[0001] The present invention relates to an integrated plant with low environmental impact
(so-called "green factory") for the production of steel hot-rolled and cold-rolled
strip in a wide dimensional range with high productivity and flexibility of the plant
and a high quality of the strip.
[0002] It is known that the production cycle for the manufacture of 4 million tons/year
of coils of steel strip is based on the so-called "integral cycle", which uses coal
for the production of metallurgical coke, lime and flux which, combined with fine
iron mineral, generate pellets and sintered after processing in special plants. Pellets
and sintered, loaded with the coke in the blast furnace, are turned into liquid cast
iron and slag.
[0003] From cast iron then you get the steel in the converter process that dramatically
reduces the carbon content. The steel is then refined in a plant for degassing and
processed in chemical analysis in special treatment installations. The steel is then
cast by continuous casting which produces slabs approximately 200-250 mm thick, 1500-2000
mm wide and 8-12 meters long.
[0004] The slabs leaving the continuous casting are then stored in a deposit and subsequently
resumed according to the production program to be heated in a furnace which takes
the slabs to the optimum temperature (about 1200°C) for the next stage of hot rolling.
This phase normally comprises the passage in a first series of stands that perform
the roughing operations and reduce the slab to a thickness of about 35-50 mm and then
the finishing rolling is performed in a train that uses up to seven stands. From here
the rolled material is sent, after cooling, to the winding on the reels that generate
the coils of rolled strip.
[0005] The hot product of this type of plant is normally in the range of thicknesses from
1,8 to 15 mm, with a great prevalence in thicknesses greater than 2,5 mm since this
type of plant is unsuitable for the production of coils of thin thickness. Thin thicknesses
are usually produced through cold cycles that use large finishing equipment, such
as pickling, cold rolling trains with five stands, annealing, galvanizing and painting
installations.
[0006] A typical integrated plant of this type, from raw material to finished products,
for a capacity of 4 million tons/year occupies very large spaces, usually from 5 to
8 millions of square meters. The typology of these plants is scarcely flexible and
involves the need of large amounts of intermediate materials put into storage (slabs,
hot-rolled coils, cold-rolled coils, etc.) for a few million tons overall, with a
consequent increase in production costs.
[0007] From an energy point of view the costs are quite high both for the material heating
costs and for the rolling costs due to a high number of stands. Also the environmental
impact is considerable and is mainly due to fine dust, particularly in coking plants
and in the blast furnace.
[0008] It is also known that with the thin slab technology it is possible to make plants
with reduced energy costs and low environmental impact, by casting thin slabs less
than 100 mm thick and in which the liquid steel is produced through by melting iron
scrap. With this type of technology it is not possible however to produce more than
1,5 million tons/year with one casting/rolling line and 3 million tons/year with two
lines, with profitability problems especially in times, such as the current times,
in which the selling price of the coils is low.
[0009] There is therefore the need to realize extremely compact factories that can produce
an amount equal to 3-4 million tons/year or more of coils of very high quality and
with high production mix, with a single continuous casting line directly connected
without solution of continuity to the finishing mill, with low investment and production
costs but environmentally responsible.
[0010] The idea underlying the present invention is to realize a factory with very low environmental
impact (green factory), with consumption per unit of product reduced by 50% for both
energy and water. This result is obtained thanks to the short distance not only between
the steel mill and the casting machine but especially between the continuous casting
and the winding reel of the hot-rolled strip, using the continuous production technology
(so-called endless) that minimizes production time and consumption thereby reducing
production costs. The green factory is also characterized by a considerable reduction
of raw materials and emissions as well as by a high recycling ratio with recovery
even of part of the heat used in the production cycle.
[0011] To this purpose, the green factory according to the present invention comprises a
foundry section for the production of liquid steel directly connected to a continuous
casting and hot rolling section, which is in turn connected to a cold rolling section
that is in connection with a finishing section (galvanic treatment, coating, annealing),
a longitudinal slitting section being able to receive coils from each of the three
above-mentioned working sections (hot rolling, cold rolling, finishing). Moreover
a vehicle shredding section produces metal scrap to be used as raw material for the
foundry, a vehicle shredding residue burning section generates current for the plant,
and finally a foundry slag treating section is dedicated to the recycling of the slag
and to the heat recovery therefrom.
[0012] A first fundamental advantage of the plant according to the present invention is
to provide a factory, with a production cycle in line, of extreme compactness in terms
of space and production cycle times such that it can be fully realized in spaces of
less than 700.000 m
2. Such a plant allows to produce, with a single continuous casting line directly connected
without solution of continuity to the finishing mill, an amount equal to 3-4 million
tons/year or more of coils of very high quality and for all applications, including
the inner and outer parts of cars, with a high mix of thicknesses and maximum respect
for the environment.
[0013] A second important advantage of the factory realized with the teachings of the present
invention lies in the fact that it has very competitive investment and processing
costs, it is highly environmentally friendly and has a minimum environmental impact,
in particular for the reduction (up to 50%) of the energy and water consumption per
unit of product and for the emission of fumes and noise reduced to a minimum, thanks
to the fact that the sections are housed in completely closed and soundproofed sheds.
[0014] A further advantage of this factory is the provision of a "human friendly" indoor
work environment where the workers, thanks to the integrated automation of all plants,
can supervise all production processes in ergonomic and soundproofed pulpits, with
no need to be in direct contact with the steel.
[0015] Further advantages and characteristics of the plant according to the present invention
will become apparent to those skilled in the art from the following detailed and non-limiting
description of an embodiment thereof with reference to the accompanying drawings in
which:
Fig.1 is a schematic view of the different sections that make up the plant and of their
connections, with the exception of the foundry slag treating section which is omitted;
Fig.2 is a schematic view in longitudinal section of the beam of the foundry slag treating
section;
Fig.3 is a schematic view in cross section of the collection basin of said slag;
Fig.4 is a perspective view partly broken away of the structure of the panels used to make
the coverage sheds of the sections;
Fig.5 is a perspective view of a continuous casting machine, in the version with the electromagnetic
brake external to the cooling circuit of the mould and depicted in the inoperative
position;
Fig.6 is a perspective view of the casting machine of Fig.5 with the electromagnetic brake
depicted in the operative position;
Fig.7 is a perspective view of a continuous casting machine, in the version with the electromagnetic
brake internal to the cooling circuit of the mould;
Fig.8 is a schematic front view that shows the magnitude of the wave generated by the turbulence
of the liquid steel introduced into the mould;
Fig.9 is a schematic top plan view showing the profile of the terminals of the magnetic
cores of the electromagnetic brake;
Fig.10 is a schematic side view showing the profile of the terminals of the magnetic cores
of the electromagnetic brake; and
Fig.11 is a diagram of the cooling circuit of the mould.
[0016] Referring to Fig.1, there is seen that a plant according to the present invention
comprises a foundry section SF for the production of liquid steel which is fed directly
to an adjacent section CCHR for the continuous casting and hot rolling to a thickness
between 0,8 and 25 mm. More specifically this section CCHR comprises a device for
the continuous casting in thin slab with liquid core reduction (LCR) followed by a
finishing mill capable of reducing the thin slab to a strip of the desired final thickness,
in addition to a device for cooling the strip thus obtained and to a final winding
station provided with relative shears for obtaining coils HRC.
[0017] The coils HRC of hot-rolled steel strip obtained in the section CCHR can be passed
for possible additional processing to an adjacent pickling and cold rolling section
PCR comprising lines with different rolling trains, for example a line with three
rolling stands to obtain a thickness between 0,2 and 1 mm.
[0018] Similarly, the coils CRC of cold rolled steel strip obtained in the section PCR can
then be passed for possible additional processing to a longitudinal slitting section
SL or to an adjacent coil finishing section CF which may comprise lines HDGL for hot
dip galvanizing treatment (typically zinc coating), lines HDGCL for hot dip galvanizing
treatment combined with an additional coating (typically paint) and lines AL for annealing.
[0019] The wide range of finished products that can be obtained with the present plant thus
comprises coils HRC of hot rolled steel strip with a thickness comprised between 0,8
and 25 mm, the maximum width being equal to the width of the mould, and coils CRC
of cold rolled steel strip with a thickness comprised between 0,2 and 2 mm that can
later be zinc coated (HDGC) or zinc coated and painted (HDGCC). A typical mix of finished
products for a production of 4 million tons/year includes 1 million of HRC and 3 millions
of CRC divided in half between lower and higher thicknesses.
[0020] In section SF the present invention adopts the most advanced melting technologies
of raw materials such as metal scrap, DRI (Direct Reduced Iron), HBI (Hot Briquetted
Iron) and cast iron to obtain the liquid steel which is then refined, processed and
loaded with the appropriate ferroalloys in order to be ready for casting in section
CCHR. These melting and refining phases of the liquid steel are carried out within
sheds that are closed and kept in depression, so as to prevent the escape of fumes
which are sucked by a special plant and filtered prior to the emission in the atmosphere
in suitable installations for reducing pollutants that use the most advanced technologies
available.
[0021] By way of example, the section SF schematized here comprises two melting electric
arc furnaces EAF, three ladle furnaces LF, two vacuum decarburization furnaces VOD
and a vacuum degassing system RH (Ruhrstahl-Heraeus).
[0022] For manufacturers of steel from electric oven the availability of scrap of good quality
in adequate quantities is critical, and for this purpose there is provided a section
AS where a mill is employed for crushing and shredding "packs" of vehicle bodies and
a procedure is used for the recovery of waste elements (metals such as lead, copper,
zinc and tin) whose presence in the steel can affect the production of high quality
steels.
[0023] In the present plant there is also provided a section ASRB where there is implemented
a process for the energy recovery of the residual consisting of a mix of various types
of materials such as plastics, rubbers, textiles, glass (so-called ASR = Automobile
Shredder Residue or "fluff"), rather than disposing of it almost entirely in a landfill
as is currently done according to the state of the art. For this purpose there is
used, as described in the Italian patent n.
1416512 herein incorporated by reference, a compact reactor and a process of pyro-gasification
of fluff optimized in terms of thermo-chemical and thermo-fluidodynamical efficiency,
thus maximizing the extraction of the energy content of the fed material.
[0024] The electricity generated from the thermal energy obtained from the fluff in section
ASRB is fed into the plant network, thus contributing to the reduction of kWh needed
to produce 1 ton of steel. In this way the calculated value, fulfilling the criteria
of PAS 2050:2011, of the carbon footprint of the finished product is less than 1300
kg CO
2/ton, in relation to 1 ton of hot-rolled carbon steel type S235 JR (low alloy) 2 mm
thick and 1500 mm wide, with an hourly production of 330 tons/h. This value includes
the raw material (mainly steel scrap), the melting process in the EAF furnace and
the endless process of continuous casting and rolling of the strip, including the
water cooling system (so-called "cradle-to-gate" value).
[0025] In the steel production process, a substantial portion of the production waste is
represented by the slag that originates in the melting processes. In particular, in
the processes based on electric melting furnaces EAF of the Siemens-Martin type the
percentage of slag produced for each unit of liquid steel is about 16% by weight.
This slag is usually discharged into areas of cooling/treatment outdoors for later
disposal, which involves emissions of steam and the remote possibility of throwing
of materials in the case of direct contact of the liquid slag with significant quantities
of water.
[0026] The basic chemistry that occurs during the slag cooling process consists of some
modifications for which the iron oxide FeO is oxidized to ferric oxide Fe
2O
3, which reacts with the oxides of lime and aluminum forming minerals after the cementation
process:
4FeO + O
2 = 2Fe
2O
3 (1)
Fe
2O
3 + nCaO = nCaO . Fe
2O
3 (2)
4CaO . FeO + O
2 = 4CaO . Fe
2O
3 (3)
4CaO . Fe
2O
3 + Al
2O
3 = 4CaO . Al
2O
3 . Fe
2O
3 (C
4AF) (4)
[0027] The silicon and alumina present in the slag also react with the portion of unbound
lime present forming minerals after the cementation process:
2CaO + SiO
2 = 2CaO . SiO
2 (C
2S) (5)
2CaO . SiO
2 + CaO = 3CaO . SiO
2 (C
3S) (6)
3CaO + Al
2O
3 = 3CaO . Al
2O
3 (C
3A) (7)
[0028] The continuous monitoring of the completion of these processes allows the reuse of
the slag thus modified both as conglomerate for roadbeds and as an inert in the production
of concrete.
[0029] Referring to Fig.2, there is seen that in the green factory object of the present
invention all activities of cooling/treatment of the slag are carried out indoors.
The section ST for treating slag FS is in fact contained in a shed built with soundproof
panels suitable to limit the propagation of noise and contain any throwing of materials.
Also the whole shed is at a slight depression to convey any emission to a centralized
fumes treatment plant through a special system ECS for capturing emissions released
from the slag FS being treated. The same kind of protection of the working environment
and of limitation of the emissions is preferably applied also to the other sections.
[0030] The slag cooling basin, shown in Fig.3, comprises a system HRS for heat recovery
from the slag which is discharged in the basin at each completion of the melting cycle
of a batch of steel, at intervals comprised between 35 and 60 minutes. The basin accumulates
a number of discharges in proportion to its size, then the basin is allowed to cool
and in the meantime there is used a twin basin to continue operations and the plant
proceeds so alternately.
[0031] The structure of the basin comprises an internal tank 1, a waterproofed external
tank 2 and a layer of thermal insulation material 3 arranged between said two tanks.
The internal tank 1 has a bottom wear layer 4 suitable to protect the structure of
the tank itself inside which pass pipes of the heat recovery system HRS.
[0032] The residence time of the cooling slag in the basin allows the transmission of heat
to the underlying structure of the internal tank 1 and, thanks to its size, there
is established a temperature regime such that the piping network of the HRS system
manages to remove the additional heat resulting from each new discharge. A control
system automatically switches the individual cooling circuits in series/parallel configuration
to adapt the flow rates/temperatures to the needs of the heat users, both inside and
outside of the factory (e.g. remote heating).
[0033] The shed of section ST, as well as the sheds of the other sections, is preferably
made with metal panels insulated with high-density mineral wool, of the type illustrated
in Fig.4. More specifically, a panel consists of an external sheet 5 with a C-shaped
cross-section suitable to support an internal sheet 6, exposed to the noise, that
has a micro-perforated surface behind which there is a sound-muffling floating lamina
7 elastically suspended between two layers 8, 8' of high-density (80-100 kg/m
3) mineral wool insulation. Furthermore, a protective foil 9 is arranged between the
micro-perforated sheet 6 and the internal layer 8 of mineral wool.
[0034] By varying the type of the intermediate sound-muffling lamina 7 and modulating the
thickness and density of the mineral wool layers 8, 8' diversified levels of sound
attenuation can be reached in relation to the presence and different sound spectrum
of the internal noise sources. Typically a panel with only the inner layer 8 of mineral
wool 80 mm thick has an attenuation of 28 ÷ 32dB in the spectrum f> 250 Hz.
[0035] The factory realized with the teachings of the present invention consists of plants
for the production of hot-/cold-rolled steel strips, galvanized and coated, that are
characterized by being as compact as possible while respecting all the phases of transformation
of steel. More specifically, the plant for the production of hot-rolled strip is based
on the "endless" technological concept which involves casting and rolling directly
connected in line without solution of continuity for the maximum exploitation of the
enthalpy of the liquid steel. Such a plant is extremely compact (length about 180
meters) and allows the production of high quality steel strips wound in coils that
cannot be obtained with other conventional plants or through other thin slab technologies
at a competitive cost, with more than 70% of the hot-rolled coils that may have a
thickness in the range from 0,8 to 1,6 mm and a width in the range from 1560 to 1800
mm.
[0036] The endless configuration, described for example in European patent
EP 1868748 and represented in Fig.1 in section CCHR, is characterized by the important aspect
consisting of the direct connection without solution of continuity of the continuous
casting and rolling stages, with a single set of stands that implements the roughing
and finishing steps. This solution, in addition to reducing the energy request practically
to that regarding only the finishing, since it eliminates the wasteful heating of
the slab replaced by a single temperature recovery between casting and the rolling
mill, is particularly favorable in terms of yield of the steel because the losses
due to oxide rather than for other wastes are minimized.
[0037] Thanks to the endless technology it is possible to obtain hot-rolled strip with a
minimum thickness up to 0,8 mm with dimensional features, internal structure and quality
typical of cold-rolled strips, in particular as regards planarity and very tight thickness
tolerances, also on the head/tail of the strip. These properties of the hot-rolled
coils HRC allow to obtain, with a subsequent step of cold rolling in section PCR,
strips having a minimum thickness of 0,2 mm with excellent geometric characteristics.
[0038] The tremendous technical progress in the field of continuous casting plants allowed
to reach higher and higher flow rates, i.e. to increase more and more the quantity
of steel per unit time output from the continuous casting. With the teachings of the
present invention it is possible to obtain a very high productivity of the continuous
casting machine capable of casting up to 10 tons/min of steel thanks to the particular
technological system composed of the plunger, the mould and the electromagnetic brake
(so-called "mould system"), as shown in figures 5 to 7.
[0039] The electromagnetic brake (EMB) is an essential component in the achievement of a
high flow rate in continuous casting and to achieve a flow rate of 10 tons/min it
was necessary to design an innovative geometry of the terminals of the magnetic cores
of the EMB, as illustrated in more detail below.
[0040] It is known, in fact, that the objectives of the introduction of an electromagnetic
brake in a continuous casting machine are primarily the stabilization of the meniscus
M in the mould, where the solidification of the steel begins with the formation of
the first solid "skin" of the product, and the reduction of the penetration depth
of the inclusions, both solid and gaseous. The molten metal passes through the static
magnetic field generated by the EMB and by virtue of the relative motion between the
metal and the field induced currents are generated within the metal that create an
induced magnetic field. The interaction of this induced field with the magnetic field
of the EMB results into a mechanical force (Lorentz force) opposite to the direction
of motion of the metal, from which results the braking action which is proportional
to the square of the magnetic field of the EMB.
[0041] In this way the speed of the molten metal is decreased and the kinetic energy lost
is converted into heat energy, in accordance with the principle of conservation of
energy. Therefore there is a redistribution of the flow of metal in the mould, which
allows to retain the inclusions in the zone of the meniscus M which, moreover, is
hotter due to the reduced turbulence.
[0042] There are two different construction types of the electromagnetic brake, which have
the same operating principle but depending of the casting machine you can have the
external arrangement or the internal one. The former is preferred in case of new machines,
the second is usually used in case of retrofit where the space available is smaller.
In both cases, the moulds must be suitable for use with the EMB, mainly as regards
the cooling water chambers which must be shaped to accommodate the cores of the brake
and be made of nonmagnetic stainless steel, so as not to affect the passage of the
magnetic field towards the mould and not decrease the effectiveness of the device.
[0043] Taking into consideration the external arrangement, shown in figures 5 and 6, the
components of the EMB are mounted externally to the mould, formed by four copper plates
CP that delimit the space in which there is poured the liquid steel fed through the
submerged nozzle SN. These components are:
- a magnetic yoke MY that allows the "magnetic closure" of the circuit and is normally
integrated in the support structure of the casting machine;
- two electric coils EC connected in series and formed from copper windings consisting
of tubes of rectangular section directly cooled with de-ionized water; coils EC are
supplied with direct current from a converter and said current flowing in the windings
creates the magnetic field and allows to obtain the braking effect on the molten metal;
- two magnetic cores MC, on which coils EC are wound, which are equipped with a supporting
and handling system to enter and exit from the water chambers WC of the mould; in
the operative position of Fig.6 the two cores MC are inserted in the water chambers
WC to take them closer to the mould so as to pass the magnetic field generated by
coils EC through the mould itself, whereas when it is necessary to replace the mould
the two cores MC are retracted by means of the handling system (preferably hydraulic)
to the inoperative position of Fig.5, so that the mould can be removed freely.
[0044] In the internal arrangement illustrated in Fig.7, all the aforesaid components of
the EMB are mounted directly on the mould which is equipped with cores MC, complete
with coils EC, that "live in symbiosis" with the mould itself, therefore one must
provide as many pairs of magnetic cores MC as are the moulds in use.
[0045] The solution object of this invention can be applied to both arrangement, external
and internal, and consists of a particular geometry of the front surface of the terminals
of the magnetic cores that are no longer made as the usual steel parallelepipeds normally
used. This geometry has been designed to have a magnetic field inside of the mould
able to guarantee optimal casting conditions even with the high flow rates typical
of the continuous process used in the present plant (so-called technology ESP = Endless
Strip Production).
[0046] The applicant has performed tests to evaluate the effectiveness of the geometry chosen
for the terminals of the EMB by analyzing the stability of the meniscus M of the molten
metal through the so-called "sheet test" (dip test) which consists in dipping in the
mould, parallel to the wide plates CP, a sheet of stainless steel having a thickness
equal to 0,2 mm. From the analysis of the sheets it is possible to obtain an indication
of the magnitude of the wave generated by the turbulence of the liquid steel introduced
into the mould through the submerged nozzle SN, measuring both the difference W
1 between the points of maximum and minimum and the difference W
2 between the maximum point and the average height of the wave, as shown in Fig.8.
[0047] For the test to be effective it is important that the time of immersion in the mould
is sufficient to allow the melting of the sheet but without being too long, so as
to obtain a realistic image of the wave that is present in the moment in which the
sheet is dipped, i.e. an instantaneous representation of the meniscus. Through the
tests performed it was verified that while with the traditional flat terminals the
statistical average of W
1 and W
2 was respectively 26 and 15 mm, with the terminals having the geometry developed by
the applicant the average of W
1 and W
2 is reduced respectively to 7 and 3 mm. It is therefore evident how the turbulence
in the mould decreases dramatically by using the geometry object of the present invention.
[0048] The studies carried out by the applicant have allowed therefore to define a geometry
of the front surface of the terminals close to the mould that is illustrated in figures
9 and 10. By indicating with L the width of each terminal and with H the difference
between the point of the terminal profile closest to the mould and that farthest from
the same, the plan view of Fig.9 shows the significant points of passage of the profile
in the horizontal plane that are then interpolated by a polynomial curve of the sixth
order
a*x6+
b*x5+
c*x4+
d*x3+
e*x2+
f*x+
g.
[0049] The values of L, H and of the coefficients of the interpolating curve are comprised
within the following ranges:
L = 400 mm ÷ 600 mm;
H = 300 mm ÷ 450 mm;
a = -3,6*10-12 ÷ -2,7*10-13,
b = 95*10-10 ÷ 8*10-9,
c = -4,3*10-6 ÷ -48*10-7,
d = 1,6*10-4 ÷ 1*10-3,
e = -9,2*10-2 ÷ -2*10-2,
f= -1,2*10-1 ÷ 8,7*10-1,
g = 0.
[0050] The side view of Fig.10 similarly shows the profile of the terminals in the vertical
plane, where S indicates the thickness of the terminals and the significant points
of passage of the profile are again interpolated by a polynomial curve of the sixth
order
a*
x6+
b*
x5+
c*
x4+
d*
x3+
e*
x2+
f*
x+
g.
[0051] The values of S and of the coefficients of the interpolating curve are comprised
within the following ranges:
S = 300 mm ÷ 400 mm;
a = 3,1*10-12 ÷ 2,3*1011,
b = -2,0*10-8 ÷ -3,8*10-9,
c = 1,5*10-6 ÷ 5,7*10-6,
d = -3,7*10-4 ÷ -1,8*10-4,
e = -3,8*10-2 ÷ -1,8*10-3,
f = -7,8*10-1 ÷ 2,6*10-1.
g = 0.
[0052] Also for the achievement of the aforementioned flow rate value, it was also necessary
to design an innovative mould cooling system of the dynamic type (DMC = Dynamic Mould
Cooling) shown schematically in Fig.11.
[0053] In fact, unlike the current state of the art which provides for constant flow rates
of cooling water regardless of the operating conditions, the DMC is a management system
for the cooling water of the copper plates of mould 10 which consists in the variation
of the cooling water flow rate as a function of the casting speed and of the thickness
of the plates themselves. This is done through the use of variable-speed pumps 11
inserted in the cooling circuit, in addition to a conventional heat exchanger 12 and
a bypass valve 13.
[0054] This management of the cooling water can make constant the heat transfer in the mould
despite considerable changes in the operating conditions, with important beneficial
effects both on the formation in the mould of the first skin of the blank and on the
life of the copper plates. On the ESP line of the Arvedi steelworks in Cremona it
was possible to obtain, with the help of the DMC, a thickness of the first skin between
10 and 15 mm at the exit of the mould and a life of the plates of over 1400 castings.
This is the result of the reduction in the formation of cracks in the copper, which
is positively reflected not only on the reduction of the defectiveness of the product
but also on the decrease in the stops of the line due to breaking of the first skin
of the blank with the consequent leakage of liquid steel (so-called break-out).
[0055] Experimental tests conducted at the plant of the Arvedi steelworks in Cremona have
shown that it is possible to cast, thanks to the innovative geometry of the terminals
of the magnetic cores of the electromagnetic brake and to the innovative system of
dynamic mould cooling, thin slabs with a thickness of 100 mm at a speed of 6 m/min
with a flow rate greater than 7,1 tons/min thus making it possible to produce, with
a single integrated line of continuous casting and rolling, an amount of hot-rolled
coils greater than 4 million tons/year with an average specific energy consumption
lower than 135 kWh/t. This has made it possible to compact the factory object of the
present invention in such a manner as to be entirely realized in spaces of 500.000-700.000
m
2.
[0056] The present invention can also be applied by replacing the endless process according
to the teachings of patent
EP 1868748 with that of patent
EP 1558408, which comprises a roughing and finishing step with an intermediate heating between
the roughing mill and the finishing mill, rather than a single rolling plant. In addition
it can also be applied to integral cycle plants, i.e. with the melting of mineral
and coal in a blast furnace, applying the best available technologies to minimize
the environmental impact.
1. Integrated plant with very low environmental impact for producing coils of hot-rolled
and cold-rolled steel strip, comprising a foundry section (SF) for producing liquid
steel directly connected to a continuous casting and hot rolling section (CCHR) with
final winding of the strip into coils, this latter section (CCHR) being in turn connected
to a cold rolling section (PCR) that is in connection with a finishing section (CF),
said plant further comprising a longitudinal slitting section (SL) suitable to receive
coils from each of said three working sections (CCHR, PCR, CF), a vehicle shredding
section (AS) suitable to produce metal scrap fit for use as raw material in said foundry
section (SF), a vehicle shredding residue burning section (ASRB) suitable to generate
current to supply the plant, and a foundry slag (FS) treating section (ST) suitable
to recycle the slag and recover heat therefrom.
2. Plant according to claim 1, characterized in that the foundry section (SF) includes electric arc melting furnaces (EAF), ladle furnaces
(LF), vacuum oxygen decarburization furnaces (VOD) and a vacuum degassing system (RH).
3. Plant according to claim 1 or 2, characterized in that the continuous casting and hot rolling section (CCHR) includes a device for the continuous
casting of thin slabs with liquid core reduction (LCR) that directly feeds a rolling
mill with a single series of stands suitable to carry out the roughing and finishing
of the thin slab until it is reduced to a strip with a thickness comprised between
0,8 and 25 mm.
4. Plant according to any of the preceding claims, characterized in that the cold rolling section (PCR) includes pickling and cold rolling lines with different
rolling mills suitable to reduce the hot-rolled steel strip to a cold-rolled strip
with a thickness comprised between 0,2 and 2 mm.
5. Plant according to any of the preceding claims, characterized in that the finishing section (CF) includes hot dip galvanizing lines (HDGL), hot dip galvanizing
and coating lines (HDGCL) and annealing lines (AL).
6. Plant according to any of the preceding claims, characterized in that the foundry slag (FS) treating section (ST) includes a slag (FS) cooling basin made
up of an internal tank (1), a waterproofed external tank (2) and a layer of thermal
insulation material (3) arranged between said two tanks (1, 2), the internal tank
(1) having a bottom wear layer (4) suitable to protect the structure of the tank itself
inside which pass pipes of a heat recovery system (HRS) comprising means for switching
single cooling circuits in series/parallel configuration in order to adapt the flow
rates/temperatures to the needs of the heat users on the basis of commands from an
automatic control system.
7. Plant according to any of the preceding claims, characterized in that at least the foundry section (SF) and the foundry slag (FS) treating section (ST),
preferably also other sections, are contained in sheds built with soundproof panels
suitable to limit the propagation of noise and to restrain possible throwing of material,
said sheds being at a slight depression so as to convey any emission to a centralized
fumes treatment system through an emission capture system (ECS).
8. Plant according to the preceding claim, characterized in that the soundproof panels are metal panels insulated with high-density mineral wool at
80-100 kg/m3, each panel consisting preferably of an external sheet (5) with a C-shaped cross-section
suitable to support an internal sheet (6) that has a micro-perforated surface behind
which there is a sound-muffling floating lamina (7) elastically suspended between
two layers (8, 8') of said high-density mineral wool insulation, a protective foil
(9) being also preferably arranged between said micro-perforated sheet (6) and the
internal layer (8) of mineral wool.
9. Plant according to any of the preceding claims, characterized in that the sections include ergonomic and soundproofed pulpits connected to the plant devices
so as to allow the operators to supervise all the production processes without being
in direct contact with the steel being worked.
10. Plant according to any of claims 3 to 9, wherein the continuous casting device includes
an electromagnetic brake (EMB) arranged along two opposite long sides of a mould,
said electromagnetic brake (EMB) being characterized by the geometry of the front surface of terminals of magnetic cores (MC) on which there
are wound electric coils (EC) that generate the magnetic field, said geometry providing
a profile in the horizontal plane defined by a length (L) of the terminal, by a difference
(H) between the point of said profile closest to the mould and the point farthest
from the mould and by significant passage points interpolated by a polynomial curve
of sixth order a*x6+b*x5+c*x4+d*x3+e*x2+f*x+g, the values of length (L), of difference (H) in distance from the mould and of the
coefficients of said polynomial curve being comprised within the following ranges:
L = 400 mm ÷ 600 mm; H = 300 mm ÷ 450 mm; a = -3,6*10-12 ÷ -2,7*1013; b = 9,5*10-10 ÷ 8*10-9; c = -4,3*10-6 ÷ -4,8*10-7; d = 1,6*10-4 ÷ 1*10-3; e = -9,2*10-2 ÷ -2*10-2; f = -1,2*10-1 ÷ 8,7*10-1; g = 0.
11. Plant according to the preceding claim, characterized in that the terminals of the magnetic cores (MC) have a geometry of their front surface providing
a profile in the vertical plane defined by a thickness (S) of the terminal, by a difference
(H) between the point of said profile closest to the mould and the point farthest
from the mould and by significant passage points interpolated by a polynomial curve
of sixth order a*x6+b*x5+c*x4+d*x3+e*x2+f*x+g, the values of thickness (S), of difference (H) in distance from the mould and of
the coefficients of said polynomial curve being comprised within the following ranges:
S = 300 mm ÷ 400 mm; H = 300 mm ÷ 450 mm; a = 3,1*10-12 ÷ 2,3*10-11; b = -2,0*10-8 ÷ -3,8*10-9; c = 1,5*10-6 ÷ 5,7*10-6; d = - 3,7*10-4 ÷ -1,8*10-4; e= -3,8*10-2 ÷ -1,8*10-3; f= -78*10-1 ÷ 2,6*10-1; g = 0.
12. Plant according to any of claims 3 to 11, wherein the continuous casting device includes
a system for managing the cooling water of wide and narrow copper plates (CP) that
make up a mould (10), characterized in that said system, through the use of variable-speed pumps (11) located in the cooling
circuit, is suitable to perform a variation of the flow rate (P) of the cooling water
depending on the steel casting speed in said mould (10) and on the thickness of said
copper plates (CP).