Migration and Emission Characteristics of Trace Elements in a 660

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Migration and Emission Characteristics of Trace Elements in a 660MW Coal-fired Power Plant of China Shilin Zhao, Yufeng Duan, Houzhang Tan, Meng Liu, Xuebin Wang, Lituo Wu, Chenping Wang, Jianhong Lv, Ting Yao, Min She, and Hongjian Tang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00450 • Publication Date (Web): 15 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016

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Energy & Fuels

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Migration and Emission Characteristics of Trace Elements in a 660MW Coal-fired Power Plant of China

4

Shilin Zhao a, Yufeng Duan a,*, Houzhang Tan b, Meng Liu a, Xuebin Wang b, Lituo

5

Wu b, Chenping Wang a, Jianhong Lv a, Ting Yao a, Min She a and Hongjian Tang a

6

a

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Education, School of Energy and Environment, Southeast University, Nanjing,

8

210096, China

9

b

1 2

Key Laboratory of Energy Thermal Conversion and Control of Ministry of

School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an

10

,710049, China

11

ABSTRACT:

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Trace elements (TEs) emitted from coal-fired power plant has caused widespread

13

concern. The onsite investigation of the TEs emission from a Chinese 660MW

14

pulverized coal (PC) boiler equipped with SCR, ESP, WFGD and WESP was

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conducted by using US EPA Method 29. Simultaneous sampling of the coal, bottom

16

ash, ESP ash, flue gas and by-products from WFGD and WESP process was

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performed. Results show that TEs mass balance rates for the entire system, furnace

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and each air pollution control device (APCD) are in acceptable range of 70-130%,

19

which confirms the validity and reliability of the field test data. The studied TEs are

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mainly distributed in bottom and ESP ash with the ratio of 2.11%-12.15% and

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87.83%-97.83% respectively while little amount of them exists in WFGD, WESP and

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stack. Coal combustion by-products like bottom ash and gypsum have little influence

23

on soil from the perspective of TEs while more attention should be paid to Ni, Zn and 1

ACS Paragon Plus Environment

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Cd in the ESP ash. Waste water from WFGD should be treated carefully especially

25

for Cr and Mn. WESP waste water has no influence on ground water except Mn, Ag

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and Sb. Zn, Ni and Sb prefer to enrich in ESP ash while accumulation of Mn occurs in

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bottom ash. Ba is enriched in both bottom and ESP ash. ESP has great removal

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efficiency for TEs with value exceeding 99.87%. Both WFGD and WESP are capable

29

to capture TEs, which results in the overall removal rate across ESP + WFGD +

30

WESP more than 99.90%. TEs concentration in the flue gas emitted from the stack is

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extremely low with the range of 0.00-1.33 µg/m3. The ultra-low emission (ULE)

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coal-fired power plant equipped with SCR + ESP + WFGD + WESP has good effects

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on TEs emission control.

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1. INTRODUCTION

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Trace elements (TEs, such as As, Cd, Se, Mn, Pb, etc.) emitted from coal 1-3

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combustion has caused great damage on the environment and public health

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can result in contamination of soil and water bodies, as well as various diseases. Since

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2009, more than 30 serious poisoning cases associated with TEs pollution have

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happened in China 4. The incidents include blood Pb excess in Children in Fengxiang

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County of Shaanxi province, the Cr contamination in Qujing city of Yunnan province,

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Cd contamination in Longjiang of Guangxi province and Liuyang of Hunan province,

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and As pollution in Hunan, Yunnan, Shangdong, Guizhou province 1. Coal is the main

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primary energy, which is responsible for almost 40% world electricity capacity.

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Recent study has found that coal will surpass crude oil as the most vital source of

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energy in the world by the year of 2020 5. In China, 3.5 billion tons of coal was

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consumed in 2011, of which, nearly 50% was used for power generation

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Coal-fired power plant is considered to be one of the main anthropogenic TEs

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emission sources besides SO2, NOx, and particulate matter (PM) 8-10. 2


. They

6, 7

.

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TEs in coal can be volatilized during coal combustion in power plants, some of

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which will exist in bottom ash. With flue gas cooling, they will undergo form

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transformation, condensation and adsorption. In general, TEs may be emitted into the

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atmosphere in gaseous or particulate state at the end. Therefore, conventional air

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pollution control devices (APCDs) such as SCR, ESP, WFGD, etc. may remove TEs

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from the flue gas. Many researchers have conducted field tests on TEs emission and

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distribution in coal-fired power plants. R.C. Bhangare et al.

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ash, and fly ash from five thermal power plants in India to study the distribution of

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TEs in coal and the combustion residues. Z. Klika et al.

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two fuidised-bed power stations to achieve the effects of boiler output on the TEs

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partition during coal combustion. Sharon M. Swanson et al. 13 also researched the TEs

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distribution in the American coal-fired power plant with determining TEs content in

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the samples of coal, bottom ash and fly ash. However, reports about direct test of TEs

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in flue gas from coal-fired power plant are rarely found due to the complexity of flue

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gas sampling system for TEs. In addition, most field tests about TEs emission are in

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the coal-fired power plant equipped with SCR, ESP/FF, or WFGD. Recently, wet

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electrostatic precipitator (WESP) has played an important role in ultrafine particles

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and aerosols, which draws extensive attention for coal-fired power plant. Researches

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about removal effects of TEs across WESP are seldom reported.

12

11

selected coal, bottom

conducted the field test in

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Chinese government has paid enough attention to pollution emissions from

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coal-fired power plants. It has put forward the ultra-low emission (ULE) for thermal

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power units, which require the limit values of dust, NOx, and SO2 are 5mg/m3, 35

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mg/m3 and 50 mg/m3, respectively in some provinces including Jiangsu and Zhejiang

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province

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characteristics of TEs was conducted on an ULE demonstration coal-fired power plant

14, 15

. In this study, the field test about the migration and emission

3


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in Hebei province, which was equipped with SCR, ESP, WFGD and WESP. Flue gas

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sampling of TEs was conducted at the five measuring point simultaneously by the US

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EPA Method 29. The main purpose includes the following: (1) TEs distribution in this

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ULE power plant, (2) Concentration and enrichment of TEs in coal combustion

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by-products, (3) Removal efficiency of TEs across air pollution control devices

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(APCDs), (4) Emission characteristic of TEs in the flue gas to the atmosphere.

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2. EXPERIMENTAL SECTION

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2.1. Utility Boiler

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The ULE demonstration coal-fired power plant is located in Dingzhou City,

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Hebei province. It is a tangentially fired, pulverized coal boiler with electricity

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generation capacity of 660MW. To achieve the ultra-low emissions, this power plant

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is installed with SCR capable of achieving NOx emission conversion rate of about

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85%, ESP used for PM removal, WFGD with SO2 removal efficiency of 96%, and

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WESP for ultrafine particles or aerosols removal. The SCR catalyst used in this power

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plant is honeycomb with the main component of V2O5-WO3/TiO2, which is arranged

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in high dust way. During the TEs sampling, four ESP felids are in operation. The

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amount of the coal used for burning during TEs sampling process is 250t/h, which is

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corresponding to the 100% output. The proximate and elemental analysis of the coal

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are shown as Table 1, the method used for which is shown in Table 2. Based on the

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National Coal Classification Standard of China (GB/T 5751-2009), the coal sample

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belongs to bituminous.

95

TEs content in the coal sample is shown as Table 3. The average TEs

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concentrations of coal in China and the world are also included in this table. It can be

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found that the average value of TEs including Co, Ni, Cu, Zn, Mo, Cd, Ba, and Pb in

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China is higher than that of the world, which reflects the importance and difficulty in 4


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TEs removal for Chinese coal-fired power plants. Besides Mn, Ag, Sb, Ba, and Pb,

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the concentrations of the remaining TEs in the table of the test coal sample are lower

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than the average value of Chinese coal. This may be due to the geological conditions

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of coal origin 16.

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2.2. Sampling Procedures and Analytical Method

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The simulation sampling locations in the test coal-fired power plant are shown as 19

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Figure 1. US EPA method 29

is used for flue gas sampling of TEs. Five flue gas

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sampling points are located at inlet/outlet of SCR, ESP, WFGD and WESP. The

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gaseous samples are withdrawn from the flue gas isokinetically through a probe with

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a filter maintaining the temperature at 120 0C followed by a series of impingers in an

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ice bath. The particulate TEs can be captured by the quartz fiber filter. Gaseous form

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of TEs is collected by 5% V/V nitric acid (HNO3) / 10% V/V peroxide (H2O2) in the

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two impingers. The first impinger is used to removal moisture in the flue gas, while

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the last impinger filled with certain amount of silica gel is to adsorb moisture from the

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former solution for protecting the following equipment. The system diagram of flue

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gas isokinetic sampling device for TEs can be found in Figure 2.

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During the field test, flue gas sampling of TEs is conducted at the five locations

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simultaneously with US Apex mercury instrument (made in America). Coal sample,

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bottom ash, ESP ash, limestone slurry, WFGD waste water, WESP fresh water, and

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WESP waste water are collected every 0.5 hour. Then the individual sample is put

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together to determine the TEs concentration respectively. The whole sampling process

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lasts for 2 hours.

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Solid samples including coal, bottom ash, ESP ash, particulate matter in the flue

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gas and flue gas desulfurization gypsum are firstly digested by a mixture of acids 5


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(HNO3: HCl: HF = 3: 1: 1) in a microwave oven. Then TEs concentration in them can

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be determined by inductively coupled plasma-mass spectrometry (ICP-MS). TEs in

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clear liquid samples such as HNO3/H2O2 solution, limestone slurry, WESP fresh

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water, and WESP waste water are detected by the ICP-MS directly. For WFGD waste

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water which is epinephelos, it should be separated into solid and clear liquid sample

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through filtration and drying. Then the TEs content in it can be achieved by

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calculating the content in solid and liquid samples. All the TEs detection process is

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done by the EPA Method 6020a which is listed in Table 2. At the same time, the

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detection limits for TEs in solid and liquid samples by using ICP-MS are shown in

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Table 4. Multifunction flue gas analyzer named MRU vario plus (made in Germany)

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is used to detect the oxygen concentration in the flue gas at the TEs sampling point,

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results of which is shown in Table 5. In addition, the flue gas temperature at the TEs

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sampling point is also shown in Table 5. The TEs concentration in flue gas at the five

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locations is unified to 6% O2 for comparison based on the individual O2 content in the

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flue gas.

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3. RESULTS AND DISCUSSION

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3.1. TEs Mass Balance Rate and Distribution

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3.1.1 TEs Mass Balance Rate of Entire System and Each APCD

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Mass balance rate is used to prove the data validity and credibility for the TEs

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field test in the coal-fired power plant. The TEs entire system mass balance rate is

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defined as the ratio of the total amount of TEs in bottom ash, ESF ash, removed in

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WFGD and WESP, and in the flue gas emitted from the stack to that in the feeding

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coal per hour. TEs mass balance rate for APCDs namely SCR, ESP, WFGD and

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WESP is defined as the total output amount of TEs to the total input amount per hour,

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which can be described in the following formula (1) - (4). Due to the complexity for 6


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the analysis process and the representativeness of the taken solid or liquid samples, it

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was acceptable for the value in the range of 70-130% generally 20, 21. R furnace = (TEs bottom ash + TEs flue gas) / TEs feeding coal

(1)

R SCR = TEs SCR, out / TEs SCR, in

(2)

R WFGD = (TEs WFGD, out + TEs WFGD, removal) / TEs WFGD, in

(3)

R WESP = (TEs WESP, out + TEs WESP, removal) / TEs WESP, in

(4)

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Where, R

furnace,

R

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furnace, the SCR, the WFGD, and the WESP, respectively. TEs bottom ash represents the

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total TEs amount in the bottom ash per hour. TEs

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amount in flue gas per hour including the gaseous and particulate form, which can be

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obtained by the concentration of the gaseous TEs multiplied by the volume of the flue

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gas plus the concentration of the TEs in the fly ash multiplied by the weight of the fly

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ash. TEs

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per hour. TEs

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the flue gas at the outlet of the SCR, the WFGD, and the WESP per hour,

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respectively. TEs SCR, in, TEs WFGD, in and TEs WESP, in represent the total TEs amount in

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the flue gas at the inlet of the SCR, the WFGD and the WESP per hour, respectively.

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TEs WFGD, removal and TEs WESP, removal represent the total amount of TEs removed in the

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WFGD and the WESP per hour, respectively.

feeding coal

SCR,

R

WFGD

and R

WESP

represent the mass balance rate for the

flue gas

represents the total TEs

represents the total TEs amount in the corresponding feeding coal

SCR, out,

TEs

WFGD, out

and TEs

WESP, out

represent the total TEs amount in

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It should be specially reminded that TEs in the flue gas contains two kinds of

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gaseous and particulate form. TEs associated with fly ash in the flue gas were named

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as the particulate TEs.

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Results of mass balance rates for the entire system and APCDs are shown as

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Table 6. It can be found that the TEs mass balance rates for the entire system are in

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the range of 71.99%-107.94% while the values for furnace and APCDs are in the 7


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range of 71.01%-129.05%, which confirms the validity and reliability of the field test

170

data.

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3.1.2 TEs Distribution in Bottom Ash, ESP Ash, WFGD, WESP and Stack

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Figure 3 shows the mass distribution of TEs in the coal-fired power plant. It can

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be found that TEs are mainly distributed in bottom ash and ESP ash, which accounts

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for 2.11%-12.15% and 87.83%-97.83% respectively. Little amount of TEs are

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distributed in WFGD and WESP as well as the stack, which has the proportion of

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-0.08%-0.05%, 0.00%-0.06% and 0.00%-0.10%, respectively. The reasons for the

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negative value removed in the WFGD can be explained as follows

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amount of TEs distributed in the flue gas emitted from ESP; (2) Flow fluctuation

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existed in gypsum, limestone slurry and WFGD wastewater; (3) Complexity in

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sampling and analysis system. For the very low amount of TEs distributed in WFGD,

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WESP and stack, which bring no distinct distinction for the researched TEs, the

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in-depth discussions are not conducted in this section. TEs distribution characteristics

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have relations with their volatility, which is dependent on the existence forms in coal,

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their own properties and the surrounding environment such as combustion

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temperature, oxidizing or reducing atmosphere, etc. In general, TEs associated with

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organics or sulfide, high furnace temperature and oxidizing atmosphere are beneficial

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for their volatilization. The ratio higher than 10% in the bottom ash for TEs are Cr,

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Mn and Ba, while the value lower than 5% are Zn, As, Mo, Cd, Sb and Pb. For TEs in

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ESP ash, the proportion less than 90% are Cr, Mn and Ba, while the value more than

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95% are Zn, As, Mo, Cd, Sb and Pb, which corresponds to the TEs in the bottom ash.

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As, Mo, Cd, Pb, et al. are usually linked with sulfur minerals in coal 24-26. During coal

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combustion, they will firstly emit with sulfur minerals decomposing and then

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condense on the fly ash as flue gas cooling, which result in little amount of them 8


22, 23

: (1) Little

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existed in bottom ash but high ratio in ESP ash. In contrast, Ba and Mn, etc. may

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occur in discrete minerals that will be highly enriched in ash matrix

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be used to explain little amount of Cr, Mn, Ba in ESP ash but high amount of them

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distributed in bottom ash.

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3.2 Concentrations and Enrichment of TEs in coal combustion by-products

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3.2.1 Concentration of TEs in Coal Combustion By-products

11, 27

, which can

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TEs concentrations in coal combustion by-products are listed in Table 7.

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Although there are no limits for TEs emission in solid and liquid coal combustion

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by-products from coal-fired power plants in China, relevant standards for soil and

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ground water are proposed by the State Technical Supervision Bureau and National

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Environmental Protection Agency. The emission limits for TEs in soil and ground

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water are also listed in Table 7. Based on application functions and protection

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objectives of the soil, the secondary standard with PH value of 6.5-7.5 which focused

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on the agricultural production and human health are chosen in this study. Considering

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the water for life drinking as well as agricultural irrigation, the third class quality

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standards of ground water are selected in this paper. For the solid samples emitted

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from the coal-fired power plant, most TEs are lower than the limits except Ni, Zn and

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Cd in ESP ash, whose values are slightly higher than the limit value. It shows that

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bottom ash and gypsum have little effects on soil in terms of TEs while attention

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should be paid to some TEs in the ESP ash such as Ni, Zn and Cd. For waste water

214

from WFGD and WESP, almost all the TEs in WFGD waste water are higher than the

215

limit value for ground water except Ag and Sb, whose values are not given.

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Concentration of Cr and Mn in the waste water from WFGD far exceeds the limits,

217

which is nearly 130 and 900 times as the value in ground water. It indicates that

218

enough emphasis should be put on the desulfurization wastewater treatment. Except 9


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for Mn, Ag and Sb, all the remining TEs in the WESP waste water are under the limit

220

value, which have no influence on ground water.

221

3.2.2 Enrichment of TEs in Bottom Ash and ESP Ash

222

Relative enrichment index (REI) is considered as the best way to evaluate

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enrichment characteristics of TEs in bottom ash and fly ash, which has been used by

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many researchers 10, 11, 25. The REI formula can be shown as formula (5): REI = CTEs, BA/FA × Acoal,ad / CTEs, coal

(5)

225

Where, CTEs, BA/FA, CTEs, coal represent the concentration of the TEs in bottom ash or fly

226

ash, and the coal respectively. Acoal,ad represents the ash content in the feeding coal on

227

the basis of air dry. Relative enrichment index of TEs in bottom ash and ESP ash is shown as Figure

228 229

4. For the TEs in ESP ash, they are in the order:

230

Zn > Ni > Sb > Ba > 1.2 > Pb > Cd > Co > Cr > Mn > Ag > Cu > As > 1 > Mo

231

For the TEs in bottom ash, they are in the order: Mn > Ba > 0.7 > Cr > Ni > Cu > Ag > Co > Zn > Cd > As > Mo > Pb > Sb

232 233

The results indicate Zn, Ni, Sb and Ba tend to accumulate in ESP ash, while the

234

enrichment of Mn and Ba occurs in bottom ash during coal combustion. JOSEÄ R, et

235

al.

236

Class I: Easily enriched in the bottom ash, such as Mn and U, etc. Class II: little

237

amount in bottom ash while large quantities in fly ash, such as Zn, Sb, Pb, Cd and As,

238

etc. Class III: Mainly existed in flue gas, such as Hg. These classifications for TEs

239

show great agreement with our studies. Four reasons can be used to explain the

240

difference of TEs enrichment in bottom ash and ESP ash, which are described as these

241

16

242

for the bottom ash and ESP ash existence, (3) Different pore structure existed in

30

divided TEs into three categories according to their volatility in coal burning.

: (1) Different material species in bottom ash and ESP ash, (2) Different temperature

10


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bottom ash and ESP ash, (4) TEs existing form in coal and during coal combustion.

244

The unburn carbon and CaO on fly ash could absorb some TEs such as As with flue

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gas cooling, which benefit for TEs enrichment. In this study, the unburn carbon

246

content of the fly as is 1.37 wt.%. High temperature and little specific surface area

247

result in few TEs in bottom ash. Mn usually occurs in coal in the form of carbonates,

248

siderites and ankerite, which are difficult to volatilize 31. In addition, Mn would like to

249

connect with Fe oxides which are mainly in bottom ash. Therefore, Mn tends to

250

accumulate in bottom ash.

251

3.3 Removal Efficiency of TEs across ESP, WFGD and WESP

252

In coal-fired power plants, air pollution control devices (APCDs) including SCR,

253

ESP, WFGD, and WESP, etc. are not only used to remove NOx, particulate matter and

254

SO2, but also used to capture TEs. The separate and overall removal rate of TEs

255

across APCDs in this study are shown in Figure 5-8, and the gaseous TEs

256

concentration along the flue gas path is listed in Table 8 as well. Since the gaseous

257

TEs content does not change across the SCR device which can be found in Table 8,

258

the removal rate is almost zero. From Figure 5, the whole researched TEs removal

259

rate is higher than 99.90% except Cr with the value of 99.87%. In the flue gas before

260

ESP, particulate TEs are the main form. Thus, high dust efficient removal

261

performance of ESP results in great TEs removal effects. Form Figure 6, the TEs

262

removal rate across WFGD higher than 60% are Co, Ni, Zn, Sb and Ba.

263

Thermodynamic studies

264

the flue gas in the form of chloride, which are easily soluble in water. Oxidation state

265

like CrO3 and Cr2O3 is the main form of Cr in flue gas, thus WFGD has little removal

266

effect on it. On the other hand, the particulate matter can be captured by WFGD,

267

which increases the TEs removal efficiency.

32

show that some TEs like Co, Ni, Zn and Sb, etc. exist in

11


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From Figure 7, it can be found that more than 60% of Mn, Co, As, Ag, Sb, Ba

269

and Pb are removed by WESP, which indicates some gaseous TEs are further

270

removed under the conditions of more water vapor and lower temperature of about 50

271

0

272

the TEs in flue gas after WESP are in the gaseous form. The negative removal rate of

273

Ni and Zn may due to the error in TEs sampling and analysis or re-release form

274

WESP water under the discharge conditions, which needs further study. Figure 8

275

shows the TEs overall removal rate across ESP + WFGD + WESP is larger than

276

99.90%, which demonstrates this ULE coal-fired power plant has excellent capture

277

effects on TEs.

278

3.4 Emission Characteristics of TEs in Flue Gas to the Atmosphere

279

3.4.1 Emission Concentration of TEs in Flue Gas to the Atmosphere

C. Table 7 shows WESP has the capacity for further particulate matter removal. All

280

The emission concentration of TEs in flue gas to the atmosphere is the

281

concentration escaped from WESP, as shown in Table 8. The concentration of the

282

whole researched TEs is in the range of 0.00-1.33 µg/m3, which is extremely low.

283

There is no particular emission standard for TEs emitted from the coal-fired power

284

plant except Hg with the value of 30 µg/m3 in China. However, Integrated Emission

285

Standard of Air Pollutants was enacted by the National Environmental Protection

286

Agency of China in 1996 33, specifying the limits of Cr, Pb, Cd and Ni were 0.08, 0.9,

287

1.0 and 5.0 mg/m3, respectively. Compared to this standard, the emission

288

concentration of TEs in this ULE coal-fired power plant is far less than the limits. The

289

European Commission also gives the limit value for TEs emitted to the atmosphere in

290

the Air Quality Standards, which permits Pb, As, Cd and Ni to be 0.5 µg/m3, 6ng/m3,

291

5ng/m3 and 20ng/m3, respectively

292

coal-fired power plant, they are almost equal to or lower than the limits except Ni.

34

. For Pb, As, Cd and Ni emitted from this ULE

12


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From the perspective of the coal-fired industry, TEs in the flue gas to the air from this

294

coal-fired power plant can be seen as the ultra-low emissions.

295

3.4.2 Atmospheric Emission Factor of TEs

296

An emission factor is a representative value that describes the amount of a

297

pollutant released to the air with an activity associated with the release of that

298

pollutant 25. In this work, emission factors of the TEs are expressed as the amount of a

299

given metal emitted through stack divided by the quantity of coal burned, as listed in

300

Table 9. It can be seen that Co, Ni, Cu, As, Mo, Ag, Cd, Sb, Ba and Pb emitted via

301

stack are lower than 3 mg/t coal while Zn is 6.58 mg/t coal. Compare to other TEs, Cr

302

and Mn have relatively high value of nearly 11 mg/t coal. In contrast to Pb, Cd and

303

Mn released from six coal-fired power plants in China

304

power plant are extremely low. Coal-fired power plants equipped with SCR + ESP +

305

WFGD + WESP can effectively control the TEs emission.

306

4. Conclusion

10

, TEs emitted from this

307

For the ULE coal-fired power plant, most of the TEs are mainly distributed in

308

bottom ash and ESP ash with the proportion of 2.11%-12.15% and 87.83%-97.83%

309

respectively while little amount of them exists in WFGD, WESP and stack. Cr, Mn

310

and Ba are mainly accumulated in bottom ash while As, Mo and Pb mainly exist in

311

ESP ash. Distribution of TEs in the coal-fired power plant is affected by their form in

312

coal and external conditions.

313

Solid coal combustion by-products like bottom ash and gypsum have little impact

314

on soil in terms of TEs but Ni, Zn and Cd in the ESP ash should be paid more

315

attention. Concentration of Cr and Mn in WFGD waste water greatly exceeds the

316

limits. All the TEs studied in this work except Mn, Ag and Sb in WESP waste water 13


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317

have no influence on ground water. Zn, Ni and Sb tend to enrich in ESP ash while

318

enrichment of Mn occurs in bottom ash. Ba is enriched in both bottom ash and ESP

319

ash.

320

Particulate TEs are the main form in the flue gas, the removal rate of TEs studied

321

in this work for ESP is higher than 99.87%. Both the WFGD and WESP are able to

322

capture TEs in flue gas. The TEs overall removal rate across ESP + WFGD + WESP

323

is larger than 99.90%. TEs concentration in the flue gas emitted from the stack is in

324

the range of 0.00-1.33 µg/m3. Co, Ni, Cu, As, Mo, Ag, Cd, Sb, Ba and Pb emitted via

325

stack are lower than 3 mg/t coal while Zn is 6.58 mg/t coal. Compared to other TEs,

326

Cr and Mn have relatively high value of nearly 11 mg/t coal. The ULE coal-fired

327

power plant equipped with SCR + ESP + WFGD + WESP has good effects on TEs

328

emission control.

329

330

AUTHOR INFORMATION

331

Corresponding Author

332

*E-mail for Yufeng Duan: [email protected] Telephone: 86+025-83795652. Fax:

333

86+025-83795652.

334

Notes

335

The authors declare no competing financial interest.

336

ACKNOWLEDGMENTS

337

This project was financially supported by the National Natural Science

338

Foundation of China (51376046，51576044), the Fundamental Research Funds for

339

the Central Universities, Graduate Student Research and Innovation Program of

340

Jiangsu Province (CXZZ13_0093, KYLX_0115, KYLX_0184, KYLX15_0071), the 14


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Scientific Research Foundation of Graduate School of Southeast University

342

(YBJJ1505), and the help from Xi’an Jiaotong University.

343

344

(1) Tian, H. Z.; Lu, L.; Hao, J. M.; Gao, J. J.; Cheng, K.; Liu, K. Y.; Qiu, P. P.; Zhu,

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C. Y. A review of key hazardous trace elements in Chinese coals: abundance,

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occurrence, behavior during coal combustion and their environmental impacts.

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C. Y.; Wang, K.; Hua, S. B. Atmospheric emission inventory of hazardous trace

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elements from China’s coal-fired power plants-temporal trends and spatial

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M. R. Distribution of trace elements from a coal burned in two different Spanish

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(5) Vejahati, F.; Xu, Z. H; Gupta, R. Trace elements in coal: Associations with coal

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and Pb from coal in China, Atmospheric Environment 2012, 50, 157–163.

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deposition from coal-fired thermal power plants. Environ Monit Assess 2015,

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coals: distribution, modes of occurrence, and environmental effects. Environ

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partitioning during coal combustion in two fuidised-bed power stations. Fuel

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coal-burning power plants in the United States. International Journal of Coal

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Anhui, China. Fuel 2013, 107, 315–322.

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genetic types, impacts on human health, and industrial utilization. International

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Journal of Coal Geology 2012, 94, 3-21.

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(18) Ketris, M. P., Yudovich, Y. E. Estimations of Clarkes for carbonaceous biolithes:

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world average for trace element contents in black shales and coals. International

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(19) Myers, J.; Kelly, T.; Lawrie, C.; Riggs, K. United States Environmental

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Protection Agency, USEPA, Method M29 Sampling and Analysis, Environmental

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Technology Verification Report. Battelle, Columbus, Ohio, 2002. pp. 15–22.

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(20) Wang, S. X.; Zhang, L.; Li, G. H.; Wu, Y.; Hao, J. M.; Pirrone, N.; Sprovieri, F.;

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Ancora, M. P. Mercury emission and speciation of coal-fired power plants in

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China, Atmospheric Chemistry and Physics 2010, 10, 1183–1192.

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(21) Quick, W. J.;Irons, R. M. A. Trace element partitioning during the firing of washed and untreated power station coals. Fuel 2002, 81, 665–672.

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(22) Córdoba, P.; Ochoa-Gonzalez, R.; Font, O.; Izquierdo, M.; Querol, X.; Leiva, C.;

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López-Antón, M. A.; Díaz-Somoano, M.; Martinez-Tarazona, M. R.; Fernandez,

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C.; Tomás, A. Partitioning of trace inorganic elements in a coal-fired power plant

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equipped with a wet Flue Gas Desulphurisation system. Fuel 2012, 92, 145–157.

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(23) Tao, Y.; Zhuo, Y. Q.; Zhang, L.; Chen, C. H.; Xu X. C. Mercury transformation

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across various air pollution control devices in a 200 MW coal-fired boiler of

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China. Asia-Pacific Journal of chemical Engineering 2010, 5, 756–762.

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(24) Zhou, C. C.; Liu G. J.; Fang, T.; Wu, D.; Lam, P. K. S. Partitioning and

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transformation behavior of toxic elements during circulated fluidized bed

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combustion of coal gangue. Fuel 2014, 135, 1–8.

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(25) Goodarzi, F.; Huggins, F. E.; Sanei, H. Assessment of elements, speciation of As,

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Cr, Ni and emitted Hg for a Canadian power plant burning bituminous coal.

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International Journal of Coal Geology 2008, 74, 1–12.

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(26) Querol, X.; Fernhndez-Turiel, J. L.; Lbpez-Soler, A. Trace elements in coal and

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their behavior during combustion in a large power station. Fuel 1995, 74(3),

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331-343.

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(27) Sia, S. G.; Abdullah, W. H. Enrichment of arsenic, lead, and antimony in

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Balingian coal from Sarawak, Malaysia: Modes of occurrence, origin, and

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partitioning behaviour during coal combustion. International Journal of Coal

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Geology 2012, 101, 1–15.

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(28) Environmental quality standard for soils, national standards of People's Republic of China, GB 15618-1995, 1995. (29) Quality standard for ground water, national standards of People's Republic of China, GB/T 14848-9, 1993.

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(30) Otero-Rey, J.; Loapez-Vilarinno, J.; Moreda-Pineiro, J.; Alonso-Rodriaduez, E.;

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Muniategui-Lorenzo, S.; Loapez-Mahiaa, P.; Prada-Rodriaguez, D. As, Hg, and 17


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Se flue gas sampling in a coal-fired power plant and their fate during coal

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combustion. Environ. Sci. Technol. 2003, 37, 5262-5267.

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(31) Zajusz-Zubek, E.; Konieczynski, J. Coal cleaning versus the reduction of mercury

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and other trace elements’’ emissions from coal combustion processes. Archives of

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Environmental Protection 2014, 40(1), 115-127.

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(32) Jano-Ito, M. A.; Reed, G. P.; Millan, M. Comparison of thermodynamic

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equilibrium predictions on trace element speciation in oxy-fuel and conventional

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coal combustion power plants. Energy & Fuels 2014, 28, 4666−4683.

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(33) Integrated Emission Standard of Air Pollutants, national standards of People's Republic of China, GB 16297-1996, 1996. (34) Air Quality Standards, European Commission, 2015, http:// ec.europa.eu /environment /air/ quality/standards.htm

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Table captions:

454

Table 1. Proximate and elemental analysis of the coal sample

455

Table 2. Analysis method used in tests

456

Table 3. TEs content in the coal sample (mg/kg)

457

Table 4. Detection limits of TEs in solid and liquid samples for ICP-MS

458

Table 5. O2 concentration in the flue gas and the flue gas temperature at the sampling

459

location

460

Table 6. Mass balance rates of trace elements in entire system and APCDs

461

Table 7. TEs concentration in the coal combustion by-products

462

Table 8. Gaseous TEs concentration along the flue gas path (Based on 6% O2, µg/m3)

463

Table 9. Emission factors of TEs in the coal-fired power plant (mg/t coal)

464 465 466

Figure captions:

467

Figure 1. Simultaneous sampling locations in tested power plant

468

Figure 2. System diagram of flue gas TEs isokinetic sampling device

469

Figure 3. Mass distribution of TEs in the coal-fired power plant

470

Figure 4. Relative enrichment index of TEs in bottom ash and ESP ash

471

Figure 5. TEs removal rate across ESP

472

Figure 6. TEs removal rate across WFGD

473

Figure 7. TEs removal rate across WESP

474

Figure 8. Overall TEs removal rate across ESP+WFGD+WESP

475

19


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476

Page 20 of 36

Table 1. Proximate and elemental analysis of the coal sample Proximate analysis

LHV

Elemental analysis

Mar %

Aar %

Var %

FCar %

Qar,net MJ/kg

Car %

Har %

Oar %

Nar %

Sar %

16.08

15.17

26.67

42.09

21.74

54.02

3.22

10.25

0.96

0.31

477

20


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478

Table 2. Analysis method used in tests

a

Sample

Method

Proximate analysis of coal Total water content in coal Total sulfur content in coal Carbon / hydrogen content in coal Nitrogen content in coal Chlorine content in coal Heat value analysis of coal TEs in solution / water / waste water TEs in coal / ash / gypsum

GB/T a 212-2008 GB/T a 211-2007 GB/T a 214-2007 GB/T a 476-2008 GB/T a 19227-2008 GB/T a 3558-2014 GB/T a 213-2008 EPA Method 6020a EPA Method 6020a

National standard of China

21


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479

Page 22 of 36

Table 3. TEs content in the coal sample (mg/kg) Cr

Mn

Co

Ni

Coal 12.3 180 5.9 9 sample China 17 15.4 116.2 7 15 18 World 16 nd 5.1 13 n.d. is shorten for “not detected”.

Cu

Zn

As

Mo

Ag

Cd

Sb

Ba

Pb

11.1

33

3

2.6

0.06

0.08

2

245

23.4

17.5 16

38 23

3.79 8.3

2.7 2.2

n.d. n.d.

0.25 0.22

0.71 0.92

159 150

15.1 7.8

22


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480

Solid (mg/kg) Liquid (µg/L)

Table 4. Detection limits of TEs in solid and liquid samples for ICP-MS Cr

Mn

Co

Ni

Cu

Zn

As

Mo

Ag

Cd

Sb

Ba

Pb

0.1

0.05

0.01

0.05

0.02

0.2

0.1

0.05

0.01

0.01

0.05

0.05

0.02

0.05

0.02

0.005

0.05

0.02

0.1

0.05

0.03

0.005

0.005

0.03

0.03

0.01

481 482

23


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483

Table 5. O2 concentration in the flue gas and the flue gas temperature at the sampling

484

location Location

Inlet of SCR

Outlet of SCR

Outlet of ESP

Outlet of WFGD

Outlet of WESP

O2 / % Temperature / 0C

3.63 370

4.38 350

4.59 114

5.04 49

5.57 48

485

24


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486

Table 6. Mass balance rates of trace elements in entire system and APCDs

Cr Mn Co Ni Cu Zn As Mo Ag Cd Sb Ba Pb

Mass balance rate in each APCD / %

Entire system /%

Furnace

SCR

ESP

WFGD

WESP

88.75 88.72 87.76 99.45 81.71 107.94 74.42 71.99 84.13 86.56 91.79 99.28 86.56

92.63 118.72 120.54 128.63 117.38 129.05 109.75 105.75 82.73 114.53 113.28 127.29 106.58

95.39 72.23 71.30 75.69 72.51 83.14 71.01 72.12 125.82 75.07 80.74 76.00 71.01

99.91 99.99 99.98 100.00 93.40 99.99 94.38 93.39 81.19 99.95 99.97 99.99 103.10

101.49 76.43 95.86 82.68 79.77 101.42 102.37 82.69 81.79 91.02 85.91 81.73 91.62

86.40 72.57 77.13 115.04 71.70 90.53 80.19 84.89 72.97 73.36 108.47 77.11 76.41

487 488

25


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489

Table 7. TEs concentration in the coal combustion by-products Solid samples (mg/kg) Bottom ash Cr Mn Co Ni Cu Zn As Mo Ag Cd Sb Ba Pb

490

Page 26 of 36

ESP ash

47.9 76.15 750 1105 14.6 37.8 30 64.35 29.6 65.4 50 270.3 3.1 16.95 2.4 14.25 0.15 0.367 0.1 0.525 1.5 14.15 1009 1710 21.2 155.2 n.g. is short for “not given”.

Liquid samples (µg/L)

Gypsum

WFGD waste water

WESP waste water

5.9 20.4 0.53 1.5 1.8 3.1 0.9 0.2 0.04 n.d. 0.1 16.9 1.5

6436.4 88589.3 1165.6 2481.6 1821.4 3149.1 1260.7 227.6 1.1 280.9 74.9 14398.9 1891.6

21.6 255 5.1 31.2 6.3 29 1.3 3.8 0.52 0.9 1.9 66 12.5

491 492

26


Relevant standards Soil 28 （mg/kg） 200 n.g. n.g. 50 100 250 25 n.g. n.g. 0.30 n.g. n.g. 300

ground water 29 (µg/L) 50 100 50 50 1000 1000 50 100 n.g. 10 n.g. 1000 50

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493

Table 8. Gaseous TEs concentration along the flue gas path (Based on 6% O2, µg/m3) TEs in flue gas Crp Crg Mnp Mng Cop Cog Nip Nig Cup Cug Znp Zng Asp Asg Mop Mog Agp Agg Cdp Cdg Sbp Sbg Bap Bag Pbp Pbg

SCR In 1254.04 2.58 24043.68 0.36 832.89 0.40 1335.76 0.75 1516.48 1.08 5107.32 2.56 396.01 1.50 331.58 0.97 5.66 0.00 11.00 0.02 275.01 0.55 35358.36 3.27 3017.25 0.98

Out 1200.42 2.02 17419.06 2.54 595.87 0.10 1014.40 0.37 1103.47 0.37 4260.97 0.60 282.96 0.17 240.40 0.18 7.13 0.00 8.28 0.00 223.06 0.10 26956.20 4.14 2372.46 0.59

ESP Out 0.59 0.99 8.50 0.38 0.29 0.00 0.49 0.39 0.50 0.08 2.08 0.25 0.13 0.01 0.11 0.04 0.00 0.00 0.00 0.00 0.11 0.03 13.15 0.47 1.19 0.04

WFGD Out 0.14 1.40 2.01 2.36 0.07 0.03 0.12 0.09 0.12 0.23 0.49 0.24 0.03 0.03 0.03 0.03 0.00 0.01 0.00 0.00 0.03 0.01 3.11 2.32 0.28 0.47

494 495

27


WESP Out 1.33 1.33 0.03 0.29 0.21 0.82 0.01 0.06 0.00 0.00 0.01 0.34 0.16

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496

TEs EF

Cr 10.71

Page 28 of 36

Table 9. Emission factors of TEs in the coal-fired power plant (mg/t coal) Mn 10.71

Co 0.25

Ni 2.35

Cu 1.73

Zn 6.58

As 0.12

Mo 0.50

Ag 0.03

28


Cd -0.02

Sb 0.05

Ba 2.74

Pb 1.27

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497

Figure 1. Simultaneous sampling locations in tested power plant

498 499

29


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500

Figure 2. System diagram of flue gas TEs isokinetic sampling device

501 502 503

30


Page 30 of 36

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504

Figure 3. Mass distribution of TEs in the coal-fired power plant

Mass distribution / %

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 90 75 60 45 30 15 0.12 0.08 0.04 0.00 -0.04 -0.08 Cr Mn Co Ni Cu Zn As Mo Ag Cd Sb Ba Pb

Trace elements

505

Bottom ash ESP ash TEs removed in WESP

TEs removed in WFGD TEs emitted in stack

31


Energy & Fuels

506

Figure 4. Relative enrichment index of TEs in bottom ash and ESP ash

1.4

Relative enrichment index

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

Bottom ash ESP ash

1.2 1.0 0.8 0.6 0.4 0.2 0.0 Cr Mn Co Ni Cu Zn As Mo Ag Cd Sb Ba Pb

507

Trace elements

508

32


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Page 33 of 36

509

Figure 5. TEs removal rate across ESP 100.2

Removal rate across ESP / %

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

100.0

99.8

99.6

99.4

510


Trace elements

511

33


Energy & Fuels

512

Figure 6. TEs removal rate across WFGD 80

Removal rate acrossWFGD / %

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

70 60 50 40 30 20 10 0 Cr Mn Co Ni Cu Zn As Mo Sb Ba Pb

513

Trace elements

514

34


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Page 35 of 36

515

Figure 7. TEs removal rate across WESP 100.25 100.00

WFGD+WESP/ %

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

99.75 99.50 99.25 99.00


Trace elements 516 517

35


Energy & Fuels

518

Figure 8. Overall TEs removal rate across ESP+WFGD+WESP 100.25

Overall removal rate across ESP+ WFGD+WESP/ %

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

100.00 99.75 99.50 99.25 99.00


Trace elements

519

36


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Migration and Emission Characteristics of Trace Elements in a 660

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