JPS6143406B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention reduces iron ore while heating and melting it,
It concerns a method of directly obtaining molten iron. (Prior art) In order to reduce iron ore and produce molten iron, there is usually a method using a blast furnace or a method in which iron ore is reduced in a shaft furnace and then melted in an electric furnace. It is based on the method of gas reduction followed by dissolution. 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 electricity requires a high amount of primary energy, and is not realistic in the current situation where Japan is dependent on overseas sources of energy. On the other hand, attempts have been made to make iron by directly using primary energy, especially the combustion heat of coal and other carbonaceous materials, but due to the extremely high reactivity of molten iron oxide, the refractory materials are severely eroded, and as a result, there have been no successful cases. do not have. 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-58-113307 discloses a method in which iron ore is pre-reduced and then charged into a melting furnace for reduction, similar to the present invention. However, 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 supposed to be carried out using 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 cannot be omitted. Furthermore, although fuel and oxygen are supposed to be 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 thus the productivity. (Objective of the Invention) The object of the present invention is to solve the above-mentioned problems of melting and reduction directly using carbonaceous materials and to perform efficient operations. (Structure and operation of the invention) In order to achieve the above 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. In other words, at the same time, it is possible to perform a certain degree of reduction 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. The second feature of the present invention is that, in order to increase the efficiency of energy use, oxygen or air is introduced into the upper part of the smelting reduction furnace, and the combustible gas (this gas (which also has reducing properties) is burned, and the generated heat heats the iron bath produced by reduction. That is, in the present invention, iron ore is preheated, further reduced in a preliminary reduction furnace, and then carbonaceous material, oxygen,
Blow it into a bottom-blowing melting furnace together with a slag-forming agent, and further blow oxygen or air into the top of the melting furnace,
A portion of the combustible gas produced by the reduction and gasification reactions of carbonaceous materials was combusted, the reduced iron bath in the furnace was heated, and the generated high-temperature gas was passed through a heat exchanger for heat recovery. Afterwards, it is mixed with a part of the gas recovered from the preliminary reduction furnace, and after decarboxylation treatment, it is heated to a predetermined temperature to determine the oxidation degree of the gas [(H ₂ O + CO ₂ )/(H ₂ + H ₂ O + CO + CO ₂ )]. 0.07
It is characterized in that it is adjusted to 0.15 and then introduced into the preliminary reduction furnace, and the preliminary reduction rate in the preliminary reduction furnace is adjusted to 0.60 to 0.75. The gist of the present invention will be explained below with reference to the drawings. 1st
The figure is an explanatory diagram showing the outline of the method of the present invention, in which 1 is an iron ore preheating furnace, 2 is a preliminary reduction furnace, 3 is a smelting reduction furnace, and an injection port 4 for carbonaceous material, oxygen, slag forming agent, etc., is used for preliminary reduction. An inlet 5 for injecting iron ore, an inlet 6 for secondary oxygen for partial combustion, a gas outlet 7, 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 heating machine, 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 or a shaft furnace to partially reduce the iron ore. As will be described later, the present invention is characterized by this preliminary reduction. The pre-reduced iron ore is blown into the furnace from the bottom of the smelting reduction furnace 3 together with carbonaceous material, oxygen, slag-forming agent, etc., and reduction is performed. Furthermore, oxygen or air is blown into the upper part of the melting reduction furnace 3 from an oxygen inlet 6, and the combustible gas generated by partial combustion of the reduced and injected carbonaceous material is combusted, and the combustible gas is reduced by the generated heat. Heat an iron bath. On the other hand, the high temperature gas generated in the smelting reduction furnace 3 is discharged from the discharge port 7, heat exchanged with a heat exchanger 8 such as a waste heat boiler, mixed with a part of the gas recovered from the preliminary reduction furnace 2, and further A part of the mixed gas is decarboxylated by the decarboxylation device 10, and the degree of oxidation is adjusted to a range of 0.07 to 0.15.
It is heated by the heater 11 and introduced into the preliminary reduction furnace 2 . Note that the high-pressure steam generated by heat exchange with the high-temperature gas by the heat exchanger 8 is used for power generation and the like. The present invention is characterized by adjusting the degree of oxidation of the gas introduced into the pre-reduction furnace to 0.07-0.15 and setting the pre-reduction rate in the pre-reduction furnace to 0.60-0.75.The reason is as follows. Explain. FIG. 2 shows the progress of reduction over time when iron ore is gas-reduced. As is clear from this figure, the rate of gas reduction of iron ore is fast up to a reduction rate of 60 to 70%, but the rate decreases beyond this point. This fact shows that gas utilization efficiency is high when the reduction is 70% or less, which is advantageous as a process. However, the direct steel 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, preliminary reduction is aimed at a reduction rate close to 100%. are doing. 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 electricity
You will be doubly disadvantaged. Furthermore, Fig. 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. Become. 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;
A reduction rate close to 100% requires a large amount of gas. Further, FIG. 4 shows changes in the amount of gas generated and the amount of reducing gas when the degree of oxidation of the gas generated by the melting reduction furnace and the reducing gas for preliminary reduction changes. Now, in a melting reduction furnace, the carbonaceous material blown into the iron bath usually undergoes the following reaction with oxygen to be partially oxidized and generate heat. C+1/2O ₂ =CO+26kca/m However, the CO gas generated here is 68kca/m
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 CO ₂ , and this combustion heat is used to heat the iron bath. This is the key to increasing energy efficiency. It is advantageous.
However, if the degree of oxidation is increased too much, it will put a burden on the CO ₂ removal process and increase the overall cost, so the upper limit of the degree of oxidation here is about 0.35. Further, in the preliminary reduction step, when the degree of oxidation of the gas increases, the reduction force decreases, and the required amount of gas increases. On the other hand, the petroleum-derived gas generated in the smelting reduction furnace of the present invention has a high CO content, and it is known that when this is heated to high temperatures, carbon will precipitate due to the reaction of 2CO → CO ₂ + C, making the furnace inoperable. Therefore, at the reduction temperature of 900° C. of the present invention, the degree of oxidation cannot be reduced to 10% or less. As explained above, in order to increase the energy efficiency of the smelting reduction furnace, it is advantageous to increase the degree of oxidation of the exhaust gas, and in order to reduce the amount of gas required for preliminary reduction, it is advantageous to reduce the degree of oxidation of the gas. It is desirable to do so. Therefore, in the present invention, a decarboxylation device is installed between these two steps to remove CO ₂ and
After removing H ₂ O, it is used for preliminary reduction. In other words, the preliminary reduction rate is 75%, which increases the required amount of reducing gas rapidly.
It is characterized by operating under operating conditions that avoid the above and also avoid a range of low preliminary reduction rates where the energy required for melting reduction increases (gas becomes surplus). (Example) Next, an example 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.

【table】

[Table] In steady operation, return rate is 65 per hour.
%, 1270Kg of pre-reduced iron ore, temperature 1500℃,
98% O ₂ 351N ³ , 806 kg of coal, and 196 kg of coal stone were injected into an iron bath with a C concentration of 3% through a tuyere provided at the bottom of the melting furnace. At the same time, when 520Nm ³ of 98% oxygen was soft blown from the top of the iron bath for secondary combustion, 1690Nm ³ of gas at 1700°C was generated. Its composition is _H2 : 11%, CO: 58
%, CO ₂ : 16%, H ₂ O: 14%, N ₂ : 1%, and the amount of dust was 84 kg. This high-temperature gas is further heat-recovered by an exhaust heat boiler installed at the top of the furnace, cooled and dehumidified, and then boosted to a pressure of 3Kg/cm ² by a compressor and mixed with 637Nm ³ of circulating gas from the preliminary reduction process, of which 1525Nm After branching ³ , the pressure was further increased to 8Kg/cm ² , sent to a decarbonizer to remove carbon dioxide and dehumidify, and then the pressure was reduced to 4.5Kg/cm ² , and the remaining part that had been branched earlier was When mixed with the gas of
H ₂ : 13%, CO: 75%, CO ₂ : 8%, H ₂ O: 2
%, N ₂ :1590 Nm ³ of 2% gas was obtained. This gas with an oxidation degree of 0.102 was heated to 900°C in a gas heating furnace and then blown into a preliminary reduction furnace. 1,500 kg of hematite ore (particle size of 2 mm or less) preheated to 850°C is supplied to this pre-reduction furnace from the top of the furnace, and it reacts with the gas to undergo fluidized reduction, producing 1,270 kg of semi-reduced ore with a reduction rate of 65%. Obtained. At this time, of the gas discharged from the preliminary reduction furnace, the remainder after branching off the 637 Nm ³ which is recycled to the reduction process as circulating gas is discharged outside the system as preliminary fuel for iron ore and fuel for power generation. Incidentally, the amount of exhaust gas at this time was 860Nm ³ and the calorific value was 1840kca/Nm ³ . In addition, 1030 kg of 3% C molten iron was produced per hour from the smelting reduction furnace. The slag generated at this time was 237 kg, basicity (CaO/SiO ₂ ) = 1.3, and FeO concentration in the slag was 5%. Furthermore, corrosion of the furnace material during the 5-hour experimental operation was not significant. For comparison, the oxidation degree of the pre-reducing furnace inlet gas was
When it was set to 0.06, carbon began to deposit on the exhaust gas dust remover about 15 minutes after the start of operation, and eventually the system became inoperable. Furthermore, when the degree of oxidation was set to 0.20, the reduction rate decreased significantly. Therefore, if the operation continues under these conditions, a large amount of gas will be required to reduce each unit of ore to the specified reduction rate, resulting in various disadvantages such as an increase in the size of the equipment and an increase in power for gas circulation. A point appears. (Effects of the Invention) As explained above, the present invention uses the pre-reduction conditions of a moderate reduction rate, which is advantageous in gas utilization rate in gas reduction, and also uses dissolved carbon in an iron bath supplied by bottom blowing. Fast reduction of semi-reduced iron ore,
In order to improve the heat exchange coefficient of the fuel, we combine various processes such as secondary fuel on an iron bath, and furthermore, adjust the oxidation degree of the gas introduced into the pre-reduction furnace to a range of 0.07 to 0.15, and By setting the preliminary reduction rate at 0.60 to 0.75, extremely high productivity can be ensured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the method of the present invention, and FIG.
The figure shows the relationship between the reduction rate and reaction time when iron ore is reduced to gas. Figure 3 shows the effect of changes in the preliminary reduction rate of iron ore on the required amount of coal, the amount of gas generated, and the amount of preliminary reduced gas. 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
...Heating machine, 12...Cooler.

Claims (1)

[Scope of Claims] 1. After preheating iron ore and further pre-reducing it in a pre-reduction furnace, it is blown into a bottom-blowing smelting reduction furnace together with carbonaceous material, oxygen, and a slag forming agent. , blowing oxygen or air to burn part of the combustible gas produced by the reduction and gasification reaction of carbonaceous materials, heat the reduced iron bath in the furnace, and use the generated high-temperature gas to After passing through a heat exchanger to recover heat, it is mixed with a part of the gas recovered from the preliminary reduction furnace, and after decarboxylation treatment, it is heated to a predetermined temperature, and the oxidation degree of the gas [(H ₂ O + CO ₂ )/(H ₂ +
H ₂ O + CO + CO ₂ )] 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. 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.