JPH09263846A - Method for recovering available metal in dust and/or sludge from stainless steel producing process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective coke adding method for treating dust and/or sludge produced in a stainless steel producing process with an electric furnace. SOLUTION: At the time of executing smelting reduction by briquetting the dust and/or the sludge containing available metals and adding the coke into this briquette, the adding quantity of the coke used to the reduction is adjusted to a quantity corresponding to the coke adding quantity (kg/T-dust, sludge) of 0.75-0.90 calculated by A [ 2.6(%total Fe/0.7773)+3.3 (%Cr2 O3 )+2.9 (%NiO)]. Further, the coke used to the reduction is adjusted so that the total of wt. ratio of each grain size of the coke mixed within the following range becomes 100%. The grain sigz and the blending ratio of the coke are <=10mm at 5-20%, 10-15mm at 35-50%, 15-20mm at 25-40% and >20mm at <=10%, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of waste such as dust and sludge generated from each process in the production of stainless steel, and more particularly to the F contained in this waste.
The present invention relates to a method for adding coke to an electric furnace in electric furnace smelting for efficiently and stably recovering valuable metals such as e, Ni and Cr.

[0002]

In the production of stainless steel, electric furnaces,
A large amount of valuable metals such as Fe, Ni, and Cr are contained in sludge generated from dust in gas discharged from processes such as a converter and VOD process and waste liquid from pickling process of stainless steel plate. Therefore, discarding these dusts and sludges as wastes is not desirable from the viewpoint of resource saving and pollution prevention. Therefore, many technologies have been proposed for treating dust and sludge and recovering valuable metals in them. Japanese Patent Publication No. 62-2013 is known as a typical prior art relating to the treatment of dust and sludge generated in the stainless steel manufacturing process. Japanese Examined Patent Publication No. 62-2013 discloses a smelting method in which, when treating dust and sludge in an electric smelting furnace, the particle size of added coke is adjusted according to the composition of the dust and sludge in order to stabilize the furnace condition. are doing. In order to put dust or sludge into an electric furnace, it is necessary to turn the dust and sludge into briquettes or pellets using a briquette or granulator. used. If the amount of slag is unreasonably small due to the composition of dust and sludge, or the ash content of coke is too small, slag material such as silica stone or limestone is added, and a part of the coke is added to the briquette. Sometimes. In the case of dust and sludge treatment, sulfur in the molten metal of the hearth is expressed by weight ratio [% S] relates to various factors such as basicity of slag, hearth temperature, and coke addition amount as a reducing agent. Sulfur [% S] in the molten metal is one of the indicators of the stability of the furnace because it shows the overall results of the electric furnace operation.

[0003]

If the coke grain size is selected according to the composition of the briquette in order to maintain a good furnace condition, cokes for each grain size suitable for each composition are prepared. The cost disadvantages such as sieving, mixing equipment for particle size adjustment, coke storage for each particle size, and overall increase in work load increase. In the case of a briquette composition that requires coarse-grained coke, the electrical resistance in the furnace decreases as the coarse-grained coke increases. Therefore, the electrode must be pulled up, and the thermal energy to the hearth Can't concentrate. In the case of an electric furnace, the main component of the reaction of valuable metals in the oxide form is the direct reduction of coke in the hearth.
Pulling up the electrode increases heat dissipation, resulting in a decrease in thermal efficiency, that is, an increase in power consumption and a decrease in processing capacity.
The basic amount of coke added is the amount necessary to remove the oxygen bound to the metal to be recovered, so it varies depending on the composition of the dust and sludge to be treated, and the coke in the furnace
In order to maintain a stable operation for a long period of time without excess or deficiency, the amount of effort must be constantly monitored and great efforts must be made to respond to fluctuations.

In order to solve the above-mentioned problems, the present invention provides a method for easily determining an appropriate amount of coke added to a change in dust and sludge composition, and a particle size of the added coke most effective for the reaction. It proposes a configuration.

[0005]

That is, the above-mentioned object is achieved by charging dust and sludge made into briquette and an amount of coke corresponding to the following equation into an electric furnace. Amount of coke = A {2.6 (total Fe / 0.7773) +3.3 (% Cr ₂ O ₃ ) +
2.9 (% NiO)} where the coke amount is (Kg / T-dust, sludge)
, (% Total Fe / 0.7773) is the weight% of the total Fe charged into the furnace, (% Cr ₂ O ₃ ), (% NiO) are the respective weight% of the dust and sludge raw material compositions, and a is a number in the range of a = _{0. 75~0. 90.}

At this time, the coke to be used has a coke particle size and a weight ratio of 10 mm or less ... 5-20% 10-15 mm ... 35-50% 15- 20 mm ... 25-40% 20 mm or more ... 10% or less, and further adjust so that the total weight ratio of coke of each particle size is 100%. Is to use.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the above formula for determining the amount of coke added, a coefficient for Fe, a coefficient for 2.6, a coefficient for Cr, 3.3,
The coefficient of Ni content, 2.9 is the reduction coke, the carbon remaining in the molten metal, and the reduction coke of the Si content that inevitably enters the molten metal. The total amount of coke added to each component is further corrected by the coefficient A. As will be described later, A is a coefficient experimentally obtained for briquettes having different compositions. A is about 0.83 and A = 0.75 to 0.90
In a relatively wide range, the power consumption rate (KWH / T-dust, sludge) is close to the minimum, and the composition fluctuates during operation, resulting in excess or deficiency in the amount of coke corresponding to that composition. If it is in the designated range of A, the operation can be continued with the electric power consumption rate close to the minimum value in the composition.

That is, if the amount of coke required for the treatment of a briquette is calculated by using A = 0.83 in the above equation, some fluctuation of the composition when it reaches the hearth and melts Of course, it is not necessary to consider, and even if the coke amount for the former briquette calculated by A = 0.83 is directly applied to the briquette of other composition, the latter amount for this coke amount is If the numerical value of A calculated back from the composition is within A = 0.75 to 0.90, stable operation can be continued. Therefore, the coke amount calculated by applying A = 0.83 to the center of the specified range of A for the typical composition of dust and sludge to be treated contains Fe, Cr, and Ni oxides of other dust and sludge. If the composition region within A = 0.75 to 0.90 is determined in advance in the combination of the amounts, the amount of dust and sludge in that region may be added by the coke amount of the previously determined representative composition. It is possible to save the trouble of calculating the coke amount corresponding to the composition variation each time.

At this time, since the coke grain size affects the reactivity, the coke grain size structure also affects the excess or deficiency of the coke. The fine-grained coke has good reactivity and high electric resistance, so if the proportion of fine-grained particles is large, the insertion depth of the electrode can be sufficiently secured and the power consumption rate decreases. However, a large amount of fine particles is not preferable because the fine particles are easily discharged outside the furnace together with the slag, and are also discharged as dust together with the exhaust gas. Therefore, we examine the appropriate grain size range and propose the following coke grain size composition.

10 mm or less ... 5 to 20% 10 to 15 mm ... 35 to 50% 15 to 20 mm ... 25 to 40% 20 mm or more ... 10% or less Each grain The diameter cokes are mixed within the weight ratio range shown here, and the weight ratios of the particle size cokes are 100% in total.

[0011]

【Example】

(Embodiment 1) FIG. 1 is a schematic view of an electric smelting furnace according to an embodiment of the present invention.
Is inserted into. The briquette 3 together with the coke 4 is charged into the furnace top of the furnace body 1 and sequentially descends to the hearth. The briquette was prepared by a usual method. That is, the pulp waste liquid is added as a binder to the dust and sludge collected from each step of stainless steel production, and the mixture is mixed into a briquette through a briquetting machine. Molten metal 5 accumulated in the hearth is taken out through an outlet 7. The molten metal 5 is covered with the slag 6 in a molten state. By the above work, the briquette containing valuable metals as shown in Table 1, a and b are treated, and the amount of added coke is displayed by using three types of parameters. KWH / T-dust, sludge). That is, (1) dust per ton and sludge Ton
Coke basic unit, (2) Magnification of the amount of added coke to the theoretical amount of coke required for reducing the valuable metal oxide contained, and (3) Amount of coke required for reduction of each metal oxide individually. The same ratio to the sum of the above, that is, the coefficient A, A = coke addition amount / {2.6 (% total Fe / 0.7773) +3.3 (% Cr
₂ O ₃ ) +2.9 (NiO}, where the unit of coke addition is (kg / T-dust, sludge).

[0012]

[Table 1]

In the method (1) in which the composition of the briquette to be treated is not taken into consideration, the amount of coke added to obtain the minimum electric power consumption rate greatly varies depending on the variation of the briquette composition. That is, it is necessary to constantly pay attention to the excess and deficiency of coke in the operation. The ratio of the excess coke amount to the theoretical coke amount required for reduction (2) takes into account the briquette composition, so the position showing the minimum power consumption unit is larger as the coke consumption unit display (1) is. Although it does not fluctuate, when there is an excess or deficiency in the optimum amount of coke, the power consumption rate increases rapidly. Strict monitoring for fluctuations and strict adjustment of coke addition amount are required. (3), which has an A value on the horizontal axis, shows a minimum value at A = 0.80 and 0.82 for group a and b respectively, and A =
In the range of 0.75 to 0.90, the power consumption rate was close to the minimum. Therefore, if the coke addition amount is determined at the central value 0.83 of A = 0.75 to 0.90, even if the coke amount is applied to briquettes having other compositions falling within the above range, the optimum condition is obtained. Can be operated at.

(Example 2) With respect to a briquette produced by using the electric furnace used in Example 1 and performing the same pretreatment as in Example 1, the grain size composition of the coke to be added is the power consumption unit. The influences given are shown in Table 2. Example 2 is a case where the particle size constitution shown in the table is selected from the range of the particle size distribution allowed for each particle size and the coefficient A is 0.80.

[0015]

[Table 2]

(Embodiment 3) Although it is within the allowable range, Embodiment 2
Example 3 in Table 2 shows the result of an experiment similar to that of Example 2 using a coke having a grain size configuration different from that of A = 0.86. Example 1 when the coke grain size is appropriate
In both No. 2 and No. 2, the electric power consumption rate was about 900 KWH / T-dust and sludge or less, and the sulfur [% S] in the molten metal showed that the furnace condition was stable.

(Comparative Example) An experiment was carried out on a briquette produced by the same process as that of the example using the electric furnace used in the example. Comparative Example 1 in Table 2 has a substantially proper coke grain size composition, but is an example in which the addition amount does not reach the range of the allowable A value.
Sulfur [% S] in the molten metal is also large and the
This indicates that the concentration of bon is insufficient, and at the same time, the power consumption rate is also large.

In Comparative Example 2, the ratio of coke having a large grain size was large, and the electric power consumption rate was increased even if A was a proper value because the electrode was pulled up because the electric resistance decreased.

In Comparative Example 3, the grain size composition is proper, but when the coke is added in excess of the proper value of A, the electric power consumption rate is inferior to that of the above-mentioned Examples.

[0020]

According to the present invention, dust containing valuable metals,
When recovering valuable metals by treating sludge with an electric furnace, it is possible to easily determine the amount of coke added that can operate at the most economical power consumption rate, even if the composition of dust and sludge fluctuates.
At that time, the unit of electric power can be reduced by determining the granularity of the coke to be used according to the present invention, and a stable furnace condition for a long period can be secured.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electric smelting furnace according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between parameters of coke addition amount and electric power consumption rate.

[Explanation of symbols]

 1 Electro-smelting furnace main body 2 Electrode 3 Briquettes 4 Cokes 5 Molten metal 6 Molten slag 7 Molten metal outlet

Claims (2)

[Claims] 1. A valuable metal-containing dust and / or sludge is formed and melt-reduced together with coke and optionally a slag-forming agent to recover valuable metal in the dust and / or sludge. In the above method, the addition amount of coke used for reduction is the addition amount of coke (Kg / T-dust, sludge) = A {2.6
(% Total Fe / 0.7773) +3.3 (% Cr ₂ O ₃ ) +2.9 (% NiO)}, A = 0.75 ~
A method for recovering valuable metals in dust and / or sludge generated from a stainless steel manufacturing process, characterized by adjusting the amount to 0.90. 2. The coke used in the reduction according to claim 1, wherein the coke particle size and the weight ratio thereof are 10 mm or less ........ 5 to 20% 10 to 15 mm .. -50% 15-20 mm ... 25-40% 20 mm or more ... 10% or less, and the total weight ratio of coke of each particle size is 100%. The method for recovering valuable metal of dust and / or sludge generated from the stainless steel manufacturing process according to claim 1, which is used after being adjusted.