JPH0776382B2 - Method for producing chrome sinter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a sinter of chromium, and more particularly to a production method in which the amount of a solvent added is devised.

[Conventional technology]

Chromium ore is useful as a raw material for ferrochrome, which is an additive for steel and the like. However, it is difficult to obtain lumpy chromium ore, and it is generally supplied as a fine-grained, fine-grained, or powdered product.

On the other hand, if such a powdery chromium ore is put into a ferrochrome refining furnace as it is for reduction refining, the furnace condition becomes extremely unstable, and in particular the gas permeability generated by the reaction in the furnace deteriorates suddenly. It is known that various gases are blown up and the ore is scattered, resulting in various adverse effects such as a decrease in product yield and an increase in power consumption.

Therefore, in order to improve the operability of the smelting furnace, attempts have been made to agglomerate the powdery ore particles of chromium ore.

Conventionally, the methods proposed to agglomerate such a powdery granular ore are roughly classified into (i) a briquetting method, (ii) a pelletizing method, and (iii) a sintered ore. Method etc. Of these, the methods (i) and (ii) have the drawbacks that the manufacturing process is complicated, the manufacturing cost is high, and it is difficult to obtain a stable quality product. Therefore, the method (iii) is most suitable. Considered an excellent method.

Chromium sinter is usually produced by a Dwightroid type or Grinwald type sinter. Since chromium ore itself is difficult to melt, it is necessary to add a solvent containing CaO, SiO ₂ , MgO, etc. in advance to make it easily soluble. The medium solvent functions to melt by the heat of combustion of coke added during the production of sinter to form slag, and to be immersed between chrome ores to maintain the bonding force between the chrome ores. That is, the structure of the produced chrome sinter is
In other words, the structure is such that chrome ore is used as an aggregate and molten solvent medium is used as a binder.

It is important to increase the bond strength between chrome ores in order to improve the yield and strength of the product sintered ore. Therefore, it is necessary to promote the formation of effective molten slag.

Examples of such a method for producing a chrome sinter include the inventions of Japanese Patent Publication Nos. 10685/50, 51-4922, and 59-7770.

First, the invention of the first Japanese Examined Patent Publication No. 10685/1975 is to add coke to chromium ore with a fine grain size, and then add a medium solvent with a fine grain size, and then burn with a Grinwald type sintering machine or a Dwightroid type sintering machine. Disclosed is a method of sintering a chromium ore consisting of binding, and
Using those containing 60 wt% of MgO and 30 to 60 wt% of SiO _2.

The invention of the second Japanese Patent Publication No. 51-4922 also discloses a similar method for producing a chromium sinter, but SiO ₂ as a medium solvent is added to
30 wt%, CaO 20-55 wt% and MgO 10-30 wt%
It uses what it contains.

Furthermore, in the invention of the third Japanese Examined Patent Publication No. 59-7770, (a) powdered coke 3 to 10% by weight, return ore 40% by weight or less, powdered limestone 3 to 15 is added to granular chromium ore 50 to 80% by weight. weight%,
Blended with 2-10 wt% silica sand, or (b) 3-10 wt% powdery coke, 40 wt% or less of return ore, 5-20 wt% powdered limestone, 3-15 wt% powdered fluorspar Add 2 to 10% of water to the blended material to make a raw material for sintering, and use the same sintering machine as above to produce (a) CaO-SiO ₂ based slag or (b) CaO-CaF ₂ based slag. A method of forming and sintering is disclosed.

[Problems to be Solved by the Invention]

However, the solvent and solvent having the compositions and blending ratios disclosed in these methods can improve the product yield of the chrome sinter ore and have some effect in imparting sufficient strength to the sinter. However, it was not yet perfect, and it was necessary to devise and optimize the component and addition amount of the solvent.

Therefore, the present inventors have examined the effect of the solvent mixture on the yield and strength from many experimental results, and found that the proper solvent mixture is CaO and SiO _{2 in} the ratio of CaO and SiO ₂ to chromium ore.
The present applicant proposes a method for producing a chrome sinter having a total amount of O ₂ of 35% by weight or more and a ratio of CaO to SiO ₂ within a range of 0.8 to 1.6. -97332. According to this method, it is possible to improve the yield of the sintered ore as a product (60% or more of the product yield of 5 mm or more) and to increase the strength of the sintered ore (tumbler index of 60 or more).

However, the proper blending of the solvent and solvent set in the method according to the above-mentioned prior application is only to increase the product yield and strength of the chromium sinter ore, and no consideration is given to the reducibility of the ore. It was not done.

In a ferrochrome refining furnace such as an electric furnace, ferrochrome is produced by reducing iron oxide and chromium oxide in chromium ore with a carbonaceous material such as coke.
The reduction reaction mainly proceeds at the interface between the slag and the carbonaceous material in which the chromium sinter is melted, but as described later (Example),
Although the refractory chromium ore particles gradually dissolve, they exist in the form of dispersion in the molten slag phase derived from the solvent until the end of reduction. The reduction rate is greatly influenced by the physical properties of the molten slag (eg viscosity, solubility of Cr oxide, etc.). In other words, the reducibility of the chromium sinter greatly depends on the composition of the molten slag phase, that is, the composition of the solvent medium. Therefore, in the production of chrome sinter, the reduction reaction in the smelting furnace is promoted and the productivity and yield are improved by optimizing the mixing of the additive solvent to improve the reducibility of the sinter. At the same time, it is important to reduce the energy used.

Therefore, the main object of the present invention is to provide a chromium sinter with a proper mixture of additive solvents based on comprehensive quality control that adds reducibility, which is as important as yield and strength as the quality of chrome sinter. It is to provide a method for producing ore.

[Means for Solving the Problems]

 MEANS TO SOLVE THE PROBLEM This invention which solved the said subject is as follows.

Powdered chromium ore and powdered solvent containing CaO and / or SiO ₂ as a main component under the following conditions (A), (B) and (C)
Is added so as to satisfy the above condition, and powdered coke is further added and kneaded, followed by sintering with a Dwightroid type or Grinwald type sintering machine to obtain a sintered ore having excellent reducibility. Method for producing chrome sinter.

Here, F _i : amount of the slag-making agent of the i-th type (kg / ton chromium ore) (CaO) _i , (SiO ₂ ) _i , (Al ₂ O ₃ ) _i , (MgO) _i : i CaO in th type Zokasu _{agent, SiO 2, Al 2 O 3} , MgO content (wt%) where the subscript i represents the i-th type of slag agent, k is the type forming agent Represents a number.

(CaO) _o , (SiO ₂ ) _o , (Al ₂ O ₃ ) _o (MgO) _o : CaO, SiO ₂ , Al ₂ O ₃ , MgO content in chromium ore (wt%) [Function] The present invention Improves product yield and strength,
Reducibility (melt-reducibility in refining temperature range of about 1550 to 1700 ℃), which has not been paid attention in the quality control of conventional chromium sinter.
In order to improve this, various studies have been conducted, and it is important to set the amount of solvent added so as to satisfy the above conditions (A), (B) and (C). There was found.

Satisfying the above conditions (A) and (B) is 5m
It is important to obtain a sintered ore having a product yield of m or more of 60% or more and a strength of 60 or more in the tumbler index. However, for this purpose, the upper limit of formula (A) is 1.
6 is enough.

When the conditions (A) and (C) are satisfied, good reducibility is obtained in the refining temperature range.

[Specific Examples of Invention]

 The present invention will be described in more detail below.

The solvent used in the method of the present invention is not limited as long as it mainly contains CaO and / or SiO ₂ effective for welding chromium ore. Examples thereof include materials such as forochrome slag, chrome bulb (water extraction residue of soda oxidation combustion product of chrome ore), coal stone, silica sand, fluorspar, serpentine, and various other slag and minerals. Actually, it is properly selected according to the composition of various solvent medium itself,
It is compounded and used so as to satisfy the conditions (A) and (C).

The particle size of this solvent is preferably as small as possible from the viewpoint of melt formation, but if it is about 3 mm, it can be used without problems.

〔Example〕

Next, the reasons and effects of numerical limitation of the present invention will be clarified by examples.

To a chromium ore raw material having the composition and particle size distribution shown in Tables 1 and 2, a solvent and powder coke having a particle size of 3 mm or less were added at a predetermined ratio, kneaded well, and then charged into a 30 kg test sintering pot. , The sintered ore sample was fired.

Limestone powder, silica sand, serpentine, and blast furnace slag were used as the solvent, and various types of sinter samples were prepared with varying amounts. After measuring the yield (product ratio of particle size of 5 mm or more) of the produced sinter, strength sample (tumbler JIS method)
Also, it was subjected to a smelting reduction test. Samples for 3 charges were prepared for various sintered ores, but for the 2nd and 3rd charges, products with a grain size of 5 mm or less were used as return ores.

The smelting reduction test is in the refining temperature range of ferrochrome 15
The method of investigating the reaction rate with carbonaceous material was used at 60 to 1710 ℃. That is, 100 g of chromium sinter sample with a grain size of 10 to 15 mm is dropped from the top into a graphite crucible (inner diameter 70 mm, outer diameter 90 mm, height 200 mm) heated to a predetermined temperature in N ₂ atmosphere, and the amount of CO gas generated Was used. The charged chromium sinter rapidly heats and melts, and the iron oxides (FeO) and chromium oxides (Cr ₂ O ₃ ) contained are reduced by the graphite crucible, which is a carbon material, to generate CO gas. To do. The reduction reaction formula is represented by formula (1).

(Fe, Mg) (Cr, Al) 2 O 4 + 4C = Fe + 2Cr + (MgO) + (Al 2 O 3) + 4CO (g) ...... (1) where, by continuously measuring the flow rate and the CO concentration of the exhaust gas Thus, the generation rate of CO gas can be obtained, and the reduction rate and reduction rate of the chromium sinter can be calculated by the equation (2).

Where Or: amount of reduced oxygen in chromium sinter sample (mole-O) _t : reduction rate at time t (min) (mole-O / min) R _t : reduction rate at time t (%) W: chrome firing Weight of sinter sample (g) (FeO) _O : FeO content in chromium sinter sample (wt%) (Cr ₂ O ₃ ) _O : Cr ₂ O ₃ content in chrome sinter (wt%) Co _t : CO concentration in exhaust gas at time t (%) CO _t-1 : CO concentration in exhaust gas at time t-1 (%) G _t : Exhaust gas flow rate at time t (Nl / min) Measurement time is 2 hours, After the measurement, the graphite crucible cooled in the N ₂ stream was taken out and the condition inside the crucible was observed. As a result, the parts that were considered to have reacted (the entire bottom surface of the crucible and a part of the side surface) were worn out so as to be thinly scooped out. And the generated metal droplets were attached. Therefore, the reduction reaction rate per unit interfacial area was calculated using the measured area of the worn portion of the crucible wall as the reaction interfacial area between the molten slag and the carbonaceous material (graphite crucible).

(Example 1) FIG. 1 and FIG. 2 show the results of measuring the step size (product ratio of +5 mm) and the strength (tumbler JIS method) of the manufactured chrome sinter. It was found that both the yield and the strength depended largely on the composition of the added solvent medium, but were almost unaffected by the composition of MgO and Al ₂ O ₃ , and were almost determined by the composition of Ca 0 and SiO ₂ . It has been found that the appropriate solvent-solvent compounding conditions that can improve the yield (60% or more of the product of 5 mm or more) and the strength (60 or more by the tumbler index) are as follows.

(Example 2) Further, a smelting reduction test was carried out on a part of the manufactured chromium sinter, and the influence of the solvent-solvent blending on the reducibility was investigated. Table 3 shows the composition of the sintered ore samples used in the test. Based on sample A, B to E are added CaO and SiO
CaO and S with the total amount of ₂ being constant (350 to 400 kg / ton Cr ore)
The ratio of iO ₂ (CaO / SiO ₂ ) is changed, and F and G are
The total amount of CaO and SiO ₂ was changed while keeping CaO / SiO ₂ constant (1.0 to 1.2). Further, H and I are obtained by adding a relatively large amount of MgO.

An example of the test results is shown in FIGS. All of these results are experimental results at 1650 ° C. Figures 3, 5 and 7 show changes in the reduction process, and Figures 4, 6 and 8 show changes in the reduction reaction rate per unit interfacial area with the reduction process. Similar experiments were conducted at 1560, 1610, 1658, and 1710 ° C in addition to 1650 ° C. The reaction rate increased with increasing temperature, but the change with the progress of reduction and the effect of sinter composition (solvent mixture) Is the temperature range (15
A similar tendency was observed at 60 to 1710 ℃.

As shown in Figs. 3 and 4, CaO / SiO ₂ (CaO
And the ratio of the added amount of SiO ₂ ) is significant, and CaO / SiO ₂
It was found that the same tendency was shown in the range of 0.8 to 1.3, while the reaction rate was remarkably reduced outside the range.
In the case of CaO / SiO ₂ = 0.6, the reaction rate gradually increased with the progress of reduction, but this is a result of the contact area (reaction interface area) with the crucible wall increasing because the molten slag vigorously formed. Almost no such foaming occurred in other sinter samples. It is considered that such a severely forming sinter may cause troubles (flooding, poor slag, etc.) in the refining furnace. From the results of the third and fourth experiments, the proper CaO / SiO ₂ (ratio of CaO and SiO ₂ ) of chromium sinter from the viewpoint of reducibility is
It was found to be 0.8-1.3.

Next, the results of examining the effect of the total amount of added CaO and SiO ₂ on the reduction rate are shown in FIGS. It was found that the smaller the amount of (CaO + SiO ₂ ), the more markedly the reduction rate decreases with the progress of reduction.

Figures 7 and 8 show the effect of adding MgO. It was found that the addition of MgO significantly reduced the reaction rate.

An experiment was also conducted in which the reagent Al ₂ O ₃ was added to the chrome sinter ore A, but it was found that the reaction rate remarkably decreased when Al ₂ O _{3 was} added.

The above experimental results, in order to produce a chromium sinter having good reducibility must be properly blended medium solvent, CaO and the ratio of SiO ₂ to be added as appropriate formulation ranges 0.8 It was 1.3, and there was a lower limit for the total amount of CaO and SiO ₂ , and an upper limit for the addition amounts of MgO and Al ₂ O ₃ .

(Example 3) When slag in the smelting reduction test was subjected to quench sampling and observed under a microscope, undissolved chromium ore particles ((Fe, Mg) (Cr, A) in the molten slag phase derived from the solvent until the end of reduction were obtained.
l) ₂ O ₄ ) was found to be dispersed. As the reduction progressed, the diameter of undissolved chromium ore particles became smaller, and the shape was found to be rounded. Further, when the molten slag phase portion was analyzed by XMA (X-ray microanalyzer), it was confirmed that the Al ₂ O ₃ and MgO concentrations increased with the progress of reduction. From the above, under the test conditions assuming ferrochromium refining conditions, the smelting reduction of chromium sinter is (1) in the solid-liquid coexisting state in which chromium ore particles are dispersed in the molten slag phase derived from the solvent medium. proceed. (2) As a result of gradual dissolution of chromium ore particles as the reduction progresses, Al ₂ O ₃
It was found that the concentrations of MgO and MgO in the molten slag phase increased.

It is considered that the reduction reaction rate is affected by the change in the physical properties due to the composition change (increased Al ₂ O ₃ and MgO concentration) in the molten slag phase with the progress of reduction. Therefore, FIGS. 9 and 10 show the relationship between the reaction rate and the (Al ₂ O ₃ + MgO) fraction in the molten slag phase by arranging the experimental results shown in FIGS. 6 and 8. Since it is difficult to measure the composition of the molten slag phase during the reduction process, the dissolution of chromium ore particles progresses in a manner proportional to the reduction rate, and as a result, (Al
₂ O ₃ + MgO) concentration was assumed to increase, and calculation was performed using the following formula.

Where X: (Al ₂ O ₃ + MgO) fraction in the molten slag phase F _i : Addition amount of i-th type solvent solvent (kg / ton Cr ore) (CaO) _i , (SiO ₂ ) _i , (Al ₂ O ₃ ) _i , (MgO) _i : i-th type solvent CaO in a _{solvent, SiO 2, Al 2 O 3} , MgO content (wt%) where the subscript i represents the i-th type of slag agents, k represents the number of types of forming agent.

Shown in CaO chromium _{ore, SiO 2, Al 2 O 3} , MgO content (wt%) Figure _{9: (CaO) O, (} SiO 2) O, (Al 2 O 3) O, (MgO) O As described above, the relationship between the smelting reduction rate and the (Al ₂ O ₃ + MgO) fraction in the molten slag phase of the three types of chromium sinter having different total amounts of added CaO and SiO ₂ was in good agreement. In the case of sinter containing MgO, the Mg content in the molten slag phase depends on the amount added.
Although the ratio of O and Al ₂ O ₃ was different, it was found that the relationship was almost the same as shown in FIG.

The smelting reduction test results shown above and other experimental results (experimental results with different concentrations, etc.) were statistically processed to determine the proper composition of CaO / SiO ₂ = 0.8-1.3 sinter ore. The following reaction rate approximation formula applicable in the temperature range of 1560 to 1710 ℃ was derived.

= 10 ⁴ × (1.367−2.463X) × Exp (−68950 / kT) where: Reduction reaction rate (mole−O / min.cm ² ) X: (MgO and Al ₂ O ₃ ) content in the molten slag phase Rate (-) k: Gas constant (= 1.9872 cal / deg · mole) T: Temperature (° K) In the above equation, the reaction rate is 20% or less compared to the X = O state (reduction rate maximum). Is regarded as a stagnation state of return, the maximum value of X that does not cause a stagnation of return is calculated to be 0.45. In order to maintain high yield and productivity in the ferrochrome smelting furnace, it is necessary to complete the reduction promptly without causing reduction stagnation. In the relation of the above equation, when the reduction rate is 100%, X is It must be 0.45 or less. That is, it is necessary to satisfy the condition of the following equation.

As described above, from the test results described in the examples, the yield, the appropriate range of the additive solvent based on the comprehensive quality control of the chromium sinter considering the reducibility considering the reducibility in addition to the strength, It was confirmed to be the above (A) to (C).

〔The invention's effect〕

As described above, according to the present invention, not only the yield and strength of the product can be improved, but also the reducibility is remarkably improved.

[Brief description of drawings]

Fig. 1 is a graph examining the effect of solvent agents on product yield, Fig. 2 is a graph examining the effect of solvent mixture on strength, and Figs. 3, 5, 7 are the results of smelting reduction tests (reduction progress). 4), Fig. 4, 6 and 8 are changes in the reaction rate with the progress of reduction, and Figs. 9 and 10 are the reduction rate and the molten slag phase (MgO + Al
₂ is a relational diagram with ₂ O ₃ ) fraction.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-58-91148 (JP, A) JP-A-58-213837 (JP, A) JP-A-52-46317 (JP, A) JP-A-53- 7522 (JP, A) Japanese Patent Sho 51-4922 (JP, B2) Japanese Patent 59-7770 (JP, B2)

Claims (1)

[Claims] 1. A chrome ore powder containing CaO and / or SiO ₂
A powdery solvent containing as a main component the following conditions (A), (B)
And (C) are added so that the powdered coke is added and kneaded, and then sintered by a Dwightroid type or Grinwald type sintering machine to obtain a sintered ore having excellent reducibility. A method for producing a chromium sinter that is characterized. Here, F _i : amount of the slag-making agent of the i-th type (kg / ton chromium ore) (CaO) _i , (SiO ₂ ) _i , (Al ₂ O ₃ ) _i , (MgO) _i : i CaO in th type Zokasu _{agent, SiO 2, Al 2 O 3} , MgO content (wt%) where the subscript i represents the i-th type of slag agent, k is the type forming agent Represents a number. (CaO) _o , (SiO ₂ ) _o , (Al ₂ O ₃ ) _o , (MgO) _o : CaO, SiO ₂ , Al ₂ O ₃ , MgO content in chromium ore (wt%)