The invention relates to a method for heating a semi-finished metal product to be further laminated.

In the metal production, but more specifically in steel production, semi-finished products need to be heated before undergoing further forming process. This is for example the case of steel slab before hot rolling which are heated, in a furnace, to temperatures above 1000°C prior to the hot rolling.

However, such a heating consumes a great amount of energy leading to emission of greenhouse gas. It is thus desirable to develop heating methods of semi-finished metal products reducing greenhouse gas emission.

It is a subject of this invention to provide such a heating method.

This is achieved by providing a method according to any one of the claims 1 to 9.

Other characteristics and advantages will become apparent from the following description of the invention.

The present invention relates to a method for heating at least one semi-finished metal product to be further laminated, by means of a heat exchanging device comprising a chamber containing solid particles, supporting means able to support said semi-finished metal product and a gas injector, comprising the successive steps of: i. injecting a gas into said chamber so as to form a fluidized bed, ii. inserting at least one hot metal product, having a temperature from 400°C to 1000°C, into said fluidized bed, wherein the temperature of said inserted at least one hot metal product is greater than the temperature of the fluidised bed such that said at least one hot metal product is able to transfer heat to said fluidized bed, iii. inserting said at least one semi-finished metal product to be further laminated, having a temperature from -20°C to 200°C into said fluidized bed, wherein the temperature of said at least one semi-finished metal product to be further laminated is smaller than the temperature of said fluidised bath such that said fluidized bed is able to transfer heat to said at least one semi-finished metal product to be further laminated, iv. taking out said at least one semi-finished metal product to be further laminated of said fluidized bed when the temperature of said at least one semi-finished metal product to be further laminated is less than 100°C below the temperature of said fluidised bed..

As illustrated in Figure 1, the heat exchanging device 1 comprises a chamber 2 containing solid particles 3, a support able to support at least one semi-finished steel product 4 and a gas injector 5. The chamber is preferentially able to receive more than two semi-finished metal products simultaneously.

The supporting means 6 is preferentially able to receive more than two semi-finished metal products and at least one metal product. The supporting means can be a mesh basket. The supporting means can be composed of several parts not necessarily connected one to another. For example, the supporting means can comprise several mesh baskets. Alternatively, the support means can be pillars/ stumps with guides inside the bed

The chamber may be a closed chamber with a closable opening through which a semifinished metal product may be conveyed, but it could also have an open roof or any configuration suitable for semi-finished steel products conveying.

In step i. of the method, a gas 6 is injected into said chamber 2 so as to form a fluidized bed 7 as illustrated in Figure 1. In both Figures 1A and IB, the chamber 2 comprises solid particles 3 but in Figure IB, a gas 6 is injected, by means of the gas injector 5, forming a fluidized bed 7. The solid particles have a direction of circulation.

Preferably, said solid particles of said fluidized bed are in a bubbling regime. The gas velocity to be applied to get a bubbling regime depends on several parameters like the kind of gas used, the size and density of the particles or the size of the chamber which are easily managed by a person skilled in the art.

In step ii., at least one hot metal product is inserted inside the fluidized bed. Said at least one hot metal product, at the time of its insertion, has a temperature from 400°C to 1000°C. The minimum temperature at which said hot metal product is inserted, 400°C, is greater than the temperature of said fluidised bed. It permits that said at least one hot metal product transfers heat to the fluidized bed, i.e. the particles composing the fluidized bed. Due to the heat transfer, the temperature of the hot metal product will decrease.

Preferably, said hot metal product is a semi-finished metal product. For example, said at least one hot metal product can be a slab or bloom that has been casted and has thus a temperature from 400°C to 1000°C.

Figure 2 embodies a chamber 2 comprising a fluidized bed 7 and three hot metal products 8 inserted inside said fluidized bed.

In step iii., at least one semi-finished metal product to be further laminated is inserted inside the fluidized bed. When inserted inside said fluidized bed, said at least one semi-finished metal product to be further laminated has a temperature from -20°C to 200°C.

The maximum temperature at which a hot semi-finished metal product is inserted, 200°C, is smaller than the temperature of the fluidised bed. It permits that said at least one hot metal product can thus transfer heat to the fluidized bed, i.e. the particles composing the fluidized bed.

The semi-finished metal product to be further laminated can, for example, be retrieved from a stock or a pile.

Figure 3 embodies a chamber comprising a fluidized bed, three hot metal products 8 inserted inside said fluidized bed and four semi-finished metal products to be further laminated 9 inside said fluidized bed.

The at least one hot metal product inserted in step ii. and the at least one semi-finished metal product to be further laminated inserted in step iii. are different products as represented in Figure 3.

Alternatively, at least one semi-finished metal product to be further laminated can be inserted inside the fluidized bed before inserting at least one hot metal product. Alternatively, hot metal products and semi-finished metal products to be rolled can be inserted alternatively inside said fluidized bed.

In step iv., at least one semi-finished metal product to be further laminated, that has previously been inserted inside said fluidized bed, is taken out of said fluidized bed when its temperature is less than 100°C below the temperature of said fluidised bed. For example, if the temperature of the fluidised bed is 350°C, then at least one semi-finished metal product to be further laminated, that has previously been inserted inside said fluidized bed, is taken out of said fluidized bed when its temperature is from 251°C to 350°C.

In the steps ii, iii. and iv., the metal product, hot or to be further laminated, may be conveyed inside and/ or outside the chamber by a rolling conveyor or may be placed inside the chamber by pick up means, such as cranes or any suitable pick up mean. For example, the system disclosed in WO 2021 064 451 can be used to as pick up means.

The method according to the invention permits to use the hot metal products heat to heat the semi-finished metal product to be further laminated.

Such a method permits to reduce the amount of greenhouse gas emission required to heat a semi-finished metal product before rolling.

Preferably, said metal products are made of steel. Preferably, said metal products can be of different steel grade.

Preferably, said metal products are a slab and/ or a bloom and/ or a billet and/ or a blank and/ or an ingot.

Preferably, said semi-finished metal products are slabs being from 150 to 250 mm thick, being from 600 to 1800 mm wide and being from 5000 to 15000 mm long. Preferably, said semifinished metal products are slabs weighing from 3.5 tons to 50 tons.

Preferably, said metal products, hot or to be further laminated, comprise a broad face. Even more preferably, said broad face is parallel to the direction of circulation of the solid particles of the fluidized bed.

Preferably, said gas injected in said chamber is heated. Preferably, said gas injected in said chamber has a temperature greater than 200°C, even more preferably greater than then temperature of the fluidised bed and even more preferably greater than 400°C.

Even preferably, said gas is at least partly heated by a renewable energy source and/or by recovered waste heat. The recovered waste heat can for example come from reused fumes.

Preferably, said gas injected in said chamber is air. Alternatively, the gas injected by the gas injector is preferably an inert gas, such as argon or helium, or nitrogen or a mix of gases.

Preferably, the gas is injected at a velocity from 1 to 30 cm.s ⁴ . Such a velocity range requires a low ventilation power and thus a reduced energy consumption Advantageously, said chamber does not comprise a heat exchanger in contact with the fluidized bed. Here a heat exchanger is to be understood as a device wherein a transfer medium is circulated. Such a chamber is advantageous because the heating method does not require the use of energy, outside of the energy brought by the hot semi-finished steel product and the gas, to heat the fluidised bed and thus the semi-finished steel product to be further laminated. It permits to reduce even more the amount of greenhouse gas emission required to heat a semi-finished metal product before rolling

Preferably, the solid particles have a size from 40 to 500 pm.

Preferably, the solid particles have a heat capacity comprised from 500 to 2000 J.kg'bK ¹ .

Preferably, the bulk density of the solid particles is from 1400 to 4000 kg.rn \

Preferably, the solid particles are ceramic particles. Preferably, the solid particles are made of glass or any other solid materials chemically stable up to 1000°C. For example, the solid particles can be made of SiC, Olivine, steel slag or alumina.

Preferably, the solid particles are inert. It avoids any reaction with the metallic product.

Preferably, in step ii., the at least one hot metal product has a temperature from 600°C to 1000°C, and even more preferably from 800°C to 1000°C.

Preferably, said at least one hot metal product is taken out of said fluidized bed when the temperature of said hot metal product is from the temperature of the fluidised bed to 100°C higher than the temperature of the fluidised bed. Even more preferably, said at least one hot metal product is taken out of said fluidized bed when the temperature of said hot metal product is from the temperature of the fluidised bed to 50°C higher than the temperature of the fluidised bed. For example, if the temperature of the fluidised bed is 315°C, then said at least one hot metal product is taken out of said fluidized bed when the temperature of said hot metal product is from 265°C to 315°C.

Preferably, at least a second hot metal product, having a temperature from 400°C to 1000°C, is inserted into said fluidized bed.

Said at least second hot metal product is inserted between the steps ii and iii and/or between the steps iii and iv and/ or after the step iv. Removing hot products having transferred heat to the fluidised bed permits to replace them with hotter semi-finished metal product so as to continuously have at least one source of heat inside the fluidized bed.

Preferably, in step iii., the at least one semi-finished product to be further has a temperature from -20°C to 200°C, and even more preferably from -20°C to 100°C.

Preferably, said at least one semi-finished metal product to be further laminated is taken out of said fluidized bed when the temperature of said semi-finished metal product to be further laminated is less than 50°C below the temperature of said fluidized bed.

Preferably, at least a second semi-finished metal product to be further laminated, having a temperature from -20°C to 200°C, is inserted into said fluidized bed.

Said at least second hot semi-finished metal product is inserted between the steps iii and iv and/ or after the step iv.

Removing the semi-finished metal product to be further laminated having underwent a temperature increase permits to replace them by other semi-finished metal product needing to be heated.

For example, the product temperature may be measured using contact thermocouples placed on the slab support and/ or using pyrometer when entering/ exiting of slab and/ or during performance tests, using embedded thermocouples on the slab similar to tests performed for reheating furnace thermal profiles.

Preferably, said fluidized bed is kept at a temperature from 100°C to 700°C. Even more preferably, said fluidized bed is kept at a temperature from 250°C to 600°C.

For example, the fluidized bed temperature may be measured using thermocouples placed at different points inside the fluidised bed with a small filter on the tip to avoid particles entrapment and/ or the air exiting the fluidized may also be measured to give an order of magnitude.

Preferably, said method comprises a step v., after the step iv. wherein said semi-finished metal product to be further laminated that has been heated in the fluidized bed is then heated in a reheating furnace to a temperature from 1100°C to 1400°C.

Even more preferably, said method comprises a step vi., after the step v. wherein said semifinished metal product to be further laminated is hot rolled. Alternatively, the method can use at least two heat exchanging devices, so as to have a cascade of heat exchanging device where hot semi-finished metal product goes in one way and the semi-finished metal product to be further laminated goes in the opposite direction.

A simulation has been performed to illustrate an embodiment of the claimed method.

In the simulations, the modelled fluidised bed has an average specific heat capacity of 0.6 kJ.kgAK ¹ and a mass of 200 000 kg. Moreover, in the simulation, the modelled hot metal products are hot steel slabs of 25 tons having an average specific heat capacity of 0.8085 kJ.kgAK ¹ . The modelled semi-finished metal products to be further laminated are steel slabs to be laminated of 25 tons having an average specific heat capacity of 0.519 kJ.kg bK ¹ .

The simulation, as illustrated in Figure 4, embodies a running process wherein the fluidised bed has a temperature of 310°C when a hot steel slab, having a temperature of 800°C, is inserted inside the fluidised bed. This corresponds to the step ii. of the claimed method. On Figure 4, the temperature of the fluidised bed is represented by a continuous line while the temperature of the hot steel slab is represented by a dash line.

Then a first steel slabs to be laminated, having a temperature of 25°C, and a second steel slabs to be laminated, having a temperature of 20°C, are inserted inside the fluidised bed. This corresponds to the step iii. of the claimed method. On Figure 4, the temperature of the steel slabs to be laminated are represented by a dash-dot line and a dash-dot-dot line.

Then the first steel slab to be laminated is taken out of the fluidised bed when its temperature around 15°C lower than that of the bath. This corresponds to the step iv. of the claimed method.