JP2983087B2 - Operation method of smelting reduction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smelting reduction method for metals, and more particularly to a smelting reduction method for iron and ferroalloys.

[0002]

2. Description of the Related Art As a method of producing pig iron and a method of producing ferroalloys without using the blast furnace method, smelting reduction has been studied and utilized in actual production. Among them, in the iron bath type smelting reduction method, in order to efficiently supply the heat necessary for the reduction of ore,
Attempts have been made to improve the secondary combustion rate of the gas generated from the furnace, increase the combustion heat per unit weight of the fuel such as coal and coke used (hereinafter referred to as carbonaceous material), and reduce the carbonaceous unit consumption. Many have been made.

In other words, the amount of heat to oxidize and burn carbon to carbon monoxide is about four times the amount of heat to burn carbon dioxide, and in the case of hydrogen, secondary combustion in which hydrogen reacts with oxygen. Otherwise, heat of combustion is not generated, and for efficient use of carbonaceous materials, it is indispensable to implement an operation method with high secondary combustion rate and good heat arrival.

For example, Japanese Patent Application Laid-Open No. 03-140405 discloses a technique for supplying a bottom-blown stirring gas and a method for supplying top-blown oxygen to obtain a high secondary combustion rate. It also describes the amount of slag for reducing the amount of dust contained. Japanese Patent Application Laid-Open No. 61-221322 discloses a technique of transmitting secondary combustion heat to slag and further stirring the slag bath with gas to transfer the heat to molten metal in a converter type container. ing.

[0005] In the smelting reduction method, ore as a main raw material is supplied from above or from the furnace bottom, and is dissolved in an iron bath or slag, and becomes a dissolved component of slag in the form of metal oxide. This metal oxide is reduced by the carbon dissolved in the molten metal or the solid carbon in the form of coke or char in the slag to become the molten metal.

[0006] In order to reduce the ore, a large amount of heat of reduction is required. Therefore, in the smelting reduction method, oxygen or air is supplied into a furnace, and carbon material supplied as fuel is burned. An operation to supplement the heat of reduction is being implemented. At this time, in order to increase the calorific value per weight of the carbonaceous material, CO and H ₂ gas generated from an iron bath or a slag bath are further converted to CO 2
Research has been actively conducted to increase the productivity by generating a large amount of heat in the furnace by the secondary combustion of burning to ₂ and H ₂ O.

[0007] Techniques for increasing the secondary combustion rate include:
It has been clarified that it is effective to effectively use the foamed molten slag existing on the iron bath as an oxygen shield, and for this purpose, the slag is also made to have a certain thickness or more. At this time, it is desirable that oxygen is blown from above the slag bath or into the slag.

In order to effectively use the heat of the secondary combustion, enhance the heat transfer efficiency, and utilize the heat of the reduction reaction and the sensible heat of the molten metal, various techniques for well stirring the slag have been studied. It is effective to blow a stirring gas from the bottom of the iron bath or a gas from the side wall for stirring.

[0009] However, in the prior art, attention has been paid only to a technique for increasing the secondary combustion rate, and no research has been sufficiently conducted to improve the heat transfer from the secondary combustion. In particular, the conventional research was carried out in a small experimental furnace having an iron bath scale of 1 to 10 tons. Therefore, when the production rate is high, that is, when the acid supply flow rate is large, an operation method for increasing the heat transfer efficiency is required. Was not sufficiently clarified, so that the production amount per hour was 20 to 50 t.
There was not enough knowledge about good production conditions when producing pig iron. Also, because the experimental furnace is small,
There was also a problem that the distance from the furnace wall to the oxygen jet was short, and stirring from the furnace wall was more effective than in a large furnace.

[0010] As a method of supplying the oxygen jet from the top blowing lance, a depression (cavity) formed by the oxygen jet in the foamed slag during the operation is formed in a layer containing a large amount of iron particles existing under the slag. He had only the knowledge to control the acid transfer conditions so as not to hit. This control method is important to keep the secondary combustion rate high,
The conditions for effectively heating the secondary combustion heat were not satisfied. As a result, although the operation with a high secondary combustion rate could be implemented, the heat could not be effectively used for the reduction reaction, the carbon unit consumption could not be reduced effectively, and the secondary combustion heat caused the generated gas. As the temperature rises, radiant heat to the bricks on the furnace wall increases, causing a problem that the wear rate of the bricks increases.

[0011]

When the operation of smelting reduction is to be carried out efficiently and economically, the following points are technical problems. In the smelting reduction furnace, the ore is melted and reduced at the same time, and a large amount of heat is consumed for this. Therefore, in order to achieve high productivity and economical operation, an iron bath and a slag bath are required. It is an important technical problem that carbon monoxide and hydrogen gas generated from the gas are subjected to secondary combustion and that this heat is effectively used.

Although various techniques have been studied for improving the secondary combustion rate and generating a large amount of heat in the smelting reduction furnace, the heat generated in the secondary combustion can be effectively reduced by using a reduction reaction site and an iron bath. Heat cannot be transferred to the furnace, and despite the increase in the secondary combustion rate, the unit consumption of coal does not decrease, and the heat is not used effectively. Problems such as damage have occurred.

Further, in the conventional experimental operation, since the operation was performed in a small furnace of a scale of 1 to 10 tons, there is no sufficient knowledge about a technique for improving heat transfer in an operation having a high production speed. However, due to the lack of experience at high production rates in large furnaces, the operation is similar to that of small furnaces, despite the high heat supply rate, so that only operations with poor heat transfer during secondary combustion can be obtained. I didn't.

That is, the heat generated by the secondary combustion is effectively transferred to the reduction reaction site and the heat bath to increase the thermal efficiency, to lower the exhaust gas temperature and to reduce the wear of the refractory, so that the melting reduction is required. Was an important issue for us. The present invention provides a smelting reduction method that effectively solves the above-mentioned problems.

[0015]

Means for Solving the Problems The present invention has been completed as a result of various studies and studies on a large-scale test furnace applicable to actual operation in order to solve the above-mentioned problems in smelting reduction. There is an iron bath type smelting reduction operation in which oxygen or air is blown from the top blowing lance to the slag bath formed on the iron bath, and the stirring gas is blown down from the tuyere below the surface of the iron bath. In the method, iron ore and stone as raw materials
Charcoal is added from above the furnace, and 1/6 to 2.0
The slag of t is formed on an iron bath, the discharge speed of oxygen or air from the nozzle at the nozzle outlet of the oxygen or air is set to 300 Nm / sec or more. The distance from the upper surface is set to be not less than 10 times and not more than 45 times the nozzle diameter in the lance.

In the above-mentioned operation, an acid supply flow rate of 1000
The operation is performed while securing a slag amount of 1.5 to 3.5 tons per Nm ³ / h. Still further, in the above-mentioned operation, a part of the top-blown oxygen is blown from the slag bath.

[0017]

As described above, in the smelting reduction, in order to enhance the secondary combustion and enhance the heat transfer efficiency, the state of the oxygen jet blown from the upper blowing lance is optimized and the molten slag is transferred to the heat transfer medium. It is important to clarify the appropriate conditions for utilizing as a raw material, and it is an important operating condition to reduce the amount of carbonaceous materials and oxygen consumption and increase productivity.

The present inventors have elucidated the above operating conditions,
In order to achieve operation with good thermal efficiency, various experimental studies were conducted on a large-scale test furnace capable of almost reproducing actual operation, and as a result, the following facts were found. As a result of this experiment,
First, it was revealed that the state of the oxygen jet from the top blowing lance plays an important role. That is, by adjusting the positional relationship between the upper blowing lance and the slag, and adjusting the discharge speed of the oxygen jet, it is found that the jet combustion state of the discharged gas flow and the heat transfer from the combustion part are kept good. Was.

Second, it was found that slag formed on the iron bath also plays an important role in heat transfer. That is, the amount of heat generated due to the secondary combustion or the amount of slag corresponding to the supply rate of oxygen is present on the iron bath, so that the molten slag that receives the primary heat and acts as a heat transfer medium can be supplied in an appropriate amount. By making it exist, the heat transfer from the slag to the reducing portion of iron oxide and the hot metal bath can be improved.

In this experiment, an experimental measurement was carried out using a smelting reduction furnace having a maximum iron bath of 120 t under the following operating conditions, and the above-mentioned fact was clarified. The outline of the test furnace is as shown in FIG. 1 described later. Royo hot metal amount up to 120t experimental conditions still bath area 22m ² of test furnace (slag - hot metal surface) pig iron amounts 50~120t slag amount 20~100t hot metal t per slag weight 0.15~2.0t molten iron production rates 15~40t / H Ore charging speed 25-60t / h Coal charging speed 20-45t / h Oxygen flow rate 15,000-30,000Nm ³ / h Hot metal temperature 1500 ℃ Top blowing lance No. of nozzles 5-18 holes Nozzle diameter 40-73mm Bottom blowing Gas Gas type N ₂ stirring power 3 kW / t-metal Raw material condition Ore Lump (> 5 mm), Fe ₂ O ₃ 97% Input from above furnace Coal Lump (> 5 mm), fixed carbon 60%, volatile matter 26% From above furnace Input For the measurement of the secondary combustion rate, gas sampling was performed from the exhaust gas duct, and each gas component was continuously measured. Further, in order to measure the heat of secondary combustion, the heat balance in the process was performed every 10 minutes, and the relationship between the heat transfer efficiency and the operating conditions was analyzed. Since the heat transfer efficiency is affected by the secondary combustion rate, the data used for the analysis has a secondary combustion rate of 40 to 45%.

First, the influence of the state of acid supply from the top blowing lance on the heat transfer efficiency was investigated and analyzed. The data used include a secondary combustion rate of 40 to 45% and an acid feed rate of 1
The amount of slag per 000 Nm ³ / h was 2 to 3 t. The investigated acid feeding conditions are the distance between the lance nozzle and the upper surface of the slag (hereinafter, referred to as the lance gap) and the discharge flow rate of oxygen. Seven types of lances are used, and the acid supply flow rate is from 20,000 Nm ³ / h to 3
It was 000 Nm ³ / h.

FIG. 2 shows the relationship between the lance gap and the heat transfer efficiency. As an index of the lance gap, a dimensionless value obtained by dividing the lance gap (H) by the nozzle diameter (D) was used. Iron bath with 1/6 to 2.0 tons of slag per t of hot metal
Under the conditions formed above, the heat transfer efficiency is high in the heat in which the ratio (H / D) of the lance gap to the nozzle diameter is in the range of 10 to 45. However, it was found that when the H / D was 10 or less or negative, the heat transfer efficiency was poor. Also, H /
It was recognized that even when D was 45 or more, the heat transfer efficiency deteriorated.

The present inventors have obtained the following conclusions as a result of various research analyses. That is, if the lance gap is too large, the rate of combustion of the oxygen jet in the space above the slag increases, and the radiant heat from the oxygen jet to the gas and refractory above the slag increases. Therefore, it has been found that the reason why the heat arrival is deteriorated when the H / D is increased is that the combustion position of such an oxygen jet shifts upward.

On the other hand, when the H / D is 10 or less or a negative value, the slag cavity covers an oxygen jet under oxygen-feeding conditions, and most of the heat of the secondary combustion is supplied to the slag cavity. Heat transfer is expected to improve when the lance gap is reduced because the heat is transmitted to the surface, whereas in reality, when the H / D is small, the heat transfer is deteriorated. I figured out what was happening. It has been clarified that the cause of this is that the flow rate of oxygen discharged from the outlet of the upper blowing lance nozzle has a large effect.

FIG. 3 shows the relationship between the flow rate of oxygen discharged from the outlet of the upper blowing lance nozzle and the heat transfer efficiency. However, the discharge flow rate of oxygen from the lance nozzle cannot be measured directly, and the actual flow rate cannot be accurately calculated due to the influence of the discharge pressure.
The gas flow rate based on the volume of the gas in the standard state was adopted, and the unit was Nm / sec.

As a result of this analysis, it was found that the heat transfer efficiency was strongly affected by the oxygen discharge flow rate. As shown in FIG. 3, slag of 1/6 to 2.0 t per hot metal t
Under the condition formed on the iron bath, the discharge flow rate of oxygen is 30
It was clarified that the case where the heat transfer rate was 0 Nm / sec or more was stable and the heat transfer efficiency was good. However, in the lance type used in this experiment, when the discharge flow rate of oxygen exceeds 450 Nm / sec, the above-mentioned H / D becomes 45 or more, so that the heat transfer efficiency is slightly deteriorated. However, on the other hand, when the oxygen discharge flow rate is 3
It has been found that when the temperature is less than 00 Nm / sec, the heating efficiency is extremely deteriorated, and the heating efficiency is rapidly deteriorated as the oxygen discharge flow rate decreases.

On the other hand, the oxygen discharge flow rate is 300 Nm.
/ Sec or less, it has been found that the heating efficiency is extremely deteriorated and the heating efficiency is rapidly deteriorated as the oxygen discharge flow rate is decreased.

This phenomenon has been elucidated as follows . If the oxygen discharge flow rate is high, the jet speed is faster than the oxygen combustion, and before the combustion is completed sufficiently, the jet reaches the bottom of the slag cavity and the remaining oxygen burns inside the slag. The contact between the high-temperature gas and the slag becomes good, and the amount of heat transfer increases. On the other hand, if the oxygen flow rate is low, most of the oxygen will burn in the jet,
As the combustion ratio inside the slag decreases,
It was found that the heat transfer efficiency from the jet to the slag was reduced due to the limited heat transfer.

Under the operating conditions where the oxygen discharge flow rate is low in this experiment, the lance gap or H / D is small or negative, that is, the lance tip is in the slag, and the lance gap and the oxygen discharge It is considered that the influence of both the flow velocity and the influence of the oxygen discharge velocity are greater at this flow velocity, and the heat transfer efficiency is degraded.

When the above analysis results are considered comprehensively, they can be summarized as follows. That is, 1/6 per hot metal t
Under the conditions of this experiment in which a slag of ~ 2.0 t was formed on an iron bath, when the H / D was 10 or less, that is, when the lance gap was small or negative, the effect of the oxygen discharge flow rate on the heat transfer efficiency was considered. Is dominant, and although the lance gap was made small, the heat arrival in the slag cavity was improved, but the heat arrival deteriorated. Also,
Under the acid feeding condition where the lance gap is more than 45 times the nozzle diameter, the part where the oxygen jet burns in the gas space above the slag increases in spite of the large oxygen discharge flow rate, and the oxygen jet flows to the upper gas and brick. Radiant heat increased, and as a result, it was found that the heat transfer efficiency deteriorated.

Next, in order to investigate the relationship between the heating efficiency of the secondary combustion and the amount of slag, the amount of slag in the furnace was increased from 20 tons to 100.
The operation of the smelting reduction was performed while changing to t. FIG. 4 shows the results of this experiment. The horizontal axis of this figure is the slag weight per bath area, and the vertical axis is the heat transfer efficiency. When the amount of slag was 1.5 t or less per 1000 Nm ³ / h of the acid supply flow rate, the number of data with the secondary combustion rate of 40 to 45%, which is the condition of adoption, was small, and the heating efficiency was 75% or less in all cases.

In the operation of such a small amount of slag, there is a problem that the thickness of the slag is thin, and the oxygen jet directly hits the hot metal bath, so that a high secondary combustion rate is hardly obtained. Further, even when the secondary combustion was at a predetermined value, the heat-releasing efficiency was poor, the basic unit of coal and oxygen was large, and the refractory was greatly worn.

Next, 1.5 t / 1000 Nm ³ / h-O ₂
With each of the above slag amounts, the heating efficiency was 80% or more. Further, as the amount of slag increases, the heating efficiency improves, and the amount of slag increases to _{2 to} ³ t / 1000 Nm ³ / h-O _2.
According to the test results, depending on the heat, the heat transfer efficiency was 95%
There were more.

However, the slag amount was 3.5 t / 1000.
In the case of heat of Nm ³ / h-O ₂ or more, the heat transfer efficiency deteriorates conversely. This is probably because the amount of the slag was too large and the slag was not sufficiently stirred. Further, in the heat of such a large amount of slag, abnormal heat of the slag was generated, and there were many heats in which it was difficult to continue the operation.

1/6 to 2.0 tons of slag per t of hot metal
When the results of the experiments in the present invention formed on an iron bath are summarized, it has been found that high heat transfer efficiency can be obtained by smelting reduction under the following acid-supplying conditions. (1) The discharge flow rate of O _{2 at} the nozzle outlet of the upper blowing lance is
300Nm / sec or more. (2) The ratio (H / D) of the lance gap to the nozzle diameter is 10
Not less than 45 and not more than 45. (3) The amount of slag is in the range of 1.5 to 3.5 t per 1000 Nm ³ / h of acid supply flow rate.

[0036]

EXAMPLE The present invention was carried out in a large smelting reduction furnace shown in FIG. In FIG. 1, reference numeral 1 denotes a furnace body lined with refractory bricks.
It is agitated by bottom blowing gas. Above the hot metal bath 2 is a foamed molten slag 3, in which the hot metal droplets and the carbon material mixed by the stirring of the hot metal are mixed. The temperature of the hot metal and slag is usually 1400 ° C to 1600 ° C. Carbon material, ore, and auxiliary materials are supplied to the molten slag from the upper raw material hopper 8, and the smelting reduction reaction mainly proceeds inside the slag.

Oxygen is blown from the top blowing lance 4 to form a jet 5. Further, part of the oxygen may be blown from a lateral blowing lance installed on the furnace wall. In order to keep the secondary combustion rate high, the slag cavity 6 formed by the jet is supplied with acid so that it does not reach the layer 7 (emulsion layer) containing hot metal droplets formed under the foamed molten slag. It is common to control the conditions. However,
Under acid feeding conditions aimed at operation with a relatively low secondary combustion rate, the cavity may reach the emulsion layer. With the progress of the smelting reduction reaction, the generated hot metal descends in the slag and accumulates in the hot metal bath. Hot metal and molten slag are periodically discharged outside the furnace.

In the above-described smelting reduction furnace, hot metal is manufactured based on each condition, and as shown in Table 1, slag amount, oxygen discharge flow rate, H /
The operation result with changing D was obtained.

[0039]

[Table 1]

The basic conditions for the operation are secondary combustion: 40 to 45.
%, Acid supply flow rate: 30,000 Nm ³ / h, iron bath stirring:
It was set to 3.3 kW / t.

In Example 1, the operation was performed under appropriate conditions for both the oxygen discharge flow rate and the H / D, so that the heat arrival efficiency was 90.2%, which was a good value. As a result, the unit consumption of coal is reduced, and a good result of 948 kg / t is obtained. In addition, because the unit consumption of coal was reduced, the unit consumption of oxygen and the amount of generated gas were also reduced.
The productivity was also good at 36.9 t / h.

Next, in Example 2, both the oxygen discharge flow rate and the H / D were within appropriate conditions, and the slag amount was set to a sufficient amount for the heat transfer of the secondary combustion heat.
This is an example of an operation that secures 4 t / 1000 Nm ³ / h-O ₂ . In this operation, the heating efficiency is further improved, and 9
It was as high as 2.2%. As a result, the basic unit of coal was 922 kg.
/ T or less, and the production speed is 39.8.
t / h was good.

On the other hand, in the comparative examples out of the proper operation conditions, the heat radiating efficiency was poor in all cases. In Comparative Example 1, since the amount of slag was small, the secondary combustion rate was slightly lower, and
Heating efficiency was as low as 74.3%. In Comparative Example 2, since the amount of slag was too large, the heating efficiency was only 83.7%. In Comparative Example 3, since the H / D was as large as 48.9 and the lance gap was excessive, heat escaped from the oxygen jet to the upper gas, and the heat transfer efficiency was reduced. In Comparative Example 4, the discharge flow rate of oxygen was 251 Nm / sec.
Therefore, the heating efficiency is also deteriorated.

As described above, according to the present invention, if the operating conditions are within the range clarified, even at a high secondary combustion rate, the heating efficiency is high and the unit consumption of coal and the production rate are good. When the three conditions affecting the above conditions were out of proper ranges, the heating efficiency was low, and as a result, both the unit consumption of coal and the productivity were deteriorated.

In this experimental facility, about 15% of the total oxygen content was blown from the side-blowing lance installed on the furnace wall in the molten slag under the same conditions as in Example 2 in Table 1. Table 2 shows that both the secondary combustion and the heat transfer efficiency were as shown in Table 1.
There was no difference from the result.

Next, Table 2 shows the operation results using reduced iron as the iron raw material.

[0047]

[Table 2]

The basic condition of the operation is the secondary combustion rate: 30 ± 5
%, Acid supply flow rate: 25,000 Nm ³ / h, iron bath stirring:
3.2 to 3.5 kW / t.

As the reduced iron, scrap, granulated pig iron, and directly reduced iron are usually used. In this embodiment, briquettes of the directly reduced iron are used. This briquette has a metallization ratio of 95% or more, and is considered to be almost completely metallic iron.
Since the operation using reduced iron does not require reduction heat, the operation was performed with a low secondary combustion rate of about 30%.

In the third embodiment in which the operation according to the present invention is carried out,
The oxygen discharge flow rate is 315 Nm / s and the H / D is 3
It was 3.3 operations. In this operation, since the condition of high heat-emission efficiency was realized, the heat-emission efficiency was 90.2.
%, And the unit coal consumption was as good as 259 kg / t. However, in the operation using reduced iron, the heat required for reduction is unnecessary and the amount of heat transfer is small, so the amount of slag per 1000 Nm ³ / h of acid transport is as follows.
Despite the small amount of 1.1 t, good heat-releasing efficiency is obtained.

Next, in the fourth embodiment, the discharge flow rate of oxygen is set to 3
The operation was 80 Nm / s and the H / D was 25.0. Since good operating conditions could be realized, the heat transfer efficiency was as high as 92.2%, and the unit coal consumption was as good as 240 kg / t. On the other hand, in Comparative Examples 5 and 6, which did not satisfy the operating conditions of the present invention, the heat-releasing efficiency was as low as about 80%,
The unit consumption of coal was 331 kg / t and 345 kg / t, respectively, which were 20 to 30% higher than the operation of the example. As a result of this operation, the production rates of the examples
In contrast, the rate is 110 t / h or more, whereas the comparative example
It stopped below 0t.

[0052]

According to the present invention, in the operation of smelting reduction, it is possible to maintain high heat-releasing efficiency even at a high secondary combustion rate and a high production rate, and as a result, the unit consumption of coal and the unit consumption of oxygen are reduced. It is possible to produce hot metal at a low production cost and improve productivity. In particular, the unit consumption of coal, which is an important factor controlling the production cost, could be reduced by about 20% compared to the prior art.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a large iron-bath smelting reduction furnace for carrying out the present invention.

FIG. 2 is a table showing a relationship between a ratio of a lance gap and a lance nozzle diameter (H / D) and heat transfer efficiency in smelting reduction.

FIG. 3 is a table showing a relationship between a discharge speed of oxygen from a lance nozzle and heat transfer efficiency.

FIG. 4 is a chart showing the relationship between the amount of slag and the heat transfer efficiency in smelting reduction.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C21B 11/02

Claims (3)

(57) [Claims] 1. An iron bath type smelting reduction method in which oxygen or air is blown from a top blowing lance toward a slag bath formed on the iron bath, and a stirring gas is blown from the tuyere below the surface of the iron bath. In the operation method, feed iron ore and coal as raw materials above the furnace.
Slag of 1/6 to 2.0 t per t of hot metal
The nozzle orifice is formed on a bath, and the outlet speed of the nozzle at the upper blowing lance of the oxygen or air is 300 Nm / sec or more, and the distance between the upper blowing lance and the upper surface of the slag is 10 times or more and 45 times or less of the nozzle diameter at the lance. An operation method for smelting reduction, characterized in that: 2. The method according to claim 1, wherein the flow rate of the acid is 1000 Nm ³ / h.
2. The operation method for smelting reduction according to claim 1, wherein the operation is performed while securing a slag amount of 5 to 3.5 t. 3. The method for smelting reduction according to claim 1, wherein a part of oxygen is blown from a tuyere immersed in a slag bath.