STUDY OF THE PROCESS OF OBTAINING SMALL-LUMP PEAT FROM HYDROMASS

S. I. Smolyaninov, V. N. Ponomarev, Yu. N. Vasiliev

(Recommended by the scientific-methodological seminar of the Faculty of Chemical Technology)

The dominant method of peat extraction in our country is the milling method—a fully mechanized and economical method. Its drawback is its great dependence on weather conditions and the poorer quality of the product in comparison with lump peat. These circumstances, as well as the need in a number of cases, in the power, gas-chemical, and domestic use of peat, to supply consumers with peat in lump form, raise the question of obtaining lump peat by a method cheaper than the excavator method.

One of the directions that has received broad development in scientific research is the creation of processes for obtaining small-lump peat. The Kalinin Peat Institute has developed a new technological process for extracting small-lump peat, the distinctive features of which are the use of surface phenomena in an intensively dispersed peat mass formed into lumps of specified dimensions [1].

We are conducting studies of the possibility of obtaining small-lump peat with satisfactory physicomechanical properties from peat hydromass that has undergone preliminary dewatering in a dewatering installation, since the hydraulic method of extraction successfully combines a productive method of excavating peat from the deposit and transporting it over long distances.

The experiments were carried out with peats from the Vasyugan deposit of varying degrees of decomposition. For comparison of the physicomechanical indices of moldings made from hydropeat that had passed through the stage of preliminary dewatering by filtration through porous partitions, moldings were made from raw peat. In the course of the work, the influence of various factors on the strength, water absorption, abrasion resistance of a small lump, and also on the duration of drying was investigated, in particular: the moisture content of the material being molded, the degree of processing, and the molding pressure.

From the initial raw peat with a degree of processing of 0.5 time (by degree of processing we mean the number of times the peat mass is passed through a mechanical meat grinder), a hydromass with a moisture content of 96% was prepared. The hydromass obtained was dewatered by filtration under a vacuum of 0.2 mm Hg to a moisture content of 91–93%, then brought by mechanical pressing on a roller press (using the principle of multistage pressing) to a moisture content of 75–80%. Peat samples were molded with degrees of processing of 0.5; 1; 2; and 3 times. Simultaneously, another batch of these peats was dried under laboratory conditions to a moisture content of 80–85%, and samples were also formed from them.

of a similar degree of processing. All samples were formed in cylindrical dies 50 mm in diameter.

The forming pressure was 3–5 kg/cm². The resulting briquettes were dried simultaneously under laboratory conditions. During drying, the linear dimensions of the samples were measured and the loss in weight was recorded. Drying was carried out until the sample reached constant weight. The dried briquettes were tested for temporary compressive strength, abrasion resistance, and water absorption.

Analysis of the drying process of formed peat was carried out on the basis of drying curves and curves of its rate. Figure 1 presents drying curves for briquettes made of peat with a degree of decomposition of 35% under single-stage processing, establishing the relationship between peat moisture content and drying time. It is not difficult to see that the drying intensity of briquettes made from hydromass dewatered to forming moisture is higher than that of briquettes made from raw peat of the same moisture content.

Fig. 1. Drying curves of formed peat:
1 — briquettes made from raw peat, degree of decomposition \(R = 35\%\), number of processing operations \(n = 1\); 2 — briquettes made from hydromass \(R = 35\%\), \(n = 1\); 3 — briquettes made from raw peat \(R = 15\), \(n = 1\); 4 — briquettes made from hydromass \(R = 15\), \(n = 1\).

Figure 2 presents graphical dependences of the abrasion resistance of peat briquettes on the degree of processing, indicating that the abrasion resistance of briquettes made from hydromass is approximately equal to, and even lower than, that of briquettes made from raw peat. Similar results were obtained in determining the water absorption of formed peat (Fig. 3).

Thus, analyzing the data obtained in the work, the following conclusions may be drawn:

1. The drying rate decreases with an increase in the degree of processing, which can be explained by the formation of a more compact and dense structure of the peat sample, hindering the movement of moisture to the outer layers of the sample.

The degree of decomposition has a significantly smaller effect on the drying rate of the briquette than the degree of processing. With an increase in the degree of decomposition, the drying rate decreases, which is more characteristic of high-moor peats.

It should be noted that the drying process proceeds considerably more intensively in samples formed from hydromass than in samples made from raw peat; moreover, with an increase in the degree of peat decomposition this is manifested more noticeably at any degree of processing.

1. In all cases, the shrinkage of the specimens increased with the degree of processing.

2. As a result of the work carried out, the influence of the initial moisture content of the formed specimen on its strength was determined. With an increase in the moisture content of the peat being formed, the compressive strength of the specimens decreases,

Fig. 2. Dependence of the abrasion of formed pieces on the degree of processing:
1 — formed pieces from hydromass, \(R = 35\%\); 2 — formed pieces from raw peat, \(R = 35\); 3 — formed pieces from hydromass, \(R = 45\); 4 — formed pieces from raw peat, \(R = 45\)

Fig. 3. Dependence of the moisture absorption of formed pieces on the degree of processing:
1 — formed pieces from raw peat, \(R = 45\%\); 2 — formed pieces from hydromass, \(R = 45\%\); 3 — formed pieces from raw peat, \(R = 35\%\); 4 — formed pieces from hydromass, \(R = 35\%\)

which is observed for all batches of formed pieces; moreover, peat specimens made from hydromass are in no respect inferior to specimens made from raw peat, and in many cases even surpass them. Reducing the moisture content of the material formed from hydromass from 80 to 75% increases the compressive strength of the specimens by more than 2–1.5 times.

The data obtained refute the opinion that it is impossible to obtain strong lump peat from hydromass because of the alleged washing out of the humus part of the peat, which, as is known, plays a definite role in creating the peat structure.

1. Tests of the specimens for abrasion showed that formed pieces from hydromass generally give a smaller percentage of fines than formed pieces from raw peat.

2. The moisture absorption of peat specimens from hydromass is lower than the moisture absorption of specimens from raw peat. This relationship holds for peats of various degrees of decomposition and various degrees of processing. A decrease in the initial moisture content of the specimens leads to a reduction in the moisture absorption of the peat.

Thus, small-lump peat from hydromass, obtained under laboratory conditions, is not inferior in its physicomechanical properties—and in some cases surpasses—specimens made from raw peat. This shows the possibility of obtaining small-lump peat of satisfactory quality from hydromass and even the advisability of doing so, proceeding from the technological scheme we have adopted for peat extraction by the hydraulic method with preliminary dewatering of the hydromass.

LITERATURE

1. G. I. Kuzhman, Theoretical Foundations and the Process of Obtaining Small-Lump Peat Fuel for Energy-Gas-Chemical Use. GEI, 1960.
2. E. N. Semenskii, Technical Analysis of Peat. GEI, 1958.