The rust removal system uses a rust removal solution to remove rust from electrical steel, and the method involves cleaning the rust removal solution.

Abstract

The invention relates to a system of descaling devices using descaling solution to descal electrical steel, comprising: a descaling tank, a concentrating tank where the concentrating tank is connected to the descaling tank, a cross-flow filter capable of producing percolation and concentrate, comprising an inlet, a percolation outlet and a concentrate outlet where the inlet is connected to the concentrating tank, and the concentrate outlet is connected to the inlet and to the concentrating tank. A method for cleaning the descaling solution in the descaling device system is also proposed.

Description

[0001] METHOD FOR PURIFYING A PICKLING SOLUTION

[0002] The present invention relates to a method and an installation for purifying a pickling solution. This method is particularly intended for a pickling solution used to pickle steel and in particular electrical steel.

[0003] The development of new steel grades leads to greater alloying element content, in particular the silicon content for steel used in electric applications. Unfortunately, the alloying elements will contaminate the pickling bath by dissolution during the pickling process.

[0004] For example, the silicon dissolved in the pickling solution can lead to the formation of monosilicic acids Si(OH)4 which then condensate to form colloidal silica and ultimately form suspension and / or co-precipitation with other substances. The silicon dissolved in the pickling tanks and more globally in the pickling installation accumulates. Eventually this silicon precipitates and reduce the lifespan of the equipment of the pickling installation. In order to remove the precipitates and eliminate the clogging, the pickling process needs to be shut down during the cleaning process.

[0005] Patent WO 201436575 describes a method of purification and desilication of spent acid pickling baths. In this method, the spent pickling solutions from the pickling installation is supplied to a collecting tank. Then the spent pickling solution is supplied to a microfiltration unit which produces a first permeate and a first retentate. This first permeate is supplied to an ultrafiltration unit which produces a second permeate and a second retentate. The second permeate is then sent to a thermal regeneration plant. The first and second retentates ends up in a sludge container to be disposed in a sewage treatment plant. However, this method requires two filtration equipments leading to a high maintenance and more frequent line stop and does not permit to recirculate the filtered pickling solution into the pickling installation. Patent EP 3 728 696 B1 describes a method of treatment of spent acid. In this method, the spent pickling solution from the pickling installation is supplied to a recirculation tank. Then the spent pickling solution is supplied to an ultrafiltration device which produces a permeate and a retentate. The permeate is supplied to the recirculation tank.

[0006] However, this method is mostly applicable to turbulent pickling installations which have recirculation tanks available and produce mostly low silicon steel grades (i.e., non-electrical steel grades).

[0007] Patent AT 411 575 relates to a method for purifying contaminated acidic pickling wastewater with the aid of cross-flow microfiltration. In order to do so, the occurring pickling solution is calmed in a settling container and then purified in a crossflow micro-filter in the temperature range from 10 to 55°C. Then it is processed according to the spray roasting principle in an acid regeneration plant. This process aims to prevent plant failure as a result of pipe encrustation, filter and nozzle blockages.

[0008] However, this method is not energy efficient as the pickling solution has to be cooled to be treated and re-heated to be used again in the pickling installation and does not permit to recirculate the filtered pickling solution into the pickling installation.

[0009] The purpose of the present invention is to provide a method and an installation able to purify a pickling solution from a pickling installation and to reuse it in said pickling installation.

[0010] To illustrate the invention, various embodiments and various non-limiting examples will be described, particularly with reference to the following figure: - Figure 1 is a schematic illustration of an embodiment of the invention,

[0011] - Figure 2 is a schematic illustration of a second embodiment of the invention.

[0012] As illustrated in Figure 1 , the invention also relates to an installation for a pickling solution used to pickle electrical steel comprising:

[0013] - a pickling tank 1 ,

[0014] - a concentration tank 3 wherein said concentration tank is connected to said pickling tank 1 ,

[0015] - a crossflow filtration device 5, able to produce a permeate and a retentate, comprising an entry side 5e, an permeate exit side 5p and a retentate exit side 5r wherein

[0016] - said entry side 5e is connected to said concentration tank 3,

[0017] - said permeate exit side 5p is connected to the pickling tank 1 ,

[0018] - said retentate exit side 5r is connected to said entry side 5e and to said concentration tank 3.

[0019] The pickling tank 1 is able to comprise a pickling solution 2, forming a pickling bath inside said pickling tank 1.

[0020] The concentration tank 3 is able to comprise a concentrated liquor 4 so that the pickling solution 2 from the pickling tank 1 can be supplied to said concentration tank 3.

[0021] The entry side 5e is connected to said concentration tank 3 so that the concentration liquor 4 can be supplied to said entry side 5e of said crossflow filtration device 5.

[0022] The permeate exit side 5p is connected to the pickling tank 1 so that the permeate can be supplied to said pickling tank 1 . The retentate exit side 5r is connected to said entry side 5e and to said concentration tank 3 so that the retentate can be supplied to the filtration device 5 and to the concentration tank 3.

[0023] A prefilter able to remove coarse particles, from 2.5 pm to 5mm, preferably from 2.5 pm to 10 pm, can be placed between the concentration tank 3 and the crossflow filtration device 5 permitting to filter the concentrated liquor flowing from the concentration tank 3 to the crossflow filtration device 5.

[0024] The crossflow filtration device 5 is made of materials withstanding acidic or basic media. For example, the crossflow filtration device can be made of polymers such as polypropylene and / or polyethylene and / or polysulfone and / or polyvinylidene difluoride, or from metallic materials such as titanium or stainless steel and / or other metals with coatings.

[0025] The crossflow filtration device is preferably a ceramic membrane crossflow filtration device.

[0026] The crossflow filtration device 5 can be an ultrafiltration device. The ultrafiltration device has preferably a membrane pore size from 5 to 500 kDa and even more preferably from 15 to 300 kDa. The ultrafiltration device has preferably a total filtering area from 10 to 600 m2and even more preferably from 20 to 450 m2.

[0027] Preferably, the ultrafiltration device comprises tubular membranes, composed of asymmetric ceramic porous structural support on which the filtering active layers are deposited. For example, the ceramic porous structural support can be made of metal oxides such as Alumina (AI2O3) or Titania (TiO2). The filtering active layers can comprise at least three layers between 3 and 80 pm thick. These active layers can also be made of metal oxides, usually AI2O3, TiO2 or ZrO2. The membranes are assembled in metallic housings (made of titanium or stainless steel or coated metals) which can include several membranes.

[0028] As illustrated in Figure 2, the pickling installation can comprise a feeding pump

[0029] 8 able to regulate the flow of concentrated liquor 4 from the concentration tank 3 to the filtration device 5.

[0030] As illustrated in Figure 2, the pickling installation preferably comprises a circulation pump 16 upstream of the filtration device 5. The pump permits to achieve preferred conditions for a crossflow filtration process.

[0031] The permeate exit 5p is preferably also connected to an intermediate collection tank and / or an acid regeneration plant (ARP).

[0032] As illustrated in Figure 2, the pickling installation preferably comprises a separation device 9 connected to the concentration tank 3 so that the concentrated liquor 4 can be supplied to said separation device 9. The separation device 9 is preferably a decanter. As illustrated in Figure 2, the pickling installation preferably comprise a purge pump 10 able to regulate the flow of concentrated liquor 4 from the concentration tank 3 to the separation device 9.

[0033] As illustrated in Figure 2, the pickling installation can comprise, in addition to the separation device 9, a dewatering system 13 connected to the separation device

[0034] 9 and connected to the concentration tank 3 and / or to the separation device 9 and / or to any other collecting means.

[0035] The invention also relates to the following method for purifying a pickling solution.

[0036] A portion of the pickling solution 2 from the pickling tank 1 is supplied to the concentration tank 3. The pickling solution 2 can be an acidic solution or an alkaline solution or a mix of both. The pickling solution preferably comprise from 0.5 to 30 weight percent of hydrochloric acid and / or sulfuric acid and / or nitric acid. Preferably, the pickling solution does not comprise hydrofluoric acid because it could damage the ceramic membrane of the filtration system.

[0037] The pickling solution 2 may comprise any alloying elements of steel products, such as Fe, Mn, Zn, Cr, Sn, SiOx or silicon-based compounds. For example, the pickling solution can comprise iron in the forms of iron salts, such as iron chlorides, and / or iron oxides. For example, the pickling solution can comprise from 60 to 350 grams per litre of iron, and from 0.001 to 20 grams per litre of manganese.

[0038] The pickling solution 2 may also comprise additives such as inhibitors for overpickling avoidance such as organic and / or inorganic compounds.

[0039] The pickling solution 2 may also comprise other elements due to the pickling of a steel product and resulting from the processing step upstream of the pickling of the steel product.

[0040] The invention is particularly intended for treating the pickling solution of electrical steel grades which can comprise up to 6.5 weight percent of silicon. The pickling solution 2 in the pickling tank 1 has preferably a silicon content from 30 to 10000 mg per litre of pickling solution. Even more preferably, the pickling solution 2 in the pickling tank 1 has preferably a silicon content from 500 to 10000 mg per litre of pickling solution. The silicon compounds can be found in the form of dissolved, colloidal or suspended particles. More than 50 % of the total silica can be in colloidal or suspended form.

[0041] The portion of the pickling solution 2 can be supplied to the concentration tank

[0042] 3 by gravity or can be pumped or any other suitable means. A steel pickling installation can comprise more than one pickling tank. A portion of the pickling solution 2 from more than one pickling tank can be supplied to the concentration tank 3.

[0043] The volume loss due to the supply of pickling solution 2 from the pickling tank 1 to the concentration tank 3 can be compensated or reduced thank to a feed of pickling solution.

[0044] A portion of the concentrated liquor 4 from the concentration tank 3 is supplied to a crossflow filtration device 5. In crossflow filtration, the filtering effect is achieved by dynamic shear stress gradients built up in the filtration direction. Compared to static filtration, it permits achieve long lasting filtration performance at high filtrate flows. The filter cake, e.g. the accumulation of the impurities on the membrane pores, can be regularly removed by means of periodic reversal of flow, i.e. backwashing, so as to clean the filtration device. This can be done by a Clean-in-place (CIP) method which is well known by the person skilled in the art. The devices and pipes pertaining to this method are not represented on Figure 1.

[0045] The purpose of the ultrafiltration device 5 is to separate the acids or base of the pickling solution from the colloidal and suspended impurities such as the alloying elements and in particular from the silicon-based compounds, eg. colloidal silica.

[0046] Then the ultrafiltration device 5, supplied in concentrated liquor 4 from the concentration tank 3, produces a retentate 6 and a permeate 7.

[0047] The retentate has a greater concentration of impurities than the concentrated liquor 4 supplied to the ultrafiltration device 5. The permeate, also known as the filtrate, has a smaller concentration of impurities than the concentrated liquor 4 supplied to the ultrafiltration device 5. In the case where a circulation pump is used upstream of an ultrafiltration device 5, the pump permits to obtain a transmembrane pressurization from 0.5 to 6 bar.

[0048] Preferably, the volume of permeate is more than 70% of the concentrated liquor 3 that enters the filtration device and preferably more than 90%. Preferably the rejection is less than 30% and more preferably less than 10%.

[0049] Preferably, the concentrated liquor may comprise a fraction of a waste liquor from the pickling solution 2, a fraction of the retentate from the filtration device 5 and a fraction of the clarified concentrated liquor 11. This mixed stream or concentrated liquor can be sent to the filtration device 5 or to the separation device 9. The concentration of silicon in this concentrated liquor ranges may be between 0.5 - 50 g / L and the temperature between 60-85°C.

[0050] The permeate 7 can supplied to the pickling tank 1 . The permeate can also be supplied to an intermediate collection tank and / or to an acid regeneration plant (ARP). The retentate 6 is recirculated through a circulation loop. Preferably, a remarkably higher, from 5 to 60 times greater than the one provided by the feeding pump 8, is recirculated through the circulation loop with the pump 16. It permits to achieve the preferred conditions for a cross-flow filtration process. Preferably, the trans-membrane pressure is from 0.5 to 6 bar and the crossflow velocity is from 2.5 to 5 meter per second. Those conditions permit to generate a turbulent regime reducing the fouling of the membranes.

[0051] Additionally, an increase of concentration in the circulation loop permits to limit fouling of the filtration devices, particularly for filtration devices having membranes, as the biggest colloidal particles are less prone to foul a filtration device. A fraction of the retentate can be recirculated to the concentration tank 3 from the filtration device 5. This installation permits to form a circulation loop is formed between the concentration tank 3 and the ultrafiltration device 5. Also, as the permeates leaves the circulation loop, the concentrated liquor 4 increase its concentration in silicon content.

[0052] The method can also comprise a step wherein, a portion of the concentrated liquor 4 from the concentration tank 3 is supplied to the separation device 9. Optionally, the method can comprise a mode of operation wherein a fraction of the retentate 6 exiting the filtration device is directly supplied to the separation device 9 skipping the concentration tank 3, in a continuous feed-and-bleed mode of operation, vie a pump or by gravity.

[0053] The installation can comprise several filtration stages (e.g. 2 to 7) operated in series or in parallel to increase process efficiency reducing total membrane area required. For example, the installation can comprise from 2 to 7 filtration stages in series or in parallel.

[0054] The separation device 9 is supplied periodically or continuously. The term periodically is to be interpreted in the sense that the supply can be turned “on” and “off”, but it is not necessarily at regular intervals of time. The supply can be managed by the purge pump 10 or by gravity.

[0055] The separation device favours the settling of the supplied concentrated liquor 4 which will result in the presence of a multiphasic solution comprising at least a clarified concentrated liquor and a darker concentrated liquor.

[0056] The clarified concentrated liquor 11 has a lower silicon content than the supplied concentrated liquor 4 from the concentration tank 3 or the retentate 6. The clarified concentrated liquor should be on the top of the separation device. The darker concentrated liquor 12 has a greater silicon content than the supplied concentrated liquor 4 from the concentration tank 3 or the retentate 6. The darker concentrated liquor should be at the bottom of the separation device.

[0057] Preferably, less than 30 percent of the flowrate entering the filtration device 5e is supplied to the separation device 9.

[0058] The clarified concentrated liquor 11 can be supplied to the pickling tank 1 and / or to the concentration tank 3 and / or to the ultrafiltration device 5 and / or to a tank.

[0059] The darker concentrated liquor can be supplied to the dewatering system 13.

[0060] The dewatering system 13 can be any system or device able to concentrate the solid fraction and separate the liquid phase. For example, the dewatering system 13 can be a filter press, a filter belt, or a centrifuge. The dewatering system 13 can also comprise more than one equipment able to concentrate the solid fraction and separate the liquid phase. For example, the dewatering system 13 can comprise a filter press and a centrifuge.

[0061] The dewatering system produces a solid fraction 14 and a liquid fraction 15. The liquid fraction can be supplied to the separation device 9 and / or to the concentration tank 3 and / or to the pickling tank 1 and / or to the ultrafiltration system 5 and / or to a collecting tank.

Claims

CLAIMS1 . A pickling installation for a pickling solution to pickle electrical steel comprising:- a pickling tank (1 ),- a concentration tank (3) wherein said concentration tank is connected to said pickling tank (1 ),- a crossflow filtration device (5), able to produce a permeate and a retentate, comprising an entry side (5e), an permeate exit side (5p) and a retentate exit side (5r) wherein- said entry side 5e is connected to said concentration tank (3),- said retentate exit side (5r) is connected to said entry side (5e) and to said concentration tank (3).

2. A pickling installation according to claim 1 , wherein said crossflow filtration device (5) is an ultrafiltration device.

3. A pickling installation according to any of claims 1 or 2, wherein said crossflow filtration device (5) is made from polymers selected between polypropylene, polyethylene, polysulfone, polyvinylidene difluoride or in combination, or made from metallic materials selected between titanium or stainless steel and / or other metals with coatings.

4. A pickling installation according to claim 2, wherein said ultrafiltration device has a membrane pore size from 5 to 500 kDa.

5. A pickling installation according to any one of the claims 1 to 4, wherein said pickling installation comprises a separation device (9) connected to the concentration tank (3).

6. A pickling installation according to claim 5, wherein said pickling installation comprises a dewatering system (13) connected to the separation device (9) and connected to the concentration tank (3).

7. A pickling installation according to any one of the claims 1 to 6, wherein said permeate exit side (5p) is connected to the pickling tank (1 ).

8. A method for purifying a pickling solution in a pickling installation according to any one of the claims 1 to 7, wherein said pickling tank (1 ) comprises a pickling solution (2), said concentration tank (3) comprises a concentrated liquor (4), comprising the steps of: i. supplying a portion of the pickling solution (2) to the concentration tank (3), ii. supplying a portion of the concentrated liquor (4) from the concentration tank (3) to a crossflow filtration device (5), iii. producing, by means of said crossflow filtration device (5), a retentate (6) and a permeate (7), iv. supplying said retentate (6) to the concentration tank (3) and to said filtration device (5).

9. A method according to claim 8 taking place in a pickling installation according to claim 6, wherein said permeate (7) is supplied to the pickling tank (1 ).

10. A method according to claim 8 or 9, wherein said pickling solution (2) in the pickling tank (1 ) has a silicon content from 30 to 10000 mg per litre of pickling solution.11 . A method according to any one of the claims 8 to 10 and taking place in a pickling installation according to claim 4, wherein a portion of the concentrated liquor (3) from the concentration tank (4) is supplied to the separation device (9).

12. A method according to claim 11 , wherein less than 30 percent of the flowrate entering the filtration device 5e is supplied to the separation device (9).

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