JPS62151531A - Method and apparatus for reducing chromium ore - Google Patents

Abstract

PURPOSE:To efficiently reduce the oxide of chromium and iron in chromium ore at a low cost by lowering pellets consisting of pulverized powder of the chromium ore and carbonaceous reducing agent in a vertical type reaction pipe consisting of a preheating chamber, combustion chamber and cooling chamber. CONSTITUTION:Powdery coke and anthracite as reducing agents are mixed with the powdery Cr or in the amt. larger than the theoretically required amt. The mixture is pelletized to pellets having about 10mm diameter by a binder such as bentonite. The pellets 8 are charged into the vertical reaction furnace 3 consisting of a preheating zone 3a, reducing zone 3b and cooling zone 3c from the upper part thereof. The pellets 8, preheated by the high-temp. reactive exhaust gas rising from below, fall into the reducing zone 3b and are indirectly heated to 1,200-1,500 deg.C in the combustion chamber 1 having a burner 2 which uses gaseous or liquid fuel. After the Cr ore is reduced at high reducibility, the Cr ore is taken out of the furnace 3 through the cooling zone 3c. The Cr ore is subjected to the solid phase reduction at the low cost by using the inexpensive fuel without using the costly electric power as a heat source for reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing reduced wavelets of chromium ore, which are suitable as additives for metallurgy.

(Prior Art) Generally, steel containing chromium is manufactured by adding chromium to iron in the form of ferrochrome. A common method for producing ferrochrome is to charge chromium ore together with a carbonaceous reducing agent and a slag-forming agent into an electric furnace and melt and smelt it. Recently, methods have also been adopted to reduce the amount of expensive electrical energy used and use cheaper heavy oil or coal energy for smelting.

That is, as seen in Japanese Patent Publication No. 46-43695, a binder is added to a mixed fine powder raw material of chromium ore and a carbonaceous reducing agent, granulated into a pellet shape, and this granulated material is inserted into a rotary kiln. A method of reducing and roasting in a solid state in an oxidizing combustion air stream is carried out. In this method, a fuel with a low energy unit price such as heavy oil or pulverized coal is selected and used, but in order to completely burn the fuel and obtain a high temperature, excess combustion air is used and oxidizing combustion air is used. directly heating the pellets. This oxidizing combustion air stream contains carbon dioxide (CO2), water vapor (H2O), and oxygen (
02) It contains a large amount of gas that is oxidizing to chromium/iron carbide, which is a reduction product, or a carbonaceous reducing agent. For this reason, the oxidation reaction proceeds on the surface of the pellet, and the reduction of chromium and iron does not proceed to a high degree, so that the actual reduction rate of the entire wavelet reaches only about 80% at most. In particular, the reduction rate of chromium is limited to about 75-. If such pellets are to be used as raw material for steelmaking, expensive electrical energy must be used to reduce the remaining portion.

On the other hand, as a solid-phase reduction method that avoids heating in an oxidizing combustion stream, a mixture of chromium ore and a carbonaceous reducing agent is charged into a vacuum furnace and heated while introducing argon (Ar) gas. A method of solid-phase reduction using
1959 etc.).

In addition, in the method of solid-phase reduction in a rotary kiln, the inner charcoal pellets of chromium ore are charged into the rotary kiln together with a large amount of carbon material, and the inner charcoal pellets are kept buried in the carbon material, so that substantially [ A method of solid phase reduction in a carbon monoxide (CO) atmosphere generated by the reduction of <Ret> is also known (see USP 2,869.850, etc.).

(Problems to be Solved by the Invention) As mentioned above, when a chromium ore internal coal wavelet is charged into a rotary kiln and reduced and roasted in an oxidizing combustion air stream, the reduction rate is about 80 degrees at most. .

In recent years, attempts have been made to make steel by directly charging chromium ore, rather than in the form of fed chromium, into a steelmaking furnace and using it as a chromium source. Reducing ore requires a large amount of energy, and there is a limit to how much energy can be reduced in a steelmaking furnace.

Therefore, if the combustion energy of cheap fuel is used to perform solid phase reduction to the highest possible degree and this highly reduced product is added to the steelmaking furnace, it will have a great effect on shortening steelmaking time and reducing energy consumption. become. In other words, the main purpose of the present invention is to utilize the energy of cheap fuel to achieve a reduction rate of 80%.
% or more highly reduced chromium ore reduced pellets.

To avoid the disadvantages of reductive roasting in an oxidizing combustion stream,
As mentioned above, attempts have been made to reduce and roast the method in an inert air stream, but there are problems with equipment to realize it on an industrial scale, and it has not yet been realized.

That is, in the method using a vacuum furnace such as that disclosed in Japanese Patent Publication No. 38-1959, a batch operation is required, which inevitably leads to a decrease in productivity. In addition, in the reduction roasting method in a rotary kiln with a large amount of exterior carbonaceous material as in USP 2,869.850, the reddish after reduction roasting and the carbonaceous material are mixed,
If this continues, it will not be possible to obtain anything that can be used directly in the steelmaking process. It is substantially difficult to separate the reduced roasted material from the exterior carbonaceous material, and no effective means have been found.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems. The present invention provides a method for indirectly heating pellets using the combustion energy of inexpensive fuel from outside of the chrome ore to obtain highly reduced chromium ore reduced Zellet, and an apparatus therefor.

The present invention will be explained in detail below.

The chromium ore used in the present invention is chromium oxide (having a Cr20ρ content of 40 to 60%).The chromium ore may be a fine ore.

Carbonaceous reducing agents include metallurgical coke, petroleum coke,
Those containing fixed carbon (FC) such as anthracite, coal, and charcoal can be used. The mixing ratio of chromium ore and carbonaceous reducing agent is determined according to the following formula.

7Cr O+ 27C→2Cr C+ 21CO(1)
7FeO+IOC-+ Fe7C3+ 7CO(2) That is, the amount of carbonaceous reducing agent required to reduce chromium oxide and iron oxide in the chromium ore to carbide may be blended. In the present invention, the carbonaceous reducing agent is not consumed by oxidation due to the oxidizing gas flow, so the blending ratio of the carbonaceous reducing agent may be a stoichiometric amount or a slight excess of the stoichiometric amount.

Since the chromium ore and the carbonaceous reducing agent are brought into intimate contact for solid phase reduction, they are mixed into a fine powder and then granulated into pellets using a suitable binder. The particle size of the mixed fine powder is 10
It is good to set it to 0 mesh or less, preferably 200 mesh or less. Further, the binder may be inorganic (for example, bentonite) or organic (for example, CMC).

The granulation method is not particularly limited, and a conventional method using a retizer can be used.

There is no particular restriction on the Klet size, as long as it is easy to handle during the manufacturing process. From the viewpoint of the reduction reaction, a diameter of about 10 mm is preferable in order to improve heat conduction.

Prior to the reduction of Zellet, it is necessary to dry and preheat the Zellet, and the drying preheating is also carried out in the upper stage of the vertical reactor, but it can also be carried out in a separate process using waste heat or the like.

By drying the pellet, it has the effect of being strong enough to withstand compression inside the vertical reaction tube.

The reduction reaction is carried out by charging the pellet from the upper end of the vertical reaction tube, and while discharging it to the lower end, the pellet is indirectly heated from the outside of the vertical reaction tube and heated at a temperature of 1200° C. or higher for 30 minutes or more.

The reason for using the vertical reaction tube here is to indirectly heat the four reactors and at the same time to make the operation continuous, thereby improving productivity. As long as the pellet is constantly moving downward inside the vertical reaction tube, sintering of the four pellets will not occur even if the four pellet temperature reaches a high temperature of 1200'C or higher.

Carbon monoxide (CO) is generated by reduction,
In order to promote the reaction, it is necessary to discharge CO out of the system. For this purpose, exhaust equipment is provided at the upper end of the vertical reaction tube to exhaust and remove the CO gas from the reaction tube after heat exchange within the reaction tube.

On the other hand, the heating necessary for reduction is achieved by heating the outside of the vertical reaction tube with combustion flame, thereby indirectly heating the pellet. In this case, fuels include heavy oil, coal, natural gas,
Any fuel such as smelting furnace waste gas can be used, and it is sufficient to select the fuel that is economically most advantageous for the plant. Moreover, the most efficient combustion conditions can be selected without being restricted by the reduction reaction. Even when such a state of complete combustion of fuel is utilized, in the case of the present invention, no oxidation phenomenon occurs on the red surface portion, and chromium ore reduced 4 red with a high reduction rate can be obtained.

The temperature at which chromium oxide in chromium ore is reduced is 1200°C or higher under normal pressure, so the inside of the vertical reaction tube is
Heat it to 200℃ or higher, and make a pellet of 1200℃.
It is necessary to adjust the processing speed so that the residence time in the temperature range of .degree. C. or higher is at least 30 minutes or more.

Since the chromium ore reduced sintered pellets obtained in this way are not affected by oxidizing combustion air currents, the condition is almost uniform from the inside of the pellet to the surface, and the reduction rate of the entire pellet is over 90 coefficients. reach.

Next, the reduction device according to the present invention will be explained.

FIG. 1 is an explanatory diagram showing the mechanism of the reduction device according to the present invention. In Figure 1, a burner 2 is installed in the combustion chamber 1 to completely burn cheap fuel such as heavy oil or pulverized coal.
Obtain a high temperature combustion air flow of 0 to 1600°C. This high-temperature combustion air stream contacts and heats the vertical reaction tube 3 disposed in the combustion chamber 1, and then is guided to the preheater 9 to preheat the raw material and the flue 7
The exhaust gas is led to a flue gas treatment device (not shown) through the exhaust gas and the waste heat is recovered.

The vertical reaction tube 3 constitutes the reduction device of the present invention, and is composed of three parts from the top: a pre-preparation zone 3a, a reduction zone 3b, and a cooling zone 3c. Of these, the reduction zone 3a is disposed within the combustion chamber 1, is heated, and receives thermal energy necessary for reducing the chromium ore from the high-temperature combustion airflow of the fuel. Therefore, this part must be able to withstand high temperatures, as well as oxidizing combustion airflow and carbon monoxide airflow, which is the reductive product. It must also be stable against the raw material chromium ore, difficult to form into sintered materials, and have excellent wear resistance. In order to exchange heat even more efficiently,
The material must have high thermal conductivity. Such materials include alumina-based, zirconia-based, silicon carbide-based, spinel-based refractories, and sialon (5i-At-
Ceramics such as 0-N solid solution) can be used.

The vertical reaction tube 3 is configured in a thin cylindrical shape in order to indirectly heat the pellet 8 loaded therein. In order to heat the pellet in the center to the reducing temperature, it is necessary to make the inner diameter 40 mm or less. If it is larger than 40 crn, heat transfer will not reach the center, resulting in poor efficiency.

In production equipment, if a plurality of thin vertical reaction tubes 3 are arranged in the combustion chamber 1 and a plurality of burners 2 are used, efficient heating can be achieved.

The preheating zone 3a in the upper part of the vertical reaction tube 3 and the cooling zone 3c in the lower part are parts having a low operating temperature. These parts only need to exchange heat efficiently, so metal materials such as copper alloys with good thermal conductivity can be used. cooling zone 3c
A cooling chamber 10 is disposed around the outer periphery of the burner 2, and if air is used for heat exchange, the air can be used as combustion air for the burner 2, for example.

It is also possible to use heat as steam.

At the upper end of the vertical reaction tube 3, a raw material granule charging mechanism 4 and a gas discharge mechanism 5 are provided. The raw material granule charging mechanism 4 is a facility for quantitatively feeding raw material granules into the vertical reaction tube 3, and is configured to have a variable supply rate. It is also provided with a structure that suppresses the inflow of air into the reaction tube as much as possible.

The gas exhaust mechanism 5 is for forcibly exhausting carbon monoxide (CO), which is a reduction product generated within the vertical reaction tube 3, out of the system, and has a discharge capacity commensurate with the amount generated. That's fine. Carbon monoxide discharged by the gas discharge mechanism 5 can be used as fuel via a gas holder (not shown).

A reduced granule discharge mechanism 6 is provided at the lower end of the vertical reaction tube 3. This is for continuously discharging the granulated material that has undergone the reduction reaction out of the system, and has a structure in which the discharging capacity is variable. Furthermore, although the reduced granules are cooled in the cooling zone 3C, they are still at a high temperature, so a heat-resistant structure is adopted. Furthermore, a sealing function is provided to suppress the inflow of air into the reaction tube 3 as much as possible.

Next, the present invention will be explained with reference to Examples.

Example 22 parts of coke powder was blended with 100 parts of chromium ore from South Africa, dried with a rotary dryer, and then ground with a ball mill to obtain a mixed fine powder of 200 mesh and 90% L pass. Table 1 shows the grades of chromium ore and coke powder used.
Shown below.

Table 1 (wt%) Next, 3.5 tons of bentonite was added as a binder to the mixed fine powder, and no. Pelletization was carried out on the left to a diameter of 12±5 mm using a pelletizer while adding water.

Use a band dryer to dry this pellet with a moisture content of 0.5.
It was dried to a temperature of less than The composition of left for drying is shown in Table 2.
It was as follows.

Table 2 (wt%) Next, for drying, the knots were placed in a vertical reduction apparatus having the structure shown in FIG.

The vertical reduction apparatus used in this example was as follows. That is, combustion chamber 1 has a diameter of 1.8 ms and a height of 2 m.
It consists of a refractory groove structure and is equipped with three heavy oil burners 2 at the bottom. Inside this combustion chamber 1 is an outer diameter of 35 crn and an inner diameter of 3 crn.
Three alumina vertical reaction tubes 2 each having a length of 0 cm and 5 m are installed so as to penetrate inside the combustion chamber 1. Combustion chamber 1
There is a preheating chamber 9 having a diameter Im and a height of 2m and having an adiabatic structure in the upper part of the chamber, through which the combustion gas in the combustion chamber 1 passes and heats the preheating zone 3 at the upper part of the vertical reaction tube 3. . Combustion chamber 1
A cooling chamber 10 made of steel plate and having a diameter of 1 m and a height of 2 m is installed at the bottom of the cooling chamber. Cooling air is introduced into the cooling chamber 10 to cool the cooling zone 3C at the bottom of the vertical reaction tube 3, and the heated air can be used as combustion air for the heavy oil burner. A rotary feeder is installed at the upper part of the vertical reaction tube 3 as a raw material granule charging mechanism 4, and the structure is such that the raw material pellets can be fed in a fixed amount while suppressing the inflow of air.

In addition, an exhaust duct is connected to the upper part of the vertical reaction tube 3,
The structure is such that it is connected to a suction blower and the carbon monoxide gas generated by the reaction is exhausted from the row side.

On the other hand, a backfly damper is installed at the bottom of the vertical reaction tube 3 as a reduced granule discharge mechanism 6, creating a structure that can continuously discharge knots produced by reduction while suppressing the inflow of air from the bottom of the vertical reaction tube. It is composed.

By charging the dry VSOTO into the vertical reactor constructed as above and heating the vertical reaction tube with a combustion flame using heavy oil as fuel, the container inside the vertical reaction tube is indirectly heated. I returned it. The temperature inside the combustion chamber 1 reaches a maximum of 1450°C, and at this time the 4let temperature inside the vertical reaction tube is 1200-1
The temperature reached 350°C.

In order to ensure a four-rest residence time of 2 hours or more in the chromium oxide reduction temperature range of 1200° C. or higher, the pellet movement speed in the reaction tube was targeted at 0.5 rry'h.

Further, the degree of opening of the suction blower was adjusted to maintain the internal pressure at the top of the vertical reaction tube 3 at -3wn Aq. The reaction gas sucked by the suction blower passes through a heat exchanger (not shown) and is stored in a gas holder (not shown).
It was used as auxiliary fuel for rotary dryers.

Since the combustion exhaust gas leaving the preheating chamber 9 still maintained a high temperature, it was led to a band dryer and used for pellet drying.

Table 3 shows the composition of the reduced pellet thus obtained.

Table 3 (wt%) Here, Sot, Cr, Sot, and Fe are Cr and Fe that are soluble in 10% sulfuric acid. In addition, (Cr, Fe) reduction rate is the proportion of oxygen atoms that are removed by reduction treatment among the oxygen atoms bonded to valuable metal atoms in the ore (
b) and is determined by the following formula.

As is clear from Figure 3, the reduced wavelet obtained by the method of the present invention was highly reduced, and there was no difference between the inside and the surface of the pellet, and the reduction was uniform. Especially when looking at the reduction rate of chromium, it is 93.5.
4 with such a high chromium reduction rate.
Reds cannot be obtained by conventional methods.

Furthermore, if the reduction apparatus according to the present invention is used, it is possible to make the operation continuous, improve productivity, and from the point of view of energy efficiency, it is possible to use a four-speed rotary kiln system. Although this example shows an example in which three vertical reaction tubes are installed, it is of course possible to install a larger number of reaction tubes, and it goes without saying that productivity and thermal efficiency can be further improved.

When the reduced wave rest obtained by the method of the present invention is directly added to a steelmaking furnace, chromium can be easily added with little energy, so it is extremely useful as a chromium additive for steelmaking.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of the reduction device of the present invention. DESCRIPTION OF SYMBOLS 1... Combustion chamber, 2... Burner, 3... Vertical reaction tube, 4... Raw material granule input mechanism, 5... Gas discharge mechanism, 6... Reduced granule discharge Mechanism, 7... Flue, 8.
... Pellet, 9... Preheating chamber, 10... Cooling chamber.

Claims (1)

[Claims] 1) After adding a binder to a powdered mixed raw material of chromium ore and a carbonaceous reducing agent and granulating it into pellets, the granulated product is charged from the upper end of a vertical reaction tube. The granules were heated to 1200°C by heating the outside of the vertical reaction tube using combustion gas.
A method for reducing chromium ore, which comprises indirectly heating the ore to 1500° C. for reduction, and continuously taking out the granulated material from the lower end of a vertical reaction tube. 2) A vertical cylindrical reaction tube made of ceramic is installed in the fuel combustion chamber, the upper end of the reaction tube is equipped with a raw material granule charging mechanism and a gas discharge mechanism, and the lower end of the reaction tube is equipped with a raw material granule charging mechanism and a gas discharge mechanism. A chromium ore reduction device comprising a reduced granule discharge mechanism.