JP2002136998A - Method for dehydrating slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for efficiently dehydrating a slurry constituted of a powder containing iron oxide or an iron compound generated in the iron industry. SOLUTION: In the method for dehydrating the slurry of the powder containing an iron compound powder with an average particle size of 1.5-40 μm by compressing the same by a dehydrator constituted of circulating and moving endless loop-shaped filter cloth and a pair of compression rolls arranged above and under the filter cloth, the number of rotations of the compression roll on the surface side carrying the slurry of the filter cloth is set to a range of <=50 rotations per min and the pressing force of the compression roll is 9,000 N or more per 1 m of the contact length of the compression roll and the filter cloth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dewatering a slurry containing iron oxide generated from a reduction, refining, rolling, pickling process or the like in the steelmaking industry. In particular, the present invention relates to a technique for facilitating dehydration of a slurry composed of powder having a small particle size.

[0002]

2. Description of the Related Art In the steelmaking industry, a large amount of dust and sludge containing iron oxide and the like are generated in large quantities because a large amount of iron is handled in a high-temperature atmosphere or a chemical solvent. First, the steelmaking industry at the integrated steel mill using the blast furnace / converter method includes the iron ore sintering process, blast furnace reduction process, converter smelting process, hot rolling process,
It consists of pickling and plating processes for steel products. From these processes, a large amount of dust, mainly iron oxide, and precipitates of iron compounds in wastewater are generated.
Also, in the steelmaking industry using the electric furnace method, a large amount of precipitate containing iron is generated from the continuous casting step, the hot rolling step, and other steps.

It is to be noted that a large amount of water collected from a precipitation pit or a thickener containing these iron compounds is contained, and a powder is suspended in water to form a mixture in a fluid state. This is called a slurry, and the water content is relatively low,
A sludge-like mixture having low fluidity is called sludge. In the following description, a slurry of a powder containing iron oxide or chloride is referred to as an iron slurry, and a sludge is referred to as an iron sludge.

[0004] Generally, the treatment of these iron slurries involves:
After increasing the powder concentration of the iron slurry in the sedimentation pit or thickener, the water content is reduced using various dehydrators, and the iron slurry is taken out of the water treatment system.

[0005] Among these iron slurries, there are powders having a particularly small powder particle size (that is, particles having a particle size of 40 microns or less). These are particularly likely to become sludge even after dehydration, and are generally difficult to dehydrate. This type includes wet dust collected from blast furnace gas dust (secondary ash from blast furnace), fine dust in converter gas dust (converter fine dust), and waste liquid containing iron ions from the pickling process of steel sheets. There are neutralized precipitates (pickling neutralized sludge), plating waste liquid precipitates (plating sludge), hot rolling scale storage pit precipitates (rolling sludge), and others. These have an average particle size of 1.5 to
It is 40 microns.

[0006] In the dehydration treatment of these iron slurries, a dehydrator model is selected according to physical conditions such as the powder concentration of the slurry and the particle diameter of the slurry. For example, a press-type dehydrator is used for dehydrating a slurry obtained by agglomerating a blast furnace secondary ash or a converter dust collected by a wet method with a thickener. In these cases, the moisture is 70-8
The 0% slurry is dehydrated to a water content of 25 to 30%. In addition, a horizontal centrifugal dewatering device called a decanter is often used for dewatering the pickling-neutralized sludge. In this dehydration treatment, the slurry containing about 90% of water is dehydrated to a state where the content of water is about 50%. As described above, in the related art, a press-type dehydrator, a horizontal centrifugal dehydrator, a vacuum dehydrator, and the like are used to dehydrate the iron slurry.

[0007] These iron sludges have a water content of 25 even after dehydration.
Since it is か か る 50%, the subsequent treatment is troublesome, so that after the dewatering, other dry dusts are mixed and finally disposed at an industrial waste disposal site. However, some may be recycled to the reduction step after being further dried.

[0008]

The iron slurry is dehydrated using a dehydrator adapted to the physical characteristics of the powder in the slurry. However, since the particle diameter of the powder is small, the iron slurry is dehydrated by a conventional method. The water content later is 25 to 50% as described above, and the property is sludge-like.

The water content after dehydration in the conventional method generally varies depending on the particle size of iron sludge. Very fine 1.5-1
For pickling neutralized sludge or converter fine particle dust composed of 0 micron particles, even if a vacuum dehydrator or horizontal centrifuge as shown in JP-A-60-9518 is used, 25 to 25
Dehydration was only possible up to 50%. Also, a relatively coarse 1
In a blast furnace secondary ash or rolled sludge composed of particles of 0 to 40 microns, even if a press-type dehydrator is used, 20 to 3 particles are used.
Dehydration was only possible up to 5%.

[0010] As a result, in the conventional dewatering method, what is produced after dehydration of the iron slurry is sludge-like sludge having strong tackiness. Handling this sludge-like sludge has various problems. In other words, it is recognized that the iron sludge may stick to conveyor equipment such as a belt conveyor or cause a phenomenon that the iron sludge cannot be discharged from the storage hopper because of its strong adhesiveness. As a result, for handling iron sludge, iron sludge is piled up in the soil surrounded by walls, placed on a truck by a club crane, a shovel loader, or the like, and transported to a drying treatment plant or a baking treatment facility.

[0011] Another problem in handling iron sludge is that when handling iron sludge, spills and scattering are liable to occur when heavy equipment is used and loaded on trucks. As a result, there is a problem in that the surroundings of the facility are soiled with sludge, and the sludge scattered around is dried and becomes scattered dust, thereby causing environmental pollution. Therefore, conventionally, attempts have been made to reduce the water content of the iron sludge after dehydration to facilitate handling.

To explain the characteristics of iron sludge, iron sludge changes from a highly sticky sludge state due to the difference in powder particle size.
The proportion of moisture that changes in a relatively dry state with a low viscosity is different. In the case of a sludge composed of extremely fine particles of 1.5 to 10 microns, the water content is about 20 to 30% or less, and a relatively dry and low tack state is obtained. Also, 10
A sludge composed of relatively coarse particles of 40 microns has a relatively dry and low tackiness with a water content of about 15 to 22%.

In other words, if the water content is reduced to the above-mentioned level, the iron sludge can be transported by a continuous transport means such as a belt conveyor, so that the transportation cost can be greatly reduced. In particular, when used in a recycling process in a steel mill, for example, in a sintering plant, a dust pellet production facility, a rotary kiln type or a rotary hearth type reduction facility, it is necessary to reduce the moisture until it can be conveyed. It is also effective for stable operation of the transfer device in the process.

However, in the conventional dehydration method, water cannot be sufficiently removed by the dehydration step alone.
After dehydration, a means for reducing the water content by performing drying using a heat source is used. As a result, the step of removing water from the iron slurry is composed of a dewatering device, a drying device, and a conveying means for connecting these, and the process has been complicated.
Moreover, the iron sludge after dewatering is sludge-like, and heavy equipment such as a club crane is required for handling the sludge in the drying process, which requires labor and is costly.

Generally, after dewatering the iron sludge, it is necessary to reduce the water content by about 10% in the drying step. In order to reduce the water content by 10%, about 300,000 kJ of heat is required per ton of iron sludge. This consumes a large amount of heat, which is a major problem in energy saving and cost.

Further, some slurries generated in the steel industry contain oil. This is a result of the mechanical oil being mixed with the scale or the like in a process such as rolling. When oil is mixed in the slurry, there is a problem that the filter is clogged in a press-type dehydrator or the like.

As described above, in the prior art, when dehydrating the iron slurry, the dewatering device alone could not reduce the water content to such a level that it could be easily handled. Therefore, there has been a demand for a new iron slurry dehydration method for reducing the iron slurry to a water content that does not exhibit stickiness with a dehydrator alone.

[0018]

The gist of the slurry dewatering method of the present invention is as follows (1) to (9).

(1) A dehydrator that pours slurry onto a circulating and moving endless loop-shaped filter cloth, squeezes it with a pair of squeezing rolls installed above and below the filter cloth, dehydrates the filter cloth, and then cleans the filter cloth. Is used, the rotation speed of the pressing roll on the side of the filter cloth on which the slurry is placed is 50 rotations per minute or less, and the pressing force of the pressing roll is 9,000 N per 1 m of the length of the contact between the pressing roll and the filter cloth. Under the above conditions, a slurry of a powder having a water content of 1.0 to 3.5 times the mass of the powder and containing an iron compound powder and having an average particle size of 1.5 to 40 microns is dewatered. A method for dewatering a slurry, comprising:

(2) The slurry is poured onto an endless loop-shaped filter cloth that moves in a circulating manner, the slurry is suctioned by a vacuum suction device provided below the filter cloth, and further a downstream process of the vacuum suction device is performed. After pressing and dewatering with a pair of pressing rolls installed above and below the filter cloth in the part, when using a dehydrator for washing the filter cloth, the rotation speed of the pressing roll on the filter cloth surface side on which the slurry is placed Is less than 50 revolutions per minute,
The pressing force of the squeezing roll is 9,000 N or more per 1 m of the length of contact between the squeezing roll and the filter cloth, and contains 1.0 to 5.5 times the water mass of the powder, and an iron compound. A slurry dewatering method, comprising dewatering a slurry of powder containing powder and having an average particle size of 1.5 to 40 microns.

(3) As a slurry of powder containing an iron compound, a wet dust collector thickener slurry of blast furnace gas dust, a wet dust collector thickener slurry of converter gas dust, a neutralized precipitate slurry of iron ions generated in the pickling process, plating The method for dewatering a slurry according to the above (1) or (2), wherein a single slurry or a mixed slurry is used for the water treatment slurry in the step and the fine scale of precipitation pits of the scale generated in the hot rolling step.

(4) The method for dewatering a slurry according to the above (1) or (2), wherein a slurry of a powder containing a metal oxide containing 10% by mass or more of a powder having a particle size of 10 μm or more is used. .

(5) When dewatering the oil-containing slurry, after squeezing with a pair of squeezing rolls, the filter cloth is washed with washing water containing a surfactant, and then washed again. The method for dewatering a slurry according to the above (1) or (2).

(6) The sludge dehydrated on the filter cloth is transferred to a pressing roll placed on the filter cloth by the method described in any one of (1) to (5) above. A dewatering method for recovering the sludge by scraping the sludge with a scraper, wherein the distance between the scraper and the pressing roll is in the range of 0.1 to 2 mm.

(7) The slurry according to any one of (1) to (6) is dewatered after adding a flocculant to a slurry containing a powder having a ratio of particles of 10 μm or less of 30% by mass or more. Dehydration method.

(8) As a coagulant, a polyacrylamide-based polymer, an acrylic acid-based polymer, or an acrylic acid-based cationic polymer is added at a ratio of 30 to 300 milligrams per 1 kg of the powder in the slurry slurry (7).
A method for dehydrating the slurry according to the above.

(9) The method for dewatering a slurry according to (7) or (8), wherein after the aqueous solution of the flocculant is added to the slurry, the slurry having the increased powder concentration is dewatered using a precipitation tank.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an apparatus for performing a method for dewatering an iron slurry according to the present invention, and the method of the present invention will be described with reference to FIG. FIG. 1 shows equipment that implements the present invention, a thickener for sedimentation of an iron slurry, a slurry transport device, a twin-roll dehydrator, a sludge transport conveyor, and
The equipment consisting of a sludge storage place is shown.

First, the iron slurry is used in an iron slurry generation process in an ironworks, for example, a neutralization tank for a waste liquid containing iron ions in a process of collecting dust from a venturi scrubber for collecting secondary ash of a blast furnace and pickling a steel plate. The iron slurry having a low concentration is sent to the thickener 1 for precipitation. In the thickener 1 for sedimentation, the particles in the iron slurry are settled by gravity to produce an iron slurry having a high particle concentration at the bottom. The iron slurry having a high particle concentration is withdrawn from the bottom of the thickener for sedimentation 1 and sent to the dehydrator 4 via the slurry pipe 3 using the slurry pump 2. Here, the iron slurry is dehydrated to have a predetermined moisture content, and is sent to the sludge storage place 6 on the belt conveyor 5.

FIG. 2 is a detailed view of the dehydrator 4 for explaining a detailed method of dehydration. In the dehydrator of the present invention, iron slurry is poured from the slurry supply port 7 to the filter cloth 8 provided in a loop. The filter cloth 8 is made of a cloth woven with fibers or felt, which is an untwisted cloth.
For example, it is made of nylon or Tetron (registered trademark). A filter cloth using a felt that absorbs the water of the slurry is particularly desirable. The filter cloth 8 moves at a steady speed toward a pair of squeezing rolls 9 and 10 installed above and below the filter cloth, and the pair of squeezing rolls 9 and 10 rotate at a steady speed. And the iron slurry 11 thereon are squeezed from above and below to reduce the water content. The powder is sent downstream of the roll with the water content reduced. Most of the water contained in the iron slurry is pressed by the pressing rolls 9 and 10 and is extruded to the lower side of the filter cloth 8. The dewatered iron sludge is separated from the filter cloth at a portion where the filter cloth 8 is bent downward by the pressing roll 10. However, since much iron sludge adheres to the filter cloth 8 and the upper pressing roll 9, it is killed off by the scraper 12.

After the dehydration is completed, iron compound powder is attached to the filter cloth 8 after the iron sludge is separated. When used in the next dehydration cycle as it is, the adhesion of powder further increases, and the filter cloth 8 is clogged. Therefore, filter cloth cleaning is performed. Water is sprayed on the cleaning nozzle 13 to clean the cleaning tank 1
In step 4, flush the water contaminated with the powder. Normally, one-stage cleaning is sufficient, so the cleaning nozzle 15 and the cleaning tank 16 shown in FIG. 2 are unnecessary. However, in order to wash the slurry containing oil, two-stage washing is performed as shown in FIG. In the first-stage washing, water containing a surfactant is sprayed from the washing nozzle 13 to drop powder and emulsify and drop oil. In the second stage, water is sprayed with the washing nozzle 15,
In the washing tank 16, the powder is washed off. The number of washing stages can be arbitrarily determined and is not limited.

By carrying out the method of the present invention, the iron sludge collected here is in a good dewatered state. At this time, the particles having an average particle size of relatively large as 10 to 40 microns have a water content of 15 to 22%, and the particles having an average particle size as small as less than 10 microns have a water content of 20 to 20%. 30%.

In the above-mentioned preferable range of the contained water content, pseudo-agglomerated particles due to the contained water become compressed flake iron sludge. Since the iron flakes in the form of flakes have relatively low water content and low adhesiveness, even if they are conveyed by the belt conveyor 5, the sludge adheres little to the conveyor belt and can be easily conveyed. The sludge can be easily transported by transport means other than a belt conveyor such as a pipe conveyor.

The inventors of the present invention used the dehydrator shown in FIG.
Various studies have been made on operating conditions for efficiently dehydrating an iron slurry containing iron compound powder, and by operating under the following conditions, it is possible to obtain a sludge having a water content in the above-mentioned good range. Elucidated.

First, there is an appropriate range for the mass ratio of the powder and the water of the iron slurry used in the present invention. If the water content is too small, the flow of the iron slurry poured on the filter cloth cannot be sufficiently ensured, and the amount of iron slurry on the filter cloth will be extremely shaded. As a result, a uniform iron slurry distribution cannot be made on the filter cloth, and the iron-slurry-rich part of the iron slurry is too thick and the squeezing becomes insufficient,
There was a problem that water could not be squeezed. When dehydrating an iron slurry containing powder of an iron compound such as iron oxide, if the mass ratio of water to powder is 1.0 or less, the flow of the iron slurry during transportation of the iron slurry becomes poor. As a result, when the flow velocity in the pipe decreases, there is a problem that a clogging phenomenon occurs in the slurry pipe 3. From this point, it is necessary that the mass ratio of water to powder is 1.0 or more. Operational conditions.

On the other hand, if the water content is too high, the iron slurry cannot be squeezed out, and the water content of the dewatered sludge is too high. FIG. 3 shows the results of the study of the upper limit of the water content ratio of the iron slurry by the present inventors as a relationship between the water content of the iron slurry, the mass ratio of the powder, and the productivity (the amount of dehydration per hour). In the example of FIG. 3, the blast furnace secondary ash having a relatively coarse particle diameter of 29 microns in the iron slurry was used.

When the ratio of water increases, the productivity tends to deteriorate under the operating conditions that make the water content of the sludge after dehydration appropriate. In particular, when the mass ratio of the water to the powder becomes 3 or more, the productivity starts to deteriorate due to the increase in the water content of the slurry. In the blast furnace secondary ash, in order to obtain a sludge with a water content of 20% or less, in which the sludge after dehydration has little tackiness, and to prevent the productivity from deteriorating, the mass ratio of the water to the powder is required. It is clarified that a value of 3.5 or less is an important condition for the dehydration operation.

As described above, in the dehydrator of FIG. 2 used in the present invention, there is a restriction on the water ratio of the iron slurry stock solution. However, the iron slurry having a higher moisture content may be dewatered. In this case, a method of vacuum-suctioning the iron slurry from below the filter cloth before pressing with a roll is effective. However, if the water content is too large, the amount of water passing through the filter cloth is too large, and the filter cloth is clogged. The present inventors conducted various experiments and found that if the water content of the iron slurry was not more than four times the mass of the powder, dehydration could be performed efficiently. That is, when the mass ratio of water to powder in the iron slurry stock solution is in the range of 1.0 to 5.5, a method of vacuum suction before squeezing is effective, and dehydration can be performed to the above-mentioned proper water content ratio. .

Further, the present inventors have clarified that there are appropriate conditions for pressing the pressing rolls during the dewatering of the iron slurry. Important squeezing roll squeezing conditions that affect dewatering performance are the rotation speed of the squeezing roll and the pressing pressure. If the rotation speed of the pressing roll is too high, sludge will be sent to the downstream side of the pressing roll without sufficient dewatering. As a result, the sludge after dehydration has a water content that is higher than the water content that does not have much tackiness. Also, if the pressing pressure of the squeezing roll is too low, a problem arises that water cannot be completely removed. Thus, the present inventors, when using a dehydrator of the type shown in FIG. 2, when dehydrating and using to a water content suitable for handling iron slurry,
It has been found that there is an appropriate range of pressing roll rotation speed and pressing pressure.

FIG. 4 shows the result of investigation on the influence of the rotation speed of the pressing roll 9 on the slurry side on the water content of the sludge. In the example of FIG. 4, the blast furnace secondary ash, in which the diameter of the particles in the iron slurry is also relatively large, is used, and the pressing force of the pressing roll is 9,0 per 1 m of the length of the contact between the pressing roll and the filter cloth.
At 00N, the diameter of the slurry-side squeezing roll 9 placed above the filter cloth is 350 mm. Rotation speed 5 per minute
At 0 rotations or less, a sludge having a water content of 20% or less, which is a state in which the sludge after dehydration has little tackiness, can be obtained. Further, when the rotation speed was 35 rotations or less per minute, the moisture content was 18% or less, and good results were obtained.

Also in the experiment results in which the diameter of the pressing roll 9 on the slurry side was set to 500 mm, good dehydration results were obtained when the pressing roll rotation speed was 50 rotations per minute or less. In the dehydrator of the type shown in FIG. 2, the present inventors consider that the time change rate of the interval between the pressing roll and the filter cloth when the pressing roll 9 presses the filter cloth affects the dewatering result. I clarified something. In other words, when the diameter of the slurry-side pressing roll is large, the time change rate of the interval between the roll and the filter cloth is not large even if the passing speed of the filter cloth is high, so that the dewatering results are equivalent. In other words, with a large-diameter pressing roll,
If the conditions for keeping the rotation speed of the roll constant are adhered to, the dewatering performance does not deteriorate even if the filter cloth speed is increased. In other words, the rotation speed of the pressing roll 9 on the slurry side is an important condition for determining the dewatering performance, and good dewatering performance can be obtained at a rotation speed of 50 revolutions per minute or less.

Next, FIG. 5 shows the result of investigation on the influence of the pressing pressure of the pressing roll on the water content of the sludge. In the example of FIG. 5 as well, the blast furnace secondary ash having relatively coarse particles in the iron slurry is used, and the rotation speed of the pressing roll 9 on the slurry side is 35 rotations per minute. The result was that the higher the pressing force of the pressing roll, the lower the water content of the iron sludge generated by dehydration. The pressing force of the pressing roll is 9,000 N / m
In the above, the water content was 20% or less of the target, and good dehydration results were obtained. However, when the pressing force of the squeezing roll is 50,000 N / m or more, a phenomenon in which the sludge adheres strongly to the squeezing roll and the filter cloth and it is difficult to remove the sludge has occurred. Therefore, the pressing force of the squeezing roll is preferably not too high. . The pressing force per 1 m of the length of the contact between the squeezing roll and the filter cloth is expressed in N / m (N is Newton).

The above experiment was carried out with a slurry of plating sludge having an average particle size as small as 6 microns. As a result, although the water content of the sludge after dehydration was 22 to 25%, which was slightly higher than that of the secondary ash in the blast furnace, stable dehydration was performed when the operation was performed under the dehydration conditions described above.
Further, even if the water content of the sludge after dehydration was 22 to 25%, the sludge was a flake-like dehydrated product with plating sludge, and the adhesion was weak. As described above, in the case of sludge having small particles, since the specific area of the particles is large, even if the moisture is several% higher than that of the sludge having large particles, physical properties such as adhesion are equivalent.

Next, the present inventors investigated the effect of the particle size of the iron slurry on the dewatering performance. When dehydrating an iron slurry composed of iron compound particles, if the particle diameter is small, it is difficult to dehydrate even if the pressing pressure is increased. When the average particle size is 1.5 microns, although the productivity is slightly lowered, the iron slurry can be dewatered to a suitable moisture having low adhesiveness. However, when the average particle diameter becomes 1.5 microns or less, the rotation speed of the pressing roll on the slurry side is reduced to 15 / min.
Even when the rotation was reduced, the water could only be dehydrated up to 30 to 35%. This sludge has tackiness and is in a state of insufficient dewatering. That is, it is an important requirement of the present invention that the average particle size of the particles in the iron slurry be 1.5 microns or more.

The present inventors have also clarified that even when the average particle diameter is small, when a relatively large particle is present, the dehydration becomes good. As a result of repeatedly performing a dehydration experiment using an iron slurry, it was found that when particles having a relatively large particle diameter of 10 μm or more were mixed at a certain ratio, dehydration was easy. It has also been clarified that if particles having a particle size of 10 μm or more are mixed in a ratio of 10% by mass or more, the productivity of dehydration is improved by 20% even if the average particle size is the same. This is because, when particles having a large particle diameter are mixed, water permeability around the particles is improved, and dehydration is facilitated. Therefore, in order to improve the dewatering performance of an iron slurry composed of particles having a small particle diameter, the particles having a particle diameter of 10 μm or more are increased by mixing with an iron slurry composed of particles having a large particle diameter. Dehydration is an effective means.

As described above, the size of the particles contained in the slurry strongly affects the performance of the dehydrator. Then, the present inventors invented that the dehydration performance was improved by agglomerating particles to form clusters in which tens to thousands of fine particles were gathered. As a result of various studies on a flocculant suitable for a slurry containing fine particles of an iron compound, particularly iron oxide or iron hydroxide, a polyacrylamide-based polymer, an acrylic acid-based polymer, or an acrylic acid-based cationic polymer was found to be good. . If these coagulants are mixed with the slurry before dehydration to aggregate fine particles of 10 μm or less, the apparent particle diameter increases, and the dehydration performance is improved. Specifically, the processing speed per 1 m of the length of the pressing roll 9 of the dehydrator 4 is improved. Also, the water content decreases. 30% by mass of particles having a particle size of 10 microns or less
Above, the effect of the flocculant is remarkable. The amount of the coagulant added is 30 to 300 per kg of powder in the slurry.
Good milligram ratio. However, since the coagulant is added in the form of an aqueous solution, when the coagulant is added, the water content of the slurry increases, and the function of the dehydrator 4 is slightly reduced. Therefore,
By installing a sedimentation tank between the thickener for sedimentation 1 and the dehydrator 4, by recovering the increased amount of water,
It is an effective method to return the slurry water entering the dehydrator 4 to the state before the addition of the flocculant.

Also, when the average particle size is too large, a problem occurs in the dehydration treatment. As described above, since the filter cloth 8 is formed by weaving fibers, if there are many particles having a large particle diameter, the particles are caught between the fibers, and the filter cloth is clogged or the fibers are damaged. Sometimes. In the case of dehydration with an iron slurry, it has been found that when the average particle size exceeds 40 microns, clogging of the filter cloth is likely to occur. Comparing the results of the long-term operation, when the average particle size is 29 microns, the average size of the filter cloth is 45 days while the filter cloth lasts 65 days.
In the case of microns, the filter cloth had to be replaced in 22 days.

The iron compound such as iron oxide has a high hardness, and the parts of the dewatering machine 4 are greatly worn. In particular, the pressing roll 9
And the wear of the scraper 12 is large.
A method is adopted in which the pressing roll 9 and the scraper 12 are not brought into direct contact. By setting the distance between the two to 0.1 to 2 mm, abrasion of the pressing roll 9 and the scraper 12 is small, and separation of sludge adhering to the pressing roll 9 can be performed without any problem.

When dewatering an iron slurry containing oil generated in the steel industry, the dewatering method of pressing with a pressing roll of the present invention as shown in FIG. 2 is effective. However, since the filter cloth 8 becomes stained with oil over time, it is effective to wash the filter cloth with a surfactant. In the present invention, the oil of the filter cloth is suspended in the first-stage washing with the surfactant in the first-stage washing, and then washed out in the second-stage washing, so that the filter cloth of up to about 1% of the total mass is removed. Iron slurry mixed with oil can be dehydrated stably for a long period of time. The target iron slurry is blast furnace secondary ash, converter fine dust, pickling neutralized sludge, plating sludge,
Rolled sludge and other powdered iron slurries.

[0050]

The results of the dehydration performed using the apparatus according to the present invention are shown in Table 1 in comparison with the conventional dehydration method. The dewatering machine according to the present invention is shown in FIG.
0 mm and a filter cloth width of 1.2 m. As Comparative Example 1 according to the conventional method, an example of the dehydration treatment of the press-type dehydrator and the dehydrator shown in FIG. 2 but in which the operating conditions are out of the range of the present invention are shown as Comparative Example 1. As the iron slurry, a slurry of the secondary ash of the blast furnace was used. The slurry water content was about twice (67% by mass) the mass of the powder, the average particle size of the powder was 25 microns, and the ratio of particles having a particle size of 10 microns or less was 23%.

Comparative Example 1 shows the results of dewatering by a filter press type dewatering machine. The water content of the sludge after dewatering is as high as 52%, the sludge is also a clay-like lump, has a strong tackiness, and is difficult to handle. there were. Comparative Example 2 is an operation using a squeeze roll type dehydrator, and the rotation speed of the squeeze roll is 6
The sludge moisture after dehydration was 31
% Was high. The properties were clay-like. Comparative Example 3
In this example, the pressing force of the pressing roll is 6000 N / m, which is an example of processing weaker than the range of the present invention. As a result of this process,
Although the dewatering speed was good, the water content of the sludge after dewatering was as high as 33%.

On the other hand, in the embodiment of the present invention, the operation is performed by a pressing roll type dehydrator, and the rotation speed of the pressing roll is 35
Rotation / min, pressing force of pressing roll is 12,000N /
m, which was within the proper treatment range in the present invention, the sludge water content after dehydration was as good as 23%. The properties of the sludge were flake-like and weakly sticky. Thus, by operating the press roll type dehydrator under the conditions of the present invention, a sludge having excellent handling characteristics could be produced.

In Example 2, the same blast furnace secondary ash was used, but the water content of the slurry was about 4.2 times the powder mass (water content 81%).
%) Was dehydrated. Since this slurry has a large amount of water, it was pre-dewatered by a vacuum suction device installed below the filter cloth before dewatering with the pressing rolls 9 and 10 of the dehydrator 4. As a result, despite the large amount of slurry water, the sludge water after dewatering was as good as 25%.

An example of a dehydration treatment in which a coagulant is added to the slurry before dehydration is shown as Example 3. In the third embodiment,
The slurry which processed the waste liquid of galvanizing was used. This was a very fine powder slurry having an average particle diameter of 4.3 microns and a ratio of particles of 10 microns or less being 87%. 44 mg of an acrylic acid-based polymer was added to 1 kg of the powder in the slurry. As a result,
The particles aggregated to an apparent average particle size of 11 microns. After the addition of the flocculant, the slurry was subjected to the precipitation concentration operation. As a result, the water content was almost the same as before the addition of the flocculant. In this treatment, the water content of the sludge after dehydration was 27%, which was very good as a fine particle sludge.
On the other hand, in Example 4, dehydration was performed without a coagulant. The dewatering conditions were the same, but the dewatering treatment speed was reduced to about 75% as compared with Example 3, and the water content of the sludge was 3%.
Although it was as high as 0%, it could be processed properly. In the case of other types of dehydrators, the water content of this sludge after dehydration is 45-60.
%, The effect of the present invention in Example 4 was recognized.

Example 5 is an example in which sludge generated in a steel rolling step containing 1% oil and having an average particle diameter of 26 microns was treated.
Shown in Water containing a surfactant was sprayed from the washing nozzle 13 of the dehydrator 4 to drop the powder and emulsify and drop the oil to perform dehydration. As a result, the water content after dehydration was as low as 18%, and the filter cloth was not clogged with oil even after one month of continuous dehydration.

Although not described in Table 1, the results of Example 6 were obtained by dewatering the same slurry of secondary ash in the blast furnace under the same conditions as in Example 1. However, in the sixth embodiment, the life of the squeezing roll 9 and the scraper 12 was compared by not bringing the scraper 12 into contact with the squeezing roll 9, and the processing was not performed in the first embodiment. In Example 6, the dewatering treatment speed and the sludge moisture after dewatering were the same as in Example 1. However, in Example 6, dehydration could be performed without polishing the pressing roll 9 for one year. Also,
The life of the scraper 12 was 5 months. On the other hand, in Example 1, since the pressing roll 9 and the scraper 12 were brought into direct contact, it was necessary to polish the pressing roll 9 every six months. The life of the scraper 12 was as short as one month.

[Table 1]

[0057]

In the operation range of the method of the present invention, a dewatering machine of the type in which the filter cloth on which the slurry is squeezed is pressed and dewatered with one or more pressing rolls, and contains an iron compound generated from the ironmaking process. The slurry of the powder to be dewatered can be dewatered to produce a low-moisture dehydrate. In addition, the effect of a dehydrator for dehydrating a slurry in which oil or the like may be mixed can be exhibited.

[Brief description of the drawings]

FIG. 1 is a system diagram of a dehydrating apparatus for performing the present invention;
It is a figure of the equipment which sends to a dehydrator from the thickener for sedimentation which concentrates a slurry, and dehydrates.

FIG. 2 is a detailed view of a dehydrator of a type in which a slurry on a filter cloth is dewatered by a pressing roll.

FIG. 3 is a diagram showing the effect of the mass ratio between the water content of the slurry and the powder on the productivity of dehydration.

FIG. 4 is a diagram showing the effect of the rotation speed of a pressing roll on sludge moisture after dewatering.

FIG. 5 is a diagram showing the effect of the pressing force of the pressing roll on the side pressing the slurry on the sludge moisture after dewatering.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thickener for sedimentation 2 Slurry pump 3 Slurry piping 4 Dehydrator 5 Belt conveyor Sludge storage place 7 Slurry supply port 8 Filter cloth 9 Squeezing roll 10 Squeezing roll 11 Iron slurry 12 Scraper 13 Washing nozzle 14 Washing tank 15 Washing nozzle 16 Washing Tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 33/44 B30B 9/24 J 33/58 B01D 33/36 B30B 9/20 9/24 (72) Invention Person Shoji Imura 1 Kimitsu, Kimitsu-shi, Nippon Steel Corporation Kimitsu Works (72) Inventor Satoshi Kondo 1 Kimitsu, Kimitsu-shi, Nippon Steel Corporation Kimitsu Works (72) Inventor Yoichi Abe 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Shigeki Takahashi 20-1 Shintomi Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Cho Aizaki Tokyo 1-6-1 Nihombashi Honmachi, Chuo-ku Marukashi Building Building TDD Corporation (72) Inventor Hirohiko Chiba 1-6-1 Nihonbashi Honmachi, Chuo-ku, Tokyo Marukashi Building Building TDK Corporation The internal F-term (reference) 4D026 BA03 BB03 BB05 BC12 BC33 BD05 BE05 BE06 BF06 BF11 BH07 4D059 AA03 AA11 AA30 BE09 BE14 BE15 BE31 BE57 BE58 BE59 CB17 CB18 DB11 DB24 EB01 EB07 EB11 EB20

Claims (9)

[Claims] 1. A dehydrator that pours a slurry onto an endless loop-shaped filter cloth that moves in a circulating manner, presses the slurry with a pair of pressing rolls disposed above and below the filter cloth, dehydrates the filter cloth, and then cleans the filter cloth. When used, the rotation speed of the pressing roll on the filter cloth surface side on which the slurry is riding is 50 rotations per minute or less,
In addition, when the pressing force of the pressing roll is 9,000 N or more per 1 m of the length where the pressing roll and the filter cloth are in contact with each other, the pressing roller contains water of 1.0 to 3.5 times the mass of the powder, and contains an iron compound. A slurry dewatering method, comprising dewatering a slurry of powder containing powder and having an average particle size of 1.5 to 40 microns. 2. A slurry is poured onto an endless loop-shaped filter cloth that moves in a circulating manner, the slurry is suctioned by a vacuum suction device provided below the filter cloth, and further, a downstream process section of the vacuum suction device. After squeezing and dewatering with a pair of squeezing rolls installed above and below the filter cloth, when using a dehydrator to wash the filter cloth, the rotation speed of the squeezing roll on the filter cloth surface side on which the slurry is riding Less than 50 revolutions per minute, and
When the pressing force of the squeeze roll is 9,000 N or more per 1 m of the length of the contact between the squeeze roll and the filter cloth, the squeeze roll contains 1.0 to 5.5 times the mass of the powder and contains the iron compound powder. A slurry dewatering method, comprising dewatering a slurry of powder having an average particle size of 1.5 to 40 microns. 3. A powdery slurry containing blast furnace gas dust, a thickener slurry of a blast furnace gas dust,
Converter dust dust wet collector thickener slurry, iron ion neutralized precipitate slurry generated in pickling process, water treatment slurry in plating process, fine pits of scale pits generated in hot rolling process as single slurry or The slurry dewatering method according to claim 1 or 2, wherein a mixed slurry is used. 4. The slurry dewatering method according to claim 1, wherein a slurry of a powder containing a metal oxide containing 10% by mass or more of a powder having a particle size of 10 μm or more is used. 5. When dewatering a slurry containing oil,
The slurry dewatering method according to claim 1 or 2, wherein the filter cloth is washed with washing water containing a surfactant after being squeezed by a pair of squeezing rolls, and then washed again. 6. The method according to claim 1, wherein the sludge dewatered on the filter cloth is transferred to a pressing roll provided on the filter cloth, and the sludge is scraped off. In a dewatering method for recovering sludge by scraping off the slurry, a distance between the scraper and the pressing roll is set in a range of 0.1 to 2 mm. 7. The method according to claim 1, wherein a dewatering is performed after adding a flocculant to a slurry containing a powder having a ratio of particles of 10 μm or less of 30% by mass or more. Dewatering method of slurry. 8. A polyacrylamide-based polymer, an acrylic acid-based polymer, or an acrylic acid-based cationic polymer as a coagulant is used in an amount of 30 to 30 kg per 1 kg of powder in a slurry.
The slurry dewatering method according to claim 7, wherein the slurry is added at a ratio of 300 milligrams. 9. The method for dewatering a slurry according to claim 7, wherein after the aqueous solution of the flocculant is added to the slurry, the slurry having the increased powder concentration is dewatered using a precipitation tank.