Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
METHOD AND SYSTEM OF TREATING A CARBON STEEL STRIP,
ESPECIALLY FOR A PICKLING TREATMENT
BACKGROUND
[0001] The present invention relates to a method for treating a steel
strip, especially for
a pickling treatment of the steel strip, by means of a treatment liquid in a
treatment station,
the treatment station comprising a treatment tank.
[0002] Furthermore, the present invention relates to a system for
treating a steel strip,
especially for a pickling treatment of the steel strip, by means of a
treatment liquid in a
treatment station, the treatment station comprising a treatment tank.
[0003] The steel strip to be treated according to the method of the
present invention and
in a system of the present invention is a carbon steel.
[0004] In pickling processes, metal surfaces are treated by removing
impurities such as
typically rust or scale using treatment liquids, or pickle liquors, typically
containing strong
acids.
[0005] These impurities may occur during metal forming processes, in
particular rolling
and/or heat treatment. During the hot rolling process of metal strips a scale
layer, mainly
consisting of different metal oxides, is formed. The scale layer needs to be
removed before
further processing the steel strip. This is typically done in an acid pickling
process, wherein
the scale layer is dissolved in the acid, followed by a rinsing section to
completely remove
the pickling solution. So-called "secondary scale" is formed as the steel
strip passes
continuously through the hot strip finishing line and over the roller table
where it cools and to
some extent also in the coiling machine, where the strip is wound up into
coils. Depending on
the grade of material, on the final thickness of the hot-rolled strip, and on
the rolling speed,
both the thickness of the scale and its chemical composition can vary.
[0006] Scale itself is chemically quite similar to rust, being made up
of iron and oxygen
bonded together in various molecular arrangements. Like rust, scale typically
develops at the
surface of the steel product where the metal surface is exposed to air.
[0007] To eliminate this scale, the most common approach today is to
use a pickling line
having one or a plurality of acid baths, typically using a plurality of
pickling tanks or pickling
stations in a row, normally containing hydrochloric acid at a certain
temperature in the range
of typically between 50 C and 95 C. Cumulatively or alternatively other
strong acids are
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used to descale or clean the metal surfaces, e.g. hydrochloric acid, sulfuric
acid, etc. may be
used as pickling agents (or treatment liquid) for pickling of e.g. ferrous
metals.
[0008] The steel strip is pulled (or pushed or both pulled and pushed)
through the
pickling line ¨ especially the treatment tank (or pickling tank) ¨ at a
certain speed (e.g. up to
a couple of meters per second), then rinsed ¨ typically with water ¨, and
dried, normally air-
dried. During pulling and/or pushing of the steel strip through the pickling
line the layer of
scale dissolves in the acid.
[0009] The concentration of the acid itself becomes depleted during the
pickling
operation, so that it is necessary to add fresh acid continuously. However,
large amounts of
spent acids are not only hazardous to the environment but usually also
expensive. Thus it is
desirable to reduce the amount of required acid for a given metal surface to
be treated or to
regenerate the spent acids for reuse. Furthermore, the pickling operation
should be carried
out such that the regeneration of the acids spent can be realized in a
comparatively simple
and comparatively environmentally compatible manner.
[0010] Since the beginning of pickling in general and strip pickling in
particular
developments in this field had the target to improve the efficiency with
regards to pickling
time, consumption of chemicals and energy, and surface quality. In the
beginning, pickling
lines were operated with H2504. Later HCI replaced H2504 due to shorter
pickling time, lower
consumption and the possibility of total regeneration of the acid. Pickling
acids are consumed
during the pickling process. The acid dissolves the oxide scale and metal
salts are formed.
H2504 mainly forms Fe504 which can be removed from the pickling liquid and has
to be
disposed and consequently has to be replaced by fresh H2504. HCI on the
contrary forms
mainly FeCl2 and a minor amount of FeCI3 during the pickling process. Both can
be
converted back to HCL in the so called pyrohydrolysis reaction using fluidized
bed or spray
roaster regeneration plants resulting in a complete recovery of the spent
pickling acid.
Another advantage of HCI as pickling liquid is the fact that HCI acts less
aggressive to the
base metal than H2504 and consequently reducing the risk of over-pickling.
[0011] Beside the type of acid which is used during the pickling
process, other factors
influence the pickling efficiency. Higher temperature of the pickling acid for
example reduces
the required time which is needed to completely remove the scale layer.
Therefore modern
strip pickling lines using HCI as pickling liquid are operated at temperatures
ranging from
about 80 C to about 90 C. Since the pickling in acid containing pickling
solutions is a
chemical or electrochemical process, the media and energy exchange between the
pickling
acid and the strip surface is highly important with regards to the pickling
efficiency.
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[0012] Today pickling lines are designed as shallow tank turbulence
installations
comprising of several consecutive pickling tanks. The steel strip is pulled or
pushed through
the treatment tanks. The complete pickling section is arranged as a cascade,
i.e. the fresh or
regenerated acid is added to the last treatment tank (i.e. the most downstream
treatment
tank according to the direction of movement of the steel strip) and is then
processed in a
countercurrent flow to the strip transport direction in order to maximize the
use of the pickling
acid. At the entry and exit of the treatment tanks, wringer rolls are
installed to remove the
pickling acid from the strip to the greatest possible extend in order to
enhance the cascade
effect. German patent disclosure DE 40 31 234 describes this technology.
[0013] Inside the treatment tank, the pickling acid is injected on both
sides of the tank
creating a high turbulence between the strip surface and the pickling acid.
[0014] The pickling acid is then overflowing from the treatment tank to
a circulation tank
from where it is again injected into the treatment tank by means of pumps. The
high
turbulence reduces the thickness of the liquid boundary layer on the strip
surface resulting in
an improved media and energy exchange and consequently reducing the required
pickling
time.
[0015] Another well-known pickling method is the spray pickling,
wherein the pickling
acid is directly sprayed onto the strip surface using several spray nozzles
installed both
above and below the steel strip, cf. e.g. document DE 42 28 808 Al. The
pickling acid is then
collected in a circulation tank from where it is pumped to the spray nozzles
and sprayed on to
the strip surface again. The spray nozzles are typically operated at a
pressure above 1 bar.
Due to the high impulse of the pickling acid sprayed onto the strip surface,
the pickling
efficiency and consequently the pickling time can be further improved. However
this
technology has never been used commercially in strip pickling lines.
Laboratory tests, carried
out for different steel grads, have proven, in particular when using HCI
containing pickling
solution, that the pickling speed of spray-pickling is up to five times higher
compared to the
shallow tank turbulence technology. However the dissolving speed of the base
metal is
increased in the same way or even further. Therefore, the pickling process is
difficult to
control with a high risk of over pickling the metal strip. One of the reasons
for this
aggressiveness with regards to the base metal is the formation of FeCI3 in the
pickling acid.
The spray nozzles used in the spray pickling technology create fine droplets
with a high
surface which are in direct contact with air. The air, in particular the
oxygen contained in the
air, dissolves in the pickling acid and oxidizes the FeCl2 together with the
HCI forming FeCI3.
While HCI is a non oxidizing acid and therefore dissolving the base metal only
slowly, FeCI3
is an oxidizing agent, consequently increasing the dissolving speed of the
base material. In a
pure spray pickling process the FeCI3 concentration can reach 60 g/I and
above.
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Another drawback of the increased FeCI3 concentration in the pickling acid is
the effect on
the regeneration process of the spent pickling acid. Spent pickling acid is
typically
regenerated using the pyrohydrolysis process. In this process FeCl2 and FeCI3
are converted
back to HCI and Fe203. FeCI3 however has a much lower evaporation temperature
than
FeCl2 and evaporates in the pyrohydrolysis reactor causing very fine Fe203
particles below 1
pm in size when converted to Fe203. These fine particles are difficult to
remove from the
process off-gases causing high dust emissions.
SUMMARY
[0016] It is therefore an object of the present invention to provide method
and a system
for an improved steel strip treatment, especially pickling, such that fixed
investment as well
as maintenance costs are reduced, the treatment and pickling process is
realized
comparatively quickly, with high quality, and in an environmentally friendly
manner.
[0017]
The object of the present invention is achieved by a method for treating a
steel
strip, especially for a pickling treatment of the steel strip, by means of a
treatment liquid in a
treatment station, the treatment station comprising a treatment tank with a
spray section and
an immersion section, and the treatment station comprising a common collection
means for
the treatment liquid,
wherein the steel strip comprises carbon steel and is a continuous steel strip
being oriented
substantially horizontally, both in its longitudinal and transverse
directions,
wherein the steel strip has a top surface and a bottom surface,
wherein the method comprises transporting the steel strip continuously through
the treatment
station in a transport direction, the transport direction being parallel to
the longitudinal
direction of the steel strip, such that
-- in a first step, the treatment liquid is sprayed onto the top surface of
the steel strip and
onto the bottom surface of the steel strip while the steel strip being in the
spray section of the
treatment station,
-- in a second step, the steel strip is immersed in the treatment liquid while
the steel strip
being in the immersion section of the treatment station,
wherein, while treating the steel strip, the treatment liquid is continuously
pumped out of the
common collection means and through both the spray section and the immersion
section of
the treatment station, wherein spraying of the treatment liquid onto the top
and bottom
surfaces of the steel strip is provided using spray nozzles.
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[0018] According to the present invention, it is thereby advantageously
possible to
provide a treatment station that requires comparatively low installation costs
as well as
reduced maintenance costs. The present invention is related to a process for
chemical or
electrochemical treatment of the surface of carbon steel, preferably strip
shaped, wherein the
material is treated with a pickling solution, preferably containing HCI, in
one or more
treatment tanks to remove an oxide scale layer which was previously formed
during the hot
rolling process of the metal strip (steel strip). This treatment is needed to
reach a clean
surface for either further processing it in a cold rolling process or for
direct commercial use.
[0019] According to an embodiment of the present invention, instead of
the steel strip
comprising carbon steel, it is also preferred that the steel strip consists of
carbon steel.
[0020] According to the present invention, it is preferred that the
process for chemical or
electrochemical treatment of the surface of carbon steel is conducted using a
pickling
solution containing HCI as the only pickling agent, wherein the advantages of
spray pickling
are used to a maximum extend. Furthermore the process shall be controllable
minimizing the
risk of over-pickling so that the process can be realized in commercially used
industrial scale
pickling lines.
[0021] According to the present invention, the spent acid of such a
process is of a
quality such that it can be treated in regeneration plants without additional
investment
considering in particular the FeCI3 concentration in such spent acid.
[0022] The present invention is also directed to the possibility to revamp
existing pickling
lines, in particular the treatment tanks, and to use more efficient pickling
technology with
improved efficiency while re-using existing equipment in order to reduce
installation costs, as
for example acid circulation circuits etc. can be reused.
[0023] According to the present invention, it is advantageously
possible that such
requirements can be achieved by the present invention, comprising a pickling
process using
an HCI containing pickling solution as the only pickling acid, wherein the
material to be
treated (i.e. the steel strip) is processed horizontally through one or more
treatment tanks
which are ¨ in case of more than one treatment tank ¨ operated as a pickling
cascade.
[0024] According to the present invention, each single treatment tank
(of the treatment
station) of the above described process comprises of one spray pickling zone
and one dip
pickling zone arranged as one unit using one common circulation circuit, i.e.
one common
circulation tank (common collection means) with several pump circuits as
required. All
pickling acid coming from the dip section and the spray section are collected
and mixed in
the common circulation tank (common collection means) and pumped back to the
above
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mentioned two pickling sections (of the treatment tank of the treatment
station). Inside the
single pickling tank (treatment tank), a guide roll underneath the strip
located between the
spray and pickling section might be required to better position the steel
strip inside the
treatment tank. Typically, a wringer roll unit ¨ as it is typically installed
between two pickling
sections ¨ is not required. Preferably the first section of the treatment tank
is a spray section
while the second section of the dip pickling type, preferably with high
efficiency such as
shallow tank turbulence technology.
[0025] According to the present invention, the steel strip is treated ¨
in the treatment
tank of the treatment station ¨ by means of a treatment liquid such that the
same treatment
liquid is used both in the spray section and in the immersion section of the
treatment tank.
Advantageously, it is thereby possible to realize the treatment station
(having both the spray
section and the immersion section) in a more cost effective manner as the same
common
collection means (as well as at least a part of the circulation system) can be
used for both the
spray section and the immersion section, hence reducing the costs for
realizing the
possibility to treat the steel strip by means of both the spray section and
the immersion
section.
[0026] According to the present invention, the steel strip comprises
carbon steel and is a
continuous steel strip being oriented substantially horizontally, both in its
longitudinal and
transverse directions, at least at the treatment station. This means that
steel strip is mostly
horizontally oriented in its transverse direction but is allowed to be sagging
in its longitudinal
direction. The height variation through the treatment station of the steel
strip in its longitudinal
direction may reach, e.g., up to 0,5 m. Preferably, also between the treatment
station or
between the plurality of treatment stations, the height variations of the
steel strip in its
longitudinal direction are also comprised up to 0,5 m. Generally, it is
preferred according to
the present invention that the height variation of the steel strip in its
longitudinal direction is
comprised between up to 0,5 m throughout the complete treatment system, that
potentially
(and typically) comprises a plurality of treatment stations one after the
other in the transport
direction of the steel strip.
[0027] According to the present invention, the treatment liquid is
sprayed ¨ in a first step
and by means of nozzles ¨ onto the top surface of the steel strip and onto the
bottom surface
of the steel strip while the steel strip is in the spray section of the
treatment station. In second
step (that is not necessarily subsequent to the first step but could also be
preceding the first
step), the steel strip is immersed in the treatment liquid while the steel
strip is in the
immersion section of the treatment station. For the treatment of the steel
strip, the treatment
liquid of the treatment station is continuously pumped out of the common
collection means
(of that treatment station) and through both the spray section and the
immersion section of
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the treatment tank, wherein spraying of the treatment liquid onto the top and
bottom surfaces
of the steel strip is provided using spray nozzles.
[0028] According to the present invention, two pickling technologies
are directly
combined in one treatment tank (i.e. in one treatment station), i.e. using
physically the same
pickling acids (or the same treatment liquid) in both pickling sections (i.e.
in both the spray
section and the immersion section of the considered treatment station), as
described. By
doing so, the concentration of FeCI3 can be kept below a critical level
throughout the entire
pickling process, guaranteeing a uniform pickling result without the risk of
over-pickling.
Furthermore the spent acid of such process can be easily regenerated in
regeneration plants
without additional investment to reach the legally required emission values,
especially
regarding dust emissions.
[0029] According to the present invention, the efficiency of the
treatment process (or
pickling process) is increased. Tests have proven that a certain increase in
the FeCI3
concentration reduces the pickling time also for the dip pickling process.
Consequently the
process according to the present invention uses the advantage of the high
efficient spray
pickling process while the efficiency of the dip pickling process is improved
as well, due to
the common use of the pickling acid (i.e. the same treatment liquid is used
both in the spray
section and the immersion section of one and the same treatment station), and
the
consequently increased FeCI3 level. Of course, in (the typical) case that more
than one
treatment stations are used in a pickling line or steel strip pickling
installation, this does not
mean that the same treatment liquid is used in all of such different treatment
stations. To the
contrary, in case of a plurality of treatment stations (i.e. having each a
treatment tank
comprising a spray section and an immersion section), a different treatment
liquid is normally
used for a different treatment station; however within the same treatment
station/treatment
tank, the same treatment liquid is used for both kinds of pickling processes
(spray and dip
pickling). Thereby, it is advantageously possible that the drawbacks of a
comparatively high
concentration in FeCI3 can be avoided that would typically arise in case of
combining spray
pickling and dip pickling using different treatment liquids in the same
treatment station.
[0030] According to the present invention, the design of the treatment
line or pickling line
is done in such a way that it is advantageously possible that the treatment
stations or
treatment tanks can easily replace existing treatment tanks in case of a
required revamp (or
refurbishment) while the circulation circuits can be reused. This is mainly
attributed to the fact
that the spray pickling technology and the dip pickling technology (i.e. the
spray section and
the immersion section) are combined in one treatment tank (i.e. as part of one
treatment
tank).
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[0031] The design of the present invention also allows the possibility
to operate the
treatment tanks without an additional (external) circulation tank ¨ or common
collection
means ¨ (i.e. external or separate to the treatment tank). In such an
embodiment, the
treatment tank itself, in particular the area underneath the spray section,
and, if required, also
underneath the dip section, is used as circulation tank (or common collection
means), i.e. the
circulation tank (or common collection means) is realized in a manner
integrated with the
treatment tank. This is advantageous for the replacement (refurbishment) of
deep bath
treatment tanks which have often been operated without circulation circuits.
In this case only
the pump circuit needs to be added while the circulation tank is incorporated
(or integrated)
in the treatment tank.
[0032] According to a preferred embodiment of the present invention,
the spray section
comprises an effective spray length in parallel to the longitudinal direction
of the steel strip
such that ¨ during the first step ¨ the top and bottom surfaces of the steel
strip receive the
treatment liquid while being located within the effective spray length,
wherein the immersion
section comprises an effective immersion length in parallel to the
longitudinal direction of the
steel strip such that ¨ during the second step ¨ the steel strip is immersed ¨
with its top and
bottom surfaces ¨ in the treatment liquid while being located within the
effective immersion
length, wherein the effective spray length and the effective immersion length
are provided
having a ratio of between and including 30:70 to 70:30, especially a ratio of
50:50.
[0033] According to the present invention, it is thereby advantageously
possible to
flexibly adapt process parameters of a pickling line to fit best with the
intended operative use
after construction. By means of defining the length of the immersion section
(at a given
transport speed of the steel strip through the pickling line), the time is
defined during which
the treatment liquid is effectively treating the steel strip in the immersion
section. By means
of defining the length of the spray section (equally at a given transport
speed of the steel strip
trough the pickling line), the maximum time of spray pickling is defined in
relation to the dip
pickling time.
[0034] According to another preferred embodiment of the present
invention, the effective
spray length and hence the ratio of the effective spray length vs. the
effective immersion
length is varied by activating only a part of the spray nozzles.
[0035] According to the present invention, it is thereby advantageously
possible to vary
the spray pickling time even during operational use of the pickling line, i.e.
by de-activating a
part of the spray nozzles. By selectively activating and/or de-activating
groups of spray
nozzles, is it advantageously possible according to the present invention,
that also the
manner or the intensity of the spray pickling step can be varied in
operational use of the
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pickling line, e.g. by using only every second spray nozzle such that spray
pickling is less
intensive in the spray section.
[0036] According to a preferred embodiment of the present invention,
the spray section
is located ¨ along the transport direction of the steel strip ¨ upstream with
respect to the
immersion section. According to an alternative preferred embodiment of the
present
invention, the spray section is located ¨ along the transport direction of the
steel strip ¨
downstream with respect to the immersion section.
[0037] According to the present invention, it is thereby advantageously
possible to
provide the possibility of different pickling line architectures. E.g., it is
advantageously
possible (in case that at least two treatment stations are used) to provide
both treatment
stations such that the spray section is located upstream with respect to the
immersion
section (i.e. the steel strip passes the spray section first and afterwards
the immersion
section): This results in a pickling sequence of the kind of a spray and dip
pickling (using a
first treatment liquid) in the first (or upstream) treatment station, followed
by a spray and dip
pickling (using a second treatment liquid) in the second (or downstream)
treatment station.
Alternatively, it is also advantageously possible (in case that at least two
treatment stations
are used) to provide the first treatment station such that the spray section
is located
downstream with respect to the immersion section (i.e. the steel strip passes
the immersion
section first and afterwards the spray section), and to provide the second
treatment station
such that the spray section is located upstream with respect to the immersion
section (i.e. the
steel strip passes the spray section (of the second treatment station) first
and afterwards the
dip section (of the second treatment station)): This results in a pickling
sequence of the kind
of a dip and spray pickling (using a first treatment liquid) in the first (or
upstream) treatment
station, followed by a spray and dip pickling (using a second treatment
liquid) in the second
(or downstream) treatment station. Of course, these building blocks of two
treatment stations
can be either repeated or combined with other treatment stations or
configurations of
treatment stations.
[0038] According to a preferred embodiment of the present invention,
the method
comprises using ¨ besides using the treatment liquid in the treatment station
¨ a further
treatment liquid in a further treatment station, the further treatment station
comprising a
further treatment tank with a further spray section and a further immersion
section, and the
further treatment station comprising a further common collection means for the
further
treatment liquid,
wherein the method comprises transporting the steel strip continuously through
the further
treatment station in the transport direction such that
-- in a third step, the further treatment liquid is sprayed onto the top
surface of the steel
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strip and onto the bottom surface of the steel strip while the steel strip
being in the further
spray section of the further treatment station,
-- in a fourth step, the steel strip is immersed in the further treatment
liquid while the steel
strip being in the further immersion section of the further treatment station,
wherein, while treating the steel strip, the further treatment liquid is
continuously pumped out
of the further common collection means and through both the further spray
section and the
further immersion section of the further treatment station , wherein spraying
of the further
treatment liquid onto the top and bottom surfaces of the steel strip is
provided using further
spray nozzles, wherein the third and fourth steps are preceding the first and
second steps or
are subsequent to the first and second steps.
[0039] According to the present invention, it is thereby advantageously
possible to
combine at least two inventive treatment stations in a pickling line. Of
course, it is also
possible and preferred according to the present invention to combine such two
inventive
treatment stations with a conventional treatment station (i.e. having solely a
spray section or
solely an immersion section in a treatment tank) or with a plurality of
conventional treatment
stations. In such an architecture of the pickling line, the two inventive
treatment station are
either located directly subsequent one after the other along the transport
direction of the steel
strip or the combination with one or a plurality of conventional treatment
stations is provided
such that the treatment station (or the first treatment station) is located
upstream according
to the transport direction of the steel strip with respect to a conventional
treatment station (or
with respect to a plurality of conventional treatment stations) and downstream
with respect to
this or these conventional treatment station(s) is located the further
treatment station (or
second treatment station) according to the present invention.
[0040] According to another preferred embodiment of the present
invention, the
treatment liquid and/or the further treatment liquid comprises
-- hydrochloric acid in a concentration ranging from and including 150 g/I to
and including
250 g/I and
-- FeCI3 in a concentration ranging from and including 10 g/I to and including
35 g/I,
especially in a concentration ranging from and including 15 g/I to and
including 30 g/I or
especially in a concentration ranging from and including 19 g/I to and
including 26 g/I and,
-- FeCl2+ ions in a concentration ranging from and including 30 g/I to and
including 300 g/I,
especially in a concentration ranging from and including 30 g/I to and
including 60 g/I or in a
concentration ranging from and including 130 g/I to and including 180 g/I or
in a
concentration ranging from and including 230 g/I to and including 300 g/I.
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[0041] According to the present invention, it is thereby advantageously
possible to
combine a high efficiency of the pickling process while retaining the
possibility to
comparatively easily regenerated the used pickling acids (treatment liquids).
[0042] The present invention also relates to a system for treating a
steel strip, especially
for a pickling treatment of the steel strip, by means of a treatment liquid in
a treatment
station, the system comprising the treatment station, wherein the treatment
station comprises
a treatment tank with a spray section, an immersion section, and the treatment
station
comprising a common collection means for the treatment liquid,
wherein the steel strip comprises carbon steel and is a continuous steel strip
being oriented
substantially horizontally, both in its longitudinal and transverse
directions,
wherein the steel strip has a top surface and a bottom surface,
wherein the system is configured to transport the steel strip continuously
through the
treatment station in a transport direction, the transport direction being
parallel to the
longitudinal direction of the steel strip, such that
-- the treatment liquid is sprayed onto the top surface of the steel strip and
onto the bottom
surface of the steel strip while the steel strip being in the spray section of
the treatment
station,
-- the steel strip is immersed in the treatment liquid while the steel strip
being in the
immersion section of the treatment station,
wherein the system is configured such that the treatment liquid is
continuously pumped out of
the common collection means and through both the spray section and the
immersion section
of the treatment station, wherein the system comprises spray nozzles such that
the treatment
liquid is sprayed onto the top and bottom surfaces of the steel strip using
the spray nozzles.
[0043] According to the present invention, it is thereby advantageously
possible to
provide a system (or a treatment station) that requires comparatively low
installation costs as
well as reduced maintenance costs. According to the present invention, it is
advantageously
possible to combine the advantages of spray pickling and dip pickling and to
minimize the
risk of over-pickling. It is furthermore advantageous that the spent acid of
such a system is of
a quality such that it can be treated in regeneration plants without
additional investment
considering in particular the FeCI3 concentration in such spent acid.
[0044] According to an embodiment of the present invention, instead of
the steel strip
comprising carbon steel, it is also preferred that the steel strip consists of
carbon steel.
[0045] According to a preferred embodiment of the present invention ¨
especially
regarding the inventive system ¨, the spray section comprises an effective
spray length in
parallel to the longitudinal direction of the steel strip such that the top
and bottom surfaces of
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the steel strip receive the treatment liquid while being located within the
effective spray
length, wherein the immersion section comprises an effective immersion length
in parallel to
the longitudinal direction of the steel strip such that the steel strip is
immersed ¨ with its top
and bottom surfaces ¨ in the treatment liquid while being located within the
effective
immersion length, wherein the effective spray length and the effective
immersion length are
provided having a ratio of between and including 30:70 to 70:30, especially a
ratio of 50:50.
[0046] According to the present invention, it is thereby advantageously
possible to
flexibly adapt process parameters of a pickling line to fit best with the
intended operative use
after construction.
[0047] According to a preferred embodiment of the present invention ¨
especially
regarding the inventive system ¨, the spray section is located ¨ along the
transport direction
of the steel strip ¨ upstream with respect to the immersion section. According
to an
alternative preferred embodiment of the present invention ¨ especially
regarding the
inventive system ¨, the spray section is located ¨ along the transport
direction of the steel
strip ¨ downstream with respect to the immersion section.
[0048] According to the present invention, it is thereby advantageously
possible to
flexibly adapt process parameters of a pickling line to fit best with the
intended operative use
after construction.
[0049] According to a preferred embodiment of the present invention ¨
especially
regarding the inventive system ¨, the common collection means for the
treatment liquid of
both the spray section and the immersion section is a collection means
separated from the
treatment tank of the treatment station.
[0050] According to the present invention, it is thereby advantageously
possible to build
the treatment tank in a very cost effective manner such that especially the
volume of the
treatment tank is comparably small (and hence less treatment liquid is to be
used). The
treatment liquid is pumped through the common collection means (or circulation
tank) that is
separated from the treatment tank.
[0051] According to a preferred embodiment of the present invention ¨
especially
regarding the inventive system ¨, the common collection means for the
treatment liquid of
both the spray section and the immersion section is a collection means
integrated with the
treatment tank of the treatment station, especially integrated such that the
bottom part of the
treatment tank forms the common collection means.
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[0052] According to the present invention, it is thereby advantageously
possible to
realize the treatment station in a very cost effective manner as no separate
common
collection means (or circulation tank) is required.
[0053] According to another preferred embodiment of the present
invention ¨related to
both the method and the system ¨, the length of the treatment station is
preferably 20 m or
less, preferably between 16 m and 20 m. The treatment station comprising both
the spray
section and the immersion section is preferably assembled using two main
components of
the treatment tank such that the treatment tank is ¨ after assembling the two
main
components ¨ integrally formed using the two main components.
[0054] According to the present invention, it is thereby advantageously
possible to
provide the two main components forming the treatment tank such that each of
the main
components have a maximum length of 11,6 m, i.e. the two main components have
a length
of 11, 6 m or less. Thereby, it is advantageously possible to transport these
main
components of the treatment tank, used in a treatment station according to the
inventive
method, such that no welding of the two main components is required.
Preferably, the main
components of the treatment tank are slid into one another. This enables a
much faster setup
of the treatment station which is especially advantageous in case of re-
furbishing existing
pickling lines, as the down-time due to the refurbishment can be considerably
reduced.
According to the present invention, it is preferred that one of the main
components of the
treatment tank realizes the spray section of the treatment station and the
other of the main
components of the treatment tank realizes the immersion section of the
treatment station.
[0055] According to a preferred embodiment of the present invention ¨
especially
regarding the inventive system ¨, the system comprises ¨ besides the treatment
liquid in the
treatment station ¨ a further treatment liquid in a further treatment station,
the further
treatment station comprising a further treatment tank with a further spray
section and a
further immersion section, and the further treatment station comprising a
further common
collection means for the further treatment liquid,
wherein the system is configured such that the steel strip is transported
continuously through
the further treatment station in the transport direction such that
-- the further treatment liquid is sprayed onto the top surface of the steel
strip and onto the
bottom surface of the steel strip while the steel strip being in the further
spray section of the
further treatment station,
-- the steel strip is immersed in the further treatment liquid while the steel
strip being in the
further immersion section of the further treatment station,
wherein the system is configured such that the further treatment liquid is
continuously
pumped out of the further common collection means and through both the further
spray
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section and the further immersion section of the further treatment station,
wherein the system
comprises further spray nozzles such that the further treatment liquid is
sprayed onto the top
and bottom surfaces of the steel strip using the further spray nozzles.
[0056] According to the present invention, it is thereby advantageously
possible to
combine at least two inventive treatment stations in a pickling line. Of
course, it is also
possible and preferred according to the present invention to combine such two
inventive
treatment stations with a conventional treatment station (i.e. having solely a
spray section or
solely an immersion section in a treatment tank) or with a plurality of
conventional treatment
stations.
[0057] According to a preferred embodiment of the present invention, the
system
comprises ¨ besides the treatment liquid in the treatment station and the
further treatment
liquid in the further treatment station ¨ a third treatment liquid in a third
treatment station, the
third treatment station comprising a third treatment tank with a third spray
section and a third
immersion section, and the third treatment station comprising a third common
collection
means for the third treatment liquid.
[0058] According to the present invention, it is thereby advantageously
possible to
combine at least three inventive treatment stations in a pickling line. Of
course, it is also
possible and preferred according to the present invention to combine such
three inventive
treatment stations with a conventional treatment station (i.e. having solely a
spray section or
solely an immersion section in a treatment tank) or with a plurality of
conventional treatment
stations.
[0059] According to a further preferred embodiment of the present
invention, the system
comprises ¨ besides the treatment liquid in the treatment station, the further
treatment liquid
in the further treatment station, and the third treatment liquid in the third
treatment station ¨ a
fourth treatment liquid in a fourth treatment station, the fourth treatment
station comprising a
fourth treatment tank with a fourth spray section and a fourth immersion
section, and the
fourth treatment station comprising a fourth common collection means for the
fourth
treatment liquid. According to other embodiments, also the combination of five
treatment
stations according to the present invention is possible and preferred
according to the present
invention.
[0060] According to another preferred embodiment of the present
invention, the
treatment liquid and/or the further treatment liquid and/or the third
treatment liquid comprises
-- hydrochloric acid in a concentration ranging from and including 150 g/I to
and including
250 g/I and
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-- FeCI3in a concentration ranging from and including 10 g/I to and including
35 g/I,
especially in a concentration ranging from and including 15 g/I to and
including 30 g/I or
especially in a concentration ranging from and including 19 g/I to and
including 26 g/I and,
-- FeCl2 in a concentration ranging from and including 30 g/I to and including
300 g/I,
especially in a concentration ranging from and including 30 g/I to and
including 60 g/I or in a
concentration ranging from and including 130 g/I to and including 180 g/I or
in a
concentration ranging from and including 230 g/I to and including 300 g/I.
[0061] According to the present invention, it is thereby advantageously
possible to
combine a high efficiency of the pickling process while retaining the
possibility to
comparatively easily regenerated the used pickling acids (treatment liquids).
[0062] These and other characteristics, features and advantages of the
present
invention will become apparent from the following detailed description, taken
in conjunction
with the accompanying drawings, which illustrate, by way of example, the
principles of the
invention. The description is given for the sake of example only, without
limiting the scope of
the invention. The reference figures quoted below refer to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] Figure 1 schematically illustrates a treatment system comprising
three different
treatment stations, each one being configured according to the present
invention, i.e. having
a treatment tank with both a spray section and an immersion section such that
a common
collection means and the same treatment liquid is used for the treatment of
the steel strip in
both the respective spray section and the immersion section.
[0064] Figure 2 schematically illustrates a first embodiment of a
treatment station having
a treatment tank and a common collection means separated from the treatment
tank, the
treatment tank having its spray section and its immersion section to treat the
steel strip with a
common treatment liquid circulating between ¨ and within ¨ the common
collection means on
the one hand, and the spray and immersion sections on the other hand.
[0065] Figure 3 schematically illustrates a second embodiment of a
treatment station
having a treatment tank and a common collection means separated from the
treatment tank,
the treatment tank having its spray section and its immersion section to treat
the steel strip
with a common treatment liquid circulating between ¨ and within ¨ the common
collection
means on the one hand, and the spray and immersion sections on the other hand.
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DETAILED DESCRIPTION
[0066]
The present invention will be described with respect to particular embodiments
and with reference to certain drawings but the invention is not limited
thereto but only by the
claims. The drawings described are only schematic and are non-limiting. In the
drawings, the
size of some of the elements may be exaggerated and not drawn on scale for
illustrative
purposes.
[0067]
Where an indefinite or definite article is used when referring to a singular
noun,
e.g. "a", "an", "the", this includes a plural of that noun unless something
else is specifically
stated.
[0068]
Furthermore, the terms first, second, third and the like in the description
and in
the claims are used for distinguishing between similar elements and not
necessarily for
describing a sequential or chronological order. It is to be understood that
the terms so used
are interchangeable under appropriate circumstances and that the embodiments
of the
invention described herein are capable of operation in other sequences than
described of
illustrated herein.
[0069]
Figure 1 schematically illustrates a treatment system comprising three
different
treatment stations 3, 31, 32 as an example of a pickling line according to the
present
invention. In one possible and preferred implementation of the pickling line
for the treatment
of a steel strip 1, represented in Figure 1, all three treatment stations 3,
31, 32 represent
treatment stations according to the present invention, i.e. having a treatment
tank with both a
spray section and an immersion section such that a common collection means and
the same
treatment liquid is used for the treatment of the steel strip in both the
respective spray section
and the immersion section. In this implementation or architecture of the
pickling line, all three
treatment stations 3, 31, 32 are realized either according to a first
embodiment of the present
invention, represented in Figure 2 for the exemplary case of the treatment
station being
represented by reference sign 3, or according to a second embodiment of the
present
invention, represented in Figure 3 for the exemplary case of the treatment
station being
represented by reference sign 3. Alternatively, a part of the three treatment
stations 3, 31, 32
is or are realized according to the first embodiment of the present invention
(Figure 2) and
another part is or are realized according to the second embodiment of the
present invention
(Figure 3). In the context of the present invention, the terms 'treatment
station' and 'first
treatment station' as well as 'further treatment station' and 'second
treatment station' are
used synonymously and only aim to differentiate the treatment stations from
one another.
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Typically, the naming convention typically (but not necessarily) relates to
the location of a
treatment station along the transport direction of the steel strip, the
transport direction being
represented by reference sign 2. In the implementation represented in Figure
1, a treatment
station (or first treatment station) 3 is located upstream of a further
treatment station (or
second treatment station) 31. The further treatment station (or second
treatment station) 31
is located upstream of a third treatment station 32. The treatment station (or
first treatment
station) 3 comprises a treatment tank (or first treatment tank) 4, and a
common collection
means (or first common collection means) 5. The further treatment station (or
second
treatment station) 31 comprises a further treatment tank (or second treatment
tank) 41, and a
further common collection means (or second common collection means) 51. The
third
treatment station 32 comprises a third treatment tank 42, and a third common
collection
means 52. In the exemplary implementation of the pickling line represented in
Figure 1
(where all treatment stations are configured according to the present
invention), all tree
treatment stations 3, 31, 32 each have a spray section and an immersion
section as part of
their respective treatment tank 4, 41, 42, i.e. the treatment station (or
first treatment station) 3
has a spray section (or first spray section) and an immersion section (or
first immersion
section) using a treatment liquid (or first treatment liquid), the further
treatment station (or
second treatment station) 31 has a further spray section (or second spray
section) (not
depicted in Figure 1) and a further immersion section (or second immersion
section) (not
depicted in Figure 1) using a further treatment liquid (or second treatment
liquid), and the
third treatment station 32 has a third spray section (not depicted in Figure
1) and a third
immersion section (not depicted in Figure 1) using a third treatment liquid.
For the exemplary
case of the treatment station 3 (first treatment station 3), a first and a
second embodiment of
the present invention is schematically shown in Figures 2 and 3.
[0070] Figure 2 schematically illustrates the first embodiment of the
treatment station 3
having the treatment tank 4 and the common collection means 5 separated from
the
treatment tank 4, the treatment tank 4 having its spray section 13 and its
immersion section
14 to treat the steel strip 1 with a common treatment liquid circulating
between ¨ and within ¨
the common collection means 5 on the one hand, and the spray and immersion
sections 13,
14 on the other hand.
[0071] Figure 3 schematically illustrates a second embodiment of a
treatment station 3
having the treatment tank 4 and the common collection means 5 separated from
the
treatment tank 4, the treatment tank 4 having its spray section 13 and its
immersion section
14 to treat the steel strip 1 with a common treatment liquid circulating
between ¨ and within ¨
the common collection means 5 on the one hand, and the spray and immersion
sections 13
on the other hand.
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[0072] Figures 1, 2 and 3 combined illustrate the inventive treatment
process and
system (or treatment station) for chemical or electrochemical treatment of the
surface of the
steel strip 1, the steel strip 1 being a carbon steel strip. The steel strip 1
is first horizontally
transported through the treatment stations 3, 31, 32 in which the steel strip
1 is treated with a
treatment liquid in the form of a pickling acid, normally containing HCI. At
least one of the
treatment stations 3, 31, 32 (or their respective treatment tanks 4, 41, 42)
comprises a spray
pickling section (as represented in Figures 2 and 3 as spray section 13 of the
treatment
station 3) and a dip pickling section (as represented in Figures 2 and 3 as
immersion section
14 of the treatment station 3) according to the present invention. Figure 1
shows an
exemplary implementation with three treatment station 3, 31, 32 (each having a
treatment
tank) as a preferred embodiment, however the number of treatment stations (and
treatment
tanks) is at least one and is not limited to three.
[0073] All treatment stations 3, 31, 32 comprise a common collection
means,
respectively (i.e. the respective treatment tanks 4, 41, 42 are connected to
respective
common collection means (or circulation tanks) 5, 51, 52), wherein the common
collection
means 5, 51, 52 are either (i.e. potentially for each treatment station 3, 31,
32 differently)
realized as separate tanks as shown in the first embodiment represented in
Figure 2 or are
realized as common collection means 5, 51, 52 integrated in the respective
treatment tank 4,
41,42 as shown in Figure 3.
[0074] In the exemplary embodiment shown in Figure 1, the common collection
means
(or circulation tanks) 5, 51, 52 are operated as a cascade, i.e. the fresh or
regenerated acid
(i.e. the treatment liquid) is added (cf. reference sign 54) to the last
common collection
means (or last circulation tank) 52 - i.e. being related to the most
downstream treatment
station 32 according to the transport direction 2 of the steel strip 1 - and
is consequently
transferred to the other common collection means (or circulation tanks) in
counter direction to
the strip transport direction 2. Thereby, the level of free acid is the
highest in the third
treatment liquid (circulating in the third treatment station 32), the level of
free acid is medium
in the further treatment liquid (second treatment liquid) (circulating in the
further (second)
treatment station 31), and lowest in the treatment liquid (first treatment
liquid) (circulating in
the (first) treatment station 3. Finally the spent acid is removed (reference
sign 55) from the
(first) common collection means (or (first) circulation tank) 5. After the
pickling treatment in
the three treatment stations 3, 31, 32 (in the exemplary implementation shown
in Figure 1),
the steel strip 1 is further processed in section 6 which comprises a rinse
section and a dryer,
if required.
[0075] According to the first embodiment of the common collection means (or
circulation
tank) 5, shown in Figure 2, the treatment station 3 comprises the treatment
tank 4 with a
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separate common collection means 5 (or separate circulation tank 5). At the
entry and exit
section, wringer rolls 12 are installed to remove pickling acid from the strip
and to guide the
steel strip 1 inside the treatment tank 4. The wringer roll 12 in the entry
section is only used
when the treatment tank is the first tank in the pickling process like the
treatment station 3 in
Figure 1. The following treatment stations (or treatment tanks), like
treatment stations 31, 32
in Figure 1, do not need such wringer roll 12. In the exemplary representation
of Figure 2 (i.e.
not necessarily), the first part (according to the transport direction of the
steel strip 1) of the
treatment tank 4 is a spray pickling section 13 or spray section 13, followed
by a dip pickling
section 14 or immersion section 14. In the spray pickling section 13, spray
nozzles 15 are
mounted above and below the surface of the steel strip 1. The pickling acid
(or treatment
liquid) is pumped from the circulation tank 5 (or common collection means 5)
by means of
pumps 17, 18 to both the spray pickling section 13 and the dip pickling
section 14. In one or
more of the pump circuits, a heat exchanger 19 is installed to heat the
pickling acid
(treatment liquid) to the required temperature. If required, a guide roll 20
can be installed
between the spray pickling section13 and the dip pickling section 14 in order
to reduce the
slack of the strip.
[0076] According to the second embodiment of the common collection
means (or
circulation tank) 5, shown in Figure 3, the treatment station 3 comprises the
treatment tank 4
with an integrated common collection means 5. The other components of the
treatment
station 3 are analogous to the description of Figure 2.
[0077] While specific embodiments of the invention have been shown and
described in
detail to illustrate the inventive principles, it will be understood that the
invention may be
embodied otherwise without departing from such principles.
[0078] For example, the pickling line is configured for a maximum width
of the steel strip
1 of 1890 mm, a maximum speed of the steel strip 1 of 255 m/min. Furthermore
exemplarily,
the distance of the spray nozzles 15 to the steel strip 1 (both from the spray
nozzles to the
top surface 1' of the steel strip 1, and to the bottom surface 1" of the steel
strip 1) is 200 mm
or approximately 200 mm. Additionally, the distance of the spray nozzles 15 to
each other in
the lateral direction of the steel strip 1 corresponds to 200 mm or
approximately 200 mm.
Additionally, the distance of the spray nozzles 15 to each other in the
longitudinal direction of
the steel strip 1 corresponds to 500 mm or approximately 500 mm. The treatment
liquid is
preferably pumped out of the spray nozzles having a pressure of between and
including 1
bar to and including 3 bar, and the amount of treatment liquid per spray
nozzle is preferably
12 l/min or approximately 12 l/min. For example, the total number of spray
nozzles per
treatment station corresponds to 306 or approximately 306, and the amount of
pumped
treatment liquid per treatment station corresponds to 220 m3/h or
approximately 220 m3/h.
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[0079] Test trials were carried out in a pilot plant. The pilot plant
consisted of two
treatment stations (each having a treatment tank) both arranged as described
in the present
invention with a first spray pickling section followed by a dip pickling
section in each of the
treatment tanks. The treatment tanks were designed so that the length of both
sections was
approximately the same. The pickling acid used was HCI with a concentration of
approx. 200
g/I total acid in both tanks. The material treated during the test runs were
different IF steel
grades (interstitial Free steel), which belong to the group of steel grades
that are more
difficult to pickle mainly due to their high recoiling temperature. The test
results have proven
that the pickling time could be reduced by 40 ¨ 45% compared to the
conventional pickling
process using dip pickling with shallow tank turbulence technology, while the
FeCI3
concentration was constantly below 30 g/I which is considered to be uncritical
as far as the
acid regeneration process is concerned. All tested materials showed uniform
pickling results
without any signs of over-pickling.
[0080] In another test using the same pilot plant, the material was
treated with a reduced
temperature of the pickling acid (treatment liquid). The results showed that
the temperature
could be reduced from 90 C down to 70 C while still reaching the same
pickling time as for
the conventional dip pickling process with shallow tank turbulence technology.
This result is
equivalent to a 20 % reduction of the energy which is needed to keep the
process
temperature in the pickling process.
[0081] As an example of the operation of the system and especially of the
use of the
treatment liquids as a cascade, an example is given of the concentration
values for an
example of using three treatment stations in a pickling line:
In the first treatment station 3, the concentration of HCI is in the range of
between and
comprising 205 g/I to and comprising 220 g/I, the concentration of FeCl2 is in
the range of
between and comprising 260 g/I to and comprising 278 g/I, the concentration of
FeCI3 is in
the range of between and comprising 22 g/I to and comprising 26 g/I. The
temperature of the
treatment liquid is in the range of between and comprising 88 C to and
comprising 91 C.
In the second treatment station 31, the concentration of HCI is in the range
of between and
comprising 201 g/I to and comprising 211 g/I, the concentration of FeCl2 is in
the range of
between and comprising 140 g/I to and comprising 146 g/I, the concentration of
FeCI3 is in
the range of between and comprising 21 g/I to and comprising 26 g/I. The
temperature of the
treatment liquid is in the range of between and comprising 88 C to and
comprising 91 C.
In the third treatment station, the concentration of HCI is in the range of
between and
comprising 193 g/I to and comprising 206 g/I, the concentration of FeCl2 is in
the range of
between and comprising 43 g/I to and comprising 47 g/I, the concentration of
FeCI3 is in the
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range of between and comprising 19 g/I to and comprising 22 g/I. The
temperature of the
treatment liquid is in the range of between and comprising 88 C to and
comprising 91 C.
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REFERENCE SIGNS
1 steel strip
2 transport direction of the steel strip
3 treatment station
4 treatment tank (of the treatment station)
5 common collection means (of the treatment station)
12 wringer roll(s)
13 spray section (of the treatment station)
14 immersion section (of the treatment station)
spray nozzles (of the treatment station)
17, 18 pumps
19 heat exchanger
guide roll(s)
15 31 further treatment station
41 further treatment tank (of the further treatment
station)
51 further common collection means (of the further
treatment station)
32 third treatment station
42 third treatment tank (of the third treatment station)
20 52 third common collection means (of the third treatment
station)
54 feeding of fresh treatment liquid
55 removing of used treatment liquid
