Study of the Effect of Heating Temperature on the Caking Capacity of Gas Coals and Their Mixtures with Certain Additives
Abstract Generated abstract
This study examines how heating temperature affects the caking ability of Kuznetsk gas coals and their mixtures with lean additives relevant to medium-temperature coking. Using Gebler softness numbers measured over a range of temperatures, the authors compare pure gas coals with mixtures containing coke dust and Anzher TS coal, and assess changes in plastic mass behavior and apparent thermal stability. The results indicate that lean additives generally reduce softness, but their effects depend strongly on temperature and additive type: TS coal can increase the thermal stability of the plastic decomposition products of Lenin gas coal G2, while coke shows a different, nonuniform leaning action. The authors suggest that these effects may reflect differences in wettability and chemical interaction during pyrolysis, with possible implications for reducing coke fissuring.
Full Text
Study of the Effect of Heating Temperature on the Caking Ability of Gas Coals and Their Mixtures with Certain Additives
I. V. GEBLER, N. M. SMOLYANINOVA
In connection with the study of the suitability of Kuzbass gas coals for medium-temperature coking, we carried out experiments to study the behavior of gas coals in the plastic state. Almost all existing studies on this question dealt with the study of the plastic properties of the above-mentioned coals mainly under the conditions of high-temperature coking. It seemed of interest to investigate the properties of coal in the plastic state at different temperatures, and especially at temperatures lower than those used in coking. It was of interest to subject to these investigations both gas coals in pure form and with additions of certain other coals. When the question of using gas coals for coking was studied, many investigators [1, 2, 3] noted the positive effect of a number of so-called “leaning” additives (coke dust, semicoke, anthracite, and coals of the additive type—PS, TS) on the quality of the solid pyrolysis residue. Taking this into account, it was of interest to test the effect of these additives on the plastic properties of gas coals at different temperatures.
The results of a study of the influence of heating temperature on the caking properties of a number of coals from the Kuznetsk Basin were published by us earlier [4]. A characteristic dependence of the softness numbers according to I. V. Gebler on the heating temperature was found, and an assumption was made regarding the possibility of using this dependence as an additional characteristic for selecting a charge.
The present work is devoted to studying the influence of certain “leaning” additives on the caking properties of Kuznetsk gas coals.
The technical analyses of the coals and additives taken are given in Table 1.
Table 1
| Mine name | Technological group | $W^a$ | A | $V^г$ | Button character |
|---|---|---|---|---|---|
| Mine named after Yaroslavsky | G1 | 2.01 | 10.91 | 36.81 | Caked, moderately dense |
| Mine named after Kirov | G2 | 1.62 | 6.65 | 42.08 | Caked, fused, weakly swollen |
| Mine name | Technological group | \(W^a\) | \(A^c\) | \(V^r\) | Coke button characteristics |
|---|---|---|---|---|---|
| Mine No. 3, seam 3rd Inner | CC | 1.82 | 7.33 | 32.50 | Caked, dense, unswollen |
| Mine “Fizkulturnik” | TC | 0.80 | 7.04 | 16.14 | Caked, dense, unswollen |
| Coke from the Gubakha Coke-Chemical Plant | — | 0.18 | 13.93 | 1.02 | — |
The working procedure was the same as previously [4]. The heating time of the coal at different temperatures was represented by us by the following values (Table 2).
Table 2
| Temperature, °C | 300 | 400 | 500 | 600 | 700 | 800 | 900 |
|---|---|---|---|---|---|---|---|
| Heating time, min. | 27.0 | 19.0 | 13.6 | 10.2 | 7.6 | 5.0 | 3.35 |
The first experiments to determine the softening numbers at different temperatures were carried out with coal G1 in pure form and then with the addition of 10% coke, ground so as to pass through a sieve of 900 openings/cm². These data are presented in Table 3.
Table 3
| Experiment No. in order | \(T^\circ\)C | Average softening numbers (M) for charges: 100% G1¹) | Average softening numbers (M) for charges: G1 + 10% coke |
|---|---|---|---|
| 1 | 350 | 10 | — |
| 2 | 400 | 93 | 35 |
| 3 | 450 | 143 | 98 |
| 4 | 500 | 168 | 120 |
| 5 | 550 | 131 | 104 |
| 6 | 600 | 112 | 85 |
| 7 | 650 | 107 | 80 |
| 8 | 700 | 99 | 72 |
| 9 | 800 | 83 | 60 |
| 10 | 850 | 73 | — |
The addition of 10% coke powder reduces the absolute value of the softening numbers, but the nature of their dependence on temperature remains the same as for pure gas coal.
¹) This coal proved to be partially oxidized.
From an analysis of the indicated data it can be seen that, at a lower temperature, gas coal is capable of accepting a larger amount of additive without greatly reducing the caking properties of the mixture.
The second series of experiments was carried out with Leninsk coal G2, in which no traces of oxidation were found, and also with coals of grade SS (Kiselevsk coals) and of technological group TS (Anzherka coals).
The effect of temperature on caking ability was studied for individual coals (G2, TS) and for mixtures of G2 with 10% TS and 50% TS, by determining their softness numbers at various temperatures (from 350 to 800°). The results of the experiments are given in Table 4.
Table 4
| No. | T°C | 100% G2 | G2 + 10% TS | G2 + 50% TS | 100% TS |
|---|---|---|---|---|---|
| 1 | 350 | 0 | — | — | — |
| 2 | 380 | 18 | — | — | — |
| 3 | 385 | 23 | 24 | — | — |
| 4 | 400 | 85 | 32 | 13 | 0 |
| 5 | 450 | — | 67 | — | — |
| 6 | 500 | 175 | 104 | 50 | 26 |
| 7 | 550 | 179 | 130 | 55 | — |
| 8 | 600 | 161 | 123 | 55 | 29 |
| 9 | 650 | — | 110 | — | — |
| 10 | 700 | 90 | 85 | 54 | 34 |
| 11 | 800 | 75 | 66 | 47 | 24 |
As can be seen from the table, the addition of 10% TS coal somewhat lowers the softness numbers, while the addition of 50% TS lowers them very strongly. Gas coal and mixtures in which it predominates differ greatly in softness numbers from TS coal.
Experiments to determine the properties of the plastic mass of coals G2 and SS showed that the “continuity” of coal G2 with SS is much worse than with TS coal, which may be explained from the standpoint of B. A. Onusaitis [5], who points to the great importance, for the caking of a coal mixture, of good wetting of the surface of a poorly softening coal by the liquefied layer of a well-softening coal. Evidently, for TS and SS coals we have an example of different wettability of their grains by the softened mass of coal G2.
Table 5
| No. | Coals and mixtures | Decrease in caking ability, in units \(M/100^\circ\text{C}\), in the temperature interval from the maximum to 800° |
|---|---|---|
| 1 | G1 | 27·3 |
| 2 | 90% G1 + 10% coke | 20·3 |
| 3 | G2 | 38·3 |
| 4 | 90% G2 + 10% TS | 25·6 |
| 5 | 50% G2 + 50% TS | 4·40 |
| 6 | TS | 4·57 |
Table 5 gives data which, in our opinion, characterize the thermal stability of the decomposition products of various coals and their mixtures; we expressed this as the decrease in units of \(M\) per \(100^\circ\text{C}\) in the temperature interval from the maximum for the given coal or mixture to \(800^\circ\).
In Fig. 1 these data are presented graphically for the mixture G2 and TS.
It is evident from this graph that the increase in the thermal stability of the plastic decomposition products of the organic substance of this mixture does not obey the law of additivity and can, in our opinion, be explained only from the standpoint of chemical interaction of the products of thermal transformation of these two coals at high temperatures. This proposition is confirmed by consideration of the thermal stability of the decomposition products for G1 and for G1 + 10% coke. In this case the thermal stability of the liquid products of transformation of the organic substance of the mixture G1 with 10% coke has almost not increased, compared with coal G1, since coke does not yield an appreciable amount of decomposition products capable of entering into chemical interaction with the melt of coal G1.
Fig. 1. Dependence of the thermal stability of the products of thermal decomposition of coal G2 on the addition of coal TS.
In Fig. 2 the leanifying action of various additives as a function of temperature is shown graphically, presented in the form of the percentage decrease in \(M\) from a definite amount of the given additive at each temperature. If I. V. Gebler [2] noted a smaller leanifying action of coke compared with non-caking coal (grade T), then the curves in Fig. 2 show that the leanifying action of coke is less than the leanifying action of coal TS only at temperatures below \(600^\circ\) (curves for G1 + 10% coke and G2 + 10% TS), whereas at temperatures of about \(850^\circ\) the leanifying action of coke becomes so large that the addition of 10% coke dust lowers \(M\) by as much as the addition of 50% coal TS lowers it.
Fig. 2. Leanifying action of various additives as a function of temperature.
Attention should be paid to the difference between the curves of the percentage decrease in caking ability as a function of temperature as a result of the action of the addition of coal TS and of coke. If, with increasing temperature, the percentage decrease in \(M\) upon addition of coal TS (in amounts of 10 and 50%)
decreases uniformly,^1) then the corresponding curve, with the addition of coke, has a minimum lying close to the maximum of the dependence of \(M\) on temperature.
This difference, in our opinion, may be explained as follows. The considerable “leaning” effect of TS coal at low temperatures is due to the fact that this coal, having greater thermal stability and a higher initial softening temperature, acts at these temperatures as an “infusible” filler; as the temperature is raised, this role naturally disappears, down to the smallest values.
Coke, however, despite its absolute infusibility, cannot be regarded as a completely inert component. It can also affect the chemical reactions occurring during coal pyrolysis. This influence will be the stronger, the closer the chemical nature of the coke is to the nature of the products interacting with it. It is precisely this phenomenon that we should observe in two cases—at the beginning of softening, when the chemical nature of the coke is close (relatively) to the nature of the condensed aromatic substance of the coal, and at higher temperatures, when condensation reactions are strongly manifested in the softened coal substance; and, finally, most likely, the nature of the coke will differ from the nature of the reacting products precisely at the moment of maximum softening of the coal.
Thus, on the basis of the data discussed above, we may conclude that the addition to Lenin gas coal G2 of a “leaning” additive in the form of Anzher TS coal greatly improves the properties of the plastic mass, increasing its thermal stability.
In our opinion, this should have a positive effect on the fissuring of the coke, since many investigators consider the low thermal stability of the plastic mass of gas coals to be one of the indirect causes of high fissuring [1, 6].
REFERENCES
- Gryaznov N. S. Coking of Kuzbass Gas Coals. Metall[[unclear: remainder not visible]]
- Gebler I. V. Izvestiya AN SSSR, OTN, No. 6, 1948.
- Podbelskii G. N. Scientific works on problems of coal processing and quality. Collection 2, Ugletekhizdat, 1952.
- Gebler I. V., Smolyaninova N. M. Coke and Chemistry, No. 3, 1957.
- Onusaitis B. A. Izvestiya AN SSSR, OTN, No. 1, 1947.
- Vekhov V. A., Gorovoi G. P. Transactions of the Chemical-Metallurgical Institute, issue 6, 1951.
^1) An increase in the leaning effect of TS coal with decreasing temperature was also noted by V. A. Vekhov and G. P. Gorovoi [6].