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

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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