RAPID METHOD FOR DETERMINING THE OPTIMUM MOISTURE CONTENT OF FINE-GRAINED MATERIALS BEFORE PELLETIZING

V. M. Vityugin, V. A. Trofimov

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

In the practice of pelletizing dispersed materials, determination of the optimum (working) moisture content is of great interest. At present, for a wide range of materials subjected to pelletizing (iron-ore concentrates, glass batches, cement raw mixes, etc.), this moisture content is established by a lengthy and labor-intensive experimental procedure when pelletizing materials under laboratory conditions, with the appropriate corrections being made in the production process. In the present work a method is proposed for determining the optimum moisture content of fine-grained materials, distinguished by modeling of the pelletizing process. From experience in the use of vibrational effects in construction, in the forming of powders, and in the compaction of soils it is known [1, 2] that in this case the densest packing of particles is achieved, approaching the theoretically possible packing. Preliminary studies have established that the porosity of briquettes formed by vibrocompaction of moist dispersed materials is identical to, or somewhat lower than, the porosity of pellets. The data in the table confirm the possibility of modeling the pelletizing process by the method of vibrational compaction of moist dispersed materials. From the practice of pelletizing fine-grained materials it is known [3] that the maximum strength of a pellet is achieved when the pores are completely filled with water, i.e., when the pore-filling coefficient \((K_w)\), according to the formula known from soil science [4], is equal to 1.

\[ K_w=\frac{W\cdot \gamma}{\varepsilon\cdot \gamma^{b}}, \tag{1} \]

where \(K_w\) is the relative content of water in the pore volume, in fractional units;
\(W\) is the gravimetric moisture content of the material, in fractional units;
\(\gamma\) is the specific weight of the material, g/cm\(^3\);
\(\gamma^{b}\) is the specific weight of water, g/cm\(^3\);
\(\varepsilon\) is the reduced porosity of the material, in fractional units.

Samples of materials differing in their physicochemical properties were selected as the objects of investigation: iron-ore concentrate from the Sokolovsko-Sarbaiskii Mining and Processing Combine, natural pulverulent quartz (marshalite) from the Balashov deposit, ground limestone from the Sokolovsko-Sarbaiskii combine, Tashlin quartz sand, and ilmenite concentrate from one of the deposits.

The studies were carried out on an electromagnetic vibrator reac-

of a standard type with a power of 100 W at a frequency of 100 Hz and an amplitude of 0.6 mm, in a special cylindrical beaker made of organic glass with a vertical height graduation. A weighed portion of dry material was moistened to the capillary state and placed in the vibrator beaker in a layer of about 30 mm. Before loading the sample, 30 sheets of filter paper were placed on the bottom of the beaker. Another 30 sheets of paper were placed on top of the sample layer. A light floating piston (surcharge) was inserted into the beaker from above to ensure better contact of the paper with the material. Vibrocompaction was carried out for 2 minutes. After compaction, the reduced porosity \((\varepsilon)\) and the moisture content from the middle of the material layer \((W_{\text{sl}})\) were determined. The moisture content of the samples determined in this way was compared with the actual pelletizing moisture content obtained under laboratory and production conditions. The results of the determinations are presented in the table.

Table 1

Comparative data on the moisture content of the vibrocompacted layer of materials and pellets, the reduced porosity of vibrocompacted samples, and the filling coefficient

As can be seen from the table, the moisture content of the compacted layer formed by vibration treatment is practically equal to the optimum pelletizing moisture content. If in formula (1) we take \(\gamma^b = 1\) and \(K_w = 1\) (as the optimum condition), then, after simple transformations of the formula, we obtain the calculation equation for determining the optimum pelletizing moisture content of fine-grained materials:

\[ W_{\text{opt}}=\frac{\varepsilon}{\gamma}, \tag{2} \]

where \(W_{\text{opt}}\) is the optimum moisture content, %;
\(\varepsilon\) is the reduced porosity of the vibrocompacted layer, %;
\(\gamma\) is the specific gravity of the material, g/cm³.

Consequently, for the purposes of practical determination of the optimum moisture content of fine-grained materials before pelletizing, it is sufficient to know only the value of the reduced porosity to which the material can be compacted with free arrangement of particles (for example, by vibrocompaction of a material layer) and its specific gravity.

REFERENCES

1. I. G. Shatalova, N. S. Gorbunov, V. I. Likhtman. Physicochemical Principles of Vibrational Compaction of Powder Materials. “Nauka,” 1965.
2. Mc. Geaty R. K. J. Amer. Ceram Soc, No. 10, Abstrs, 49, 1961.
3. V. N. Korotich. Theoretical Principles of Pelletizing Iron-Ore Materials. “Metallurgiya,” 1966.
4. V. A. Priklonskii. General Soil Science. L., 1943.