METHOD AND DEVICE FOR COOLING A STEEL STRIP TRAVELLING IN A CONTINUOUS LINE COOLING SECTION

Abstract

Process and device for cooling a steel strip (1) running through the cooling section (2) of a continuous line, whereby cooling is achieved by projecting the strip with an aqueous solution of formic acid with a concentration of formic acid between 0.1% and 6%, and preferably between 0.5% and 2%.

Claims

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 a projecting solution, said 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.

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 claim 1, where the solution is projected onto the steel strip by spraying.

4. Process as per claim 1, 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 solutionfrom 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%.

5. Process as per claim 4, where the liquid solution to be projected following the injection has a formic acid concentration between 0.5% and 2% by mass.

6. Process as per claim 1, 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.

7. Process as per claim 1, where the solution drawn off from the recirculation unit (13) undergoes a deoxygenation process before being projected.

8. Process as per claim 1, 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.

9. 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 claim 1.

10. Device as per claim 9, which includes a system of membranes (4) arranged to deoxygenate the solution, said membranes being swept with nitrogen on one side and with vacuum extraction on the other side.

Description

[0078] On this drawing, FIG. 1 is a schematic view of an assembly method for a cooling section as per the invention. This assembly method being in no way limiting, there may in particular be variations of the invention that only include a selection of the 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.

[0079] FIG. 1 shows a cooling section of a continuous galvanizing line comprising a first part 2 within which a steel strip 1 is running vertically from top to bottom and cooled with a liquid projection as per the invention. Nozzles 3, arranged on both sides of the strip 1 project the coolant liquid onto the strip. Upstream of these nozzles in a liquid circuit, a membrane system 4 extracts dissolved oxygen in the solution. Alternatively, a bubbling system 31 using nitrogen or another inert gas is placed in a projection tank 13 to amplify natural deoxygenation. The level of dissolved oxygen in the solution is measured in the projection tank 13 using a sensor 35. At the exit of area 2, in the direction of the strip running, there is a set 5 of liquid knives for removing the majority of run-off liquid from the strip. The set 5 of liquid knives is followed, in the direction of the strip running, by a set 6 of gas knives for removing the remaining liquid from the strip. The strip then passes through a return tank 7 where the coolant liquid projected by the nozzles 3 and set 5 of liquid knives is collected. In this tank, a second set 8 of gas knives is designed to remove any remaining liquid from the strip. The strip then passes through an area 9 where heating tubes 10 eliminate all traces of liquid on the strip. On leaving this area 9, the strip passes through an atmosphere sealing device 11 between wet areas 2, 7, 9 and areas 12 downstream in the direction of the strip running. In this atmosphere sealing device, gas injection and/or aspiration allow to improve atmosphere separation between the sections up and downstream of the sealing device.

[0080] The liquid projected onto the strip by the nozzles 3 and set 5 of liquid knives is collected in the return tank 7 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 tank is equipped with cascading compartments 32 to keep particles as much as possible in the first compartments. Electromagnets 33 placed under the tank 27, together with a system of drawers 34, can collect and remove metallic particles without draining the tank. The liquid then passes through a set 28 of external filters to eliminate residual metallic particles before being sent back to the projection tank 13 by means of a pump 30. The set 28 of external filters and the pump 30 are doubled-up so that these elements can be maintained without stopping the installation.

[0081] Supply circuits 14 including a pump 15 and a heat exchanger 16 allow to supply the nozzle rows 3 in area 2 with coolant liquid at the required pressure and temperature, using the liquid held in the projection tank 13. The supply circuits 14 include a diversion circuit 17 enabling some of the liquid pumped to tank 13 to be sent to another tank 18. Alternatively, the diversion circuit 17 is fed from the recirculation tank 27. The diversion circuit 17 is activated when some of the liquid in the cooling section needs to be renewed to maintain its performance within the desired operating range.

[0082] A vapor collector 19 is placed in area 2 above the nozzle rows 3. The vapors collected are sent to a wet scrubber 20 where they are condensed and sent to the tank 18. Exiting the scrubber, gas with the vapor removed is sent to a chimney 21.

[0083] The liquid collected in the tank 18 is sent to a processing assembly 22 where the used formic acid solution is dosed with oxygenated water to obtain a mixture of formic acid and hydroxides of iron (III) and of the steel's alloying elements. This mixture is then filtered with a filter press (not shown) to separate the formic acid from the iron (III) hydroxides, the latter being removed with conveyors 23. The re-generated formic acid is re-used and re-injected as a new solution using a circuit 24 into a tank 25. Fresh formic acid is also introduced into this tank 25 using a circuit 26.

[0084] The liquid collected in tank 25 can then be sent to the projection tank 13 using a circuit 29 with a pump (un-numbered) located in tank 25.

[0085] Of course, the invention is not limited to the examples described above and numerous adjustments can be made to these examples without moving outside the frame of the invention. Moreover, the invention's various characteristics, forms, variants and assembly methods can be linked to one another in different combinations to the extent that they remain compatible and do not exclude one another.