The invention is related to a method to control the cooling of a flat metal product.
In steel production, but more generally in metal production, there are several plants wherein hot metal products are manufactured and must be cooled. The cooling rate of those products is of high importance to get the desired microstructure and the associated properties. It is even more true for highly alloyed steel grades for which an inadequate cooling rate may lead to breaks of the product or to poor quality and discard of the product. This may happen notably for slabs at the exit of the casting strand or to plates at the exit of the rolling mill.
There is so a need for a method which allows to control the cooling rate of metal products.
Document U.S. Pat. No. 3,957,111 describes a cooling method wherein in slabs are put in a chamber having cooling walls which receive heat released from the slabs by radiation. Water is flowing under pressure within passages within the cooling walls and removes heat from those cooling walls. The control of the water temperature allows to control the slab cooling speed. A gas, such as vapor, fills the space between the slabs and the cooling walls to further control the cooling speed of the slabs. In this method the control is difficult to handle because both gas and water flow rate must be considered. Moreover, the required equipment is a heavy one and the cooling time is long.
Document EP 0 960 670 describes a cooling method wherein a slab is dipped into a vessel of water further equipped with nozzles to spray water on the slab. The distance between the nozzles and the slab may notably be adjusted to control the cooling rate. This method requires a lot of water as the vessel as to be refilled regularly to guarantee the efficiency.
It is an object of the present invention to provide a method which allows to control the cooling rate of flat metal products which overcome the above-mentioned drawbacks.
The method according to the invention allows controlling the cooling rate of the flat metal product without detrimental impact on the quality of the metal product. For example, it neither involves detrimental chemical impact on the metal product, nor has any physical impact on its surface which could create surface defects.
This problem is solved by a method according to the invention wherein a metal product having a broad face and a temperature over 400° C. is put in contact with a fluidized bed of solid particles, the solid particles having a direction of circulation (D) and capturing the heat released by the metal product and transferring said captured heat to a transfer medium wherein:
The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:
The invention will be better understood upon reading the description which follows, given with reference to the following appended figures:
In
Those flat products are usually semi-finished products, which means that they will be subjected to further manufacturing steps before being sold. For those subsequent steps it is important that the product is exempt of defects and notably that its flatness is guaranteed. For example, if a slab has a vertical bending of few millimeters it may raise difficulties during its further rolling or even make it impossible to roll which would imply the discarding of said slab.
In
The chamber 2 contains solid particles and comprises gas injection means 4, gas being injected to fluidize the solid particles and create a fluidized bed of solid particles 5 in a bubbling regime, the solid fluidized particles circulating along a circulation direction (D). The hot flat metal products 3 are placed into the chamber 2 on support means so that their broad face 3a is parallel to the direction (D) of circulation of the fluidized particles. In a preferred embodiment, the direction (D) is vertical and the slab 3 is placed on the support along its edge 3c so that its broad face is parallel to the vertical direction. This allows to promote heat transfer efficiency but also to avoid deformation of the product. The hot flat metal products have a temperature above 400° C. when placed into the chamber 2 and are for example slabs or plates and maybe made of steel.
As illustrated in
The gas can be nitrogen or an inert gas such as argon or helium and in a preferred embodiment, air. It is preferably injected at a velocity between 5 and 30 cm/s which requires a low ventilation power and thus a reduced energy consumption. The injection flow rate of gas is controlled to match a defined cooling path of the hot metal products 3. The cooling path to be matched is first defined considering the product parameters of the metal product to be cooled. It may notably consider the chemistry of the metal product, its metallurgical state or its initial and final temperature. It can be predetermined according to abacus for example and/or it can be monitored online through temperature measurements performed on the products. This may be advantageous for metal products whose quality is impacted by cooling rate, such as steel, but also be advantageous for the plant to regulate production.
The solid particles preferentially have a thermal capacity comprised between 500 and 2000 J/Kg/K. Their density is preferentially comprised between 1400 and 4000 kg/m3. They maybe ceramic particles such as SiC, Alumina or steel slag. They may be made of glass or any other solid materials stable up to 1000° C. They preferably have a size comprised between 30 and 300 μm. These particles are preferably inert to prevent any reaction with the hot metal product 3.
The device 1 further comprises at least one heat exchanger 6 wherein a transfer medium is circulating, the heat exchanger being in contact with the fluidized bed 5. This heat exchanger may be composed, as illustrated in
In a preferred embodiment the transfer medium 10 circulating in the heat exchanger is pressurized water which, once heated by the heat released by the fluidized solid particles, is turned into steam 11. Pressurized water may have an absolute pressure between 1 and 30 Bar. Pressurized water may then be turned into steam by a flash drum 7 or any other suitable steam production equipment. Preferentially the water remains liquid inside the heat exchanger. The produced steam 11 may then be reused within the metal production plant by injection within the plant steam network, for hydrogen production for example or for RH vacuum degassers or CO2 gas separation units in the case of a steel plant. Having both steam reuse plant and metal product manufacturing plant within the same network of plant allows to improve the overall energy efficiency of said network.
The transfer medium 10 circulating in the heat exchanger may also be air or molten salts having preferably a phase change between 400 and 800° C. which allow to store the capture heat. The transfer medium 10 may comprises nanoparticles to promote heat transfer.
In a further embodiment the metal product 3 may comprise scale particles on its surfaces. By chemical or physical interaction with the solid fluidized particles, those scale particles may be removed from the metal product 3 and drop down at the bottom of the fluidized bed. In such a case the equipment 1 is provided with a scale removal device, such as a removable metallic grid to frequently remove the scale particles from the fluidized bed.
With the method according to the invention metal products may be cooled down from 900° C. to 350° C. in less than 60 minutes.
The method according to the invention may be performed at the exit of a casting plant, in a slab yard or at the exit of a rolling or levelling stand.
The method according to the invention allows a fast and homogeneous cooling of the metal product while respecting a given cooling path without detrimental impact on the product, and notably on its flatness.
It further allows to recover at least 90% of the heat released by the metal products. Moreover, the device according to the invention is quite compact and can be adapted to the available space.
A simulation was performed to show how a method according to the invention may be applied. Results of the simulation are illustrated in
The grey curve is a predefined cooling path which must be followed. This cooling path comprises three portions (a, b, c) with different cooling rates.
For this simulation we considered a slab having dimensions 12 m×1.5 m×0.2 m which corresponds approximately to a weight of 28 tons. The slab having an initial temperature of 800° C. is placed in an equipment comprising solid particles of silicon carbide.
Temperature of the fluidized bed was of 400° C. A heat exchanger as the one illustrated in
The black curve illustrates the evolution of temperature versus time of said slab. As can be seen in
A simulation was performed to evaluate the product impact in terms of deformation of a cooling method according to prior art and according to the invention.
In both scenario A and B, a slab made of a commercial low carbon steel grade and having a length L of 10 m, a width W of 1 m and a thickness T of 0.25 m, is placed in an equipment comprising solid particles of silicon carbide with a density of 320 kg/m3 and a Sauter diameter of 50 μm, those particles being fluidized in a bubbling regime thanks to the injection of air at 5 cm/s and circulating vertically, the bottom of the chamber being the horizontal direction.
A heat exchanger as the one illustrated in
For both scenarios the deformation of said slab is simulated and illustrated in
The method according to the invention allows thus to monitor the cooling path of the flat product without detrimental impact on the product and notably without involving a deformation of said product as shown in
Number | Date | Country | Kind |
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PCT/IB2018/055110 | Jul 2018 | IB | international |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2019/055882 | 7/10/2019 | WO | 00 |