JPS6167727A - Method for melting and reducing chrome ore - Google Patents

Abstract

PURPOSE:To melt and reduce without expensive electric power by selecting the relation between the existed amount of coke in a melt-reducing furnace and an oxygen blow speed of said furnace enhancing the second combustion ratio and reheating a chrome ore in a rotary kiln. CONSTITUTION:A coke 39 and a lime stone 41 are added to a chrome ore pellet 40 loaded internally with carbon component in a rotary kiln 21, preheated and supplied to a melt-reducing furnace 22. In the furnace 22, a coke and a flux are added from a hopper 26 and molten, deoxidized by oxygen blowing from a tuyere 23, lance 25. At this time, a production amount of slag in the furnace 22 is >=approximately 300kg/t-metal, the relation between the oxygen blow speed and the existed amount of coke in the furnace is selected to be >=50% of the second combustion ratio [CO2%/(CO%+CO2%)]X100% and the high temperature exhausted gas is induced in the kiln 21 for preheating. At the same time, NOx in the exhausted gas and a hexad chrome in dust are deoxidized to solve a peroxide problem.

Description

Detailed Description of the Invention (Industrial Application Field) This invention pre-reduces chromium ore or chromium oxide, for example, in a rotary kiln, and the semi-reduced product obtained in this pre-reduction process is subjected to top-bottom blowing. This method is used to melt and reduce chromium ore by charging carbonaceous materials, flux, and oxidizing gas into a converter-type reaction vessel, and can suppress the production of sulfur oxides and nitrogen oxides to extremely low levels. Regarding the method.

(Prior Art) Conventionally, high chromium alloys, such as ferrochrome containing 50 parts or more of Cr, have been used as chromium ore in a low shaft type electric furnace as disclosed in Japanese Patent Application Laid-open No. 138.418/1983! has been produced by heating, melting, and reducing the semi-reduced product. However, this method has the following problems.

(1) Since expensive electricity is used as reduction energy, manufacturing costs are high, especially in Japan.

(2) Cr CI) in the slag discharged outside the furnace is 2~
It has a high ratio of 5, and the chrome loss is thick. C in the broken slag
The high r% limits the range in which the slag can be used effectively.

Therefore, we developed the so-called smelting reduction method, which replaces the reduction energy with primary energy that is cheaper than electricity (particularly the heat of combustion of carbonaceous solids such as coal and coke). If conditions can be found to sufficiently reduce the cost, the advantage would be enormous.

Therefore, the inventors proposed in Japanese Patent Application No. 53-66939 (Japanese Unexamined Patent Publication No. 54-158320 No. 111) a method for melting chromium ore in which electric energy was partially replaced with energy (coke, etc.) as the reduction energy. A reduction process was proposed.

This process uses equipment consisting of a combination of a pre-reduction furnace such as a rotary kiln and a top-bottom blown converter reactor to produce high chromium alloys from chromium ore or chromium oxide. The process involves preliminary reduction of chromium ore or chromium oxide to obtain a semi-reduced product, and a top-bottom blown converter type reaction of the semi-reduced product of chromium ore or chromium oxide, carbonaceous material, flux, and oxidizing gas. The method consists of a step of supplying the chromium ore or chromium oxide to a container and melting and reducing the chromium ore or chromium oxide.

(Problems to be Solved by the Invention) In the melting and reduction process of chromium ore, etc. using the above-mentioned top-bottom blown converter reactor, the heating and melting of raw materials, the energy for reducing oxides, etc. It must be supplied by the oxidative exotherm of the material.

In the case of Zorothes, which relies on the heat generated by oxidation of carbonaceous materials for the energy for reducing metal oxides, the problem is how low the amount of sulfur oxides or nitrogen oxides produced can be suppressed. The technical problem of this invention is to pre-reduce chromium ore or chromium oxide using equipment consisting of a combination of a pre-reduction furnace such as a rotary kiln and a top-bottom blowing converter type reaction vessel.
The object of the present invention is to provide an operating method that can suppress the production of sulfur oxides and nitrogen oxides in the subsequent melting and reduction process.

(Means for Solving the Problems) The technical problem of this invention as described above is that molten iron, pre-reduced chromium ore granules, carbonaceous materials and oxygen In the smelting reduction process in which oxides are reduced and melted by supplying chromium ore, the secondary combustion rate in the reaction vessel is set to 50% or less, and the high-temperature exhaust gas from the reaction vessel is used to pre-reduce chromium ore. A method for melting and reducing chromium ore, which is characterized in that the chromium ore is preheated in the kiln, and the dust contained in the exhaust gas from the reaction vessel is reduced together with the chromium ore in the kiln. nru.

The present invention will be explained in detail below.

This invention is implemented using, for example, the equipment shown in FIG.

An example of equipment used to carry out the present invention is shown in FIG.
6 is carbon material, hotz+ for flux, 27 is bath water, 2
8 is slag, 29 is chromium pellet, 30 is carbon material, 31
3 is a bubble, 32 is a pellet storage tank, 33 is a scoop feeder for lime, 34 is a scoop feeder for coke, 35 is an air port, 36 is a raw material chute, 37 is an exhaust fan, 3
8 is a pellet discharge port and a smelting-reduction furnace generated gas path, 39
40 is coke, 40 is pellets, 41 is limestone, 42 is an air nozzle, 43 is a blower, 44 is a pressure measuring device in a tuyere pipe, and 45 is an exhaust gas analyzer f. This equipment consists of a combination of a rotary kiln 21 and a top-bottom blowing converter type melting reduction furnace 22. First, the rotary kiln 21 is mainly operated using exhaust gas emitted from the smelting reduction furnace as fuel, and heats various raw materials charged into the smelting reduction furnace 22. For example, after pulverizing chromium ore and carbonaceous materials such as coke, the rotary kiln 21 is formed into pellets. Pre-reducing some of the iron oxide and chromium oxide by heating the charcoal-filled chromium pellets to obtain preheated semi-reduced pellets; It is used to preheat wood, preheat lime used as flux, and roast limestone. The rotary kiln 21 can also utilize the sensible heat of the high-temperature gas discharged from the bath fusion reduction furnace 22, and can raise the heating temperature compared to other types of pre-reduction furnaces to reduce chromium oxide, which is difficult to reduce. Since the furnace is heated by 50 to 70 degrees, it is suitable as a preheating pre-reduction furnace using exhaust gas. By using this, as a result of preheating and preliminary reduction of the raw material, it is possible to reduce the amount of heat generated per production amount required in the melting reduction furnace. For example, the chromium content in chromium ore is 7.
If it is possible to charge the coke into the smelting reduction furnace in a state in which the iron and coke are pre-reduced and preheated to 1000°C, compared to the case where the coke is charged without preheating or pre-reducing. The required calorific value in the melting reduction furnace (this is generated by burning carbonaceous material with oxygen) may be about 30%. In addition, if most of the iron content in the chrome pellets charged into the smelting reduction furnace is pre-reduced, the (T, Fe%) of the slag produced when the pellets are melted in the smelting reduction furnace can be lowered. It also has the effect of reducing erosion. Furthermore, it is possible to increase the rate constant in the zero-order reaction zone of the pellets introduced into the melting reduction furnace, which is advantageous in advancing the reduction reaction.

The smelting reduction furnace 22 receives pre-reduced chromium pellets and a flux mainly composed of charcoal lime such as coke, melts them, and reduces residual chromium and iron oxides. The reaction progresses, and finally chromium-iron alloy melt and MgO-5102-CaO-AZ2
This is a device for obtaining slag containing 03 as the main component. The converter shape is convenient for achieving strong stirring of the slag, which is essential for the progress of the reaction. A tuyere 23 (there may be a plurality of tuyeres) for blowing oxygen-containing gas from the bottom and a top blow lance 24 for blowing oxygen into the furnace from above are attached.

The function of the bottom blowing tuyere is to adjust the temperature of the metal by blowing oxygen-containing gas into the metal, and as a result, achieve strong stirring of the slag through stirring of the metal. Accordingly, metal removal is performed to adjust the carbon content of the finished product. Stirring alone can be done using an inert gas such as Ar or nitrogen, but in that case, it is preferable to use a gas containing oxygen because of the gas cost for stirring and the loss of sensible heat carried out of the system by stirring. is advantageous. In order to blow gas containing oxygen into metal,
For example, by using a double pipe lining, a small amount of hydrocarbons can be released from the outer pipe.
Blow a cooling gas such as Ar + N2 to protect the tuyere from melting.

Oxygen supply from the top blowing lance is the main means of controlling the exothermic conditions in the smelting reduction furnace. The shape of the nozzle is determined by the amount of oxygen to be supplied, the size of the furnace, the exhaust gas conditions, etc. It is possible to adjust the distance between the lance tip and the slag surface according to the operating conditions. The shape of the smelting reduction furnace is basically similar to a normal steelmaking converter, but (1) ) If there is a large amount of slag produced due to the composition of the ore used, the diameter of the upper part where the slag accumulates should be made larger than the part where the metal accumulates to reduce the relative thickness of the slag; (2) the furnace. If increasing the secondary combustion rate within the reactor places a large load on the refractories in the upper part of the furnace, countermeasures are taken such as creating a water-cooled structure for that part.

The best refractory material for the smelting reduction furnace is magnesia cardinal brick for the lower half of the furnace (the part that is almost always exposed to slag and metal). For the upper half of the furnace (the part exposed to the co-co□-based high-temperature gas atmosphere), magnesia charcoal brick or chromium magnesia brick is also suitable. Which is best depends on the exhaust gas CO/
It depends on what value is selected as the CO2 ratio (from the operation of the smelting reduction furnace, any value can be taken within the range of CO/CO2≧0.3).

Note that a pellet storage tank is provided between the rotary kiln and the bath melting furnace as a buffer for matching the two as necessary. Either the rotary kiln is operated on an irregular basis to match the raw material supply and main turn required from the smelting reduction furnace, or the equipment consists of a combination of one rotary kiln and two smelting reduction furnaces. In the case where the raw material supply pattern is stabilized as the sum of two units by shifting the operation cycles of the two units, the storage tank can be made smaller or even removed.

The operating method using the above equipment is as follows.

The rotary kiln is equipped with carbon and charged with Taflom ore pellets and coke lumps, and uses high-temperature gas from the smelting reduction furnace as the heat source. Heavy oil and other fuels are added as needed, and the air nozzle 42, air port Combustion is controlled by supplying air or oxygen-enriched air through a furnace such as 35, and the temperature range of the grain cylinder in the kiln is maintained at 1400° C. or higher, which is necessary to promote the reduction of chromium.

It is desirable to supply all of the carbon material required by the bath smelting furnace through a rotary kiln, except for some adjustment purposes. This is because increasing the amount of carbon in the kiln prevents re-oxidation of the pellets in the high temperature range, making it possible to maintain a high reduction rate of the chrome pellets supplied to the smelting reduction furnace. This is because the material itself is preheated, which improves the thermal lance of the smelting reduction furnace. However, if it becomes a problem that the amount of gas at the kiln outlet cannot be lowered to a sufficiently low value because there is a large amount of carbon material charged to the kiln, some of the carbon material may be scooped out from the middle of the kiln, for example. It may be supplied by a feeder.

Depending on the composition of the chromium ore and carbonaceous materials used, the flux may be lime, and if necessary, silica stone or CaO and 510
A slag containing 2 (e.g., generated in a stainless steel manufacturing process) is added to a smelting reduction furnace. These fluxes are added almost in proportion to the amount of chromium pellets added, or they are added in advance rather than in proportion to the amount of chromium pellets added, taking into consideration the time required for slag formation.

These fluxes may be directly charged into the melting reduction furnace from the hopper 26, but they may also be charged after being preheated through a rotary kiln. In particular, it is also possible to use limestone as the lime source, roast it in a kiln, and feed the preheated quicklime to the smelter reduction furnace.

However, if there is a risk that the chromium pellets and flux will react with each other in the kiln, lowering the melting point and forming a layer in the kiln, the flux should be added near the bottom of the kiln through the scoop feeder 33, or the flux should be preheated. Alternatively, a separate preheating device may be used for roasting.

Note that rotary kiln operation is difficult when the storage tank is large, or when two smelting reduction furnaces are operated with staggered operation cycles and the sum of pellets supplied to them is almost constant over time. Operate close to steady state. In other cases, unsteady operation is performed to match the raw material supply pattern required from the smelting reduction furnace.

When starting up a smelting reduction furnace, it can be charged with iron or iron-chromium molten metal obtained from another melting furnace, or with coke and mold pig iron or solid ferrochrome and blown acid to produce metal. Dissolve and use as seed water. From the second heat onwards, for example, 80 or more of the slag generated in Moe heat and about 2/3 of the high chromium m hot water are tapped out, and about 1/3 of the amount of Akigaku bath water is left in the furnace as seed hot water. Continue operations.

In the course of continuing research on melting and reducing chromium ore or chromium oxide using a top-bottom blown converter reactor, the inventors discovered that
It has been found that there is a significant correlation between the secondary combustion rate and the generation of sulfur oxides (SOX) and nitrogen oxides (NOx). This is shown in FIGS. 2 and 3.

The sulfur source of SOx is mainly input coke (charcoal material). As is clear from FIG. 2, when the secondary combustion rate exceeds 50%, the amount of SOX generated increases rapidly.

Apparently, the secondary combustion rate can be changed largely depending on the combination of the blowing acid conditions and the amount of coke remaining in the furnace.

On the other hand, if the amount of SOx generated increases during the finishing reduction stage, although the sulfur (S) in the slag decreases, (S)/[S]
Since Fi does not change much, sulfur [8] in the metal does not decrease much.

On the other hand, if the amount of SOx generated does not increase in the final reduction period, (S 2 )/[S 2 ) increases in the final reduction period, so that [S] decreases on the contrary.

As described above, if the secondary combustion rate is too high, the number of SOx generation caps increases, but the desulfurization ability of the slag decreases, so there is a drawback that [8] this does not lead to a decrease.

The nitrogen sources of NOx are coke (charcoal material) and air entering the furnace. As shown in FIG. 3, the amount of NOx generated has a clear correlation with the secondary combustion rate (CO2/(CO+Co2)), and increases rapidly when the secondary combustion rate exceeds 50 to 60.

Furthermore, even under the same secondary combustion rate, the amount of NOx generated during the smelting reduction period is lower than that during the final reduction period because heat is removed from the coke surface by the chromium reduction reaction and the degree of superheating of the coke is reduced. It is thought that.

1, there is a tendency for the amount of NOx generated to increase as the amount of residual coke increases. This is thought to be because the introduced coke stays on the slag surface for an increased amount of time, making it easier to overheat.

Thus, in order to reduce the amount of NOx generated, it is desirable to reduce the secondary combustion rate and the degree of superheating of coke.

Next, the amount of dust generated from the top-bottom blowing converter type reaction vessel is 30 to 50 g per INm3 of the furnace gas, and this dust contains a high proportion of chromium.

In the process of this invention, high-temperature exhaust gas from the melting and reduction process in the top-bottom blown converter type reaction vessel is introduced into a preliminary reduction furnace such as a rotary kiln to preheat the chromium ore.

The chromium ore is agglomerated together with carbonaceous material, and further subjected to solid phase reduction (preliminary reduction) in the presence of exterior coal.

The outer coal is charged into a top-bottom blown converter reactor together with the pre-reduced chromium ore pellets, but the dust that was present in the high-temperature exhaust gas from the top-bottom blown converter reactor is also removed. It is reduced and charged into a top-bottom blown converter reactor together with the outer coal.

By doing so, the dust containing chromium can be reduced and transferred into the chromium alloy without leaving the system.

(Example) Rated amount of molten metal (i.e. amount of bath water immediately before tapping) is 50 tons
Using two top-bottom blowing converters as reaction vessels, ferrochrome was produced using semi-reduced chromium pellets as a raw material.
3 (approximately 33 tons) was tapped, leaving 1 and V3 in semi-continuous operation. Four bottom blowing tuyeres (double tubes with an inner tube diameter of 20 m) are installed at the bottom of the melting reduction furnace, with pure oxygen flowing through the inner tube and zolopane gas flowing through the outer tube as a protective gas. The top blowing lance has a total of 7 nozzles (1 hole in the center and 6 holes around the periphery).

Chromium ore, which is the main raw material for smelting and reduction, is extracted from a mixed powder frame and granulated into pellets along with coke, and after drying, it is charged into a rotary kiln, and the high-temperature gas emitted from the smelting and reduction furnace is used as a heating source to pre-reduce, preheat, and dust. We made a reduction. The 80% of carbon material supplied to the smelting reduction furnace is charged into the rotary kiln as outer coal to improve the reduction rate of the semi-reduced pellets and to preheat the carbon material to be supplied to the smelting reduction furnace. The rotary kiln operates normally. (kiln rotation speed 0.4r,
p, m, pellet steady continuous discharge). The pellets are fed to one of the two melting reduction furnaces using a distribution device.

The average composition and temperature of the semi-reduced chromium pellets supplied to the smelting reduction furnace are as follows.

T, Cr: 35%, T, Fe: 23%, Cr reduction rate: 66%, iron reduction rate: 92%%MgO: 10
Person, Az,, o3: 10%, 810□: 9%,
Temperature 1 [1300℃.

-Smelting reduction smelting first stage- Preheated reduction pellets, carbonaceous material, and lime are charged into 17 tons of remaining hot water while blowing oxygen-containing gas from the top and bottom.

The acid blowing speed is 14000 Nm3/hr for top blowing and 1 for bottom blowing.
60 ONm''/hr x 4. The charging rate of the prereduced pellets is adjusted so that the temperature of the molten alloy phase is controlled between 1580 and 1630°C.

64 tons of semi-reduced pellets and 20 tons of carbon material in 45 minutes.

Coal 7. Charge Ot. During this first stage of smelting reduction smelting, the amount of blown acid from the top blowing lance and the amount of carbonaceous material supplied were controlled in order to keep the secondary combustion rate below 40 coefficients.

The slag composition, amount and temperature at the end of this period are as follows.

CaO: 25%, 8102: 26%, MgO:
19%, At20. : 19%, T-Cr
: 6.8%, T, Fa: 1.1%, Slag i
l: 36 t, temperature: 1630°C.

The amount of metal is 45t1 and the amount of free carbon material I is 3t.

-Second phase of smelting reduction smelting- The supply of semi-reduced pellets is stopped, and 100 kg of carbonaceous material is introduced into the bath smelting reduction furnace every 3 minutes from the carbonaceous material supply hole. The bottom blown oxygen amount was kept constant, and the top blown acid amount was changed every 5 minutes to 850 ONm3/hr and 400 ONm3/hr.
hr s ONm"/hr to promote reduction of Cr in the slag. Metal temperature is 1600 to 163
It was maintained in the 0°C range. During this second stage of smelting reduction smelting,
The amount of oxygen sent from the top blowing lance was controlled in order to keep the secondary combustion rate below 40 coefficients.

The amount of free carbon material/the amount of bath molten slag is in the range of 60 to 100 kg/l.

The final slag composition of the bath melting furnace was: CaO: 28%, S
IO2: 28%, MgO=20%
, A t203: 20%, T, C
r: O 15%, T, Fe: 0.7%.

of slag throughout this period. At203 = 18-20 section is within the range of

The components of the tapped metal are as follows.

Cr: 53%, Fe: 37%, C: 6.5%, S
I: 05, S: 00015qb, P: 0.
0035 width.

In this way, the first stage of smelting reduction is 45 minutes, while the second stage is 15 minutes, the decarburization stage is 20 minutes, the slag and hot water are tapped for 1°, and the time required to supply pellets to each smelting reduction furnace is as follows. The time during which pellets were not fed was 45 minutes, and the operations of one rotary kiln and two melting reduction furnaces were matched.

(Effects of the Invention) As described above, the present invention has improved the production method of ferrochrome, which has conventionally been carried out using expensive electric power as energy.
It is a smelting reduction method that maintains the generation of SOx and NOx at extremely low levels and uses inexpensive carbonaceous materials and oxygen as a heat source, and it is also able to achieve a higher chromium recovery yield than the conventional electric furnace method. It has a great industrial effect in that it is possible to supply ferrochrome, which is cheaper than the conventional method.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of an apparatus for carrying out this invention, Fig. 2 is a diagram showing the correlation between the secondary combustion rate and the amount of SOX generated in the process of this invention, and Fig. 3 is a diagram of this invention. FIG. 3 is a diagram showing the correlation between the secondary combustion rate and the amount of NOx generated in the process. (”dd) X09 (Wdd) x□H

Claims (1)

[Claims] Molten iron is placed in a reaction vessel that can blow oxygen-containing gas from the top to the bottom.
In the melt reduction process in which granules of pre-reduced chromium ore, carbonaceous material, and oxygen are supplied to reduce and melt oxides, the secondary combustion rate in the reaction vessel is set to 50% or less, and the introducing the high-temperature exhaust gas into a kiln for pre-reducing chromium ore, preheating the chromium ore in the kiln, and reducing dust contained in the exhaust gas from the reaction vessel together with the chromium ore in the kiln. A method for melting and reducing chromium ore, which is characterized by: