FR2493876A1 - Carburised ferrochromium prodn. from chromium mineral - using tilting, rotary, oxygen-blown reactor - Google Patents

Abstract

Carburised ferrochromium is produced by (a) charging a tilting rotary reactor with chromium mineral and carbonaceous reductant; (b) heating the charge to at least 1000 (pref. at least 1200) deg.C; (c) making successive addns. of solid carbonaceous reductant and oxygen blowing while rotating the reactor in the inclined position to give a liq. ferrochromium bath covered by a low chromium content slag; and (d) tapping and separating the ferrochromium and the slag. A wide range of carbon-saturated ferrochromium alloys can be produced, at low cost and high productivity, even from low quality minerals and variable quality solid reductants.

Description

The present invention relates to a process for the production of ferro-chrome fueled by means of a reactor in which the energy is supplied by the combustion of a carbonaceous material in an oxidizing gas.

Ferro-chromium and, in particular fuel-ferro-chromium, is usually produced in an electric arc furnace, by melting a charge of chromium ore, a carbonaceous reducer, and a certain number of additions intended to form, with the constituents of the ore, a slag of suitable fluidity. This production, which results in ferro-chromium which can contain from 50 to 65 OD of Cr, and 6 to 10 Ó of C, consumes at least 5,000 kwh / ton for quality at 60 Ó of Cr.It involves the use heavy equipment: electric ovens from 3Q to 5Q MW, fully closed to allow the recovery and purification of smoke, which requires the use of very regular loads both in chemical composition and in particle size; the use of friable or very fine ores, and of heterogeneous composition is therefore excluded, or, at least, is only possible at cost. expensive preparations (agglomeration, or pelletization for example).

In a certain number of cases, for example when the electric power distribution network is insufficient, or the price per kilowatt hour is too high, we would like to have a process in which the energy necessary for fusion and the reduction of the ore would not be provided by electric current, but for the greater part by solid carbonaceous products, even of average or mediocre quality, which are found in abundance, and in deposits of easy exploitation, in a certain number of countries and only in a small or zero proportion. by high-priced fuels such as natural gas or petroleum derivatives.

The present invention provides a solution to this problem.

It consists of a process for the production of fuel-ferro-chromium in which a chromium ore is treated by a solid carbonaceous reducer, at temperature C: -high, in a reactor constituted by a substantially cylindrical refractory enclosure which can rotate around its axis, the axis being tiltable in any position from the vertical to the horizontal, and the combustion gases of the carbonaceous reducer being able to be recovered, this process comprising the following steps -We introduce into the reactor a charge of chromium ore and carbonaceous reducer .

- The load is brought to a temperature at least equal to 10,000 C and preferably at least equal to approximately 12,000 C by any known heating means.

- A succession of additions of solid carbonaceous reducer is introduced onto the charge, and oxygen is blown to cause the combustion of said additions, the reactor being rotated, and its axis being inclined, until d '' a liquid ferro-chromium bath covered with a slag substantially depleted in chromium.

- We pour and separate, in a known manner, the ferro-chromium fuel and the slag exhausted.

For the implementation of the process, the solid carbonaceous reducing agent can preferably be coke, but also different types of natural carbon products such as hard coal, anthracite, lignites, charcoal.

One can, moreover, introduce various additives to adjust the composition of the final product, for example iron or iron ore if one seeks to produce a chromium cast iron, and also, additives to adjust the composition of the slag, for example to give it fluidity.

appropriate deity; taking into account the composition of the ore. This additive can be, for example, quartz.

The charge can be preheated by various known means, either in the reactor itself, by means of a gas or oil burner, or by pulverized solid fuel or, outside the reactor, using, at least partially, as a source of heat, the combustion gases recovered at the outlet of the reactor.

The chromium ore can be used in the raw state, simply crushed and mixed with the reducing agent, or in the form of agglomerate. In the latter case, the ore is finely ground and mixed with the carbon reducer, also
crushed. One can then agglomerate with the ball press, after possible addition of a binder of known type, or put the load in the form of pellets (or "pellets") by means of a conventional pelletizing plate, with addition of 5 to 15 ó of water. Drying of the pellets can be ensured by using, at least partially, the combustion gases from the reactor during operation.

The agglomerates can be loaded as such into the reactor or be prereduced in an auxiliary oven heated, at least partially, by the combustion gases of the reactor. The reduction rate can reach up to 90 m for chromium and up to 95 Ó for iron.

It is possible to control the flow of oxygen supplied to the temperature of the combustion gases, which is fixed at a predetermined value or at a range of values.

The inclination of the axis of the reactor with respect to the horizontal and the speed of rotation of the reactor around its axis are determined, so as to ensure the reduction of the ore in the minimum time, and not to cause excessive wear rapid refractory lining. We can operate with an inclination C (of the axis between 30 and 5 (10 relative to the horizontal, and a speed of rotation of a few revolutions per minute at the start, to homogenize the load and the temperature, and 15 at 25 rpm during oxygen blows, without these values being absolute limits.

FIG. 1 represents a reactor for implementing the invention.

 I1 comprises a substantially cylindrical metal casing (1), a lining (2), generally based on magnesia, a means of rotation (3) around its axis (4) and a means of tilting (not shown) around of two pin journals (5) fixed on the external metal casing.

The reactor is capped with a hood (6) connected to any known system for capturing and recovering combustion gases and dust (not shown). Oxygen is injected by a lance (7) which can be adjusted in inclination and in length of penetration into the reactor.

The fact that one can obtain an almost total reduction of the chromium ore while one breathes oxygen continuously on the load is explained at the same time by the use of a rotating reactor, in inclined position, and by the mode of insufflation of oxygen, on the surface of the load, at a relatively low angle of incidence.

The area of combustion of coke in oxygen is limited to the upper part of the charge. The heat given off is transmitted in part by conduction to the middle zone of the charge, and, in large part, by radiation and convection, to the part (9) of the refractory lining situated above the charge. Due to the rotation of the reactor, the heat accumulated in the zone (9) of the lining is, during the following half-turn, transferred, by conduction, to the lower part (10) of the load which, protected from the oxygen, and in the presence of the coke initially introduced, gradually undergoes a reduction in chromium and metallic iron.

The intermediate zone (11), between the lower reduction zone and the upper combustion zone is in substantially balanced conditions from the oxidation-reduction point of view.

The implementation of the invention is explained in the examples which follow, in which all the volumes of gas are expressed in cubic normometers.

Example 1
A reactor with a nominal capacity of 3 tonnes of steel is used, of substantially cylindrical shape, with a diameter of 1.35 m and a depth of 2.70 m, lined with refractory bricks based on magnesia.

2 tonnes of chromium ore are loaded (all coming, 0 to 100 mm) having the following composition
Cr203 39.2 0 (Cr / Fe = 1.45)
FéO 24.0 Ó
Si02 7.5 Ó
A1203 14.4 Ó
CaO 1.6%
MgO 11.7 Ó (+ various 1.6 S) and 400 kg of coke in pieces of 20 to 40 millimeters.

Firstly, preheating is carried out with a conventional burner with liquid or gaseous fuel, so as to bring the load to approximately 12,000 C. To ensure uniformity of temperature, the reactor is put into intermittent slow rotation (2 to 3 turns , every minute), the axis of rotation being inclined at about 40 relative to the horizontal. Towards the end of preheating, 400 kg of coke are added in pieces of 20 to 40 mm, to facilitate the initiation of the combustion reaction.

Then, the reactor is rotated at 12 revolutions per minute and blown, at the top of the charge, by means of a lance, oxygen at a rate of 10 m 3 / minute.

After having blown 300 in3 of oxygen, one reloads 200 kg of coke on the load, which is approximately 16000 C. From this moment, one controls the blowing of oxygen to the temperature of the combustion gases which one fixes at around 13000 C.

After having blown 200 m3 of oxygen, which corresponds substantially to the combustion of the 200 kg of coke, the temperature of the charge reaches approximately 17000 C. We again charge 150 kg of coke and we blow 150 m3 of oxygen, by slaving the temperature of the combustion gases at 13,000 C. After this blowing, the temperature of the charge rose to 1,700-180 ° C. and the metal and slag bath began to form.

The penetration of the lance into the reactor is then reduced, and it is inclined so that its angle of incidence with the plane of the charge is less than 150, to prevent oxygen from entering the charge. From this moment, we proceed by successive small additions of coke (100 kg) corresponding to blowing of 100 m3 of oxygen, to prevent the coke from being coated in slag and thus escaping combustion. We also load 50 kg of quartz intended for the fluidization of the slag. The temperature is maintained between 1800 and 18500 C. As soon as the whole of the charge is melted, the reaction accelerates and is manifested by gassing and foaming of the slag; the oxygen supply is reduced so as to maintain the temperature of the fumes between 600 and 8000 C.

It is checked on a slag sample that the exhaustion of chromium has been practically obtained, by the white color of the ground slag.

We can then pour into a pocket, then clean the slag and pour the metal into an ingot mold.

The entire operation, preheating, reduction and pouring, lasted 3.5 hours.

We recovered: 945 kg of metal at 54, 1 S of Cr and 8.4% of C (ie a chromium yield of 95.4) and 1050 kg of slag at 2.1 Ó of Cr203.

EXAMPLE 2
In the same reactor as in Example 1, pellets of agglomerated chromium ore were introduced, obtained by grinding the ore to a particle size of less than 0.5 mm, having the following composition
Ore. 100 parts by weight
Coke ............... 20 parts by weight
Bentonite * 3 parts by weight and pelletizing by means of a conventional pelletizing plate with the addition of 10 0 of water, followed by drying in an oven. The composition of the ore is identical to that of Example 1.

The 1600 kg of pellets are loaded with 150 kg of coke, in the reactor set in slow rotation (1 to 2 revolutions per minute). The reactor, which had just been used for a previous operation, was already at a temperature of around 12,000 C, which accelerated the preheating of the load. 150 kg of coke are added and oxygen is blown at the rate of 3 m3 per minute. After about an hour, the temperature rose to 14500 C. The rotation is then accelerated to 15 revolutions / minute, and loads of 150 and then 100 kg of coke are then added by blowing oxygen, at at the rate of 15 m3 per minute and at the rate of 100 m3 of oxygen per 100 kg of ceke. After blowing 400 m3 of oxygen, the temperature rose to 19,000 C. The oxygen flow is reduced and the temperature is maintained at 19,000 C, by controlling the oxygen flow so as to have a smoke temperature between 600 and 8000 C. 50 kg of quartz are then added, it is poured into a pocket, the slag is scoured and finally poured into an ingot mold.

400 kg of metal are obtained, having the composition
Chrome 62.74%
Carbon 9.12 X
Silicon .... 0.05 X
Iron and miscellaneous impurities: balance
Example 3
With the same ore and under the same conditions as in Example 2, 1600 kg of agglomerated pellets were prepared, which were dried and then reduced in a rotary oven, for two hours, using partially, as a heat source , the fumes and combustion gases from the reactor, which still contain a certain proportion of carbon monoxide. After two hours, it was noted that the rate of reduction of chromium was between 75 and 90, and the rate of reduction of iron, between 90 and 95 X.

The pre-reduced pellets were introduced into the still hot reactor, after a previous operation, with 100 kg of coke. Then, 100 m3 of oxygen were injected, at a flow rate of 3m3 per minute, the reactor being put into slow rotation (1 to 2 revolutions per minute), and we continued as in Examples 1 and 2, and we obtained 400 kg of fuel ferro-chromium having a composition substantially identical to that of Example 2.

Example 4
800 kg of agglomerates of chromium + coke, dosed with 22 X carbon and 100 kg of coke in pieces of 20 to 40 mm, are loaded into a reactor preheated to 10,000 ° C.

The mixture is heated to 12,500 C using a fuel-air burner while rotating, the reactor at 3 revolutions per minute for 2 hours. It is found that the charge thus treated has undergone a partial reduction of the iron and of the Cr contained (approximately 75 X of the Cr and 90 X of the Fe).

Then 750 kg of finely cut scrap is added, plus 200 kg of coke, the reactor is made to turn at 20 revolutions per minute and 400 m3 of oxygen are blown using the lance. This gives a metal bath covered with a slag at a temperature of 16500 C. 950 kg of "chromium cast iron" having the following composition are poured
Chrome ............ 15.97
Carbon 5.27% Silicon 0.05 0.05 ó
Balance iron
The implementation of the invention makes it possible to obtain, according to the types of ores used, and the possible additions, the whole range of ferro-chromium substantially saturated with carbon in equipment that is both simple, robust, and does not require d heavy investment, whose productivity is relatively high, and which can accommodate poor quality ores; reliable or very fine, heterogeneous, and solid carbon reducers of very diverse natures and of uneven quality.

This process can thus constitute an alternative to the electrometallurgical processes currently practiced.

Claims (9)

10) Process for the production of fuel chrome iron consisting in treating an ore with a solid carbonaceous reducer, at high temperature, in a reactor constituted by a substantially cylindrical refractory enclosure, able to rotate around its axis, the axis being tiltable in all positions from vertical to horizontal and the combustion gases from the solid carbonaceous reducer recoverable, characterized by the succession of the following stages - a charge of chromium ore and carbonaceous reducer is introduced into the reactor. - The load is brought to a temperature at least equal to 10,000 and preferably at least equal to 12,000 C by any known means. - A series of additions of solid carbonaceous reducer are introduced onto the charge, and oxygen is blown to cause the combustion of said additions, the reactor being rotated, its axis being inclined, until obtaining a liquid ferrochrome bath covered with a slag substantially depleted in chromium. - We pour, and we separate in a known way, the ferro-chrome and the spent slag. 20) A method of producing ferro-chromium fuel, according to claim 1, characterized in that there is also introduced into the feed, an additive intended to adjust the composition of ferro-chromium, such as iron or l 'iron oxide. 30) Process for the production of fuel ferro-chromium according to claim 1 or 2, characterized in that at least one additive intended to adjust the composition of the slag is introduced into the feed. 40) A method of producing ferro-chromium fuel according to any one of claims 1 to 3, characterized in that the solid carbonaceous reducing agent is chosen from coke, coal, anthracite, lignite, charcoal. 50) Process for the production of ferro-chromium fuel according to any one of claims 1 to 4, characterized in that the charge is brought to at least 1 0000 C and preferably to 12000 C by means of a liquid fuel burner or gaseous or solid pulverized.  60) Process for the production of ferro-chromium fuel according to any one  of claims 1 to 5, characterized in that the filler is prea  lably raised to 10,000 C and preferably at least 120 in C by  passage in an oven heated, at least partially, by gases  combustion from the reactor.  70) Process for the production of fuel-ferro-chromium according to any one  as in claims 1 to 4, characterized in that the load is  consisting of agglomerates of finely ground chromium ore,  crushed solid carbonaceous reducer and a binder.  80) Process for the production of fuel-ferro-chromium according to the claim  tion 7, characterized in that the agglomerates are previously duits.-  90) Process for the production of fuel-ferro-chromium according to the claim  tion 8, characterized in that the agglomerates are previously  pre-reduced in an oven heated, at least partially, by gases  combustion from the reactor.  POO) Process for the production of ferro-chromium fuel according to any one  as in claims 1 to 8, characterized in that the oxygen flow  is controlled at a predetermined temperature of the combustion gases  leaving the reactor.  110) Process for the production of fuel-ferro-chromium according to any one  as in claims 1 to 10, characterized in that the speed of  reactor rotation is between 1 and 25 revolutions per minute.