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Effect of lignite addition and steam on the pyrolysis of Turkish oil shales
Effect of lignite addition and steam pyrolysis of Turkish oil shales Ersan Putun”, Ekrem Ekinci, Murat Citiroglu, Christopher J. Lafferty? and Colin E. Snapet
Gordon
fnstanbul Technical University, Dept of Chemical Engineering, Turkey “Anadolu University, Dept of Chemical Engineering, Eskisehir, tuniversity of Strathclyde, Dept of Pure & Applied Chemistry, (Received 23 January 7992; revised 7 July 1992)
on the
D. Lovet,
Maslak,
80626
Turkey Glasgow
Gl
Istanbul,
IXL,
UK
Steam was found to be a more effective sweep gas than nitrogen at low velocities in fixed-bed pyrolysis of Goynuk oil shale but, at higher velocities and in fluidized-bed pyrolysis, the differences were considerably less marked. Relatively small but significant synergistic effects were observed between lignites and the two oil shales investigated - Goynuk and Seyitomer - under static retorting conditions. These effects were more pronounced with large concentrations of oil shales but disappeared in fluidized-bed pyrolysis, where conversions are considerably higher because mass transfer limitations largely disappear. (Keywords:
lignite; oil shale; pyrolysis)
has vast reserves of both oil shales and high-sulphur lignites, much of the former having particularly low mineral matter contents. The objective of research has been to identify ways in which significantly higher oil yields and oils of better quality can be obtained than under the normal static conditions used in retorting tests such as the Gray-King and Fischer assays. It is well established that, although fairly high oil yields (in the range lo-40 wt% daf) can be achieved from lignites and oil shales under static retorting conditions, as in those assays, the oil yields are mass transfer-limited. Indeed, the authors have reported elsewhere’ .’ that the use of well-swept fixed-bed reactors and hydrogen under pressure gives oil yields of > 70 wt% daf for two shales ~ Goynuk and Seyitomer - which can be classified as immature type I/II kerogens3. Two other possibilities are to consider (1) the use of steam to overcome mass transfer limitations and avoid retrogressive char-forming reactions more effectively than inert gases such as nitrogen, and (2) co-pyrolysis of lignites with oil shales. Minkova ef a1.4 and Rubel and Coburn’ have found that the use of steam, like nitrogen, as a sweep gas gives rise to marked increases in oil yield for coals and oil shales respectively. However, it is uncertain whether steam has a distinct chemical role during pyrolysis other than passivating clay minerals from catalysing retrogressive char-forming reactions, for example the coupling of phenols to form furans”. Indeed, in fluidized beds, the differences in conversion between nitrogen and steam for oil shales are generally small’ and may partly arise from the fact that steam is more effective for collecting light oils. The co-processing of coals and heavy oils in direct liquefaction has already received considerable attention. Co-pyrolysis
of a lignite and an Australian oil shale (Rundle) has recently been reported by Sato and Saxby’. They found that the addition of lignite gave a slight synergistic effect in terms of increasing the oil yield from the shale and also reduced the molecular weights of the resulting oils considerably. For the Turkish reserves, co-pyrolysis is an attractive option, as the lignites and oil shales lie in close proximity and, in the case of the Goynuk and Seyitomer deposits, much of the shale forms an overburden for the lignite. In this study, the effect of steam on the pyrolysis of Goynuk oil shale in the Heinze retort and in a fluidized reactor and the co-pyrolysis of two Turkish lignites with Goynuk and Seyitomer oil shales have been investigated.
Presented at ‘Eastern Oil Shale Symposium’, 13-15 November 1991, Lexington, KY, USA
“Includes analysis
Turkey
001~2361/92/12151 l&O4 C. 1992 Butterworth-Heinemann
Ltd.
EXPERIMENTAL The proximate and ultimate analyses of the Goynuk and Seyitomer oil shales and the lignites used are summarized in Table I. Seyitomer oil shale contains a significant amount of carbonates and, from thermogravimetric analysis, it is estimated that carbonate-derived CO, in
Table 1
Analyses of the lignites and oil shales (wt%)
Seyitomer
Yatagan
Seyitomer
lignite
lignite
oil shale
Goynuk oil shale
30.9 15.6 30.0 23.5 36.3 3.5 0.9 1.1
14.8 41.4 34.0 9.8 23.7 2.9 5.5 0.7
3.5 69.0 20.ta 1.4 10.1 1.1 0.1 0.3
5.1 24.4 56.3 13.6 49.9 6.4 3.3 1.1
._ Moisture Ash Vol. matter Fixed carbon C H S N CO,
estimated
FUEL,
to
be
1992,
10 wt%
from
thermogravimetric
Vol 71, December
1511
Pyrolysis of Turkish oil shales: E. Ekinci et al. Table 2 Yields from atmospheric pressure oil shale at 550°C ( wt% daf shale)
experiments
Goynuk Char
Oil
Heinze retort static steam, 0.7 cm s 1 steam, 1.3 cm s-r steam, 3.3 cm s-r nitrogen, 3.3 cm s-r
55 46 40 25 47
33 40 44 55 39
Fixed bed static nitrogen,
48 23
38 61
22 cm s-r0
on Goynuk
Seyitomer
static steam, 4.3 cm s-r steam, 7.7 cm s-’ steam, 12.3 cm s-r
“Total hydrocarbon gas yield 2.8 wt% comprising 0.8 wt /O ethane and 0.4 wt% ethene
Char
Oil
64 51 46 42
28 38 42 45
_ _
_
0.9 wt% methane,
the volatiles accounts for - 10 wt% of the shale. This accounts for the fact that the volatile matter as determined is significantly higher than the organic carbon content (Table I). Goynuk oil shale and Yatagan lignite were pyrolysed in a Heinze retort at 550°C under static conditions (self-generated atmosphere) and using both nitrogen and steam as sweep gases up to superficial gas velocities of 0.3 m s- ‘. Char yields were determined from the weight losses for the retort. Oils were separated from the liquor and recovered for analysis. In addition, experiments at 550°C were also conducted with nitrogen using (1) a fixed-bed reactor (0.8 cm i.d.) with a much smaller sample size (5 g, vs. 30 g in the Heinze retort) to facilitate the use of larger sweep gas velocities and (2) a 3 cm diameter silica reactor in which the sample (30 g) is fluidized and slowly heated (5 K min-‘) from ambient temperature; the superficial gas velocity of 6.0 cm s-l corresponds to twice the minimum fluidizing velocity. Co-pyrolysis of mixtures of Goynuk oil shale with Yatagan lignite and Seyitomer oil shale with Seyitomer lignite ( ~200 pm) was carried out in the Heinze retort at 550°C under static conditions as described above. Sample sizes were 30 and 50 g for the Goynuk and Seyitomer oil shale mixtures respectively; the larger sample size was used for Seyitomer oil shale owing to its low organic matter content. The mass ratio of lignite to oil shale was varied between 1:3 and 3:l. To investigate the effect of a sweep gas on co-pyrolysis phenomena, the Goynuk oil shale-Yatagan lignite mixtures (212-350 pm) were heated to 550°C in the reactor used for the fluidized-bed experiments described above. For comparison with the Heinze retort, co-pyrolysis experiments were also carried out in this reactor using a static (non-fluidizing) atmosphere and a nitrogen flow rate of 2.0 cm s- ’ (below minimum fluidizing velocity). The oils from a number of tests in the Heinze retort were fractionated by silica gel adsorption chromatography into alkanes, aromatics and polars. Where appropriate, the alkanes and aromatics were analysed by gas chromatography and ‘H n.m.r. respectively.
with steam and nitrogen. Although gas yields were not determined for the Heinze retort, it is expected that these will be similar to the figure of k 9 wt % daf shale obtained in the fixed-bed reactor with nitrogen (Tab/e 2). As expected, the use of a sweep gas increased the oil yield considerably, and the total conversions ( lOO- wt% char) in the region of 80% achieved using a fixed-bed reactor with a relatively high superficial gas velocity and using a fluidized-bed reactor are close to the volatile matter content of the shale (Tables 1 and 2). Steam is much more effective than nitrogen at low sweep gas velocities in the Heinze retort. The oil yield achieved with a steam velocity of 3.3 cm s-l is nearly as high as that with a nitrogen velocity seven times as high in the small fixed-bed reactor. For the other oil shale, Seyitomer, which has a much lower organic matter content ( - I5 wt%), it was found that a much greater steam velocity is required to overcome retrogressive reactions (Table 2). The compositions of the Goynuk shale oils from the Heinze retort are compared in Figure 1, which indicates that, compared with static retorting, the yields of alkanes and aromatics increase markedly and polars decrease slightly, using either nitrogen or steam as sweep gas. However, the effect is more pronounced with steam, indicating that alkanes must be involved in retrogressive reactions leading to char formation, probably via dehydrogenation to alkenes and subsequent cyclization. Indeed, g.c. analysis of the alkane fractions and ‘H n.m.r. analysis of the aromatics qualitatively indicated that alkene concentrations broadly increase with increasing steam velocity. Thus, either the steam is actually promoting bond cleavage reactions, creating a greater demand for transferable hydrogen, or is merely providing a more protective environment, limiting the extent of cyclization and aromatization of the alkenes by passivating the acidic clay minerals. Evidence that the steam may actually promote bond cleavage was provided by Minkova et a1.4, who found that the sulphur contents of the oils obtained with steam were lower.
60
0 0
Asphaltenes Aromatics q Polars l Alkanes
50
40 a, z YI v4
30
s 3 20
10
RESULTS
AND DISCUSSION
Steam pyrolysis Tub/e 2 compares the oil and char yields obtained from Goynuk oil shale in the different regimes investigated
1512
FUEL, 1992, Vol 71, December
0 Static
Figure
1
Compositions
Steam
Nitrogen 3.3 ems
ofGoynuk
-1
0.7cms
Steam -1
shale oils prepared
3.3cms
-1
in Heinze retort
Pyrolysis
I
20 r 0
0 0
I 40
I 20 Oil
Figure 2
Actual Predicted
shale
I 60
content
Oil yields from Goynuk
of
blend
oil shale-Yatagan
I 80
I 100
(wt%)
lignite mixtures
of Turkish oil shales: E. Ekinci et al.
a relatively poor solvent for the phenolic material from the lignites. Further information on the interactions between the lignites and oil shales during static pyrolysis can be obtained from the compositions of the resulting oils. Figure 4 indicates that the concentrations of alkanes and aromatics increase and the concentrations of polars decrease more than those predicted from the compositions of the individual oils. This provides further evidence that the interactions between the oil shales and lignites go some way to limiting retrogressive reactions which are probably catalysed to a large extent by the clay minerals. In particular, the well-established increases in overall aromaticity under static retorting conditions9%i0 are probably attributable in part to cyclization of acyclic alkanes and alkyl moieties. Table 3 lists the char and tar yields from the fluidized-bed experiments with Yatagan lignite, Goynuk oil shale and their mixtures. Under static conditions, a distinct synergistic effect is observed as in the Heinze retort for a 1:2 mixture (1ignite:oil shale, Figure 2). As expected, the use of nitrogen as a sweep gas gave rise to significantly higher conversions and, with the maximum sweep gas velocity of 6.0 cm s-i, the conversions of the oil shale and lignite are slightly higher than their volatile matter contents (Table 1). However, the char and tar yields for the 1:2 mixture are similar to the predicted yields. Therefore synergism would appear to be evident
O Actual 0 Predicted
0' 0
Figure 3
I
I
I
I
I
20
40
60
80
100
Oil shale
content
Oil yields from Seyitomer
of blend oil shale-lignite
(wt%) mixtures
- ---
Co-pyrolysis Figures 2 and 3 present the actual and predicted oil yields from the Heinze retort experiments with the Goynuk oil shale-Yatagan lignite and Seyitomer oil shale-Seyitomer lignite mixtures respectively; the predicted yields were simply deduced from those of the separate components. The actual oil yields for the mixtures are consistently higher than those predicted. The differences of 2-5 wt% daf oil shale or asphaltiteelignite are considerably greater than the estimated experimental errors of0.5-1.0 wt%. For the oil shale-lignite mixtures, the increases in oil yield are highest for the 3:l mass ratio of oil shale to lignite and would appear broadly to increase with increasing oil shale content. Thus the oil shale is reasonably effective in partly preventing retrogressive char-forming reactions for the lignite. However, relatively large amounts of oil shale are probably required, because compatibility between the shale and lignite is relatively poor. It has been found that the shale oils are highly aliphatic in character’.2, and during the initial stages of pyrolysis, the pyrobitumen which is the precursor of the shale oil is expected to be
0
0
I
I
I
I
I
20
40
60
80
100
Oil shale Figure 4 mixtures
Predicted
Compositions
content
of oils
of blend from
(wt%)
Seyitomer
oil
shale-lignite
Table 3 Yields from experiments on Yatagan lignite and Goynuk shale in fluidized-bed reactor (wt% daf blend)
oil
Sample
Sweep gas
Char
Oil
Total gas”
Goynuk Yatagan 1:2 mixture
Staticb Staticb Static*
45 44 37 [45]’
43 24 40 1371
12 32 23
1:2 mixture 1:2 mixture
2cms-’ 6cms-’
::
42 54 [SS]
25 24
Goynuk Yatagan
6cms-’ 6cms-’
15 38
74 28
11 34
1231
“By difference and including water bNo sweep gas, no fluidization ‘Values in square brackets are predicted
yields
FUEL, 1992, Vol 71, December
1513
Pyrolysis
of Turkish oil shales: E. Ekinci et al.
under static conditions or with a low sweep gas velocity where there are severe mass transfer limitations on the release of volatiles. In well-swept reactors, such as the fuidized-bed reactor used here, the contact between lignite and oil shale particles is likely to be considerably poorer than in fixed-bed static reactors, and pyrolysis of the two components proceeds more or less independently. only
REFERENCES I 2
3 4 5 6 7
ACKNOWLEDGEMENT
8
The authors thank NATO and the Science & Engineering Research Council with British Gas (CASE studentship, GDL) for financial support.
1514
FUEL,
1992,
Vol 71, December
9 10
Citiroglu, M.: Snape, C. E., Lafferty, C. J., Ekinci, E. and Bartle, K. D. Erdiil Kohlr, Erdyas, Petrochem. 1990, 43, 142 Ekinci, E., Citiroglu, M., Putun, E., Lafferty, C. J. and Snape, C. E. In Proc. 1991 Int. Conf. on Coal Science. Paper no. ACC:33 Putun, E., Ekinci, E., Akar, A., Frere, B., Bartle, K. D., Citiroglu, M. and Snape, C. E. J. Per. Geol. 1991, 14, 459 Minkova, V., Angelova, G., Ljustzkanov, L., Goranova, M. and Razvigorova, M. In Proc. 1987 Int. Conf. on Coal Science, p. 671 Rubel, A. M. and Coburn, T. T. In Proc. 1981 US Eastern Oil Shale Symposium, University of Kentucky, p. 21 Ross, D. S., Loo. B. H., Tse, D. S. and Hirschon. A. S. Fuel 1991,70. 289 Carter, S. D. and Taulbee, D. L. Flrel Process. T&no!. 1985, 3, 251 Sato, S. and Saxby, J. D. In Proc. 1989 Int. Conf. on Coal Science, p, 619 Burnham, A. K. and Happe. J. A. Furl 1984. 63. 1353 Wilson. M. A., Lambert, D. E. and Collin. P. J. Furl 1985, 64. 1647
Gordon
fnstanbul Technical University, Dept of Chemical Engineering, Turkey “Anadolu University, Dept of Chemical Engineering, Eskisehir, tuniversity of Strathclyde, Dept of Pure & Applied Chemistry, (Received 23 January 7992; revised 7 July 1992)
on the
D. Lovet,
Maslak,
80626
Turkey Glasgow
Gl
Istanbul,
IXL,
UK
Steam was found to be a more effective sweep gas than nitrogen at low velocities in fixed-bed pyrolysis of Goynuk oil shale but, at higher velocities and in fluidized-bed pyrolysis, the differences were considerably less marked. Relatively small but significant synergistic effects were observed between lignites and the two oil shales investigated - Goynuk and Seyitomer - under static retorting conditions. These effects were more pronounced with large concentrations of oil shales but disappeared in fluidized-bed pyrolysis, where conversions are considerably higher because mass transfer limitations largely disappear. (Keywords:
lignite; oil shale; pyrolysis)
has vast reserves of both oil shales and high-sulphur lignites, much of the former having particularly low mineral matter contents. The objective of research has been to identify ways in which significantly higher oil yields and oils of better quality can be obtained than under the normal static conditions used in retorting tests such as the Gray-King and Fischer assays. It is well established that, although fairly high oil yields (in the range lo-40 wt% daf) can be achieved from lignites and oil shales under static retorting conditions, as in those assays, the oil yields are mass transfer-limited. Indeed, the authors have reported elsewhere’ .’ that the use of well-swept fixed-bed reactors and hydrogen under pressure gives oil yields of > 70 wt% daf for two shales ~ Goynuk and Seyitomer - which can be classified as immature type I/II kerogens3. Two other possibilities are to consider (1) the use of steam to overcome mass transfer limitations and avoid retrogressive char-forming reactions more effectively than inert gases such as nitrogen, and (2) co-pyrolysis of lignites with oil shales. Minkova ef a1.4 and Rubel and Coburn’ have found that the use of steam, like nitrogen, as a sweep gas gives rise to marked increases in oil yield for coals and oil shales respectively. However, it is uncertain whether steam has a distinct chemical role during pyrolysis other than passivating clay minerals from catalysing retrogressive char-forming reactions, for example the coupling of phenols to form furans”. Indeed, in fluidized beds, the differences in conversion between nitrogen and steam for oil shales are generally small’ and may partly arise from the fact that steam is more effective for collecting light oils. The co-processing of coals and heavy oils in direct liquefaction has already received considerable attention. Co-pyrolysis
of a lignite and an Australian oil shale (Rundle) has recently been reported by Sato and Saxby’. They found that the addition of lignite gave a slight synergistic effect in terms of increasing the oil yield from the shale and also reduced the molecular weights of the resulting oils considerably. For the Turkish reserves, co-pyrolysis is an attractive option, as the lignites and oil shales lie in close proximity and, in the case of the Goynuk and Seyitomer deposits, much of the shale forms an overburden for the lignite. In this study, the effect of steam on the pyrolysis of Goynuk oil shale in the Heinze retort and in a fluidized reactor and the co-pyrolysis of two Turkish lignites with Goynuk and Seyitomer oil shales have been investigated.
Presented at ‘Eastern Oil Shale Symposium’, 13-15 November 1991, Lexington, KY, USA
“Includes analysis
Turkey
001~2361/92/12151 l&O4 C. 1992 Butterworth-Heinemann
Ltd.
EXPERIMENTAL The proximate and ultimate analyses of the Goynuk and Seyitomer oil shales and the lignites used are summarized in Table I. Seyitomer oil shale contains a significant amount of carbonates and, from thermogravimetric analysis, it is estimated that carbonate-derived CO, in
Table 1
Analyses of the lignites and oil shales (wt%)
Seyitomer
Yatagan
Seyitomer
lignite
lignite
oil shale
Goynuk oil shale
30.9 15.6 30.0 23.5 36.3 3.5 0.9 1.1
14.8 41.4 34.0 9.8 23.7 2.9 5.5 0.7
3.5 69.0 20.ta 1.4 10.1 1.1 0.1 0.3
5.1 24.4 56.3 13.6 49.9 6.4 3.3 1.1
._ Moisture Ash Vol. matter Fixed carbon C H S N CO,
estimated
FUEL,
to
be
1992,
10 wt%
from
thermogravimetric
Vol 71, December
1511
Pyrolysis of Turkish oil shales: E. Ekinci et al. Table 2 Yields from atmospheric pressure oil shale at 550°C ( wt% daf shale)
experiments
Goynuk Char
Oil
Heinze retort static steam, 0.7 cm s 1 steam, 1.3 cm s-r steam, 3.3 cm s-r nitrogen, 3.3 cm s-r
55 46 40 25 47
33 40 44 55 39
Fixed bed static nitrogen,
48 23
38 61
22 cm s-r0
on Goynuk
Seyitomer
static steam, 4.3 cm s-r steam, 7.7 cm s-’ steam, 12.3 cm s-r
“Total hydrocarbon gas yield 2.8 wt% comprising 0.8 wt /O ethane and 0.4 wt% ethene
Char
Oil
64 51 46 42
28 38 42 45
_ _
_
0.9 wt% methane,
the volatiles accounts for - 10 wt% of the shale. This accounts for the fact that the volatile matter as determined is significantly higher than the organic carbon content (Table I). Goynuk oil shale and Yatagan lignite were pyrolysed in a Heinze retort at 550°C under static conditions (self-generated atmosphere) and using both nitrogen and steam as sweep gases up to superficial gas velocities of 0.3 m s- ‘. Char yields were determined from the weight losses for the retort. Oils were separated from the liquor and recovered for analysis. In addition, experiments at 550°C were also conducted with nitrogen using (1) a fixed-bed reactor (0.8 cm i.d.) with a much smaller sample size (5 g, vs. 30 g in the Heinze retort) to facilitate the use of larger sweep gas velocities and (2) a 3 cm diameter silica reactor in which the sample (30 g) is fluidized and slowly heated (5 K min-‘) from ambient temperature; the superficial gas velocity of 6.0 cm s-l corresponds to twice the minimum fluidizing velocity. Co-pyrolysis of mixtures of Goynuk oil shale with Yatagan lignite and Seyitomer oil shale with Seyitomer lignite ( ~200 pm) was carried out in the Heinze retort at 550°C under static conditions as described above. Sample sizes were 30 and 50 g for the Goynuk and Seyitomer oil shale mixtures respectively; the larger sample size was used for Seyitomer oil shale owing to its low organic matter content. The mass ratio of lignite to oil shale was varied between 1:3 and 3:l. To investigate the effect of a sweep gas on co-pyrolysis phenomena, the Goynuk oil shale-Yatagan lignite mixtures (212-350 pm) were heated to 550°C in the reactor used for the fluidized-bed experiments described above. For comparison with the Heinze retort, co-pyrolysis experiments were also carried out in this reactor using a static (non-fluidizing) atmosphere and a nitrogen flow rate of 2.0 cm s- ’ (below minimum fluidizing velocity). The oils from a number of tests in the Heinze retort were fractionated by silica gel adsorption chromatography into alkanes, aromatics and polars. Where appropriate, the alkanes and aromatics were analysed by gas chromatography and ‘H n.m.r. respectively.
with steam and nitrogen. Although gas yields were not determined for the Heinze retort, it is expected that these will be similar to the figure of k 9 wt % daf shale obtained in the fixed-bed reactor with nitrogen (Tab/e 2). As expected, the use of a sweep gas increased the oil yield considerably, and the total conversions ( lOO- wt% char) in the region of 80% achieved using a fixed-bed reactor with a relatively high superficial gas velocity and using a fluidized-bed reactor are close to the volatile matter content of the shale (Tables 1 and 2). Steam is much more effective than nitrogen at low sweep gas velocities in the Heinze retort. The oil yield achieved with a steam velocity of 3.3 cm s-l is nearly as high as that with a nitrogen velocity seven times as high in the small fixed-bed reactor. For the other oil shale, Seyitomer, which has a much lower organic matter content ( - I5 wt%), it was found that a much greater steam velocity is required to overcome retrogressive reactions (Table 2). The compositions of the Goynuk shale oils from the Heinze retort are compared in Figure 1, which indicates that, compared with static retorting, the yields of alkanes and aromatics increase markedly and polars decrease slightly, using either nitrogen or steam as sweep gas. However, the effect is more pronounced with steam, indicating that alkanes must be involved in retrogressive reactions leading to char formation, probably via dehydrogenation to alkenes and subsequent cyclization. Indeed, g.c. analysis of the alkane fractions and ‘H n.m.r. analysis of the aromatics qualitatively indicated that alkene concentrations broadly increase with increasing steam velocity. Thus, either the steam is actually promoting bond cleavage reactions, creating a greater demand for transferable hydrogen, or is merely providing a more protective environment, limiting the extent of cyclization and aromatization of the alkenes by passivating the acidic clay minerals. Evidence that the steam may actually promote bond cleavage was provided by Minkova et a1.4, who found that the sulphur contents of the oils obtained with steam were lower.
60
0 0
Asphaltenes Aromatics q Polars l Alkanes
50
40 a, z YI v4
30
s 3 20
10
RESULTS
AND DISCUSSION
Steam pyrolysis Tub/e 2 compares the oil and char yields obtained from Goynuk oil shale in the different regimes investigated
1512
FUEL, 1992, Vol 71, December
0 Static
Figure
1
Compositions
Steam
Nitrogen 3.3 ems
ofGoynuk
-1
0.7cms
Steam -1
shale oils prepared
3.3cms
-1
in Heinze retort
Pyrolysis
I
20 r 0
0 0
I 40
I 20 Oil
Figure 2
Actual Predicted
shale
I 60
content
Oil yields from Goynuk
of
blend
oil shale-Yatagan
I 80
I 100
(wt%)
lignite mixtures
of Turkish oil shales: E. Ekinci et al.
a relatively poor solvent for the phenolic material from the lignites. Further information on the interactions between the lignites and oil shales during static pyrolysis can be obtained from the compositions of the resulting oils. Figure 4 indicates that the concentrations of alkanes and aromatics increase and the concentrations of polars decrease more than those predicted from the compositions of the individual oils. This provides further evidence that the interactions between the oil shales and lignites go some way to limiting retrogressive reactions which are probably catalysed to a large extent by the clay minerals. In particular, the well-established increases in overall aromaticity under static retorting conditions9%i0 are probably attributable in part to cyclization of acyclic alkanes and alkyl moieties. Table 3 lists the char and tar yields from the fluidized-bed experiments with Yatagan lignite, Goynuk oil shale and their mixtures. Under static conditions, a distinct synergistic effect is observed as in the Heinze retort for a 1:2 mixture (1ignite:oil shale, Figure 2). As expected, the use of nitrogen as a sweep gas gave rise to significantly higher conversions and, with the maximum sweep gas velocity of 6.0 cm s-i, the conversions of the oil shale and lignite are slightly higher than their volatile matter contents (Table 1). However, the char and tar yields for the 1:2 mixture are similar to the predicted yields. Therefore synergism would appear to be evident
O Actual 0 Predicted
0' 0
Figure 3
I
I
I
I
I
20
40
60
80
100
Oil shale
content
Oil yields from Seyitomer
of blend oil shale-lignite
(wt%) mixtures
- ---
Co-pyrolysis Figures 2 and 3 present the actual and predicted oil yields from the Heinze retort experiments with the Goynuk oil shale-Yatagan lignite and Seyitomer oil shale-Seyitomer lignite mixtures respectively; the predicted yields were simply deduced from those of the separate components. The actual oil yields for the mixtures are consistently higher than those predicted. The differences of 2-5 wt% daf oil shale or asphaltiteelignite are considerably greater than the estimated experimental errors of0.5-1.0 wt%. For the oil shale-lignite mixtures, the increases in oil yield are highest for the 3:l mass ratio of oil shale to lignite and would appear broadly to increase with increasing oil shale content. Thus the oil shale is reasonably effective in partly preventing retrogressive char-forming reactions for the lignite. However, relatively large amounts of oil shale are probably required, because compatibility between the shale and lignite is relatively poor. It has been found that the shale oils are highly aliphatic in character’.2, and during the initial stages of pyrolysis, the pyrobitumen which is the precursor of the shale oil is expected to be
0
0
I
I
I
I
I
20
40
60
80
100
Oil shale Figure 4 mixtures
Predicted
Compositions
content
of oils
of blend from
(wt%)
Seyitomer
oil
shale-lignite
Table 3 Yields from experiments on Yatagan lignite and Goynuk shale in fluidized-bed reactor (wt% daf blend)
oil
Sample
Sweep gas
Char
Oil
Total gas”
Goynuk Yatagan 1:2 mixture
Staticb Staticb Static*
45 44 37 [45]’
43 24 40 1371
12 32 23
1:2 mixture 1:2 mixture
2cms-’ 6cms-’
::
42 54 [SS]
25 24
Goynuk Yatagan
6cms-’ 6cms-’
15 38
74 28
11 34
1231
“By difference and including water bNo sweep gas, no fluidization ‘Values in square brackets are predicted
yields
FUEL, 1992, Vol 71, December
1513
Pyrolysis
of Turkish oil shales: E. Ekinci et al.
under static conditions or with a low sweep gas velocity where there are severe mass transfer limitations on the release of volatiles. In well-swept reactors, such as the fuidized-bed reactor used here, the contact between lignite and oil shale particles is likely to be considerably poorer than in fixed-bed static reactors, and pyrolysis of the two components proceeds more or less independently. only
REFERENCES I 2
3 4 5 6 7
ACKNOWLEDGEMENT
8
The authors thank NATO and the Science & Engineering Research Council with British Gas (CASE studentship, GDL) for financial support.
1514
FUEL,
1992,
Vol 71, December
9 10
Citiroglu, M.: Snape, C. E., Lafferty, C. J., Ekinci, E. and Bartle, K. D. Erdiil Kohlr, Erdyas, Petrochem. 1990, 43, 142 Ekinci, E., Citiroglu, M., Putun, E., Lafferty, C. J. and Snape, C. E. In Proc. 1991 Int. Conf. on Coal Science. Paper no. ACC:33 Putun, E., Ekinci, E., Akar, A., Frere, B., Bartle, K. D., Citiroglu, M. and Snape, C. E. J. Per. Geol. 1991, 14, 459 Minkova, V., Angelova, G., Ljustzkanov, L., Goranova, M. and Razvigorova, M. In Proc. 1987 Int. Conf. on Coal Science, p. 671 Rubel, A. M. and Coburn, T. T. In Proc. 1981 US Eastern Oil Shale Symposium, University of Kentucky, p. 21 Ross, D. S., Loo. B. H., Tse, D. S. and Hirschon. A. S. Fuel 1991,70. 289 Carter, S. D. and Taulbee, D. L. Flrel Process. T&no!. 1985, 3, 251 Sato, S. and Saxby, J. D. In Proc. 1989 Int. Conf. on Coal Science, p, 619 Burnham, A. K. and Happe. J. A. Furl 1984. 63. 1353 Wilson. M. A., Lambert, D. E. and Collin. P. J. Furl 1985, 64. 1647