EFFECT OF ADDITIONS OF IRON ORE AND FLUXES ON THE PROPERTIES OF PEAT AS A METALLURGICAL FUEL

I. V. Gebler, S. I. Smolyaninov, V. E. Potapenko, V. I. Kosolapov

The iron ores of Tomsk Oblast belong to the type of lean siliceous–phosphorus–vanadium ores. The average iron content in them is 36%. The shortcomings of the ores are their dustiness and low mechanical strength [1]. Dusty ores are smelted in a blast furnace with difficulty. The large carryover of ore in the form of flue dust greatly complicates smelting, and successful smelting of such ores is possible only if they are agglomerated [2].

The direct use of lean ores is possible in low-shaft furnaces operating with oxygen-enriched blast [3, 4]. Low-shaft furnaces have a number of advantages, one of which is the reduced requirements imposed on the mechanical strength of the blast-furnace fuel and on the size of its pieces, owing to the small height of the column of charge materials. However, for the same reason it is necessary to achieve maximum contact between the ore and the reducing agent [5].

An orientation toward using air-dry molded peat with an admixture of the necessary amount of iron ore in the blast furnace can solve both the problem of achieving close bonding between the ore and the fuel and that of agglomerating dusty ores. Moreover, the production of such fuel–ore materials can apparently be carried out effectively on ordinary peat-molding machines.

There are no works in the literature in this direction. Methods have been proposed for obtaining peat–iron briquettes [6] from milled peat by heating it to 300–310° and subsequent pressing, in the hot state, at a pressure of 50–100 atmospheres.

We carried out experiments on adding iron ore from the Bakchar deposit [1] to peat at the moment of molding, in an amount up to 160% relative to the raw \((W^{p}—85\%)\) peat mass (samples with the maximum addition of iron ore proved completely unsatisfactory in mechanical properties, and therefore the results of their tests are not presented).

The general experimental procedure and the approach to evaluating the quality of the samples obtained were the same as previously [7]. The ore (degree of grinding 1–0 mm) was added to the raw peat mass, which had been passed once through a meat grinder. The components were thoroughly mixed, and the mixture was again processed twice in the meat grinder.

It could be expected that the addition of iron ore would accelerate the natural drying of molded peat, both as a result of the coagulating-

effect on peat colloids, and as a result of a peculiar drainage effect. The experiments showed that the addition of ore noticeably accelerates the drying of peat. The difference in the time required for the specimens to reach the air-dry state amounts to four days. The final moisture content in specimens with iron ore is several (4–5) percent lower. It should also be noted that freshly molded specimens with an ore addition are more resistant to deformation under their own weight, and during drying they undergo uniform shrinkage. Specimens with additions of 5, 10, and 12% iron ore, calculated on the wet mass, differ only insignificantly from one another in drying rate, which apparently indicates the predominance of the coagulating action of the ore.

The results of tests for mechanical strength are presented graphically in Fig. 1. As can be seen from the figure, the strength index of molded peat in all cases decreases with increasing ore content in the mixtures. This decrease is especially strong for air-dry specimens; when the latter are heated to 400–1000°, the strength index changes much less. It is interesting to note that, with an ore addition up to 3%, the strength index of the specimens at all temperatures is higher than that of peat without additives.

The abrasion of air-dry specimens is practically independent of the addition of iron ore up to a content of the latter of 12% of the wet mass of the peat. At 400° the abrasion decreases with increasing ore addition. At 500° an iron-ore addition up to 8% reduces abrasion, while a further increase in the ore content rapidly increases abrasion. Heating the specimens to temperatures above 500° intensifies the negative effect of the ore addition. Beginning with a 3–4% addition, abrasion increases sharply, and the more so the higher the final heating temperature of the specimen.

Fig. 1. Mechanical strength (strength index and abrasion coefficient) of air-dry peat (a/d) and coke made from it at various final heating temperatures (figures by the curves), as a function of the addition of iron ore to wet ($W^p = 85\%$) peat.

Thus, the addition of iron ore to peat at the moment of its molding in order to obtain fuel-ore lump materials for blast-furnace smelting is of definite interest. Under conditions of natural peat drying, the acceleration of drying under the action of iron ore may be of practical value. An ore addition up to 3% generally improves the mechanical strength of the molded pieces under all the conditions tested. An ore addition up to 5% may, apparently, be entirely permissible.

The gangue remaining in the course of blast-furnace smelting after reduction of the iron oxides can only rarely be independently smelted into a slag suitable for the production of pig iron in terms of physical properties and chemical composition. Usually it requires the addition of a flux, the quantity and quality of which are determined by a special calculation for each case. When working with mineral fuel, flux is necessary both for slagging the ash of the fuel and for binding its sulfur. The flux may be basic (limestone or lime-magnesian) or acidic (siliceous). Since the gangue of ore usually contains an excess of silica, then when

in smelting on coke they resort to the basic flux, for which limestone is used [8].

New directions in ferrous metallurgy, associated with intensification of the blast-furnace process, raise the question of developing new methods for preparing raw materials—obtaining fuel-and-smelting materials. In this case the slag-forming substances can be fully released only in the combustion zone, i.e., when the slag constituents have already been sufficiently heated. This ensures the fluidity of the slags, which is of particular importance in smelting with oxygen-enriched blast [9].

To assess the possibility of obtaining this type of material on a peat basis, we carried out work on adding a certain amount of fluxing material to raw peat at the moment of its forming.

The raw peat mass, thoroughly mixed with flux and processed three times in a meat grinder (W^r—85%), was formed and treated according to the procedure reported earlier [7].

Samples were prepared with additions of 3, 2, 1, and 0.5% limestone, based on the raw mass of peat. The limestone had the following screen composition: fraction 1.0–0.5 mm—41%; 0.5–0.25 mm—2.3%; 0.25–0.01 mm—55.8%. One batch of formed pieces contained 2% limestone, ground to 100% passage through a 0.25 mm sieve. An addition of slaked lime (“pushonka”) in an amount of 1% was also tested.

Natural drying of the formed peat is, in general, noticeably accelerated when limestone is added to the raw peat. The addition of lime proved especially effective in this respect.

In this case, during drying, the peat formed pieces lose 70–80% of their weight 4–5 days earlier than pure peat. In the other cases the drying is accelerated by 3–4 days. The formed pieces with an addition of calcium hydroxide are less resistant to deformation under their own weight and crack more strongly during further drying; nevertheless, the strength of individual pieces remains very high. As the limestone content in the mixture is increased within the range 0.5–3.0%, the drying rate changes practically not at all.

Visual observations established that coarse flux grains are centers of crack formation during coking. Samples with fine-ground additions give almost no cracks.

From the graphs (Fig. 2) it is clear that the strength index of the formed peat decreases with an increase in the percentage of limestone addition at all test temperatures. The limestone addition has an especially strong effect on samples heated in the temperature interval up to 300°. At high (above 500°) final heating temperatures the strength index from limestone additions in amounts up to 1% changes only slightly, and at temperatures close to 1200° it even increases somewhat from the addition of 0.5% flux.

The strength index of samples with a 2% addition of limestone, crushed to pass through a 0.25 mm sieve, at heating temperatures up to 300° practically does not differ from this value for samples with an addition of coarse limestone. However, at higher temperatures samples with an admixture of fine limestone are 15–20% stronger than the corresponding mixtures of peat with coarse limestone. As for the addition of calcium hydroxide, these samples of formed peat have increased strength (approximately to the same degree as the preceding ones) throughout the tested temperature interval, except at 400°, where the strength of the corresponding samples is practically the same (data for the addition of fine limestone and lime are not shown in Fig. 2).

The abrasion of peat briquettes with flux additions at low temperatures (up to 200°) is practically independent of the amount of limestone. With a further increase in temperature, abrasion begins to increase with increasing flux content, and at temperatures of 700–1200° reaches 100% for specimens containing 3% calcium carbonate. Within the indicated temperature range, a sharp increase in abrasion is already observed when more than 1% flux is added.

A substantial difference in abrasion is observed for specimens with an addition of 2% coarse and fine limestone. If the abrasion of the former is very high and reaches 85% at 900°, then the abrasion of the latter over the entire temperature interval up to 1200° proves to be lower than for any of the mixtures tested by us, including pure peat. As for the addition of calcium hydroxide, the abrasion of these specimens in the temperature range 200–600° differs little from the abrasion of specimens with the corresponding amount of coarse limestone addition. Above 500° the picture changes, and specimens with lime are abraded approximately half as much.

Fig. 2. Mechanical strength (strength index and abrasion coefficient) of air-dry peat \((W^p — 85\%)\) and coke from it at various final heating temperatures (figures by the curves), as a function of limestone addition to raw peat.

Thus, the addition to raw peat of fluxes in the form of limestone (fraction 1.0–00 mm) in amounts up to one percent does not substantially reduce the mechanical properties of briquetted peat. It is interesting to note that with greater grinding of the flux, the addition of even 2% limestone not only did not impair the strength of the specimens, but imparted better mechanical properties to them.

The addition of lime, in all probability, has no advantages over limestone, at least with respect to the mechanical properties of the briquetted peat material.

The acceleration of the natural drying of peat under the action of the limestone additive should also have practical significance.

Conclusions

1. The addition of iron ore and fluxes to raw peat accelerates the subsequent natural drying of peat and promotes more uniform shrinkage.

2. The addition of ore up to 3% and limestone up to 2% to the raw \((W^p — 85\%)\) peat mass improves the mechanical properties of briquetted peat and the coke made from it.

LITERATURE

1. Babin A. A. et al. Vestnik ZSGU, No. 1, 49, 1957.
2. Chizhevsky N. P. Selected Works, vol. 1, Publishing House of the Academy of Sciences of the USSR, Moscow, 1958.
3. Krasavtsev N. I. Prospects for the Development of Blast-Furnace Production. Metallurgizdat, Moscow, 1958.

1. Koppenberg G., Ventsel V. Oxygen blast in a shaft furnace. Metallurgizdat, Moscow, 1959.

2. Tsytsev et al. In the collection New Principles of Coal Coking. Publishing House of the USSR Academy of Sciences, Moscow, p. 89, 1955.

3. Klimov B. K. New methods of thermal processing of peat. GONTI, Moscow–Leningrad, 1930.

4. Gebler I. V., Smolyaninov S. I., Martynov A. F., Severin B. M. Peat Industry, No. 8, p. 16, 1959.

5. Pavlov M. A. Metallurgy of Pig Iron, Part 1. Publishing House of the USSR Academy of Sciences, 1948.

6. Sapozhnikov L. M. In the collection New Principles of Coal Coking. Publishing House of the USSR Academy of Sciences, Moscow, p. 5, 1955.