Intensification of the Granulation Process of Coal Blends for Coking
Abstract Generated abstract
This paper examines ways to intensify granulation of coal blends for coking, addressing the low productivity, excessive rolling time, and adhesion problems associated with earlier water or tar granulation methods. Laboratory experiments used a pan granulator and vibratory feeder to form nuclei from pre-moistened coal, while adding lower-moisture coal with a small kerosene additive to improve mobility and prevent sticking. The results indicate that OS and coking coals granulated better than gas and fat coals, and that selective granulation of suitable components in plant blends increased bulk density, with the best reported dry-basis increase reaching 12.6 percent. On this basis, the authors propose a modified coal-preparation scheme for the Kemerovo Coke-Chemical Plant and recommend semi-plant and plant-scale testing.
Full Text
INTENSIFICATION OF THE GRANULATION PROCESS OF COAL CHARGES FOR COKING
V. M. Vityugin, G. D. Speshchii, Yu. F. Lutsenko
(Presented by the scientific seminar of the Faculty of Chemical Technology)
In the technological processes proposed by various researchers for granulating coal charge with water and with tar, there are a number of major shortcomings that do not allow granulation to be used under production conditions. One of these shortcomings is the low productivity of the granulators, caused by the long rolling time. In addition, granulation with water requires an increased moisture content of the charge, which disrupts the rolling process.
The purpose of the present studies is to develop a more advanced and productive technology for rolling coal charge.
It is generally known that the binder for granulation can be supplied in three ways:
a) by spraying it with a nozzle onto the surface of the mass in the granulator,
b) by preliminary moistening of the charge,
c) by a combined method incorporating both of these methods.
A study of all three methods revealed the advantage of the preliminary-moistening method (greater strength, uniformity, lower moisture content). But the use of this method did not promise an increase in granulator productivity, since, at the high moisture content of the charge supplied for granulation, the mass adhered to the pan and the granulation process was disrupted. Granulation proceeded only at a low pan filling coefficient and with a long rolling time.
A solution was found in the use of a vibratory feeder and in creating a bed from charge of plant moisture content with a micro-addition of kerosene.
The use of the vibratory feeder made it possible to intensify the process of forming granule nuclei with a uniform distribution of moisture, while the use of a bed with a micro-addition of kerosene prevented the mass from adhering to the pan and increased the mobility of the mass; thus conditions were created for the normal course of the process.
For granulation, coals were used with the following particle-size characteristic: 91% of particles were 0–3 mm.
Granulation was carried out on a pan granulator 1 m in diameter, with stepwise variation of the speed from 15.5 to 25.5 rpm and smooth adjustment of the rim height from 90 to 140 mm. Granule nuclei were obtained on a vibratory feeder with stepwise variation of the vibration frequency from 1000 to 2000 oscillations/min and a constant amplitude of 12 mm.
Pre-moistened coal with a moisture content of 16–17% was fed to the vibratory feeder. Simultaneously, onto the rotating pan—
Table 1
| Coal grade | Amount of coal supplied to the vibrator, kg | Moisture content of coal supplied to the vibrator, % | Amount of coal supplied to the granulator, kg | Moisture content of coal supplied to the granulator, % | Sieve composition, %: +10 | Sieve composition, %: 7–10 | Sieve composition, %: 5–7 | Sieve composition, %: 3–5 | Sieve composition, %: 0–3 | Moisture content of granulated coal, % | Bulk weight of granules, kg/m³ |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Gas coal | 5 | 17.04 | 5 | 11.22 | 2.16 | 5.69 | 15.76 | 40.1 | 36.1 | 12.76 | 0.85 |
| Coking coal | 5 | 16.25 | 5 | 8.49 | 12.4 | 24.8 | 18.6 | 19.7 | 24.6 | 10.29 | 0.875 |
| Fat coal | 5 | 16.23 | 5 | 8.11 | 13 | 28.4 | 15 | 25.8 | 55 | 11.26 | 0.82 |
| OS with supply of 5 kg of ungranulated charge | 4.4 | 15.07 | 1 | 5.69 | 18.55 | 14.35 | 24.3 | 25.3 | 17.6 | 11.52 after charge supply 9.076 | 0.914 |
Table 2
| No. | Charge composition | Supplied to vibrator | Supplied to granulator | Additional | Granulometric composition, %: +5 | Granulometric composition, %: +3 | Granulometric composition, %: −3 | Moisture after granulation, % | Bulk weight, kg/m³ | Increase in bulk weight: on wet charge, % | Increase in bulk weight: on dry charge, % |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Coal G—40%, Zh—20%, K—20%, OS—20% | 50% charge | 50% charge | — | 22.69 | 23.41 | 53.9 | 11.14 | 825 | 10.7 | 6.4 |
| 2 | Same | 30%—G, 20%—OS | 50% | — | 26.4 | 21.8 | 51.8 | 11.22 | 825 | 10.7 | 6.25 |
| 3 | Plant charge: G—38%, Zh—16%, K—20%, OS—26% | 38%—G, 26%—OS | 36% | — | 29.33 | 23.4 | 46.83 | 11.6 | 833 | 11.8 | 6.8 |
| 4 | Plant charge: G—38%, Zh—16%, K—20%, OS—26% | 26%—OS | 13%—G, 26%—OS | 61% | 18.69 | 13.3 | 68.61 | 8.25 | 846 | 13.5 | 12.6 |
| 5 | Plant charge: G—38%, Zh—16%, K—20%, OS—26% | 38%—G | 26%—OS | 36% | 11.76 | 18.84 | 69.4 | 11.67 | 832 | 11.8 | 6.8 |
| 6 | Plant charge: G—38%, Zh—16%, K—20%, OS—26% | 40% | 20% | 40% | 15.55 | 16.9 | 67.55 | 10.54 | 805 | 8.1 | 4.5 |
coal with a moisture content of 7–9% and a kerosene microadditive of 1% was fed uniformly. Using this procedure, experiments were carried out on granulation of the following coal grades: G, OS, K₂, and Zh, which are part of the blend of the Kemerovo Coke-Chemical Plant.
The experiments were conducted as follows: coal of the required grade was weighed out on technical scales in an amount of 10 kg; one half by weight was moistened to 16–17% and fed to the vibrating feeder, while the other half was moistened to 7–9% and, after introduction of the kerosene microadditive, was fed to the plate. The moisture content was monitored by sampling. Coal was fed to the granulator for 5 min, then rolling was continued for another 1 min. After this the material was discharged, and an average sample was taken for moisture and screening by size classes. The density was evaluated by dropping the granulated coal from a height of 1.8 m. The experimental data are given in Table 1.
Analyzing these data, it may be noted that the best granulation is obtained with OS and K₂ coals, characterized by a higher degree of metamorphism. These same coals also yield the strongest granules. Coals of grades G and Zh granulated worse, with the poorest result obtained in granulating grade Zh coal.
The bulk density of the granulated blend decreased to some extent in comparison with the ungranulated blend. An increase in it is observed only after blending.
The second series of experiments was carried out on a plant blend, but with different variants of feeding to the vibrating feeder and the plate, without blending and with blending. The experimental data are given in Table 2.
The bulk density of the experimental blends in all cases proved to be greater than that of the plant ungranulated blend. The highest bulk density was 848 kg/m³; in this case the increase in bulk density, recalculated to the dry blend, was 12.6%, with a significant increase in the granulation rate. On the basis of analyses of the experiments carried out, a basic scheme of coal preparation using selective granulation was proposed to the Kemerovo Coke-Chemical Plant.
The existing scheme up to the batchers located after the silos remains unchanged. In all, 64% of the total coal mass is sent to granulation; 50% of it is fed to the vibrating feeder, and part of the gas coal is used as the bed. Coking and fat coals are sent for blending.
Thus, it is proposed to make use of the better granulating ability of OS coal, to compact into granules precisely those coals on whose coking this has a favorable effect, and also to maintain a ratio between the granulated and ungranulated parts of the blend close to the optimum in order to ensure the greatest possible increase in bulk density.
After the mixer, the scheme remains unchanged. Water and the microadditive may be supplied by spraying onto the material moving along the conveyor. Drying of the granules is proposed to be carried out using the heat released during dry quenching of coke.
It is proposed to test this technology under semi-plant and plant conditions.
The economic expediency of the proposed change in technology is explained by the fact that the costs of granulation are offset by an increase in the productivity of the installation, owing to densification of the coke-oven charge.