Effect of the Composition of Fuel and Smelting Materials on the Reduction Rate
Abstract Generated abstract
This paper examines how the ore to peat ratio in peat-based fuel-smelting materials affects the reduction of iron oxides during shaft-furnace processing. Two laboratory smelting tests in a 200-liter shaft furnace compared briquettes made from magnetite concentrate and lowland peat with different ratios of nonvolatile carbon to iron, while monitoring furnace conditions, gas composition, and the metallization of charge samples taken from different furnace heights. The results indicate that a higher peat content markedly accelerates reduction despite a lower shaft temperature, with reduction in the high-peat material largely completed by the zone where coking ends. The study attributes this intensification mainly to peat and its thermal decomposition products, rather than to the conventional reduction mechanism by furnace gases.
Full Text
EFFECT OF THE COMPOSITION OF FUEL-SMELTING MATERIALS ON THE RATE OF REDUCTION
V. S. Arkhipov, S. I. Smolyaninov
(Presented by the scientific-methodological seminar of the Chemical-Technology Faculty)
In the manufacture of fuel-smelting materials (FSM) based on peat, the choice of the ratio between the ore and peat components is of great importance not only from the standpoint of strength, but also from the standpoint of the reducibility of iron oxides.
When FSM are processed in a shaft furnace, the following reduction paths may be distinguished:
- By coke-combustion gases (hearth gases).
- By vapor-gas products of peat pyrolysis.
- By the solid carbon of peat coke.
Under shaft-furnace conditions all three factors may act simultaneously; however, the action of the second and third is predominantly confined to quite definite zones. Reduction by the vapor-gas products of pyrolysis proceeds in the upper zone of the furnace, while reduction by solid carbon occurs most intensively in the high-temperature zone, where the coking process has already been completed.
The introduction of peat into the charge may cause the following consequences in reduction:
Table 1
Characteristics of charge materials
| Material | $A^c$ | $V^c$ | $C^c_{\mathrm{nonvol}}$ | $\mathrm{Fe}_{\mathrm{total}}$ | $\mathrm{SiO_2}$ | $\mathrm{CaO}$ | $\mathrm{Al_2O_3}$ | l.o.i. |
|---|---|---|---|---|---|---|---|---|
| Coke | 10.6 | 1.7 | 87.7 | 0.6 | 5.3 | 0.6 | 2.3 | |
| Limestone | 0.14 | 2.36 | 52.80 | 1.05 | 41.44 | |||
| FSM, test I | 45.2 | 43.9 | 10.9 | 21.7 | 5.27 | 3.05 | 2.93 | |
| FSM, test II | 29.8 | 49.7 | 20.5 | 11.3 | 6.4 | 3.6 | 1.4 |
- Removal of heat in the upper zone of the furnace with cooling of the charge and a decrease in the rate of reduction.
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Increasing the rate of reduction by enriching the gas with vapor-gas products of peat pyrolysis.
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Increasing the rate of reduction as a result of a relative increase in the content of the peat component in the FCM [1].
Clarification of the influence of the FCM composition on iron reduction was one of the tasks set during testing of peat-based FCM in a 200-liter laboratory shaft furnace [2].
Table 2
Operating parameters
| Parameters | Test I | Test II |
|---|---|---|
| Duration of the test, h–min | 27–30 | 15–17 |
| Charge composition, g: coke | 1000 | 1000 |
| Charge composition, g: FCM | 650 | 2145 |
| Charge composition, g: limestone | 110 | 111 |
| Calculated coefficients, kg/kg of metal: coke consumption | 6.99 | 5.86 |
| Calculated coefficients, kg/kg of metal: slag yield | 1.50 | 1.54 |
| Basicity of ternary slag | 1.03 | 0.8 |
| Blast: flow rate, nm³/h | 91 | 69 |
| Blast: temperature in the annular air duct, °C | 400 | 638 |
| Grate-gas temperature, °C | 448 | 313 |
| Intensity of coke combustion in the tuyere zone, kg/m²·h | 186 | 154 |
Two tests were carried out in which FCM prepared from magnetite concentrate from the Abagur sinter plant and lowland peat were used. In the first test, FCM with a ratio of nonvolatile carbon to iron of 0.5 was used; in the second, 1.82 (Table 1).
The use of coke in the charge and its high consumption per 1 kg of metal were caused by the large heat losses of the furnace. From the standpoint of the thermal regime, the reduction conditions were more favorable in the first test. This is explained by the higher coke consumption per 1 kg of metal (Table 2), the increased intensity of furnace operation, and the smaller removal of heat in the upper zone for peat coking. The temperature of the grate gas can serve as an indicator of the thermal state of the furnace; in the first test it was maintained at a level of 450°, while in the second it gradually decreased and by the end of the smelting amounted to 200°C.
Differences in the composition of the gas phase are insignificant: in the second experiment the high content of TPM in the charge (63%) leads to the appearance of hydrogen and methane in the gas (Table 3).
Table 3
Average gas composition
according to analyses on an KhL-3 chromatograph
| Experiment | CO | CO₂ | H₂ | CH₄ | N₂ | O₂ |
|---|---|---|---|---|---|---|
| I | 30.0 | 2.0 | 65.6 | 2.4 | ||
| II | 30.7 | 2.3 | 3.8 | 0.8 | 61.0 | 1.4 |
The results of the analysis (Table 4) show a significant difference in the course of reduction. If in the first experiment metallic iron appears in the layer 900–800 mm above the tuyere level, then in the second experiment the reduction process has already been completed in this layer. In the first experiment it was not possible to trace reduction down to the tuyere zone, since
Table 4
Analysis of TPM extracted from the furnace
| Charge layer, mm above tuyere level | I experiment Fetot | I experiment Femet | II experiment Fetot | II experiment Femet |
|---|---|---|---|---|
| 1500–1400 | 26.8 | 0.2 | 11.0 | 0.5 |
| 1400–1300 | 28.0 | 0.4 | 13.8 | 0.5 |
| 1300–1200 | 32.1 | 0.1 | 16.0 | 0.5 |
| 1200–1100 | 18.6 | 8.0 | ||
| 1100–1000 | 38.6 | 0.2 | 18.6 | 19.0 |
| 1000–900 | 42.5 | 0.1 | 20.9 | 20.6 |
| 900–800 | 40.0 | 1.7 | 21.8 | 17.5 |
| 800–700 | 40.4 | 3.5 | 24.5 | 20.6 |
| 700–600 | 41.0 | 4.8 | 26.2 | 21.3 |
| 600–500 | 40.4 | 5.6 | 27.2 | 24.5 |
| 500–400 | 24.7 | 22.2 | ||
| 400–300 | 38.6 | 27.3 | 24.0 | |
| 300–200 | 32.1 | 27.8 | 25.7 | |
| 200–100 | 29.8 | 28.7 | 25.3 | |
| 100–0 | 41.2 | 27.4 | 19.3 |
the lower charge layers were oxidized during cooling; however, the increased iron content in the slags of the first smelt (1.4–10.4%) compared with the second (1.8–6.0%) indicates incomplete reduction in the first experiment.
Judging from ash content and volatile-matter yield (Figs. 1, 2), coking ends in the 1000–900 mm layer. Thus, in the second experiment the coking and reduction processes are completed simultaneously, whereas in the first experiment reduction continues below the coking zone as well, evidently down to the tuyere level.
Thus, the tests carried out make it possible to state with complete certainty that increasing the peat content in fuel-ore materials significantly intensifies the reduction processes, despite the decrease in the temperature of the furnace shaft. The sharp difference in the pattern of reduction in the two tests indicates the predominant role of peat and of the products of its decomposition as a reducing agent, and the subordinate importance of the usual mechanism of reduction in shaft furnaces by furnace gases.
Fig. 1. Change in the ash content of fuel-ore materials over the height of the furnace: 1 — first test, 2 — second test
Fig. 2. Loss of volatiles from fuel-ore materials over the height of the furnace: 1 — first test, 2 — second test
Conclusions
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Metallurgical tests of peat-ore briquettes were carried out in a large laboratory shaft furnace.
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The processes of reduction of iron oxides in briquettes with different contents of the peat component were studied.
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A sharp intensification of reduction reactions by the products of thermal decomposition of peat was demonstrated.
References
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P. V. Geld. Uspekhi khimii, 26, pp. 1070–1083, 1957.
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A. M. Chernyshev et al. New methods for preparing fuel and fuel-ore materials and their metallurgical processing. ITI, vol. 22, 1963.