E nergy S ou rces , 2 2 :4 97 ] 5 13 , 20 00
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The Drama Lignite Deposit, Northern Greece:
Insights from Traditional Coal Analyses,
Rock-Eval Data, and Natural
Radionuclides Concentrations
ANDRE AS GE O RGAKO PO ULO S
De partme nt of Mine ralogy } Pe trology }
School of Ge ology
Aristotle U nive rsity of The ssaloniki
The ssaloniki , Gree ce
E conomic Ge ology
In the present study the results of traditional m ethods for characterizing 25 lignite
sam ples, representing a continuous sequence of the Dram a deposit, N orthern
G reece, are presented. The m oisture, the v olatile m atter, and the ash contents are
high, while the sulfur content rem ains at low lev els. R ock-E v al analysis was
perform ed on the sam e sam ples. The Tm ax v alues obtained do not correlate with
coal type and rank and are higher than those expected for lignites. T he reflectiv ity
v alues are lower than 0.2%. In v alues - 0.5% R m and ) 1.5% R m , Tm a x does not
correlate with R m . It is also noticed that the difference in hydrogen contents is not
2 38
2 35
related to the Tm ax v alues as would be expected. T he concentrations of
U,
U,
226
2 10
228
228
40
Ra, Pb,
Ra,
T h, and K, determ ined in sam ples D2 and D5, are sim ilar
to those reported in the literature for G reek lignites. The concentrations of uranium series isotopes are am ong the higher for lignites worldwide.
Keywords
Dram a, Gre ece , lignite , radionuclide s, Rock-Eval pyrolysis
More than 60 basins in Gre e ce forme d during Ne oge ne and Q uate rnary time s
include coal de posits. The rank of the coal varie s from pe at up to the subbituminous coal stage . The most abundant type of coal in Gre e ce is lignite . Lignite
de posits forme d from the Mioce ne to the Ple istoce ne in mire s of intram ontane and
paralic basins , such as the basins of Ptole m ais , Florina , and Dram a in Northe rn
Gre e ce and the basin of Me galopolis in Southe rn Gre e ce . The prove d lignite
Received 5 March 1999; accepte d 20 May 1999.
The pre sent work has be en m ade possible thanks to the Institute of Geology and
Mineral Exploration (IGME ). I warmly thank J. Broussoulis and P. Yiakkoupis of IGME for
providing the core samples and for fruitful discussions. The author is espe cially indebte d to
FrancË ois Marquis and Je an Espitalie for the Rock-Eval pyrolysis analyse s and for their
advice during the interpre tation of the re sults. I am particularly grate ful to Asst. Prof. M.
Manolopoulou for the radioactivity me asure ments and for he r valuable help in the comprehension of the re sults. The assistance of Asst. Prof. T. Soldatos and Le cture r A. Koroneos is
highly appre ciate d. I wish also to thank Prof. S. V alceva, University of Sofia, Bulgaria, for
having assiste d me through he lpful discussions, and Asst. Prof. K. Christanis, University of
P atras , Gre ece , for his critical re vie w and sugge stions for improve me nt of this article.
Addre ss to corre spondence to Dr. Andre as Ge orgakopoulos , Department of Mineralogy } Pe trology } Economic Geology, School of Ge ology, Aristotle University of The ssaloniki, 540 06 The ssalonki, Gree ce . E-m ail:ageorgak@ geo.auth.gr
497
498
A . G eorgakopoulos
re serve s are e stim ate d up to 6 ,750 Mt without adding the 4 ,300 Mm 3 of the
Philippi pe at , about 150 km in the e ast of The ssaloniki , Northe rn Gre e ce. The
e conom ically re cove rable lignite rese rve s re ach 3 ,900 Mt , approxim ate ly 58% of
the total. The calorific value is ve ry low: 1400 kcal r kg in Ptole m ais ] Amynte o , only
900 kcal r kg in Me galopolis. The ash content is always high , in contrast to the
sulfur conte nt which is always low. O pe ncast mining take s place in the basins of
Ptole m ais , Amynteo , and Me galopolis. The annual production e xce e ds 60 Mt, of
which 98% is use d for e le ctricity ge ne ration. The total installe d c ap acity of the
powe r plants is 4 ,833 MW . A num ber of public ations have re ferre d to the ge ology ,
pe trology , mine ralogy , and ge oche m istry of Gree k pe ats and lignite s , such as those
of Cam e ron e t al. (1984 ) , Christanis (1983 , 1987 , 1994 ) , Kaouras (1989 ) , Goodarzi
e t al. (1990 ) , Ge ntzis e t al. (1990 , 1996 , 1997 ) , B roussoulis e t al. (1991 ) , Kalkreuth
e t al. (1991 ) , Fowle r e t al. (1991 ) , Kaouras e t al. (1991 ) , Antoniadis (1992 ) ,
Antoniadis e t al. (1992 ) , B otis e t al. (1993 ) , V alce va & Ge orgakopoulos (1993 ) ,
V alce va e t al. (1995 ) , Filippidis e t al. (1996 ) , Sakorafa & Michailidis (1997 ) , and
Antoniadis & Rie ber (1997 ). The pre se nt article inte grate s conve ntional analyse s
of lignite s from the Dram a de posit with a pure ge oche mical analysis } Rock-E val
pyrolysis } and me thods of me asureme nt of the quantity of the naturally occuring
prim ordial radionuclide s which will be re le ase d , to some e xte nt, to the e nvironme nt
afte r the lignite combustion.
Geological Setting
The 700-km 2 intram ontane basin of Dram a is a tectonic grabe n forme d since the
Mioce ne by post-alpidic tectoge ne sis (Figure 1 ). Te ctonic move m e nts during the
E arly-Middle Ple istoce ne se parate d the Dram a basin from the Se rre s grabe n in
the we st. Pre-Ne oge ne me tamorphic and igne ous rocks of the Rhodope m assif ,
such as gne isse s , schists , m arble s , and granite s , constitute the m argins of the
Dram a basin (Me lidonis , 1969 , 1981 ). The Ne oge ne -Q uate rnary form ations of the
basin consist of clay , mud , sand , conglome rate , m arl , pe at , and lignite . The lignite
de posit e xte nds all ove r the ce ntral plain are a of the Dram a basin. In the Lowe r
Ple istoce ne , a lacustrine e nvironm e nt gradually de ve lope d in a large part of the
basin. Lacustrine , c alcare ous gyttja was de posite d , constituting the floor of the
lignite de posit and occurring in m any othe r m arginal parts of the basin. As the lake
gradually shallowe d , e xte nde d pe at-forming mire s , cove red by he rbace ous ve ge tation , forme d. It was on the se pe at-form ing m ire s that the ge ne sis of Dram a lignite s
starte d 1 m illion ye ars ago (V an De r W ie l & W ijmstra, 1987 ). O ve r most of the
basin , clastic m ate rial from alluvial fans de posite d at diffe rent time s. The e xte nsions of the fans in the are a of the Dram a lignite de posit se parate the limno-te lm atic
de posits into thre e distinct lignite se am s (A , B , and C ; se e Figure 2 ). The form ation
of the Dram a lignite in a limno-te lm atic e nvironme nt is confirme d by pe trographic
and palynological inve stigations (Kaouras e t al., 1991 ). M aximum growth of all
three lignite se am s is found in the are a of Agia P araske vi (Figure 1 ). Se am C is not
de ve lope d in the north of the village of Ne rofraktis; se am B is not de ve lope d as far
north as the village of Koudounia , and se am A se e ms to e xte nd furthe r to the
north. The minable lignite rese rve s are e stim ate d to e xce e d 1 ,430 Mt, with more
than 1 ,060 Mt be longing to se am A , which is the thicke r and more e xte nsive one .
The Dram a lignite de posit has not bee n e xploite d ye t.
499
Figure 1. Simplifie d ge ological m ap of Dram a basin (after Me lidonis, 1969 ).
500
A . G eorgakopoulos
Figure 2. Ge ne ralize d profile s of the Dram a lignite de posit (after Filippidis et al., 1996 ).
Samples and Analytical Methods
Twe nty-five lignite sam ple s repre se nting a continuous se que nce of the Dram a
de posit we re obtaine d from the DR 84 r 86 core . The coring site is loc ate d about
1.2 km in the north of Agia P araske vi village (Figure 1 ). Drilling and sampling was
c arrie d out by the Institute of Ge ology and Mine ral E xploration (IGME ) , Athe ns.
The Dram a L ignite Deposit, N orthern G reece
501
E ach sam ple repre sents a se am inte rval 0.2 to 1.6 m thick. Figure 2 shows the
stratigraphic and are al e xte nt of the sam ple d lignite s. The sample s we re air-drie d
afte r being crushe d in coarse fragm e nts. The n the sam ple s we re crushe d to pass a
1-mm sie ve . The num ber and thickne ss of e ach sam ple is give n in Table 1.
Proxim ate and ultim ate an alyse s we re pe rforme d according to ISO standards. The
moisture , the ash content (on a dry basis ) , the volatile m atte r (on a dry and dry,
mine ral m atte r-fre e basis ) , the c arbon content (on a dry basis ) , and the total sulfur
and organic sulfur content we re de term ine d. The calorific value was de te rmine d by
the rmogravime tric an alysis using an isothe rm al bomb calorime te r. Polishe d se ctions of the sam ple s we re pre pare d for m icroscopic obse rvation. The lignite
sam ple s we re mounte d in e poxy re sin and the n ground and polishe d according to
the standard me thod (Stach e t al., 1982 ). The re fle ctance was de termine d in
imme rsion oil at a monochrom atic light ( l s 546 nm ). Re fle ctance me asureme nts
we re take n on e u-ulminite A (dark ). Fluore sce nce spe ctra an alysis has not bee n
c arrie d out.
Organic Geochemistry: The Rock-Ev al Pyrolysis Method
The Rock-E val pyrolysis me thod uses a spe cial de vice in which coals or rocks with
organic substance are subje cte d to sustaine d pyrolysis unde r an ine rt atmosphe re ,
which allows faste r study of the organic m atte r and its stage of e volution. The m ain
part of the instrume nt is a sm all ove n in which a pulve rize d rock sam ple (about 100
mg ) is he ate d in a he lium atm osphe re (E spitalie e t al., 1977 ). In the c ase of coals ,
the recom me nde d sam ple size of 100 mg m ay ove rload the flame ioniz ation
de te ctor (FID ) (Pe ters , 1986 ). In pre vious studie s 5-mg aliquots we re used (Fowle r
e t al. , 1991; Syke s e t al. , 1994 ). In the prese nt study, be twe e n 10 and 16 mg of
lignite we re use d. This am ount of sam ple provide s good re sults for both TO C and
S 2 value s. Afte r a fe w minute s’ purge for trace s of air , the de vice he ats the sam ple
progre ssive ly from 180 8 C up to 600 8 C at a constant rate of 15 8 C r min. During the
assay , the hydroc arbons , which are fre e in the sample at the tim e of sam pling , are
first volatilize d at a m ode rate tempe rature. The quantity of the se hydroc arbons is
re corde d as a function of time by me ans of a flame ionization de tector (FID ) ,
giving a first pe ak (S 1 ). The se cond pe ak (S 2 ) is repre se ntative of the hydrocarbons
and hydrocarbon-like compounds ge ne rate d by the rm al cracking and othe r re actions of the organic m atte r (lignite in our case ). The organic m atte r pyrolysis also
ge ne rate d oxyge n-containing volatile s , i.e ., carbon dioxide (CO 2 ) and wate r. The
me asure me nt of CO 2 (S 3 pe ak ) is limite d to the range 180 ] 390 8 C , in orde r to
include the m ain stage of CO 2 ge ne ration from organic m atte r and to avoid othe r
source s of CO 2 (de composition of carbonate s , bic arbonate s , e tc. ). From S 1 and S 2
the microproce ssor de termine s the total production inde x (TPI ) , which is the ratio
S 1 r (S 1 q S 2 ). S 1 , S 2 , S 3 are c alculate d in milligram s of products (hydrocarbons ,
CO 2 ) pe r gram of sam ple . A fourth param e ter is the tem pe rature , Tm ax (in de gre e s
Ce lsius ) at which the m aximum rate of ge ne ration of hydrocarbons occurs (top of
the S 2 pe ak ). This param e ter is use d mostly for e valuation of the m aturation stage .
For the purposes of this study, the O il Show Analyze r (O .S.A.) ve rsion of Rock-E val
an alyze rs was used. In the O il Show Analyze r the de term ination of the total
organic carbon (TO C ) is not optional , as in the case of the RO CK-E V AL II
apparatus , and is re alize d in place of the an alysis of the CO 2 coming from the
organic m atte r cracking (S 3 pe ak ). From the above-me ntione d param e te rs the
hydroge n inde x (HI ) and the oxyge n inde x (O I ) are calculate d by me ans of S 2 , S 3 ,
502
D.1
D.2
D.3
D.4
D.5
D.6
D.7
D.8
D.9
D.10
D.11
D.12
D.13
D.14
D.15
D.16
D.17
D.18
D.19
D.20
D.21
D.22
D.23
D.24
D.25
Sample
Table 1
C
C
C
C
C
C
B
B
B
B
B
B
A
A
A
A
A
A
A
A
A
A
A
A
A
Lignite
se am
45.00
62.20
63.50
64.70
68.60
75.00
102.70
106.60
109.40
113.05
113.55
117.10
134.90
144.50
148.00
150.80
156.70
159.50
163.00
166.60
174.20
183.00
186.30
187.60
200.40
De pth
bene ath
surface
(m )
0.90
0.80
0.80
0.60
0.90
0.70
0.50
0.80
0.70
0.50
1.05
1.00
0.80
0.50
0.50
0.70
0.30
0.50
1.00
0.50
0.30
0.30
0.30
0.50
0.50
Ply
thickne ss
(m )
59.0
66.0
68.0
65.0
63.8
66.0
59.0
65.0
62.0
69.0
68.5
68.0
64.0
61.8
63.3
57.7
66.0
55.0
61.0
62.9
60.0
54.9
55.0
54.6
62.0
Moisture
(% a.r.)
44.0
31.3
27.6
27.0
45.8
26.2
43.6
33.8
47.9
31.2
26.1
23.4
42.9
27.2
28.9
41.9
41.0
45.1
42.9
40.5
42.1
45.3
48.4
46.1
37.2
Ash
(% d.b.)
40.0
42.0
44.9
47.2
36.2
45.1
38.0
41.8
35.8
44.6
47.0
45.7
38.2
43.6
42.0
37.3
21.5
36.2
36.4
24.0
37.8
34.3
31.1
31.4
41.1
V olatile
m atte r
(% d.b.)
2660
3587
3645
3600
2731
3756
2980
3476
2879
3765
3935
4120
2813
3757
3549
2927
2200
2712
3154
2070
3009
2445
2278
2615
3549
Net
calorific
value
(d.b.)
69.1
64.3
65.8
65.3
67.4
61.4
68.2
63.2
69.6
64.3
63.8
62.1
67.3
66.0
64.7
66.9
50.2
65.4
68.9
58.1
68.7
68.0
69.6
67.8
64.9
V olatile
matte r
(% dmmf )
4790
5143
5298
5100
5231
5123
5306
5550
5467
5378
5460
5541
5012
5602
5678
5248
4934
5400
5786
5142
5598
5345
5432
4986
5619
Ne t
calorific
value
(dmmf )
31.00
37.50
35.60
35.50
33.90
40.20
33.30
36.80
30.10
36.30
35.80
39.20
32.50
35.70
35.10
31.80
47.20
34.60
32.60
44.90
34.10
33.30
30.80
32.00
35.70
Fixed
carbon
(% dmmf)
4.00
2.00
2.70
2.50
1.30
1.90
2.30
2.70
2.90
3.60
3.30
3.00
4.00
3.40
1.90
3.80
2.20
2.90
5.00
1.90
4.20
3.40
3.90
3.00
4.20
Total
sulfur
(% d.b.)
Proxim ate and ultim ate analyse s and calorific value s (kc al r kg ) for the Dram a lignite s (% dmmf is pe rce nt on a dry,
m ine ral m atte r-fre e basis; % d.b. is dry basis at standard conditions; % a.r. is as-re ce ive d basis )
1.7
0.4
0.5
0.4
0.1
0.4
0.4
0.7
1.1
0.7
0.5
0.2
0.6
0.9
0.4
1.9
0.3
0.9
1.1
0.3
1.2
1.2
0.6
0.4
1.2
V olatile
sulfur
(% )
The Dram a L ignite Deposit, N orthern G reece
503
and TO C content. The y are respe ctive ly e xpresse d in m illigram s of HC pe r gram of
TO C and in m illigram s of CO 2 pe r gram of TO C. The oxyge n inde x and the S 3
pe ak are not include d in the O il Show Analyze r me asureme nts. The Rock-E val
pyrolysis an alyse s we re pe rforme d at the Laboratory of O rganic Ge oche m istry,
Institut FrancË ais du Pe trole , Rue il-M alm aison , France .
Radioactiv ity
Two lignite sam ple s (D2 and D5 ) we re se le cte d to me asure the quantitie s of the
naturally occurring radionuclide s. The sam ple s we re homoge nize d , package d to
pre clude radon e m an ation , and the n counte d for natural gam m a radiation on a
low-background , high-purity Ge de te ctor , linke d to an appropriate data acquisition
syste m (Manolopoulou , 1990; Manolopoulou & Pap aste fanou , 1992 ). The refore ,
23 8
235
22 6
210
228
22 8
40
the conce ntrations of
U,
U,
Ra,
Pb ,
Ra,
Th , and K (in B q r kg )
we re de termine d. The radioactivity me asure me nts we re pe rforme d at the Nucle ar
Physics De partme nt , Aristotle Unive rsity of The ssaloniki.
Results and Discussion
Chemical Analyses
Re sults from traditional proxim ate and ultim ate an alysis and calorific value s of the
Dram a lignite s are re porte d in Table 1. The studie d lignite s are characte rize d by
low value s of fixe d carbon (30.10 ] 47.20% ) and high ash conte nts (23.4 ] 48.4% , on a
dry basis ). The as-re ceive d moisture varie s within the range 54.6 ] 69% . After
combustion in the boile r , re sidual m ine ral m atte r must be disposed off in the form
of ash (Unsworth e t al., 1991 ). Such disposal always has an e conom ic pe nalty, which
will be se ve re for the Dram a de posit, as the ash conte nt of all Dram a sample s is
quite high. The volatile m atte r , on a dry basis , range s from 21.5% to 47.2% , while
on a dry, mine ral m atte r-fre e basis , it varie s be twe e n 50.2% and 69.6% . Such
volatile m atte r contents are conside re d high , but are within the range of low-rank
coals such as lignite s. The total sulfur conte nt varie s for se am C from 1.3% to
4.0% , whe re as the value s for the volatile sulfur are from 0.1% to 1.7% . For se am
B , the total sulfur content varie s from 2.3% to 3.6% , with value s of volatile sulfur
from 0.4% to 1.1% . Finally, for se am A , total sulfur value s vary from 1.9% to 5.0% ,
whe re as volatile sulfur value s vary from 0.3% to 1.9% . Ge ne rally, the volatile
sulfur am ounts in ave rage approxim ate ly 20% of total sulfur (the diffe rence from
the total sulfur re m ains in ash ). In the pre sent study the ``ne t’’ c alorific value of the
sam ple s is give n. It diffe rs m ost signific antly from the ``gross’’ value due to the fact
that the lignite sample s have a high moisture content. The ``ne t’ ’ calorific value is
quote d to a dry and to a dry, m ine ral m atte r-fre e basis , afte r re calculation. The
ave rage ne t calorific value on a dry basis for se am C is 3 ,330 kcal r kg , for se am B is
3 ,526 kcal r kg and for se am A is 2 ,852 kcal r kg. O n a dry, mine ral m atte r-fre e basis
the value s are 5 ,114 , 5 ,450 , and 5 ,367 kcal r kg , respe ctive ly.
Rock-Ev al Pyrolysis
The re sults of Rock-E val pyrolysis are pre se nte d in Table 2. Rock-E val pyrolysis
has be e n applie d to coal sample s (Te ichm ulle
È r & Durand , 1983; Durand & Paratte ,
1983; Be rtrand , 1984; V e rhaye n e t al., 1984; Ge orgakopoulos , 1984; Pe te rs , 1986 ;
504
D.1
D.2
D.3
D.4
D.5
D.6
D.7
D.8
D.9
D.10
D.11
D.12
D.13
D.14
D.15
D.16
D.17
D.18
D.19
D.20
D.21
D.22
D.23
D.24
D.25
Sample
C
C
C
C
C
C
B
B
B
B
B
B
A
A
A
A
A
A
A
A
A
A
A
A
A
Lignite
se am
45.00
62.20
63.50
64.70
68.60
75.00
102.70
106.60
109.40
113.05
113.55
117.10
134.90
144.50
148.00
150.80
156.70
159.50
163.00
166.60
174.20
183.00
186.30
187.60
200.40
De pth
(m )
14.8
12.2
13.5
14.1
12.0
12.6
13.1
9.4
12.9
15.9
12.2
13.4
12.3
10.2
12.1
16.9
11.2
10.3
15.3
12.5
12.0
10.2
12.0
10.2
10.8
Sample
we ight
(mg )
Table 2
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
R ate
(8 C r min )
0.20
0.40
0.51
0.14
0.66
0.31
0.30
0.10
0.46
0.37
0.57
0.07
0.32
0.29
0.49
0.76
0.53
0.09
0.19
0.40
0.16
0.09
0.00
0.00
0.27
S1
(mg r g of
sample )
19.05
82.86
77.85
39.14
31.50
40.07
71.29
36.59
65.19
55.72
65.90
40.07
46.74
68.52
51.57
62.54
21.51
41.94
62.41
27.92
46.00
53.33
24.58
22.25
36.11
S2
(mg r g of
sample )
420
427
420
442
442
446
422
437
436
429
419
427
431
416
436
430
440
441
441
443
446
434
438
439
428
(8 C )
Tm ax
Rock-E val data for Dram a lignite sample s
113
186
172
150
136
107
164
74
193
151
154
97
127
158
154
189
149
210
193
111
143
146
112
82
115
H.I.
16.79
44.61
45.19
26.08
23.22
37.43
43.50
49.56
33.71
36.93
42.77
41.25
36.86
43.42
33.46
33.12
14.40
20.01
32.32
25.11
32.18
36.55
21.89
27.26
31.51
TO C
(% )
1.19
0.90
1.13
0.54
2.84
0.83
0.69
0.20
1.36
1.00
1.33
0.17
0.87
0.67
1.46
2.29
3.68
0.45
0.59
1.59
0.50
0.25
0.00
0.00
0.86
S1 r TO C
15.19
37.70
38.69
22.82
20.55
34.08
37.56
46.51
28.26
32.27
37.25
37.92
32.95
37.71
29.14
27.87
12.57
16.52
27.12
22.76
28.35
32.12
19.85
25.41
28.49
RC
(% )
0.90
0.85
0.86
0.87
0.89
0.91
0.86
0.94
0.84
0.87
0.87
0.92
0.89
0.87
0.87
0.84
0.87
0.83
0.84
0.91
0.88
0.88
0.91
0.93
0.90
RC r TO C
The Dram a L ignite Deposit, N orthern G reece
505
Kalkreuth & Macaule y, 1987; B oudou e t al. , 1990; Fowle r e t al. , 1991 ; M arquis e t
al. , 1992; Suggate & B oudou , 1993; Syke s e t al. , 1994; B ostick & D aws , 1994 ;
Ne wm an e t al., 1997 ) , and it was e vide nt that a ve ry cautious interpretation of the
re sults should be m ade . Typically, the application of pyrolysis e xpe rim e nts on
diffe re nt coal sam ple s has be e n unde rtake n to confirm the ide a that coals m ay
provide a source of oil and gas accum ulations. The most volatile compounds (gue st
bitume n ) appe ar in the first P 1 pe ak. The are a S 1 of this pe ak is ve ry low for all
Dram a sam ple s. Sim ilar low value s have alre ady be e n reporte d for a large coal
se rie s (Te ichmulle
È r & Durand , 1983 ). As Te ichmulle
È r and Durand (1983 ) , B ostick
and Daws (1994 ) , and othe rs have also noted , S 1 is sm all in coals and doe s not
incre ase with incre asing rank. Furthe rmore , pe ats and lignite s have much highe r S 1
value s than bituminous coals (Sugg ate & B oudou , 1993 ). The hydrocarbon-like
products and re late d volatile bitume ns , forme d by the rm al cle avage from the
organic m atte r , appe ar in the se cond pe ak P 2 . For the uppe r se am C , the value s of
S 2 (in mg HC r g ) vary from 19.05 to 82.86 . For se am B , the value s of S 2 vary from
36.59 to 71.29 , whe re as for the lowe r se am A , the value s vary be twe e n 21.51 and
68.52 . The se S 2 value s indic ate that only m inor hydrocarbon e xpulsion occurs from
the Dram a lignite s. The Tmax value s for all sam ple s vary be twe e n 416 and 446 8 C.
Some sam ple s show high T max value s , although all sam ple s are obtaine d from only
a 160-m-de e p we ll and are of the sam e low rank. In ge ne ral , for te rre strial organic
m atte r in the e arly stage s of e volution the Tmax value s vary be twe e n 395 and 420 8 C.
It m ust also be notice d that the diffe rence s in the mine ral m atte r content of the
sam ple s do not influe nce the T max value s. For the sam ple s showing high Tm ax
value , the latte r doe s not corre late with both coal type and rank. A ccording to
Ne wm an e t al. (1997 ) , any re lationship be twe e n coal type and Tmax is e rratic at the
lowe st coal rank (high-volatile bituminous B ) the y have inve stigate d. The re fore , it
c an be conclude d that the relationship betwe e n Tmax and coal type is also e rratic
for lignite s. In all sam ple s the refle ctivity value s are lowe r than 0.2% (Table 3 ).
B e twe e n 0.5% R m (Tm ax f 425 8 C ) and 1.5% R m (Tm ax f 475 8 C ) , the corre lation
be twe e n R m and Tm ax is fairly line ar. In value s - 0.5% R m and ) 1.5% R m , Tm ax
incre ase s more quickly than R m (Te ichmulle
È r & Durand , 1983 ). Som e scatte ring is
also notice able : this is not only due to ince rtitude s of me asurem e nts , but also due
to diffe re nt significance s of R m and Tm ax : R m is me asured on huminite (e u-ulminite
A ) , while T max is me asured on whole coal (huminite q liptinite q ine rtinite ). In a
pre vious work , Kaouras e t al. (1991 ) pre se nte d a pe trographic and palynological
study, conducte d on a set of sam ple s from one borehole of the Dram a lignite
de posit. The authors e stablishe d that the m ace rals of the huminite group in 9
sam ple s vary from 61.49 % to 81.72% , those of the liptinite group from 8.42% to
31.76 % , and those of the ine rtinite group from 6.01% to 24.72 % . The se value s
point out that T max cannot corre late pe rfe ctly with R m . In othe r words , Tm ax is
influe nce d by the pe trographic composition , beside s the rank , the latte r de te rmine d on the basis of huminite refle ctance . The hydroge n inde x value s vary from
107 to 186 for se am C , from 74 to 193 for se am B , and from 82 to 210 for se am A.
It is notice d that the diffe rence s in hydroge n conte nts are not re late d to the Tm ax
value s as would be e xpe cte d. Apart from that , the value s of Tmax and those of the
de pth are not relate d to e ach othe r. The O il Show Analyze r de vice de te rmine s
total organic carbon (TO C ) in we ight pe rce nt of sam ple , by summing up the
pyrolyze d organic carbon (de duced from the total am ount of hydrocarbons S 1 q S 2 )
with the re sidual organic carbon (RC ) obtaine d afte r oxidation. In Figure 3 , the
506
A . G eorgakopoulos
Table 3
Me an random re fle ctance s (% R m , oil ) me asured on e u-ulminite s A
of the Dram a lignite sam ple s
R andom re fle ctance
in oil (% )
E u-ulm inite A
Se am
De pth (m )
D.1
D.2
D.3
D.4
D.5
D.6
C
C
C
C
C
C
45.00
62.20
63.50
64.70
68.60
75.00
0.20
0.12
0.13
0.13
0.17
0.19
"
"
"
"
"
"
0 ,02
0 ,03
0 ,05
0 ,03
0 ,05
0 ,03
D.7
D.8
D.9
D.10
D.11
D.12
B
B
B
B
B
B
102.70
106.60
109.40
113.05
113.55
117.10
0.20
0.15
0.17
0.11
0.13
0.14
"
"
"
"
"
"
0 ,03
0 ,02
0 ,03
0 ,02
0 ,03
0 ,03
D.13
D.14
D.15
D.16
D.17
D.18
D.19
D.20
D.21
D.22
D.23
D.24
D.25
A
A
A
A
A
A
A
A
A
A
A
A
A
134.90
144.50
148.00
150.80
156.70
159.50
163.00
166.60
174.20
183.00
186.30
187.60
200.40
0.14
0.12
0.17
0.13
0.17
0.17
0.12
0.14
0.14
0.14
0.17
0.17
0.18
"
"
"
"
"
"
"
"
"
"
"
"
"
0 ,03
0 ,01
0 ,02
0 ,02
0 ,02
0 ,02
0 ,01
0 ,02
0 ,02
0 ,03
0 ,03
0 ,02
0 ,03
Sam ple
Rock-E val TO C value s are relate d to fixe d carbon as de term ine d by proxim ate
an alysis for the Dram a lignite sam ple s. For a part of the sam ple s the value s are
almost the sam e , but for the re st the re is a signific ant diffe rence . It is difficult to
provide a satisfactory e xplan ation about this phe nome non. The total organic
c arbon can be divide d into two fractions: the first, conne cte d to the hydrocarbons
that are re le ase d during the cracking of the coal , is found in the pyrolyz ate . The
se cond fraction is the re sidual c arbon (RC ) or ``de ad carbon ,’’ which constitute s the
ine rt carbon that re acts only in oxidation. The se two carbon forms we re studie d by
Gransch and E ism a (1970 ) , who originally proposed the ``carbon ratio’ ’ (C R r C T ).
The re sidual carbon C R (or RC ) is re late d to the abundance of polyarom atic
nucle i. The volatile fraction C T minus C R (C T be ing the total organic carbon ) is
re late d to the abundance of aliphatic chains and oxyge n-containing functional
groups which are lost during pyrolysis. For the same type of organic m atte r the
ratio C R r C T incre ase s with the de gre e of m aturation , re aching approxim ate ly the
507
Figure 3. Relationship betwee n Rock-Eval TO C value s with fixed carbon content as dete rmined by proxim ate analysis for the Dram a lignite .
508
A . G eorgakopoulos
value 1 in the case of graphite . In addition , high C R r C T value s m ay be obtaine d
from type III organic m atte r or coals , e ve n at low stage s of m aturation. In the
Dram a sam ple s , the value s of the carbon ratio vary from 0.83 to 0.94. Inde pe nde nt
of the me thodology that is used , the diffe re nce be twe e n TO C and C R corre sponds
to the c arbon that is libe rate d during pyrolysis , terme d C p . The re fore , the re lation:
C T y C R s C P is form e d. During pyrolysis this C P is libe rate d in the form of
hydrocarbons , CO , and CO 2 . The quantitie s of CO are ve ry low and can be ignored
(Souron e t al., 1975 ). The quantity of carbon that is relate d to the CO 2 libe rate d
during pyrolysis is , of course , large r than the quantity of carbon that is re late d to
the CO , but still rem ains at ve ry low le ve ls. In the case of re ce nt se dime nts
originating from highe r plants , the quantity of carbon re late d to the CO 2 constitute s just 8% of the total organic c arbon. In the case of lignite s (as in the Dram a
c ase ) , this pe rce ntage falls to 4% , whe re as for type III rock sam ple s in the
be ginning of the m ature stage it is 2% (Souron e t al. , 1975 ). From the above it is
cle ar that the gre ate st part of the volatile organic c arbon (C P ) is re late d to the
hydrocarbons libe rate d during pyrolysis cracking and is repre se nte d by the S 2 pe ak ,
le ading to an e xce lle nt corre lation betwe e n S 2 are a and TO C y RC diffe rence .
Natural Radionuclides
238
23 5
22 6
21 0
228
228
T able 4 pre sents the conce ntrations of
U,
U,
Ra,
Pb ,
R a , Th , and
40
K (in Bq r kg ) , de te rmine d in sam ple s D2 and D5 , both obtaine d from se am C.
Conce ntrations of U and Th are also calculate d in ppm , while the conce ntration of
K is calculate d in we ight pe rce nt. The re sults show a similar distribution of the
naturally ocurring radionuclide s be twe e n the two sample s. It se e m s that radioactive
238
22 6
22 6
210
e quilibrium e xists betwe e n
U and
R a and also be twe e n
R a and
Pb. This
fact me ans that the rate of form ation of the radioactive daughter product is e qual
to the rate of de cay. According to Cole s e t al. (1978 ) , secular e quilibrium doe s e xist
23 8
235
226
Table 4
21 0
228
228
40
Conce ntrations of
U , U , R a,
Pb , R a , Th , and K for sam ple s
D2 and D5 obtaine d from the uppe r se am C of the Dram a lignite de posit
D2
B q r kg
238
U
U
226
Ra
210
Pb
228
Ra
228
Th
40
K
U (ppm )
Th (ppm )
K (% )
235
121.0
6.5
125.3
160.0
16.9
14.5
106.0
9.80
3.90
0.34
" 1 s : standard deviation.
D5
" 1s
14.0
2.1
2.6
15.0
1.2
1.3
6.8
12.0%
5.5%
6.4%
Bq r kg
95.0
4.8
108.4
118.0
20.7
19.7
103.0
7.70
5.00
0.33
" 1s
12.0
0.9
1.3
12.0
0.7
0.8
3.4
12.0%
2.6%
3.3%
The Dram a L ignite Deposit, N orthern G reece
509
be twe e n all the nuclide s of the uranium serie s chain in the coals. This radioactive
238
226
238
e quilibrium doe s not e xist be twe e n
U and
R a in the Ptole m ais lignite s ( U :
226
22 6
210
22 6
210
R a s 1.7 " 0.4 ) , whe re as it doe s e xist be twe e n
R a and
Pb ( R a:
Pb s
1.0 " 0.2 ) (M anolopoulou , 1990; Manolopoulou & Pap aste fanou , 1992 ). The me an
238
235
isotopic ratio
U:
U for the two sam ple s inve stigate d is 19.4 " 3.7 (B q ) and is
in fairly good agre e me nt with the natural one , 21.44 " 0.02 (Bq ). In ge ne ral , the
conce ntrations of natural radionuclide s in type s of coal are le ss than those in the
23 8
e arth’s crust. The ave rage activity conce ntrations in coal are 20 Bq r kg of
U , 20
23 2
40
238
23 2
B q r kg of
Th , and 50 B q r kg of K, and all the de cay products of
U and
Th
are in radioactive e quilibrium with the ir pre cursors (UNSCE AR , 1982 ). Lignite
radioactivity has be e n ve ry scarce ly cove re d by the international bibliography.
The re fore a com parison is unde rtake n betwe e n the re sults of the prese nt study and
those re porte d by seve ral authors conce rning highe r-rank coals. A ve ry compre he nsive study by Ge ntzis and Goodarzi (1997 ) reports on the concentration of radionuclide s in subbituminous coals use d e xclusive ly for powe r ge ne ration in Albe rta ,
C an ada. The authors compare the radioactivity me asure d in coals from the
Highvale Mine and the W hite wood Mine with the sam e conce ntrations in othe r
C an adian fee d coals (E vans e t al., 1985 ) , in Australian coals , and in coals from the
Unite d State s and the Unite d Kingdom (Sm ith , 1987 ). The y have found that the
23 2
activity of
Th range s from 10 to 40 B q r kg , whe re as the range in Australian coals
is from 11 to 69 , in the U.K. coals from 7 to 19 , and in the U.S. coals from 4 to 21
22 6
B q r kg. For
R a the activity range s from 10 to 40 B q r kg , whe re as the range in
Australian coals is from 19 to 24 , in the U .K. coals from 8 to 22 , and in the U .S.
21 0
coals from 9 to 59 B q r kg. For
Pb the authors have found an activity range from
10 to 40 Bq r kg , ve ry sim ilar to those of Australian coals (16 ] 28 ) and lowe r than
those of U.S. coals (4 ] 52 ). From all the above value s it is cle ar that , in the case of
Dram a, the radium-226 and uranium-238 conce ntrations are within the highe r
range for world coals. Uranium and its daughter nuclide s are associate d with the
organic m ate rial of lignite s (coal m atrix ) , while thorium and its daughte r nuclide s
as we ll as potassium are associate d with inorganic m ate rials (ash m atrix). The
22 6
228
diffe re nt be havior be twe e n the two isotope s of radium ,
R a and
R a in the
22 6
studie d lignite s , is probably due to the fact that
R a has highe r m obility in
228
23 2
the coal m atrix than
R a , which is associate d (as its pare nt
Th ) with alum inosil23 8
icate s. R adium-226 (and its pre cursor
U ) has bimodal be havior e ithe r in the
volatile form of uraninite or in the silicate form of coffinite wU (SiO 4 )1 y X (O H )4 X x
(Cole s e t al., 1978; Manolopoulou & Pap aste fanou , 1992 ). O bviously, the sm all
numbe r (2 ) of lignite sam ple s which we re inve stigate d for the conce ntrations of
naturally occurring radionuclide s doe s not pe rmit significant conclusions to be
m ade , but similar conce ntrations are also re fe rre d for the Ptole m ais lignite s , in
which U has pre dominantly an organic mode of occurre nce (Manolopoulou , 1990 ).
Conclusion
The prese nt study was carrie d out to de termine the quality param e te rs which
re fle ct the rm al value and any de le terious te nde ncie s it m ay have for proce ss
e fficie ncy and r or the e nvironm e nt. Traditional an alyse s such as proxim ate , ultim ate , and c alorific value do not show substantial variability am ong the thre e lignite
se am s of the Dram a de posit. The moisture , the volatile m atte r , and the ash
contents are always high , while the sulfur conte nt of Dram a lignite s always re m ains
510
A . G eorgakopoulos
at low le ve ls. A spe cific te chnique involving a pyrolysis proce ss (Rock-E val pyrolysis ) has be e n used toge the r with conve ntional me thods. Rock-E val analysis was not
de signe d for coal characte rization , and has not be e n e valuate d rigorously for
re producibility in this regard. This me thod has be e n applie d only a ve ry few time s
in lignite studie s , the re fore , the se results m ay be ve ry inte resting.
The Tmax of re le ase of gase ous spe cie s unde r ine rt atmosphe re (hydrocarbons ,
H 2 ) or unde r oxidizing atmosphe re (H 2 O , CO 2 , SO 2 , . . . ) allow a wide ning of the
rank dom ain to be asse sse d , com pare d to the Tmax of the Rock-E val pyrolysis ,
which conce rns only the dom ain of 0.5 to 1.5% R m .
The S 1 as we ll as S 2 value s de te rm ine d from the Rock-E val pyrolysis for the set
of Dram a sam ple s de monstrate that:
1. S 1 and S 2 corre late with coal type and rank , while Tm ax doe s not.
2. Rock-E val S 2 indicate s only minor hydrocarbon e xpulsion from Dram a
lignite s.
3. Comparison of the Rock-E val an alysis data (TO C ) with those of the
proxim ate analysis (fixe d carbon ) re ve als that som e time s the Rock-E val
te chnique unde restim ate s and som e time s it ove restim ate s the carbon
content.
Inte rpretation of the results of the Rock-E val an alysis is important for the
e valuation of the pe trole um-source potential of coals , but is of no value for lignite s
since the y have no pe trole um-source pote ntial. Howe ve r , this an alytical me thod ,
although unconve ntional for lignite s , com bine d with some othe r , also unconve ntional an alytical me thods , is valuable in relation to coal utiliz ation (in hydrolique faction , gasification , combustion , e tc. ).
The concentrations of the naturally occurring radionuclide s , which to some
e xte nt will be re le ase d to the e nvironme nt afte r the combustion of the lignite , are
am ong the highe r for lignite s worldwide . A s Cole s e t al. (1978 ) have re porte d , a
238
part of
U which is associate d with silicate s or which is mine ralize d as coffinite in
23 8
the lignite (coal m atrix ) re m ains with the bottom ash , whe re as the
U part
associate d with the uraninite (UO 2 ) in the coal m atrix forms volatile compounds ,
such as UO 3 . R a-226 also form s volatile com pounds such as R a (O H ) 2 and late r
conde nse s out on the fine r fly ash particle s (fly ash m atrix ).
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