Energy Fuels 2010, 24, 123–130 Published on Web 09/02/2009
: DOI:10.1021/ef9005127
Effects of Indigenous and Added Minerals on Transformation of Organic and Inorganic Sulfur in Density Separated Coal Fractions during CO2-Pyrolysis† Dangzhen Lv, Minghou Xu,* Hong Yao, Xiaowei Liu, Wei Jiang, Huilong Cao, and Zhonghua Zhan State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, 430074, China Received May 25, 2009. Revised Manuscript Received August 12, 2009
The present paper was addressed toward the impacts of indigenous and added minerals on the organic and inorganic sulfur transformations during CO2-pyrolysis in a fixed-bed reactor at a temperature range of 400-800 °C. A Chinese bituminous coal was separated into three density fractions using the float-sink method: light (2.0 g/cm3). The sulfur retention of the three coal fractions was characterized in detail to study the influence of indigenous minerals on organic and inorganic sulfur transformation. Moreover, the role of added minerals was investigated by adding NaCl and kaolinite. The results indicated that indigenous minerals promoted the sulfur retention in coal char, especially in C>2.0, but had little effect on the decomposition of inorganic sulfur. Meanwhile, it was found that the added minerals also increased the sulfur retention. NaCl had a remarkable effect on sulfur retention at a low temperature range but appeared to have little capacity of sulfur retention due to the volatilization of itself at high temperatures above 700 °C. As for kaolinite, it was observed that there was an indistinct ability to retain sulfur during CO2-pyrolysis in our study. In comparison with added minerals, indigenous minerals had more significant effects on sulfur transformation because they were inherently embedded in the organic matrix of coal, while added minerals were physically dispersed within coal.
to pollutants formation. However, previous studies were mainly concerned with sulfur transformation during N2-pyrolysis.4-18 The sulfur transformation behavior under high CO2 concentration in oxy-fuel combustion is not clear.19-21 Meanwhile, sulfur exists in coal as two major forms simultaneously, that is, organic and inorganic sulfur. Both of them might influence each other due to the interaction or competition reaction with minerals during pyrolysis.6,17,18 Additionally, sulfur reacting with the mineral matter in coal, particularly with alkali and alkali earth metals, may cause slagging, fouling, agglomeration, and defluidization during coal utilization.22 Therefore, it is necessary to study the effects of minerals in coal on the organic and inorganic transformations during CO2 pyrolysis. To clarify the effects of minerals on the sulfur transformation, we used density fractionation techniques to get coal fractions with various mineral contents from the same coal. The float-sink method was widely used in the studies for
1. Introduction Coal has been and will continue to be a primary energy source, especially with the increasing world population and the continuous imcrease of human demands. Drastic increases the use of coal will certainly cause severe adverse health effects and environmental pollution. Sulfur in coal, a major pollution source, inhibits the effective and extensive utilization of coal. Thus, desulfurization before, during, and after coal combustion has been a topic of great importance for coal utilization. Presently, oxy-fuel combustion has been recognized as one of the most promising technologies to implement CO2 capture and simultaneously realize high desulfurization efficiency. During oxy-fuel combustion, the CO2 concentration may be enriched up to 90% using O2 and recycled flue gas to replace air for coal combustion. Pyrolysis, as an initial and important intermediate stage in combustion and other coal thermochemical conversion processes, has still received many researchers0 considerable attentions.1-3 In the pyrolysis process, sulfur in coal undergoes complex transformations that have significant impacts on the subsequent reactions related
(10) Pemsler, J. P.; Lam, R. K. F.; Litchfield, J. K.; Dallek, S.; Larrick, B. F.; Beard, B. C. Electrochem. Soc. 1989, 72 (1), 111–126. (11) Watkinson, A. P.; Germain, C. Can. Metall. Q. 1972, 11, 535– 547. (12) Boyabat, N.; et al. Fuel Process. Technol. 2003, 85 (2-3), 179– 188. (13) Chen, H.; Li, B.; Zhang, B. Fuel 2000, 79 (13), 1627–1631. (14) Gryglewicz, G.; Jasienko, S. Fuel 1992, 71 (11), 1225–1229. (15) Monteiro, J. L. F. Can. J. Chem. Eng. 1981, 59 (4), 511–516. (16) Liu, F.; et al. Fuel 2007, 86 (3), 360–366. (17) Telfer, M.; Zhang, D. Fuel 2001, 80 (14), 2085–2098. (18) Yani, S. Zhang, D. InThe 32nd International Symposium on Combustion, Montreal, Canada, 2008. (19) Duan, L. B.; Zhao, C. S.; Zhou, W.; Qu, C. R. Chen, X. P. Energy Fuels 2009, DOI: 10.1021/ef9002473. (20) Jamil, K.; Hayashi, J.; Li, C. Z. Fuel 2004, 83 (7-8), 833–843. (21) Messenbck, R. C.; Dugwell, D. R.; Kandiyoti, R. Energy Fuels. 1999, 13 (1), 122–129. (22) Vuthaluru, H. B.; Linjewile, T. M.; Zhang, D. K. Fuel 1999, 78 (4), 419–425.
† Presented at the 2009 Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies. *To whom correspondence should be addressed. Telephone: 86-2787546631. Fax: 86-27-87545526. E-mail:
[email protected]. (1) Van Heek, K. H.; Hodek, W. Fuel 1994, 73 (6), 886–896. (2) Cypres, R.; Furfari, S. Fuel 1981, 60 (9), 768–778. (3) Arendt, P.; Van Heek, K. H. Fuel 1981, 60 (9), 779–787. (4) Attar, A. Fuel 1978, 57 (4), 201–212. (5) Khan, M. R. Fuel 1989, 68 (11), 1439–1449. (6) Yan, J.; Yang, J.; Liu, Z. Environ. Sci. Technol. 2005, 39 (13), 5043–5051. (7) Patrick, J. W. Fuel 1993, 72 (3), 281–285. (8) Ibarra, J. V.; Palacios, J. M.; Moliner, R.; Bonet, A. J. Fuel 1994, 73 (7), 1046–1050. (9) Coats, A. W.; Bright, N. F. H. Can. J. Chem. 1966, 44 (10), 1191– 1195.
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Energy Fuels 2010, 24, 123–130
: DOI:10.1021/ef9005127
Lv et al.
Table 1. Weight Percent of Each Coal Fraction (ad) density (g/cm3)
coal
weight percent (wt %)
2.0
C2.0
30.28 58.52 11.20
Table 2. Proximate and Ultimate Analysis of the Three Density Coal Fractions proximate analysis (w t%, db)
ultimate analysis (wt %, db)
coal
Ad
FCd
Vd
C
H
Oa
N
Sa
C2.0
4.34 28.92 79.48
68.33 49.71 3.99
27.33 21.37 16.53
81.33 56.10 6.65
5.41 3.19 0.49
3.94 7.49 8.06
1.42 0.93 0.19
3.56 3.37 5.13
a
O: by difference; S: according to the total sulfur.
determining major and trace element affinities in coal,23-25 particulate matter emission,26 char structure, and burnout.27 Few studies had been reported about the sulfur transformation in the case of density-separated coal fractions. The main objective of this paper is to investigate the behaviors and mechanisms of organic and inorganic sulfur transformations during CO2-pyrolysis based on systematically comparing the sulfur transformations of the density-separated coal fractions. Furthermore, the roles of indigenous and added minerals on the sulfur transformation are also investigated by adding sodium and kaolinite.
Figure 1. Schematic diagram of the fixed-bed reactor.
samples of C
