JP2706142B2 - Recycling method of steelmaking dusts in electric furnace with scrap preheating furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for recycling CaO-containing steelmaking dust, oil-containing and water-containing scales in an electric furnace having a scrap preheating furnace.

[Conventional technology]

In a steel mill, a large amount of dust is generated in a manufacturing process, and a dust collecting device for improving the environment is installed and collected.

Most of the collected dust contains valuable components such as Fe, Ni, and Cr, and is being reused as an iron source or an auxiliary material.

In particular, the amount of steelmaking dust generated in the steelmaking process is large, and it is required to reuse the entire amount.

The steelmaking dust has a lot of fine powder and needs to be aggregated into pellets and briquettes. When briquetting, it is necessary to provide a binder that provides crushing strength that can withstand handling up to an auxiliary raw material hopper and the like provided on the steelmaking furnace. The crushing strength varies depending on the handling conditions, but generally 7 kg / pellet or more that can obtain a powdering rate of 10% by weight or less when dropped from a height of 3 m is sufficient for practical use.

However, steelmaking dust contains CaO, and when its content is high, when briquetting is performed, the hydration reaction with water when added causes expansion and collapse after briquetting, and the granulated material ( Pellets) were powdered again, and the yield was low.

Japanese Patent Application Laid-Open No. 56-65670 discloses a method of adding water for stabilizing CaO, digesting CaO by a hydration reaction, and then performing a granulation treatment.

The steelmaking dust is dry dust collected by a dry dust collector.

On the other hand, in a rolling process, a pickling process, and the like, there is a sludge called B-scale, which is a fine powder which is collected by a wet dust collector, separated by a thickener or the like, and collected on the overflow side and difficult to dewater.

This B scale also contains valuable components, and is reused in the same manner as steelmaking dust. However, this B
The scale has a high moisture content, and it is necessary to dehydrate to make the moisture content suitable for granulation to enable handling for reuse.

Furthermore, since the B scale has a high oil content, the dust particles are covered with an oil film during granulation, making it difficult to contact with the binder, and the strength is insufficient. is necessary.

For this reason, oil-containing iron-containing sludge is tillage-dried using the sun, and then a mixture of a cement-based binder and dry powder is supplied in advance to granulate it. After kneading the dried powder and the dry powder, a method in which a mixture of a hardening agent and a dry powder containing no oil in advance are supplied and granulated is disclosed in JP-B-57-43622, JP-A-54-1979. It is disclosed in Japanese Patent Publication No. 107478.

As a dehydration drying method other than solar drying, there is a method of granulating after drying by the heat of oxidation reaction of FeO by grinding and kneading by utilizing the fact that converter dust contains a large amount of FeO. It is disclosed in Japanese Unexamined Patent Publication No. 58-140328.

Examples of the dust collected in addition to the steelmaking dust and the B scale include the following.

In the refining process, there is a shot scale with a large amount of coarse powder collected by a dry dust collector.

This contains a lot of shot grains, which are metallic iron components that have become fine powder due to wear and the like during shot blasting.

Also, in the rolling step, pickling step, etc., there is a large amount of coarse powder collected on the sedimentation side separated by a wet dust collector and separated by a thickener etc. There is a pit scale of the time.

The scales described above are relatively easy to handle and are often used alone.

A place where such dust and scales are reused is, for example, electric furnace steelmaking.

In this electric furnace steelmaking, for example, JP-B-63-49153
As disclosed in Japanese Unexamined Patent Publication, scrap preheating for reducing energy costs and effectively using the same is performed.

The preheating temperature for scrap preheating is generally 200-300 ° C
However, it has also been attempted to increase the temperature by providing two or more scrap preheating furnaces and sequentially heating them in a range where the cost required for preheating and the profit obtained by preheating are commensurate.

In such electric furnace steelmaking, when the above-mentioned dust and scales are used, the pellets are charged from the auxiliary furnace hopper on the electric furnace. It is considered to be advantageous from the viewpoint of effective utilization of input energy. Loading the pellets together with the scrap has the advantage that pellet recycling equipment such as an auxiliary raw material hopper is not required when reusing dust. However, for that purpose, in addition to the room temperature crushing strength, it is necessary to maintain the crushing strength such that the pellets are not powdered when charged into the electric furnace after preheating and the residual strength after heat treatment.

In the conventional granulation method, unfired pellets
Although no binder is added as described in -65670, a hydraulic cement binder in which the required amount of crushing strength can be obtained at least after a sufficient curing period has been disclosed. However, in an electric furnace having the above-mentioned scrap preheating furnace, when pellets using a hydraulic cement-based binder are preheated, CaO hydrate evaporates, and water rapidly disappears during preheating. As a result, the bonding strength of the cement decreases. There is also a problem that the brittle pellets are powdered by being exposed to a high-temperature preheating gas.

Further, when a hydraulic cement-based binder is used, there is a problem that a large indoor curing yard is required.

Further, there is a method of adding a mixed powder of a dry powder and a binder in a granulation step to form a pellet having a two-layer structure in order to remove the effect of the oil content for recycling B scale having a high oil content. .

However, this method has a drawback that the process and the equipment are complicated because the processing equipment for each of the dry and wet powders is required.

There is also a method of activating and drying the FeO contained in the FeO-containing powder, but it requires a grinding and kneading machine such as a ball mill which requires a long time to manage, and also requires time and effort to control the temperature.

[Problems to be solved by the invention]

The problem to be solved in the present invention is to solve the problems at the time of processing for recycling valuable waste such as the above-mentioned conventional steelmaking dust. By producing the necessary room temperature crushing strength and utilizing the preheating process of electric furnace steelmaking, it is possible to produce unfired pellets that can further increase the crushing strength without being powdered even when exposed to the high-temperature gas and scrap. An object of the present invention is to provide a recycling method that can be used in an electric furnace having a preheating furnace.

[Means for solving the problem]

The method for recycling steelmaking dust in an electric furnace having a scrap preheating furnace according to the present invention includes a step of adding water while stirring CaO-containing steelmaking dust to cure and form a granulated raw material; A water glass of 3 to 7% by weight is added, and a process of granulating and curing by moisture-mixing and kneading, and a step of charging the granulated material after curing into a preheating furnace containing scraps, to a preheating temperature of the scrap. Heating and then charging it into the electric furnace together with the scrap.

Further, the present invention can be used for reuse of a water-containing scale together with CaO-containing steelmaking dust.

That is, the step of using the granulated raw material as the granulated raw material can be a step of mixing the CaO-containing steelmaking dust with oil-containing and water-containing scales dehydrated to a water content of 50% by weight or less, curing the mixture, and curing the mixture.

Further, in the step of using the granulated raw material, the CaO-containing steelmaking dust can be mixed with an oil-containing scale and a water-containing scale dehydrated to a water content of 50% by weight or less, cured, and then mixed with the dried organism.

[Action]

In the present invention, water is added while stirring CaO-containing steelmaking dust, or a mixture containing a water-containing scale is stirred to disperse water in the dust, thereby promoting the CaO hydration reaction and digesting CaO. Curing for 1 to 2 days to stabilize to obtain a granulated raw material having a water content of 2 to 10% by weight, and utilizing the reaction between water glass and CaO hydration product added during granulation. Thus, the hardening of the pellet can be promoted, and the hardness can be greatly increased by preheating the pellet.

If the water content of the oil-containing and water-containing scale in the step of using the above-mentioned granulated raw material exceeds 50% by weight, it is difficult to handle the kneading machine and this method is uneconomical, so that the water content of the water-containing scale is 50% by weight. It is specified below.

The mixing ratio of the granulated raw materials is 50% for CaO-containing steelmaking dust.
If the content of oil-containing and water-containing scales is less than 20% by weight, the content of undigested CaO becomes excessively higher than that of the hardening reaction by water glass in the next step, and causes expansion powdering during preheating.
If the amount exceeds 10% by weight, the water content becomes excessive, the curing time becomes longer, and the margin of the added amount of water glass in the next step decreases.

The amount of water added in the process of forming granulated raw material is 3% by weight
If it is less than 10%, undigested CaO remains, and after the granulation, the hydration reaction of the undigested CaO occurs, causing expansion and pulverization of the pellets.If it exceeds 15% by weight, the water content becomes excessive and the curing days become longer,
The margin of the added amount of water glass in the next step is reduced.

While supplying the granulated raw material to a rolling granulator such as a pan pelletizer, the granulated material is subjected to humidity control and kneading so that the pellet moisture after granulation is 10 to 15% by weight, and granulated. After pelletizing, hydrated Ca (OH) ₂ and xCaO, SiO ₂ .nH ₂ O
Is reacted with water glass to cure the sodium silicate to cure the pellets, and then cured for one day or more. By using water glass as a binder that does not powder even if it is blown to a preheated gas of residual strength and high heat after heat treatment,
Starting with the B scale, which is difficult to process, various types of dust collection powder having different properties generated in an iron mill can be subjected to a collective granulation process collectively.

The water glass used in the present invention is used for forming a die mold using 2CaO · SiO ₂ as a curing agent, and its curing mechanism is based on the following reaction.

_{CaO + H 2 O → Ca (} OH) 2 Ca (OH) 2 → Ca 2 + 2OH - The Ca ²⁺ occur gelation of sodium silicate by the presence of ions, the reaction scheme is as follows.

Na ₂ O, SiO ₂ .nH ₂ O + 2CaO, SiO ₂ → 8CaO, SiO ₂ .nH ₂ O + SiO ₂ + NaOH The above reaction is said to proceed in a shorter time as the temperature is higher. By the way, although the steelmaking dust fluctuates in a considerable range depending on the operating conditions of the electric furnace, etc., 9 to 20 wt%
It contains CaO, of which free CaO is present at 2 to 10% by weight.

Therefore, when water glass is used as a binder for the pellets in the reuse of steelmaking dust in an electric furnace having a scrap preheating furnace, a reaction similar to the above-described curing mechanism occurs.

If the amount of water glass added in the granulation step is less than 3% by weight, the residual strength after heat treatment is insufficient, and if it exceeds 7% by weight, it becomes uneconomical. The total water content when added exceeds the water content that can be granulated, making granulation impossible.

Room temperature crushing strength of the pellets treated in the above process is
Cured after 5 days after granulation, 10kg / pellet or more, and residual strength after heat treatment after high-temperature preheating at 900 ° C of 10kg / pellet or more, and the powdering rate of 5% by weight or less can be obtained. .

〔Example〕 Example 1 A steelmaking dust having a CaO content of 10.5% by weight shown in Table 1 was subjected to a granulation treatment according to the process shown in FIG. 1, and was used in an electric furnace after preheating. CaO-containing steelmaking dust mixing tank length 2500m
While supplying the powder to a pug mixer of 7 m, 7% by weight of water was added to 100% by weight of the dust, dispersed and mixed, and allowed to stand in a pallet for 1 day to perform natural curing. After curing, the water content was 2% by weight.

Transfer the granulated material after curing from the pallet to the hopper,
1500mm inner diameter, 250mm depth, 10r rotation speed using vibration feeder
While continuously supplying 1T / hr to the Pam pelletizer at pm, JIS3
No. water glass is added 6% by weight based on 100% by weight of the granulated raw material, and moisture-kneaded and kneaded so that the pellet moisture after granulation is 13 to 14% by weight to obtain pellets having a particle size of 10 to 15 mm. Was.

The pellets were allowed to stand on a pallet for 5 days to perform natural curing. After curing, its room temperature crush strength was 12.8 kg / pellet.

The cured pellets were transferred from a pallet to a charging chute, and the pellets were charged onto scraps previously stored in a preheating bucket having a connection portion for a high-temperature exhaust gas passage from an electric furnace in an upper lid as a preheating furnace.

Next, cover the upper lid, connect the high-temperature exhaust gas inlet pipe, pass the gas into the bucket,
After the primary heating to 0 to 300 ° C, the supply of the high-temperature exhaust gas was stopped, and after the tapping of the electric furnace, the preheated bucket was transferred to a standby electric furnace furnace port, and the pellets and scraps were transferred to the electric furnace. After charging into the inside, secondary heating was performed at 700 to 900 ° C., and then melting was performed.

Also, during the melting operation, the steelmaking dust collected was not found to have increased particularly as compared with the case where no pellet was used.

In addition, a part of the above pellets was taken out, and the residual strength after the heat treatment and the daily change of the room temperature crushing strength were examined.

Residual strength after heat treatment uses pellets for 5 days of curing period,
It is charged into the Erema electric furnace, heated to 900 ° C. by the heating pattern shown in FIG. 6, and kept at each temperature for 10 minutes.
The test pellet was taken out, its crushing strength (residual strength after heat treatment) was measured by a universal testing machine, and the strength was estimated during the heating before melting in the preheating furnace and the electric furnace.

The result is shown in FIG. From the figure, the residual strength after heat treatment increased significantly from 12.8 kg / pellet at room temperature to 23.8 kg / pellet at 300 ° C, showing the characteristics of water glass at 700 ° C.
However, it is presumed that when the pellets were heated and heated to a high temperature, the hydrate of CaO decomposed and evaporated to form fine nests inside the pellets.

If the temperature exceeds 900 ° C., the pellets are presumed to be sintered, thereby increasing the strength. FIG. 5 shows the daily change of the room temperature crushing strength.
8.9 kg / pellet, enough strength to withstand handling.

Example 2 A steelmaking dust having a CaO content of 10.5% by weight and an oil-containing, water-containing scale A, B and a pit scale shown in Table 1 were subjected to granulation by the process shown in FIG. After preheating, it was treated in an electric furnace.

A scale, B scale, and pit scale are each accumulated in the outdoor yard for one month, drained, mixed and collected with a cultivator with a shovel, and then dried in the sun for 5 days, and mixed and stirred with the cultivator. And dehydrated to a water content of 21% by weight. 50% by weight of the dewatered mixed raw material and 50% by weight of CaO-containing steelmaking dust were supplied to a high-speed stirring type mixer having an inner diameter of 2500 mm, dispersed and kneaded, and sufficiently mixed. . After curing, its water content was 8.3% by weight.

Transfer the granulated material after curing from the pallet to the hopper,
Add 6 wt% of JIS No. 3 water glass to 100 wt% of granulated raw material while continuously supplying at 1T / h to a pan pelletizer with an inner diameter of 1500 mm, depth of 250 mm, and rotation speed of 10 rpm using a table feeder. Of the pellets was adjusted to a moisture content of 10 to 12% by weight to obtain pellets having a particle diameter of 10 to 15 mm.

The pellets were allowed to stand on a pallet for 5 days to perform natural curing. After curing, its cold crush strength was 14.2 kg / pellet.

The cured pellets were transferred from a pallet to a charging chute, and charged onto scraps stored in a preheating bucket in advance.

Next, the lid was covered, a high-temperature exhaust gas inlet pipe was connected, the gas was passed into the bucket, and the scrap was discharged.
After the primary heating to 0 to 300 ° C., the supply of the high-temperature exhaust gas was stopped, the preheating bucket that performed the preheating was transferred to the standby furnace opening, and the pellets and scrap were charged into the furnace.
Secondary heating was performed at 700 to 900 ° C., and then melting was performed.

Also, during the melting operation, it was not recognized that the steelmaking dust collected was particularly increased as compared with the case where pellets were not used.

A part of the pellet was taken out, and the residual strength after the heat treatment and the chronological change of the room temperature crushing strength in Example 1 were determined.
Investigated in the same manner as. The results are shown in FIGS.

As is clear from those figures, the same tendency as in the first embodiment is shown.

Example 3 Granulation was carried out using the dusts and scales shown in Table 1 by the steps shown in FIG. 3, and after preheating, they were used in an electric furnace.

A-scale, B-scale and pit scales, which are oil-containing and water-containing scales, are each accumulated in the outdoor yard for one month, drained, mixed and accumulated with a cultivator equipped with a shovel, and dried in the sun for 5 days. The mixture was mixed and stirred by a cultivator and dehydrated to a water content of 22% by weight. 50% by weight of the dewatered mixed raw material and 50% by weight of CaO-containing steelmaking dust
The mixture was supplied to a 500 mm high-speed stirring type mixer, dispersed and kneaded, and sufficiently mixed. After that, the mixture was allowed to stand in a pallet for 1 day to perform natural curing. After curing, its water content was 9.4% by weight.

90% by weight of the mixed raw material after curing and 10% by weight of a shot scale, which is a dry scale, are supplied to a pug mixer having a mixing tank length of 2500 mm by a conveyor, and dispersed and mixed to form a granulated raw material having a water content of 8.5% by weight. This is 1500m inside diameter
JIS No. 3 water glass was added 7% by weight to 100% by weight of granulated raw material while continuously supplying at 1T / h to a pan pelletizer with m, depth 250mm, and rotation speed 10rpm.
The mixture was conditioned and kneaded so as to have a concentration of 13 to 14% by weight to obtain pellets having a particle size of 10 to 15 mm. The pellets were allowed to stand on a pallet for 5 days to perform natural curing. After curing, its cold crush strength is 14.7
kg / pellet.

The cured pellets were transferred from a pallet to a charging chute, and charged onto scraps stored in a preheating bucket in advance.

Next, cover the upper lid, connect the high-temperature exhaust gas inlet pipe, pass the gas into the bucket,
After primary heating to 0 to 300 ° C., the contents were charged into the electric furnace, and then secondary heated to 700 to 900 ° C., followed by melting operation.

Also, during the melting operation, it was not recognized that the steelmaking dust collected was particularly increased as compared with the case where pellets were not used.

A part of the pellet was taken out, and the residual strength after the heat treatment and the chronological change of the room temperature crushing strength in Example 1 were determined.
Investigated in the same manner as. The results are shown in FIGS.

As is clear from those figures, the same tendency as in the first embodiment is shown.

In the present embodiment, the dry scale is added after kneading and curing the oil-containing and water-containing scale and the CaO-containing steelmaking dust, but may be added when the oil-containing and water-containing scale is dehydrated.

Comparative Example A pellet was produced by the treatment process of the third example of the present invention using a cement-based binder instead of the water glass of the present invention as a binder, and was used in an electric furnace after preheating. Portland cement was used as the cement binder, and 15% by weight was added to 100% by weight of the granulation raw material.

Further, similarly to each example of the present invention, a part of the above-mentioned pellet was taken out, and the post-heat treatment residual strength and the normal temperature crushing strength were examined over time. The results are shown in FIGS.

From Fig. 4, the residual strength after heat treatment increased from 5.9 kg / pellet at room temperature to 8.4 kg / pellet at 300 ° C, but slightly increased to 300 ° C.
Over 1.9 kg / pellet, even at 900 ° C
It is almost flat at 2.1kg / pellet and cannot withstand handling after heating.

In addition, during the melting operation, it was recognized that the amount of steelmaking dust collected increased compared to when pellets were not used. The reason is that when heated, the moisture quickly disappears from the cement binder and its strength cannot be maintained,
It is presumed that the powder was further exposed to high-temperature gas and rapidly powdered.

From FIG. 5, it is considered that the room-temperature crushing strength of the cement-based binder tends to increase as the curing days become longer, which is considered to be because the strength of the pellets largely depends on the hydraulic property of the cement. As described above, the curing mechanism of the reaction between the glass and the components of the granulation raw material is completely different.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(1) Water or a water-containing scale is mixed with steelmaking dust in advance, and the CaO contained in the steelmaking dust is digested and stabilized by a hydration reaction, and water generated by the hydration reaction by using water glass as a binder. In addition to obtaining the required crushing strength in a short time by the hardening reaction of the water glass, the pellets are heated in a preheating furnace to further increase the crushing strength and are exposed to hot air for preheating. There is a synergistic effect of not being powdered.

(2) Since the required crushing strength is developed at an early stage, the curing space for pellets after granulation can be significantly reduced.

(3) Dust generated from an electric furnace steel mill, etc., and those with different scale properties, particle size distributions, etc. are mixed and complement each other as granulation raw materials to obtain dense pellets. Can be reused effectively.

[Brief description of the drawings]

FIG. 1 to FIG. 3 show processing steps in each embodiment of the present invention. FIG. 4 is a diagram showing the residual strength after heat treatment of the pellets treated according to each example and the comparative example. FIG. 5 is a diagram showing the daily change of the room-temperature crushing strength of the pellets treated according to each of the examples and the comparative examples, and FIG. 6 is a diagram showing a heating pattern of an Erama electric furnace for examining the residual strength after heat treatment of the pellets. is there.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Ueda 2-25-1 Shimada, Hikari-shi, Yamaguchi Prefecture (72) Inventor Masakazu Yamaguchi 1508-5, Oji, No. 1-8-5, Yawatanishi-ku, Kitakyushu-shi, Fukuoka (72) Inventor Takafumi Nagamatsu 1-9-6 Kogura, Kokurakita-ku, Kitakyushu-shi, Fukuoka

Claims (3)

(57) [Claims] 1. A process in which water is added to a CaO-containing steelmaking dust while stirring to cure the granulated raw material, and a granulated raw material is added, and 3 to 7% by weight of water glass is added to 100% by weight of the granulated raw material. , Kneading, kneading, granulating and curing, putting the cured granules into a preheating furnace containing scraps, heating them to the scrap preheating temperature, and charging them together with the scraps into an electric furnace. A method for recycling steelmaking dusts in an electric furnace having a scrap preheating furnace. 2. An electric furnace having a scrap preheating furnace according to claim 1, wherein the step of forming a granulated raw material comprises mixing and curing an oil-containing and water-containing scale dehydrated to a water content of 50% by weight or less with CaO-containing steelmaking dust. For recycling steelmaking dust in Japan. 3. The method according to claim 1, wherein the step of forming a granulated raw material comprises mixing a CaO-containing steelmaking dust, an oil-containing and water-containing scale dehydrated to a water content of 50% by weight or less, and curing.
A method for reusing steelmaking dust in an electric furnace having a scrap preheating furnace for mixing the living organism and the dry scale.