the kmter large - costar-mines.org · (figure7).theinstallationis underconstructionatthepo...
TRANSCRIPT
THE KMTER PROCESS FOR RETORTING
LARGE PARTICLE OIL SHALE
YEFIMOVV.M.
(The Oil Shale Research Institute, Kohtla-Jarve, Estonian SSR)
ROOKS I. H.
(The V. I. Lenin PO "Slantsekhim", Kohtla-Jarve, Estonian SSR)
In recent years considerable interest has been shown to
the experience of commercial-scale processing of oil shale as
an alternative feedstock for theproduction of liquid fuels. The
evaluation of different retort systems, however, should be
madewith due consideration of the specific properties ofdif
ferent oil shales, influencing the efficiency of the retorting
process. Our studies of oil shale samples extracted from the
world's largest oil shale formations in the USA and Brazil as
well as those of kukersite (Baltic oil shale) processed in the
USSR on a commercial scale, show that the latter is charac
terized by several technological properties which complicate
it's thermal processing.
As can be seen from Tables 1 and 2, kukersite is charac
terized by high levels of free moisture, high organic matter
content, as well as high levels of calcium carbonate in inor
ganic matter. Upon heating of kukersite the bulk of
thermobitumen is formed at temperatures near 400 degrees
C. Themechanical strength of kukersite is as low as half that
of theGreenRiver oil shale. Kukersite yields oilwhich is rep
resented essentially by aromatic and oxygen compounds
including large quantities ofphenols. As a result the kuker
site oil has a relatively low pour point.
The above properties of kukersite cause relativelyhigh
specific heat requirements on retorting, i.e. the heat con
sumed by kukersite in the semicoking zone of the retort
appreciablyexceeds that for retorting Green River and Irati
oil shales. According toour calculations these values are as
high as 1.100, 670 and680 KJ/kg, respectively.
Biturninization of kukersite (i.e. passingthrough a plastic
stage uponheating), its relatively
low mechanical and ther-
momechanical strength, result in a necessity of utilizing oil
shale in a particle size range of 25-125 mm, thus limiting the
possibility of intensification of its industrial scale retorting.
Relatively high levels of specific heat consumption for the
retorting process and a high organic matter content make it
necessary to process kukersite in special retorting systems, e.
g. in generators, providing for relatively high temperatures of
the heat carrier gas entering the retorting chamber as well as
that of the oil vapours and gas in the gas collectors, i.e. 800-
900 and 200-250 degrees C, respectively. These factors are
considered to have a negative effect upon the process. Due to
the specific properties of kukersite the concept employing
cross current flow of heat carrier gas through the shale bed
proved to be most acceptable for the retorting of this par
ticular shale. Compared with the traditionally employed
countercurrent flow of heat carrier gas this concept is more
preferable providing for more uniform distribution of the
heat carrier through the fuel bed. It enables to modify the
height of the retorting chamber and thus to practically
eliminate the dependence of the unit throughput rate on the
velocity of the heat carrier gas in the retorting chamber, and
to perform the process in a thin oil shale bed.
Therefore, generators employing cross current heat car
rier flow (the Kiviter process) are widely applied in the
U.S.S.R. for retorting ofkukersite, characterized by a high or
ganic content and biturninization upon heating. The first
modification of the retort presented in Figure 1 incorporat
ing a single retorting chamber had a daily throughput ofabout
200 1 of oil shale, the shale oil yield as high as 75-78 per cent
of the Fischer assay.
256
The necessity of reequipment of the oil shale industryin
the Baltic basin led to the intensification of efforts aimed at
developing a new generation of oil shale retorts providing for
both higher unit throughput rates and higher shale oil yields.
The development of a new retort inevitably led to a con
siderable expansionof the overall dimensions as compared to
those of the 200 ton-per-day module, to difficulties in ensur
ing a uniform heat carrier gas distribution in the fuel bed, and
a uniform downward passage of the latter in the retort. The
above difficulties were the most serious to overcome in
developing a new 1,000 ton-per-day generator.
The concept of the successfully commercialized 200ton-
per-day generators could not be used because a single
retorting chamber in a 1,000 ton-per-day unit would result in
unreasonable increase of the height of the retort, e. g. the
limitation of the thickness of the fuel bed in the retorting
chamber to maximum 1.5 m to avoid difficulties due to oil
shale biturninizationwouldmake it necessary to increase the
unit height to 60-70m. For these reasons amodification of the
Kiviter processwas developed employing two parallel retort
ing chambers arranged in the retorting zone. (Figure 2).
This concept also enabled to arrange uniform distribution
of the heat carrier in the fuel bed, mainly due to the employ
ment of two charging devices one for each retorting chamber
and introduction of additional heat into each of the retorting
chambers through side combustion chambers. To provide
better heat recovery of the discharged spent shale, thelatter
is cooled with recycle gas in a cooling zone arranged in the
lower part of the retort, as is widely used in different solid
fuels retorting systems in the world.
The first 1,000 ton-per-day generator built at the PO
"Slantsekhim"
at Kohtla-Jarve (Estonian SSR) was put into
operation in January 1981 (Figure 3). The retort is erected on
an open site.The outer diameter of the cylindrical retort ves
sel is 9.6m., its height is 21 m.The overall height of the retort,
including the oil shale bin is 35 m.
Subsequently, the operating experience of the first 1,000
ton-per-daygeneratorwas taken into consideration to design
and construct two similar units also at the PO "Slantsekhim",
which started operation in January 1987 (Figure 4).
Since then the design throughput rate of the retorts has
been achieved amounting to 950-1050 tons ofoil shaleper day
with a daily oil yield about 170 tons (80-82 per cent of the Fis
cher assay). The operation of the 1,000 ton-per-day generator
revealed a problem of carry-over of finely divided solid par
ticles with oil vapours. The amount of fine solid particles
carried over from a 1,000 ton-per-daygenerator several times
exceeds that from the 200 ton-per-day units. As a result, the
concentration of fine solids (mechanical impurities) in the
heavy shale oil fraction, amounting to 30-40 per cent of the
total oil, makes up at times to 10-15 per cent particularly at
the end of runs. The generator has been on stream 85-90 per
cent of calendar time. To cool the oil vapours and off-gas the
condensation system is provided with air-cooled bare tube
coolers with a total heat exchange surface of 930m squared.
Each cooler is composed of three stacked-up sectionswith in
termediate draw-off of the product shale oil (Figure 5).
Further research on the Kiviter process resulted in the
development of another designmodification employing a cir
cular retorting chamber, encircling the retort by perimeter
(Figure 6, modification C). This concept provides a 1.5-fold
increase of the net volume of the retorting shaft with no
change in the thickness of the shale bed,which is ofparticular
importance for normal retorting of kukersite. Moreover, this
design eliminates the side walls of the retorting chamber
responsible for an uneven distribution of the heat carrier in
the fuel bed, as well as difficulties in uniform oil shale
downward passage in the retort, and other negative
phenomena.Due to special features of the design a dailyunit
throughput rate of 1,500 tons ofoil shale canbe expectedwith
an oil yield of 83-85 per cent of the Fischer assay oil without
changing the overall dimensions of the 1,000 ton-per-day
prototype retort. In 1987 the design and engineering of the
modified retort were completed and the construction started
of an installation comprising four prototype modified retorts
with an overall throughput of 6,000 tons of oil shale per day
257
(Figure 7). The installation is under construction at the PO
"Slantsekhim"atKohtla-Jarve and is scheduled to start opera
tion by 1992-1993.
Thus, over the past decade, the development of new sys
tems for retorting large particle size oil shale in the USSR as
well as the updating of the existing units has resulted in attain
ing a substantial increase in retort throughput rates with a
simultaneous increase in shale oil yields. It ispertinent to note
that the first generators built at Kohtla-Jarve in 1924 had a
throughput rate of 33 tons of oil shale per day.
It is a fact that the majority of oil shales occurring
throughout theworldmaybe classified as poor in organicmat
ter and, as a rule, are not readily beneficiated. To design
adequate retorting technology the following aspects should be
taken into consideration. Firstly, the use of low organic shales
makes it possible to reduce the size of feed oil shale particles.
Lean shales with a Fischer assay oil yield ofmaximum 10-12
per cent are not practically bituminized upon heating. As a
rule, they are characterized by a fairly high mechanical and
thermomechanical strength, which enables to retain the ini
tial oil shale particle size in the retorting process. This makes
itpossible to utilize small particle size oil shale in a range from
6-8 mm to 60-70 mm as retort feed. This in its turn results in
a substantial(two- or three-fold) increase in the retort
throughput.
Secondly, the use of low organic oil shale enables to attain
a higher filling factor of the retort. Lean oil shale is not
bituminized upon heating and therefore there are no
obstacles for an increase in the fuel bed sizein the retort.This
factor enables to double the retortthroughput as compared
to retorting kukersite,what due to its biturninization proper
ties should be processedin a relatively thin bed.
The third factor impliesthe possibilityofmaintaining rela
tively lowtemperatures of the heat carrier gas injected into
the retort, aswell as those of the
retort off-gas, amounting to
500-600 degree C and 60-80 degree C, respectively. This is
possible due to a relativelylow specific heat consumption for
thedecomposition of lean oil
shales and to a low organiccon-
tent of the shale.
The above specific featuresmake it possible to appreciab
ly improve the efficiency of the retorting of lean oilshales in
generators as compared to that of retorting kukersite. So it is
considered possible to develop retorts based on the Kiviter
process capable of retorting low organic oil shales at unit
throughput rates of 5,000-10,000 tons of oil shale per day.
258
TABLE 1
SAMPLES OF DIFFERENT OIL SHALES - Properties
Green
River
(USA)
Irati
(Brazil)
Baltic
Basin
(USSR)
Moisture content, wt %
Proximate analysis, wt %
(dry basis):Carbon dioxide
Ash
Organicmatter
(by difference)
Sulfur (total), wt %
Heating value (by combustionin bomb calorimeter), MJ/kg
Fischer Assay product balance,wt%
Oil
Water
Spent shale
Gas and losses
(by difference)
Fischer Assay oil, per centof organic matter
Ash composition, wt %
Si02CaO
MgO
Al>3
Fe2Q3Na>
K2O
SO3Total
Thermobitumen yield (max.)at 390-400 degree C:
Per cent of oil shale
Per cent of organicmatter
0.7
5.36
2.4
67.4
5.3
5.61
3.5
39.8
9.0
17.3
68.3
2.6
79.8
18.7
46.5
14.4 17.6 34.8
0.65 4.19 1.85
13.40
9.7 7.0 23.6
1.2 1.3 1.8
86.7 88.2 69.5
5.1
67.8
44.3 60.3 23.1
20.5 2.8 56.5
7.4 3.1 4.2
12.8 13.2 4.9
5.5 12.0 4.4
3.5
2.8
16.9 12.5
2.4 1.7 3.3
99.2 100.0 98.9
6.0 21.6
39.9 - 56.1
TABLE 2
FISCHER ASSAY PRODUCT PROPERTIES
SHALE OIL:
Density (20 degree C), kg/m 3Molecular weight (average)Heating value (by combustionin bomb calorimeter),
MJ/kg'
Pour point, degree C
Ultimate analysis, wt %C
H
S
N
O (by difference)
Chemical group composition,wt%:
Saturated hydrocarbons
Unsaturated hydrocarbonsAromatic hydrocarbonsNeutral heteroatomic
compounds
Phenols and carboxylic
acids
SPENT OIL SHALE:
Proximate analysis, wt %
(dry basis):Carbon dioxide
Ash
Carbon
Sulfur (total)
Heating value (by combustionin bomb calorimeter), MJ/kg
Green
River
(USA)
}
Irati
(Brazil)
Baltic
Basin
(USSR)
927
233
918
210
978
285
42,6
+ 25
42,2 39,7
-20
83.9
11.9
0.8
1.3
2.1
84.4
11.0
1.3
0.6
2.7
81.5
10.0
0.8
0.2
7.5
35.6
27.2
13.7
16.7
48.4
4.1
5.8
42.0
36.0 19.5 25.9
1.2 1.7 22.2
19.5 2.7 27.6
78.2 90.0 63.8
2.7 6.1 8.5
0.4 3.1 1.3
0.92 2.34 3.26
260
OIL SHALE OIL SHALE
3rtMTSHHMr-1
FIGURE 1. Gas generatorwith crosscurrent flow of
the heat carrier gas (modification A): 1 -
charging
device; 2 - oil shale retorting chamber; 3- heat
carrier preparation and distribution chamber; 4- oil
vapours collecting and evacuation chamber; 5- gas
outlet; 6-
gasifier; 7- gas blower; 8 - spent shale
discharge device
OIL VAPORSAND BAB
SPENT SHALE
AA
FIGURE 2. 1,000 ton-per-day gas generator(modification B): 1 -
charging device; 2- oil shale
retorting chamber; 3- central heat carrier prepar
ation and distribution chamber; 4- oil vapours
collecting and evacuation chamber; 5- side
combustion chambers; 6- gas burners; 7 - recycle gas
inlets for heat carrier preparation; 8- recycle gas
inlets for cooling spent shale; 9- spent shale
discharge device
m^fW*?""'~
-^tJt^ *m m
FIGURE 3. General view of the 1,000 ton-per-day prototype generatorwith condensation system
261
c<u
o
c
o
<u
3
-a
oo
W
DaHH
Ph
ex
&o
3 2
c
a
Ih
<u
o
Wo
a o
262
2 / 3
<^rs
0.0 '0
<?/> \
I ?o . ir 13
0
/ <? 3
FIGURE 6. Modification of gas generators with cross currentflow ofheat carrier gas (the Kiviter process): 1 -
retortingchamber; 2
- heat carrier preparation and distribution chamber;3 - oil vapours collecting and evacuation chamber
FIGURE 7. General view of a unit under construction comprising four 1,500 ton-per-day generators
263