JP2006212569A - Slurry concentrating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slurry concentrating method capable of obtaining concentrated slurry with high concentration in a well mixed state by concentrating slurry containing a powder with low specific gravity and a powder with high specific gravity. <P>SOLUTION: In a case that the slurry containing the powder with low specific gravity and the powder with high specific gravity is concentrated, the slurry is loaded with a flocculant and a revolving stream is formed and stirred so that a Reynolds number Re becomes 1,500 or above by rotating the flocculant-loaded slurry in a flocculation reaction tank 2 by stirring blades 3 and the flocculated powder is subsequently sedimented in a sedimentation tank 5 to obtain a slurry having a predetermined high concentration without separating the powder low in specific gravity and the powder with high specific gravity at the time of sedimentation. Further, by controlling the stagnation time of the slurry in the sedimentation tank 5 to a definite time range when the concentration of the slurry is set to 45-55 mass%, the concentrated slurry can be well discharged without closing the concentrated slurry discharge piping provided to the bottom part of the sedimentation tank while keeping the concentration of the slurry after concentration high. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a slurry concentration method for concentrating a slurry containing a plurality of types of powder having a large specific gravity difference to a high concentration.

  In the steel industry, a large amount of iron is handled in a high-temperature atmosphere or a chemical solvent, so a large amount of dust and sludge containing iron oxide and the like are generated. First of all, the steel manufacturing industry in the integrated steelworks using the blast furnace / converter method consists of iron ore sintering process, blast furnace reduction process, converter smelting process, hot rolling process, pickling process of steel products, plating It consists of processes. From these steps, a large amount of dust, mainly iron oxide, and precipitates of iron compounds in the wastewater are generated. Also in the steel industry using the electric furnace method, a large amount of precipitates containing iron is generated from the continuous casting process, hot rolling process, and other processes.

  In general, these iron slurries are treated with precipitation pits or thickeners, and after increasing the powder concentration of the iron slurries, various dehydrators are used to lower the water content, resulting in water treatment as iron sludge. Out of the system.

  Among the slurries generated at these steelworks, converter gas, for example, is collected by a non-combustion gas processing device, so-called OG device, and collected, and then used as fuel gas for power generation and heating of steel materials. . The OG device has a venturi scrubber type dust collector and collects dust while applying water. The converter dust in the collected water is first separated into coarse particles in a primary settling tank and poured into a thickener. In the thickener, fine converter dust is precipitated and the concentrated one is dehydrated to 20-30% with a dehydrator.

  In order to use a large amount of particulate converter dust, it is effective to recycle to a blast furnace. However, fine converter dust contains zinc, and its use in a blast furnace is restricted as it is. As a countermeasure against this problem, if the fine converter dust is dezinced, it can be used in a blast furnace. If the rotary hearth method is used, the dezincification rate is as high as 90% or more, and reduced iron can be obtained. Therefore, examples of being used as a dezincification process are increasing.

  The rotary hearth method is a process mainly consisting of a type of firing furnace in which a disk-shaped refractory hearth lacking a central part rotates on a rail at a constant speed under a fixed refractory ceiling and side walls. It is used for the reduction of metal oxides and the treatment of iron dust. In order to use iron oxide-containing powder such as fine-grain converter dust in a rotary hearth reduction furnace, the powder raw material alone or a mixture with other iron oxide-containing powder can be used. It is mixed with a powder containing carbon such as spherical pellets.

  Patent Document 1 describes a metal oxide reduction facility using a rotary hearth type reduction furnace for reducing dust and sludge containing metal oxides. A mixing tank and a stirring device are installed as a device for well mixing raw material powder (a mixture of metal oxide-containing powder and carbon-containing powder) that contains a lot of moisture and is in a slurry state. In order to uniformly stir the raw material powder in a slurry state in a short time, it is necessary to contain a large amount of moisture. If the slurry-containing water at the time of mixing is 100% or more with respect to the mass of the powder, the fluidity is high, the time for uniform mixing is shortened, and the power for stirring is small. The mixed slurry is sent to a dehydrator. Dehydration is performed with a dehydrator so that the moisture content is in the range of 16 to 26% of the mass of the powder. In the case of dehydrating a slurry made of fine powder having an average particle size of 120 μm or less, it is difficult to make the water content of the dehydrated product 16 to 26% with a general dehydrator, and a special dehydrator is used. As a dehydrator used in this case, it is effective to use a dehydrator having a belt-like filter that receives a powder mixture containing moisture and a twin roll that sandwiches and compresses the filter.

  Patent Document 2 describes an invention for reducing fine powder converter dust by a rotary hearth method. First, fine converter dust generated together with converter gas is collected by a bench yuri scrubber. The converter dust and water slurry is separated into large particles by a coarse particle separator, and then the dust is concentrated by a thickener and the water content is adjusted to 20 to 35% by mass with a dehydrator. Other fine sludges and powder coke supplied from the slurry storage tank and the powder coke storage tank are mixed in the mixing tank, and the water content is 55 mass% or more (that is, the slurry concentration is 45 mass% or less). Make a mixed slurry. This mixed slurry is dehydrated with a dehydrator. The moisture after dehydration is 17 to 27% by mass. A cylindrical or granular shaped body of about 10 to 40 mm is produced from this dehydrated product with a molding apparatus. This compact is supplied to a rotary hearth type reduction furnace and fired and reduced.

JP 2001-234220 A JP 2003-82418 A

  In the method described in Patent Document 1, the water content of the slurry when mixing the powder containing metal oxide and the powder containing carbon is 100% or more (that is, the slurry concentration is 50% by weight or less) with respect to the powder mass. . In this method, it is necessary to dehydrate a wide concentration slurry having a slurry concentration of 50% by mass or less, and the dehydrator has a lower production capacity as the slurry concentration of the slurry to be dehydrated is lower (the higher the moisture content is). Even when the slurry concentration is low, it is necessary to install many dehydrators so that the raw material can be stably supplied to the rotary hearth. Therefore, there has been a problem that the equipment cost and operating cost of the dehydrator are increased.

  In the method described in Patent Document 2, the fine powder converter dust slurry is once adjusted to 20 to 35% using a dehydrator, then mixed with the powder coke in a mixing tank, and dehydrated by a dehydrator. That is, it is necessary to perform the dehydration process twice, which leads to an increase in equipment cost and operation cost for the dehydration process. Although a method of using fine powder converter dust without dehydration is also described, in this case, unless a large amount of carbon source or other dust containing a small amount of water is used, the water content after mixing is 55% or less (that is, The slurry concentration cannot be 45% by mass or more.

  The slurry when mixing the powder containing metal oxide and the powder containing carbon has a high water content, and if the powder of the mixed slurry can be precipitated and concentrated, dehydration is performed using a slurry with a low water content. As a result, the production capacity of the dehydrator can be increased. Further, it is not necessary to perform the dehydration step twice, or it is not necessary to use a large amount of carbon source or other dust having a low water content.

  However, when a slurry in which a powder with a high specific gravity such as metal oxide and a powder with a low specific gravity such as a carbon source are mixed is precipitated in a settling tank and concentrated, the sedimentation rate of the powder with a high specific gravity is set. Is faster than the sedimentation rate of the powder having a low specific gravity, and the powder having a high specific gravity settles first, so that the sediment is separated in the sedimentation tank, and a normal mixture cannot be obtained. For stable operation of a reduction furnace such as the rotary hearth method, it is necessary to adjust the raw material so that the content ratio of metal oxide and carbon source (reducing agent) in the raw material is always an appropriate value. Concentration in the tank causes the content ratio of the metal oxide and carbon source in the raw material to deviate and fluctuate, so that the reduction reaction in the reduction furnace changes over time and sometimes the reduction rate decreases. Or sometimes the reaction gas becomes excessive. Moreover, since the concentration of the slurry after concentration is high, the concentrated slurry discharge pipe at the bottom of the settling tank is blocked, and it may be difficult to discharge the concentrated slurry.

  An object of the present invention is to provide a slurry concentration method capable of concentrating a slurry containing a low specific gravity powder and a high specific gravity powder and obtaining a high concentration concentrated slurry in a good mixed state.

  In the present invention, the slurry concentration (mass%) means a value obtained by subtracting the moisture content (mass%) from 100%.

  In the case of concentrating a slurry containing a low specific gravity powder and a high specific gravity powder, the present inventors add a flocculant to the slurry and then stir under predetermined appropriate conditions, and then agglomerate in a sedimentation tank. It was found that if the powder thus prepared is allowed to settle, the low specific gravity powder and the high specific gravity powder do not separate at the time of sedimentation, and a slurry having a predetermined high concentration can be obtained.

  The inventors also have an appropriate time range for the slurry residence time in the settling tank, and by controlling the residence time within this appropriate time range, the concentration of the slurry after concentration is kept high while concentrating at the bottom of the settling tank. It was found that the concentrated slurry can be discharged well without blocking the slurry discharge piping.

The present invention has been made based on the above findings, that is, the gist thereof is as follows.
(1) 30% by mass or more of the solid content is particles having a particle size of 10 μm or less, including low specific gravity powder and high specific gravity powder, and the high specific gravity powder has a true specific gravity more than twice that of the low specific gravity powder. In a method of concentrating a slurry, the Reynolds number Re calculated by the following formula (1) is 1500 or more by rotating the stirring blade 3 in the agglomeration reaction tank 2 for the slurry to which the flocculant is added. A method for concentrating a slurry, characterized in that a swirling flow is formed and stirred, and then the aggregated powder is settled in a settling tank 5.
Re = ρ × n × d ² / μ (1)
Where ρ: liquid density (kg / m ³ ), n: rotation speed of the stirring blade (sec ⁻¹ ), d: diameter of the stirring blade (m), μ: liquid viscosity (kg / m · sec).
(2) The low specific gravity powder includes at least one of pulverized coal and coke powder, and the high specific gravity powder includes at least one of iron oxide, chromium oxide, nickel oxide, and manganese oxide. The method for concentrating a slurry according to 1).
(3) When a slurry having a slurry concentration of 20 to 40% by mass is processed and concentrated to a slurry concentration of 45 to 55% by mass, the residence time of the slurry in the settling tank 5 is controlled within a certain time range. The method for concentrating a slurry according to (1) or (2) above.
(4) When the residence time in the settling tank 5 exceeds a predetermined time, the concentrated slurry is extracted from the lower part of the settling tank and charged again into the settling tank. .
(5) The interface level between the concentrated slurry and the supernatant liquid in the settling tank 5 is detected or estimated, and when the interface level exceeds a preset upper limit, the slurry feeding to the settling tank 5 is stopped and preset. The slurry concentration method as described in (3) or (4) above, wherein the slurry feeding to the settling tank 5 is resumed when the lower limit is exceeded.
(6) As a flocculant, a weak anionic polymer flocculant or a nonionic polymer flocculant is added in an amount of 0.01 to 0.07% by mass with respect to the mass of the solid substance in the slurry. The slurry concentration method according to any one of 1) to (5).
(7) The slurry according to any one of (1) to (6) above, wherein dust or sludge generated in a steel manufacturing process is included as one or both of the low specific gravity powder and the high specific gravity powder. Concentration method.

  In the present invention, when a slurry containing a low specific gravity powder and a high specific gravity powder is concentrated, a swirling flow is formed in a range of a predetermined Reynolds number in an aggregation reaction tank after adding a flocculant to the slurry. By stirring, when the powder aggregated in the sedimentation tank is subsequently settled, the low specific gravity powder and the high specific gravity powder are not separated at the time of sedimentation, and a slurry having a predetermined high concentration can be obtained.

  In the present invention, the slurry residence time in the settling tank is controlled within an appropriate time range so that the concentrated slurry discharge pipe at the bottom of the settling tank is not blocked while maintaining the slurry concentration after concentration high. The concentrated slurry can be discharged.

  The slurry concentration method of the present invention will be described based on FIG.

  The slurry to be concentrated by the present invention is a particle having a solid content of 30% by mass or more and a particle size of 10 μm or less, and includes a low specific gravity powder and a high specific gravity powder, and the high specific gravity powder has a low true specific gravity. It is more than twice the specific gravity powder.

  When the powder particles in the slurry are settled in the settling tank 5 to concentrate the slurry, the sedimentation speed of the powder particles is proportional to the square of the particle diameter and proportional to the true specific gravity. Therefore, if the slurry contains a low specific gravity powder and a high specific gravity powder, the high specific gravity powder has a true specific gravity more than twice that of the low specific gravity powder, the high specific gravity powder is compared with the low specific gravity powder. As a result, the sedimentation rate is twice or more larger, and the high specific gravity powder settles first. Therefore, in the slurry containing two kinds of powders having different specific gravities as described above, the sediment is separated in the sedimentation tank.

  Since the present invention aims to achieve slurry concentration without causing separation in such a slurry, it includes a low specific gravity powder and a high specific gravity powder, and the high specific gravity powder has a true specific gravity and a low specific gravity powder. The slurry was limited to twice or more of the slurry.

  The present invention is directed to a slurry in which 30% by mass or more of the solid content is particles having a particle size of 10 μm or less. This is because the effect of the present invention is exhibited in the slurry containing the powder having such a small particle diameter. That is, in the sedimentation and concentration of the slurry, the smaller the particle size (especially, 10 μm or less), the more difficult it is to settle (they tend to flow out together with the supernatant), and the proportion of the small particle size powder is high (30% This is because the components of the concentrated slurry greatly change when they flow out without being settled.

  In the slurry concentration method of the present invention, a flocculant is added to the slurry, the slurry is agitated in the agglomeration reaction tank to agglomerate solids in the slurry, and then the agglomerated powder is settled in the sedimentation tank. To concentrate the slurry. In the case shown in FIG. 1, the coagulant supplied from the coagulant supply device 4 is supplied to the pre-concentration slurry in the aggregation reaction tank 2. Aggregated agglomerates are mixed uniformly with high specific gravity powder and low specific gravity powder, so there is no difference in specific gravity between the agglomerates, so that uniform sediment can be obtained in the subsequent sedimentation tank. It becomes.

  In the present invention, the slurry is stirred by rotating the stirring blade 3 in the aggregation reaction tank 2. Usually, a cylindrical agglomeration reaction tank 2 is prepared, and agitation is performed using an agitation blade 3 having a rotation axis that coincides with the axis of the agglomeration reaction tank 2. As the stirring blade 3, a propeller type, a paddle type, a spiral type, an anchor type, a comb type, and a turbine type can be used, but a paddle type or an anchor type with a gentle stirring and less shearing effect is preferable. By rotating the stirring blade 3, a swirl flow swirling in the horizontal plane is generated in the agglomeration reaction tank 2, and the slurry is gradually moved from the bottom to the upper part of the agglomeration reaction tank 2 while swirling the slurry. Therefore, new slurry is supplied from the bottom of the agglomeration reaction tank 2, overflows from the upper part of the agglomeration reaction tank 2, and is supplied to the settling tank 5.

In the present invention, the stirring is performed by forming a swirl flow so that the Reynolds number Re calculated by the following formula (1) is 1500 or more when stirring.
Re = ρ × n × d ² / μ (1)
Where ρ: liquid density (kg / m ³ ), n: rotation speed of the stirring blade (sec ⁻¹ ), d: diameter of the stirring blade (m), μ: liquid viscosity (kg / m · sec).

  If the Reynolds number Re is too small, an aggregate obtained by agglomerating the high specific gravity powder and the low specific gravity powder is deposited on the bottom of the agglomeration reaction tank 2. When the Reynolds number Re is 1500 or more, the agglomeration reaction is satisfactorily finished without being accumulated, and discharged together with the slurry from the upper part of the agglomeration reaction tank.

  On the other hand, if the Reynolds number Re is too large, the agglomerated particles are destroyed and the aggregating effect cannot be exhibited. If the Reynolds number Re is 2100 or less, the aggregated effect of the present invention can be exhibited without destroying the aggregated particles.

  In the present invention, it is preferable that the low specific gravity powder includes at least one of pulverized coal and coke powder, and the high specific gravity powder includes at least one of iron oxide, chromium oxide, nickel oxide, and manganese oxide. In the slurry having such a composition, the true specific gravity when coke powder is used as the low specific gravity powder is about 1.8 to 1.9, and the true specific gravity when iron oxide is used as the high specific gravity powder is 5. The ratio of the true specific gravity of the high specific gravity powder and the low specific gravity powder is twice or more. For this reason, the conventional slurry concentration method cannot perform uniform concentration, and it is possible to perform uniform concentration only by using the method of the present invention.

  In the present invention, when the slurry having a slurry concentration of 20 to 40% by mass is processed and concentrated to a slurry concentration of 45 to 55% by mass, the residence time of the slurry in the settling tank 5 is controlled within a certain time range. preferable.

  In order to uniformly mix the slurry containing the low specific gravity powder and the high specific gravity powder, the slurry concentration before concentration is preferably 20 to 40% by mass. If the slurry concentration before concentration is too low, it becomes difficult to concentrate the slurry to a sufficiently high concentration in the sedimentation tank 5, but sufficient concentration can be performed if the slurry concentration is 20% by mass or more. If the slurry concentration before concentration is too high, it is difficult to uniformly mix the solid content in the slurry, but uniform mixing can be performed if the slurry concentration is 40% by mass or less.

  In the present invention, the concentration of the slurry after concentration is 45 to 55% by mass. If the concentration of the slurry after concentration is too low, it will be difficult to perform sufficiently efficient dewatering in the subsequent dewatering step. However, if the concentration of the slurry after concentration is 45% by mass or more, dewatering is performed with good efficiency. It becomes possible. Further, if the concentration of the slurry after concentration is too high, it becomes difficult to discharge the slurry from the bottom of the settling tank 5 and the possibility of clogging the piping increases. However, the concentration of the slurry after concentration is 55% by mass or less. If it exists, it becomes possible to perform a favorable operation | work, without obstruct | occluding piping.

  In the present invention, the preferable range of the slurry concentration after the concentration of the slurry is very narrow as 45 to 55% by mass, and therefore it is important to perform control for maintaining this preferable range. In the present invention, the slurry concentration in the sedimentation tank 5 is controlled within a certain time range to maintain the concentration of the slurry after concentration in a suitable range.

The concentration of the slurry after concentration varies depending on the residence time of the slurry in the settling tank 5. The longer the residence time, the higher the concentration of the slurry after concentration, and the shorter the residence time, the lower the slurry concentration. And if residence time was 30 minutes or more and less than 60 minutes, it discovered that the slurry density | concentration after concentration was controllable in the suitable range of 45-55 mass%. Here, the residence time of the slurry in the settling tank means a value obtained by dividing the internal volume of the settling tank 5 by the slurry inflow amount 11 (m ³ / hr).

  The slurry concentrated to a slurry concentration of 45 to 55% by mass (water content 45 to 55% by mass) is extracted from the settling tank 5, and then dehydrated by a dehydrator 7 to reduce the water content to 17 to 27%. In the present invention, since the slurry concentration is concentrated to 45 to 55% by mass at the stage of charging into the dehydrator 7, the water content after dehydration can be reduced as compared with the prior art, and the treatment of the dehydrator 7 is performed. Capability can be improved, and the number of installed dehydrators 7 can be reduced or the size of the dehydrators 7 can be reduced.

  The dehydrator 7 for further dehydrating the slurry concentrated by the slurry concentration method of the present invention may be of any type as long as the water content after dehydration becomes the value indicated, but the slurry is placed on the filter cloth. A type dehydrator, a filter press dehydrator, a vacuum drum dehydrator, or a centrifugal dehydrator that is poured and squeezes the slurry and filter cloth with a pair of upper and lower pressing rolls is preferable.

As described above, the residence time of the slurry in the settling tank 5 means a value obtained by dividing the internal volume of the settling tank 5 by the slurry inflow amount 11 (m ³ / hr). Since the internal volume of the settling tank 5 is constant, the residence time of the slurry is determined by the slurry inflow amount 11. Therefore, when the supply amount 12 of the slurry before concentration is lowered, the slurry inflow amount 11 is also lowered accordingly, and the residence time of the slurry is increased. If the residence time exceeds the upper limit of the preferred range, the concentration of the slurry after concentration becomes too high, and it may be difficult to discharge the slurry from the bottom of the settling tank.

  In the present invention, when the residence time in the settling tank 5 exceeds a predetermined time, the above problem is solved by extracting the concentrated slurry from the lower part of the settling tank and introducing it again into the settling tank. That is, when the slurry supply amount before concentration decreases and the residence time in the settling tank 5 exceeds a predetermined time, the concentrated slurry is extracted from the lower part of the settling tank and is again put into the settling tank. If the amount of slurry added again is the circulation amount 13, the slurry inflow amount 11 to the settling tank 5 becomes a value obtained by adding the slurry supply amount 12 and the circulation amount 13, and as a result, the residence time in the settling tank is shortened, which is preferable. A good residence time. As a result, the concentration of the slurry after concentration can be maintained in a suitable concentration range.

  In the settling tank, there is an interface (hereinafter referred to as “slurry interface 17”) between the concentrated slurry and the supernatant liquid precipitated at the bottom. It has been found that when the slurry interface 17 exceeds a certain upper limit position and becomes a high position, the concentration of the slurry after concentration becomes too high and it becomes difficult to discharge the slurry from the bottom of the settling tank 5. That is, if the slurry interface 17 can be grasped, when the slurry interface 17 exceeds a certain upper limit, the slurry concentration after concentration is reduced to a certain preferable range by taking measures to reduce the slurry concentration after concentration. Can be maintained.

  In order to change the slurry discharge amount 15 in accordance with the operation state of the dehydrator 7 (number of operating units, dehydration speed, etc.), it is necessary to change the slurry supply amount 12 accordingly. In the present invention, the interface level (slurry interface 17) between the concentrated slurry and the supernatant liquid in the settling tank 5 is detected or estimated, and when the slurry interface level exceeds a preset upper limit, the slurry is fed to the settling tank. When the pressure falls below the preset lower limit, the slurry supply to the settling tank is restarted to maintain the balance between the slurry supply amount and the slurry discharge amount, and keep the concentration of the slurry after concentration within a suitable range. Made possible.

  In thickeners (sedimentation tanks) such as converter dust, concentrated slurry flows by draining slurry from the bottom of the sedimentation tank when the waste water containing dust continuously flows in and the slurry interface in the sedimentation tank exceeds the set value. Can be obtained. In this case, since the discharge of the concentrated slurry is intermittent, a storage facility for the concentrated slurry (water tank, stirring device, pump) is required to supply the dehydrator continuously. However, in the present invention, the concentrated slurry is stored by intermittently supplying the slurry to the settling tank by detecting or estimating the slurry interface in the settling tank so that the concentrated slurry can be continuously discharged from the bottom of the settling tank. Equipment is no longer needed.

  The slurry interface 17 can be detected by an interface meter using ultrasonic waves. Further, the slurry interface can be estimated by the following method.

  In general, a circular cylinder portion called a center well 6 is disposed in the center of the settling tank 5, and slurry is supplied into the center well 6. The liquid level 19 in the center well 6 is higher than the liquid level 18 outside the center well, and a level difference may occur. And it turned out that this level difference becomes large, so that the slurry interface 17 in a sedimentation tank becomes high. Therefore, by grasping the relationship between the liquid level difference and the slurry interface 17 in advance, it is possible to detect the liquid surface level difference inside and outside the center well and to estimate the slurry interface level therefrom. Since the liquid level 18 outside the center well is normally kept constant, it is possible to measure the liquid level difference inside and outside the center well by detecting only the liquid level 19 inside the center well. is there.

  As the flocculant used in the present invention, it is preferable to use a weak anionic polymer flocculant or a nonionic polymer flocculant. The reason why the weak anionic polymer flocculant is preferable is that the surface of the metal oxide particles is positively charged, so that the negatively charged polymer flocculant effectively acts on the aggregation. The reason why the nonionic polymer flocculant is preferable is that it can be used for a relatively wide range of powders because the charge is intermediate between positive and negative.

  The amount of the flocculant added is preferably 0.01 to 0.07% by mass relative to the mass of the solid substance in the slurry. If the amount of the flocculant added is too small, the powder particles will be insufficiently aggregated and separated in the sedimentation tank, and a low specific gravity and small particle size powder will flow out to the supernatant in large quantities. If 0.01 mass% or more is added with respect to the mass of the solid substance, the problem does not occur. In addition, if the amount of the flocculant added is too large, the aggregate becomes too large and accumulates in the agglomeration reaction tank, or the concentration of the slurry after concentration becomes too high, and the discharge pipe at the bottom of the sedimentation tank is blocked. If the addition amount is 0.07% by mass or less with respect to the mass of the solid substance in the slurry, the problem does not occur.

  In the present invention, it is particularly preferable that one or both of the low specific gravity powder and the high specific gravity powder include dust or sludge generated in the steel manufacturing process. From the steel manufacturing process, dust, mainly iron oxide, and precipitates of iron compounds in wastewater are generated in large quantities. In addition, carbon sources such as pulverized coal and powdered coke are generated as dust and sludge from the steel manufacturing process. By applying the slurry concentration method of the present invention using a slurry containing a large amount of carbon source among these dust and sludge as a low specific gravity powder and using a slurry containing a high specific gravity powder containing a lot of iron oxide, Since a highly concentrated slurry containing a carbon source and an iron oxide source can be efficiently produced, the highly concentrated slurry can be further dehydrated and used as a raw material for producing reduced iron.

  The present invention was applied when a slurry containing coke powder as a low specific gravity powder and a slurry containing iron oxide as a high specific gravity powder were mixed, and the slurry was concentrated and dehydrated to produce a reduced iron production raw material. The slurry containing iron oxide uses fine powder converter dust generated in the wet dust collection process of the converter gas in the iron manufacturing process. The true specific gravity of the coke powder as the low specific gravity powder is 1.8, the true specific gravity of the iron oxide as the high specific gravity powder is 5.2, and the specific gravity difference between the two is more than twice.

  In the slurry before concentration, the ratio of coke powder was 13 to 15.5% by mass and the ratio of iron oxide was 70.1 to 72.6% by mass in the total solid content. Moreover, the ratio of the particle | grains with a particle size of 10 micrometers or less among solid content was 54 mass%. The slurry concentration in the slurry before concentration is around 25% by mass.

  The slurry was concentrated using the apparatus shown in FIG. First, the slurry to which the coagulant is added from the coagulant supply device 4 is stirred by rotating the stirring blade 3 in the coagulation reaction tank 2, and then the powder is settled and concentrated in the settling tank 5, and the concentrated slurry is taken out. The dehydrator 7 was supplied.

The agglomeration reaction tank 2 has an inner diameter of 1.2 m and an inner volume of 1.7 m ³ , and the slurry is stirred using a stirring blade 3 having a diameter of 1.1 m disposed therein. The stirring blade 3 has two blades. By changing the rotation speed of the stirring blade 3 from 53 rpm to 90 rpm, the Reynolds number calculated by the equation (1) was changed from 1350 to 2290. The liquid density (ρ) for the Reynolds number Re calculation was 1259 kg / m ³ , and the liquid viscosity (μ) was 1.0 kg / m · sec.

  As the flocculant, a nonionic polymer flocculant (specifically, Tedeflok TKI-318 (manufactured by TDE)) was used, and the amount of flocculant added was 0.02% with respect to the solid content mass in the slurry.

The sedimentation tank 5 has an internal volume of 46.0 m ³ , a center well 6 is disposed in the center of the tank, and slurry is supplied into the center well 6. The target residence time of the slurry was 30 to 60 minutes. The supply amount of the slurry is 57 m ³ / hr, and the actual residence time is 48.4 minutes.

The slurry interface level in the settling tank was detected by measuring the liquid level 19 in the center well and estimating the slurry interface level from this liquid level.
(Example of the present invention)
The slurry was concentrated by setting the stirring blade rotation speed of the agglomeration reaction tank 2 to 65 rpm and the Reynolds number Re calculated by the formula (1) to 1650.

  The slurry before and after the concentration was collected every hour for 4 hours after the start of the slurry concentration, and the slurry concentration and the components were evaluated. The results are shown in Table 1. As is clear from Table 1, the concentration of the slurry after concentration is maintained in a favorable range of 45 to 55 mass% over 4 hours, and the Fe content and C content in the slurry after concentration are uniformly maintained. I was able to.

(Comparative Example 1)
The slurry was concentrated by setting the rotation speed of the stirring blade of the agglomeration reaction tank to 90 rpm and the Reynolds number Re calculated by the formula (1) to 2290.

  Since the Reynolds number Re was too large, the particles aggregated in the aggregation reaction tank were destroyed. Therefore, the carbon content could not be completely settled in the settling tank, and the carbon powder flowed into the overflow water, resulting in a decrease in the carbon component ratio in the concentrated slurry as shown in Table 2.

(Comparative Example 2)
The slurry was concentrated by setting the rotation speed of the stirring blade of the agglomeration reaction tank to 53 rpm and the Reynolds number Re calculated by the formula (1) to 1350.

  Since the Reynolds number Re was too low, slurry was deposited at the bottom of the agglomeration reaction tank, and stirring became impossible.

  Under the same conditions as in the inventive example of Example 1, the slurry was concentrated and dehydrated to produce a reduced iron production raw material. The slurry concentration at the inlet of the coagulation reaction tank was 32.3%. Moreover, in order to make the slurry density | concentration after concentration into the range of 45-55%, it turns out that what is necessary is just to control the residence time of the slurry in a settling tank in the range for 30 to 60 minutes.

  Table 3 shows the results.

  No. in Table 3 No. 1 to 3 do not perform “circulation” in which the concentrated slurry is extracted from the lower part of the settling tank and is again charged into the settling tank. The residence time in the settling tank fluctuated due to fluctuations in the amount of slurry supplied. No. No. 1 had a residence time as short as 23 minutes, and the slurry concentration after concentration was 42.6%, which was less than the target slurry concentration. No. No. 2 had a good residence time of 55 minutes, and the slurry concentration after concentration was also in a good range. No. No. 3 had too long a residence time, and the slurry concentration after concentration was too high.

  Therefore, No. in Table 3 In No. 4, no. “Circulation” was performed at the same slurry supply amount as in No. 3. As a result, the residence time in the sedimentation tank was in a good range, and the slurry concentration after concentration could be in the good range.

It is a conceptual diagram which shows the slurry concentration method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material tank 2 Agglomeration reaction tank 3 Agitation blade 4 Coagulant supply apparatus 5 Settling tank 6 Center well 7 Dehydrator 11 Slurry inflow 12 Slurry supply 13 Circulation 14 Overflow water 15 Slurry discharge 16 Slurry 17 Slurry interface 18 Liquid surface 19 Liquid Level P Pump

Claims (7)

30% by mass or more of the solid content is a particle having a particle size of 10 μm or less, and includes a low specific gravity powder and a high specific gravity powder. The high specific gravity powder is a slurry having a true specific gravity that is twice or more that of the low specific gravity powder. In the method of concentrating,
The slurry to which the flocculant is added is stirred by forming a swirling flow so that the Reynolds number Re calculated by the following formula (1) is 1500 or more by rotating the stirring blade in the aggregation reaction tank, A method for concentrating a slurry, wherein the powder aggregated in a settling tank is allowed to settle.
Re = ρ × n × d ² / μ (1)
Where ρ: liquid density (kg / m ³ ), n: rotation speed of the stirring blade (sec ⁻¹ ), d: diameter of the stirring blade (m), μ: liquid viscosity (kg / m · sec).   The low specific gravity powder includes at least one of pulverized coal and coke powder, and the high specific gravity powder includes at least one of iron oxide, chromium oxide, nickel oxide, and manganese oxide. The method for concentrating the slurry as described.   The slurry residence time in the settling tank is controlled within a certain time range when a slurry having a slurry concentration of 20 to 40% by mass is processed and concentrated to a slurry concentration of 45 to 55% by mass. Or the method for concentrating slurry according to 2 above.   The method for concentrating a slurry according to claim 3, wherein when the residence time in the settling tank exceeds a predetermined time, the concentrated slurry is extracted from the lower part of the settling tank and charged again into the settling tank.   When the interface level between the concentrated slurry and the supernatant liquid in the settling tank is detected or estimated, and when the interface level exceeds the preset upper limit, the slurry feed to the settling tank is stopped and falls below the preset lower limit The slurry concentration method according to claim 3 or 4, wherein the slurry feeding to the settling tank is resumed.   A weak anionic polymer flocculant or a nonionic polymer flocculant is added as the flocculant in an amount of 0.01 to 0.07% by mass with respect to the mass of the solid substance in the slurry. 6. The method for concentrating a slurry according to any one of 5 above.   The method for concentrating slurry according to any one of claims 1 to 6, wherein dust or sludge generated in a steel manufacturing process is included as one or both of the low specific gravity powder and the high specific gravity powder.

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