JPS60145307A - Reducing method of iron ore by melting - Google Patents

Abstract

PURPOSE:To reduce iron ore and to produce efficiently and directly molten iron by preheating iron ore and reducing preliminarily the iron ore with the waste gas from a melt reduction furnace then blowing the iron ore to the melt reduction furnace, blowing carbonaceous material and oxygen thereto and heating the iron bath. CONSTITUTION:Iron ore is preheated in a preheating furnace 1 and is fed into a preliminary reduction furnace 2 where the iron ore is subjected to reduction to some extent to decrease the content of iron oxide and thereafter the iron ore is bottom-blown together with a carbonaceous material, oxygen, slag forming agent, etc. through blow ports 4, 5 into a melt reduction furnace 3. Secondary oxygen is top-blown through a blow port 6 into the furnace to burn a part of the combustible gas generated by the gasification reaction of the carbonaceous material, thereby reducing the iron ore and heating the iron bath. The molten iron is thus obtd. The high-temp. gas formed in this stage is passed through a heat exchanger 8, by which heat is recovered. The gas is further mixed with part of the gas recovered from the furnace 2 and the geseous mixture is passed through a decarbonizing device 10 where the degree of oxidation of the gaseous mixture (H2O+CO2)/(H2+H2O+CO+CO2) is adjusted to 0.07-0.15. The gas is heated in a heater 11 and is introduced into the furnace 2 to make the preliminary reduction ratio therein 0.60-0.75.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for directly obtaining molten iron by reducing iron ore while heating and melting it.

(Prior art) To reduce iron ore and produce molten iron, there are usually methods using a blast furnace or methods in which iron ore is reduced in a shaft furnace and then melted in an electric furnace, but these methods basically involve gas reduction. It is based on the method of dissolving after performing

On the other hand, various attempts have been made to reduce iron ore while heating it and melting it as a smelting reduction method. One of them uses electric power as a heating means, and arc furnaces and plasma furnaces are used. However, considering power generation efficiency, the method of using electric power requires a high amount of secondary energy, and is not practical in our country's current dependence on overseas energy sources. On the other hand, attempts have been made to make iron by directly using secondary energy, especially the heat of combustion of carbonaceous materials such as coal. There are no examples.

Furthermore, in order to increase the utilization efficiency of the latent heat possessed by carbonaceous materials, it is necessary to increase the degree of oxidation of the atmosphere, but this is contrary to the purpose of reducing iron ore.

As described above, it can be concluded that the disadvantages of this process are that the above-mentioned methods have poor energy utilization efficiency and high fuel consumption.

Further, JP-A-58-1.13307 discloses a method in which iron ore is pre-reduced and then charged into a melting furnace and reduced in the same manner as the present invention. However, in this method, the melting furnace is filled with coke, and reduction and melting are performed within the coke packed bed. This is exactly the same phenomenon that occurs in the lower part of a blast furnace. Preliminary reduction is performed using the high-temperature recovered gas generated from the melting furnace, and this process is the same as the phenomenon occurring in the upper part of the blast furnace. In other words, this method can be said to be a process in which the blast furnace is divided into upper and lower parts.

However, this method requires coke to be charged into a melting furnace, and the coke oven can be omitted. Furthermore, although fuel and oxygen are often blown into the coke-filled bed at the tuyeres, there is a limit to the permeability of the coke-filled bed, which limits the amount of injection and therefore the productivity.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems of melting and reducing directly using carbonaceous materials and to perform efficient operations.

(Structure and operation of the invention) In order to achieve such an object, the present invention first aims to effectively utilize the reducing gas discharged from the smelting reduction furnace, so that the gas is used to pre-reduce iron ore. It is characterized by doing the following. At the same time, a certain degree of reduction is performed before being charged into the smelting reduction furnace to reduce the iron oxide content of the contents in the smelting reduction furnace and to significantly reduce the corrosivity of the refractory. This is possible. The second feature of the present invention is that, in order to improve energy utilization efficiency, oxygen or air is introduced into the upper part of the smelting-reduction furnace. This gas also has a reducing property) is combusted, and the generated heat is used to heat the iron bath produced by reduction.

In short, in the present invention, iron ore is preheated, further pre-reduced in a pre-reducing furnace, and then blown into a bottom-blowing melting furnace together with carbonaceous material, oxygen, and a slag-forming agent, and then heated in the upper part of the melting furnace. To,
Oxygen or air is injected to combust part of the combustible gas generated by the reduction and gasification reactions of carbonaceous materials, and the reduced iron bath in the furnace is heated, and the generated high-temperature gas is transferred to a heat exchanger. After passing through and recovering heat, it is mixed with a part of the gas recovered from the preliminary reduction furnace, and after decarbonation treatment, it is heated to a predetermined temperature, and the oxidation degree of the gas [(H20+C02)/(H2+H20+CO+CO□
)] was adjusted to 0.07-015 and introduced into the pre-reduction furnace, and the pre-reduction rate in the pre-reduction furnace was adjusted to 0.60-0.
．． 75.

The present invention will be explained in detail below with reference to the drawings. Figure 1 (5) is a diagram showing the outline of the method of the present invention. 1 is an iron ore preheating furnace, 2 is a preliminary reduction furnace, and 3 is a smelting reduction furnace. Port 4, pre-reduced iron ore injection port 5
, a secondary oxygen inlet 6 for partial combustion, a gas exhaust lower, etc. are provided. 8 is a heat exchanger such as a waste heat boiler that exchanges heat with the high temperature gas discharged from the melting reduction furnace 3; 9 is a gas holder; 10 is a decarboxylation device; 11 is a heater; and 12 is a cooler.

To reduce iron ore according to the method of the present invention, iron ore is first charged into a preheating furnace 1 and preheated, and then charged into a prereduction furnace 2. This preliminary reduction furnace 2 uses a fluidized bed, a shaft furnace, or the like to partially reduce the iron ore. As will be described later, the present invention is characterized by this preliminary reduction. Pre-reduced iron ore is a carbonaceous material.

It is blown into the furnace from the bottom of the melting reduction furnace 3 together with oxygen, a slag forming agent, etc., and reduction is performed. Furthermore, oxygen or air is blown into the upper part of the melting reduction furnace 3 through an oxygen inlet 6,
Burn the combustible gas generated by partial combustion of the reduced and injected carbonaceous materials, and (6) heat the reduced iron bath with the generated heat. On the other hand, the high-temperature gas generated in the eye smelting reduction furnace 3 is discharged from the exhaust lower, and is used as waste heat. The heat is exchanged by a heat exchanger 8 such as a filter, and mixed with a part of the gas recovered from the preliminary reduction furnace 2. A part of the mixed gas is further decarboxylated by a decarbonator 10 and oxidized. After the temperature is adjusted to a range of 0.07 to 0.15, it is heated by a heating device 11 and introduced into the preliminary reduction furnace 2. The high-pressure steam generated is used for power generation, etc.

The present invention reduces the degree of oxidation of the gas introduced into this preliminary reduction furnace to 0.
．． This method is characterized by adjusting the voltage to 0.07~15vc and setting the preliminary reduction rate in the preliminary reduction furnace to 0.60 to 0.75.The reasons for this will be explained below.

FIG. 2 shows the progress of reduction over time when iron ore is gas-reduced. As is clear from this figure, the gas reduction rate of iron ore is 60-7
It is fast up to 0%, but speed decreases above this. This fact shows that the gas utilization efficiency is high when the reduction is 70% or less, which is advantageous as a process. However, the direct iron manufacturing method that is currently in practical use uses a system that melts reduced iron using an electric furnace, and in order to reduce the electricity consumption rate in the melting part, the preliminary reduction has a reduction rate of close to 100. oriented.

However, as is clear from FIG. 2, it takes a long time to achieve a reduction of more than 90%, and it goes without saying that such a high reduction rate is disadvantageous from the viewpoint of gas reduction. Using more expensive power is doubly penalizing.

Figure 3 shows the change in the amount of coal required for the smelting reduction furnace when the preliminary reduction rate of the charged ore is changed. As is clear from this figure, when the preliminary reduction rate is low, the reduction rate in the smelting reduction furnace is high, so the required amount of heat is large and the carbon material consumption rate is high, but on the other hand, the amount of reducing gas generated is large. That's it. On the other hand, when the preliminary reduction rate increases, the amount of carbon material consumed in the smelting reduction furnace decreases, but at the same time, the amount of generated gas decreases. Further, when the required amount of reducing gas in the pre-reduction furnace is displayed with respect to the pre-reduction rate, it is as shown in FIG. 3. The amount of reducing gas required in the preliminary reduction step is small at low reduction rates, but increases as the reduction rate increases, and a large amount of gas is required at reduction rates close to 100%.

Furthermore, FIG. 4 shows changes in the amount of generated gas 1' and reducing gas amount when the degree of oxidation of the gas frequently generated in the melting reduction furnace and the reducing gas for preliminary reduction changes.

Now, in a smelting reduction furnace, the carbonaceous material blown into the iron bath usually undergoes the following force reaction with oxygen and is partially oxidized to generate heat.

C+HO2= Co -1-261<cavrnot However, the CO gas generated here is 68 ]<cat^t
Although this CO gas is useful as a reducing gas for preliminary reduction, it is disadvantageous in terms of the energy efficiency of the smelting reduction furnace. Therefore, as shown in Figure 4, by increasing the degree of oxidation of the generated gas, a part of the CO is further combusted to CO2, and this combustion heat is used to heat the iron bath to increase energy efficiency. advantageous in a sense.

(9) If the oxidation degree of the scallop is increased too much, it will put a burden on the CO2 removal process and increase the overall cost, so the oxidation degree here is set at about 0.35.

In addition, in the preliminary reduction step, when the degree of oxidation of the gas increases, the driving force for reduction decreases, so the required amount of gas increases. - It is known that the coal-derived gas generated in a smelting reduction furnace like the one invented by Rikiki has a high CO acid content, and that when this is heated to high temperatures, carbon precipitates due to the reaction 2Co→CO2+C, making it impossible to operate. Therefore, at the reduction temperature of 900° C. of the present invention, it is difficult to reduce the degree of oxidation to 10% or less.

As mentioned above, it is advantageous to increase the oxidation degree of the exhaust gas in order to increase the energy efficiency of the smelting reduction furnace, and to reduce the amount of gas required for preliminary reduction, it is advantageous to increase the oxidation degree of the gas. It is desirable to do so. Therefore, in the present invention, a decarboxylation device is installed between these two steps, and CO2 is removed from the highly oxidized gas discharged from the melting reduction furnace.
and (10) used for preliminary reduction after removing N20. In other words, it is characterized by operating under operating conditions that avoid a preliminary reduction rate of 75 or higher, where the required amount of reducing gas increases rapidly, and avoid a low preliminary reduction rate range, where the required energy for smelting reduction increases (gas becomes surplus). It is a thing that is called.

(Example) Next, examples of the present invention will be shown.

Coal having properties shown in Table 1 and iron ore having properties shown in Table 2 were prepared.

(11) In steady operation, 1270k17 of pre-reduced iron ore was heated at a temperature of 1500°C and a reduction rate of 65% for 1 hour.
In the iron bath of concentration 3, 98 chi 02351Nm, 806kt
? of coal and 196 kg of limestone were injected through a tuyere located at the bottom of the melting furnace. At the same time, for secondary furnace firing, soft blowing was performed from the top of the same 98% acid i25ONm'i iron bath, and 1690N of gas at 1700°C was found.
m' gas was generated. Its composition is N2: 11%
, Co: 58ji.

C02:16%, N20:14t, N2:1% and the amount of dust is 84! It was 9.

This high-temperature gas is then cooled and dehumidified by recovering heat using an exhaust heat dissipator installed at the top of the furnace.
! l) The pressure was increased to 3 kg/Qn2, and the circulation from the pre-reduction step was mixed with 637 Nm' of gas, of which 1525 Nm3f was branched, further increased to a pressure of 8 kg/Qn2, and sent to the decarbonation gas equipment. After removing carbon dioxide gas and dehumidifying it, the pressure was reduced to 4.5 kg/cm2, and when mixed with the remaining gas that had been branched earlier, N2
: 13, Co: 75%, CO2: 8.

(13) HO: 2%, N2: 2qb gas 1590 Nm
was gotten. This gas having an oxidation degree of 0.102 was heated to 900° C. in a gas heating furnace and then blown into a preliminary reduction furnace. This pre-reduction furnace has 15
57 hematite ore (particle size of 2 or less) is supplied to 00, and reacts with the gas to perform fluidized reduction, resulting in a reduction rate of 65.
1,270 kg of semi-reduced ore was obtained. At this time, of the gas discharged from the preliminary reduction furnace, the residue obtained by branching off the 637 Nm, which is recycled to the reduction process as circulating gas, is discharged outside the system as fuel for preheating iron ore and fuel for power generation. By the way, the amount of exhaust gas at this time was 86O
Nm.

The calorific value was 1840 kcat/Nm.

Further, from the smelting reduction furnace, 103Q kg of D1/hour was produced with C: 3% molten iron. The slag generated at this time was 237kl? , basicity (CaO/S10□)=1.3
1 The FeO concentration in the slag was 5 qb. Furthermore, corrosion of the furnace material during the 5-hour experimental operation was not significant.

For comparison, the oxidation degree of the preliminary reduction furnace inlet gas was set to 0.06.
However, approximately 15 minutes after the start of operation (14), carbon began to precipitate in the exhaust gas dust remover, and eventually operation became impossible. Also, when the oxidation degree was set to 0.20,
There was a significant decrease in the reduction rate. Therefore, if the operation continues under these conditions, a large amount of gas will be required to reduce a unit of ore to the specified reduction rate, and the installation will become larger.
Disadvantages of glazes such as increased power for gas circulation appear.◎ (Effects of the invention) As explained above, the present invention provides preliminary reduction conditions that are advantageous in terms of gas utilization rate in gas reduction, which is a medium reduction rate. It also combines various processes such as high-speed reduction of semi-reduced iron ore with dissolved carbon in the iron bath supplied by bottom blowing, secondary combustion on the iron bath to improve the thermal efficiency of the fuel, and further pre-reduction. Oxidation degree of gas introduced into the furnace i0.07-0.1
By adjusting the reduction rate within the range of 0.5 and setting the preliminary reduction rate in the preliminary reduction furnace to 0.60 to 0.75, extremely high productivity can be ensured.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an example of the method of the present invention, Figure 2 is a diagram showing the relationship between the reduction rate and reaction time when iron ore is gas-reduced, and Figure 3 is a diagram showing the preliminary reduction rate of iron ore. Diagrams showing the effects of changes on coal requirements, gas generation, and pre-reduction gas amounts;
FIG. 4 is a diagram showing changes in the degree of oxidation of the smelting reduction furnace generated gas and preliminary reducing gas, the amount of generated gas, and the preliminary reducing gas. 1: Preheating furnace, 2: Pre-reduction furnace, 3: Melting reduction furnace, 4: Inlet (charcoal material, oxygen, slag forming agent, etc.), 5: Inlet (iron ore)
, 6: Inlet (secondary oxygen), 7: Gas outlet, 8: Heat exchanger, 9: Gas holder, 10: Decarboxylation device, 11: Heater, 12: Cooler ,20θO

Claims (2)

[Claims] (1) After preheating iron ore and pre-reducing it in a pre-reduction furnace, it is blown into a bottom-blowing smelting reduction furnace together with charcoal, oxygen, and a slag-forming agent. A part of the combustible gas produced by the reduction and gasification reaction of carbonaceous material is combusted, heating the reduced iron bath in the furnace, and the generated high-temperature gas is passed through a heat exchanger to generate heat. After recovery, it is mixed with a part of the gas recovered from the preliminary reduction furnace, and after decarbonation treatment, it is heated to a predetermined temperature to reduce the oxidation degree of the gas [()(20-+C02y(H2+)
H20+C0-I-CO2] is adjusted to 0.07 to 0.15 and introduced into a preliminary reduction furnace, and the preliminary reduction rate in the preliminary reduction furnace is set to 0.60 to 0.75. Melting reduction method (2) The method for melting and reducing iron ore according to claim 1, wherein the preliminary reduction furnace is a fluidized bed or a shaft furnace.