Heat transfer device
By introducing an oxide scale collection and removal device into the heat transfer unit, the problem of fluidized bed instability caused by oxide scale particles was solved, and efficient oxide scale management and energy utilization were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ARCELORMITTAL SA
- Filing Date
- 2023-11-27
- Publication Date
- 2026-06-09
AI Technical Summary
In existing heat transfer devices, the generation and accumulation of oxide scale particles during the cooling and reheating of semi-finished steel products leads to instability in fluidized bed operation, affecting heat transfer efficiency and the continuity of device operation.
A heat transfer device was designed, comprising a fluidized bed, a gas ejector, a heat exchanger, and an oxide scale collection and removal device. The device effectively collects and removes oxide scale through structures such as gas nozzles and grooves, ensuring the stable operation of the fluidized bed.
Effective oxide scale management was achieved, ensuring efficient operation of the heat transfer device, avoiding fluidized bed volume increase and overflow, and improving energy utilization efficiency.
Smart Images
Figure CN122180791A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to heat transfer devices. In particular, this invention relates to heat transfer devices with improved designs for cooling or reheating semi-finished steel products. Background Technology
[0002] In steel production, due to the potential delay between the manufacture of semi-finished products and their hot rolling, several plants cool steel semi-finished products, such as slabs, after production for a period of time. Therefore, the stored semi-finished products must be reheated before hot rolling. These cooling-and-reheating steps result in direct energy loss. Consequently, methods have been developed to reduce the energy loss caused by these steps.
[0003] EP3821171 discloses a heat transfer device for cooling a slab, wherein the slab is placed in a chamber and contacted with a fluidized bed of solid particles to capture the heat released by the slab and transfer it to a heat transfer medium such as water.
[0004] WO2023 / 111760 describes a method for reheating a semi-finished product such as a slab using similar equipment, wherein heat is transferred from a heat transfer medium to the slab by using a fluidized bed containing solid particles.
[0005] However, when steel semi-finished products are cooled and reheated, they produce oxide scale. When using this type of equipment, the solid particles in the fluidized bed remove the oxide scale from the product as they come into contact with it. This produces oxide scale particles that mix with the solid particles in the fluidized bed and, when present in excess, can alter the operation of the equipment. Oxide scale particles can also be generated by the thermal gradient between the steel semi-finished product and the solid particles, as well as by the action of devices (e.g., slab clamps) that place and remove semi-finished products within the fluidized bed. Summary of the Invention
[0006] This invention discloses a heat transfer device for cooling or reheating steel semi-finished products, which has an improved design that allows for good scale management.
[0007] The first object of the present invention is a heat transfer device comprising:
[0008] - Chamber 1, comprising a fluidized bed of solid particles 2, which exchange heat with the semi-finished metal product 16, the solid particles 2 circulating in a circulation direction.
[0009] - Gas injector 3, which is used to inject gas into the chamber 1.
[0010] - A heat exchanger 4 having a circulating heat transfer medium, the heat exchanger 4 being in contact with the fluidized bed, allowing the solid particles 2 to exchange heat with the heat transfer medium.
[0011] - A device for collecting oxide scale particles 5 released from the metal semi-finished product into the chamber 1.
[0012] - A device for removing oxide scale particles 5 from the chamber 1.
[0013] The heat transfer device according to the invention may also have the following optional features, either individually or in combination:
[0014] - The gas injector 3 consists of a plurality of fluidizing nozzles 6, each fluidizing nozzle 6 having an opening facing the bottom of the chamber 1.
[0015] - The apparatus for collecting oxide scale particles 5 includes means for blowing gas toward the oxide scale particles 5 to move them.
[0016] - The device for collecting oxide scale particles 5 includes a groove 8 located at the bottom of the chamber 1.
[0017] - The device for blowing gas consists of a plurality of gas nozzles 9, each gas nozzle 9 having an opening facing the groove 8.
[0018] - The device for blowing gas consists of a plurality of nozzles 14, each nozzle 14 having two openings, a first opening facing the groove 8 and a second opening facing the bottom of the chamber 1.
[0019] - The bottom of chamber 1 has a sloping shape to further promote the accumulation of the oxide scale particles 5.
[0020] - The bottom of chamber 1 includes a channel 15 to further promote the accumulation of the oxide scale particles 5.
[0021] - The bottom of chamber 1 is formed into a tiled roof shape to promote the accumulation of the oxide scale particles 5, and the device for blowing gas is located below the tiles.
[0022] - The device for removing the oxide scale particles is a tube with an endless screw 11.
[0023] A second object of the present invention is a method for removing oxide scale from a heat transfer device according to the invention, wherein oxide scale particles 5 are collected using a device for accumulating oxide scale particles and a device for removing oxide scale particles and then removed from the chamber 1 of the device, and wherein solid particles 2 from the fluidized bed that are removed together with the oxide scale particles are recycled back into the fluidized bed.
[0024] The method for removing oxide scale according to the present invention may also have the following optional features, either individually or in combination:
[0025] - By blowing gas toward the cavity 8 via a nozzle, the oxide scale particles 5 are accumulated in the cavity 8 at the bottom of the chamber 1. The nozzle has at least one opening toward the cavity 8.
[0026] - The gas blowing is pulsed.
[0027] - The gas blowing by the nozzle alternates between a first opening toward the recess and a second opening toward the bottom of the chamber. Attached Figure Description
[0028] The invention will be described in a non-limiting manner with reference to the following figures:
[0029] - Figure 1 Based on the overall view of the heat transfer device of the prior art,
[0030] - Figure 2 A view of an embodiment of the heat transfer device according to the present invention.
[0031] - Figure 3 A view of a second embodiment of the heat transfer device according to the present invention.
[0032] - Figure 4 A view of a third embodiment of the heat transfer device according to the present invention.
[0033] - Figure 5 A view of an embodiment of the chamber bottom and recess.
[0034] - Figure 6 : Overall view of the slab. Detailed Implementation
[0035] Figure 1 A heat transfer device according to the prior art is shown. The device includes a chamber 1 in which a metal semi-finished product, such as a slab 16, is placed. The chamber contains solid particles 2 and includes a gas injection device 3 that injects gas into the chamber 1 to fluidize the solid particles 2 and create a fluidized bed of solid particles 2 in a bubbling state, circulating in the circulation direction. The metal semi-finished product is placed on a support device in the chamber 1, preferably with its wide face parallel to the circulation direction of the fluidized particles. The device also includes at least one heat exchanger 4 in which a heat transfer medium circulates, the heat exchanger 4 contacting the fluidized bed.
[0036] This invention uses a similar apparatus to reheat or cool the metal semi-finished product 16. In the cooling case, the hot metal semi-finished product is immersed in a fluidized bed of solid particles 2, which are then able to capture the heat released by the hot metal semi-finished product. This allows for uniform cooling of the semi-finished product, as all parts of the semi-finished product are in contact with the fluidized solid particles 2. The solid particles 2 are kept in motion by gas ejected by means of a jetting device 3 and are in contact with a heat exchanger 4, in which they release the captured heat to a heat transfer medium circulating therein. The flow rate of the heat transfer medium within the heat exchanger 4 can be adjusted to control the cooling rate; in fact, the more medium circulating within the heat exchanger 4, the more heat is released from the solid particles 2. In the reheating case, the same mechanism is applied, but the solid particles 2 capture heat from the heat exchanger 4 and release the captured heat to the cold semi-finished product placed in the chamber 1.
[0037] The surface of hot steel is prone to oxidation. After continuous casting or during reheating, scale forms on the steel semi-finished product. Inside the unit, scale is removed from the semi-finished product due to the action of the semi-finished product flow device, the thermal gradient between the fluidized bed and the semi-finished product, or repeated contact of the fluidized solid particles 2 on the semi-finished product, and scale particles 5 are released into chamber 1 and mixed with the solid particles 2. This can cause fluidization disturbance, thereby reducing heat transfer efficiency. It can also lead to an increase in the fluidized bed volume and may cause overflow. The more scale in chamber 1, the more severe the disturbance may be. Therefore, it is important to have a heat transfer device that includes means to manage scale.
[0038] To achieve better management of oxide scale, the present invention improves upon the previous design by adding devices for collecting oxide scale particles and devices for removing oxide scale particles from chamber 1.
[0039] Figure 2 An embodiment of a heat transfer device according to the present invention is shown. It includes: a chamber 1 comprising a fluidized bed of solid particles 2 for exchanging heat with a semi-finished product, a gas ejector 3, a heat exchanger 4 having a circulating heat transfer medium, means for collecting oxide scale particles released from the flat metal product into the chamber 1, and means for removing oxide scale particles from the chamber 1.
[0040] In the preferred embodiment shown in Figure 2, the gas injector 3 comprises a plurality of fluidizing nozzles 6, each nozzle including an opening facing the bottom of the chamber 1. The fluidizing nozzles 6 allow for the formation of a fluidized bed.
[0041] Several fluidization states exist. Fluidization is the operation of converting solid particles 2 into a fluid state by suspending them in a gas or liquid. The behavior of the particles varies depending on the fluid velocity. In the gas-solid system, which is one of the inventions, as the flow rate increases beyond the minimum fluidization, significant instabilities accompanied by gas bubbling and channeling are observed. At higher velocities, agitation becomes more intense, and the movement of the solids becomes more violent. Furthermore, the bed does not expand much beyond its volume at the minimum fluidization stage. At this stage, the fluidized bed is in a bubbling state, which is the state required by the invention to achieve good circulation of the solid particles 2 and a uniform temperature in the fluidized bed. The gas velocity applied to obtain a given state depends on several parameters, such as the type of gas used, the size and density of the particles, or the size of the chamber 1. This can be easily managed by those skilled in the art.
[0042] The fluidizing nozzles 6 are preferably arranged in several rows in the chamber 1. This ensures that all solid particles 2 are in a bubbling state, so that the fluidized bed occupies the entire volume of the chamber 1. All fluidizing nozzles 6 are connected to the main gas path 7.
[0043] The gas can be nitrogen or an inert gas such as argon or helium, and in a preferred embodiment, it is air. It is preferably injected at a velocity of 1 cm / s to 30 cm / s, which requires lower ventilation power, thus reducing energy consumption. The gas flow rate is preferably monitored by the main valve 12.
[0044] To manage the oxide scale entering the fluidized bed, the method used in this invention is to remove the oxide scale from chamber 1. However, since the oxide scale particles 5 are released into the fluidized bed from various parts of the flat product, direct removal of the oxide scale can be very difficult. Therefore, the method includes a first step of collecting the oxide scale particles 5. Therefore, the heat transfer device according to the invention includes means for collecting the oxide scale particles 5.
[0045] exist Figure 2 In the illustrated embodiment, the device for collecting oxide scale particles 5 includes a groove 8 located at the bottom of chamber 1. Since the density of oxide scale particles 5 is higher than that of solid particles 2, they naturally fall to the bottom of chamber 1. This invention utilizes this fact, and the groove 8 allows the oxide scale to be collected naturally therein. The groove 8 is preferably located on one side of chamber 1, such as... Figure 2 As shown.
[0046] The apparatus for collecting oxide scale particles preferably includes a means for blowing gas toward the oxide scale to move it. Since not all oxide scale will naturally fall into the groove 8, this means for blowing gas allows the oxide scale that has fallen to the bottom of the chamber 1 but is outside the groove 8 to be moved. They are moved toward the groove 8 so that they fall into the groove 8, so that most of the oxide scale particles 5 are collected in the groove 8.
[0047] like Figure 2 As shown, the device for blowing gas preferably consists of a plurality of gas nozzles 9, each nozzle 9 having an opening facing the groove 8. They are preferably arranged in several rows within the chamber 1. The gas nozzles 9 are connected to an auxiliary gas path 10, which is different from the main gas path 7. Gas blowing is preferably pulsed, as it allows for better optimization of the blowing process. Gas nozzles 9 farther from the groove 8 move the oxide scale below nozzles 9 closer to the groove 8, and so on. Pulsed gas prevents the use of gas when no oxide scale needs to be moved, thus preventing gas waste. Each gas nozzle 9 is connected to the auxiliary gas path 10 and controlled by an auxiliary valve 13. The blowing of gas should push the oxide scale particles 5 towards the groove 8 without disturbing the fluidization of the solid particles 2.
[0048] Another embodiment of the device for blowing gas is a plurality of nozzles 14, each nozzle 14 having two openings, a first opening facing the recess 8 and a second opening facing the bottom of the chamber 1. All nozzles 14 are connected to the main gas passage 7 and have a means of alternating between the first opening for blowing gas to move the oxide scale and the second opening for fluidizing the solid particles 2. Preferably, some fluidizing nozzles 6 are replaced by nozzles 14 with two openings. This configuration is shown in... Figure 3 middle.
[0049] To facilitate the collection of oxide scale particles 5, the bottom of chamber 1 preferably has a sloping shape facing the groove 8, such as... Figure 2 As shown. This allows gravity to be used to facilitate the blowing of oxide scale particles 5 into grooves 8.
[0050] Figure 5 A preferred embodiment of the bottom of chamber 1 is shown. It forms a plurality of channels 15 pointing towards grooves 8. The channels 15 allow for initial collection of oxide scale particles 5 as they fall naturally into the channels 15. The means for blowing gas, in this case a gas nozzle 9, is positioned above the channels 15. This configuration allows for better overall collection because it ensures that most of the oxide scale particles 5 are collected into the grooves 8 and do not permanently accumulate elsewhere.
[0051] Another embodiment has a tiled roof-like structure at the bottom of chamber 1, with a device for blowing gas located below the tiles. This is shown in... Figure 4 middle.
[0052] After collecting the oxide scale particles 5, they need to be removed from chamber 1. In a preferred embodiment, a terminal screw 11 is used to continuously remove the oxide scale particles 5 from groove 8 as they fall into groove 8, such as... Figure 2 As shown. However, any device used for removing oxide scale particles 5 from chamber 1 can be used.
[0053] Since the apparatus used to remove the oxide scale particles 5 from chamber 1 may also remove solid particles 2 from the fluidized bed, as is the case with the endless screw 11, these solid particles 2 removed along with the oxide scale particles 5 are recycled back into the fluidized bed to avoid reducing the volume of the fluidized bed and thus reducing the efficiency of the heat transfer device. In a preferred embodiment, a magnetic separator is used to separate the solid particles 2 and oxide scale particles 5 removed from the chamber.
[0054] The apparatus for collecting oxide scale particles and the apparatus for removing oxide scale particles can also be used to remove any unwanted particles from the fluidized bed, as long as such unwanted particles have a density greater than the solid particles 2 of the fluidized bed.
[0055] Figure 6 The diagram shows a slab 16, an example of a semi-finished product. The slab 16 has a parallelepiped shape and includes a top 16a and a bottom wide face, two narrow faces 16b, and two edges 16c. The wide faces define the slab's width W and length L, where the width W is typically 700 mm to 2500 mm, the length L is 5000 mm to 15000 mm, and the thickness T is typically 150 mm to 350 mm. More generally, a flat product can be defined as a parallelepiped where the smallest dimension (e.g., thickness T) is negligible compared to other dimensions (e.g., length L), for example, the smallest dimension is at least 15 times smaller than the largest dimension. The wide faces of the parallelepiped are those excluding the smallest dimension. Other examples of semi-finished products are billets, large square billets, shaped billets, or coils.
[0056] The solid particles 2 preferably have a heat capacity of 500 J / kg / K to 2000 J / kg / K. Their density is preferably 1400 kg / m³ to 4000 kg / m³. They can be ceramic particles, such as SiC, alumina, olivine, or steel slag. They can be made of glass or any other solid material stable up to 1400°C. They preferably have a size of 30 µm to 500 µm. These particles are preferably inert to prevent any reaction with the slab 16.
[0057] The heat exchanger 4 may consist of: a first conduit through which a heat transfer medium is circulated to carry it to the heat exchanger 4; a second conduit through which the heat transfer medium is recovered; and a third conduit connecting the first and second conduits and passing through the fluidized bed of chamber 1 and solid particles 2.
[0058] The heat transfer medium circulating in heat exchanger 4 is preferably pressurized water, which, once heated by the heat released by the fluidized solid particles 2, becomes steam. The pressurized water can have an absolute pressure between 1 bar and 30 bar. The pressurized water can then be converted into steam via a flash tank or any other suitable steam production equipment. Preferably, the water remains liquid inside heat exchanger 4. The generated steam can then be reused within the metal production plant by injecting it into the plant's steam network, for example, for hydrogen production, or, in the case of a steel plant, for RH vacuum degassing machines or CO2 gas separation units. Having both a steam reuse plant and a metal product manufacturing plant within the same plant network allows for improved overall energy efficiency of the network.
[0059] The heat transfer medium circulating in heat exchanger 4 can also be air or molten salt, which preferably undergoes a phase change between 400°C and 800°C, allowing the trapped heat to be stored. The heat transfer medium may contain nanoparticles to facilitate heat transfer.
[0060] The heat stored during the cooling step can be reused during the reheating step. Two or more devices according to the invention can be used together for the cooling and reheating steps.
[0061] The heat transfer device according to the invention allows for good scale management, thereby allowing continuous operation without reducing its efficiency.
Claims
1. A heat transfer device, comprising: - A chamber (1) comprising a fluidized bed of solid particles (2) that exchange heat with a metal semi-finished product (16) and the solid particles (2) circulating in the circulation direction; - Gas injector (3), which is used to inject gas into the chamber (1); - A heat exchanger (4) having a circulating heat transfer medium, the heat exchanger (4) being in contact with the fluidized bed, such that the solid particles (2) exchange heat with the heat transfer medium; - A device for collecting oxide scale particles (5) released from the metal semi-finished product into the chamber (1); - A device for removing oxide scale particles (5) from the chamber (1).
2. The heat transfer device according to claim 1, wherein the gas injector (3) comprises a plurality of fluidizing nozzles (6), the fluidizing nozzles (6) including openings toward the bottom of the chamber (1).
3. The heat transfer device according to claim 1 or 2, wherein the means for collecting the oxide scale particles (5) includes means for blowing gas toward the oxide scale particles (5) to move them.
4. The heat transfer device according to any one of claims 1 to 3, wherein the means for collecting oxide scale particles (5) includes a groove (8) located at the bottom of the chamber (1).
5. The heat transfer device according to claim 4, wherein the device for blowing gas comprises a plurality of gas nozzles (9), each gas nozzle (9) having an opening facing the groove (8).
6. The heat transfer device according to claim 4, wherein the device for blowing gas comprises a plurality of nozzles (14) having two openings, the first opening facing the groove (8) and the second opening facing the bottom of the chamber (1).
7. The heat transfer device according to any one of claims 4 to 6, wherein the bottom of the chamber (1) has a sloping shape to further promote the accumulation of the oxide scale particles (5).
8. The heat transfer device according to claim 7, wherein the bottom of the chamber (1) includes a channel (15) to further promote the accumulation of the oxide scale particles (5).
9. The heat transfer device according to claim 7, wherein the bottom of the chamber (1) is formed in the shape of a tile roof to promote the accumulation of the oxide scale particles (5), and wherein the device for blowing gas is located below the tiles.
10. The heat transfer device according to any one of the preceding claims, wherein the means for removing the oxide scale particles is a tube with an endless screw (11).
11. A method for removing oxide scale from a heat transfer device according to any one of the preceding claims, wherein oxide scale particles (5) are collected using a device for accumulating oxide scale particles and a device for removing oxide scale particles, and then the oxide scale particles (5) are removed from a chamber (1) of the device, and wherein solid particles (2) from a fluidized bed removed together with the oxide scale particles are recycled back to the fluidized bed.
12. The method for removing oxide scale according to claim 11, wherein the oxide scale particles (5) are accumulated in the groove (8) at the bottom of the chamber (1) by blowing gas toward the groove (8) via a nozzle, the nozzle having at least one opening facing the groove (8).
13. The method for removing oxide scale according to claim 12, wherein the gas blowing is pulsed.
14. The method for removing oxide scale according to claim 13, wherein the gas blowing performed by the nozzle alternates between a first opening facing the groove (8) and a second opening facing the bottom of the chamber (1).