ON THE ISSUE OF INCREASING THE BULK DENSITY OF THE CHARGE IN A COKE OVEN CHAMBER¹

I. V. GEBLER, N. I. GNEDIN

Compaction of coke charges, that is, an increase in the bulk density of the charge in a coke oven chamber, as is known, has a twofold significance.

First, when the charge is compacted, the productivity of coke ovens increases without increasing the existing capacities. Taking this circumstance into account, and also taking into account considerations of a technological nature, directive instructions from Glavkoks provided for a certain increase in the coking period (with some reduction of the temperature in the flues), which, of course, inevitably leads to a decrease in the productivity of coke installations.

The latter circumstance can be compensated chiefly by increasing the loading of the charge, that is, by compacting it in the coke oven.

Second, compaction of charges proceeds in parallel with their relative depletion with respect to caking capacity; that is, the higher the bulk density of the charge, the leaner it may be in caking capacity without reducing the quality of the coke under the same coking-regime conditions.

At the greatest degree of charge compaction, when the bulk density reaches 1100–1150 kg/m³, which can be achieved by tamping, even charges very lean in caking capacity, as shown by the work of N. P. Chizhevsky [1], yielded good coke, whereas from the same charges with ordinary top charging the coke obtained was so friable that it was impossible to push it out by machine and it had to be extracted from the oven by hand.

The indicated works of N. P. Chizhevsky, and later of other investigators as well, are of extremely great significance in general and, in particular, for eastern plants, where to this day it is still necessary to introduce into the charges a large percentage of fat coals.

The bulk density of crushed coal depends on its moisture, temperature, and granulometric composition, and, for charges loaded into a coke oven, also on the loading conditions. The dependence of bulk density on moisture is well known. The bulk density of wet coal decreases up to a moisture content of 7–10%. Further incre—

The increase of moisture in the charge leads to an increase in bulk density. However, the use of charges with a high moisture content does not seem feasible, if only for the reason that, as it increases in the charge, the coking period increases by approximately 0.5 hours for each 1% of moisture, which leads to a reduction in oven turnover and, consequently, to a decrease in plant productivity.

The influence of temperature on the magnitude of the bulk density of crushed coal in the direction of increasing it is manifested at temperatures below 0°, i.e., when the moisture passes into the solid state, provided that freezing does not occur. Observations carried out at plants in this direction have shown, however, that during the usual passage through coal preparation the coal is not overcooled even under severe winter conditions, and that on an inclined conveyor the charge is cooled below 0° only when the outside air temperature is not less than 30°C \[2\]. Thus, the use of freezing of the charge for a seasonal increase in bulk density requires special operating conditions in coal-preparation shops.

In addition, possible difficulties are noted when using charges cooled below zero, owing to their increased flowability.

In the Journal of the Chemical Industry \[3\] an abstract was published giving a description of experiments on coking coal with different grain sizes, in which the bulk density of the charge was determined. From dry coal (volatile matter yield 26.2%, ash 7.4%) samples with different grain sizes were prepared (Table 1).

Table 1

Of the individual samples, a high bulk density was obtained with sample No. 2; the maximum bulk density was obtained with sample No. 9, when the air spaces of the coarse-grained coal were filled with coal “flour.”

The use of coal of such coarse crushing for coke charges, as is known, is not practiced, but similar relationships are also observed for coals with a greater degree of crushing, and this is the densifying effect of differential grinding. However, the possibility of such a method is very limited under the operating conditions of coal-preparation shops.

To increase the bulk density of the charge, it has been proposed to wet it with small quantities, 0.1–0.3%, of hydrocarbon liquids—kerosene and certain oils from coke-chemical production (the method of the ENIN, Academy of Sciences of the USSR). Of such oils, the most readily available in practice for plants should be considered filtered anthracene oil, after the separation of crude anthracene. The addition of such oil is recommended in the amount of 0.3 to 0.8%, and the bulk density of the charge (with a moisture content of 4.9–5.8%) should increase by 5–7.9% [4,5].

On average, the yield of tar during coking is 3% of the working charge, and the amount of anthracene oil obtained in the distillation of tar is about 16–20%; thus, the yield of anthracene oil relative to the charge is 0.5–0.6%. Therefore, an addition of anthracene oil greater than 0.6% is not feasible for a plant using its own oil. At the lower of the indicated limits, 0.3%, one half of the entire oil production is consumed. At the same time, in the ordinary practice of coal-preparation shops at eastern plants, the increase in bulk density, according to testimony of the technical management of the plants, amounted to 150–200 kg per oven, i.e., at most 1.2%, and not 5%, as indicated in the literature. The reason for this, apparently, lies in the great difficulty of satisfactorily mixing the charge with such a small amount of oil under production conditions, especially in cold weather, at a charge temperature of, for example, +5°C, ±2°C, when the oil thickens and, with the increase in its viscosity, achieving complete mixing becomes still more difficult.

In addition, the consumption of anthracene oil, as well as of other oils (kerosene), for oiling the charge, if only its compaction in the coke-oven chamber is pursued thereby, is hardly expedient also because it leads to an increase in production cost.

Thus, for anthracene oil, with its cost of 670 rubles per ton and with the addition of oil in an amount of 0.3%, the additional expenditure per ton of charge will be:

\[ 670 \times 0.003 = 2.01 \text{ rubles.} \]

If the increase in the bulk density of the charge with an addition of 0.3% anthracene oil is taken as 2%, and the coke yield as 75% of the working charge, then the additional profit from the increase in the amount of metallurgical coke obtained when the amount of charge is increased by 2%,¹ at a coke price of 120 rubles per ton, relative to one ton of charge without oiling, will be:

\[ (120 \times 0.75)(1.0117 - 1) = 1.05 \text{ rubles;} \]

whereas the cost of the oil per 1 t of charge will be:

\[ 670 \times 0.003 = 2.01 \text{ rubles.} \]

Thus, the cost of oiling the charge is not covered by the profit from the additional coke and, under the conditions of the example taken from practice, costs production 0.96 rubles per 1 t of charge. Consequently, from an economic standpoint, the use for charge compaction even of such an oil product as anthracene oil—the most readily available at coke plants—is unprofitable.

Compaction of the charge in the chamber of a coke oven can be achieved—

purely by mechanical means. The greatest compaction is achieved, as is known, by tamping the charge with the aid of a special machine outside the oven chamber, with subsequent introduction into it of the coal block obtained in this way; in this case the weight of a unit volume of coal can be brought up to \(1200\ \mathrm{kg/m^3}\) [6].

With ordinary top charging of ovens, the bulk density of the charge may vary with the conditions of charging and leveling.

According to P. L. Hertzberg [7], it is impossible to adopt any single charging method that would be generally optimal. The sequence of emptying the bunkers is not the same with one or two standpipes, in view of the resistance of the gas flows. The magnitude of the bulk density is influenced by the height and density with which the bunkers of the charging car are filled with charge, and by the degree to which graphite has been cleaned from the charging holes. The charging method has no effect on the bulk density of the charge when the moisture content is less than \(4\%\).

With regard to leveling, the literature indicates [8] that the insertion of the leveling bar into the chamber should be increased gradually from 2–3 to \(8\ \mathrm{m}\) with the discharges always full; this leads to a gradual redistribution of excess amounts of coal and reduces its ejection by the leveling bar.

From the practice of coke-oven operation it is known that some operators of charging cars give a larger charge than others. Thus, for example, at one plant a case was recorded in which the charge (in summer) loaded by one of the operators was \(2.7\%\) greater than the planned amount.

Various working methods are observed in leveling: the number of double movements (insertion of the leveling bar into the chamber and its withdrawal) ranges from 8 to 15, with varying degrees of extension.

Systematic control of the charging and leveling process is not being carried out properly, and optimal conditions for this, generally speaking, have not been developed. Meanwhile, rationalization of the charging process in order to increase the bulk density and, accordingly, the tonnage of the chamber should be the simplest and cheapest means for this purpose.

Leveling in itself leads to compaction of the charge, and in this respect the design of the leveling bar is important. Apparently the most successful is the leveling bar of engineer B. S. Filippov, which has a number of pressing devices (“irons”) in the form of triangular prisms arranged along the working length of the leveling rod. According to data from one plant, such a leveling bar gives compaction of the charge of from 2 to 3% in comparison with a leveling bar of ordinary design. The compaction produced by the leveling bar does not penetrate deeply; it is concentrated only in the upper layers of coal directly under the leveling bar. This is evident from the figures given to characterize the compacting action of the leveling bar under the influence of sagging of the leveling rod [9]. Data on this matter are given in Table 2.

Table 2

Change in the bulk density of the charge in the chamber of a coke oven

As can be seen, the bulk density of coal is not the same either along the length or over the height in the coke-oven chamber. The greatest bulk density of coal is observed in the layers at a distance of 0.5 m from the top of the charge. In this case, the increase in bulk density occurs due to the pressing forces of the bar leveling the coal charge. A certain increase in bulk density is also observed in the very lowest layers of the coal charge, which occurs because of compaction of the charge as it falls from the charging car. At a distance of 1.4 m from the top of the charge, the bulk density of the coal is the lowest.

It is known that compaction of a coal charge by tamping is carried out layer by layer, with layer thicknesses on the order of 300 mm; with a greater layer thickness, the degree of compaction decreases, since the pressure acting on the surface of the crushed coal is gradually expended in overcoming friction between its particles.

The data on changes in the bulk density of the coal charge in the coke-oven chamber, given in Table 2, are confirmed by studies by other authors who have carried out work in this direction.

Proceeding from these circumstances, it is necessary to keep in mind the possibility of the favorable action on the coal charge in the coke-oven chamber, along its length, of the use of one or two additional leveling bars. This measure should contribute to significant compaction of the charge and to equalization of its bulk density. As a result, there should follow an increase in coke yield when using charges of a definite composition, as well as the possibility of introducing larger quantities of lean coals for coking without reducing the quality of the coke obtained.

The latter circumstance is of especially great importance in connection with the shortage of coking and fat coals used for coke production.

Proceeding from the considerations indicated, we carried out work to study the compacting effect on coke charges by means of certain methods. In the work carried out, special attention was paid to the selection of such methods of compacting coke charges as would not complicate the technological process or, in general, the servicing of coke-oven installations.

The work was carried out with a model of a coke-oven chamber corresponding to the chamber of a PK oven in the hot state at 1/10 of the natural size of the latter, i.e., it had the following dimensions: length 1.25 m, average width 0.039 m, height 0.31 m (Fig. 1).

Fig. 1. Model of a coke-oven chamber, 1/10 natural size.
A—shutter for emptying the chamber; Б—shutters at the charging hoppers; В—common shutter for all hoppers.

The chamber model had four charging hoppers, which could be emptied either simultaneously, by opening one common slide gate, or selectively, for which purpose each hopper was also provided with a separate slide gate. Discharge of the oven chamber was carried out by means of the sliding shutter A, which served

under the floor of the oven chamber. The discharged coal fell into a box located directly under the oven floor, as did gate A, along the entire length. The box could also be freely pulled out; therefore the weighing of the charge unloaded from the oven chamber was carried out without any difficulty after each experiment.

In all the experiments conducted, the charge intended for loading into the bunkers was selected according to the following sieve composition:

The moisture content of the charge was 4.00%.

In layer-by-layer leveling, carried out with three levelers, each of which was located at 1/3 of the height of the oven chamber, the charge was loaded in three stages.

In the first stage, the charge was loaded only to one third of the oven height, with simultaneous partial discharge from all four charging holes.

The leveler was constructed in the form of a rod with smoothing shoes.

The form of distribution of the charge after the first discharge to the indicated height is shown in Fig. 2¹.

Fig. 2. Arrangement of the charge in the chamber after loading 1/3 of the charge.

After the first discharge of the charge, it was leveled with from 3 to 9 movements. One movement is taken to mean the insertion of the leveler into the oven and its withdrawal back. Then a second loading of the charge into the oven chamber was carried out, already to 2/3 of its height, simultaneously from 4 charging holes, after which another leveling followed with the same number of movements.

The general appearance of the arrangement of the charge after its second discharge is shown in Fig. 3.

Subsequently, the final loading of the oven chamber from all the hoppers was carried out (Fig. 4), followed by the final leveling.

Fig. 3. Arrangement of the charge in the chamber after lower leveling and loading of the second portion of the charge.

Single-pass (ordinary) leveling with one upper leveling bar was also carried out after all four hoppers had been emptied to refusal.

The change in the bulk density of the charge as a function of the leveling method is presented in Table 3.

Table 3

As can be seen, the number of passes of the leveling bar has a substantial effect on the compaction of the charge.

Taking nine double movements as normal leveling, with three leveling bars we obtain, all other conditions being equal, an increase in the bulk density of the charge of 5.3%.

If the bulk density of the charge ($W = 6\%$) in ovens with the leveling bar of Engineer Filippov’s system is approximately 760 kg/m³, then with three leveling bars, assuming a 5.3% increase in density, it will be 806 kg/m³.

In order to take into account the corresponding increase in coke yield, it is necessary to allow for the technological coking period, which, as is known, lengthens with an increase in the bulk density of the charge.

The duration of the coking period (\(Z\) hours), depending on the bulk density (\(i \, \mathrm{kg/m^3}\)) of the contents of the chamber, changing from the state of coal to the state of coke, may be expressed as follows:

Fig. 4. Arrangement of the charge in the chamber after completion of charging and the last leveling.

\[ Z=\psi i, \]

where

\[ i=\frac{i_{\text{coal}}+i_{\text{coke}}}{2}, \]

and \(\psi\) is a quantity depending on the width of the oven, the temperature, the thermal conductivity of the coal, the coke, and the heating wall, and in the present case remains constant.

The bulk density of coke in the chamber may likewise be taken as constant and equal to \(950 \, \mathrm{kg/m^3}\).

For the value of \(i\) we have:

\[ \text{with one leveling, } \quad i_1=\frac{760+950}{2}=855 \, \mathrm{kg/m^3}; \]

\[ \text{with three levelings, } \quad i_3=\frac{806+950}{2}=878 \, \mathrm{kg/m^3}. \]

Since \(\psi\) in the present case is constant, then

\[ \frac{Z_3}{Z_1}=\frac{i_3}{i_1}. \]

Taking \(Z_1\) (with one leveling) as equal to 14 hours, we find the coking period with three levelings (\(Z_3\)):

\[ Z_3=\frac{Z_1 \times i_3}{i_1}=\frac{14 \times 878}{855}=14.38 \text{ hours}. \]

Let the useful volume of the oven chamber be \(20.19 \, \mathrm{m^3}\), and the gross yield of coke be 75.0% of the weight of the charge; the number of ovens discharged per day will be:

with one leveling bar

\[ \frac{24}{14}=1.71 \text{ ovens,} \]

with three leveling bars

\[ \frac{24}{14.38}=1.67 \text{ ovens.} \]

The amount of coke per oven per day will accordingly be:

with one leveling bar

\[ \frac{20.19 \times 760 \times 0.75 \times 1.71}{1000}=19.68 \, t, \]

with three leveling bars

\[ \frac{20.19 \times 806 \times 0.75 \times 1.67}{1000}=20.38 \, t. \]

Thus, the productivity of the ovens in terms of gross coke output with triple leveling increases by 3.55%.

By an analogous calculation it can be determined that, with two leveling bars—middle (at \(2/3\) of the height from the floor) and upper—and with compaction of the charge by 3.9%, the increase in gross coke output is 2.39%.

As can be seen, when two additional leveling bars are used, the effect obtained is one and a half times greater than with one additional middle leveling bar.

An increase in the productivity of coke ovens in terms of coke output by 3.55%, with only a slight additional expenditure of energy for the operation of the additional leveling bars, is of considerable importance; for example, for a plant with a capacity of \(5000 \, t\) of coke per day, the additional amount amounts to \(177.5 \, t\) per day, or \(53{,}250 \, t\) per year, including approximately \(50{,}055 \, t\) of metallurgical coke; at a price of 120 rubles per ton for the latter, this gives 6 million rubles per year additionally.

The implementation of three-layer leveling in practice presents no difficulties and can be carried out either by installing two additional leveling rods, similar in design to the ordinary leveling bar, or in the form of a frame moving up and down, carrying one leveling rod. The design of the coke pusher permits both, but the second variant is apparently more convenient.

In the present work, questions of design and installation are not considered.

According to the Coke Chemist’s Handbook¹, the ordinary leveling process, with respect to time, proceeds as follows:

1) hooking the door of the leveling hatch onto the winch hook — 10 sec,
2) opening the leveling hatch — 6 sec,
3) leveling — 90 sec,
4) closing the leveling hatch — 28 sec,

Total: 134 sec.

Consequently, very little time is spent on it—slightly more than two minutes—and increasing this time to 6–7 minutes should not cause difficulties; this can also be confirmed by the fact that, in practice, charging crews work differently, and, when timing the leveling process at some plants with a stopwatch in hand, we often observed considerably longer times than that indicated above as normal.

The leveling process itself should be automated, as is done in the coke shops of the Zaporozhye and Zhdanov plants [11].

Conclusions

1. An increase in the bulk density of the coal charge in the chamber of a coke oven can be achieved by layer-by-layer leveling during the charging of the charge, without the addition of any substances that promote dense packing of the coal grains.

2. With layer-by-layer leveling, a more uniform distribution of coal over the height and length of the oven chamber is achieved, which, in turn, contributes to obtaining coke of more uniform quality.

3. Layer-by-layer leveling leads to an increase in the productivity of coke ovens in terms of coke, all other conditions being equal. With three-layer leveling this increase amounts to as much as 3.55%.

4. Since leveling is a short-term process and the power of the leveling bar motor, when it is moved by means of a cable wound on a drum, is 27–30 kW, the energy consumption for additional leveling is negligible.

Literature

1. Chizhevsky I. P. Coke and Chemistry, No. 10, 1932.
2. Agroskin A. A., Zagrobelnaya V. S. Izvestiya of the Academy of Sciences of the USSR, Department of Technical Sciences, No. 1, 1947.
3. Journal of the Chemical Industry, No. 5–6, 1910.
4. Agroskin A. A. and Pitin R. I. Izvestiya of the Academy of Sciences of the USSR, Department of Technical Sciences, No. 2, 1946.
5. Agroskin A. A. and Loskutova E. N. Izvestiya of the Academy of Sciences of the USSR, 1947.
6. Feldman Ya. and Meikson L. Coke and Chemistry, No. 4, 1932.
7. Gertsberg P. L. Coke and Chemistry, No. 5, 1935.
8. Coke Chemist’s Handbook, 4, 398. 1939, Scientific-Technical Publishing House of Ukraine.
9. Coke Chemist’s Handbook, 4, 339. 1939.
10. Coke Chemist’s Handbook, 4, 420. 1939.
11. Shvarts G. A. Coke and Chemistry, No. 2, 1955.

1. Coke Chemist’s Handbook, p. 420, 1939. ↩↩↩↩