cl or Cl2 with the generation of H2O by O2 at high temperature. Then Hg0 was further oxidized by oxidative Cl or Cl2. If this postulation was correct, high concentration H2O would affect Hg0 oxidation by hindering the reaction (6), and moreover, the oxidative Cl would be detected definitely during the experiment. Figure 3 showed the influence of H2O on Hg0 oxidation with different HCl concentration in the simulated flue gas in OEC. As shown in the Figure 3-a to 3-d, Hg0 oxidation efficiency decreased linearly with increasing of H2O concentration from 0% to 40% in the simulated OEC 7


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flue gas. For example, Hg0 oxidation efficiency decreased from 69% to 11% when H2O concentration increased from 0% to 40% in the simulated flue gas with 30 ppm HCl in OEC. These results directly showed that the Hg0 oxidation efficiency was obviously impacted by high H2O content, which might inhibit Hg0 oxidization, and the inhibition on Hg0 oxidization proceeded by inhibiting the generation of oxidative Cl2 in the reaction (6). 3.1.2. Influence of HCl and H2O on oxidative Cl generated in the simulated flue gas in OEC Based on the discussion of 3.1.1, high HCl concentration and high temperature could improve the Hg0 oxidation; high H2O concentration could inhibit Hg0 oxidation. However, during the process of Hg0 oxidation in the reaction (5), the chemical valence of chloride ion (Cl-) remained. Consequently, an intermediate step should proceed and it would convert HCl to oxidative Cl by the reaction (6), and then oxidative Cl would oxidize Hg0 to Hg2+; Simultaneously, the oxidative Cl was reduced to Cl-. According to the results and postulation above, the root cause of high H2O concentration inhibiting Hg0 oxidation was that the high H2O concentration could inhibit the conversion from HCl to oxidative Cl. In the simulated flue gas in OEC, the oxidative Cl was detected by using the standard method of HJ/T30-1999. It firstly investigated the influence of HCl concentration and temperature on generation of oxidizing Cl in the simulated OEC flue gas with high 30% H2O. As shown from Figure 4-a to 4-d, the conversion efficiency of oxidative Cl increased in different degree with the increase of HCl concentration. The higher temperature had a favourable influence on the conversion efficiency of oxidative Cl. It appeared that the temperature played a bigger role than the HCl concentration on the conversion efficiency of oxidative Cl based on Figure 4. As shown in Figure 4, although only a small proportion of HCl was converted to oxidative Cl, the absolute amount of generated oxidative Cl was much more than that of Hg0 and was enough to oxidize Hg0 in the chemical reaction balance system. The conversion efficiency of oxidative Cl was below 5% at 700℃ as shown in Figure 4-a. At the temperature of above 900℃， the conversion efficiency of oxidative Cl apparently increased with the increase of HCl concentration and the correlation became very clear especially at 1150℃. It indicated that HCl concentration also impacted the oxidative Cl in the higher temperature regime. By contrast with f Figure 4 and Figure 2, the oxidative Cl, temperature and HCl concentration shared the same tendency with Hg0 oxidation efficiency, temperature and HCl 8


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concentration. It could conclude that both the formation of oxidative Cl and the Hg0 oxidation efficiency benefited from the higher temperature and HCl concentration in the same manner. For example, the conversion efficiency of oxidative Cl rose from 7 % to 19 % and increased by about 2.7 times in Figure 4-d. Hg0 oxidation efficiency rose from 29% to 79% and also increased by about 2.7 times in Figure 2-e. Both experiments were conducted under the same condition with the increase of HCl concentration from 15ppm to 120ppm. The inhibitory efficiency of oxidative Cl was used to evaluate the influence of H2O on Cl conversion from the initial non-oxidative Cl (HCl) to the oxidative Cl (Cl2 etc.), and its definition was presented in Section 2.2.3. Figure 5 showed the influence of H2O on the inhibitory efficiency of oxidative Cl. The changes on the inhibitory efficiency of oxidative Cl appeared small within 15% with the increase of H2O concentration from 5% to 40% at a given HCl concentration. However, the average absolute values of inhibitory efficiency of oxidative Cl were as high as about 40%, 65%, 85% and 90% with HCl concentration of 15ppm, 30ppm, 60ppm and 120 ppm, respectively. It indicated that, firstly, the simulated flue gas in OEC with H2O would greatly inhibit the generation of oxidative Cl compared with that without H2O. Secondly, the HCl concentration change impacted the inhibitory efficiency of oxidative Cl apparently more strongly than the H2O concentration change. Accordingly, it could be inferred that HCl and H2O have a big difference in quantity. In this experiment, the magnitude of HCl concentration was part per million (ppm), while the magnitude of H2O concentration was percent (%). The H2O concentration would be higher but less sensitive than the HCl concentration during the reaction. In the other words, compared to the H2O concentration, the HCl concentration is dominant in this reaction. Based on the discussion above, it indicated that the inhibitory efficiency of oxidative Cl was obvious and high when H2O was present in the simulated flue gas in OEC, and it would keep rising with the increase of HCl concentration. It could be inferred that the presence of H2O could inhibit the generation of oxidative Cl, the inhibitory effect of which was mainly impacted by the change of HCl concentration. However, the change of H2O concentration imposed an important influence on the Hg0 oxidation efficiency as shown in Figure 3. It might be inferred that the change of H2O concentration affected the kinetic reaction of Hg0 oxidation by oxidative Cl, which needs further investigation on the kinetic process in other papers. 3.1.3. The influence of SO2 and H2O on Hg0 oxidation in the simulated flue gas in OEC 9


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The influence of SO2 on Hg0 oxidation with high H2O content in the simulated flue gas in OEC was shown in Figure 6. Here, the oxidative Cl was simulated by the Cl2. As shown in Figure 6, the Hg0 oxidation efficiency decreased obviously when SO2 concentration increased at different temperature. For example ,when the SO2 concentration increased from 50 ppm to 1000 ppm at 300℃, the Hg0 oxidation efficiency decreased from 52% to 12%. Which showed that SO2 inhibited the oxidation of Hg0 in the simulated flue gas in OEC. The previous research suggested [21] that the inhibitory effect of SO2 on Hg0 oxidation resulted from SO2 reacting with oxidative Cl. The reaction probably proceeded as follow: （7）

Cl2+SO2+H2O⇆2HCl+SO3

According to the reaction above, high H2O content could enhance this reaction. In order to confirm this postulation, the further experiment was conducted on the influence of SO2 and H2O on the consumption efficiency of oxidative Cl in the simulated flue gas in OEC, and the result was shown in Figure 7. The consumption efficiency of oxidative Cl rose rapidly with the increase of SO2 concentration at different temperatures. For example, the consumption efficiency of oxidative Cl increased from 41% to 87% with the increase of SO2 concentration from 50 ppm to1000ppm at 300℃. In terms of Figure 6 and Figure 7, it could conclude that the added SO2 consumed the oxidative Cl in the simulated flue gas in OEC with the high content of H2O, which inhibited the oxidation of Hg0. High temperature would also enhance the consumption efficiency of oxidative Cl by SO2 and H2O.

3.2. The influence of ash on Hg0 oxidation in the simulated heterogeneous flue gas in OEC The homogeneous reactions between Hg0 and other gas components (such as HCl, Cl2, SO2, O2, etc.) were subject to the limited dynamic of chemical reaction and the short residence time in the boiler tail. Nevertheless, many literatures presented that unburned carbon (UBC) of fly ash imposed an important influence on the Hg speciation

[22-25]

. Anton [23] also reported that fly ash

could impact the oxidation and adsorption of Hg. In order to discover the influence of H2O on Hg0 oxidation in the heterogeneous flue gas during, it made a simple simulated experiment to compare the Hg0 oxidation efficiency in 10


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homogeneous and heterogeneous flue gas in OEC. The ash from combustion of Maijiayu Coal, a popular coal used by power plants in the east of China, was used in a fixed bed to simulate the heterogeneous condition in this experiment. Table 2 showed the main ingredients of the ash (by X Ray Fluorescence) used in the experiment. Figure 8 showed the different Hg0 oxidation efficiencies between the simulated homogeneous and heterogeneous flue gas in OEC. The Hg0 oxidation efficiency increased obviously in the heterogeneous flue gas with ash in OEC. For example, under the same condition (30% H2O, 6% O2, 60ppm HCl, 700℃), the Hg0 oxidation efficiency was 37 % in the simulated homogeneous flue gas in OEC while the Hg0 oxidation efficiency was 80 % in the simulated heterogeneous flue gas with ash in OEC. The Hg0 oxidation efficiency rose by 43% due to the addition of ash. It indicated that ash could overcome the inhibitory effect of high H2O concentration on Hg0 oxidation. In other words, the inhibitory effect of H2O on Hg0 oxidation could be weakened in the heterogeneous flue gas in OEC. The previous research [25] showed that fly ash, as the medium and catalyst of reaction between Hg0 and flue gas components, could promote significantly Hg0 oxidation. The reason might be that UBC of ash have lots of active sites, which could not only promote the conversion from HCl to oxidative Cl but also provide favorable sites for Hg0 oxidation.

4．CONCLUSIONS In this work, the influence mechanism of H2O on Hg0 oxidation in the simulated flue gas during OEC on a fixed bed test bench was studied. Based on the experimental results and the discussion above, it was convincing that the generation of HgCl2 by the reaction between Hg0 and HCl needed the high temperature above 500℃ in the simulated homogeneous flue gas in OEC. The Hg0 oxidation efficiency increased with the increase of HCl concentration. A key intermediate reaction step was needed to complete the reaction between Hg0 and HCl. HCl was firstly oxidized to oxidative Cl with the generation of H2O by O2 at high temperature; then Hg0 was further oxidized by oxidative Cl. It was apparent that the Hg0 oxidation efficiency was impacted by high H2O content and it was because that the high H2O concentration could inhibit the conversion from HCl to oxidative Cl. The inhibitory efficiency of oxidative Cl was impacted by the change of HCl 11


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concentration much more than by the change of H2O concentration. However, the change of H2O concentration imposed a more important influence on the Hg0 oxidation efficiency, and it might because the change of H2O concentration impacted the kinetic reaction of Hg0 oxidation by oxidative Cl, which needs further investigation on kinetic process in the following work. The added SO2 consumed the oxidative Cl in the simulated flue gas with high H2O content in OEC, and consequently it resulted in a negative effect on the oxidation of Hg0. The Hg0 oxidation efficiency increased obviously in the heterogeneous flue gas with ash in OEC. Hence, the inhibitory effect of H2O on Hg0 oxidation could be weakened in the heterogeneous flue gas in OEC. This work would be helpful to reveal the mechanism of high H2O concentration on the inhibition of Hg oxidation. It was insightful on understanding the transformation of Hg species in the flue gas in OEC, and was significant for developing Hg control technology for the flue gas in OEC and reducing Hg pollution emission from coal-fired power plants.

AUTHOR INFORMATION Corresponding Author 1：： Chang-xing Hu Fax：+86 0574-88130650, E-mail:

[email protected]

Corresponding Author 2：： Rui-tang Guo E-mail:

[email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This research was supported by the Chinese National Natural Science Foundation (No: 51306162) and Zhejiang Provincial Natural Science Foundation of China (No: LY13E060008).

12


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Phys. Chem. A 2009, 113 (24), 6633-6639. [14] Wilcox, J.; Okano, T. Ab initio-based mercury oxidation kinetics via bromine at postcombustion flue gas conditions. Energy & Fuels 2011, 25 (4), 1348-1356. [15] Wilcox, J.; Robles, J.; Marsden, D. C. J.; Blowers, P. Theoretically predicted rate constants for mercury oxidation by hydrogen chloride in coal combustion flue gases. Environ. Sci. Technol.2003, 37 (18), 4199–4204. [16] Van, O. B.; Fry, A.; Adams, B.; et al. Mercury measurements from pilot-scale furnaces under air- And oxy-fired conditions. Air and Waste Management Association - Power Plant Air Pollutant Control "MEGA" Symposium 2012, 1: 562-579. [17] Van O, B.; Fry, A.; Adams, B.; Bool, L. Mercury speciation and emission from pilot-scale PC furnaces under air- and oxy-fired conditions. 28th Annual International Pittsburgh Coal Conference 2011, PCC 2011(3), 1854-1864. [18] Liu, Y.H.; Zheng, C.G.; You, X.Q.; Qiu, J.R. Effect of chlorine on the speciation of mercury in flue gases. Acta Scien. Circum. 2001, 1, 69-73. [19] Zhao, B.; Liu, X.W.; Si, J.P.; et al. Impact of SO2 and H2O on mercury removal by activated Carbon in simulated flue gas of oxy-coal combustion. Proceedings of the CSEE 2013, 33(17), 24-29. [20] Zhao, L.P. Kinetics study of homogenous and heterogeneous mercury oxidation on the surface of unburned carbon by halogen in coal-fired flue gas. Huazhong University of Science& Technology. 2014. [21] Wu, H. Experimental and mechanism study on mercury emission and transformation during coal combustion. Huazhong University of Science& Technology. 2011. [22] Hower, J.C.; Senior, C.L.; Suuberg, E.M.; et al. Mercury capture by native fly ash carbons in coal-fired power plants. Prog. Energy Combust. Sci. 2010, 36(4), 510-529. [23] López-Antón, M.A.; Abad-Valle, P.; Díaz-Somoano, M.; et al. The influence of carbon particle type in fly ashes on mercury adsorption. Fuel 2009, 88(7), 1194-1200. [24] Zhong, L.C., Zhang, Y.S., Liu, Z.; et al. Study of mercury adsorption by selected Chinese coal fly ashes. J. Therm. Anal. Calorim. 2014, 116(3), 1197-1203. [25] Luo, J.J.；Zhang, L.D.；Huang, H.W.；Zhang, J.R. Effects of flue gas components and fly ash on mercury oxidation. Journal of University of Science and Technology Beijing 2011, 06, 771-776. 14


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Energy & Fuels

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List of tables Table 1 Concentration range of each simulated flue gas component used in the experiment Table 2 The main ingredients of ash used in the experiments

List of Figures Figure 1. Schematic diagram of the experimental system Figure 2. The influence of HCl and temperature on Hg0 oxidation in the simulated OEC flue gas with 30% H2O Figure 3. The influence of H2O on Hg0 oxidation in the simulated OEC flue gas with different HCl Figure 4. The influence of HCl and temperature on oxidative Cl generated in the simulated OEC flue gas with 30% H2O Figure 5. The influence of H2O on the inhibitory efficiency of oxidative Clin the simulated OEC flue gas with different HCl Figure 6. The influence of SO2 on Hg0 oxidation in the simulated OEC flue gas with 30% H2O Figure 7. The influence of SO2 on the consumption efficiency of oxidative Cl in the simulated OEC flue gas with 30% H2O Figure 8. Different Hg0 oxidation efficiency between the homogeneous and heterogeneous flue gas condition

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Energy & Fuels

Table 1 Concentration range of each simulated flue gas component used in the experiment Component

Concentration unit

0

Concentration range

3

Hg

µg/m

18±2

O2

%.

6

H2O

%

0, 5, 10, 20, 30, 40

HCl

ppm

15, 30, 60, 120

Cl2

ppm

10

SO2

ppm

50, 100, 150, 200, 600, 1000

CO2

%.

Balance

Table 2 The main ingredients of ash used in the experiments Coal type

SiO2

Al2O3

Fe2O3

CaO

C

Maijiayu

43.74%

46.89%

2.90%

1.80%

0.36%

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Na2O 0.52%

Energy & Fuels

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MFC 3

O2 CO2

SO 2

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6

MFC 3

MFC N2

6 4

3

8

MFC 3

H2O

11

HCl/Cl2 MFC 3 5 9

1 2 6 ven

7

10

Figure 1. Schematic diagram of the experimental system 1：Flow controller；2：Temperature controller；3：The simulated gases； 4：Mixed gas box；5：Reaction furnace ；6：Electric heating tape ；7：Activated carbon fixed adsorption；8：Mercury vapor generator ；9：Data record computer；10：Mercury and oxidizing Cl analyser ；11：Water injector

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100

600℃

Hg oxidation efficiency (%)

80

60

40

700℃

80

60

40

0

0


100

20

0

20

0 0

15

30

45

60

75

90

105

120

135

0

15

30

60

75

90

105

120

135

105

120

135

2-b 100


900℃

80

60

1000℃

80

60

40

0

40

0


100

45

HCl concentration （ ppm）

HCl concentration （ ppm） 2-a

20

20

0

0 0

15

30

45

60

75

90

105

120

135

0

HCl concentration （ ppm） 2-c 100

15

30

45

60

75

90

HCl concentration （ ppm） 2-d

1150℃

80

60

40

0


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Energy & Fuels

20

0 0

15

30

45

60

75

90

105

120

135

HCl concentration （ ppm） 2-e

Figure 2. The influence of HCl and temperature on Hg0 oxidation in the simulated OEC flue gas with 30% H2O 0 3 [Hg =18±2 µg/m ; O2=6%; HCl=15/30/60/120ppm; H2O=30%; CO2=equilibrium gas；T=600、700、 900、1000、1150℃]

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Energy & Fuels

100

HCl=15ppm

80

HCl=30ppm


80

60

40

60

40

0

0


100

20

20

0 -5

0

5

10

15

20

25

30

35

40

0

45

-5

0

5

H2O content (%) 3-a

10

15

20

25

30

35

40

45

H2O content (%) 3-b

100

100

HCl=60ppm

HCl=120ppm

80


80

60

60

40

0

40

0


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20

20

0

0 -5

0

5

10

15

20

25

30

35

40

-5

45

0

5

10

15

20

25

30

35

40

45

H2O content (%) 3-d

H2O content (%) 3-c

Figure 3. The influence of H2O on Hg0 oxidation in the simulated OEC flue gas with different HCl [Hg0=18±2 µg/m3, O2=6%; HCl=15/30/60/120ppm; H2O=0/5%/10%/20%/30%/40%; CO2=equilibrium gas; T=900℃]

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40

700

Conversion efficiency of oxidizing Cl (%)


40 35 30 25 20 15 10 5

900

35 30 25 20 15 10 5 0

0 0

15

30

45

60

75

90

105

120

0

135

15

30

40

40

1000


35 30 25 20 15 10 5 0 0

15

30

45

60

75

90

45

60

75

90

105

120

135

105

120

135

HCl concentration（ ppm) 4-b

HCl concentration（ ppm) 4-a


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

105

120

1150

35 30 25 20 15 10 5 0 0

135

15

30

45

60

75

90

HCl concentration（ ppm) 4-d

HCl concentration（ ppm) 4-c

Figure 4. The influence of HCl and temperature on oxidative Cl generated in the simulated OEC flue gas with 30% H2O [O2=6%; HCl=15/30/60/120ppm; H2O=30%; CO2=equilibrium gas]

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Energy & Fuels

100

HCl=15ppm

Inhibitory efficiency of oxidizing Cl (%)


100

80

60

40

20

HCl=30ppm

80

60

40

20

0

0 0

5

10

15

20

25

30

35

40

45

0

5

10

H2O content (%) 5-a 100

15

20

25

30

35

40

45

H2O content (%) 5-b 100

HCl=60ppm



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80

60

40

20

HCl=120ppm

80

60

40

20

0

0 0

5

10

15

20

25

30

35

40

0

45

5

10

15

H2O content (%) 5-c

20

25

30

35

40

45

H2O content (%) 5-d

Figure 5. The influence of H2O on the inhibitory efficiency of oxidative Clin the simulated OEC flue gas with different HCl [O2=6%; HCl=15/30/60/120ppm; H2O=5%/10%/20%/30%/40%; CO2=equilibrium gas; T=900℃]

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100

100

100

200

80

Hg oxidation efficiency （ % ）

0

60

40

20

0

Hg oxidation efficiency （ %）

80

0

60

40

20

0 0

100

200

300

400

500

600

700

800

900

1000 1100

0

100

200

300

SO2 concentration （ ppm） 6-a 100

100

300

500

600

700

800

900

1000 1100

400

80


60

40

20

0

0

Hg oxidation efficiency（ %）

400

SO2 concentration （ ppm） 6-b

80

60

40

20

0

0 0

100

200

300

400

500

600

700

800

900

0

1000 1100

100

100

200

300

400

500

600

700

800

900

1000 1100

SO2 concentration （ ppm） 6-d

SO2 concentration （ ppm） 6-c 500

80

60

40

20

0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0 0

100

200

300

400

500

600

700

800

900

1000 1100

SO2 concentration （ ppm） 6-e

Figure 6. The influence of SO2 on Hg0 oxidation in the simulated OEC flue gas with 30% H2O [Hg0=18±2 µg/m3, O2=6%; Cl2=10ppm; H2O=30%; SO2=50/100/150/200/600/1000ppm; CO2=equilibrium gas]

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Energy & Fuels

100

100

Consumption efficiency of oxidizing Cl （ %）

Consumption efficiency of oxidizing Cl（ %）

100

80

60

40

20

0

200

80

60

40

20

0 0

100

200

300

400

500

600

700

800

900

1000 1100

0

100

200

300

400

SO2 concentration（ ppm） 7-a 300

100

80

60

40

20

0 0

100

200

300

400

500

600

700

800

900

600

700

800

900

1000 1100

900

1000 1100

400

80

60

40

20

0

1000 1100

0

SO2 concentration（ ppm） 7-c 100

500

SO2 concentration（ ppm） 7-b

Consumption efficiency of oxidizing Cl（ % ）

Consumption efficiency of oxidizing Cl（ %）

100

Consumption efficiency of oxidizing Cl （ %）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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100

200

300

400

500

600

700

800

SO2 concentration（ ppm） 7-d

500

80

60

40

20

0 0

100

200

300

400

500

600

700

800

900

1000 1100

SO2 concentration（ ppm） 7-e

Figure 7. The influence of SO2 on the consumption efficiency of oxidative Cl in the simulated OEC flue gas with 30% H2O [O2=6%; H2O=30%; Cl2=10ppm; SO2=50/100/150/200/600/1000ppm; CO2=equilibrium gas]

24


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100

100

homogeneous-600 heterogeneous-600

80

homogeneous-700 heterogeneous-700

80


60

40

20

0

0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0

60

40

20

0 0

15

30

45

60

75

90

105

120

135

0

HCl concentration （ ppm） 0 8-a

15

30

45

60

75

90

105

120

135

HCl concentration （ ppm） 8-b

Figure 8. Different Hg oxidation efficiency between the homogeneous and heterogeneous flue gas condition [Hg0=18±2 µg/m3, O2=6%; HCl=15/30/60/120ppm; H2O=30%; CO2=equilibrium gas; Mash=50mg]

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Influence of H2O on Hg0 Oxidation in the Simulated Flue Gas in

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