Thermal Balance of Peat-Bloomery Smelting
Abstract Generated abstract
This paper examines the thermal balance of blast-furnace smelting when peat is used as fuel, a practice known to lower shaft temperatures because of peat moisture and high volatile content. Using established blast-furnace calculation schemes, the authors estimate the thermal equivalent and required consumption of Tagan-type lowland peat in a simplified burden of ore, limestone, and peat, accounting for drying, semicoking products, tar, gas, ash slagging, and heat losses. The calculation gives a peat consumption of about 6.8 kg per kg of pig iron, broadly consistent with reported industrial tests. The resulting heat balance indicates that only about 20 percent of the heat supports iron smelting, while roughly 60 percent is consumed in processing the peat itself, making the furnace function largely as a gas generator with slag removal.
Full Text
THERMAL BALANCE OF PEAT-FUELED BLAST-FURNACE SMELTING
S. I. Smolyaninov, V. S. Arkhipov
(Presented by the KhTF scientific-methodological seminar)
The practice of using peat as a fuel in industrial blast furnaces [1], as well as tests of peat fuel-fluxing materials in laboratory shaft furnaces [2], have shown that the use of peat invariably leads to a decrease in temperatures in the furnace shaft, and sometimes to disruption of the smelting process, if appropriate measures are not taken. This phenomenon is explained by the high moisture content of peat (35–40%) and by a volatile yield on the order of 65% of the dry matter.
The water vapor, tar, and gas released in the shaft carry away a considerable amount of heat, which is normally expended on heating the burden and on indirect reduction. Sometimes the heat expenditure for evaporating the moisture of the peat is so great that the furnace turns into a drying unit [1]. Thus, a significant part of the heat from the combustion of the nonvolatile carbon of the peat is spent on “self-servicing,” while the actual reduction processes play a subordinate role in the thermal balance. At the same time, drying the peat in the shaft furnace may be regarded as a positive factor, since the excess heat of the outgoing gases is usefully utilized.
In this connection, the question of the rational consumption of peat per unit of pig iron and of the distribution of heat among the items of the thermal balance when peat is used as fuel in a shaft furnace is of interest, regardless of whether it is used in the form of a fuel-fluxing material or in the form of separate pieces.
It is most convenient to perform such a calculation for the blast-furnace process, since calculation schemes have been developed for it in detail and the necessary experimental reference data are available.
Taking as given the smelting conditions adopted by A. N. Ramm for calculating the thermal equivalents of iron ores, and taking into account the calculated thermal characteristics of Sokolovsko-Sarbaisk ore and of normal flux [3], we shall determine the thermal equivalent of peat and its consumption per 1 kg of conditioning pig iron. For simplicity, we shall limit ourselves to a burden consisting of only three components: ore, limestone, and peat. The quality of the peat (Table 1) adopted for the calculation is characteristic of Tagan peat, which was used for making experimental fuel-fluxing materials at the Tomsk Polytechnic Institute.
The yield of semicoking products and the composition of the coking gas are taken according to N. P. Bogdanov [4] for the conditions of gasification of lump peat 35–40 mm in size in industrial gas generators.
Table 1
Characteristics of peat
| Technical analysis, % | Technical analysis, % | Technical analysis, % | Technical analysis, % | Technical analysis, % | Yield of semicoking products, % on dry peat | Yield of semicoking products, % on dry peat | Yield of semicoking products, % on dry peat | Yield of semicoking products, % on dry peat |
|---|---|---|---|---|---|---|---|---|
| $W^p$ | $A^c$ | $V^c$ | $C_{\text{nonvol.}}^c$ | $S^c$ | coke | pyrogenetic moisture | tar | gas |
| 20,00 | 9,46 | 61,20 | 29,64 | 1,00 | 38,8 | 17,0 | 11,0 | 33,2 |
The thermal equivalent of peat was determined by the formula derived for coke, but taking into account the heat expenditures for evaporation and superheating of water vapor and tar.
The obtained value of the relative consumption of peat—6.83 kg/kg of pig iron—is close to the data of industrial tests—4–6 kg/kg of pig iron—which indicates the reliability of the calculation.
If one takes as a basis air-dried peat with a final moisture content of 35–40%, still higher peat consumptions should be expected.
On the basis of the data obtained, the heat balance of peat-blast-furnace smelting was compiled (Table 2).
Table 2
Heat consumption per 1 kg of pig iron in peat-blast-furnace smelting
| Item No. | Expenditure items | kcal/kg | % |
|---|---|---|---|
| 1. | Heat consumption for producing pig iron from iron ore, taking into account slagging of the barren rock | 1506 | 20,0 |
| 2. | Heat consumption for the processes of drying, coking, and slagging of peat ash: | ||
| a) evaporation and superheating of working and pyrogenetic moisture | 2075 | 27,7 | |
| b) evaporation and superheating of tar | 173 | 2,3 | |
| c) sensible heat of pyrolysis gas | 225 | 3,0 | |
| d) slag formation and losses with slag | 1988 | 26,5 | |
| 3. | Sensible heat of bosh gas (after deducting pyrolysis gas) | 1025 | 13,7 |
| 4. | External heat losses | 506 | 6,8 |
| 5. | Total | 7498 | 100,0 |
First of all, attention is drawn to the high heat consumption per 1 kg of pig iron in peat-blast-furnace smelting—7498 kcal—in comparison with smelting on coke—1657 kcal [5]. The reduction processes proper occupy only 20% in the heat balance of peat smelting, as against 76.4% in coke smelting; the remaining amount of heat is expended on drying the peat (28%), slagging the ash (26.5%), and heat losses (20.5%). Thus, 60% of the balance heat is consumed by the peat itself. The blast furnace in this case is transformed into a gas generator with liquid slag removal, in which 20% of the excess heat is used for producing pig iron.
Conclusions
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The consumption of lowland peat with an ash content of 10% and a moisture content of 20% is 6.8 kg of dry peat per 1 kg of cast iron.
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In peat-blast-furnace smelting, 60% of the heat is expended on processing the peat, and only 20% on processes associated with smelting cast iron.
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The heat expenditures for coking the peat are small and amount to about 5% of the heat-balance total.
Literature
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Peat and Its Chemical Utilization, ed. M. A. Pavlov, ONTI NKTP, pp. 93–121, Moscow, 1935.
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Conducting an experimental smelting in an enlarged laboratory blast furnace and metallurgical evaluation of peat-ore briquettes of the Tomsk Polytechnic Institute. Report on Topic No. 358—3, IMet im. A. A. Baikov, Moscow, 1966.
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Blast-Furnace Production. Metallurgizdat, Moscow, vol. 1, 1963.
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N. N. Bogdanov. Semi-coking and Gasification of Peat, Gosenergoizdat, Moscow, 1947.
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A. D. Gotlib. The Blast-Furnace Process, 2nd ed., Metallurgiya Publishing House, Moscow, 1966.