On the Coking of Coal-Tar Pitch

Based on the materials of a technical design for an installation for the production of pitch (electrode) coke, prepared by the Department of Apparatus of the Tomsk Industrial Institute named after S. M. Kirov for the Kemerovo Coke-Chemical Plant.

N. N. Norkin, M. S. Pribytkov, V. V. Kazmina, S. N. Volkov,
A. F. Timofeev, V. S. Biryukov, A. D. Anisimov.

I. Introduction

In the article presented to the reader, the principal provisions are set forth of the technical design for an installation for the coking of pitch, prepared by the authors—staff members of the Department of Apparatus of the Tomsk Industrial Institute named after S. M. Kirov¹. The design was prepared directly at the Kemerovo Coke-Chemical Plant during the period from July 6 to August 29, 1938, and was approved by Glavkoks on October 7, 1938.

The question of the industrial coking of pitch is of great significance for the national economy, and its solution must proceed not only along the line of adapting existing coke ovens, but, primarily, along the line of creating new rational designs of furnace installations.

In designing the installation, a whole series of additional considerations arose which could not be reflected in the design; the purpose of the present article is to acquaint the reader both with the content of the design and with those additional considerations which go beyond the limits of the designed installation and may serve as certain material in the design of new installations.

II. The Techno-Economic Significance of the Problem of Producing Pitch Electrode Coke

The consumer of pitch (electrode) coke is the aluminum industry; coke serves as the raw material for the production of electrodes used in the electrolysis of aluminum. The specific consumption of electrodes per 1 ton of aluminum amounts to 18% of the cost of aluminum.

Coke for electrodes serving as anodes in electrolytic aluminum baths must have the following properties:

1) Total ash content within 0.5%
2) The ash must contain: no more than 0.06% \(Fe_2O_3\)
3) Sulfur in the coke no more than 0.7%
4) Volatiles in the coke no more than 0.6%
5) Content of fines (up to 5 mm) no more than 5%.

Until 1933, the raw material for electrodes in the USSR was coke from petroleum residues:

a) still coke from direct distillation of petroleum residues;
b) cracking coke (residues from petroleum cracking);
c) pyrogenetic coke (Baku petroleum installation).

Beginning in 1933, thanks to the work of the Kharkov Coal-Chemical Institute and, in particular, of full member N. A. Nikolsky, the raw-material base for electrode production was expanded through coke from coal-tar pitch. In 1935, the first installation in the USSR for coking coal-tar pitch was put into operation at the Staromakeevka Coke-Chemical Plant. Since 1938, production of pitch coke has been under development at the Kemerovo Coke-Chemical Plant (Kuzbass). Mastering the production of pitch (electrode) coke is important not only in the sense of expanding the raw-material base, but also in the sense of improving coke quality: 1) lower ash content; 2) increased strength; 3) high yield of coarse-lump coke. In addition, productivity per ton of raw material is greater when coking coal-tar pitch than when coking pitch from petroleum residues.

Table 1 gives a comparative characterization of pitch coke and coke from petroleum residues.

Table 1.

Comparative characterization of pitch coke and coke from petroleum residues.

Without presenting in the present article detailed characteristics of the pitch raw material and the results of its experimental coking in a crucible and retort, and of industrial coking in coke ovens (we refer to the original sources), it is necessary to state, on the basis of the experimental material, that the statics of the coking processes have been studied quite fully (maximum temperature of evolution and composition of products), but the kinetics of the process (duration of coking, intensity of gas evolution in the various periods of coking, and other phenomena), which would make it possible confidently to develop a rational design for an industrial installation, have not been sufficiently studied on a production scale.

Therefore, the introduction of production of pitch (electrode) coke in the reconstructed Olivier–Piett system coke ovens at the Kemerovo Coke-Chemical Plant makes it possible, in addition to the experience of industrial coking at the Staro-Makeevka Plant, to construct a rational technological coking regime in ovens specially designed for this purpose.

III. Technological scheme of the installation for the production of pitch (electrode) coke.

The following principles were laid as the basis for developing the technological scheme for the production of pitch (electrode) coke at the Kemerovo Coke-Chemical Plant:

1. Transportation of liquid pitch is, where possible, by gravity or under pump pressure; extrusion of liquid pitch under the pressure of water steam is not used.

2. Charging of liquid pitch into the ovens is batchwise. With an overall coking duration of 24 hours, charging is carried out over 10 hours, approximately 1 ton of pitch every hour and a half.

3. Coking of pitch is carried out in Olivier–Piett system coke ovens (12 ovens), adapted for charging liquid pitch.

4. Condensation of tar vapors from the pitch gas is carried out in a barillet by intensive irrigation of the barillet with water. The standpipes from the ovens to the barillet are kept as low as possible in height in order to avoid condensation of tar vapors before the barillet and clogging of the standpipes. In view of this, the standpipes and barillet of the old coke ovens proved unsuitable.

5. The pitch gas is combined with the direct coal-coking coke gas and therefore is not subjected to purification separately from the coke gas.

6. Recovery of pitch tar from the barillet water is carried out by settling and melting in special apparatus (mixers and clarifiers).

In the structural development of the project, the design materials of the Kharkov Coal-Chemical ...

Institute (UKhIN) and the operating characteristics of the unit at the Staro-Makeevka plant.

The technological scheme developed in the design for the Kemerovo plant is as follows (see Fig. No. 1—Axonometric view of the pitch-coking unit).

In the tar-distillation shop, liquid pitch is forced out by steam at a temperature of 200°C into a thermocistern and delivered to the pitch receivers in this thermocistern, mounted on a four-axle railway car. The capacity of the cistern is 50 m³; the length of the cylindrical part is 7310 mm; the diameter is 2950 mm; the thickness of the insulation is 120 mm; the insulation material is asbestos.

From the thermocistern the pitch flows by gravity (pitch-line slope 0.020) into 2 heated pitch receivers. The pitch receivers are in one common setting. They are heated by separate gas-fired remote furnaces using coke gas. The purpose of the heated pitch receivers is to warm the pitch to a temperature of 200°C. The capacity of each pitch receiver is 30 m³. The dimensions of the riveted steel shell of the pitch receiver are: length 7500 mm, diameter 2200 mm, wall thickness 18 mm. The first flues of the pitch receivers are lined with fireclay brick. The pitch receivers are located in a brick building, with a fire-resistant floor on reinforced-concrete beams. The floor level of the pitch-receiver building is “3051” mm relative to the level of the thermocistern rail head (for gravity flow of the pitch). Between the thermocistern and the pitch receivers there is a special bypass device of semi-oval cross-section, 1000 mm long, to accelerate emptying of the thermocistern.

The pitch heated in the pitch receivers is forced by gear pumps into a tubular preheater. The pitch pumps are located in a special brick building with a fire-resistant floor on reinforced-concrete beams (the pump house); in the pump house, in addition to the pitch pumps, there are piston steam pumps for pumping pitch tar from tar mixers and centrifugal pumps for supplying water to the barillet. The pump-house pit is 2940 mm below the rail-head level, to ensure operation of the pitch pumps under flooded suction. The pitch line from the pump house to the tubular preheater is arranged on external (above-ground) metal columns.

The tubular preheater is two-section, consisting of radiant and convection chambers. The purpose of the tubular coil is to heat the pitch to a temperature of 200°C. Such high preheating of the pitch is necessary because, first, at the furnaces the pitch is discharged from the pitch line by means of valves; the slightest cooling of the valves or clogging of them will lead to rapid solidification of the pitch; second, since the pitch is charged into the furnaces periodically, continuous circulation in the pitch lines is necessary; this circulation is carried out between the measuring tank and the pitch receiver, with a total pitch-line length of 150 m. The tubular coil is fired with coke gas (consumption 65 m³/hour). In the radiant part of the tubular coil there are 34 heating tubes, and in the convection chamber—

Installation for the Production of Pitch Coke

Fig. 16.

Labels visible in the schematic:

• Storage area for the production of pitch coke
• Direct coke-oven gas, 1100°
• Gas channel
• Light components
• Pitch
• Superheater
• Direct contact with water
• Pitch pipeline
• Pump B
• Pitch pipeline
• Direct contact with water
• Pitch pipeline
• Recirculation pitch line
• Steam pipeline
• Tar pipeline
• Main water line
• Mixer
• Preheater
• Pre-oxidizer
• [[unclear: label resembling “enricher”]]
• Pitch pumps
• Steam pipeline
• Recirculation line, direct
• Recirculation line to pumps
• Pitch withdrawal
• Recycled pitch
• Pitch receiver
• Branch line for supplying heated tank cars

Reconstructed “Olivier Plett” furnace for coking pitch.

1—Pitch collector. 2—Pitch-gas standpipe. 3—Pitch-gas babifilet. 4—Pitch-gas pipeline. 5—Steam supply to the coking chamber. 6—Coke-gas standpipe. 7—Coke-gas barillet. 8—Coke-gas pipeline. 9—Coking chamber. 10—Uprights. 11—Daunkers. 12—Measuring tank. 13—Pitch pipeline.

Fig. 2.

65 tubes; tube length 1300 mm, internal diameter 38 mm. In summer there may be no need to heat the pitch in the tubular heater; in that case the pitch is fed by a bypass line directly into the measuring tank, bypassing the tubular heater.

From the tubular heater the pitch is fed into a measuring tank located on the end concrete platform of the coke-oven battery. The purpose of the measuring tank is, first, to deliver pitch in batches to the coke ovens (750 kg each) and, second, to create the pressure necessary for conveying the pitch through the pipelines on the ovens. The pressure created by the pitch is about 1500 mm water column. The measuring tank, with a steam jacket, is provided with two inspection funnels. When the measuring tank is full, the pitch is returned through the circulation line back to the pitch receivers.

The pitch header on the ovens is provided with 12 valves for charging pitch into the ovens; one valve is provided for each oven; charging is carried out through one valve on the coke side. The slope of the pitch header is 0.020; diameter 100 mm, length about 12 m. The pitch header is provided with an external steam jacket; the valves are steam-heated. The design concept of the pitch line and valves was borrowed from the materials of the UkhIN project, but was redesigned accordingly in connection with the installation of the measuring tank on the ovens.

Additional equipment on the ovens. For coking pitch, 12 ovens of the Olivier-Piett system are intended, with the following dimensions: coking-chamber height 1.72 m, width 0.32 m, length 10.47 m; when 6 tons of pitch are charged, the height of the pitch layer is 1.53 m. In connection with this, the following additional equipment is installed: 1) a new barillet is installed on brackets of the anchor columns on the machine side of the battery. The need to install a new barillet is due to the arrangement of low standpipes (to avoid tarring and clogging of the standpipes with tar), intensive spraying, and the introduction of an independent operating regime for the ovens. 2) The standpipes are designed for special installation, similar to the shortened standpipes of Olivier-Piett ovens; however, it is more expedient to install Becker-type standpipes (of the type shown in the drawing, Fig. 2). The steam formed during the coking of pitch is removed from the ovens through the standpipes and the barillet into a gas main that is being newly installed. To secure the gas main on the ovens, a special frame metal structure has been designed. The pitch gas main is then connected to the direct coke-oven gas main. The installation of a special gas main for pitch gas (and not the introduction of the gas into the old barillet) is dictated by the need to have an independent operating regime for the pitch ovens. Between the pitch gas main and the pitch barillet an intermediate downcomer chamber is installed, sprayed with water to wash from the gas the condensing tar vapors. To clean the oven crown of soot and graphite, steam is supplied into the under-crown space.

The arrangement of the additional equipment on the ovens is shown in Fig. 2. (Reconstructed Olivier-Piett oven for coking pitch).

Condensation equipment. To separate the tar from the supernatant water coming together from the barillet and the down-comer chamber, two consecutively connected mixers and one clarifier are installed. The dimensions of the mixers (cylindrical tanks) are: length 9900 mm, diameter 2180 mm. In the mixers, tar and water are separated according to specific gravity; inside, the mixers are equipped with steam coils. The tar is pumped by steam pumps to the tar-distillation unit of the old plant; the supernatant water passes through the clarifier and is delivered by centrifugal pumps into the supernatant-water pipeline and, with the aid of nozzles, is sprayed into the barillet and the down-comer chamber.

The coke is discharged from the ovens by means of a pusher into a quenching car; for this purpose, the equipment for the old ovens is used without any additional alterations. For storage of pitch coke, a special pitch-coke warehouse has been designed, with a special platform for loading coke into railway cars by means of three belt mobile conveyors. The capacity of the warehouse is for three days’ output of the installation.

IV. Principal indicators of the technological calculation of the apparatus and equipment of the installation.

The capacity of the installation for producing pitch (electrode) coke has been determined from the conditions of obtaining pitch from the tar-distillation shop and from the duration of pitch coking adopted in the design, equal to 24 hours. The capacity indicators are given in Table No. 2.

Table 2.

Capacity indicators of the installation for pitch coking.

) Note:* In calculating the annual capacity, oven downtime for current repairs has been assumed at 25% of working time.

The number of Olivier-Cetta ovens reconstructed for pitch coking is 12, each with a useful capacity of 6 tons of pitch.

As indicated in the technological flow sheet, delivery of the liquid pitch is carried out in an insulated tank with a capacity of about 50 tons. Loading of the pitch into the thermal tank is carried out by displacement—

with steam from the pitch separator; the delivery of the liquid pitch into the pitch receivers takes place by gravity, through a special trough-shaped transfer device, which makes it possible to maneuver the thermocistern unit over a distance of 1 m; with a calculated rate of cooling of the liquid pitch, based on heat losses to the surrounding environment in winter, equal to 2.5 degrees/hour, and a minimum permissible temperature of cooling of the pitch in the cistern to 100° C, the thermocistern is covered with a layer of thermal insulation 130 mm thick.

The pitch receivers are installed in the form of two fire-tube boilers, enclosed in a common brick setting, with a total capacity of up to 75 tons; this capacity is justified by the need to ensure continuous circulation of pitch between the pitch receivers and the coke ovens. The furnaces in front of each pitch receiver are gas-fired, of the uptake type; the consumption of coke-oven gas for heating the pitch receivers is 65 m³/hour of coke-oven gas, with a thermal efficiency of the pitch receivers of 65%. The temperature distribution in the flues of the pitch receivers is as follows: temperature in the furnace 1100° C; temperature in the first (lined) flue—the fire tube—750° C; in the second flue—the side flue (unlined)—650° C, and the temperature in the third (lower) flue 400° C. The distribution of heating surfaces in the flues is as follows: in the 1st flue 2.97 m², in the second—1.3 m², in the third—3.82 m²; the total heating surface is 8 m². The chimney for both pitch receivers is one iron stack, 16 m high.

The pipelines for transferring pitch to the coke ovens and for return circulation are seamless steel pipes, 100 mm in diameter, with external steam heating in the form of a pipe 150 mm in diameter. At the places where compensators are installed on the overhead line, for ease of installation, instead of a steam jacket, steam chambers are installed, in which the compensators are also located. The calculated head loss in the pitch pipelines, including also the tubular furnace up to the measuring tank at the ovens, with a total length (along the developed line) of 250 m, is 35 m water column. Of this total length, 81 m falls on the external (overhead) line.

The coking regime is intended to be as follows: by means of the measuring tank, 750 kg of liquid pitch is charged into the oven through the pitch collector, with the valve above the oven open; after 1½ hours, another portion of 750 kg is charged, and so on. Thus, the number of batch charges is 8 over 12 hours. In the interval between batch charges, partial coking takes place; final coking is completed during the remaining 12 hours, since the full coking period is taken in the design as equal to 24 hours. The need for batch charging, according to the materials of UKhIN for the Staro-Makeevka coke-chemical plant and according to the instructions of N. A. Nikolsky, is due to the fact that during the coking of pitch there occurs a brief, vigorous evolution of gas; in order to avoid a strong incre—

of pressure in the coking chamber and of the plugging of the standpipes with tar during vigorous gas evolution, and batch charging was provided for. Special experiments carried out to study this phenomenon under laboratory conditions (the laboratory of the Department of Apparatus of the Tomsk Industrial Institute) clearly confirm this. Into an electrically heated furnace, preheated to 800°C, pitch was poured in an amount of 4 kg. During the first 2 hours gas evolution was slow, and then the gas began to be evolved vigorously, so that as a result an irrigated standpipe 75 mm in diameter could not cope with passing the gas through its open cross-section, and the gas, together with tar vapors, seeped intensively through the brickwork and through the flanges.

From the heat balance compiled for reconstructed ovens of the Olivier-Pietta system without regeneration, it follows that the heat consumption for coking 1 kg of pitch is 1050 cal., and the thermal efficiency is 35%. It is appropriate to note that the heat consumption for coking pitch in Becker-system ovens (according to literature data) in the USA is 18% lower, which is explained by the shorter coking period (16 hours instead of 24) and by heat regeneration in Becker-system ovens. In the USSR at the present time the production of pitch coke is carried out at the Staro-Makeevka and Kemerovo coke-chemical plants, and the use of flame ovens now under repair (Krivoi Rog) is also proposed.

During the period of operation of the ovens on liquid pitch, certain negative aspects of their operation came to light: thus, for example, in his article (Coke and Chemistry, Nos. 4–5, 1939), the representative of Glavkoks, S. Gorelik, points out:

Liquid coal-tar pitch corrodes the fireclay brickwork and the joints, creating leaks, which leads to the penetration of pitch into the burner flues, regenerators, and tunnel. The head brick of the chamber was especially subject to corrosion.

It was necessary to carry out systematic repairs of the oven—to replace the oven heads, to do deep raking-out of the joints, and to put in “patches” along the length of the partition up to 4 m².

In conclusion, the question is raised of the need to select an appropriate refractory composition—one capable of resisting the destructive action of liquid pitch at high temperatures.

V. Additional studies necessary for creating more rational equipment for the production of pitch (electrode) coke

In designing, a number of difficulties were encountered because of the absence of data on the behavior of pitch during transport, its preheating, and coking. Therefore, in the future additional studies are necessary, which should experimentally (on a laboratory and plant scale) provide additional mate-

materials for designing a more rational construction of thermal equipment. In particular, it is necessary to determine the coefficient of friction when liquid pitch flows through pipelines. At present, when pitch pipelines are designed, the value adopted for the coefficient of friction is taken equal to the coefficient of friction for tar. Knowledge of the magnitude of the coefficient of friction as a function of temperature would make it possible to establish the relationship between the expenditure of head and the degree of heating of the pitch. When liquid pitch is transported through pipelines, three means are used as motive forces: steam under a certain pressure, pumps, and gravity flow under the influence of a difference in levels. The use of steam is most widespread. In this connection there arises the need to study the influence of steam on the conditions of pitch coking: the duration of coking, the yield of coke, and the yield of gas and pitch tar.

The regime of pitch coking has also been little clarified. In American practice (according to the literature), liquid pitch is continuously poured into the oven for 3 hours; then the charging of pitch is stopped and coking takes place. In German practice (also according to the literature), solid lump pitch is charged into the oven; in the operating practice of the Staro-Makeevka coke-chemical plant the charging of pitch is by portions; the same method of charging has been adopted in the design for the Kemerovo coke-chemical plant. With the latter method of charging it is inevitable that the first portions of pitch are coked for the full period (24 or 36 hours), while the subsequent portions are coked for a shorter time and, finally, the last portion for only half of the total time. Under these conditions, uneven coking must be expected; unfortunately, careful observations of the quality of the coke have not been made.

In contrast to metallurgical coke, pitch electrode coke is not required to have pieces of a definite size; therefore, in order to increase the productivity of ovens for pitch coking, the law of the quadratic dependence of the productivity of heating (coking) on the thickness of the coal (pitch) is, in practice, more applicable than for ovens used in the coking of bituminous coal; that is, it is entirely logical to assume that pitch must inevitably be coked in a very thin layer. If at present pitch coking is carried out in ovens intended for the coking of bituminous coal, then it is obvious that in the near future there will inevitably arise the need to create entirely different oven designs, distinct from the standard types.

Also of interest is the problem of utilizing the gas obtained in the coking of pitch; the gas obtained has a composition different from coke-oven gas; pitch gas contains up to 75% hydrogen; therefore it is hardly expedient to mix coke-oven gas with pitch gas; this will entail the organization of an independent gas system at pitch-coking installations.

References

1. S. Petrov, Maidanovskaya et al.—On the question of manufacturing electrodes from the coal-tar pitch of Kuzbass coals. Journal Coke and Chemistry, No. 3, 1933, and Proceedings of the Siberian Physico-Technical Institute. Tomsk, vol. II, 1933.

2. I. Ya. Postovsky and V. N. Novikov,—On the characterization of pitches. Journal Coke and Chemistry, No. 8, 1934.

3. N. A. Nikolsky and M. A. Stepanenko,—Production of electrode coke from pitch in a plant installation by the UChIN method. Journal Coke and Chemistry, No. 10, 1931.

4. V. M. Kopeliovich,—Coking of coal-tar pitch for the purpose of obtaining low-ash coke for electrode production in the USA. Journal Coke and Chemistry, No. 4, 1935.

5. N. A. Nikolsky, M. A. Stepanenko, N. A. Kabachenko,—Coking of pitch resin. Journal Coke and Chemistry, No. 4, 1986.

6. V. M. Kopeliovich,—Results of the work of the Kharkov Coal-Chemical Institute on the occasion of the 20th anniversary of October. Journal Coke and Chemistry, No. 11, 1937.

7. S. Gorelik,—Production of pitch coke. Journal Coke and Chemistry, Nos. 4–5, 1939.

1. In carrying out the design, consultations were provided by: the head of the design-and-technical department of the Kemerovo Coke-Chemical Plant—M. P. Tokarev; full member of the Ukrainian Scientific-Research Institute—N. A. Nikolsky; and the chief technologist of the plant—engineer B. S. Filippov. Students Suslova and Shirokova worked as draftsmen. ↩