FUEL-SMELTING MATERIALS FROM REDUCED-MOISTURE PEAT

S. I. Smolyaninov, G. G. Krinitsyn

(Presented by the organic section of the scientific seminar of the Chemical-Technological Faculty)

The use of peat in metallurgy has long attracted interest; however, in practice very little has yet been done in this direction.

The modern direction of progress in ferrous metallurgy is characterized by the search for ways to intensify the blast-furnace process. One of the main links in solving this problem is the thorough preparation of raw materials for blast-furnace smelting, which ultimately may be embodied in the creation of a “monoclast,” i.e., a granulated mixture homogeneous in chemical and physical composition, containing fuel, ore, and fluxes in the required ratio.

Investigations carried out at the Tomsk Polytechnic Institute [1] showed that from peat, by mixing it with ore and fluxes in a definite proportion, it is possible to obtain a material whose mechanical qualities are not inferior to coke. The basis for the production of these materials is the process of obtaining machine-formed peat, which is based on the excavator method of peat extraction.

However, at the present time a number of new processes have appeared for the production of machine-formed peat, surpassing the excavator method in economic indices. These should include first of all the milling (surface-layer) and fine-lump methods of extraction [2]. The latter may prove most suitable for the production of peat-flux-ore moldings.

One of the features of obtaining fine-lump peat, as well as milled peat, is that the operating moisture content of the industrial deposit is considerably reduced. This circumstance creates conditions for increasing labor productivity and reducing cost in peat extraction. According to S. G. Solopov [4], a reduction in the moisture content of a peat deposit by 10% causes a reduction in the cost of peat extraction by 15%. At the same time, reduction of moisture content makes peat forming more difficult and creates the need for intensive dispersion of the latter. Work carried out at the Kalinin Peat Institute [3] showed that, with intensive dispersion, it is possible to form peat with a moisture content of up to 75%.

According to modern concepts, the strength of peat moldings is influenced by a whole series of factors, the most important of which are the forces of intermolecular adhesion, depending on the surface of the contacting peat particles, on the thickness of their solvate layers.

...of shells, on the zeta potential of colloidal particles, etc. The introduction into the peat briquette of new components—iron ore and limestone—must undoubtedly affect the quality of the briquette obtained. It may be expected that peat–flux–ore briquettes obtained from peat of reduced moisture content will prove stronger than briquettes obtained from peat with higher moisture content.

When the moisture content of peat is reduced, the adsorption shells of the colloidal particles decrease in size. This promotes an increase in the forces of intermolecular adhesion. In addition, the less moist the peat during briquetting, the less the structure of the briquette changes during drying. The introduction of iron ore into the peat mass leads to the appearance in the system of iron ions, which, even in the most insignificant quantities, cause a decrease in the thickness of the adsorption shells and promote coagulation.

Because the ore and fluxes are added in a finely ground form, the surface area of the contacting particles increases, which should also lead to an increase in the forces of intermolecular adhesion.

The purpose of the present work was to investigate the possibility of obtaining a strong peat–flux–ore briquette from peat of reduced moisture content. Peat from the Bakchar district of Tomsk Oblast was studied (Table 1).

Table 1

The peat was sedge–hypnum, lowland. Degree of decomposition—35%. Botanical composition: hypnum moss—50%, Omsk sedge and woolly-fruited sedge—35%, bogbean—10%, herbaceous residues—5%. Iron ore from the Bakchar deposit (Tomsk Oblast) was used as the ore component.

The iron content in the ore was 40%. This ore was ground until 75% passed through a 0.075 mm sieve. Limestone from the Sergeevskoe deposit in Tomsk Oblast served as the flux. Four batches of peat with different moisture contents were prepared: 85, 80, 76, and 74%. The choice of the initial moisture content was determined as follows. In peat, according to the classification of A. P. Rebinder [7], there are three types of bonding of the solid substance with water: chemical, physicochemical, and mechanical. In addition, peat contains unbound water. The content of chemically bound water is small. Physicochemically, mainly sorption water is retained. Capillary intracellular water is bound to the peat physicomechanically. When the initial moisture content of peat is lowered to 80%, a point is reached at which only bound water remains in the peat, mainly intracellular and sorption water. To check the change in briquette quality upon attaining this state of the peat, samples with the above-mentioned initial moisture content were taken.

From peat of each given moisture content, three batches of briquettes were prepared with the following conventional degrees of processing: 3, 8, 15. As the conventional unit, the degree of processing of peat during a single passage of the latter through a meat grinder was adopted.

Sedimentation analysis of peat with the given degrees of processing showed that particles of the class \(1\,\mu\) and smaller are present after 3-fold processing in an amount of 4.44%; after 8-fold, 8.14; and after 15-fold, 10.2%.

The technology for preparing the briquettes was in all cases as follows: after a single processing the peat was thoroughly mixed with the ore, then the resulting mass was additionally processed the required number of times and molded.

Drying of the briquettes was carried out under natural conditions at an air temperature of 291–293°K and a relative humidity of 30–32%. To bring the briquettes under these conditions to constant weight, the drying period required at an initial peat moisture content of 85% was 28 days, at 80%—26 days, at 76%—23 days, and at 74%—18 days. After drying, briquettes with an initial peat moisture content of 85 and 80% retained the shape obtained in the raw state, and their cracking was insignificant. The briquette could be broken only by applying considerable force. In briquettes made from peat with an initial moisture content of 76%, after drying cracks appeared, dividing the briquette approximately into two equal parts. The greatest cracking was found in briquettes made from peat with a moisture content of 74%.

After drying, the crushing resistance and abrasion resistance of the briquette material were studied in the air-dry state and after thermolysis at 673 and 1073°K. To determine crushing resistance, the samples were prepared in the form of regular parallelepipeds.

Figure 1 presents data on determining the crushing resistance of briquettes with a degree of processing of 8. It is interesting to note

Fig. 1. Dependence of the crushing resistance of peat briquettes with ore and fluxes in the air-dry state (curve 1) and after heating to 673°K (curve 2) and 1073°K (curve 3) on the initial moisture content of the peat.

that the dependence obtained for peat fuel-smelting materials is the reverse of the picture observed when testing briquettes—

briquettes made of pure peat [6]. A decrease in moisture content from 76 to 74% has an especially strong effect on strength.

The abrasion test was carried out in a drum 70 mm in diameter and 125 mm long. To create severe conditions inside the drum, there were 15 metal balls 15 mm in diameter, and a rib was welded along the generatrix of the cylinder. Pieces of the test sample measuring 10–15 mm were loaded into the drum. After 1500 revolutions, the yield of fines smaller than 3 millimeters was determined as a percentage of the initial charge; this was taken as the measure of abrasion. Figure 2 shows the dependence of abrasion on the conditional degree of processing for samples with different initial moisture contents.

As can be seen from the figure, this dependence is quite definite under all the conditions we tested. The strength of the briquettes increases most markedly when the degree of processing is increased to 8 (in arbitrary units). For air-dry samples, the effect of the initial moisture content and the degree of processing is not pronounced. These factors act much more significantly in samples heated to 673 and 1073°K, especially in the latter case.

Fig. 2. Dependence of abrasion of fuel-smelting materials at different stages of pyrolysis on the degree of processing of peat with different initial moisture contents.
a) dotted lines—air-dry samples: 1—initial moisture content, 85%; 2—80%; 3—76%; 4—74%;
b) dashed-dotted lines—samples heated to 673°K: 5—initial moisture content, 85%; 6—80%; 7—76%; 8—74%.
c) solid lines—samples heated to 1073°K; 9—initial moisture content, 85%; 10—80%; 11—70%; 12—74%.

Thus, the use of peat with reduced moisture content makes it possible to obtain much stronger fuel-smelting materials. The best samples in terms of strength were obtained from peat with a moisture content of 74%. However, processing such peat is associated with a considerable expenditure of energy for grinding; therefore, it may be more expedient not to reduce the moisture content below 76%. Increasing the degree of processing favorably affects the strength of the briquettes at all stages of pyrolysis; nevertheless, excessive grinding is inadvisable,

since the subsequent effect decreases. All this cannot be a consequence of the weak action of the processing apparatus used by us.

Conclusions

1. From reduced-moisture peat it is possible to obtain stronger fuel-smelting materials than from peat of the usual moisture content used in the excavator method of extraction.

2. Increasing the degree of processing up to a certain limit increases the strength of peat-flux-ore molded pieces.

3. The most favorable conditions for obtaining strong fuel-smelting materials are: initial peat moisture content—76%, conventional degree of processing—6–8.

References

1. I. V. Gebler et al. The influence of additions of iron ore and fluxes on the properties of peat as a metallurgical fuel. Izv. TPI, vol. 111, 1961.

2. I. V. Gebler, S. I. Smolyaninov, A. G. Nezvanov. The influence of the degree of comminution of ore and fluxes on the quality of fuel-smelting materials based on peat. Izv. TPI, vol. 112, 1963.

3. G. I. Kuzhman, N. I. Malinin. Some results of experimental work on the creation of a new technological process for obtaining fine-lump peat. Trudy MTI, issue 8, 1958.

4. S. G. Solopov. Technological principles for the production of high-quality fuel in the development of deposits of reduced operational moisture content. Scientific Reports of Higher Education Institutions. Mining, No. 1, 1958.

5. S. G. Solopov. The influence of dispersion on the structure and physicomechanical properties of peat. Trudy MTI, issue 8, 1958.

6. I. V. Gebler et al. The influence of pressure and moisture content on the properties of peat as a metallurgical fuel. Peat Industry, No. 8, 1959.

7. P. A. Rebinder. On the forms of bonding of moisture with material, 1956.