Ways to Intensify the Granulation Process of Alkali-Containing Glass Batches
Abstract Generated abstract
This study examines intensification of granulation for alkali-containing window-glass batches by replacing calcined soda with sodium carbonate monohydrate. Sodium carbonate monohydrate was prepared from decahydrate and compared with calcined soda in particle size, specific surface area, plastic strength of moistened batches, and laboratory pan granulation behavior under varying moisture and temperature conditions. The results indicate that monohydrate, being more finely dispersed and readily soluble, lowers the moisture required to reach the working granulation state by about 20 to 25 percent and removes the need for preliminary thermal plasticization. Its use permits granulation at lower temperatures and higher rates, producing denser granules with a more uniform size distribution, although excessive initial moisture can prevent successful granulation.
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Ways of Intensifying the Process of Granulating Alkali-Containing Glass Batches
V. M. Vityugin, L. G. Lotova, V. A. Trofimov
(Presented by the scientific seminar of the Department of General Chemical Technology)
Intensification of the granule-formation process for alkali-containing glass batches, with the production of granules of satisfactory quality, is possible by increasing the caking capacity of the batch and, above all, by increasing its plasticity. The most expedient way to increase the plasticity of the batch is by heating it to the dehydration temperature of soda and sodium sulfate \((>35^\circ\mathrm{C})\). The technology of thermal granulation of alkali-containing glass batches based on this principle [1] made it possible to reduce the working moisture of the caked material in comparison with the usual “cold” method, while simultaneously improving the quality of the granulate and increasing the rate of the granule-formation process.
The effect of thermal granulation is mainly a consequence of preliminary thermal plasticization of the batch at a temperature of \(50\text{--}55^\circ\mathrm{C}\). This was confirmed by direct experiments on batch granulation and by studying the structural state of the system in terms of the plastic-strength parameter [2]. It was established that temperature holding of a moistened soda batch promotes the initial formation in the system of finely dispersed, readily soluble sodium carbonate monohydrate, which increases the plasticity of the batch. However, in the continuous method of granulation the time of thermal plasticization, and consequently the amount of monohydrate formed, is limited. A reserve for further intensification of the granule-formation process and improvement of granule quality is the replacement of calcined soda by sodium carbonate monohydrate.
In the present work, results are presented from studies on the use of soda monohydrate in granulating window-glass batch. The monohydrate was obtained from decahydrate soda compounds by the method of weath—
Table 3
Results of slag granulation in which soda is partially or completely replaced by monohydrate
| No. | Amount of monohydrate introduced together with soda (%) | Initial slag moisture, % | Granulation time, min | Slag temperature during granulation, °C | Granule moisture, % | Granule density, g/cm³ | Note |
|---|---|---|---|---|---|---|---|
| 1 | 100* | 14 | — | — | — | — | Slag is not granulated because of excess moisture |
| 2 | 100* | 12 | 1.5 | 29 | 10.5 | 2.14—2.17 | Granules are well rolled, comparatively strong |
| 3 | 100 | 11 | 1.5—2 | 27 | 9.9 | 2.17—2.24 | Granules with a diameter of 3—10 mm predominate (up to 60—65%) |
| 4 | 50 | 12 | 2.5 | 27 | 10.6 | 1.99—2.11 | Much fines are formed in the form of weakly granulated grains, about 50% |
| 5 | 50* | 13 | 2.0 | 31 | 11.4 | 1.89—1.96 | Slag granulates well; granules with a diameter of 5 mm predominate |
| 6 | 20 | 13 | 2.5 | 32 | 11.6 | 1.82—1.86 | Much ungranulated fines, about 50% |
* Results of slag granulation at an initial temperature of 50—53°C; in the remaining cases the temperature did not exceed 31—32°C.
stirring. With intensive blowing of air through soda decahydrate (the decahydrate was obtained by the standard procedure [3]), a finely dispersed (Table 1), readily soluble powder of sodium carbonate monohydrate is formed, with a specific surface area* of 4080 to 6000 cm²/g (for comparison, the specific surface area of soda is 2800–3000 cm²/g).
Table 1
Comparative granulometry of soda and its monohydrate
| Fraction, μm | Calcined soda | Sodium carbonate monohydrate |
|---|---|---|
| +30 | 39.20 | 22.20 |
| 25—30 | 6.95 | 4.00 |
| 20—25 | 9.56 | 4.00 |
| 15—20 | 17.40 | 4.80 |
| 10—15 | 9.15 | 25.50 |
| 10 | 17.74 | 39.50 |
Note. In carrying out the dispersion analysis, ethyl alcohol was used as the liquid medium.
A comparative assessment of the structural state of batches with monohydrate and with ordinary soda (Table 2) showed that, other conditions being equal, the plastic strength of the experimental (monohydrate) batch is lower than that of the ordinary one. It had previously been established [2] that the working state for granulation of an alkali-containing glass batch is characterized by plastic-strength values of 10–13 N/cm². Consequently, the granulation moisture corresponding to the working state is lower for the monohydrate batch than for the ordinary batch, and is about 10–11%.
Laboratory granulation tests were carried out on a pan granulator; the pan diameter was 0.3 m, and the rotational speed was 32 rpm. In preparing the batch, part or all of the soda was replaced by the monohydrate. The granulation results are given in Table 3.
Table 2
Results of determining the plastic strength of glass batches at different moistures and temperatures
| Batch moisture, % | 100% Na₂CO₃·H₂O, 27°C | 100% Na₂CO₃·H₂O, 33°C | 100% Na₂CO₃·H₂O, 40°C | 100% Na₂CO₃·H₂O, 50°C | 100% Na₂CO₃, 27 | 100% Na₂CO₃, 33 | 100% Na₂CO₃, 40 | 100% Na₂CO₃, 50 |
|---|---|---|---|---|---|---|---|---|
| 8 | 124.6 | 40 | 32.5 | 26.4 | 71.2 | 61.5 | 49 | 43.2 |
| 10 | 99.1 | 18.2 | 15.1 | 12.4 | 68.0 | 57.3 | 35.0 | 16.9 |
| 12 | 75.0 | 7.0 | 6.1 | 5.6 | 67.3 | 53.8 | 27.6 | 12.3 |
| 14 | 56.2 | 4.6 | — | — | 66.5 | 39.4 | 17.3 | 10.8 |
| 22 | 12 | — | — | — | 16.0 | 6.2 | 5.4 | — |
Analysis of the results obtained shows that the use of its monohydrate instead of calcined soda leads to a decrease in the working granulation moisture by approximately 20–25%. When soda is replaced by the monohydrate, the need for preliminary thermal plasticization of the batch is eliminated. The granulation process is carried out at lower temperatures and at an increased rate. The granules obtained are denser and more uniform in size.
REFERENCES
- Author’s certificate No. 357155 C 03c 1/00, published 31.10.72.
- L. G. Lotova, V. A. Trofimov, V. M. Vityutin. Effect of temperature on the structural-mechanical properties of moistened alkali-containing glass batches. Izv. TPI, vol. 257, Tomsk, 1973.
- E. V. Lesnova. Practicum in Inorganic Synthesis. Moscow, “Vysshaya shkola,” 1969, 65–66.
* The specific surface area was determined on a PSKh-4 instrument.