JPH01152210A - Method for adjusting gas characteristic for pre-reduction in smelting reduction - Google Patents

Abstract

PURPOSE:To increase utilizing ratio of energy and to improve pre reduction ratio of ore by reforming a part of generating gas from a smelting reduction furnace, mixing with gas introduced into a pre-reduction furnace and raising temp. of this mixed gas. CONSTITUTION:The generating gas from the smelting reduction furnace 20 secondarily burnt is passed through a gas pipe 1 connected with furnace top opening hood 20a and distributed to the branched gas pipes 1a. After passing the gas through a wet type dust collector 3, blower 4 and decarbonic acid device 5, it is joined with gas in the other gas pipe 1a by gas pipe 2 and mixed. Further, by passing through a hot cyclone 6 and partial combustor 7, it is introduced into the pre-reduction furnace 30 as the gas for pre-reduction. Or, after passing the exhaust gas discharged from the pre-reduction furnace 30 through the blower and the decarbonic acid device, it is mixed with the gas introduced into the pre-reduction furnace 30. By adjusting this gas characteristic, the secondary combustion can be increased and the consumption of coal being necessary to obtain the molten metal can be reduced.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention pre-reduces ore containing metal oxides, such as iron ore, in a solid state in a pre-reduction furnace and then transfers it to a smelting reduction furnace. This relates to a method of adjusting the properties of preliminary reduction gas in smelting reduction, which involves melting and final reduction.In particular, it reduces the consumption of coal, which is a reactant, and increases the energy utilization rate of the entire process. The present invention relates to a method for adjusting the properties of preliminary reduction gas in smelting reduction.

(Conventional technology) The smelting reduction method is a method for producing iron and ferroalloys by reducing ores containing metal oxides, such as iron ore (iron oxide), in a molten state. This technology has recently attracted attention for its adaptability, and research and development for its practical application is underway. The expected features of this method are as follows. In other words, compared to the blast furnace method, as a steel manufacturing method, it is possible to use cheaper raw materials, omit pre-processing steps such as agglomeration of fine ore, and downsize equipment, and as a method for manufacturing ferroalloys,
For example, it is possible to put a process that does not depend on electricity into practical use.

Various processes have been proposed for the smelting reduction method, and there are various types of reduction furnaces, but a typical type is a metal bath furnace type smelting reduction furnace. For example, in steel manufacturing, this is a reduction furnace in which iron ore is charged together with coal and oxygen into an iron bath (molten iron), and this is reduced to obtain molten iron (pig iron). (It can be reduced at a rate more than 100 times faster than that in the solid state.)
, has been adopted in many processes due to its simple equipment format.

On the other hand, the energy utilization rate of the smelting reduction process using this method is very poor, and most of the energy of the coal, which is the heat source, escapes with the exhaust gas. is multiplied several times.

a) Application of secondary combustion technology: Secondary combustion refers to blowing oxygen (or a gas containing oxygen) into the gas space in the smelting reduction furnace to remove some of the combustible gas coming out from the metal bath surface. This is a combustion technology. If the heat generated by this is recovered in the metal bath, the amount of coal consumed can be reduced by that amount, and the energy utilization rate will be increased. The proportion of combustible gas out of the combustible gas emitted from the bath surface is
This is called the secondary combustion rate.

In a smelting reduction furnace, the basic reaction equation when reducing iron oxide, for example, changes as follows depending on the presence or absence of secondary combustion. First, when there is no secondary combustion (secondary combustion rate is 0%, gas temperature in the furnace is 1450°C), 1.430 J nee PetO* + 1.293 kg-C
+ 0.905Nm'-0t (25℃) (25℃) (2
5℃) On the other hand, the secondary combustion rate was set to 30% and the gas temperature in the furnace was set to 160℃.
When the temperature is 0℃, if we compare formula (■) and formula (2), the consumption m of C (coal) and 0 necessary to obtain molten iron at the car position in the smelting reduction furnace is:
It can be seen that it is reduced by applying secondary combustion.

In addition, in the case of formula ■ (secondary combustion rate 30%), the added energy is the combustion heat of C, which is 0.679 kgX 810
0kcal/kg = 5500kcal.

On the other hand, the heat used effectively is Fetos (1kg
) heat of reduction 1d1759kcal and heat of solution of re 239
Since the total value of kcal is 1998 kcal, the energy utilization rate is 199g15500, or 36%
It is.

When looking only at smelting reduction furnaces, as mentioned above, the higher the secondary combustion rate, the higher the energy utilization rate.

b) Application of preliminary reduction process: This is a technique in which the ore is not directly melted and reduced, but is preliminary reduced in a solid state, and then finally reduced in a smelting reduction furnace as described above. In the preliminary reduction, the high-temperature gas generated during the final reduction in the smelting reduction furnace is mainly used as the reducing gas, so that energy can be used effectively. Most pre-reduction furnaces are of the fluidized bed type, where the ore forms a fluidized bed and contacts and reacts with the above gases, and the reaction temperature is around 800°C.
The reduction rate (preliminary reduction rate) in the preliminary reduction furnace is 70 to 95.
It is set to %.

Note that the reduction rate indicates the reduction rate of oxygen when the raw material ore is based on six metal oxides, for example, FctO*
If this is the standard (return rate 0%), the return rate is 11.1%.
33.3% to Fe+Oa, 33.3% to FcO, and 1% to FcO.
At 00%, it will be continuously illuminated by Fe. In order to obtain a desired preliminary reduction rate, the composition and temperature of the reducing gas introduced into the preliminary reduction furnace must be appropriate.

In a process consisting of such a pre-reduction furnace and a smelting reduction furnace, when the pre-reduction rate is set to 75%, that is, when Fat's is reduced to a mixed state of FcO and F6 in the pre-reduction furnace, , the basic reaction formula is as follows.

(In preliminary reduction furnace) 1.430kg4atOs+ 1.29ONm”CO→
0.625kg-Pe(s)+0.482kg-FcO
+0.838Nm3・CO+0.451Nm"COt
...■ (in the smelting reduction furnace) Here, the added energy is the combustion heat of C, 0.6
31kgX 8100kcal/kg= 5111kc
al, the energy utilization rate is 39%.

The reason for adding more m of CO than is chemically required in equation (2) is that in order to reduce Fe, 03 to Fe at 800°C, it is necessary to C on the right side)
This is due to the fact that the o/(CO+Cot) ratio must be kept at 65% or more (see Figure 3).

In the smelting reduction furnace, if C is added to ensure this C0ftd and CO is used as a coolant to balance the heat balance accompanying this exothermic reaction, the relationship shown in equation (2) will be obtained.

Two methods a) and b) for increasing the energy utilization rate have been shown above, but in recent melting reduction, a combination of both is often employed.

In other words, if secondary combustion technology is applied to the smelting reduction furnace, the gas generated from this will be used to burn ore to 70 to 95
The common process is to pre-refund to a return rate of 1.5%.

However, simply combining these two methods does not necessarily improve the energy utilization rate of the entire process. In other words, if you increase the secondary combustion rate,
This is because reducing components such as CO are reduced in the gas generated from the smelting reduction furnace, so unless the amount of C as energy is increased, the preliminary reduction rate will decrease. for example,
In order to achieve a secondary combustion rate of over 35% and a preliminary reduction rate of 70%, an infinite amount of C is theoretically required, and the energy utilization rate is equal to zero.

Therefore, conventionally, the following methods have been used to increase the energy utilization rate of the entire process.

b) By limiting the secondary combustion rate to 30% or less, a high preliminary reduction rate (70 to 95%) as described above is ensured. In this case, the gas generated from the melting reduction furnace contains
Since it contains sufficient reducing components, this gas is used for preliminary reduction by adjusting only the flow rate and temperature.

a) By reforming the gas generated from the smelting reduction furnace and increasing the reducing components (CO and II) in the gas and using it as preliminary reduction gas, a high secondary combustion rate (up to about 40%) can be achieved. Balancing the preliminary return rate (Japanese Patent Application Laid-Open No. 59-22250
No. 8).

C) A portion of the exhaust gas from the pre-reduction furnace will be decarbonated and reheated, and then mixed with the gas generated from the smelting reduction furnace to be used as pre-reduction gas, resulting in a high secondary combustion rate and high Balancing the preliminary return rate (COIN process, etc.).

(Problems to be Solved by the Invention) In any of the above conventional methods, the amount of coal (C) required to reduce the ore (metal oxide) and obtain total yield is large. The problem of insufficient energy utilization still remains. For example, when iron ore is reduced by method (a), the energy utilization rate is at most 40%, and if the blast furnace method is used, it is more than 50%. It's hard to say.

Since the consumption m of C is large, the consumption of 02 is also large, and therefore, in reality, not only will there be a negative impact on the generation of slag i7k and the consumption m1 of lime, but also the loss of produced metals into the slag. This will also increase the burden on equipment related to this.

In addition, in methods (a) and (c) above, the secondary combustion rate can be higher than in method a), so the energy utilization rate is somewhat higher, but in order to ensure a high preliminary reduction rate,
It is necessary to significantly adjust the gas properties (reforming or decarboxylation), which requires enormous equipment and operating costs.

(Purpose of the Invention) The present invention was made with the aim of solving the above problems, and by adjusting the properties of the preliminary reduction gas, the energy utilization rate can be significantly improved. The goal is to minimize the consumption of lime, etc.
The present invention aims to provide a method for adjusting the properties of preliminary reduction gas in melt reduction.

(Means for Solving the Problems) The gist of the present invention for achieving the above-mentioned object is to pre-reduce ore containing metal oxides in a solid state in a pre-reduction furnace, and then reduce the ore in a smelting reduction furnace. At the same time, the gas generated in the smelting reduction furnace and having a reducing ability is introduced into the preliminary reduction furnace. By reforming a part of the exhaust gas from the reduction furnace, mixing it with the gas introduced into the pre-reduction furnace, and raising the temperature of this mixed gas, the preliminary permissibility of the ore in the pre-reduction furnace can theoretically be increased to 33. The gas composition and temperature should be adjusted so that the

(Function) According to the method of adjusting the properties of the preliminary reduction gas of the present invention,
Ore containing metal oxides is pre-reduced in a preliminary reduction furnace until the preliminary reduction rate is approximately 33%, and then finally reduced in a smelting reduction furnace with a high reduction rate. has a property that achieves the pre-reduction rate with a slight adjustment, so that the secondary combustion rate can be made sufficiently high in the smelting reduction furnace, and therefore the energy utilization rate of the entire process can be maximized.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a smelting and reduction system diagram for iron manufacturing relating to a first embodiment of the present invention. In the figure, 20 is a melting reduction furnace, 30
is a pre-reduction furnace, in which the iron ore is pre-reduced in a solid state in the pre-reduction furnace 30 and then melted in the smelting-reduction furnace 20 for final reduction. A method is shown in which gas is introduced into the preliminary reduction furnace 30 as a reducing gas.

As shown in the figure, the molten iron 20a (and slag 20b) of the smelting reduction furnace 20 includes a pre-reduction furnace 3.
In addition to iron ore (preliminary reduced iron, from the transfer pipe 34) that has been pre-reduced at 0, coal and lime (from the blowing pipe 22)
, oxygen and, if necessary, said carbon dioxide gas (blow tube 2
3) etc. These react in the melting reduction furnace 20, for example, as shown in equation (2) and are reduced in a molten state.

In the melting reduction furnace 20, combustible gas containing CO and the like is generated from the bath of the molten iron 20a due to such a reduction reaction, so oxygen is blown into the furnace gas space 20c from the blowing pipe 21 as described above. , performs secondary combustion.

In this embodiment, the gas generated from the melting reduction furnace 20 through secondary combustion is passed through the gas pipe l connected to the furnace mouth hood 20d, and a portion is distributed to the gas pipe 1a branched from the gas pipe l. Wet type dust collector 3, blowing air (via Shigeru 4 and decarboxylation device 5), and then combining and mixing with gas from the other branched gas pipe 1b in gas pipe 2, and then hot Zyclone 6 and partial combustor 7. The gas is introduced into the preliminary reduction furnace 30 as a preliminary reduction gas.

Note that the wet dust collector 3 is not limited to this, and any device that can cool and remove dust from gas may be used, and the decarboxylation device 5 may also be used for other gas reforming devices, such as hydrocarbons or pulverized coal.
Ol to CO or 11. 6 is good if it is modified to The partial combustor 7 raises the gas temperature by blowing oxygen (or a gas containing oxygen) into a part of the gas and burning part of the combustible components, but it is also possible to use other means such as a heating device. It may be possible to raise the temperature by

The illustrated preliminary reduction furnace 30 is a fluidized bed type reduction furnace, and the powdery iron ore charged through the ore charging pipe 31 is the preliminary reduction furnace introduced into the furnace through the gas pipe 2 as described above. Flow P7J3 on the dispersion plate (straightening plate) 30a by the reducing gas
0b is formed, and in this state it contacts and reacts with a reducing gas to undergo preliminary reduction.

The preliminary reduced iron is discharged from the discharge pipe 32 or 33, transferred within the transfer pipe 34 by, for example, gas transfer, and charged into the melting reduction furnace 20. On the other hand, the gas used for preliminary reduction is discharged from the exhaust gas pipe 8.

In this example, in order to increase the energy utilization rate of the entire process, the properties of the preliminary reduction gas are adjusted so that the iron ore is reduced to almost PeO in the preliminary reduction furnace 30, and the The secondary combustion rate is set at 60% or more. PQv in the pre-reduction furnace
When reduced to O3h'FQO, the preliminary reduction rate is 33.3%, but in addition to PetO5, the iron ore actually used as a raw material contains Fe5, which has a slightly lower oxygen m content.
Since some 0+ is included, the actual preliminary return rate is 3.
The value is slightly lower than 3.3%.

The reason why the preliminary reduction rate and the secondary combustion rate are set in this way by adjusting the properties of the preliminary reduction gas in the process shown in the figure will be explained below.

As described above, the preliminary reduction rate in the preliminary reduction furnace 30 is determined by m (ratio) of CO contained in the preliminary reduction gas. In addition, this COm is determined by the claw and secondary combustion rate of C (coal) charged into the smelting reduction furnace 20, and m of this C is the preliminary reduction rate of iron ore charged into the smelting reduction furnace 20. It changes depending on. These trends can be seen in the basic reaction equations ■ to
This can be easily understood by looking at a known reduction equilibrium diagram using O gas.

If we consider the above points regularly, we can find that a unit amount of molten iron Fe(I
It is believed that it is possible to find an appropriate preliminary reduction rate and secondary combustion rate that minimize the consumption m of C to obtain 2), or in other words, maximize the energy utilization rate. Therefore, the inventors set realistic conditions (properties of iron ore and coal, heat radiation loss in each part, etc.), determined these through calculations, and conducted further confirmation experiments. The results thus obtained are as follows.

i) The consumption m of coal (C) is the minimum when the secondary combustion rate is 20% or more and the preliminary reduction rate is 33%, and these values are the minimum when the secondary combustion rate is less than 20%. Coal consumption m
less than. Further, when the preliminary reduction rate is 33%, the amount of coal consumed decreases as the secondary combustion rate is higher than 20%.

i) When the secondary combustion rate exceeds 60%, C0ff1 in the gas generated from the smelting reduction furnace decreases, so the preliminary reduction rate of 33% cannot be achieved unless this gas is reformed.

In summary, keeping the preliminary reduction rate at 33% and increasing the secondary combustion rate as high as possible will reduce coal consumption m. For example, when the secondary combustion rate is 50% and the preliminary reduction rate is 33%, the coal consumption m is approximately 0% less than the previous example (secondary combustion rate 0%, preliminary reduction rate 75%). From this, we can see the magnitude of the degree of reform caused by this.

However, if the secondary combustion rate is set to 60% or more in order to further reduce coal consumption m, the gas generated from the smelting reduction furnace 20 cannot be used as it is as the preliminary reduction gas for the purpose of i) above. I'm not going. In this example, the preliminary reduction rate was increased to 33% by adjusting the properties of the preliminary reduction gas.
The reason why the degree and two-fire combustion rate were set at 60% or more is due to the above reasons.

In this embodiment, the secondary combustion rate in the melting reduction furnace 20 is set to 6.
5% and the generated gas is a gas pipe! Gas pipes 1a and l
Regarding the gas properties in each part of the gas pipe (points A-G in Fig. 1) when 50% of the combustible components in the gas are combusted in the partial combustor 7. The trial calculation results are shown below.

According to the above calculation, 11.0 of 67Nm3 is removed by cooling and removing dust from the gas in the wet dust collector 3, and 293Nm3, which is 90% of the gas, is removed in the decarboxylation device 5.
It is assumed that CO1 of ' is removed, and the temperature drop of the gas in each device and gas pipe, as well as the shift reaction of the gas accompanying this, are also taken into consideration.

Of the above values, what is noteworthy is the gas composition at point G (the exit of the pre-reduction furnace 30).

The gas here contains CO and 11 as reducing components.
However, these ratios are high, with a preliminary return rate of 33%.
(reducing iron ore to FeO). That is, if there are CO and I+ in the gas, the conditions for obtaining FeO at 800°C are Co/Co
, > 0.35, but the trial calculation results show that Co/Co,
= 0.36, which is satisfied.

By adjusting the properties of the preliminary flashing gas as described above, if the secondary combustion rate is increased to 65% while maintaining the preliminary reduction rate at about 33%, the secondary combustion rate can be increased to 50%. Coal consumption is further reduced by several percent compared to the previous case.

Regarding coal consumption m when the secondary combustion rate exceeds 20%, it increases rapidly when the preliminary reduction rate exceeds 33%, but when the preliminary reduction rate decreases to 33% or less, the coal consumption m Since m increases only a little, the preliminary reduction rate in actual operation may be any value between a dozen percent and 33 percent. In the method of this embodiment, by increasing the gas m distributed to the gas pipe 1a and reforming a large amount of gas, it is possible to further increase the secondary combustion rate, and therefore it is also possible to further reduce coal consumption. It is. On the other hand, even if the secondary combustion rate is 60% or less, adjusting the gas properties using this method can increase the reducing power of the pre-reducing gas. Refund rate (about 33%)
There are many benefits, such as being able to achieve

Next, a second embodiment of the present invention will be described based on FIG. 2. This embodiment shows the same smelting and reduction process for steel manufacturing as in the first embodiment, but the gas generated from the smelting and reducing furnace 20 and introduced into the preliminary reduction furnace 30 via the gas pipe 1 contains cooling and The present invention is characterized in that a part of the dust-removed exhaust gas from the preliminary reduction furnace 30 is reformed and then mixed. That is, the gas pipe 8 exits from the preliminary reduction furnace 30.
The exhaust gas passing through the wet collection 11! ! ! After cooling and removing dust in machine 3, it is branched into gas pipes 8a and 8b, and gas pipe 8b
At the same time, the gas on the side of the gas pipe 8a is passed through the blower 4 and the decarboxylation device 5 to join and mix with the gas in the gas pipe I. As in the first embodiment, the gas thus mixed is partially combusted in the partial combustor 7 to raise its temperature, and then introduced into the preliminary reduction furnace 30 as a preliminary reduction gas.

Further, in this embodiment, in order to more accurately adjust the properties of the preliminary reduction gas, a part of the gas generated from the melting reduction furnace 20 can be discharged from the gas pipe 1c as necessary. The gas led to the gas pipe 1c may be discharged after being merged with the gas in the gas pipe 8b. In addition, the gas emitted in this way contains flammable components, so
For example, it can be used as a fuel in steel plants.

In the drawings, parts common to those in the first embodiment are designated by the same reference numerals.

In this embodiment as well, the gas composition and temperature are adjusted so that the preliminary reduction rate of iron ore in the preliminary reduction furnace 30 is about 33%, so a high secondary combustion rate can be achieved in the smelting reduction furnace 20, which is better than the conventional method. Molten iron can be obtained with less coal consumption.

However, in this case, CO and 11. In order to reform the exhaust gas from the preliminary reduction furnace 30 where m is smaller, it is necessary to introduce more gas (for example, 70 to 80% of the total exhaust gas) into the gas pipe 8a and decarbonate it. On the other hand, according to this embodiment, even when the amount of gas generated m changes based on changes in the operating state of the smelting reduction furnace 20, the gas m distributed to the gas pipe 8a or the gas m discharged from the gas pipe 1c can be controlled. There is an advantage that the pre-reduction gas tank can be adjusted by increasing or decreasing the amount. In this point, the preliminary reduction furnace 30
This is particularly advantageous if the system is of the fluidized bed type, in which the flow m of the reducing gas must be precisely regulated.

The above-described method of adjusting gas properties for preliminary reduction in smelting reduction according to the present invention is not limited to the case where iron is obtained by reducing iron ore.
It can also be applied to the case where other metals are melted and reduced by a similar process, such as obtaining ferrochrome by reducing 2O4).

(Effects of the Invention) According to the method for adjusting the properties of the preliminary reduction gas in smelting reduction of the present invention configured as described above, the following effects can be obtained.

1) Since the secondary combustion rate can be increased, the consumption of coal necessary to obtain molten metal is significantly reduced.

2) Along with the above 1), consumption of oxygen, lime, etc. is also reduced.

3) Along with the above l) and 2), the amount of exhaust gas generated m is reduced.

4) The above 1) and 2) reduce the number of slag formations in the molten metal, thereby reducing metal loss and improving the metal manufacturing yield.

5) In line with l) to 4) above, coal and lime conveyance equipment, oxygen supply equipment, and exhaust gas treatment stage 4! Since the if can be downsized, equipment costs and operating costs can be reduced.

6) Since the preliminary reduction rate is low, the 8 jaws of the preliminary reduction furnace can be made smaller.

7) Since the reducing ability (amount of reducing components) of the preliminary reduction gas may be low, it is only necessary to reform a part of the gas generated from the smelting reduction furnace or the exhaust gas from the preliminary reduction furnace,
Therefore, the equipment cost and operating cost of the reformer can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a melting reduction system diagram showing a first embodiment of the present invention, Fig. 2 is a melting reduction system diagram showing a second embodiment of the present invention, and Fig. 3 is a melting reduction system diagram showing a second embodiment of the present invention.
The figure is an equilibrium diagram of the reduction of iron by CO gas. 1, la, lb, lc, 2, 8.8a, 8b・-
・Gas pipe, 3-Q, formula % formula %

Claims (3)

[Claims] (1) Ore containing metal oxides is pre-reduced in a solid state in a pre-reduction furnace and then melted in a smelting reduction furnace for final reduction, and the gas with reducing ability generated in the smelting reduction furnace is prepared as a reserve. Depending on the method of introduction into the reduction furnace,
When performing smelting reduction of the ore, a part of the gas generated from the smelting reduction furnace or the exhaust gas from the pre-reduction furnace is reformed and mixed with the gas introduced into the pre-reduction furnace, and this mixed gas is A method for adjusting gas properties for preliminary reduction in smelting reduction, characterized by adjusting gas composition and temperature by increasing temperature so that the preliminary reduction rate of ore in a preliminary reduction furnace is theoretically about 33%. (2) A part of the gas generated from the smelting reduction furnace or the exhaust gas from the pre-reduction furnace is cooled and dust removed, and then mixed with the gas introduced into the pre-reduction furnace via a blower and decarboxylation device. The method of adjusting gas properties for preliminary reduction in smelting reduction according to claim 1, wherein a part of the mixed gas is combusted to raise the temperature to adjust the gas composition and temperature. (3) After cooling and removing dust from the gas generated from the smelting reduction furnace or the exhaust gas from the pre-reduction furnace, a part of it is mixed with the gas introduced into the pre-reduction furnace via a blower and decarboxylation device. The method of adjusting gas properties for preliminary reduction in smelting reduction according to claim 1, wherein a part of the mixed gas is combusted to raise the temperature to adjust the gas composition and temperature.