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Flash pyrolysis of coals A new approach of classification
Journal
of Analytical
and Apphed
Pyrolysi\
JOURNALot ANALYTICAL and APPLIED PYROLYSIS
3s (199.5) 77 91
Flash pyrolysis of coals A new approach of classification
Abstract Flash pyrolysis-gas chromatography:mass spectrometry constitutes. in combination with statistical methods such as principal component analysis (PCA) and hierachical cluster analysis (HCA), an advantageous technique in an attempt to characterize and classify coals of different origin. Eight coals comprising three from South Africa. two from Australia. and one from U.S.A.. Columbia and Indonesia. respectively. have been pyrolyzed at 750°C. Observed differences in the composition of the pyrolyzate have been elucidated by studying nine parameters: (A) the content of long-chain aliphatic compounds: (B) the content of benzene; (C) the content of toluene; (D) the content of toluene in the aromatic fraction: (E) the content of naphthalene relative to the content of benzene+ naphthalene: (F) the content of cresols in the aromatic fraction; (G) the content of cresols relative to the content of’ toluene + cresols: (H) the content of o-cresol in the cresol fraction; and (I) the content of styrene relative to the content of naphthalene + styrene. The data obtained have been treated statistically by means of PCA and HCA, demonstrating a high degree of similarity between the three South African coals, whereas a somewhat less pronounced similarity between the Australian coals was shown. The results are discussed based on an analogous study applying conventional coal analyses such as elemental analysis. maceral composition. vitrinite reflectance. ash content, etc. A further comparison with studies applying ash composition data has been included. Kc~~~~rtls: Coal classification;
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78
L. Carlsen, J. V. Chrisliansrn ! J. Anal. Appl. P.vrolysis 35 (1995) 77-91
1. Introduction Coals cannot be described as well-defined structures, but should rather be considered as a series of well-defined substructures bound together in a complicated three-dimensional network. Thus, coals consist of a macromolecular matrix containing a variety of aliphatic, aromatic and polyaromatic moieties interconnected through either ether or carbon-carbon linkages. In addition, different heteroatomcontaining sub-units are present in various amounts as a reflection of the origin of the single coal. The actual composition and structure of a given coal obviously reflect the original plant material used in nature’s production of the coal. However, temperature and pressure conditions prevailing over the geological time scale at the site at which the coal has been produced also have a determining role. In addition to the matrix material, coals typically also consist of a mobile phase of low molecular weight compounds trapped within the coal matrix [l-3]. Several attempts to construct coal structures based on existing data on the content of subunits have been made (see, for example, Ref. [2]), suggesting the molecules with molecular weights from around 1000 up to above 100 000 can be present in a single coal sample. Coals of different origin may behave quite differently upon combustion, and it seems reasonable to assume that the organic fraction plays a dominant role in this context, although the inorganic fraction cannot immediately be left out of consideration. Thus, not only should the actual elemental composition but also the nature of the three-dimensional coal matrix, as well as the trapped mobile fraction, be a priori considered. Seen from an environmental as well as from a combustion technology point of view, it appears highly desirable to develop a classification system based on simple laboratory measurements to predict the combustion behaviour of a given coal, thus thereby being able to optimize the combustion process with respect both to the energy output and the environmental impact. Eventually the system could be applied as a guide prior to the purchase of large quantities of an unknown coal for power production, as the coal could be classified and thus compared to a selection of coals exhibiting well-documented properties. The present paper describes preliminary studies on the possible classification of coals based on variations in the relative concentrations of a series of simple aliphatic and aromatic compounds found in the pyrolyzates of single coals following pyrolysis at 750°C [4]. The obtained data have been treated statistically and compared to results obtained analogously based on conventional coal analyses, e.g. elemental analyses, maceral composition, vitrinite reflectance, ash content, etc.
2. Experimental Flash pyrolysis experiments were carried out using a PYROLA-85 foil pulse pyrolyer (PYROL AB, Lund, Sweden) connected to a Varian Saturn II GC/MS system. The pyrolysis products were separated on a Chrompack CP Sil-5 CB
column (25 m x 0.25 mm i.d.) and identified in an ion trap mass spectrometer operated in the electron impact mode. Samples of coal were placed directly on the platinum foil in the pyrolysis chamber operated at 150°C. Samples were pyrolyzed at 750°C for 2 s. The loading procedure has been described previously [5]. The study included in total eight coals of different origin. supplied by ELSAM: three coals from South Africa (SAl, SA2. SA3). two coals from Australia (AU]. AU2), and one coal each from North America (US2). Columbia (CO1 ) and Indonesia (ID]), respectively [6]. It is unrealistic to quantify the single compounds or groups of compounds in absolute terms, as it requires a comparison with a complete range of isomers: this obviously. is not available. Thus, we have based the quantification on the integration of 1-~I! characteristic ions representing single compounds. Consequently, the calculated percentages should be regarded as the relative contributions to the pyrolyzates of the single compounds from the different coals. The relative yield of a given compound (or group of compounds) is given by C x lOO:CR, where C is the yield of the characteristic ion (or ions) representing the compound in question, and CR represents the total yield of ions used for quantification of the compounds given in Table 1. Conventional coal analysis data comprising the content of volatiles, the elemental composition. the moisture content, the ash content, the vitrinite reflectance, the maceral composition and the ash composition were supplied. together with the coals. by ELSAM [6,7].
I
Table
Retention
times and ions used for the quantification
C‘ompound
Retention (min)
of selected products
time
Selected ions. ,,I 1 -_
Benzene
I.13
Toluene
I.31
91
Styrene
1.78
I 03
78
Phenol
2.20
,I-Cresol
7.80
107 + IOX
lndene
2.86
Il5+
,rr,~~-Cresol
3.00
I07 + 108
C2-Phenols
Y4 II6
127
Naphthalene
4.28
I -Methylnaphthalene
5.63
131 + 147
2-Methylnaphthalene
5.83
I41 + 143
C2-Naphthalenes
I28
141 + I56
Brphenyl
6.65
I54
Acenapthylene
7.46
157
Phenanthrene
I I ,35
17X
Anthracene
I I .45
I78
Cl6
-C?9.
C’l6C29.
unsaturated saturated
55 + 69 + 83 57+71+85
80
L. Cdsen,
1 J. Anal. Appl. Pyrolysis 35 (1995) 77 -91
J. V. Christinnsrn
60
40
E
30 I 20 0 10-m
of long-chain
.
l
SA3
SA2
SAl
I
o.,.,.,.,.,.,. US2 Fig. 1. The content
p
aliphatic
compounds
AU1
AU2
in the pyrolyzate
ID1
-
I’ CO1
following
pyrolysis
at 750°C.
The statistical treatment including principal component and hierarchical cluster analyses of the data, has been performed by applying the SYSTAT 5 soft-ware package (OSYSTAT, inc.), version 5.1 for Macintosh computers [8]. In the case of PCA, the input parameters are automatically standardized, whereas a standardization of the parameters is carried out prior to HCA in order to ensure equal weighting of the single parameters. The PCA is carried out on the correlation matrix. The similarity between two samples i and j, S,j, determined by HCA, is given by S, = 1 - d,,/d,,,,, where d,, and d,,, are the distance between samples i and j and the maximum distance between samples, respectively.
3. Results Obviously, a wide variety of compounds present in the pyrolyzates could a priori be used as indicators for the single coals. In the present study, we have chosen to focus on compounds and groups of compounds exhibiting major variations. Hence, the following parameters have been selected (see Table 1): (A) the content of long-chain aliphatic compounds; (B) the content of benzene; (C) the content of toluene; (D) the content of toluene in the aromatic fraction; (E) the content of naphthalene relative to the content of benzene + naphthalene; (F) the content of cresols in the aromatic fraction; (G) the content of cresols relative to the content of toluene + cresols; (H) the content of o-cresol in the cresol fraction; and (I) the content of styrene relative to the content of naphthalene + styrene. 3.1. The content
of /ong-chain
aliphatic
compounds
Various coals exhibit significant differences in the content of long-chain aliphatic compounds. In Fig. 1 are displayed the percentages of long-chain aliphatic compounds (see Table 1) in the pyrolyzate of the eight coals. It is noted that the coals are grouped according to their apparent contents of long-chain aliphatic compounds in the pyrolyzates. Four coals, i.e. the three South African coals (SAlSA2,
L. Carlsm.
J. V. Christiansrn
)/J.
Anal.
Appl.
Pwoiy.sis
.I_5 (1995)
77-91
XI
SA3) and the U.S. coal (US2), exhibited approximately 10% of the long-chain aliphitics in the pyrolyzates, whereas the pyrolyzate corresponding to the Columbian coal, COl, contained as much as around 50%. For the three remaining coals. i.e. AUl. AU2 and IDl, contents between 25 and 35% were determined. 3.2. The content
oj’ benzene,
toluene and nuphthcrlene
Benzene is the simplest aromatic compound and is. as such, a reasonable parameter to include. It was noted, however, that the benzene contents of the pyrolyzates originating from the eight coals. in general, are low. i.e. 3- 7%. Nevertheless, it can immediately be noted (Fig. 2a) that the coals can be separated into three groups according to the concentration of benzene in the pyrolyzates: (1) CO1 and US2 (approximately 2%); (2) IDl, AU2 and AU1 (approximately 333.5%); and (3) SAl, SA2 and SA3 (667%). As in the case of benzene, the toluene concentration is one of the rather simple aromatic parameters that possibly displaying variations between the single coals. However, in contrast to benzene, toluene appears as one of the dominating aromatic compounds in the pyrolyzates. In Fig. 2b, the contents of toluene in the single pyrolyzates are summarized (1) relative to the total pyrolyzate; and (2) relative to the aromatic fraction of the pyrolyzate, the latter being calculated by subtracting the above estimated content of aliphatics from the total pyrolyzate. It is noted that the observed variations are virtually identical apart from in the coals CO1 and US2, which apparently shift positions due to the extreme content of aliphatics present in the pyrolyzate of COl, which is about five times that originating from US2. Although the grouping of the coals based on the toluene content is not as clear as that based on the benzene data, a close-to-identical grouping can be noted. Thus, especially, the grouping of the two Australian and the three South African coals. respectively, is emphasized. Turning to the condensed aromatic compounds, naphthalene is the simplest possible in this context. The content of naphthalene in the pyrolyzate ranges from I to 4%. In order to estimate variations in the formation of condensed relative to non-condensed aromatics, the naphthalene contents in the eight pyrolyzates are displayed (Fig. 2c) relative to the combined benzene and naphthalene contents. Obviously, the Indonesian coal, IDl, is separated from the others by a rather low naphthalene value (approximately 22%). A tendency to a separation of CO1 (approximately 30%) from the remaining six coals, all with naphthalene values around 3540’%, can be noted. The grouping of the three South African and the two Australian coals, respectively, emphasized. 3.3. The content
of’cresols
Cresols, i.e. the three possible isomers of methylphenol, appear to be rather characteristic products following the pyrolysis of coals and as such seem to act as potentially important parameters for the possible grouping of the single coals. In
82
L. Curlsm, J. V. Christiansen /J. Anal. Appl. Pyrolysis 35 (1995) 77791
the present study we have chosen to elucidate the participation of cresols in three different ways (Fig. 3). The content of cresols in the aromatic fraction of the pyrolyzates (Fig. 3a) obviously separates the eight coals into three distinct groups: (1) the three South African coals, which together with the Australian coal AU1 exhibit the lowest cresol content (2530%); (2) the coals COl, AU2 and ID1 with a cresol content around 40%; and (3) the US coal, US2, exhibiting a cresol content of about 50%. 6
a
7-
fl l
6-
E
n
P e
540 n
3-
s
q
n
2-p , l!,
.
,
.
,
.
,
.I
-
I
-
1.
I
CO1
US2
ID1
AU2
AU1
SAl
SA2
SA3
CO1
US2
ID1
AU1
AU2
SA3
SAl
SA2
q
I
0
50 -
cl 0
40 -
lil
0
I
30 -
20
.
p
.
, ID1
.
, . , . , . , . , . , . , 1 CO1 AU1 US2 SA3 AU2 SA2 SAl
Fig. 2. (a) Content of benzene in the pyrolyzates. (b) Content of toluene in (1) the total pyrolyzates and (2) the aromatic fraction of the pyrolyzate. (c) Content of naphthalene relative to the combined benzene and naphthalene content in the pyrolyzate.
L. Corlsm, J. V. Chrhtiunsen ; J. And.
SA2 90
SAl
SA3
Appl. Pvo!,..si.\ 1.5(1945) 77 41
AU1
CO1
AU2
ID1
x3
us2
,
70
n
n
E
I
60 q
40.
,
.
SA2
20!,
. US2
,
.
,
SAl
, ID1
.
,
SA3
AU2
AU2
CO1
r,.
,
.
,
.
AU1
.
, SA3
.
, ID1
.
,
.
SAl
, . , CO1 US2
, AU1
.
, SA2
Fig. 3. Content of cresols (a) in the aromatic fraction and (b) relatke to the combined toluene cresol fraction of the pyrolyzate. (c) Content of o-cresol in the cresol fraction in the pyrolyzatc.
and
An alternative view, displaying the cresol content relative to the combined cresol and toluene content (Fig. 3b) disclosed a less clear separation. However, the same trend, i.e. a certain grouping of the South African coals and, in this case, the Autrahan coals, respectively, can be noted. The analytical procedure does allow the separation of o-cresol from the meta and para isomers, the latter two, however, not being separated. Displaying the contents
84
L. Carlsm,
J. V. Christiansen
I J. Anal. Appl. Pyrolysis 35 (1995) 77-91
of o-cresol in the cresol fractions (Fig. 3c) suggests content in the US2 and ID1 coals, whereas no distinct six coals was revealed.
a somewhat lower o-cresol separation of the remaining
3.4. The content oj’styrene The last parameter included in the present study is the content of styrene. Typically the styrene content in the pyrolyzate is up to a few per cent. Styrene may, in this context, be regarded as a degradation product from fused carbon moieties. Thus, we have chosen to use the styrene content relative to the combined content of naphthalene and styrene as a possible parameter characteristic for the single coals (Fig. 4). Immediately, three distinct groups are noted (1) the South African coals (approximately 33%); (2) the Australian coals and the coals US2 and CO1 (approximately 45-50%); and (3) the Indonesian ID1 coal exhibiting a styrene value around 75%.
4. Discussion Obviously the nine different parameters described above each give valuable information on similarities and dissimilarities between the eight coals included in the present study. However, an overall picture is virtually impossible to develop with-out applying statistical techniques. In the following, the statistical treatment of the data based on principal component analysis (PCA) and hierarchical cluster analysis (HCA) is discussed [8]. The PCA reduces the multivariant data set by summarizing the nine parameters applying a limited number of variables, i.e. the principal components. In the present study, the first three principal components have been included, which apparently explain more than 95% of the total variance. Alternatively, HCA, applying the average linkage method with the euclidean metric (i.e. root-mean-square distances), was employed to produce dendrograms to visualize the actual degree of similarity between the single coals included in the study.
SAl
942
SA3
Fig. 4. Content of styrene relative to the pyrolyzates following pyrolysis at 750°C.
AU2 combined
US2 content
AU1
CO1
ID1
of naphthalene
and
styrene
in the
L. Carlsen, J. V. Christiansrn
//J. Anal. Appl. P,wly.ri.c .U (1995) 77 91
x5
PC-2
Fig. 5. Principal
component
analysis
based on pyrolysis
data
In Fig. 5 the results of the PCA based on the above nine described parameters derived from the flash pyrolysis experiments are visualized, the three first principal components accounting for 73.72% 13.01% and 8.85% of the total variance. respectively, the corresponding component loading being given in Table 2. It is immediately seen that the three South African coals and the two Australian coals, respectively, are located rather close in the three-dimensional space set by the first three principal components, whereas the remaining three coals are found Table 2 Principal
components
estimated
from pyrolysis
data ’
Parmaeter
PC 1
PC2
PC3
Component loadings A: Aiiphatics B: Benzene C: Toluene 1 D: Toluene 2 E: Naphthalene F: Cresol I G: Cresol 2 H: Cresol 3 I: Styrene
- 0.656 0.891 0.982 0.957 0.751 -0.891 0.740 -0.951 - 0.849
0.646 0.079 0.008 - 0.030 - 0.400 -0.399 0.523 - 0.220 0.326
0.31 I -0.331 -0.156 -0.160 0.509 0.070 0.370 0.100 -0.360
6.635
I.171
0.796
73.711
13.009
8.848
Variance
explained
by components
Per cent of total variance
d The weights given.
explained
of the single parameters
and the relative
and cumulative
parts
of the total variance
are
86
L. Carlsen, J. V. Christiansen
SA3
/J.
Anal. Appl. Pyrolysis
35 (1995) 77-91
-
I
ID1 I
1
I
I
I
Sij = l_ dij/d,,,
I
r 0
Fig. 6. Dendrogram representing the relationships between the eight coals based on pyrolysis data.
“scattered” throughout the space. Obviously, this is not surprising based on simple geographic considerations. It can be noted, however, that the PCA predicts SA3 to be slightly different from SAl and SA2. This is nicely reflected by the HCA, Fig. 6 displaying the resulting dendrogram. Thus, it is noted that SAl and SA2 show similarities of more than 85%, whereas the similarity between SA3 and the SAI/SA2 group amounts to about 68.5%. Analogously, the two Australian coals show a similarity of about 68.5%. In contrast to this, it is noted that the Indonesian coal, IDI, and the South African coals show a similarity of less than 20%. Traditionally, the characterization of coals is based on the content of volatiles, the elemental composition, the moisture and ash content, and the vitrinite reflectance as well as the maceral composition. In order to compare the above-described classification based on pyrolysis data with a classification based on conventional analytical data, a PCA was carried out applying the conventional analytical data for the eight coals as input parameters. In Fig. 7 the results of the analysis are shown, the three first principal components accounting for 58.02%, 25.98% and 10.51% of the total variance, respectively, the corresponding components loading being given in Table 3. Immediately, it is noted that, also based on the conventional analytical data, the PCA discloses a rather close connection between the three South African coals, whereas the grouping together of the two Australian coals is not equally demonstrated. On the other hand, apart from IDl, the coals apparently are predicted to be more closely related than was observed based on pyrolysis data (see Fig. 8). This is further substantiated through the HCA, Fig. 8 displaying the resulting dendrogram. Thus, based on the conventional data, SAl and SA2 show similarities of more than 92%, whereas the similarity between SA3 and the SAl/SA2 group amounts to slightly less than 90%. The two Australian coals show a similarity of about 77.5%. It is noted especially that AU2 and SA3 show a similarity of about 86.5%. The Indonesian coal, IDI, shows a similarity of approximately 57% to the group consisting of the remaining seven coals.
Obviously the analyses based on the conventional coal data demonstrate significantly less variation between the single coals than do the analyses based on pyrolysis data, suggesting the latter to be the more suitable for detailed classification purposes. Furthermore, it should be emphasized that by no means can the nine selected pyrolysis-derived parameters be claimed as the eventual choice. A detailed study aiming at an optimal selection of parameters may be expected to further improve the applicability of the method. Thus, the results of the PCA based on the conventional data (see Table 3) indicate significant contributions to the third principal component by the heteroatoms sulfur and oxygen as well as by the moisture and ash contents. Consequently it may seem appropriate to include, for example. heteroatom-containing compounds, other than the cresols, in future studies. As mentioned in the Introduction the inorganic constituents in the coals cannot immediately be left out of consideration, as the thermal conversion of the coals obviously may be influenced by these species, e.g. through catalytic effects. Thus, it may be appropriate to try to classify the coals based on the content of these inorganic constituents exclusively. Consequently, we carried out a PCA based on the composition of the ash taking into account SiO,, Al,O,, TiOz, P,O,, SO,. Fe?O,, CaO, MgO, Na,O and K,O [6,7]. In Fig. 9 the result of the analysis is visualized, the three first principal components accounting for 49.22% 35.08% and 11 .OO% of the total variance, respectively, the corresponding component loading being given in Table 4. Not surprisingly, a somewhat more scattered picture is obtained (Fig. 9) although apparently the three South African coals are still resonably closely grouped. No evident grouping of the remaining six coals can be deduced. This is further reflected in the dendrogram originating from the corre,-
AU
A' 7
PC-2 (25.95%) -2 -3 Fig. 7. Principal
component
analysis
based
PC-l (58.02%) on conventlonal
coal analyses.
88 Table 3 Principal
L. Carlsen, J. V. Christiansen
components
estimated
/J.
Anal. Appl. Pyrolysis
from conventional
coal analyses
35 (1995) 77-91
*
Parameter
PC1
PC2
PC3
Component loadings % Volatiles % Carbon % Hydrogen % Sulphur ‘%INitrogen % Oxygen ‘l/n Water ‘%IAsh Vitrinite reflectance % Vitrinite % Exinite % Intertinite % Huminite %I Liptinite
- 0.922 0.834 - 0.622 -0.094 0.915 -0.763 - 0.834 0.503 0.863 0.086 0.907 0.836 -0.878 - 0.878
-0.317 - 0.445 - 0.675 -0.787 0.298 0.473 0.153 0.518 - 0.035 - 0.987 0.006 0.526 0.450 0.450
0.112 -0.021 0.277 0.483 -0.201 0.405 -0.516 0.660 0.424 -0.108 0.027 - 0.057 0.152 0.152
8.123
3.636
1.471
58.019
25.975
10.506
Variance
explained
by components
Per cent of total variance
explained
a The weights of the single parameter
and the relative and cumulative
part of the total variance
are given.
sponding HCA (Fig. 10). The coals SAl and SA2 show a similarity of about 76.5%, whereas the similarity between these two coals and the third South African coal, SA3, amounts to about 60% only. Likewise, the analysis predicts the similarity between the two Australian coals to be slightly above 55% only. ID1 us2 co1 AU1 AU2
-
SA3
-
-
SAl SA2 I
1 Fig. 8, Dendrogram analyses.
representing
I
1
I
s.. 3 l_ ‘1
the relationships
I
dii/d,,,
between
r 0
the eight coals based
on conventional
coal
L. Curlsen. J. V. Christiansen
! J. Anal. Appl. Pyrolysis -1.5(1995) 77-91
xs
us2
.SA2
1
AU1
-1
-2 Fig. 9. Principal
component
-2
analysis
PC-1 (49.22%) based
on ash composition.
Although the same overall picture was obtained based on PCA and HCA of the available ash data, it seems clear that this system does not constitute as ideal for coal classification purposes. The most striking feature developed throughout the above described analyses is the similarities of the three South African coals. although apparently they are grouped into two subgroups consisting of (1) SAl and SA2 and (2) SA3, respectively. It is in this connection interesting to note that from a power production point of view these three coals behave differently, i.e. SAl and SA3 behave similarly during combustion, whereas a different behaviour of SA2 has been observed. resulting in an increased burning-out time [7]. Apparently none of the three described characterization techniques are able to reflect this. us2 ,
SA3
1
1 Fig. 10. Dendrogram
h
-I
representing
I
1
I
I
Sij=l-dij/d,,, the relationships
between
r
0
the eight coals based on ash composition.
90 Table 4 Principal
L. Curlsen, J. V. Christiunsen
components
estimated
from ash composition
Parameter
35 (1995) 77-91
d
PCI
Component % SiOz ‘%IAl,03 ‘%ITiOz ‘%IP*Or ‘%Iso, ‘%IFezOl ‘%ICaO ‘%IMgO ‘%INa,O ‘%IK,O Variance
i J. Anal. Appl. Pyrolysis
PC2
PC3
loadings
explained
- 0.772 0.923 0.784 0.941 0.661 -0.383 0.848 0.504 - 0.406 -0.502
-0.605 -0.165 ~ 0.268 -0.155 0.639 0.863 0.418 0.640 0.776 0.824
-0.192 0.327 0.534 0.036 -0.254 0.315 - 0.207 - 0.484 0.480 0.000
4.922
3.508
1.100
49.218
35.078
11.002
by components
Per cent of total variance
explained
* The weights of the single parameter
and the relative and cumulative
part of the total variance
are given.
The pyrolysis technique applied in the present study only reveals the eventual products generated during the pyrolysis process. Since the elemental compositions of, for example, the three South African coals show only minor differences, it may not be surprising that the pyrolysis product compositions analogously show a high degree of identity. However, the pyrolysis technique will not disclose any time dependence of the formation of these products, e.g. due to significant differences in the average molecular sizes of the three coals. Thus, it is suggested that the time-dependent formation of volatiles from the three coals should be studied possibly similarly to previous studies by Carlsen et al. [9].
5. Conclusions It has been demonstrated that flash pyrolysis in combination with statistical methods constitutes an advantageous technique for the characterization and classification of coals of different origin. Eight coals comprising three from South Africa, two from Australia, and one from the U.S.A., Colombia and Indonesia, respectively have been pyrolyzed at 750°C and differences in the compositions of the pyrolyzates have been elucidated based on nine parameters. The data obtained have been treated statistically by means of PCA and HCA, demonstrating a high degree of similarity between the three South African coals, whereas a somewhat less pronounced similarity between the Australian coals was shown. Similar results are obtained by applying conventional coal analyses. In order, eventually, to predict the combustion behaviour of a given coal, it is suggested that the parameters applied
should include data based rate of volatiles formation components.
on the time-resolved pyrolysis of the coal, such as the for whole and possibly the rate of formation of single
Acknowledgments This work has been partly financed by the Danish Technical and the Danish power companies ELSAM and ELKRAFT financial support.
Research Council are thanked for
References [I] P.H. Given. A. Marzec, W.A. Barton, L.J, Lynch and B.C. Gerstetn. Fuel. 65 (1986) 155. [2] H. Shinn. Fuel, 69 (1984) 1187. [3] N.E. Vanderbourgh. J.M. Williams, Jr. and H.-R. Schultcn. J. Anal. Appl. Pyrolysis. 8 (1985) 271 [4] J.V. Christiansen. A. Feldthus and L. Carlsen, J. Anal. Appl. Pyrolysis, 32 (1995) 51. [S] J.V. Christiansen. A. Feldthus, H. Egsgaard and L. Carlsen. J. Anal. ,Appl. Pyrolysis. 24 (1993) 31 I, [6] J.V. Christiansen. A. Feldthus, H. Egsgaard. C. Jespersen. E. Larsen and L. Carlsen. Flash-pyrolyse of kul. I. Pyrolyse ved modstandsopvarmning, Rise-R-771 (pt.1) (D-\). Rise National Laboratory. Roskilde. September 1994. [7] P. Torslev, ELSAM, Personal communication. [8] L. Wilkinson. SYSTAT: The System for Statistics, SYSTAT. Inc., Evanston, IL. 1989. [9] L. Carlsen, A. Feldthus and P. Bo, J. Anal. Appl. Pyrolysis. 19 (1991) I5 27.
of Analytical
and Apphed
Pyrolysi\
JOURNALot ANALYTICAL and APPLIED PYROLYSIS
3s (199.5) 77 91
Flash pyrolysis of coals A new approach of classification
Abstract Flash pyrolysis-gas chromatography:mass spectrometry constitutes. in combination with statistical methods such as principal component analysis (PCA) and hierachical cluster analysis (HCA), an advantageous technique in an attempt to characterize and classify coals of different origin. Eight coals comprising three from South Africa. two from Australia. and one from U.S.A.. Columbia and Indonesia. respectively. have been pyrolyzed at 750°C. Observed differences in the composition of the pyrolyzate have been elucidated by studying nine parameters: (A) the content of long-chain aliphatic compounds: (B) the content of benzene; (C) the content of toluene; (D) the content of toluene in the aromatic fraction: (E) the content of naphthalene relative to the content of benzene+ naphthalene: (F) the content of cresols in the aromatic fraction; (G) the content of cresols relative to the content of’ toluene + cresols: (H) the content of o-cresol in the cresol fraction; and (I) the content of styrene relative to the content of naphthalene + styrene. The data obtained have been treated statistically by means of PCA and HCA, demonstrating a high degree of similarity between the three South African coals, whereas a somewhat less pronounced similarity between the Australian coals was shown. The results are discussed based on an analogous study applying conventional coal analyses such as elemental analysis. maceral composition. vitrinite reflectance. ash content, etc. A further comparison with studies applying ash composition data has been included. Kc~~~~rtls: Coal classification;
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78
L. Carlsen, J. V. Chrisliansrn ! J. Anal. Appl. P.vrolysis 35 (1995) 77-91
1. Introduction Coals cannot be described as well-defined structures, but should rather be considered as a series of well-defined substructures bound together in a complicated three-dimensional network. Thus, coals consist of a macromolecular matrix containing a variety of aliphatic, aromatic and polyaromatic moieties interconnected through either ether or carbon-carbon linkages. In addition, different heteroatomcontaining sub-units are present in various amounts as a reflection of the origin of the single coal. The actual composition and structure of a given coal obviously reflect the original plant material used in nature’s production of the coal. However, temperature and pressure conditions prevailing over the geological time scale at the site at which the coal has been produced also have a determining role. In addition to the matrix material, coals typically also consist of a mobile phase of low molecular weight compounds trapped within the coal matrix [l-3]. Several attempts to construct coal structures based on existing data on the content of subunits have been made (see, for example, Ref. [2]), suggesting the molecules with molecular weights from around 1000 up to above 100 000 can be present in a single coal sample. Coals of different origin may behave quite differently upon combustion, and it seems reasonable to assume that the organic fraction plays a dominant role in this context, although the inorganic fraction cannot immediately be left out of consideration. Thus, not only should the actual elemental composition but also the nature of the three-dimensional coal matrix, as well as the trapped mobile fraction, be a priori considered. Seen from an environmental as well as from a combustion technology point of view, it appears highly desirable to develop a classification system based on simple laboratory measurements to predict the combustion behaviour of a given coal, thus thereby being able to optimize the combustion process with respect both to the energy output and the environmental impact. Eventually the system could be applied as a guide prior to the purchase of large quantities of an unknown coal for power production, as the coal could be classified and thus compared to a selection of coals exhibiting well-documented properties. The present paper describes preliminary studies on the possible classification of coals based on variations in the relative concentrations of a series of simple aliphatic and aromatic compounds found in the pyrolyzates of single coals following pyrolysis at 750°C [4]. The obtained data have been treated statistically and compared to results obtained analogously based on conventional coal analyses, e.g. elemental analyses, maceral composition, vitrinite reflectance, ash content, etc.
2. Experimental Flash pyrolysis experiments were carried out using a PYROLA-85 foil pulse pyrolyer (PYROL AB, Lund, Sweden) connected to a Varian Saturn II GC/MS system. The pyrolysis products were separated on a Chrompack CP Sil-5 CB
column (25 m x 0.25 mm i.d.) and identified in an ion trap mass spectrometer operated in the electron impact mode. Samples of coal were placed directly on the platinum foil in the pyrolysis chamber operated at 150°C. Samples were pyrolyzed at 750°C for 2 s. The loading procedure has been described previously [5]. The study included in total eight coals of different origin. supplied by ELSAM: three coals from South Africa (SAl, SA2. SA3). two coals from Australia (AU]. AU2), and one coal each from North America (US2). Columbia (CO1 ) and Indonesia (ID]), respectively [6]. It is unrealistic to quantify the single compounds or groups of compounds in absolute terms, as it requires a comparison with a complete range of isomers: this obviously. is not available. Thus, we have based the quantification on the integration of 1-~I! characteristic ions representing single compounds. Consequently, the calculated percentages should be regarded as the relative contributions to the pyrolyzates of the single compounds from the different coals. The relative yield of a given compound (or group of compounds) is given by C x lOO:CR, where C is the yield of the characteristic ion (or ions) representing the compound in question, and CR represents the total yield of ions used for quantification of the compounds given in Table 1. Conventional coal analysis data comprising the content of volatiles, the elemental composition. the moisture content, the ash content, the vitrinite reflectance, the maceral composition and the ash composition were supplied. together with the coals. by ELSAM [6,7].
I
Table
Retention
times and ions used for the quantification
C‘ompound
Retention (min)
of selected products
time
Selected ions. ,,I 1 -_
Benzene
I.13
Toluene
I.31
91
Styrene
1.78
I 03
78
Phenol
2.20
,I-Cresol
7.80
107 + IOX
lndene
2.86
Il5+
,rr,~~-Cresol
3.00
I07 + 108
C2-Phenols
Y4 II6
127
Naphthalene
4.28
I -Methylnaphthalene
5.63
131 + 147
2-Methylnaphthalene
5.83
I41 + 143
C2-Naphthalenes
I28
141 + I56
Brphenyl
6.65
I54
Acenapthylene
7.46
157
Phenanthrene
I I ,35
17X
Anthracene
I I .45
I78
Cl6
-C?9.
C’l6C29.
unsaturated saturated
55 + 69 + 83 57+71+85
80
L. Cdsen,
1 J. Anal. Appl. Pyrolysis 35 (1995) 77 -91
J. V. Christinnsrn
60
40
E
30 I 20 0 10-m
of long-chain
.
l
SA3
SA2
SAl
I
o.,.,.,.,.,.,. US2 Fig. 1. The content
p
aliphatic
compounds
AU1
AU2
in the pyrolyzate
ID1
-
I’ CO1
following
pyrolysis
at 750°C.
The statistical treatment including principal component and hierarchical cluster analyses of the data, has been performed by applying the SYSTAT 5 soft-ware package (OSYSTAT, inc.), version 5.1 for Macintosh computers [8]. In the case of PCA, the input parameters are automatically standardized, whereas a standardization of the parameters is carried out prior to HCA in order to ensure equal weighting of the single parameters. The PCA is carried out on the correlation matrix. The similarity between two samples i and j, S,j, determined by HCA, is given by S, = 1 - d,,/d,,,,, where d,, and d,,, are the distance between samples i and j and the maximum distance between samples, respectively.
3. Results Obviously, a wide variety of compounds present in the pyrolyzates could a priori be used as indicators for the single coals. In the present study, we have chosen to focus on compounds and groups of compounds exhibiting major variations. Hence, the following parameters have been selected (see Table 1): (A) the content of long-chain aliphatic compounds; (B) the content of benzene; (C) the content of toluene; (D) the content of toluene in the aromatic fraction; (E) the content of naphthalene relative to the content of benzene + naphthalene; (F) the content of cresols in the aromatic fraction; (G) the content of cresols relative to the content of toluene + cresols; (H) the content of o-cresol in the cresol fraction; and (I) the content of styrene relative to the content of naphthalene + styrene. 3.1. The content
of /ong-chain
aliphatic
compounds
Various coals exhibit significant differences in the content of long-chain aliphatic compounds. In Fig. 1 are displayed the percentages of long-chain aliphatic compounds (see Table 1) in the pyrolyzate of the eight coals. It is noted that the coals are grouped according to their apparent contents of long-chain aliphatic compounds in the pyrolyzates. Four coals, i.e. the three South African coals (SAlSA2,
L. Carlsm.
J. V. Christiansrn
)/J.
Anal.
Appl.
Pwoiy.sis
.I_5 (1995)
77-91
XI
SA3) and the U.S. coal (US2), exhibited approximately 10% of the long-chain aliphitics in the pyrolyzates, whereas the pyrolyzate corresponding to the Columbian coal, COl, contained as much as around 50%. For the three remaining coals. i.e. AUl. AU2 and IDl, contents between 25 and 35% were determined. 3.2. The content
oj’ benzene,
toluene and nuphthcrlene
Benzene is the simplest aromatic compound and is. as such, a reasonable parameter to include. It was noted, however, that the benzene contents of the pyrolyzates originating from the eight coals. in general, are low. i.e. 3- 7%. Nevertheless, it can immediately be noted (Fig. 2a) that the coals can be separated into three groups according to the concentration of benzene in the pyrolyzates: (1) CO1 and US2 (approximately 2%); (2) IDl, AU2 and AU1 (approximately 333.5%); and (3) SAl, SA2 and SA3 (667%). As in the case of benzene, the toluene concentration is one of the rather simple aromatic parameters that possibly displaying variations between the single coals. However, in contrast to benzene, toluene appears as one of the dominating aromatic compounds in the pyrolyzates. In Fig. 2b, the contents of toluene in the single pyrolyzates are summarized (1) relative to the total pyrolyzate; and (2) relative to the aromatic fraction of the pyrolyzate, the latter being calculated by subtracting the above estimated content of aliphatics from the total pyrolyzate. It is noted that the observed variations are virtually identical apart from in the coals CO1 and US2, which apparently shift positions due to the extreme content of aliphatics present in the pyrolyzate of COl, which is about five times that originating from US2. Although the grouping of the coals based on the toluene content is not as clear as that based on the benzene data, a close-to-identical grouping can be noted. Thus, especially, the grouping of the two Australian and the three South African coals. respectively, is emphasized. Turning to the condensed aromatic compounds, naphthalene is the simplest possible in this context. The content of naphthalene in the pyrolyzate ranges from I to 4%. In order to estimate variations in the formation of condensed relative to non-condensed aromatics, the naphthalene contents in the eight pyrolyzates are displayed (Fig. 2c) relative to the combined benzene and naphthalene contents. Obviously, the Indonesian coal, IDl, is separated from the others by a rather low naphthalene value (approximately 22%). A tendency to a separation of CO1 (approximately 30%) from the remaining six coals, all with naphthalene values around 3540’%, can be noted. The grouping of the three South African and the two Australian coals, respectively, emphasized. 3.3. The content
of’cresols
Cresols, i.e. the three possible isomers of methylphenol, appear to be rather characteristic products following the pyrolysis of coals and as such seem to act as potentially important parameters for the possible grouping of the single coals. In
82
L. Curlsm, J. V. Christiansen /J. Anal. Appl. Pyrolysis 35 (1995) 77791
the present study we have chosen to elucidate the participation of cresols in three different ways (Fig. 3). The content of cresols in the aromatic fraction of the pyrolyzates (Fig. 3a) obviously separates the eight coals into three distinct groups: (1) the three South African coals, which together with the Australian coal AU1 exhibit the lowest cresol content (2530%); (2) the coals COl, AU2 and ID1 with a cresol content around 40%; and (3) the US coal, US2, exhibiting a cresol content of about 50%. 6
a
7-
fl l
6-
E
n
P e
540 n
3-
s
q
n
2-p , l!,
.
,
.
,
.
,
.I
-
I
-
1.
I
CO1
US2
ID1
AU2
AU1
SAl
SA2
SA3
CO1
US2
ID1
AU1
AU2
SA3
SAl
SA2
q
I
0
50 -
cl 0
40 -
lil
0
I
30 -
20
.
p
.
, ID1
.
, . , . , . , . , . , . , 1 CO1 AU1 US2 SA3 AU2 SA2 SAl
Fig. 2. (a) Content of benzene in the pyrolyzates. (b) Content of toluene in (1) the total pyrolyzates and (2) the aromatic fraction of the pyrolyzate. (c) Content of naphthalene relative to the combined benzene and naphthalene content in the pyrolyzate.
L. Corlsm, J. V. Chrhtiunsen ; J. And.
SA2 90
SAl
SA3
Appl. Pvo!,..si.\ 1.5(1945) 77 41
AU1
CO1
AU2
ID1
x3
us2
,
70
n
n
E
I
60 q
40.
,
.
SA2
20!,
. US2
,
.
,
SAl
, ID1
.
,
SA3
AU2
AU2
CO1
r,.
,
.
,
.
AU1
.
, SA3
.
, ID1
.
,
.
SAl
, . , CO1 US2
, AU1
.
, SA2
Fig. 3. Content of cresols (a) in the aromatic fraction and (b) relatke to the combined toluene cresol fraction of the pyrolyzate. (c) Content of o-cresol in the cresol fraction in the pyrolyzatc.
and
An alternative view, displaying the cresol content relative to the combined cresol and toluene content (Fig. 3b) disclosed a less clear separation. However, the same trend, i.e. a certain grouping of the South African coals and, in this case, the Autrahan coals, respectively, can be noted. The analytical procedure does allow the separation of o-cresol from the meta and para isomers, the latter two, however, not being separated. Displaying the contents
84
L. Carlsm,
J. V. Christiansen
I J. Anal. Appl. Pyrolysis 35 (1995) 77-91
of o-cresol in the cresol fractions (Fig. 3c) suggests content in the US2 and ID1 coals, whereas no distinct six coals was revealed.
a somewhat lower o-cresol separation of the remaining
3.4. The content oj’styrene The last parameter included in the present study is the content of styrene. Typically the styrene content in the pyrolyzate is up to a few per cent. Styrene may, in this context, be regarded as a degradation product from fused carbon moieties. Thus, we have chosen to use the styrene content relative to the combined content of naphthalene and styrene as a possible parameter characteristic for the single coals (Fig. 4). Immediately, three distinct groups are noted (1) the South African coals (approximately 33%); (2) the Australian coals and the coals US2 and CO1 (approximately 45-50%); and (3) the Indonesian ID1 coal exhibiting a styrene value around 75%.
4. Discussion Obviously the nine different parameters described above each give valuable information on similarities and dissimilarities between the eight coals included in the present study. However, an overall picture is virtually impossible to develop with-out applying statistical techniques. In the following, the statistical treatment of the data based on principal component analysis (PCA) and hierarchical cluster analysis (HCA) is discussed [8]. The PCA reduces the multivariant data set by summarizing the nine parameters applying a limited number of variables, i.e. the principal components. In the present study, the first three principal components have been included, which apparently explain more than 95% of the total variance. Alternatively, HCA, applying the average linkage method with the euclidean metric (i.e. root-mean-square distances), was employed to produce dendrograms to visualize the actual degree of similarity between the single coals included in the study.
SAl
942
SA3
Fig. 4. Content of styrene relative to the pyrolyzates following pyrolysis at 750°C.
AU2 combined
US2 content
AU1
CO1
ID1
of naphthalene
and
styrene
in the
L. Carlsen, J. V. Christiansrn
//J. Anal. Appl. P,wly.ri.c .U (1995) 77 91
x5
PC-2
Fig. 5. Principal
component
analysis
based on pyrolysis
data
In Fig. 5 the results of the PCA based on the above nine described parameters derived from the flash pyrolysis experiments are visualized, the three first principal components accounting for 73.72% 13.01% and 8.85% of the total variance. respectively, the corresponding component loading being given in Table 2. It is immediately seen that the three South African coals and the two Australian coals, respectively, are located rather close in the three-dimensional space set by the first three principal components, whereas the remaining three coals are found Table 2 Principal
components
estimated
from pyrolysis
data ’
Parmaeter
PC 1
PC2
PC3
Component loadings A: Aiiphatics B: Benzene C: Toluene 1 D: Toluene 2 E: Naphthalene F: Cresol I G: Cresol 2 H: Cresol 3 I: Styrene
- 0.656 0.891 0.982 0.957 0.751 -0.891 0.740 -0.951 - 0.849
0.646 0.079 0.008 - 0.030 - 0.400 -0.399 0.523 - 0.220 0.326
0.31 I -0.331 -0.156 -0.160 0.509 0.070 0.370 0.100 -0.360
6.635
I.171
0.796
73.711
13.009
8.848
Variance
explained
by components
Per cent of total variance
d The weights given.
explained
of the single parameters
and the relative
and cumulative
parts
of the total variance
are
86
L. Carlsen, J. V. Christiansen
SA3
/J.
Anal. Appl. Pyrolysis
35 (1995) 77-91
-
I
ID1 I
1
I
I
I
Sij = l_ dij/d,,,
I
r 0
Fig. 6. Dendrogram representing the relationships between the eight coals based on pyrolysis data.
“scattered” throughout the space. Obviously, this is not surprising based on simple geographic considerations. It can be noted, however, that the PCA predicts SA3 to be slightly different from SAl and SA2. This is nicely reflected by the HCA, Fig. 6 displaying the resulting dendrogram. Thus, it is noted that SAl and SA2 show similarities of more than 85%, whereas the similarity between SA3 and the SAI/SA2 group amounts to about 68.5%. Analogously, the two Australian coals show a similarity of about 68.5%. In contrast to this, it is noted that the Indonesian coal, IDI, and the South African coals show a similarity of less than 20%. Traditionally, the characterization of coals is based on the content of volatiles, the elemental composition, the moisture and ash content, and the vitrinite reflectance as well as the maceral composition. In order to compare the above-described classification based on pyrolysis data with a classification based on conventional analytical data, a PCA was carried out applying the conventional analytical data for the eight coals as input parameters. In Fig. 7 the results of the analysis are shown, the three first principal components accounting for 58.02%, 25.98% and 10.51% of the total variance, respectively, the corresponding components loading being given in Table 3. Immediately, it is noted that, also based on the conventional analytical data, the PCA discloses a rather close connection between the three South African coals, whereas the grouping together of the two Australian coals is not equally demonstrated. On the other hand, apart from IDl, the coals apparently are predicted to be more closely related than was observed based on pyrolysis data (see Fig. 8). This is further substantiated through the HCA, Fig. 8 displaying the resulting dendrogram. Thus, based on the conventional data, SAl and SA2 show similarities of more than 92%, whereas the similarity between SA3 and the SAl/SA2 group amounts to slightly less than 90%. The two Australian coals show a similarity of about 77.5%. It is noted especially that AU2 and SA3 show a similarity of about 86.5%. The Indonesian coal, IDI, shows a similarity of approximately 57% to the group consisting of the remaining seven coals.
Obviously the analyses based on the conventional coal data demonstrate significantly less variation between the single coals than do the analyses based on pyrolysis data, suggesting the latter to be the more suitable for detailed classification purposes. Furthermore, it should be emphasized that by no means can the nine selected pyrolysis-derived parameters be claimed as the eventual choice. A detailed study aiming at an optimal selection of parameters may be expected to further improve the applicability of the method. Thus, the results of the PCA based on the conventional data (see Table 3) indicate significant contributions to the third principal component by the heteroatoms sulfur and oxygen as well as by the moisture and ash contents. Consequently it may seem appropriate to include, for example. heteroatom-containing compounds, other than the cresols, in future studies. As mentioned in the Introduction the inorganic constituents in the coals cannot immediately be left out of consideration, as the thermal conversion of the coals obviously may be influenced by these species, e.g. through catalytic effects. Thus, it may be appropriate to try to classify the coals based on the content of these inorganic constituents exclusively. Consequently, we carried out a PCA based on the composition of the ash taking into account SiO,, Al,O,, TiOz, P,O,, SO,. Fe?O,, CaO, MgO, Na,O and K,O [6,7]. In Fig. 9 the result of the analysis is visualized, the three first principal components accounting for 49.22% 35.08% and 11 .OO% of the total variance, respectively, the corresponding component loading being given in Table 4. Not surprisingly, a somewhat more scattered picture is obtained (Fig. 9) although apparently the three South African coals are still resonably closely grouped. No evident grouping of the remaining six coals can be deduced. This is further reflected in the dendrogram originating from the corre,-
AU
A' 7
PC-2 (25.95%) -2 -3 Fig. 7. Principal
component
analysis
based
PC-l (58.02%) on conventlonal
coal analyses.
88 Table 3 Principal
L. Carlsen, J. V. Christiansen
components
estimated
/J.
Anal. Appl. Pyrolysis
from conventional
coal analyses
35 (1995) 77-91
*
Parameter
PC1
PC2
PC3
Component loadings % Volatiles % Carbon % Hydrogen % Sulphur ‘%INitrogen % Oxygen ‘l/n Water ‘%IAsh Vitrinite reflectance % Vitrinite % Exinite % Intertinite % Huminite %I Liptinite
- 0.922 0.834 - 0.622 -0.094 0.915 -0.763 - 0.834 0.503 0.863 0.086 0.907 0.836 -0.878 - 0.878
-0.317 - 0.445 - 0.675 -0.787 0.298 0.473 0.153 0.518 - 0.035 - 0.987 0.006 0.526 0.450 0.450
0.112 -0.021 0.277 0.483 -0.201 0.405 -0.516 0.660 0.424 -0.108 0.027 - 0.057 0.152 0.152
8.123
3.636
1.471
58.019
25.975
10.506
Variance
explained
by components
Per cent of total variance
explained
a The weights of the single parameter
and the relative and cumulative
part of the total variance
are given.
sponding HCA (Fig. 10). The coals SAl and SA2 show a similarity of about 76.5%, whereas the similarity between these two coals and the third South African coal, SA3, amounts to about 60% only. Likewise, the analysis predicts the similarity between the two Australian coals to be slightly above 55% only. ID1 us2 co1 AU1 AU2
-
SA3
-
-
SAl SA2 I
1 Fig. 8, Dendrogram analyses.
representing
I
1
I
s.. 3 l_ ‘1
the relationships
I
dii/d,,,
between
r 0
the eight coals based
on conventional
coal
L. Curlsen. J. V. Christiansen
! J. Anal. Appl. Pyrolysis -1.5(1995) 77-91
xs
us2
.SA2
1
AU1
-1
-2 Fig. 9. Principal
component
-2
analysis
PC-1 (49.22%) based
on ash composition.
Although the same overall picture was obtained based on PCA and HCA of the available ash data, it seems clear that this system does not constitute as ideal for coal classification purposes. The most striking feature developed throughout the above described analyses is the similarities of the three South African coals. although apparently they are grouped into two subgroups consisting of (1) SAl and SA2 and (2) SA3, respectively. It is in this connection interesting to note that from a power production point of view these three coals behave differently, i.e. SAl and SA3 behave similarly during combustion, whereas a different behaviour of SA2 has been observed. resulting in an increased burning-out time [7]. Apparently none of the three described characterization techniques are able to reflect this. us2 ,
SA3
1
1 Fig. 10. Dendrogram
h
-I
representing
I
1
I
I
Sij=l-dij/d,,, the relationships
between
r
0
the eight coals based on ash composition.
90 Table 4 Principal
L. Curlsen, J. V. Christiunsen
components
estimated
from ash composition
Parameter
35 (1995) 77-91
d
PCI
Component % SiOz ‘%IAl,03 ‘%ITiOz ‘%IP*Or ‘%Iso, ‘%IFezOl ‘%ICaO ‘%IMgO ‘%INa,O ‘%IK,O Variance
i J. Anal. Appl. Pyrolysis
PC2
PC3
loadings
explained
- 0.772 0.923 0.784 0.941 0.661 -0.383 0.848 0.504 - 0.406 -0.502
-0.605 -0.165 ~ 0.268 -0.155 0.639 0.863 0.418 0.640 0.776 0.824
-0.192 0.327 0.534 0.036 -0.254 0.315 - 0.207 - 0.484 0.480 0.000
4.922
3.508
1.100
49.218
35.078
11.002
by components
Per cent of total variance
explained
* The weights of the single parameter
and the relative and cumulative
part of the total variance
are given.
The pyrolysis technique applied in the present study only reveals the eventual products generated during the pyrolysis process. Since the elemental compositions of, for example, the three South African coals show only minor differences, it may not be surprising that the pyrolysis product compositions analogously show a high degree of identity. However, the pyrolysis technique will not disclose any time dependence of the formation of these products, e.g. due to significant differences in the average molecular sizes of the three coals. Thus, it is suggested that the time-dependent formation of volatiles from the three coals should be studied possibly similarly to previous studies by Carlsen et al. [9].
5. Conclusions It has been demonstrated that flash pyrolysis in combination with statistical methods constitutes an advantageous technique for the characterization and classification of coals of different origin. Eight coals comprising three from South Africa, two from Australia, and one from the U.S.A., Colombia and Indonesia, respectively have been pyrolyzed at 750°C and differences in the compositions of the pyrolyzates have been elucidated based on nine parameters. The data obtained have been treated statistically by means of PCA and HCA, demonstrating a high degree of similarity between the three South African coals, whereas a somewhat less pronounced similarity between the Australian coals was shown. Similar results are obtained by applying conventional coal analyses. In order, eventually, to predict the combustion behaviour of a given coal, it is suggested that the parameters applied
should include data based rate of volatiles formation components.
on the time-resolved pyrolysis of the coal, such as the for whole and possibly the rate of formation of single
Acknowledgments This work has been partly financed by the Danish Technical and the Danish power companies ELSAM and ELKRAFT financial support.
Research Council are thanked for
References [I] P.H. Given. A. Marzec, W.A. Barton, L.J, Lynch and B.C. Gerstetn. Fuel. 65 (1986) 155. [2] H. Shinn. Fuel, 69 (1984) 1187. [3] N.E. Vanderbourgh. J.M. Williams, Jr. and H.-R. Schultcn. J. Anal. Appl. Pyrolysis. 8 (1985) 271 [4] J.V. Christiansen. A. Feldthus and L. Carlsen, J. Anal. Appl. Pyrolysis, 32 (1995) 51. [S] J.V. Christiansen. A. Feldthus, H. Egsgaard and L. Carlsen. J. Anal. ,Appl. Pyrolysis. 24 (1993) 31 I, [6] J.V. Christiansen. A. Feldthus, H. Egsgaard. C. Jespersen. E. Larsen and L. Carlsen. Flash-pyrolyse of kul. I. Pyrolyse ved modstandsopvarmning, Rise-R-771 (pt.1) (D-\). Rise National Laboratory. Roskilde. September 1994. [7] P. Torslev, ELSAM, Personal communication. [8] L. Wilkinson. SYSTAT: The System for Statistics, SYSTAT. Inc., Evanston, IL. 1989. [9] L. Carlsen, A. Feldthus and P. Bo, J. Anal. Appl. Pyrolysis. 19 (1991) I5 27.