JPH032922B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for operating a so-called vertical melting reduction furnace, and in particular, to a method of operating a so-called vertical furnace, and in particular to the preparation of carbonaceous material as a lump solid reducing agent to be filled inside the vertical furnace. By appropriately adjusting the composition of the reducing exhaust gas generated from the vertical furnace, it is possible to reduce the amount of difficult-to-reducible ores such as chromium ore in the pre-reduction of powdery ore in the fluidized bed pre-reduction furnace. However, the aim is to achieve an accurate preliminary reduction rate by using only exhaust gas from a vertical furnace.

In recent years, raw material ores mainly composed of various metal oxides, including iron ore, have become more common than lump ores.
Powder and granular ore are becoming more common, and their proportion is expected to continue to increase. Conventionally, the conventional smelting method using powder and granular ore is to pre-reduce the powder and granular ore using a fluidized bed, and then melt and reduce the pre-reduced ore in an electric furnace, converter, or other melting furnace. It is.

In this case, there are many methods in which a binder is added to the pre-reduced ore to agglomerate it, and the agglomerate is melted and reduced in a melting furnace. However, this method not only requires materials for agglomeration, processing costs, and processing energy, but also requires firing at that time. Another drawback is that it costs a lot of money to treat NO _x , SO _x and dust in the gas discharged from the furnace.

In addition to the above-mentioned method, a method has also been proposed in which pre-reduced ore is melted and reduced without agglomeration or calcination using an arc furnace or a furnace that uses plasma or pure oxygen. The method using a furnace not only consumes a huge amount of power, but also has restrictions on location, and the method using a furnace that uses plasma also consumes a tremendous amount of power, making it currently difficult to apply even on an industrial scale. Furthermore, with the method using a furnace that uses pure oxygen, even though it is easy to obtain a high-temperature atmosphere, it is difficult to maintain a reducing atmosphere and the amount of oxygen used increases, both of which require technical solutions. It's fraught with problems.

By the way, the present inventors have previously disclosed in Japanese Patent Application No. 56-63294 that a packed layer of carbonaceous solid reducing agent, mainly coke, is continuously formed inside a vertical blast furnace. The reducing exhaust gas discharged from the vertical furnace is used to produce powder,
The partially reduced ore obtained by pre-reducing the granular ore is further added with flux if necessary, and is blown into the tuyere.800
We have proposed a method for melting and reducing powder and granular ores in a vertical furnace, in which the partially reduced ore is melted and reduced by blowing air at a temperature of ~1300°C or oxygen-enriched air into the vertical furnace.

The development of the smelting reduction method using such a vertical furnace has made it possible to smelt powder and granular ores extremely effectively.

However, in the above smelting reduction method, coke is generally used as the solid reducing agent, and the reducing component in the exhaust gas is mainly CO.
For materials that are difficult to reduce, such as chromium ore, it is difficult to achieve a satisfactory preliminary reduction by using exhaust gas alone, making it difficult to operate smoothly.

Therefore, when pre-reducing chromium ore, coke is used as a CH ₄ source because hydrocarbon gas (hereinafter simply abbreviated as CH ₄ ) whose main component is methane is more effective as a reducing agent than CO gas. Using furnace gas, etc., these gases are introduced into the fluidized bed together with the vertical furnace exhaust gas for preliminary reduction, and the obtained partially reduced ore is entrained in oxidizing gas and blown into the vertical furnace. By doing so, melting reduction was performed.

Therefore, as mentioned above, when pre-reducing ores that are difficult to reduce such as chromium ore, CH ₄
This method requires a large amount of coke oven gas as a source and also requires preheating, which increases costs, and requires equipment for supplying coke oven gas, which adds to the equipment burden.

In this respect, it would be extremely advantageous if appropriate preliminary reduction could be achieved even with the use of exhaust gas only, even for hard-to-reducible ores.

This invention advantageously meets the above requirements.
It does not require separate coke oven gas, and can be used as a backup for difficult-to-reducible powder and granular ores such as chromium ore by using only the exhaust gas generated in a vertical furnace through smelting reduction. The purpose of this study is to propose a method for operating a vertical smelting reduction furnace that enables reduction and even smelting reduction.

Now, in the actual operation of the smelting reduction method for powder and granular ores using a vertical furnace, if coal is added to the coke, which is usually used as a lump solid reducing agent to fill the furnace, the exhaust gas was found to contain _CH4 .

The inventors focused on CH ₄ contained in this exhaust gas, and as a result of numerous experiments and studies regarding the effective use of such CH ₄ , (a) CH ₄ was charged into a vertical furnace. (b) The amount of CH ₄ generated increases as the blending ratio of coal increases; If the proportion of coal in the reducing agent is within a specified range, there should be no problem in melting and reducing in a vertical furnace.

(d) Therefore, by appropriately changing the proportion of coal in the total lump solid reducing agent and adjusting the exhaust gas composition (the amount of hydrocarbons whose main component is CH ₄ ), only the exhaust gas from the vertical furnace can be reduced. It was discovered that by using this method, even difficult-to-reducible ores such as chromium ore can be pre-reduced easily and accurately to the desired reduction rate.

This invention is based on the above findings.

In other words, this invention continuously forms a packed layer of bulk solid reducing agent inside a vertical furnace, while injecting oxidizing gas under preheating through a group of tuyeres provided on the lower body wall of the vertical furnace. The partially reduced ore obtained by pre-reducing the granular ore using the reducing exhaust gas discharged from the furnace is entrained in the oxidizing gas stream and blown into the vertical furnace. When performing vertical furnace smelting reduction, lump coal is mixed into the lump solid reducing agent as a CH ₄ generation source, and the blending amount of this lump coal is adjusted to match the partially reduced ore with the desired preliminary reduction rate. The above-mentioned problem is solved by adjusting the vertical furnace exhaust gas to be generated in accordance with the fluidized pre-reducing gas having the gas composition.

This invention will be specifically explained below.

FIG. 1 shows a vertical smelting reduction furnace suitable for carrying out the present invention together with a fluidized bed pre-reduction furnace, where numeral 1 is a supply device for granular ore, 2 is a fluidized bed pre-reduction furnace, and 3 is a fluidized bed pre-reduction furnace. It is a vertical melting reduction furnace, 4 is a lump coal hopper, 5 is a hopper of other lump solid reducing agent such as coke, 6 is the hopper 4,
A feeding device for mixing coal and coke from 5 to continuously form a packed layer inside the vertical furnace; A plurality of tuyere groups are arranged, and 8 is an exhaust port for exhaust gas.

In actual operation, the packed layer in the vertical furnace 3 is combusted by preheating and blowing an oxidizing gas such as air or oxygen-enriched air through the tuyeres 7 and 7'. The reducible high-temperature exhaust gas generated in the mold furnace 3 is guided from the exhaust port 8 through the branch pipe 8' to the bottom of the preliminary reduction furnace 2 to remove the refractory powdery ore charged into the furnace 2. The pre-reduced partially reduced ore is led from the ore discharge port 9 to the tuyere 7, 7' through the ore feed pipe 9' shown by the broken line, and is blown into the vertical furnace 3 together with preheated air for charging. As a result, it is melted and reduced in the furnace. In the figure, 10 is a gas heating furnace, 11 is a booster, and 12 is a tap.

Now, in such smelting reduction, the preliminary reduction rate is determined in order to carry out optimal operation by taking various operating conditions into consideration. It varies depending on the amount of _CH4 in it. For example, for powdered chromium ore, as shown in Figure 2, which shows the effect of the amount of CH ₄ in the exhaust gas on the preliminary reduction rate of the ore, the preliminary reduction rate of powdered chromium ore depends on the amount of CH ₄ in the exhaust gas. Increases and decreases proportionally and almost linearly. Therefore, once the preliminary reduction rate to be reduced in the fluidized bed is set, the proportion of coal in the bulk solid reducing agent is adjusted in order to generate exhaust gas containing an appropriate amount of CH ₄ to achieve this preliminary reduction rate. By adjusting the amount, preliminary reduction at a predetermined reduction rate can be easily achieved, thus achieving smooth melt reduction.

The lump coal is mixed here as a source of reducing gas (CH ₄ ) to be sent to the preliminary reduction furnace, but after carbonization, it becomes coke and is consumed as fuel and reducing agent in the lower part of the furnace. From a quality perspective, cheap non-caking coal is preferable to expensive caking coal in order to avoid caking and agglomeration reactions in the furnace, and its size is determined to prevent agglomeration during carbonization in the upper part of the furnace. Also, from the viewpoint of maintaining air permeability, it is preferable that the material be in the form of a block.

Further, coke is generally suitable as a solid reducing agent other than lump coal to be charged into a vertical furnace, and it is preferable that the size of the coke is lump-like.

The blending ratio of this lump coal and solid reducing agent such as coke is determined according to the desired preliminary reduction rate as described above, but in the case of hard-to-reducible ores, the range is 10 to 35% based on experimental results. If it exceeds 85%, the permeability of the packed layer will decrease due to the somewhat low strength of the coke generated from coal in the furnace, and the exhaust gas will increase due to the increase in volatile content. Adverse effects include problems such as erosion and blockage at the inlet of the pre-reduction furnace. On the other hand, when it was less than 10%, a satisfactory effect on reduction could not be obtained.

Next, as an example of the present invention, a case of manufacturing ferrochrome will be described.

The experiment was carried out in a test reactor according to the system system shown in Fig. 1 under the following operating conditions.

1 Vertical furnace inner diameter: 1.2m 2 Pre-reduction furnace inner diameter: 1.1m 3 Ore brand: Powdered chromium ore Average particle size: 0.2mm Supply amount: 190Kg/h 4 Coal type: Non-caking coal Particle size: 10-30mm Supply amount: 100Kg/h 5 Type of solid reducing agent: Coke Particle size: 10-30mm Supply amount: 130Kg/h 6 Air flow to vertical furnace: 650Nm ³ /h Air blowing temperature: 1250℃ (upper stage) 7. Target preliminary reduction rate: 30% 8. Target amount of _CH4 in exhaust gas: 100Nm 3 /t-metal The operation was started under operating conditions of 100Nm ³ /t-metal or higher, and the amount of CH4 generated in the vertical furnace was When the exhaust gas was introduced into the pre-reduction furnace, it was possible to accurately pre-reduce the difficult-to-reducible powdered chromium ore to the desired reduction rate of 30%, and in turn achieved smooth smelting reduction.

For reference, the exhaust gas components of a vertical furnace are shown below.
It was as follows.

CH ₄ : 1.2-1.3%, CO: 35-37% N ₂ : 60-62%, CO ₂ : 0.3-0.4%... Also, the amount of ferrochrome produced is 100 kg/h, and its composition is Cr: 56%, C : 8%, Si: 2%,
Furthermore, the amount of slag discharged was 170 kg/h.

In the above embodiments, the present invention was mainly explained for the case where it was applied to the preliminary reduction of powdered chromium ore, but it can also be applied to other easily reducible ores such as silica and nickel ore, as well as manganese which is difficult to reduce like chromium ore. Needless to say, the same method can be applied to ores.

Thus, according to the present invention, by appropriately adjusting the amount of CH ₄ in the exhaust gas generated in the vertical furnace, it is possible to pre-reduce powdery ore prior to smelting reduction even by using only this exhaust gas, and moreover to achieve the desired reduction. Accurate preliminary reduction to the preliminary reduction rate can be achieved, and as a result, smooth operation of melt reduction can be achieved.

In particular, for hard-to-reducible ores, the coke oven, which was previously considered indispensable, is no longer necessary, and the preheating process for the coke oven gas can also be eliminated, and furthermore, the use of high-temperature exhaust gas reduces the heat in the pre-reducing oven. Since consumption can also be reduced, it is useful for cost reduction.

In addition, as for the coal used in this invention, cheap non-caking coal is preferable to expensive caking coal in order to avoid the caking and agglomeration reaction in the furnace, so the increase in cost due to the combination of coals is rare.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a vertical furnace suitable for carrying out the present invention together with a preliminary reduction furnace, and Fig. 2 shows the preliminary reduction rate of chromium ore and the vertical furnace exhaust gas introduced into the preliminary reduction furnace. 2 is a graph showing an example of the relationship with the amount of CH ₄ in the water.

Claims (1)

[Scope of Claims] 1. While a packed layer of bulk solid reducing agent is continuously formed inside a vertical furnace, oxidizing gas under preheating is passed through a group of tuyeres provided on the lower body wall of the vertical furnace. The partially reduced ore obtained by pre-reducing the powdery ore using the reducing exhaust gas discharged from the furnace is entrained in the oxidizing gas stream and blown into the vertical furnace. When melting down ore,
In the lump solid reducing agent, lump coal is blended as a source of hydrocarbon gas mainly composed of methane, and the blending amount of the lump coal is adjusted to the gas composition to obtain partially reduced ore with the desired preliminary reduction rate. 1. A method for operating a vertical melting reduction furnace, which comprises adjusting the vertical furnace exhaust gas to be generated in accordance with the fluidized preliminary reducing gas. 2. The method according to claim 1, wherein the proportion of lump coal in the total lump solid reducing agent is 10 to 85% by weight.