Backwashing water treatment system based on zero wastewater discharge of steel rolling production line and working method

Abstract

The invention relates to the technical field of steel rolling production line sewage treatment, and particularly discloses a steel rolling production line wastewater zero discharge-based backwashing water treatment system and a working method.The steel rolling production line wastewater zero discharge-based backwashing water treatment system comprises a backwashing water precipitation unit, a sludge concentration unit and a dehydration unit, and the backwashing water precipitation unit is used for treating backwashing water generated by a bypass filter; backwashing water is subjected to primary precipitation through the backwashing water precipitation unit to form supernate, the supernate returns to the circulating water system, and muddy water obtained after primary precipitation is input into the muddy water concentration unit; the sludge concentration unit is used for carrying out secondary precipitation concentration on the mud water subjected to primary precipitation, supernate returns to the backwashing water precipitation unit, and the mud water subjected to secondary precipitation is input into the dehydration unit; the dewatering unit is used for further separating sludge from water, and the separated water enters the backwashing water precipitation unit for further cyclic utilization; zero emission of the backwashing water is realized, clean water treated by the backwashing water is recycled, and ferric oxide in the backwashing water is recycled and sold as a byproduct, so that the cost is reduced, and the benefit is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment for steel rolling production lines, and in particular to a backwash water treatment system and a working method based on zero discharge of wastewater from steel rolling production lines. Background Art

[0002] The circulating water of the steel rolling production line is generally treated by bypass filters. After the water quality is treated by bypass filters, the content of suspended solids and grease in the circulating water is significantly reduced. The treated circulating water is then reused in the pool. The backwash water of the bypass filter is a kind of wastewater generated after the circulating water is treated. It contains a large amount of suspended solids and oil pollution. Direct discharge will cause serious pollution to the environment.

[0003] Generally, hot rolling production lines will be equipped with a mud treatment system to treat backwash water. Traditional hot rolling mud treatment systems are generally composed of sedimentation tanks, plate and frame filter presses, etc., but they have the problems of large footprint and low treatment efficiency. With the continuous advancement of technology, advanced hot rolling production line mud treatment generally adopts equipment and treatment processes such as advection tank scraping, sludge concentrator concentration, centrifuge dehydration, etc. with small footprint and high treatment efficiency. However, the above mud treatment equipment has the following technical problems in actual operation:

[0004] Sludge scraping in a horizontal flow tank is a method of collecting sludge through a scraper after the sludge is settled. However, the operation of the scraper is affected by factors such as the amount of sludge accumulation, and its operating efficiency is low. It is also easy to cause blockage of the sludge primary lifting pump.

[0005] Sludge concentrator is a method of treating the primary sludge by secondary sedimentation and concentration, but the sludge concentrator is prone to cause blockage of the secondary lifting and feeding pump.

[0006] Centrifuge is a method of separating mud and water from secondary sedimentation concentrated sludge, but the centrifuge is greatly affected by the uniformity of the incoming material. Uneven incoming material can easily cause problems such as centrifuge blockage, high water content in the discharge material, and low discharge efficiency.

[0007] The centrifuge needs to be installed on a high platform, and the sludge precipitation in the sewage pipe will cause the pipe to be blocked.

[0008] During the backwash water treatment process, the sludge concentrator and centrifuge will still discharge wastewater, and it is impossible to achieve "zero discharge" of wastewater.

[0009] Therefore, in the existing treatment methods, there are still problems such as low treatment efficiency, sludge clogging equipment, low discharge efficiency, and inability to achieve complete wastewater circulation.

[0010] In order to solve the above problems, it is necessary to provide a new method for backwash water treatment that can improve the backwash water treatment efficiency and achieve zero wastewater discharge. Summary of the invention

[0011] In view of the problems existing in the prior art, the purpose of the present invention is to provide a backwash water treatment system and working method based on zero discharge of wastewater from a steel rolling production line, so that the mud and water in the backwash water can be efficiently separated, the generated sludge can be recycled, the backwash water can be reused, and no polluted water is generated, thereby achieving "zero discharge" of wastewater.

[0012] The technical solution adopted by the present invention to solve its technical problems is: a backwash water treatment system based on zero discharge of wastewater from a steel rolling production line, including a backwash water sedimentation unit, a sludge concentration unit and a dehydration unit, the backwash water sedimentation unit is used to treat the backwash water generated by the bypass filter, the backwash water is precipitated once in the backwash water sedimentation unit to form a supernatant, the supernatant is returned to the circulating water system, and the muddy water after the first precipitation is input to the muddy water concentration unit; the sludge concentration unit is used to perform secondary precipitation and concentration on the muddy water after the first precipitation, the supernatant is returned to the backwash water sedimentation unit, and the muddy water after the second precipitation is input to the dehydration unit; the dehydration unit further separates the sludge and water, and the separated water enters the backwash water sedimentation unit for further recycling.

[0013] Specifically, the backwash water sedimentation unit includes a bypass filter backwash pump, a pipeline mixer, a regulating tank, a scraper, and a primary sludge lifting pump. The regulating tank includes a clear water area and a sludge area of ​​the regulating tank. The regulating tank is divided into partitions for further separation of mud and water. The rear of the bypass filter backwash pump is connected to the pipeline mixer, which is used to fully mix the agent with the backwash water. The rear of the pipeline mixer is connected to the regulating tank. The clear water area of ​​the regulating tank is connected to the circulating water system and the disc oil remover. A scraper is installed in the sludge area of ​​the regulating tank, and a primary sludge lifting pump is also installed in the sludge area of ​​the regulating tank.

[0014] Specifically, compressed air is introduced into the sludge area of ​​the regulating tank for aeration so that the sludge and water are fully mixed.

[0015] Specifically, the sludge thickening unit includes a sludge sedimentation tank, a sludge thickener, a secondary sludge lifting pump, a mixing tank, and a tertiary sludge lifting pump. The sludge sedimentation tank is connected to the sludge area of ​​the regulating tank through a primary sludge lifting pump. A sludge thickener is installed on the sludge sedimentation tank. The rear of the sludge thickener is connected to the secondary sludge lifting pump. The rear of the secondary sludge lifting pump is connected to the mixing tank. The rear of the mixing tank is connected to the tertiary sludge lifting pump.

[0016] Specifically, an air-water flushing mechanism is provided at the bottom discharge pipe of the sludge thickener to prevent the thick iron oxide sludge from clogging the inlet pipeline of the secondary sludge lifting pump.

[0017] Specifically, compressed air is introduced into the mixing tank for aeration and uniform mixing.

[0018] Specifically, the dehydration unit includes a horizontal screw centrifuge, a screw conveying device, a dosing device, and a slag pool. The horizontal screw centrifuge is connected to a tertiary sludge lifting pump, the dosing device is installed on the horizontal screw centrifuge, the rear of the horizontal screw centrifuge is connected to the screw conveying device, and the rear of the screw conveying device is connected to the slag pool.

[0019] Specifically, an overflow pipe is arranged on the feed pipeline of the horizontal screw centrifuge, and an elevated sewage pipe is adopted as the sewage pipe of the horizontal screw centrifuge, and the sewage is refluxed by setting an inclination angle.

[0020] A working method of a backwash water treatment system based on zero discharge of wastewater from a steel rolling production line comprises the following steps:

[0021] S1. The backwash water is input into the regulating tank through the bypass filter backwash pump. During the input process, the backwash water and the flocculation and coagulant are fully mixed by the pipeline mixer by adding flocculation and coagulant agents. The mixed backwash water enters the regulating tank and is precipitated through the regulating tank. The regulating tank has a certain slope, which is convenient for the scraper to collect sludge better. After precipitation, the sludge enters the sludge area of ​​the regulating tank through the scraper, and the supernatant enters the clear water area of ​​the regulating tank through the overflow weir, and is returned to the circulating water system through the clear water lifting pump for reuse. A disc deoiler is set in the clear water area of ​​the regulating tank for further deoiling. Aeration is set in the sludge area of ​​the regulating tank, and the concentrated sludge is aerated with compressed air to fully mix the sludge with water to obtain uniform sludge water, so as to prevent the lumps of sludge from clogging the sludge lifting pump. The uniform sludge water enters the sludge concentration unit through the primary sludge lifting pump for further treatment.

[0022] S2. The sludge treated by the backwash water sedimentation unit enters the sludge sedimentation tank for sedimentation; the sludge sedimentation tank is cylindrical with a conical bottom, which is convenient for the sludge to be graded and scraped by the sludge thickener after the sludge is precipitated; the supernatant after the sludge is concentrated enters the clear water area of ​​the backwash water regulating tank to further concentrate the mud and water; the sludge after sedimentation and concentration is scraped and collected by the sludge thickener; the sludge thickener has multi-stage blades, which can transfer the sludge step by step during the rotation process; the discharge pipe at the bottom of the sludge thickener is provided with air and water flushing; the inlet pipeline of the secondary sludge lifting pump is made of stainless steel, which makes the sludge conveying process smoother; the concentrated sludge enters the mixing tank through the secondary sludge lifting pump; the mixing tank is aerated and mixed with compressed air, and the uniform mud and water enter the horizontal screw centrifuge through the tertiary sludge lifting pump;

[0023] S3. The muddy water further concentrated by the sludge thickener enters the horizontal screw centrifuge; through the dosing device such as flocculation and coagulant; the muddy water reacts with the flocculation and coagulant in the horizontal screw centrifuge, and the mud and water are separated by the high-speed rotation of the horizontal screw centrifuge. The separated solid sludge enters the slag pool through the screw conveyor, and the dry slag is taken out; an overflow pipe is set on the feeding pipeline of the horizontal screw centrifuge to avoid large sludge clumps from being unable to be processed when they are fed into the horizontal screw centrifuge, resulting in blockage of the horizontal screw centrifuge equipment; the sewage from the horizontal screw centrifuge is returned to the regulating tank in the backwash water sedimentation unit through the elevated sewage pipe for further treatment.

[0024] The present invention has the following beneficial effects:

[0025] The backwash water treatment system and working method designed in the present invention based on zero discharge of wastewater from a steel rolling production line achieve zero discharge of backwash water, reuse clean water through backwash water treatment, and recover iron oxide in the backwash water and sell it off as a by-product, thereby reducing costs and increasing efficiency.

[0026] The backwash water treatment system and working method designed by the present invention based on zero discharge of wastewater from a steel rolling production line solves the problem of incomplete reaction between reagents and backwash water due to the short water transmission distance from the bypass filter to the backwash water sedimentation unit.

[0027] The backwash water treatment system and working method designed in the present invention based on zero discharge of wastewater from a steel rolling production line solves the problem of iron oxide-containing sludge clogging the conveying pipeline and treatment equipment during sludge transportation in the backwash water treatment process of a traditional steel rolling production line, reduces problems such as equipment failure shutdown and pipeline unblocking, and realizes the full process cycle of backwash water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the structural block diagram of the backwash water treatment system based on zero discharge of wastewater from steel rolling production lines.

[0029] In the figure: 1- bypass filter backwash water, 2- sewage treatment agent, 3- backwash water after the agent is fully mixed, 4- separated waste oil, 5- supernatant, 6- compressed air, 7- primary precipitated sludge, 8- aerated mixed sludge, 9- secondary precipitated sludge, 10- concentrated sludge, 11- mixed sludge, 12- dehydrated sludge, 13- dehydrator sewage, 101- bypass filter backwash pump, 102- pipeline mixer, 103- regulating Pool saving, 104-clear water area of ​​regulating tank, 105-sludge scraper, 106-sludge area of ​​regulating tank, 107-primary sludge lifting pump, 108-disc deoiler, 201-sludge sedimentation tank, 202-sludge thickener, 203-secondary sludge lifting pump, 204-mixing tank, 205-tertiary sludge lifting pump, 301-horizontal screw centrifuge, 302-screw conveying device, 303-dosing device, 304-slag tank, 401-circulating water system. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely further describe the technical solutions in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, a method for backwash water treatment based on zero discharge of wastewater from a steel rolling production line is provided, wherein the system involved in the method comprises a backwash water sedimentation unit, a sludge concentration unit, and a dehydration unit; the backwash water sedimentation unit is used to treat the backwash water generated by the bypass filter, and the backwash water is precipitated once in the backwash water sedimentation unit to form a supernatant 5, and the supernatant 5 is returned to the circulating water system 401, and the muddy water after the first precipitation is input to the muddy water concentration unit; the sludge concentration unit is used to perform a second precipitation and concentration on the muddy water after the first precipitation, and the supernatant 5 is returned to the backwash water sedimentation unit, and the muddy water after the second precipitation is input to the dehydration unit; the dehydration unit further separates the sludge and water, and the separated water enters the backwash water sedimentation unit for further recycling.

[0032] The backwash water sedimentation unit includes a bypass filter backwash pump 101, a pipeline mixer 102, a regulating tank 103, a scraper 105, a primary sludge lifting pump 107, and a disc oil remover 108 which are connected in sequence. The bypass filter backwash pump 101 is connected to the pipeline mixer 102 at the rear, and the pipeline mixer 102 is used to fully mix the agent with the backwash water. The pipeline mixer 102 is connected to the regulating tank 103 at the rear, and the clear water area 104 of the regulating tank is connected to the circulating water system 401 and the disc oil remover 108. The scraper 105 is installed in the sludge area 106 of the regulating tank, and the primary sludge lifting pump 107 is also installed in the sludge area 106 of the regulating tank.

[0033] The bypass filter backwash water is input into the regulating tank 103 through the bypass filter backwash pump 101. However, during the backwash water input process, flocculation and coagulant agents are added to improve the backwash water treatment effect. However, since the process distance is too short, the agent and the backwash water cannot fully react, which will cause the agent flocculation effect to deteriorate. By setting a pipeline mixer 102, the present invention ensures that the agent and the backwash water are fully mixed through the rotation of the impeller, thereby increasing the reaction speed and solving the problem of poor flocculation effect in a short process.

[0034] The backwash water after sufficient mixing reaction enters the regulating tank 103 for sedimentation and regulation. The regulating tank 103 is divided into a regulating tank clean water area 104 and a regulating tank sludge area 106. By zoning the regulating tank 103, it is convenient to further separate the sewage and water. At the same time, it can play a certain isolation role to ensure that the treated clean water is not polluted. The supernatant 5 enters the regulating tank clean water area 104 through the overflow weir, and is returned to the circulating water system 401 for reuse through the clean water lifting pump. The disc deoiler 108 is set in the regulating tank clean water area 104 for further deoiling. The sludge that has been initially precipitated enters the regulating tank sludge area 106 through the scraper 105 for sludge collection.

[0035] The sludge area 106 of the regulating tank has a certain slope, which is convenient for the sludge to gather in the sludge area 106 of the regulating tank, so that the scraper 105 can collect the sludge better; after sedimentation, the sludge enters the sludge area 106 of the regulating tank through the scraper 105; the iron oxide sludge accumulated in the sludge area 106 of the regulating tank is thick, and the transportation by the primary sludge lifting pump 107 may cause blockage and other problems. The present invention introduces compressed air into the sludge area 106 of the regulating tank for aeration, so that the sludge and water are fully mixed to obtain uniform muddy water, thereby preventing thick sludge from clogging the primary sludge lifting pump 107; the uniform muddy water enters the sludge concentration unit through the primary sludge lifting pump 107 for further treatment.

[0036] The sludge thickening unit includes a sludge settling tank 201, a sludge thickener 202, a secondary sludge lifting pump 203, a mixing tank 204, and a tertiary sludge lifting pump 205. The sludge settling tank 201 is connected to the sludge area 106 of the regulating tank through the primary sludge lifting pump 107, the sludge thickener 202 is installed on the sludge settling tank 201, the rear of the sludge thickener 202 is connected to the secondary sludge lifting pump 203, the rear of the secondary sludge lifting pump 203 is connected to the mixing tank 204, and the rear of the mixing tank 204 is connected to the tertiary sludge lifting pump 205.

[0037] The sludge treated by the backwash water sedimentation unit enters the sludge sedimentation tank 201 for sedimentation; the sludge sedimentation tank 201 is cylindrical with a conical bottom, which is convenient for the sludge to be graded and scraped by the sludge thickener 202 after the sludge is precipitated; the supernatant 5 after the sludge is concentrated enters the clean water area 104 of the backwash water regulating tank to achieve clean water reuse and further concentration of muddy water; the sludge after sedimentation and concentration is scraped and collected by the sludge thickener 202; the sludge thickener 202 has multi-stage blades, which can transfer the sludge step by step during the rotation process, and the sludge is collected by the middle conical funnel and enters the secondary sludge lifting pump 203, and the sludge When the sludge enters the secondary sludge lifting pump 203, since the iron oxide content in the sludge generated by the backwash water of the steel rolling production line is relatively high, the thick iron oxide will cause the lifting pump to be blocked. The present invention adopts a method of adding flushing to the discharge pipe at the bottom of the sludge concentrator 202, and introduces a mixed gas-water mixture of compressed air and water with a pressure of about 0.6MPa into the feed pipe, which effectively prevents the thick iron oxide sludge from clogging the inlet pipeline of the secondary sludge lifting pump; the inlet pipeline of the secondary sludge lifting pump 203 is changed to a stainless steel pipeline to increase the corrosion resistance and wear resistance of the pipeline, so that the sludge is smoother during transportation.

[0038] The iron oxide sludge transported by the secondary sludge lifting pump 203 may have large lumps of sludge. The large lumps of sludge entering the dehydration unit may cause the horizontal screw centrifuge 301 to overload, and in severe cases may cause the centrifuge to be blocked. A mixing tank 204 is provided before the sludge enters the dehydration unit. The mixing tank 204 collects the sludge transported by the secondary sludge lifting pump 203, and compressed air is introduced into the mixing tank 204 for aeration to break up the large lumps of sludge, so that the mud and water in the mixing tank are evenly mixed, and the even mud and water enter the dehydration unit through the tertiary sludge lifting pump 205.

[0039] The dehydration unit includes a horizontal screw centrifuge 301, a screw conveying device 302, a dosing device 303, and a slag pool 304. The muddy water concentrated by the sludge concentrator enters the horizontal screw centrifuge 301 for dehydration; the dosing device 303 is installed on the horizontal screw centrifuge 301, the rear of the horizontal screw centrifuge 301 is connected to the screw conveying device 302, and the rear of the screw conveying device 302 is connected to the slag pool 304.

[0040] During the operation of the decanter centrifuge 301, flocculation and coagulant agents are added through the agent device 303; the mud and water react with the agent in the decanter centrifuge 301, and the mud and water are separated by the high-speed rotation of the decanter centrifuge 301; the decanter centrifuge 301 has limited working capacity during the actual dehydration process, and large lumps of sludge will cause the load of the decanter centrifuge 301 to increase, and even cause equipment blockage in severe cases. The present invention adds an overflow pipe to the feeding pipeline of the decanter centrifuge 301 to connect the decanter centrifuge 301 and the sludge sedimentation tank 201 of the sludge concentration unit, so that when the sludge is transported to the decanter centrifuge 301, the excess large lumps of sludge that cannot be processed return to the sludge sedimentation tank 201 through the overflow pipe, thereby preventing the excess large lumps of sludge that cannot be processed from staying in the decanter centrifuge 301 and causing equipment blockage.

[0041] The solid sludge separated by the horizontal screw centrifuge 301 enters the slag pool 304 through the screw conveyor 302, and the dry sludge is sold out; the sewage discharged from the horizontal screw centrifuge 301 is returned to the regulating tank 103 in the backwash water sedimentation unit for further treatment; in actual use, the sewage discharged from the horizontal screw centrifuge 301 is returned to the backwash water sedimentation unit by gravity in the form of a buried pipeline, but in actual operation, the sewage contains more sludge, and the gravity sewage discharge is at a low terrain, which will cause sludge precipitation and then cause the sewage pipe to be blocked. The present invention adopts an elevated sewage pipe to make the sewage return at a certain inclination angle to avoid sludge precipitation caused by low terrain to block the pipeline.

[0042] The present invention realizes zero discharge of backwash water by adopting the above backwash water treatment method and physical treatment method, and completely separates the iron oxide-containing sludge into qualified clean water and sludge. The clean water is returned to the circulating water system for reuse, and the sludge is sold out to achieve cost reduction and efficiency improvement. The water content of the sludge is reduced from 45% to below 15%, and the iron content is above 55%.

[0043] The invention solves the problem of incomplete reaction between the reagent and the backwash water caused by a short process from the bypass filter to the backwash water precipitation unit.

[0044] The present invention solves the problem of iron oxide-containing sludge clogging the conveying pipeline and treatment equipment during the backwash water treatment process of the traditional steel rolling production line, reduces the problems of equipment failure shutdown, pipeline unblocking, etc., and realizes the full process cycle of backwash water treatment.

[0045] The present invention is not limited to the above-mentioned implementation modes, and anyone should be aware of the structural changes made under the enlightenment of the present invention, and all those having the same or similar technical solutions as the present invention fall within the protection scope of the present invention.

[0046] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A backwash water treatment system based on zero discharge of wastewater from a steel rolling production line, characterized in that: It includes a backwash water sedimentation unit, a sludge concentration unit and a dehydration unit. The backwash water sedimentation unit is used to process the backwash water generated by the bypass filter. The backwash water is precipitated once in the backwash water sedimentation unit to form a supernatant, which is returned to the circulating water system. The muddy water after the first precipitation is input into the muddy water concentration unit; The sludge concentration unit is used to conduct secondary sedimentation and concentration of the sludge water after the primary sedimentation, and the supernatant is returned to the backwash water sedimentation unit, and the sludge water after the secondary sedimentation is input into the dehydration unit; The dehydration unit further separates the sludge and water, and the separated water enters the backwash water sedimentation unit for further recycling.

2. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 1 is characterized in that: The backwash water sedimentation unit includes a bypass filter backwash pump, a pipeline mixer, a regulating tank, a scraper, and a primary sludge lifting pump. The regulating tank includes a clear water area and a sludge area of ​​the regulating tank. The regulating tank is divided into partitions for further separation of mud and water. The rear of the bypass filter backwash pump is connected to the pipeline mixer, which is used to fully mix the agent with the backwash water. The rear of the pipeline mixer is connected to the regulating tank. The clear water area of ​​the regulating tank is connected to the circulating water system and the disc oil remover. The scraper is installed in the sludge area of ​​the regulating tank, and a primary sludge lifting pump is also installed in the sludge area of ​​the regulating tank.

3. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 2 is characterized in that: Compressed air is introduced into the sludge area of ​​the regulating tank for aeration so that the sludge and water are fully mixed.

4. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 2 is characterized in that: The sludge thickening unit includes a sludge sedimentation tank, a sludge thickener, a secondary sludge lifting pump, a mixing tank, and a tertiary sludge lifting pump. The sludge sedimentation tank is connected to the sludge area of ​​the regulating tank through a primary sludge lifting pump. A sludge thickener is installed on the sludge sedimentation tank. The rear of the sludge thickener is connected to the secondary sludge lifting pump. The rear of the secondary sludge lifting pump is connected to the mixing tank. The rear of the mixing tank is connected to the tertiary sludge lifting pump.

5. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 4 is characterized in that: The bottom discharge pipe of the sludge concentrator is provided with an air-water flushing mechanism to prevent the thick iron oxide sludge from clogging the inlet pipeline of the secondary sludge lifting pump.

6. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 4 is characterized in that: Compressed air is introduced into the mixing tank for aeration and uniform mixing.

7. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 4 is characterized in that: The dehydration unit comprises a horizontal screw centrifuge, a screw conveying device, a dosing device, and a slag pool. The horizontal screw centrifuge is connected to a tertiary sludge lifting pump, the dosing device is installed on the horizontal screw centrifuge, the rear of the horizontal screw centrifuge is connected to the screw conveying device, and the rear of the screw conveying device is connected to the slag pool.

8. The backwash water treatment system based on zero discharge of wastewater from steel rolling production line according to claim 7 is characterized in that: The feed pipeline of the horizontal screw centrifuge is provided with an overflow pipe, and the sewage discharge pipe of the horizontal screw centrifuge adopts an elevated sewage discharge pipe, and the sewage is refluxed by setting an inclination angle.

9. The working method of the backwash water treatment system based on zero discharge of wastewater from a steel rolling production line according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. The backwash water is input into the regulating tank through the bypass filter backwash pump. During the input process, the backwash water and the flocculation and coagulant are fully mixed by the pipeline mixer by adding flocculation and coagulant agents. The mixed backwash water enters the regulating tank and is precipitated through the regulating tank. The regulating tank has a certain slope, which is convenient for the scraper to collect sludge better. After precipitation, the sludge enters the sludge area of ​​the regulating tank through the scraper, and the supernatant enters the clear water area of ​​the regulating tank through the overflow weir, and is returned to the circulating water system through the clear water lifting pump for reuse. A disc deoiler is set in the clear water area of ​​the regulating tank for further deoiling. Aeration is set in the sludge area of ​​the regulating tank, and the concentrated sludge is aerated with compressed air to fully mix the sludge with water to obtain uniform sludge water, so as to prevent the lumps of sludge from clogging the sludge lifting pump. The uniform sludge water enters the sludge concentration unit through the primary sludge lifting pump for further treatment. S2, the sludge treated by the backwash water sedimentation unit enters the sludge sedimentation tank for sedimentation; The sludge sedimentation tank is cylindrical and has a conical bottom, so that the sludge can be graded and scraped by the sludge thickener after sedimentation. The supernatant after sludge concentration enters the clear water area of ​​the backwash water regulating tank to further concentrate the mud and water. The sludge after sedimentation and concentration is scraped and collected by the sludge thickener. The sludge thickener has multi-stage blades, which can transfer the sludge step by step during the rotation process. The discharge pipe at the bottom of the sludge thickener is equipped with air and water flushing; the inlet pipe of the secondary sludge lifting pump is made of stainless steel, making the sludge conveying process smoother; The concentrated sludge enters the mixing tank through the secondary sludge lifting pump; the mixing tank is aerated with compressed air for uniform mixing, and the uniform muddy water enters the horizontal screw centrifuge through the tertiary sludge lifting pump; S3. The muddy water further concentrated by the sludge thickener enters the horizontal screw centrifuge; through the dosing device such as flocculation and coagulant; the muddy water reacts with the flocculation and coagulant in the horizontal screw centrifuge, and the mud and water are separated by the high-speed rotation of the horizontal screw centrifuge. The separated solid sludge enters the slag pool through the screw conveyor, and the dry slag is taken out; an overflow pipe is set on the feeding pipeline of the horizontal screw centrifuge to avoid large sludge clumps from being unable to be processed when they are fed into the horizontal screw centrifuge, resulting in blockage of the horizontal screw centrifuge equipment; the sewage from the horizontal screw centrifuge is returned to the regulating tank in the backwash water sedimentation unit through the elevated sewage pipe for further treatment.

Images