JP6389066B2 - Steel-based wastewater treatment method - Google Patents

Description

  The present invention relates to a method for treating steel-based wastewater. More specifically, in the treatment of steel-based wastewater in which treated water is used again as cooling water after removing suspended solids, a large amount of particles such as metal powders and oils with a particle size of 50 μm or more that are generated in large quantities at steelworks From the wastewater containing various suspended solids, the suspended solids can be coagulated and settled at once, while still containing these coarse suspended solids, and the treated water is circulated and used. In particular, the present invention relates to a method for treating steel-based wastewater that can remarkably suppress the occurrence of calcium scale that is likely to occur at locations where heat load is high and the wetness and thirst of cooling water are repeated.

  For example, wastewater generated at steelworks includes direct cooling wastewater in continuous casting processes, direct cooling wastewater in rolling processes, dust collection wastewater in blast furnaces, converters, and electric furnace processes, and rainwater wastewater generated from outdoor raw material storage yards. But the amount is large. Moreover, in these wastewaters, as described below, not only fine suspended substances, but also particle sizes of metal powder such as iron, granulated slag, coal powder and coke powder are 50 μm or more. Of coarse suspended solids (hereinafter also referred to as coarse SS). When removing suspended substances from such waste water, first, the coarse suspended substances are previously removed by a method such as sedimentation separation, and then the removed waste water is further treated with various flocculants, In many cases, fine suspended solids (hereinafter also referred to as fine SS) having a particle size of less than 50 μm are removed by coagulation sedimentation.

  FIG. 5 shows an example of a conventional method for removing suspended matter (SS) containing coarse SS and fine SS as described above contained in wastewater, but directly in the rolling process of the steel material rolling line. An outline of the treatment of cooling wastewater is schematically shown. As shown in FIG. 5, the direct cooling wastewater is recycled as direct cooling water after the SS is removed to become treated water. Therefore, the treated water is desired to be clearer with less suspended matter. Below, with reference to FIG. 5, the processing procedure of the conventional direct cooling wastewater is demonstrated. First, in a rolling process, cooling water is sprayed on the steel material surface from a spray nozzle etc., and steel material is cooled. The cooling water used at that time flows down to an open soot called scale sluice indicated by 1 in FIG. This is called direct cooling wastewater and contains various suspended substances. Specifically, in this direct cooling wastewater, a large suspended substance having a particle size of 50 μm or more called a scale peeled off from the surface of the steel material, a roll shaft lubricating oil used for casting or rolling, or rolling Oil, fine iron powder generated by friction between these rolls and steel materials, and the like are included, and at least coarse SS and fine SS are mixed. In addition, the direct cooling waste water produced in the continuous casting process in the steel material production line has the same property, and the treatment is often performed in the same manner as described above.

  The large amount of directly cooled wastewater that has flowed down into the scale sluice 1 is drained by a violent flow into a tank called a scale pit indicated by 3 in FIG. 5 and stored in the pit. The scale pit is mainly intended for precipitation separation of large scale (coarse SS) having a large particle size that is present in the cooling wastewater directly. It is a relatively small tank with an Over Flow Rate of about 10 m / hr or more. is there.

  As described above, in the conventional treatment for the direct cooling wastewater generated from the continuous casting process and the rolling process, first, suspended matter (coarse SS) having a large particle diameter is precipitated and separated in the scale pit 3. After that, the waste water from which the coarse SS has been removed is mainly separated into fine particles (that is, fine particles having a particle size of less than 50 μm) by means of a coagulation sedimentation facility 8, a filter 9, and an electromagnetic filter (not shown) provided later. SS) is removed. Then, after removing the coarse SS and the fine SS as described above, the treated water is cooled by passing it through the cooling tower 4 or the like, and is directly supplied to the factory again as cooling water.

  In the conventional method for removing suspended substances from directly cooled wastewater, which is performed as described above, a flocculant is used for the purpose of efficiently sedimenting suspended substances. The flocculant to be used is selected according to the properties of the wastewater, and it is common to use various flocculants in combination. For example, Patent Document 1 relating to a water treatment method for steel rolling wastewater has a step of injecting polyaluminum chloride (PAC), which is an inorganic flocculant, and an organic flocculant into raw water obtained by collecting water used for steel rolling. Based on this assumption, the concentration of suspended solids can be more greatly and advantageously reduced by adjusting these injection amounts. Further, in Patent Document 2, when oil-containing wastewater generated from the steel industry or the like is treated with PAC, a cationic dispersion type (co) polymer that is an organic flocculant is added, and then subjected to aggregation precipitation treatment and dehydration treatment. A method has been proposed. Patent Document 3 proposes to add a specific cationic organic flocculant to wastewater mixed with mineral oil such as automobile industrial wastewater, and then add an anionic organic flocculant to aggregate and separate flocs. Yes.

Furthermore, in Patent Document 4, in the water treatment method of direct cooling wastewater in the rolling process described above, when sulfuric acid bands or PACs of inorganic flocculants are used, sulfate ions and chlorine ions in the cooling water increase, and cooling water and There is a problem of promoting corrosion of equipment such as rolling mills and rolls in contact with each other and generating fine iron oxide (Fe ₂ O ₃ ) in the cooling water. It cannot be removed. And in the technique described in Patent Document 4, as a countermeasure, aggregation treatment is performed using a cationic organic flocculant such as ammonia, an aliphatic primary amine, an aliphatic secondary amine or a polycondensate of alkylenediamine and epichlorohydrin. However, it is said that it is effective to add a scale inhibitor specific to the treated water.

  Here, since a large amount of cooling water is required in the steel industry, the direct cooling wastewater is used for cooling the steel material in the rolling process of the steel material rolling line, and as shown in FIG. It is recycled and used directly as cooling water. Then, the following processing is performed in order to enable circulation use.

  The direct cooling system circulating water used in the continuous casting process and hot rolling process of steelworks is affected by suspended solids and oil in the circulating water, causing problems such as increased strainer differential pressure, spray nozzle and spray tip clogging. In order to generate | occur | produce, the removal process of the suspended matter and oil from circulating water is needed. On the other hand, in the conventional method, it is difficult to sufficiently remove the suspended matter and the oil so that the treated water becomes transparent, and the spray caused by the suspended matter and the oil remaining in the cooling water is difficult. In order to avoid problems caused by blockage of nozzles or the like, the inside of the system is regularly cleaned.

  In addition, because the suspended matter and oil removal treatment and cleaning work described above cannot remove calcium dissolved in the circulating water, scale precipitation due to dissolved calcium is inevitable. In order to avoid the problem of clogging caused by precipitates firmly fixed to a spray nozzle or the like, the work for removing the precipitates is frequently performed. The above-described cleaning work and deposit removal process must be performed while the operations of the continuous casting process and hot rolling process of the steel mill are stopped, which causes a reduction in productivity. Precipitation of scale is important because calcium contained in cooling water may precipitate as scale in various parts, resulting in various operational failures and loss of manufacturing stability. It is a problem.

  On the other hand, for example, in Patent Document 5, there are problems such as corrosion of peripheral equipment such as rolls and frames and blockage of spray nozzles of the spray unit in the rolling mill in the direct cooling water system in the circulating hot rolling process of the steel mill. In the prevention method, it is said that it is effective to use a chlorine agent and a specific scale inhibitor together.

JP 2012-139633 A JP 2008-006382 A Japanese Patent No. 4072075 Japanese Patent No. 3868521 Japanese Patent No. 3427859

  When removing suspended substances from the directly cooled wastewater used in the steel works mentioned above, as described above, multiple types of flocculants selected from various inorganic and organic flocculants Is used. Since the amount of direct cooling wastewater in the steelworks is large, the cost for the flocculant becomes large, and therefore there is a demand for the development of technology that achieves high coagulation sedimentation efficiency at a lower cost and in a smaller amount. In the prior art, even if multiple types of flocculants are added separately to the wastewater, the point of addition is usually after entering the water treatment facility. For example, in the example shown in FIG. 5, a flocculant may be added in the scale pit 3 described above, which is the first treatment tank in the water treatment facility, for the purpose of further precipitating the coarse SS. The flocculant used here is usually an inorganic flocculant. On the other hand, the organic flocculant is used to agglomerate fine SS into large flocs and agglomerate and settle. In the example shown in FIG. 5, the fine SS in the waste water after the coarse SS is precipitated in the scale pit 3 is used. It is used for the purpose of coagulating and precipitating SS. In the example shown in FIG. 5, for example, an organic flocculant is added to the vast sedimentation basin 8 constituting the coagulation sedimentation facility. In this case, as a method for promoting the mixing, for example, a method in which a stirrer is installed in the settling basin, or a method in which a stirrer is provided in front of the settling basin and the flocculant is mixed in advance in the stirrer. In these cases, in addition to the cost of the organic flocculant used, the equipment and maintenance costs for the stirrer and stirrer tank are required separately. Therefore, the suspended solid removal method without the use of a stirrer, etc. Development is desired.

  In the conventional treatment method, as described above, after the coarse SS is precipitated in the scale pit, the waste water from which the coarse SS has been removed is treated in the coagulation sedimentation facility. As described above, the suspended matter in the wastewater flowing into the stirring tank provided in the preceding stage of the settling basin is fine particles (fine SS) having a particle size of less than 50 μm. For this reason, even if it uses various flocculants as a floc, the sedimentation speed is about 2-3 m / hr at most, and it is not quick. Therefore, in the conventional treatment method, a large sedimentation basin having a size of Over Flow Rate that is lower than the sedimentation speed of flocs composed of the fine SS is required. This means that the scale of the processing facility becomes extremely large, and if this point is improved, it is extremely effective.

In addition, as described above, in the conventional removal of suspended substances in the direct cooling wastewater generated from the continuous casting process or rolling process, only the inorganic flocculant or the inorganic flocculant and the organic flocculant are used. to combination, Cl derived from inorganic coagulant ^- because it happens to or SO ₄ ^2-like corrosive anions are mixed into the treated water, there are the following problems. These treated water is cooled in a cooling tower or the like and supplied to the factory again as cooling water. At that time, the water evaporates and the concentration of the corrosive anions increases, resulting in the circulation of piping and sprays in the circulation system. There is a risk of accelerating the corrosion of the nozzle.

  Moreover, in the removal process of suspended solids in the direct cooling wastewater, a large amount of high oil sludge in which the oil and suspended solids such as fine iron powder are firmly adsorbed is generated in the sedimentation basin. This high oil content sludge is disposed of as industrial waste or recycled as a raw material for iron making, and in most cases, a process of concentration and dehydration is required. In addition, high oil sludge is prone to poor concentration and dehydration, and is very flammable, so the oil contained therein cannot be burned sufficiently in the sintering machine, generating oil vapor and collecting exhaust gas dust. It is feared that it accumulates in the device and causes spontaneous ignition or explosion, and is not suitable for recycling.

  As a solution to the problems such as poor concentration and poor dehydration in the high oil sludge described above, there are a method of concentrating and dewatering after mixing with other sludge having a low oil content, and a method of incineration. However, these methods cannot be used when the amount of low oil sludge to be mixed with the high oil sludge is limited or when the remaining capacity of the incinerator is not large. And is not a fundamental solution to the problem of poor dehydration. For this reason, it would be extremely useful if a fundamental solution to the problem in the high oil content sludge generated in a large amount by the conventional method could be found.

  From the situation as described above, the present inventors can obtain the following effects, particularly in a method for removing suspended substances in wastewater including various suspended substances generated in steelworks, and at least the following effects: Even if it contains coarse suspended matter and fine suspended matter in wastewater, and even those that contain oil, these are simultaneously put together and the Over Flow Rate such as scale pits is 10 m / hr or more. It would be recognized that it would be extremely useful to provide a technique that enables separation and removal treatment in a relatively small water tank. In particular, (1) Treated with simplified equipment for various wastewater containing suspended solids of direct cooling wastewater that is often used in steelworks, for example, from continuous casting and rolling processes. (2) Low maintenance costs, (3) If possible, without using an inorganic flocculant that can adversely affect the treated water, (4) Metals in the wastewater Even if oils are suspended in addition to suspended substances such as water and coke, it is extremely effective if an economical and simple method for removing suspended substances in wastewater that does not generate sludge that is difficult to recycle can be realized. It is.

  Furthermore, the present inventor can realize the above-described economical and simple method for removing suspended substances in wastewater from various wastewaters containing suspended substances in direct cooling wastewater generated from continuous casting processes and rolling processes. However, dissolved calcium cannot be removed, and there is a problem of clogging of spray nozzles and the like due to scale deposition due to calcium. I realized that it would be. As described above, when the scale is deposited, it is necessary to remove the precipitate, but the removal treatment must be performed by stopping the operation of the continuous casting process or hot rolling process of the steel mill, This causes a reduction in productivity. On the other hand, the problem of scale precipitation due to calcium can be suppressed by adding a scale inhibitor to the circulating cooling water, but the amount of water in the direct cooling system circulating water in the steelworks as described above is large. There is a problem that the cost of the medicine is high.

  Accordingly, an object of the present invention is to provide steel-based wastewater containing suspended solids in a system in which treated water after removing suspended solids is used as cooling water, for example, directly generated from a continuous casting process or rolling process in a steelworks. When separating and removing suspended matter in wastewater in which coarse SS and fine SS coexist, which are generated in cooling wastewater, the following points that could not be achieved with conventional technology were achieved at the same time, It is an object of the present invention to provide an industrially extremely useful method for treating steel-based wastewater, which can also achieve the suppression of scale precipitation due to calcium dissolved in direct cooling wastewater. That is, one of the objects of the present invention is a conventional processing method in which the coarse SS and the fine SS are coagulated and settled in the same process in the removal process of the suspended matter. In addition to achieving quick and clear water treatment with the same or better quality than that achieved in the previous step, the total amount of flocculant used can be reduced compared to the conventional method by enabling the same treatment. Furthermore, the equipment cost and the maintenance cost can be reduced by greatly simplifying the equipment. In addition, the recycling cost of the generated aggregated sediment is reduced. An object of the present invention is to provide a technique capable of achieving reduction of a substance that promotes corrosion of piping mixed into treated water due to use. Furthermore, in addition to the excellent effects listed above, another object of the present invention is to realize a technique capable of suppressing the precipitation of scale due to dissolved calcium, so that calcium dissolved in circulating water is precipitated. However, the problem of causing the clogging of the spray tip and the spray nozzle is more preferably solved without using a scale dispersant (a scale inhibitor). It is to improve productivity in the continuous casting process and hot rolling process of a steel mill by making it possible to reduce the number of times of the removal process of the precipitate.

  The above object is achieved by the present invention described below. That is, the present invention provides at least a coarse suspended substance and a fine suspended substance in a method for treating steel-based wastewater containing a suspended substance of a system that uses treated water after removing suspended substances as cooling water. And at least one organic flocculant coexisting in turbulent water at a flow rate of 0.5 m / second or more, and the coarse suspended substance and the fine The suspended solids are coagulated and settled in the same treatment, and these suspended solids are removed at the same time, and at least the pH of the treated water after removing the suspended solids is 8.3 or less. Thus, the present invention provides a method for treating steel-based wastewater, characterized in that it is configured to suppress scale precipitation due to calcium in a system in which the treated water is circulated and used as cooling water.

  The following point is mentioned as a preferable form of the removal processing method of the suspended matter in the wastewater of the above-mentioned this invention. After the steel-based wastewater coagulates and settles the coarse suspended solids and the fine suspended solids in the same treatment to remove these suspended solids, the treated water is used as direct system cooling circulating water. In the vicinity of the entrance of a water treatment facility for purifying the organic flocculant from the point where the waste water in which coarse suspended substances and fine suspended substances coexist is generated. To the waste water at any point up to the point, and the direct system cooling circulating water does not contain a scale dispersant; the addition amount of the organic flocculant is 0.1 mg / L or more, and The pH is 7.0 or more and 8.3 or less; the pH is 7.5 or more and 8.1 or less; the coarse suspended substance has a particle size of 50 μm or more; The fine suspended substance has a particle size of less than 50 μm, and this The ratio of the coarse suspended solid concentration to the fine suspended solid concentration (rough / fine) is 0.5 or more by mass ratio; the lay nozzle of the turbulent water The number is 8,000 or more.

In addition, as a preferred embodiment of the above-described method for removing suspended substances in waste water of the present invention, the organic flocculant is any one of the monomers represented by the following general formula (1) and the following general formula (2). The main component is a cationic or amphoteric copolymer derived from a raw material monomer containing 5 mol% or more as one or both essential components, and the weight average molecular weight of the copolymer and the square of the cation colloid equivalent at pH 7 When the multiplied value is N, the N value is 5 million to 60 million; the organic flocculant further has a weight average molecular weight of 2 million to 13 million, and a cation colloid equivalent at pH 7 is 0. .7 to 4.1.
(In the above formula, R ₁ and R ₂ each independently represent CH ₃ or C ₂ H ₅ , and R ₃ represents either H, CH ₃ or C ₂ H _5. X ⁻ represents an anion. Represents sex counter ion.)

  In the steel wastewater treatment method of the present invention, at least one organic flocculant is vigorously added and coexisted in steel wastewater such as direct cooling wastewater in which coarse SS and fine SS coexist, In the case of normal steel-based wastewater, metal powder and oil components having a particle size of 50 μm or more are obtained by a very simple method of adjusting the pH of the wastewater to 8.3 or less in the state where an acid is added and the organic flocculant coexists. From the waste water containing coarse SS, etc., all suspended solids can be removed by coagulating and sedimenting efficiently in a state in which these coarse SS are contained, and the treated water becomes extremely clear. Therefore, the occurrence of clogging caused by suspended substances remaining in the circulating water is effectively reduced, and further, the scale dispersant (scale inhibitor) is used by setting the pH of the treated water to 8.3 or less. Calcium that dissolves without Formation and deposition of scale by the beam can be markedly suppressed.

  According to the present invention, first, a coarse SS and a fine system of a system that uses treated water after removing suspended solids as cooling water, such as direct cooling wastewater generated from a continuous casting process or rolling process of an ironworks. When separating and removing suspended substances in steel-based wastewater containing suspended substances in which SS coexists, for example, in a relatively small tank with an Over Flow Rate of 10 m / hr or more, a coarse SS and a fine SS In the same treatment, SS can be quickly settled, and the obtained treated water can be made to have a clear water quality that could not be achieved by the conventional treatment method. It is possible to provide an industrially extremely useful method for treating steel-based wastewater that can suppress the precipitation of scale due to calcium dissolved in the steel. In other words, by adopting the steel wastewater treatment process of the present invention, the total amount of flocculant used can be reduced compared to the conventional one, and the equipment and maintenance costs are reduced by greatly simplifying the equipment. In addition, when the treated water is circulated and reused directly as cooling wastewater, the treated water can be made clearer than by the conventional suspended matter removal treatment method, so clogging caused by suspended substances remaining in the treated water is possible. Can be significantly reduced. Furthermore, by adopting the steel-based wastewater treatment process of the present invention, it is possible to reduce the occurrence of clogging caused by the above-mentioned suspended substances, and to suppress the precipitation of scale due to calcium dissolved directly in the cooling wastewater. Therefore, productivity in the continuous casting process and hot rolling process of an ironworks can be improved.

  In addition, according to the present invention, by adopting the treatment process of the present invention, it is possible to coagulate and settle coarse SS and fine SS in the same treatment and more clearly compared to the prior art. The equipment can be greatly simplified, and the equipment cost and maintenance cost can be reduced. The agglomerate / sediment agglomerated and settled by the treatment process of the present invention is easy to handle, easy to handle, and suitable for recycling. Therefore, the cost for treatment of agglomerate / sediment is significantly higher than that of conventional methods. In this respect as well, a high economic effect can be realized. Furthermore, since the treated water obtained by the treatment process of the present invention exhibits a clear water quality equivalent to or higher than that achieved by the conventional treatment method, it can be recycled as it is. Since the precipitation of scale due to calcium dissolved in the circulating water can be remarkably suppressed by an extremely simple means, the economic effect from this point is extremely great.

It is a schematic diagram which shows an example at the time of applying the coagulation sedimentation processing method of the suspended solid prescribed | regulated by this invention to the direct cooling wastewater process of a continuous casting process. In addition, when the pH of treated water is not adjusted by methods, such as adding an acid, it becomes a reference example. It is a schematic diagram (Example 1) which shows an example which applied the coagulation sedimentation processing method of the suspended solids prescribed | regulated by this invention to the direct cooling wastewater process in a hot rolling process. In addition, when the pH of treated water is not adjusted by methods, such as adding an acid, it becomes a reference example. It is a figure of the photograph which shows the scale deposition condition in the case of the method of an Example. It is a photograph showing the scale deposition situation in the case of the method of the comparative example. It is a schematic diagram of the removal processing method of the suspended solid with respect to the direct cooling wastewater of the conventional hot rolling process. It is a figure which shows the range of the organic flocculent which can be used suitably for the coagulation sedimentation processing method of the suspended solids prescribed | regulated by this invention.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. First of all, the present inventors suspended in a steel-based wastewater in which coarse SS and fine SS coexisted in direct cooling wastewater generated from a continuous casting process or rolling process of an ironworks as described above. In order to achieve efficiency in separating and removing substances, intensive studies were conducted. As a result, while stopping the use of the inorganic flocculant, when the organic flocculant coexists, or after the addition of the organic flocculant, the organic flocculant, coarse SS and fine SS , Existing in wastewater, or present in wastewater by a very simple method of generating a state of coexistence while becoming a turbulent flow state at a high flow rate of 0.5 m / second or more The surprising fact which overturned the common sense of the prior art that coarse SS and fine SS can be coagulated and settled very efficiently and rapidly by the same process was discovered. According to said method prescribed | regulated by this invention, in the removal process of the suspended solid in steel-type wastewater, the various effects mentioned below can be acquired compared with the conventional method. First, there is no need to use an inorganic flocculant that has been used to promote sedimentation of coarse SS, and it is not necessary to remove fine SS after the treatment of coarse SS. Therefore, the facility cost and the maintenance cost can be reduced as compared with the conventional processing method. Furthermore, in addition to being able to agglomerate and settle these SSs very quickly with the same treatment, the coarse SS and the fine SS, and the agglomeration / sediment (sediment) is the sludge produced by the conventional treatment. Is completely different, because the dehydration is good and the oil content is low, the subsequent treatment is very easy, and the equipment and maintenance costs required for the conventional treatment for the treatment of the precipitate are greatly increased. Can be reduced. Further, the precipitate has a property suitable for recycling. Furthermore, the treated water obtained does not have the problem of mixed chlorine ions and sulfate ions due to the use of the inorganic flocculant, and compared with the treated water obtained by the conventional method for removing suspended solids. The water quality is clearly clear and has very little residue of suspended matter, and it is an epoch-making thing that can be reused as good cooling water as it is without removing fine SS in the subsequent stage.

  In the steel wastewater treatment method of the present invention, at least one organic flocculant is used, at least coarse SS and fine SS coexist, flow velocity is 0.5 m / second or more, and turbulent flow state is present. By producing a state in which the organic flocculant coexists in water, the removal of suspended substances in wastewater can be made extremely efficient. Action and effect are obtained. Below, the removal processing method of a suspended substance prescribed | regulated with the processing method of the steel-type wastewater of this invention is explained in full detail.

  Wastewater generated at steelworks is usually treated as coarse SS with a particle size of 50 μm or more and as fine SS with a particle size of less than 50 μm. These are processed by coagulation sedimentation and the like. In the present invention, these coarse SS and fine SS are coagulated and settled by the same process, and these can be removed simultaneously. It is said. Although the coexistence state of coarse SS and fine SS in the wastewater to be treated is not particularly limited, according to the study by the present inventors, the ratio of coarse SS concentration to fine SS concentration (rough / fine) is the mass ratio. If it is the waste water which is 0.5 or more, these can be satisfactorily treated together in a stable state. Further, according to the study by the present inventors, the ratio of the coarse SS concentration to the fine SS concentration (coarse / fine) may be 0.5 or more, and if it is rather large, good processing can be performed. Even if the ratio of the coarse SS concentration to the SS concentration is about 100, it can be processed without any problem. As a result of confirmation by the present inventors, the ratio of the coarse SS concentration to the fine SS concentration (coarse / fine) of the wastewater generated in the steel works depends on the specific gravity of the suspended substance. It was about ~ 100 or about 10-70. Furthermore, according to the study by the present inventors, by applying the treatment method of the present invention to any of these wastewaters, suspended substances of different sizes in the wastewater can be treated with the same treatment, For example, in a relatively small tank with an Over Flow Rate of 10 m / hr or more, it can be settled very quickly, and in addition to this, the treated water cannot be easily achieved by the conventional treatment. It will be something.

  The meaning of “flow velocity of 0.5 m / second or more and turbulent state” as defined in the present invention means that the use state of the organic flocculant is treated in the conventional gentle flow state while stirring. Instead, it means that coarse SS, fine SS, and organic coagulant coexist in a vigorous fluid state where the remarkable effects of the present invention are obtained. The flow rate may be in a state of flowing at a speed of 0.5 m / second or more, but more preferably, the flow rate is in a state of flowing at a speed of 1.0 m / second or more. Further, the flow state needs to be a turbulent flow state. More specifically, the number of water lay nozzles is 8000 or more, and more preferably, the number of water lay nozzles is 10,000 or more. The coarse SS and the fine SS may coexist, and the organic coagulant may coexist. The above-mentioned configuration defined in the present invention does not need to be achieved by providing a separate agitation facility or the like as in the case of the conventional suspension treatment method. As described below, the wastewater generated in the factory is intense. Since it can be achieved by skillfully using the flow for the removal of suspended matter, the equipment benefits are very large.

  Examples of a method for producing the above-described water state defined in the present invention include a method of adding an organic flocculant to waste water in such a state as described in (1) below, and a coarse SS as described in (2) below. And a method of adding an organic flocculant in advance to the water (circulated water) before becoming waste water in which the fine SS is coexisted.

(1) An organic flocculant is added to waste water in a turbulent state where a coarse SS and a fine SS coexist, the flow rate is 0.5 m / second or more. In this case, a preferable addition position of the organic flocculant includes any point from the point where the waste water where coarse SS and fine SS coexist to the vicinity of the inlet of the water treatment facility.
(2) The organic flocculant is added in advance to the circulating water before becoming waste water in which coarse SS and fine SS coexist, and further, this water is used as cooling water, so that coarse SS and fine SS are used. In addition, the organic flocculant can coexist in turbulent water at a flow rate of 0.5 m / second or more. As an example of the position of addition of the organic flocculant in that case, the water before becoming the waste water in which the coarse SS and the fine SS coexist is converted into the coarse SS and the fine SS in the presence of the organic flocculant. In the system where the treated water obtained by coagulating and sedimenting in the same treatment and removing them simultaneously is circulated and used again as cooling water, the addition of the organic flocculant is satisfied until the use criteria such as direct cooling wastewater are satisfied. It may be carried out at any point from the point where the circulating water is treated to the water supply point where the circulating water is used.

  As for the above (1) and (2), the direct cooling wastewater generated in the continuous casting process and rolling process of an ironworks will be specifically described as an example. "Any point from the point where the coexisting wastewater is generated to the vicinity of the entrance of the water treatment facility" includes the following points. First, when cooling water is sprayed from the spray nozzle or the like onto the surface of the steel material to cool the steel material, the cooling water becomes direct cooling waste water, so this point is a “waste water generation point”. In addition, “any point from the point where the wastewater is generated to the vicinity of the entrance of the water treatment facility”, after cooling the steel material, directly becomes cooling wastewater and flows down into an open rod called scale sluice. It flows to the scale pit, which is a water treatment facility, meaning a series of points in the meantime and nearby points.

  As described above, in the present invention, the addition of the organic flocculant is performed at a point where the coarse SS and the fine SS coexist in the wastewater in which the coarse SS and the fine SS coexist. Or may be added in the vigorous stream immediately before being drained into the scale pit, added near the scale pit inlet, or added near the suction of the scale pit pump.

  In addition, the “any point from the point where the water is treated before the use standard is met to the point where the water is supplied” as referred to in the above (2) refers to the sedimentation basin, the filtration tank after the scale pit Circulating flow from the exit point of the suspended solids removal equipment such as the machine, electromagnetic filter, etc. (that is, the treated water discharge port) to the waste water generation point through the cooling tower and from the downstream side of the scale pit to the scale sluice It means from the vicinity of the suction of the scale pit pump that generates the water to the waste water generation point described above.

  According to the study by the present inventors, at least one kind of organic flocculant is produced by coexisting coarse SS and fine SS, and coexisting in a state of being vigorously flowing with water, It turned out that a high effect is acquired. More specifically, when the organic flocculant coexists with the coarse SS and fine SS in a vigorous mixed state, the coagulation / aggregation / sedimentation effect of the organic flocculant is more prominent, and the coarse SS and fine SS With the same treatment, the solution rapidly aggregates and settles at a speed that could not be achieved by the prior art, and the supernatant liquid becomes clear (transparent) that has not existed before. Further, for example, 2 is shown in FIG. 1 and FIG. 2 from the fact that a higher effect can be obtained by ensuring a certain amount of time during which they are vigorously flowing in the coexistence state and the ease of the addition work. It was also found that it is preferable to add the organic flocculant as far as possible from the scale pit 3 of the scale sluice. If comprised in this way, an organic flocculant, coarse SS, and fine SS will be in a vigorous mixing state in any point where cooling wastewater flows through a scale sluice, for example. As a result, surprisingly, when discharged into the scale pit 3, the suspended matter containing coarse SS and fine SS directly in the cooling wastewater is coagulating / aggregating, or has already coagulated / aggregated. Therefore, it separates quickly into precipitate and clear treated water. Also, in a system that circulates and uses treated water as cooling water, as the point as far as possible from the scale pit 3, for example, the treated water obtained before the waste water generation point described above is used as irrigation water (circulated water). It is also effective to select up to the water supply point to be added and add the organic flocculant to the water before becoming waste water.

  The present inventors consider the reason why the above excellent effect is obtained by the configuration of the present invention as follows. When the organic flocculant is added to waste water or water at the above points, it is vigorously mixed. In that state, first, the organic flocculant has a particularly high agglomeration effect on the coexisting coarse SS, and a stronger coagulation effect. As a result, coagulation / aggregation of coarse SS occurs rapidly, and at this time, coexisting fine SS is taken into the coarse aggregate formed by this organic coagulant, It is considered that the excellent effect of the present invention, that is, quick and efficient good coagulation sedimentation by the same treatment, was obtained. In particular, when the wastewater is flowing in a ditch or a liquid channel, the fine SS is actively moving in the wastewater, so it is inferred that the fine SS is more easily taken into the coarse aggregate. ing. Furthermore, the aggregate / sediment obtained by the treatment method of the present invention, which is considered to be obtained by such a mechanism, is the conventional sludge obtained by adding a flocculant and allowing it to settle in a sedimentation tank. It is clearly different and has good dehydration and low oil content. For this reason, subsequent processing becomes extremely easy, and it is possible to significantly reduce the cost conventionally required for the secondary treatment of sedimentation / precipitate. In addition, the obtained aggregate / sediment does not become a high oil content, so that it is suitable for recycling.

  One of the features of the steel wastewater treatment method of the present invention is that the effective suspension material removal method described above is applied, and the coarse SS and the fine SS in the direct cooling wastewater are coagulated at once. The treated water that can be settled and is obtained after removing the agglomerates / sediments is extremely clear. For this reason, treated water can be directly circulated and used directly as system cooling water. Since the treated water obtained is extremely clear, even if it is used as it is, problems such as increased strainer differential pressure, spray nozzles, and spray tip clogging caused by suspended solids and oil remaining in the water occur. Can be suppressed. Furthermore, in order to prevent the occurrence of such troubles, the number of periodic cleaning operations in the system that were necessary to remove residual suspended solids and oil from the treated water should be reduced. Can do.

  However, according to the study by the present inventors, even if the suspended water and oil are effectively agglomerated and settled and removed by the above method, the treated water can be made unprecedented and clear, Since calcium dissolved in water could not be removed, it was found that there was another problem described below. That is, even when the above-described clear treated water is circulated, precipitation of calcium dissolved in the circulated water cannot be avoided, and this precipitate causes a problem of clogging such as a spray nozzle. In order to maintain a stable manufacturing state, it is necessary to stop the manufacturing line and frequently remove precipitates, which causes a decrease in productivity in a continuous casting process, a rolling process, and the like. On the other hand, the present inventor has investigated the places where precipitates are likely to be generated in a system in which treated water after removing suspended substances is used as cooling water.・ Check that the thirst is repeated, and more specifically, by repeating wetting and drying by spraying, scales due to calcium dissolved in the circulating water are deposited, and the spray tip and spray nozzle are easily clogged. did. As mentioned above, it is generally known that calcium scale precipitation can be suppressed by adding a scale dispersant to the circulating water, and various agents have been proposed, but they are used in steelworks. Direct cooling system circulating water has a large amount of water, and there is an economic problem that the cost of the medicine becomes enormous.

  As a result of intensive studies by the present inventors on the above-mentioned problems, the method of coagulating and sedimenting coarse SS and fine SS in steel-based direct cooling wastewater defined in the present invention at once is effective. When the treated water is removed to make clear treated water and used again as circulating water, it is compared with the case where the pH is not adjusted by a very simple method of simply reducing the pH of the circulating water to 8.3 or less. It has been found that calcium scale precipitation is dramatically reduced. In the clear treated water obtained by coagulating and sedimenting coarse SS and fine SS at a time and removing the aggregate and sediment, the SS in the treated water is about 10 mg / L or less, and the oil content is It is about 2 mg / L or less. The pH of the treated water is usually about 8.5 to 8.7. In this case, the present inventors have found that the precipitation of calcium scale that occurs when the circulating water is used is drastically reduced only by adjusting the pH of the treated water to be used to 8.3 or less. . FIG. 4 is a diagram showing the state of the spray nozzle after 2.5 months when the circulating water is circulated in a state of about 8.5 without adjusting the pH of the circulating water. FIG. 3 shows the pH of the circulating water. Although it is a figure which shows the state of the spray nozzle after 2.5 months at the time of adjusting and circulating to about 8.1-8.2 with an acid, the difference is clear. In either case, the precipitates that had adhered to the spray nozzle before the start of the test were removed to obtain a similar state.

  Although the pH adjustment of the circulating water performed in the present invention may be performed by any method, in the case of steel wastewater, the pH is often about 8.5 to 8.7 as described above. Usually, an acid may be added to adjust the pH. The acid used for adjusting the pH may be any known inorganic acid or organic acid that is generally used, and is not particularly limited. Specific examples include inorganic acids such as sulfuric acid, hydrochloric acid and phosphoric acid, and organic acids such as citric acid.

  In the method for treating steel-based wastewater of the present invention, it is necessary to make the pH of the circulating water 8.3 or less as described above. However, considering the influence on the piping and the like, the pH is 7.0 or more and 8 .3 or less, more preferably, the pH may be 7.5 or more and 8.1 or less. The remarkable effect of the present invention can be obtained by simply lowering the pH of the circulating water, which was about 8.5, to 8.3 or less. The reason for this is as follows. thinking. First, the present inventors analyzed the component of the deposit | attachment which has produced the obstruction | occlusion of the spray nozzle. As a result, most of the components were found to be calcium carbonate. Here, the concentration of carbonate ions in water greatly varies depending on the pH, and it was confirmed that the concentration of carbonate ions was tripled in the case of 8.5 compared to the pH of the solution of 8.0. In addition, if the pH of the circulating water is adjusted to suppress the precipitation of scale, the precipitation and growth of calcium scale can be further reduced by treating the concentration of suspended matter and oil in the circulating water as low as possible. It was confirmed. From these things, in this invention, after using directly for cooling water etc., the treated water for using as circulating water again reduces suspended matter and oil to the extent which is not in the past, and Both effects of lowering the pH of the circulating water and lowering the abundance ratio of carbonate ions are considered to be the difference in the amount of calcium carbonate deposited.

The organic flocculant used in the present invention is not particularly limited, and for example, an organic flocculant selected from acrylic, polyamine, and diallylammonium compounds can be used. According to the study by the present inventors, a more remarkable effect can be obtained by using the organic flocculants listed below. Specifically, a cationic or amphoteric copolymer derived from a raw material monomer containing at least 5 mol% of one or both of the monomers represented by the following general formula (1) and the following general formula (2) as an essential component. An organic flocculant having an N value of 5 to 60 million when N is a value obtained by multiplying the weight average molecular weight of the copolymer by the square of the cation colloid equivalent at pH 7 It is preferable to use it. Furthermore, it is effective to use an organic flocculant having a weight average molecular weight of 2 million to 13 million and a cation colloid equivalent at pH 7 of 0.7 to 4.1, and a weight average molecular weight of 4 million to 1300. More preferably, an organic flocculant having a cation colloid equivalent at pH 7 of 1.1 to 3.5 is used.
(In the above formula, R ₁ and R ₂ each independently represent CH ₃ or C ₂ H ₅ , and R ₃ represents either H, CH ₃ or C ₂ H _5. X ⁻ represents an anion. Represents sex counter ion.)

  The organic flocculant mainly composed of the above-mentioned cationic or amphoteric copolymer that can be suitably used in the treatment method of the present invention is a monomer represented by the above formula (1) and / or (2). Although it can derive from the raw material monomer containing more than mol%, it is preferable to use what designed the monomer composition so that said requirements may be satisfy | filled in that case. As a specific synthesis method, for the cationic copolymer, the synthesis method described in Patent Document 4 mentioned above can be used. In addition, as described in, for example, Japanese Patent No. 3352835, the amphoteric copolymer is a cationic monomer represented by the above formula (1) and / or (2), and itaconic acid as another monomer. It can be obtained by the same method by appropriately mixing an anionic monomer such as acrylic acid or the like to obtain a raw material monomer.

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

  For the organic flocculant obtained from the raw material monomer as described above, the present inventors have stated that “the coarse SS and the fine SS are coexisting from the wastewater in a state where the coarse SS and the fine SS coexist. It was examined in detail from the viewpoint of "removing turbid substances by the same treatment". As a result, in order to achieve the above-mentioned object stably at a higher level, a cation derived from a raw material monomer containing 5 mol% or more of the monomer represented by the formula (1) and / or (2) described above It has been found that the above-described remarkable effects of the present invention can be achieved at a higher level when the copolymer of the sex or amphoteric satisfies the following requirements. The inventors of the present invention are intended when the weight average molecular weight of the copolymer is 2 million to 13 million and the cation colloid equivalent value at pH 7 is 0.4 meq / g or more. It was found that the cohesiveness of (1) When the cation colloid equivalent value is small, the copolymer having a large molecular weight tends to have a larger effect as described above. (2) When the cation colloid equivalent value is large, the copolymer having a small molecular weight is low. It was found that coalescence tends to have a greater effect as described above.

  The inventors of the present invention have an extremely great technical effect by achieving “removing these suspended solids from wastewater in a state where coarse SS and fine SS coexist by the same treatment”. Therefore, in order to further increase the industrial value, the organic flocculant used was examined in more detail. As a result, among the copolymers derived from the raw material monomers, when the N value obtained by multiplying the weight average molecular weight of the copolymer by the square of the cation colloid equivalent at pH 7 is 5 million to 60 million, It has been found that it functions as an excellent organic flocculant. The cation colloid equivalent value used in the present invention is a value obtained by measuring the cation colloid equivalent value per gram of the active ingredient in the organic flocculant by a colloid titration method (a method of titrating with a potassium polyvinyl sulfate solution). The weight average molecular weight is a value measured by a GPC (gel permeation chromatography) method in terms of polystyrene.

  FIG. 6 is a diagram showing a range of organic flocculants that can be suitably used in the suspended matter coagulation sedimentation treatment method defined in the present invention. FIG. 6 is a weight average molecular weight derived from a raw material monomer containing 5 mol% or more of the monomer represented by the general formula (1) and / or (2) as an essential component, which was performed by the present inventors; Examination results of evaluating the difference in the aggregation / sedimentation effect obtained in 4 stages A to D when various copolymers having different cation colloid equivalents at pH 7 were added to waste water using each as an organic flocculant. Is shown. In AD, the effects of the present invention are recognized, but a significant effect is recognized in the order of A> B> C> D. Although D was not without the effect of coagulation / sedimentation, D was evaluated as inappropriate in view of implementation. Based on these results, the present inventors are one of the objects of the present invention “to remove these suspended solids from wastewater in a state where coarse SS and fine SS coexist by the same treatment. A detailed examination of the range of organic flocculants that can be realized, and the N value obtained by multiplying the weight-average molecular weight of the copolymer and the square of the cation colloid equivalent at pH 7 is 5 to 60 million. It was concluded that a remarkable effect can be realized. The range is indicated by a broken line in FIG. Furthermore, among those within this range, when the weight average molecular weight is 2 million to 13 million and the cation colloid equivalent at pH 7 is 0.7 to 4.1, the weight average molecular weight is 4 million to 13 million, In addition, when the cation colloid equivalent at pH 7 is 1.1 to 3.5, a more prominent effect tends to be obtained. In terms of the N value, it is more preferable to use an organic flocculant having a balance between a weight average molecular weight and a colloid equivalent equivalent to about 15 to 55 million.

  From the above, it was found that if the weight average molecular weight of the copolymer which is the main component of the organic flocculant is too small, it is difficult to obtain a sufficient SS removal effect. On the other hand, if the weight average molecular weight is too large, the viscosity increases and it becomes difficult to use. The cation colloid equivalent value used above indicates the cation density in the organic flocculant, that is, the amount of the functional group exhibiting cationic property. As described above, one of the objects of the present invention is “to remove these suspended solids from wastewater in a state where coarse SS and fine SS coexist by the same treatment”. It was found that there is an optimum cation colloid equivalent value range in consideration of the weight average molecular weight, and that a remarkable effect can be surely obtained by using a copolymer within the range satisfying the above characteristics as an organic flocculant. .

  The organic flocculants exemplified above are cationic or amphoteric, but the present invention is not limited to this, and an anionic or nonionic organic flocculant may be used depending on the target wastewater. You can also. For example, according to the study by the present inventors, in the case of dust collection wastewater from a converter, it is more effective to use an anionic organic flocculant than to use a cationic organic flocculant. can get. In addition, when treating wastewater containing carbon-based dust such as coal and coke from rainwater drainage in a coal yard, the use of a slightly anionic or nonionic organic flocculant is suitable.

  According to the study by the present inventors, the organic flocculant mainly composed of the copolymer as described above is discharged in a large amount from, for example, a hot rolling process of a steel mill, or a metal such as iron powder or rolled. Directly cooled wastewater in which coarse SS and fine SS coexist and suspended, in which oil such as oil is suspended, is 0.1 mg / L or more, for example, about 2 mg / L, relative to the treated wastewater. By adding only a small amount, the suspended matter in the wastewater quickly aggregates and settles, and the supernatant becomes extremely clear with no turbidity observed visually. On the other hand, when this organic flocculant is used for the coagulation sedimentation treatment performed after removing coarse SS from wastewater in advance as in the prior art, the remarkable effect as described above cannot be obtained, and the fine SS Although there was a tendency to flocculate and settle, the supernatant was turbid with the naked eye and apparently not sufficient. This is because the remarkable coagulation / aggregation / sedimentation effect of the present invention brought about by the organic coagulant described above is exhibited when a coarse SS having a particle size of 50 μm or more coexists with fine SS. This indicates that it is important to treat waste water in a state where coarse SS and fine SS coexist and float.

  Further, according to the study by the present inventors, the organic flocculant is, as described above, for example, the direct cooling wastewater from the hot rolling process reaches the “scale pit” which is a water treatment facility. A higher effect can be obtained if it is added to a groove or liquid channel called “scale sluice” where the waste water up to this point is flowing vigorously. Suspended substances in wastewater generated at steelworks contain a large amount of iron powder with a large specific gravity. Therefore, it is necessary to prevent sedimentation of suspended substances. The flow of scale sluice is 1-5 m / sec. It is extremely fast. According to the study by the present inventors, the requirements defined in the present invention can be satisfied by simply adding an organic flocculant to this fast wastewater stream, and as a result, the above-described remarkable effects can be obtained. Further, as described above, in this case, it is more effective to add the organic flocculant to the “scale pit” that is the water treatment facility more upstream. In particular, by adding the organic flocculant in the vicinity of the wastewater generation point, it will ensure a longer time for the wastewater to flow violently until it reaches the “scale pit” via the “scale sluice”. Although it becomes possible to do this, a higher effect can be obtained more quickly with respect to the aggregation / sedimentation of the suspended substance. When organic flocculant is added, it is better to add the organic flocculant to the place where the wastewater is flowing vigorously and react the organic flocculant with coarse SS and fine SS in a vigorous mixed state. It shows that the coagulation / aggregation / sedimentation effect due to the use of the agent is more rapidly and more prominently exhibited. As mentioned earlier, in the grooves and liquid channels called scale sluice, wastewater flows violently in a fast flow, for example, skillfully using this point before the wastewater is introduced into the water treatment facility In this case, it is not necessary to provide a separate apparatus such as a stirrer, and it is possible to obtain an industrially excellent effect by a simple means of appropriately designing a point where the organic flocculant is added. For this reason, in order to achieve the requirements stipulated in the present invention, which is essential for effectively aggregating and sedimenting suspended substances, conventional grooves and liquid channels called scale sluices are used as they are. However, in some cases, the flow may be devised so that the flow becomes more turbulent, for example, by installing an obstacle, a rotating blade, or the like in the groove or the liquid channel. In any case, in the steel wastewater treatment method of the present invention, it is necessary to react the organic flocculant with the coarse SS and the fine SS, which are the targets of the removal treatment, in a vigorous mixed state. The following remarkable effects (1) to (4) of the present invention can be obtained. Furthermore, in the present invention, the scale of calcium in the system in which the treated water is circulated and used as cooling water by adjusting the pH of the treated water after removing suspended substances from the wastewater to 8.3 or less. Precipitation can be suppressed, and the following significant effect (5) can be obtained.

  According to the steel wastewater treatment method of the present invention, various industrially useful effects described below can be obtained by the above-described extremely simple method. Hereinafter, main effects or merits obtained by the processing method of the present invention will be described.

(1) Simplification of water treatment process In the method for removing suspended solids defined in the present invention, coarse SS and fine SS in waste water are separated from organic flocculant only by devising the addition point of organic flocculant. By mixing well, fine iron powder and oil and large-scale scale can be agglomerated and settled very quickly. Conventionally, they are removed in scale pits for processing coarse suspended solids. Even fine iron powder and oil that could not be settled and separated in a scale pit or a relatively small tank like this, and mixing of suspended solids was reduced to the same level or higher on the exit side of the scale pit. Since extremely clear treated water can be obtained, simple and rapid treatment becomes possible.
As a result, the fine iron powder and oil separation facilities such as a sedimentation basin, a filter, and an electromagnetic filter, which are required in the conventional process for removing fine SS in wastewater, are not required. In connection with this, the backwashing waste water treatment equipment required when using a stirrer, a filter, and an electromagnetic filter becomes unnecessary.
Further, in the suspended substance removal treatment method defined in the present invention, an inorganic flocculant is not required, and therefore, facilities such as a tank, a pump, a stirrer, and a liquid feed line are not required.
Therefore, when constructing a new suspended solids removal treatment facility for wastewater that is generated in large quantities at steelworks and coexists with coarse SS and fine SS, it is related to the above. Equipment space and construction costs can be greatly reduced.
(2) Reduction of operation and maintenance costs The suspended solids removal treatment method defined in the present invention eliminates the need for a sedimentation basin and a filter, and is necessary because the treated water can be sent directly to the cooling tower from the exit side of the scale pit. The number of pumps can be reduced, and maintenance costs including electricity costs can be greatly reduced.
(3) Reduction of corrosion Since the method for removing suspended solids defined in the present invention does not require an inorganic flocculant, the corrosiveness contained in inorganic flocculants represented by polyaluminum chloride and sulfuric acid bands. It is possible to remarkably reduce the presence of anions, such as Cl ^- and SO ₄ ^2-, in the treated water. For this reason, when the coagulated sediment and the treated water cooled are supplied again to the factory, it is possible to reduce the corrosion of the piping system and the surface of the steel material to be produced.
(4) Promotion of recycling of iron sludge In the suspended solids removal treatment method defined in the present invention, the particle size of the particles generated in the scale pits by coagulating and sedimenting coarse SS and fine SS by the same treatment Sludge composed of large scale, fine iron powder, and oil has good dewaterability and concentration, and has a low oil content per weight, and therefore can be easily transported and recycled.

In the steel-based wastewater treatment method of the present invention, the above-described various effects are realized by applying a suspended substance removal treatment method having a specific configuration, and a very clear treatment with reduced contamination of suspended substances. Although water is obtained, it is further necessary that at least the pH of the treated water after removal of suspended solids is 8.3 or less. As a result, the following remarkable effect (5) is obtained. can get.
(5) Suppression of scale deposition due to calcium Scaling precipitation due to calcium in the system in which treated water is circulated and used as cooling water is markedly suppressed. It can be significantly reduced. Since it is necessary to stop the operation of the manufacturing apparatus, the calcium scale removal treatment work leads to an improvement in production efficiency. Furthermore, if the spray tip or spray nozzle is blocked by the calcium scale, good operation cannot be performed and the product quality may be deteriorated, which can contribute to product quality maintenance. In addition, although the problem of a calcium scale can be solved also by utilizing a scale dispersing agent (scale inhibitor), according to this invention, the expense concerning a chemical | medical agent can be reduced.

  Next, the present invention will be described in more detail with reference to examples and comparative examples. The present invention is not limited to these examples.

[Confirmation test example-Confirmation of superiority of coagulating and precipitating coarse SS and fine SS by the same treatment]
First, the confirmation test was performed as follows about the superiority of coagulating and sedimenting coarse SS and fine SS by the same treatment. In the examination, the inflow water to the scale pit 3 generated in the actual hot rolling process shown in FIG. 5 was sampled and used for the confirmation test. Specifically, the scale pit 3 inflow water sampled is divided into two, one scale pit inflow water is used for the test as it is, and the other scale pit inflow water has a particle size of 50 μm or more. What removed SS (coarse SS) was used. Add the same amount of the following organic flocculant to each of the water described above and mix well, then place the same amount in a plurality of vertically long cylindrical containers of the same shape, and the longest for 20 minutes. The sedimentation state at each time point was observed. Then, in order to objectively evaluate the sedimentation state, treated water having different standing times is collected from a certain height from the bottom surface of the cylindrical container, and each collected water (treated water) is JIS K0102. The SS concentration was analyzed according to In the test, acrylamide / [2- (acryloyloxy) ethyl 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. A cationic compound containing benzyldimethylammonium chloride / [2- (acryloyloxy) ethyl] trimethylammonium chloride copolymer (molar ratio = 60/20/20) as a main component was used. The weight average molecular weight was 11 million, and the cation colloid equivalent value at pH 7 was about 1.2 to 2.2 meq / g. The N value is 158.44 to 53.24 million.

  Table 1 shows the test results. As a result, as shown in Table 1, the “system with coarse SS” in which the coarse SS and the fine SS are treated in the same manner as defined in the present invention, and “no coarse SS” used in the conventional process are used. It was confirmed that there is a big difference in the sedimentation rate in For example, the sedimentation time for obtaining treated water with an SS concentration of 15 mg / L is only 2 minutes in the “system with coarse SS”, whereas “no coarse SS” is used in the conventional treatment. The "system" required 8 minutes. From this, it is possible to precipitate SS very quickly as compared with the conventional method by using the “system with coarse SS” that treats coarse SS and fine SS identically defined in the present invention. confirmed.

  In the comparison test between the above-described case of processing with the “system without coarse SS” conventionally performed and the case of processing with the “system with coarse SS” newly performed in the present invention, the sedimentation rate of SS was increased. Regarding the reason for the remarkable difference, the present inventors added an organic flocculant to the water to be treated in a state where the coarse SS and the fine SS coexist when the treatment is performed in the “system with coarse SS”. Thus, since the aggregates of both SSs were rapidly formed, the sedimentation rate was the same as in the case of the treatment with only the coarse SS performed before the processing of the “system without coarse SS” in the prior art. I think that it was because of over.

  From the result of the above-described confirmation test, when processing with the conventional “system without coarse SS”, the coarse SS is processed in a relatively small tank (for example, design Over Flow Rate: about 10 to 50 m / hr). A large sedimentation tank (for example, design Over Flow Rate: about 0.5 to 4.0 m / hr) is used for the subsequent processing of fine SS using a certain scale pit. On the other hand, by applying the “system with coarse SS” defined in the present invention, by using only a relatively small tank such as the scale pit described above, it is equal to or more than the conventional processing method. It was suggested that the quality of treated water was obtained. In other words, the test results described above are never obtained by the coagulation sedimentation treatment performed in the “system without coarse SS” of the prior art by the treatment in the “system with coarse SS” newly defined in the present invention. It was confirmed that a remarkable effect that could not be achieved was achieved.

<Reference Examples 1 and 2, Comparative Reference Example>
The outline of this reference example is shown in FIG. In this reference example, as shown in FIG. 1, the organic flocculant 2 is flown at the most upstream portion of the scale sluice 1 where the spray cooling wastewater flows with respect to the spray cooling wastewater generated in the continuous casting process. Added. And the supernatant water obtained by the scale pit 3 was processed by the electromagnetic filter 5, cooled by the cooling tower 4, and used again as cooling water. In this example, as the organic flocculant 2, acrylamide / [2 derived from a raw material monomer each containing 20 mol% each of the two types of monomers represented by the general formulas (1) and (2) as essential components. Uses a cationic compound mainly composed of-(acryloyloxy) ethyl] benzyldimethylammonium chloride / [2- (acryloyloxy) ethyl] trimethylammonium chloride copolymer (molar ratio = 60/20/20) It was. The weight average molecular weight was 11 million, and the cation colloid equivalent value at pH 7 was about 1.2 to 2.2 meq / g. And with respect to the waste water in scale sluice 1, this organic flocculant is set to 0 mg / L (no addition, comparative reference example), 1 mg / L (reference example 1), 2 mg / L (reference example 2). Added continuously. In addition, ratio (rough / fine) of coarse SS and fine SS in the spray system cooling wastewater processed above was about 5-20 in the mass ratio.

  And after said process, according to JISK0102, SS density | concentration and the n-Hex extract substance density | concentration (oil content) of the spray return water 6 (process water A) and the spray direct water 7 (process water B) were measured. In addition, spray return water here is the water (supernatant water) of the exit side of scale pit 3, and spray direct feed water is the water cooled after processing with the electromagnetic filter 5 (cooling water after a process). ). Further, as Comparative Example 1, the SS concentration and the n-Hex extract substance concentration (oil content) were also measured when no organic flocculant was added.

  Table 2 shows the results of the above-described organic flocculant addition test. As Reference Example 1, by adding an organic flocculant to 1 mg / L, the SS concentration of spray return water becomes 19 mg / L, and the n-Hex extract substance concentration becomes 5 mg / L. Compared with the addition, it was confirmed that the concentration of both pollutants was halved. Moreover, in spray direct water, good water quality with an SS concentration of 10 mg / L and an n-Hex extract substance concentration of 4 mg / L was obtained.

  Furthermore, as a reference example 2, when an organic flocculant was added in an amount of 2 mg / L and tested in the same manner as described above, the SS concentration of spray return water was 9 mg / L, and the n-Hex extract substance The concentration was 2 mg / L. The water quality of the spray return water is equivalent to the water quality of the direct spray water which is treated with the electromagnetic filter 5 at the subsequent stage when the addition concentration of the organic flocculant is 1 mg / L. Therefore, when an organic flocculant is added so that it may become 2 mg / L, even if the process by the electromagnetic filter 5 is stopped, it is thought that favorable water quality can be maintained.

[Confirmation test example-Confirmation of suppression effect of scale deposition by calcium]
Coarse grains were added to the actual spray cooling wastewater at the steel mill hot rolling plant shown in FIG. 2 to prepare a sample for a simulation test, and the following test was performed. Specifically, a spray system cooling wastewater obtained by adding 5000 mg / L of coarse particles having a particle diameter of 50 μm or more settled in a scale pit was used. In addition, when processing, in both cases of Example 1 and Comparative Example, the superiority was confirmed as described above, and a state in which coarse SS and fine SS defined in the present invention are coagulated and settled by the same processing is realized. Therefore, the treatment was performed with high-speed stirring. In Example 1 and Comparative Example 1, by stirring at high speed, coarse SS and fine SS coexist, and the flow rate is 0.5 m / second or more, and the organic flocculant is in the turbulent water. A coexisting state was created. In Comparative Example 2, no organic flocculant characterizing the present invention was added. Furthermore, in the treatment test of Example 1 and Comparative Example 2, the treatment was performed such that the pH during the stirring treatment was 8.3 or less. That is, using the above-described sample for simulation test, Example 1 performs a process that satisfies the requirements defined in the present invention, and Comparative Examples 1 and 2 do not satisfy any of the requirements defined in the present invention. Processing was performed to confirm the remarkable effect of the processing defined in the present invention.

<Example 1>
An organic flocculant 1 mg / L and sulfuric acid 2 mg / L were added to the sample for the above-described simulation test and stirred at high speed for 30 seconds with a stirrer. After the stirring was stopped, treated water was collected from the intermediate layer of the water tank so that the overflow rate was 30 m / hr, and the water quality was examined. As shown in Table 1, since the pH was 7.8, in this example, the stirring treatment was performed under the condition of pH 7.8. In this example, the following organic flocculants were used. Acrylamide / acryloyloxyethyltrimethylammonium chloride copolymer (molar ratio) derived from a raw material monomer containing 35 mol% each of the two types of monomers represented by the general formulas (1) and (2) as essential components = 60/20/20), which is a cationic component. The weight average molecular weight was 8 million, and the cation colloid equivalent value at pH 7 was 1.0 to 2.1 meq / g. The N value is 8 million to 485.1 million.

<Comparative Example 1>
The same organic flocculant as that used in Example 1 was used for the above-mentioned sample for simulation test, 1 mg / L of the organic flocculant was added, and the mixture was stirred at high speed for 30 seconds with a stirrer. After the stirring was stopped, treated water was collected from the intermediate layer of the water tank so that the overflow rate was 30 m / hr, and the water quality was examined. As shown in Table 1, since the pH was 8.5, the stirring treatment was performed under the same conditions as in Example 1 except that the treatment was performed under the condition of pH 8.5. Become.

<Comparative Example 2>
2 mg / L of sulfuric acid was added to the above-described sample for simulation test, and the mixture was stirred at high speed for 30 seconds with a stirrer. After the stirring was stopped, treated water was collected from the intermediate layer of the water tank so that the overflow rate was 30 m / hr, and the water quality was examined. As shown in Table 1, since the pH was 7.8, in this example, the stirring treatment was performed under the condition of pH 7.8 as in Example 1.

<Evaluation>
(Water quality analysis result-1)
Table 3 shows the water quality analysis results for each treated water obtained by the treatment in Example 1 and Comparative Examples 1 and 2.

  The Langelia index (saturation index) in Table 3 is an index of the corrosiveness of water in the water supply system, and is a numerical value indicating the precipitation tendency of calcium carbonate in water. This is a measure of the ease of formation. Conventionally, in cooling water frequently used in the steel industry, the tendency of calcium carbonate scale formation is evaluated using the Langeria index as an index. The Langeria index (saturation index) is a value obtained from the difference between the actual pH of water and the theoretical pH (pHs: pH when the calcium carbonate in water is in an equilibrium state where neither dissolution nor precipitation of calcium carbonate occurs). It is said that the smaller the Langeria index, the easier the calcium carbonate dissolves and the stronger the corrosivity. The target value of the comfortable water quality item in the water supply system is set to “approximately −1 or more and as close to 0 as possible”.

  As shown in Table 3, the treated water obtained by the treatment of Comparative Example 1 has a relatively large Langelia index, which is an indicator of the tendency of scale formation of calcium carbonate as described above, compared to the other examples. It can be said that it tends to generate scale. On the other hand, in both the treated water of Example 1 and Comparative Example 2 in which acid was added to the high-speed stirring treatment conditions in Comparative Example 1 to adjust the pH during the treatment, the Langeria index was approximately ± 0. This indicates that the production of at least calcium carbonate scale can be suppressed only by adjusting the pH. This point coincides with the common technical knowledge that the ease of adhesion of scales to piping and the like as seen from the Langeria index is more likely to adhere as the pH value increases.

(Water quality analysis result-2)
As shown in Table 4, the treated water treated in Example 1 and the treated water treated in Comparative Example 2 showed the same value for the Langeria index. According to the above detailed examination, in the actual system, when both were compared, it was found that the degree of scale adhesion to the piping and the like was completely different.

  Therefore, using the treated water obtained in Example 1 and Comparative Examples 1 and 2, an adhesion test was carried out in batches as described below, and an adhesion rate (abbreviated as MCM) was obtained for comparative examination. . Specifically, 1 L of each treated water is taken in a glass beaker, 40 mm × 20 mm × 3 mm cold rolled steel plate (SPCC) is used as a test piece, and this is immersed in a glass beaker, and each treated water is placed in a test piece. The adhesion test was conducted by rotating the magnetic stirrer so that the flow rate was about 1.0 m / s. At that time, each treated water was kept at 40 ° C. in a thermostatic bath, water was changed once a day, and stirring was continued for 14 days. Then, the adhesion amount of the scale adhering to the test piece surface was measured, and the adhesion rate was determined by the following equation. The results are shown in Table 4.

  As shown in Table 4, from the comparison between Example 1 and Comparative Example 1, the adhesion rate (MCM) was 25 from only adjusting the pH during high-speed stirring treatment from 8.5 to 7.8. It was confirmed that it was reduced to 10 or less by half. In addition, when the treated water of Example 1 having the same Langeria index and the treated water of Comparative Example 2 were compared, the MCM of the treated water of Example 1 having a lower SS concentration in water was further reduced. confirmed. From these facts, it was confirmed that in order to suppress the precipitation of scale due to the precipitation and growth of calcium, the reduction of the SS concentration in water and the pH value during the coagulation treatment are important.

<Example 2 and Comparative Example 3>
From the test results using the sample for the above-mentioned simulation test, it was concluded that it is useful to apply the present invention particularly to the direct system cooling circulating water used in large quantities at steelworks. The effect was confirmed in an actual system. Specifically, as shown in FIG. 1, the organic flocculant 2 similar to that used in Example 1 is added to the uppermost stream of the scale sluice 1 without adding the inorganic flocculant to the scale pit 3. It added so that it might become a density | concentration of 3 mg / L. Furthermore, in Example 2, about 2 mg / L of sulfuric acid was added so that the circulating cooling water had a pH of 8.1. On the other hand, in Comparative Example 3 in which no sulfuric acid was added, the pH of the circulating cooling water was about 8.5. When operated continuously for two and a half months in this state, as shown in FIG. 3, the effect of Example 2 was extremely remarkable.

Examples of utilization of the present invention include a large amount of waste water in which coarse SS and fine SS coexist, steel factory direct cooling wastewater in continuous casting process, direct cooling of steel in rolling process Although it can be applied to the treatment of wastewater, it is possible to realize the great economic effect that can be achieved in these wastewater treatment and the improvement of productivity in the continuous casting process and hot rolling process of steelworks. The practical value is extremely high. That is, in the method for treating steel-based wastewater according to the present invention, the addition position of the organic flocculant is devised, and the pH of the treated water from which suspended substances are removed is set to 8.3 or less. From the steel-based wastewater as described above, coarse SS and fine SS can be coagulated and settled very quickly by the same treatment, and can be easily removed and treated with SS removed. Since the water is extremely clear without turbidity, the treated water can be circulated as it is simply by cooling and adjusting the pH, and further, the treated water generated when the treated water is circulated is used. A remarkable effect is obtained in that the precipitation of scale due to calcium dissolved in the water is dramatically suppressed.
Since the steel-based wastewater treatment method of the present invention can be greatly simplified as compared with the conventional methods as described below, its economic effect is remarkable and its application is expected. The method for treating steel-based wastewater according to the present invention does not require separate treatment of coarse SS and fine SS as in the conventional method, so the type and amount of organic flocculant to be used can be reduced. In addition, it is possible to eliminate the need for a vast sedimentation tank that was necessary for the coagulation and sedimentation of fine suspended solids, and compared with those obtained by conventional treatment, It can be very simple, and there is a possibility that facilities such as electromagnetic filters and filters can be dispensed with, and the conventional treatment method is completely overturned, and the facilities that have been required so far, and the operation and maintenance that accompanies them are unnecessary. Therefore, the treatment method for steel wastewater according to the present invention is expected to have a very large economic effect.
Moreover, the precipitate (scale sludge) formed by the coagulation / aggregation of the organic flocculant, coarse SS and fine SS, which has been removed by the treatment method of the present invention, is easy to handle and can be dredged with crumb heavy machinery. In addition, it has a strong coagulation, so that the influence on the water quality of the supernatant liquid during the operation is small, which greatly simplifies the treatment of the precipitate. Processing becomes possible.
The means for suppressing the precipitation of scale due to calcium, which is defined in the method for treating steel wastewater according to the present invention, is a very simple one in which the pH of ordinary treated water is slightly lowered to 8.3 or less. However, the effect of suppressing scale deposition is dramatic, and its use is expected.
In the steel wastewater treatment method of the present invention, there is no need to use an inorganic flocculant, and there is a problem of adverse effects due to chlorine ions mixed in the treated water, which has been a concern in conventional methods using an inorganic flocculant. This is also very economical from this point.

1: Scale sluice (open)
2: Organic flocculant 3: Scale pit 4: Cooling tower 5: Electromagnetic filter 6: Spray return water (treated water A)
7: Direct spray water (treated water B)
8: Sedimentation basin 9: Filter

Claims (7)

In the method for treating steel-based wastewater containing suspended solids in a system in which treated water after removing suspended solids is used as cooling water,
A coarse suspended substance having a particle size of 50 μm or more containing at least one of metal powder, granulated slag, coal powder or coke powder, and a fine suspended substance having a particle size of less than 50 μm coexist, and At a flow rate of 0.5 m / second or more, a state in which at least one flocculating / sedimenting agent of the suspended substance coexists in turbulent water,
The coarse suspended substance and the fine suspended substance are coagulated and settled by the same treatment, and these suspended substances are removed simultaneously,
Furthermore, by setting the pH of the treated water after removing suspended substances to 8.3 or less , the treated water can be circulated and used as cooling water without using a scale dispersant . Configured to suppress scale precipitation due to dissolved calcium in
The aggregating / sedimenting agent is cationic or amphoteric derived from a raw material monomer containing 5 mol% or more of any one or both of the monomers represented by the following general formula (1) and the following general formula (2) as essential components. When the value obtained by multiplying the weight average molecular weight of the copolymer by the square of the cation colloid equivalent at pH 7 is N, the N value is 5 to 60 million. A method for treating steel-based wastewater.
(In the above formula, R ₁ and R ₂ each independently represent CH ₃ or C ₂ H ₅ , and R ₃ represents either H, CH ₃ or C ₂ H _5. X ⁻ represents an anion. Represents sex counter ion.) After the steel-based wastewater coagulates and settles the coarse suspended solids and the fine suspended solids in the same treatment to remove these suspended solids, the treated water is used as direct system cooling circulating water. System
Either from the point where the waste water in which the coarse suspended substance and the fine suspended substance coexist is generated to the vicinity of the inlet of the water treatment facility for purifying the waste water The method for treating steel-based wastewater according to claim 1, wherein the direct-system cooling circulating water is added to the wastewater at a point of no and does not contain a scale dispersant.   The method for treating steel-based wastewater according to claim 1 or 2, wherein an addition amount of the flocculant / sedimentation agent is 0.1 mg / L or more, and the pH is 7.0 or more and 8.3 or less.   The said pH is 7.5 or more and 8.1 or less, The processing method of the steel-type wastewater of any one of Claims 1-3.   The coexistence state of the coarse suspended substance and the fine suspended substance indicates that the ratio of the coarse suspended substance concentration to the fine suspended substance concentration (rough / fine) is 0. It is 5 or more, The processing method of the steel-type wastewater of any one of Claims 1-4.   The method for treating steel-based wastewater in wastewater according to any one of claims 1 to 5, wherein the number of lay nozzles of the turbulent water is 8000 or more.   The aggregating / sedimenting agent further has a weight average molecular weight of 2 million to 13 million and a cation colloid equivalent at pH 7 of 0.7 to 4.1. Treatment method for steel wastewater.