JPS6136575B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for preliminary reduction of hard-to-reducible ores, and particularly when melting and reducing hard-to-reducible ore powder such as chromium ore powder by a vertical furnace smelting reduction method. This is intended to enable smooth preliminary reduction of ore powder.

In recent years, raw material ores mainly composed of various metal oxides, including iron ore, have become more common than lump ores.
Powdered ore is becoming more common, and its proportion is expected to continue to increase.

This tendency is the same for chromium ore, which is difficult to reduce. Conventionally, when producing ferrochrome from granular chromium ore, the melting furnace was
Electric furnaces have been mainly used. However, in the production of ferrochrome using an electric furnace, the electricity consumption per unit is several thousand.
KWH/t, which had the disadvantage of extremely high costs.

Incidentally, recently, the smelting reduction method for directly obtaining molten metal from raw ore powder has been attracting attention as a technology for producing ferrochrome and other ferroalloys that does not rely on electricity, and the inventors previously published Japanese Patent Application Laid-Open No. 57-198205. In the publication, while a packed layer of carbonaceous solid reducing agent is continuously formed inside the vertical furnace, it is discharged from the vertical furnace through a group of tuyeres arranged on the lower body wall of the vertical furnace. The pre-reduced ore obtained by partially reducing the granular ore using reducing exhaust gas is subjected to pneumatic conveyance using air at a temperature of 300 to 1300°C or oxygen-enriched air, with additional flux added if necessary. We proposed a vertical furnace smelting reduction method for powdery ore, in which the pre-reduced ore is blown into a vertical furnace and smelted and reduced.

Such a vertical furnace smelting reduction method can be applied to the smelting of various powdery ores, but when applied to the production of ferroalloy from hard-to-reducible ores such as chromium ore, the following I had a problem like this.

In other words, in the preliminary reduction furnace, high-temperature exhaust gas from the vertical furnace is used as reducing gas to reduce the
Even if an attempt is made to reduce a chromium ore, for example, chromium oxide (Cr ₂ O ₃ ) is more difficult to reduce than the iron oxide (FeO) contained in the ore, the chromium ore as a whole cannot be reduced to a specified reduction rate. The point is that it is difficult to make a return.

In addition, as a preliminary reduction method for chromium ore, a method using heavy oil or coal as a reducing agent has also been proposed, but in this case, the temperature inside the reactor is set to 1100 -
Since it is necessary to maintain the temperature at a high temperature of 1300℃, it is not suitable when the exhaust gas temperature from a vertical furnace is low.

In this respect, when chromium ore is used, hydrocarbon gases such as methane (CH ₄ ) are used as reducing agents that reduce at low temperatures.
However, the reduction reaction of chromium ore with hydrocarbon gas is a large endothermic reaction, so even if the sensible heat of the high-temperature exhaust gas from the vertical furnace is used, the reduction reaction will not be effective. It was difficult to maintain a temperature of 950 to 1150 degrees Celsius for smooth progress.

This invention advantageously solves the above problem, and even when pre-reduction is performed at a low temperature using a hydrocarbon gas, it is possible to effectively reduce the temperature drop caused by the endothermic reaction of the hydrocarbon gas. This paper proposes a method for pre-reducing refractory ores, which can achieve smooth pre-reduction while avoiding such problems.

This invention solves the problem of a temperature drop in the furnace due to an endothermic reaction when pre-reducing hard-to-reducible powdery ore using a hydrocarbon gas. This can be advantageously avoided by introducing gas or air to cause a partial combustion exothermic reaction with the combustible components in the carbon material in the furnace or the gas generated in the furnace, thus reducing the temperature in the furnace to the appropriate reaction temperature of 950°C. It is based on new knowledge that it can be maintained at 1150℃.

That is, the present invention provides a vertical furnace smelting reduction method using a fluidized bed pre-reduction furnace for pre-reducing powdery ore and a vertical furnace for melting and reducing the pre-reduced ore. When pre-reducing the ore, a pre-reduction furnace is placed in which the powdered ore is supplied.
A fluidized bed is formed by supplying hydrocarbon gas along with carbonaceous materials to the vertical furnace exhaust gas, while oxygen-containing gas is blown into at least the region above the low reduction region above the fluidized bed. This is a preliminary reduction method for hard-to-reducible ores.

This invention will be specifically explained below.

FIG. 1 schematically shows a pre-reduction furnace suitable for carrying out the present invention, and number 1 in the figure is a pre-reduction furnace consisting of a fluidized bed reactor, and its shape is usually vertical and cylindrical. 2 is a supply port for hard-to-reducible ores such as powdered chromium ore, and 3 is a supply port for carbonaceous materials such as coke and coal, as well as flux.
These carbonaceous materials and fluxes can also be mixed with chromium ore and supplied from the supply port 2 at the same time. 4
5 is the inlet for the vertical furnace exhaust gas which is the fluidized bed reducing gas, 5 is the injection port for the hydrocarbon gas as the reducing agent, 6 is the outlet for the pre-reduced granular pre-reduced ore, and 7 is the inlet for this. In this example, this is an oxygen-containing gas injection port opened in the freeboard portion of the preliminary reduction furnace 1. Note that 8 is a gas distribution plate, and 9 is a combustion gas exhaust port.

Now, the powdery chromium ore supplied into the furnace from the powdery ore supply port 2 forms a fluidized bed 10 by introducing the vertical furnace exhaust gas, and at the same time forms a fluidized bed 10 at the injection port 5.
It is reduced by hydrocarbon gas supplied from By the way, since the reduction reaction of chromium ore by this hydrocarbon gas is a large endothermic reaction as described above, smooth reduction cannot be carried out if the temperature inside the furnace is significantly lowered.

Therefore, in this invention, an oxygen-containing gas such as oxygen gas or air is separately blown into the furnace.
A predetermined reaction temperature is ensured by causing a partial combustion reaction with the combustible components in the carbon material in the furnace or the gas generated in the furnace, and by utilizing the combustion heat.

However, when introducing this oxygen-containing gas into the furnace, there are problems such as sintering of pre-reduced chromium ore particles due to local overheating near the oxygen-containing gas injection port, operational problems, and recycling of pre-reduced chromium ore particles. This involves various problems such as a reduction in the reduction rate due to oxidation, and it is impossible to inadvertently introduce oxygen-containing gas into the fluidized bed, so the introduction position is important.

Therefore, the inventors conducted various studies regarding this point and found that the oxygen-containing gas injection region was changed to the area above the low reduction area at the top of the fluidized bed, that is, the area at the top of the fluidized bed where the preliminary reduction rate of chromium ore was low. and/
Alternatively, by using a freeboard section, the appropriate reaction temperature can be maintained without the risk of causing the above-mentioned problems.
They found that it is possible to achieve effective preliminary reduction by ensuring that

That is, as shown in FIG. 1, oxygen-containing gas is introduced into the freeboard section 11 above the fluidized bed 10 and is combusted in the freeboard section 11 with combustible components in the fluidized bed gas. The combustion heat can effectively heat the fluidized bed 10. At this time, if the supply port 2 for the granular ore is installed at the upper part of the freeboard part 11 as shown in the figure, in addition to the above-mentioned effect, the chromium ore itself can also be heated, which is even more effective.

Next, FIG. 2 illustrates another method of blowing the oxygen-containing gas. In this example, the inside of the fluidized bed 10 is multi-staged using, for example, a multi-stage device 12, and the fluidized bed 1
In the process of changing from chromium ore to pre-reduced chromium ore, oxygen-containing gas is generated in the upper part of the fluidized bed where reduction has not yet progressed sufficiently and most of the chromium ore remains as chromium ore. Even with this injection method, heat can be evenly transferred into the fluidized bed without the above-mentioned problems such as sintering of the chromium ore particles.
A predetermined temperature can be ensured. In this case, it is desirable that the reduction rate of the ore at the point where the oxygen-containing gas is introduced is 10% or less on average.

Furthermore, although Figures 1 and 2 only show cases in which oxygen-containing gas is injected into the furnace only in the freeboard section and the upper part of the fluidized bed, it goes without saying that both can be carried out simultaneously. Nor. Regarding the amount of oxygen blown, it is desirable to set the amount of oxygen blown to about 300 Nm ³ or less per ton for chromium ore, for example, since blown in too much oxygen may cause hard sintering. Furthermore, when blowing the oxygen-containing gas, it is more advantageous to preheat it if necessary in order to obtain the desired effect.

Examples of the present invention will be described below.

Preliminary reduction of chromium ore was carried out under the following operating conditions using the pre-reduction furnace shown in FIG. 2 above.

(1) Chromium ore: Chromium ore from the Philippines Composition: Cr ₂ O ₃ 49.2% FeO 23.8% Particle size: 28-48 mesh 7.9% 48-100 mesh 86.7% Less than 100 mesh 5.4% Supply rate: 85Kg/h (2 ) Charcoal material: Coke {CDQ (coke dry quencher) dust} Particle size: 48 to 100 mesh Supply amount: 38Kg/h (3) Vertical furnace exhaust gas supply amount: 890Nm ³ /h (4) Hydrocarbon type Gas: Methane gas Supply amount: 10Nm ³ /h (5) Supply oxygen amount: 11Nm ³ /h (6) Target preliminary reduction rate: 35% When chromium ore was preliminary reduced under the above operating conditions, the preliminary reduction furnace The internal temperature is 1030℃, which can maintain the appropriate reaction temperature when using hydrocarbon gas.
In addition, the achieved preliminary return rate met the target value of 35%.

In the above embodiments, the case where preliminary reduction of chromium ore is mainly explained, but it goes without saying that the present invention can also be applied to preliminary reduction of other difficult-to-reducible ores such as manganese ore.

Thus, according to the present invention, even when a hydrocarbon gas is used as a reducing agent for preliminary reduction of hard-to-reducible ores, smooth preliminary reduction can be achieved without causing a temperature drop in the furnace. is possible,
It's advantageous.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a preliminary reduction furnace suitable for use in carrying out the present invention, and FIG. 2 is a schematic diagram of another preferred preliminary reduction furnace. 〓〓〓〓

Claims (1)

[Scope of Claims] 1. In a vertical furnace smelting reduction method using a fluidized bed pre-reduction furnace for pre-reducing powdery ore and a vertical furnace for melting and reducing the pre-reduced ore, When pre-reducing the granular ore, a pre-reducing furnace is placed in which the granular ore is supplied.
A fluidized bed is formed by supplying hydrocarbon gas along with carbonaceous materials to the vertical furnace exhaust gas, while oxygen-containing gas is blown into at least the region above the low reduction region above the fluidized bed. Preliminary reduction method for refractory ores.