JPH01191719A - Method for operating smelting reduction furnace - Google Patents

Abstract

PURPOSE:To exhaust gas generated with secondary combustion as the gas having low oxidized degree at low temp. and to reduce damage of refractory at upper part in a furnace by blowing fine powdered coal from a nozzle ar ranged at the side wall in the furnace body just at upper part of the secondary combustion zone. CONSTITUTION:In the smelting reduction furnace 3, CO and H2 in the furnace 3 are reacted with oxygen in the secondary combustion zone 18 just above slag 13 and the gas having high oxidizing degree is generated at high temp. Just at upper part of this secondary combustion zone 18, the fine powdered coal is blown from a furnace wall nozzle 15 arranged at the side wall in the furnace. The gas from the secondary combustion zone 18 passing through reforming reaction zone 20 blowing the fine powdered coal lowers the temp. and the oxidizing degree with endothermic of heat decomposition reaction of the line powdered coal and is exhausted to the out of the furnace. By this method, the treating equipment of heat exchanger, decarbonic acid device, etc., for introducing the exhaust gas into pre-reducing process can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of operating a smelting reduction furnace that performs secondary combustion.

<Conventional Technology> Recently, the smelting reduction refining method has been attracting attention as a steelmaking technology that can replace the blast furnace/converter method. The smelting reduction furnace used in this method is capable of producing molten iron alloys with smaller-scale equipment without being restricted by the raw materials used, and of effectively recovering the heat generated during the refining reaction. It was developed for this purpose.

In order to increase the productivity of a smelting reduction furnace, it is important to efficiently supply heat.
It is proposed in the publication No.-192513. The secondary combustion exhaust gas is treated, for example, according to the flow proposed in Japanese Patent Application Laid-open No. 145307/1983.

That is, high-temperature gas generated in the smelting reduction furnace is discharged from the exhaust port and heat exchanged with a heat exchanger such as a waste heat boiler. This gas is then mixed with a portion of the gas recovered from the pre-reduction furnace and stored in a gas holder.

Then, after a part of the mixed gas is adjusted to an oxidation degree in the range of 0.07 to 0.15 by decarboxylation in a decarboxylation device,
It is heated by a heater and introduced into a preliminary reduction furnace.

<Problems to be Solved by the Invention> When a smelting reduction furnace is operated to obtain a high secondary combustion rate by the method described in JP-A-62-192513, the exhaust gas becomes high in temperature and has a high degree of oxidation. A large number of processing equipment such as a heat exchanger and a decarboxylation device as shown in the flow of JP-A-60-145307 are required, and the processing capacity thereof is also required to be large.

Therefore, the present invention aims to reform and recover the heat of the secondary combustion gas in the smelting reduction furnace without affecting the secondary combustion zone, and to discharge it as a gas with a lower temperature and low oxidation degree. It was developed to simplify or omit some of the gas processing equipment.

Means for Solving the Problems〉 The operating method of the smelting reduction furnace of the present invention is to inject pulverized coal into which high-temperature, highly oxidized gas generated by secondary combustion is blown directly above the secondary combustion zone in the furnace. It is characterized by reacting with the gas and discharging it outside the furnace as a gas with a lower oxidation degree at a lower temperature.

This will be explained in detail below using the drawings. FIG. 1 shows an example in which the present invention is applied to a converter-type melting reduction furnace.

That is, there is hot metal 12 in the lower part of the smelting reduction furnace, and above it there is a slag phase 13 in which carbonaceous materials are suspended, and from the surface of the slag phase 13 there is CO gas generated by reduction reaction and combustion of carbon, and thermal decomposition products of coal. 11. Gas etc. are generated. When secondary combustion is performed using top-blown oxygen 17, this oxygen jet engulfs the surrounding gas, and the CO, H2, and 1, CO+ in the gas are
The reaction of □02 → 1120 occurs, and the gas becomes high temperature due to the heat of combustion, collides with the slag surface and transfers heat, supplying the heat necessary for reducing and melting the ore. Some of the heat becomes sensible heat of the combustion generated gas and increases its temperature. In particular, when operating to increase the secondary combustion rate, the temperature of the combustion gas increases. In the secondary combustion zone 18, part of the combustion product gases is again involved in the oxygen jet and forms a circulating flow, whereas in the upper region 2° of the secondary combustion zone the gases form an upward flow. When about 1 mm of pulverized coal is injected into this region, the degree of oxidation of the gas is high and the following reactions occur easily when the temperature is about 1500 to 2000°C: CO! 10C → 2CO ■, thO+c → CO+H! When this occurs and volatile matter is present in the pulverized coal, CO and H2 are generated by the thermal decomposition reaction. Raw material charging chute 2
The carbonaceous material in the raw material charged from 1 needs to be supplied above the slag 13 against the gas upward flow in the upper region 20 of the secondary combustion zone 18, so that the average particle size of the carbonaceous material The diameter is on the order of several fences and is larger than pulverized coal 19. On the other hand, the upper region 20
Since the reactions (1) and (2) and the thermal decomposition reaction strongly depend on the particle size, only a small amount of this reaction occurs due to the carbonaceous material in the raw material charged from the raw material charging chute 21. Therefore, in order to actively cause this reaction, it is necessary to blow the pulverized coal 19 into the upper region 20 from the pulverized coal injection nozzle 15.

The temperature of the gas passing through this region 20 and the amount of oxidation blown are adjusted. If this reaction zone 20 is temporarily called a reforming reaction zone, when the degree of oxidation of the gas passing through the reforming reaction zone 20 is 0.5 or more and the temperature is 1500°C or more, the coal charged into the furnace is Pulverized coal corresponding to 30% or less of the material amount is blown into the reforming reaction zone 20 from the nozzle 15. Modification reaction zone 20
The temperature of the gas passing through decreases to 700-1300℃ due to the endothermic reaction of reactions ① and ② and the thermal decomposition reaction of pulverized coal.
The degree of oxidation also decreases to 0.1 to 0.5 and is discharged from the furnace.

At this time, the amount of gas increases by about 30% at most. If the amount of pulverized coal injected into the reforming reaction zone 20 is too large, reactions (2) and (2) will not proceed sufficiently due to the temperature drop, and some unburned carbon will be drawn into the secondary combustion zone 18 and secondary combustion will occur. This reduces the efficiency of heat supply to the iron bath. Furthermore, the carbon content in the exhaust gas also increases.

As one of the methods of blowing pulverized coal into the reforming reaction zone, the second
As shown in the figure, if three or more nozzles are installed horizontally at an angle α of 15 to 45 degrees from the center and pulverized coal is blown into the reforming reaction zone, a greater reforming effect can be obtained. In this case, a swirling flow is formed in the reforming reaction zone, promoting the reactions (1) and (2) between the ascending gas flow and the pulverized coal. If the inclination angle is less than 15 degrees, a sufficient swirling flow will not be formed, and if it exceeds 45 degrees, the injected gas and pulverized coal will easily collide with the furnace wall, forming an effective reforming reaction zone. Can not do it.

Furthermore, as one method for injecting pulverized coal into the reforming reaction zone, as shown in Figure 3, a lance 2 is inserted diagonally from above the furnace mouth.
2 may be inserted to blow pulverized coal into the reforming reaction zone.

In this case, since the lance is movable, pulverized coal can be blown into any height position depending on the situation inside the furnace to form a reforming reaction zone.

As the temperature of the gas that passes through the reforming reaction zone decreases, damage to the furnace wall refractories in the upper part of the furnace is reduced, the thermal load on the hood through which the exhaust gas passes in the upper part of the furnace is reduced, and the heat generated by the radiated heat is reduced. Losses are also reduced. Furthermore, it is also possible to reduce the number of heat exchangers, gas reforming equipment, etc. that are introduced as part of the exhaust gas preliminary reduction process.

<Example> 1. An example in which the present invention was implemented using the converter-type melting reduction furnace shown in FIG. 1 will be described.

Preliminarily reduced ore and coal are continuously charged into a smelting reduction furnace 3 in which hot metal 12 and slag 13 are present through a charging port 21 provided above. Hot metal and slabs are 1450-15
It is kept at 50°C. Oxygen is blown into the furnace through tuyeres 14 provided at the bottom of the furnace. The charged ore is reduced by the carbon in the hot metal and the carbonaceous material in the slag, and the bottom-blown oxygen reacts with the oxygen in the hot metal to generate CO gas. In addition, H and gas are generated by thermal decomposition of coal.

Here, 60-70% of this generated gas is discharged from the top blowing lance 16.
02 gas was blown in an amount equivalent to burning %. In the secondary combustion zone 18 directly above the slag, the generated gas and the oxygen jet underwent a combustion reaction, and heat was transferred to the bath surface. A part of the combustion gas formed a circulating flow in the secondary combustion zone. The gas leaving the secondary combustion zone has an oxidation degree of 0.6 to 0.7 and a temperature of 1700 to 1800.
It was °C. Here, from the furnace wall nozzle 15, a particle size of 0.1
Pulverized coal having a volatile content of 30 to 40% was blown into the coal in an amount equivalent to 20 to 25% of the coal charged above. Due to this effect, exhaust gas with an oxidation degree of 0.3 to 0.4 and a temperature of 800 to 1000''C was obtained at the mouth of the melting reduction furnace.

2. An inclined pulverized coal blowing nozzle shown in FIG. 2 was installed in a converter-type melting and reduction furnace similar to that in Example 1.

From Example 1, when ore with a high preliminary reduction rate and coal were supplied to a smelting reduction furnace and the amount of top blowing oxygen was reduced, the degree of oxidation of the gas leaving the secondary combustion zone was 0.5 to 0.6, and the temperature was 1600～
The temperature was 1700°C. Here, the furnace wall nozzle 15 (angle α=
30°), particle size 0.5 mark or less, volatile content 30-40%
When pulverized coal was injected in an amount equivalent to 15 to 20% of the above-injected coal, the reaction progressed sufficiently in the reforming reaction zone despite the lower temperature and coarser grain size of the pulverized coal, and oxidation degree 0.3-0.4, temperature 800-10
00°C exhaust gas was obtained.

3. A lance 22 for blowing pulverized coal from an oblique direction as shown in FIG. 3 was installed in a converter type melting reduction furnace similar to that in Example 1.

When pre-reduced ore containing a large gangue component and coal were supplied to a smelting reduction furnace and operated in the same manner as in Example 1, a large amount of slag was generated at the same time as hot metal was produced, and the slag level increased. As the slag level rose, the top-blown oxygen lance was raised, and the secondary combustion zone also moved upward. In line with this, the pulverized coal injection position was changed by gradually raising the lance, and we were able to secure a sufficient reforming reaction zone.

<Effects of the Invention> As described above, in the present invention, the gas oxidized in the secondary combustion zone above the slag of the smelting reduction furnace reacts with the pulverized coal injected in the space directly above the secondary combustion zone. A reforming reaction zone is formed in which the gas is reformed and the heat is recovered by reducing the gas oxidation degree and exhaust gas temperature before being discharged to the outside of the furnace. Therefore, treatment equipment such as a heat exchanger and a decarboxylation device for introducing this exhaust gas into the preliminary reduction step can be saved or omitted. Additionally, since the gas temperature decreases above the reforming reaction zone, damage to the refractories at the top of the smelting-reduction furnace is reduced, and the thermal load on the exhaust gas hood is reduced, as well as heat loss due to radiated heat. The effect of this can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example in which the present invention is applied to a converter-type melting reduction furnace, FIG. 2 is a diagram showing an example of a furnace cross section when the nozzle according to claim 2 is used, and FIG. FIG. 2 is a diagram showing an example of pulverized coal injection using a lance inserted from outside the furnace. Figure 2 Figure 3

Claims (3)

[Claims] (1) In a smelting reduction furnace, semi-reduced ore supplied from a preliminary reduction furnace is reduced and refined using carbon in an iron bath and carbonaceous materials in slag, and at the same time secondary combustion is performed using top-blown oxygen. Alternatively, a method for operating a smelting reduction furnace characterized by injecting pulverized coal 19 from a pulverized coal injection nozzle 15 provided on the side wall of the furnace body directly above the secondary combustion zone 18 where H_2 is reacting with oxygen. (2) At least three or more pulverized coal injection nozzles 15 are installed horizontally and tilted in the same direction at 15 degrees to 45 degrees with respect to the furnace center direction directly above the secondary combustion zone 18 of the reduction furnace to generate pulverized coal. 2. The method of operating a melting reduction furnace according to claim 1, characterized in that the method comprises blowing 19. (3) In the smelting reduction furnace, the semi-reduced ore supplied from the preliminary reduction furnace is reduced and refined using carbon in the iron bath and carbonaceous materials in the slag, and at the same time secondary combustion is performed using top-blown oxygen. Alternatively, a method for operating a smelting reduction furnace, characterized in that pulverized coal is injected directly above the secondary combustion zone 18 where H_2 is reacting with oxygen using a lance 22 inserted from diagonally above the outside of the reduction furnace.