In-line silicon deposition in pickling plants

Abstract

The present invention relates to a device and a method for depositing undissolved materials, in particular undissolved silicon compounds, from a pickling fluid in a pickling plant. The pickling circuit of the pickling plant comprises a pickling tank for pickling metal strip, a return line between the pickling tank and the circuit tank, a circulation pump for circulating the main volumetric flow of pickling fluid from the pickling tank, and a heating device arranged in the pressure line between the circuit tank and the pickling tank. The device according to the invention comprises a flocculation device capable of introducing at least one flocculating agent into the main volumetric flow, and a deposition device, preferably designed as an inclined clarification device, arranged in the circuit tank for settling undissolved materials directly from the main volumetric flow. For example, when pickling silicon-containing steel strip (electrical steel strip), at least two stages of flocculation can be carried out using two or more mixing zone vessels.

Description

[Technical Field]

[0001] The present invention relates to a device and method for depositing insoluble silicon compounds in a pickling circuit in a pickling plant. [Background technology]

[0002] In pickling plants, scale formed during the hot rolling process is removed from the surface of rolled metal strip, e.g., steel strip, to enable further processing of the metal strip. For this purpose, the scale layer is attacked by a suitable pickling fluid, e.g., a pickling solution containing hydrochloric acid (HCl) or sulfuric acid (H2SO4). Conventionally, the scaled metal strip passes successively through several pickling vessels. The scale layer (in the case of steel strip, which consists mainly of iron oxide) goes into solution in the pickling fluid, or insoluble components precipitate as so-called pickling sludge. The pickling sludge also contains chemical compounds of accompanying elements (e.g., carbon) and even alloying elements depending on the composition of the original metal strip. After pickling, any remaining pickling fluid residues are usually cleaned from the descaled metal strip by rinsing with a washing fluid, and the strip is then dried.

[0003] The spent pickling solution (hereinafter referred to as pickling liquor) is treated in a separate regeneration plant. The iron oxides thereby obtained constitute valuable chemical raw materials in the chemical industry, and it is therefore desirable to separate such oxides in as high a purity as possible.

[0004] For example, when steel strip with a high silicon content (i.e., a silicon content of more than 2 weight percent) is pickled in a hydrochloric acid-based pickling plant, insoluble colloids in the form of gel-like silicate sludge (silica) form in the pickling solution, which cannot be separated without great expense. Steel strip with a high silicon content includes, in particular, so-called electrical steel strip. The silicate sludge accumulates in the tubes and other sections of the pickling plant, leading to repeated clogging or blockages (so-called fouling) and, in the worst case, to the failure of the entire plant components. This also applies to other alloying elements of the steel strip, such as Al, C, etc., which also affect the regeneration plant.

[0005] To maintain the performance of the pickling plant, these deposits must be removed at regular intervals, which is associated with corresponding maintenance costs. The conventional method for removing insoluble residues is, on the one hand, to flush the relevant subsections with alkaline solutions (e.g., sodium hydroxide - NaOH), and, on the other hand, to manually and mechanically remove these residues. Both methods imply a reduction in the availability of the pickling plant. Furthermore, to flush with alkaline solutions that render the substances irrelevant to the process, special expensive equipment is required, or related concepts for treating or disposing of this cleaning solution are needed.

[0006] Another method for eliminating deposits is separation by microfiltration. Due to process conditions (high pH or high temperature of the pickling fluid), the membranes used for this have a short service life, making such a method uneconomical. Furthermore, this type of filtration is only limitedly suitable for large volume flows, since the microfilters used have a very small pore structure. For example, Patent Document 1 discloses a method for reducing the content of undesirable accompanying elements, in particular silicon compounds (silica), by pressing the resulting pickling fluid downward in a settling vessel and then cleaning it using a cross-flow microfilter at a temperature range of 10°C to 55°C. While effective deposition of undesirable colloids from the pickling fluid is possible in the described method, in addition to using the aforementioned microfilter in a conventional pickling plant for steel strip, the invention of Patent Document 1 also requires cooling of the pickling fluid to be cleaned, especially since electrical steel strip is pickled at a relatively high temperature range of up to 90°C.

[0007] A method for sedimenting silicon compounds from pickling fluid in a pickling plant is known from US Pat. No. 5,699,999. In this case, a volumetric flow of pickling fluid of the order of 3 to 15 cubic meters per hour is cooled to 60°C by a heat exchanger, after which a first flocculation aid is added and stirred with the pickling fluid in a mixing tank. A second flocculation aid is then added, after which the pickling fluid is subsequently transferred into a conical settling tank. The precipitated silicon compounds are sucked out from the bottom of the settling tank, and the clarified pickling fluid is skimmed off through an overflow weir and transported back into the pickling plant.

[0008] It is known from US Pat. No. 5,699,999 to deposit silicon compounds from pickling fluid in a pickling plant with several pickling tanks. The main volume flow of pickling fluid is circulated between the pickling tank and the respective circuit tank or directly between the pickling tanks. The circuit tanks are connected to a common device for regenerating the pickling fluid. The regenerated pickling fluid is returned from the associated circuit tank to the pickling tank via the respective heat exchanger. Furthermore, at least one pickling tank or circuit tank is followed by a secondary circuit, by which the pickling fluid is transported from the associated pickling or circuit tank via a deposition device for silicon compounds and returned to the pickling or circuit tank. In the deposition device, the silicon compounds from the pickling fluid transported in the secondary circuit are deposited by utilizing a flocculation device and a settling tank.

[0009] It is known from US Pat. No. 5,699,999 to separate amorphous, partially dissolved silicon from a treatment solution conveyed in a circuit for the chemical treatment of iron-silicon alloy strips, without the addition of a flocculation aid. In this case, a portion of the treatment solution containing silicon is withdrawn and conveyed to a receiving vessel in which the solution is subjected to pressure-driven membrane filtration. In this case, the filtrate substantially freed from silicon is conveyed back to the treatment fluid, while the silicon-enriched solution is conveyed back into the receiving vessel and the highly silicon-enriched solution is withdrawn from the receiving vessel and discarded.

[0010] The prior art also discloses pickling plants with multiple pickling tanks through which the metal strip to be pickled passes successively, each assigned its own pickling circuit in which the pickling fluid is heated and circulated. The concentration of dissolved and undissolved scale compounds is greatest in the first pickling tank through which the strip passes, and their concentration decreases relatively in subsequent pickling tanks. The total circulating volumetric flow of the pickling circuit is, for example, 300 to 500 cubic meters per hour and is hereinafter referred to as the main volumetric flow of the pickling circuit. The pickling circuit comprises at least the associated pickling tank, a circuit tank, a circulation pump, and a heating device. The piping extending between the pickling tank and the circuit tank is referred to as the return line of the associated pickling tank. The circuit tank has a volume larger than the volume of the assigned pickling tank (usually about twice the volume of the pickling tank) and is used as a so-called receiving vessel during the pickling operation. This receiving vessel is only partially filled with pickling fluid, for example, about 30% to 50%, and its volume is hereinafter also referred to as the receiving volume of the circuit tank. This receiving volume serves as a buffer, for example, to compensate for fluctuations in the fill level in the assigned pickling tank. Furthermore, the circuit tank is used to receive pickling fluid from the assigned pickling tank during emergency drainage, i.e., when pickling fluid has to be quickly released from the pickling tank, for example, in the event of an operational interruption.

[0011] For cleaning the pickling fluid in the pickling circuit, a distinction is further made between so-called in-line and so-called offline operation. In the case of in-line operation, at least one partial flow is taken from the main volumetric flow of the pickling circuit and conveyed to a device for separating insoluble substances, such as insoluble silicon compounds. After separation, the cleaned pickling fluid is conveyed back into the pickling circuit. On the other hand, during offline operation, part of the pickling fluid is first conveyed to a device for separating insoluble substances, and the pickling fluid cleaned of insoluble substances is then conveyed to a separate regeneration plant for separating dissolved components (e.g., iron chloride compounds). Correspondingly, during in-line operation, the accumulation of insoluble substances in the plant components of the pickling plant itself is at least partially prevented (depending on the ratio of the partial flow to the main volumetric flow), while during offline operation, accumulation in the regeneration plant is completely prevented, improving the quality of the reusable material obtained from the regeneration plant. In principle, in-line and offline operations can be combined with each other.

[0012] The process conditions in the pickling tank are the main volume flow of the circulating pickling fluid and its process temperature T p In addition to the deposition of dissolved scale components, the circulation of the pickling fluid generates in each pickling tank the flow of pickling fluid required for the pickling process. Furthermore, the heat loss of the pickling fluid in each pickling tank is compensated for by the heating devices of the pickling circuit.

[0013] In particular for the pickling of the aforementioned steel strips having a relatively high silicon content, pickling plants are further known from the prior art which have corresponding deposition devices for depositing insoluble substances (e.g. silicon dioxide) arising from the pickling fluid during pickling. These in-line deposition devices separate the insoluble components from the pickling fluid during in-line operation, but they only deposit those from a partial stream of the overall circulation stream in the pickling circuit, and a device for cooling the partial stream is also required. After cleaning the partial stream and before returning it to the pickling circuit, the heat removed from the partial stream (in addition to the overall heat loss during the pickling process) must be replenished, which entails increased energy consumption.

[0014] Furthermore, it is known from US Pat. No. 5,623,699 to continuously convey the pickling fluid to be purified, in particular the pickling fluid from a hydrochloric acid pickling plant for electrical steel strip with a high silicon content, from the acid receiving vessel of the pickling plant first to a pre-cleaning vessel, in which most of the suspended solids are deposited by sedimentation. Some of the partially purified pickling fluid is then conveyed from the overflow area of ​​the pre-cleaning vessel to an acid regeneration plant, while the acid-sludge mixture is periodically withdrawn from the bottom area of ​​the pre-cleaning vessel and subjected to a cleaning treatment by utilizing a flocculant. Since the disclosed volumetric flows (of the order of a few cubic meters per hour) are significantly lower than the volumetric flows of conventional pickling circuits, the disclosed invention is not suitable for purifying the main volumetric flow in the pickling circuit of a pickling plant. Furthermore, the additional vessels and piping required for this invention entail significant space requirements.

[0015] A drawback associated with such methods and devices known from the prior art for depositing silicon compounds from pickling fluids during in-line operation is that, on the one hand, the insoluble material is only cleaned from a portion of the main volume flow, and therefore, in the case of pickling steel strips with a high silicon content, the availability of such pickling plants is still significantly reduced, with correspondingly increased cleaning costs compared to operations in which only strips without a high silicon content are pickled. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Austrian Patent No. 411575 [Patent Document 2] Chinese Patent No. 1238562 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005200697 [Patent Document 4] German Patent No. 4116353 [Patent Document 5] German Patent No. 4242619 Summary of the Invention [Problem to be solved by the invention]

[0017] It is therefore an object of the present invention to overcome the drawbacks of the aforementioned systems and to significantly improve the availability of pickling plants with only a small additional space requirement. [Means for solving the problem]

[0018] This object is achieved according to the invention by a device having the features of claim 1 and a method having the features of claim 9.

[0019] The dependent claims relate to advantageous configurations of the invention.

[0020] The device according to the invention for depositing insoluble silicon compounds from a pickling fluid in a pickling plant having at least one pickling circuit comprises an agglomeration device and a deposition device. The pickling circuit comprises a pickling tank of the pickling plant for pickling metal strips, a return line between the pickling tank and the circuit tank, and a pressure line between the circuit tank and the pickling tank. The pickling circuit comprises a circulation pump with a maximum pumping capacity of 500 to 600 cubic meters per hour for circulating a main volumetric flow of pickling fluid from the pickling tank through the return line into the circuit tank and back into the pickling tank via the pressure line, and a process temperature T prevailing in the pickling tank, which is in the range of up to 90°C. p and a heating device disposed in the pressure line for heating the pressure to

[0021] The expression "maximum pump capacity" refers to the amount of pickling fluid that the circulation pump can output or circulate per hour in continuous operation at its maximum operating performance. However, if necessary, the circulation pump may be operated at a lower operating performance, thereby outputting a correspondingly smaller amount of pickling fluid per hour. By using the maximum pump capacity, the total amount of pickling fluid present in the pickling circuit may be circulated multiple times per hour, for example, 5 to 10 times per hour, and passed through and thereby cleaned by the deposition device a corresponding number of times. In this case, the total amount of pickling fluid present in the pickling circuit consists of the pickling fluid in the pickling tank, the coalescing device, the deposition device, the return line, and the pressure line.

[0022] The coalescing device is preferably arranged in the return line and comprises one or more mixing zone vessels for introducing at least one coalescing aid into the main volume flow. Alternatively, the coalescing device may also be arranged in the pickling tank or in the pressure line. In this case, the introduced at least one coalescing aid is heated to a temperature equal to or higher than the process temperature T of the pickling fluid. pThe deposition device is arranged in a circuit tank of the pickling circuit and is configured to deposit the insoluble silicon compound directly from the main volume flow conveyed through the circuit tank.

[0023] The device according to the invention makes it possible to carry out an in-line operation in which the deposition process for insoluble silicon compounds extends over the entire main volume flow, so that the pickling fluid for the pickling process is consequently made available with a consistent quality. Furthermore, compared to the methods known from the prior art, energy can be saved since separate cooling and reheating of the pickling fluid to be cleaned is avoided, and due to the integration of the deposition device into the circuit tank, only smaller heat losses of the pickling fluid occur during the deposition of insoluble substances.

[0024] Preferably, the circuit tank has a volume that is multiple times, e.g., two to three times, larger than the volume of the pickling tank in the associated pickling circuit, and the deposition device comprises at least a settling zone, a settling zone, and a receiving zone, wherein a first overflow is disposed between the settling zone and the settling zone, and a second overflow is disposed between the settling zone and the receiving zone.

[0025] The aforementioned volume of the circuit tank, which is two to three times larger than the volume of the pickling tank in the associated pickling circuit, allows the deposition device to be integrated directly into the circuit tank, thereby avoiding the need for additional piping compared to deposition devices that are conventionally located outside the circuit tank.

[0026] For example, the pickling tank has a volume of 30 to 40 cubic meters and the circuit tank according to the invention has a volume of 75 to 100 cubic meters. In this case, the settling zone may be dimensioned so that the entire main volumetric flow of pickling fluid passing through the circuit tank during normal operation of the pickling plant has more than 90% of the undissolved material, in particular undissolved silicon compounds, cleaned therefrom, whereby the time between maintenance intervals required for the pickling plant can be significantly increased.

[0027] In the settling zone, the disturbances created when the pickling fluid entered the circuit tank can flow away, so that the transfer of the pickling fluid to the subsequent settling zone takes place in the form of a settled flow, which is further assisted by the first overflow. The second overflow between the settling zone and the receiving zone prevents the transfer of pickling sludge from the settling zone into the subsequently located receiving zone.

[0028] According to another preferred configuration of the device according to the invention, the coalescence device has at least two mixing zone vessels for adding at least two different coalescence aids into the main volume flow of the pickling circuit. In this way, the type and concentration of the coalescence aids introduced into the main volume flow can be adapted to the chemical composition of the metal strip currently being pickled in the pickling plant. For this purpose, the composition and concentration of scale components in the pickling fluid can be determined, for example, with the aid of a pickling model which takes into account the chemical composition of the metal strip and the pickling fluid.

[0029] For example, by utilizing multiple mixing zone vessels during the pickling of a metal strip containing primarily carbon, the first flocculating aid need only be added to the first mixing zone vessel, and not to any of the other mixing zone vessels. Alternatively, when, for example, a metal strip containing silicon is being pickled in an associated pickling plant, the addition of the first flocculating aid to the first mixing zone vessel may be omitted, while single-stage or multi-stage flocculation is performed by one or more of the other mixing zone vessels.

[0030] In one preferred configuration of the device according to the invention, the total volume of all mixing zone vessels is between 8 cubic meters and 25 cubic meters. In this way, the residence time of the passing pickling fluid is a few minutes (e.g., 1 to 3 minutes), allowing the undissolved silicon compounds in the pickling fluid to solidify together to form larger or heavier particles that settle more quickly in the settling zone.

[0031] Preferably, the deposition device is configured as a lamella separation device, which comprises a plurality of parallel flow channels through which the pickling fluid passes, and insoluble materials, such as insoluble silicon compounds, are deposited from the pickling fluid by gravity in a settling process, so that the lamella separation device has no moving parts and, as a result, has a long operating time with relatively low maintenance costs.

[0032] Preferably, the flow channels are inclined at an angle α to the vertical and are made of an acid- and heat-resistant material that can permanently withstand temperatures of at least 90°C. The angle α is preferably in the range of 15° to 60°, preferably 25° to 35°. Preferably, the vertical distance d between adjacent flow channels (by which we mean the distance between the geometric centers of the cross-sectional areas in cross sections perpendicular to the longitudinal direction of adjacent flow channels) is at least 50 mm, preferably at least 75 mm. In one particularly preferred configuration, to increase mechanical stability, the lamellar separation device is configured as a honeycomb arrangement of parallel-running flow channels.

[0033] Lamellar separation devices are known from the prior art, consist for example of thermoplastic material and, on the one hand, can be produced economically, for example by means of 3D printing methods, and can be adapted to any geometrical requirements. On the other hand, lamellar separation devices having the aforementioned dimensions are mechanically more robust at little cost and at the same time less susceptible to obstruction by undissolved substances from the pickling fluid than, for example, the microfilters used in the prior art.

[0034] The advantages and technical effects of the method according to the invention correspond to those of the device according to the invention. In the method according to the invention for depositing insoluble silicon compounds from a pickling fluid in at least one pickling circuit of a pickling plant, the pickling circuit comprises: - pickling tanks of a pickling plant for pickling metal strips; - a return line between the pickling tank and the circuit tank; - a pressure line between the circuit tank and the pickling tank; - a circulation pump; a heating device disposed in the pressure line; - a main volume flow of 500-600 cubic meters per hour of pickling fluid is circulated by a circulation pump from the pickling tank through a return line into the circuit tank and back into the pickling tank via a pressure line; - at least one flocculating aid is introduced into the main volume flow by a flocculating device having one or more mixing zone vessels, - the insoluble silicon compounds are deposited directly from the main volume flow by a deposition device located in the circuit tank, - The main volume flow is heated to the process temperature T by a heating device. p It is heated until

[0035] The method according to the invention for removing insoluble silicon compounds from the pickling fluid is preferably carried out during the pickling of the metal strip in the associated pickling plant. However, as an alternative to this, the method according to the invention can also be used during the time when the metal strip is not being pickled in the pickling plant, for example, in order to particularly thoroughly clean the corresponding insoluble pickling residues from the pickling fluid after pickling of some metal strips with a high silicon content. In this case too, the main volumetric flow of the pickling circuit is circulated with the aid of a circulation pump.

[0036] In one configuration of the method according to the invention, - when pickling the first type of metal strip through the first mixing zone vessel, a first flocculating aid is introduced into the main volumetric flow; When pickling the second type of metal strip exclusively through the second and / or third mixing zone vessel, at least a second flocculating aid is introduced into the main volumetric flow.

[0037] In other words, when pickling a first type of metal strip, a first flocculating aid is introduced into the main volumetric flow by the first mixing zone vessel, while the addition of further flocculating aids into the second and third mixing zone vessels is omitted, so that the main volumetric flow simply flows passively through the second and third mixing zone vessels. When pickling a second type of metal strip, i.e., a type different from the first, the addition of flocculating aid into the first mixing zone vessel is omitted, while only a second flocculating aid is added into the second mixing zone vessel, or the second and third flocculating aids are added into the main volumetric flow in both the second and third mixing zone vessels.

[0038] The first type of metal strip may, for example, include steel strip having a particular carbon content, while the second type may include steel strip having a high silicon content (and / or other insoluble alloying elements of the steel strip).

[0039] The above-described characteristics, features, and advantages of the present invention, and the manner in which they are achieved, will become clearer and easier to understand in connection with the following description of exemplary embodiments, which are explained in more detail in connection with the figures, in which the same details are respectively indicated by the same reference symbols in all figures. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a schematic diagram showing a simple pickling circuit of a pickling plant as known from the prior art; FIG. [Figure 2] 1 is a schematic diagram showing silicon deposition in a partial stream of a pickling circuit of a pickling plant, as known from the prior art; [Figure 3] 1 shows an exemplary diagram of a pickling circuit with a device according to the invention, with a deposition device in the circuit tank; DETAILED DESCRIPTION OF THE INVENTION

[0041] FIG. 1 shows a schematic representation of a pickling plant 1 comprising three pickling tanks 11, 12, and 13, each filled with a pickling fluid 2, through which the metal strip 6 to be pickled passes continuously (represented in FIG. 1 by arrows from left to right) in the production direction P. Each of the pickling tanks 11, 12, and 13 is assigned its own pickling circuit 8, with only the pickling circuit 8 of the first pickling tank 11 being represented in FIG. 1. In the following, the connecting arrows between two subsections represent the respective connecting piping. In addition to the pickling tank 11 itself, the represented pickling circuit 8 comprises a circuit tank 20, a circulation pump 22, and a heating device 24, the subsections of which are connected to each other in series via piping. The line extending between the pickling tank 11 and the circuit tank 20 is in this case referred to as the return line 3 , and the line extending between the circuit tank 20 and the pickling tank 11 is referred to as the pressure line 4 .

[0042] The pickling fluid 2 used in the pickling plant 1 is conveyed through the individual pickling tanks 11, 12 and 13 in the direction opposite to the production direction P of the metal strip 6, and new pickling fluid 2 is introduced into the last pickling tank 13 and conveyed in succession (as represented in FIG. 1 by the curved arrows between the individual pickling tanks 11, 12 and 13) in the direction opposite to the production direction P up to the first pickling tank 11. In this case, molten material (e.g., iron Fe 2+) and the concentration of undissolved substances (e.g. silicon dioxide) increases in the pickling fluid 2. From the first pickling tank 11, the pickling fluid 2 is first extracted via a return line 3 into a circuit tank 20 in the form of a so-called main volume stream 7, the majority of which is then conveyed by a circulation pump 22 via a heating device 24 and a pressure line 4 back to the pickling tank 11. A partial stream 5' is branched off from the pressure line 4 and conveyed to treatment in a regeneration plant 26. The cleaned partial stream 5' corresponding to the extracted partial stream 5' is heated to a conventional process temperature T of up to 90°C, which prevails in the pickling tanks 11, 12 or 13. p A partial stream 5 of the reprocessed pickling fluid 2, heated to .degree. C., is conveyed back to the final pickling tank 13.

[0043] The volume of each of the pickling tanks 11, 12, or 13 is, for example, 30 to 40 cubic meters, the respective main volumetric flow 7 is, for example, up to 500 cubic meters per hour, and the piping of each pickling circuit has a total additional volume of approximately 10 cubic meters. The partial flow 5' branched off to the regeneration plant 26 is, for example, approximately 15 cubic meters per hour. During normal pickling operation, the circuit tank 20 is approximately one-third filled with pickling fluid. To allow for the collection of pickling fluid released from the pickling tank and associated piping in the event of an emergency discharge, the associated circuit tank has a volume of, for example, approximately 70 cubic meters.

[0044] 2 shows a pickling plant 1 known from the prior art for pickling metal strip 6 containing a high silicon content (more than 2 percent by weight). In addition to the embodiment depicted in FIG. 1, in the pickling plant 1 according to FIG. 2, a first partial stream 5′ of pickling fluid 2 is branched off from the pressure line 4 during in-line or offline operation, and a second partial stream 5″ of pickling fluid 2 is branched off from the pressure line 4 during offline operation, and is conveyed via a cooling device 27 or 27′ to a deposition device 28 or 28′, respectively, for separating undissolved silicon compounds. The pickling fluid 2 of partial stream 5′ cleaned of undissolved silicon compounds is further conveyed via a valve 29 into a regeneration plant 26 during offline operation, or conveyed back into the circuit tank 20 during in-line operation.

[0045] 3 shows diagrammatically by way of example a pickling circuit 8 of a pickling tank 11 with a coalescing device 31 and a circuit tank 20 equipped with a deposition device 30 according to the invention for depositing insoluble substances, preferably silicon compounds, from the pickling fluid 2. A pickling plant 1 with three pickling tanks 11, 12 and 13 is shown by way of example, but the invention may also be used in pickling plants with more or less than three pickling tanks.

[0046] According to Fig. 3, the deposition device 30 is arranged in the circuit tank 20 of the first pickling tank 11, since the pickling fluid 2 therein has the highest concentration of scale compounds formed during pickling and therefore the need for their deposition, in particular of undissolved silicon compounds, is greatest in this pickling circuit. The pickling circuits of the further pickling tanks 12 and 13, which have a lower concentration of undissolved substances, may be configured as conventional pickling circuits according to Fig. 1 (this is not shown in Fig. 3). However, it is also possible to configure some (for example the first two or three) or all of the pickling circuits of the pickling plant 1 with deposition devices 30 according to Fig. 3.

[0047] In FIG. 3, the metal strip 6 passes successively in the production direction P through three pickling tanks 11, 12, and 13, each filled with pickling fluid 2. The pickling tanks 11, 12, and 13 each have a volume of approximately 30 to 40 cubic meters, and the connecting piping of the pickling circuit 8 has a total volume of approximately 10 cubic meters. From the first pickling tank 11, a main volume flow 7 of pickling fluid 2, comprising approximately 500 cubic meters per hour, is conveyed out of the pickling tank 11 via a return line 3 and then passes successively through three mixing zone vessels 32, 32', and 32'' of a coalescing device 31 arranged in the return line 3.

[0048] In the mixing zone vessels 32, 32' and 32" the preparation of the corresponding flocculation aid is carried out by means of the corresponding dosing device 33, 33' and 33", respectively. For example, the respective flocculation aid is introduced in solid form from the corresponding storage vessel 34, 34' or 34" into the respective dosing device 33, 33' and 33", and dissolved in a liquid (e.g., water), thereby providing and introducing the flocculation aid into the main volumetric flow 7 at the concentration required for the assigned mixing zone vessel 32, 32' and 32", in order to promote settling of undissolved material in the main volumetric flow into the subsequent settling zone 36. Alternatively, the respective flocculation aid may be present in the respective storage vessel 34, 34' or 34" in the form of a pre-concentrated liquid and diluted to the desired concentration in the respective dosing device 33, 33' and 33". As another alternative, the respective flocculation aid may also be introduced in solid form from the corresponding storage container 34, 34' or 34" directly into the respective mixing zone vessel 32, 32' or 32" by the respective dosing device 33, 33' or 33", in which case the dosing device 33, 33' or 33" is configured as a dosage device. If no flocculation aid is added into the main volumetric flow 7 by one of the mixing zone vessels 32, 32' or 32", the main volumetric flow 7 will only passively flow through the corresponding mixing zone vessel 32, 32' or 32".

[0049] The transport of the pickling fluid 2 between the individual mixing zone vessels 32, 32' and 32'' may in this case be carried out by natural gradient or with the aid of pumps (not shown in Figure 3). In the exemplary embodiment according to Figure 3, up to three different flocculation aids may be introduced into the main volumetric flow 7 of the pickling circuit 8, each in the required concentration. The flocculation aids promote the solidification of undissolved substances in the pickling fluid 2, such as undissolved silicon compounds, to form larger particles 43, which, due to their size, can be more easily deposited with the aid of the subsequent deposition device 30.

[0050] After the mixing zone vessels 32, 32' and 32'', the main volumetric flow 7 of the pickling circuit 8 is conveyed via the return line 3 into the circuit tank 20, which according to the invention comprises a settling zone 35, a settling zone 36 and a receiving zone 39 and has a total volume of 75 to 100 cubic meters. The settling zone 35 is used to settling the main volumetric flow 7 and to minimize disturbances. By means of a first overflow 38, the settling pickling fluid 2 flows into the settling zone 36, in which a deposition device 30 configured as a lamella separation device 37 is arranged.

[0051] The lamella separation device 37 has a plurality of parallel flow channels 44, which are arranged next to each other at a vertical distance d of at least 50 to 70 mm and inclined at an angle α to the vertical. In the flow channels, the insoluble matter of the pickling fluid 2 solidified to form particles 43 settles toward the bottom region of the settling zone 36 due to the effects of gravity in the settling process. The lower ends of the flow channels 44 are separated vertically by a height h of at least 200 mm from the bottom of the circuit tank 20. The flow channels 44, which define the flow direction of the passing pickling fluid 2 (represented in FIG. 3 by an arrow pointing diagonally upward), may be formed from parallel-arranged tubes or hollow prisms, each with a closed boundary in a plane perpendicular to the flow direction. This gives the lamella separation device 37 an overall honeycomb structure (not visible in FIG. 3).

[0052] The pickling sludge that collects in the settling zone 36 or in the bottom region of the circuit tank 20 when the pickling fluid 2 flows through the lamella separation device 37 is extracted therefrom and transported through the extraction opening 40 to the filtration device 41. The bottom of the circuit tank 20 is preferably configured so that automatic transport of the sediment to the extraction opening 40 is ensured (e.g., by a corresponding chamfer or rounding in the bottom surface) (e.g., the circuit tank 20 may be configured as a recumbent cylinder with a rounded bottom and a diameter of, e.g., 4 to 4.5 meters). Alternatively, the sediment may be extracted from the circuit tank 20 by a suitable transport device (e.g., a pump not shown in FIG. 3). In the filtration device 41, configured for example as a chamber filter press, the solid components of the pickling sludge are separated as dry material (filter cake) and transported to a collection container 42 for subsequent disposal, while the remaining liquid part of the pickling sludge (filtrate) is transported to the regeneration plant 26.

[0053] Via the second overflow 38', the pickling fluid 2 cleaned of undissolved substances flows into a receiving zone 39 of the circuit tank 20, from which the main volume flow 7 is conveyed back into the first pickling tank 11 via the pressure line 4 with the aid of the circulation pump 22. A heating device 24 is arranged in the pressure line 4, which heats the pickling fluid 2 passing through it to a process temperature T, typically up to 90°C. p Before the heating device 24, a partial flow 5' of, for example, 12 to 18 cubic meters per hour is branched off from the main volume flow 7 and conveyed to a regeneration plant 26. [Explanation of symbols]

[0054] 1. Pickling plant 2. Pickling fluid 3 Return line 4 Pressure Lines 5, 5', 5'' partial flow 6 metal strips 7 Main volume flow 8. Pickling Circuit 11, 12, 13 Pickling tanks 20 Circuit Tank 22 Circulation pump 24 Heating Devices 26 Regeneration Plant 27, 27' Cooling Device 28, 28' Deposition Device 29 valves 30 Deposition Device 31 Coagulation Device 32, 32', 32'' Mixing Zone Vessel 33, 33', 33'' delivery device 34, 34', 34'' storage container 35 Suppression Zone 36 Subsidence Zone 37 Lamellar Separation Device 38, 38' Overflow 39 Receptive Zone 40 Extraction opening 41 Filtration Devices 42 Collection container 43 particles 44 flow channels d vertical distance h height P Manufacturing direction T p Process Temperature α angle

Claims

1. A device for depositing insoluble silicon compounds from a pickling fluid (2) in a pickling plant (1) having at least one pickling circuit (8), said pickling circuit (8) comprising: pickling tanks (11, 12, 13) of said pickling plant (1) for pickling metal strips (6); a return line (3) between the pickling tanks (11, 12, 13) and a circuit tank (20); a pressure line (4) between the circuit tank (20) and the pickling tanks (11, 12, 13); a circulation pump (22) for circulating the main volume flow (7) of pickling fluid (2) with a maximum pumping capacity of 500 to 600 cubic meters per hour; The main volume flow (7) is heated to a process temperature (T ｐ a heating device (24) arranged in said pressure line (4) for heating the pressure to a regeneration plant (26) for separating dissolved components of the spent pickling fluid (2), the regeneration plant (26) being connected to the main volumetric flow (7) and the pickling tanks (11, 12, 13) by partial flows (5, 5'), one partial flow (5') being branched off from the main volumetric flow (7) of the pressure line (4), the device comprising: a coalescing device (31) having one or more mixing zone vessels (32, 32', 32'') for introducing at least one coalescing aid into said main volumetric flow (7); a deposition device (30) arranged in said circuit tank (20) for depositing an insoluble silicon compound directly from said main volume flow (7).

2. 2. The device according to claim 1, wherein the circuit tank (20) has a volume two to three times larger than the pickling tanks (11, 12, 13) in the pickling circuit (8), and the deposition device (30) comprises at least a settling zone (35), a settling zone (36) and a receiving zone (39), a first overflow (38) being arranged between the settling zone (35) and the settling zone (36), and a second overflow (38') being arranged between the settling zone (36) and the receiving zone (39).

3. 3. Device according to claim 1 or 2, wherein the coalescing device (31) has at least two mixing zone vessels (32, 32', 32'') for adding at least two different coalescing aids to the main volumetric flow (7).

4. 4. The device of claim 1, wherein the total volume of all of the mixing zone vessels is between 8 cubic meters and 25 cubic meters.

5. The device according to any one of claims 1 to 4, wherein the deposition device (30) is configured as a lamella separation device (37) comprising a number of flow channels (44) parallel to one another.

6. 6. The device of claim 5, wherein the flow channel (44) is inclined at an angle (α) to the vertical and is made of an acid- and heat-resistant material that can permanently withstand temperatures of at least 90°C.

7. The device according to claim 6, wherein said angle (α) is between 15° and 60°.

8. 8. A device according to claim 6 or 7, wherein the vertical distance (d) between adjacent flow channels (44) is at least 50 mm.

9. 1. A method for depositing insoluble silicon compounds from a pickling fluid (2) in at least one pickling circuit (8) of a pickling plant (1), said pickling circuit (8) comprising: pickling tanks (11, 12, 13) of said pickling plant (1) for pickling metal strips (6); a return line (3) between the pickling tanks (11, 12, 13) and a circuit tank (20); a pressure line (4) between the circuit tank (20) and the pickling tanks (11, 12, 13); a circulation pump (22) for circulating the main volume flow (7) of pickling fluid (2) with a maximum pumping capacity of 500 to 600 cubic meters per hour; a heating device (24) arranged in the pressure line (4); a regeneration plant (26) for separating dissolved components of the spent pickling fluid (2), the regeneration plant (26) being connected to the main volumetric flow (7) and the pickling tanks (11, 12, 13) by partial flows (5, 5'), one partial flow (5') being branched off from the main volumetric flow (7) of the pressure line (4), The main volume flow (7) of 500 to 600 cubic meters per hour of pickling fluid (2) is circulated by the circulation pump (22) from the pickling tank (11, 12, 13) through the return line (3) into the circuit tank (20) and back into the pickling tank (11, 12, 13) via the pressure line (4); At least one flocculating aid is introduced into said main volumetric flow (7) by means of a flocculating device (31) having one or more mixing zone vessels (32, 32', 32''), Insoluble silicon compounds are deposited directly from the main volume flow (7) by a deposition device (30) located in the circuit tank (20), The main volume flow (7) is heated to a process temperature (T ｐ ) heated to a temperature of 1000°C.

10. When pickling a first type of metal strip (6) through a first mixing zone vessel (32), a first flocculation aid is introduced into said main volumetric flow (7), 10. The method according to claim 9, wherein at least a second flocculation aid is introduced into the main volumetric flow (7) when pickling a second type of metal strip (6) only through the second and / or third mixing zone vessels (32', 32'').

Images