in Coal-Fired Power Plants on Arsenic Emissions

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Effect of Coordinated Air-Pollution Control Devices (APCD) in Coal-Fired Power Plants on Arsenic Emissions Jiawei Wang, Yongsheng Zhang, Zhao Liu, Pauline Norris, Carlos E. Romero, Hong Xu, and Wei-Ping Pan Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 24 Jun 2017 Downloaded from http://pubs.acs.org on June 24, 2017

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Effect of Coordinated Air-Pollution Control Devices (APCD) in Coal-Fired Power Plants on Arsenic Emissions Jiawei Wang a, Yongsheng Zhang a,1, Zhao Liu a, Pauline Norris b, Carlos E. Romero c, Hong Xu a, Wei-Ping Pan a, b a. Key Laboratory of Condition Monitoring and Control for Power Plant Equipment, Ministry of Education, North China Electric Power University, Beijing, 102206, P.R. China; b. Institute of Combustion Science and Environmental Technology, Western Kentucky University, Bowling Green, KY 42101, USA; c. Energy Research Center, Lehigh University, 117 ATLSS Drive, Bethlehem, PA 18015-4729, USA

Abstract: An arsenic emission study was performed at nine coal-fired power plants in China and the US that are equipped with various air-pollution-control devices (APCDs). On average over 90% of the arsenic in the flue gas is captured by the dry particulate matter collection system. Less than 3% of the arsenic remains in the boiler slag and 3% is captured by the desulfurization system. Another 1% is captured by wet precipitators. The remaining arsenic is emitted from the stack. Ultra-low emissions technology with a low-temperature economizer before the ESP promotes the capture of more arsenic compounds. It was found that reactions between arsenic and the

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Corresponding author E-mail: [email protected] 1

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denitrification catalyst make it difficult to reach a perfect arsenic mass balance in a power plant, excluding plants that are equipped with a Hot ESP installed before the SCR system. Arsenic speciation depends greatly on the temperature of the flue gas and the location of the measurement. There are no significant differences between US and Chinese coals in regard to the behavior of arsenic during combustion and its interaction with power plant APCD systems. Key words: Arsenic emission; Mass balances; Particle size; SCR poisoning

1. Introduction Arsenic is a metalloid element that has acute toxicity. Though it is an essential trace element for human beings, its toxicological impact cannot be ignored under long-term intake of arsenic and its derivatives.1-6 The largest part of anthropogenic arsenic emissions are originated from stationary sources, such as copper smelting, coal combustion and other nonferrous metal industries.7,

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Uncontaminated soil

contains on average about 7 micrograms per gram (µg/g) of arsenic, however, levels in the range between 200 and 2,500 µg/g have been detected near stationary sources, and up to 700 µg/g in agricultural soils treated with arsenic-containing pesticides (WHO1987).9 It has been reported that about 19.6 million people in China are at health risk from contaminated water with high values of arsenic.10 Power plants in China and the United States use large amounts of coal. Coal consumption in the electric power industry accounts for about 46% of the coal

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consumption in China in 2013 and about 92% of the coal consumption in the United States in 2010.11 Chemical and physical speciation of arsenic varies from coal, fly ash, gypsum and residue, of which coal utilization in a power plant would be a great potential risk for the environment and human health. The average arsenic concentration in Chinese coals is 5.78 µg/g.3 The average arsenic concentration in U.S. coal is reported at 6.50 µg/g.3 There are three dominant arsenic species in coal: arsenate, and pyritic and organic arsenic.3, 12-15 X-ray Absorption Fine Structure (XAFS) results from Zielinski indicate that most of the arsenic in coal is in the form of As-bearing pyrite caused by epigenetic introduction of hydrothermal fluids.16 Tian came to the conclusion that arsenic content follows a descending order in coals: sulfide > organic > arsenate > silicate > soluble and exchangeable fractions.3 The relationship between arsenic and sulfur has also been mentioned for various coals.17, 18 According to the summary of Yudovich, the dominant arsenic form in bituminous coals is sulfuric and only a minor portion is in ionic exchangeable form.13 In sub-bituminous coals, arsenic is mainly uniformly distributed in the sulfide, carbonate, and organic matter forms. In the U.S coals, even average arsenic content does not mask an evident As-Spyr relationship.19 Power plants are nowadays equipped with air pollution control devices (APCD), such as selective catalytic reduction (SCR) systems for nitrogen oxide (NOX) emissions control. Electrostatic precipitators (ESPs) for particulate matter control and wet flue gas desulfurization (WFGD) systems for sulfur dioxide (SO2) control. Because of coal quality and emissions requirement for different power plants, 3


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installation of APCDs is not exactly the same in China as it is in the United States. Different devices have different impacts on the transformation of arsenic and its removal. Senior et.al., concluded that gaseous As2O3, or its dimer As4O6, could adhere and block some of the micropores in the catalyst and it would react with the vanadium oxide in the catalyst, while deactivated it.20-22 It is evident that differences in SCR design and catalyst formulation from power plant to power plant will vary the effect on arsenic. Arsenic concentrations in coal and the capture of arsenic by fly ash have been studied by several groups. Meij etc. concluded that most of the arsenic in coal could be captured and enriched to the fly ash particles, especially on the finer size distribution, and relative enrichment (RE) factor indicated the concentration of target elements on the fly ash particles, and RE value increased when the temperature of flue gas or the particle size decreased.5,

23-25

Cheng carried out several full-scale

experiments and the results indicate that ESP could reach 97% efficiency on arsenic removal. Tang5 concluded that 83% of As was removed by the ESP unit. 26 Linak and Wendt have put forward several possible routes for the mechanisms governing the fate of trace elements during coal combustion.27 Arsenic distributes into vapor phase, sub-micrometer and super- micrometer particles.27 Sub-micrometer particles can be captured as ash or residues in the furnace, economizer and ESP while super-micrometer particles may be partially captured in FGDs and emitted into the

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atmosphere. Arsenic in their vapor phase would be redistributed into liquid, solid and gaseous phases in wet FGD wet scrubbers. WESPs are nowadays used to remove fine particles and sulfuric acid aerosols in coal-fired power plant.28, 29 In theory, removing fine particulate matter from flue gas would

decrease the amount of arsenic released into the environment. Research has

shown that fine particulate matter after the WESP is mainly derived from desulfurization gypsum.29 Although, there are several studies that have evaluated the effects of ESP on arsenic, there is very limited research reporting the effect of WESP on arsenic. The effect of WESP on arsenic is poorly understood. Coal-fired power plants in China and the United States have different configurations that are designed for the type of coal being burned. There is also very limited information available on the impact of the coordinated APCD train in coal-fired power plants on arsenic emissions. Particularly, in recent years, many existing power plants in China have been retrofitted to meet ultra-low emissions technology standards.29 Changes to existing SCR and ESP units, upgrading of FGD scrubbers and/or the use of new equipment such as low temperature economizers and WESPs have been successfully introduced to obtain very low emissions of conventional PM, SO2 and NOx pollutants.29-33 However, there is insufficient information on the impact of these technologies upgrades or the adoption of new equipment on arsenic emissions. Thus, research on the effect of ultra-low emissions technologies on arsenic partitioning during coal combustion is of great interest to

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equipment manufactory, boiler operators and environment protection government agencies. In this study, the partitioning of arsenic at nine electric power plants (EPPs) was investigated. Five of these EPPS are in China and the other ones are in the US. This study evaluates the impact of different APCDs on arsenic partitioning and removal. In addition, this study evaluates the effect of ultra-low emissions technologies on arsenic partitioning during coal combustion. 2. Experimental procedure The sampling program for the American power plant was carried out during 2003 and 2004, while the sampling time for the Chinese power plant was during 2012 and 2016. Coal, flue gas, fly ash, slag, limestone and gypsum samples were collected from nine power plants. The APCDs for each power plant are shown in Table 1. Unit #2 and Unit #9 are located at the same power plant. Unit #9 is retrofitted with a low temperature economizer to lower the flue gas temperature down to 90℃ before entering the ESP, and a wet ESP is installed to enhance the capture efficiency of particulate matter to meet ultra-low emission standards. None of the US coal-fired power plants (#5-8) in this study is equipped with a low temperature economizer or wet ESP system. There is only one plant with a hot ESP included in this study power plant #6. During the arsenic sampling periods, the boiler flue gas samples were extracted from were operated under the following conditions: 1) consistent load at more than

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85%; 2) consistent coal supply and 3) bringing down the coal storage level to a minimum in the coal hoppers before changing to a new coal. Pulverized coal was collected from the pipes leading from the pulverizer to the boiler. The fly ash systems consist of four banks ESPs in China and two banks ESPs in the US. In all cases, the first row of hoppers was sampled in China and in the US. Grab samples of slag, limestone and gypsum were synchronized with hopper fly ash sampling. The flue gas streams were sampled at the inlet and outlet of the APCDs. The arsenic in the flue gas was sampled in accordance with EPA Method 29 "Determination of Metals Emissions from Stationary Sources".23,

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The sampling

equipment consists of the Ontario isokinetic sampling instrument from American APEX Instruments. This system is composed of a sampling probe, filter, filter tank, absorption bottle package (a total of four groups, placed in an ice water bath) and the master control box (including dry gas flowmeter, vacuum gauge, pump and ancillary equipment), as shown in Figure 1. In the process of sampling, the flue gas is sampled by the probe from a flue probe, where the flue gas passes through a heated quartz fiber membrane, the absorption bottle package, the control box, and a dry gas flowmeter metering the dry flue gas volume. Arsenic in the flue gas is collected by acidification of H2O2. Flue gas samples were collected at Unit #1, Unit #2, Unit #5, Unit #6 and Unit #9. All analyses of liquid and solid samples were performed at the North China Electric Power University and the Institute for Combustion Science and Environmental Technology, at the Western Kentucky University. The analyses of 7


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arsenic in the coal, fly ash, slag, limestone and gypsum in China were performed following Chinese Method GB/T 3058-2008, using automatic hydride generation atomic fluorescence spectrometry (PSA10.055 Millennium Excalibur, PSA Company). The analyses of arsenic in the coal, fly ash and slag in the US were performed following ASTM method D6357-OOa, using LECO renaissance inductively coupled plasma-time of flight mass spectrometry (ICP-TOFMS). Flue gas samples were analyzed using automatic hydride generation atomic fluorescence spectrometry (PSA10.055 Millennium Excalibur, PSA Company), in China and in the US, according to the sample pretreatment and analytical guidelines of EPA’s Method 29. The linearity of the calibration curve for these analyses was 0.999, and the limit of detection was 0.35 ng/g. Coal analyses were performed following standard ASTM guidelines (moisture, ash and volatile matter-ASTM D-5142-02a; sulfur-ASTM D-4239-02a; chlorine-ASTM D 4208-02). Major oxides and minor elements were analyzed by ICP-AES (Leeman Labs Prodigy) in China and by X-ray fluorescence on a Rigaku RIX 3001 XRF in the US. In order to ensure the accuracy of arsenic test results, each group of samples was tested three times. The data were deemed valid if the relative deviation values were within ±10%. Additionally, for every five samples to be tested, a known concentration of standard liquid was used to validate instrument operational error, if the standard liquid test results were within ±10%, the test data was considered with good enough accuracy to be used in the study. 3. Results and discussion 3.1 Emission and balance of Arsenic 8


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Proximate and ultimate analysis data, fly ash composition and arsenic concentration are shown in Tables 2-4: As shown in Table 2, all the US coals have high volatility (32-37%), moderate ash content (9-12%), and wide range of sulfur contents (0.6-2.9%). Coal #7 has a relatively high sulfur concentration (2.9%). The Chinese coals have a wide ash content range (15-38%) with relatively low sulfur content, except coal #4 (1.7%). As shown in Table 3, the major differences in the fly ash composition are among the Al, Ca, and Fe concentrations. As shown in Table 4, the arsenic concentration in the Chinese coals is between 0.85-3.34 µg/g and the arsenic concentration in the US coal is between 2.5-22.3 µg/g. Arsenic concentrations in flue gas are very low at both Chinese and US plants. Only a small amount of arsenic is emitted from the stack (Unit #1: 0.21 µg/m3, Unit #2: 0.52 µg/m3 (flue gas after ESP), Unit #5: 0.57 µg/m3, Unit #6: 0.71 µg/m3 and Unit #9: 0.10 µg/m3). It was found that most of the arsenic in the coal was retained in the fly ash except at the CFB #4 unit. General, for a PC boiler, the arsenic content in the fly ash is 5~10 times the arsenic content in the coal, while the arsenic content in the slag is at the same level that in coal.

For CFB boilers, the

arsenic content in the slag is higher than in fly ash, with both levels about 5 times the equivalent concentration in coal. It is known that arsenic is readily volatilized during the combustion process, after combustion in the boiler it will tend to enrich the fly and bottom ash. The fireside temperature of a PC boiler is significantly higher than that of a CFB boiler, thus arsenic would more condense after combustion, and the arsenic content in the slag of a CFB would be expected to be higher. It should be noticed that 9


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for these sampled power plants, the arsenic content in limestone and gypsum was low, with concentrations between 1 to 2 µg/g. 3.1.1 Balance of Arsenic Field measurement of arsenic is more difficult than with conventional pollutants, such as dust, sulfur dioxide and nitrogen oxides. Arsenic measurement accuracy and reliability is typically asserted by mass balance.26, 35 Gas and solid measurements can be used to calculate a general equilibrium constant i. Balance of arsenic is calculated under the following equation:26 RI =

ெ௢௨௧ ெ௜௡

（1）

where RI represents the recovery index of arsenic; a value of RI equal to 1 represents a complete mass balance. An acceptable sampling error is between 70 and 130%,24 considering the repeatability and precision both in the sampling and analysis. Min refers to the overall input of arsenic including coal (Mcoal) and limestone (Mlim). Mout refers to the overall input of arsenic including the amount of arsenic in flue gas (Mflue), bottom ash (Mba), precipitator ash (Mfa) and desulfurization gypsum (Mgy). An arsenic balance should also include all the water inputs using for the FGD reagent slurry and the makeup water, while all the water output is used as the gypsum slurry in a power plant. In order to simplify the test program, what considered in the material balance accounting were only solid samples of limestone and gypsum, without any liquid (the water in the FGD process). During combustion, arsenic is released into the flue gas and get partitioned to vapor and particulate phases. Arsenic partitioning between vapor and particulate 10


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phase is due to the chemical interactions of arsenic with fly ash.2 Figure 2 shows Mass balances 1 (RI 1) for arsenic in Unit #2, Unit #5 , Unit #6 and Unit #9 have been calculated, assuming that the input is the arsenic content from the combusted coal. The particulate arsenic concentration in the filter ash collected during the flue gas sampling at the ESP inlet is used as the arsenic concentration in the fly ash. The mass balance results are shown in Figure 3. The recovery of arsenic (RI 1) is 81.92, 88.20, 95.20 and 71.63% for Units #2, #5, #6 and #9, respectively. Flue gas only was taken after the FGD in Units #1 and #9, thus, mass balance 2 (RI 2) was adopted. Mass balance 2 (RI 2) for arsenic in Unit #1 and Unit #9 where calculated assuming that the input is the arsenic content from the combusted coal and limestone. Arsenic will associate with the fly ash, slag, gypsum and in-stack arsenic in the form of particulate and gas phases, respectively. Arsenic mass balance (RI 2) results are shown in Figure 3. The recovery of arsenic is 72.24 and 73.11% for Units #1 and #9, respectively. The overall mass balance for arsenic in this study is around 70-85%. This relatively low mass balance may be due to the effect of the APCD system as discussed in the following sections. 3.2. Effect of SCR on arsenic removal The recovery of arsenic is low for Units #1, #2 and #9 with equipped SCR systems, see Table 5. Arsenic recovery was high for Unit #5 (without a SCR system) and Unit #6 (with a hot ESP). The recovery index for Units #5 and #6 was 88.20 and 95.20%, respectively. Unit #9 has three catalyst layers, and Unit #2 only has two layers. The RI 1 values for Units #9 and #2 are 71.63 and 81.92%, respectively. The 11


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flue gas passes through the SCR before it reaches the ESP inlet. It can be thought that partial gas phase As2O3 solidifies on both active and non-active sites in the vanadium-based catalysts that are used in the SCR system, which reduces the activity of the catalyst.36 When compared with the other units, about 15% of the arsenic may be retained in the SCR system. Unit #6 has the highest arsenic recovery rate. This may be due to the location of the hot ESP, which is located before the air preheater, operated at around 3500C. Most of arsenic compounds could be captured in the hot ESP before the flue gas enters any of the other APCD system. This explains the excellent arsenic mass balance which layout of the APCD system. However, few power plants have a hot ESP to minimize arsenic poisoning on the catalyst in the SCR system. Most power plants select low arsenic coal to limit catalyst poisoning. It may be difficult to obtain a high recovery rate for arsenic in the SCR system. 3.3. The effect of ESP on arsenic removal In order to investigate the arsenic capturing efficiency for fly ash, ESP fly ash samples from nine units were collected and analyzed for arsenic. The ESP arsenic capturing efficiencies were calculated and the results are shown in Figure 4. Results from Unit #5 and Unit #6 indicate that the hot ESP has a significant, positive effect on arsenic removal. As mentioned in the last section, this means that using hot ESPs can reduce SCR catalyst poisoning and improve the service life of the catalyst. In this study, it was found that the particulate precipitators collect about 90% of the arsenic present. The particulate removal efficiency for the effect of ESP units was determined by the particulate matter measurements carried out. Based on the 12


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particulate removal efficiency, the average arsenic removal efficiency of the ESP unit should be about 95%. Unit #2 and #9 are located at the same station. Unit #9 is retrofitted with ultra-low emissions standards technology. The arsenic removal efficiency of the ESP for Units #2 and #9 is 95.87 and 98.22%, respectively. Enhancing the particle matter capture efficiency increased the arsenic removal efficiency by 2.35%. The low temperature economizer reduces flue gas temperature at the ESP entrance to approximately 90oC. Thus, the resistivity of the fly ash and the flow of flue gas are both reduced.29, 32 The ESP particulate matter removal efficiency is improved. It has been suggested that SOx, HCl, and H2O in the flue gas would condense and absorb on surface of the fly ash particles and a liquid membrane would be formed on surface of the fly ash.33 The conductivity and viscosity of the surface of the fly ash would also be increased. Thus, the opportunity for the arsenic compounds to be captured by the fly ash would increase. Agglomeration of smaller particles to form larger particles will occur and improve fly ash capture efficiency. Fly ash particle size is another factor that has been measured in the literature that affects arsenic capturing efficiency. The ESP ash particle size will decrease when the flue gas flows from Row 1 to Row 4 in the ESP system.5, 35 And some scholars have demonstrated that fly ash specific surface area increases as the particle size decreases.5, 23, 25, 35 In this study, the arsenic concentrations in ashes from the first two rows of hoppers were compared. Three sets of ash samples collected from Rows 1 and 2 show a consistently larger arsenic concentration in Row 2. This trend is shown in 13


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Figure 5. The arsenic absorption capacity increases with increasing fly ash specific surface area. Hence, the arsenic partitioning in the ESP fly ash will be in accordance with its size; the smaller sized particles will have increased arsenic content. Although, the off-gas at the ESP outlet contains only very small amounts of fine fly ash, the enrichment of arsenic in these particulates would increase the risk of contaminate after release of the ash into the environment. 3.4. FGD on the effect of arsenic removal Limestone and gypsum samples from Units #1 and #9 were collected and analyzed for arsenic to investigate the arsenic capturing efficiency in the FGD system. A small amount of arsenic (less than 3.49%) was collected by the FGD at Units #1 and #9. There was less arsenic than expected in the ESP fly ash which suggests that arsenic in particulate phase was enriched on the fine particles in the flue gas, which could escape from ESP unit and removed by the wet scrubber. The particulate arsenic was insoluble during the FGD process and easily incorporated into solid portion of the slurry in the scrubber tanks. 3.5. The effect of WESP on arsenic removal Wet electrostatic precipitators (WESPs) are used to control fine particulate as well as sulfuric acid aerosols and trace metals.37, 38 WESPs are designed to control fine particles.39 For particulate matter removal efficiency could reach 90%, affected on humid gases and sticky particles.37, 40-42 It was found in this study that arsenic is more easily enriched in fine particles. In theory, fine particle removal would greatly impact arsenic removal. Arsenic concentrations in the flue gas were 0.130 µg/m3 and 14


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0.098 µg/m3 at the Unit #9 WESP inlet and outlet, respectively. The arsenic removal efficiency at the WESP was 24.6%. Capturing arsenic is a co-benefit of the WESP system, but the amount of arsenic is very small in the total mass balance. Unit #9 was retrofitted with a low temperature economizer, an ESP high frequency power supply and a WESP. The APCDs in Unit #9 were found to be able to remove 99.93% of the arsenic from the flue gas stream. This indicates that ultra-low emissions retrofits increase arsenic capture ability in a coal-fired power plant. 3.6. Effect of components in fly ash and coal on arsenic removal High concentrations of acidic gas such as HCl and SO2 in the flue gas might compete for the CaO active sites. Under oxidizing atmosphere, CaO and SO2 would produce CaSO4 between 600-1000℃ while HCl could generate CaClOH with CaO between 100-600℃.43 The relationship between arsenic and chlorine, sulfur and CaO in the ESP fly ash was investigated in this study. Fly ash samples were collected at the ESP, Row 2 hoppers at Units #5 and #6. No obvious relationship between arsenic and CaO or chlorine content was found. The results indicate that the CaO concentration in the fly ash is more than sufficient to capture all the arsenic. On the other hand, the arsenic content is in similar proportion to the sulfur concentration. The arsenic concentration increases with increasing sulfur concentration for both units. The root mean square of the correlation between arsenic and sulfur for Units 5 and 6 is 0.819 and 0.872, respectively, as shown in Figure 6. This shows that sulfur has a first order impact on arsenic in the fly ash. The sulfophile property of arsenic may explain this trend, sulfide-bound arsenic is the most predominant mode, ranging from 42 to 88%.15 15


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The mode of occurrence of trace elements in coal provides very useful information to understand their behavior during coal cleaning and combustion. Figure 7 shows that the arsenic concentration increases with increasing sulfur concentration in coal, and the root mean square of this correlation is 0.873. This shows that sulfur is a very important parameter influencing arsenic in coal. Arsenic in coal is primarily present in the forms of realgar (As2S2), orpiment (AsS), and arsenopyrite (FeAsS), which could explain the observed trend. High arsenic concentrations in coal shorten the lifetime of the catalyst. This may partially counteracts the financial savings from burning low cost, high sulfur coal. However, if arsenic pyrite forms dominate in the feed coal, conventional coal cleaning may be an efficient tool for the removal of arsenic from coal. The relationship between arsenic content and sulfur content was also observed in the Chinese coals as well. 3.7. Arsenic concentrations in ash at different locations Arsenic capture on ash involves physic-sorption and chemic-sorption. Temperature affects both of process.44 In this study, the arsenic concentrations in the ashes collected at different locations (from the boiler bottom, economizer and ESP hoppers) were correlated with their temperatures. Figure 8 shows arsenic concentration in different ashes from Units #1 to 9 vs. location temperature, based on the data of Table 4 and the temperature at the sampling location. The arsenic concentration in ash sharply decreases as the temperature increases. The arsenic distribution in the ash at different locations at the same unit strongly depends on the temperature of the location. High arsenic residue in the slag at Unit #4 may be due to 16


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the addition of limestone in the CFB system; The limestone could adsorb arsenic and prevent the arsenic into the flue gas. 4. Conclusions For Chinese and US coals, the ESP is the most important unit in the APCD system to capture arsenic compounds. More than 90% of the arsenic in the flue gas is captured by cold ESP systems in US and Chinese power plants tested in this study. Less than 2.9% of the arsenic is in the slag. Another 3% is captured by the WFGD system. Less than 1% is captured by WESP systems. Less than 0.5% of the arsenic is emitted in the stack. Ultra-low emissions technology and lower flue gas temperatures also promote capture of more arsenic compounds in the ESP. The installation of a hot ESP before SCR systems seems to prevent the chemical reaction between arsenic and the SCR catalysts. The WESP also demonstrated the ability to capture a small amount of arsenic compounds with the fly ash. Acknowledgements Financial support for this study was provided by the Key Projects in the National Science & Technology of China (No. 2015BAA05B02), the Fundamental Research Funds for the Central Universities (2017JQ002) and 111 Project of China (B12034) and this support is gratefully acknowledged. References [1] DeSesso, J.; Jacobson, C.; Scialli, A.; Farr, C.; Holson, J. An assessment of the developmental toxicity of inorganic arsenic 1. Reproductive Toxicology. 12 (1998) 385-433. 17


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[2] Zeng, T.; Sarofim, A. F.; Senior, C. L. Vaporization of arsenic, selenium and antimony during coal combustion. Fuel and Energy Abstracts. 43 (2002) 254. [3] Tian, H. Z.; Lu, L.; Hao, J. M.; Gao, J. J.; Cheng, K.; Liu, K. Y.; Qiu, P. P.; Zhu, C. Y. A Review of Key Hazardous Trace Elements in Chinese Coals: Abundance, Occurrence, Behavior during Coal Combustion and Their Environmental Impacts. Energy Fuels. 27 (2013) 601-614. [4] Zhou, C.; Liu, G.; Yan, Z.; Fang, T.; Wang, R. Transformation behavior of mineral composition and trace elements during coal gangue combustion. Fuel. 97 (2012) 644–650. [5] Quan, T.; Liu, G.; Yan, Z.; Sun, R. Distribution and fate of environmentally sensitive elements (arsenic, mercury, stibium and selenium) in coal-fired power plants at Huainan, Anhui, China. Fuel. 95 (2012) 334-339. [6] Nriagu, J. O.; Pacyna, J. M. Quantitative Assessment of Worldwide Contamination of Air, Water and Soils by Trace Metals. Nature. 333 (1988) 134-139. [7] Mandal, B. K.; Suzuki, K. T. Arsenic round the world: a review. Talanta. 58 (2002) 201–235. [8] Kabata-Pendias, A.; Pendias, H. K. Trace elements in soils and plants. Trace Elements in Soils & Plants. 34 (1992) 951-974. [9] Group, W. B. Pollution prevention and abatement handbook, 1998 : toward cleaner production. World Bank Group, 1999. [10] Rodríguez-Lado, L.; Sun, G.; Berg, M.; Zhang, Q.; Xue, H.; Zheng, Q.; Johnson, 18


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C. A. Groundwater arsenic contamination throughout China. Science. 341 (2013) 866-868. [11] Cen, K. F.; Ni, M. J.; Gao, X.; Luo, Z. Y.; Wang, Z. H.; Zheng, C. H. Progress and Prospects on Clean Coal Technology for Power Generation. Chinese Journal of Engineering Science. 17 (2015) 49-55. [12] Shah, P.; Strezov, V.; Stevanov, C.; Nelson, P. F. Speciation of Arsenic and Selenium in Coal Combustion Products†. Energy & Fuels. 21 (2006) 506-512. [13] Yudovich, Y. E.; Ketris, M. P. Arsenic in coal: a review. International Journal of Coal Geology. 61 (2005) 141-196. [14] Yu, K.; Liu, G.; Chou, C. L.; Ming, H. W.; Zheng, L.; Rui, D. Arsenic in Chinese coals: distribution, modes of occurrence, and environmental effects. Science of the Total Environment. 412-413 (2011) 1–13. [15] Liu, H. M.; Pan, W. P.; Wang, C. B.; Zhang, Y. Volatilization of Arsenic During Coal Combustion Based on Isothermal Thermogravimetric Analysis at 600–1500° C. Energy & Fuels. 30 (2016) 6790-6798. [16] Zielinskia, R. A.; Fosterb, A. L.; Meekera, G. P.; Brownfielda, I. K. Mode of occurrence of arsenic in feed coal and its derivative fly ash, Black Warrior Basin, Alabama. Fuel. 86 (2007) 560–572. [17] Spears, D. A.; Zheng, Y. Geochemistry and origin of elements in some UK coals. International Journal of Coal Geology. 38 (1999) 161-179. [18] Hower, J. C.; Robertson, J. D.; Wong, A. S.; Eble, C. F.; Ruppert, L. F. Arsenic and lead concentrations in the Pond Creek and Fire Clay coal beds, eastern 19


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Kentucky coal field. Applied Geochemistry. 12 (1997) 281-289. [19] Attia, Y. A. Processing and utilization of high sulfur coals. Elsevier Science Pub.co.inc.new York Ny, (1984). [20] Senior, C. L.; Lignell, D. O.; Sarofim, A. F.; Mehta, A. Modeling arsenic partitioning in coal-fired power plants. Combustion and Flame. 147 (2006) 209-221. [21] Hilbrig, F.; Goebel, H. E.; Knoezinger, H.; Schmelz, H.; Lengeler, B. ChemInform Abstract: Interaction of Arsenious Oxide with DeNOx-Catalysts: An X-Ray Absorption and Diffuse Reflectance IR Spectroscopy Study. Cheminform. 22 (1991) 168-176. [22] Hums, E. A catalytically highly-active, arsenic oxide resistant V-Mo-O phase — results of studying intermediates of the deactivation process of V2 O5 -MoO3 -TiO2 (ANATASE) DeNOx catalysts. Research on Chemical Intermediates. 19 (1993) 419-441. [23] Guo, X.; Zheng, C. G.; Xu, M. H. Characterization of arsenic emissions from a coal-fired power plant, Energy & Fuels. 18 (2004) 1822-1826. [24] Yokoyama, T.; Asakura, K.; Matsuda, H.; Ito, S.; Noda, N. Mercury emissions from a coal-fired power plant in Japan. Science of the Total Environment. 259 (2000) 97-103. [25] Meij, R. Trace element behavior in coal-fired power plants. Fuel Processing Technology. 39 (1994) 199-217. [26] Cheng, C. M.; Hack, P.; Chu, P.; Chang, Y. N.; Lin, T. Y.; Ko, C. S.; Chiang, P. H.; 20


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He, C. C.; Lai, Y. M.; Pan, W. P. Partitioning of Mercury, Arsenic, Selenium, Boron, and Chloride in a Full-Scale Coal Combustion Process Equipped with Selective Catalytic Reduction, Electrostatic Precipitation, and Flue Gas Desulfurization Systems†. Energy & Fuels. 23 (2009) 4805-4816. [27] Linak, W. P.; Wendt, J. O. L. Trace metal transformation mechanisms during coal combustion. Fuel Processing Technology. 39 (1994) 173-198. [28] Wang, X.; Chang, J.; Xu, C.; Wang, P.; Cui, L.; Ma, C. Electrical characteristics of electrostatic precipitator with a wet membrane-based collecting electrode. Journal of Electrostatics. 80 (2016) 85-94. [29] Sui, Z.; Zhang, Y.; Peng, Y.; Norris, P.; Cao, Y.; Pan, W.P. Fine particulate matter emission and size distribution characteristics in an ultra-low emission power plant. Fuel. 185 (2016) 863-871. [30] Zhang, Y.; Wei, S. Z.; Hu, J. T. 350 mw unit of flue gas pollutants near zero emissions research and practice. Thermoelectric technology. (2015) 1-5. [31] Wang, S. M.; Song, C.; Chen, Y. B.; Sun, P. Technology research and engineering applications of near-zero air pollutant emission coal-fired power plant. Research of Environmental Sciences. 28 (2015) 487-494. [32] Huang, Y. C.; Yang, S.; Chen, C.; Chen, Y. Discussion on smoke clean emissions technology in coal-fired power plant. Energy and Energy Conservation. (2015) 126-129. [33] Zhao, Y. M.; Ma, S. M.; Yang, J. P.; Zhang, J. Y.; Zheng, C. G. Status of ultra-low emission technology in coal-fired power plant. Journal of China Coal Society. 40 21


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(2015). [34] Zevenbergen, C.; Bradley, J. P.; Reeuwijk, L. P. V.; Shyam, A. K.; Hjelmar, O.; Comans, R. N. J. Clay Formation and Metal Fixation during Weathering of Coal Fly Ash. Environ. sci. technol. 33 (1999) 3405-3409. [35] Guo, X.; Zheng, C. G.; Dan, C. Characterization of Arsenic Emissions from a Coal-Fired Power Plant. Environmental Science. 27 (2006) págs. 1822-1826. [36] Beér, J. M. Developments in NOx Abatement and Control By Herminé N. Soud and Kazunori Fukusawa. IEA Coal Research: London, 1996, Energy Fuels. (1998). [37] Staehle, R. C.; Triscori, R. J.; Kumar, K.; Ross, G.; Paternak, E. The Past, Present, and Future of Wet Electrostatic Precipitators in Power Plant Applications. In: Mega Symposium. May, 2003, pp. 19-22. [38] Wang, S.; Zhang, Y.; Gu, Y.; Wang, J.; Zhang, Y.; Cao, Y.; Romero, C. E.; Pan, W. P. Using modified fly ash for mercury emissions control for coal-fired power plant applications in China. Fuel. 181 (2016) 1230-1237. [39] Altman, R.; Offen, G.; Buckley, W.; Ray, I. Wet electrostatic precipitation demonstrating promise for fine particulate control - Part II. Power Engineering. 105 (2001) 37-39. [40] Bologa, A.; Paur, H. R.; Seifert, H.; Wäscher, T.; Woletz, K. Novel wet electrostatic precipitator for collection of fine aerosol. Journal of Electrostatics. 67 (2009) 150-153. [41] Jaworek, A.; Krupa, A.; Czech, T. Modern electrostatic devices and methods for 22


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exhaust gas cleaning: A brief review. Journal of Electrostatics. 65 (2007) 133-155. [42] Kim, H. J.; Han, B.; Woo, C. G.; Kim, Y. J.; Ono, R.; Oda, T. Performance evaluation of dry and wet electrostatic precipitators used in an oxygen-pulverized coal combustion and a CO2 capture and storage pilot plant. Journal of Aerosol Science. 77 (2014) 116-126. [43] Jozewicz, W.; Gullett, B. K. Reaction Mechanisms of Dry Ca-Based Sorbents with Gaseous HCl. Ind.eng.chem.res. 34 (1995) 607-612. [44] Senior, C. L.; Zeng, T.; Che, J.; Ames, M. R. ; Sarofim, A. F.; Olmez, I.; Huggins, F. E.; Shah, N.; Huffman, G. P.; Kolker, A.; Mroczkowski, S.; Palmer, C.; Finkelman, R. Distribution of trace elements in selected pulverized coals as a function of particle size and density. Fuel Processing Technology. 63 (2000) 215-241.

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Figure captions Figure 1. EPA 29 schematic diagram Figure 2. Air-pollution control devices and mass balance range Figure 3. Mass balance of arsenic in flue gas at Unit #1, 2, 5, 6 and 9 Figure 4. ESP arsenic capturing efficiency for five units Figure 5. Arsenic concentration in ESP fly ash at the hoppers for different rows Figure 6. Arsenic to Sulfur in ESP fly ash Figure 7. Arsenic vs sulfur for different coals Figure 8. Arsenic concentrations in ash at different locations

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Page 25 of 38

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Energy & Fuels

Temperature Sensor

Glass Probe Tip

Temperature Sensor

Glass Probe Liner Glass Filter Holder

Manometer

Heated Area

Vacuum Line Empty 5%HNO3/10%H2O2 Silica Gel (Optional)

Vacuum Gauge

Orifice By-pass Valve

Main Valve

Dry Gas Meter Air-Tight Pump

Figure 1. EPA 29 schematic diagram

25


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

Figure 2. Air-pollution control devices and mass balance range

26


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Page 27 of 38

100

In-Stack Gas Output of FGD Slag Fly Ash

RI 1 Unit 1、 2、 5 、 6 and 9 As Mass Balance (%)

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

80

RI 2 60

8 6 4 2 0

Unit 2-RI 1 Unit 5-RI 1 Unit 6-RI 1 Unit 9-RI 1 Unit 1-RI 2 Unit 9-RI 2

Figure 3. Mass balance of arsenic in flue gas at Unit #1, 2, 5, 6 and 9

27


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

ESP Arsenic Capturing Efficiency at five Units (%)

Energy & Fuels

100

95.87

98.98

Page 28 of 38

RI 1 97.48

RI 2

98.22

96.23 90.1

80

60

40

20

0

Unit 2-RI 1 Unit 5-RI 1 Unit 6-RI 1 Unit 9-RI 1 Unit 1-RI 2 Unit 9-RI 2

Figure 4. ESP arsenic capturing efficiency at five units

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60

Row #1 Row #2

Unit 7 ESP Ash Arsenic vs.ESP Row No. 50

47.1 40.6

40

36 As 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

30.3

30

22

21.3

20

10

0 Test #1

Test #2

Test #3

Figure 5. Arsenic concentration in ESP fly ash at the hoppers for different rows

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Energy & Fuels

160

Unit 5 and 6 ESP Ash As vs. S 140

Unit 5

120 2

R =0.819 As 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

Page 30 of 38

100

80

60

2

R =0.872

40

Unit 6

20 0.10

0.15

0.20

0.25

0.30

0.35

S wt%

Figure 6. Arsenic to Sulfur in ESP fly ash

30


0.40

Page 31 of 38

25

As vs. S in Coal 20

15

As 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

2

R =0.873 10

5

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

S wt%

Figure 7. Arsenic vs sulfur for different coals

31


Energy & Fuels

180 Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9

12

160

ESP Ash

8

As µg/g

140 120

As 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

Page 32 of 38

Slag

4

ECO Ash

100

1

40

0 1100

ESP Ash

1200

1300 o

Temperature ( C)

ESP Ash

20

Slag

Slag

ECO Ash 0 0

200

400

600

800

1000

1200

1400

o

Temperature ( C)

Figure 8. Arsenic concentrations in ash at different locations

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Energy & Fuels

Table captions Table1. Electric power plant data Table 2. Ultimate/Proximate analysis of coal samples (Dry Basis) Table 3. Fly ash major and minor composition analysis (%) Table 4. Arsenic concentration of all samples Table 5. Recovery values for arsenic at different units

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Page 34 of 38

Table1. Electric power plant data Unit ID

Unit#1

Unit#2

Unit#3

Unit#4

Unit#5

Unit#6

Unit#7

Unit#8

Unit#9

Unit Capacity

200MW

300MW

200MW

300MW

300MW

500MW

508MW

125MW

300MW

Country

CHN

CHN

CHN

CHN

US

US

US

US

CHN

Boiler

PC

PC

PC

CFB

PC

PC

PC

PC

PC

WESP

NO

NO

NO

NO

NO

NO

NO

NO

YES

NO

NO

FGD

NO

FGD

Injection SO2 control

FGD

FGD

FGD

limestone into furnace

Particulate

cold

cold

cold

cold

cold

Hot

cold

cold

cold

Control

ESP

ESP

ESP

ESP

ESP

ESP

ESP

ESP

ESP

NO

NO

NO

NO

NO

NO

NO

NO

YES

SCR

SCR

SCR

NO

NO

NO

SCR

NO

SCR

Low temperature economizer NOx control Fuel type

bituminous coal

Note: PC represent Pulverized coal furnace, CFB represent Circulating fluidized bed furnace, FGD represent Flue gas desulfurization equipment, ESP represent Electrostatic precipitator equipment SCR represent Selective catalytic reduction equipment.

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Energy & Fuels

Table 2. Ultimate/Proximate analysis of coal samples (Dry Basis) Boiler

Proximate analysis (%)

Ultimate analysis (%)

V

A

FC

C

H

O

N

S

1#

30.74

15.67

53.58

64.91

4.36

13.77

0.86

0.43

2#

28.28

16.41

55.31

64.34

4.06

13.93

0.84

0.42

3#

25.89

28.43

45.68

60.07

4.37

6.01

0.63

0.49

4#

23.71

38.62

37.67

48.39

3.30

7.11

0.89

1.69

5#

32.12

12.59

55.30

71.49

4.94

8.41

1.32

1.25

6#

33.54

11.27

55.19

73.02

4.96

8.77

1.36

0.62

7#

37.88

10.57

51.56

65.92

5.53

13.69

1.39

2.90

8#

33.78

9.86

56.36

75.79

5.00

6.28

1.77

1.30

9#

29.31

18.48

52.21

63.43

4.21

12.24

0.89

0.75

Note: V represent volatile, A represent ash, FC represent fixed carbon, C represent carbon, , H represent hydrogen, O represent oxygen, N represent Nitrogen, S represent sulfur.

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Page 36 of 38

Table 3. Fly ash major and minor composition analysis (%) Boiler 1# 2# 3# 4# 5#

Al2O3 31.03 19.57 21.09 29.45 19.56

CaO 2.76 11.74 6.24 1.40 2.13

6#

20.03

7#

15.56

8# 9#

Major and Minor analysis Na2O MgO P2O5 SiO2 0.51 0.52 0.71 50.10 2.27 0.84 0.53 46.60 1.55 0.11 0.87 49.87 0.26 0.36 0.69 54.64 0.01 0.70 0.17 51.79

TiO2 1.31 0.82 0.79 1.10 1.57

2.70

0.11

0.79

0.10

54.97

2.16

0.21

0.75

0.07

39.66

12.38

1.86

0.47

1.00

0.24

7.10

2.34

2.18

0.76

0.62

Fe2O3 2.62 7.25 7.92 5.20 7.40

K2O 2.73 2.62 3.75 1.54 2.29

1.69

5.33

1.12

23.17

25.11

1.45

18.87

12.52

BaO 0.08 0.08 0.13 0.03

MnO 0.02 0.16 0.11 0.12

SrO 0.27 0.72 0.38 0.12

0.04

0.02

0.08

1.68

0.11

0.03

0.09

1.00

0.03

0.02

0.03

50.59

1.43

0.20

0.02

0.11

48.53

0.81

0.07

0.13

0.65

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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 4. Arsenic concentration of all samples unit

coal

fly ash

slag

economizer ash

limestone

gypsum

flue gas

（emissions）

flue gas

（out of ESP）

flue gas（out of FGD）

µg/g

µg/g

µg/g

µg/g

µg/g

µg/g

µg/m3

µg/m3

µg/m3

1#

1.03±0.06

5.05±0.03

3.11±0.16

ND

1.48±0.04

2.08±0.07

2#

0.85±0.08

4.84±0.09

1.60±0.12

ND

1.12±0.06

1.68±0.01

0.21±0.02

ND

0.21±0.02

ND

0.52±0.04

ND

5#

11.53±0.03

91.51±0.25

7.50±0.08

ND

ND

ND

0.57±0.02

0.57±0.02

ND

6#

2.53±0.08

23.96±0.45

5.06±0.04

16.24±0.12

ND

ND

0.71±0.01

0.71±0.01

ND

9#

1.26±0.05

5.57±0.24

0.83±0.03

ND

1.68±0.02

1.46±0.06

0.10±0.01

0.15±0.01

0.13±0.01

3#

3.05±0.01

10.53±0.16

2.67±0.07

ND

ND

ND

ND

ND

ND

4#

3.34±0.06

16.16±0.34

21.27±0.03

ND

ND

ND

ND

ND

ND

7#

22.25±0.04

160.20±0.52

12.16±0.06

110.31±0.32

ND

ND

ND

ND

ND

8#

4.00±0.05

42.23±0.21

2.86±0.03

ND

ND

ND

ND

ND

ND

Note: ND represent that there is no such solid or gas samples collected

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Energy & Fuels

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Page 38 of 38

Table 5. Recovery values for arsenic at different units Unit #1

Unit #2

Unit #5

Unit #6

Unit #9

RI 1 (%)

/

81.92

88.20

95.20

71.63

RI 2 (%)

72.24

/

/

/

73.11

38


in Coal-Fired Power Plants on Arsenic Emissions

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