Powder recovery method and powder recovery equipment

Abstract

To provide a method for recovering a powder and an apparatus for recovering a powder capable of reducing oil removal energy from an oil-containing powder and enhancing an oil removal rate and a solid-liquid separation rate.SOLUTION: There is provided a method for recovering a powder from an oil-containing powder 10, which comprises: a slurrying step of mixing an oil-containing powder having a specific gravity of more than 1.05 and water 20 so that the viscosity is 0.003 to 2.00 PaS to generate slurry 30; an emulsification step of adding a volatile hydrophilic solvent 50 having a specific gravity of more than 1.05 and less than 2.0 to the slurry, followed by mixing to form an emulsion 40; and a powder phase separation step of filtering a solvent phase 50a and a water phase 20a while performing phase separation by centrifugal force to separate the powder phase, wherein the powder phase separation step is performed by a filtration type centrifugal separator having a scraping mechanism of a powder phase and when filtering the solvent phase and water phase, a powder phase deposited on the filtration surface is accumulated by the scraping mechanism.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a powder recovery method and a powder recovery system. [Background technology]

[0002] In various manufacturing industries, including the steel industry, large amounts of mixtures in which powders containing hydrophilic particles are dispersed in water or aqueous solutions are discharged. The mixtures are often discharged in the form of aqueous slurries. The powders contained in the mixtures are diverse, and in the steel industry, for example, they include scale, grinding waste, dust, leaching residues, fly ash, slag powder, and ore powder. All of these are also hydrophilic particles.

[0003] For example, scale and grinding dust are contaminated with oil and moisture (for example, rolling oil, lubricating oil, and cooling water used in rolling) that are inevitably generated during industrial production. Such scale and grinding dust containing oil and moisture contain 5 to 50% moisture and a few percent oil. Therefore, for the purpose of recycling or efficient use, it is necessary to remove the oil and moisture from powder such as scale and grinding dust.

[0004] Conventionally, a method of removing oil from powder containing oil (hereinafter also referred to as oil-containing powder) has been known to involve combustion treatment using a rotary kiln or the like. However, since the oil concentration of the oil-containing powder is low, a fuel supporting the combustion is required for the combustion treatment, which poses a problem of requiring a large amount of energy. In particular, when the oil concentration of the oil-containing powder is lower, high-grade (expensive) energy such as COG (coke oven gas) or heavy oil may be used as the fuel supporting the combustion, and in such cases, the above problem becomes more serious. In addition, when the powder is combusted, CO2 emissions also increase, which goes against the CO2 reduction that has become a particular issue in recent years.

[0005] Furthermore, in the case of scale with oil attached (hereinafter also referred to as oil-containing scale), the scale after combustion treatment to remove the oil is often used as an iron source in the sintering process, etc. However, there is a problem that FeO, the main component in the scale, is oxidized to Fe2O3 during the combustion treatment, which increases the amount of coke used in the sintering process.

[0006] In order to cope with such problems, various methods for separating oil from oil-containing powders have been investigated. For example, Patent Document 1 discloses a method for extracting oil from oil-containing scale into an organic solvent by mixing the oil-containing scale with an organic solvent as an extractant and stirring the mixture. Patent Documents 2 and 3 also disclose techniques for separating oil from a mixture containing oil-containing powder and recovering the powder. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-132011 A [Patent Document 2] JP 2017-177018 A [Patent Document 3] Japanese Patent Application Publication No. 7-116960 Summary of the Invention [Problem to be solved by the invention]

[0008] However, none of the techniques disclosed in Patent Documents 1 to 3 can fully solve the above-mentioned problems.

[0009] In light of the above, in a method for removing oil from oil-containing powder to recover high-purity powder, there is a strong demand for a method that consumes less energy when removing the oil (oil removal energy) and can remove the oil more stably and quickly.

[0010] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a powder recovery method and powder recovery equipment that can reduce the energy required to remove oil from oil-containing powder and increase the oil removal rate and solid-liquid separation rate. [Means for solving the problem]

[0011] The gist of the present invention is as follows.

[0012] [1] A method for recovering powder comprising the steps of: separating oil from a powder having oil attached thereto and recovering the powder, the method comprising the steps of: a slurrying step of mixing the oil-containing powder having a specific gravity of more than 1.05 with water to produce a slurry having a viscosity in the range of 0.003 to 2.00 Pa·S; an emulsification step of adding a first volatile hydrophobic solvent having a specific gravity of more than 1.05 and less than 2.0 to the slurry and then mixing to form an emulsion; a powder phase separation step of breaking down the emulsion by centrifugal force, and further separating the emulsion into an aqueous phase, a solvent phase, and a powder phase by centrifugal force, and filtering the solvent phase and the aqueous phase to separate the powder phase; a powder phase recovery step of recovering the separated powder phase; having The powder phase separation step is carried out by a filtration type centrifugal separator having a mechanism for scraping the powder phase, a collecting mechanism for collecting powder, the collecting mechanism being configured to collect the powder phase deposited on a filtration surface when filtering the solvent phase and the aqueous phase in the powder phase separation step, so that a thickness of a portion of the powder phase on the filtration surface is reduced. [2] The method for recovering powder described in [1] above, characterized in that, in the powder phase separation step, when the powder phase is accumulated by the scraping mechanism, the powder phase is accumulated on one end face side of the filtration surface, thereby imparting a gradient to the thickness distribution of the powder phase within the filtration surface and reducing the thickness of a portion of the powder phase. [3] The method for recovering powder described in [1] or [2] above, characterized in that the scraping mechanism for the powder phase in the powder phase separation process has a plate-shaped scraping plate, and the scraping plate is inserted into the centrifugal separator to accumulate the powder phase, thereby reducing the thickness of a portion of the powder phase. [4] The method for recovering powder according to the above-mentioned [1] or [2], characterized in that the scraping mechanism for the powder phase in the powder phase separation step is composed of the filtration surface inclined with respect to a plane parallel to the rotation axis of the centrifugal separator, and the inclination of the filtration surface reduces a thickness of a portion of the powder phase when centrifugal force is applied. [5] The method for recovering powder according to any one of the above [1] to [4], wherein the boiling point of the first volatile hydrophobic solvent at normal pressure is less than 95°C. [6] The method for recovering powder according to any one of the above [1] to [5], characterized in that the powder phase obtained in the powder phase recovery step is dried at a temperature higher than the boiling point of the first volatile hydrophobic solvent. [7] The method for recovering powder according to any one of the above [1] to [6], characterized in that the powder phase obtained in the powder phase recovery step is placed in a hot water tank having a water temperature higher than the boiling point of the first volatile hydrophobic solvent, the first volatile hydrophobic solvent is volatilized and removed, and then a slurry containing the powder is dehydrated in a dehydrator to recover the powder phase. [8] In the powder phase separation step, The method for recovering powder according to any one of the above items [1] to [7], further comprising a rinsing step of filtering the solvent phase and the aqueous phase to separate the powder phase, adding a second volatile hydrophobic solvent to the separated powder phase, and further applying centrifugal force to separate the solvent phase remaining in the powder phase, followed by filtration. [9] The method for recovering powder according to any one of the above [1] to [8], characterized in that a plurality of successive steps from the powder phase separation step to the powder phase recovery step are carried out in a single filtration-type centrifugal separator.

[10] The method for recovering powder described in [8] or [9] above, characterized in that the boiling point of the second volatile hydrophobic solvent at normal pressure is less than 95°C.

[11] The method for recovering powder according to any one of the above [8] to

[10] , characterized in that the powder phase obtained in the powder phase recovery step is dried at a temperature higher than the higher of the boiling points of the first volatile hydrophobic solvent and the second volatile hydrophobic solvent.

[12] The method for recovering powder according to any one of the above items [8] to

[11] , characterized in that the powder phase obtained in the powder phase recovery step is introduced into a hot water bath having a water temperature higher than the higher of the boiling points of the first volatile hydrophobic solvent and the second volatile hydrophobic solvent, the first volatile hydrophobic solvent and the second volatile hydrophobic solvent are removed by volatilization, and then a slurry containing the powder is dehydrated in a dehydrator to recover the powder phase.

[13] The method for adjusting the amount of the second volatile hydrophobic solvent added in the rinsing step includes: A solvent phase containing an oil is collected from the solvent phase separated in the rinsing step by gravity separation; Measure the absorbance of the oil-containing solvent phase; The amount of oil remaining in the powder phase after the powder phase recovery step is estimated from the measured absorbance value obtained; The method for recovering powder according to any one of the above [8] to

[12] , characterized in that the amount of the second volatile hydrophobic solvent added in the rinsing step is adjusted so that the estimated value of the residual oil content is equal to or less than a target value.

[14] The method for recovering powder according to any one of the above [1] to

[13] , characterized in that a surfactant is added in the emulsification step.

[15] A method for recovering powder according to any one of the above [1] to

[14] , characterized in that the oily powder is one or a mixture of two or more of the following: oily scale, oily grinding swarf, and oily coke powder.

[0013]

[16] A powder recovery system for separating oil from powder having oil attached thereto and recovering the powder, comprising: A slurrying device that mixes the oil-containing powder having a specific gravity of more than 1.05 with water to produce a slurry; an emulsifier for adding a first volatile hydrophobic solvent having a specific gravity of more than 1.05 and less than 2.0 to the slurry and then mixing to form an emulsion; a powder phase separation device for breaking down the emulsion by centrifugal force, and further separating the emulsion into an aqueous phase, a solvent phase, and a powder phase by the centrifugal force, and filtering the solvent phase and the aqueous phase to separate the powder phase; having The powder phase separation device is a filtration type centrifugal separator having a mechanism for scraping the powder phase, The scraping mechanism includes: A powder recovery system, characterized in that it is a mechanism for collecting the powder phase that has accumulated on a filtration surface when the solvent phase and the aqueous phase are filtered.

[17] The powder recovery equipment described in

[16] above, characterized in that the scraping mechanism has a plate-shaped scraping plate, and the scraping plate is inserted into the centrifugal separator to accumulate the powder phase.

[18] The powder recovery equipment described in

[16] above, characterized in that the scraping mechanism is composed of the filtering surface inclined with respect to a plane parallel to the rotation axis of the centrifugal separator. Effect of the Invention

[0014] According to the above aspects of the present invention, it is possible to provide a powder recovery method and powder recovery equipment that can reduce the energy required to remove oil from oil-containing powder and increase the oil removal rate and solid-liquid separation rate. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing the state of oil and water in oil-containing scale. [Diagram 2] FIG. 2 is a flowchart illustrating the powder recovery method according to this embodiment. [Diagram 3] FIG. 3 is a schematic diagram for explaining an overview of the powder recovery method according to this embodiment. [Figure 4]FIG. 4 is a schematic diagram for explaining the modification of the powder surface by a surfactant in the emulsification step of this embodiment. [Diagram 5] FIG. 5 is a schematic diagram showing a powder recovery facility 1 according to this embodiment and a continuous treatment (continuous process) using the same. [Figure 6] FIG. 6 is a schematic cross-sectional view of a powder phase separation device (filtration centrifuge) 80 in which a continuous filtration centrifuge is used. [Figure 7] FIG. 7 is a schematic cross-sectional view of a batch-type filtering centrifuge applied as a powder phase separation device (filtering centrifuge) 80. As shown in FIG. [Figure 8] FIG. 8 is a graph showing the relationship between the blending ratio of water and powder (water / powder (g / g)) and the viscosity (Pa·s) of the slurry in Examples 1-6 to 1-10. [Figure 9] FIG. 9 is a graph showing the relationship between the viscosity (Pa·s) of the slurry and the oil removal rate (%) in Examples 1-6 to 1-10. [Figure 10] FIG. 10 is a graph showing the relationship between the compounding ratio of cleaning solvent to powder (cleaning solvent / powder (g / g)) and the oil removal rate (%) in Examples 1-11 to 1-14. [Figure 11] FIG. 11 is a graph showing the relationship between the oil concentration in the solvent and the absorbance of the solvent phase in Example 5. [Figure 12] FIG. 12 is a graph showing the relationship between the absorbance of the solvent phase and the oil concentration in the cake in <Example 5>. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The powder recovery method and powder recovery equipment according to the present embodiment will be described with reference to the drawings. In this specification and the drawings, components having substantially the same functional configurations are given the same reference numerals to avoid repeated explanation. A numerical range expressed using "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits.

[0017] First, the object to be treated, the solution, etc. in the powder recovery method will be described together with new findings obtained by the present inventors.

[0018] The object to be treated in the powder recovery method of this embodiment is a powder having oil attached thereto (oil-containing powder), such as scale generated in a rolling process, grinding dust, etc. The scale referred to here is scale containing oil and moisture, and is also called oil-containing scale or oil-containing sludge.

[0019] The particle size of the oil-containing powder to be treated is not particularly limited, but for example, the oil-containing powder may be one having an average particle size of 5 μm to 200 μm. The particle size of the powder can be measured by a laser diffraction / scattering method, and the average particle size is based on the volume.

[0020] Next, the state of existence of oil and water in oil-containing scale will be described using an example in which the oil-containing powder is oil-containing scale. Fig. 1 is a schematic diagram showing the state of oil and moisture in oil-impregnated scale. For the sake of convenience, the shapes and dimensional ratios of the components shown in Fig. 1 are illustrated to be different from the actual shapes, but the oil-impregnated powder in this embodiment is not limited to Fig. 1. As shown in Fig. 1, moisture and oil in oil-impregnated scale exist as oil and moisture in the bulk, oil and moisture in gaps, oil and moisture in capillaries, and oil and moisture adsorbed on the scale. Oil and moisture refers to a state in which oil and moisture are mixed. Moreover, the bulk here refers to the area that does not touch the interface of the scale particles.

[0021] Oil and moisture in the bulk refers to the moisture and oil present around scale particles. Oil and moisture in pores refers to the moisture and oil surrounded by gaps formed by aggregations of large and small solid particles such as scale. Oil and moisture in capillaries refers to the moisture and oil bound together by capillary pressure within the capillaries on the surface of the scale. Oil and moisture adsorbed to particles such as scale refers to the moisture and oil chemically adsorbed to the scale.

[0022] The oil and moisture in the bulk have almost no binding strength with particle groups such as scale, and are easily separated by applying external pressure. They can be separated by mechanical force, for example, dehydration and deoiling using a pressurized dehydrator or centrifugal dehydrator, or by natural dehydration and deoiling by leaving to stand.

[0023] On the other hand, because the oil and water in the gaps are surrounded by solid particles such as scale, it is very difficult to separate them by dehydration / de-oiling using mechanical force or by leaving them to stand.

[0024] Furthermore, the oil and moisture in the capillaries is moisture and oil that is held inside the capillaries on the surface of particles such as scale by capillary force, and like the oil and moisture in the voids, it is difficult to separate it by dehydration / deoiling using mechanical force or by leaving it to stand.

[0025] Furthermore, the oil and moisture adsorbed to particles such as scale is water and oil that is chemically bound to the surface or inside of the particles, and can only be separated by evaporation due to an increase in temperature or by chemical reaction.In other words, the oil and moisture in the gaps, in the capillaries, and adsorbed to the particles cannot be easily separated by normal dehydration and deoiling operations (mechanical dehydration and deoiling operations using a centrifugal dehydrator or filter press, or natural dehydration and deoiling by leaving to stand, etc.).

[0026] To address these issues, the inventors have investigated a method of using a solvent as a means of separating and removing oil and water, particularly oil. As a result of the investigation, it was thought that the oil in the bulk, gaps, and capillaries, as well as the oil adhering to the particles, could be adsorbed by a solvent and separated from the powder, and further investigations were carried out.

[0027] When an organic solvent is added to oil-containing scale and then stirred to extract the oil from the scale, the oil in the bulk is easily extracted because it comes into contact with the organic solvent. On the other hand, the oil in the gaps and capillaries is surrounded by scale, and water is also present in the gaps and capillaries at the same time as the oil. Therefore, the oil in the gaps and capillaries and the organic solvent are blocked by the water and scale, and the organic solvent cannot easily come into contact with the oil in the gaps and capillaries. In other words, when it comes to the oil in the gaps and capillaries, the oil in the oil-containing scale is not easily extracted by simply adding an organic solvent and stirring, and the oil content is not easily reduced.

[0028] The inventors have discovered that the oil content in oil-containing scale can be reduced by replacing the oil in the gaps and capillaries, which cannot be easily separated by ordinary dehydration and deoiling operations, with an easily volatile hydrophobic organic solvent (hereinafter also referred to as a volatile hydrophobic solvent), and then volatilizing the volatile hydrophobic solvent in the gaps and capillaries.

[0029] In addition, it was discovered that by selecting as a volatile hydrophobic solvent an organic solvent that has a boiling point of less than 95°C at normal pressure and is liquid at room temperature and pressure, it is possible to suppress the evaporation of water and to allow the organic solvent to evaporate primarily.

[0030] In addition, when a hydrophobic organic solvent is used as a means for separating oil from oil-containing powder, if a mixture of the organic solvent and oil-containing powder is left to stand after strong stirring, it becomes an emulsion in which many powder particles are dispersed in the aqueous phase between the solvent droplets. However, it was found that if the mixture is not fully emulsified, the oil extraction by the solvent does not proceed. In the region where the mixture is not emulsified, the powder does not have sufficient fluidity in the slurry consisting of water and oil-containing powder, so the solvent is not mixed uniformly and it is thought that the oil extraction does not proceed easily. Therefore, when emulsifying a mixture of an organic solvent and oil-containing scale, it is important to determine the mixing ratio of the oil-containing powder, water, and solvent after fully understanding the region where the emulsion will be formed.

[0031] In addition, generally, when a mixture of a hydrophobic organic solvent and water is strongly stirred and left to stand, an emulsion is temporarily formed, but the emulsion state is often dissolved in a short time. However, when a mixture containing a fine powder with high hydrophilicity (wettability), such as the above-mentioned mixture of fine oil-containing powder and organic solvent, is strongly stirred and left to stand, the emulsion may not be easily broken and may become stable. This is because the fine powder, which is a solid content, functions as an emulsifier, and the fine powder is present at the interface between the fine water droplets and the organic solvent phase, or the interface between the fine organic solvent droplets and the aqueous phase, thereby stabilizing the emulsion. When the emulsion is stabilized, the hydrophobic organic solvent and water cannot be easily separated, so it is necessary to break the emulsion.

[0032] Therefore, the present inventors have investigated a method of breaking down an emulsion by applying centrifugal force using a filtration type centrifugal separator. As a result, they have found that it is possible to break down an emulsion and separate it into a solvent, an aqueous phase, and a powder phase, and to filter the solvent phase and the aqueous phase and recover only the powder phase. In this way, by applying centrifugal force to an emulsion, the fine powder present in the aqueous phase between the solvent droplets is moved in the direction of the centrifugal force, resulting in an emulsion consisting of only water and solvent. As a result, the solvent droplets coalesce and become larger, and the emulsion is dissolved (demulsified), i.e., broken, in a short time.

[0033] The present invention has been made based on the new findings described above. Next, a powder recovery method and a powder recovery system according to an embodiment of the present invention will be described with reference to the drawings.

[0034] <1. Powder recovery method> Fig. 2 is a flow chart showing the powder recovery method according to the present embodiment, and Fig. 3 is a schematic diagram for explaining the outline of the powder recovery method according to the present embodiment. As shown in FIG. 2, the powder recovery method according to this embodiment includes a slurrying step S1, an emulsifying step S2, a powder phase separating step S3, and a powder phase recovering step S4. Each step will be described below with reference to Fig. 3. For ease of explanation, Fig. 3 shows a case where a batch-type filtering centrifuge and a centrifugation container 200 are used, but the powder recovery method according to this embodiment is not limited by the device used.

[0035] (Slurrying step S1) The slurrying step S1 is a step in which oil-containing powder 10 and water 20 are mixed in a container 100 to produce a slurry 30 (FIG. 3(a)). In the slurrying step S1, first, powder 10 and water 20 are charged into a container 100 and stirred (mixed) to disperse powder 10 in water 20 and generate slurry 30.

[0036] The oil-containing powder 10 is a particle having a specific gravity of more than 1.05. The oil-containing powder 10 preferably contains hydrophilic particles, and examples of the hydrophilic particles include scale and grinding chips. The hydrophilic particles are particles that have an affinity for water and have the property of being easily mixed with water. The oil-containing powder 10 is more preferably composed of only hydrophilic particles, but may contain other types of particles, such as hydrophobic particles, as long as the effects of the present invention are not impaired. The hydrophobic particles are particles that are hydrophobic to water, and examples of the particles that constitute the oil-containing powder 10 include coke powder and plastic powder. Most of the particles that constitute the oil-containing powder 10 may be hydrophobic particles.

[0037] In the case where most of the oil-containing powder 10 is hydrophobic particles, when the oil-containing powder 10 is emulsified and then phase-separated using a filtration-type centrifuge, the gaps in the cake made of hydrophobic particles are filled with the hydrophobic solvent. Therefore, when the aqueous phase passes through next, it becomes a resistance and makes filtration difficult, but by scraping, the filterability of the aqueous phase is improved. The same is true for a mixture of hydrophobic particles and hydrophilic particles; when deliquified using a filtration-type centrifuge, the gaps in the cake made of the mixture are filled with the hydrophobic solvent, and when the aqueous phase passes through next, it becomes a resistance and makes filtration difficult, but by scraping, the filterability of the aqueous phase is improved.

[0038] The specific gravity of the oil-containing powder 10 is more than 1.05 and is greater than the specific gravity of the first volatile hydrophobic solvent (hereinafter also referred to as the cleaning solvent) 50 used in the subsequent emulsification step S2. This allows the oil-containing powder 10 to move to the solvent phase 50a when the emulsion is subsequently broken to effect phase separation. That is, the water 20 present between the particles of the oil-containing powder 10 can be replaced by the first volatile hydrophobic solvent 50. Note that, when hydrophobic particles are contained in the oil-containing powder 10, the hydrophobic particles move to the solvent phase 50a.

[0039] The particle size of the oil-containing powder 10 is not particularly limited, but the volume-based 50% particle size (d 50 ) is preferably 200 μm or less. In this embodiment, the water 20 present between the particles of the oil-containing powder 10 is replaced with the first volatile hydrophobic solvent 50, thereby reducing the energy required for drying the oil-containing powder 10 and efficiently recovering the powder. The first volatile hydrophobic solvent 50 evaporates with lower energy than the water 20. Therefore, by replacing the water 20 present between the particles of the oil-containing powder 10 with the first volatile hydrophobic solvent 50, the energy required for drying the oil-containing powder 10 can be reduced. And, the smaller the particle diameter of the oil-containing powder 10, the larger the gaps present between the particles of the oil-containing powder 10, so that more water 20 can be replaced with the first volatile hydrophobic solvent 50, and as a result, the above-mentioned effect is enhanced. From this viewpoint, it is preferable that the particle diameter of the oil-containing powder 10 is small, and the volume-based 50% particle diameter (d 50 ) is preferably 100 μm or less. More preferably, it is 80 μm or less, and even more preferably, it is 50 μm or less. On the other hand, if the volumetric 50% particle size of the oil-containing powder 10 is less than 1 μm, the amount of capillary water and adsorbed water will be greater than the interstitial water described in FIG. 1, and the hydrophilicity of the oil-containing powder 10 will be very high, and even if the treatment of this embodiment is performed, it may be difficult to remove the water 20 present between the particles of the oil-containing powder 10. Therefore, the lower limit of the volumetric 50% particle size of the oil-containing powder 10 is preferably 1 μm or more.

[0040] The volumetric 50% particle size (d 50) can be measured, for example, by the following measurement method using a laser diffraction particle size distribution analyzer. That is, the sample to be measured is slurried with water, and a small amount of sodium hexametaphosphate solution is added as a dispersant. Next, the sample is dispersed in the mixed liquid by stirring the mixed liquid and irradiating it with ultrasonic waves. Next, this mixed liquid is placed in the laser diffraction particle size distribution analyzer, and the particle size distribution is measured.

[0041] The oil-containing powder 10 may be any one of oily scale, oily grinding chips, and oily coke powder, or a mixture of two or more of them. As described above, the oil-containing powder 10 is preferably made of hydrophilic particles, but is more preferably scale or grinding chips. This is because there is a strong demand for recycling or efficient use of these oil-containing powders.

[0042] Scale is generated, for example, during hot rolling. Specifically, scale is generated on the surface of a slab by preheating the slab. Such scale is finely crushed during hot rolling and discharged together with the coolant water. In other words, a water-containing slurry (water-containing scale) in which fine scale particles are dispersed in the coolant water is discharged. The water-containing slurry generated during hot rolling often contains 3 to 8 mass % oil (mass % relative to the total mass of the powder).

[0043] The amount of water 20 added in the slurrying step S1 is equal to or greater than the amount that causes the powder 10 to become slurried in the water 20. In the subsequent emulsifying step, the first volatile hydrophobic solvent 50 is added to the slurry 30, and the viscosity of the slurry 30 increases. Therefore, it is better to set the viscosity in the slurrying step S1 lower than the target viscosity. Specifically, water 20 is added to the powder 10 so that the viscosity of the slurry in the slurrying step S1 is 2.00 Pa·S or less. The viscosity of the slurry is preferably 0.65 Pa·S or less, more preferably 0.50 Pa·S or less, and even more preferably 0.35 Pa·S or less. On the other hand, if too much water is added in the slurrying step S1, the probability of contact between the oil-containing powder 10 and the first volatile hydrophobic solvent 50 decreases in the emulsifying step S2 and subsequent steps, so it is necessary to lengthen the time required for the emulsifying step S2 and subsequent steps, i.e., the time required to extract the oil from the powder 10, or to increase the stirring intensity. Therefore, it is preferable to add water 20 to the oil-containing powder 10 so that the viscosity of the slurry in the slurrying step S1 is 0.003 Pa·S or more.

[0044] Here, the reason for limiting the viscosity in the slurrying step S1 will be explained below together with the results of the inventor's investigation. The present inventors have studied the correlation between the degree of emulsification in the emulsification step S2 described below and the progress of oil extraction, and have found that when emulsification is insufficient, the progress of oil extraction by the cleaning solvent is also insufficient. This is thought to be because, when emulsification is insufficient, the powder to which the oil is attached does not have sufficient fluidity in the slurry, so that the cleaning solvent is not mixed uniformly even when it is added, and the extraction of the oil is not promoted. Therefore, when emulsifying a mixture of the slurry and the cleaning solvent, it is important to adjust the mixing ratio so that the mixture is sufficiently emulsified. Therefore, the present inventors have focused on the viscosity of the slurry and found that by controlling the viscosity of the mixture of water and powder to a predetermined value or less, i.e., 2.00 Pa·S or less, when mixing the water and powder to form a slurry in the slurrying step S1, the mixture can be sufficiently emulsified in the emulsification step described below.

[0045] In order to extract the oil from the powder in the emulsion obtained by mixing and stirring the oil-containing powder, water, and cleaning solvent, each particle of the powder needs to come into contact with a droplet of the cleaning solvent. To do this, it is necessary to make the powder move freely in the aqueous phase. As a result of examining an index for evaluating this "free movement in the aqueous phase," the present inventor found that it can be evaluated by the viscosity of the slurry. When the solid concentration in the slurry, that is, the ratio of the powder, increases, the viscosity of the slurry increases rapidly and the fluidity of the slurry decreases significantly, so that even if the emulsion is subsequently formed, the opportunity for the powder to come into contact with the droplets of the cleaning solvent decreases rapidly. For this reason, in this embodiment, as described above, it is important to set the viscosity of the slurry in the slurrying step S1 to 2.00 Pa·S or less.

[0046] In this embodiment, the powder 10 and the water 20 are mixed in advance to form a slurry, and then the first volatile hydrophobic solvent 50 is added to the slurry 30. However, when the powder 10, the water 20, and the first volatile hydrophobic solvent 50 are mixed at the same time, the mixing of the water 20 and the powder 10 is difficult to proceed, and emulsification may be difficult. In particular, when the water / powder mixing ratio (g / g) is small, emulsification becomes difficult and the oil removal performance decreases. Therefore, in the slurrying step S1, it is preferable to mix the water 20 and the powder 10 in advance, form a slurry, add the first volatile hydrophobic solvent 50, mix, and emulsify.

[0047] The mixing device used in the slurrying step S1 is not particularly limited, but for example, a vessel equipped with stirring blades for stirring the mixture of the powder 10 and water 20, a line mixer, or the like can be used.

[0048] (Emulsion process S2) The emulsification step S2 is a step of adding a first volatile hydrophobic solvent 50 to the slurry 30 produced in the slurrying step S1 and stirring the mixture to form an emulsion 40 (FIG. 3(b)). In the emulsification step S2, first, a first volatile hydrophobic solvent 50 having a specific gravity of more than 1.05 and less than 2.0 is added to a container 100 containing a slurry 30 consisting of powder 10 and water 20, and the mixture is further stirred to form an emulsion 40. Note that in the emulsification step S2, a container other than the container 100 may be used to form the emulsion 40 by stirring.

[0049] In general, an emulsion means a dispersion solution of two immiscible liquids, one of which is dispersed as fine droplets in the other liquid, and is also called an emulsion. The emulsion 40 according to this embodiment means a dispersion solution in which two liquids (water 20 and a first volatile hydrophobic solvent 50) with different specific gravities and solid powder 10 are suspended.

[0050] The first volatile hydrophobic solvent 50 is a liquid having volatility and hydrophobicity, that is, a liquid having a property of low affinity for water (difficult to dissolve in water or difficult to mix with water). The first volatile hydrophobic solvent 50 is, for example, a liquid having a solubility in water of 0 g / L or more and 10.0 g / L or less at room temperature (25° C.). If the solubility of the first volatile hydrophobic solvent 50 in water is high, a large amount of water 20 remains in the first volatile hydrophobic solvent 50 when the water 20 present between the particles of the powder 10 is replaced with the first volatile hydrophobic solvent 50. In this case, there is a possibility that the energy required for drying the powder 10 after the powder phase recovery step S4 cannot be sufficiently reduced. From this viewpoint, the solubility of the first volatile hydrophobic solvent 50 in water is preferably 10.0 g / L or less at room temperature, more preferably 5.0 g / L or less. In this case, the water 20 remaining in the first volatile hydrophobic solvent 50 can be further reduced.

[0051] In this embodiment, "hydrophobic" may also mean a property including lipophilicity, and the first volatile hydrophobic solvent 50 may be, for example, an organic solvent or various oils having hydrophobicity.

[0052] The specific gravity of the first volatile hydrophobic solvent 50 is greater than that of water and less than that of the powder 10 to be collected. Specifically, the specific gravity of the first volatile hydrophobic solvent 50 is greater than 1.05 and less than 2.0. As a result, by breaking the emulsion in the powder phase separation step S3 described later, the phase structure in the centrifuge container 200 becomes, from the top, an aqueous phase 20a, a solvent phase 50a, and a powder phase 10a (see FIGS. 3(c) and (d)).

[0053] The boiling point of the first volatile hydrophobic solvent 50 is preferably less than 95° C. at normal pressure. If the upper limit of the boiling point is less than 95° C., the first volatile hydrophobic solvent 50 can be easily removed (for example, with steam, which is an inexpensive energy source) in the subsequent powder phase recovery step S4. There is no particular limit to the lower limit of the boiling point of the first volatile hydrophobic solvent 50, but since the oil extraction operation is easily carried out at room temperature, it is preferably 50° C. or higher.

[0054] In addition, the volatile heat value of the first volatile hydrophobic solvent 50 is preferably smaller than that of water. In this case, the first volatile hydrophobic solvent 50 can be easily removed by volatilization in the powder phase recovery step S4, and can be easily separated from the powder 10.

[0055] In addition, as the solvent used as the first volatile hydrophobic solvent 50, it is preferable to select a solvent with a large KB value (kauri-butanol value) in order to remove oil from the powder 10 more efficiently. By using a solvent with a large KB value as the first volatile hydrophobic solvent 50, the oil can be more easily absorbed. From the viewpoint of the KB value, it is preferable to use, for example, trichloroethylene, 1-bromopropane, etc. as the first volatile hydrophobic solvent 50. In addition, hydrofluoroether may be used as the first volatile hydrophobic solvent 50.

[0056] It is preferable that the amount of the first volatile hydrophobic solvent 50 added to the powder 10 to which oil is attached, that is, the rate of the cleaning solvent addition, is appropriately controlled from the viewpoint of the efficiency of extracting the oil. As described above, if the emulsification step S2 is not sufficiently performed, the extraction of the oil by the first volatile hydrophobic solvent 50 does not proceed sufficiently. In the region where the emulsion is not performed, the fluidity of the slurry 30 is low, so that the first volatile hydrophobic solvent 50 has few opportunities to come into contact with the powder to which oil is attached, and it is considered that the extraction of the oil does not proceed easily. Therefore, when the mixture of the slurry 30 and the first volatile hydrophobic solvent 50 is made into an emulsion, it is preferable to control the blending ratio of the mixture so that the viscosity of the slurry is within the above range.

[0057] In this embodiment, when the emulsion is broken to separate the phases in the powder phase separation step S3, the powder 10 is moved to the hydrophobic solvent phase 50a. In order to sufficiently move the powder 10 to the hydrophobic solvent phase 50a, it is effective to increase the affinity between the powder 10 and the solvent phase 50a. Therefore, in this embodiment, when the powder 10 contains hydrophilic particles, it is preferable to add a surfactant 90 to the slurry 30 in addition to the first volatile hydrophobic solvent 50 in the emulsification step S2. The manner of adding the surfactant 90 is not particularly limited. For example, the surfactant 90 may be added to the slurry 30 separately from the first volatile hydrophobic solvent 50, or may be added simultaneously.

[0058] FIG. 4 is a schematic diagram for explaining the modification of the surface of the powder 10 by the surfactant 90 in the emulsification step S2 of this embodiment. As shown in FIG. 4, the surfactant 90 has a hydrophilic group 91 and a hydrophobic group 92. The hydrophilic group 91 of the surfactant 90 faces the surface side of the powder 10, and the hydrophobic group 92 faces the outside of the powder 10. This can change the surface of the powder 10 from hydrophilic to hydrophobic, so that the amount of water 20 accompanying the powder 10 can be reduced when the powder 10 is moved from the aqueous phase 20a to the solvent phase 50a. That is, the water 20 surrounding the powder 10 can be replaced with a larger amount of the first volatile hydrophobic solvent 50. As a result, after the powder phase recovery step S4, the energy required for drying the powder 10 can be further reduced, and an improvement in the dryness can be expected. Note that FIG. 4 shows the state in which the surface of the powder 10 is modified by the surfactant 90, and the powder 10 is in a state of moving to the solvent phase 50a. As shown in FIG. 4, it can be seen that the water 20 is not attached to the part of the surface of the powder 10 to which the surfactant 90 is attached.

[0059] The surfactant 90 may be an oil-soluble surfactant, and is mainly an anionic surfactant, but may also be a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant. More specific examples include sodium sulfonate (also called Na sulfonate), calcium sulfonate (also called Ca sulfonate), magnesium sulfonate (also called Mg sulfonate), and the like, which are oil-soluble anionic surfactants. The surfactant 90 may be used alone or in combination of two or more types. The surfactant 90 is preferably stable at the temperature at which the surfactant is used, the functional group portion is preferably ionized at the pH of the slurry 30, and is preferably soluble in the first volatile hydrophobic solvent 50 at the temperature at which the surfactant is used to a concentration of 1 mg / L or more, more preferably 1 g / L or more. The amount of the surfactant 90 to be added is not particularly limited. As shown in the examples described later, the more the amount of the surfactant 90 to be added, the more the water 20 can be replaced by the first volatile hydrophobic solvent 50. As a result, the energy required for drying the powder 10 can be further reduced. However, as the amount of surfactant 90 added increases, the reduction in the amount of energy required to dry the powder 10 reaches a plateau. At this point, the amount of surfactant 90 added becomes a substantial upper limit.

[0060] (Powder phase separation process S3) The powder phase separation step S3 is a step in which the emulsion 40 formed in the emulsification step S2 is broken down by centrifugal force, and then the emulsion 40 is separated by centrifugal force into an aqueous phase 20a, a solvent phase 50a, and a powder phase 10a, and the solvent phase 50a and the aqueous phase 20a are filtered to separate the powder phase 10a (Figures 3(c) to (f)).

[0061] The powder phase separation step S3 can be carried out using a filtration type centrifugal separator, and for example, a powder phase separation device (filtration type centrifugal separator) 80 provided in the powder recovery equipment 1 according to this embodiment described later may be used. The powder phase separation step S3 of the present embodiment involves applying centrifugal force to the emulsion 40 to effect phase separation, while filtering the solvent phase 50a and the aqueous phase 20a to separate the powder phase 10a.

[0062] In the powder phase separation step S3, as shown in FIG. 3(c), first, the emulsion 40 in the centrifuge container 200 is broken by centrifugal force. The emulsion 40 of this embodiment is stable due to the presence of many powder particles 10 in the water 20 between the solvent droplets as shown in FIG. 3(b). In addition, the filtration resistance of the emulsion 40 is very large, so that the time required for filtration is long in a general suction filtration method. Therefore, in this embodiment, as shown in FIG. 3(c), centrifugal force is applied to the emulsion 40, so that the powder particles 10 present in large amounts in the water phase 20a between the solvent droplets can be moved in the direction in which the centrifugal force acts (the direction of the arrow in FIG. 3(c)). Furthermore, the solvent droplets are united to form the solvent phase 50a, and as a result, the emulsion 40 can be destroyed. At this time, the oil adhering to the surface of the powder particles 10 is absorbed into the first volatile hydrophobic solvent 50 (solvent phase 50a).

[0063] By applying centrifugal force in this manner to break the emulsion 40, the powder 10 moves to the solvent phase 50a. At this time, most of the water 20 present around the powder 10, particularly the water 20 present between the particles of the powder 10, is replaced with the first volatile hydrophobic solvent 50. Note that by adding a surfactant 90 in the preceding emulsification step S2, more water 20 can be replaced with the first volatile hydrophobic solvent 50.

[0064] When the emulsion 40 is broken, as shown in FIG. 3(d), the aqueous phase 20a, the solvent phase 50a, and the powder phase 10a are separated in this order from the top of the centrifugation vessel 200 (the opposite side to the filtration surface 201). At this time, the gaps in the powder phase 10a are mainly filled with the solvent phase 50a, and only a small amount of water 20 is present around the powder 10. Therefore, for example, at point A in FIG. 3(d), the filtration resistance of the solvent phase 50a is smaller than the centrifugal force, so that the solvent phase 50a is easily filtered from the filtration surface 201. That is, although phase separation progresses after the breakage of the emulsion 40, the solvent phase 50a can be discharged to the outside of the centrifugation vessel 200 without waiting for the completion of phase separation.

[0065] After the solvent phase 50a passes through the powder phase 10a and is discharged from the filtration surface 201, the aqueous phase 20a passes through the powder phase 10a, but as shown in Fig. 3(e), a large amount of the remaining first volatile hydrophobic solvent 50 remains in the gaps in the powder phase 10a. Therefore, for example, at point B in Fig. 3(e), the filtration resistance of the aqueous phase 20a is greater than the centrifugal force, so that the aqueous phase 20a cannot easily pass through the powder phase 10a and is difficult to be discharged by the centrifugal force alone. Therefore, in this embodiment, a scraping mechanism for the powder phase 10a is provided in the filtration type centrifugal separator, and the scraping mechanism promotes the discharge of the aqueous phase 20a. Specifically, as shown in FIG. 3(f), the powder phase 10a deposited on the filtration surface 201 is first accumulated in a portion of the filtration surface 201 (the portion on the left side of the figure) by the scraping mechanism. This reduces the amount of powder phase 10a located in other portions of the filtration surface 201 (the portion on the right side of the figure). That is, the thickness of a portion of the powder phase 10a in the filtration surface 201 is reduced. The thickness of a portion of the powder phase 10a may be zero. In the portion of the powder phase 10a where the thickness is reduced (the portion surrounded by the dotted line in FIG. 3(f)), the filtration resistance is reduced, so that the aqueous phase 20a easily passes through the powder phase 10a. As a result, the aqueous phase 20a can be discharged from the filtration surface 201 to the outside of the system, and the powder phase 10a can be separated from the aqueous phase 20a. In other words, by accumulating the powder phase 10a deposited on the filtration surface 201 using a scraping mechanism, it is possible to promote the discharge of the aqueous phase 20a out of the system, thereby increasing the solid-liquid separation speed. In Fig. 3(d) to Fig. 3(f), the direction of the arrows illustrated below the filtration surface 201 indicates the discharge direction of the solvent phase 50a and the aqueous phase 20a, and the thickness of the arrows indicates the degree of discharge. That is, for example, Fig. 3(f) shows that the discharge amount of the aqueous phase 20a discharged from the filtration surface 201 is large in the region where the powder phase 10a is thin and is small in the region where the powder phase 10a is thick.

[0066] The scraping mechanism will be described in detail later in the powder recovery equipment 1 according to the present embodiment, but may be, for example, a plate-shaped scraping plate. In this case, the plate-shaped scraping plate is inserted into the centrifuge container 200, and the powder phase 10a is scraped and accumulated, thereby reducing the thickness of a part of the powder phase 10a.

[0067] The scraping mechanism may be configured such that the filtering surface 201 is inclined with respect to a plane parallel to the rotation axis of the centrifugal separator. In other words, by configuring the filtering surface 201 to be inclined, deposition of the powder phase 10a on the entire filtering surface 201 can be suppressed, and part of the powder phase 10a can be accumulated on the end surface side of the filtering surface 201 by the action of centrifugal force.

[0068] When the powder phase 10a deposited on the filtration surface 201 is accumulated by the scraping mechanism as described above, the accumulation position and shape are not particularly limited as long as a region of the powder phase 10a with a reduced thickness is formed. For example, the powder phase 10a may be accumulated toward the outer periphery of the filtration surface 201 to provide a gradient in the thickness distribution of the powder phase 10a in the filtration surface 201, thereby reducing the thickness of a portion of the powder phase 10a. By reducing the thickness of a portion of the powder phase 10a in the filtration surface 201 in this manner, the filtration resistance of the portion is significantly reduced, and the aqueous phase 20a can be easily and quickly discharged from the filtration surface 201, thereby improving the solid-liquid separation speed.

[0069] The centrifugal force in the powder phase separation step S3 is preferably 10 G or more. If the centrifugal force is 10 G or more, the solvent phase 50a can easily pass through the powder phase 10a. Although there is no particular upper limit to the centrifugal force, if the centrifugal force exceeds 10,000 G, there are almost no applicable filtration type centrifugal separators, so the centrifugal force is preferably 10,000 G or less.

[0070] (Rinsing process S3´) In the powder phase separation step S3, the solvent phase 50a and the aqueous phase 20a are filtered to separate the powder phase 10a, and then a rinsing step S3' may be performed in which a second volatile hydrophobic solvent 51 (hereinafter also referred to as the rinsing solvent) is further added to the separated powder phase 10a to separate the solvent phase 50a remaining in the powder phase 10a.

[0071] As shown in FIG. 3(f), the separated powder phase 10a may contain a solvent phase 50a that has not been filtered. Since the residual solvent phase 50a' is a phase that has adsorbed oil but has not been filtered, it is preferable to thoroughly separate and remove the residual solvent phase 50a' in order to increase the purity of the powder 10. In this embodiment, it is preferable to perform a rinsing step S3' in which a second volatile hydrophobic solvent (rinsing solvent) 51 is added to the powder phase 10a containing such a residual solvent phase 50a' and the residual solvent phase 50a' is separated and removed from the powder phase 10a by centrifugal force. By additionally performing such a rinsing step S3' in the powder phase separation step S3, the residual solvent phase 50a' containing the oil remaining in the powder phase 10a can be thoroughly removed, and the powder 10 with high purity can be recovered.

[0072] The amount of the second volatile hydrophobic solvent 51 to be added is preferably calculated as follows. First, the residual solvent phase 50a' separated and removed in the rinsing step S3' is separated by gravity separation into an aqueous phase containing almost no oil and a solvent phase containing oil, and the absorbance of the solvent phase containing oil is measured. From the measured absorbance value obtained, the amount of residual oil in the powder phase after the powder phase recovery step S4 is estimated, and the amount of the second volatile hydrophobic solvent 51 added is adjusted so that the estimated value of the residual oil amount is equal to or less than a target value. That is, when the residual solvent phase separated and removed by the rinsing step S3' contains a large amount of oil (when the absorbance is high), it can be determined that a large amount of oil that was not completely removed from the powder phase 10a remains, and in that case, the amount of the second volatile hydrophobic solvent 51 added is increased. On the other hand, when there is almost no oil remaining in the residual solvent phase separated and removed by the rinsing step S3' (when the absorbance is low), it can be said that the oil has been sufficiently removed from the powder phase 10a, so the amount of the second volatile hydrophobic solvent 51 added can be reduced. This allows the residual solvent phase 50a' to be efficiently separated and removed from the powder phase 10a. In addition, the amount of residual oil in the powder phase after recovery can be controlled by the absorbance of the residual solvent phase 50a' containing oil separated by the rinsing step S3'.

[0073] The absorbance of the residual solvent phase 50a' containing the oil separated by the rinsing step S3' is measured, for example, by placing the residual solvent phase 50a' to be measured in a sealed cell and measuring the absorbance with an absorbance meter. Since oil is generally yellowish, an absorption wavelength of about 350 to 500 nm may be used when measuring the absorbance of the residual solvent phase 50a' containing the oil.

[0074] The second volatile hydrophobic solvent (rinsing solvent) 51 used in the rinsing step S3' may be the same as the first volatile hydrophobic solvent 50 described above, or may be different. As described later, the oil-containing solvent phase recovered from the cleaning waste liquid is distilled and then regenerated as an oil-free volatile hydrophobic solvent. This regenerated volatile hydrophobic solvent can be used as the first volatile hydrophobic solvent or the second volatile hydrophobic solvent. In addition, the solvent phase recovered from the rinsing waste liquid can also be used as the first volatile hydrophobic solvent (cleaning solvent) since it contains a small amount of oil. For these reasons, it is preferable to use the same solvent for the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51.

[0075] (Powder phase recovery process S4) The powder phase recovery step S4 is a step of recovering the powder phase 10a separated in the powder phase separation step S3.

[0076] In the powder phase recovery step S4, first, the powder phase 10a is recovered from the centrifugation container 200. Specifically, after the discharge (filtration) of the aqueous phase 20a is completed as shown in Fig. 3(f), the powder phase 10a remaining in the centrifugation container 200 is recovered. Note that the powder phase 10a after the discharge of the aqueous phase 20a is often a cake-like mass of the powder 10 agglomerated, and is also called a "powder cake" or simply a "cake".

[0077] Next, the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 remaining in the collected powder phase 10a are removed. Since the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 that have not been completely discharged remain in the collected powder phase 10a, they need to be removed. Specifically, these solvents may be removed by, for example, drying removal or volatilization removal.

[0078] When the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 are removed by drying, the drying temperature is preferably a temperature higher than the boiling point of the first volatile hydrophobic solvent 50. This allows each solvent to be efficiently dried and removed from the powder phase 10a. When a hydrophobic solvent different from the first volatile hydrophobic solvent 50 is used as the second volatile hydrophobic solvent 51 in the rinsing step, the solvent may be dried and removed at a temperature higher than the boiling points of the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51.

[0079] The drying means is not particularly limited, but for example, an indirect heating type dryer, a vacuum indirect heating type dryer, or the like may be used for drying.

[0080] When the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 are removed by volatilization, the powder phase 10a is first put into a hot water bath with a water temperature higher than the boiling point of the first volatile hydrophobic solvent 50 to volatilize and remove the first volatile hydrophobic solvent 50. Since the powder phase 10a put into the hot water bath is slurried, the slurry is dehydrated in a dehydrator after the solvent is volatilized and removed. This makes it possible to recover the powder 10 from which each solvent has been removed. In addition, when a hydrophobic solvent different from the first volatile hydrophobic solvent 50 is used as the second volatile hydrophobic solvent 51 in the rinsing step, the water temperature of the hot water bath may be set to the higher of the boiling points of the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51.

[0081] As described above, most of the liquid contained in the powder phase (powder cake) 10a after the powder phase separation step S3 is the first volatile hydrophobic solvent 50 or the second volatile hydrophobic solvent 51, so the powder phase 10a can be dried with less energy (heat of vaporization). Therefore, the CO2 generated during drying of the powder phase 10a can be reduced. As shown in the examples described later, the energy required to dry the powder phase can be measured by differential scanning calorimetry (DSC), but it can also be measured by other methods, such as the Karl Fischer method.

[0082] Although the powder recovery method according to the present embodiment has been described above, the temperature and pressure during each step are not particularly limited, and may be performed, for example, at room temperature and pressure. In the present embodiment, it is preferable to perform a plurality of consecutive steps from the powder phase separation step S3 to the powder phase recovery step S4 using a single filtration type centrifugal separator.

[0083] In addition, in the powder recovery method according to this embodiment, each of the steps from the slurrying step S1 to the powder phase recovery step S4 can be carried out as a batch process. However, from the viewpoints of the solid-liquid separation speed, the powder recovery speed, and productivity, it is preferable to carry out these steps as a continuous process in which these steps are carried out simultaneously in parallel.

[0084] According to the powder recovery method of this embodiment, a filtration type centrifugal separator is used to extract and remove oil using a volatile hydrophobic solvent, so that the energy required for removing oil from oil-containing powder can be significantly reduced compared to conventional combustion treatment methods. In addition, after the emulsion is broken down by the filtration type centrifugal separator and separated into a powder phase (powder cake), an oil-containing solvent, and water, the powder phase is scraped and accumulated on the filtration surface, so that the water phase can be quickly discharged from the area where the thickness of the powder phase is reduced, and the powder phase can be recovered quickly and efficiently. In addition, since most of the voids in the recovered powder phase are volatile hydrophobic solvents, they can be easily removed, and low-moisture, high-purity powder containing almost no oil can be efficiently recovered. That is, according to the powder recovery method of this embodiment, a new and improved powder recovery method can be provided that can increase the oil removal rate and solid-liquid separation speed.

[0085] <2. Powder recovery equipment> Next, an embodiment of a powder recovery equipment for carrying out the powder recovery method of the present embodiment will be described. That is, the powder recovery equipment of the present embodiment is an equipment for separating oil from oil-adhered powder and recovering the powder. In addition, each device in the powder recovery equipment of the present embodiment may be provided in a batch manner, or may be provided so as to perform so-called continuous processing in which each device is operated simultaneously to proceed with processing continuously. Note that, from the viewpoint of powder recovery speed and productivity, it is preferable that the powder recovery process be a continuous processing (continuous process). In the following description, a case where continuous processing is carried out will be taken as an example of the recovery equipment of this embodiment.

[0086] FIG. 5 is a schematic diagram showing a powder recovery facility 1 according to this embodiment and a continuous treatment (continuous process) using the same. The powder recovery equipment 1 of this embodiment includes a slurrying device 60, an emulsifying device 70, and a powder phase separation device 80 that separates the powder phase by filtering the solvent phase and the aqueous phase while separating the powder phase by centrifugal force. Note that, although Fig. 5 shows a case where a continuous filtering centrifuge is used as the powder phase separation device 80, the present invention is not limited thereto, and various filtering centrifuges can be used.

[0087] The slurrying device 60 is a device that performs the slurrying step S1, and stirs and mixes the oil-containing powder 10 having a specific gravity of more than 1.05 with water 20 to generate the slurry 30. Any known device can be used as the slurrying device 60, and for example, a vessel equipped with a stirring blade and a motor for stirring the mixture of the powder 10 and the water 20, a line mixer, or the like can be used.

[0088] When the powder recovery method is performed as a continuous process, the slurrying apparatus 60 can be connected to the downstream emulsifying apparatus 70, for example, via piping. The slurry 30 generated in the slurrying apparatus 60 is sent to the emulsifying apparatus 70 through the piping. A pump P1 is connected to the piping, and the slurry 30 in the piping is sent to the emulsifying apparatus 70 by the pump P1.

[0089] The emulsification device 70 is a device that carries out the emulsification step S2, in which a first volatile hydrophobic solvent 50 having a specific gravity of more than 1.05 and less than 2.0 is added to the slurry 30, and then stirred and mixed to form the emulsion 40. A known emulsification device 70 can be used, and for example, a vessel equipped with a stirring blade and a motor for stirring the mixture of the slurry 30 and the first volatile hydrophobic solvent 50, a line mixer, or the like can be used.

[0090] When the powder recovery method is performed as a continuous process, the emulsification apparatus 70 can be connected to the downstream powder phase separation apparatus 80, for example, via a pipe, and the generated emulsion 40 is sent through the pipe to the powder phase separation apparatus 80. A pump P2 is connected to the pipe, and the emulsion 40 in the pipe is sent to the powder phase separation apparatus 80 by the pump P2.

[0091] The slurry 30 and the first volatile hydrophobic solvent 50 are introduced into the emulsifier 70. The slurry 30 is introduced into the emulsifier 70 from the slurryifier 60 through a pipe. The first volatile hydrophobic solvent 50 is introduced into the emulsifier 70, for example, from a solvent storage tank (not shown). In FIG. 5, the first volatile hydrophobic solvent 50 is supplied to a pipe that delivers the slurry 30, and is introduced into the emulsifier 70 together with the slurry 30. The first volatile hydrophobic solvent 50 may be directly introduced into the emulsifier 70 through a pipe separate from that for the slurry 30.

[0092] The emulsification device 70 stirs and mixes the slurry 30 and the first volatile hydrophobic solvent 50 by rotating the stirring blades with the motor M. As a result, the powder 10, the water 20, and the first volatile hydrophobic solvent 50 are strongly stirred, so that the above-mentioned emulsion 40 can be produced, and further, the first volatile hydrophobic solvent 50 acts as an extractant for the oil, so that the oil is extracted from the powder 10.

[0093] The powder phase separation device 80 is a filtration type centrifugal separator (filtration type centrifuge) that breaks down the emulsion by centrifugal force, and further separates the emulsion into an aqueous phase, a solvent phase, and a powder phase by centrifugal force, while filtering the solvent phase and the aqueous phase to separate the powder phase.

[0094] When each step of the powder recovery method is performed in a continuous process, the emulsion 40 is introduced into the filtration type centrifuge (powder phase separation device) 80 from the emulsification device 70 via piping, and then the emulsion 40 is centrifuged.

[0095] When the powder is collected in a continuous process, it is preferable to use a continuous filtering centrifuge as shown in Fig. 5 as the filtering centrifuge which is the powder phase separation device 80. It is more preferable to use a continuous filtering centrifuge which can use a volatile solvent and can separate various solvents and waste liquids such as the filtered solvent phase and the second volatile hydrophobic solvent 51 used in the Suzuki process from each outlet.

[0096] The filtering centrifuge (powder phase separation device) 80 in this embodiment has a scraping mechanism 81 for scraping the powder phase 10a separated by centrifugal force. The scraping mechanism 81 is a mechanism for accumulating the powder phase 10a deposited on a screen (filtering surface) 82 on a part of the filtering surface when filtering the solvent phase and the aqueous phase. By providing the scraping mechanism 81 in the filtering centrifuge 80, it is possible to achieve efficient and high-speed solid-liquid separation. In this embodiment, the scraping mechanism 81 is a scraper made of a spiral plate extending along the axial direction of the rotating shaft. The scraper is fixed to the rotating shaft. The outer peripheral end of the scraper is located near the inner surface of the filtering surface 82. The scraper rotates together with the rotating shaft to gradually move the powder phase 10a on the filtering surface 82 downward.

[0097] FIG. 6 shows a schematic cross-sectional view of a filtration centrifuge (powder phase separation device) 80 in the case where a vertical continuous filtration centrifuge is used. In the case of a vertical continuous filtration centrifuge, the emulsion 40 supplied from a supply port provided at the top of the machine is broken by centrifugal force, and the emulsion 40 is separated into a powder phase 10a, a solvent phase 50a, and an aqueous phase 20a on the filtration surface 82. The separated phases are arranged in the order of the powder phase 10a, the solvent phase 50a, and the aqueous phase 20a from the filtration surface 82 side. The solvent phase 50a in the emulsion 40 passes through the holes 82a in the screen (filtration surface) 82 rotating at high speed under the centrifugal force, and is discharged outside the system. On the other hand, the powder phase 10a in the emulsion 40 remains inside the screen 82 and is transported downwards in the machine by a scraper inside the rotor. The transported powder phase 10a is fed into a drying device (not shown) provided below the filtration centrifuge 80, or is discharged from an outlet provided below the filtration centrifuge 80 and transported via piping or the like to a drying device provided outside the system of the filtration centrifuge 80.

[0098] When a continuous filtering centrifuge is used as the filtering centrifuge (powder phase separation device) 80, this scraper corresponds to the scraping mechanism 81. Here, in the case of a vertical continuous filtration centrifuge, the solvent phase 50a of the emulsion 40 supplied from the top is filtered and discharged outside the system immediately after the centrifugal force acts on it, but the aqueous phase 20a has difficulty passing through the gaps in the powder phase 10a as described above. Therefore, in this embodiment, the powder phase 10a is scraped and accumulated by the scraper, and the aqueous phase 20a is discharged outside the system from the area where the thickness of the powder phase 10a is reduced.

[0099] 6 is provided so as to have a cross-sectional shape that is generally in the shape of an eight from the top to the bottom (upstream to downstream) of the machine body, i.e., a shape that diverges toward the bottom, about the rotation axis, but the shape of the screen 82 is not particularly limited to this. That is, the screen 82 may be parallel to the rotation axis, or may be provided so as to have a cross-sectional shape that is generally in the shape of an inverted eight from the top to the bottom (upstream to downstream) of the machine body, about the rotation axis, that is, so that the diameter of the screen 82 becomes smaller toward the bottom when the machine body is viewed in plan.

[0100] In the case of a vertical continuous type powder phase separation device (filtering type centrifuge) 80 as shown in FIG. 6, the emulsion 40 is transported downward by a scraper (scraping mechanism) 81, while being phase-separated by centrifugal force. At this time, the phase-separated powder phase 10a is scraped by the scraper 81 and deposited on the lower surface of the scraping surface of the scraper 81, but the deposited powder phase 10a tends to spread along the entire surface of the screen 82 due to the centrifugal force, and the area where the thickness of the powder phase 10a is small decreases, that is, the thickness of the powder phase 10a may become approximately uniform due to the centrifugal force. On the other hand, when the screen 82 is parallel to the rotation axis (perpendicular to the centrifugal force), or when it is inclined so as to form an inverted eight shape in cross section from the top to the bottom of the machine body (from upstream to downstream) about the rotation axis, the centrifugal force does not easily act to spread the powder phase 10a scraped by the scraper over the entire surface of the screen 82. This makes it possible to maintain the area of ​​the powder phase 10a having a small thickness, and allows the aqueous phase 20a to be discharged to the outside of the system quickly and efficiently.

[0101] The above describes the case where a continuous filtration centrifuge is used as the powder phase separation apparatus (filtration centrifuge) 80. However, a batch filtration centrifuge can also be used as the powder phase separation apparatus (filtration centrifuge) 80 of this embodiment, and in that case, the same structure and technical concept as the continuous type can also be applied.

[0102] Next, a powder phase separation device (filtering centrifuge) 80A in the case where a batch-type filter centrifuge is applied will be described. FIG. 7 shows a cross-sectional view of a powder phase separation device (filtering centrifuge) 80A in the case where a batch-type filtering centrifuge is used. In the powder recovery equipment of this embodiment, when a batch-type filtering centrifuge is used as the powder phase separation device, as shown in FIG. 7, the filtering surface 201 inclined with respect to the rotation axis becomes a scraping mechanism. That is, by inclining the filtering surface 201 (when the inclination angle α in FIG. 7 is 0°), which is usually installed parallel to the rotation axis, with respect to a plane parallel to the rotation axis, it is possible to suppress deposition of the powder phase 10a on the entire filtering surface 201 and promote accumulation of the powder phase 10a. Regarding the inclination angle α of the filtering surface 201, if the inclination angle α is more than 0°, the above-mentioned effect can be exhibited. Although the upper limit of the inclination angle α is not particularly limited, if the inclination angle α is excessively large, the length of the batch-type filtering centrifuge container 200 becomes large, and the centrifuge device becomes large, so that the inclination angle α is preferably 60° or less.

[0103] The inclination direction of the filtration surface 201 of the batch-type powder phase separation apparatus (filtration type centrifuge) 80A is not particularly important. That is, when the centrifuge container 200 containing the emulsion is placed in the powder phase separation apparatus 80A, the filtration surface 201 may be inclined in a direction in which the upper end side of the filtration surface 201 is inclined toward the rotation shaft (see FIG. 7), or the filtration surface 201 may be inclined in a direction in which the lower end side of the filtration surface 201 is inclined toward the rotation shaft. Regardless of the inclination direction, the effect of suppressing deposition of the powder phase 10a on the entire surface of the filtration surface 201 and promoting accumulation of the powder phase 10a can be obtained.

[0104] The powder phase separation apparatus 80, 80A has been described above. However, the powder phase (cake) separated by the powder phase separation apparatus 80, 80A contains volatile hydrophobic solvents, which must be removed. Specifically, these solvents can be removed by drying removal or volatilization removal. For example, when a vertical continuous filtration centrifuge is used as the powder phase separation apparatus (filtration centrifuge) 80, a hot water tank (not shown) can be provided below the machine, and the powder phase can be directly introduced into the hot water tank from the powder phase outlet. When the solvent is removed by drying removal, the cake discharged from the bottom of the machine can be introduced into a dryer using a pump for transferring the cake, or the like. EXAMPLES

[0105] Next, examples (experimental examples) of this embodiment will be described. In each of the examples described below, various tests were performed to confirm the effects of this embodiment. Note that each of the following examples was performed at room temperature and normal pressure.

[0106] <Example 1> The powder, hydrophobic solvent (cleaning solvent) and water were mixed and stirred under the conditions shown in Table 1A, and centrifuged under the conditions shown in Table 1B to recover the powder phase.

[0107] [Table 1A]

[0108] [Table 1B]

[0109] In Comparative Example 1-1, the ingredients (powder and hydrophobic solvent) and water shown in Table 1A were mixed under the mixing conditions shown in Table 1A. Specifically, oily scale and water were placed in a 100 ml glass container, sealed, and manually shaken to mix and form a slurry. After that, a hydrophobic solvent (cleaning solvent) was added to the slurry, which was then sealed, and further manually shaken to mix and stir. After stirring, the mixture was in an emulsion state. The emulsion was then poured into a general centrifuge vessel without a filtering surface at the bottom, and the centrifuge vessel was rotated in a batch-type tabletop centrifuge to apply centrifugal force for 10 seconds at a centrifugal acceleration of 1750 G. The phase separation state in the centrifuge vessel was then observed, and the powder phase (cake) that had settled at the bottom of the vessel was collected, and the heat of vaporization and the oil content in the powder phase were measured, and the oil removal rate was calculated.

[0110] In Comparative Example 1-2, the ingredients (powder and hydrophobic solvent) and water shown in Table 1A were mixed under the mixing conditions shown in Table 1A. Specifically, oily scale and water were placed in a 100 ml glass container, sealed, and manually shaken to mix and form a slurry. After that, a hydrophobic solvent (cleaning solvent) was added to the slurry, which was then sealed, and further manually shaken to mix and stir. After stirring, the mixture was in an emulsion state. The emulsion was then poured into a filtration-type centrifugation vessel with a filtration surface on the bottom (the filtration surface was parallel to the rotation axis, and the inclination angle α was 0 degrees), and this centrifugation vessel was rotated in a batch-type tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750 G. After that, the state of phase separation in the centrifugation vessel was observed, and the cake that had settled at the bottom of the vessel was collected, and the heat of vaporization and the oil content in the powder phase were measured, and the oil removal rate was calculated.

[0111] In Example 1-3, Comparative Examples 1-4 to 1-5, and Examples 1-6 to 1-10, the ingredients (powder and hydrophobic solvent) and water shown in Table 1A were mixed under the mixing conditions shown in Table 1A. Specifically, oily scale and water were placed in a 100 ml glass container, sealed, and manually shaken to mix and form a slurry. After that, a hydrophobic solvent (cleaning solvent) was added to the slurry, the container was sealed, and the container was further manually shaken to mix and stir. Then, a mixture of the slurry and the hydrophobic solvent was put into a filtration type centrifugation vessel having a filtration surface on the bottom (the filtration surface is parallel to the rotation axis, and the inclination angle α is 0 degrees), and the centrifugation vessel was rotated in a batch type tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. After that, the cake deposited on the bottom (filtration surface) of the centrifugation vessel was scraped by a scraping mechanism (spoon), and then the centrifugation vessel was rotated again in a tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. Note that the "number of scraping steps" in Table 1B is counted as one series of steps (centrifugal force action - scraping - centrifugal force action) described above. In addition, the phase separation state of the centrifugation vessel was observed every time the scraping step was performed, and the scraping operation and the centrifugation operation were repeated until the aqueous phase was discharged and disappeared. The number of scraping operation steps is shown in Table 1B. After the aqueous phase was discharged, the cake that had settled to the bottom of the vessel was collected, and the heat of vaporization and the oil content in the powder phase were measured to calculate the oil removal rate.

[0112] In Examples 1-11 to 1-17 and 1-21 to 1-24, the ingredients (powders and hydrophobic solvent) and water shown in Table 1A were mixed under the mixing conditions shown in Table 1A. Specifically, various powders and water were placed in a 100 ml glass container, sealed, and manually shaken to mix and form a slurry. After that, a hydrophobic solvent (cleaning solvent) was added to the slurry, sealed, and further manually shaken to mix and stir. Then, the emulsion was poured into a filtration type centrifugation vessel having a filtration surface (the filtration surface is parallel or oblique to the rotation axis, the inclination angle α is 0 to 30 degrees) on the bottom, and the centrifugation vessel was rotated in a batch type tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. Then, an oil-free volatile hydrophobic solvent (rinsing solvent) in the same amount as the cleaning detergent was poured into the centrifugation vessel, and the centrifugation vessel was further rotated in a tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. Then, the cake deposited on the bottom (filtration surface) of the centrifugation vessel was scraped up with a spoon, and the centrifugation vessel was rotated again in the tabletop centrifuge, and centrifugal force was applied for another 10 seconds at a centrifugal acceleration of 1750G. The state of phase separation in the centrifugation vessel was observed after each scraping step, and the scraping and centrifugation steps were repeated until the aqueous phase was completely discharged. The number of scraping steps is shown in Table 1B. After the aqueous phase was completely discharged, the cake that had settled at the bottom of the vessel was collected, and the heat of vaporization and the oil content in the powder phase were measured, and the oil removal rate was calculated.

[0113] In Examples 1-18 to 1-20, the ingredients (powder and hydrophobic solvent) and water shown in Table 1A were mixed under the mixing conditions shown in Table 1A. Specifically, scale and water were placed in a 100 ml glass container, sealed, and manually shaken to mix and form a slurry. Then, a hydrophobic solvent (cleaning solvent) was added to the slurry, sealed, and further manually shaken to mix and stir. At this time, a surfactant (Na-sulfonate) was added to the cleaning solvent at the addition rate shown in Table 1A. The addition rate of the surfactant shown in Table 1A is the addition rate relative to the powder (mass%, outside numbers). Then, the emulsion was poured into a filtration type centrifugation vessel having a filtration surface on the bottom (the filtration surface was parallel to the rotation axis, and the inclination angle α was 0 degrees), and the centrifugation vessel was rotated in a batch type tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. Then, an oil-free volatile hydrophobic solvent (rinsing solvent) in the same amount as the surfactant-containing cleaning solvent was poured into the centrifugation vessel, and the centrifugation vessel was further rotated in a tabletop centrifuge, and centrifugal force was applied for 10 seconds at a centrifugal acceleration of 1750G. Then, the cake deposited on the bottom (filtration surface) of the centrifugation vessel was scraped up with a spoon, and the centrifugation vessel was rotated again in the tabletop centrifuge, and centrifugal force was applied for another 10 seconds at a centrifugal acceleration of 1750G. The state of phase separation in the centrifugation vessel was observed after each scraping step, and the scraping and centrifugation steps were repeated until the aqueous phase was completely discharged. The number of scraping steps is shown in Table 1B. After the aqueous phase was completely discharged, the cake that had settled at the bottom of the vessel was collected, and the heat of vaporization and the oil content in the powder phase were measured, and the oil removal rate was calculated.

[0114] Next, the test results will be described.

[0115] As shown in Comparative Examples 1-1 to 1-2 and Example 1-3, it can be said that the oil content in the powder phase after recovery is lower and the heat of vaporization can be reduced in a filtering type centrifuge vessel having a filtering surface (Comparative Example 1-2) than in a general conventional centrifuge vessel having no filtering surface (Comparative Example 1-1). Furthermore, it can be said that the oil content in the powder phase after recovery is lower and the heat of vaporization can be reduced by using a filtering type centrifuge vessel having a filtering surface and then performing a scraping process, as in Example 1-3 of the invention.

[0116] In addition, Comparative Examples 1-4 to 1-5 and Invention Examples 1-6 to 1-10 are examples in which the mixing ratio of the cleaning solvent to the powder (cleaning solvent / powder (g / g)) was kept constant (0.29 (g / g)), and only the mixing ratio of water to powder (water / powder (g / g)) was changed from 0.18 to 1.06 (g / g). When the water / powder ratio was 0.33 (g / g) or less (Comparative Examples 1-4 and 1-5), the slurry could not be made, and when the viscosity of the slurry was measured, the measurement range was exceeded (exceeding 100 Pa·S), and the measurement itself could not be performed. In addition, in Comparative Examples 1-4 and 1-5, the slurry could not be made, and the emulsion state was also poor. On the other hand, when the water / powder ratio was 0.47 (g / g) or more (Invention Examples 1-6 to 1-10), the emulsion could be sufficiently made, and all were 2.00 Pa s or less. In addition, the emulsion state was good in all of Invention Examples 1-8 to 1-10, but the slurry viscosity was slightly higher in Invention Examples 1-6 and 1-7, and the emulsion state was slightly inferior to Invention Examples 1-8 to 1-10, but not enough to inhibit the effects of the present invention.

[0117] 8 and 9 are graphs showing the relationship between the blending ratio of water and powder (water / powder (g / g)) and the slurry viscosity (Pa·s), as well as the relationship between the slurry viscosity (Pa·s) and the oil removal rate (%) in Examples 1-6 to 1-10, respectively. As shown in the graphs of Figures 8 and 9, as the water / powder ratio decreases, the viscosity of the slurry increases, and mixing with the cleaning solvent becomes insufficient, resulting in a tendency for the oil removal rate to decrease. For example, when the viscosity of the water slurry is 1.98 Pa·S (Example 1-6), the oil removal rate is 42 mass%, and it was confirmed that oil can be removed. On the other hand, when the viscosity exceeds 100 Pa·S (Comparative Example 1-4 and Comparative Example 1-5), the oil removal rate is 10% or less, and it was found that almost no oil can be removed. When the viscosity of the slurry is 0.61 Pa·S (Invention Example 1-7), the oil removal rate increases to 52% by mass, and when the viscosity of the slurry is 0.35 Pa·S or less (Invention Examples 1-8 to 1-10), the oil removal rate increases significantly to 64 to 70% by mass and becomes almost constant. From this, it is considered that by making the viscosity of the slurry 0.35 Pa·S, the powder can move freely in the aqueous phase of the emulsion, and the contact between the solvent droplets in the emulsion and the powder does not become the rate limiting factor. The amount of heat of vaporization did not vary significantly depending on the viscosity of the aqueous slurry. In view of the above, the viscosity of the slurry prepared by mixing the powder with water is set to 2.0 Pa·S or less, preferably 0.65 Pa·S or less, more preferably 0.50 Pa·S or less, and even more preferably 0.35 Pa·S.

[0118] In Examples 1-8 and 1-11, the presence or absence of a rinsing step is compared. From the results of Examples 1-8 and 1-11, it can be said that the oil removal rate is increased by performing the rinsing step. This is because the cleaning solvent containing the oil remaining between the particles cannot be completely removed in the powder phase separation step. In other words, by performing the rinsing step in the powder phase separation step, the cleaning solvent containing the oil remaining between the particles can be sufficiently removed.

[0119] FIG. 10 is a graph showing the relationship between the compounding ratio of cleaning solvent to powder (cleaning solvent / powder (g / g)) and the oil removal rate (%) in Examples 1-11 to 1-14. In Examples 1-11 to 1-14, the cleaning solvent / powder ratio was changed from 0.21 to 1.23 (g / g). As shown in the graph of FIG. 10, the oil removal rate increased as the cleaning solvent / powder ratio increased, and the oil removal rate reached approximately 97 mass % when the cleaning solvent / powder ratio was 0.3.

[0120] Furthermore, in Examples 1-11 and 1-15 to 1-17, the inclination angle α of the filtration surface of the filtration-type centrifugal separation vessel was changed from parallel (0 degrees) to 30 degrees with respect to the rotation axis. Note that the inclination direction was such that the upper end side of the filtration surface was inclined toward the rotation axis direction, as shown in FIG. As is clear from Examples 1-11 and 1-15 to 1-17, the aqueous phase in the centrifuge vessel can be discharged with fewer scraping steps by inclining the filtration surface rather than setting the inclination angle α of the filtration surface at 0 degrees. This phenomenon will be explained below.

[0121] As shown in Figure 3, after the emulsion is broken, it is separated into a powder phase (cake), solvent phase, and water by centrifugal force. The solvent phase passes through the cake and is discharged from the filtration surface, and then the aqueous phase is discharged. Specifically, first, centrifugal force acts on the powder in the emulsion, concentrating it at the place farther from the rotation axis, i.e., the bottom surface of the container (filtration surface), and forming a powder phase (cake). Usually, the inside of the cake contains a lot of solvent, so the filtration resistance is high for water to pass through, and filtration takes time. However, if the filtration surface is installed at an angle (if the inclination angle is greater than 0 degrees), the cake accumulates in one direction, resulting in an area where the cake is thin and a filtration surface that is not covered by the cake. In such an area with a thin cake thickness or on a filtration surface that is not covered by the cake, the filtration resistance is small, and the aqueous phase can be filtered quickly. It is believed that such a phenomenon occurred in Examples 1-15 to 1-17.

[0122] Furthermore, the effect of the heat of vaporization due to the addition of a surfactant was investigated in Examples 1-11 and 1-18 to 1-20. It was found that the heat of vaporization can be reduced by adding a surfactant together with the cleaning solvent in the emulsification process, and the heat of vaporization decreases as the amount of surfactant increases. Note that even in Example 1-20, in which a larger amount of surfactant was added than in the other examples, the heat of vaporization was 13 J / g-dry, resulting in a small amount of water, etc. being present between the particles. This is thought to be because the surfactant made all the surfaces of the powder (scale) particles hydrophobic, and all the water, etc. between the particles was replaced with the hydrophobic solvent, but the result was thought to be due to a small amount of water being dissolved in the solvent.

[0123] Furthermore, in Example 1-21 of the invention, grinding dust with oil attached thereto was used as the powder, but it was confirmed that the oil could also be separated from the grinding dust in the present invention example, and that the oil could be removed from the grinding dust.

[0124] Furthermore, in Examples 1-22 to 1-24, it was confirmed that oil could be removed by using trichloroethylene and hydrofluoroether as the hydrophobic solvent (cleaning solvent).

[0125] The oil content of the powder before oil removal and the recovered cake (powder phase) was measured as follows. First, the powder before oil removal and the collected cake were each dried in a dryer at 105°C for 2 hours, and then the oil was extracted with n-hexane using a Soxhlet extractor. Subsequently, the mixture containing the extracted n-hexane and oil was heated to volatilize the n-hexane, and the weight of the residue (oil) was measured, and the oil content in the powder before oil removal and the cake before oil removal were calculated. The oil removal rate is a value obtained by subtracting the oil content of the cake (powder phase) after oil removal from the oil content of the powder before oil removal as the numerator and the oil content of the powder before oil removal as the denominator.

[0126] The heat of vaporization of the recovered cake was measured as follows. First, 5 to 8 mg of sample was taken from the cake deposited at the bottom of the centrifuge container, and the wet sample was quickly placed in a differential scanning calorimetry (DSC) device (DSC8230, manufactured by Rigaku Corporation). Next, the sample was heated from room temperature to 80°C, and the heat of vaporization at this time was measured. Since the amount of sample was very small, the volatile hydrophobic liquid in the sample evaporates between the weighing operation and the differential scanning calorimetry measurement. Therefore, it is presumed that the measured heat of vaporization is the heat of vaporization due only to the moisture in the sample. In other words, the smaller the heat of vaporization, the smaller the amount of water etc. brought into the cake, and the less energy is required to dry the cake after collection.

[0127] The average particle size of the powder was measured by a laser diffraction / scattering method to determine the volume-based average particle size.

[0128] The viscosity of the slurry was determined by first measuring the viscous resistance torque using a rotational viscometer and converting the obtained viscous resistance torque into viscosity. Specifically, 300 ml of the prepared slurry was placed in a tall beaker and the rotor of the rotational viscometer was immersed in the slurry and rotated to measure the viscous resistance torque of the slurry acting on the rotor. The obtained viscous resistance torque was then converted into viscosity. The rotational viscometer used was a "VISCOMETER DVL-8 model (manufactured by Toki Sangyo)."

[0129] <Example 2> First, water was added to the oil-adhered scale (water content 20 mass%, oil content 5 mass%-dry) and mixed to prepare a slurry (solid content: 50% mass) in the slurrying process.The slurry prepared in the slurrying process was then fed into an emulsifying device at 2.0 kg / min, and a cleaning solvent (1-bromopropane, specific gravity: 1.35, boiling point: 71°C) was further fed at 0.29 kg / min and stirred to prepare an emulsion.

[0130] Next, the emulsion prepared in the emulsification process was fed at 2.29 kg / min into the vertical continuous filtration centrifuge shown in Figures 5 and 6. The same rinsing solvent as the cleaning solvent (1-bromopropane, specific gravity: 1.35, boiling point: 71°C) was fed at 0.29 kg / min. The vertical continuous filtration centrifuge used was designed so that a series of steps, namely the powder phase separation step, the rinsing step, and the powder recovery step, could be performed continuously in the vertical direction from upstream to downstream. After feeding the rinsing solvent, the filtration surface was rotated by applying centrifugal force so that the centrifugal acceleration was 1750 G. The slit width of the filtration surface was 50 μm.

[0131] In addition, the rotation speed of the scraper, which is the scraping mechanism, was set to 30 rpm slower than the rotation speed of the filtration surface, so that the scale accumulated on the filtration surface was scraped downstream. The cleaning solvent containing mainly oil and the cleaning waste liquid mainly composed of water, which were separated by the filtering centrifuge, as well as the rinsing solvent containing almost no oil separated in the rinsing process and the rinsing waste liquid mainly composed of water, were each collected from the outlets installed on the sides of the filtering centrifuge. In addition, the scale (cake) remaining after separating the cleaning solvent, rinsing solvent and water was discharged and collected from the outlet installed below the filtering centrifuge. The oil content and heat of vaporization of the collected cake were measured. The results are shown in Table 2.

[0132] In this embodiment, the inclination angle α of the filtering surface was set to the following three cases. In CASE 1, the rotation axis of the centrifuge and the direction of scraping the cake are parallel, that is, the filtration surface is parallel to the rotation axis (α is 0 degrees). In CASE 2, the filtration surface is arranged so that the rotation axis and the scraping direction intersect, that is, the filtration surface is roughly inverted cone-shaped when viewed in cross section, and α is set to 10 degrees. In CASE 3, the filtration surface is arranged so that the scraping direction moves away from the rotation axis as it moves downstream of the centrifuge, that is, the filtration surface is roughly cone-shaped when viewed in cross section, and α is set to -10 degrees. Comparative Example 2-1 and Invention Example 2-2 were CASE 1, Invention Examples 2-3 and 2-5 were CASE 2, and Invention Example 2-4 was CASE 3. In Invention Example 2-5, a surfactant (Na-sulfonate) was added to the cleaning solvent and rinsing solvent, and the surfactant was added to the scale amount of 0.5 mass %.

[0133] In Comparative Example 2-1, only water was used without using any volatile hydrophobic solvent (cleaning solvent, rinsing solvent). Specifically, water was used instead of the cleaning solvent, water was used instead of the rinsing solvent, and no surfactant was added. The results for Comparative Example 2-1 and Invention Examples 2-2 to 2-5 are shown in Table 2. In Comparative Example 2-1, in which no volatile hydrophobic solvent was used, the oil was hardly removed. Furthermore, the moisture content in the cake after recovery was 21%, and the heat of vaporization was 530 J / g-dry.

[0134] On the other hand, in Examples 2-2 to 2-5, the oil content in the cake after recovery was 0 mass% in all examples, which was significantly reduced compared to Comparative Example 2-1. It was also confirmed that the heat of vaporization was reduced in Examples 2-2 to 2-5. Among the invention examples 2-2 to 2-4, which have different inclination angles (α) of the filtration surface, the heat of vaporization was the smallest in the case of invention example 2-3 (α was 10 degrees). This revealed that installing the filtration surface so that the scraping direction crosses the rotation axis reduces the amount of residual moisture in the cake. Furthermore, in invention example 2-5, in which a surfactant was added, the heat of vaporization was reduced to about one-tenth of that in invention example 2-3, in which no surfactant was added, confirming the effect of hydrophobizing the scale surface by the surfactant.

[0135] The oil content and heat of vaporization of the scale and the cake after recovery were measured by the same method as in Example 1.

[0136] [Table 2]

[0137] <Example 3> 1 kg of the cake collected in Example 2-3 was put into 2 liters of hot water adjusted to 90°C and stirred for 1 minute to volatilize the hydrophobic solvent remaining in the collected scale. The slurried cake was then collected and subjected to a centrifugal force of 1750G for 30 seconds in a batch centrifuge to perform solid-liquid separation, and a cake was obtained again. When the residual solvent content in the cake after the water removal was measured, no residual solvent was detected.

[0138] Next, 1 kg of the cake recovered in Example 2-5 was crushed, thinly spread on a drying dish to a thickness of 5 mm or less, and dried for 10 minutes in a drying oven adjusted to 120° C. to volatilize the hydrophobic solvent remaining in the scale. After drying, the residual solvent content in the cake was measured, and no residual solvent was detected.

[0139] In the present examples, the residual solvent content in the cake was measured as follows. The cake from which the solvent had been evaporated was mixed with pure water to prepare sample water, which was then placed in a sealed container. The sample was then heated for 10-20 minutes at a temperature 30-50°C higher than the boiling point of the solvent, causing the solvent components to volatilize from the sample water into the air layer in the sealed container. The gas phase in the sealed container was then sampled with a syringe, and the gas components in the syringe were measured by gas chromatography to calculate the residual solvent concentration in the cake.

[0140] <Example 4> The cleaning waste liquid recovered in Example 2-3 was left to stand, and was separated into an oil-containing solvent phase (oil-containing solvent phase) and an aqueous phase by gravity separation, and only the oil-containing solvent phase was recovered. The recovered oil-containing solvent phase was put into a distillation apparatus adjusted to 120°C, and only the solvent component was evaporated and then coagulated, so that the oil-containing solvent phase was separated into oil and solvent. The separated solvent was colorless and transparent, and it was confirmed that it did not contain oil. From this, it was confirmed that the separated solvent could be reused as the first volatile hydrophobic solvent (cleaning solvent) or the second volatile hydrophobic solvent (rinsing solvent). On the other hand, the separated oil contained 2.1 mass% of residual solvent, but it was confirmed that most of the solvent could be recovered by distillation.

[0141] The residual solvent content in the oil separated from the oil-containing solvent phase was measured as follows. First, the bromine content in the separated oil was measured by combustion ion chromatography. Next, the residual solvent content in the oil was calculated, assuming that all the bromine in the separated oil was 1-bromopropane. The combustion apparatus used was the AQF-100 manufactured by Mitsubishi Chemical Analytech Co., Ltd., and the ion chromatography apparatus (IC apparatus) used was the ICS-2000 manufactured by Thermo Fisher Scientific Co., Ltd.

[0142] <Example 5> In Example 2-3, the test was carried out under the same conditions except that the input amount of the rinsing solvent was changed from 0.03 kg / min to 0.4 kg / min, and the washing waste liquid, the rinsing waste liquid, and the cake were collected. The collected rinsing waste liquid was left to stand and separated into an aqueous phase and a solvent phase by gravity separation. The separated solvent phase was filtered with a filter paper of "Type 5 A" specified in JIS P 3801 to remove small amounts of scale, and the filtered solvent was collected.

[0143] When the relationship between the oil concentration in the recovered filtered solvent and the absorbance of the solvent phase at an absorption wavelength of 400 nm was investigated, the relationship shown in Figure 11 was obtained. From this relationship, it was found that in the region of absorbance 2 or less, there is an almost positive correlation between the oil concentration in the solvent and the absorbance of the solvent phase.

[0144] In addition, when the relationship between the absorbance (absorption wavelength 400 nm) of the solvent phase after filtration and the oil concentration in the cake was examined, the relationship shown in FIG. 12 was obtained. From this relationship, it can be said that the oil concentration in the cake can be estimated by measuring the absorbance of the solvent phase in the rinsing waste liquid. From this, when it is desired to make the oil concentration in powder such as scale below a certain target value, for example, it is sufficient to estimate the amount of residual oil in the cake from the absorbance of the solvent phase in the rinsing waste liquid and adjust the amount of rinsing solvent added so that the estimated value of the residual oil amount is below the target value. In this way, the oil concentration in the powder can be efficiently made below the target value, and the amount of rinsing solvent used can be appropriately controlled, thereby suppressing losses such as excessive input of solvent. For example, looking at the relationship in Figure 12, it can be said that in order to reduce the oil concentration in the cake (powder) to 0.2% or less, the absorbance needs to be 0.25 or less, and the amount of rinsing solvent added is adjusted so that the absorbance falls within that range.

[0145] In addition, when the absorbance (absorption wavelength 400 nm) of the solvent phase in the rinse waste liquid was 0.25, the oil concentration in this solvent was small at 11 mg / ml of solvent, and it was confirmed that it can be used as the first volatile hydrophobic solvent (cleaning solvent). [Explanation of symbols]

[0146] 1 Powder recovery equipment 10 Powder (oil-containing powder) 10a Powder phase 20 water 20a aqueous phase 30 Slurry 40 Emulsion 50 First volatile hydrophobic solvent (cleaning solvent) 50a Solvent phase 50a´ Residual solvent phase 51 Second volatile hydrophobic solvent (rinsing solvent) 60 Slurrying Equipment 70 Emulsifier 80 Powder phase separation device (filter type centrifuge) 81 Scraper mechanism 82 Filtration surface 90 Surfactants 100 containers 200 Centrifugation vessels 201 Filtration surface

Claims

1. A method for recovering powder comprising the steps of: separating oil from a powder having oil attached thereto and recovering the powder, the method comprising the steps of: A slurrying step of mixing the powder having a specific gravity of more than 1.05 to which oil has been attached with water to produce a slurry having a viscosity in the range of 0.003 to 2.00 Pa·S; an emulsification step of adding a first volatile hydrophobic solvent having a specific gravity of more than 1.05 and less than 2.0 to the slurry and then mixing to form an emulsion; a powder phase separation step of breaking down the emulsion by centrifugal force, and further separating the emulsion into an aqueous phase, a solvent phase, and a powder phase by centrifugal force, and filtering the solvent phase and the aqueous phase to separate the powder phase; a powder phase recovery step of recovering the separated powder phase; having the first volatile hydrophobic solvent is trichloroethylene, 1-bromopropane, a hydrofluoroether, or a liquid having a solubility in water of 0 g / L or more and 10.0 g / L or less at room temperature (25° C.) and a boiling point of less than 95° C. at normal pressure; The powder phase separation step is carried out by a filtration type centrifugal separator having a mechanism for scraping the powder phase, The mechanism for scraping the powder phase is as follows: The filtering type centrifugal separator has a filtering surface that is inclined with respect to the rotation shaft in a cross-sectional view passing through the rotation shaft, or the filtering type centrifugal separator has a scraper made of a spiral plate material that rotates together with the rotation shaft of the filtering type centrifugal separator in the vicinity of the filtering surface of the filtering type centrifugal separator, a collecting mechanism for collecting powder, the collecting mechanism being configured to collect the powder phase deposited on a filtration surface when filtering the solvent phase and the aqueous phase in the powder phase separation step, so that a thickness of a portion of the powder phase on the filtration surface is reduced.

2. The filtration type centrifuge is a continuous type, The scraper mechanism includes a scraper that is fixed to a rotation shaft of the centrifugal separator and is disposed along an inner surface of the filtering surface while extending along the axial direction, The method for recovering powder according to claim 1, characterized in that the powder on the filtration surface is moved by rotating the scraper, and the powder phase is accumulated to reduce a thickness of a portion of the powder phase.

3. The filtration type centrifuge is a vertical type, 3. The method for recovering powder according to claim 2, wherein the filtering surface is parallel to the rotation axis or inclined so as to form an inverted eight shape in a cross section passing through the rotation axis.

4. The filtration type centrifuge is a batch type, The centrifugal separator includes a filtering surface inclined with respect to the rotation axis in a cross section passing through the rotation axis, as the scraping mechanism, 2. The method for recovering powder according to claim 1, wherein the thickness of a portion of the powder phase is reduced by inclining the filtration surface when centrifugal force is applied.

5. The method for recovering powder according to any one of claims 1 to 4, characterized in that the powder phase obtained in the powder phase recovery step is dried at a temperature above the boiling point of the first volatile hydrophobic solvent.

6. The powder recovery method according to any one of claims 1 to 5, characterized in that the powder phase obtained in the powder phase recovery step is put into a hot water tank having a water temperature higher than the boiling point of the first volatile hydrophobic solvent, the first volatile hydrophobic solvent is volatilized and removed, and then a slurry containing the powder is dehydrated in a dehydrator to recover the powder phase.

7. The method for recovering powder according to any one of claims 1 to 6, characterized in that the powder phase separation step through the powder phase recovery step are carried out using a single filtration type centrifugal separator.

8. In the powder phase separation step, The method for recovering powder according to any one of claims 1 to 7, further comprising a rinsing step of filtering the solvent phase and the aqueous phase to separate the powder phase, adding a second volatile hydrophobic solvent similar to the first volatile hydrophobic solvent to the separated powder phase, and further applying centrifugal force to separate the solvent phase remaining in the powder phase and then filtering the resultant.

9. The method for recovering powder according to claim 8, characterized in that the powder phase obtained in the powder phase recovery step is dried at a temperature above the boiling points of the first volatile hydrophobic solvent and the second volatile hydrophobic solvent.

10. 9. The method for recovering powder according to claim 8, characterized in that the powder phase obtained in the powder phase recovery step is put into a hot water tank having a water temperature higher than the boiling points of the first volatile hydrophobic solvent and the second volatile hydrophobic solvent, the first volatile hydrophobic solvent and the second volatile hydrophobic solvent are volatilized and removed, and then a slurry containing the powder is dehydrated in a dehydrator to recover the powder phase.

11. The method for adjusting the amount of the second volatile hydrophobic solvent added in the rinsing step includes the steps of: A solvent phase containing an oil is collected from the solvent phase separated in the rinsing step by gravity separation; Measure the absorbance of the oil-containing solvent phase; The amount of oil remaining in the powder phase after the powder phase recovery step is estimated from the measured absorbance value obtained; The method for recovering powder according to any one of claims 8 to 10, characterized in that the amount of the second volatile hydrophobic solvent added in the rinsing step is adjusted so that the estimated value of the residual oil content is equal to or less than a target value.

12. The method for recovering powder according to any one of claims 1 to 11, characterized in that a surfactant is added in the emulsification step.

13. The method for recovering powder according to any one of claims 1 to 12, characterized in that the oily powder is one or a mixture of two or more of the following: oily scale, oily grinding dust, and oily coke powder.

14. A powder recovery system that separates oil from a powder having oil attached thereto and recovers the powder, A slurrying device for mixing the oil-containing powder having a specific gravity of more than 1.05 with water to produce a slurry; an emulsifier for adding a first volatile hydrophobic solvent having a specific gravity of more than 1.05 and less than 2.0 to the slurry and then mixing to form an emulsion; a powder phase separation device for breaking down the emulsion by centrifugal force, and further separating the emulsion into an aqueous phase, a solvent phase, and a powder phase by the centrifugal force, and filtering the solvent phase and the aqueous phase to separate the powder phase; having The powder phase separation device is a filtration type centrifugal separator having a mechanism for scraping the powder phase, The scraping mechanism includes: The filtering type centrifugal separator has a filtering surface that is inclined with respect to the rotation axis in a cross-sectional view passing through the rotation axis, or has a scraper made of a spiral plate material in the vicinity of the filtering surface, A powder recovery system, characterized in that it is a mechanism for collecting the powder phase that has accumulated on a filtration surface when the solvent phase and the aqueous phase are filtered.

15. The filtration type centrifuge is a continuous type, The scraper mechanism includes a scraper that is fixed to a rotation shaft of the centrifugal separator and is disposed along an inner surface of the filtering surface while extending along the axial direction, The powder recovery equipment according to claim 14, characterized in that the powder on the filtration surface is moved by rotating the scraper, and the powder phase is accumulated.

16. The filtration type centrifuge is a vertical type, 16. The powder recovery facility according to claim 15, wherein the filtering surface is parallel to the rotation axis or inclined so as to form an inverted eight shape in a cross section passing through the rotation axis.

17. The filtration type centrifuge is a batch type, 15. The powder recovery facility according to claim 14, characterized in that the scraping mechanism comprises a filtering surface inclined with respect to the rotation axis in a cross section passing through the rotation axis of the centrifugal separator.

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