CAST IRON

BLAST-FURNACE OPERATION WITH AUTO~IATIC STABILIZATION OF THE THEORETICAL TUYERE-HEARTH TEMPERATURE IN THE CASE OF A VARIABLE HOT-BLAST TEMPERATURE N. M. Bondarenko, A. F. Gri~hchenko, Yu. I. Grinberg, O. V. Mitasov, P. V. Sorokin, and I. Ya. Ustimenko

UDC 669.22.012.23

The efficiency of blast-furnace operation when the entire blast is fed through the stoves was substantiated in articles by L. D. Sharkevich in Metallurgy of Cast Iron, a collection of scientific researches at the Donetsk Scientific-Research Institute of Ferrous Metallurgy [Vol~ 24, Donetsk (1971), pp. 127-143] and by N. M. Babushkin, F. R. Shklyar, P. Bo Fedotov, e t a ! . , [Metallurg, No. 8,.8-11 (1976)]. It was noted in these articles that it is best to maintain a constant theoretical combustion temperature (Tteor) when the temperature of the hot blast is variable and that such a practice makes it possible to reduce fluctuations in the physical heating and composition of the pig iron. During ordinary blast-furnace operation, stabilization of the hot-blast temperature is the method used to stabilize the. thermal state of the hearth. Blast temperature is stabilized by supplying a certain amount of cold blast through the mixer valve. Operation of a furnace with a closed mixer valve makes it possible to more fully utilize the heating capacity of the stoves, although the thermal state of the hearth in time changes with the changes in the hotblast temperature. Thus, to stabilize Tteor and the thermal state of the hearth when hot-blast temperature decreases by IO~ it is necessary to reduce natural gas consumption by 0.13-0.14% of the blast. Blast-furnace No. 4 at the Kramatorsk Metallurgical Plant, used to make conversion pig iron, was changed over to operation without stabilization of hot-blast temperature through the mixer valve after raw ore in the charge was replaced by pellets in January 1981. The furnace is serviced by three stoves operating in a sequential regime and fired by blast-furnace gas from the same furnace. The dome temperature in the stoves does not exceed 1200~ Changeover of the furnace to the new technology made it possible to increase the temperature of the hot blast an average of 30~ To reduce fluctuations in hearth heating caused by an average drop in hot-blast temperature of 50-70~ during the stove-cooling period and to stabilize Tteor , an automatic system was introduced on the furnace to regulate the ratio of the hot blast temperature to the consumption of natural gas, with correction for the consumption of cold blast (ACS, for automatic control system). The initial ratio of the consumptions of natural gas and cold blast for furnace No. 4, working on an air blast with a temperature of IO00~ was 4.0-4.5%. This value is considered optimal for the existing charging conditions and was confirmed by trial heats with different consumptions of natural gas and by long experience; Tteor here is 19752025~ Figure i shows a functional diagram of the ACS. It is based on moving-coil instruments~ Ferrodynamic transducers FT have been included in instruments la, ic, Id, 2b, and 3b to convert an angle of rotation (proportional to the temperature and the consumption of cold blast and natural gas) into alternating voltage which is then used in the control circuit of the ACS.

Donetsk Scientific-Research Institute of Ferrous Metallurgy (DonNllchermet). Kramatorsk Metallurgical Plant. Donetsk Polytechnic Institute. Translated from Metallurg, No. 6, pp. 18-19, June, 1984.

0026-0894/84/0506-0189508.50

9 1985 Plenum Publishing Corporation

189

Ho~-blast line

Cold-blast line

Natural-gas line

Fig. I. Functional diagram of s y s t e m t o control the "hot-blast-temperature -- natural-gas-consumption" ratio with a correction for cold-blast consumption: 2) contracting device (diaphragm) to measure consumption of cold blast; 2a) differential manometer; 3) contracting device (diaphragm) to measure the consumption of natural gas; 3a) differential manometer; 4a) actuator control switch (remaining notation explained in text).

The ACS for the "hot-blast-temperature -- natural-gas-consumption" ratio works as follows. The temperature of the hot blast is measured by the set of instruments 1 and la. An alternating current proportional to the measured temperature is sent from the recorder la to the input of the adder lb. The consumption of cold blast is measured by the set of instruments 2, 2a~ and 2b. A transducer TF built into the recorder 2b sends an electrical signal proportional to the cold-blast consumption to the second input of the adder lb. An electrical signal propotional to the consumption of natural gas goes from the recorder 3b to the input of the measurement block of the relay-type control instrument 4. The controlling variable in our ACS is the hot-blast temperature (with a correction for cold-blast consumption), while the controlled variable is the consumption of natural gas, Since the furnace is operated with a variable blast consumption, the electrical signal proportional to the controlling parameter is corrected in the adder ib with allowance for the cold-blast consumption. To multiply the electrical signal of the controlling variable by the coefficient expressing the ratio, we use a converter to convert voltage into current (ic in the figure). There is a linear relationship between the output current of the converter and the voltage on the frame of the ferrodynamic transducer id [K. I. Didenko and Zh. A. Gusev, New Monitoring and Control Equipment [in Russian], Mashgiz, Moscow (1961)]. The output current of the transducer ic is proportional to the input voltage from the adder lb. The coefficient expressing the ratio of the controlling and controlled variables is determined by the angle of rotation of the frame of the transducer of control-point setting mechanism id. Electrical signals proportional to the controlling and controlled variables are summed algebraically in the measurement block of the control instrument 4. This sum is formed in accordance with the chosen control law and, acting through a contactless reversing starter 4b, it controls the electric actuator 3c. The latter moves the control element and thus changes the consumption (flow rate) of natural gas. The control instrument 4 controls natural gas consumption in accordance with the prescribed ratio. The control error with regard to the ratio is 5% Presented below are performance indices of the furnace with a closed mixer valve before and after introduction of the ACS (periods A and B correspond to January of 1981 and 1982, respectively):

190

A Production, tons/day . . . . . . . . . . . . . . Useful-volume utilization factor, m3/ton.day . . . . . . . . . . . . . . . .... Slag yield, tons/ton pig . . . . . . . . . . . . Fe content of iron-bearing part, % . . . . . . . Percentage of pellets in iron-bearing part. Blast: consumption, m3/min . . . . . . . . . . . . . . pressure, MPa, (psig) . . . . . . . . . . . . . temp., ~ . . . . . . . . . . . . . . . . . . . content of 02, % . . . . . . . . . . . . . . Top gas: pressure, MPa, (psig) . . . . . . . . . . . . . temp., ~ . . . . . . . . . . . . . . . . . . . Composition, %: CO . . . . . . . . . . . . . . . . . . . . . . CO2 . . . . . . . . . . . . . . . . . . . . . H2 . . . . . . . . . . . . . . . . . . . . . . Content in pig, %: Si . . . . . . . . . . . . . . . . . . . . . . Mn . . . . . . . . . . . . . . . . . . . . . . S. . . . . . . . . . . . . . . . . . . . . . . Slag basicity CaO/Si02 . . . . . . . . . . . . . Consumption of materials, kg/ton pig: pellets . . . . . . . . . . . . . . . . . . . iron ore . . . . . . . . . . . . . . . . . . . metallic additions . . . . . . . . . . . . . . limestone . . . . . . . . . . . . . . . . . . . dolomitized limestone . . . . . . . . . . . . . dry coke . . . . . . . . . . . . . . . . . . . dry coke, adjusted Natural gas consumption, m3/ton pig . . . . . . . Downtime, % . . . . . . . . . . . . . . . . . . . Slow-speed operation, % . . . . . . . . . . . . .

o

B

1274

1320

0~81! 576 59.18 88.2

0.783 623 58.65 75.7

1998 0.189(1o89) 956 21.0

1904 0.293(2.93) 1073 21.0

0.95(9.5) 182

0.108(i.08) 183

25.6 15.0 4.2

26.4 14.2 4.3

1.07 1.01 0.041 1.20

0.91 1.17 0.033 1.17

1440 193 68 496 46 689 689 64 0.6 i0.0

1282 413 78 449 109 663 684 88 0.9 0~

The lower hot-blast temperature in January of 1981 was due to a shortage of blastfurnace gas for heating the stoves. It can be seen from the above data that the introduction of the ACS reduced silicon content in the pig by 0.16% and decreased the adjusted consumption of coke by 5 kg/ton pig. The amount of pig iron produced which did not meet plant specifications for silicon content (no higher than 1.20%) decreased from 13.3 to 2.3%. Statistical analysis of the thermal state of the hearth, expressed through the silicon content of the pig iron, showed that stabilization of Tteor led to a reduction in fluctuations of silicon content: Operating regime

Mean silicon content, % Number of meas . . . . . . . . . . . SD, % . . . . . . . . . . . . . . . Coeff. of variation . . . . . . . .

Without stabilization of Tteor 1.07 207 0.32 0.30

With stabilization of Tteor 0.91 168 0.24 0.26

Thus, introduction of the automatic system to stabilize theoretical combustion temperature in the tuyere hearths during operation of a blast furnace with a variable hot-blast temperature made it possible to reduce the silicon content of the pig by 0.16%, reduce the amount of pig made which does not meet plant standards on silicon content by 11%, and reduce coke consumption by 5 kg/ton pig, or 0.72%.

191

FROM THE EDITOR The above method of stabilizing Tteor simultaneously destabilizes the consumption of reducing agents per unit amount of materials reduced, a situation aggravated by the fact that the decrease in natural gas consumption is accompanied by a synchronous reduction in hotblast temperature.. Conversely, an increase in blast temperature is accompanied by an increase in natural gas consumption. Thus, there are harmonic fluctuations of both heat input and the quantity of reducing gases available. Rather than compensating for each other, these fluctuations mutually reinforce the undesirable consequences with respect to both overheating of the materials in the hearth and the stability of the chemical composition of the pig at tapping. In connection with this, the editor believes that the above method is in need of additional testing before it can be recommended for broad adoption.

AUTOMATIC MONITORING OF LIQUID SMELTING PRODUCTS IN THE BLAST-FURNACE HEARTH* V. G. Makienko, Yu. V. Serov, V. A. Seredenko, A. A. Ii'yashov, Yu. V. Fedulov, L. S. Mkrtchan, I. M. Peftiev, V. A. Kalachev, and V. N. Rudenko

UDC 669.162.263.44:66.012.1

Work is being done in the USSR and abroad to develop new methods and equipment for monitoring the operation of blast furnaces. Mathematical models developed in the USSR, Japan, Italy, and other countries, based on indirect computer-assisted monitoring of hearth temperatures, are complicated, involve a large number of nominal and indirect theoretical parameters describing the thermal state of the hearth, and have a low prediction reliability and accuracy Along with their advantages, present direct methods of monitoring the operation of the blast-furnace hearth also have several serious shortcomings. For example, lance-enclosed temperature transducers (TsNIIchermet, Moscow Institute of Steel and Alloys, All Union Scientific-Research Institute of Heat Engineering in Metallurgy) provide only for monitoring of the tuyere hearth, the parameters of which nonlinearly characterize the temperature of the smelting products due to fluctuations in the oxidizing-reducing and heat-exchange work of the gas and charge. The accumulation of pig iron and slag in the hearth can be evaluated indirectly by the use of domestic devices which record so-called "internal electrical effects" on the steel shell of the furnace, the existence of which is argued by the authors (at the Novolipetsk combine and other plants) of the ion theory of melts. However, these devices do not provide for direct monitoring of the parameters of the liquid smelting products in a blasfurnace hearth. The well-known direct means of monitoring the tuyere zone of the hearth proposed and once used by crews under M. A. Pavlov and I. P. Bardin, involving the insertion of water-cooled probes through special ports, permitted only one-time measurement of the tuyerehearth parameters, was complicated, and was labor-intensive. To monitor the parameters of molten smelting products directly in the hearth of a blast furnace, TsNIIchermet has developed the TEGRA-I device. The device is designed so as to ensure continuous automatic monitoring during the entire campaign of the furnace (10-15 years) while not disturbing the air-tightness of the lining of the furnace. It is reliable and simple to use, has constant metrological characteristics, and permits the use of GSP-series heat-engineering equipment.

*Participating in this study were V. N. Khurshchev, S, V. Botman, N.A. Krimamli, N. I. Shpagin, A. V. Syrovatskii, N. A. Tereshchenko (Ii'ich Zhdanov Combine), V. V. Besfamil'nyi, M. A. Mikheev, V. A. Zavidonskii (Magnitogorsk combine), V. S. Polyanichko, and B. L. Fridman ("Azovstal'" combine).

Central Scientific-Research Institute of Ferrous Metallurgy (TsNIIchermet). from Metallurg, No. 6, pp. 20-22, June, 1984.

192

0026-0894/84/0506-0192508.50

9 1985 Plenum Publishing Corporation

Translated