Patent Application
20250010345
The present invention relates to a steel product processing plant, in particular comprising at least one rolling mill provided with a plurality of stands arranged in series and adapted 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. Said plant, in particular said lines are further provided with:
Steel product cleaning systems are, for example, water jet descaling machines.
The steel product processing process includes several steps in which the product is at a high temperature, for example during casting and subsequent rolling. This metal in contact with the environment undergoes an oxidation process which causes the formation of scale, a generic name with which iron oxide compounds are identified in the sector which compromise the quality aspect of the product if they are rolled (so-called rolled-in scale), and which lead to a decrease in the weight of the finished product. Therefore, in the production of hot rolled articles it is necessary to remove such scale from the metal surface in some specific steps, for example before or during the rolling. Descaling machines are used for this purpose, which generally remove the scale with high pressure water jets on the metal surface, possibly with the aid of mechanical devices. A descaling machine is generally formed by one or more spraying bars with nozzles which send the pressurized water jets across the material, so as to cause the detachment of the scale. The scale resulting from the rolling and continuous casting processes is also removed in the product cooling steps by direct cooling, by means of which a set of nozzles spray water and/or air on the metal product so as to decrease the temperature thereof (for example in the secondary cooling step of casting, or between the rolling stands). It is evident that this type of process employs considerable amounts of water (in a plant for long products, for example, it employs over 1,000 m3/h, while a plant for flat products easily comes to use 10 times as much), which is mixed with clumps of scale possibly dirty with lubricating oil. To collect the mixtures of water and scale which are formed during the product processing steps, deep scale pits are currently created, which in addition to the collection of this mixed sludge, allow the subsequent process of separation from the water of the coarse, heavy scale by decanting or sedimentation by gravity and the return of the water, still however containing the fine and light scale, to the water treatment plant (WTP) of the plant.
The muddy waters are then all conveyed together to the so-called scale pit, in which the extraction of the sedimented coarse, heavy scale is performed by means of, for example, automatic buckets.
To allow the separation of the coarse/heavy scale, the scale pit is sized to have a hydraulic load equal to ˜20 m3/m2/h. The scale pit which collects all the water from the direct descaling/cooling circuit requires high depths. In this regard, there is a need to have basins or tanks made, usually circular with a very deep inverted conical trunk bottom, typically 12-15 metres deep with respect to the ground floor 0 on which the steel plant stands. Very high investments are incurred to make such scale pits: civil works costs, long construction times, construction site problems (piling, dewatering, interference, extension of the construction sites, etc.), maintenance, installation of machines, etc. Furthermore, this sludge recovery and separation system is not selective, thus several steps are necessary to properly separate water and scale.
JP S62 137112 A describes the collection of muddy water in a single pit, while Reitmeyer and Diem (Reitmeyer, D. et al., “Neue Hochleistungs-Zunderseparation im Kühlwasser-Recycling bei den Badischen Stahlwerken/New High-Capacity Scale Separation for Cooling Water Recycling at Badische Stahlwerke”, Stahl und Eisen vol. 125, n. 10, 2005, 39-44) describe a subdivision of the muddy water flows of a rolling mill according to the size of the scale in order to consider the needs of the subsequent separation in hydrocyclones.
The object of the invention is to overcome the aforesaid drawbacks and to propose a steel product processing plant with steel product direct cooling or cleaning systems and a sludge mixture separation system comprising at least water and sludge deriving from the direct cooling and/or cleaning, which reduces the expense of civil works, which is applicable to various configurations of rolling and/or continuous casting plants and which is simple to maintain. Another object of the invention is to provide a relative separation process of mixtures comprising at least water and scale deriving from the above cleaning and/or direct cooling. Further objects or advantages of the invention will become apparent from the following disclosure.
In a first aspect of the invention, the object is achieved by a steel product processing plant according to the first claim and as defined above in which the separation system comprises:
If the pits are placed below ground level, their depth essentially corresponds to the excavation depth necessary to receive them starting from ground level.
In a preferred embodiment of the invention, each pit comprises:
The overall depth is to be understood as the sum of the depth of the channel or the channel system and the tank, or as the excavation depth necessary to receive the set of elements listed. In the case of the first pit, the channel can have, for example, a depth of 3.50 m and the tank of 2.50 m, resulting in a total pit depth of 6.00 m, while in the case of the second pit the channel has a depth of 3.50 m and the relative tank of 3 m, resulting in a total depth of 6.50 m. If portions of the channel or channel system and the related collection tank are at least partially on the same level, the overall depth is understood as the sum of the depth of the channel/channel system and the depth of the tank minus the depth of the portions on the same level.
The division of the sole classic pit into two or more distinct pits has made it possible to reduce their overall depth since the mixtures can be divided between all these pits.
The rolling stands comprise relative direct cooling systems. The mixtures deriving from the casting, from the descaling machine and/or from the direct cooling of the rolling mill are therefore divided into at least two flows, a first deriving advantageously from the secondary cooling of the casting, the descaling machine and the first stands of the rolling mill, all components which generally produce large, heavy scale, separable by means of the dredging device, and a second flow deriving from subsequent stands which gradually produce increasingly fine scale, which is small and light; the second flow can be pumped from the relative collection tank of the mixtures directly to a longitudinal clarifier, while in the prior art all the mixtures of the entire plant were conveyed together in a single pit and it was then necessary to separate the heavy, large scale from the entire volume of the collected mixtures, while in the invention it is sufficient to carry out this separation only for a portion of the mixtures, and precisely from the first flow. Both systems, classic and new, can have a hydraulic load equal to 20 m3/m2/h.
Preferably, the channels or channel systems of the pits do not exceed 4 m in depth.
In a very advantageous embodiment of the invention, the first pit comprises a dredging device, in particular a mechanical scraping conveyor. Advantageously, the dredging device is arranged in the tank and the mixture, in particular coming from casting and first part of the rolling mill, comprising at least water and large-size scale collected from the channel or channel system of the first pit, is directed directly to the dredging device. Preferably, as mentioned, the dredging device is a scraping conveyor which comprises along its longitudinal extension a channel with wear-resistant plates within which run, guided by relative rollers of which at least one motorized, in relative circuits, two parallel chains between which scraping blades (scraping beams) are transversely fixed parallel to each other so that they are capable of scraping the mixtures, i.e., the sludge of water and coarse scale along said channel plates, accumulating it and advancing the decanted scale in the conveyor channel. Advantageously, near the entrance of the mixtures into the tank, located above the conveyor, the chains of the same circuit are further spaced apart from each other by a further sending roller. Alternatively, belt dredging systems with a series of buckets can be used which are adapted to collect and transport the scale accumulated on the bottom of the tank.
With such a dredging device, in particular a scraping conveyor, the scale is continuously and automatically removed, and it is thus not necessary to periodically perform removals with the bucket.
The invention is particularly applicable to hot rolling mills for long products, fast finishing blocks (FFB), mini-mills, heavy products (HSeM, Heavy Section Mill) and systems consisting of continuous casting and rolling in general, but is also designable for rolling mills and casting machines for flat products adapted for the production of strips (Hot Strip Mills, HSM).
In an embodiment of the invention it is included that the first pit has inclined side walls, in particular with an inclination between 45 and 75°, preferably between 55 and 65°, more preferably about 60°. With an inclination of 60° and the same dredging system, it is possible to double the decantation surface with respect to 90° walls.
Preferably, the channel or the channel system comprises a distribution hood which forms the entrance into said at least one collection tank of the mixtures of the first pit. This thus avoids preferential routes with the accumulation of scale in difficult areas, hindering the correct dredging process. For example, the hood is positioned in the centre of the tank.
In a preferred embodiment of the invention, said at least one tank for collecting the mixtures of said first pit is provided in the upper edge along the perimeter, preferably along the entire perimeter, with a plurality of clarified water overflow channels which feed a further clarified water collection tank included for such a purpose in said first pit, preferably next to said first collection tank of the mixtures of water and scale. This expedient helps to avoid preferential routes with possible leakage of suspended solids into the clarified water.
These expedients make it possible to increase the processable flow rate of the dredging system, for example from 250 m3/h to 500 m3/h for rolling mills and from 300 m3/h to 600 m3/h for continuous casting machines.
Further embodiments of the invention, described below, ensure, by virtue of the elimination of sections which can cause difficulties during use, better management and maintenance.
In this regard, the plant according to the invention further comprises an emergency tank, preferably arranged on the side of said at least one collection tank of the mixtures of said first pit, or on the side of the dredging device. Preferably, the emergency tank is made of reinforced concrete. The emergency tank allows to remove a tank with an emergency basket on the entrance of the dredging device. This avoids the problems of removing the lid with water and scale which continues to arrive and the difficulties of reinserting the emergency basket due to the residual scale in the tank, etc. For example, the emergency tank is capable of collecting scale for a work day, thus allowing special maintenance that may be required by the equipment. Furthermore, advantageously, the entrance to said at least one collection tank of the mixtures of said first pit is made, preferably as a closed pipe, with an emergency by-pass adapted to feed said emergency tank. The use of a closed pipe instead of an open channel and a lid on an emergency basket avoids splashes of water and scale with consequent dirt and accumulations of scale.
With respect to a clarified water collection tank under the mixture collection tank and therefore under the dredging device, a tank, preferably in reinforced concrete, can be included at the side of the mixture collection tank. This facilitates periodic cleaning, no longer necessary in a confined and narrow space.
In a particularly preferred embodiment of the invention, the pits are at least partially arranged below said at least one steel product direct cooling or cleaning system, or of said other system adapted to spray water on the product being processed. In particular, it is advantageous to include the channel or channel system at least partially below these systems. The tanks themselves, as part of the channel or channel system, can be located to the side of said systems, but advantageously always below ground and lower than the channel or channel system. The reduced depth of the pits, preferably between 5 and 7 m, makes it possible to advantageously locate them inside the factory building which houses the steel product processing plant and not outside the factory building, as often envisaged by the state of the art.
A second aspect of the invention relates to a process for separating mixtures comprising water and scale deriving from a direct cooling and/or descaling of steel products comprising the following steps:
The water and scale mixtures described in the disclosure of the invention are mixtures comprising water and scale, thus they contain at least water and scale, but can contain other components, such as lubrication oils or greases.
Another aspect of the invention includes that the steel product processing plant also comprises only a continuous casting machine with unloading of the casting products directly in a downstream plate, this machine being provided with direct cooling, wherein the separation unit comprises only a pit with depth <10 m, with a water/scale mixture collection tank with a dredging device and an overflow system for separating the clarified water.
The features and advantages disclosed for one aspect of the invention may be transferred mutatis mutandis to other aspects of the invention.
The industrial applicability is obvious from the moment wherein it is possible, with the same good results in the water's purification from scale, a considerable saving of CAPEX (abbreviation of CAPital EXpenditure). The subdivision of the flows, grouping on one side the mixtures with coarse scale, for example from casting, from the descaling machine and from the first flattening stands, and on the other side the remaining water containing gradually finer scale, allows to have to separate the coarse scale only from a portion of the dirty water and allows to pump and pass the water with finer scale through pipes. In fact, the rapid sedimentation of large, heavy scale is envisaged in the first pit along with its extraction, dredging and unloading in a dedicated container, perhaps directly on a truck or a transport vehicle. The overflow water from the tank of the first pit can be pumped into the water treatment plant for final purification, for example in a longitudinal clarifier, where medium particles are removed by sedimentation and oil and grease by an oil skimmer. The second flow can instead be collected in a rather small tank (or several tanks), of circular shape, for example, used to avoid the deposit of materials and with submerged pumps which remove the collected mixtures to the water treatment plant. This avoids the unwanted deposit of scale, and in any case, for any inconvenience, the pumping stations can wash the partially cleaned water in the channel during the re-stranding/maintenance steps. The scale coming from a continuous casting machine can be grouped in the scale of the first flow mentioned above (i.e., deriving from the first stands of a rolling mill), indeed the scale is even heavier, especially in the straightening section of the products, and the aforesaid system can be adopted, in particular the pit with dredging, but since the water is almost free of oil (normally used in rolling), it can be sent directly after the separation of the scale to the collection tank of the clarifier overflow for the final filtration.
The key concept of plant waste water treatment is to have a plurality of water recovery pits from the direct cooling of a rolling mill, which are less deep with respect to the background art, which envisages only one very deep pit with great expense in plant/construction terms.
The division into several pits is carried out starting in particular from the assumption that during the rolling, following the heating in the furnace, the oxide which is created on the product, also known as scale, decreases in size and quantity as the rolling continues. This means that in the early steps there is a high production of oxidation scale, which is very small towards the end. Therefore, the inventors consider it inadvisable to mix the dirty water with this type of scale size and treat it all together to clean it, but recommend dividing the water according to the different scale sizes and such as to be able to treat them specifically, creating simpler and less expensive plants.
Said objects and advantages will be further highlighted in the disclosure of preferred examples of embodiments of the invention given by way of non-limiting example.
Variant and further features of the invention are the subject matter of the dependent claims. The description of preferred embodiment examples of the plant and of the process according to the invention is given, by way of example and not of limitation, with reference to the attached drawings. In particular, unless otherwise specified, the number, shape, size and materials of the plant and of the individual components may vary, and equivalent elements may be applied without deviating from the inventive concept.
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.
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).
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.
Lastly,
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 m3, 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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021000029639 | Nov 2021 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/061247 | 11/22/2022 | WO |
