Abstract
The invention relates to a steel product processing plant, in particular including a rolling line and preferably upstream thereof a continuous casting line including at least one steel product direct cooling or cleaning system, or another system suitable to spray water on the product being processed; and a system for the separation of mixtures, in particular of a muddy nature, including water and scale deriving from said systems, which is provided with at least two pits (F1, F2) for collecting the mixtures, wherein at least a first pit (F1), advantageously provided with a dredging system for continuously removing the scale, is fed by water with coarse scale and at least a second pit (F2) with water with fine scale and wherein said pits each have a maximum overall depth <10 m, preferably even less.
Claims
1. A steel product processing plant, comprising at least one rolling mill provided with a plurality of stands arranged in series and suitable to progressively reduce the thickness of the product to be rolled in the advancement direction, and optionally a descaling machine and a continuous casting line arranged upstream of said rolling mill and of said descaling machine, wherein said plant is further provided with: (a) at least one steel product direct cooling or cleaning system, or other system suitable to spray water on the product being processed; (b) at least one system for separating mixtures, in particular mixtures of a muddy nature, comprising water and scale, deriving from said at least one steel product direct cooling or cleaning system, or from said other system suitable to spray water on the product being processed comprising: (b-1) at least a first collection pit (F1) of the mixtures; (b-2) at least a second collection pit (F2) of the mixtures; wherein said pits (F1, F2) each have an overall depth <10 m, preferably <8 m, still more preferably <6.50 m; and wherein said at least a first pit (F1) is fed with mixtures deriving from the casting or from said descaling machine and/or from one or more of the initial stands of the rolling mill and wherein said at least a second pit (F2) is fed by one or more groups formed by the remaining stands of the rolling mill.
2. The plant according to claim 1, wherein each pit (F1, F2) comprises: (i) a channel or a channel system, (ii) at least one collection tank of the mixtures into which said channel or said channel system opens.
3. The plant according to claim 1, wherein said first pit (F1) comprises: (c) a dredging device, in particular a scraping conveyor.
4. The plant according to claim 1, wherein said first pit (F1) comprises inclined walls, in particular with an inclination between 45 and 75.
5. The plant according to claim 2, wherein said channel or said channel system of said first pit (F1) comprises a distribution bell which forms the inlet in said at least one collection tank of the mixtures of said first pit (F1).
6. The plant according to claim 1, wherein said at least one collection tank of the mixtures of said first pit is provided in the upper edge along the perimeter, with one or more channel(s) of clarified water overflow which feed(s) at least one clarified water collection tank included for such a purpose in said first pit.
7. The plant according to claim 6, wherein said clarified water collection tank is arranged next to said at least one collection tank of the mixtures of said first pit.
8. The plant according to claim 1, wherein it further comprises an emergency tank, preferably at the side of said at least one collection tank of the mixtures of said first pit, and wherein the inlet to said at least one collection tank of the mixtures of said first pit is made as a closed pipe with an emergency by-pass adapted to feed said emergency tank.
9. The plant according to claim 1, wherein said pits (F1, F2) are at least partially arranged below said at least one steel product direct cooling or cleaning system, or other system suitable to spray water on the product being processed.
10. A process for separating mixtures comprising water and scale deriving from a direct cooling and/or descaling of steel products comprising the following steps: (I) producing metal scale in an oxidation process of a steel product in continuous casting and/or rolling processes; (II) water jet descaling and/or direct cooling of the continuous casting and/or rolling product resulting in scale accumulation in the descaling and/or direct cooling water forming said mixtures comprising water and scale; (III) conveying the mixtures with large size scale, in at least a first pit (F1) with an overall depth of less than 10 m and preferably provided with a dredging device, such as a scraping conveyor, and removing the large size scale, in particular >500 m, with said dredging device in a special container and diverting the clarified water, in particular by means of overflow elements present in said first pit (F1); (IV) conveying the mixtures with scale of fine particle size, in particular 500 m, into at least a second pit with a depth less than 10 m; and preferably removing the mixtures with pumps, without separation of the scale from the water, from the second pit.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 depicts a principle scheme of scale separation in a rolling mill according to the state of the art.
[0046] FIG. 2 depicts a principle scheme of the scale separation in a rolling mill according to the invention.
[0047] FIG. 3 depicts means for separating the scale in a steel product processing plant according to the state of the art.
[0048] FIG. 4 depicts means for separating the scale in a steel product processing plant according to the invention.
[0049] FIG. 5 depicts in section a scale separation system according to the invention in comparison with a scale separation system according to the state of the art.
[0050] FIGS. 6 a-c depict in different views an embodiment example of a collection tank of water with scale with a scraping conveyor according to the invention.
[0051] FIGS. 7a-d depict in various more detailed views a scraping conveyor in a dirty water collection tank according to the invention; and
[0052] FIG. 8 depicts another example embodiment of the tank for collecting scale of medium-large size.
DETAILED DESCRIPTION
[0053] FIG. 1 depicts a principle scheme of the system for collecting and separating the scale in a rolling mill according to the state of the art. A rolling mill 100 is preferably preceded by a descaling machine 102. A metal product 104 passes through the descaling machine 102 and into the rolling mill 100 to be rolled. The direct cooling water flows (arrows) from the descaling machine 102 and the rolling mill 100 (but possibly also from the secondary cooling of a casting arranged upstream, not shown) are collected in a channel 108, for example which reaches the yield end point at a depth of 9 m, and subsequently feed a scale pit/collection tank 110 through a distribution hood 111. The collection tank 110 can typically be located outside the factory building. When the water level 116 has reached the overflow of the tank 110, the clarified water (the bulk of the scale (not shown) due to its weight tends to sediment on the bottom of the tank 110) overflows and pours into the tank 112 for collecting the clarified water, from where it is conveyed by means of a pumping station 114 to further treatments, for example to a longitudinal clarifier (not shown). The tank 112 is preferably circular, with a diameter for example of 9 m. The overall depth P (channel 108+tank 110=pit F) is approximately 14 m and is located below the ground 106.
[0054] FIG. 2 depicts a principle scheme of the scale separation in a rolling mill according to the invention. Here, too, there is a rolling mill 200 preceded by a descaling machine 202, and possibly a continuous casting machine (not shown), through which a metal product 204 advances, decreasing in width/thickness. A first channel 208a and a second channel 208b are provided below the metal product processing line. The first channel 208a collects the water with scale from the descaling machine 202, from the casting secondary, if any, and from the first stands of the rolling mill 200, for example flattening stands; the second channel 208b collects the direct cooling water from the remaining stands of the rolling mill 200 and from any downstream quenching systems (not shown). From the first channel 208a, the waters with heavy scale reach a collection tank 210 in which a scraping conveyor 270, or dredge, is placed, driven by means 268 which remove the sedimented scale 217 and drop it (arrow S) into a special container for evacuation (not shown). The overflow water reaches a clarified water collection tank 212a from where it is pumped through a pumping station 214a towards a longitudinal clarifier (not shown). The waters collected by the second channel 208b and comprising lighter scale are instead fed to a collection tank 212b of water with scale from which the water is directly pumped by means of a relative pumping station 214b to the longitudinal clarifier (not shown). Seen from the ground, in an exemplary manner, the depth P.sub.1 is about 3.35 m, the depth P.sub.2 about 5.70 m and the depth P.sub.3, which corresponds to the overall depth of the pit system, about 6.30 m. The collection tank 212b is preferably circular and has a diameter for example of 5 m. The channel 208a and the tank 210, with the tank 212a, form the first pit F1, and the channel 208b and the tank 212b form the second pit F2.
[0055] FIG. 3 depicts the separation of scale in a steel product processing plant according to the state of the art. From various metal processing plants 4, 6, such as cooling systems of continuous casting machines, 2, 8, such as descaling units, rolling mills, direct cooling and quenching systems, etc., not only does water emerge dirty with oils and greases due to the lubrication of components such as the rolling rollers, but also as seen of scale detached following the handling of the product and its processing. The dirty water is directed to scale pits/pretreatment tanks 22 normally divided into two chambers 22a and 22b separated by an overflow 32. A level gauge 24 detects the water level in the tank 22. In the first chamber 22a the largest scale falls by gravity, with can be withdrawn with a relative magnetic crane or bucket 20. Normal maintenance activities must be carried out for the crane bucket and hoist 20. If the scale extraction bucket/hoist fails, the volume of the scale pit allows an accumulation of scale for 2-3 days to allow repairs to be performed without stopping the water purification plant.
[0056] In the second chamber 22b, an oil skimmer 26 removes the oil from the surface. First pumping means 30 withdraw the water to perform the washing of the water and scale transport channels and reintroduce it to a new treatment in the first chamber 22a. Second pumping means 28 withdraw the water to feed a longitudinal sedimentation tank (not shown) and subsequent sand filters. From the hardening and tempering plants of bars or rods 8, or from the cooling for strips, the dirty water with fine scale is instead directed to a recovery tank 38, provided with a water level meter 34 where the fine scale remains in suspension and the water is pumped with a pumping system 36 to further filtration treatments (not shown).
[0057] FIG. 4 depicts the scale separation in a steel product processing plant according to the invention. From different product processing areas, such as a continuous casting machine 4, 6 provided with secondary cooling or a rolling mill 2 with possible descaling system, cooling and descaling waters emerge, in particular dirty water with scale from the product processing steps, which is directed to a collection tank 40 in which there is a dredging system 46 adapted to convey the scale directly to a container or removal means 50. The part 40a of the tank is separated, comprises a level gauge 42 and collects the clarified water which is pumped with a relative pumping system 44 to further treatments (not shown). The tank 40 is contained in a larger basin 48 which can comprise further tanks, for example an emergency tank (not shown). For the treatment of dirty water from hardening, treatment and tempering plants of bars or rods 8, characterized by a limited presence of small-sized scale, nothing changes with respect to the state of the art illustrated with reference to FIG. 3. The dirty water from the casting, descaling machine, and rolling mill 2, instead incorporating larger-sized scale, is divided into two flows 53 (based on the dimensional composition of the scale, as illustrated above with reference to FIG. 2) of which the first is directed to a dredging plant as described above for the water from the plants 4 and 6, while the second reaches a collection tank 52 with a level meter 56 and a pumping system 58 for pumping the water with fine scale to further purification treatments (not shown).
[0058] FIG. 5 depicts in section a scale separation system according to the invention in comparison with a scale separation system according to the state of the art. The collection tank 62 of the dirty water can be seen on the left, located below a rolling plant 66 inside a factory building 60. A scraping conveyor 70 supported by poles 75 and driven by a motor 68 removes the sedimented scale, separating it from the dirty water coming from the rolling mill 66 and entering through the channel 64 in the tank 62. The conveyor 70 fills a scale evacuation container or means 72. The cloud on the right in FIG. 5 instead depicts the principle according to the state of the art in which there is a single, very deep pit F outside the factory building 60 and in which a device with a hoist and bucket B is used for the periodic extraction of the scale C accumulated in the pit F.
[0059] FIGS. 6 a-c depict in different views an embodiment example of a collection tank of water with scale with a scraping conveyor according to the invention. FIG. 6a is a side sectional view of a tank 62 for collecting coarse scale dirty water with a dredging system 70 in the form of a scraping conveyor. The supports 75 support a channel 73 on which the scale falls from an inlet 76 along the water level 74, and where a chain system 71 with scraping blades moved by a motor 68 and guided around two sending rollers 69 drags the scale into a container or means 72 for the evacuation of the collected scale. FIG. 6b shows the conveyor 70 with the drive motor 68 from above. Scraping blades 79 are arranged between two parallel chains 71, which scrape along the plates 77 resistant to the wear of the channel and accumulate and transport the scale. Lastly, FIG. 6c is a cross-sectional view which clearly highlights the inlet 76 which feeds the conveyor 70 and the tank 62 through a channel or a closed pipe.
[0060] FIGS. 7a-d depict different views of a scraping conveyor 170 usable in the invention and arranged in a containment tank 162 below the ground 163. The supports 175 support a channel 173 on which water with coarse scale portions enters from the inlet 176 in the form of a distribution hood. The scale sediments on the channel 173. The motor 168 drives the chains 171 supported on two sending rollers 169 in the direction of the arrow A. In FIG. 7b, the same system is seen in a plan view from above and the scraping blades 179 collecting the scale are seen, scraping on the plates 177 of the channel 173. A collection tank 167 is noted around the inlet 176 provided with a channel 165 for collecting clarified overflow water. The collection tank 167 is located in the greater containment tank 162 (not shown, but visible in FIG. 7a). In the top view in FIG. 7c, a grid 182 for operator access can be noted. The bell-shaped inlet 176 is preferably fed by two closed pipes 176a. A door for accessing the interior for maintenance work is noted on the electrical panel 180. The front view of FIG. 7d clearly shows two closed pipes 176a for transporting the dirty water which open into the distribution hood 176.
[0061] Lastly, FIG. 8 depicts in a plan view another example embodiment of the tank for collecting medium-large scale. A main containment tank 362 can be noted in which a smaller tank 367 is located for collecting the dirty water, in which there is a scraping conveyor 370 which transports the coarse scale in a special container 396. The tank 367 is provided with a drain channel with overflow 365 which can feed the laterally collocated clarified water tank 390 by means of the pipe 392. The dirty water arrives through a closed pipe 384 which is divided into a pipe 388 to feed the inlet 376 and a by-pass pipe 386 which feeds the tank 391 that serves, alternatively, as an emergency tank in case of the need for extraordinary maintenance of the automatic dredging system; from the emergency tank 391, where the scale with volume decants for some autonomous hours to allow the restoration of the dredge, the water reaches the clarified water tank 390 through an overflow. A pump station 394 serves to empty the tank 390 and to dedicate the removed water to different destinations (not shown).
[0062] The solution with two tanks with lower depth according to the invention allows to halve the necessary depth of the pits, to reduce the amount of reinforced concrete volume needed by over 1000-1500 m.sup.3, to reduce the construction time of the civil works from about six months to about one month, a reduction in energy consumption, despite the need to have two pumping stations, even up to about 100 MW/year. The dredge is reliable and easy to maintain: typically every six months the scale transport cross-beams (flights) must be turned and complete maintenance must be carried out every year: changing the chains, flights and wear plates of the inclined bottom.
[0063] The costs for excavations and reinforced concrete works are also lowered by more than one million euros. The absolute volume of savings obviously depends on the size of the plants made. Furthermore, the system according to the invention unloads the coarse scale well separated from the water.
