Patent Application
20250187066
The present invention refers to a steel plant for the production of long products, in particular bars, rods, profiles, wires and the like, or for flat products, in particular strips, sheets and the like comprising:
Steel plants for the production of flat and long products generally provide, upstream of the rolling line, a continuous casting machine or a plate for loading material to be rolled, followed by a descaler, an emergency shear, preferably a reheating furnace, a further emergency cutting device, optionally another descaler, roughing cages, another shear, a possible further reheating furnace, for example an induction one, an intensive or accelerated cooling device and a further descaler, pre-finishing and/or finishing cages, a laminar cooling device, a further shear for cutting to size the rolled product and then winders for the products to be wound, or discharge plates for the bars or a coil-shaping head and a conveyor belt for the rod. Along the line, coolings are necessary, for example for the product, the parts of the devices used, the rolling rolls, etc., which can be made by direct coolings or indirect coolings.
Direct cooling is for example applied in rolling and in pre-finishing of a metal product and can involve detaching oxides from the product, called scale, which in general at this phase of processing has large dimensions, other direct coolings are carried out in the finishing and quenching of the rolled product, and the detachment in water of a finer scale takes place, being the temperatures lower and a larger scale detachment having already occurred upstream. The cooling waters accumulate under the machinery and drag the scale coming from the rolling, reheatings and accessory processings, thus assuming different characteristics in terms of quantity/concentration and dimensions of the contained scale. Scale concentrations in the waters also depend on the volume of waters used and the quantity of scale produced. For example, in flat products, which use a lot of water (in the order of magnitude of several thousand m3/h), the average scale concentration will be lower than in the rolling plants for long products, which on the contrary use less water for the different cooling phases.
Usually cooling plants in a steel plant for the production of flat products, such as direct quenching or the accelerated cooling in the rolling mills or laminar cooling have a dedicated water treatment plant (Water Treatment Plant, WTP) in order to treat and cool the water, and return it to the cooling systems. This circuit is separate from the main circuit that feeds the rest of the line. The demand for water from such cooling systems is generally intermittent depending on the cooling phases that the product has to undergo. The accelerated cooling circuit and the side spray units produce less dirty waters, while the rolling mills, the descalers and the reheating furnaces produce greater quantities of scale in the water.
By long products are generally meant rods, wires, bars and profiles. The cast products or those loaded via the plate are rolled and undergo high reductions and intermediate reheatings, leading, during direct cooling in the different phases, to the detachment of high quantities of scale compared to flat products, which, using a lot of water, have a greater dilution capacity.
In steel plants for the production of long products, usually, the flows coming from quench cooling systems are sent to the WTP to treat and cool the water and this takes place in parallel with the water flows coming from the rolling mills. This means that WTP must treat the sum of the flow rates coming from quenching, rolling and finishing and therefore must be oversized in terms of the size of the treatment units.
The WTP of any steel plant mainly requires the following treatment/cooling sections: collecting tanks, pumping stations and pump room, sand filters and relative sludge treatment, cooling towers, civil works and relative buildings, electrical and automation devices and plants, pipings, and in specific cases units for dosing chemicals.
The steel plants referred to above provide for separate water treatment circuits (production of flat products) for machinery producing more or less dirty waters to adapt the treatment to the needs or scale content or a circuit that treats together (production of long products) all the waters deriving from the machinery, regardless of whether these machineries produce waters that are lean or rich in scales, this results in high costs and extensive and complex circuits and in the need for a large number of cooling water treatment devices.
The expense in terms of devices needed to treat the waters is considerable, on the one hand for the large quantities of waters to be filtered and purified, on the other hand to have to provide for more than one circuit to treat the waters differently charged with scales, an expense that results in a significant increase in the capacity and/or number of water treatment devices. This need has a negative impact on OPEX and CAPEX values. OPEX is the operating expense, which stands for Operating Expense, i.e. the cost necessary to manage a product, business or system. Its counterpart, CAPEX (which stands for Capital Expenditure), is the cost to install, develop or provide durable assets for the product or the system.
The invention aims to overcome the above drawbacks and to propose a steel plant as initially defined which is less complex, which simplifies the direct cooling water treatment circuit(s), which requires less water and reduces the apparatus necessary to separate the scale from the cooling waters. Further objects or advantages of the invention will result from the following description.
In a first aspect of the invention, the object is achieved by a steel plant as initially defined which is characterized in that
The connection in series reduces the quantity of water needed to cool all machinery as the second group of machinery uses the same cooling water exiting the first group of machinery. This makes it possible to reduce the water treatment devices as the volume of the cooling water has been reduced and is to be cleaned only after leaving the second group of machinery. The inventors have therefore, deviating from the traditional way, identified the opportunity to send the cooling water exiting the first group of machinery directly, i.e. preferably without particular purification and cooling, in the second group of machinery, a connection in series made possible also by the fact that the flow rates of both groups of machinery are comparable. This applies to the production of long products and to the production of flat products.
The optimization proposed by the invention therefore consists in the possibility of directly reusing the water discharged from the sections of the machinery of the first group, for example quenching machinery, in other users, for example rolling mills. These downstream users require a certain water quality and an inlet temperature that the water exiting the first group of machinery satisfies.
In a preferred embodiment of the invention, between said direct cooling systems of said first group and said direct cooling systems of said second group at least one collecting tank is provided along the water flow. The collecting tank allows to compensate for any hydraulic imbalances in the management in series of the two groups of machinery and to take over in the moments of machine downtime or flow rates that are not always completely compatible between the two groups and can be filled not only by the first group of machinery, but also by other sources.
Advantageously, the cleaning of the cooling waters exiting the second group of machinery takes place in the water treatment circuit, in particular realized as a single circuit, which comprises a succession of water treatment devices. In this regard, the cooling water treatment circuit arranged downstream of said second group of machinery comprises a succession of water treatment devices, in turn, comprising, in the following order, at least one tank, preferably at least two tanks for separating scale and/or oil, said tank(s) preferably being divided into several chambers separated by means of one or more weirs, at least one filter unit and at least one cooling tower provided with at least one tank for collecting cooled water and connected to said direct cooling systems of said first group of machinery and/or, if present, to said at least one collecting tank. The cooled water collecting tank can also feed any descaler or continuous casting machinery and relative sprayers present in the steel plant or other users.
The number of the single elements of the circuit may vary, such as the number of the cooling towers, and additional water treatment devices may be integrated. For separating scale, different devices can be envisaged in the relative tanks, such as buckets or magnetic devices that collect the settled scale, scrapers or dredging conveyors, lamellar filters. These systems, as well as the suitable oil separators, are well known to the person skilled in the art. The tank for separating scale and oil is usually oblong in extension. It is also conceivable to replace mentioned elements with others, for example other types of tanks for separating scale.
A first tank could be a simple scale pit, and a second tank an oblong clarifier with two chambers.
In a preferred embodiment of the invention, said steel plant is a plant for the production of long products, in particular bars, rods, profiles, wires and the like wherein the first group comprises at least one piece of machinery selected from the group consisting of quenching units and tempering units and that said second group comprises at least one piece of machinery selected from the group consisting of fast finishing blocks, rolling mills and reheating furnaces. In the case of steel plants for the production of long products it has proved to be preferable that said collecting tank also feeds the at least one scale and/or oil separation tank, in particular a second scale and/or oil separation tank, preferably the most downstream chamber of the tank. This can be useful for managing the hydraulic conditions of the system and avoids scale and oil removal processes where not necessary.
In another preferred embodiment of the invention, said steel plant is a plant for the production of flat products, in particular strips, sheets and the like and said first group of machinery comprises at least one piece of machinery selected from the group consisting of accelerated cooling units, side sweep spray units, direct quenching units, laminar cooling units and that said second group of machinery comprises at least one piece of machinery selected from the group consisting of hot rolling mills and reheating furnaces.
Advantageously, descalers and continuous casting machinery are not directly fed by the first group, but only from clean waters in respective water treatment devices after passing the second group of machinery.
Advantageously, the machinery of said second group are therefore suitable for use in the direct cooling system, without affecting the quality of the product that produce, during use, the waters coming from said cooling systems of said first group of machinery that therefore have characteristics suitable to be able to feed the second group of machinery. Suitable characteristics concern the total suspended solids content, the inlet temperature and the oil and grease content.
A second aspect of the invention refers to a process for treating direct cooling waters of a steel plant for the production of long products, in particular bars, rods, profiles, wires and the like, or for flat products, in particular strips, sheets and the like, comprising the following steps:
To define whether a machinery belongs to the first or second group of machinery, the content of total suspended solids expressed in mg/l or ppm of the cooling water exiting the machinery is advantageously assessed. Preferably, the scale lean waters comprises total suspended solids ≤70 mg/l, preferably from 20 to 60 mg/l, in the case of a steel plant for the production of long products, and ≤50 mg/l, preferably from 5 to 20 mg/l, in the case of a steel plant for the production of flat products. The total suspended solids content is preferably determined according to the Standard Method (Standard Methods) SM 2540 D (Determination of Total Suspended Solids) accessible for example on the website www.standardmethods.org. The standard deviation to be considered in determining the values is 2.8 mg/l.
Preferably, the waters to be transferred to the machinery of the second group contain for both types of steel plants only traces of oils and/or greases therefore the relative machinery of the first group preferably produce waters with only traces of oils and/or greases, quantifiable in ≤2 mg/l. The oils and greases content is preferably determined according to the standard method (Standard Methods) SM 5520 B (Determination of Oil and Grease) accessible for example on the website www.standardmethods.org. The standard deviation to be considered in determining the values is 0.2 mg/l.
These values are not to be understood as an aim to be achieved by the individual machinery, but they are values that occur during normal use of the machinery and allow their division into a first and a second group of machinery according to the invention.
Advantageously, the waters exiting the first group of machinery have a ΔT with respect to the inlet temperature required by the second group of machinery which corresponds to ≤8° C. in the case of a steel plant for the production of long products and a ΔT of ≤5° C. in the case of a steel plant for the production of flat products. For long products, between a classic plant and the plant according to the invention the inlet temperature in the second group of machinery can increase for example from 35° C. to 43° C.; while increases from 30° C. to 33.5° C. are for example observed for flat products.
The above shown values are respected by the machinery that make up the first group. Therefore, there are no particular contraindications in reusing the cooling water used in them in the users that make up the second group of machinery. The solution according to the invention, optimized with respect to the state of the art, allows to reduce the flow rates of the cooling towers by about 40%, to almost halve the number of sand filters or self-cleaning filters and to reduce by about 20% the size of any sludge thickeners used in connection with the filter units. In addition, reductions in the powers of the pumps, piping lengths/diameters, number of pumps, size of the tanks and pump room are feasible.
Compared to the state of the art, where the waters used in the second group of machinery are purified and cooled waters, the water for the users within the second group, such as rolling mills, in terms of TSS (for long products on average from 30 to 70 mg/l) compared to the quality of the circulating water in the classic solution (containing TSS <50 mg/l) may have a lower quality which is however acceptable. In a preferred embodiment of the invention, this phenomenon can be mitigated by applying more wear and clogging resistant spray nozzles to the cages of the rolling mill. The increase in water temperature for the users of the rolling mill (for example 43° C.) compared to the temperature of the circulating water in the classical solution (for example 35° C.) in the production of long products, can be mitigated, in case of wet bulb values below certain thresholds, by cooling the water to suitable temperatures. For example: when the wet bulb is <26° C., it is possible to cool the water to or below 30° C., consequently the water temperature for the users of the rolling mill will have increased only to 38° C., in the case of the chosen example. The greater complexity in the hydraulic balance of the management in series is manageable with a control unit that controls the various flow rates. The savings in terms of CAPEX and OPEX are important, too. In the case of the invention, relatively to a steel plant for the production of long products, CAPEX sees savings in relation to the electro-mechanical equipment, civil works, installation activities. Also in terms of OPEX savings can be noted for energy, chemicals and water/sludge conditioning.
The invention has significantly optimized the water treatment plant for the production of long and flat products in terms of CAPEX and OPEX, reusing the water discharged from the first group of machinery (e.g. from accelerated cooling and direct quenching) directly into the direct cooling users in the second group of machinery (e.g. rolling mills), and this without any dedicated WTP for each group of machinery. The principle is applicable to many types of plants: to rolling mills of various kind, for the production of thin strips, sheets, rods, narrow strips, profiles, wires, etc. ranging within a large range of diameters, thicknesses, widths, types of section, etc.; to various types of direct cooling, such as accelerated cooling, laminar cooling; and to quenching units and tempering units of various kind.
In the case of the production of flat products, the users downstream of the first group of machinery are a little more demanding in terms of TSS and ΔT, but the machinery of the first group of machinery, such as accelerated cooling and quenching, still respect the characteristics required by usually supplying waters with a TSS between 5 and 20 ppm, only traces of oil and grease and a ΔT between 2 and 5° C. The envisaged temperature increase at the first group of machinery is generally already compensated upstream, in the WTP, without any effort considering the wet bulb temperature at the plant site.
The optimization proposed by the invention makes certain advantageous modifications to the plant: the cooling towers for the first group of machinery are eliminated, the same applies to sand filters and sludge treatment, dosing units for chemical treatments are no longer needed, while the pumping station of the classic solution can be used, but the pump room WTP is no longer needed and the collecting tanks have been resized.
Obviously, even in the case of the production of flat products, the quality of water for the users of the second group of machinery compared to the classic solution is worse in terms of TSS, but it is still an acceptable quality. The greater complexity in the hydraulic balance of the two circuits in series can be controlled by a relative control unit of the plant, and the increase in temperature at the first group of machinery is not problematic considering a suitable wet bulb temperature in the plant.
The features and advantages described for one aspect of the invention may be transferred mutatis mutandis to the other aspects of the invention.
The industrial applicability is obvious from the moment that the following situation occurs: The connection in series of the two groups of machinery manages to achieve considerable savings in terms of CAPEX and OPEX, to considerably lower the volume of cooling water required for direct cooling of all users and to reduce the space required by up to 35%. Having also reduced the number of water treatment devices, civil works and necessary maintenance are reduced, too.
The objects and advantages will be further highlighted in the description of preferred embodiment examples of the invention given by way of non-limiting example only.
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 non-limiting example, with reference to the attached drawings. In particular, unless otherwise specified, the number, shape, size and materials of the individual components of the plant may vary, and equivalent elements may be applied without deviating from the inventive concept.
In all drawings, level gauges are designated with I, pumps with p and agitators with a. The flow rates indicated below are just an example and vary with the size of the plant. The water treatment circuit includes a second part dedicated to the treatment of water deriving from hot rolling mills for the production of strips at high pressure with flow rates around 3,700 m3/h 36 or at low pressure (with flow rates about 240 m3/h) 38 and descalers (flow rate of about 350 m3/h) 40 and reheating furnaces (flow rate of about 30 m3/h) 42 which all feed a tank 44 with a first chamber 44a and a second chamber 44b, and precisely feed the first chamber 44a provided with a crane with a bucket 46 and with an oil separator 48, the surface water (freed from oil and heavy scale) overflows into the chamber 44b, from where it is pumped into a circuit again in the chamber 14a in order to be cleaned a second time or, passing through a two-chamber clarifier 76 with oil and scale separation devices (not represented) in a filter 50 which feeds a cooling tower 52 that collects the cooled water in a single-chamber tank 54. The tank can also be fed with make-up water 56 or from a tank 58 for storing and dosing conditioning chemicals, while the tank 44 can also be fed with waters coming from a sludge thickener 60. The filter 50 is manageable with backwash air 62 and washing water 64, drain water 66 is drained. The water of the tank 54 can feed the filter 50 for its backwash with clean water, the dirty water producers 38, 40 and 42 and, with a pump and line dedicated to take into consideration the large flow rate, the user 36; this line provides a blowdown system 68, also available from the line exiting from the tank 14 to feed the cooling water users 10 and 12 or the tank 34. The tank 44 can be fed by a polyelectrolyte source 70 or by a tank 72.
The plant for the production of flat products also includes a water treatment plant for water deriving from indirect cooling, waters that due to the nature of the indirect treatment (for example from reheating furnaces (flow rates about 400 m3/h)), hot strip rolling mills (flow rates about 1,300 m3/h) and electric motors (with flow rates around 215 m3/h) do not require special purifications and can be transferred directly to a cooling tower (equipped with a water make-up service well known to the person skilled in the art, where necessary with filters and brine pits). These indirect cooling waters are not covered by the invention.
For the different dirty water producers or cooling water users, two distinct cooling circuits C1 and C2 can be noted, while the invention combines the circuits into a single circuit C putting in series the two groups of producers (10, 12 and 36, 38, 40 and 42), as represented in
The drainage water 60 after an appropriate treatment can return to the tank 76, this treatment involves a collection in a tank from which it is conveyed in a sludge thickener from which it is always introduced into the tank 76 or through a passage through a further tank it continues in a drainage system to eliminate the sludge that must be taken to the landfill. Additives can be added to the thickener or to the drainage or dehydration system (dewatering unit). This part of the plant is well known to the expert and is not illustrated in more detail. The quality, the flow rate and the temperature of the water exiting the users 10 and 12 is therefore suitable for distribution among the users 36, 38, 40 and 42.
The tanks 13, 34 and 44 and their connections allow compensating for any flow rate imbalances in feeding the users. The inlet temperatures in the users 36, 38, 40 and 42 are little influenced by the passage from the classic version to the invention.
The flow rates of the users 86, 88, 90 and 92 are by way of example respectively 700-1300 m3/h, 600 m3/h, about 270 m3/h and 600 m3/h and the inlet temperature Ti is about 35° C.
The example of the state of the art (
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022000003797 | Mar 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/051836 | 2/28/2023 | WO |
