INFLUENCE OF VARIOUS FACTORS

ON THE STRENGTH OF PEAT THERMAL BRIQUETTES

S. I. SMOLYANINOV, S. G. MASLOV

(Presented by the scientific-methodological seminar of the KhTF)

This article presents some results of work on studying the influence of briquetting pressure, holding under pressure, and degree of comminution on the strength of peat thermal briquettes during slow heating. The experiments were carried out with a series of peats from the Vasyugan peat massif of Tomsk Oblast. Their characteristics are given in Table 1. The method for obtaining and testing thermal briquettes was described earlier [1, 2].

Table 1

Characteristics of peat samples

From the data obtained (Fig. 1) it is evident that the strength of thermal briquettes increases rapidly at first with increasing pressure, and then changes hardly at all. It may be assumed that initially strengthening occurs through the packing of grains and the realization of brittle deformations. At the same pressure, contact between peat particles is probably achieved, and the plastic products of thermal decomposition are distributed uniformly throughout the entire volume of the briquetted material. With further compression of the pressed mass, elastic deformations apparently begin to predominate in it, and an increase in pressure does not lead to a noticeable effect.

The decisive role in the process of realization of plastic products should be played by polymerization and polycondensation reactions [3].

The solid residue of the thermal decomposition of peat is involved in these reactions; it possesses high activity and thus is not merely an inert filler.

It may be assumed that pressure also affects the nature of the course of the reactions, namely, it accelerates the reactions of realization of plastic products.

The pressure required in thermal briquetting depends on the degree of decomposition of the peat. For peats of medium and high degree of decomposition,

it is equal to \(200 \cdot 10^5\ \text{N}/\text{m}^2\), and for peat of a low degree of decomposition it is \(100 \cdot 10^5\ \text{N}/\text{m}^2\) higher. Such a difference obviously arises as a result of the greater frictional force between the particles of slightly decomposed peat, owing to their anisometric structure and the smaller yield of pyrobitumens.

The reason for the reduction in pressure in thermal briquetting as compared with ordinary briquetting methods is the lubricating action

Fig. 1. Influence of briquetting pressure on the strength of thermobriquettes. 1—peat with a degree of decomposition of 5%; 2—25%; 3—55%.

of the plastic products of thermal decomposition and a different mechanism for forming a strong briquette structure. Thus, according to the data of D. P. Zverev and Yu. P. Pushkarev, the specific frictional force during briquetting of peat heated to the temperature of thermal briquetting is 2.4 times lower than during briquetting of cold drying material [4].

Apparently, the plastic deformation of peat at the moment of its thermal decomposition plays a most important role [3].

The pressing rate and the holding time under pressure determine not only the strength of the briquette, but also the productivity of the presses. Above all, with an increase in the holding time, the number of transitions of elastic deformations of peat particles into plastic ones increases, and relaxation of stresses in the briquette occurs. The time factor must also play a decisive role in the completeness of the chemical reactions by which binding substances are formed.

The results of the studies are presented in Fig. 2. It is evident from the figure that, with increasing holding time, the strength of the briquettes first increases considerably and then practically does not change. Evidently, by this time the hardening reactions of the plastic products are essentially completed and relaxation of elastic deformations into plastic ones occurs.

As can be seen from Fig. 2, for peat of a low degree of decomposition a longer holding time under pressure is necessary, which is probably due to the anisometric (fibrous) structure of its particles and, as a consequence, to a longer relaxation time of plastic deformations.

The results of our studies (Fig. 3) indicate a dependence of the particle size of peat before thermal briquetting on its degree of decomposition. Apparently, this is explained by the increasing anisometry of the particles, which reaches its greatest value in peats of low degree of decomposition.

Fig. 2. Influence of holding time under pressure on the strength of thermo-briquettes. 1 — peat with a degree of decomposition of 5%, 2 — 25%, 3 — 55%.

Fig. 3. Influence of the coarseness of peat particles on the strength of thermo-briquettes. 1 — peat with a degree of decomposition of 5%, 2 — 25%, 3 — 55%.

Conclusions

1. The dependence of the strength of thermo-briquettes on briquetting pressure, holding time under pressure, and the coarseness of peat particles has been determined.

2. The influence of the degree of peat decomposition on the indicated factors has been shown.

References

1. S. I. Smolyaninov, A. M. Denisov. Influence of briquetting temperature and pressure on the mechanical properties of peat thermo-briquettes. Izv. TPI, vol. 112, 82, 1963.

2. I. V. Gebler, S. I. Smolyaninov, A. F. Martynov, B. M. Severin. Influence of pressure and moisture on the properties of peat as a metallurgical fuel. Peat Industry, 8, 16, 1959.

3. V. E. Rakovskii, F. L. Kaganovich, E. A. Novikova. Chemistry of Pyrogenic Processes. Publishing House of the Academy of Sciences of the BSSR, Minsk, 1959.

4. D. P. Zverev, Yu. V. Pushkarev. Production of thermo-briquettes — a way to improve the quality indicators of peat fuel. Chemistry of Solid Fuel, 4, 55, 1967.