Subscriber access provided by University of Chicago Library
Environmental and Carbon Dioxide Issues
Distribution and Speciation Transformation of Hazardous Trace Element Arsenic in Particulate Matter of a Coal - fired Power Plant Shilin Zhao, Yufeng Duan, Cong Chen, Hao Wu, Deye Liu, Meng Liu, Jianhong Lu, and Xiaobing Gu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00472 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 14, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 21 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
1
Distribution and Speciation Transformation of Hazardous Trace Element
2
Arsenic in Particulate Matter of a Coal - fired Power Plant
3
Shilin Zhao a, b, Yufeng Duan a, *, Cong Chen a, Hao Wu a, Deye Liu c, Meng Liu a, Jianhong Lu a,
4
Xiaobing Gu d
5
a
6
Energy and Environment, Southeast University, Nanjing, 210096, China
7
b
8
Canada
9
c
Jiangsu Provincial Center for Disease Control and Prevention, Nanjing 210009, China
10
d
Datang Environmental Industry Group Co., Ltd, Beijing, 100097, China
11
ABSTRACT: Particle matter (PM) emitted from coal combustion can cause great
12
harm on human health and the environment. The existence of hazardous trace element
13
arsenic (As) in PM intensifies its toxicity. In this work, four particle sizes of fly ash
14
PM (PM10) before the electrostatic precipitator (ESP) in a
15
600 MW coal-fired power plant was sampled by a Dekati Low Pressure Impactor
16
(DLPI). The coal sample, bottom ash, ash from ESP (ESP ash) were collected
17
simultaneously. Concentrations of total and valent As (As3+ and As5+) in the sample
18
were determined by the inductively coupled plasma-mass spectrometry (ICP-MS) and
19
high performance liquid chromatography (HPLC) coupled with ICP-MS, respectively.
20
The morphological structure and chemical components of the PM surface were
21
characterized by the scanning electron microscope (SEM) and X-ray fluorescence
22
spectrometry (XRF). Results show that the coal used for the power plant is low-sulfur
23
and low-chlorine bituminous coal with 3.851 mg/kg of As. Total As content in the
24
ESP ash is 11.44 times of that in the bottom ash (only 1.637 mg/kg). Arsenic is prone
25
to enrich in ESP ash while dissipate in bottom ash. With fly ash particle diameter
26
decreasing, concentration of total As increases from 9.599 mg/kg to 20.088 mg/kg and
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, T6G 1H9,
1
ACS Paragon Plus Environment
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
27
the corresponding relative enrichment index increases from 0.68 to 1.42. The main As
28
form in coal-fired fly ash is As5+, which occupies 90.98%-98.63% of the total As
29
amount. Toxic As3+ has a little higher ratio in bottom ash with value of 21.01%. More
30
As physical adsorption and chemisorption active sites on the smaller fly ash PM with
31
higher specific area contribute to increase in the concentration of total As and As5+ as
32
the particle sizes decrease. Moreover, the transformation mechanism of As to PM
33
during coal combustion was discussed.
34
KEYWORDS: Coal-fired power plant; Fine particulate matter; Arsenic; Distribution;
35
Speciation transformation
36
1. INTRODUCTION
37
Coal is a major primary source of energy in China, which accounts for 67.3% of
38
primary energy consumption 1. Particle matter (PM), especially nanoparticles, emitted
39
from coal combustion can enter human lungs and cause various respiratory diseases
40
such as asthma, lung cancer
41
can diffuse in environment and damage the body's immune system, emission of
42
arsenic (As) and its compounds in coal combustion process has caused the widespread
43
concern in the world
44
plants, coal-fired power plant is known as one of the largest anthropogenic sources of
45
PM and As
46
pollutants, such as NOx, SO2, and PM, more and more coal-fired power plants has
47
been installed with the air pollution control devices (APCDs), like selective catalytic
48
reduction (SCR), electrostatic precipitator (ESP), or fabric fibers (FFs), and wet flue
49
gas desulfurization (WFGD) in China 12. Although these APCDs have the synergistic
50
control effects on emission of PM and As
51
ESP or FFs for fine particles, especially the PM with diameter of less than 0.5 µm 10, 17.
2-6
. Due to the high toxicity and carcinogenicity, which
7-9
. With the large amounts of coal consumed in thermal power
10, 11
. Facing the increasingly stringent requirements on the conventional
13-16
, there is little removal efficiency of
2
ACS Paragon Plus Environment
Page 2 of 21
Page 3 of 21 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
52
At high furnace temperature, arsenic escape from the coal in the vapor phase. With
53
flue gas cooling, it is prone to be enriched in fine PM 18. Thus, it increases the toxicity
54
of ultra-fine and nano-fine particles undoubtedly, which needs to be given enough
55
attention 19-23. The combination of PM and As has been investigated by several authors
56
24
10, 24-31
.
57
Wang et al.
collected PM before an ESP of a 660 MW coal-fired power plant
58
located in Nanchang by the Dekati Gravimetric Impactor (DGI), results of which
59
showed that concentration of As, Cd, Cr, Pb increased with decreasing the particle
60
size. Yu et al. 25 sampled PM at the inlet of ESP in a coal-fired power plant in Beijing
61
through an Andersen 8-stage Stack Impactor with aerodynamic diameter separation to
62
study the distribution of As, Pb, Cr, Cd, Ni, Co, Cu, Zn in fine PM. It was found that
63
obvious enrichment of those 8 hazardous trace elements occurred in fly ash with small
64
particle diameter, and concentration of most volatile As in smallest PM (Aerodynamic
65
diameter: 0-0.71 µm) was 30 times of that in the largest PM (10.97-17.54 µm). Yi et al.
66
26
67
V, Zn, Mn, Fe in fine fly ash at the inlet and outlet of FFs in a 220 MW power plant
68
by the Electrical Low Pressure Impactor (ELPI), finding that enrichment trends of all
69
elements after FFs were basically the same as the inlet of it. Wang et al.
70
investigated the enrichment of trace elements in PM entering and leaving the novel
71
ESP of a 660 MW coal-fired power plant, results of which indicated enrichment
72
factors of As, Cd, Cr, Pb in PM were 31.2-41.4, 20.1-26.8, 12.2-14.0, 4.8-6.0,
73
respectively. However, the current studies were only focused on the enrichment
74
characteristic of hazardous trace elements in PM. The content of different forms of As
75
(As3+ is more toxic than As5+ 32) in PM, and the transformation mechanism of As to
76
PM during coal combustion are seldom studied.
studied the size-classified relative enrichment factors of As, Hg, Se, Cd, Cr, Cu, Al,
3
ACS Paragon Plus Environment
10
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
77
In this study, the PM at the inlet of ESP in a 600 MW coal-fired power plant was
78
sampled by a Dekati Low Pressure Impactor (DLPI). The content of total As in
79
different sizes of PM was detected by the inductively coupled plasma-mass
80
spectrometry (ICP-MS). Valent As, namely As3+ and As5+ in PM was determined by
81
the high performance liquid chromatography (HPLC) coupled with ICP-MS. The
82
scanning electron microscope (SEM) and X-ray fluorescence spectrometry (XRF)
83
were used to characterize the physical and chemical properties of the PM surface. The
84
contents includes: (1) Enrichment characteristics of total As in the samples; (2)
85
Content and proportion of valent As in the samples; (3) SEM, XRF analysis of the
86
samples; (4) Transformation mechanism of As to PM in coal combustion process. The
87
objective is to explore the distribution and speciation transformation of hazardous
88
trace element As in PM, which hopes to provide a guidance for the effective control of
89
PM with As.
90
2. EXPERIMENTAL SECTION
91
2.1. Plant Description, PM Sampling and Coal analysis
92
The field test was conducted in a 600 MW coal-fired power plant located in
93
Inner Mongolia. To control the conventional air pollutant emission, SCR and ESP
94
were used to remove NOx and PM in flue gas, respectively. WFGD was adopted for
95
the SO2 removal as well as the fine PM. The combination of SCR, ESP and WFGD is
96
the most popular APCDs in coal-fired power plants in China. PM in flue gas at the
97
inlet of ESP was sampled by a DLPI (Dekati Ltd, Finland), which has 13 stages (12
98
channels) with 50% cutpoints ranging from 0.0281, 0.0565, 0.0944, 0.154, 0.258,
99
0.377, 0.605, 0.936, 1.58, 2.36, 3.95, 6.6 to 9.8 µm (in aerodynamic diameter),
100
respectively. To collect enough amount of the PM for As determination, the sampling
101
was conducted twice. For each time, the PM sampling lasted for 3 hours with gas flow 4
ACS Paragon Plus Environment
Page 4 of 21
Page 5 of 21 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
102
rate of 10 L/min. To avoid the interference of water vapor condensation in flue gas,
103
the temperature of DLPI was kept above 100 °C. And working pressure of the device
104
was 100 mbar. After the sampling, four particle sizes of PM (named PM10), which was with aerodynamic diameter of less than 1 µm, 1-2.5 µm,
106
2.5-10 µm, larger than 10 µm, respectively, in the two sampling processes were mixed
107
for the determination of As speciation and concentration.
108
In the whole PM sampling process, the corresponding coal sample, bottom ash,
109
and ash removed by ESP (ESP ash) were gotten about per hour. Then, the same kind
110
sample was putted together evenly, which minimized errors in sample collection. The
111
electricity generation capacity was maintained at about 480 MW. The proximate and
112
ultimate analyses of the coal sample are shown in Table 1. Based on Chinese
113
classification method for coal used in boiler, the coal belongs to bituminous coal. The
114
chlorine content (0.01%) is lower than the average value in Chinese and American
115
coal, which is 0.022% and 0.0614%, respectively 33. According to the concentration of
116
sulfur in Chinese coal within the range of 0.2%-8% 34, the sulfur content (0.90%) in
117
the coal sample is relatively low. Table 1. Proximate and elemental analysis of the coal sample a
118
Proximate analysis (%)
Element analysis (%)
Qnet, ar
M
A
V
FC
MJ/kg
C
H
O
N
S
Cl
17.90
23.38
23.22
35.51
16.98
44.01
2.60
10.52
0.69
0.90
0.01
119
Note: a: All the value is on the as received basis
120
2.2. As Speciation and Concentration Determination
121
Concentration of total As in solid samples, such as coal, PM, bottom ash, ESP
122
ash was determined by the ICP-MS (Agilent Technologies 7700x, US) after digestion
123
by the mixture of concentrated nitric acid (HNO3) and perchloric acid (HClO4).
5
ACS Paragon Plus Environment
Energy & Fuels
124
Because different As speciation has different toxicities, it is meaningful to know their
125
content in the solid samples. Concentration of As3+ and As5+ can be determined by the
126
HPLC (Shimadzu LC20-AB, Japan) coupled with ICP-MS (named HPLC-ICP-MS)
127
in this work, which has been used in some studies successfully
128
PM, bottom ash, ESP ash was digested by 10 mL of 0.1% (v/v) HNO3 to release the
129
As completely. Then the solution was purified in a centrifuge at 7000 rpm for 10
130
minutes to obtain the supernatant. The content of As3+ and As5+ in the clear solution
131
can be directly detected by HPLC-ICP-MS. The accuracy of As3+ and As5+
132
concentration in samples was determined through a mixed solution of GBW08667
133
and GBW08666 as standard reference material. The chromatogram of As3+ and As5+
134
gotten from the GBW08667 and GBW08666 is shown in Figure 1. In order to ensure
135
the accuracy, all the measurements of As speciation were conducted in several times
136
to achieve parallel results with relative standard deviation less than 5%.
35, 36
. About 0.01g of
22500 As3+
20000 75ppb
17500 15000
Intensity (cps)
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 6 of 21
12500
As5+
10000
125ppb
7500 5000 2500 0 -2500 -100
0
100
200
300
400
500
600
700
800
Time (s)
137 138
Figure 1. Chromatogram of As3+ and As5+ based on mixed solution of GBW08667
139
and GBW08666
140 141
2.3. Relevant Characterization Methods Burning weight loss method was used to obtain the unburned carbon (UBC) in 6
ACS Paragon Plus Environment
Page 7 of 21 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
142
the ESP ash and bottom ash. The samples were firstly dried in an oven at 102 °C for 8
143
hours to remove moisture and then kept in a muffle furnace with 850 °C for 3 hours.
144
The ratio of the mass difference between the dried and the burned sample to that of
145
dried sample was defined as the UBC content 37. The SEM was used to acquire the
146
physical structure of PM, ESP ash, and bottom ash on a Hitachi s-4800 microscope
147
(made in Japan). The XRF (ARL ADVANT’ XP, Switzerland) was applied to
148
determine the major elements and oxides on the surface of PM and ESP ash.
149
3. RESULTS AND DISCUSSION
150
3.1. Enrichment Characteristics of Total As in the Samples
151
Concentration of total As in the coal determined by ICP-MS is 3.851 mg/kg,
152
which is little higher than the average content in Chinese coal (3.79 mg/kg) while less
153
than that in world’s coal (8.30 mg/kg) 38. Figure 2 gives the total As content in bottom
154
ash, ESP ash, and PM, which ranges from 1.637 mg/kg (bottom ash) to 20.088 mg/kg
155
(PM10, PM2.5-10, PM1-2.5, and PM10
PM2.5-10
PM1-2.5
PM10, PM2.5-10, PM1-2.5, and PM10
0.192
8.733
9.599
90.98
9
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 21
PM 2.5-10
n.d.
11.982
12.365
96.91
PM 1-2.5
n.d.
13.431
14.606
91.95
PM 10
47
. The
Page 11 of 21 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
PM 2.5-10
PM 1-2.5
PM 10
to PM 1-2.5 then decreases from PM 1-2.5 to PM
11
ACS Paragon Plus Environment
10
to PM 1-2.5 then increases from PM 1-2.5 to PM
10
17.67
18.95
3.68
2.40
33.39
40.53
5.15
3.42
PM 2.5-10
18.05
18.62
3.24
2.04
34.10
39.84
4.54
2.91
PM 1-2.5
21.02
24.61
2.95
2.46
39.72
52.65
4.12
3.51
PM
