On the Granulation of Glass Batches with a High Content of Alkali Components

V. M. Vitogin, L. G. Lotova, V. A. Trofimov

(Presented by the scientific seminar of the Department of General Chemical Technology)

Improving the technology for preparing the batch is one of the most important ways of intensifying the melting process. This direction includes a number of methods differing in their nature and complexity of implementation: moistening of the batch, fine grinding of individual components, briquetting, sintering, and granulation. All these methods are aimed at preventing dusting, stratification, and segregation of the batch during transportation and storage; at increasing the uniformity of the batch and, consequently, the homogeneity of the glass melt; and ultimately at increasing the productivity and service life of glass-melting furnaces.

Unfortunately, so far only moistening and briquetting of batches have been introduced, and even then only in low-tonnage production of special glasses [1, 2].

The simplest and most effective method—granulation of batches—despite its obvious advantages, is still at the research stage. In contrast to briquetting, this method does not require expensive pressing equipment and can be used for large-tonnage glass production.

Some disagreements among researchers regarding the rate of glass melting on granulated batch are explained by differences in the technological schemes tested. Some researchers (Gur’yanova [3], Leffler [4], Demidovich [5], Knapp [1]) either ground the batch or introduced binding additives into it: liquid glass, starch, Portland cement, hydrated lime. Others (Yamamoto, Komatsu [6]) replaced a significant portion of the soda (about 50%) with caustic soda.

Differences in granulation conditions naturally led to the production of granules with different properties in terms of moisture content, density, size, uniformity, and degree of recrystallization of the soluble components.

The imperfection of the technology is the main obstacle to introducing granulation into glass production. Above all, this concerns the difficulty of maintaining continuity in a high-capacity process, the frequent need to introduce expensive additives, the high moisture content of the granules (from 17 to 28%), and the need for a drying operation.

In the present work, several ways of eliminating these shortcomings have been analyzed. As the object of study, one of the

of the most widely used batches for producing window glass (the batch for producing window glass at the Anzhero-Sudzhensk Glass Plant). The composition of the batch and the particle-size distribution of the components are given in Table 1.

Table 1

Batch composition and particle-size characteristics of the components

Studies have shown that a glass batch with a significant content of alkaline components (up to 21%) can be granulated without additives at a temperature and moisture content of the granulated mass of, respectively, 30–32°C and 14%.

The granulation process is carried out by forming lumps—granules—from a previously moistened (approximately to the optimum moisture content) hot batch, with their structure being fixed during crystallization of the hydrates of soda and sodium sulfate by cooling in the course of rolling and transportation.

When testing pelletizing apparatuses, it turned out that stable granulation is easier to carry out in a drum than on a pan. During granulation on a pan, the incoming hot batch, coming into contact with the granules that have formed, melts the crystallohydrates in them, and the thermal regime of the process is disturbed. Therefore, it is practically difficult to make the granulation process on a pan continuous.

In a drum granulator the incoming batch practically does not come into contact with the granulate. In addition, the drum granulator is a closed apparatus, which is very important for maintaining a constant thermal regime [7].

At present, industrial introduction of the granulation technology for glass batch of the indicated composition is being carried out at the Anzhero-Sudzhensk Glass Plant. The technological scheme of the process for obtaining granules is shown in Fig. 1.

The components of the glass batch—sand, soda, sulfate, fuel oil, feldspar, dolomite, and water—are fed through a skip into the batch mixer for the first mixing. After 4 min of mixing, the comparatively homogeneous batch mass is transported, with simultaneous mixing by an auger, to a pan (or belt) feeder and then, in strictly metered fashion, to a two-shaft paddle mixer. In the mixer, additional moistening of the batch to the optimum working state (≈ up to 13%) takes place. The moist, thoroughly mixed batch

Fig. 1. Technological scheme for thermal granulation of the batch.

Flow diagram:

Dosing of components
↓
First mixing ← Water, 8%
↓
Second mixing
↓
Dosing of batch with \(W = 8\%\)
↓
Additional moistening ← Water, 4%
↓
Granulation ← Water, 1–1.5%
↓
Transportation with simultaneous cooling
↓
Storage hopper

enters the drum for pelletizing. (Drum dimensions: length 8 m, diameter 1.6 m.)

A small amount of water, approximately 1–1.5%, is fed directly into the drum to moisten the working surface and to create fluctuations in moisture content. The strength of the raw granules is insufficient for transporting them to the storage hopper. Therefore, to fix their structure, cooling devices are installed on the conveyor belts (at the plant, fans are installed). The slight residual moisture of the granules, about 10–11%, makes it possible to eliminate the drying stage.

The characteristics of the granulate obtained under industrial conditions are given below (Table 2).

Practice has shown that the process of granule formation can be regulated by changing the amount of batch and water supplied. With an increase in the amount of water (approximately up to 15%), the size of the granules increases, and granules of size from 7 to

Table 2

Characteristics of the granulate

15 mm. As the water consumption is reduced to 12%, the granules decrease to 3–7 mm. When the moisture content is reduced to 10%, the granule sizes again increase to 10–15 mm, but at the same time about 30% of the batch is practically not rolled into granules. With stable granulation, fluctuations in moisture content should not exceed 2–3%.

A condition for the stable formation of granules is strict dosing and continuous movement of the material through the drum. The temperature of the mass being granulated plays a significant role and should not be below 27° or above 32°C. Fluctuations in the batch temperature are leveled out by water supplied to the batch before the drum.

The capacity of the granulator is determined by the residence time of the material in the drum, which, in turn, depends on the angle of inclination of the drum and on its rotational speed. At an inclination angle of 5° and a rotational speed of 12.4 rpm, the maximum capacity of the factory granulator is 4 tons/hour.

Conclusions

1. Ordinary glass batches containing about 20% alkali components (\(Na_2CO_3\), \(Na_2SO_4\)) can be successfully granulated at a mass temperature and moisture content of 30°C and 14%, respectively.

2. A process of continuous granulation was carried out in a drum granulator.

3. For better plasticization of the mass, it is necessary that, during moistening with mixing, the batch pass through temperatures of 50–60°C.

4. The necessary conditions for stable granule formation are minimal deviations in dosing and moistening of the batch, and stability of the operating temperature.

References

1. O. Knapp. Brikettieren und granulieren des Glasgemenges. “Glas—Email—Keramo—Technik,” 1969, No. 5, 166–169 (FRG).

2. Method for briquetting batch for glass melting. Japanese Patent Class 21 A2, No. 10718, published 29.06.63.

3. Gurov A. M. F. Granulation of glass batch. “Glass and Ceramics,” 1959, No. 5, pp. 14–16.

4. Granulation of glass batch. H. Läffer. Granulierung von Glasgemenge. “Glastechnische Bericht,” 1953, No. 7, p. 224.

5. M. A. Matveev, B. K. Demidovich. Granule formation in glass batch. “Glass and Ceramics,” 1967, No. 10, pp. 20–23.

6. Granulation of glass batch. J. Jamamoto, E. Komatsu. Pelletizing the Glass batch. “The Glass Industry,” 1968, 49, No. 9, 491–493.

7. I. E. Ruchkin, D. G. Khokhlov. The process of nodulizing finely ground concentrates and the operation of nodulizers. Proceedings of the Uralmekhanobr Institute, 1969, issue 16, pp. 67–95.