JP6853682B2 - Oil-impregnated sludge treatment method - Google Patents

Description

The present invention relates to a method for treating oil-containing sludge containing a large amount of oil as much as 3 to 15% by mass in addition to coarse particles and fine particles. The oil-containing sludge containing the above is classified into fine particles having a high oil content in which oil is concentrated and coarse particles having a low oil content that can be recycled as they are, and at that time, the coarse particles are classified as much as possible. The present invention relates to a method for treating oil-impregnated sludge, which can improve the recycling rate of iron powder and the like by realizing an increase in the amount of iron powder.

In a steel mill, a large amount of wastewater containing a large amount of iron or the like as a coarse-grained or fine-grained suspended substance (SS), such as direct-cooled wastewater in a continuous casting process or direct-cooled wastewater in a rolling process, is generated. In these direct cooling wastewaters, SS in the wastewater is solid-liquid separated and removed, and then the obtained treated water is circulated and used again as direct cooling water. On the other hand, SS in wastewater is solid-liquid separated as oil-containing sludge containing, for example, about 50% by mass of iron and about 10% by mass of oil in the above wastewater treatment. As described above, since the oil-impregnated sludge contains a large amount of iron, it is returned to the iron-making process and recycled. Then, as described below, when recycling, it is necessary to remove the oil content in the oil-containing sludge.

As a method of recycling oil-impregnated sludge, there is also an example in which oil-impregnated sludge is used as it is in a sintering raw material as it is as a part of a granulating raw material for granulation, and then charged into a sintering machine as a sintering raw material for pseudo particles. Not without. However, in this case, there arises a problem that the oil contained in the sintered raw material is vaporized, which adversely affects the operation. Therefore, it is difficult to reuse the oil-containing sludge as it is as a raw material for steelmaking, and the oil content in the oil-containing sludge is removed at the time of recycling.

As a method for removing oil in oil-containing sludge, for example, a technique of burning oil in oil-containing sludge in a kiln-type incinerator and recovering iron as an effective resource is known (see Patent Document 1). Has been done. However, although this method can completely remove oil by combustion, a large amount of oil-containing sludge generated in a steel mill is burned in an incinerator to remove oil, which requires a large amount of incineration capacity. It's not the best way to do it.

As another method, for example, it has been proposed to bring oil-containing sludge into contact with a solvent to dissolve the oil in the solvent, then perform solid-liquid separation, and further purify the solid content. However, in this case, there is a problem of cost required for a solvent or the like used in a large amount, and a problem of cost required for secondary treatment such as treatment of wastewater used for purification treatment of solid content. On the other hand, for oil-containing granules composed of aggregates of coarse particles and fine particles and containing oil, a grinding step of reducing the particles by friction between the particles and a classification step of coarse particles and fine particles are performed. There is a method that enables the reuse of iron while reducing the cost of chemicals and water treatment compared to the conventional method by further removing the oil from the separated coarse particles in the washing process. It has been proposed (see Patent Document 2). It is said that this method can be applied even when the target value of the degree of cleanliness of the particles to be reused is high.

Japanese Unexamined Patent Publication No. 10-169956 Japanese Patent No. 5417933

As described above, although a large amount of oil-containing sludge generated in a steel mill contains a high concentration of iron, it is necessary to remove the oil content in the oil-containing sludge in order to reuse it. On the other hand, it is possible to remove the oil by treating the oil-containing sludge as it is, but in that case, the combustion efficiency of the oil is poor and the amount to be treated becomes enormous. It is difficult in reality because it requires the addition of a large-scale incineration facility. Further, as described above, in the prior art, it is necessary to remove oil by using a large amount of chemicals by a complicated operation, which is the most suitable method for practical use in which iron can be reused by a simple method. Not. Since the amount of oil-containing sludge that requires oil removal treatment is extremely large compared to the conventional oil-containing sludge treatment method described above, at present, oil-containing sludge can effectively utilize the resources contained in the oil-containing sludge. It is often disposed of without being used.

Therefore, an object of the present invention is, for example, to effectively regenerate more active ingredients such as iron from oil-containing sludge by a simple method at the lowest possible cost for oil-containing sludge generated in a large amount in a steel mill. The purpose is to provide a technique for treating oil-impregnated sludge that can be made available.

The above object is achieved by the following invention. That is, in the present invention, water is added to an oil-containing sludge containing coarse particles and fine particles and an oil content of 3 to 15% by mass to form a slurry, and the slurry-like oil-containing sludge is supplied to a liquid cyclone to be 15 μm or more and 20 μm or more. A classification step of separating coarse particles and fine particles using the following as a classification point, and a dehydration step of dehydrating fine particles having a particle size less than the classification point, in which the oil is concentrated by classifying in the classification step. The present invention provides a method for treating oil-containing sludge, which comprises an incineration step of incinerating the dehydrated sludge dehydrated in the dehydration step to remove an oil component.

Moreover, as a preferable form of the present invention described above, it is mentioned that it has the following structure. Adjusting the slurry concentration (SS) of the slurry-like oil-impregnated sludge so as to be 15% by mass or more; the oil-containing sludge contains iron powder and oil generated in the process wastewater treatment process in a steel mill. It is sludge; in that case, the recovery rate of the coarse particles is 35% or more and the oil content is 1% by mass or less; the incineration residue obtained in the incineration step is Along with the coarse grain content, the recovered iron content may be reused at the steel mill.

Further, as a preferred embodiment of the present invention, there is an oil-impregnated sludge treatment method in which a polymer flocculant containing polyacrylamide as an active ingredient is added when dehydrating the fine particles in the dehydration step.

（上記式中の、Ｒ₁、Ｒ₂は、それぞれ独立にＣＨ₃又はＣ₂Ｈ₅を表し、Ｒ₃は、Ｈ、ＣＨ₃又はＣ₂Ｈ₅のいずれかを表す。Ｘ^-は、アニオン性対イオンを表す。） Examples of the polymer flocculant include polyacrylamide and cationized metamorphic products of polyacrylamide. Specifically, it is cationic or amphoteric derived from a raw material monomer containing 5 mol% or more of one or both of the monomers represented by the following general formula (1) and the following general formula (2) as essential components. The main component is a copolymer, and the value obtained by multiplying the weight average molecular weight (Mw) of the copolymer by the square of the cationic colloid equivalent (CE) at pH 7 and further dividing by 1 million is defined as N. In some cases, a polymer flocculant having an N value of 5 to 60 can be mentioned.

(In the above formula, R ₁ and R _{2 independently represent CH 3} or C ₂ H ₅ , respectively, R ₃ represents either H, CH ₃ or C ₂ H ₅ , and X ^- is an anion. Represents sex counterion.)

According to the present invention, oil-containing sludge containing coarse particles and fine particles containing oil, for example, oil-containing sludge containing a large amount of iron content of about 50% by mass and oil of about 10% by mass, which is generated in a large amount in a steel mill or the like, is reused. To the available resources, a method for treating oil-containing sludge that can be easily and efficiently provided is provided. That is, according to the present invention, the oil content is increased (for example, the oil content is concentrated to about 15%) by simply supplying the oil-containing sludge into a slurry and supplying it to the liquid cyclone and classifying it at a specific classification point. It can be separated into a component and a coarse particle with the oil content reduced to 1% by mass or less, and the recovery rate as the coarse particle can be increased. Since the coarse particle has a low oil content, the oil content can be used as an iron source. It can be used as it is in a sintering factory with an acceptance standard value of 1% by mass or less. For this reason, it is sufficient to remove the oil by incineration after the dehydration treatment only for the fine particles having a high calorific value in which the oil is concentrated. Therefore, in addition to being able to reduce the amount of oil to be treated, it is possible to improve the incineration efficiency. .. The residue after incineration can be used for recycling together with the above-mentioned coarse particles having a low oil content. Further, according to a preferred embodiment of the present invention, when dehydrating the above-mentioned fine particles, if a specific polymer flocculant is used, drainage is improved and high dehydration efficiency can be realized. Therefore, when dehydrated sludge is incinerated. The efficiency of the oil-containing sludge is improved, and as a result, the oil-impregnated sludge can be recycled into a reusable resource more efficiently.

It is a flow figure which shows typically the method of treating the oil-impregnated sludge of this invention. It is a graph which shows the particle size distribution of each coarse grain obtained by making the actual oil-impregnated sludge of a steel mill into a slurry, supplying it to a liquid cyclone under different operating conditions, and classifying it, and the particle size distribution of the slurry before classification. ..

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. As a result of diligent studies to solve the problems of the prior art described above, the present inventors have used a liquid cyclone, which has been conventionally known as a classifier, and used coarse particles and fine particles contained in oil-impregnated sludge. When classifying into minutes, just by setting a specific classification point, the oil content can be almost transferred to the classified fine particles side and concentrated, and at the same time, the coarse particles can be made almost free of oil, and the coarse particles can be made. The present invention was completed by finding that a high recovery rate as a minute can be realized (see FIG. 1).

For example, the oil-containing sludge obtained in the process of treating the directly cooled wastewater of a steel mill contains an iron content of about 50% by mass and an oil content of about 3 to 15% by mass. The present invention is suitable for treating oil-containing sludge having such properties. Specifically, the process is performed according to the following procedure. First, water is added to the oil-impregnated sludge to form a slurry. At that time, the slurry concentration (SS) may be appropriately adjusted, but it is preferable to adjust the slurry concentration (SS) so as to be 15% by mass or more. In the method for treating oil-impregnated sludge of the present invention, such slurry-like oil-containing sludge is supplied to a liquid cyclone, and by adjusting the classification conditions of the liquid cyclone, a classification point of 15 μm or more and 20 μm or less is set as a classification point, and coarse particles and fine particles are used. It is characterized by being separated into minutes.

Here, the classification performed by the liquid cyclone will be described. When the slurry is press-fitted into the liquid cyclone, the particles are arranged in a satellite pattern by centrifugal force so that the particles have a larger specific gravity and particle size toward the peripheral wall and a smaller specific gravity and particle size toward the center. A downward flow is generated along the taper of the cyclone on the peripheral wall, and along this flow, those with a large specific gravity and particle size are guided to the bottom nozzle and discharged, while the central part rises on the contrary. A flow is generated, and those with a small specific gravity and particle size are glued to this flow and discharged to the top nozzle.

As will be described later, the coarse particle content and the fine particle size classified at a specific classification point by such a principle show the following properties, respectively. That is, for example, when the oil-impregnated sludge is an oil-containing sludge containing iron powder and oil generated in the process wastewater treatment process in a steel mill, the coarse particles having a particle size equal to or higher than the classification point have an oil content of 1% by mass. Hereinafter, the oil content is preferably 0.8% by mass or less, which is low in oil content. Further, when the SS weight was examined, it was found that the recovery rate of the coarse particles in this case was 35% or more, further 40% or more, more preferably 50% or more. On the other hand, it was found that most of the oil content in the slurry-like oil-containing sludge was transferred to the fine particles having a particle size less than the classification point, and the oil content was concentrated.

Therefore, the coarse particles having a low oil content obtained by the above-mentioned classification treatment can be recycled and used as they are, for example, as a material for iron making at a sintering factory or the like, without performing the next treatment. On the other hand, the oil content of the classified fine particles can be efficiently removed by the following procedure, and the residue can be used for recycling. As described above, in the classification treatment specified in the present invention, coarse particles can be obtained with a high recovery rate, so that the amount of fine particles for removing oil can be small, and oil-containing treatment requiring oil removal treatment is required. The amount of sludge can be significantly reduced (volume).

According to the study by the present inventors, when the oil-containing sludge containing iron powder and oil generated in the process wastewater treatment process in the above-mentioned steel mill is treated, the oil content of the slurry-like oil-containing sludge supplied to the liquid cyclone is included. It was found that most of, specifically, more than 90% of the oil content was transferred to the classified fine particles, and the oil content was efficiently concentrated. In the present invention, utilizing this fact, in the dehydration step, the fine particles in a state where such oil is concentrated are dehydrated, and in the subsequent incineration step, the dehydrated sludge dehydrated in the dehydration step is incinerated. , It has become possible to efficiently remove the oil content in the oil-containing sludge. According to the study by the present inventors, the calorific value in the combustion process specified in the present invention is such that the oil content is highly concentrated in the fine particles to be incinerated, so that the oil-containing sludge is incinerated as it is to remove the oil content. Compared with the conventional method, the calorific value is nearly 1.5 times, and as a result, the amount of the combustion improver added can be reduced and the incineration process can be performed efficiently. Further, the incineration residue obtained in the above-mentioned incineration step from which the oil content has been removed in this manner can be recycled at the steelworks as the recovered iron content together with the above-mentioned coarse particles having almost no oil content.

Furthermore, the present inventors can improve the dehydration efficiency by using a specific polymer flocculant in the above-mentioned dehydration step because the water separation is improved and the dehydration property is improved, and as a result, the dehydration efficiency can be improved. We have found that the efficiency of the above-mentioned incineration is further improved. Specifically, when a polymer flocculant containing polyacrylamide as an active ingredient is used as the polymer flocculant, the effect of improving the dehydration property of fine particles in the dehydration step can be remarkably obtained. all right. Examples of the polyacrylamide-based polymer flocculant preferably used in the treatment method of the present invention include polyacrylamide, a Mannig variant or Hoffmann decomposition product of polyacrylamide, and dimethylaminoalkyl (meth) acrylate and acrylamide. Examples thereof include cationized variants of polyacrylamide such as the copolymer of. The Mw of this polymer flocculant is preferably 1,000,000 to 20,000,000 for both the homopolymer and the copolymer.

To give a specific example in which a polyacrylamide-based polymer flocculant is applied to the treatment method of the present invention, for example, one or both of the monomers represented by the following general formula (1) and the following general formula (2) are essential. The main component is a cationic or amphoteric copolymer derived from a raw material monomer containing 5 mol% or more as a component, and the weight average molecular weight (Mw) of the copolymer is 2 of the cationic colloid equivalent (CE) at pH 7. When the value multiplied by the power is further divided by 1 million and N is defined as N, a polymer flocculant having an N value of 5 to 60 is added when the fine particles are treated in the dehydration step. The sex can be greatly improved. The amount of the polymer flocculant used is not particularly limited, but is preferably about 0.5 to 1.0% by mass with respect to the amount of SS. Details of the polymer flocculants exemplified above are described in Japanese Patent Application Laid-Open No. 2016-13541, and in the present invention, a polymer flocculant containing such polyacrylamide as an active ingredient is used. It can be used as appropriate.

（上記式中の、Ｒ₁、Ｒ₂は、それぞれ独立にＣＨ₃又はＣ₂Ｈ₅を表し、Ｒ₃は、Ｈ、ＣＨ₃又はＣ₂Ｈ₅のいずれかを表す。Ｘ^-は、アニオン性対イオンを表す。）

(In the above formula, R ₁ and R _{2 independently represent CH 3} or C ₂ H ₅ , respectively, R ₃ represents either H, CH ₃ or C ₂ H ₅ , and X ^- is an anion. Represents sex counterion.)

A cationic or amphoteric copolymer that can be used as a polymer flocculant that has an effect of improving dehydration by dehydrating fine particles is derived from the above-mentioned specific raw material monomer. Specifically, it can be obtained by designing the above-mentioned monomer composition so as to satisfy the requirements for the N value specified in the present invention. As a specific synthesis method, the synthesis method described in Japanese Patent No. 3868521 can be used for the cationic copolymer. Further, the copolymer of both sexes is, for example, as described in Japanese Patent No. 3352835, the cationic monomer represented by the above formulas (1) and / or (2), and itaconic acid as another monomer. It can be obtained by the same method by appropriately mixing anionic monomers such as or acrylic acid to obtain a raw material monomer.

Typical examples of the monomer represented by the above formula (1) include acryloyloxyethyltrimethylammonium chloride, hydrochloride of dimethylaminoethyl acrylate and the like. Moreover, acryloyloxyethyldimethylbenzylammonium chloride is mentioned as a typical example of the monomer represented by the formula (2). Examples of other monomers copolymerizable with these monomers include (meth) acrylamide, N-methyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide and the like.

The present invention will be described in more detail with reference to Examples and Comparative Examples. These examples do not limit the present invention. Hereinafter,% is based on mass unless otherwise specified.

<Examination test example-1>
An oil-containing sludge containing iron powder and 3 to 15% by mass of oil actually generated at a steel mill was subjected to a classification test using a liquid cyclone to examine whether or not the object of the present invention could be achieved. .. In the classification test for classifying into coarse particles and fine particles, the slurry concentration (SS) of the oil-containing sludge to be supplied to the liquid cyclone was appropriately adjusted, and the operating conditions of the liquid cyclone were appropriately changed. Then, the target of classification to be good is that the oil content transferred to the coarse particle content (bottom liquid) can be reduced to 1% or less, and the recovery amount of such coarse particle content that can be recycled as it is is 35% or more. , Preferably, studies were conducted to find the optimum conditions that can realize the maximum recovery amount. Specifically, the target value is to recover the coarse particles having an oil content of 1% or less at a recovery rate of 40% or more, and the oil-containing sllur to be supplied to the liquid cyclone in order to achieve this target value. The three conditions of the slurry concentration, the cyclone inlet operating pressure, and the cyclone outlet operating pressure were examined, and tests were conducted under the combination conditions 1 to 7 shown in Table 1 in order to find the optimum conditions for each. As a result, it was found that the operating conditions of conditions 2, 3 and 5 are optimum.

A classification test using a liquid cyclone was performed by repeating the test conditions shown in Table 1 twice. The specific operating conditions selected are shown in Table 2. Then, the oil content of the coarse particle content (bottom liquid) and the SS of the fine particle content (top liquid) were measured for each of the coarse particle content and the fine particle content classified in the classification test conducted under the operating conditions shown in Table 2. The measurement results are summarized in Table 2. Further, in Table 2, the ratio of the SS value (SS of the slurry-SS of the top liquid) of the classified coarse particles (bottom liquid) to the SS value of the slurry (object to be treated) supplied to the liquid cyclone is shown. The bottom recovery rate (%) is also shown.

As shown in Table 2, when the classification is performed under operating conditions 2, 3 or 5, the oil content transferred to the coarse particle content (bottom liquid) can be reduced to 1% or less, and the oil content is low. It was found that the amount of coarse particles that can be recycled as it is can be recovered with a high recovery rate of 40% or more. More specifically, the slurry concentration (SS) supplied to the liquid cyclone is 15% by mass or more, the cyclone inlet pressure is 0.2 MPa or more, and the cyclone outlet pressure is 0.07 MPa or more. It was found that when classified, sludge (coarse grain content) having an oil content of 1% or less can be recovered with a bottom recovery rate of 40% or more.

<Examination test example-2>
Next, the slurry concentration (SS) supplied to the liquid cyclone, which has the remarkable effect described above, is set to 15% by mass or more, the oil content is set to 3 to 15% by mass, and the inlet pressure of the cyclone is set to 0.2 MPa or more. Moreover, when the cyclone outlet pressure is classified under the condition of 0.07 MPa or more, what is the classification point at which the coarse particles and fine particles contained in the oil-impregnated sludge are classified into coarse particles and fine particles, respectively? A detailed examination test was conducted to find out what was happening.

Specifically, the laser diffraction type particle size distribution is obtained for each of the coarse particles obtained by the four types of operating conditions 1, 2, 5 and 7 shown in Table 2 under the operating conditions of the liquid cyclone. The particle size distribution was measured using the measuring method. The measurement results are shown in Table 3 and FIG. The particle size distribution of the supplied slurry (called raw mud slurry) used in the classification test was also measured, and the results are also shown in Table 3 and FIG. The coarse particle content obtained as a result of classification under operating condition 1 had a low oil content of 0.3%, but a low bottom recovery rate of 20% or less, and was obtained as a result of classification under operating condition 7. Although the recovery rate of the coarse particle content was as high as 50% or more, the oil content was 1.5%, which was not the coarse particle content intended by the present invention.

As shown in Table 3 and FIG. 2, it was confirmed that the raw material slurry (raw mud slurry) in which coarse particles and fine particles from 1.0 μm to 100 μm are distributed broadly can achieve the object of the present invention. By the classification treatment under the operating condition 2 or 5, the classified coarse particles show a distribution close to a normal distribution having a median value in the vicinity of 40 to 50 μm. Further, from the results of the above particle size distribution, the classification points at which the oil content of the classified coarse particles is 1% or less and the coarse particle recovery rate is 40% or more are from the value of "x10" in Table 3. It was concluded that it was 15 to 20 μm. Therefore, if the raw mud slurry is treated under the conditions specified in the present invention, the coarse particles having an oil content of 1% or less, which can be recycled as iron as they are after classification, have a bottom (coarse particle) recovery rate of 40%. It was found that it can be obtained in a high state.

As shown in Table 3 and FIG. 2, the coarse particle content obtained as a result of classification under the operating condition 1 is compared with the coarse particle content classified under the operating condition 2 or 5 specified in the present invention. It is considered that the distribution of the larger particle size is high and the distribution of the smaller particle size is small, and the bottom recovery rate is low due to this. Further, the coarse particles obtained as a result of classification under the operating condition 7 have a high distribution of those having a small particle size, and due to this, the bottom recovery rate is high, but the particle size is small. Since the oil content is also classified at the same time, it is considered that the oil content concentration contained in the coarse particle content has increased.

<Examination test example-3>
As shown in the previous test example, by treating the oil-containing sludge containing coarse particles, fine particles, and oil under the conditions specified in the present invention, the coarse particle recovery rate of coarse particles having an oil content of 1% or less can be obtained. It is obtained in a high state of 35% or more (40% or more in the above test result). On the other hand, most of the oil content of the oil-containing sludge (supplied slurry used in the classification test) is transferred to the fine particles (top liquid). The classified fine particles are dehydrated in the dehydration step, and then the dehydrated sludge dehydrated in the dehydration step is incinerated and disposed of in the incineration step. Therefore, it is important that sufficient dehydration is performed before incineration in terms of improving the efficiency of processing the classified fine particles.

On the other hand, as shown below, it has been found that it is extremely effective to add a specific polymer flocculant specified in the present invention to perform the dehydration treatment when the fine particles are dehydrated. It was. Specifically, when the fine particles (top liquid) obtained by classifying under the operating condition 2 performed in Study Test Example-1 are dehydrated, the case where the polymer flocculant is added and the case where the polymer flocculant is not added. The remarkable effect obtained by performing dehydration treatment by the above two methods and adding a specific polymer flocculant to dehydrate was found.

The above polymer flocculant contains acrylamide / [2-] derived from a raw material monomer containing 20 mol% each of the two types of monomers represented by the general formulas (1) and (2) as essential components. (Acryloyloxy) ethyl] benzyldimethylammonium chloride / [2- (acryloyloxy) ethyl] trimethylammonium chloride copolymer (molar ratio = 60/20/20) as the main component was used. .. Its weight average molecular weight is 3 million and its cationic colloid equivalent at pH 7 is 2.0 meq / g. Therefore, the N value of this copolymer is 12 (L value = 1.5). For details of the polymer flocculant used, refer to the description in JP-A-2016-13541. The amount of the polymer flocculant added to the fine particles (top liquid) was 1000 mg / L, and after the polymer flocculant was added, the mixture was vigorously stirred and then dehydrated.

The results are shown in Table 4. As shown in Table 4, when the polymer flocculant is not added to the fine particles (top liquid), good dehydration is not performed even after dehydration treatment, and the fine particles flow out. The SS capture rate was 2.2%, which was close to zero. On the other hand, by adding a specific polymer flocculant to the fine particles (top liquid) and then dehydrating, dehydrated sludge with a water content of 45% can be obtained, and the SS capture rate is significantly 99.9%. It was confirmed that it can be improved. Therefore, if the treatment is performed as described above, almost all the oil content obtained by the classification treatment as described above is transferred from the oil-containing sludge containing coarse particles, fine particles and oil content, and the oil content is concentrated. Since the dewatered sludge that captures SS almost completely can be obtained from the fine particles having a high calorific value, the dehydrated filtrate has good water quality. Therefore, the above method is extremely effective when discharging the dehydrated filtrate to the outside of the system.

<Effects obtained by applying the present invention>
(Effect of reducing the amount of incineration)
In comparison with the conventional method of treating oil-impregnated sludge containing coarse particles, fine particles and oil from a steel mill without performing classification treatment, the treatment method of the present invention is used to classify coarse particles and fine particles. The efficiency of the treatment obtained by the above is shown in Table 5 in comparison with the amount of treatment performed by the monthly incineration treatment. Specifically, the treatment method of the present invention is applied to the treatment amount and specific gravity of oil-impregnated sludge (raw mud) captured by a filter after introducing hot-rolled wastewater into a settling basin and filtering it with a filter. Finally, Table 5 shows the amount of oil-containing sludge that requires oil treatment and its specific gravity. By applying the treatment method of the present invention for classifying coarse particles and fine particles, in the method of the present invention, it is the fine particles (top liquid) classified from the oil-containing sludge that finally requires oil treatment. become. As a result, as shown in Table 5, the reduction rate of the treated amount of oil-impregnated sludge from the steel mill is as large as about 50% in both capacity and weight by applying the method of the present invention. Was confirmed. Further, by applying the treatment method of the present invention, from oil-containing sludge containing coarse particles, fine particles and oil, coarse particles that can be reused as they are, have a small amount of oil and contain a large amount of active ingredients such as iron are efficient. The good classification is clear from the fact that the specific gravity of 1.90 in the raw mud decreased to 1.60. As described above, by applying the treatment method of the present invention, the amount of treatment required for the final incineration can be reduced by almost 50%, and the effect is that the oil-impregnated sludge from the steelworks can be reduced. Since the amount is enormous, the economic effects such as improvement of work efficiency and simplification of equipment brought about by the reduction will be extremely large.

(Effects due to differences in the properties of dehydrated sludge to be incinerated)
The comparison was made according to the difference in the properties of the sludge after the dehydration treatment, which is the target of the incineration treatment. A specific comparison was made by measuring the oil content and calorific value of the sludge subject to incineration. The measurement results are summarized in Table 6.

As a result, as shown in Table 6, the oil content of the oil-containing sludge was 9.3% by mass in the conventional case, but when the treatment method of the present invention was applied, the oil content of the oil-containing sludge was increased. It was 17.4% by mass, and it was found that the oil content was about twice as concentrated as in the past. Since the oil content is greatly concentrated in this way, the calorific value when incinerating sludge after dehydration and drying is also increased by about 1.5 times, and by applying the treatment method of the present invention, in the incineration step. Combustion efficiency can be greatly improved. As described above, by applying the treatment method of the present invention, the amount of fine particles that need to be removed by incineration by incineration is about 55% by weight as compared with the case of the conventional method. Therefore, the amount of incineration can be greatly reduced. Further, in addition to the above effects, as described above, since the oil content is concentrated in the fine particles, the calorific value of the fine particles processed in the incineration step is increased, so that the combustion efficiency can be improved. As a result, in addition to being able to recycle a larger amount of resources as compared with the case of processing by the prior art, improvement of work efficiency and simplification of equipment at that time can be achieved, which is brought about by the processing method of the present invention. Its economic effect will be greater.

Claims (5)

Oil-impregnated sludge containing coarse particles and fine particles and 3 to 15% by mass of oil (however, the particles are made smaller by friction between the particles with respect to the oil-containing granules composed of aggregates of coarse particles and fine particles and containing oil. In the process of adding water to a slurry ( excluding those treated in the grinding step), the slurry concentration (SS) of the slurry-like oil-containing sludge is adjusted to be 15% by mass or more.
A classification step in which the adjusted slurry-like oil-containing sludge is supplied to a liquid cyclone and separated into coarse particles and fine particles with a classification point of 15 μm or more and 20 μm or less to obtain coarse particles having an oil content of 1% by mass or less. When,
A dehydration step of dehydrating fine particles having a concentrated oil content and a particle size of less than the classification point, which is obtained by classifying in the classification step.
A method for treating oil-containing sludge, which comprises an incineration step of incinerating dehydrated sludge dehydrated in the dehydration step to remove oil. The method for treating oil-impregnated sludge according to claim 1, wherein the oil-impregnated sludge is oil-impregnated sludge containing iron powder and oil generated in a process wastewater treatment process in a steel mill. Method of processing oil-bearing sludge according to claim 1 or 2 coarse fraction collection rate is 35% or more. The method for treating oil-impregnated sludge according to claim 2 or 3 , wherein the incineration residue obtained in the incineration step is to be reused as recovered iron in the steelworks together with the coarse particles. The oil-containing sludge treatment method according to any one of claims 1 to 4 , wherein a polymer flocculant containing polyacrylamide as an active ingredient is added when the fine particles are dehydrated in the dehydration step.

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