JPS6040482B2 - How to operate a blast furnace - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of operating a blast furnace, and particularly to a method of operating a blast furnace in a stable and efficient manner by controlling the shape and position of the softened cohesive zone. In a blast furnace, ores and coke are placed in bags from the top of the furnace in layers, and heated and smelted using air blown from the tuyeres. The ores charged from the top of the furnace are heated and reduced by the rising gas while descending inside the furnace, and begin to soften and fuse at around 1250 qo, and melt and drip at around 1400 qo. This softening cohesive zone has extremely poor ventilation, so in order to ensure ventilation in the furnace in this area, the height of the softening cohesive zone temperature range should be different in the direction of the furnace fleas, and the ore It is necessary to allow gas to flow into the coke layer between the steel and the ores. Furthermore, if the position in the furnace is too low, the furnace heat will fluctuate due to poor reduction, and if it is too high, the high-temperature castle will expand, leading to deterioration of ventilation, so it is necessary to keep the blast furnace in a stable and efficient state. For operation, it is necessary to appropriately control the height of this softening cohesive zone temperature castle within the furnace. On the other hand, in conventional operating methods, stable operation is maintained by converting the gas composition and temperature distribution in the radial direction of the furnace obtained by an in-furnace gas sampler installed at the top of the furnace into an index and keeping these within an appropriate range. However, this often provides only qualitative information about the height of the softened cohesive zone in the furnace, which is intertwined with other factors, and is therefore not appropriate. This resulted in a hindrance. The object of the present invention is to
The object of the present invention is to provide a method for stabilizing and increasing the efficiency of blast furnace operation by understanding the isothermal distribution in the radial direction within the furnace of 400 oo and controlling it within an appropriate range. The key point of the present invention is that during blast furnace operation, the temperature in all directions of the furnace diameter measured by a gas sampler installed directly above the charge surface, and the C○, C02, Day2, N2, etc. in the direction of the furnace surface. The shape and position of the softened cohesive zone can be determined based on the gas component distribution and operating conditions.
Quantitatively determined as an isothermal distribution in all directions of the furnace diameter at 0qC, the height Am from the tuyere level at a position of 1400qC at the furnace center,
The lowest value of the height of the isotherm from the tuyere level is Rm, the hearth radius is Rh, and the temperature of coke entering the tuyere tip combustion zone is calculated as 75% of the theoretical combustion temperature at the tip. This is a blast furnace operating method characterized by stable and efficient operation by actively controlling the shape of the softening adhesion zone so that when Tad is Am and Bm satisfy the following ■, Tsukuda formula. . Wind. Madarami Shaimo Aozora Mi・-73 legs 0.7×cos {(0
．． 001 x Tad - 2)
xcos {(0.001xTad-2)×n} ten 0.8
Hereinafter, details and embodiments of the present invention will be described with reference to the accompanying drawings. First, we will discuss a method for understanding the shape of the softened adhesion zone inside a blast furnace. According to dismantling surveys of blast furnaces and laboratory experiments, the charge charged from the top of the furnace descends through the furnace while maintaining its layered structure, and the ores are heated and reduced during the descent, softening and melting at approximately 125,000 ℃. It is known that it starts to deposit and melts and drips at about 1400°C. Therefore, at any position in the direction of the furnace, 25,000 and 14
If the height of 00qo is known, the isothermal distribution obtained by connecting this height in the direction of the furnace fleas will indicate the cross-sectional shape and position of the cohesive zone. On the other hand, if we assume that there is no distribution in the pressure, temperature, etc. within the furnace in all directions of the furnace diameter, and that these distributions exist only in the height direction, then the top gas temperature and components obtained as a result of operation are A method is known in which the reaction amount in the furnace is determined based on the material balance and heat balance from operating conditions such as combined air blowing conditions, and the temperature distribution in the furnace height direction is calculated from the reaction temperature and heat transfer rate. Therefore, if the blast furnace is divided into multiple rings and each divided area can be regarded as an independent blast furnace, the furnace top gas temperature and gas composition in each divided area can be easily determined from the furnace cavity direction gas sampler on the charge surface. Therefore, the temperature distribution in the direction of the furnace recess of each divided region can be determined in the above-mentioned direction, and the shape and position of the Europeanized cohesive zone can be determined from the isotemperature line distribution obtained by connecting the isotemperature positions of each region. As a result of various studies conducted by the present inventors regarding this method, it was found that the actually measured temperature distribution in the furnace and the calculated results were significantly different. The reason for this is that when the blast furnace is divided into multiple rings, the movement of material between each divided area is negligible from the charge surface to the softening and adhesion zone. This is because the situation below the belt is different from that above. This will be explained with reference to FIG. 1, a partial sectional view of a blast furnace.
That is, there is a blade □ 2 at the bottom of the blast furnace 1, and the multiple ring-shaped dividing boundary 3 of the blast furnace is shown by a dot Sunsen. A dripping substance 5 is dripping from the softened cohesive zone 4. During the process in which the front gas 6 is distributed to each divided area in the dripping zone, CO gas generated by direct reduction of ores mixes with the front gas 6 and the European cohesive zone 4
Since the composition of the gas that reaches the furnace differs for each divided region, large errors occur in the calculation of material balance and heat balance, and the actual temperature distribution inside the furnace differs greatly from the calculated results. Furthermore, considering the CO gas (hereinafter referred to as mixed CO) generated from the immediate reduction of steel ores mixed in the gas before the tuyere, if the blast furnace is divided into multiple rings, each divided area can be regarded as an independent blast furnace. It was found that the temperature distribution inside the furnace can be estimated with high accuracy using the method described above. A method of estimating the temperature distribution in the furnace by considering the following mixed CO will be explained. This method consists of the following four steps. Step 1: Calculating the charge descent velocity distribution in the direction of the furnace Step 2: Calculating the reaction force using mass balance and heat balance Step 3
:Evaluation of distribution of descending velocity of baggies Step 4: Calculation of temperature distribution inside the furnace Divide the blast furnace into n multiple rings corresponding to the measurement points of the gas sampler installed directly above the baggies. n is the number of measurement points of the gas sampler and is usually 4 to 10. Further, the subscript i of each symbol below indicates the i-th area from the center side. Step 1; Since the rate of descent of the bags in the blast furnace has a nearly linear distribution in the radial direction, the rate of descent of the bags in the i region is given by the formula '1}, and the parameter A is set to an initial value of 1 to 5. gives any negative integer. Field i=AX [Ri-Masuri] River B...Here UBi
: Descending speed of rhombus in the i region [m/h] UB: Average descending speed of the rhombus in the blast furnace [m/h] SS, Si: Average cross-sectional area of the blast furnace and average cross-sectional area of the i-region [〆] Ri: Distance from the center of the defect that divides the area of area i into two [m] Step 2: For each divided area, solve the following simultaneous equations regarding material balance and heat balance* to calculate the amount of dry gas at the top of the furnace per unit air flow rate. VT
OPi [N〆/1 pi Nm3-blast], pig iron production amount PIG1 [k9/1 pi Nm3-blast], solution loss carbon chapter CSOLi [kg/1 and Nm3-bl
[ast], the amount of water vapor in the furnace top gas generated by indirect reduction of ores TH2 [k9/1 pi Nm31 blast]
, mixed CO amount COMIXi [Nm3/1 piNm3-bl
ast]. From the nitrogen balance, from the hydrogen balance, from the carbon balance, 1 public IC○i + TC02) x VTOPi = CBV + CS
OLi ten CIMmXPIGi+12×COMIXi
．． ．． ．． [4,2240
224 Oxygen balance to 16XnC side 2XTC. 4th referee XTH 2 = OBV side MPXP/Gi 116 x OB
YFEXRSXPIGi2240
55
．． 85 22・4. ．．・{5} From the heat balance, here TTOPi, TN2, TC0j, TC02, T
H2: Furnace top gas temperature in i region

[00] and N2 in the furnace top dry gas. C○, C02, daily concentration [%] NBV, HBV, OBV, CBV: Nitrogen, hydrogen, and oxygen that the blast brings into the furnace and the carbon that is combusted with this oxygen [kg
/1 pi Nm3- blast] CN, CH, FIXC: Nitrogen, hydrogen, carbon content in coke [1] NCOKE, HCOKE; Nitrogen, hydrogen generated from coke burning in front of the tuyere [k9/1 pi Nm3
-blast] CIMP, 01MP; Carbon and oxygen in CO generated by reduction of Si, Mn, P, and Ti in pig iron [k9/1piNm3
-blast] OBYFE; Atomic ratio of oxygen and iron combined with iron in iron ores [1] Ratio of iron derived from ores to iron in pig iron [1] Q,; Considering heat of moisture decomposition Sensible heat of air blast [kcal/1piNm3-blast] Q2: Combustion heat of heavy oil considering sensible heat and decomposition heat of heavy oil [〃
] Pi: Heat of coke combustion [〃] Q4: Heat of indirect reduction by CO gas of iron ores [〃] Q:
Sensible heat held by mixed CO [〃] Pi: Sensible heat of molten iron [〃] Q? : Slag head heat [〃] Q8: Pig Sj, Mn, T;, heat of reduction of P and heat of dissolution of C [〃] Q: Heat of solution Soros reaction [〃] Q, o: Hydrogen gas reaction [〃] Q. : Heat of moisture evaporation [〃] Q, 2: Sensible heat of furnace gas [〃] Q, 3: Heat loss [〃] Ores OREi [k9/1] consumed per 10ONm3 of air blown in the i-th area pi Nm3-blast], coke COKEi [k9/1 pi Nm3-blast], reduction pellet amount REDPi [k9/1 pi Nm3-blas]
t] is determined by the following equation using the solution of this simultaneous equation. OREi = Dohan Noh 9 --- (7' Reishenteifu /
main? *E1 CSLi ten plate side i…■ REDPi=W Yorume XP・Gi Here, TFE: Iron content ratio of ores [1] CCOKE;
Carbon in coke burned in front of the blade by blowing 1000Nm3 [k9/1piNm3-blast] WREDP, WPIG: Reduction pellet usage, tap iron production [k9/1piNm3-blast]
ton/dy] Step 3; Amount of air blown distributed to each distribution area BVi [1 piNm3/h
] and the furnace top gas pressure VVTOPi [Nm3/h] are determined by the following formula. UBixSi
...[9}BVi:. pEi/pore+COKEi/pc. keju REDP
i/PREOPVVTOPi=VTOPi×BVi
...(10) Here, pore, pCO
KE, PREDP: Ore, coke, reduced pelleting density [k9/〆] Next, the furnace top gas temperature and dry gas composition are determined from the calculation results of each divided area using the following formula. T.T.C. =ZTC○jxVVTOPi. ．． ．． (,
,)ZVVTOPiTTC02=ZTC02xVVTO
Pi. ．． ．． (,2)ZVVTOPiTTN2
=2TN public x VVTOPi. ．． ．． (,5
)2VVTOPiTTH2=ZTH public x VVTOPi
．． ．． ．． (,3) 2VVTOPi where...
TTC○, TTC02, TTN2, TTH2; C○, C02, N2, daily concentration of furnace top dry gas for the entire blast furnace [
%] TTT: Top gas temperature of the entire blast furnace

[00] CPC○, CPC02, CPN2, CPH2, CPH2
0: C○, C02, N2, day 2, day 20 specific heat [kea
l/Nm3°C] Using these values, the charge descent velocity distribution is evaluated using the following formula. Let the evaluation value be EA. Hiroshi: Taishika Mepui Taki Pre-furnace gas temperature [℃], C0, C02 concentration [%] Here, return to step 1 again and set the value of A to an arbitrary small positive value (for example, 0.01, 0 A value such as .001) is added, this is set as A again, and the calculations in steps 1 to 3 are performed to obtain EA. In this way, step 1 increases A little by little until the value of A does not exceed the absolute value of the initially set value of A.
Repeat calculations up to 3. On the other hand, the evaluation value EA will be a large value if the parameter A is inappropriate and the descending speed distribution expressed by equation [1} is significantly different from the actual one, and if A is appropriate, EA' approaches zero. That is, when EA is at its minimum, the m formula is closest to the rhombite fall rate distribution in the furnace, and the calculated value at this time best represents the condition in the blast furnace. Therefore, in the calculation of step 4, E
Use the calculation results of steps 1 to 3 when A is the minimum. Step 4: In the blast furnace, the charge is 950o from the charge side.
The reaction heat and heat loss are small until the reaction heat and heat loss reach about
Zj, TGZi] is determined by the following equation as a function of depth [m] from the surface of the charge. Here, TSO: Temperature at the time of bagging the charge [°C] HV: Heat transfer coefficient between gas and solid [kcal/h・〇0] AA
i: Cross-sectional mirror [elbow] of area i in Z direction CCi: Heat capacity flow rate of solid in area i [kcal/h・℃] GTUi:
Heat capacity flow rate ratio of gas and solid in region i [1] Next, the temperature distribution in the furnace height direction in the region where the temperature of the bagged material is 95,000 or higher is determined as follows. (The charge is divided into minute sections of distance △Z in the furnace height direction from the position where the charge reaches 95,000 at 160,000 sheep. At any boundary position Z of this minute section, the heat capacity of the charge and gas, the flow rate ,,○.,Charge weight W per 100 m3 of air blowing
, and moth volume VV, warm shellfish in bag, gas temperature T
, is known, the gas temperature L is calculated from the charge temperature at the next boundary position Z + △Z, and the average temperature of the charge and gas between this Z + △Z is L, To, using the following formula. be done. et al. 10AQ2XBV length DFXAQI ---(・8
) Here, P = R Yoshisha Hisao
Solution loss heat of reaction at p [kcal/1 piNm3
-blast]AQ2=HV×Sixno- et al.) Transfer from gas to solid △Z×BVi heat amount [kcal/1piNm3-blast] Ratio=day. -2 drops of water P and average heat capacity flow rate of solid [kcal/h. OC] CGP: Specific heat of gas [kcal
/Nm300] DF: Contribution rate of solid to solution loss reaction heat [1] However, since , To are unknown, ra,
By giving to, , To=T, as the initial value of To, t2 and T2 can be found. T again here. = (t, +ra)/2, To = (T, 10T2)/2, and above 2, T2 is expressed as (18), (19)
t2, T2 by calculating convergence by repeating this operation.
is found. At this time, the temperature of the charge and gas at Z + △Z, the heat capacity flow rate of the rhombite and gas, the weight of the charge and the gas volume per m3 on the 100 side of the blast are also determined from the solution loss reaction amount, so the following minute Various calculations can be made for the section, and by sequentially repeating these calculations, the temperature distribution in the furnace height direction can be obtained. On the other hand, the position where the charge temperature reaches 950 do is determined by equation (16), and the gas temperature is determined by equation (17). Heat capacity flow rate of charge and gas at this position, blowing 10
The solid weight and gas volume per m3 are respectively (CPO
RE×OREi ten CPCOKE×COKEi+CPRE
DP×REDPi)×BVi, CPG×VVTOPi,
(OREj+COKEj+REDPj), VTOPi. Therefore, the temperature distribution in the direction of the furnace height when the bag temperature is 95,000 can be calculated using the method described below using these as the initial values at the start of calculation, and the softening temperature can be calculated from the isotemperature line obtained by connecting the positions of 125,000 and 1,400 qo in each divided area. The shape of the cohesive zone can be understood quantitatively. The most important feature of the estimation of the temperature distribution in the blast furnace described above is that the amount of reaction in each divided region is determined by taking into consideration the mixed CO, which cannot be estimated at all by conventional methods. Next, a method of operating a blast furnace according to the present invention will be explained. As mentioned above, the shape and position of the softened cohesive zone is such that the aeration of the cohesive zone is extremely poor. It is necessary to make the gas flow into the coke layer between the ores, and if the position in the furnace is too downward, the furnace heat will fluctuate due to poor reduction. It is also necessary to control it within an appropriate range because if it is too high, the high temperature region will expand, resulting in poor ventilation and wind pressure fluctuations. Based on this idea, the actual 2000-4000
In that blast furnace, the position, shape and operation of the softened cohesive zone were determined by changing the radial charge distribution using the ore/coke ratio (hereinafter referred to as ○/C), the blowing temperature, and the movable armor. After investigating the condition, it was found that stable and efficient operation could be ensured if the position and shape of the softened cohesive zone estimated by calculation were within the following range. In other words, the height of the 1400oo radial isotherm line from the blade □ level at the center of the furnace obtained by calculation is Am■), and the lowest value of the height from the blade □ level in the radial direction of the isothermal line is R.
m (m), and the temperature of the coke entering the tip of the blade is 75% of the theoretical combustion temperature of the tip of the blade, Tad.
(°C), and the hearth radius at the tuyere level is Rh (m), then the normal theoretical combustion temperature range (2150<Tad<25
00) Then it's Hadashago. -Ne〇. 7XCOS {〇. 〇. IXTad-2)X stroke}10.5<1.2×cos{(
It has been found that stable and efficient operation can be ensured by controlling the temperature to 0.001 x Tad-2) x 0.8.
Next, the above restriction expression will be explained. In a blast furnace, ores and coke are charged alternately, so the two are accumulated in layers inside the furnace, and they descend through the furnace while maintaining this layered structure.
It is known that the ores begin to soften and coalesce when the charge reaches about 125,000, and melt and drip at about 140,000. In particular, the softened and fused materials of ores are highly permeable, so in the softened brood zone 4 shown in FIG. 1, gas flows through the coke layer sandwiched between the softened and fused materials as shown in the figure. Therefore, the size of Am-Bm corresponds to the number of coke layers sandwiched between the softened layers, and if Am-Bm is large, it is good for ensuring ventilation in the furnace, but if it is too large, it will cause the center blow-through and gas This causes a decrease in utilization rate, deterioration of reactor condition, and increase in fuel ratio. On the other hand, when Am-Bm decreases to 4.0, the ventilation resistance inside the furnace increases due to the decrease in the coke layer, and the furnace condition becomes unstable. Therefore, in order to stabilize and improve the efficiency of blast furnace operation, it is necessary to set upper and lower limits for Am-Bm. However, it is clear that regulating only Am-Bm is insufficient when considering the size of blast furnaces. In other words, in a blast furnace with a large hearth diameter, the amount of air blown is naturally large, so
In order to keep the ventilation resistance in the cohesive layer approximately constant regardless of the size of the blast furnace, the larger the blast furnace, the larger the number of coke layers, that is, the larger Am-Bm. Therefore, by setting (Am-Bm)/Rh, it is possible to standardize the number of coke layers sandwiched between the fused materials in consideration of the size of the blast furnace. However, in a blast furnace, the tuyeres are installed to protrude from the furnace down to the inside of the furnace by approximately 40 mm, and from the perspective of the gas flow in the lower part of the furnace, the net hearth tuyeres are calculated by subtracting this 40 mm, which is Rh-0.4. So, the standardization is (Am-Bm)/(
Rh-0.4) is appropriate. From this point of view, both the furnace condition and fuel ratio will be good in actual operation (Am-B
The range of m)/(Rh-0.4) was investigated. Next, the latter equation including Tad and Bm will be explained. In order to improve the fuel efficiency of a blast furnace, it is necessary to determine the length of the blast furnace's lumpy zone, that is, the distance from the surface of the furnace charge to the position where the ores start softening and fusion, as is clear from Figure 1. Although it differs depending on the direction of the furnace, it is necessary to lengthen this distance and increase the indirect reduction rate of ores. However, if this distance is too large, the ore will reach the hearth with insufficient reduction and insufficient heat transfer, causing a drop in furnace heat, and in the worst case, there is a risk of serious accidents such as cooling. . In general, blast furnaces are affected by charging conditions such as the movable armor position at the top of the furnace and the charging schedule, and the lowest softened cohesive zone level is located on the furnace wall side, approximately from the inner surface of the furnace wall. It is within the range of about 3 hours. This region is directly exposed to the high-temperature gas in front of the tuyeres, and the ores melt at about 40,000 degrees Celsius, are rapidly heated to about 1,500 degrees by the high-temperature tuyere gases, and reach the hearth. Therefore, if the position of the European cohesive zone in this area is too low, there will be a lack of furnace heat due to poor heat transfer, and if it is too high, the amount of heat supplied will be excessive, leading to a decrease in fuel efficiency and an increase in wind pressure in the so-called hot area. However, the furnace condition becomes unstable. When trying to stabilize the fuel ratio and furnace conditions in this way, there should be upper and lower limits to the height of the softened cohesive zone (Bm in the case of the present invention) at the position where the softened cohesive zone is the lowest. It is. On the other hand, iron ores melt at a substantially constant temperature of about 140,000°C, but the heat transfer from the gas to the molten material after melting largely depends on the temperature difference between the two. In other words, since the temperature at which iron ores melt is almost constant, it largely depends on the gas temperature in front of the tuyere. Therefore, the front gas temperature (theoretical combustion temperature Tad)
If Tad is high, heat transfer is ensured even if the lower limit of Bm is small, but if Tad is low, heat transfer will be insufficient unless the lower limit of Bm is large. On the other hand, when the upper limit of Bm is high, Tad is high, the heat transfer from the gas to the melt is large, so if the difference from the lower limit is small, the heat transfer becomes surplus, whereas when Tad is low, the heat transfer from the gas to the melt is large. Since heat transfer to objects becomes relatively small, B
The difference between the upper and lower limits of m is allowed to be within a larger range than when Tad is high. In this way, it is necessary to reduce Bm in order to reduce the blast furnace fuel ratio, but there are upper and lower limits to this, and this is thought to be closely related to the theoretical combustion temperature. As a result of investigating and studying the range in which both the condition and the fuel ratio are favorable in terms of the relationship between Bm and Tad, the relational expression of the present invention was found.
In particular, 0.7×cos {(〇.〇.1XTad-2)
The cos of 0.8 is obtained by adapting the boundaries between insufficient furnace heat and the appropriate operating range and between overheating of the furnace and the appropriate operating range as an empirical formula, which were obtained as a result of the investigation. . Next, as a method to control (Am-Bm)/(Rh-0.4) and Bm, for the former, the amount of coke or ore charged per time, the height of the charging line, This can be easily achieved by adjusting the order of injection, the position of the mover puller, and the chute angle in a bellless blast furnace, and the latter can be easily controlled by controlling the air temperature, humidity, air flow rate, heavy oil injection weight, and the position of the moveable armor. I can do it. Example 1 This is an example in which the cohesive zone is determined using a calculation formula using measured values.
Based on the various operating conditions mentioned above and the measured values of C○, C02, Day2, and N2 of the gas sampler directly above the charge at each measurement position from the center (Table 1) in the blast furnace that was operated in 1996. Figure 2 shows the results of calculating the isotherm distribution inside the furnace. Table 1 Example 2 Tables 2 and 3 have ○/C of 3.90 and 4.00, respectively.
The position of the movable armor, theoretical combustion temperature, Bm, for the present invention example and the comparative example not according to the present invention when
(Am-Bm)/(Rh-0.4) and an index representing the furnace condition are shown. From Tables 2 and 3 (Am-Bm)/(Rh-0.4)
When Bm and Bm are controlled within the range according to the present invention, the fuel cost is lower than in the comparative example, and stable and efficient operation is ensured with fewer fluctuations in hot metal Si, ventilation fluctuations in the furnace, and number of abnormalities in dropping of the charge. It is clear that Table 2 * Shows the degree of dispersion of wind pressure measurements every minute; the larger the number, the greater the variation. Table 3 By setting an appropriate range for the shape and position of the softened cohesive zone in the furnace, the present invention enables unified operation length because conventionally the operation is based on information that includes the operating conditions of a gas sampler and internal phenomena. By eliminating the difficulty in controlling the condition and controlling the softened cohesive zone shape and position to keep it within an appropriate range, the operating condition of the blast furnace can be maintained in good condition. In the present invention, (Am-Bm)/(Rh-0.4) and B
The operating condition of the blast furnace can be maintained in good condition by controlling the
A similar effect can be expected by approximating a curve and displaying its slope or curve. Furthermore, although the present invention uses the temperature and gas components measured by a gas sampler directly above the shaft, it is natural that the temperature distribution inside the furnace can be similarly estimated using the measured values from the gas sampler installed at the top of the shaft. It is. Brief Description of the Drawings Figure 1 is a sectional view showing the distribution of insect encroachments in a blast furnace and the gas flow from the tuyere, and Figure 2 is an isothermal line showing an example of the temperature distribution in a blast furnace calculated according to the present invention. It is a diagram. 1... Blast furnace, 2... Feather ○, 4... Fusion body, 5... Dropped material. Figure 1 Figure 2

Claims (1)

[Claims] 1. In blast furnace operation, the temperature in the radial direction of the furnace measured by a gas sampler installed directly above the charge surface and the C in the radial direction of the furnace.
Based on the distribution of gas components such as O, CO_2, H_2, N_2 and operating conditions, the shape and position of the softened cohesive zone can be determined by
Quantitatively determined as the isothermal line distribution in the radial direction of the furnace at 00°C, the height Am from the tuyere level at the position of 1400°C at the center of the furnace,
The minimum height of the isotherm from the tuyere level is Bm, the hearth radius is Rh, and the theoretical combustion temperature calculated by assuming that the temperature of coke entering the tuyere tip is 75% of the theoretical combustion temperature at the tuyere tip is Tad. A blast furnace operating method characterized in that stable and efficient operation is achieved by actively controlling the shape of the softened cohesive zone so that Am and Bm satisfy the following formulas (A) and (B) when . (A) 0.58≦(Am-Bm)/(Rh-0.4)
≦1.73(B) 0.7×cos {(0.001×T
ad-2)×π}+0.5≦Bm≦1.2×cos{
(0.001×Tad−2)×π}+0.8