INLINE SILICON DEPOSITION IN A PICKLING PLANT

Abstract

A device and a method for depositing undissolved materials, in particular undissolved silicon compounds, from a pickling fluid in a pickling plant. A pickling circuit of the pickling plant has a pickling tank for pickling metal strips, a return line between the pickling tank and a circuit tank, a circulation pump for circulating a main volume flow of pickling fluid from the pickling tank, and a heating device arranged in a pressure line between the circuit tank and the pickling tank. The device includes a flocculation device for introducing at least one flocculant into the main volume flow, and a deposition device in the circuit tank and preferably designed as an inclined clarifying device, for the sedimentation of undissolved materials directly from the main volume flow. When pickling silicon-containing steel strips (electrical steel strips), an at least two-stage flocculation can be carried out using two or more mixing zone containers.

Claims

1-10. (canceled)

11. A device for depositing undissolved silicon compounds from a pickling fluid in a pickling plant having at least one pickling circuit, the pickling circuit comprising: a pickling tank of the pickling plant for pickling metal strips; a return line between the pickling tank and a circuit tank; a pressure line between the circuit tank and the pickling tank; a circulation pump having a maximum pump capacity of from 500 to 600 cubic meters per hour for circulating a main volume flow of pickling fluid; and a heating device arranged in the pressure line for heating the main volume flow to a process temperature; wherein the device comprises: a flocculation device having one or more mixing zone containers configured to introduce at least one flocculation aid into the main volume flow; and a deposition device arranged in the circuit tank configured to deposit undissolved silicon compounds directly from the main volume flow.

12. The device as claimed in claim 11, wherein: the circuit tank has a volume from 2 to 3 times greater than the pickling tank in the pickling circuit; the deposition device comprises at least a settling zone, a sedimentation zone, and a reception zone; a first overflow is arranged between the settling zone and the sedimentation zone; and a second overflow is arranged between the sedimentation zone and the reception zone.

13. The device as claimed in claim 11, wherein the flocculation device has at least two mixing zone containers configured to add at least two different flocculation aids into the main volume flow.

14. The device as claimed in claim 11, wherein a sum of volumes of all of the mixing zone containers is from 8 to 25 cubic meters.

15. The device as claimed in claim 11, wherein the deposition device is configured as a lamella separating device comprising a multiplicity of mutually parallel flow channels.

16. The device as claimed in claim 15, wherein the flow channels are inclined at an angle relative to a vertical and consist of an acid-resistant and heat-resistant material which permanently withstands temperatures of at least 90? C.

17. The device as claimed in claim 16, wherein the angle is 15-60?.

18. The device as claimed in claim 16, wherein a normal distance between neighboring flow channels is at least 50 mm.

19. A method for depositing undissolved silicon compounds from a pickling fluid in at least one pickling circuit of a pickling plant, the pickling circuit comprising: a pickling tank of the pickling plant for pickling metal strips; a return line between the pickling tank and a circuit tank; a pressure line between the circuit tank and the pickling tank; a circulation pump; and a heating device arranged in the pressure line; wherein the method comprises: circulating, by the circulation pump, a main volume flow of from 500 to 600 cubic meters per hour of pickling fluid from the pickling tank through the return line into the circuit tank and via the pressure line back into the pickling tank; introducing, by a flocculation device, at least one flocculation aid into the main volume flow having one or more mixing zone containers; depositing, by a deposition device arranged in the circuit tank, undissolved silicon compounds directly from the main volume flow; and heating, by the heatin device, the main volume flow to a process temperature.

20. The method as claimed in claim 19, wherein: when pickling a first type of metal strips by means of a first mixing zone container, a first flocculation aid is introduced into the main volume flow; and when pickling a second type of metal strips exclusively by means of a second and/or a third mixing zone container, at least a second flocculation aid is introduced into the main volume flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The above-described properties, features and advantages of this invention, as well as the way in which they are achieved, will become clearer and more comprehensible in connection with the following description of exemplary embodiments, which are explained in more detail in connection with the drawings. Details which are the same are respectively denoted by the same references in all the figures.

[0050] FIG. 1 shows a schematic representation of a simple pickling circuit, known from the prior art, of a pickling plant,

[0051] FIG. 2 shows a schematic representation of silicon deposition, known from the prior art, in a partial flow of the pickling circuit of a pickling plant, and

[0052] FIG. 3 shows an exemplary representation of a pickling circuit having a device according to the invention, comprising a deposition device in the circuit tank.

DETAILED DESCRIPTION

[0053] FIG. 1 (FIG. 1) schematically shows a pickling plant 1 comprising three pickling tanks 11, 12 and 13, which are respectively filled with pickling fluid 2 and through which a metal strip 6 to be pickled passes successively in a production direction P (symbolized in FIG. 1 by an arrow from left to right). Each pickling tank 11, 12, 13 is assigned its own pickling circuit 8, only the pickling circuit 8 of the first pickling tank 11 being represented in FIG. 1. In what follows, a connecting arrow between two subsections respectively symbolizes a connecting pipeline. Besides the pickling tank 11 itself, the pickling circuit 8 represented comprises a circuit tank 20, a circulation pump 22 and a heating device 24, these subsections being connected to one another in series via pipelines. A line running between the pickling tank 11 and circuit tank 20 is in this case referred to as a return line 3, and a line running between the circuit tank 20 and pickling tank 11 is referred to as a pressure line 4.

[0054] The pickling fluid 2 used in the pickling plant 1 is conveyed counter to the production direction P of the metal strip 6 through the individual pickling tanks 11, 12 and 13, fresh pickling fluid 2 being introduced into the last pickling tank 13 and conveyed in a cascade (symbolized in FIG. 1 by curved arrows between the individual pickling tanks 11, 12 and 13) counter to the production direction P to the first pickling tank 11. In this case, the concentration of dissolved substances (for example iron Fe.sup.2+) and undissolved substances (for example silicon dioxide) increases in the pickling fluid 2. From the first pickling tank 11, pickling fluid 2 is first extracted via the return line 3 in the form of the so-called main volume flow 7 into the circuit tank 20, then a large part thereof is delivered by means of the circulation pump 22 via the heating device 24 and the pressure line 4 back to the pickling tank 11. A partial flow 5 is branched off from the pressure line 4 and delivered to processing in a regeneration plant 26. A partial flow 5 of reprocessed pickling fluid 2, corresponding to the withdrawn partial flow 5 and cleaned and heated to a conventional process temperature T.sub.p of up to 90? C. prevailing in the pickling tanks 11, 12 or 13, is delivered back to the last pickling tank 13.

[0055] The volume of the pickling tank 11, 12 or 13 is, for example, respectively from 30 to 40 cubic meters with a respective main volume flow 7 of, for example, up to 500 cubic meters per hour, the pipelines of the respective pickling circuit in total having an additional volume of about 10 cubic meters. The partial flow 5 branched off to the regeneration plant 26 is, for example, about 15 cubic meters per hour. During normal pickling operation, the circuit tank 20 is about one third filled with pickling fluid. In order to be able to collect the pickling fluid released from a pickling tank and the associated pipelines in the event of an emergency discharge, the associated circuit tank has a volume of about 70 cubic meters, for example.

[0056] FIG. 2 (FIG. 2) shows a pickling plant 1 known from the prior art for pickling steel strips 6 which contain an elevated silicon content (more than two percent by weight). In addition to the embodiment represented in FIG. 1, in the pickling plant 1 according to FIG. 2 a first partial flow 5 of pickling fluid 2 is branched off during inline or offline operation and a second partial flow 5 of pickling fluid 2 is branched off during offline operation from the pressure line 4 and respectively delivered 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 the partial flow 5, from which undissolved silicon compounds have been cleaned, is either during offline operation conveyed further via valves 29 into a regeneration plant 26 or, during inline operation, delivered back into the circuit tank 20.

[0057] FIG. 3 (FIG. 3) shows by way of example and schematically a pickling circuit 8 of a pickling tank 11 having a flocculation device 31 and a circuit tank 20, which comprises a deposition device 30 according to the invention for depositing undissolved substances, preferably silicon compounds, from the pickling fluid 2. A pickling plant 1 comprising three pickling tanks 11, 12 and 13 is represented by way of example, although the invention may also be used for pickling plants having more or fewer than three pickling tanks.

[0058] 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 the pickling and there is therefore the greatest need for deposition thereof, in particular of undissolved silicon compounds, in this pickling circuit. The pickling circuits of the further pickling tanks 12 and 13 may also be configured as a conventional pickling circuit according to FIG. 1 because of their lower concentration of undissolved substances (this is not represented in FIG. 3). It is, however, also possible to configure several (for example the first two or three) or all of the pickling circuits of a pickling plant 1 with a deposition device 30 according to FIG. 3.

[0059] In FIG. 3, a metal strip 6 passes successively in the production direction P through three pickling tanks 11, 12 and 13 respectively filled with a pickling fluid 2. The pickling tanks 11, 12 and 13 respectively have a volume of about 30 to 40 cubic meters, and the connecting pipelines of the pickling circuit 8 have a total volume of about 10 cubic meters. From the first pickling tank 11, a main volume flow 7 of pickling fluid 2 comprising about 500 cubic meters per hour is conveyed out of the pickling tank 11 via the return line 3 and subsequently passes successively through three mixing zone containers 32, 32 and 32 of a flocculation device 31 arranged in the return line 3.

[0060] In the mixing zone containers 32, 32 and 32, the preparation of corresponding flocculation aids is respectively carried out with the aid of corresponding application devices 33, 33 and 33. For example, the respective flocculation aid is introduced in solid form from a corresponding storage container 34, 34 or 34 into the respective application device 33, 33 and 33 and dissolved in a liquid (for example water) so that it can be provided and introduced into the main volume flow 7 in the concentration required for the assigned mixing zone container 32, 32 and 32, in order to promote the sedimentation of the substances undissolved therein in a subsequent sedimentation zone 36. Alternatively, the respective flocculation aid may already be in concentrated liquid form in the respective storage container 34, 34 or 34 and diluted to a desired concentration in the respective application 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 by means of the respective application device 33, 33 or 33 into the respective mixing zone container 32, 32 or 32, the application device 33, 33 or 33 in this case being configured as a dosing device. If a flocculation aid is not added into the main volume flow 7 by one of the mixing zone containers 32, 32 or 32, the main volume flow 7 only flows passively through the corresponding mixing zone container 32, 32 or 32.

[0061] The transport of the pickling fluid 2 between the individual mixing zone containers 32, 32 and 32 may in this case take place either because of a natural gradient or with the aid of pumps (not represented in FIG. 3). In the exemplary embodiment according to FIG. 3, up to three different flocculation aids may be introduced in a respectively required concentration into the main volume flow 7 of the pickling circuit 8. The flocculation aids promote the coagulation of undissolved substancesfor example undissolved silicon compoundsin the pickling fluid 2 to form larger particles 43, which can be deposited more easily with the aid of a subsequent deposition device 30 because of their size.

[0062] After the mixing zone containers 32, 32 and 32, the main volume flow 7 of the pickling circuit 8 is conveyed from the return line 3 into the circuit tank 20, which according to the invention comprises a settling zone 35, a sedimentation zone 36 and a reception zone 39 and has a total volume of from 75 to 100 cubic meters. The settling zone 35 is used to pacify the main volume flow 7 and minimize turbulence. Via a first overflow 38, the pacified pickling fluid 2 flows into the sedimentation zone 36 in which a deposition device 30 configured as a lamella separating device 37 is arranged.

[0063] The lamella separating device 37 has a multiplicity of flow channels 44 running parallel, which are arranged at a normal distance d of at least 50 to 70 mm next to one another and are inclined at an angle ? relative to the vertical. In the flow channels, undissolved substances of the pickling fluid 2, which are coagulated to form particles 43, settle because of the effect of gravity in a sedimentation process in the direction of the bottom region of the sedimentation zone 36. The lower end of the flow channels 44 is separated in the vertical direction at a height h of at least 200 mm from the bottom level of the circuit tank 20. The flow channels 44 forming a flow direction (symbolized in FIG. 3 by arrows pointing obliquely upward) for the pickling fluid 2 passed through may be formed from tubes or hollow prisms arranged parallel to one another, which respectively have a closed boundary in a plane normal to the flow direction so that the lamella separating device 37 overall has a honeycomb structure (not visible in FIG. 3).

[0064] The pickling sludge which gathers in the bottom region of the sedimentation zone 36, or of the circuit tank 20, when the pickling fluid 2 flows through the lamella separating device 37 is extracted from there and delivered through an extraction opening 40 to a filtering device 41. The bottom of the circuit tank 20 is preferably configured in such a way that automatic transport of the sediment to the extraction opening 40 is ensured (for example by a corresponding chamfer or rounding in the bottom face; for example, the circuit tank 20 may be configured as a recumbent cylinder with rounded bottoms and a diameter of for example from 4 to 4.5 meters). Alternatively, the sediment may also be extracted from the circuit tank 20 by suitable conveyor devices (for example a pump, not represented in FIG. 3). In the filtering device 41, which is configured for example as a chamber filter press, the solid constituents of the pickling sludge are separated as a dry substance (filter cake) and delivered to a collection container 42 for the purpose of subsequent disposal, while the remaining liquid fraction of the pickling sludge (filtrate) is delivered to the regeneration plant 26.

[0065] Via a second overflow 38, the pickling fluid 2 from which undissolved substances have been cleaned flows into the reception zone 39 of the circuit tank 20, from where the main volume flow 7 is delivered back into the first pickling tank 11 with the aid of a circulation pump 22 via a pressure line 4. Arranged in the pressure line 4, there is a heating device 24 which heats the pickling fluid 2 passed through to a process temperature T.sub.p of generally up to 90? C. Before the heating device 24, a partial flow 5for example from 12 to 18 cubic meters per houris branched off from the main volume flow 7 and delivered to a regeneration plant 26.

LIST OF REFERENCE SIGNS

[0066] 1 pickling plant [0067] 2 pickling fluid [0068] 3 return line [0069] 4 pressure line [0070] 5,5, 5 partial flow [0071] 6 metal strip [0072] 7 main volume flow [0073] 8 pickling circuit [0074] 11, 12, 13 pickling tank [0075] 20 circuit tank [0076] 22 circulation pump [0077] 24 heating device [0078] 26 regeneration plant [0079] 27, 27 cooling device [0080] 28, 28 deposition device [0081] 29 valve [0082] 30 deposition device [0083] 31 flocculation device [0084] 32, 32, 32 mixing zone container [0085] 33, 33, 33 application device [0086] 34, 34, 34 storage container [0087] 35 settling zone [0088] 36 sedimentation zone [0089] 37 lamella separating device [0090] 38, 38 overflow [0091] 39 reception zone [0092] 40 extraction opening [0093] 41 filtering device [0094] 42 collection container [0095] 43 particle [0096] 44 flow channel [0097] d normal distance [0098] h height [0099] P production direction [0100] T.sub.p process temperature [0101] ? angle