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Activated Carbon for Capturing Hg in Flue Gas under O2/CO2 Combustion Conditions. Part A: Experimental and Kinetic Study Hui Wang, Shen Wang, Yufeng Duan, Ya-ning Li, Yuan Xue, and Zhanfeng Ying Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03380 • Publication Date (Web): 12 Jan 2018 Downloaded from http://pubs.acs.org on January 13, 2018

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Activated Carbon for Capturing Hg in Flue Gas under O2/CO2 Combustion Conditions. Part A: Experimental and Kinetic Study Hui Wang*, a, b , Shen Wangc, Yufeng Duan*, b, Ya-ning Lib, Yuan Xue d, Zhanfeng Ying a a

School of Energy and Power Engineering, Nanjing University of Science and

Technology, Nanjing, 210094, China. b

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,

Southeast University, Nanjing, 210096, China. c

School of Chemical and Material Engineering, Nanjing Polytechnic Institute, Nanjing

210048, China. d

Hua-Neng Nanjing Jinling Power Generation Co. Ltd, Nanjing, 210034, China.

KEYWORDS. Mercury; Oxy Combustion; O2/CO2; Adsorption Mechanism; Kinetic Model

ABSTRACT: This study evaluated the mercury sorption by activated carbon(AC) under the O2/CO2 atmosphere in a fixed-bed reactor. Effects of the oxygen concentration on the mercury sorption efficiency under both the air and oxy-fuel atmosphere were explored.

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The kinetic studies were also used to predict the mercury sorption process by the pseudofirst-order model and the intraparticle diffusion model in this work. The experimental results indicated that the mercury sorption capacity of AC increased with the increased oxygen concentration under both the air and oxy-fuel atmosphere. Oxygen might increase the oxidation of mercury by the Mars-Maessen way. A high CO2 concentration promoted AC to generate more active sites under the oxy-fuel atmosphere. Besides, the results of the kinetic analysis illustrated that the pseudo-first-order model showed a better agreement with the experimental data compared to the intraparticle diffusion model. These experimental and theoretical results in this work are helpful in mercury capture under the oxy-fuel atmosphere.

1. INTRODUCTION More than 170 countries signed the Paris Agreement to make a proof for the carbon emission reduction1, and China is going to reduce the carbon emission per unit of GDP in 2020 by 40%-45% from its 2005 level2. Thus, it is of great significance to develop new technologies for the carbon emission control3. The oxy-fuel combustion is one of the most promising technologies helpful in controlling the carbon emission4. Ha-Na Jang’s observations5 showed that CO2 concentration was higher and steam was larger under oxy-fuel than that of air-fuel combustion; the findings from Gao6 suggested that NOx concentration was lower under oxy-fuel combustion due to the attack by CO; high partial pressure of CO2 can affect the formation of SOx from Duan’s results7; the reactivity of char combustion can be affected by H2O gasification reaction under oxy-fuel combustion8. Compared to the air atmosphere, the level of the flue gas components and combustion characteristics ( such as


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CO25, NOx6, SOx 7 and H2O8, 9 and so on) under the oxy-fuel atmosphere are different, leading to a different theory and mechanism of the mercury control4. There have been some reports about the mercury speciation under the oxy-fuel atmosphere. Yoshiaki Mitsui10 found that the Hg concentration was higher under the oxyfuel atmosphere than that under the air atmosphere at the SCR inlet through the experiments on the Babcock-Hitachi’s 1.5MWth combustion condition. By the thermodynamic modeling, Yang11 concluded that the primary mercury specie was Hg0 under the oxy-fuel atmosphere. Our recent studies also indicated that the Hg2+ percentage was higher under the oxy-fuel atmosphere compared to that under the air atmosphere. Besides, mercury behaviors under the oxy-fuel atmosphere were studied by other researchers12-14. As well known, mercury pollution is a grave threat to human health and environment15,

16

. Especially, mercury can destroy the CO2 storage system by the

amalgam reaction17. Chinese power plant air pollutants emission standard (GB 132232011)18, 19, which was published in 2011, concluded that mercury should be controlled to levels below detectable limits for the safety of the CO2 storage system. Thus, it is essential to explore the suitable sorbents for the mercury removal. There exist three primary forms of mercury in the flue gas20: elemental mercury (Hg0), oxidized mercury (Hg2+) and particulate-bound mercury(Hgp). Hg0 is hard to remove due to its insolubility and volatility, whereas Hg2+ and Hgp can be removed due to their physical characteristics. Therefore, it is critical to know how to remove the elemental mercury.


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AC has been widely chosen as a sorbent for the mercury control in the laboratory experiment and the coal-fired power plant. Zhou et al.21 studied the mercury sorption by AC and AC-Br (modified AC by 1% NH4Br) in a fixed-bed reactor. Results showed that temperature could influence the mercury sorption rate, and AC-Br showed a better performance than AC at 150 oC and 200 oC. Zhong et al.22 investigated the mercury sorption in the AC modified by the iodine steam vapor (AC-I). Results showed that the mercury sorption capacity of AC-I was much higher than that of AC-Br. Zhao et al.23 explored the effects of CO2, SO2 and H2O on the mercury control by AC under the oxyfuel atmosphere in a fixed-bed reactor. Results indicated that a high CO2 concentration could not change the capacity of AC for mercury removal, whereas SO2 and H2O inhibited its capacity for mercury removal. Though the Hg0 sorption by AC has been widely studied, researches about the mechanism of mercury sorption by AC under the oxy-fuel atmosphere are limited. As the mercury capture under the oxy-fuel atmosphere varies greatly from the air atmosphere2427

, the mercury sorption by AC under the oxy-fuel atmosphere needs to be further studied. The mercury sorption mechanism by AC, which includes the physical sorption and

the chemical sorption, is extremely complicated. Mercury removed by AC is divided by three steps22: mass transfers from the outer membrane, intraparticle diffusion, and Hg sorption on the active sites. Hude et al.28 evaluated the mercury sorption process by the kinetic study and found that the pseudo-first-order sorption kinetic model could describe the sorption process. A.Fuente-Cuesta et al.29 used the kinetic model to predict the mercury adsorption mechanism by sorbents, and the results indicated that the YoonNelson model showed a better explanation for mercury capture. There were some


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reports30-32 about the kinetic models to explore the mercury adsorption mechanism by AC. However, the dynamic mechanism of mercury sorption by AC under the oxy-fuel atmosphere is still limited. Thus, it is essential to conduct the experimental and kinetic study of mercury sorption by AC under the oxy-fuel atmosphere. This paper conducted the experimental and kinetic study of the mercury capture by AC under the oxy-fuel atmosphere. The experiments were conducted in a fixed-bed reactor and the kinetic analysis of experimental results was also carried out to explore the mercury sorption mechanism. All of these results contribute to a better understanding of the mercury sorption process. Besides, the study in this work is beneficial for developing an independent mercury control technology under the oxy-fuel atmosphere to the energy and environmental industry. 2. EXPERIMENTAL SECTION 2.1 Sorbent. The commercial activated carbon was selected in this work as the mercury sorbent. It was produced by crushing, grinding and screening, with the particle diameter of about 0.075-0.08 µm. Then they were dried in an oven at 45 oC for 12 h. The ultimate and structural analysis of activated carbon was listed in Table 1. As shown in Table 1, the specific surface area and the micropore were excellent for the sorbent. 2.2 Experimental Setup. A bench-scale device was established in this experiment, as shown in Figure 1. The experimental setup mainly consisted of a gas distribution device, a mercury vapor generator, a vertical tube furnace reaction device (1100 mm length with an outer diameter of 20 mm), a mercury online measuring instrument and an exhaust gas purification device. Mercury was measured by the EMP-2 mercury vapor monitor (Nippon Instruments Corporation., Japan).


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The total gas flow rate was 2000 ml/min. The carrier gas rate of the Hg0 vapor was 200 ml/min. The sorption experiments were conducted for 2 h at 120 oC, by packing 200 mg sorbent in the middle of the tube under different conditions with the mercury vapor concentration of 40±1 µg/m3. The Hg0 vapor was generated by a standard Hg0 permeation tube (VICI Metronics Inc., USA). The baseline sorbent experiments were conducted for 2 h at 120 oC by packing 200 mg sorbent under the O2/N2 and O2/CO2 atmosphere with the mercury vapor concentration of 0 µg/m3. The treated sorbent was analyzed by GC-FTIR (Thermo Nicolet Corporation, USA). 2.3 Evaluation of sorbents. 2.3.1 Breakthrough Rate η. The breakthrough rate (η) was calculated from the following equation: 0 Cout η = 0 ×100% Cin

Eq.1

Where, η is the breakthrough rate; Cin0 is the mercury concentration at the inlet of the reactor, µg/m3; Cout0 is the mercury concentration at the outlet of the reactor, µg/m3. 2.3.2 The Sorption Capacity. The sorption capacity of the sorbent at ‘t’ min (qt) was calculated from the following equation ct + cti +∆t   q t = ∫ [(c 0 − c) V/ m]d τ = (V/ m) ∫ ( c 0 − c ) d τ ≈ (V/ m)∑  c0 − i ∆t 0 0 2 τ =0   t

t

ti

Eq.2

Where, qt is the sorption capacity of the sorbent at ‘t’ min, µg Hg/g sorbents;


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V is the volume flow rate of the simulated flue gas, m3/min; m is the mass of the sorbent, g; ∆t is the time interval between the two sampling points, min; t is the sorption time, min;

cti is the mercury concentration at the i sampling point, µg/m3; cti +∆t is the mercury concentration at the i+1 sampling point, µg/m3. 2.4 Sorption Kinetic Models and Parameters. The amount of the absorbed Hg and the rate of the absorbed Hg were two key factors for estimating the properties of the sorbent. Kinetic models could display the sorption process. This work adopted the pseudo-firstorder kinetic model and the intraparticle diffusion kinetic model to explore the mercury sorption mechanism. The pseudo-first-order kinetic model, derived from Lagergren equation33, was used to calculate the mercury migration on the surface of AC. This model was expressed as: dq = k1 ( qe − q ) dt

Eq.3

By integrating the boundary condition t = 0, q = 0; t = t, q = q , Eq.3 was transformed to

ln(qe − q) = ln qe − k1t

Eq.4

Another form of Eq.4 was

q = qe (1 − e−tk1 )

Eq.5

Where, qe is the equilibrium absorbed amount, µg/g; q is the absorbed amount at time t, µg/g;


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k1 is the kinetic constant of the pseudo-first-order kinetic equation. The intraparticle diffusion kinetic model, created by Weber and Morris34, was applied in exploring the mercury sorption in the interior of AC, This model was expressed as: q = k p t 1/ 2 + c

Eq.6

Where, q is the absorbed amount at time t, µg/g; kp is the kinetic constant of the intraparticle diffusion kinetic equation; c is the boundary layer effect. 3. RESULTS AND DISCUSSION 3.1 Baseline Sorbent Test. To illustrate the effects of the baseline atmosphere on the chemical structure of the sorbent, the blank experiments under different atmospheres without mercury were tested in the first step. From Figure 2, it could be observed that AC, AC-O2/N2 (sorbent treated under the O2/N2 atmosphere for 2h at 120 oC) and AC-O2/CO2 (sorbent treated under the O2/CO2 atmosphere for 2h at 120 oC) had the similar FTIR spectra and spectra intensity, which indicated that the chemical structure of these sorbents was similar, and the type and the number of surface functional groups were almost same. Hui Wu35 investigated the baseline Hg0 oxidation by experiments with different baseline gas (N2, O2/N2, CO2, O2/CO2), and found that the Hg0 oxidation couldn’t occur at a temperature lower than 873 K. Minghou Xu36 obtained a similar conclusion by using detailed chemical kinetics: the highest Hg0 oxidation rate by O2 alone was only 1.5%-6%. In summary, the baseline atmosphere alone had little impact on the chemical structure of AC sorbent.


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3.2 Effect of Oxygen Concentration on Mercury Breakthrough Rate under O2/N2 Atmosphere. The oxygen concentration was one of the key factors influencing the mercury breakthrough rate37. The experimental results of the mercury breakthrough rate under the O2/N2 atmosphere provided a significant guideline to analyze the mercury breakthrough rate under the O2/CO2 atmosphere. As shown in Figure 3, the Hg0 breakthrough rate of AC increased with time, but reduced with the oxygen concentration under the O2/N2 atmosphere. The Hg0 breakthrough rate of AC was limited to 57.23%64.68% after the 120 min sorption experiment, with the lowest Hg0 breakthrough rate of about 20% in the first 10 min. From Figure 2, it could be inferred that O2 might increase the mercury oxidation through the Mars-Maessen way, as shown in R1-R538-40. Moreover, the enriched oxygen could generate much more oxygen-containing functional groups which increased the sorption rate. Thus, a high O2 concentration intensified the mercury sorption capacity of AC.

Hg (g) → Hg (ads)

R1

Hg (ads) + M xOy → HgO(ads) + M xOy −1

R2

M xOy −1 + 1 O2 → M xOy 2

R3

HgO(ads) → HgO( g )

R4

HgO(ads) + M xOy → HgM xOy +1

R5

3.3 Effect of Oxygen Concentration on Mercury Breakthrough Rate under O2/CO2 Atmosphere. Compared to the O2/N2 atmosphere, the CO2 concentration was a key factor on the mercury control under the O2/CO2 atmosphere41,


42

. A high CO2

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concentration could generate the reducing atmosphere43, which was not beneficial for the mercury removal. As shown in Figure 4, the Hg0 breakthrough rate in the sorption experiment was limited to 38.17%-50.79% after the 120 min sorption experiment, with the lowest Hg0 breakthrough rate of about 6.5% in the first 10 min. The results from Figure 4 showed that the mercury breakthrough rate decreased with the decrease of the CO2 concentration under the O2/CO2 atmosphere. It could be indicated that CO2 inhibited the mercury removal by AC under the O2/CO2 atmosphere. Besides, the O2 concentration could increase the sorption rate of AC, indicating that R1-R5 was still the dominant mechanism. 3.4 Effect of Atmosphere on Mercury Breakthrough Rate. Though the oxy-fuel combustion technology had a lot of advantages, the difference of the mercury control under the O2/CO2 atmosphere from that under the air atmosphere was still unclear. Effects of the atmosphere on the mercury breakthrough rate were shown in Figure 5. The results illustrated that the mercury breakthrough rate under the O2/CO2 atmosphere was lower than that under the O2/N2 atmosphere with the same oxygen concentration. As discussed in the published reports35, 44 , CO2 couldn’t oxidize mercury directly. It could be inferred that a high CO2 concentration promoted AC to generate more active sites43, which could help to adsorb more mercury in the form of the physical sorption. Results were contradictory to the analysis from Figure 4, thus effects of CO2 on the mercury removal might be the competition of two mechanisms. In summary, compared to the O2/N2 atmosphere, CO2 promoted the sorption rate of mercury under the O2/CO2 atmosphere.


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3.5 Kinetic Analysis of Mercury Uptake on AC by Pseudo-First-Order Kinetic Model. In this work, the primary kinetic models were used to explore the mechanism of the mercury control by activated carbon. The dynamic equation was calculated to compare with the experimental data, and the correlation coefficient R2 represented the difference between the calculated curves and the experimental data. A high value of R2 meant a good prediction of the kinetic model to the experimental data. Figure 6 and Figure 7 showed the equilibrium absorbed capacity with different oxygen concentrations under the O2/N2 and O2/CO2 atmosphere by the pseudo-first-order kinetic model. The parameters involved were listed in Table 2. In Figure 6, it illustrated a good agreement between the calculated curves by the pseudo-first-order kinetic model and the experimental data. The correlation coefficient R2 was higher than 0.9997, which revealed that the pseudo-first-order kinetic model could perfectly described the mercury sorption process by AC under the O2/N2 atmosphere. The slope of tangent represented the mercury sorption rate constant k1t at t min. From Figure 6, it could also be found that k1t decreased with time. As shown in Table 1, as the oxygen concentration increased, k1 decreased at first and then increased, which indicated that the oxygen concentration could affect the kinetic constant, and 4% O2 under the O2/N2 atmosphere exhibited the highest k1 value (0.00361). Besides, it also revealed that the oxygen concentration promoted the mercury sorption by AC within the range of 4%-8%, whereas it inhibited the mercury sorption by AC within the range of 8%-10%. The value of R2 decreased with different oxygen concentrations, which indicated that effects of the oxygen concentration on the external mass transfer were negative under the O2/N2 atmosphere. These results agreed well with the prior reports21, 45.


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Figure 7 illustrated that the calculated curves agreed well with the experimental data under the O2/CO2 atmosphere. The correlation coefficient R2 was higher than 0.9997, which revealed that the pseudo-first-order kinetic model could perfectly describe the mercury sorption process under the O2/CO2 atmosphere. There were massive fluctuations in the kinetic constant k1 when the O2 concentration changed from 4% to 10% and k1 changed from 0.0045 min-1 to 0.00106 min-1, which showed that the oxygen concentration inhibited the mercury sorption by AC. Thus, effects of the oxygen concentration on the external mass transfer were positive under the O2/CO2 atmosphere. 3.6 Kinetic Analysis of Mercury Uptake on AC by Intraparticle Diffusion Kinetic Model. The intraparticle diffusion was the process of mercury molecules on the surface of AC moving to its inner active site, with the concentration gradient and van der Waals interaction contributing to this phenomenon. Results were displayed in Figure 8 and Figure 9, with parameters of kp, c, R2 displayed in Table 2. Compared to the pseudo-first-order kinetic model, both of the two figures showed that the correction efficiency by the intraparticle diffusion kinetic model was lower than 0.977. From Figure 8 and Figure 9, deviation could be observed between the calculated curves and the experimental data. Therefore, it illustrated that this model might not be suitable to display the mercury sorption by AC, and the intraparticle diffusion was not the only rate-controlling step46. As shown in Table 2, the kinetic constant kp increased with the increased oxygen concentration under both the two atmospheres, with a higher kp under the oxy-fuel atmosphere, which indicated that the intraparticle diffusion rate increased with the


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increased oxygen concentration, and the intraparticle diffusion rate was greater under the oxy-fuel atmosphere. The slope of tangent represented the mercury sorption rate constant kpt at t min by the intraparticle diffusion, and kpt decreased with time. kpt showed a similar trend with k1t, indicating that the mercury sorption process was influenced by both the surface diffusion and the intraparticle diffusion. The surface diffusion was the dominant sorption form due to active sites on the surface of AC at the beginning. Then, the intraparticle diffusion became the main sorption mechanism, as active sites of AC were occupied21. 4. CONCLUSION Effects of the oxygen concentration on the mercury sorption by AC under the air and oxy-fuel atmosphere have been investigated. A series of experimental tests has been conducted in a fixed-bed reactor, and the kinetic analysis of the experimental results has been carried out by the pseudo-first-order model and the intraparticle diffusion kinetic model. A high O2 concentration was beneficial for the mercury sorption capacity of AC under the O2/N2 atmosphere, whereas CO2 inhibited the mercury removal under the O2/CO2 atmosphere. Moreover, O2 might increase the oxidation of mercury by the MarsMaessen way under both the O2/N2 and O2/CO2 atmosphere. The sorption process obeyed the pseudo-first-order kinetic model. The intraparticle diffusion, which was not the only rate-controlling step, might not be suitable to display the mercury sorption by AC. Effects of the oxygen concentration on external mass transfer were negative under the O2/N2 atmosphere, but were positive under the O2/CO2 atmosphere. The intraparticle


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diffusion rate increased with the increased oxygen concentration under both the O2/N2 and O2/CO2 atmosphere. Besides, the intraparticle diffusion rate was greater under the oxy atmosphere than that under the air atmosphere. AUTHOR INFORMATION Corresponding Author *E-mail for Hui Wang: [email protected]. Tel/Fax: 86+25-84314965. *E-mail for Yufeng Duan: [email protected]. Tel/Fax: +86-025-83795652. NOTES The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (No 51706104 ); the Natural Science Foundation of Jiangsu Province (BK20170849); the National Key R&D Program of China (2016YFC0201105). REFERENCES (1).

Rogelj, J.; Den Elzen, M.; Höhne, N.; Fransen, T.; Fekete, H.; Winkler, H.;

Schaeffer, R.; Sha, F.; Riahi, K.; Meinshausen, M., Paris Agreement climate proposals need a boost to keep warming well below 2C. Nature 2016, 534, (7609), 631-639. (2).

Yuan, J.; Hou, Y.; Xu, M., China's 2020 carbon intensity target: Consistency,

implementations, and policy implications. Renewable and Sustainable Energy Reviews 2012, 16, (7), 4970-4981. (3).

Zhao, C.; Chen, X.; Zhao, C., CO2 absorption using dry potassium-based sorbents

with different supports. Energ Fuel 2009, 23, (9), 4683-4687.


S14

Page 15 of 32 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

(4).

de las Obras-Loscertales, M.; Izquierdo, M.; Rufas, A.; de Diego, L.; García-

Labiano, F.; Abad, A.; Gayán, P.; Adánez, J., The fate of mercury in fluidized beds under oxy-fuel combustion conditions. Fuel 2016, 167, 75-81. (5).

Jang, H.-N.; Kim, J.-H.; Back, S.-K.; Sung, J.-H.; Yoo, H.-M.; Choi, H. S.; Seo,

Y.-C., Combustion characteristics of waste sludge at air and oxy-fuel combustion conditions in a circulating fluidized bed reactor. Fuel 2016, 170, 92-99. (6).

Gao, Y.; Tahmasebi, A.; Dou, J.; Yu, J., Combustion characteristics and air

pollutant formation during oxy-fuel co-combustion of microalgae and lignite. Bioresource Technol 2016, 207, 276-284. (7).

Duan, Y.; Duan, L.; Anthony, E. J.; Zhao, C., Nitrogen and sulfur conversion

during pressurized pyrolysis under CO2 atmosphere in fluidized bed. Fuel 2017, 189, 98106. (8).

Xu, J.; Su, S.; Sun, Z.; Si, N.; Qing, M.; Liu, L.; Hu, S.; Wang, Y.; Xiang, J.,

Effects of H2O Gasification Reaction on the Characteristics of Chars under Oxy-Fuel Combustion Conditions with Wet Recycle. Energ Fuel 2016, 30, (11), 9071-9079. (9).

Wang, H.; Duan, Y.; Li, Y.-n.; Xue, Y.; Liu, M., Prediction of Synergic Effects of

H2O, SO2, and HCl on Mercury and Arsenic Transformation under Oxy-Fuel Combustion Conditions. Energ Fuel 2016, 30, (10), 8463-8468. (10).

Mitsui, Y.; Imada, N.; Kikkawa, H.; Katagawa, A., Study of Hg and SO3 behavior

in flue gas of oxy-fuel combustion system. Int J Greenh Gas Con 2011, 5, S143-S150. (11).

Yang, J.; Zhao, Y.; Zhang, J.; Zheng, C., Chapter 7 - Mercury Behavior and

Retention in Oxy-fuel Combustion. In Oxy-Fuel Combustion, Academic Press: 2018; pp 151-170.


S15

Energy & Fuels 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

(12).

Page 16 of 32

Gao, Q.; Li, S.; Xu, Y.; Yao, Q., Effect of CO2/H2O on the incipient ultrafine

particulate matter formation in oxy-fuel combustion of high-sodium lignite. Energ Fuel 2017. (13).

Li, W.; Xu, M.; Li, S., Calcium sulfation characteristics at high oxygen

concentration in a 1MWth pilot scale oxy-fuel circulating fluidized bed. Fuel Process Technol 2018, 171, 192-197. (14).

Zhang, L.; Yi, B., Pulverized Coal Combustion Characteristics in Oxy-fuel

Atmospheres. In Oxy-Fuel Combustion, Elsevier: 2018; pp 63-85. (15).

Liu, Y. x.; Zhang, J., Photochemical oxidation removal of NO and SO2 from

simulated flue gas of coal-fired power plants by wet scrubbing using UV/H2O2 advanced oxidation process. Ind Eng Chem Res 2011, 50, (7), 3836-3841. (16).

Liao, Y.; Chen, D.; Zou, S.; Xiong, S.; Xiao, X.; Dang, H.; Chen, T.; Yang, S.,

Recyclable naturally derived magnetic pyrrhotite for elemental mercury recovery from flue gas. Environmental science & technology 2016, 50, (19), 10562-10569. (17).

Treharne, R. W.; Cox, C. M. Carbon Dioxide Reduction with Alkali-metal

Amalgams; Charles F Kettering Research Lab Yellow Springs Oh: 1968. (18).

Mep, A., GB 13223-2011, emission standard of air pollutants for thermal power

plants. China Environmental Science Press, Beijing Google Scholar 2011. (19).

Shi, Y.; Xia, Y.-f.; Lu, B.-h.; Liu, N.; Zhang, L.; Li, S.-j.; Li, W., Emission

inventory and trends of NOx for China, 2000–2020. Journal of Zhejiang University Science A 2014, 15, (6), 454-464. (20).

Goldman, L. R.; Shannon, M. W.; Health, C. o. E., Technical report: mercury in

the environment: implications for pediatricians. Pediatrics 2001, 108, (1), 197-205.


S16

Page 17 of 32 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

(21).

Zhou, Q.; Duan, Y.-F.; Hong, Y.-G.; Zhu, C.; She, M.; Zhang, J.; Wei, H.-Q.,

Experimental and kinetic studies of gas-phase mercury adsorption by raw and bromine modified activated carbon. Fuel Process Technol 2015, 134, 325-332. (22).

Zhong, L.; Li, W.; Zhang, Y.; Norris, P.; Cao, Y.; Pan, W.-P., Kinetic studies of

mercury adsorption in activated carbon modified by iodine steam vapor deposition method. Fuel 2017, 188, 343-351. (23).

Zhao, B.; Liu, X.; Si, J.; Wang, C.; LI, D.; Wu, W.; Xu, M., 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. (24).

Fernández-Miranda, N.; Lopez-Anton, M. A.; Díaz-Somoano, M.; Martínez-

Tarazona, M. R., Mercury oxidation in catalysts used for selective reduction of NOx (SCR) in oxy-fuel combustion. Chem Eng J 2016, 285, 77-82. (25).

Fernández-Miranda, N.; Rumayor, M.; Lopez-Anton, M. A.; Díaz-Somoano, M.;

Martínez-Tarazona, M. R., Mercury retention by fly ashes from oxy-fuel processes. Energ Fuel 2015, 29, (4), 2227-2233. (26).

Lopez-Anton, M.; Rumayor, M.; Díaz-Somoano, M.; Martínez-Tarazona, M.,

Influence of a CO2-enriched flue gas on mercury capture by activated carbons. Chem Eng J 2015, 262, 1237-1243. (27).

Yang, J.; Zhao, Y.; Chang, L.; Zhang, J.; Zheng, C., Mercury adsorption and

oxidation over cobalt oxide loaded magnetospheres catalyst from fly ash in oxyfuel combustion flue gas. Environmental science & technology 2015, 49, (13), 8210-8218. (28).

Huda, M. N.; Li, W.; Dai, M.; Lin, L., Kinetic study on mercury sorption from

fuel gas. Energ Fuel 2017, 31, (2), 1820-1824.


S17

Energy & Fuels 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

(29).

Page 18 of 32

Fuente-Cuesta, A.; Diamantopoulou, I.; Lopez-Anton, M.; Diaz-Somoano, M.;

Martínez-Tarazona, M.; Sakellaropoulos, G., Study of mercury adsorption by low-cost sorbents using kinetic modeling. Ind Eng Chem Res 2015, 54, (21), 5572-5579. (30).

Skodras, G.; Diamantopoulou, I.; Pantoleontos, G.; Sakellaropoulos, G., Kinetic

studies of elemental mercury adsorption in activated carbon fixed bed reactor. J Hazard Mater 2008, 158, (1), 1-13. (31).

Mohan, D.; Singh, K. P., Single-and multi-component adsorption of cadmium and

zinc using activated carbon derived from bagasse—an agricultural waste. Water Res 2002, 36, (9), 2304-2318. (32).

Saleh, T. A.; Sarı, A.; Tuzen, M., Optimization of parameters with experimental

design for the adsorption of mercury using polyethylenimine modified-activated carbon. Journal of Environmental Chemical Engineering 2017, 5, (1), 1079-1088. (33).

Lagergren, S., About the theory of so-called adsorption of soluble substances.

1898. (34).

Saleh, T. A.; Siddiqui, M. N.; Al-Arfaj, A. A., Kinetic and intraparticle diffusion

studies of carbon nanotubes-titania for desulfurization of fuels. Petrol Sci Technol 2016, 34, (16), 1468-1474. (35).

Wu, H.; Liu, H.; Wang, Q. H.; Luo, G. Q.; Yao, H.; Qiu, J. R., Experimental

study of homogeneous mercury oxidation under O2/CO2 atmosphere. P Combust Inst 2013, 34, 2847-2854. (36).

Xu, M.; Qiao, Y.; Zheng, C.; Li, L.; Liu, J., Modeling of homogeneous mercury

speciation using detailed chemical kinetics. Combust Flame 2003, 132, (1), 208-218.


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Page 19 of 32 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

(37).

Liu, T.; Xue, L.; Guo, X.; Liu, J.; Huang, Y.; Zheng, C., Mechanisms of

Elemental Mercury Transformation on α-Fe2O3(001) Surface from Experimental and Theoretical Study: Influences of HCl, O2, and SO2. Environmental science & technology 2016, 50, (24), 13585-13591. (38).

Granite, E. J.; Pennline, H. W.; Hargis, R. A., Novel sorbents for mercury

removal from flue gas. Ind Eng Chem Res 2000, 39, (4), 1020-1029. (39).

Yang, J.; Zhao, Y.; Zhang, J.; Zheng, C., Removal of elemental mercury from flue

gas by recyclable CuCl2 modified magnetospheres catalyst from fly ash. Part 2. Identification of involved reaction mechanism. Fuel 2016, 167, 366-374. (40).

Liu, D.; Zhou, W.; Wu, J., Effect of Ce and La on the activity of CuO/ZSM-5 and

MnOx/ZSM-5 composites for elemental mercury removal at low temperature. Fuel 2017, 194, 115-122. (41).

Zhang, B.; Zeng, X.; Xu, P.; Chen, J.; Xu, Y.; Luo, G.; Xu, M.; Yao, H., Using

the Novel Method of Nonthermal Plasma To Add Cl Active Sites on Activated Carbon for Removal of Mercury from Flue Gas. Environmental science & technology 2016, 50, (21), 11837-11843. (42).

Wang, H.; Duan, Y.; Li, Y.-n.; Liu, M., Experimental Study on Mercury

Oxidation in a Fluidized Bed under O2/CO2 and O2/N2 Atmospheres. Energ Fuel 2016, 30, (6), 5065-5070. (43).

Liu, Y.; Wei, H.-m.; Xu, J.-r.; ZHOU, J.-h.; CEN, K.-f., Effect of O2/CO2 and Air

on Mercury Speciation in Coal Fired Flue Gases. Proceedings-Chinese Society Of Electrical Engineering 2008, 28, (11), 48.


S19

Energy & Fuels 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

(44).

Page 20 of 32

Font, O.; Cordoba, P.; Leiva, C.; Romeo, L. M.; Bolea, I.; Guedea, I.; Moreno, N.;

Querol, X.; Fernandez, C.; Diez, L. I., Fate and abatement of mercury and other trace elements in a coal fluidised bed oxy combustion pilot plant. Fuel 2012, 95, (1), 272-281. (45).

Zhang, J.; Duan, Y.; Zhou, Q.; Zhu, C.; She, M.; Ding, W., Adsorptive removal of

gas-phase mercury by oxygen non-thermal plasma modified activated carbon. Chem Eng J 2016, 294, 281-289. (46).

Liu, W.; Vidic, R. D.; Brown, T. D., Impact of flue gas conditions on mercury

uptake by sulfur-impregnated activated carbon. Environmental science & technology 2000, 34, (1), 154-159.


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Page 21 of 32 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

FIGURE CAPTIONS Figure 1. Schematic diagram of a fixed-bed reactor system Figure 2. FTIR spectra of sorbents treated by baseline atmosphere Figure 3. Effect of oxygen concentration on mercury breakthrough rate under O2/N2 atmosphere Figure 4. Effect of oxygen concentration on mercury breakthrough rate under O2/CO2 atmosphere Figure 5. Effect of atmosphere on mercury breakthrough rate (O2/N2 and O2/CO2) Figure 6. Kinetic analysis of mercury uptake on AC by pseudo-first-order kinetic model (Different oxygen concentration under O2/N2 atmosphere) Figure 7. Kinetic analysis of mercury uptake on AC by pseudo-first-order kinetic model (Different oxygen concentration under O2/CO2 atmosphere) Figure 8. Kinetic analysis of mercury uptake on AC by intraparticle diffusion kinetic model (Different oxygen concentration under O2/N2 atmosphere) Figure 9. Kinetic analysis of mercury uptake on AC by intraparticle diffusion kinetic model (Different oxygen concentration under O2/CO2 atmosphere) TABLE CAPTIONS Table 1 Ultimate and structural analysis of activated carbon Table 2 Kinetic parameters obtained from two kinetic models


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Energy & Fuels 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

T

Page 22 of 32

Heater Heater Control

Gas Mixer Hg Sorbent

Hg Gas Analyzer

Valve MFC

Activated Carbon

Hg Analyzer

Water Btah

Figure 1. Schematic diagram of a fixed-bed reactor system


S22

Page 23 of 32

AC

AC-O2/N2

4000

3500

645 1085

1429

2367

3035

AC-O2/CO2 3818 3679 3452

Transmittance (%)

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

3000

2500

2000

1500

1000

500

-1

Wavenumbers (cm

)

Figure 2. FTIR spectra of sorbents treated by baseline atmosphere


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Energy & Fuels

N2+ 4% O2

100

Breakthough Rate (%)

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

Page 24 of 32

N2+ 8% O2 N2+10% O2

80 60 40 20 0

20

40

60

80

100

120

140

Time (min) Figure 3. Effect of oxygen concentration on mercury breakthrough rate under O2/N2 atmosphere


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Page 25 of 32

CO2+ 4% O2

100


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

CO2+ 8% O2 CO2+ 10% O2

80 60 40 20 0 0

20

40

60

80

100

120

140

Time (min) Figure 4. Effect of oxygen concentration on mercury breakthrough rate under O2/CO2 atmosphere


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Energy & Fuels

100


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

80

Page 26 of 32

N2+4% O2

CO2+4% O2

N2+8% O2

CO2+8% O2

N2+10% O2

CO2+10% O2

60 40 20 0 0

20

40

60

80

100

120

140

Time (min) Figure 5. Effect of atmosphere on mercury breakthrough rate (O2/N2 and O2/CO2)


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Page 27 of 32

30 N2+ 4% O2

Mercury Uptake (µg/g)

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

N2+ 8% O2

25

N2+10% O2 Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 6. Kinetic analysis of mercury uptake on AC by pseudo-first-order kinetic model (Different oxygen concentration under O2/N2 atmosphere)


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Energy & Fuels

35 CO2+ 4% O2


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

Page 28 of 32

30

CO2+ 8% O2 CO2+10% O2

25

Calculated

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 7. Kinetic analysis of mercury uptake on AC by pseudo-first-order kinetic model (Different oxygen concentration under O2/CO2 atmosphere)


S28

Page 29 of 32

30


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

25

Experimental： N2+ 4% O2

Calculated： N2+ 4% O2

N2+ 8% O2

N2+ 8% O2

N2+10% O2

N2+10% O2

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 8. Kinetic analysis of mercury uptake on AC by intraparticle diffusion kinetic model (Different oxygen concentration under O2/N2 atmosphere)


S29

Energy & Fuels

35


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

30 25

Page 30 of 32

Experimental： CO2+ 4% O2

Calculated： CO2+ 4% O2

CO2+ 8% O2

CO2+ 8% O2

CO2+10% O2

CO2+10% O2

20 15 10 5 0 0

20

40

60

80

100

120

140

Time (min) Figure 9. Kinetic analysis of mercury uptake on AC by intraparticle diffusion kinetic model (Different oxygen concentration under O2/CO2 atmosphere)


S30

Page 31 of 32 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

Table 1 Ultimate and structural analysis of activated carbon Specific

Total pore

Micropore

Mean pore

surface area

volume

volume

diameter

m2•g-1

cm3•g-1

cm3•g-1

755.1

0.358

0.314

Cdaf

Hdaf

Odaf

Ndaf

Sdaf

nm

%

%

%

%

%

1.895

93.98

0.98

4.80

0.20

0.04


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Energy & Fuels 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

Page 32 of 32

Table 2 Kinetic parameters obtained from two kinetic models Pseudo-first-order Atmosphere

O2/N2

O2/CO2

O2

qe

k1

µg/g

min-1

4%

59.72

0.00361

8%

59.76

10%

Intraparticle diffusion R2

R2

kp

c

µg/(g•min1/2)

µg/g

0.9998

2.270

-5.37585

0.9738

0.00415

0.9997

2.546

-5.94871

0.9766

78.13

0.00344

0.9997

2.795

-6.74382

0.9735

4%

68.14

0.0045

0.9997

3.071

-6.97928

0.9770

8%

261.66

0.00106

0.9997

3.363

-8.72876

0.9627

10%

180.91

0.00162

0.9999

3.421

-8.54200

0.9635

R2: Correlation Coefficient


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Experimental and Kinetic Study - American Chemical Society

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