PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
awarded the Order of the October Revolution and the Order of the Red Banner of Labor
named after S. M. Kirov

Vol. 198 1974

METALLURGICAL EVALUATION OF FUEL-SMELTING MATERIALS BASED ON TESTING IN THE IMET FURNACE

G. G. Krinitsyn, V. S. Arkhipov, S. I. Smolyaninov

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

Laboratory tests for strength and reducibility of peat-ore briquettes provide a basis for experimental industrial verification of FSM. However, it is not known how this fundamentally new material will behave under conditions of counterflow of gases and burden, during slag formation, or how much interference will be caused by the gas and tar of peat pyrolysis. Finally, the composition of blast-furnace gases is of substantial importance as a raw material for chemical processing.

All these questions can be resolved only under conditions of a blast-furnace process. Carrying out a sufficient number of smelts under industrial, or even semi-industrial, conditions would require extremely large expenditures (material ones). Therefore it was decided to conduct preliminary tests in the laboratory blast furnace of the A. A. Baikov Institute of Metallurgy. Such installations have more than once been used in research on blast-furnace production [1, 2]. Staff members of the Institute of Metallurgy note that the specific features of the IMET laboratory shaft furnace do not allow it to be considered a model of a blast furnace, but rather a special enlarged laboratory apparatus for comprehensive comparative metallurgical testing of small quantities of new burden materials under counterflow conditions in a reducing atmosphere, with a large temperature gradient from 450–500°C at the grate to 2300°C in the coke combustion zone at the tuyeres [3].

The quantity of fuel-smelting material is characterized, according to the smelting results, by the following indicators: furnace operation, indicators of operating intensity, material balance, and the characteristics of the materials extracted from the furnace; comparison is used as the basis for all assessments. The results of smelting with FSM are compared with the results of smelting with a standard burden. This method of evaluation makes it possible, with greater or lesser reliability, to extrapolate the data obtained to industrial furnaces. The standard burden used consisted of coke, easily reducible ore, and limestone. The experimental burden consisted of fuel-smelting materials, fluxes (red brick and limestone), and coke, which was added because of the large heat losses of the laboratory blast furnace.

The operation of the furnace makes it possible to judge the behavior of the material being tested. If the material is strong and retains its structure up to the tuyere zone, then

the furnace accepts the blast without delays; no slips or surges in blast pressure are observed. Under the effect of thermal and mechanical loads, a weak material begins to break down; fines and dust clog the passages and channels in the burden column, dark pieces of unheated materials appear at the tuyeres, and the blast pressure changes sharply when gas flow is impeded. In the transition from the standard burden to the experimental one, no complications connected with the use of weak materials were noted. The operation of the furnace during the tests was exceptionally even, and the descent rate of the burden increased markedly. The increase in furnace operating rate is quite natural.

Table 1

Technical analysis of the fuel used in the experimental smelting

This is borne out by the technical-analysis data, which show that the peat-ore briquetting contains 57% volatile substances (Table 1). The volatiles are removed mainly up to a temperature of 800-850°C. This leads to substantial volumetric shrinkage of the materials in the furnace shaft. It must also be taken into account that the peat coke formed as a result of heat treatment burns in the tuyere zone at a much higher rate than hard-coal coke. Owing to the uniformity and evenness of the experimental burden in terms of screen composition, it has good gas permeability. The sum of these factors gives an increase in the rate of passage of materials through the shaft from 30.50 charges per hour to 38.6, and a reduction in the residence time of materials in the shaft from 1 h 42 min to 1 h 21 min, i.e., by 20%.

At the same time, the temperature in the furnace shaft decreased noticeably. A decrease in temperature in the furnace shaft during the transition to peat fuel had previously been observed by researchers [4]. The results of measurements of temperature over the depth of the shaft during operation on the standard and experimental burdens, carried out with a platinum-platinum-rhodium thermocouple, show (Fig. 1) that the temperature decreased over all levels of the furnace shaft. Nevertheless, the temperature in the combustion zone did not decrease and, according to some observations, even increased. The decrease in temperature is explained by the combination of the processes of peat coking and ore reduction. The short duration of smelting on the experimental burden does not make it possible to draw substantiated conclusions about the influence of this phenomenon on the thermal regime.

The intensity of furnace operation is expressed by the coefficient of utilization of the useful furnace volume (CUFV), by the residence time of the materials in the furnace, and by the combustion intensity in the tuyere zone, in kg per 1 m² of hearth section.

CUFV is defined as the useful furnace volume per ton of daily pig-iron output. CUFV is inversely proportional to the operating intensity only when the consumption of materials is constant. It may take different values at unchanged operating intensity but with changing quality of the raw material. The test results showed that, with the transition to the experimental burden, CUFV increased from 0.668 to 0.821 m³/t per day. A significant role in this change was played by the qual-

raw material. In view of the high yield of volatiles, the volumetric consumption of the experimental burden per unit of metal was higher than that of the standard burden, which also caused an increase in KIPO. Therefore, in this case KIPO does not reflect the actually increased intensity of the process.

When changing from the standard burden to the experimental one, the intensity of coke combustion decreased from 535 kg/m²·h to 488 kg/m²·h. The reason for this phenomenon is that the amount of nonvolatile carbon per unit weight of burden was reduced in the experimental burden to 35% in comparison with its content in the standard burden, which was 53%. Thus, comparison of the combustion intensity in this case is of a very conditional nature.

Fig. 1. Temperature distribution: 1 — smelting on ore, 2 — smelting on TPM

From the appearance of the materials extracted from the furnace, one can judge how they change while moving from the stockline to the hearth. Analysis shows how iron reduction proceeds. The picture is especially important in the tuyere zone, where the material is subjected to particularly strong thermal and mechanical effects. A material that is mechanically and thermally unstable will yield a large amount of fines, clogging the hearth and impeding the movement of gases. The lack of experience in working with a burden similar to the experimental one led to the fact that, after the furnace was stopped, during its cooling the tuyeres located in the upper part of the shaft were sooted up to a horizon 500 mm above the tuyere level. Naturally, the presence of air in the cooling blast furnace affected the properties also of that material which was not sooted. Dismantling of the preserved materials showed that, in the course of movement, the material changes its properties: it undergoes considerable shrinkage and, depending on the temperature, changes its strength; while partially breaking down, it basically retains its shape up to the zone of maximum temperatures. The strength of the material is noticeably reduced in this process. It would seem that such material should break down under the severe conditions of the IMET furnace, leading to complications in the furnace operation, as indicated above. In practice, however, this was not observed, which is also confirmed by the material balance. The material balance makes it possible to assess the strength of the material from the standpoint of removal of burden in the form of dust. A disintegrating and weak material gives high values of carryover of fines with the gases. Of particular val-

Table 2

Results of chemical analyses of FSM extracted from the blast furnace

… is the iron balance, which shows what fraction of the iron was carried off with the dust. An iron loss of no more than 20% is considered normal. Calculations show that the iron loss amounted to 6.2%, which indicates a fairly high strength of the fuel-smelting materials. At the same time, the mechanical characteristics of the materials extracted from the furnace do not confirm this conclusion. It is therefore necessary to carry out further studies to clarify the behavior of the fuel-smelting materials in the furnace.

Changes in the chemical composition of the briquettes are given in Table 2. Of greatest interest is the process of iron reduction. As can be seen from the table, already in the zone 300 mm above the tuyere level, where the temperature is 750°C, the amount of reduced iron is 56%. In the next horizon the degree of reduction is 99%. Thus, when entering the high-temperature zone, the iron is practically in the reduced state.

A comparison of the indicators considered does not reveal any factors that would categorically prevent the use of fuel-smelting materials in a blast furnace, and it shows the fundamental possibility of using peat-ore briquettes for smelting pig iron.

REFERENCES

1. Taylor, Louni, Hay. Study of the tuyere combustion zone. Problems of Modern Metallurgy. IL Publishing House, No. 2 (38), 1958.

2. I. F. Koval. On the question of the influence of blast-furnace blast temperature on the dimensions of the oxidizing zone. Stal’, No. 6, 1959.

3. Report on the work “Conducting an experimental smelting in an enlarged laboratory blast furnace and metallurgical evaluation of peat-ore briquettes of the Tomsk Polytechnic Institute.” A. A. Baikov Institute, Moscow, 1966.

4. N. P. Chizhevsky. Peat in the blast furnace. Stal’, No. 10, 1933.