JPS62230924A - Manufacture of smelted and reduced iron - Google Patents

Abstract

PURPOSE:To stably maintain high operational efficiency when smelted and reduced iron is manufactured by combining reduction in a fluidized bed with smelting and reduction, by specifying the rate of prereduction of iron ore in a prereducing stage and the efficiency of secondary combustion in a smelting and reducing furnace. CONSTITUTION:Powdery iron ore is preheated with a preheater 1 and sent to a fluidized bed type carbon coating tower 2, where the ore is brought into contact with tar or the like fed to the tower 2 to coat the surface of the ore with carbon. The ore is sent to a fluidized bed prereducing furnace 3, prereduced at 75-95% rate of prereduction and sent to a smelting and reducing furnace 4, where the ore is finally reduced with gaseous CO produced by the reaction of a carbonaceous material with oxygen. At the same time, quick lime is blown to carry out dephosphorization and secondary combustion is carried out with <=40% efficiency of combustion by further blowing oxygen. Molten iron is discharged from the lower part of the furnace 4 and slag from the upper part.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing molten reduced iron, and more specifically,
The present invention relates to a method for obtaining reduced iron by combining flow reduction, reduction, and fusion reduction in a flow iIJ layer, which can stably maintain operational efficiency at a high level.

[Prior art] In the indirect iron manufacturing method using a blast furnace-converter method or the direct iron manufacturing method using a shaft furnace, the raw material iron ore is subjected to agglomeration treatment (by pellets, sintering, briquettes, etc.) in advance, or iron ore in the form of lumps is processed in advance. Although it is necessary to use stones, this method involves pre-reducing powdered iron ore by making it fluidized with reducing gas! I! III-layer reduction method The inter-layer reduction method has great expectations because it simplifies the preliminary treatment of raw materials. However, this fluidized bed reduction method has not yet been completed as a system, and many problems remain unresolved.

[Problems to be Solved by the Invention] The most problematic problem in the fluidized bed reduction method as described above is the sticking phenomenon (described later). In other words, in order to improve the reduction rate in the fluidized bed pre-reduction process, it is sufficient to raise the reduction temperature to a certain extent, but under high temperature conditions, reduced iron forms in whiskers on the surface of powdered iron ore, becomes entangled with each other, and becomes agglomerated. A sticking phenomenon occurs in which fluidity is lost. Therefore, fluidized bed pre-reduction must be carried out while the temperature is kept low, making it impossible to sufficiently increase the reduction efficiency. Therefore, the present inventors conducted various studies to establish measures to prevent sticking. As a result, sticking was prevented by adhering carbonaceous material to the surface of powdered iron ore prior to fluidized bed pre-reduction, and it was found that sticking could be prevented under high temperature conditions. 1) Coal is the most economical raw material for carbonaceous materials, and a coal carbonization fluidized bed facility is attached to the direct reduction facility to reduce the carbon produced by carbonization. We have confirmed that carbonaceous material can be uniformly adhered to the surface of iron ore by bringing the contained gas or liquid component into contact with powdered iron ore in a reducing atmosphere, and have filed a separate patent application.

On the other hand, iron ore that has been pre-reduced as described above (hereinafter sometimes referred to as semi-reduced iron ore) is generally introduced into a smelting reduction furnace, where it undergoes final reduction, unless it is to be commercialized as briquettes, etc. and separation from gangue components.

That is, in the smelting reduction furnace, CO (2C + 02 = 2C) generated by blowing oxygen (or air) and carbonaceous material
O) At the same time, it is necessary to melt the reduced iron for separation and refining of gangue components, and the amount of heat required for the melting and associated equipment including a fluidized bed pre-reduction furnace etc. In order to secure the necessary amount of heat, secondary combustion (post-compression) of the reducing generated gas is performed on an iron bath. The high-temperature combustion exhaust gas obtained in this way is sent to the fluidized bed reduction furnace after adjusting its temperature and composition to a temperature and composition suitable for preliminary reduction.

By the way, in order to increase the operational efficiency in the above-mentioned series of reduced iron production processes, especially in the smelting reduction furnace,
It is desired to increase the pre-reduction efficiency in the fluidized bed pre-reduction furnace to reduce the reduction load in the smelting reduction furnace and to increase the post-compression combustion efficiency. However, increasing the combustion efficiency of post-compassion increases the amount of oxidizing gases (Co, H2O) in the generated gas, which not only increases the reforming load in the reforming equipment, but also causes problems when reforming is insufficient. In this case, the pre-reduction efficiency in the fluidized bed pre-reduction furnace decreases. Moreover, when the concentration of oxidizing gas in the generated gas increases, the carbonaceous material adhering to the surface of the powdery iron ore is consumed by solution loss reaction (C+Co2-2CO) and water gas reaction (C+H2O-C0+H2), resulting in a sticking prevention effect. will no longer be effective.

As is clear from the above trends, in order to prevent the occurrence of the sticking phenomenon in the fluidized bed pre-reduction reactor and to ensure smooth operation without causing excess or deficiency of heat in the smelting reduction reactor, it is necessary to It is thought that it is necessary to appropriately adjust the pre-reduction efficiency in the fluidized bed pre-reduction furnace and the secondary combustion efficiency in the smelting reduction furnace, taking into consideration their mutual relationship. Sufficient research has not been conducted, and as a result, it cannot be said that satisfactory operational efficiency has been achieved.

The present invention has been made with attention to these circumstances, and its purpose is to appropriately control the pre-reduction efficiency in the fluidized bed pre-reduction furnace and the secondary combustion efficiency in the smelting-reduction furnace while considering their mutual relationship. without causing sticking and without causing excess or deficiency in the amount of heat required for operation.
The present invention aims to provide a method for producing molten reduced iron that can stably obtain excellent operational efficiency.

[Means for Solving the Problems] The structure of the method according to the present invention is that after pre-reducing powdery iron ore to which carbon is attached in a fluidized bed method, it is melted and reduced in a smelting reduction furnace. A method for producing molten reduced iron in which the gas generated in the process is secondary-combusted on an iron bath and the high-temperature generated gas is supplied to a preliminary reduction furnace.The preliminary reduction rate of iron ore in the preliminary reduction process is controlled to 75 to 95%. At the same time,
The gist of this method is to control the secondary combustion efficiency in the smelting reduction furnace to 40% or less.

[Operation] Fig. 1 shows a basic flowchart when carrying out the present invention, in which powdery iron ore (grain ore) is preheated in a preheater 1 and then transferred to a fluidized bed carbon coating tower 2. In the coating tower 2, the surface of the grain ore is coated with carbon by bringing it into contact with tar or the like supplied from a coal carbonization tower (not shown). The carbon-coated grain ore is sent to a fluidized bed pre-reduction furnace 3 for preliminary reduction, and then sent to a smelting reduction furnace 4. In the smelting reduction furnace 4, final reduction is carried out using CO gas produced by the reaction of carbonaceous material and oxygen, which are supplied separately, and dephosphorization is carried out by blowing quicklime etc., and molten iron is extracted from the lower layer and removed from the upper layer. discharges slag. Then, oxygen is separately blown onto the iron bath of the melting reduction furnace 4,
The reducing gas produced in the reduction furnace 4 is subjected to secondary combustion to generate thermal energy, and the necessary amount of heat for the treatment system is ensured by taking into account the reaction heat of the carbonaceous material and oxygen for the reduction. The high-temperature exhaust gas generated in the melting reduction furnace 4 is cooled down to an appropriate temperature by mixing with recycled gas, which will be described later, and then sent to the preliminary reduction furnace 3, and then passed through the carbon coating bath 2 and then cooled in the cooler 5. A part of the gas is sent to the compressor 6 as a recycled gas, and the rest is extracted from the system as a reducing surplus gas. The recycled gas pressurized by the compressor 6 removes carbon dioxide gas in the decarbonator 7 to increase its reduction potential, and then is mixed with an appropriate amount of high-temperature exhaust gas from the smelting reduction furnace 4 and sent to the preliminary reduction furnace 3.

In order to carry out this series of molten reduced iron production processes efficiently, for the reasons mentioned above, the preliminary reduction efficiency in the preliminary reduction furnace 3 and the secondary combustion efficiency in the smelting reduction furnace 4 must be
They must be controlled appropriately while taking into account their mutual relationships.

As a result of conducting various studies from this perspective, we found that if the preliminary reduction rate in the preliminary reduction furnace 3 is kept at 75-95% and the secondary combustion rate in the smelting reduction furnace 4 is suppressed to 40% or less, the above series of results can be achieved. It has been found that operations can be carried out smoothly and without waste.

The reasons for determining the preliminary reduction rate and secondary combustion rate will be explained in detail below.

First, if the preliminary reduction rate is less than 75%, not only will the reduction load in the smelting reduction furnace 4 increase, but also the oxidizing gas (C
O2 + H20) concentration becomes high (7% or more), and the amount of carbon consumed by gasification due to the solution loss reaction and water gas reaction increases in the pre-reduction furnace 3, making it easier for the sticking phenomenon to occur, resulting in unstable operation. state is no longer available.

On the other hand, in order to increase the preliminary reduction rate to 95% or more, it is necessary to extremely lengthen the residence time of the grain ore in the preliminary reduction furnace 3, which not only significantly reduces productivity but also requires a long preliminary reduction process. It is also economically unfavorable because a furnace must be used.

In addition, if the secondary combustion rate exceeds 40%, the temperature inside the smelting reduction furnace 4 will become too high and the deterioration of the lining refractory will become significant, and the exhaust gas temperature will also become very high, causing the heat in the gas transmission piping to become too high. Deterioration becomes significant, and furthermore, the concentration of oxidizing gas (C02 + H20) in the exhaust gas becomes too high, making it easy to cause a sticking phenomenon in the preliminary reduction furnace 3, and in addition, the absolute amount of reducing gas in the recycled gas is insufficient. This will make it difficult to secure a predetermined preliminary return rate, and the continuous operation itself will fail.

By the way, Figure 2 is based on a total system computer program that combines subprograms that calculate the material balance and heat balance for each piece of equipment in the manufacturing process of molten reduced iron shown in Figure 1. , is a graph showing appropriate conditions for various combinations of preliminary reduction rate and secondary combustion rate.

In Figure 2, the straight line a-b indicates the limit at which the amount of recycled reducing gas becomes essentially zero, and under conditions above this, the actual amount of recycled gas becomes; Continuous operation becomes impossible because the reduction rate cannot be obtained.

In addition, the straight line c-d shows that the combustion heat of the surplus gas is used to: 1. preheat the grain ore, 2. generate the steam necessary for removing 002 from the recycled gas, and 2. generate electrical energy to produce oxygen to be blown into the smelting reduction furnace. ■The power required to boost the pressure of recycled gas, and also ■The total energy required for processing steps after this facility, such as casting and rolling of molten reduced iron (I Gcal)
) indicates the limit at which energy can be supplied corresponding to As a result, it will be necessary to consider a system for supplying reducing gas to areas other than this facility. Therefore, in order to maintain the supply and demand balance of reducing gas (including its function as a heat source) within this facility, it is best to operate along the above straight line c - d, but surplus reducing gas can be used for other purposes. It is also possible to operate in the area below the straight line c-d if a system has been established to utilize it.

The straight line e-f indicates the limit at which the oxidizing gas (CO2+H20) concentration in the gas entering the preliminary reduction furnace 3 is 7% (the upper limit that can prevent sticking), and in the region to the left of this, oxidation When the concentration of toxic gas components reaches 7% or more, carbon on the surface of the grain ore is oxidized and consumed in the pre-reduction furnace 3, making it easy to cause sticking.

In addition, the straight line g-h indicates the conditions under which the pre-reduction rate in the pre-reduction furnace is 95%, and operating in the area to the right of this line is difficult from a facility standpoint for the reasons mentioned above. This is extremely disadvantageous in terms of productivity.

The above Figure 2 shows the results of a case study in which various combinations of the reduction rate in the fluidized bed reduction process and the secondary combustion rate in the smelting reduction furnace were carried out using the total system computer program as described above. The following 3rd ~
This was determined by combining the results shown in Figure 5.

In other words, Figure 3 shows the flow rate (%) and surplus gas amount (N m3/THM) when the secondary combustion rate is varied.
) (flow rate per ton of molten iron), and the values of reduction rate and secondary combustion rate (i, j) at which the amount of surplus gas becomes zero
From this, the straight line a-b in FIG. 2 can be found.

Figure 4 shows the relationship between the fluidized bed reduction rate and surplus heat (Gcal/THM) when the secondary combustion rate is changed. The reduction rate and secondary combustion rate (k
, 1), the straight line c-d in FIG. 2 can be found.

Figure 5 also shows the fluidized N reduction rate (%) and (Co
2+H20) concentration (%), and the (CO
2+H20) concentration is 7% (dashed line in the figure: limit concentration that can prevent the occurrence of sticking in the fluidized bed reduction furnace).
), the straight line e-f in FIG. 2 can be found.

By the way, Figure 6 shows 4
Reduction rate and reduction time when the gas pressure is varied in the range of 0 to 7 g/cm' under the condition that iron ore whose surface is coated with % by weight of carbon is subjected to fluidized bed reduction at 850℃. This is a graph showing the relationship, and it can be seen that increasing the reduction rate to 95% or more by fluidized bed reduction is inefficient.

As is clear from the above results, the more preferred operating range in the present invention is the range surrounded by 1jfh shown in Figure 2, and the preferred operating range when the requirement of maintaining energy balance within this facility is added. The range is the range surrounded by 1jkl.

In the example shown in FIG. 1, as a method for attaching carbon to grain ore, a fluidized bed type carbon coating bath 2 is provided in front of the fluidized bed pre-reduction furnace 3, and the carbon material is coated in a fluidized state under a reducing atmosphere. This method allows the carbonaceous material to adhere evenly and evenly to all of the grain ores, effectively preventing sticking during fluidized bed pre-reduction. I can do it. The type of carbonaceous material to be attached to the surface of the grain ore is not particularly limited, and examples include coal-based or petroleum-based tar, pitch, coke, etc., but the most advantageous is coal-based carbonaceous material, which is cheap and abundant. .

When coal is used as a carbonaceous material, the method of adhesion to iron ore is ■
Mixing powdered coal with powdered iron ore in a fluid state3
A method of heating to about 00 to 600 degrees Celsius (at this temperature, powdered coal becomes caking and adheres to the iron ore surface), or
A separate coal gasifier is installed to thermally decompose the coal to generate CO-rich gas, which is mixed with powdered iron ore using the carbon coating base 2 to precipitate C on the surface of the iron ore (2C).
O-CO2+C) method, ■ A method in which a coal carbonization device is separately provided, coal is carbonized to generate tar, etc., and this is attached to the surface of powdered iron ore with a carbon coating base 2, ■ In the same carbon coating column, Tar that has been liquefied in advance by heating or other means,
Typical methods include a method in which carbon is deposited on the surface of powdered iron ore by injecting a carbonaceous material such as pitch or solvent-refined coal.

The amount of carbonaceous material attached to the surface of the iron ore is not particularly limited, but it has been confirmed through experiments that it is 2 to 10% by weight, particularly preferably 3.5 to 5% by weight, based on the iron ore. By attaching carbonaceous material of ifc%, sticking during fluidized bed reduction can be more reliably prevented.

As described above, according to the present invention, by appropriately controlling the reduction rate in the preliminary reduction furnace 3 and the secondary combustion rate in the smelting reduction furnace 4, a series of processes from preliminary reduction to smelting reduction can be carried out smoothly without waste. However, in order to further reduce the load on the smelting reduction furnace 4 and further increase processing efficiency, it is advantageous to blow the carbon-coated granules and carbonaceous material into the smelting reduction furnace 4 using a hot charge method. In particular, if a method is adopted in which a coal carbonization device shown in (■) above is installed and tar or the like is used as a carbon material for adhering to the surface of granules, the char produced in the carbonization process is supplied to the smelting reduction furnace 4. By using it as a carbon material, the advantages of the hot charging method described above can be utilized more effectively.

That is, when trying to blow ordinary coal into the smelting reduction furnace 4 using the hot charge method, if the carrier gas temperature is raised too high, there is a risk that the pressure inside the pipe will increase due to rapid gas generation or that the coal will cause coking. It is not possible to raise the blowing temperature extremely. However, the char from which the volatile matter has been removed by carbonization is semi-coked, and even when exposed to considerably high temperatures, problems such as increased pressure in the atmosphere due to thermal decomposition, adhesion of particles to each other, coarsening, and even coking do not occur. Therefore, hot charging into the melting reduction furnace 4 can be performed without any problem. In this case, the char discharged from the coal carbonization equipment has a considerably high temperature (approximately 550
℃), so leave this as it is? By hot charging at Mr degree, the sensible heat of the char can be effectively utilized. Further, by hot-charging the powder w (approximately 800 to 1100° C.) that has been pre-reduced to the melting reduction furnace 4 while maintaining this high temperature, it is possible to eliminate waste of sensible heat. However, with regard to pre-reduced ore powder, if the hot charge temperature exceeds 1100°C, some of the reduced iron may become sticky and stick to each other, forming blocks, and there is a risk that they will accumulate in the pipes and become impossible to feed. Therefore, the temperature should be kept below 1100°C.

By adopting a method of hot charging the raw material blown into the smelting reduction furnace 4 in this way, the amount of heat consumed in the smelting reduction furnace 4 is reduced, and the amount of carbon material used can be reduced by the amount of the reduction. .

Incidentally, Figure 7 shows that when pre-reduced grain ore with a pre-reduction rate of 86% is melt-reduced, the secondary combustion rate is varied from 0 to 6.
This shows the results of investigating the relationship between the amount of coal required for operation and the raw material (pre-reduced grain ore and char) injection temperature when the temperature is changed to 0%. As the amount of coal increases, the amount of coal required will decrease significantly.

The dashed line C-D in the figure is the amount of coal required to completely reduce semi-reduced iron ore with a preliminary reduction rate of 86%, and the dashed line E-F is the total energy required for this facility and auxiliary equipment (I Gcal/THM
) and the amount of coal required to maintain equilibrium, and the chain line GH indicates the upper limit temperature of the blowing temperature that can be adopted, respectively. In this diagram, the conditions that can effectively achieve the above purpose are AB'
EF'D'C'
This is a condition that falls within the area surrounded by E'.

Furthermore, in order to effectively utilize the purpose of reducing the coal consumption rate by hot charging, it is necessary to set the raw material injection temperature to 2 of the above conditions.
It is preferable to set the temperature to 00°C or higher, more preferably 400°C or higher.

[Example] Example 1 Figure 8 is a flow diagram showing an example of the present invention, in which the preliminary reduction rate was 86%, the secondary combustion rate was 30%, and the carbon coverage rate on the surface of grain ore was 2.7. The material balance and heat balance of each part are shown when each part is set to %. In this example, powdered coal is used as the carbon material supply source, and after being preheated in a coal preheater 9, it is carbonized in a coal carbonization fluidized bed 8, and the generated tar is used as a carbon material for coating the surface of the granule ore. The resulting char is used as a carbon material to be supplied to the melting reduction furnace 4.

Further, Table 1 below shows the flow rate, temperature, and gas composition in each line No. shown as ■ to @ in FIG. 8.

As is clear from FIG. 8 and Table 1, it can be seen that the present invention can be effectively implemented as a total system.

Example 2 According to the flowchart shown in Figure 8 above, the preliminary return rate was set to 86.
%, the secondary combustion rate is set to 20%, and the injection temperature of powdered raw material to the smelting reduction furnace is set at 30°C and 550°C, respectively. A comparison of the amount of oxygen included and the surplus energy discharged outside the system as reducing gas resulted in the results shown in Table 2 below.

Table 2 As is clear from Table 2, by combining the present invention with the hot charging method, it is possible to significantly reduce the amount of carbonaceous material and oxygen used, and it is possible to significantly reduce operating costs.

[Effects of the Invention] The present invention is constructed as described above, and by appropriately controlling the preliminary reduction rate in the preliminary reduction furnace and the secondary combustion rate in the smelting reduction furnace, thermal energy can be reduced without causing a sticking phenomenon. It is possible to maintain stable operating conditions with excellent productivity without causing excess or deficiency. In addition to this method, if a hot charge method is adopted for injecting raw materials into the smelting reduction furnace, the amount of carbon material used can be significantly reduced, and the economical efficiency of operation can be further improved.

[Brief explanation of drawings]

Figure 1 is a basic flow diagram showing an embodiment of the present invention, Figure 2 is a graph showing the interaction between reduction rate and secondary combustion rate, and Figures 3 to 5 are graphs showing the interaction between reduction rate and secondary combustion rate.
The figure is a graph showing the basis data for drawing the conclusion in Figure 2,
Figure 6 is a graph showing the relationship between reduction time and reduction rate, Figure 7 is a graph showing the relationship between raw material injection temperature into the smelting reduction furnace and the required amount of coal, and Figure 8 is the material balance obtained in the example. It is a flow diagram which also shows heat balance. 1... Preheater 2... Fluidized bed type carbon coating bath 3... Fluidized bed preliminary reduction furnace 4... Melting reduction furnace

Claims (2)

[Claims] (1) After pre-reducing carbon-coated iron ore using a fluidized bed method, it is melted and reduced in a smelting reduction furnace, and the gas generated in the smelting reduction furnace is secondaryly combusted on an iron bath to generate a high-temperature In a method for producing molten reduced iron in which generated gas is supplied to a preliminary reduction furnace, the preliminary reduction rate of iron ore in the preliminary reduction step is controlled to 75 to 95%, and the secondary combustion efficiency in the smelting reduction furnace is controlled to be 40% or less. 1. A method for producing molten reduced iron, which is characterized by controlling: (2) The manufacturing method according to claim 1, wherein the amount of carbon material supplied to the smelting reduction furnace is reduced by supplying raw materials into the smelting reduction furnace using a hot charge method.