JP2843604B2 - Production method of molten iron by combined smelting reduction and scrap melting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for producing hot metal by a smelting reduction / scrap melting combined method, and more particularly to an iron bath type smelting reduction furnace for mainly producing iron oxide. The present invention relates to a method for producing hot metal by combining smelting reduction of a raw material containing iron and melting of iron-based scrap.

This is used in a field in which it is possible to produce hot metal by responding to various needs while giving flexibility to the operation of the furnace.

(Prior Art) In recent years, smelting reduction ironmaking has been actively studied as a process that replaces the coke production, ore agglomeration, and blast furnace process. If this smelting reduction steelmaking method is put into practical use, large-scale new investment such as a smelting reduction furnace, a pre-reduction furnace, and an oxygen gas production apparatus as an integrated process is required.

On the other hand, the blast furnace has been suspended due to various circumstances, and accordingly, the converter and the continuous casting machine have also been suspended, and ironworks in which only rolling equipment moves have begun to appear. In such a steel mill, a converter, a combined casting machine, an oxygen generation facility,
The power generation facilities, raw fuel unloading transportation facilities, etc. will be idle.

However, depending on the product mix, sales volume and price, and delivery time, if the smelting reduction method or scrap melting method with minimum capital investment utilizing these idle facilities can be applied, part of the billet will be manufactured. Can be significantly advantageous.

Incidentally, in the smelting reduction of iron ore, there is a secondary combustion rate as an operating factor affecting productivity and variable costs. In the smelting reduction method, a large amount of Fe ₂ O ₃ is reduced, but at this time, a large amount of heat is consumed. Set C as much as possible to compensate for this heat
By increasing the secondary combustion that burns up to CO _2, it becomes possible to reduce the oxygen intensity and coal intensity.

As an invention for improving the secondary combustion rate and the heat transfer efficiency and consequently improving the productivity and reducing the oxygen and carbonaceous unit consumption, for example, an iron-based alloy described in JP-A-61-213310 is disclosed. There is a method for producing molten metal.

The point is that (1) the amount of slag is 250kg per ton of molten metal
The above, preferably, by 300 to 400 kg, by preventing the molten iron alloy layer and the splash generated by the bottom blow from coming into contact with a high-contact high-temperature atmosphere,
Improving the secondary combustion rate (2) Heating efficiency by maintaining the bubbling state of the slag moderately by leaving carbon content of 20% or more of the slag weight in the slag to prevent slopping Has been improved. As a result, it has become possible to significantly improve the secondary combustion rate as compared with the conventional method, while maintaining the heat arrival efficiency at about 90% or more.

The above publication states that the same concept can be applied to scrap melting. By the way, as for scrap dissolution, an example in which a large amount of slag is applied is disclosed in JP-A-61-1986.
Japanese Patent No. 221322 discloses a method for melting and refining metal raw materials.

(Problems to be solved by the invention) However, in both the smelting reduction of iron ore and the melting of scrap in a large-volume slag combined converter,
It was found that the productivity (also called hot metal production rate) and the flexibility of surplus energy (also called recovered gas heat per unit time) to the post-process were unexpectedly small.

To improve productivity in smelting reduction of iron ore,
Due to the limited capacity of oxygen generation equipment and oxygen piping,
It is common practice to maximize the acid transfer rate (Nm ³ / hr) to improve the secondary combustion rate and the heat transfer efficiency, and to reduce the oxygen gas intensity and coal intensity per unit of hot metal. .

However, in the smelting reduction method, the unit heat of coal and oxygen is high because a large amount of reduction heat of iron ore is required. For example, oxygen is 500-800 (Nm ³ / T), and the improvement of productivity is limited. There is. For example, even if 30,000 (Nm ³ / hr) large oxygen generating equipment is used, the productivity is as low as 1000 to 1500 tons / day. In addition to this, there is also a problem that the amount of gas generated in the smelting reduction furnace is large due to the high coal intensity.

Thus, when using surplus gas as fuel for power generation, for example, power consumption in the city is large in the daytime, and there is no problem even if the amount of generated gas is large, but at nighttime, the electrode consumption decreases. A problem arises in that the generated gas cannot be digested.

On the other hand, in the scrap melting method alone, the oxygen intensity is 150
Although there is no productivity problem because it is as small as ~ 250 (Nm ³ / T), the amount of gas generated is small as 1/4 to 1/5 of the smelting reduction method due to the small unit consumption of coal. I can not cope. For this reason, in the power generation equipment, the shortage of generated gas must be compensated for by expensive heavy oil or natural gas.

Here, it has a converter, an electric furnace, a private power generation facility, an oxygen generation facility, a continuous casting machine, and a rolling facility.
The above-mentioned problem will be described more specifically with an example of a steel mill having a system for operating an electric furnace, an oxygen generating facility, a rolling facility, and the like using the self-supplied power and the purchased power.

As is well known, the unit price of purchased power during a daytime period when power demand is high is significantly higher than that at midnight. Considering the energy demand of the steelworks, it is desirable in terms of cost to increase the energy of the exhaust gas from the converter in order to increase the amount of private power generation during the high demand time period in the daytime.

On the other hand, at midnight, on the other hand, it is preferable to increase the amount of inexpensive purchased power to reduce the energy of exhaust gas. Also,
In order to produce hot metal at low cost, it is important to select the cheapest combination from a wide selection of raw materials while considering raw material prices.

That is, it is known that the relative prices of ore, coal, oxygen gas, and scrap, particularly the scrap price, fluctuate greatly in time series. Further, the sales amount, that is, the production amount also changes in time series. In some cases, it is necessary to reduce the production of hot metal due to repair of a rolling mill or the like.

However, the flexibility of the operation corresponding to the needs such as the increase or decrease of the surplus energy in the post-process can be slightly made possible by the increase and decrease of the secondary combustion rate, but both the smelting reduction method and the scrap melting are small by themselves, The result is that the problem as described above exists.

Therefore, there is a strong demand for a method that has great flexibility in the operation mode during operation, that is, in the surplus energy to the subsequent process, the selection of raw materials, the productivity, and the like.

The present invention has been made in view of the above-described problems, and its purpose is to allow the ratio of surplus energy to the post-process and the production amount to be changed over a wider range, and in particular, to optimize energy supply and demand, An object of the present invention is to provide a method for producing hot metal that can realize an inexpensive production mode.

(Means for Solving the Problems) The gist of the present invention is to use iron ore and scrap as an iron source, and use a carbon material and coal in addition to the iron source as a raw material.
In the method of producing hot metal by combining smelting reduction of raw materials containing iron ore and melting of scrap, secondary combustion is performed by blowing oxygen gas upward on foamed slag in which carbon material is suspended, and oxygen gas flow rate, iron ore Another object of the present invention is to make it possible to widely change the calorific value of the recovered gas per unit time from the smelting reduction furnace and the production rate of the hot metal by changing the combination of the respective levels of the ratio of iron and scrap and the secondary combustion rate.

In other words, the production of hot metal is based on a combined method of smelting reduction of iron ore and scrap melting, and by changing the above combination, surplus energy to the subsequent process, raw material selection, flexibility such as productivity will be greatly improved. It is assumed that.

(Operation) First, operations that focus on the relationship between power supply and demand will be described.

Inexpensive times of purchase increase the rate of scrap melting compared to normal levels. In this case, since the oxygen consumption rate of scrap melting is significantly reduced as compared with the smelting reduction, the productivity can be kept constant even when the oxygen flow rate is reduced. If the secondary combustion rate is constant, the energy of the exhaust gas can be reduced by an amount corresponding to the decrease in the oxygen flow rate.

In addition, if the secondary combustion rate is improved, it is possible to further reduce the energy of exhaust gas. That is, since the amount of gas to be recovered is reduced, relatively expensive power generated by the recovered gas can be replaced with inexpensive purchased power.

Conversely, during periods of expensive power, the rate of scrap melting is reduced, the flow rate of oxygen gas is increased, the amount of recovered gas is increased, and the amount of power generated by generated gas energy is increased. It is also possible to change the generated gas energy by increasing or decreasing the secondary combustion rate.

That is, if the secondary combustion rate is reduced, the unit energy of coal increases and the energy of the generated gas can be increased. If there is enough acidity, reduce the rate of scrap dissolution,
By further increasing the amount of acid transfer, the generated gas energy can be further increased. Conversely, if the secondary combustion rate is increased, it is possible to reduce the generated gas energy and cope with a case where the gas demand is small.

Table 1 shows the combinations of the scrap dissolution ratio, the oxygen gas flow rate, and the level of the secondary combustion rate, and the resulting exhaust gas energy and productivity, including other cases.

It is natural that the standard work in Table 1 is set according to local conditions such as capacity balance and energy balance at the steelworks. The amount of coal charged (ton / h
r) is a function of the oxygen flow rate (Nm ³ / hr) and the secondary burn rate and the rate of scrap dissolution.

(Embodiment) The present invention will be described in detail as a standard embodiment, taking as an example the case of operating using an iron bath type smelting reduction furnace shown in FIG.

In FIG. 1, 1 is a smelting reduction furnace, 2 is hot metal, and 3 is slag. 4 is an oxygen lance for supplying oxygen gas, 5 is a sub-lance for measuring the temperature and sampling of the hot metal 2 and slag 3, 6 is a coal supply hopper, and 7 is an ore supply hopper. Further, reference numeral 8 denotes a supply hopper for supplying fine ore and coal, 9 denotes a scrap supply conveyor, 10 denotes an exhaust gas recovery duct, and 11 denotes a dust catcher. 12 is
A bottom blowing tuyere that supplies N ₂ , CO, O _2, etc. as a bottom blowing gas, and 13 is a gas pipe that supplies the bottom blowing gas to the bottom blowing tuyere 12.

Now, the furnace volume of the smelting reduction furnace body 1 in this embodiment is
The furnace body 1 is 200 m ³ and is lined with firebrick. In such a smelting reduction facility, first, when the furnace body 1 is tilted after the smelting reduction and melting of the scrap for tapping and discharging, for example, 40 to 100 tons of hot metal is left as seed water, and 20 to 50 tons of slag is left. Keep it.

The lower limit of the remaining hot metal is determined by securing an efficient bath depth of the bottom-blown stirring gas, for example, 400 mm or more, and the upper limit of the hot metal secures the incremental hot metal and slag amounts to be produced. It is decided based on the amount of extra room.

After tapping and discharging, 20 to 100% of the amount of scrap to be charged in one heat is charged into the furnace before blowing. It is necessary that melting of the initially charged scrap is completed at the time of measuring the iron bath temperature in the latter half of blowing. This is because the temperature measurement is performed in a sublance, and if there is any unmelted scrap at this temperature measurement, the sublance probe and the unmelted scrap may come into contact with each other and break the probe.

Therefore, as a result of investigating the melting characteristics of scrap,
The upper limit of the scrap size for almost complete dissolution within 40 minutes, which is the melting time required in normal operation time, is about 250 mm in thickness for plate-like bodies and 300 mm square for bloom etc. regardless of shape Was up to. Thus, it is preferable that the initially loaded scrap is smaller than the above-mentioned size.

Next, acid supply is started from the oxygen lance 4 shown in FIG. 1, and the acid supply rate is increased to a predetermined acid supply rate within one minute. During this time, the carbonaceous material floating on the slag 3 is suspended in the slag. 3. Prevent overflow from the furnace opening due to excessive foaming.
At this time, the amount of the carbon material is preferably set to 20% or more of the total weight of the slag.

After reaching a predetermined acid supply rate, when the hot metal temperature is about 1350 ° C. or higher, continuous or semi-continuous charging of coal, iron ore, lime, and scrap is started. If the charging is started before the temperature reaches 1350 ° C., the dissolution of iron ore into the slag is delayed and the reaction rate becomes insufficient, and the (FeO) concentration in the slag increases, or abnormal slopping occurs. You have a problem. Thus, the hot metal temperature is about 1350 ° C
After confirming the above, it is important to start the charging.

The particle size of the coal and the iron ore is not particularly limited, and as shown in FIG. 1, the massive coal and the iron ore are dropped into the coal supply hopper 6 and the ore supply hopper 7 using gravity by gravity. It was adopted.

For the purpose of preventing scattering of powdery raw materials such as coal and iron ore, it is possible to adopt a method of injecting into slag or spraying it together with carrier gas from a furnace shoulder.

In this embodiment, as shown in FIG. 1, a spraying method from a furnace shoulder was employed, and spraying was performed at a speed of 20 to 100 m / min to effectively prevent scattering of the powdery raw material.

Scraps other than those used for the initial charging are also supplied by the supply conveyor 9 from the furnace, but for example, shredder chips, lump dull, dull powder, etc. are press-molded to an appropriate size in advance so as to be easily charged. It is preferable to cut or cut.

It is important that the scrap introduced during these acid transfers be rapidly dissolved, and in order to enable such rapid dissolution, plate-shaped scrap is 10 mm or less, and granular
It was necessary to make the size less than 13mm.

The amount of lime charged should be such that the slag basicity (CaO / SiO ₂ ) is 1.0 to 1.5, preferably about 1.3, in order to maintain an appropriate slag foaming state, and mixed with the lump ore described above. A method of loading using gravity from above was adopted.

Moisture is harmful because it burns the fixed carbon in the coal and worsens the thermal efficiency. Therefore, it is desirable that the coal and iron ore to be charged are dried so that the attached moisture is 2% or less. More preferably, the iron ore and scrap are charged with preheating.

The upper blow of the oxygen gas is a soft blow using a so-called secondary combustion lance having a main hole and 3 to 15 sub holes. At that time, the ratio L _S / L _SO of the slag recess depth L _S by the top-blown oxygen jet and the thickness L _SO of the foamed slag layer is 0.7
It is good to set as follows.

That is, as a factor of the decrease in the secondary combustion rate, there is contact between the oxygen gas in the top blow and the carbon source in the hot metal, but if the soft blow is performed within the above range, the oxygen jet and the hot metal come into direct contact with each other. In addition, generation of carbon monoxide gas and reduction of the secondary combustion rate can be prevented.

In order to stir the iron bath and the slag to promote the mass / heat transfer, a bottom blow gas is blown from the bottom blow tuyere 12 shown in FIG. Normally, N ₂ is used as the bottom-blown gas, but if it can exert the stirring function, for example, CO ₂ , CO, O
₂ , LPG or the like may be used.

The gas flow rate at this time is desirably 1 to 6 kW / T-metal in the stirring energy density formula shown by the following formula (1).

Where: stirring energy density (kW / T-metal), k: volume change coefficient due to reaction in iron bath, eg 2.0 for CO ₂ gas, 1.0 for N ₂ , Ar gas, Q: bottom blown gas flow rate (Nm ³ / s), W _T : Hot metal weight (t) ρ: Hot metal density (kg / m ³ ), h: Hot metal height (m), P: Furnace internal pressure (Pa, absolute pressure), T ₁ : Inlet gas temperature (K), T ₂ : Bath (hot metal or slag) temperature (K), When the stirring power is weak, melting of the scrap becomes slow, and the temperature cannot be measured by the sublance 5. The phenomenon that the stirring of the slag becomes insufficient and the heat of the secondary combustion becomes poor. In particular, in the present invention, the melting of the scrap becomes important for the operation, and when the stirring power is less than 1 kW / T-metal, the temperature is measured for 45 minutes or more due to the large amount of the initially charged unmelted scrap. Could not. Conversely, with strong stirring of more than 6 kW / T-metal, it was also observed that the hot metal was blown up by the bottom blown gas to increase iron-based dust loss and that the hot metal and oxygen contacted and the secondary combustion rate decreased. .

The gas generated from the smelting reduction furnace is recovered from a non-combustion type exhaust gas recovery duct 10. The generated gas recovered in the recovery duct 10 is remarkably regenerated by a waste heat boiler attached to the recovery duct 10 and then removed by a dust catcher 11, and then used as a reducing gas for fuel or ore. I do. The dust thus removed is supplied to the furnace via the supply hopper 8 together with other powder materials.

In this embodiment, the ore used was not reduced. However, it is also possible to use a partially reduced ore by installing a preliminary reduction furnace.

In addition, during operation in the present embodiment, measurement of hot metal temperature, sampling of slag and hot metal are periodically performed using the sub-lance 5, the composition thereof is measured, and the generated gas is continuously discharged from the top of the collection duct 10. Sampling and exhaust gas analyzer 14
The gas composition and the secondary combustion rate are continuously measured, and the operation status is confirmed and controlled.

If the temperature of the hot metal or the secondary combustion rate of the exhaust gas deviates from the above-mentioned target values, the supply rate of the ore, the height of the upper blowing lance, and the supply rate of the coal (that is, the charged carbon, oxygen, ) Can be restored to the target value.

In order to reduce iron loss in slag at the time of slag disposal, if the ratio of scrap melting to total hot metal production is low and the FeO content of slag is 5% or more, ore In some cases, the supply of sulfur is stopped and the finish reduction for reducing FeO in the slag is performed.

Thus, when a predetermined amount of hot metal is obtained, the oxygen blowing is stopped, and tapping and slag leaving a predetermined amount of seed water and slag are left as described above.

In the present invention, the ore-to-scrap ratio (hereinafter referred to as scrap mixing ratio), the secondary combustion rate, and the oxygen gas flow rate are changed based on a combination of a predetermined level set in advance. Thus, the energy supply and demand, the operation cost, and the productivity are selected by selecting an operation method most suitable for various conditions at that time.

Therefore, as the operation method, first, control of productivity and generated gas amount by the secondary combustion rate will be described.

Increasing the secondary combustion rate increases the calorific value per coal / oxygen, thus improving productivity with respect to oxygen supply capacity.
Generated gas energy is reduced. For example, in the present embodiment, when the unreduced ore is used, the operation is performed at an oxygen flow rate of 45,000 Nm ³ / hr, and the secondary combustion rate is 35%, the productivity is 41.7 T / hr, the generated gas energy is 195 Gcal / hr (4.7 cal / hr). In contrast, when the secondary combustion rate was 45%, the productivity was 62.5 T / hr and the generated gas energy was 179 Gcal / hr (2.8 Gcal / T). That is,
Productivity is improved by improving the secondary combustion rate by 10%.
5 times and gas energy per hot metal tun to about 60
%.

As a method of controlling the secondary combustion rate, there are a method of changing the volatile matter (hereinafter referred to as VM) of the coal used, a method of changing the above-mentioned L _S / L _SO , and a method of changing the bottom blown gas amount. .

FIG. 2 shows an example of the results of a study on the relationship between the VM and the maximum secondary combustion rate under conditions of good heat arrival in the equipment of the present embodiment. As the VM decreases, the secondary combustion rate increases. You can see what you can do.

Similarly, FIG. 3 shows an example of the result of investigation on the relationship between L _S / L _SO and the maximum secondary combustion rate, and the secondary fuel transfer rate can be increased as L _S / L _SO becomes lower. .

Next, the effect of the scrap mixing ratio on the productivity and the amount of generated gas will be described.

Since scrap does not require heat for reduction, the unit of coal source and the unit of oxygen are smaller than those of ore reduction. FIG. 4 shows an example of the results of a study on the relationship between the scrap mixing ratio, productivity, and generated gas energy.

As can be seen from FIG. 4, by changing the scrap mixing ratio, the productivity also changes. As the scrap mixing ratio increases, the productivity improves, and conversely, the generated gas energy decreases.

As described above, by changing the secondary combustion rate, scrap mixing ratio, and oxygen flow rate as appropriate, it is possible to meet the planned production volume and the required amount of energy used inside and outside the steelworks, and achieve the most economical It became possible to perform a typical operation.

Next, a description will be given of a combination of the secondary combustion rate, the scrap mixing ratio, and the oxygen flow rate, and a method of controlling the same so that the surplus energy and productivity of the post-process can be changed in a wide range.

As described above, there are many combinations of the secondary combustion rate, the scrap mixing ratio, and the oxygen flow rate that change the surplus energy and productivity. For this reason, it is naturally preferable to select an operating method that enables the production of hot metal at the lowest cost while satisfying the operating conditions. Generally, productivity Pr, generated gas energy E, and production cost C are as follows (2) to (4).
It is expressed by an equation.

Pr = F (SCR, PCR, COAL, FO ₂ ,…) (2) E = G (SCR, PCR, COAL, FO ₂ ,…) (3) C = H (SCR, PCR, COAL,…) FO ₂ , ORE,…) …… (4) where SCR: Scrap mixing ratio PCR: Secondary combustion rate FO ₂ : Oxygen flow rate COAL: Coal component ORE: Ore component In this embodiment, it is shown in FIG. In the process computer 15, the type and amount of the raw material to be used based on the input signals from the coal feeder 18 and the ore feeder 19 are determined based on the input signal from the drive motor 20 of the scrap supply conveyor 9. Flow regulating valve
An oxygen flow rate, a bottom blown gas flow rate, and the like are input based on input signals from 17 and a bottom blown gas flow regulating valve 16, respectively.

The unit price of various raw materials,
Influence factors for the basic unit of each operating condition are stored in advance, and the most economical operating method is satisfied while satisfying the operating condition and the set production amount and generated gas energy at the operating time. Calculate automatically based on equation (4).

A control signal is issued from the process computer 15 based on the calculation result, and the oxygen gas flow rate is controlled by the oxygen flow regulating valve 17, and the scrap mixing ratio is controlled by the coal feeder 18, the ore feeder 19, the drive motor 20, and the like. Is done. Further, the secondary combustion rate is also controlled by controlling the flow rate of the bottom-blown gas by the bottom-blown gas flow regulating valve 16 in addition to the control described above.

FIGS. 5 to 8 show specific examples of the above-mentioned optimum combinations based on various operating conditions as shown in Table 2. FIG.

5 to 8, the solid line shows the combination of the scrap mixing ratio and the secondary combustion rate for simultaneously satisfying the operating conditions of productivity and generated gas energy, and the dotted line shows the oxygen generator capacity of 60,000 Nm ³ / hr. An oxygen intensity limit line obtained from a certain constraint condition is shown, and a dashed line shows an equal cost line based on the cost calculation result.

If the secondary combustion rate is too high as a constraint on the operation, the refractory of the furnace body 1 is greatly worn away. Therefore, the maximum value of the secondary combustion rate was set to 65%.

Example (1) is an example of an operation with high productivity and large digestive capacity of generated gas, and an example in which the scrap price is relatively expensive.

The combination of the scrap mixing ratio and the secondary combustion rate under these operating conditions is shown by a solid line in FIG. 5, but when the scrap mixing ratio is 44% or less, the operation cannot be performed due to insufficient oxygen supply capacity.

Therefore, under such conditions of productivity and generated gas amount, the scrap mixing ratio is between 44 and 100%. On the other hand, as a result of the cost calculation under these operating conditions, the lower the scrap mixing ratio, the lower the cost, as can be determined from the isocost line in FIG. As described above, in this example, the operation was performed under the conditions of a scrap mixing ratio of 44% and a secondary combustion rate of 48%, as indicated by ● in FIG.

Next, in Example (2), the conditions of productivity and generated gas are the same as those of Example (1), but the price of scrap is higher than the ore price, and is substantially equal to the sum of the ore price and the energy price of smelting reduction. This is an example.

The equal cost line in the present embodiment is almost parallel to the line of the combination of the scrap mixing ratio and the secondary combustion rate shown by the solid line. Therefore, in the present embodiment, the scrap mixing ratio is indicated by ● in FIG. The minimum cost condition was 77% and the secondary combustion rate was 38%.

Next, in Example (3), the restriction on the amount of generated gas is the same as in Examples (1) and (2), but is an example under operating conditions of low productivity. The scrap price in this example was as high as in Example (1).

FIG. 7 shows that the combination of the operable scrap mixing ratio and the secondary combustion rate is a condition of a lower secondary combustion rate or a lower scrap mixing ratio than in Examples (1) and (2). In addition, because of low productivity, the limitation of the oxygen generator is loose, and operation at a lower scrap mixing ratio is also possible.

Since the scrap price is expensive, the lower the scrap mixing ratio, the lower the production cost. In this embodiment, the operation was performed under the conditions of a scrap mixing ratio of 16% and a secondary combustion rate of 38%, as indicated by ● in FIG. .

Next, the embodiment (4) is an example in the case where the allowable amount of the generated gas is small. As can be seen from FIG. 8, when the allowable amount of generated gas is small, it is necessary to operate at a higher scrap mixing ratio and a higher secondary combustion rate.

In this example, when the scrap mixing ratio was 50% or less, the secondary combustion rate exceeded the limit of 65%, so the range of the scrap mixing ratio of 50 to 100% was the operating range. Therefore, operation at a low scrap mixing ratio, ie, 50%, was the most economical as restrictions allowed, due to the high scrap prices.

(Effects of the Invention) By implementing the present invention, the combined smelting reduction and scrap melting method is adopted according to the needs and circumstances such as the required amount of surplus energy, productivity, and the increase and decrease of the scrap price. If the ratio, the secondary combustion rate, and the acid supply rate are appropriately changed, it becomes possible to flexibly deal with surplus energy, raw material selection, productivity, and the like for the subsequent processes.

[Brief description of the drawings]

FIG. 1 is a block diagram of a well-known iron-bath smelting reduction furnace for explaining an operation method based on the present invention, and FIG. 2 is a diagram showing a VM and a maximum secondary combustion under a condition of good heat application. FIG. 3 is a chart showing an example of the results of the investigation on the relationship with the rate of slag, and FIG. 3 shows the depth L _S of the slag recessed by the top-blown oxygen jet and the thickness L of the foamed slag layer.
Chart showing an example of a survey of the relationship between the ratio (L _S / L _SO) and maximum post combustion ratio of the _SO, Fig. 4, scrap mixture ratio and productivity, findings of the relationship between evolved gas energy FIG. 5 to FIG. 8 are charts showing specific examples of the optimal combination of the scrap mixing ratio, the secondary combustion rate, and the cost condition under various operating conditions according to the present invention. 1: Furnace body for smelting reduction, 2: Hot metal 3: Slag, 4: Oxygen lance 5: Sub lance, 6: Coal supply hopper 8: Ore supply hopper 8: Powder ore and coal supply hopper 9: Scrap supply conveyor 10: Exhaust gas Recovery duct 11: Dust catcher 12: Bottom blowing tuyere, 13: Gas piping 14: Exhaust gas analyzer 15: Process computer 16: Bottom blowing gas flow control valve, 17: Oxygen flow control valve 18: Coal feeder, 19: Ore feeder 20: Drive motor

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Ogata Chikuko Hachimancho 1 Sakai City, Osaka Prefecture Nippon Steel Corporation Sakai Works (72) Inventor Tsutsumi Honda 1 Chikko Yawatacho Sakai City Osaka Prefecture Nippon Steel Corporation Sakai Works (56) References JP-A-60-218407 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21B 11/00

Claims (1)

(57) [Claims] 1. An iron ore and scrap as an iron source,
In a method for producing hot metal by combining smelting reduction of a raw material containing iron ore and melting of scrap using a carbon material and coal in addition to the iron source as described above, oxygen gas is supplied to a foaming slag in which the carbon material is suspended. The secondary combustion is performed by blowing, and by changing the combination of each level of the oxygen gas flow rate, the ratio of iron ore to scrap, and the secondary combustion rate, the recovered gas heat per unit time from the smelting reduction furnace and the hot metal production rate The method for producing hot metal by the combined smelting reduction and scrap melting method, characterized in that the melting temperature can be changed over a wide range.