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The present invention relates to a high-productivity steel heating furnace,
particularly for rolling plants.
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Heating furnaces for heating steel products, such as billets, slabs, rods, et
cetera, before rolling them are known.
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Heating furnaces of old design are generally constituted by a furnace
body in which a heating chamber is provided being delimited by respective
side walls, by a bottom wall and by a ceiling or roof having a characteristic
shape with multiple nose-like portions in order to divide the heating chamber
into a plurality of regions. Also the bottom of the chamber is generally
shaped like the roof in order to divide the chamber into various heating
regions.
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Inside the heating chamber there is a surface for supporting the products
to be heated which is arranged horizontally and on which the products are
made to advance, usually by pushing, from an inlet toward an outlet.
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In these furnaces, heating is achieved by means of burners which are
applied to the roof, above the product supporting surface, and, if one wishes
to heat the products also from below, to the bottom of the chamber below the
supporting surface.
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These furnaces have the problem of having a very complicated structure
which is mainly due to the shape of the roof and bottom of the heating
chamber. Moreover, these furnaces have a rather limited productivity.
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More recently designed heating furnaces have a heating chamber which is
delimited, in an upward region, by a roof which is shaped so as to divide the
chamber into two main regions: a region for heating by convection, which is
located proximate to the product inlet, and a region for heating by radiation,
which lies between the convection heating region and the product outlet.
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More particularly, the roof of the furnace lies on a substantially
horizontal plane in the radiation heating region and has a shallower portion,
proximate to the inlet, in order to form the convection heating region.
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The products introduced in the furnace are heated by means of burners
which are arranged on the roof of the furnace in the radiation heating region
and by means of the stream of combustion gases conveyed through the
convection heating region.
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When these gases leave the convection heating region, they are used in a
regenerator, arranged above the furnace roof, to heat the combustion air that
feeds the various burners. Usually, in view of the high temperature of the
gases, in order to avoid damage to the regenerator it is necessary to mix said
gases with dilution air at the inlet of the regenerator.
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The combustion air is then conveyed to the various burners by means of a
plurality of insulated ducts arranged above the roof of the furnace.
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These furnaces, too, have problems.
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The presence of the burners and of the ducts for conveying the preheated
combustion air on the roof of the furnace in fact increases the structural
complexity of the furnace roof and has a significant effect on the
manufacturing costs of these furnaces.
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Moreover, the convection heating region, by forcing a particular shape of
the furnace roof, further increases these costs.
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The use of the regenerator also constitutes a considerable increase in
plant complexity which affects furnace production and maintenance costs.
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The presence of the convection heating region, in addition to slowing the
advancement rate of the heated products because in order to achieve the
necessary heating efficiency it requires a reduction in the height of the
furnace in said region, also limits the gap of the furnace inlet, making it
difficult to perform maintenance through said inlet.
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As regards the general operation of these furnaces, there is a limit to
productivity which is mainly due to the type of burner used and to the
heating of the products performed in two separate steps: a scarcely effective
convection step and a more effective radiation step.
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The aim of the present invention is to solve the above-noted problems, by
providing a steel heating furnace, particularly for rolling plants, which is
structurally simpler and able to achieve higher productivities than
conventional heating furnaces.
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Within this aim, an object of the invention is to provide a heating furnace
which, by virtue of its great structural simplicity, can be produced at a lower
cost than conventional heating furnaces.
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Another object of the invention is to provide a heating furnace which
allows simple maintenance.
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This aim and these and other objects which will become better apparent
hereinafter are achieved by a steel heating furnace, particularly for rolling
plants, comprising a furnace body which contains a heating chamber in
which means for supporting the products being heated are arranged, said
chamber having an inlet door for the products to be heated and an outlet door
for the heated products, said heating chamber being delimited by a bottom,
by side walls and by a ceiling or roof of said furnace body, means for
heating said heating chamber being provided, characterized in that said
ceiling or roof is substantially flat and in that said heating means are
constituted by burners arranged on the side walls of the furnace body.
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Further characteristics and advantages of the invention will become better
apparent from the description of a preferred but not exclusive embodiment
of the heating furnace according to the invention, illustrated only by way of
non-limitative example in the accompanying drawings, wherein:
- Figure 1 is a schematic sectional side view, taken along a vertical plane,
of the heating furnace according to the invention;
- Figure 2 is a schematic sectional view of Figure 1, taken along the line II-II;
- Figure 3 is an enlarged-scale schematic sectional view of Figure 1, taken
along the line III-III;
- Figure 4 is an enlarged-scale schematic sectional view of Figure 1, taken
along the line IV-IV.
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With reference to the figures, the heating furnace according to the
invention, generally designated by the reference numeral 1, comprises a
furnace body 2 in which there is a heating chamber 3 in which means 4 for
supporting the products 5 being heated are arranged.
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The chamber 3 is delimited by substantially vertical side walls 6, 7, 8 and
9, by a bottom 10, and by a ceiling or roof 11.
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The furnace is provided with means for heating the chamber 3.
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According to the invention, the ceiling or roof 11 is substantially flat and
preferably horizontal along its entire extension, and the heating means are
constituted by burners 12 and 13 arranged on the side walls of the furnace
body.
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The chamber 3 has an inlet door 14 for the products 5 to be heated and an
outlet door 15 for the heated products.
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The inlet door 14 is arranged on an inlet opening formed in the side wall
6 that constitutes the front wall of the furnace, while the outlet door 15 is
arranged on an outlet which is formed in the side wall 7 that constitutes the
rear wall of the furnace.
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The doors 14 and 15 are constituted by gates which, if the products 5 are
made to advance in the heating chamber 3 by pushing, can move vertically
from a minimum opening position, in which they allow only the passage of
the products 5 entering or leaving the heating chamber 3, to a maximum
opening position, in which their lower side is substantially at the same level
as the roof 11.
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If the advancement of the products 5 in the heating chamber 3 is achieved
in another manner, for example by using a supporting surface with movable
portions (movable-hearth advancement), the doors 14 and 15 may also be
closed completely.
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Since the flat shape of the roof 11 allows the inlet and the outlet to
occupy substantially completely the front wall 6 and the rear wall 7 of the
furnace, during maintenance or when rapid cooling of the inside of the
furnace is required it is possible to open the doors 14 and 15 completely,
providing very wide access openings which facilitate maintenance and allow
rapid evacuation of the air and gases present inside the furnace.
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The burners are preferably constituted by regenerative burners, preferably
of the type disclosed in patent application MI98A-001595 in the name of
this same Applicant.
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The burners 12 and 13 are arranged on the mutually opposite side walls 8
and 9 of the furnace body 2 and are arranged in pairs, i.e., each burner 12, 13
arranged on one side wall faces, and is preferably aligned with, a
corresponding burner 12, 13 arranged on the opposite side wall 9 of the
furnace.
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Preferably, each burner 12, 13 is designed to operate alternately with
respect to the facing burner.
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Substantially, while one burner 12, 13 is active, the gases produced by the
combustion of the active burners are aspirated through the burner that faces
said active burner. These gases are passed through heat exchange elements
arranged inside the burner so as to heat them, and said heat exchange
elements transfer their heat content to the combustion air, which is fed to the
burner when it is activated.
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In this manner, high thermal efficiency for the burners is achieved.
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Moreover, for the furnace according to the invention preference is given
to burner management of the on-off type, i.e., each burner, when it is
activated, is made to run at full capacity. The heating of the chamber 3 is
achieved, according to a preset heating pattern, from the inlet door 14 toward
the outlet door 15, by operating the various burners 12, 13 according to a
preset sequence.
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The supporting means 4 are preferably constituted by a grid of tubular
elements 20 (commonly known as skids) which form a substantially
horizontal surface for the support and sliding of the products 5 being heated.
Such tubular elements 20 are connected to ducts 21 for supplying and
circulating a cooling fluid, for example water, which is circulated inside the
tubular elements 20 in order to cool them adequately so that they cannot be
damaged by the high temperatures reached inside the chamber 3.
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The tubular elements 20 are conveniently supported by said side walls 8
and 9 of the furnace body.
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The burners 12 are arranged above the supporting surface formed by the
tubular elements 20, and if required it is also possible to provide burners 13
below the supporting and sliding surface formed by the tubular elements 20
at least along a section of the heating chamber 3 that starts from the inlet
door 14.
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In this case, the bottom 10 of the furnace has a shallower part exclusively
in the region where the products 5 are to be heated from below as well.
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According to requirements, the sliding and supporting surface for the
products 5 can be constituted entirely by the tubular elements 20 or, as
shown, the tubular elements 20 can be used to support the products 5 only
along part of the extension of the chamber 3, while the remaining part of the
supporting surface can be constituted by a refractory cladding.
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For the sake of completeness in description, it should be noted that the
internal surface of the furnace is lined with refractory material in a per se
known manner.
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Operation of the heating furnace according to the invention is as follows.
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The products 5 to be heated are gradually introduced in the chamber 3
through the inlet door 14 and are made to advance toward the outlet door 15,
for example by means of the thrust of products 5 inserted subsequently in the
chamber 3.
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It should be noted that the products 5, as soon as they are inserted in the
heating chamber 3, are heated by radiation, thus producing a much more
rapid heating of said products 5 than allowed in the convection heating
region of conventional heating furnaces.
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During advancement inside the chamber 3, the products 5 are gradually
heated to the intended temperature until they exit from the outlet door 15.
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It should be noted that the particular shape of the roof 11 of the furnace
and the arrangement of the burners on the side walls of the furnace body 2
make the furnace roof extremely simple from a structural standpoint,
allowing to reduce significantly the production costs of the heating furnace
according to the invention with respect to those entailed by conventional
heating furnaces. Moreover, since the heating furnace according to the
invention does not have a convection heating region, it can provide for
heating of the products 5 from below starting from the inlet door 14, thus
achieving even higher effectiveness in heating the products 5.
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Substantially, the heating furnace according to the invention, for an equal
length or equal roof surface, is capable of ensuring a markedly higher
productivity than conventional heating furnaces.
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The heating furnace according to the invention, by virtue of its particular
roof, of the arrangement of the burners, and of the use of regenerative
burners, does not require regenerators and complicated ducts for feeding the
combustion air to the various burners, thus achieving further plant
simplification and reducing production costs even further.
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Since the burners are arranged exclusively on the side walls, access to the
roof during maintenance is also improved.
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It should be noted that in the furnace according to the invention the use of
regenerative burners allows to access the burners while they are not active in
order to perform any maintenance, without necessarily requiring furnace
shutdown.
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Moreover, the heating furnace according to the invention ensures control
over the level of oxidation of the heated products 5, improving the yield and
also reducing the production of scale on the product surface.
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In practice it has been observed that the heating furnace according to the
invention fully achieves the intended aim and objects, since it allows, with a
simpler structure, to achieve distinctly higher productivities than
conventional heating furnaces.
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The heating furnace thus conceived is susceptible of numerous
modifications and variations, all of which are within the scope of the
inventive concept; all the details may further be replaced with other
technically equivalent elements.
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In practice, the materials employed, so long as they are compatible with
the specific use, as well as the dimensions, may be any according to
requirements and to the state of the art.
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The disclosures in Italian Patent Application No. MI2000A001564, from
which this application claims priority, are incorporated herein by reference.
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Where technical features mentioned in any claim are followed by
reference signs, those reference signs have been included for the sole
purpose of increasing the intelligibility of the claims and accordingly such
reference signs do not have any limiting effect on the scope of each element
identified by way of example by such reference signs.
