JP5644491B2 - Water treatment system for steel rolling wastewater - Google Patents

Description

  The present invention relates to a water treatment system for steel rolling wastewater, and more specifically, recovers water (rolling wastewater) used in a rolling production process of steel products, for example, a hot rolling production process of seamless steel pipe, to adjust pH and remove impurities. The present invention relates to a water treatment system for steel rolling wastewater that can significantly and advantageously reduce the concentration of impurities, particularly suspended solids (abbreviated as SS), in the water treatment process.

Generally, water (rolling wastewater) used in a steel product rolling manufacturing process (mill line) is collected and subjected to water treatment. The water entering the water treatment process is called raw water. In the water treatment process, raw water is subjected to pH adjustment and removal of impurities so as to meet predetermined water quality standards, and then part of the raw water is called recirculated water and reused in the mill line system, and the rest is discharged outside the system. Is done.
The pH adjustment and impurity removal are generally performed as follows.

Suspended particles, which are soil elements, are floating in the raw water. This is because the surface is negatively charged and repels and does not agglomerate and is difficult to separate from water. Therefore, by adding an inorganic flocculant, the suspended particles are electrically neutralized (charge neutralization) to promote the aggregation and form fine flocs (lumps having a particle size of several mm). Polyaluminum chloride is used as the inorganic flocculant. This is an acidic liquid drug having a chemical formula of [Al ₂ (OH) _n Cl _6-n ] _m and abbreviated as PAC and having a pH of 2 to 3, and has a positive charge. Has the effect of However, if the pH of the raw water is lowered by addition of PAC and deviates from the effective range (pH 5.0 to 7.5), the effect is significantly weakened. Therefore, caustic soda (pH 11 to 12) is used together with PAC for the purpose of keeping the pH within the effective range. Caustic soda is also used to finally neutralize water.

However, since it is still difficult to remove suspended particles only by making fine flocs, the fine flocs are aggregated into coarse flocs by adding a polymer flocculant. The polymer flocculant is anionic and has an adhesive element, and the fine flocs are aggregated by the cross-linking effect to form coarse flocs.
With regard to this technical field, Patent Document 1 purifies the steel manufacturing wastewater containing oil and persistent organic matter to make the oil and COD in the alkaline wastewater in a rolling process of the steel manufacturing industry into a good state. As a method, it is described that after performing a flocculation pressure flotation or a flocculation precipitation treatment with a flocculant, a chemical oxidation treatment is further performed with an oxygen-based oxidant in the presence of a metal catalyst. About 200 to 1000 mg, the amount of the polymer flocculant used may be 1 to 2 mg per liter of raw water.

  In addition, Patent Document 2 aims to efficiently remove a suspension in suspension water as coarse floc by adding an optimum amount of a pH adjusting agent and an inorganic adjusting agent to alkaline degreasing wastewater (raw water). As a method for treating alkaline degreasing wastewater, while measuring the flow rate and pH value of the treated water led to the pH adjustment tank, the optimum pH value and the required inorganic content of the suspended water in the pH adjustment tank 3 determined according to the pH value of the raw water The correlation between the flocculant addition concentration is obtained in advance, and the pH adjuster and the inorganic flocculant are adjusted so that the suspended water in the pH adjustment tank has the optimum pH value and the required inorganic flocculant addition concentration by using the correlation. It is described that, by adding, a suspension in suspension water is efficiently condensed to form coarse floc.

JP 2007-252969 A JP 2001-170653 A

  In factories, the operation control value of the water treatment facility is usually set to be stricter than the water quality regulation value of the residence (municipalities, etc.). For example, against the water quality regulation values of Sakai City (pH: 5.8 to 8.6, SS: less than 30 ppm, oil content: less than 2 ppm, COD: less than 20 ppm, nitrogen: less than 20 ppm, phosphorus: less than 2 ppm) In the seamless steel pipe rolling manufacturing plant, the operation control values of the water treatment facility (also referred to as the circulating water facility) for the rolling wastewater are pH: 6.0 to 8.4, SS: less than 5 ppm, oil content: less than 2 ppm, COD: less than 18 ppm, nitrogen: 15 ppm, phosphorus: less than 1.5 ppm. Note that 1 ppm = 1 mg / L. However, there is an unsolved problem that the SS concentration of the circulating water sometimes exceeds the management target value by about several ppm and the quality of the product steel pipe becomes unstable. This problem is not considered in Patent Document 1 and Patent Document 2. Moreover, in the method described in Patent Document 1, there is a concern that an existing facility needs to be modified.

  Then, an object of this invention is to provide the water treatment system of the steel rolling waste water which can hold | maintain the SS density | concentration of circulating water stably to a very low level, without requiring the modification of existing facilities.

  The inventors have intensively studied to solve the above problems, and as a result, even if the raw water having the same SS concentration is subjected to water treatment under the same conditions, the rolled material that produced the raw water (before becoming the raw water) The SS concentration after water treatment differs depending on the Cr amount grade of the rolled material that was being rolled when the water was being used for rolling in the mill line, and the higher the Cr amount grade, the higher the SS concentration after water treatment. In addition, it was found that the SS concentration after water treatment changes depending on the rolling size for the rolled material having the highest Cr amount grade. And as a result of further examination, not only based on the SS concentration in the raw water, but also based on the Cr amount grade information and the rolling size information of the rolled material that produced the raw water, the PAC and the polymer flocculant in the raw water It has been found that the SS concentration after water treatment can be stably maintained at a very low level by optimally controlling the injection amount, and the present invention having the following gist configuration has been made.

(1) In a system for performing water treatment of steel rolling wastewater having a step of injecting PAC and a polymer flocculant into raw water obtained by collecting water used for steel rolling, for each Cr amount grade of the rolled material and It holds the target value of the injection amount of PAC and polymer flocculant determined according to the SS concentration in the raw water, and receives the SS concentration information in the current raw water received from time to time, the Cr amount grade information of the rolled material that produced the current raw water An injection amount adjuster for adjusting the opening degree of the PAC injection gate and the polymer flocculant injection gate so that the injection amount matches the target value held corresponding to the SS concentration value and the Cr amount grade value ,
Information for generating the Cr amount grade information of the rolled material that produced the current raw water from the rolling record data, and generating SS concentration information in the current raw water from the raw water quality inspection record data, and transmitting these information to the injection amount adjuster A water treatment system for steel rolling wastewater, characterized by comprising a generation transmitter.

(2) The target value held by the pouring amount adjuster is also determined for each rolling size, and the pouring amount adjuster also corresponds to the rolling size in the rolling size information of the rolled material that produced the current raw water. An injection amount adjuster that adjusts the opening so that the injection amount matches the target value
In addition to Cr amount grade information and SS concentration information, the information generation transmitter further generates rolling size information of the rolled material that produced the current raw water from the rolling record data,
This rolling size information is also transmitted to the pouring amount adjuster, the water treatment system for steel rolling wastewater according to (1) above.

  ADVANTAGE OF THE INVENTION According to this invention, the SS density | concentration of the circulating water which is a recycle form in the steel rolling system of the water after water treatment can be stably hold | maintained to a very low level, and it contributes to the quality improvement of steel products. There is also an advantage that the existing equipment is not required to be modified. Furthermore, there is an effect of improving water treatment efficiency by automating the PAC and polymer flocculant charging process.

Water treatment flow chart showing an example of an embodiment of the present invention

  FIG. 1 is a water treatment flow diagram showing a case where the present invention is applied to a water treatment facility attached to a mill line 1 that performs seamless steel pipe forming and rolling as an example of an embodiment of the present invention. In this water treatment facility, the water used for pipe making and rolling in the mill line 1 is collected and temporarily stored in the scale pit 2 and sent to the primary sedimentation tank 3 as a common matter with the conventional one. In the primary sedimentation tank 3, foreign substances in water are precipitated to a certain extent, and the remaining supernatant is sent to the aggregation reaction tank 4 as raw water for the next aggregation reaction treatment stage. In the agglomeration reaction tank 4, PAC, a polymer flocculant, and a neutralizing agent (NaOH) are injected for the purpose described above, and the suspension in the raw water is agglomerated into coarse floc. The water containing the coarse floc is sent to the pressurized flotation tank 5, and the floating scum formed by floating the coarse floc is removed by injection of pressurized water. It moves to the treated water tank 8, and it sends to the mill line 1 as recycle water from there, and reuses. The levitated scum is dehydrated sludge from the thickener tank through a dehydrator.

Conventionally, the SS concentration information of raw water is obtained from the water quality inspection in the primary sedimentation tank 3, and the injection amount of the PAC and the polymer flocculant is determined based on this information. In contrast, in the present invention, the target value of the injection amount of the PAC and the polymer flocculant determined to be different for each SS concentration in the raw water and for each Cr amount grade of the rolled material is held, and is received at any time. PAC injection gate so that the injection amount matches the target value held corresponding to the SS concentration value in the Cr amount grade information of the rolled material that produced the current raw water and the Cr amount grade value. 11 and an injection amount adjuster 20 for adjusting the opening degree of the polymer flocculant injection gate 12;
Information for generating the Cr amount grade information of the rolled material that produced the current raw water from the rolling record data, and generating SS concentration information in the current raw water from the raw water quality inspection record data, and transmitting these information to the injection amount adjuster Generation transmitter 30. Thereby, not only based on the SS concentration information of the raw water, but also the rolled material (the rolled material that was being rolled when the water before becoming the raw water was being used for rolling in the mill line 1) that produced the raw water. Quantity grade information is obtained, and the injection amount of PAC and polymer flocculant is determined based on this information. In this determination, prepared in advance a table that defines the target value of the injection amount of PAC and polymer flocculant different for each SS concentration in the raw water, each Cr amount grade of the rolled material and each rolling size change, With reference to the table, the target value corresponding to the SS concentration value and the Cr amount grade value in the information is set as the determination value of the injection amount. Then, the opening degree of the PAC injection gate 11 is adjusted so that the opening degree corresponds to the determined value of the PAC injection amount, and the opening degree corresponding to the determined value of the polymer flocculant injection amount is adjusted. The opening degree of the flocculant injection gate 12 is adjusted.

  The above table is a beaker test in which the raw water SS concentration value and the raw material water with different grades of Cr amount of the rolled material that produced the raw water are used as test water, and the injection amount of PAC and polymer flocculant is changed. Thus, the PAC and the polymer flocculant injection amount at which the SS concentration in the test water decreases the fastest is obtained, and the result is verified by a factory experiment or further corrected to obtain a target value.

  According to the investigations by the inventors, in the case of a rolled material with a high Cr content (specifically, 12 mass% or more), the optimum PAC injection amount and the optimum polymer flocculant injection amount depend on the rolling size. I know it will change. Therefore, the table is a table in which target injection values of PAC and polymer flocculant are set for each rolling size, especially for the Cr amount grade value having a high Cr amount. In addition to the quantity grade information and the SS concentration information, it is preferable to further generate the rolling size information of the rolled material that produced the current raw water from the rolling record data and transmit it to the injection amount adjuster 20.

  Further, the amount of NaOH injected is determined according to the amount of PAC injected as in the conventional case.

(Example)
In the embodiment in which the present invention is applied to the water treatment using the water treatment facility shown in FIG. 1, when the SS concentration in the raw water (supernatant water in the primary sedimentation tank 3) is about 20 to 50 ppm, the PAC injection amount and the high The table shown in Table 1 was used to determine the target value of the molecular flocculant injection amount. In this table, three kinds of “ordinary steel”, “low Cr steel”, and “high Cr steel” are adopted as the index regarding the Cr amount grade of the rolled material in the order of the Cr amount grade, and the high Cr steel is rolled. “Steel pipe finishing outer diameter” is adopted as an index relating to the size, and target values for the PAC injection amount and the polymer flocculant injection amount that are different for each index are determined. On the other hand, when the SS concentration in the raw water is other than about 20 to 50 ppm, the target value is given by a function that increases linearly with an increase in SS concentration. And it takes the Cr amount grade information and finish outer diameter information of the rolled material from the mill line, and also takes the SS concentration information of the raw water born from the rolled material, and the index or the function in the table corresponding to these information The PAC injection amount and the polymer flocculant injection amount with respect to the raw water were adjusted so as to coincide with the target value determined from the above.

On the other hand, conventionally, the target value is given as a function that increases linearly with an increase in SS concentration regardless of the Cr amount grade. Then, SS information of the raw water was taken, and the PAC injection amount and the polymer flocculant injection amount for the raw water were adjusted so as to match the target value determined from the function corresponding to this information.
The circulating water SS concentration in the Examples stably remained at 2 ppm or less, and was able to be maintained at a much lower level of stability than when the conventional circulating water SS concentration was 4 to 7 ppm. In addition, in the examples, although the amount of the polymer flocculant used was slightly increased on average on a monthly basis, the amount of PAC and NaOH used was significantly reduced compared to the conventional case, leading to a reduction in the overall use cost. It was.

DESCRIPTION OF SYMBOLS 1 Mill line 2 Scale pit 3 Primary sedimentation tank 4 Aggregation reaction tank 5 Pressurization float tank 6 Filtration raw water tank 7 Filter 8 Processed water tank 11 PAC injection gate 12 Polymer flocculant injection gate 20 Injection amount adjuster 30 Information generation transmitter

Claims (2)

In a system for performing water treatment of steel rolling wastewater having a step of injecting PAC and a polymer flocculant into raw water obtained by collecting water used for steel rolling, for each Cr amount grade of rolled material and in raw water The target value of the injection amount of PAC and polymer flocculant determined according to the SS concentration is held, and the SS concentration information in the current raw water received at any time, the SS in the grade information on the Cr amount of the rolled material that produced the current raw water An injection amount adjuster that adjusts the opening degree of the PAC injection gate and the polymer flocculant injection gate so that the injection amount matches the target value held corresponding to the concentration value and the Cr amount grade value;
Information for generating the Cr amount grade information of the rolled material that produced the current raw water from the rolling record data, and generating SS concentration information in the current raw water from the raw water quality inspection record data, and transmitting these information to the injection amount adjuster A water treatment system for steel rolling wastewater, characterized by comprising a generation transmitter. The target value held by the injection amount adjuster is determined for each rolling size, and the injection amount adjuster corresponds to the roll size in the rolling size information of the rolled material that produced the current raw water. Is an injection amount adjuster that adjusts the opening degree so that the injection amount coincides with
In addition to Cr amount grade information and SS concentration information, the information generation transmitter further generates rolling size information of the rolled material that produced the current raw water from the rolling record data,
The water treatment system for steel rolling wastewater according to claim 1, wherein the rolling size information is also transmitted to the injection amount adjuster.

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