JPS61213310A - Production of molten ferrous alloy - Google Patents

Abstract

PURPOSE:To improve remarkably thermal efficiency in smelting using a top and bottom blown converter by combining adequately operating conditions, shutting off an oxidative atmosphere and the formed metal and transmitting efficiently the heat formed by a reaction CO CO2 to the melt. CONSTITUTION:A raw material contg. iron oxide, carbonaceous reducing agent, flux and gaseous oxygen are supplied to the converter which permits top and bottom blowing of gas, by which a molten ferrous alloy is produced. The converter is operated under the conditions satisfying the following four conditions: (1) The amt. of slag is maintained at >=250kg/t-metal. (2) The conditions expressed by the formula I. (3) The conditions expressed by the formula II. (4) The conditions expressed by the formula III. The foaming of the slag is suppressed and the heat utilizing rate is increased by controlling optionally the degree of combustion of the generated gaseous CO to CO2 in the converter when the converter is operated in the above-mentioned manner.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention mainly relates to a method for reducing a raw material containing iron oxide to obtain a molten iron-based alloy.

(Conventional technology) The current mainstream method for manufacturing iron using iron ore as a raw material is to go through a blast furnace (95% or more). The method of melting this in an electric furnace accounts for many of the remaining products.

However, the method using a blast furnace (1) requires an agglomeration process for powder, (2) requires a coking process for coal, (3) requires enormous equipment costs, and (4) has poor production flexibility. On the other hand, the method using sponge iron has the disadvantage of high energy costs for mass production processes.

Therefore, as a method for producing large amounts of molten metal in place of the blast furnace method, a method using a more direct process and more sophisticated equipment, that is, the smelting reduction method, is recommended.
It has been studied from various directions over the years. However, none of them have reached the stage of practical use.

The principle of the smelting reduction method is that carbonaceous materials (coal or coke),
Ore, oxidizing gas (oxygen, etc.) and flux (lime, etc.) coexist, and the heat generated by burning carbonaceous materials or a part or most of the resulting co gas with CO2i is used. Then, the reduction reaction by C in the ore, ``n01n + iC-nF・+T Co2 (n: 1~
3. m: 1 to 4) and melt the various raw materials to separate the molten alloy and molten slag.

At this time, the greater the amount of heat generated per unit amount of carbonaceous material, the more advantageous it is in terms of the process. When comparing the case where the product when C is combusted is CO and the case where 002 is the product, the latter generates about four times as much heat. That is, the higher the degree of formation of the generated gas, the greater the amount of heat generated per unit amount of carbonaceous material.

However, the main purpose of smelting reduction is to reduce metal oxides;
From the viewpoint of effective resource utilization, a method must be able to reduce the concentration of metal oxides in the slag discharged outside the system to a level comparable to that of the current method. Also, if the generated heat is not used effectively for the reaction, various problems will occur.

How to balance the carbon material oxidation reaction and metal oxide reduction reaction, which generate heat, and how much heat is generated by the reaction if the oxidation reaction in the atmosphere is promoted by some means? How can these be effectively used in the progress of the reduction reaction of oxides?
The fact that no technical solution has been found is the reason why the smelting reduction method has not been put into practical use to date, and is a fundamental table problem.

Therefore, an intermediate method is to burn carbonaceous materials to achieve high CO/C
A method of obtaining gas with a high O2 ratio and a high H2/H20 ratio and considering this gas as a product (gasification), or a method with a high CO/CO2
, a method has been proposed in which high H2/H20 gas is used for preliminary reduction of ore in equipment separate from the smelting reduction furnace.

These are all methods to avoid the difficulty of having an oxidation reaction and a reduction reaction coexist due to heat generation, but the smelting reduction method has the inherent advantages in terms of equipment costs and operational freedom. It must be said that this significantly reduces the number of deaths.

(Problems to be Solved by the Invention) This invention achieves the ideal state of the smelting reduction method, that is, the reduction reaction of metal oxides proceeds to reduce their concentration in the slag, and at the same time, the atmosphere is strongly oxidized and generated. The present invention provides a method for increasing the amount of heat and efficiently transmitting the generated heat to the molten material.

(Means for Solving the Problems) The above-mentioned object of the present invention is to suppress the oxidizing atmosphere by appropriately combining various operating conditions in smelting under strong stirring using a top-bottom blowing converter. This is achieved by stably blocking the generated metal and efficiently transmitting the heat generated by the CO/CO2 reaction to the melt so that it can be used for the reduction reaction.

A specific method for realizing the present invention will be described below.

Unlike conventional shaft-type smelting furnaces, in the present invention, strong stirring of the molten material is an essential condition for the smelting reduction furnace, and the equipment is capable of stably blowing gas into the molten material layer for stirring. 1. For example, a converter that can blow oxygen from the top to the bottom is used. The purpose of bottom blowing in this case is to stir the melt, and blowing powder is not an essential requirement. Rather, as will be described later, there is an upper limit to the proportion of raw materials (ore, reducing agent) that may be bottom-blown. Since the main purpose of the gas to be blown is to stir the melt by bubbles, there are no particular restrictions on the type of gas. From the viewpoint of supplying a portion of the oxygen gas necessary for the progress of the reaction in the furnace, it is naturally possible to use oxygen or a gas containing oxygen. In addition,
When oxygen or a gas containing oxygen is used, there is an advantage that depending on the selection of operating conditions, 0% of the finished molten metal can be reduced below the carbon saturation value. In addition to oxygen, N2
゜Ar * Gas such as CO2 + hydrocarbon, or a combination thereof, or co2. generated in this process. It is also possible to recycle gas containing co as a main component.

These gases are blown into the melt through double tube tuyeres or other inlets.

Most of the oxygen gas is blown onto the melt using a top blow lance. The purpose of top-blown oxygen gas is to convert C09H2 produced by combustion of carbonaceous materials or reduction reactions into CO, H2
This is to achieve a high calorific value by burning up to O.

Among the raw materials (ore, reducing agent, 7lux, etc.), lumps are introduced from the top. The powder may be agglomerated and introduced from above, or may be sprayed onto the melt layer through a lance or the like while remaining powder.

Note that it is also possible to use scrap as part of the raw material.

The method of utilizing the gas discharged from the converter-like smelting-reduction reaction vessel can be carried out in various ways depending on the requirements of the place where the reactor is installed, such as the following.

(,) Combination of fluidized bed or rotary kiln,
Gas is used for preheating and preliminary reduction of ore.

(b) By combining y-iller, the gas is completely combusted and converted into steam, which is used for power generation, etc. Or, use it for power generation in combination with a turbine.

(e) Gas is passed through equipment for dust removal and CO2 removal as necessary and stored in a gas holder.

The operating method using these equipment is as follows.

Before starting regular operation, a layer of molten iron alloy (for example, F.-0 series) is created in the smelting reduction furnace. The amount is sufficient to ensure stable bottom blowing (in other words, it does not include blowouts etc.)
Depending on the conditions, the height is usually 30 to 60 cm or more. Such a layer of molten iron alloy can be formed by charging the molten metal made in a separate furnace, or by charging the solid metal in this furnace.

By adding alloy and carbonaceous material such as coke, Kl12 (
Depending on the mixture, hydrocarbons) are supplied to generate heat and melt the mixture. Once the operation begins, in the second and subsequent cycles, the operation is repeated with some of the produced molten iron alloy remaining.

In the present invention, iron ore or its pre-reduced product, a solid carbonaceous reducing agent such as coal or coke, and 7 lacs such as lime and silica stone are added to such a molten iron alloy, and then acid blowing is performed to form a molten iron alloy. By keeping the slag produced in the manufacturing process in an appropriate state, high CO
Let's address the previously unsolved technical problems of stable coexistence of the oxidizing atmosphere of 2qIb and the reducing melt, and of efficiently using the heat generated by the combustion of C0-4CO2 to proceed with the reduction reaction. That is.

For this purpose, a high-temperature zone generated by combustion of CO gas is generated in the vicinity of the melt to be heated.

If the molten iron alloy is exposed to the atmosphere, even if an attempt is made to create a high-temperature zone caused by the combustion of CO gas in the vicinity, the reaction of CO2+ Fe -+ Co + PeO or CO□+9→2CO will occur. In the former case, since it is a reoxidation reaction, the reduction reaction as a whole is inhibited.

In addition, in the latter case, it is an endothermic reaction, and as a result of the CO reaction, the m-'-1 of the gas decreases.
+ co.

become. Conventional back copper converter increases COx s value C
The method called "secondary combustion" was to generate heat by causing a reaction of CO+102→CO□ at a location away from the zone where the molten iron alloy exists.

However, there is a problem in that the farther the molten iron alloy is exposed to the atmosphere, the more disadvantageous it becomes to heat transfer and the lower the thermal efficiency becomes.

In contrast, in the present invention, the molten iron alloy layer and its slush produced by bottom blowing are brought into direct contact with the high-temperature atmosphere by keeping the amount of slag above a predetermined value. The amount of slag required for this purpose is based on the premise that foaming of the slag is suppressed to a predetermined value or less by the method described below, and the amount of slag required (kg/t-metal) ≧ 250.
(1). Especially 300-480
A range of kli/t-metal is optimal. Under these conditions, the amount of carbon (the amount of carbonaceous solids present on the slag and the amount of Co gas generated) +
7) Depending on the dynamic balance), in particular by controlling the combination of the amount of blown acid and the amount of carbonaceous solids present, arbitrarily high values can be obtained. In this case, instead of the secondary combustion described above, a main combustion zone (i.e., a high-temperature zone due to combustion) is formed in a portion where oxygen and carbon associate.

In this case, the molten material adjacent to the high temperature zone due to combustion is not a molten iron alloy but a molten slag layer. Therefore, the molten slag layer is transformed into an endothermic reaction site, i.e. FeO+nC→mFe+nc.

In order to maintain the temperature of n, it is desirable that a proportion of the raw material (ore or its reduced product, carbonaceous solid) above a certain lower limit be added directly to the slag layer rather than to the molten iron alloy layer.

FIG. 1 shows the relationship between the ratio of the added ore + carbonaceous reducing agent (hereinafter referred to as carbonaceous material) to the total weight of the slag layer and the heat utilization efficiency. Raw materials (ore + carbon) added directly to the slag layer instead of the metal layer
It is recognized that the higher the proportion of , the higher the heat utilization efficiency, and it is desirable that 30% or more, preferably 60% or more, be added directly to the slag layer.

In addition to the above reasons, the following may be cited as causes for this.

(1) A portion of added materials such as ore and carbonaceous material floats on the slag, and its surface acts as an efficient site for absorbing heat from the atmosphere.

(2) Compared to the case where slag is added through the metal layer, the reduction reaction sites are moved to the upper part on average, so the degree of slag foaming can be reduced even if the amount of gas generated is the same.

As for the method of directly adding ore (or its pre-reduced product) and carbonaceous material to the slag layer, it is originally possible to add lumps (more than 5 mm) to the slag layer.
In the case of powdery material, it is sufficient to charge it from the top, and in the case of powdery material, it is sprayed onto the slag surface through the upper lance and penetrated into the molten slag by inertial force. A mixture of two or more types is made into a turikerat (concave mold 5 or roller compaction) or an islet and is poured from above.

In addition, in the part where the powder is directly added to the metal layer, the powder is blown into the bottom blowing tuyere, for example. Bottom-blowing an appropriate amount of powder (particularly coal powder) may be effective for purposes other than heating, such as suppressing erosion of the tuyere and adjusting the molten metal to 0% by carburization.

As shown in Figure 2, the volumetric ratio of the total amount of blown acid to the amount of bottom blown gas has a large effect on the heat utilization efficiency.

If the total amount of bottom-blown gases (oxygen, hydrocarbons, etc.) is too small or the melt is stirred too weakly, the heat generated by combustion cannot be sufficiently absorbed, resulting in a decrease in heat utilization efficiency. On the other hand, if the total amount of bottom-blown gas is too large, the amount of the blown gas or the gas generated thereby passing through the slag layer will increase, and the slag will swell accordingly, resulting in a decrease in heat utilization efficiency. Furthermore, as the proportion of bottom-blown oxygen increases, increasing the CO2% of the exhaust gas becomes more and more restricted. Therefore, the optimum ratio of the amount of bottom blown gas (to the total amount of blown acid) is in the range of 3% to 40%, preferably 3% to 30%.

The aim of the present invention is to completely suppress the 7 ohm (bubbling) of the slag, to cause combustion to occur close to the slag surface up to Co2, and to efficiently transfer the generated heat to the slag and use it for the reduction reaction. I have to. Slag containing a large amount of gas makes the combustion site unstable and acts as a barrier against heat. 7 Ohming (bubbling) of slag is caused by the amount of gas generated below the slag surface as mentioned earlier.
In addition to the location where the gas is generated, the ease with which gas escapes is affected by the slag composition. The influence of slag composition on heat utilization efficiency is shown in Figures 3 and 4.
The S i O2 ratio and (MgO+At203)% are related. It is desirable to keep CaO/S+02 in the range of 0.8-1.9 and MgO+At203 at 23% or less.

In order to satisfy both the conditions of the slag amount (defined by formula (1)) and the above-mentioned slag composition, a flux such as lime or silica stone is added. Alternatively, some of the slag from the previous heat may remain, or the slag that has been discharged outside the furnace may be used as an IJ sieve.

If the above-mentioned bottom blowing gas amount condition is satisfied and the molten material is stirred as much as necessary to carry out the present invention, the temperature of the molten material layer of both metal and slag will be almost uniform, and the difference will be ignored. As small as possible. In order to perform bottom blowing stably, the temperature of the molten material must be 920° C. or more higher than the liquidus temperature of the molten metal, but there are no other operational restrictions.

However, if the temperature is low, foaming tends to occur due to the viscosity of the slag, which tends to reduce heat utilization efficiency. On the other hand, if the temperature is too high, the exhaust gas temperature increases, which is a loss. Therefore, 1450° to 1550°C
is the optimum operating temperature. Note that the definition of heat utilization efficiency used in this specification is the following general term υ.

After the operation is carried out to satisfy the above conditions and the added ore (or its semi-reduced product) is melted and reduced, if necessary, the amount of iron oxide in the slag is further reduced, If you want to proceed with the desulfurization reaction using slag at the same time, if you stop the supply of ore (or its half-reduced product) and continue blowing acid for a specified period of time, the slag iron oxide content will increase to an arbitrary value depending on the time. can be lowered.

In addition, compared to the case where a molten alloy with a chromium or manganese content of 20% or more is obtained by the smelting reduction method, when the iron ratio is even higher, the oxide is also reduced by C in the molten alloy. Since this is possible, the reduction reaction on the surface of the molten alloy layer tends to proceed, and as a result, the slag as a whole tends to be 7 ohming. To suppress this, (
1) Operations should be carried out with a carbon content of 20% or more of the weight of the slab remaining in the slag and a large interface area between the slag and the carbonaceous material. This is the difference between the carbon content in the carbon material added to the molten metal and (the amount of carburized into the molten metal) + (the dust containing CO, CO2, and C in the exhaust gas). (11) Adjust the slag composition, add carbonaceous material containing lime to the top of the GiD slag, and suppress 7 ohming by the foaming effect of the generated gas ( For this purpose, it is desirable that approximately 60% or more of the total carbonaceous material be added from above the slag).

By the method described above, it is possible to combust COt-CO2 up to a predetermined value and to efficiently use the heat generated by the combustion to proceed with the reduction reaction.

In addition, if fuel gas is required unsteadily due to location conditions, it is possible to control the amount of blown acid and the ratio of carbon remaining in the slag while detecting the composition of the exhaust gas. ,
CO/CO2 of exhaust gas can be changed arbitrarily. By removing dust and CO2 from this discharged gas if necessary, and then guiding it to a gas holder, the required amount of the required composition gas can be obtained.

(Example) Top-bottom blowing converter with rated molten metal capacity of 120 tons [4 bottom blowing tuyere, triple pipe; inner tube (inner diameter 16 mm, wall thickness 1 period): CO/CO2 mixing (1800 Nm'/hr ) For coal powder injection by carrier, second pipe (inner diameter 20cm, wall thickness 1m): 0□For gas injection: Outermost pipe (inner diameter 24m): Cooling gas propane e
60 Nm') for blowing], Fa-C (4.2%)
-ss (o, 3s) Charge tv'm hot water 140.

Iron ore (T, Fe: 67%, 8102: 4
．． 6%, Tie,: 0, 2%, P2O5: 0
．． 2 pieces) are sieved, and those with more than 5 pieces (5 pieces of the total charge) are sieved.
5%) is fed into the furnace from the hollow above the furnace, and after mixing 30% by weight of coal powder for those less than 5 m long, the compacted powder compacted by rolls is fed into the furnace from the arm of another hollow. Put it inside.

Coal (TC: 73% mV, M (volat
ile matter): 15chi: Ash: 12S,
P: 0.08chi, S: 0.6%) is sieved and 10m
Those of m or more are directly supplied into the furnace from the hole a4- on the furnace. The bottom of the sieve is crushed to 1 inch or less, a part is used for roll compression with the ore mentioned above, and the total charge of 10 inches is blown into the furnace through the bottom blowing tuyere to remove the remaining residue. Ha, Uebuki 2
(7 holes in total, one in the center is for coal powder injection with Co/CO2 mixed gas, the other 6 holes are for oxygen injection)
00 Nm”/hr).

Note that lump coke accounts for approximately 5% by weight of the amount of coal used.

Blowing acid (top blowing 20,000 Nm”/hr, bottom blowing 1,800 Nm”/hr
(Nm3/hr), measure the temperature of the molten material in the furnace, add iron ore so that it is in the range of 1450 to 1520°C, and adjust the amount of slag accordingly to 300±40kl.
iF/t-metal, slag composition is Cab/SiO2;
1.2±0.3Mg0 + AL20. = 8±6%
Add so that

Further, the amount and composition of the exhaust gas are detected, and the amount of coal coke input is adjusted according to the C balance formula so that the amount of carbon remaining in the slag in the furnace is 25% and 5% of the amount of slag.

There are 281 types of operation depending on the time of day.

Metal being tapped (70% of production), slag (
The ingredients for approximately 90 g of the production amount are listed above.

In case of B, the following rules apply.

Metal (molten iron alloy) C-t%) Sla'
(wt%) After tapping, the above-mentioned operation is repeated using the remaining hot water.

(Effects of the Invention) As described above, the present invention utilizes equipment similar to existing top-bottom blowing converters for steelmaking, and adopts operating conditions that are completely different from those of ordinary steelmaking methods. , which is characterized by the ability to obtain molten iron alloy from ore with high thermal efficiency and the ability to flexibly change the generated gas depending on the location conditions, and has economical effects as a solution to the drawbacks of the conventional blast furnace method. is large 0

[Brief explanation of drawings]

Figure 1 shows the relationship between the ratio of what is added to the slag layer to the total weight of added ore + carbonaceous material and the heat utilization efficiency. Figure 3 shows the effect of the ratio of total gas amount on heat utilization efficiency.
4 and 4 are diagrams showing the influence of slag composition on heat utilization efficiency. Figure 1 Figure 4 Mf engineer Al: z03 (%)

Claims (1)

[Claims] In producing a molten iron-based alloy by supplying a raw material containing iron oxide, a carbonaceous reducing agent, flux, and gaseous oxygen in a converter-like reaction vessel capable of blowing gas upward and downward, ) slag amount 2
Keep it at 50kg/t-metal or more (2) [Ore and carbonaceous materials added to the slag layer (weight)] /
[Total added ore + carbon material (weight)] x 100≧30%
(3) [Total amount of bottom blown gas (Nm^3)]/[Total amount of blown acid (Nm^3)] x 100 = 3 to 40% (4) Satisfy the conditions of MgO + Al_2O_3≦23% of slag at the same time By operating under such conditions, the foaming of the slag is suppressed and the CO gas generated inside the furnace is reduced.
A method for producing a molten iron-based alloy, characterized by increasing heat utilization efficiency while arbitrarily controlling the degree of burnup to O_2.