Sulfuric acid circulating system of stainless steel pickling line and control method thereof

Abstract

The invention discloses a stainless steel pickling line sulfuric acid circulating system and a control method thereof, belongs to the technical field of ferrous metallurgy production, and solves the problems that an ion resin adsorption method of an existing stainless steel pickling line is poor in sulfuric acid filtering effect, and the treatment burden of a wastewater treatment station is large. The device comprises a plurality of pickling circulation tanks, the pickling circulation tanks are connected with a sulfuric acid line, a water supply line and an exhaust pipe respectively, the bottoms of the pickling circulation tanks are all provided with waste acid discharge pipes, the waste acid discharge pipes are connected with circulation pipes, the circulation pipes are connected with the pickling circulation tanks, and the circulation pipes are provided with waste acid tanks and filtering devices. The circulating system is simple in structure and stable in operation, waste sulfuric acid is discharged to the waste acid tank and then filtered, the whole circulating system reduces the consumption of sulfuric acid per ton of steel by efficiently recycling the waste sulfuric acid, the production cost of strip steel and the cost for treating the waste sulfuric acid in a waste water station are greatly reduced, and the circulating system has very high practicability and wide popularization and application prospects.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel metallurgical production, and particularly relates to a sulfuric acid circulation system for a stainless steel pickling line and a control method thereof. BACKGROUND

[0002] The biggest environmental protection problem of the stainless steel pickling line lies in efficient recovery of waste acid to reduce its impact on the environment. Ion resin adsorption method, as a simple and efficient method with high automation degree, does not require special maintenance and is introduced for treatment of waste sulfuric acid.

[0003] At present, ion resin adsorption method has exposed many problems in actual operation: first, waste sulfuric acid is coarsely filtered by filter cloth, and the sludge on the filter cloth cannot be removed in time, resulting in that the amount of sulfuric acid treated by coarse filtration is seriously insufficient and far cannot meet the treatment demand of three ion resin beds; second, due to the small amount of waste sulfuric acid entering the ion resin bed, the content of metal ions in the sulfuric acid solution of the main production line is high, thereby reducing the pickling efficiency of sulfuric acid; third, the decline of pickling efficiency affects the normal pickling process of the strip steel, and the iron oxide scale on the surface of part of the strip steel cannot be completely removed, resulting in strip steel defects caused by residual oxide scale in the subsequent process, and finally causing product downgrading; fourth, in order to deal with the problem of high content of metal ions in the sulfuric acid solution, when the treatment capacity of the sulfuric acid recovery system is insufficient, the production line can only directly discharge the waste sulfuric acid to the wastewater treatment station and supplement new acid to reduce the concentration of metal ions. This method not only increases the consumption of new acid and increases the cost of the enterprise, but also increases the burden of the wastewater treatment station to treat waste sulfuric acid, which has an adverse impact on the environment. SUMMARY

[0004] The purpose of the present application is to provide a sulfuric acid circulation system for a stainless steel pickling line to solve the problems of ion resin adsorption method of the existing stainless steel pickling line, poor sulfuric acid filtration effect and heavy burden of the wastewater treatment station.

[0005] Another purpose of the present application is to provide a control method of the sulfuric acid circulation system for the stainless steel pickling line.

[0006] The technical solution of the present application is: a sulfuric acid circulation system for a stainless steel pickling line, comprising a plurality of pickling circulation tanks, the plurality of pickling circulation tanks are connected with a sulfuric acid line, a water supply line and an exhaust pipe respectively, a waste acid discharge pipe is arranged at the bottom of each pickling circulation tank, one end of the waste acid discharge pipe is connected with a circulation pipe, the other end of the circulation pipe is connected with the pickling circulation tank, a waste acid tank and a filter are arranged on the circulation pipe in sequence, a backflushing water pipe is arranged on the water outlet end of the filter, a backflushing water valve is arranged on the backflushing water pipe, and a drain pipe is arranged on the water inlet end of the filter.

[0007] As a further improvement of the present application, a resin bed is connected with the water outlet of the filter, an acid injection pipe is arranged on the acid outlet of the resin bed, and the acid injection pipe is connected with the plurality of pickling circulation tanks.

[0008] As a further improvement of the present invention, a thermometer is also provided on the backwash water pipe to ensure that the water temperature of the backwash water remains constant above 70°C during the main line shutdown.

[0009] As a further improvement of the present invention, multiple circulation pumps are provided on the circulation pipe to avoid insufficient flow in the circulation pipe.

[0010] A control method for a sulfuric acid circulation system in a stainless steel pickling line includes the following steps: A. The waste sulfuric acid discharged from the pickling circulation tank is discharged into the circulation pipe through the acid discharge pipe, so that the waste sulfuric acid is transported to the waste acid tank for storage by the circulation pump; B. The waste sulfuric acid from the waste acid tank is transported to the filter by a circulating pump, so that the sludge in the waste sulfuric acid is filtered out in the filter. The filtered waste sulfuric acid is then transported to the resin bed for purification, so that the metal ions of the filtered waste sulfuric acid are adsorbed in the resin bed.

[0011] C. The purified sulfuric acid is transported to the pickling circulation tank through the acid injection pipe; D. After the periodic purification of sulfuric acid, the sulfuric acid circulation system is shut down for maintenance. During maintenance, the bottom acid outlet of the circulating acid washing tank and the circulating pump are closed to ensure that no waste sulfuric acid passes through the sulfuric acid circulation system. The backwash water valve is kept closed. Hot water is injected into the backwash water pipe to create pressure. The backwash water valve is then opened to flush the filter. The sludge on the surface of the filter cloth is automatically removed after being backwashed by the hot water and the internal compressed air. The flushed water is discharged through the drain pipe. The sludge that falls off the filter is also periodically discharged.

[0012] The beneficial effects of this invention are: 1. This invention adds a circulation pipe to the waste acid discharge pipe and a filter device to the circulation pipe to recover sulfuric acid from the sulfuric acid sludge that was originally directly discharged into the pit. This reduces the amount of sulfuric acid entering the wastewater treatment plant, reduces the amount of red mud generated in the wastewater treatment plant, and significantly reduces the amount of lime used in the wastewater treatment plant to treat sulfuric acid, thereby effectively improving the treatment effect of the wastewater treatment plant.

[0013] 2. This invention also adds a backwash pipe to the filter, using hot water to backwash the filter, so that the sludge on the filter dissolves at the hot water temperature, avoiding the situation where sludge and crystals clog the filter, resulting in reduced flow and reduced filtration capacity. The thermometer on the backwash pipe can also be used to check at any time whether the hot water meets the cleaning standard.

[0014] 3. This invention has a simple structure and stable operation. By discharging waste sulfuric acid into a waste acid tank and then filtering it, the problem of excessive metal ion content in the sulfuric acid solution is avoided. By adding a backwash water pipe to the filter, the filtration effect of sulfuric acid in the pickling line is enhanced. The entire circulation system reduces the consumption of sulfuric acid per ton of steel through efficient recovery of waste sulfuric acid, which greatly reduces the production cost of strip steel and the cost of waste sulfuric acid treatment at the wastewater station. It has strong practicality and broad prospects for promotion and application. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the present invention.

[0016] In the diagram: 1. Pickling circulation tank; 2. Waste acid discharge pipe; 3. Sulfuric acid line; 4. Water supply line; 5. Circulation pipe; 6. Waste acid tank; 7. Filter; 8. Resin bed; 9. Acid injection pipe; 10. Backwash water pipe; 11. Drain pipe; 12. Thermometer; 13. Backwash water valve; 14. Circulation pump; 15. Exhaust pipe. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 like Figure 1 As shown, a sulfuric acid circulation system for a stainless steel pickling line includes multiple pickling circulation tanks 1. The multiple pickling circulation tanks 1 are respectively connected to a sulfuric acid line 3, a water supply line 4, and an exhaust pipe 15. Each pickling circulation tank 1 is equipped with a waste acid discharge pipe 2 at its bottom. One end of the waste acid discharge pipe 2 is connected to a circulation pipe 5, and the other end of the circulation pipe 5 is connected to the pickling circulation tank 1. A waste acid tank 6 and a filter 7 are sequentially arranged on the circulation pipe 5. A backwash water pipe 10 is provided at the outlet end of the filter 7, and a backwash water valve 13 is provided on the backwash water pipe 10. A drain pipe 11 is provided at the inlet end of the filter 7.

[0019] A resin bed 8 is connected to the outlet of the filter 7. The acid outlet of the resin bed 8 is equipped with an acid injection pipe 9, which is connected to multiple acid washing circulation tanks 1.

[0020] A thermometer 12 is also installed on the backwash water pipe 10 to ensure that the water temperature of the backwash water is kept constant above 70°C during the main line shutdown, so that the water temperature of the backwash filter reaches 60°C to 65°C, thereby improving the dissolution capacity of ferrous sulfate.

[0021] Multiple circulation pumps 14 are installed on the circulation pipe 5 to ensure the flow rate in the circulation pipe 5, so that the sulfuric acid circulation system of the pickling line can meet the processing capacity requirement of 6m³ / h.

[0022] A control method for a sulfuric acid circulation system in a stainless steel pickling line includes the following steps: A. The waste sulfuric acid discharged from the pickling circulation tank 1 is discharged to the circulation pipe 5 through the acid discharge pipe 2, and the waste sulfuric acid is transported to the waste acid tank 6 for storage by the circulation pump 14. B. The waste sulfuric acid in the waste acid tank 6 is transported to the filter 7 by the circulation pump 14, so that the sludge in the waste sulfuric acid is filtered out in the filter 7. The filtered waste sulfuric acid is then transported to the resin bed 8 for purification, so that the metal ions of the filtered waste sulfuric acid are adsorbed in the resin bed 8. C. The purified sulfuric acid is transported to the pickling circulation tank 1 through the acid injection pipe 9; D. After the sulfuric acid is purified periodically, the sulfuric acid circulation system is shut down for maintenance. During maintenance, the bottom outlet of the circulating acid washing tank 1 and the circulating pump 14 are closed to prevent waste sulfuric acid from passing through the sulfuric acid circulation system. The backwash water valve 13 is kept closed. Hot water is injected into the backwash water pipe 10 to create pressure. The backwash water valve 13 is then opened to flush the filter 7. The sludge on the surface of the filter cloth of the filter 7 is automatically removed after backwashing by the hot water and the internal compressed air. The flushed water is discharged through the drain pipe 11, and the sludge that has fallen from the filter 7 is discharged periodically.

[0023] Meanwhile, to optimize the efficiency of the pickling line, the pickling process values ​​were adjusted accordingly. By optimizing the sulfuric acid pickling parameters within the pickling line, the sulfuric acid usage in the stainless steel pickling line was adjusted to reduce the risk of ferrous sulfate crystallization, prevent crystallization on filter 7, avoid filter cloth clogging of filter 7, and reduce filtration efficiency. At the same time, the concentration of metal ions in the sulfuric acid solution was reduced, thus reducing the consumption of sulfuric acid per ton of steel. Specific adjustment data are shown in Tables 1 and 2 below: Table 1 Table 2 The sulfuric acid concentration for 430 stainless steel was reduced from the initial 220-250 g / L to 170-220 g / L to slow down over-corrosion of the strip in sulfuric acid, thereby reducing the iron content in the sulfuric acid and facilitating stable and smooth operation of the sulfuric acid circulation system. Simultaneously, the lower sulfuric acid concentration increases the solubility of ferrous sulfate, preventing crystallization of ferrous sulfate caused by temperature fluctuations during the operation of the recovery system.

[0024] Other martensitic and ultrapure stainless steels continue to use the improved sulfuric acid process concentration of 430 stainless steel to reduce the load on the sulfuric acid recovery system and increase the amount of waste sulfuric acid recovered; pickling of non-ferrous metals such as titanium plates and zirconium does not use sulfuric acid to reduce the sulfuric acid load.

[0025] By reducing the concentration of waste sulfuric acid to the lower limit of the process, while completely removing the oxide scale from the strip steel, the low sulfuric acid concentration increases the solubility of ferrous sulfate, making it less prone to crystallization on the filter cloth of filter 7. This ensures the filtration effect of the filter and avoids reducing the processing capacity of the sulfuric acid recovery system due to ferrous sulfate crystallization. It also prevents clogging of the filter cloth of filter 7 caused by ferrous sulfate crystallization after large temperature fluctuations. Simultaneously, the low concentration of sulfuric acid slows down the over-corrosion of the strip steel substrate during pickling, thereby reducing the amount of ferrous sulfate in the sulfuric acid solution and also reducing the risk of ferrous sulfate crystallization.

[0026] The consumption of sulfuric acid per ton of steel continued to decrease, from 15.9 kg / t to 11.7 kg / t, a decrease of about 27%. At the same time, the amount of red mud in the wastewater treatment plant decreased from 122 tons / day to 48 tons / day, a decrease of 21%. This proves that the amount of sulfuric acid treated by the wastewater treatment plant has been reduced, the sulfuric acid circulation system has been effectively protected, and the measures have been effective.

[0027] After the above methods were adopted, the sulfuric acid recovery system has been operating stably so far, the consumption of sulfuric acid per ton of steel has continued to decrease, and the amount of red mud generated after the wastewater treatment plant processes sulfuric acid has continued to decrease. This has solved the huge problems of high sulfuric acid consumption and large amount of red mud used in the wastewater treatment plant, which has great environmental significance.

Claims

1. A sulfuric acid circulation system for a stainless steel pickling line, comprising multiple pickling circulation tanks (1), wherein the multiple pickling circulation tanks (1) are respectively connected to a sulfuric acid line (3), a water supply line (4), and an exhaust pipe (15), characterized in that: The bottom of the pickling circulation tank (1) is equipped with a waste acid discharge pipe (2). The waste acid discharge pipe (2) is connected to one end of the circulation pipe (5). The other end of the circulation pipe (5) is connected to the pickling circulation tank (1). The circulation pipe (5) is equipped with a waste acid tank (6) and a filter (7) in sequence. The outlet end of the filter (7) is equipped with a backwash water pipe (10). The backwash water pipe (10) is equipped with a backwash water valve (13). The inlet end of the filter (7) is equipped with a drain pipe (11).

2. The sulfuric acid circulation system for a stainless steel pickling line according to claim 1, characterized in that: The filter (7) is connected to a resin bed (8) at its outlet. The acid outlet of the resin bed (8) is provided with an acid injection pipe (9), which is connected to multiple acid washing circulation tanks (1).

3. A sulfuric acid circulation system for a stainless steel pickling line according to claim 1 or 2, characterized in that: A thermometer (12) is also provided on the backwash water pipe (10).

4. The sulfuric acid circulation system for a stainless steel pickling line according to claim 1, characterized in that: Multiple circulation pumps (14) are provided on the circulation pipe (5).

5. A control method for a sulfuric acid circulation system in a stainless steel pickling line, characterized in that, Includes the following steps: A. The waste sulfuric acid discharged from the pickling circulation tank (1) is discharged to the circulation pipe (5) through the acid discharge pipe (2), so that the waste sulfuric acid is transported to the waste acid tank (6) for storage through the circulation pump (14); B. The waste sulfuric acid in the waste acid tank (6) is transported to the filter (7) by the circulation pump (14) for filtration, so that the sludge in the waste sulfuric acid is filtered into the filter (7), and the filtered waste sulfuric acid is transported to the resin bed (8) for purification, so that the metal ions of the filtered waste sulfuric acid are adsorbed into the resin bed (8). C. The purified sulfuric acid is transported to the pickling circulation tank (1) through the acid injection pipe (9); D. After the sulfuric acid is purified periodically, the sulfuric acid circulation system is shut down for maintenance. During maintenance, the bottom outlet of the circulating acid washing tank (1) and the circulating pump (14) are closed to prevent waste sulfuric acid from passing through the sulfuric acid circulation system. The backwash water valve (13) is kept closed. Hot water is injected into the backwash water pipe (10) to make the hot water pressurized. The backwash water valve (13) is opened to flush the filter (7). The sludge on the surface of the filter (7) is automatically dropped after being backwashed by hot water. The flushed water is discharged through the drain pipe (11) and the dropped sludge from the filter (7) is discharged periodically.

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