Energy Fuels 2010, 24, 5289–5290 Published on Web 09/01/2010
: DOI:10.1021/ef100652h
Distribution of Hg, As, Pb, and Cr in a Coke Oven Plant Jing-Jing Ma,† Hong Yao,*,† Guang-Qian Luo,† Ming-Hou Xu,† Jun Han,‡ and Xuan-Ming He‡ †
State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, Hubei, China, 430074, and ‡ Hubei Coal Conversion and New Carbon Materials Key Laboratory, Wuhan University of Science and Technology, Wuhan, Wuhan, Hubei, China, 430081 Received May 26, 2010. Revised Manuscript Received August 22, 2010
Trace metals in coal are in widely varying concentrations, depending on the rank and geological origin. During coal utilization, these metals transform from solid phase to gas phase or liquid phase at high temperature, which magnify their adverse impact on environment.1-5 Over the last few decades, much research6-10 has been conducted on the distribution and transformation of trace metals during coal thermal processing. Among them, most investigations focused on combustion and gasification due to the huge consumption of coal, and just a few researchers11-14 studied pyrolysis. Coking is a kind of pyrolysis. Coke produced by coal coking in a coke oven is a necessary raw material for modern iron and steel making. Besides the electric power industry and the chemicals industry, the coke industry is another major coal consumer, especially in China. About 10% of coals produced in the world are processed into coke.14 As the largest coke producer and consumer in the world, China consumed 460 million tons coal and produced 350 million tons coke in 2009, which accounts for over 59% of the total world output. Moreover, with the capacity expansion of the iron and steel industry of China, coke production and consumption are still increasing.15 Unfortunately, it is difficult to predict or control heavy metal emissions from a full scale coking process due to lacking of related basic data. This study is trying to provide some useful information about distribution and transformation of trace metals such as Hg, As, Pb, and Cr during coking process by investigating a full-scale coke oven in China. Furthermore, the research also has a positive influence on estimating the total emission of Hg, As, Pb, and Cr in the coke industry of China. The experiments were carried out in a large-scale coke oven plant in an iron and steel complex. The height of the chamber
Table 1. Coal Blending Ratio of Coking Plant coal
QF coal typea coal blending 6 ratio (%)
coal 2 FM 5
coal 3
coal 4
coal 5
1/3 JM1 1/3 JM2 JM1 24 12 14
coal 6 JM3 25
coal coal 7 8 SM1 SM2 7 7
a Coal types were defined by the Chinese coal classification standard (GB 5751-86). QF, gas-fat coal; FM, rich coal; 1/3 JM, 1/3 coking coal; JM, coking coal; SM, lean coal. The subscripts mean different origin.
Table 2. Proximate and Ultimate Analyses of the Coal Samples proximate analysis (ad) sample
ash
blending 9.42 coal 1 7.21 coal 2 9.32 coal 3 9.17 coal 4 7.86 coal 5 9.85 coal 6 9.73 coal 7 10.12 coal 8 10.25
ultimate analyze (daf)
VM
M
FC
C
H
O
N
S
28.01 41.75 31.86 33.14 35.43 25.09 24.04 17.66 15.76
1.48 2.19 2.10 1.35 1.22 1.58 1.7 1.81 1.18
61.09 48.85 56.72 56.34 55.49 63.48 64.53 70.41 72.81
78.86 78.14 79.13 82.43 82.45 78.75 78.99 81.25 82.19
4.60 4.99 4.53 3.90 3.99 4.51 4.76 4.28 4.27
6.46 5.49 5.14 6.19 6.97 5.82 5.16 4.03 3.72
1.49 1.59 1.44 1.54 1.53 1.43 1.53 1.56 1.51
0.69 1.58 1.35 0.45 0.46 0.64 0.62 0.59 0.81
Table 3. Content of As, Pb, Hg, and Cr in Coking Coals
*To whom correspondence should be addressed. Phone and Fax: þ86-27-87545526. E-mail:
[email protected]. (1) Finkelman, R. B.; Palmer, C. A.; Krasnow, M. R. Energy Fuels 1990, 4, 755–766. (2) Swaine, D. J. Fuel Process. Technol. 2000, 65-66, 21–33. (3) Seames, W. S.; Wendt, J. O. L. Fuel Process. Technol. 2000, 63, 179–196. (4) Shah, P.; Strezov, V.; Prince, K.; Nelson, P. F. Fuel 2008, 87, 1859– 1869. (5) Dastoor, A. P.; Larocque, Y. Atmos. Environ. 2004, 38, 147–161. (6) Galbreath, K. C.; Zygarlicke, C. J. Fuel Process. Technol. 2000, 65, 289–310. (7) Hsi, H.; Chen, S. G.; Rostam-Abadi, M.; Rood, M. J.; Richardson, C. F.; Carey, T. R.; Chang, R. Energy Fuels 1998, 12, 1061–1070. (8) Sorum, L. F.; Flemming, J.; Hustad, J. E. Fuel 2004, 83, 1703–1710. (9) Meij, R. Fuel Process. Technol. 1994, 39, 199–217. (10) Guffey, F. D.; Bland, A. E. Fuel Process. Technol. 2004, 85, 521–531. (11) Elwira, Z. Z.; Jan, K. Fue 2003, 82, 1281–1290. (12) Ruixia, G.; Jianli, Y.; Zhenyu, L. Fuel 2004, 83, 639–643. (13) Wang, M.; Keener, T. C.; Khang, S. Fuel Process. Technol. 2000, 67, 147–161. (14) Akira, O.; Kota, S.; Shomei, T.; Akira, I.; Tsunenori, N.; Hirokazu, T. Powder Technol. 2008, 180, 30–34. (15) China Coking; 2009; http://www.cncoke.com. r 2010 American Chemical Society
coal 1
sample
As (μg/g)
Pb (μg/g)
Hg (μg/g)
Cr (μg/g)
blending coal 1 coal 2 coal 3 coal 4 coal 5 coal 6 coal 7 coal 8
10.81 14.02 12.66 15.69 12.65 12.81 9.63 14.29 11.12
4.11 2.30 4.02 3.94 2.85 4.09 4.98 5.26 5.28
0.23 0.18 0.19 0.21 0.25 0.22 0.20 0.33 0.35
11.78 9.44 10.86 11.63 10.45 12.22 12.28 13.06 12.89
Figure 1. Schematic diagram of coke oven plant and sampling points.
of the coking oven is 6.0 m. The capacity of the oven is 140 t/h, and the operating temperature range was 950-1050 °C. The 5289
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Energy Fuels 2010, 24, 5289–5290
: DOI:10.1021/ef100652h
Table 4. As, Pb, Hg, and Cr Concentration in Coking Products from a Coke-Oven Plant No. Hg As Cr Pb
tar (μg/g) ammonia (μg/mL) coke (μg/g) tar (μg/g) ammonia (μg/mL) coke (μg/g) tar (μg/g) ammonia (μg/mL) coke (μg/g) tar (μg/g) ammonia (μg/mL) coke (μg/g)
1
2
3
4
5
6
7
8
9
10
11
0.27 0.06 0.09 26.30 0.72 4.24 12.33 1.58 9.96 4.16 1.26 3.44
0.45 0.07 0.07 38.68 1.05 5.48 12.25 1.49 11.58 3.53 1.07 3.51
0.33 0.07 0.06 25.88 0.77 4.01 12.16 1.54 10.86 4.22 1.28 3.51
0.43 0.06 0.04 35.54 1.01 4.34 12.15 1.89 11.23 3.27 0.99 3.48
0.44 0.06 0.10 32.59 0.74 4.31 12.84 1.39 10.08 5.71 1.73 3.23
0.28 0.07 0.10 34.39 1.17 4.3 13.88 1.25 10.13 3.66 1.11 2.93
0.31 0.06 0.10 35.24 0.95 4.48 13.65 2.17 10.51 3.99 1.21 3.15
0.40 0.07 0.09 33.39 1.01 4.60 14.61 1.81 11.33 3.43 1.04 3.32
0.32 0.06 0.05 32.41 1.14 5.11 15.02 1.62 11.58 3.71 1.12 3.69
0.55 0.06 0.10 32.72 0.91 4.87 15.61 2.58 11.1 3.14 0.95 3.59
0.46 0.07 0.09 35.41 0.92 4.44 14.64 2.03 12.71 4.82 1.46 3.75
feedstock is a blend of 8 types of bituminous coal. The coal blending ratio designed for the coke oven plant is listed in Table 1. Table 2 shows the proximate and ultimate analyses of coal samples. The product and byproducts include coke, tar, ammonia, and coke gas. The schematic diagram of the coke oven plant and sampling points are illustrated with Figure 1. The Hg in coke gas was used by the Ontario hydro method (OHM), but As, Pb, and Cr in the coke gas (including fine particles) were not mesured. For the samples of coal, coke, and tar, Cr and Pb were analyzed by a hydride generation atomic absorption spectrometry (HG-AAS) based on the national standard method of China, GB/T 16658-1996. As for Hg, the samples were digested according to US EPA7473 and were measured by hydride generation atomic fluorescence spectrometry (HGAFS). Arsenic was also analyzed by the HG-AFS according to the national standard method of China, GB/T 3058-1996. The concentrations of As, Pb, Hg, and Cr in ammonia samples were analyzed using the national standards of China for the examination of water and wastewater, including SL 327.12005, CJ/T 65-1999, SLa 327.2-2005, and GB 7466-87. The average contents of As, Pb, Hg, and Cr in coal samples are listed in Table 3. Content ranges of As, Pb, Hg, and Cr are 9.63-15.69, 2.30-5.28, 0.18-0.35, and 9.44-13.06 μg/g, respectively. Table 4 shows As, Pb, Hg, and Cr concent in coking products from a coke-oven plant. The coking products were sampled every day in 11 consecutive days. In the coking plant, the yields of coke, tar, ammonia, and gas were 75.9, 3.5, 4.1,
Figure 2. As, Pb, Hg, and Cr distribution in coking products (As, Pb, and Cr in the coke gas were not mesured).
and 16.5%, respectively. The distribution of As, Pb, Hg, and Cr in coking products is shown in Figure 2. For Hg, 25-28% was retained in coke, 5-9% was in the tar, 4-8% in the ammonia, and 55-66% was released in the gas. For As, 30-35% was retained in coke, 10-15% was in the tar, and 1-3% was in the ammonia. For Pb, 58-67% was retained in coke, 3-7% was in the tar, and 6-8% was in the ammonia. For Cr, 67-75% was retained in coke, 3-6% was in the tar, and 3-5% was in the ammonia. There result shows that it is most important to remove Hg and As in gas, second in coke. In contrast, more effort should be made to remove Pb and Cr in coke, second in gas. Acknowledgment. This work was supported by the National Natural Science Foundation of China (50721140649, 50721005), and the Programme of New Century Excellent Talents in University (No. NCET-08-0227) is also acknowledged.
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