- Email: [email protected]
Characterization of fly ash from a power plant and surroundings by micro-Raman spectroscopy
Available online at www.sciencedirect.com
International Journal of Coal Geology 73 (2008) 359 – 370 www.elsevier.com/locate/ijcoalgeo
Characterization of fly ash from a power plant and surroundings by micro-Raman spectroscopy A. Guedes a,⁎, B. Valentim a , A.C. Prieto b , A. Sanz b , D. Flores a,c , F. Noronha a,c b
a Centro de Geologia da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía. Universidad de Valladolid, Valladolid, Spain c Departamento de Geologia da Faculdade de Ciências, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
Received 26 August 2006; received in revised form 7 September 2007; accepted 13 September 2007 Available online 22 September 2007
Abstract Fly ash samples were collected from a Portuguese power plant that burns low-sulphur coals from South Africa, U.S.A., Colombia, and Australia. The fly ashes were collected from the hoppers of the economizers, air heaters, electrostatic precipitators, and from the stack. The power plant air monitoring system was also sampled. The fly ash characterization was conducted by microRaman spectroscopy (MRS). The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents. The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman parameters reveal that despite the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered. The different features of the Raman spectra observed for carbon particles collected from the stack, together with the high range of variation of the Raman parameters, confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of WD1, FWHMD1, FWHMG, WG and ID1/IG obtained. © 2007 Elsevier B.V. All rights reserved. Keywords: Micro-Raman spectroscopy; Fly ash; Organic constituents; Inorganic constituents
1. Introduction Fly ash from coal combustion is a complex and heterogeneous by-product, and many techniques have been applied to their characterization including microRaman spectroscopy (Scheetz and White 1985; Vangrieken and Xhoffer, 1992; Fermo et al., 1999; Escribano et al., ⁎ Corresponding author. Tel.: + 351 220114524; fax: +351 220114540. E-mail address: [email protected] (A. Guedes). 0166-5162/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2007.09.001
2001; Sze et al., 2001; Landman and de Waal, 2004; Mertes et al., 2004; Potgieter-Vermaak et al., 2005, 2006). Micro-Raman spectroscopy (MRS) is a highly sensitive technique used to characterize materials based on unique fingerprint-type spectra. In a Micro-Raman spectrometer, the sample under examination is irradiated with an intense source of monochromatic radiation, usually from a laser, and the scattered light is analysed by the spectrometer. A small fraction of the scattered light, the Raman component, has shift frequencies due to the
360
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
interactions of photons with the sample that result in changes in the vibrational or rotational energy of chemical bonds in molecules or crystals and in the vibration of crystal lattice. The shifted frequencies can be used to identify the molecules groups and their structure. The usefulness of MRS in characterizing the state of structural order of carbonaceous material and their structural variation during heat treatment has been previously discussed (Tuinstra and Koenig, 1970; Wopenka and Pasteris, 1993; Lespade et al., 1984; among many others). The Raman spectra of carbon materials is characterised by a G band at ∼1580 cm− 1 typical for graphite crystals, a D1 band at ∼1350 cm− 1 as a consequence of structural disorder. D2 at 1620 cm− 1, D3 at 1500 cm− 1 and S2 at 2900 cm− 1 usually appear in the spectra. All these bands have been previously described and discussed by several authors (Tuinstra and Koenig, 1970; Nemanich and Solin, 1979; Lespade et al., 1984; Beny-Bassez and Rozaud, 1985; Wopenka and Pasteris, 1993; Beyssac et al., 2000, 2002, 2003; Lee, 2004). Since fly ash is a residue consisting of a variety of individual particles, the objectives of this work are: (i) to use the micro-Raman spectroscopy technique to identify different materials present in the fly ash; (ii) to study the structural evolution of the unburned carbon/char material during their path through the power plant; and, (iii) to compare these materials with the ones found in the surroundings of the power plant. 2. Materials and methods The samples for this study were collected in a Portuguese power plant which uses bituminous coals and generates approximately 630 MW/h of electricity. This power plant burns low-sulphur coals (b1%) with ∼ 10% of ash and is equipped with low-NOx burners. About 99.8% of the fly ash is captured in the electrostatic precipitators. In 2004 about 95% of the fly ash produced by this power plant was utilized in the cement industry. For three days, the feed coals were collected before pulverization simultaneously with the fly ash collected from the hoppers of the economizers, air heaters, and the electrostatic precipitators (first line hopper 12, and final line hopper 42). During this period, the fly ashes were also sampled from the stack using an ANDERSEN “Universal Stack Sampler” and from the air monitoring system located on the surroundings of the power plant: Coal Park; Regional Road 5, located in the Power plant limits; and Regional Road 6 located at 40 km from the Power plant. The fly ash collected from the hoppers of the economizers, air heaters, and electrostatic precipitator
were analysed petrographically using polished epoxybound pellets with a Leitz Wetzlar microscope equipped with a magnification of ×600 and reflected-light oilimmersion objectives. The point counter method was carried on with a Swift Model F for the fly ash quantification. The fly ash morphology was determined by Scanning Electron Microscopy (SEM) and was carried out on a JEOL JSM-35C microscope equipped with an energy dispersive X-ray spectrometer analyser EDS NORAN-VOYAGER, a high resolution of 1.3 nm (30 keV)/1.5 nm (15 keV) and magnifications from ×10 to ×500,000 in a secondary and backscatter electron modes. This allowed the identification of the morphology of the particles, their size, and semi-qualitative chemical composition. Raman microprobe measurements, single spectra (MRS) and images, were performed using a Jobin-Yvon Horiba LabRam-HR (high resolution) system interfaced with an Olympus BX41 optical microscope. The system was also equipped with automated x–y micro-sampling stage, 1200 grooves/mm diffraction grating, and a Peltiercooled charge-coupled device (CCD) detector. Spectra were excited using the 632.8 nm emission line of a He–Ne laser. An Olympus ×100 objective (numerical aperture 0.95) was used. The system was operated in the confocal mode (confocal diaphragm and entrance aperture set at 400 μm). With this configuration, the lateral resolution was ∼1 μm, and the spectral resolution was determined to be 1 cm− 1. Extended scans were performed on each sample. The Raman spectra of carbon materials were measured with a density filter to avoid thermal decomposition of samples. Several micro-Raman analyses were conducted directly on fly ash grains, however most of the analysis was performed on polished epoxy-bound pellets used for petrographic analysis. Spectra obtained on representative unburned carbon materials were selected and deconvoluted and in order to determine the precise frequencies, bandwidths, and the relative intensities of the bands of the carbon materials, Raman parameters were calculated. Adequate fits to the experimental data were obtained using a mixed Gaussian-Lorentzian curve-fitting procedure in a Labspec program of Dilor-Jobin Yvon. 3. Results In order to identify and characterise the different materials present in the fly ash, optical petrography, SEM/EDS, and MRS analyses were performed on samples from the different sampling sites. The petrographic characterization of the fly ashes studied from the different sites is shown in Table 1. Fly ashes consist dominantly of glass, to a lesser extent
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370 Table 1 Fly ash petrography (vol. %) Char Glass Quartz Fe-oxides Other Economizer
21 36 31 22 21 13 Air-heater 2 3 2 0 1 2 Precipitator Hopper 12 11 64 52 13 12 5 Hopper 42 20 38 34 30 18 6
77 62 66 71 76 85 88 84 79 78 90 91 84 30 47 81 86 92 79 61 66 69 81 93
1 b1 1 2 1 0 9 11 15 13 5 2 2 5 1 2 0 0 0 0 0 0 0 0
1 2 1 4 2 2 1 2 4 9 4 5 2 b1 b1 4 2 3 1 0 0 1 1 1
0 0 1 b1 0 0 1 0 0 0 0 0 b1 1 0 0 0 0 0 1 0 0 0 b1
unburned carbon/char, and moderate occurrence of mineral matter (quartz, Fe-oxides, and others). 3.1. SEM/EDS analysis The SEM/EDS analysis performed on fly ash collected before the stack revealed high amounts of char (Fig. 1), and glass cenospheres (Fig. 2). Their EDX
361
spectra show a variety of compositions and combinations (Fig. 2B–H). Fe-oxide cenospheres, generally referred to as ferrospheres/ferrispheres, occur in very moderate concentrations (Fig. 2D, E). The particles from the stack are essentially composed by glassy cenospheres, composed of: (i) calcium aluminosilicates with Fe, Mg and Ti, (ii) aluminosilicate spheres with Fe, Na, P, S, K, Ca and Ti and, (iii) unburned carbon. SEM/EDS did not provide any relevant observation for the filters from the power plant surrounding air monitoring system, since particles were deeply submerged and bound together with the filter material. 3.2. MRS analysis In the MRS spectra, the assignments of the vibration modes and symmetric species of the different Raman bands followed those of Farmer (1974), Nakamoto (1986) and Socrates (2004) and these are shown in Table 2. 3.2.1. Inorganic constituents The micro-Raman analysis performed on several mineral fragments resulted in Raman spectra characteristic of quartz (SiO2), with the main Raman shift at 463 cm− 1. Additionally, relatively strong lines occur also at 203 and 265 cm− 1 (Fig. 3 and Table 2). The spectra obtained on the ferrospheres and ferrispheres indicate the presence of iron oxides (Fig. 4). In the hematite (Fe2O3) spectrum (Fig. 4B), the shifts appear at 227, 247, 294, 413, 498 and 614 cm− 1 (Table 2). In the magnetite (Fe3O4) spectrum (Fig. 4C) the shifts occur at 213, 288, 348, 441, 537, 653 and 905 cm− 1 (Table 2).
Fig. 1. A: SEM micrograph of char, secondary electron mode. Ash sample collected from electrostatic precipitator, hopper 12; magnification ×180; B: EDS spectrum of char.
362
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 2. A: SEM micrograph of glassy cenospheres with the identification of the particles or part of the particles analysed by EDS (electrostatic precipitator, hopper 12); EDS spectra- B: aluminosilicate glass; C: complex (Na, Mg, Fe, S) calcium-rich aluminosilicate; D and E: iron-rich two phases particle; F: iron-rich aluminosilicate; G and H: calcium and iron-rich aluminosilicate.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370 Table 2 Assignments of the Raman bands obtained in the studied inorganic constituents Raman spectra
Wavenumber (cm− 1)
Quartz (Fig. 3B)
202 265 463 Hematite (Fig. 4B) 226 247 293 413 498 614 Magnetite, ferrites + glass 213 (Fig. 4C) 288 348 441 537 653 905 Calcite (Fig. 5B) 158 282 711 1087 Cements, hydroxides 858 (Fig. 6) 3425 3626 Aluminium oxides 683 (Fig. 7) Fe-oxides, glass and 213 Fe2(SO4)3 (Fig. 8B) 328 480 640 707 826 898 1014 1103
Assignment (Species) α-SiO2 (A1) α-SiO2 (Et + El) α-SiO2 (A1) Fe+ 3 displacements (A1g) Fe+ 3 displacements (Eg) Fe+ 3 displacements (Eg) O=displacements (p1-Eg) O=displacements (a-A1g) O=displacements (a-Eg) FeFe2O4 (T2g) FeFe2O4 (Eg) FeFe2O4 (T2g) ν(α-SiO2 glass) FeFe2O4 (T2g) FeFe2O4 (A1g) ν(α-SiO2 glass) ν14 (CaCO3) (Eg) ν13 (CaCO3) (Eg) νg4 (CaCO3) (Eg) νg1 (CaCO3) (A1g) ν (CaOAl2O3) νOH [Al(OH)3] νOH [Ca(OH)2] ν(Al2O3) Fe− 2Fe− 32O4 (T2g) Fe− 2Fe− 32O4 (T2g) ν2[Fe2(SO4)3]; FeFe2O4 (T2g) Fe− 2Fe− 32O4 (A1g) ν(Al–O) ν(Si–O–Si) (B2) ν(Si–O–Na) (A1) ν1[Fe2(SO4)3] ν3[Fe2(SO4)3]; ν(SiONa) (A1)
The carbonate phases, in the form of crystalline calcite, are present (Fig. 5). A Raman spectrum with characteristic Raman bands at 158, 282, 712 and 1087 cm− 1 (Fig. 5B and Table 2). Clearly identified features in some Raman spectra are the bands at 858, 3425 and 3626 cm− 1, characteristic of Ca-and Al-hydroxides (Fig. 6 and Table 2), and a welldefined Raman shift at 684 cm− 1, characteristic of Aloxides (Fig. 7 and Table 2). The composition of the glassy spheres is very complex and shows mixtures of different components (Fig. 8 and Table 2). Some of the glassy phases were specifically identified as being composed of Fe-oxides and sulphates (Fig. 8B and Table 2)
363
3.2.2. Organic constituents Complex spectra of unsaturated organic matter appear frequently in the Raman analysis. However, in this study, only the char and other carbon fragments were characterized in detail following the classification of Hower et al. (1995). The Raman analyses were performed on both cenospheric and inertinitic chars and also on other carbon particles (Fig. 9). Several Raman parameters have been used to characterize the structural ordering of carbon materials, namely the integrated D1/G intensity ratio; the frequency and full width at half maximum of the G band (ν and FWHM, respectively); and the width and asymmetry of the S1 band in the second-order spectrum (Tuinstra and Koenig, 1970; Lespade et al., 1984; Pasteris and Wopenka, 1991; Wopenka and Pasteris, 1993; Bustin et al., 1995; Beyssac et al., 2002, 2003; Lee, 2004). In this study, the identified bands were G (1582 cm− 1), D1 (1350 cm− 1), one band around 1100–1200 cm− 1, and D3 (1500 cm− 1) (Figs. 9–11). The latter two bands are associated with the disorder effects and the D3 was associated by Mernagh et al. (1984) with the effect of exposure to the laser and attributed to C–O vibrations of surface carboxylates or related oxidized species. In these chars, the bands D2 (1620 cm− 1), S1 (2700 cm− 1) and S2 (2900 cm− 1) were not identified. Finally, the Raman parameters used to characterize the structural ordering of unburned carbon were the frequency and full width at half maximum of the G (1600 cm− 1) and D1 (1350 cm− 1) bands, and the integrated intensity ratio ID1/IG. The Raman parameters calculated for the carbon particles are shown in Table 3. The presence of the D1 band and the absence of the S1 band in the analysed carbon materials from the economizer, air heater, and electrostatic precipitators, indicate that although high temperatures (∼ 1500 °C) were reached, these materials are still structurally disordered (Lespade et al., 1984; Wopenka and Pasteris 1993; Bustin et al., 1995), i.e., did not reach the structural ordering of the graphite. The ID1/IG values obtained (Table 3 and Fig. 12A) for the char particles indicate that a structural variation occurs in the char from the economizer (average of 3.7) up to the electrostatic precipitators where the char shows higher ID1/IG values (average of 4.7 for hopper 12 and average of 4.9 for hopper 42) and consequently is structurally more disordered. The average values of FWHM of the D1 and G bands (117 cm− 1 to 132 cm− 1 and 53 cm− 1 to 57 cm− 1, respectively (Table 3, Fig. 12B) obtained on the chars of the economizer, air heater, and electrostatic precipitators are similar with the values obtained from Escribano et al.
364
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 3. A: Quartz grain from the economizer (reflected light); B: Raman spectra of different quartz particles.
Fig. 4. A: Examples of Fe-oxide particles collected from the air heater (reflected light); Raman spectra of Fe-oxides-B: three Raman spectra of hematites; C: Raman spectrum of magnetite with some glass and other oxides.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 5. A: Calcite particle (reflected light); B: Raman spectrum of calcite. Ash collected from electrostatic precipitator.
Fig. 6. Raman spectrum of calcium and aluminium hydroxides-Ca(OH)2 and Al (OH)3. Ash collected from the air heater.
Fig. 7. Raman spectrum of aluminium oxide. Ash collected from the economizer.
365
366
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 8. A: Glass particle; B: Raman spectrum of a mixture of glass, Fe-oxides and Fe2(SO4)3. Ash sample collected from the economizer.
(2001) on activated carbon (FWHMD1 ∼ 120 cm− 1 and FWHMG ∼ 70 cm− 1). The different features of the Raman spectra observed for carbon particles collected from the stack (Fig. 10) together with the high range of variation of the Raman parameters (WD1 between 1318 and 1354 cm− 1, FWHMD1 between 114 and 277 cm− 1, WG between 1564 and 1590 cm− 1, FWHMG between 53 and 126 cm− 1 and ID1/IG between
1.9 and 5.5) (Table 3, Fig. 12) confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). In the filters from the surroundings (ER5, ER6 and PC) appear carbon particles with Raman parameters different from the ones obtained in the chars from the economizer, air heater, electrostatic precipitators, and stack (Table 3, Fig. 12). The highest values of WD1
Fig. 9. A: Inertinitic char (CI); B: Isotropic cenospheric char (CC). Ash from the economizer; C: Raman spectra of inertinitic and cenospheric char; D1: D1 Raman band; D3: D3 Raman band; G: G band (for explanation see the text).
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
367
Fig. 10. A: Carbon fragment from stack; B: Raman spectra from stack particles.
(average between 1332 cm− 1 and 1357 cm− 1 for the different sites), FWHMD1 (average between 219 cm− 1 and 296 cm− 1 for the different sites) and FWHMG (average between 1572 cm− 1 and 1585 cm− 1 for the different sites) and the lowest values of WG (average between 69 cm− 1 and 117 cm− 1 for the different sites) and ID1/IG (average between 3.1 and 3.2 for the different sites) obtained these particles, suggest that the majority of the particles are from other sources rather then the power plant. The FWHMD1 and FWHMG values obtained are similar to diesel and environmental particles collected at Madrid (Spain) and Ontario (Canada) by Escribano et al. (2001). The observation of a displacement of D1 band to higher frequencies in most of the carbon particles from the surrounding filters (Fig. 12C) is in agreement with
the work of Sze et al. (2001) and thus confirming that these are diesel particles. However the values obtained in the studied samples are lower than those obtained by Sze et al. (2001) since he used an excitation wavelength of 514.5 nm and we used 632.8 nm (Vidano et al., 1981). 4. Conclusions The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents. The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman
Fig. 11. A: Raman spectrum of carbon particles from the coal park; B: Raman spectra of carbon particles from the surrounding filters; C: Raman spectra of carbon particles from stack.
368
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Table 3 Raman parameters obtained and calculated in the studied samples Sampling location
Carbon type
WD1
FWHMD1
WG
FWHMG
WD3
ID1/1C
Air heater
CI
1328 1332 1330
97 136 117
1599 1598 1599
53 59 56
1521 1523 1522
3.6 3.8 3.7
CC
1330 1331 1330 1330 1325 1324 1332 1327 1329
128 137 151 117 143 91 124 118 126
1590 1598 1595 1597 1592 1595 1597 1598 1595
63 58 68 51 58 49 56 54 57
1500 1530 1508 1525 1519 1535 1522 1526 1521
3.2 3.9 3.0 4.1 4.3 3.3 3.8 3.9 3.7
CI
1329 1329 1330 1329
132 131 133 132
1599 1599 1602 1600
57 58 53 56
1533 1529 1548 1537
4.4 4.3 5.5 4.7
CC
1336 1329 1329 1328 1331
154 140 115 113 131
1604 1597 1600 1599 1600
53 54 53 50 53
1549 1533 1532 1537 1538
6.1 4.8 4.1 4.7 4.9
1332 1324 1333 1322 1354 1329 1322 1324 1318 1320 1324 1326 1327
145 131 213 114 277 233 206 184 169 116 148 178 176
1590 1582 1580 1586 1577 1564 1570 1589 1589 1590 1587 1581 1582
55 76 126 65 80 116 84 62 53 57 63 66 75
1521 1421
1511 1530 1534 1518 1470 1499
4.3 1.9 2.3 2.3 4.0 3.6 3.3 5.3 5.5 4.0 3.6 4.3 3.7
PC
1322 1342 1327 1337 1332
193 260 222 199 219
1585 1585 1584 1586 1585
67 61 65 83 69
1510 1515 1511 1501 1509
4.3 4.5 4.9 2.8 4.1
FC
1372 1345 1350 1334 1383 1357
319 350 251 219 342 296
1580 1591 1564 1572 1586 1579
103 168 101 130 82 117
3.0 2.3 3.8 1.2 5.3 3.1
FC
1323 1358 1332 1307 1335 1339 1332
312 293 225 139 227 321 253
1588 1583 1567 1559 1561 1576 1572
86 94 118 145 110 95 108
5.6 3.7 3.9 0.9 1.9 3.9 3.3
Average Economizer
CI
Average Electrostatic precipitator Hopper 12
Average Electrostatic precipitator Hopper 42
CI Average Stack
FC
Average Surroundings Coal Park
Average Surroundings Regional road 5
Average Surroundings Regional road 6
Avearage
1485
Carbon types−CI: inertinitic char; CC: cenospheric char; FC: carbon fragment. Raman parameters−WD1: frequency of 1350 cm− 1 band; WG: frequency of 1580 cm− 1 band; WD3: frequency of 1500 cm− 1 band; FWHMD: Full Width at Half Maximum of D1 band; FWHMG: Full Width at Half Maximum of G band; ID1/IG: integrated intensity ratio of D1 and G bands.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
369
tion, and is a useful short time consuming technique for fly ash analysis of individual particles. Acknowledgements This work has been supported by FCT and by POCI 2010. The authors are gratefully acknowledged to the anonymous reviewers and Dr. J. Hower for their help in improving the manuscript. References
Fig. 12. Plot of Raman parameters for the different carbon particles- A: ID1/IG; B: FWHM D1 versus FWHMG; C: WG versus WD1. Legend-S: stack; AH: air heater; E: economizer; PE: electrostatic precipitator; ER5: surroundings, regional road 5; ER6: surroundings, regional road 6; PC: surroundings, coal park.
parameters reveal that although the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered. The different features of the Raman spectra observed for carbon particles collected from the stack together with the high range of variation of the Raman parameters, WD1, FWHMD1, WG, FWHMG and ID1/IG confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of WD1, FWHMD1, FWHMG, WG and ID1/IG obtained. The future utilization of the obtained images and spectra will probably simplify the application of the technique since MRS does not require sample prepara-
Beny-Bassez, C., Rozaud, J.N., 1985. Characterization of carbonaceous materials by correlated electron and optical microscopy and Raman microspectroscopy. Scanning electron microscopy 119–132. Beyssac, O., Goffé, B., Chopin, C., Rouzaud, J.N., 2002. Raman spectra of carbonaceous material in metasediments: a new geothermometer. Journal of Metamorphic Geology 20, 859–871. Beyssac, O., Goffé, B., Petitet, J.-P., Froigneux, E., Moreau, M., Rouzaud, J.-N., 2003. On the characterization of disorder and heterogeneous carbonaceous materials by Raman spectroscopy. Spectrochimica Acta Part A 59, 2267–2276. Beyssac, O., Goffé, B., Rouzaud, J.N., Clinard, C., Cassareuil, J., Catel, N., 2000. From anthracites to graphite: influences of temperature pressure and shear. In: Li, B.Q., Liu, Z.Y. (Eds.), Prospects for Coal Science in the 21st Century. Shanxi Science and Technology Press, pp. 29–32. Bustin, R.M., Ross, J.V., Rouzaud, J.-N., 1995. Mechanisms of graphite formation from kerogen: experimental evidence. International Journal of Coal Geology 28, 1–36. Escribano, R., Sloan, J.J., Siddique, N., Sze, N., Dudev, T., 2001. Raman spectroscopy of carbon-containing particles. Vibrational Spectroscopy 26, 179–186. Farmer, V.C., 1974. The infrared spectra of minerals. Mineralogical Society Vol. 4 London. Fermo, P., Cariati, F., Pozzi Demartin, F., Tettamanti, M., Collina, E., Lasagni, M., Pitea, D., Puglisi, O., Russo, U., 1999. The analytical characterization of municipal solid waste incineration fly ash: methods and preliminary results. Fresenius' Zeitschrift fuÉr Analytische Chemie 365, 666–673. Hower, J.C., Rathbone, R.F., Graham, U.M., Groppo, J.G., Brooks, S.M., Robl, T.L., Medina, S.S., 1995. Approaches to the petrographic characterization of fly ash. 11th International Coal Testing Conference. Lexington, KY, pp. 49–54. , May 10–12. Landman, A.A., de Waal, D., 2004. Fly ash as a potential starting reagent for the synthesis of ultramarine blue. Materials Research Bulletin 39, 655–667. Lee, Y.-J., 2004. The second order Raman spectroscopy in carbon crystallinity. Journal of Nuclear Materials 325, 174–179. Lespade, P., Marchand, A., Couzi, M., Cruege, F., 1984. Caracterisation de materiaux carbones par microspetrometrie Raman. Carbon 22 (4/5), 375–385. Mernagh, T.P., Cooney, R.P., Johnson, R.A., 1984. Raman spectra of graphon carbon black. Carbon 22 (1), 39–42. Mertes, S., Dippel, B., Schwarzenbock, A., 2004. Quantification of graphitic carbon in atmospheric aerosol particles by Raman spectroscopy and first application for the determination of massabsorption efficiencies. Journal of Aerosol Science 35 (3), 347–361. Nakamoto, K., 1986. Infrared and Raman spectra of inorganic and coordination compounds, 4th. John Wiley & Sons.
370
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Nemanich, R.J., Solin, S.A., 1979. First-and second-order Raman scattering from finite-size crystals of graphite. Physical Reviews B20, 392–401. Pasteris, J., Wopenka, B., 1991. Raman spectra of graphite as indicators of degree of metamorphism. Canadian mineralogist 29, 1–9. Potgieter-Vermaak, S.S., Potgieter, J.H., Belleil, M., DeWeerdt, F., Van Grieken, R., 2006. The application of Raman spectrometry to the investigation of cement. Part II: A micro-Raman study of OPC, slag and fly ash. Cement and Concrete Research 36, 663–670. Potgieter-Vermaak, S.S., Potgieter, J.H., Kruger, R.A., Spolnik, Z., van Grieken, R., 2005. A characterisation of the surface properties of an ultra fine fly ash (UFFA) used in the polymer industry. Fuel 84, 2295–2300. Scheetz, B.E., White, W.B., 1985. Characterization of crystalline phases in fly ash by microfocus Raman spectroscopy. Proceedings of the Materials Research Society Symposia 43, 53–60. Socrates, 2004. Infrared and Raman Characteristic Group Frequencies: Tables and Charts. John Wiley & Sons.
Sze, S.-K., Siddique, N., Sloan, J.J., Escribano, R., 2001. Raman spectroscopy characterization of carbonaceous aerosols. Atmospheric Environment 35, 561–568. Tuinstra, F., Koenig, J.L., 1970. Raman spectrum of graphite. Journal of Chemical Physics 53 (3), 1126–1130. Vangrieken, R., Xhoffer, C., 1992. Microanalysis of individual environmental particles. Journal of Analytical Atomic Spectrometry 7 (2), 81–88. Vidano, R.P., Fischbach, D.B., Willis, L.J., Oler, T.M., 1981. Observation of Raman band shifting with excitation wavelength for carbons and graphites. Solid state Communications 39, 341–344. Wopenka, B., Pasteris, J., 1993. Structural characterization of kerogens to granulite-facies graphite: Applicability of Raman microprobe spectroscopy. American Mineralogical 78, 533–577.
International Journal of Coal Geology 73 (2008) 359 – 370 www.elsevier.com/locate/ijcoalgeo
Characterization of fly ash from a power plant and surroundings by micro-Raman spectroscopy A. Guedes a,⁎, B. Valentim a , A.C. Prieto b , A. Sanz b , D. Flores a,c , F. Noronha a,c b
a Centro de Geologia da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía. Universidad de Valladolid, Valladolid, Spain c Departamento de Geologia da Faculdade de Ciências, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
Received 26 August 2006; received in revised form 7 September 2007; accepted 13 September 2007 Available online 22 September 2007
Abstract Fly ash samples were collected from a Portuguese power plant that burns low-sulphur coals from South Africa, U.S.A., Colombia, and Australia. The fly ashes were collected from the hoppers of the economizers, air heaters, electrostatic precipitators, and from the stack. The power plant air monitoring system was also sampled. The fly ash characterization was conducted by microRaman spectroscopy (MRS). The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents. The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman parameters reveal that despite the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered. The different features of the Raman spectra observed for carbon particles collected from the stack, together with the high range of variation of the Raman parameters, confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of WD1, FWHMD1, FWHMG, WG and ID1/IG obtained. © 2007 Elsevier B.V. All rights reserved. Keywords: Micro-Raman spectroscopy; Fly ash; Organic constituents; Inorganic constituents
1. Introduction Fly ash from coal combustion is a complex and heterogeneous by-product, and many techniques have been applied to their characterization including microRaman spectroscopy (Scheetz and White 1985; Vangrieken and Xhoffer, 1992; Fermo et al., 1999; Escribano et al., ⁎ Corresponding author. Tel.: + 351 220114524; fax: +351 220114540. E-mail address: [email protected] (A. Guedes). 0166-5162/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2007.09.001
2001; Sze et al., 2001; Landman and de Waal, 2004; Mertes et al., 2004; Potgieter-Vermaak et al., 2005, 2006). Micro-Raman spectroscopy (MRS) is a highly sensitive technique used to characterize materials based on unique fingerprint-type spectra. In a Micro-Raman spectrometer, the sample under examination is irradiated with an intense source of monochromatic radiation, usually from a laser, and the scattered light is analysed by the spectrometer. A small fraction of the scattered light, the Raman component, has shift frequencies due to the
360
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
interactions of photons with the sample that result in changes in the vibrational or rotational energy of chemical bonds in molecules or crystals and in the vibration of crystal lattice. The shifted frequencies can be used to identify the molecules groups and their structure. The usefulness of MRS in characterizing the state of structural order of carbonaceous material and their structural variation during heat treatment has been previously discussed (Tuinstra and Koenig, 1970; Wopenka and Pasteris, 1993; Lespade et al., 1984; among many others). The Raman spectra of carbon materials is characterised by a G band at ∼1580 cm− 1 typical for graphite crystals, a D1 band at ∼1350 cm− 1 as a consequence of structural disorder. D2 at 1620 cm− 1, D3 at 1500 cm− 1 and S2 at 2900 cm− 1 usually appear in the spectra. All these bands have been previously described and discussed by several authors (Tuinstra and Koenig, 1970; Nemanich and Solin, 1979; Lespade et al., 1984; Beny-Bassez and Rozaud, 1985; Wopenka and Pasteris, 1993; Beyssac et al., 2000, 2002, 2003; Lee, 2004). Since fly ash is a residue consisting of a variety of individual particles, the objectives of this work are: (i) to use the micro-Raman spectroscopy technique to identify different materials present in the fly ash; (ii) to study the structural evolution of the unburned carbon/char material during their path through the power plant; and, (iii) to compare these materials with the ones found in the surroundings of the power plant. 2. Materials and methods The samples for this study were collected in a Portuguese power plant which uses bituminous coals and generates approximately 630 MW/h of electricity. This power plant burns low-sulphur coals (b1%) with ∼ 10% of ash and is equipped with low-NOx burners. About 99.8% of the fly ash is captured in the electrostatic precipitators. In 2004 about 95% of the fly ash produced by this power plant was utilized in the cement industry. For three days, the feed coals were collected before pulverization simultaneously with the fly ash collected from the hoppers of the economizers, air heaters, and the electrostatic precipitators (first line hopper 12, and final line hopper 42). During this period, the fly ashes were also sampled from the stack using an ANDERSEN “Universal Stack Sampler” and from the air monitoring system located on the surroundings of the power plant: Coal Park; Regional Road 5, located in the Power plant limits; and Regional Road 6 located at 40 km from the Power plant. The fly ash collected from the hoppers of the economizers, air heaters, and electrostatic precipitator
were analysed petrographically using polished epoxybound pellets with a Leitz Wetzlar microscope equipped with a magnification of ×600 and reflected-light oilimmersion objectives. The point counter method was carried on with a Swift Model F for the fly ash quantification. The fly ash morphology was determined by Scanning Electron Microscopy (SEM) and was carried out on a JEOL JSM-35C microscope equipped with an energy dispersive X-ray spectrometer analyser EDS NORAN-VOYAGER, a high resolution of 1.3 nm (30 keV)/1.5 nm (15 keV) and magnifications from ×10 to ×500,000 in a secondary and backscatter electron modes. This allowed the identification of the morphology of the particles, their size, and semi-qualitative chemical composition. Raman microprobe measurements, single spectra (MRS) and images, were performed using a Jobin-Yvon Horiba LabRam-HR (high resolution) system interfaced with an Olympus BX41 optical microscope. The system was also equipped with automated x–y micro-sampling stage, 1200 grooves/mm diffraction grating, and a Peltiercooled charge-coupled device (CCD) detector. Spectra were excited using the 632.8 nm emission line of a He–Ne laser. An Olympus ×100 objective (numerical aperture 0.95) was used. The system was operated in the confocal mode (confocal diaphragm and entrance aperture set at 400 μm). With this configuration, the lateral resolution was ∼1 μm, and the spectral resolution was determined to be 1 cm− 1. Extended scans were performed on each sample. The Raman spectra of carbon materials were measured with a density filter to avoid thermal decomposition of samples. Several micro-Raman analyses were conducted directly on fly ash grains, however most of the analysis was performed on polished epoxy-bound pellets used for petrographic analysis. Spectra obtained on representative unburned carbon materials were selected and deconvoluted and in order to determine the precise frequencies, bandwidths, and the relative intensities of the bands of the carbon materials, Raman parameters were calculated. Adequate fits to the experimental data were obtained using a mixed Gaussian-Lorentzian curve-fitting procedure in a Labspec program of Dilor-Jobin Yvon. 3. Results In order to identify and characterise the different materials present in the fly ash, optical petrography, SEM/EDS, and MRS analyses were performed on samples from the different sampling sites. The petrographic characterization of the fly ashes studied from the different sites is shown in Table 1. Fly ashes consist dominantly of glass, to a lesser extent
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370 Table 1 Fly ash petrography (vol. %) Char Glass Quartz Fe-oxides Other Economizer
21 36 31 22 21 13 Air-heater 2 3 2 0 1 2 Precipitator Hopper 12 11 64 52 13 12 5 Hopper 42 20 38 34 30 18 6
77 62 66 71 76 85 88 84 79 78 90 91 84 30 47 81 86 92 79 61 66 69 81 93
1 b1 1 2 1 0 9 11 15 13 5 2 2 5 1 2 0 0 0 0 0 0 0 0
1 2 1 4 2 2 1 2 4 9 4 5 2 b1 b1 4 2 3 1 0 0 1 1 1
0 0 1 b1 0 0 1 0 0 0 0 0 b1 1 0 0 0 0 0 1 0 0 0 b1
unburned carbon/char, and moderate occurrence of mineral matter (quartz, Fe-oxides, and others). 3.1. SEM/EDS analysis The SEM/EDS analysis performed on fly ash collected before the stack revealed high amounts of char (Fig. 1), and glass cenospheres (Fig. 2). Their EDX
361
spectra show a variety of compositions and combinations (Fig. 2B–H). Fe-oxide cenospheres, generally referred to as ferrospheres/ferrispheres, occur in very moderate concentrations (Fig. 2D, E). The particles from the stack are essentially composed by glassy cenospheres, composed of: (i) calcium aluminosilicates with Fe, Mg and Ti, (ii) aluminosilicate spheres with Fe, Na, P, S, K, Ca and Ti and, (iii) unburned carbon. SEM/EDS did not provide any relevant observation for the filters from the power plant surrounding air monitoring system, since particles were deeply submerged and bound together with the filter material. 3.2. MRS analysis In the MRS spectra, the assignments of the vibration modes and symmetric species of the different Raman bands followed those of Farmer (1974), Nakamoto (1986) and Socrates (2004) and these are shown in Table 2. 3.2.1. Inorganic constituents The micro-Raman analysis performed on several mineral fragments resulted in Raman spectra characteristic of quartz (SiO2), with the main Raman shift at 463 cm− 1. Additionally, relatively strong lines occur also at 203 and 265 cm− 1 (Fig. 3 and Table 2). The spectra obtained on the ferrospheres and ferrispheres indicate the presence of iron oxides (Fig. 4). In the hematite (Fe2O3) spectrum (Fig. 4B), the shifts appear at 227, 247, 294, 413, 498 and 614 cm− 1 (Table 2). In the magnetite (Fe3O4) spectrum (Fig. 4C) the shifts occur at 213, 288, 348, 441, 537, 653 and 905 cm− 1 (Table 2).
Fig. 1. A: SEM micrograph of char, secondary electron mode. Ash sample collected from electrostatic precipitator, hopper 12; magnification ×180; B: EDS spectrum of char.
362
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 2. A: SEM micrograph of glassy cenospheres with the identification of the particles or part of the particles analysed by EDS (electrostatic precipitator, hopper 12); EDS spectra- B: aluminosilicate glass; C: complex (Na, Mg, Fe, S) calcium-rich aluminosilicate; D and E: iron-rich two phases particle; F: iron-rich aluminosilicate; G and H: calcium and iron-rich aluminosilicate.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370 Table 2 Assignments of the Raman bands obtained in the studied inorganic constituents Raman spectra
Wavenumber (cm− 1)
Quartz (Fig. 3B)
202 265 463 Hematite (Fig. 4B) 226 247 293 413 498 614 Magnetite, ferrites + glass 213 (Fig. 4C) 288 348 441 537 653 905 Calcite (Fig. 5B) 158 282 711 1087 Cements, hydroxides 858 (Fig. 6) 3425 3626 Aluminium oxides 683 (Fig. 7) Fe-oxides, glass and 213 Fe2(SO4)3 (Fig. 8B) 328 480 640 707 826 898 1014 1103
Assignment (Species) α-SiO2 (A1) α-SiO2 (Et + El) α-SiO2 (A1) Fe+ 3 displacements (A1g) Fe+ 3 displacements (Eg) Fe+ 3 displacements (Eg) O=displacements (p1-Eg) O=displacements (a-A1g) O=displacements (a-Eg) FeFe2O4 (T2g) FeFe2O4 (Eg) FeFe2O4 (T2g) ν(α-SiO2 glass) FeFe2O4 (T2g) FeFe2O4 (A1g) ν(α-SiO2 glass) ν14 (CaCO3) (Eg) ν13 (CaCO3) (Eg) νg4 (CaCO3) (Eg) νg1 (CaCO3) (A1g) ν (CaOAl2O3) νOH [Al(OH)3] νOH [Ca(OH)2] ν(Al2O3) Fe− 2Fe− 32O4 (T2g) Fe− 2Fe− 32O4 (T2g) ν2[Fe2(SO4)3]; FeFe2O4 (T2g) Fe− 2Fe− 32O4 (A1g) ν(Al–O) ν(Si–O–Si) (B2) ν(Si–O–Na) (A1) ν1[Fe2(SO4)3] ν3[Fe2(SO4)3]; ν(SiONa) (A1)
The carbonate phases, in the form of crystalline calcite, are present (Fig. 5). A Raman spectrum with characteristic Raman bands at 158, 282, 712 and 1087 cm− 1 (Fig. 5B and Table 2). Clearly identified features in some Raman spectra are the bands at 858, 3425 and 3626 cm− 1, characteristic of Ca-and Al-hydroxides (Fig. 6 and Table 2), and a welldefined Raman shift at 684 cm− 1, characteristic of Aloxides (Fig. 7 and Table 2). The composition of the glassy spheres is very complex and shows mixtures of different components (Fig. 8 and Table 2). Some of the glassy phases were specifically identified as being composed of Fe-oxides and sulphates (Fig. 8B and Table 2)
363
3.2.2. Organic constituents Complex spectra of unsaturated organic matter appear frequently in the Raman analysis. However, in this study, only the char and other carbon fragments were characterized in detail following the classification of Hower et al. (1995). The Raman analyses were performed on both cenospheric and inertinitic chars and also on other carbon particles (Fig. 9). Several Raman parameters have been used to characterize the structural ordering of carbon materials, namely the integrated D1/G intensity ratio; the frequency and full width at half maximum of the G band (ν and FWHM, respectively); and the width and asymmetry of the S1 band in the second-order spectrum (Tuinstra and Koenig, 1970; Lespade et al., 1984; Pasteris and Wopenka, 1991; Wopenka and Pasteris, 1993; Bustin et al., 1995; Beyssac et al., 2002, 2003; Lee, 2004). In this study, the identified bands were G (1582 cm− 1), D1 (1350 cm− 1), one band around 1100–1200 cm− 1, and D3 (1500 cm− 1) (Figs. 9–11). The latter two bands are associated with the disorder effects and the D3 was associated by Mernagh et al. (1984) with the effect of exposure to the laser and attributed to C–O vibrations of surface carboxylates or related oxidized species. In these chars, the bands D2 (1620 cm− 1), S1 (2700 cm− 1) and S2 (2900 cm− 1) were not identified. Finally, the Raman parameters used to characterize the structural ordering of unburned carbon were the frequency and full width at half maximum of the G (1600 cm− 1) and D1 (1350 cm− 1) bands, and the integrated intensity ratio ID1/IG. The Raman parameters calculated for the carbon particles are shown in Table 3. The presence of the D1 band and the absence of the S1 band in the analysed carbon materials from the economizer, air heater, and electrostatic precipitators, indicate that although high temperatures (∼ 1500 °C) were reached, these materials are still structurally disordered (Lespade et al., 1984; Wopenka and Pasteris 1993; Bustin et al., 1995), i.e., did not reach the structural ordering of the graphite. The ID1/IG values obtained (Table 3 and Fig. 12A) for the char particles indicate that a structural variation occurs in the char from the economizer (average of 3.7) up to the electrostatic precipitators where the char shows higher ID1/IG values (average of 4.7 for hopper 12 and average of 4.9 for hopper 42) and consequently is structurally more disordered. The average values of FWHM of the D1 and G bands (117 cm− 1 to 132 cm− 1 and 53 cm− 1 to 57 cm− 1, respectively (Table 3, Fig. 12B) obtained on the chars of the economizer, air heater, and electrostatic precipitators are similar with the values obtained from Escribano et al.
364
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 3. A: Quartz grain from the economizer (reflected light); B: Raman spectra of different quartz particles.
Fig. 4. A: Examples of Fe-oxide particles collected from the air heater (reflected light); Raman spectra of Fe-oxides-B: three Raman spectra of hematites; C: Raman spectrum of magnetite with some glass and other oxides.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 5. A: Calcite particle (reflected light); B: Raman spectrum of calcite. Ash collected from electrostatic precipitator.
Fig. 6. Raman spectrum of calcium and aluminium hydroxides-Ca(OH)2 and Al (OH)3. Ash collected from the air heater.
Fig. 7. Raman spectrum of aluminium oxide. Ash collected from the economizer.
365
366
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Fig. 8. A: Glass particle; B: Raman spectrum of a mixture of glass, Fe-oxides and Fe2(SO4)3. Ash sample collected from the economizer.
(2001) on activated carbon (FWHMD1 ∼ 120 cm− 1 and FWHMG ∼ 70 cm− 1). The different features of the Raman spectra observed for carbon particles collected from the stack (Fig. 10) together with the high range of variation of the Raman parameters (WD1 between 1318 and 1354 cm− 1, FWHMD1 between 114 and 277 cm− 1, WG between 1564 and 1590 cm− 1, FWHMG between 53 and 126 cm− 1 and ID1/IG between
1.9 and 5.5) (Table 3, Fig. 12) confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). In the filters from the surroundings (ER5, ER6 and PC) appear carbon particles with Raman parameters different from the ones obtained in the chars from the economizer, air heater, electrostatic precipitators, and stack (Table 3, Fig. 12). The highest values of WD1
Fig. 9. A: Inertinitic char (CI); B: Isotropic cenospheric char (CC). Ash from the economizer; C: Raman spectra of inertinitic and cenospheric char; D1: D1 Raman band; D3: D3 Raman band; G: G band (for explanation see the text).
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
367
Fig. 10. A: Carbon fragment from stack; B: Raman spectra from stack particles.
(average between 1332 cm− 1 and 1357 cm− 1 for the different sites), FWHMD1 (average between 219 cm− 1 and 296 cm− 1 for the different sites) and FWHMG (average between 1572 cm− 1 and 1585 cm− 1 for the different sites) and the lowest values of WG (average between 69 cm− 1 and 117 cm− 1 for the different sites) and ID1/IG (average between 3.1 and 3.2 for the different sites) obtained these particles, suggest that the majority of the particles are from other sources rather then the power plant. The FWHMD1 and FWHMG values obtained are similar to diesel and environmental particles collected at Madrid (Spain) and Ontario (Canada) by Escribano et al. (2001). The observation of a displacement of D1 band to higher frequencies in most of the carbon particles from the surrounding filters (Fig. 12C) is in agreement with
the work of Sze et al. (2001) and thus confirming that these are diesel particles. However the values obtained in the studied samples are lower than those obtained by Sze et al. (2001) since he used an excitation wavelength of 514.5 nm and we used 632.8 nm (Vidano et al., 1981). 4. Conclusions The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents. The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman
Fig. 11. A: Raman spectrum of carbon particles from the coal park; B: Raman spectra of carbon particles from the surrounding filters; C: Raman spectra of carbon particles from stack.
368
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Table 3 Raman parameters obtained and calculated in the studied samples Sampling location
Carbon type
WD1
FWHMD1
WG
FWHMG
WD3
ID1/1C
Air heater
CI
1328 1332 1330
97 136 117
1599 1598 1599
53 59 56
1521 1523 1522
3.6 3.8 3.7
CC
1330 1331 1330 1330 1325 1324 1332 1327 1329
128 137 151 117 143 91 124 118 126
1590 1598 1595 1597 1592 1595 1597 1598 1595
63 58 68 51 58 49 56 54 57
1500 1530 1508 1525 1519 1535 1522 1526 1521
3.2 3.9 3.0 4.1 4.3 3.3 3.8 3.9 3.7
CI
1329 1329 1330 1329
132 131 133 132
1599 1599 1602 1600
57 58 53 56
1533 1529 1548 1537
4.4 4.3 5.5 4.7
CC
1336 1329 1329 1328 1331
154 140 115 113 131
1604 1597 1600 1599 1600
53 54 53 50 53
1549 1533 1532 1537 1538
6.1 4.8 4.1 4.7 4.9
1332 1324 1333 1322 1354 1329 1322 1324 1318 1320 1324 1326 1327
145 131 213 114 277 233 206 184 169 116 148 178 176
1590 1582 1580 1586 1577 1564 1570 1589 1589 1590 1587 1581 1582
55 76 126 65 80 116 84 62 53 57 63 66 75
1521 1421
1511 1530 1534 1518 1470 1499
4.3 1.9 2.3 2.3 4.0 3.6 3.3 5.3 5.5 4.0 3.6 4.3 3.7
PC
1322 1342 1327 1337 1332
193 260 222 199 219
1585 1585 1584 1586 1585
67 61 65 83 69
1510 1515 1511 1501 1509
4.3 4.5 4.9 2.8 4.1
FC
1372 1345 1350 1334 1383 1357
319 350 251 219 342 296
1580 1591 1564 1572 1586 1579
103 168 101 130 82 117
3.0 2.3 3.8 1.2 5.3 3.1
FC
1323 1358 1332 1307 1335 1339 1332
312 293 225 139 227 321 253
1588 1583 1567 1559 1561 1576 1572
86 94 118 145 110 95 108
5.6 3.7 3.9 0.9 1.9 3.9 3.3
Average Economizer
CI
Average Electrostatic precipitator Hopper 12
Average Electrostatic precipitator Hopper 42
CI Average Stack
FC
Average Surroundings Coal Park
Average Surroundings Regional road 5
Average Surroundings Regional road 6
Avearage
1485
Carbon types−CI: inertinitic char; CC: cenospheric char; FC: carbon fragment. Raman parameters−WD1: frequency of 1350 cm− 1 band; WG: frequency of 1580 cm− 1 band; WD3: frequency of 1500 cm− 1 band; FWHMD: Full Width at Half Maximum of D1 band; FWHMG: Full Width at Half Maximum of G band; ID1/IG: integrated intensity ratio of D1 and G bands.
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
369
tion, and is a useful short time consuming technique for fly ash analysis of individual particles. Acknowledgements This work has been supported by FCT and by POCI 2010. The authors are gratefully acknowledged to the anonymous reviewers and Dr. J. Hower for their help in improving the manuscript. References
Fig. 12. Plot of Raman parameters for the different carbon particles- A: ID1/IG; B: FWHM D1 versus FWHMG; C: WG versus WD1. Legend-S: stack; AH: air heater; E: economizer; PE: electrostatic precipitator; ER5: surroundings, regional road 5; ER6: surroundings, regional road 6; PC: surroundings, coal park.
parameters reveal that although the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered. The different features of the Raman spectra observed for carbon particles collected from the stack together with the high range of variation of the Raman parameters, WD1, FWHMD1, WG, FWHMG and ID1/IG confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot). The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of WD1, FWHMD1, FWHMG, WG and ID1/IG obtained. The future utilization of the obtained images and spectra will probably simplify the application of the technique since MRS does not require sample prepara-
Beny-Bassez, C., Rozaud, J.N., 1985. Characterization of carbonaceous materials by correlated electron and optical microscopy and Raman microspectroscopy. Scanning electron microscopy 119–132. Beyssac, O., Goffé, B., Chopin, C., Rouzaud, J.N., 2002. Raman spectra of carbonaceous material in metasediments: a new geothermometer. Journal of Metamorphic Geology 20, 859–871. Beyssac, O., Goffé, B., Petitet, J.-P., Froigneux, E., Moreau, M., Rouzaud, J.-N., 2003. On the characterization of disorder and heterogeneous carbonaceous materials by Raman spectroscopy. Spectrochimica Acta Part A 59, 2267–2276. Beyssac, O., Goffé, B., Rouzaud, J.N., Clinard, C., Cassareuil, J., Catel, N., 2000. From anthracites to graphite: influences of temperature pressure and shear. In: Li, B.Q., Liu, Z.Y. (Eds.), Prospects for Coal Science in the 21st Century. Shanxi Science and Technology Press, pp. 29–32. Bustin, R.M., Ross, J.V., Rouzaud, J.-N., 1995. Mechanisms of graphite formation from kerogen: experimental evidence. International Journal of Coal Geology 28, 1–36. Escribano, R., Sloan, J.J., Siddique, N., Sze, N., Dudev, T., 2001. Raman spectroscopy of carbon-containing particles. Vibrational Spectroscopy 26, 179–186. Farmer, V.C., 1974. The infrared spectra of minerals. Mineralogical Society Vol. 4 London. Fermo, P., Cariati, F., Pozzi Demartin, F., Tettamanti, M., Collina, E., Lasagni, M., Pitea, D., Puglisi, O., Russo, U., 1999. The analytical characterization of municipal solid waste incineration fly ash: methods and preliminary results. Fresenius' Zeitschrift fuÉr Analytische Chemie 365, 666–673. Hower, J.C., Rathbone, R.F., Graham, U.M., Groppo, J.G., Brooks, S.M., Robl, T.L., Medina, S.S., 1995. Approaches to the petrographic characterization of fly ash. 11th International Coal Testing Conference. Lexington, KY, pp. 49–54. , May 10–12. Landman, A.A., de Waal, D., 2004. Fly ash as a potential starting reagent for the synthesis of ultramarine blue. Materials Research Bulletin 39, 655–667. Lee, Y.-J., 2004. The second order Raman spectroscopy in carbon crystallinity. Journal of Nuclear Materials 325, 174–179. Lespade, P., Marchand, A., Couzi, M., Cruege, F., 1984. Caracterisation de materiaux carbones par microspetrometrie Raman. Carbon 22 (4/5), 375–385. Mernagh, T.P., Cooney, R.P., Johnson, R.A., 1984. Raman spectra of graphon carbon black. Carbon 22 (1), 39–42. Mertes, S., Dippel, B., Schwarzenbock, A., 2004. Quantification of graphitic carbon in atmospheric aerosol particles by Raman spectroscopy and first application for the determination of massabsorption efficiencies. Journal of Aerosol Science 35 (3), 347–361. Nakamoto, K., 1986. Infrared and Raman spectra of inorganic and coordination compounds, 4th. John Wiley & Sons.
370
A. Guedes et al. / International Journal of Coal Geology 73 (2008) 359–370
Nemanich, R.J., Solin, S.A., 1979. First-and second-order Raman scattering from finite-size crystals of graphite. Physical Reviews B20, 392–401. Pasteris, J., Wopenka, B., 1991. Raman spectra of graphite as indicators of degree of metamorphism. Canadian mineralogist 29, 1–9. Potgieter-Vermaak, S.S., Potgieter, J.H., Belleil, M., DeWeerdt, F., Van Grieken, R., 2006. The application of Raman spectrometry to the investigation of cement. Part II: A micro-Raman study of OPC, slag and fly ash. Cement and Concrete Research 36, 663–670. Potgieter-Vermaak, S.S., Potgieter, J.H., Kruger, R.A., Spolnik, Z., van Grieken, R., 2005. A characterisation of the surface properties of an ultra fine fly ash (UFFA) used in the polymer industry. Fuel 84, 2295–2300. Scheetz, B.E., White, W.B., 1985. Characterization of crystalline phases in fly ash by microfocus Raman spectroscopy. Proceedings of the Materials Research Society Symposia 43, 53–60. Socrates, 2004. Infrared and Raman Characteristic Group Frequencies: Tables and Charts. John Wiley & Sons.
Sze, S.-K., Siddique, N., Sloan, J.J., Escribano, R., 2001. Raman spectroscopy characterization of carbonaceous aerosols. Atmospheric Environment 35, 561–568. Tuinstra, F., Koenig, J.L., 1970. Raman spectrum of graphite. Journal of Chemical Physics 53 (3), 1126–1130. Vangrieken, R., Xhoffer, C., 1992. Microanalysis of individual environmental particles. Journal of Analytical Atomic Spectrometry 7 (2), 81–88. Vidano, R.P., Fischbach, D.B., Willis, L.J., Oler, T.M., 1981. Observation of Raman band shifting with excitation wavelength for carbons and graphites. Solid state Communications 39, 341–344. Wopenka, B., Pasteris, J., 1993. Structural characterization of kerogens to granulite-facies graphite: Applicability of Raman microprobe spectroscopy. American Mineralogical 78, 533–577.