JPS61223143A - Method for prereducing chromium ore fines - Google Patents

Abstract

PURPOSE:To stabilize behaviour balance of powder in fluidized layer, and to prevent mixing of impurity in carbon powder, by controlling grain size ranges of Cr ore fines and solid carbon powder so that they are not overlapped, in preliminary reduction of Cr ore by fluidized layer. CONSTITUTION:Or ore fines and coal fines are charged to a fluidized bed 1 of reducing apparatus from supplying sources 2, 3 respectively, and counter current gas is supplied from under. Recovered gas is cleaned by a gas treating means 6 provided in circulation passage of counter current gas, and deficinet quantity thereof is supplied from source of gas such as steam, CH4 through a heater 7. The bed 1 is held to reducing temp. of Cr ore by a heating means 8. Thereat, overlapping of respective grain size ranges of Cr ore fines and coal fines is prevented. In such a way, Cr ore fines is reduced, the reduced part is passed through a slanted sieve 9 to sieve unburnt coal fines and ash without passing them therethrough, reduced Cr fines part is recovered, and sent to the following process by a carrying means 13.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for prereducing chromium ore.

More specifically, the present invention provides a method for preliminary reduction of chromium ore using a fluidized bed, in which unburned solid carbon as a reducing agent and ash are separated from the chromium ore, and are removed from the chromium ore, which are harmful to the chromium reduction reaction in the next step. The present invention relates to a method for removing components, improving the efficiency of chromium smelting, and reducing overall manufacturing costs.

BACKGROUND OF THE INVENTION Conventionally, stainless steel or chromium alloy steel has been produced by reducing chromium ore with coke in an electric furnace to produce high carbon ferrochrome, and using this as a raw material.

In other words, this method requires high temperatures to proceed with the reduction of ores with high CRL%, so this process is carried out in an electric furnace in the presence of an excessive amount of carbonaceous material (coke), and the resulting ferrochrome is melted again with the iron source,
It is a two-step method to decarburize and produce stainless steel or chrome steel.

However, this method, which is called ``indirect manufacturing method'', has
When viewed as a consistent flow from chrome ore to stainless steel, there are the following problems.

(1) Expensive electricity is used as the large amount of energy required to reduce chromium oxide.

(2) In general, 7 ferrochrome manufacturing plants and steelmaking plants are located far apart, so high carbon ferrochrome is manufactured as a molten product, but it is once solidified and then remelted during the steelmaking process, resulting in large energy losses.

(3) Since a large amount of slag is refined in contact with femchrome with a high [Cr%], the (Cr%) in the slag
It is difficult to lower the chromium loss, and the loss of chromium is large.

Therefore, in order to reduce the cost of melting chromium steel, it is necessary to solve these problems, and the following measures have been considered. In other words, (1) to maximize the use of inexpensive primary energy rather than electricity as reduction energy for chromium ore, - (2) to minimize energy loss in the integrated process from chromium ore to stainless steel. (3) It is important to minimize the amount of slag and create a reaction or reaction environment with a high Cr recovery rate.

Based on this technical idea, methods of directly reducing chromium ore with carbonaceous materials and melting reduction have been actively researched in recent years. Currently in practical use, green pellets obtained by mixing chromium ore powder with carbonaceous materials are pre-reduced at high temperatures in a rotary kiln, and the resulting pellets are charged into an electric furnace or other melting furnace. There is a way to do it.

However, in such a method, the unburned content and ash content of the carbonaceous material are directly charged into the smelting furnace, so that the P content in the carbonaceous material, especially the ash content, is 0. Impurities such as , 5iOa, and (S) are also introduced into the molten steel, requiring extra flux and a refining step to remove them. Especially P2O,
Since the dephosphorization reaction proceeds in an oxidizing atmosphere, it can hardly be removed in the stainless steel refining process.
There is a limit to the amount of pre-reduced pellets that can be used, making it impossible to achieve the above objectives.

That is, in pre-reduced pellets produced by conventional methods, in order to reduce the P content, one is forced to select a carbon material with a low P content, or the charging amount is limited to a P content that is within an allowable range. .

Problems that the invention attempts to solve The purpose of the present invention is to solve the problems of the prior art described above.

It is an object of the present invention to provide a method for pre-reducing chromium ore which can be used suitably for Cr refining in an electric furnace or other melting furnace.

More specifically, the object of the present invention is to provide a method for pre-reducing chromium ore with carbonaceous material, which involves reducing chromium ore under conditions such that the P content and ash in the carbonaceous material do not mix into the ore;
The objective is to improve the efficiency and reduce the cost of the next step of chromium reduction and refining, and at the same time to expand the range of choices for the type of carbon material used for preliminary reduction.

Means for Solving the Problems In order to solve the problems of the prior art described above and achieve the purpose of the present invention, the present inventors have completed the present invention as a result of repeated experiments and research on a method for pre-reducing chromium ore. It is something.

That is, according to the present invention, chromium ore powder and solid carbon powder whose particle size ranges do not overlap are supplied to a fluidized bed using an inert gas or a reducing gas as a countercurrent gas, and the chromium ore powder is reduced. A method for preliminary reduction of chromium ore powder is provided, which comprises classifying the reduced material to recover reduced chromium ore powder.

These chromium ore and solid carbon powder are 1-2,
It is preferable that the granularity range differs with a certain value of the city range as the boundary.

Further, according to one embodiment of the present invention, after the countercurrent gas is recovered, one or more of steam, CH4, or Cs Ht= is mixed with the recovered gas and recycled into the fluidized bed.

The fluidized bed may be a single-fan type or a multi-layered type,
Furthermore, either an internal combustion method or an external combustion method may be used.

In the case of an external combustion type fluidized bed, it is preferable to recover unburned solid carbon powder from the fluidized bed and combust it to heat the fluidized bed to the reduction temperature of chromium ore.

The solid carbon powder may be bituminous coal, coke, or char, and the temperature of the countercurrent gas and fluidized bed may be adjusted depending on which material is selected.

Function As explained above, the present invention uses chromium ore powder and solid carbon powder whose particle size ranges do not overlap when performing pre-reduction of chromium ore in a fluidized bed, and allows them to be easily sieved after pre-reduction. , is characterized in that both can be completely separated. The chromium ore powder pre-reduced by the method of the present invention and obtained by sieving does not contain unburned solid carbon powder or its ash, which is harmful to the refining reaction in a refining furnace such as an electric furnace in the next step. P2O3, S
iO*, (S), etc. will no longer be brought in.

In other words, the particle size of chromium ore powder and solid carbon powder does not change much even after the reduction reaction in the fluidized bed, so it is possible to separate and recover the solid carbon content from the chromium ore powder after reduction.
This is because it can be easily carried out using a sieve, for example.

Furthermore, compared to solid carbon powder, chromium ore powder has a higher specific gravity, and by providing a difference in particle size, it is easier to balance the behavior of the particles in the fluidized bed. That is, it is extremely important to maintain the product dρ of the particle diameter d and specific gravity ρ constant in order for the reaction to proceed uniformly in the fluidized bed.

By the way, the specific gravity of chromium ore powder is generally 3.5, and the specific gravity of solid carbon powder is 2.0. At this time, when the particle diameter of the chromium ore powder is dl and the particle diameter of the solid carbon powder is d2, the behavior of the particles in the fluidized bed is likely to be balanced when the following equation holds.

3.5d+ = 2. Oda Therefore, if the particle size d+ of the chromium ore powder is 0.8 mm, the particle size d of the solid carbon powder is l, 4 mm. Making the particle size ranges of the solid carbon powder and the chromium ore powder different in this way is extremely convenient for reactions within the fluidized bed.

The material subjected to the preliminary reduction treatment according to the method of the present invention can be easily separated into chromium ore components and unburned solid carbon components and ash components using a sieve or the like. Therefore, the reduced chromium ore sent to the next chromium refining process is not contaminated with impurities from the carbon material, providing the following advantages.

(Impurities in the next refining reaction are reduced, eliminating the need for extra 7 lux and refining.)

(Support)) Since there is no risk of contamination with impurities in solid carbon, an inexpensive carbon material can be selected.

EXAMPLES Hereinafter, the present invention will be explained with reference to examples, but these examples are merely illustrative of the present invention, and of course do not limit the scope of the present invention.

FIG. 1 of the accompanying drawings is a schematic diagram of a fluidized bed reduction apparatus used to carry out the method of the present invention.

As shown in the figure, the reduction apparatus includes a fluidized bed 1 into which ore and reducing agent are charged from above and countercurrent gas is supplied from below. In the illustrated example, the fluidized bed 1 is connected above with a source 2 of chromium ore powder and a source 3 of coke powder.

On the other hand, a countercurrent gas supply pipe 4 and a recovery pipe 5 are installed at the bottom and top of the fluidized bed, respectively, so that countercurrent gas is supplied in the direction of the arrow at the bottom of the fluidized bed 1 and recovered at the top of the fluidized bed 1. It is connected. More specifically, it is preferable that the countercurrent gas supply pipe 4 is uniformly supplied from the periphery of the fluidized bed 1 to maintain the particle suspension balance within the fluidized bed 1.

Further, the countercurrent gas supply pipe 4 and the recovery pipe 5 form a circulation path, and a gas processing means 6 is interposed in the circulation path to purify the recovery gas.

Furthermore, the circulation path is provided with steam, CH,
Alternatively, it is connected to a gas supply source (not shown) such as Ca H- to replenish the insufficient amount of countercurrent gas.

The illustrated fluidized bed reduction apparatus is of an external heating type, and a heating means 8 is provided so as to surround the fluidized bed 1.

A sieve 9 is installed at an angle in the lower part of the fluidized bed 1, so that the chromium ore after the reduction reaction passes through the sieve while moving on the sieve 9, while unburned solid carbon powder and ash do not pass through. It is composed of meshes. Further, at the lowest part of the reduction device below the fluidized bed 1, a conveying means 13 such as a belt conveyor is provided to collect the reduced reduced chromium ore that falls after passing through the sieve 9, and then transfers it to the next process. Send reduced chromium ore.

On the other hand, the reduction device further includes a recovery pipe 10 adjacent to the lower end of the slanted sieve 9 for recovering unburned solid carbon and ash that do not pass through the sieve 9 out of the fluidized bed. On the other hand, the recovery pipe 10 is connected to an ash treatment means 11. The ash treatment means 11 removes ash from the material on the sieve 9 and sends only unburned solid carbon to the heating means 8 via the pipe 12.

The above is an outline of the fluidized bed reduction apparatus used to carry out the method of the present invention, and its operation will be explained below.

In the illustrated example, the chromium ore powder supplied from the chromium ore supply source 2 is, for example, chromium sand produced in South Africa or chromium sand produced in the Philippines, and generally has a particle size of less than 1 mm. If necessary, it may be further pulverized in order to have a good floating balance.

On the other hand, the solid carbon powder may be any carbon material such as coke powder, char powder, or non-caking coal, but the particle size is 1 to 3 m.
It has undergone processing such as classification so that it falls within the range of m.

Countercurrent gas is an inert gas that is still a reducing gas, but
As shown in the figure, heated steam or a reducing gas such as CH, C3H, etc. may be mixed.

The fluidized bed 1 is maintained at the reduction temperature of chromium ore powder,
The optimum holding temperature is determined, for example, as shown in the following table, depending on the type of solid carbon powder and countercurrent gas used.

The temperatures shown in the table above are suitable temperatures for the reduction reaction,
It is also possible to use a reaction temperature higher than this.

Further, in the case of the method of the present invention, the type of solid carbon powder does not matter, but in consideration of reduction reaction efficiency and heat balance, char powder is preferable to coal powder.

As explained above, the present invention relates to an improvement of a method for reducing chromium ore using a fluidized bed, and by adjusting the particle size ranges of chromium ore powder and solid carbon powder, which is a reducing agent, so that they do not overlap, the fluidized bed reduction method is achieved. In addition to stably maintaining the behavior balance of the powder in the powder, P2O in the solid carbon powder is added to the reduced chromium ore.
It is characterized by recovering reduced chromium ore while preventing the contamination of impurities such as 5, 3i02 and (S).

Therefore, the method of the present invention has the following advantages.

■ High reduction efficiency can be achieved because fine chromium ore is used.

(2) In particular, since reduced chromium ore with low P 20 s can be obtained, it is possible to reduce the use of flux for dephosphorization in the next step of melting and refining, or eliminate the need for dephosphorization treatment.

■ Regardless of the chemical composition and type of carbon material, especially high P1 and high S
An inexpensive carbonaceous material can be used.

(2) Since the pre-reduced chromium ore produced by the method of the present invention does not contain P2O, there is no restriction on the amount of P2O to be charged.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a fluidized bed reduction apparatus used to carry out the method of the present invention. (main reference number)

Claims (6)

[Claims] (1) Chromium ore powder and solid carbon powder whose particle size ranges do not overlap are supplied to a fluidized bed using an inert gas or a reducing gas as a countercurrent gas, and the chromium ore powder is reduced, and the reduced material is A method for preliminary reduction of chromium ore powder, which comprises classifying and recovering reduced chromium ore powder. (2) With a specific numerical value in the range of 1 to 2 mm as the boundary, the maximum particle size of the chromium ore powder is less than the specific value, and the maximum particle size of the solid carbon powder is greater than or equal to the specific value. A method for pre-reducing chromium ore powder according to claim 1. (3) After recovering the countercurrent gas, at least one gas selected from the group consisting of steam, CH_4 and C_3H_8 is mixed with the recovered gas and recirculated into the fluidized bed. A method for pre-reducing chromium ore powder according to any one of Items 1 and 2. (4) The method for preliminary reduction of chromium ore powder according to any one of claims 1 to 3, wherein the fluidized bed is heated to the reduction temperature of the chromium ore by an internal heating method. . (5) The method for pre-reducing chromium ore powder according to any one of claims 1 to 3, wherein the fluidized bed is heated to the reduction temperature of the chromium ore using an external heating method. . (6) The method for preliminary reduction of chromium ore powder according to claim 5, characterized in that unburned solid carbon powder is recovered from a fluidized bed and combusted to heat the fluidized bed.