Note: Descriptions are shown in the official language in which they were submitted.
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HEATING METHOD OF A METALLIC PRODUCT
The invention relates to a method for heating a semi-finished steel product.
In the steel production, but more generally in metal production, steel
products need to be
reheated before undergoing forming process or heat treatment. This is for
example the case of
billets or bloom before hot rolling which are generally reheated, from room
temperature to
temperature above 1000 C, in a furnace.
However, such a reheating consumes a great amount of energy leading to
emission of
greenhouse gas. It is thus desirable to develop heating methods of semi-
finished product that
reduce the process impact on the environment.
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
10.
Other characteristics and advantages will become apparent from the following
description
of the invention.
The present invention relates to a method for heating a semi-finished steel
product 2, being
a slab, a billet or a bloom, comprising
- a pre-heating step, performed in a pre-heating device comprising a
chamber 3 containing
solid particles 4, a heat exchanger 5, a support 6 able to support said semi-
finished steel
product, a gas injector 7, and
- a heating step, performed in a furnace, wherein said semi-finished steel
product is heated
to a temperature from 1000 to 1400 C,
- a hot rolling step, after the heating step, wherein said semi-finished
steel product is hot
rolled,
wherein,
said pre-heating step comprises the steps of:
i. injecting a gas 12 into said first chamber 3 so as to form a first
fluidized bed 8,
ii. heating said fluidized bed 8 by means of said heat exchanger 5,
iii. putting said semi-finished steel product 2, into said fluidized bed 8
such that said
semi-finish steel product 2 is supported by said support 6 and such that said
fluidized bed 8 is able to transfer heat to said semi-finished steel product
2,
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iv. taking out said semi-finished steel product 2 when its temperature is from
200 C
to 1000 C,
and said heating step comprises the step of heating said semi-finished steel
product to a
temperature from 1100 to 1400 C.
Figure 1 illustrated an embodiment of a device wherein the claimed method can
be
performed.
Figure 2 illustrated an embodiment of multiple pre-heating device where the
pre-heating is
performed by at least two pre-heating devices.
Preferably, said semi-finished steel product, being a slab or a billet or a
bloom is to be
laminated.
This device comprises a chamber 3 containing solid particles 4, a heat
exchanger 5, a
support able to support a semi-finished steel product 6 and a gas injector 7.
The chamber is
preferentially able to receive more than one semi-finished steel product. The
support 6 is
preferentially able to receive more than one semi-finished steel product. The
support can be a mesh
basket. Preferably, in step iii., the semi-finished steel product lies on said
support.
The semi-finished steel product may be conveyed inside and 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. Even more preferably, said support is not used move said semi-
finished product
inside or outside the chamber 3. Dissociating the support system and the
transport system, e.g.
pick-up means, permits to reduce the number of transport system in case
several semi-finished
steel products are pre-heated simultaneously.
The chamber may be a closed chamber with a closable opening through which a
semi-
finished steel product maybe 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 pre-heating step, a gas is injected into said chamber 3 so
as to form a
fluidized bed 8. This injection is done by means of the gas injector 7.
Preferably, said gas injected in said chamber is heated. Even more preferably,
said gas has
a temperature from 200 to 1000 C. It permits to reduce the energy required to
heat the fluidized
bed at the preferred temperature range. Even more preferably, said gas is at
least partly heated by
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a renewable energy source and/or by recovered waste heat. The recovered waste
heat can for
example come from reused fumes.
Even more preferably, said gas injected in said chamber is heated by means of
heating
means powered in part or all by CO2 neutral electricity.
CO2 neutral electricity includes notably electricity from renewable source
which is defined
as energy that is collected from renewable resources, which are naturally
replenished on a human
timescale, including sources like sunlight, wind, rain, tides, waves, and
geothermal heat. In some
embodiments, the use of electricity coming from nuclear sources can be used as
it is not emitting
CO2 to be produced.
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., the fluidized bed is heated by means of the heat exchanger. The
heat exchanger
5 is able to transfer heat to said fluidized bed 8. An entry pipe 9 is
connected to said heat exchanger
such that a transfer medium can be introduced into the heat exchanger by said
entry pipe 9. An
exit pipe 11 is connected to said heat exchanger such that the transfer medium
can be drained away
from the heat exchanger by said exit pipe 11. The walls of the chamber 3 can
contain the heat
exchanger.
Preferably, in step ii., said fluidized bed is heated at a temperature from
400 to 700 C,
preferably from 500 to 700 C, and even more preferably from 600 to 700 C.
Preferably, a transfer medium is circulating in said heat exchanger and is
introduced into
said heat exchanger at a temperature from 250 C to 1500 C.
Preferably, said transfer medium is at least partly heated by a renewable
energy source.
Preferably, a transfer medium is circulating in said heat exchanger and is
exiting said heat
exchanger at a temperature from 150 C to 1000 C.
Even more 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.
The step ii. happens simultaneously as the step i., so that while the solid
particles form a
fluidized bed, they are heated.
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In step iii., the semi-finished steel product is put inside the fluidized bed
such that it can be
heated by the fluidized bed. So, the steps i. and ii. are performed during the
step iii. to allow the
heat transfer from the heat exchanger to the fluidized bed and also from the
heat exchanger to the
semi-finished steel product.
Preferably, said semi-finished steel product is at ambient temperature before
being brought
into the fluidized bed.
Preferably, the whole semi-finished steel product is inside said fluidized
bed.
In step iv., the semi-finished steel product is taken out of the fluidized bed
when it reaches
a determined temperature.
Preferably, said semi-finished steel product is taken out when its temperature
is from 500 C
to 700 C. Even more preferably, said semi-finished steel product is taken out
when its temperature
is from 600 C to 700 C.
In the heating step, the semi-finished steel product is heated in a furnace to
a temperature
from 1100 C to 1400 C. Such a heating range permits to perform a hot rolling.
Preferably, said method comprises a hot rolling step, after the heating step,
wherein said
semi-finished steel product is hot rolled.
--- PREFERRED EMBODIMENTS ---
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, said gas injected in said chamber as a temperature close, or
higher, to the one
of the fluidised bed.
Preferably, the gas is injected at a velocity from 1 to 30 cm.s'. Such a
velocity range requires
a low ventilation power and thus a reduced energy consumption
Preferably, the solid particles have a size from 40 to 500
Preferably, the solid particles have a heat capacity comprised from 500 to
2000 J.kg-1.K-1.
Preferably, the bulk density of the solid particles is from 1400 to 4000 kg.m-
3.
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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
semi-finished steel
5 product.
The method according to the invention permits to heat, at least partly a semi-
finished steel
product by means of renewable energy and/or recovered waste energy, in the pre-
heating step.
Alternatively, as illustrated in Figure 2, the pre-heating step is performed
by at least two
pre-heating devices (1, 100).
Said at least two pre-heating devices are arranged such that the exit pipe
(11) of a first pre-
heating device (1) is connected to an entry pipe (90) of a second pre-heating
device (100).
In that case, the pre-heating step comprises the steps of
i. injecting a gas (12, 120) into the chamber (3, 30) of said first and second
pre-heating
devices so as to form fluidized beds (4, 40),
ii. heating said fluidized beds (4, 40) by means of heat exchanger (5, 50),
iii. putting said semi-finished steel product 2, into the fluidized bed (80)
of said second pre-
heating device (100) and onto said support (60) such said fluidized bed (80)
is able to transfer heat
to said semi-finished steel product 2,
iv. taking out said semi-finished steel product 2 when its temperature is from
300 C to
500 C,
v. putting said semi-finished steel product 2, into the fluidized bed (8) of
said second pre-
heating device (1) and onto said support (6) such said fluidized bed (8) is
able to transfer heat to
said semi-finished steel product 2,
vi. taking out said semi-finished steel product 2 when its temperature is from
500 C to
700 C.
Such a pre-heating steps permits to heat the semi-finished steel product in
several steps so
as to increase the efficiency of the transfer medium passing through the heat
exchangers.
The invention also relates to a method for heating a semi-finished steel
product 2,
comprising:
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a pre-heating step, performed in a pre-heating device 1 comprising a chamber 3
containing
solid particles 4, a heat exchanger 5, a support 6 able to support said semi-
finished steel
product, a gas injector 7, and
a rolling step performed in a rolling mill, wherein
said pre-heating step comprises the steps of:
i. injecting a gas 12 into said first chamber 3 so as to form a first
fluidized bed 8,
ii. heating said fluidized bed 8 by means of said heat exchanger 5,
iii. putting said semi-finished steel product 2, into said fluidized bed 8
such that said
semi-finish steel product 2 is supported by said support 6 and such that said
fluidized bed 8 is able to transfer heat to said semi-finished steel product
2,
iv. taking out said semi-finished steel product 2 when its temperature is from
150 C
to 350 C, and
said rolling step comprises the step of rolling said semi-finished steel
product at a
temperature from 150 to 300 C.
