EP3601623B1 - Method and device for cooling a steel strip travelling in a continuous line cooling section - Google Patents

Method and device for cooling a steel strip travelling in a continuous line cooling section Download PDF

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Publication number
EP3601623B1
EP3601623B1 EP18715224.4A EP18715224A EP3601623B1 EP 3601623 B1 EP3601623 B1 EP 3601623B1 EP 18715224 A EP18715224 A EP 18715224A EP 3601623 B1 EP3601623 B1 EP 3601623B1
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EP
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Prior art keywords
solution
formic acid
liquid
advantageously
cooling
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EP18715224.4A
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German (de)
French (fr)
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EP3601623A1 (en
Inventor
Eric MAGADOUX
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Fives Stein SA
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Fives Stein SA
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Priority to PL18715224T priority Critical patent/PL3601623T3/en
Priority to RS20210951A priority patent/RS62170B1/en
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/667—Quenching devices for spray quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
    • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
    • C23G1/08—Iron or steel
    • C23G1/088—Iron or steel solutions containing organic acids
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
    • C23G3/023—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously by spraying
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G3/00—Apparatus for cleaning or pickling metallic material
    • C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
    • C23G3/027—Associated apparatus, e.g. for pretreating or after-treating
    • C23G3/028—Associated apparatus, e.g. for pretreating or after-treating for thermal or mechanical pretreatment

Definitions

  • the invention relates to the wet cooling sections of continuous lines for annealing or galvanizing steel strips.
  • galvanizing the present description relates to all dip coatings, whether they are zinc, aluminum, zinc and aluminum alloys, or any other type of coating.
  • the steel strip can typically enter at a temperature between 500 ° C and 1000 ° C, for example 800 ° C, and can exit at a temperature close to room temperature or at a temperature intermediate.
  • Gas cooling typically carried out by spraying on the steel strip a mixture of N 2 H 2 at high speed and with a high hydrogen content, makes it possible to achieve cooling speeds of up to 200 ° C / s for steel strips 1 mm thick. Since this cooling is carried out by means of a reducing gas, the steel strip is not oxidized after having passed through this type of cooling. Galvanization of the strip is then possible without any intermediate chemical step, such as pickling. However, the cooling rate being limited to 200 ° C / s, gas cooling does not make it possible to produce steels with high mechanical and metallurgical properties which require higher cooling rates.
  • An aim of the invention is to provide a method for cooling a steel strip which improves the performance of the methods according to the state of the art.
  • Another object of the invention is to provide a cooling process with greater efficiency than the processes according to the state of the art.
  • Another aim of the invention is to provide a cooling process that is less expensive than the processes according to the state of the art.
  • At least one objective of the invention is achieved with a process for cooling a steel strip traveling in a cooling section of a continuous line, comprising spraying said steel strip with an aqueous solution to spraying, said aqueous solution to be sprayed being a liquid solution or a mixture comprising a liquid and a gas, the volume proportion of liquid in the mixture being for example between 1% and 5%.
  • the formic acid concentration of said solution is between 0.1% and 6% by mass of the solution.
  • the liquid of said mixture has a formic acid concentration also of between 0.1% to 6% by mass.
  • the gas present in the mixture to be sprayed is advantageously an inert gas, for example nitrogen, or hydrogenated nitrogen.
  • Tests were carried out by the applicant on different types of steels, standard steels and steels alloyed with conventional alloying elements. such as manganese and silicon, in order to determine the ideal concentration of formic acid. These tests consist for example in placing a sample of 100 mm x 40 mm x 1 mm between two connecting pieces and bringing it rapidly to a temperature of 800 ° C, under an N 2 H 2 atmosphere at 5% H 2 and a dew point of -60 ° C, by circulating an electric current through the sample. A formic acid solution is then sprayed onto the sample for a determined period of time so that it reaches a temperature of 50 ° C.
  • the sample is reheated to a temperature of 80 ° C while it is swept with N 2 H 2 at 5% H 2 and a dew point of -60 ° C. It resulted from these tests that a formic acid solution with a concentration of between 0.1% and 6% by mass of the solution is sufficient to obtain a steel strip which can be galvanized without requiring intermediate chemical treatment.
  • the concentration of formic acid in the liquid solution is adjusted according to the content of the steel in alloying elements with high redox potential, such as aluminum, manganese or silicon. The higher it is, the more the solution will have a high concentration of formic acid.
  • the concentration of formic acid is between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4%, advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5 %, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45% and 2.5% by mass of the solution.
  • the concentration of formic acid is between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0 , 49% and 2.1% by mass of the solution. Even more advantageously, the concentration of formic acid is between 0.5% and 2% by mass of the solution.
  • the formic acid solution used to cool the strip rapidly does not require any further chemical treatment to be carried out on the strip after it has cooled. It also does not require rinsing the strip with water after rapid cooling. Only drying can be carried out. It is therefore particularly advantageous for galvanizing lines since the strip can be immersed in the zinc bath at the end of the wet cooling, after a simple drying of the strip.
  • Formic acid is the simplest of the carboxylic acids. Its chemical composition being very simple, the risk of creating complex carbonaceous deposits, adhering to the steel strip, or on the walls of the equipment, which would prevent the implementation of a galvanizing step without other intermediate treatment, is very limit. More complex acids, for example citric acid, can leave heavy carbon deposits on the belt which can prevent good galvanization.
  • Formic acid also called methanoic acid, with the chemical formula HCOOH or CH 2 O 2 , and the products of its decomposition, have very reducing properties which are ideal for the application of the invention.
  • the spray solution may take the form of a mist, a water knife, or other forms.
  • the decomposition of formic acid takes place mainly by decarboxylation while it takes place mainly by dehydration when formic acid is in gaseous form.
  • the aqueous solution to be sprayed is sprayed onto the steel strip by spraying
  • the solution to be sprayed is an aqueous solution.
  • An aqueous solution has the advantage, over other solutions, of respecting the environment better, since it does not produce toxic or harmful discharges during its use.
  • An aqueous solution is also less expensive than other solutions.
  • the aqueous solution to be sprayed can be mainly composed of demineralized water.
  • deposits on the steel strip are further limited. This solution does not lead to rejections going against the environmental standards of steel producing countries and does not entail too great an additional cost per tonne of steel produced.
  • part of the solution produced by the thermochemical reaction of the sprayed solution and of the steel strip is recovered in a recirculation unit, preferably in a recirculation tank, and the solution to be sprayed is taken in a unit of projection, preferably in a projection tank, connected to the recirculation unit. It is thus possible to reuse the planned solution, that is to say to minimize operating costs.
  • the flow rate of solution to be used for cooling the strip is between 200 and 1000 m 3 / h, and more generally around 500 m 3 / h.
  • Only a small proportion of the sprayed solution is altered by its chemical reaction with the steel strip and its thermal decomposition. In order not to achieve prohibitive consumption and production costs, it is therefore important to reuse, or even to recycle, a very large part of this solution.
  • at less than 50% of the solution is recycled. Even more advantageously, at least 60%, advantageously at least 70%, advantageously at least 80%, advantageously at least 90% of the solution is recycled.
  • At least 91%, advantageously at least 92%, advantageously at least 93%, advantageously at least 94%, advantageously at least 95%, advantageously at least 96%, advantageously at least 97%, advantageously at least 98%, advantageously at least 99% of the solution is recycled. In an even more advantageous embodiment, 100% of the solution is recycled.
  • the method according to the invention can comprise a control, continuous or periodic, for example every hour, of the solution present in the recirculation unit, which control comprises a measurement of at least one physicochemical datum of said solution. chosen from the group comprising the pH, the density and the concentration of formic acid, or a combination of these physicochemical data, and, when this measurement does not fall within a predetermined tolerance range, a predetermined volume of the solution present in the recirculation unit is withdrawn and a same predetermined volume of a formic acid solution is injected into the projection unit (13), said predetermined volume of an injected formic acid solution having an acid concentration formic such that the liquid solution to be sprayed has, after injection, an acid concentration formic is between 0.1% to 6% by mass.
  • control comprises a measurement of at least one physicochemical datum of said solution. chosen from the group comprising the pH, the density and the concentration of formic acid, or a combination of these physicochemical data, and, when this measurement does not
  • the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4%, advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5%, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45 % and 2.5% by mass.
  • the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0.49% and 2.1% by weight.
  • the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.5% and 2% by mass.
  • the predetermined volume of the solution withdrawn from the recirculation unit is determined according to the difference in the concentration of formic acid between the measured value and the minimum value of the predetermined tolerance range and the concentration of formic acid of the injected solution so that the formic acid concentration of the sprayed solution again exhibits a desired concentration.
  • the tolerance range is for example +/- 10% of the set value, whether this is for example a formic acid concentration value, a density value or a pH value.
  • the formic acid concentration and the tolerance range can be adjusted as a function of the addition elements of the steel constituting the strip and in particular its sensitivity to oxidation.
  • the concentration of formic acid and the tolerance range can be adjusted according to the configuration of the line, its operating mode and the nature of the steels treated, depending on whether these favor more or less the formation of oxides at the strip surface.
  • the formic acid concentration and the tolerance range can for example be determined by tests carried out on samples which are subjected to a thermal cycle representative of those carried out on the line.
  • the recirculation system reduces consumption of formic acid. However, the solution taken is lost. This is why the invention proposes, according to a particular embodiment, to recycle this sampled solution.
  • the solution taken is treated by oxidation with hydrogen peroxide and then filtered to extract therefrom iron III hydroxides and other alloying elements, the injected solution coming from a recirculation of the filtered solution or fresh solution.
  • the present description is aimed at a solution having a formic acid concentration of between 0.1% to 6 by mass of the solution.
  • the new solution has a concentration of formic acid of between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4% , advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5%, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45% and 2.5% by mass of the solution.
  • the new solution has a formic acid concentration of between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0.49% and 2.1% by mass of the solution. Even more advantageously, the new solution has a formic acid concentration of between 0.5% and 2% by mass of the solution.
  • the solution taken can be treated with hydrogen peroxide in order to obtain a mixture of formic acid and iron III hydroxide.
  • This mixture can then be filtered in order to separate the formic acid from the iron III hydroxides.
  • the formic acid treated and filtered can be used again and reinjected into the circuit.
  • This method has the advantage of making it possible to precisely measure the quantity of hydrogen peroxide necessary to react with the quantity of iron III hydroxide present in the solution. This not only makes it possible to control the chemical reaction so that all the hydrogen peroxide is consumed, but above all, to implement a reaction which is almost instantaneous.
  • the consumption of the system is therefore mainly hydrogen peroxide and the only discharges, apart from the gaseous discharges, are iron III hydroxides and other alloying elements of the steel strips.
  • the formic acid solution can be completely or partially recirculated.
  • Oxidation with hydrogen peroxide can restore the desired concentration of formic acid. Filtration can make it possible to extract the metal oxides, for example by a filter press. Thus, the releases only include iron III hydroxides and other metal alloying elements.
  • the dissolved oxygen present in the solution is a source of oxidation of the strip. By removing this source of oxidation, the surface condition of the strip is only better.
  • the solution taken from the recirculation unit can be treated by deoxygenation before being projected.
  • the level of dissolved oxygen remaining in the spraying solution can be less than 1 ppm.
  • Dissolved oxygen can be removed from solution through a system of nitrogen swept membranes on one side and vacuum on the other.
  • dissolved oxygen can be removed from the solution by bubbling it with nitrogen, or another neutral gas, to enhance natural deoxygenation.
  • the method can further comprise a collection of vapors which results from the projection of the solution to be projected onto the steel strip, a condensation of said collected vapors, and an injection of said condensed vapors into a fluid circuit. in which said solution to be sprayed is taken.
  • the vapor collection can be carried out by a vapor collector placed above a unit for spraying the solution to be sprayed.
  • the gas resulting from the condensation of the vapors can be sent to a chimney.
  • the condensation of the collected vapors can be carried out by a washing tower.
  • a cooling device arranged to cool a steel strip traveling in a cooling section of a continuous line comprising means arranged to implement a cooling method such as described above by spraying on said steel strip an aqueous solution, said aqueous solution being a liquid solution or a mixture of a liquid solution and a gas, the formic acid concentration of said aqueous solution being included in 0.1% and 6% by mass, the device comprising a system of membranes designed to deoxygenate said solution.
  • the means of the device according to the invention may comprise an enclosure comprising a unit for projecting a solution to be projected, preferably nozzles, arranged to project a liquid, or a mixture comprising a gas and a liquid, onto the strip of steel.
  • the membrane system designed to remove oxygen dissolved in the solution to be sprayed is placed upstream of these nozzles.
  • the means of the device may comprise, at the outlet of the enclosure, in the direction of travel of the strip, a set of liquid knives arranged to remove most of a runoff liquid present on the strip.
  • the means of the device may comprise, downstream of the set of liquid knives, a set of gas knives arranged to remove the liquid still present on the strip.
  • the means of the device may comprise, downstream of the enclosure and, where appropriate, of the set of liquid knives, and where appropriate of all or part of the set of gas knives, a return tank arranged to collect the liquid. coolant sprayed from the nozzles.
  • the return bin can be arranged so as to be located below the path of the tape at the outlet of the enclosure.
  • the return tank may include a second set of gas knives arranged to remove the liquid still present on the strip.
  • the means of the device may comprise a recirculation tank and means for transferring liquid from the return tank to the recirculation tank.
  • the liquid transfer means may comprise a filter designed to remove the metal particles present in the solution.
  • the means of the device may comprise supply circuits comprising a pump and an exchanger for supplying the projection unit.
  • the supply circuit may include a bypass circuit making it possible to send a liquid part pumped by the pump in the recirculation tank to another tank.
  • the means of the device may comprise means for actuating the bypass circuits, said means being actuated when it is necessary to renew part of the liquid contained in the cooling section in order to maintain the performance thereof within a range of predetermined operation.
  • the means of the device may comprise a system of membranes designed to deoxygenate the solution, said membranes being nitrogen swept on one side with vacuum on the other.
  • the membrane system can be positioned immediately upstream of the spray unit, the pump can be placed upstream of the membrane system, in which case the formic acid solution management circuit does not need to be isolated from oxygen sources.
  • the pump can also be placed between the diaphragm system and the spray system which allows the pressure in the diaphragms to be lowered.
  • the membrane system can be positioned on a recirculation loop on the blast pan or between the blast pan and the recirculation pan.
  • the remainder of the solution management circuit is preferably sealed against oxygen.
  • All tanks can be gas-tight and swept by an inert atmosphere, preferably nitrogen.
  • the means of the device can comprise a treatment assembly in which the solution withdrawn can be treated with hydrogen peroxide.
  • the treatment assembly can include a filter, for example a filter press, the waste of which can be removed by conveyors.
  • the treatment assembly can comprise means for injecting a solution at the outlet of the filter into the projection tank.
  • the invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be dealt with more explicitly below with regard to an exemplary embodiment described with reference to the appended drawing, but which does not 'is in no way limiting.
  • Figure 1 is a schematic view of one embodiment of a cooling section according to the invention.
  • This embodiment is in no way limiting, it is in particular possible to produce variants of the invention comprising only a selection of characteristics described below, as described or generalized, isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.
  • a cooling section of a continuous galvanizing line comprising a first part 2 in which a steel strip 1 running vertically from top to bottom is cooled by spraying a liquid according to the invention.
  • Nozzles 3, arranged on either side of the strip 1, project the cooling liquid onto the strip. Upstream of these nozzles in a liquid circuit, a membrane system 4 makes it possible to remove the oxygen dissolved in the solution.
  • bubbling 31 with nitrogen or another neutral gas is placed in a projection tank 13 to amplify the natural deoxygenation.
  • a measurement of the level of oxygen dissolved in the solution is carried out in the projection tank 13 by means of a probe 35.
  • At the outlet of part 2, in the direction of travel of the strip there is a set of knives 5.
  • the strip then passes through a return tank 7 in which the cooling liquid projected by the nozzles 3 and the assembly 5 of liquid knives is collected. In this tank, a second set 8 of gas knives is intended to remove the liquid still present on the strip.
  • the strip then passes through a part 9 equipped with heating tubes 10 making it possible to remove all traces of liquid on the strip.
  • the strip passes through an airlock 11 for separating the atmosphere between the wet parts 2, 7, 9 and parts 12 located downstream in the direction of travel of the strip. In this atmosphere separation lock, an injection and / or a suction of gas make it possible to reinforce the separation of atmospheres between the sections upstream and downstream of the lock.
  • the liquid projected onto the strip by the nozzles 3 and the assembly 5 of liquid knives is collected in the return tank 7 and then sent to the projection tank 13.
  • the liquid is transferred from the return tank 7 to a recirculation tank 27.
  • This tray is equipped with 32 compartments in cascade to maintain a maximum of particles in the first compartments.
  • Electromagnets 33 placed under the tank 27 and a system of drawers 34 make it possible to recover and remove the metal particles without having to empty the tank.
  • the liquid then passes through a set 28 of external filters in order to remove the residual metal particles before being returned to the projection tank 13 by means of a pump 30.
  • the set 28 of external filters and the pump 30 are doubled in order to ensure the maintenance of this equipment without stopping the installation.
  • Supply circuits 14 comprising a pump 15 and a heat exchanger 16 make it possible to supply the rows of nozzles 3 of part 2 with cooling liquid at the pressure and temperature required from the liquid contained in the tank 13 projection.
  • the supply circuits 14 include a bypass circuit 17 making it possible to send a liquid part pumped in the tank 13 to a tank 18.
  • the bypass circuit 17 takes its source in the recirculation tank 27.
  • the bypass circuit 17 is actuated when it is necessary to renew part of the liquid contained in the cooling section in order to maintain the performance thereof within the desired operating range.
  • a vapor collector 19 is placed in part 2 above the rows of nozzles 3.
  • the collected vapors are sent to a wet scrubber 20 in which the vapors are condensed and sent to the tank 18.
  • the gas freed of its vapors is sent to a chimney 21.
  • the liquid collected in the tank 18 is sent to a treatment unit 22 in which the spent formic acid solution is dosed with hydrogen peroxide in order to obtain a mixture of formic acid and iron III hydroxide and alloying elements of steel.
  • This mixture is then filtered through a filter press (not shown) in order to separate the formic acid from the iron III hydroxides, the latter being discharged by conveyors 23.
  • the regenerated formic acid is used again and reinjected as new solution. by means of a circuit 24 in a tank 25.
  • a supply of new formic acid is also made in this tank 25 by means of a circuit 26.
  • the liquid collected in the tank 25 can then be sent to the projection tank 13 by means of a circuit 29 comprising a pump (not numbered) placed in tray 25.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Metallurgy (AREA)
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  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
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  • General Chemical & Material Sciences (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)

Description

L'invention est relative aux sections de refroidissement humide des lignes continues de recuit ou de galvanisation de bandes d'acier. Par galvanisation, la présente description vise tous les revêtements au trempé, qu'il s'agisse de revêtements de zinc, d'aluminium, d'alliages de zinc et d'aluminium, ou tout autre type de revêtement. Dans ces sections de refroidissement, la bande d'acier peut typiquement entrer à une température comprise entre 500 °C et 1000 °C, par exemple de 800 °C, et peut en ressortir à une température proche de la température ambiante ou à une température intermédiaire.The invention relates to the wet cooling sections of continuous lines for annealing or galvanizing steel strips. By galvanizing, the present description relates to all dip coatings, whether they are zinc, aluminum, zinc and aluminum alloys, or any other type of coating. In these cooling sections, the steel strip can typically enter at a temperature between 500 ° C and 1000 ° C, for example 800 ° C, and can exit at a temperature close to room temperature or at a temperature intermediate.

Selon l'état de l'art, il existe deux types de technologies pour refroidir les bandes d'acier dans les applications de ligne continue : le refroidissement par gaz et le refroidissement humide.According to the state of the art, there are two types of technologies for cooling steel strip in continuous line applications: gas cooling and wet cooling.

Le refroidissement par gaz, typiquement réalisé par projection sur la bande d'acier d'un mélange de N2H2 à haute vitesse et à haute teneur en hydrogène, permet d'atteindre des vitesses de refroidissement allant jusqu'à 200 °C/s pour des bandes d'acier d'épaisseur 1 mm. Ce refroidissement étant réalisé au moyen d'un gaz réducteur, la bande d'acier n'est pas oxydée après être passée dans ce type de refroidissement. Une galvanisation de la bande est alors possible sans aucune étape intermédiaire à caractère chimique, telle qu'un décapage. Cependant, la vitesse de refroidissement étant limitée à 200 °C/s, le refroidissement par gaz ne permet pas de réaliser des aciers à hautes propriétés mécaniques et métallurgiques qui nécessitent des vitesses de refroidissement plus élevées.Gas cooling, typically carried out by spraying on the steel strip a mixture of N 2 H 2 at high speed and with a high hydrogen content, makes it possible to achieve cooling speeds of up to 200 ° C / s for steel strips 1 mm thick. Since this cooling is carried out by means of a reducing gas, the steel strip is not oxidized after having passed through this type of cooling. Galvanization of the strip is then possible without any intermediate chemical step, such as pickling. However, the cooling rate being limited to 200 ° C / s, gas cooling does not make it possible to produce steels with high mechanical and metallurgical properties which require higher cooling rates.

Le refroidissement humide avec de l'eau, par projection d'eau ou par projection d'un mélange d'eau et de gaz sur la bande d'acier ou par immersion de la bande d'acier dans un bac d'eau, peut permettre d'atteindre des vitesses de refroidissement de l'ordre de 1000 °C/s pour une bande d'acier d'épaisseur 1 mm. Ces vitesses de refroidissement permettent ainsi de réaliser des aciers à hautes propriétés mécaniques et métallurgiques. Cependant, avoir recours à l'eau comme fluide de refroidissement oxyde la bande et rend impossible l'utilisation de ce type de refroidissement sur une ligne de galvanisation sans une étape de décapage intermédiaire.Wet cooling with water, by spraying water or by spraying a mixture of water and gas on the steel strip or by immersing the steel strip in a water pan, can allow cooling speeds of the order of 1000 ° C / s to be achieved for a 1 mm thick steel strip. These cooling rates thus make it possible to produce steels with high mechanical and metallurgical properties. However, resorting to water as a coolant oxidizes the strip and makes it impossible to use this type of cooling on a galvanizing line without an intermediate pickling step.

La demande internationale WO2015/083047 de la déposante propose l'utilisation d'une solution aux propriétés décapantes ou non oxydantes vis-à-vis du fer et des éléments d'alliage de l'acier pour réaliser le refroidissement, par exemple une solution d'acide formique de pH inférieur à 5, permettant d'obtenir des vitesses de refroidissement de l'ordre de 1000 °C/s pour une bande d'acier d'une épaisseur d'environ 1 mm tout en n'oxydant pas la bande.International demand WO2015 / 083047 of the applicant proposes the use of a solution with pickling or non-oxidizing properties with respect to iron and the alloying elements of steel to achieve cooling, for example a formic acid solution of lower pH to 5, making it possible to obtain cooling speeds of the order of 1000 ° C./s for a steel strip with a thickness of approximately 1 mm while not oxidizing the strip.

Un but de l'invention est de proposer un procédé de refroidissement d'une bande d'acier qui améliore les performances des procédés selon l'état de l'art.An aim of the invention is to provide a method for cooling a steel strip which improves the performance of the methods according to the state of the art.

Un autre but de l'invention est de proposer un procédé de refroidissement d'une plus grande efficacité que les procédés selon l'état de l'art.Another object of the invention is to provide a cooling process with greater efficiency than the processes according to the state of the art.

Un autre but de l'invention est de proposer un procédé de refroidissement moins onéreux que les procédés selon l'état de l'art.Another aim of the invention is to provide a cooling process that is less expensive than the processes according to the state of the art.

On atteint au moins un objectif de l'invention avec un procédé de refroidissement d'une bande d'acier en défilement dans une section de refroidissement d'une ligne continue, comprenant une projection sur ladite bande d'acier d'une solution aqueuse à projeter, ladite solution aqueuse à projeter étant une solution liquide ou un mélange comprenant un liquide et un gaz, la proportion volumique de liquide dans le mélange étant par exemple comprise entre 1 % et 5 %.At least one objective of the invention is achieved with a process for cooling a steel strip traveling in a cooling section of a continuous line, comprising spraying said steel strip with an aqueous solution to spraying, said aqueous solution to be sprayed being a liquid solution or a mixture comprising a liquid and a gas, the volume proportion of liquid in the mixture being for example between 1% and 5%.

Lorsque la solution à projeter est une solution liquide, la concentration en acide formique de ladite solution est comprise en 0,1 % et 6 % en masse de la solution. Lorsqu'un mélange comprenant un liquide et un gaz est projeté, le liquide dudit mélange présente une concentration en acide formique également comprise entre 0,1 % à 6 % en masse. Le gaz présent dans le mélange à projeter est avantageusement un gaz inerte, par exemple de l'azote, ou de l'azote hydrogéné.When the solution to be sprayed is a liquid solution, the formic acid concentration of said solution is between 0.1% and 6% by mass of the solution. When a mixture comprising a liquid and a gas is sprayed, the liquid of said mixture has a formic acid concentration also of between 0.1% to 6% by mass. The gas present in the mixture to be sprayed is advantageously an inert gas, for example nitrogen, or hydrogenated nitrogen.

Des tests ont été menés par la déposante sur différents types d'aciers, des aciers standards et des aciers alliés avec des éléments d'alliage classiques tels que le manganèse et le silicium, dans le but de déterminer la concentration idéale d'acide formique. Ces tests consistent par exemple à placer un échantillon de 100 mm x 40 mm x 1 mm entre deux pièces de raccordement et à le porter rapidement à une température de 800 °C, sous une atmosphère N2H2 à 5 % de H2 et un point de rosée de -60 °C, en faisant circuler un courant électrique dans l'échantillon. Une solution d'acide formique est ensuite projetée sur l'échantillon pendant une durée déterminée pour qu'il atteigne une température de 50 °C. Dès l'arrêt de la pulvérisation de la solution acide, l'échantillon est réchauffé jusqu'à une température de 80 °C alors qu'il est balayé par du N2H2 à 5 % de H2 et un point de rosée de -60 °C. Il a résulté de ces essais qu'une solution d'acide formique de concentration comprise entre 0,1 % et 6 % en masse de la solution est suffisante pour obtenir une bande d'acier pouvant être galvanisée sans nécessiter de traitement chimique intermédiaire. La concentration en acide formique dans la solution liquide est ajustée selon la teneur de l'acier en éléments d'alliage à fort potentiel redox, tels que l'aluminium, le manganèse, ou silicium. Plus elle sera importante, et plus la solution aura une concentration élevée en acide formique.Tests were carried out by the applicant on different types of steels, standard steels and steels alloyed with conventional alloying elements. such as manganese and silicon, in order to determine the ideal concentration of formic acid. These tests consist for example in placing a sample of 100 mm x 40 mm x 1 mm between two connecting pieces and bringing it rapidly to a temperature of 800 ° C, under an N 2 H 2 atmosphere at 5% H 2 and a dew point of -60 ° C, by circulating an electric current through the sample. A formic acid solution is then sprayed onto the sample for a determined period of time so that it reaches a temperature of 50 ° C. As soon as the spraying of the acid solution is stopped, the sample is reheated to a temperature of 80 ° C while it is swept with N 2 H 2 at 5% H 2 and a dew point of -60 ° C. It resulted from these tests that a formic acid solution with a concentration of between 0.1% and 6% by mass of the solution is sufficient to obtain a steel strip which can be galvanized without requiring intermediate chemical treatment. The concentration of formic acid in the liquid solution is adjusted according to the content of the steel in alloying elements with high redox potential, such as aluminum, manganese or silicon. The higher it is, the more the solution will have a high concentration of formic acid.

Avantageusement, la concentration en acide formique est comprise entre 0,1 et 5,5 %, avantageusement entre 0,1 et 5 %, avantageusement entre 0,1 et 4,5 %, avantageusement entre 0,1 et 4 %, avantageusement entre 0,1 et 3,5 %, avantageusement entre 0,1 et 3 %, avantageusement entre 0,1 et 2,5 %, avantageusement entre 0,15 % et 2,5 %, avantageusement entre 0,2 et 2,5 %, avantageusement entre 0,3 % et 2 %, avantageusement entre 0,35 % et 2,5 %, avantageusement entre 0,4 % et 2,5 %, avantageusement entre 0,45 % et 2,5 % en masse de la solution. De manière plus avantageuse, la concentration en acide formique est comprise entre 0,46 % et 2,4 %, avantageusement entre 0,47 % et 2,3 %, avantageusement entre 0,48 % et 2,2 %, avantageusement entre 0,49 % et 2,1 % en masse de la solution. De manière encore plus avantageuse, la concentration en acide formique est comprise entre 0,5 % et 2 % en masse de la solution.Advantageously, the concentration of formic acid is between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4%, advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5 %, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45% and 2.5% by mass of the solution. More advantageously, the concentration of formic acid is between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0 , 49% and 2.1% by mass of the solution. Even more advantageously, the concentration of formic acid is between 0.5% and 2% by mass of the solution.

Avantageusement, il a été constaté que l'utilisation d'une solution d'acide formique de concentration comprise entre 0,5 % et 2 % en masse de la solution permet de traiter des nuances d'aciers peu sensibles à l'oxydation, par exemple à faible teneur en manganèse, aluminium ou silicium.Advantageously, it has been observed that the use of a solution of formic acid with a concentration of between 0.5% and 2% by mass of the solution makes it possible to treat steel grades that are not very sensitive to oxidation, for example example low in manganese, aluminum or silicon.

De manière avantageuse, la solution à projeter à un pH compris entre 1.5 et 3.Advantageously, the solution to be sprayed at a pH of between 1.5 and 3.

La solution d'acide formique utilisée pour refroidir rapidement la bande, par exemple en 1 à 3 secondes, ne nécessite pas d'effectuer d'autre traitement chimique sur la bande après son refroidissement. Elle ne nécessite pas non plus de rincer la bande avec de l'eau après le refroidissement rapide. Seul un séchage peut être réalisé. Elle est donc particulièrement avantageuse pour les lignes de galvanisation puisque la bande peut être immergée dans le bain de zinc dès la fin du refroidissement humide, après un simple séchage de la bande.The formic acid solution used to cool the strip rapidly, for example in 1 to 3 seconds, does not require any further chemical treatment to be carried out on the strip after it has cooled. It also does not require rinsing the strip with water after rapid cooling. Only drying can be carried out. It is therefore particularly advantageous for galvanizing lines since the strip can be immersed in the zinc bath at the end of the wet cooling, after a simple drying of the strip.

L'acide formique est le plus simple des acides carboxyliques. Sa composition chimique étant très simple, le risque de créer des dépôts carbonés complexes, adhérents à la bande d'acier, ou sur les parois des équipements, qui empêcheraient la mise en œuvre d'une étape de galvanisation sans autre traitement intermédiaire, est très limité. Des acides plus complexes, par exemple l'acide citrique, peuvent laisser des dépôts carbonés importants sur la bande qui peuvent empêcher une bonne galvanisation.Formic acid is the simplest of the carboxylic acids. Its chemical composition being very simple, the risk of creating complex carbonaceous deposits, adhering to the steel strip, or on the walls of the equipment, which would prevent the implementation of a galvanizing step without other intermediate treatment, is very limit. More complex acids, for example citric acid, can leave heavy carbon deposits on the belt which can prevent good galvanization.

Lors du refroidissement de la bande d'acier chaude par la solution, deux réactions chimiques indépendantes se produisent :

  • une décomposition thermique de la solution,
  • une réaction chimique entre la bande et la solution et entre la bande et les produits de la décomposition thermique.
When cooling the hot steel strip by the solution, two independent chemical reactions occur:
  • thermal decomposition of the solution,
  • a chemical reaction between the tape and the solution and between the tape and the products of thermal decomposition.

L'acide formique, également appelé acide méthanoïque, de formule chimique HCOOH ou CH2O2, et des produits de sa décomposition, possèdent des propriétés très réductrices idéales pour l'application de l'invention.Formic acid, also called methanoic acid, with the chemical formula HCOOH or CH 2 O 2 , and the products of its decomposition, have very reducing properties which are ideal for the application of the invention.

En effet, à basse température, l'acide formique se décompose par décarboxylation en eau et monoxyde de carbone selon la réaction :

        HCOOH → H2O + CO

Indeed, at low temperature, formic acid decomposes by decarboxylation into water and carbon monoxide according to the reaction:

HCOOH → H 2 O + CO

A plus haute température, à partir de 150 °C environ, l'acide formique se décompose par déshydratation en dihydrogène et en dioxyde de carbone selon la réaction :

        HCOOH → H2 + CO2

At a higher temperature, from around 150 ° C, formic acid decomposes by dehydration into dihydrogen and carbon dioxide according to the reaction:

HCOOH → H 2 + CO 2

Une fois projetée, la solution à projeter peut prendre une forme de brouillard, de couteau d'eau, ou d'autres formes.Once sprayed, the spray solution may take the form of a mist, a water knife, or other forms.

Sous forme liquide, la décomposition de l'acide formique se fait principalement par décarboxylation alors qu'elle se fait principalement par déshydratation lorsque l'acide formique est sous forme gazeuse.In liquid form, the decomposition of formic acid takes place mainly by decarboxylation while it takes place mainly by dehydration when formic acid is in gaseous form.

Selon l'invention, la solution aqueuse à projeter est projetée sur la bande d'acier par pulvérisationAccording to the invention, the aqueous solution to be sprayed is sprayed onto the steel strip by spraying

Dans les deux cas, la décomposition de l'acide formique produit des gaz réducteurs, d'une part CO, d'autre part CO2 et H2.In both cases, the decomposition of formic acid produces reducing gases, on the one hand CO, on the other hand CO 2 and H 2 .

De préférence, la solution à projeter est une solution aqueuse. Une solution aqueuse a pour avantage, par rapport à d'autres solutions, de mieux respecter l'environnement, car elle ne produit pas de rejets toxiques ou nocifs au cours de son utilisation. Une solution aqueuse est par ailleurs moins onéreuse que d'autres solutions.Preferably, the solution to be sprayed is an aqueous solution. An aqueous solution has the advantage, over other solutions, of respecting the environment better, since it does not produce toxic or harmful discharges during its use. An aqueous solution is also less expensive than other solutions.

De préférence, la solution aqueuse à projeter peut être principalement composée d'eau déminéralisée. Ainsi, les dépôts sur la bande d'acier sont encore limités. Cette solution n'entraîne pas de rejets allant à l'encontre de normes environnementales des pays producteurs d'acier et n'entraîne pas non plus un surcoût trop important de la tonne d'acier produit.Preferably, the aqueous solution to be sprayed can be mainly composed of demineralized water. Thus, deposits on the steel strip are further limited. This solution does not lead to rejections going against the environmental standards of steel producing countries and does not entail too great an additional cost per tonne of steel produced.

Avantageusement, une partie de la solution produite par la réaction thermochimique de la solution projetée et de la bande d'acier est récupérée dans une unité de recirculation, de préférence dans un bac de recirculation, et la solution à projeter est prélevée dans une unité de projection, de préférence dans un bac de projection, reliée à l'unité de recirculation. Il est ainsi possible de réutiliser la solution projetée, c'est-à-dire de minimiser les coûts d'exploitation.Advantageously, part of the solution produced by the thermochemical reaction of the sprayed solution and of the steel strip is recovered in a recirculation unit, preferably in a recirculation tank, and the solution to be sprayed is taken in a unit of projection, preferably in a projection tank, connected to the recirculation unit. It is thus possible to reuse the planned solution, that is to say to minimize operating costs.

À titre d'exemple, pour des productions d'aciers usuelles, le débit de solution à utiliser pour refroidir la bande est compris entre 200 et 1000 m3/h, et plus généralement d'environ 500 m3/h. Seule une petite proportion de la solution projetée est altérée par sa réaction chimique avec la bande d'acier et sa décomposition thermique. Afin de ne pas atteindre des consommations et des coûts de production rédhibitoires, il est donc important de réutiliser, voire de recycler une très grande partie de cette solution. Avantageusement, au moins 50 % de la solution est recyclée. De manière plus avantageuse encore, au moins 60 %, avantageusement au moins 70 %, avantageusement au moins 80 %, avantageusement au moins 90 % de la solution est recyclée. Dans un mode de réalisation plus avantageux, au moins 91 %, avantageusement au moins 92 %, avantageusement au moins 93 %, avantageusement au moins 94 %, avantageusement au moins 95 %, avantageusement au moins 96 %, avantageusement au moins 97 %, avantageusement au moins 98 %, avantageusement au moins 99 % de la solution est recyclée. Dans un mode de réalisation encore plus avantageux, 100 % de la solution est recyclée.By way of example, for standard steel productions, the flow rate of solution to be used for cooling the strip is between 200 and 1000 m 3 / h, and more generally around 500 m 3 / h. Only a small proportion of the sprayed solution is altered by its chemical reaction with the steel strip and its thermal decomposition. In order not to achieve prohibitive consumption and production costs, it is therefore important to reuse, or even to recycle, a very large part of this solution. Advantageously, at less than 50% of the solution is recycled. Even more advantageously, at least 60%, advantageously at least 70%, advantageously at least 80%, advantageously at least 90% of the solution is recycled. In a more advantageous embodiment, at least 91%, advantageously at least 92%, advantageously at least 93%, advantageously at least 94%, advantageously at least 95%, advantageously at least 96%, advantageously at least 97%, advantageously at least 98%, advantageously at least 99% of the solution is recycled. In an even more advantageous embodiment, 100% of the solution is recycled.

L'interaction de la solution d'acide formique en phase liquide ou en phase gazeuse, ainsi que celle de ses produits de décomposition en phase liquide ou en phase gazeuse, avec la bande met en œuvre des réactions dont la compréhension n'est pas aisée, notamment par leurs rapidités et leurs niveaux inhabituels de température. La cinétique des interactions entre les éléments en présence est également rendue complexe par une vaporisation de la solution au contact de la bande et le phénomène de Leindenfrost qui en résulte. Il y a ainsi des réactions chimiques entre des phases gazeuses et des phases liquides issues de la solution acide et la bande, dont la contribution à l'effet observé sur la surface de la bande par une approche expérimentale est difficile à quantifier.The interaction of the formic acid solution in the liquid phase or in the gas phase, as well as that of its decomposition products in the liquid phase or in the gas phase, with the strip implements reactions which are not easy to understand. , in particular by their speed and their unusual temperature levels. The kinetics of the interactions between the elements present are also made complex by vaporization of the solution in contact with the strip and the resulting Leindenfrost phenomenon. There are thus chemical reactions between gaseous phases and liquid phases resulting from the acid solution and the strip, the contribution of which to the effect observed on the surface of the strip by an experimental approach is difficult to quantify.

Avantageusement le procédé selon l'invention peut comprendre un contrôle, continu ou périodique, par exemple toutes les heures, de la solution présente dans l'unité de recirculation, lequel contrôle comprend une mesure d'au moins une donnée physico-chimique de ladite solution choisie dans le groupe comprenant le pH, la densité et la concentration en acide formique, ou une combinaison de ces données physico-chimique, et, lorsque cette mesure n'appartient pas à une plage de tolérance prédéterminée, un volume prédéterminé de la solution présente dans l'unité de recirculation est prélevé et un même volume prédéterminé d'une solution d'acide formique est injecté dans l'unité (13) de projection, ledit volume prédéterminé d'une solution d'acide formique injecté présentant une concentration en acide formique telle que la solution liquide à projeter présente, après injection, une concentration en acide formique est comprise entre 0,1 % à 6 % en masse. Avantageusement, la solution liquide à projeter présente, après injection, une concentration en acide formique comprise entre 0,1 et 5,5 %, avantageusement entre 0,1 et 5 %, avantageusement entre 0,1 et 4,5 %, avantageusement entre 0,1 et 4 %, avantageusement entre 0,1 et 3,5 %, avantageusement entre 0,1 et 3 %, avantageusement entre 0,1 et 2,5 %, avantageusement entre 0,15 % et 2,5 %, avantageusement entre 0,2 et 2,5 %, avantageusement entre 0,3 % et 2 %, avantageusement entre 0,35 % et 2,5 %, avantageusement entre 0,4 % et 2,5 %, avantageusement entre 0,45 % et 2,5 % en masse. De manière plus avantageuse, la solution liquide à projeter présente, après injection, une concentration en acide formique comprise entre 0,46 % et 2,4 %, avantageusement entre 0,47 % et 2,3 %, avantageusement entre 0,48 % et 2,2 %, avantageusement entre 0,49 % et 2,1 % en masse. De manière encore plus avantageuse, la solution liquide à projeter présente, après injection, une concentration en acide formique comprise entre 0,5 % et 2 % en masse. Le volume prédéterminé de la solution prélevé dans l'unité de recirculation est déterminé selon l'écart de concentration en acide formique entre la valeur mesurée et la valeur minimale de la plage de tolérance prédéterminée et la concentration en acide formique de la solution injectée de sorte que la concentration en acide formique de la solution projetée présente à nouveau une concentration souhaitée.Advantageously, the method according to the invention can comprise a control, continuous or periodic, for example every hour, of the solution present in the recirculation unit, which control comprises a measurement of at least one physicochemical datum of said solution. chosen from the group comprising the pH, the density and the concentration of formic acid, or a combination of these physicochemical data, and, when this measurement does not fall within a predetermined tolerance range, a predetermined volume of the solution present in the recirculation unit is withdrawn and a same predetermined volume of a formic acid solution is injected into the projection unit (13), said predetermined volume of an injected formic acid solution having an acid concentration formic such that the liquid solution to be sprayed has, after injection, an acid concentration formic is between 0.1% to 6% by mass. Advantageously, the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4%, advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5%, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45 % and 2.5% by mass. More advantageously, the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0.49% and 2.1% by weight. Even more advantageously, the liquid solution to be sprayed has, after injection, a formic acid concentration of between 0.5% and 2% by mass. The predetermined volume of the solution withdrawn from the recirculation unit is determined according to the difference in the concentration of formic acid between the measured value and the minimum value of the predetermined tolerance range and the concentration of formic acid of the injected solution so that the formic acid concentration of the sprayed solution again exhibits a desired concentration.

Ainsi, une mesure en continu de la performance de la solution d'acide formique permet de vérifier qu'elle se trouve dans la plage de tolérance prédéterminée. La plage de tolérance est par exemple de +/- 10 % de la valeur de consigne, que celle-ci soit par exemple une valeur de concentration en acide formique, une valeur de densité ou une valeur de pH.Thus, continuous measurement of the performance of the formic acid solution makes it possible to verify that it is within the predetermined tolerance range. The tolerance range is for example +/- 10% of the set value, whether this is for example a formic acid concentration value, a density value or a pH value.

La concentration en acide formique et la plage de tolérance peuvent être ajustées en fonction des éléments d'addition de l'acier constituant la bande et notamment sa sensibilité à l'oxydation.The formic acid concentration and the tolerance range can be adjusted as a function of the addition elements of the steel constituting the strip and in particular its sensitivity to oxidation.

La concentration en acide formique et la plage de tolérance peuvent être ajustées en fonction de la configuration de la ligne, son mode d'exploitation et la nature des aciers traités, selon que ceux-ci favorisent plus ou moins la formation d'oxydes à la surface de la bande.The concentration of formic acid and the tolerance range can be adjusted according to the configuration of the line, its operating mode and the nature of the steels treated, depending on whether these favor more or less the formation of oxides at the strip surface.

La concentration en acide formique et la plage de tolérance peuvent par exemple être déterminées par des tests réalisés sur des échantillons auxquels on fait subir un cycle thermique représentatif de ceux réalisés sur la ligne.The formic acid concentration and the tolerance range can for example be determined by tests carried out on samples which are subjected to a thermal cycle representative of those carried out on the line.

Le système de recirculation permet de réduire les consommations en acide formique. Toutefois, la solution prélevée est perdue. C'est pourquoi l'invention propose, selon un mode de réalisation particulier, de recycler cette solution prélevée.The recirculation system reduces consumption of formic acid. However, the solution taken is lost. This is why the invention proposes, according to a particular embodiment, to recycle this sampled solution.

Au contact de l'acier et des oxydes créés par les molécules d'eau, l'acide formique réagit selon la réaction :

        2CH2O2 + FeO → (CHO2)2Fe + H2O

In contact with steel and oxides created by water molecules, formic acid reacts according to the reaction:

2CH 2 O 2 + FeO → (CHO 2 ) 2 Fe + H 2 O

La solution prélevée peut alors être traitée par oxydation du (CHO2)2Fe avec du peroxyde d'hydrogène, aussi désigné sous le nom d'eau oxygénée dans la présente description, afin d'obtenir la réaction suivante :

        2(CHO2)2Fe + H2O2 + 2CH2O2 → 2(CHO2)3Fe + 2H2O

The solution taken can then be treated by oxidation of (CHO 2 ) 2 Fe with hydrogen peroxide, also referred to as hydrogen peroxide in the present description, in order to obtain the following reaction:

2 (CHO 2 ) 2 Fe + H 2 O 2 + 2CH 2 O 2 → 2 (CHO 2 ) 3 Fe + 2H 2 O

Après la formation de formiate ferrique, une seconde réaction peut être réalisée, régénérant l'acide formique et créant des hydroxydes de fer III :

        (CHO2)3Fe + 3H2O → 3CH2O2 + Fe(OH)3

After the formation of ferric formate, a second reaction can be carried out, regenerating formic acid and creating iron III hydroxides:

(CHO 2 ) 3 Fe + 3H 2 O → 3CH 2 O 2 + Fe (OH) 3

La réaction est ici présentée pour l'oxyde de fer, mais des réactions similaires se produisent avec les oxydes des éléments d'addition.The reaction is shown here for iron oxide, but similar reactions occur with addition element oxides.

Selon une particularité de l'invention, la solution prélevée est traitée par oxydation avec de l'eau oxygénée puis filtrée pour en extraire des hydroxydes de fer III et d'autres éléments d'alliage, la solution injectée provenant d'une recirculation de la solution filtrée ou d'une solution neuve. Par solution neuve, la présente description vise une solution présentant une concentration en acide formique comprise entre 0,1 % à 6 en masse de la solution. Avantageusement, la solution neuve présente une concentration en acide formique comprise entre 0,1 et 5,5 %, avantageusement entre 0,1 et 5 %, avantageusement entre 0,1 et 4,5 %, avantageusement entre 0,1 et 4 %, avantageusement entre 0,1 et 3,5 %, avantageusement entre 0,1 et 3 %, avantageusement entre 0,1 et 2,5 %, avantageusement entre 0,15 % et 2,5 %, avantageusement entre 0,2 et 2,5 %, avantageusement entre 0,3 % et 2 %, avantageusement entre 0,35 % et 2,5 %, avantageusement entre 0,4 % et 2,5 %, avantageusement entre 0,45 % et 2,5 % en masse de la solution. De manière plus avantageuse, la solution neuve présente une concentration en acide formique comprise entre 0,46 % et 2,4 %, avantageusement entre 0,47 % et 2,3 %, avantageusement entre 0,48 % et 2,2 %, avantageusement entre 0,49 % et 2,1 % en masse de la solution. De manière encore plus avantageuse, la solution neuve présente une concentration en acide formique comprise entre 0,5 % et 2 % en masse de la solution.According to a particular feature of the invention, the solution taken is treated by oxidation with hydrogen peroxide and then filtered to extract therefrom iron III hydroxides and other alloying elements, the injected solution coming from a recirculation of the filtered solution or fresh solution. By new solution, the present description is aimed at a solution having a formic acid concentration of between 0.1% to 6 by mass of the solution. Advantageously, the new solution has a concentration of formic acid of between 0.1 and 5.5%, advantageously between 0.1 and 5%, advantageously between 0.1 and 4.5%, advantageously between 0.1 and 4% , advantageously between 0.1 and 3.5%, advantageously between 0.1 and 3%, advantageously between 0.1 and 2.5%, advantageously between 0.15% and 2.5%, advantageously between 0.2 and 2.5%, advantageously between 0.3% and 2%, advantageously between 0.35% and 2.5%, advantageously between 0.4% and 2.5%, advantageously between 0.45% and 2.5% by mass of the solution. So more advantageously, the new solution has a formic acid concentration of between 0.46% and 2.4%, advantageously between 0.47% and 2.3%, advantageously between 0.48% and 2.2%, advantageously between 0.49% and 2.1% by mass of the solution. Even more advantageously, the new solution has a formic acid concentration of between 0.5% and 2% by mass of the solution.

Ainsi, la solution prélevée peut être traitée avec de l'eau oxygénée afin d'obtenir un mélange d'acide formique et d'hydroxyde de fer III. Ce mélange peut alors être filtré afin de séparer l'acide formique des hydroxydes de fer III.Thus, the solution taken can be treated with hydrogen peroxide in order to obtain a mixture of formic acid and iron III hydroxide. This mixture can then be filtered in order to separate the formic acid from the iron III hydroxides.

L'acide formique traité puis filtré peut être utilisé de nouveau et réinjecté dans le circuit. Cette méthode a pour avantage de permettre de doser précisément la quantité d'eau oxygénée nécessaire pour réagir avec la quantité d'hydroxyde de fer III présente dans la solution. Cela permet non seulement de contrôler la réaction chimique de façon à ce que toute l'eau oxygénée soit consommée, mais surtout, de mettre en œuvre une réaction qui est quasi instantanée.The formic acid treated and filtered can be used again and reinjected into the circuit. This method has the advantage of making it possible to precisely measure the quantity of hydrogen peroxide necessary to react with the quantity of iron III hydroxide present in the solution. This not only makes it possible to control the chemical reaction so that all the hydrogen peroxide is consumed, but above all, to implement a reaction which is almost instantaneous.

La consommation du système est donc principalement de l'eau oxygénée et les seuls rejets, hormis les rejets gazeux, sont les hydroxydes de fer III et d'autres éléments d'alliage des bandes en aciers.The consumption of the system is therefore mainly hydrogen peroxide and the only discharges, apart from the gaseous discharges, are iron III hydroxides and other alloying elements of the steel strips.

La solution d'acide formique peut être entièrement ou en partie recirculée.The formic acid solution can be completely or partially recirculated.

L'oxydation avec de l'eau oxygénée peut permettre de retrouver la concentration souhaitée en acide formique. La filtration peut permettre d'extraire les oxydes métalliques, par exemple par un filtre-presse. Ainsi, les rejets ne comprennent que des hydroxydes de fer III et autres éléments d'alliage métalliques.Oxidation with hydrogen peroxide can restore the desired concentration of formic acid. Filtration can make it possible to extract the metal oxides, for example by a filter press. Thus, the releases only include iron III hydroxides and other metal alloying elements.

Il est possible d'améliorer l'efficacité de cette solution, et ainsi d'améliorer l'aptitude de la bande à être galvanisée, en retirant l'oxygène dissous présent dans cette solution. En effet, l'oxygène dissous présent dans la solution est une source d'oxydation de la bande. En enlevant cette source d'oxydation, l'état de surface de la bande n'en est que meilleur.It is possible to improve the efficiency of this solution, and thus improve the ability of the strip to be galvanized, by removing the dissolved oxygen present in this solution. Indeed, the dissolved oxygen present in the solution is a source of oxidation of the strip. By removing this source of oxidation, the surface condition of the strip is only better.

Selon une caractéristique avantageuse du procédé selon l'invention, la solution prélevée dans l'unité de recirculation peut être traitée par désoxygénation avant d'être projetée.According to an advantageous characteristic of the method according to the invention, the solution taken from the recirculation unit can be treated by deoxygenation before being projected.

Avantageusement, le niveau d'oxygène dissous restant dans la solution à projeter peut être inférieur à 1 ppm.Advantageously, the level of dissolved oxygen remaining in the spraying solution can be less than 1 ppm.

L'oxygène dissous peut être retiré de la solution grâce à un système de membranes balayées d'azote d'un côté et en tirant au vide de l'autre. En variante, l'oxygène dissous peut être retiré de la solution grâce à un bullage de celle-ci à l'azote, ou un autre gaz neutre, pour amplifier la désoxygénation naturelle.Dissolved oxygen can be removed from solution through a system of nitrogen swept membranes on one side and vacuum on the other. Alternatively, dissolved oxygen can be removed from the solution by bubbling it with nitrogen, or another neutral gas, to enhance natural deoxygenation.

Dans une version avantageuse, le procédé peut en outre comporter une collecte de vapeurs qui résulte de la projection de la solution à projeter sur la bande d'acier, une condensation desdites vapeurs collectées, et une injection de desdites vapeurs condensées dans un circuit de fluide dans lequel est prélevée ladite solution à projeter.In an advantageous version, the method can further comprise a collection of vapors which results from the projection of the solution to be projected onto the steel strip, a condensation of said collected vapors, and an injection of said condensed vapors into a fluid circuit. in which said solution to be sprayed is taken.

La collecte de vapeur peut être réalisée par un collecteur de vapeurs disposé au-dessus d'une unité de projection de la solution à projeter.The vapor collection can be carried out by a vapor collector placed above a unit for spraying the solution to be sprayed.

Le gaz résultant de la condensation des vapeurs peut être envoyé vers une cheminée.The gas resulting from the condensation of the vapors can be sent to a chimney.

La condensation des vapeurs collectées peut être réalisée par une tour de lavage.The condensation of the collected vapors can be carried out by a washing tower.

Selon un deuxième aspect de l'invention, il est proposé un dispositif de refroidissement agencé pour refroidir une bande d'acier en défilement dans une section de refroidissement d'une ligne continue comprenant des moyens agencés pour mettre en œuvre un procédé de refroidissement tel que décrit précédemment précédentes par projection sur ladite bande d'acier d'une solution aqueuse, ladite solution aqueuse étant une solution liquide ou un mélange d'une solution liquide et d'un gaz, la concentration en acide formique de ladite solution aqueuse étant comprise en 0,1 % et 6 % en masse, le dispositif comportant un système de membranes agencé pour désoxygéner ladite solution.According to a second aspect of the invention, there is provided a cooling device arranged to cool a steel strip traveling in a cooling section of a continuous line comprising means arranged to implement a cooling method such as described above by spraying on said steel strip an aqueous solution, said aqueous solution being a liquid solution or a mixture of a liquid solution and a gas, the formic acid concentration of said aqueous solution being included in 0.1% and 6% by mass, the device comprising a system of membranes designed to deoxygenate said solution.

Les moyens du dispositif selon l'invention peuvent comprendre une enceinte comportant une unité de projection d'une solution à projeter, de préférence des buses, agencées pour projeter un liquide, ou un mélange comprenant un gaz et un liquide, sur la bande d'acier.The means of the device according to the invention may comprise an enclosure comprising a unit for projecting a solution to be projected, preferably nozzles, arranged to project a liquid, or a mixture comprising a gas and a liquid, onto the strip of steel.

Le système à membranes agencé pour retirer de l'oxygène dissous dans la solution à projeter est disposé en amont de ces buses.The membrane system designed to remove oxygen dissolved in the solution to be sprayed is placed upstream of these nozzles.

Les moyens du dispositif peuvent comprendre, en sortie de l'enceinte, dans le sens de défilement de la bande, un ensemble de couteaux de liquide agencé pour supprimer l'essentiel d'un liquide de ruissellement présent sur la bande.The means of the device may comprise, at the outlet of the enclosure, in the direction of travel of the strip, a set of liquid knives arranged to remove most of a runoff liquid present on the strip.

Les moyens du dispositif peuvent comprendre, en aval de l'ensemble de couteaux de liquide, un ensemble de couteaux de gaz agencé pour supprimer le liquide encore présent sur la bande.The means of the device may comprise, downstream of the set of liquid knives, a set of gas knives arranged to remove the liquid still present on the strip.

Les moyens du dispositif peuvent comprendre, en aval de l'enceinte et le cas échéant de l'ensemble de couteaux liquide, et le cas échéant de tout ou partie de l'ensemble de couteaux de gaz, un bac de renvoi agencé pour collecter le liquide de refroidissement projeté par les buses. Le bac de renvoi peut être disposé de sorte à se trouver en dessous du trajet de la bande en sortie d'enceinte.The means of the device may comprise, downstream of the enclosure and, where appropriate, of the set of liquid knives, and where appropriate of all or part of the set of gas knives, a return tank arranged to collect the liquid. coolant sprayed from the nozzles. The return bin can be arranged so as to be located below the path of the tape at the outlet of the enclosure.

Le bac de renvoi peut comprendre un second ensemble de couteaux de gaz agencé pour supprimer le liquide encore présent sur la bande.The return tank may include a second set of gas knives arranged to remove the liquid still present on the strip.

Les moyens du dispositif peuvent comprendre, un bac de recirculation et des moyens de transfert de liquide du bac de renvoi au bac de recirculation.The means of the device may comprise a recirculation tank and means for transferring liquid from the return tank to the recirculation tank.

Les moyens de transferts du liquide peuvent comprendre un filtre agencé pour éliminer les particules métalliques présentes dans la solution.The liquid transfer means may comprise a filter designed to remove the metal particles present in the solution.

Les moyens du dispositif peuvent comprendre, des circuits d'alimentation comprenant une pompe et un échangeur pour alimenter l'unité de projection.The means of the device may comprise supply circuits comprising a pump and an exchanger for supplying the projection unit.

Le circuit d'alimentation peut comprendre un circuit de dérivation permettant d'envoyer une partie liquide pompée par la pompe dans le bac de recirculation vers un autre bac.The supply circuit may include a bypass circuit making it possible to send a liquid part pumped by the pump in the recirculation tank to another tank.

Les moyens du dispositif peuvent comprendre des moyens d'actionnement des circuits de dérivation, lesdits moyens étant actionnés lorsqu'il est nécessaire de renouveler une partie du liquide contenu dans la section de refroidissement afin de maintenir les performances de celui-ci dans une plage de fonctionnement prédéterminée.The means of the device may comprise means for actuating the bypass circuits, said means being actuated when it is necessary to renew part of the liquid contained in the cooling section in order to maintain the performance thereof within a range of predetermined operation.

Les moyens du dispositif peuvent comprendre un système de membranes agencé pour désoxygéner la solution, lesdites membranes étant balayées d'azote d'un côté avec un tirage au vide de l'autre.The means of the device may comprise a system of membranes designed to deoxygenate the solution, said membranes being nitrogen swept on one side with vacuum on the other.

Le système de membranes peut être positionné immédiatement en amont de l'unité de projection, la pompe pouvant être placée en amont du système de membranes, auquel cas le circuit de gestion de la solution d'acide formique n'a pas besoin d'être isolé de sources d'oxygène.The membrane system can be positioned immediately upstream of the spray unit, the pump can be placed upstream of the membrane system, in which case the formic acid solution management circuit does not need to be isolated from oxygen sources.

La pompe peut également être placée entre le système à membranes et le système de projection ce qui permet d'abaisser la pression dans les membranes.The pump can also be placed between the diaphragm system and the spray system which allows the pressure in the diaphragms to be lowered.

Le système de membranes peut être positionné sur une boucle de recirculation sur le bac de projection ou entre le bac de projection et le bac de recirculation.The membrane system can be positioned on a recirculation loop on the blast pan or between the blast pan and the recirculation pan.

Lorsque le système de membranes est positionné au niveau d'un apport en eau déminéralisée, le reste du circuit de gestion de la solution est de préférence étanche à l'oxygène.When the membrane system is positioned at the level of a supply of demineralized water, the remainder of the solution management circuit is preferably sealed against oxygen.

Tous les bacs peuvent être étanches au gaz et balayés par une atmosphère inerte, préférablement de l'azote.All tanks can be gas-tight and swept by an inert atmosphere, preferably nitrogen.

Les moyens du dispositif peuvent comprendre un ensemble de traitement dans lequel la solution prélevée peut être traitée avec de l'eau oxygénée.The means of the device can comprise a treatment assembly in which the solution withdrawn can be treated with hydrogen peroxide.

L'ensemble de traitement peut comprendre un filtre, par exemple un filtre-presse, dont les déchets peuvent être évacués par des convoyeurs.The treatment assembly can include a filter, for example a filter press, the waste of which can be removed by conveyors.

L'ensemble de traitement peut comprendre des moyens d'injection d'une solution en sortie du filtre dans le bac de projection.The treatment assembly can comprise means for injecting a solution at the outlet of the filter into the projection tank.

L'invention consiste, mises à part les dispositions exposées ci-dessus, en un certain nombre d'autres dispositions dont il sera plus explicitement question ci-après à propos d'un exemple de réalisation décrit en référence au dessin annexé, mais qui n'est nullement limitatif.The invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be dealt with more explicitly below with regard to an exemplary embodiment described with reference to the appended drawing, but which does not 'is in no way limiting.

Sur ce dessin, la Figure 1 est une vue schématique d'un mode de réalisation d'une section de refroidissement selon l'invention. Ce mode de réalisation n'étant nullement limitatif, on pourra notamment réaliser des variantes de l'invention ne comprenant qu'une sélection de caractéristiques décrites par la suite, telles que décrites ou généralisées, isolées des autres caractéristiques décrites, si cette sélection de caractéristiques est suffisante pour conférer un avantage technique ou pour différencier l'invention par rapport à l'état de la technique.In this drawing, the Figure 1 is a schematic view of one embodiment of a cooling section according to the invention. This embodiment is in no way limiting, it is in particular possible to produce variants of the invention comprising only a selection of characteristics described below, as described or generalized, isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.

Il est représenté en Figure 1, une section de refroidissement d'une ligne continue de galvanisation comprenant une première partie 2 dans laquelle une bande d'acier 1 en défilement vertical de haut en bas est refroidie par projection d'un liquide selon l'invention. Des buses 3, disposées de part et d'autre de la bande 1, projettent le liquide de refroidissement sur la bande. En amont de ces buses dans un circuit de liquide, un système 4 à membranes permet de retirer l'oxygène dissous dans la solution. En variante, un bullage 31 à l'azote ou un autre gaz neutre est placé dans un bac 13 de projection pour amplifier la désoxygénation naturelle. Une mesure du taux d'oxygène dissous dans la solution est réalisée dans le bac 13 de projection au moyen d'une sonde 35. En sortie de la partie 2, dans le sens de défilement de la bande, se trouve un ensemble 5 de couteaux de liquide destiné à supprimer l'essentiel du liquide de ruissellement présent sur la bande. L'ensemble 5 de couteaux de liquide est suivi, dans le sens de défilement de la bande, par un ensemble 6 de couteaux de gaz destiné à supprimer le liquide encore présent sur la bande. La bande traverse ensuite un bac 7 de renvoi dans le lequel est collecté le liquide de refroidissement projeté par les buses 3 et l'ensemble 5 de couteaux de liquide. Dans ce bac, un second ensemble 8 de couteaux de gaz est destiné à supprimer le liquide encore présent sur la bande. La bande traverse ensuite une partie 9 équipée de tubes chauffants 10 permettant de supprimer toute trace de liquide sur la bande. En sortie de cette partie 9, la bande traverse un sas 11 de séparation d'atmosphère entre les parties humides 2, 7, 9 et des parties 12 situées en aval dans le sens de défilement de la bande. Dans ce sas de séparation d'atmosphère, une injection et/ou une aspiration de gaz permettent de renforcer la séparation d'atmosphères entre les sections en amont et en aval du sas.It is represented in Figure 1 , a cooling section of a continuous galvanizing line comprising a first part 2 in which a steel strip 1 running vertically from top to bottom is cooled by spraying a liquid according to the invention. Nozzles 3, arranged on either side of the strip 1, project the cooling liquid onto the strip. Upstream of these nozzles in a liquid circuit, a membrane system 4 makes it possible to remove the oxygen dissolved in the solution. As a variant, bubbling 31 with nitrogen or another neutral gas is placed in a projection tank 13 to amplify the natural deoxygenation. A measurement of the level of oxygen dissolved in the solution is carried out in the projection tank 13 by means of a probe 35. At the outlet of part 2, in the direction of travel of the strip, there is a set of knives 5. liquid intended to remove most of the runoff liquid present on the belt. The set 5 of liquid knives is followed, in the direction of travel of the band, by a set 6 of gas knives intended to remove the liquid still present on the band. The strip then passes through a return tank 7 in which the cooling liquid projected by the nozzles 3 and the assembly 5 of liquid knives is collected. In this tank, a second set 8 of gas knives is intended to remove the liquid still present on the strip. The strip then passes through a part 9 equipped with heating tubes 10 making it possible to remove all traces of liquid on the strip. On leaving this part 9, the strip passes through an airlock 11 for separating the atmosphere between the wet parts 2, 7, 9 and parts 12 located downstream in the direction of travel of the strip. In this atmosphere separation lock, an injection and / or a suction of gas make it possible to reinforce the separation of atmospheres between the sections upstream and downstream of the lock.

Le liquide projeté sur la bande par les buses 3 et l'ensemble 5 de couteaux de liquide est collecté dans le bac 7 de renvoi puis envoyé vers le bac 13 de projection. A cet effet, le liquide est transféré depuis le bac 7 de renvoi dans un bac 27 de recirculation. Ce bac est équipé de compartiments 32 en cascade pour maintenir un maximum de particules dans les premiers compartiments. Des électro-aimants 33 placés sous le bac 27 et un système de tiroirs 34 permettent de récupérer et d'évacuer les particules métalliques sans devoir vidanger le bac. Le liquide passe ensuite dans un ensemble 28 de filtres externes afin d'éliminer les particules métalliques résiduelles avant d'être renvoyé vers le bac 13 de projection au moyen d'une pompe 30. L'ensemble 28 de filtres externes et la pompe 30 sont doublés afin d'assurer la maintenance de ces équipements sans arrêter l'installation.The liquid projected onto the strip by the nozzles 3 and the assembly 5 of liquid knives is collected in the return tank 7 and then sent to the projection tank 13. For this purpose, the liquid is transferred from the return tank 7 to a recirculation tank 27. This tray is equipped with 32 compartments in cascade to maintain a maximum of particles in the first compartments. Electromagnets 33 placed under the tank 27 and a system of drawers 34 make it possible to recover and remove the metal particles without having to empty the tank. The liquid then passes through a set 28 of external filters in order to remove the residual metal particles before being returned to the projection tank 13 by means of a pump 30. The set 28 of external filters and the pump 30 are doubled in order to ensure the maintenance of this equipment without stopping the installation.

Des circuits d'alimentation 14 comprenant une pompe 15 et un échangeur de chaleur 16 permettent d'alimenter les rangées de buses 3 de la partie 2 en liquide de refroidissement à la pression et à la température requises à partir du liquide contenu dans le bac 13 de projection. Les circuits d'alimentation 14 comprennent un circuit 17 de dérivation permettant d'envoyer une partie liquide pompée dans le bac 13 vers un bac 18. En variante, le circuit de dérivation 17 prend sa source dans le bac 27 de recirculation. Le circuit 17 de dérivation est actionné lorsqu'il est nécessaire de renouveler une partie du liquide contenu dans la section de refroidissement afin de maintenir les performances de celui-ci dans la plage de fonctionnement souhaitée.Supply circuits 14 comprising a pump 15 and a heat exchanger 16 make it possible to supply the rows of nozzles 3 of part 2 with cooling liquid at the pressure and temperature required from the liquid contained in the tank 13 projection. The supply circuits 14 include a bypass circuit 17 making it possible to send a liquid part pumped in the tank 13 to a tank 18. As a variant, the bypass circuit 17 takes its source in the recirculation tank 27. The bypass circuit 17 is actuated when it is necessary to renew part of the liquid contained in the cooling section in order to maintain the performance thereof within the desired operating range.

Un collecteur 19 de vapeurs est placé dans la partie 2 au-dessus des rangées de buses 3. Les vapeurs collectées sont envoyées vers une tour de lavage (scrubber en anglais) humide 20 dans laquelle les vapeurs sont condensées et envoyées vers le bac 18. En sortie de la tour de lavage, le gaz débarrassé de ses vapeurs est envoyé vers une cheminée 21.A vapor collector 19 is placed in part 2 above the rows of nozzles 3. The collected vapors are sent to a wet scrubber 20 in which the vapors are condensed and sent to the tank 18. At the outlet of the washing tower, the gas freed of its vapors is sent to a chimney 21.

Le liquide collecté dans le bac 18 est envoyé dans un ensemble de traitement 22 dans lequel la solution usée d'acide formique est dosée avec de l'eau oxygénée afin d'obtenir un mélange d'acide formique et d'hydroxyde de fer III et d'éléments d'alliage de l'acier. Ce mélange est alors filtré par un filtre-presse (non représenté) afin de séparer l'acide formique des hydroxydes de fer III, ces derniers étant évacués par des convoyeurs 23. L'acide formique régénéré est utilisé de nouveau et réinjecté comme solution neuve au moyen d'un circuit 24 dans un bac 25. Un apport en acide formique neuf est également réalisé dans ce bac 25 au moyen d'un circuit 26.The liquid collected in the tank 18 is sent to a treatment unit 22 in which the spent formic acid solution is dosed with hydrogen peroxide in order to obtain a mixture of formic acid and iron III hydroxide and alloying elements of steel. This mixture is then filtered through a filter press (not shown) in order to separate the formic acid from the iron III hydroxides, the latter being discharged by conveyors 23. The regenerated formic acid is used again and reinjected as new solution. by means of a circuit 24 in a tank 25. A supply of new formic acid is also made in this tank 25 by means of a circuit 26.

Le liquide collecté dans le bac 25 peut alors être envoyé dans le bac 13 de projection au moyen d'un circuit 29 comportant une pompe (non numérotée) disposée dans le bac 25.The liquid collected in the tank 25 can then be sent to the projection tank 13 by means of a circuit 29 comprising a pump (not numbered) placed in tray 25.

Bien sûr, l'invention n'est pas limitée aux exemples qui viennent d'être décrits et de nombreux aménagements peuvent être apportés à ces exemples sans sortir du cadre de l'invention. De plus, les différentes caractéristiques, formes, variantes et modes de réalisation de l'invention peuvent être associés les uns avec les autres selon diverses combinaisons dans la mesure où ils ne sont pas incompatibles ou exclusifs les uns des autres.Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to these examples without departing from the scope of the invention. In addition, the different characteristics, forms, variants and embodiments of the invention can be associated with each other in various combinations as long as they are not incompatible or exclusive of each other.

Claims (9)

  1. Cooling process for a steel strip (1) running through the cooling section (2) of a continuous line, including a projection onto the said strip of an aqueous projecting solution, said aqueous solution being a liquid or a mixture of a liquid solution and a gas, characterized by the said liquid solution having a formic acid concentration of between 0.1% and 6% by mass and in that the solution is projected onto the steel strip by spraying.
  2. Process as per claim 1, where the liquid solution has a formic acid concentration of between 0.5% and 2% by mass.
  3. Process as per any of preceding claims, also including a continuous or periodic check of the solution to be projected, said check including a measurement of at least one physico-chemical datum of the said solution from the group including pH, density and formic acid concentration, or a combination of these physico-chemical data, and, when this measurement does not fall within a predetermined range of tolerance, a predetermined volume of the projected solution is drawn off and the same predetermined volume of a formic acid solution is injected into the projection unit (13), said predetermined volume of formic acid solution having a concentration of formic acid such that the liquid solution to be projected, following the injection, is of a concentration of formic acid between 0.1% and 6%.
  4. Process as per preceding claim, where the liquid solution to be projected following the injection has a formic acid concentration between 0.5% and 2% by mass.
  5. Process as per any of preceding claims, where the solution drawn off is treated through oxidation with oxygenated water, then filtered to extract the hydroxides of iron (III) and other alloying elements, the solution injected deriving from a recirculation of the filtered solution or a new solution.
  6. Process as per any of preceding claims, where the solution drawn off from the recirculation unit (13) undergoes a deoxygenation process before being projected.
  7. Process as per any of preceding claims, also including a vapors collection resulting from the projection of the solution being projected onto the steel strip, condensing said collected vapors, and injecting said condensed vapors into a fluid circuit from which the projected solution is drawn.
  8. Cooling device arranged to cool a steel strip (1) running through a cooling section (2) of a continuous line, comprising elements arranged to carry out a cooling process as per any of preceding claims by projection onto the said strip of an aqueous projecting solution, said aqueous solution being a liquid or a mixture of a liquid solution and a gas, the said liquid solution having a formic acid concentration of between 0.1% and 6% by mass and in that the solution is projected onto the steel strip by spraying.
  9. Device as per preceding claim, wherein said membranes are swept with nitrogen on one side and with vacuum extraction on the other side.
EP18715224.4A 2017-03-22 2018-03-22 Method and device for cooling a steel strip travelling in a continuous line cooling section Active EP3601623B1 (en)

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PL18715224T PL3601623T3 (en) 2017-03-22 2018-03-22 Method and device for cooling a steel strip travelling in a continuous line cooling section
RS20210951A RS62170B1 (en) 2017-03-22 2018-03-22 Method and device for cooling a steel strip travelling in a continuous line cooling section

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR1752352A FR3064279B1 (en) 2017-03-22 2017-03-22 METHOD AND DEVICE FOR COOLING A STRIP OF STEEL THROUGHOUT A COOLING SECTION OF A CONTINUOUS LINE
PCT/FR2018/050705 WO2018172713A1 (en) 2017-03-22 2018-03-22 Method and device for cooling a steel strip travelling in a continuous line cooling section

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EP3601623A1 EP3601623A1 (en) 2020-02-05
EP3601623B1 true EP3601623B1 (en) 2021-04-28

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US (1) US11162156B2 (en)
EP (1) EP3601623B1 (en)
JP (2) JP2020520409A (en)
KR (2) KR102556572B1 (en)
CN (1) CN110546283A (en)
ES (1) ES2882291T3 (en)
FR (1) FR3064279B1 (en)
PL (1) PL3601623T3 (en)
PT (1) PT3601623T (en)
RS (1) RS62170B1 (en)
WO (1) WO2018172713A1 (en)

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FR3064279B1 (en) * 2017-03-22 2020-06-26 Fives Stein METHOD AND DEVICE FOR COOLING A STRIP OF STEEL THROUGHOUT A COOLING SECTION OF A CONTINUOUS LINE
FR3104178B1 (en) 2019-12-09 2022-12-02 Fives Stein DEVICE AND METHOD FOR HEAT TREATMENT OF STEELS INCLUDING WET COOLING
CN111304424A (en) * 2020-04-27 2020-06-19 唐山曹妃甸区首燕机械有限公司 Stove nose humidifier
CN113604635B (en) * 2021-07-27 2023-05-09 中国华电科工集团有限公司 Tempering equipment and tempering method for solar heat collector manufacturing system

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KR20230065369A (en) 2023-05-11
KR20190132430A (en) 2019-11-27
ES2882291T3 (en) 2021-12-01
PL3601623T3 (en) 2021-11-02
FR3064279B1 (en) 2020-06-26
CN110546283A (en) 2019-12-06
JP2020520409A (en) 2020-07-09
JP2022163112A (en) 2022-10-25
WO2018172713A1 (en) 2018-09-27
JP7422822B2 (en) 2024-01-26
US11162156B2 (en) 2021-11-02
KR102556572B1 (en) 2023-07-18
PT3601623T (en) 2021-07-26
FR3064279A1 (en) 2018-09-28
US20200017934A1 (en) 2020-01-16
RS62170B1 (en) 2021-08-31
EP3601623A1 (en) 2020-02-05

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