EP2304060B1 - Method and device for regulating the cooling and energy recovery of a steel strip in an annealing or galvanisation phase - Google Patents

Description

The present invention relates to a method and a device for regulating the cooling necessary for forced cooling of a continuous circulating steel strip in an installation suitable for continuous annealing or continuous dipping according to the preambles of claims 1 and 6.

In particular, the invention relates to continuous annealing furnaces for the heat treatment of cold rolled steel strips, particularly rapid cooling of said strips.

The cold rolling of the steel causes hardening by hardening of the steel which causes a fragility making problematic or prohibiting the subsequent shaping of the rolled strips.

In order to restore the ductility of these strips, a heat treatment called "recrystallization annealing" is implemented. To do this, as an alternative to static treatments in batch annealing on the rolls of rolled strips, specialized (annealing) lines have been constructed in order to carry out the treatment of these strips in continuous scrolling.

• une section d'entrée comprenant une ou deux dérouleuses (1) de bande, une cisaille guillotine (2), une soudeuse de raboutage (3) permettant de raccorder une queue d'une bande issue d'une des dérouleuses à la tête d'une prochaine bande issue de l'autre dérouleuse et assurant ainsi un fonctionnement continu de la ligne, un accumulateur de bande (4) qui, à son aval, restitue de la bande préalablement accumulée lorsque le déroulement en amont de l'accumulateur est figé pour réaliser la soudure de raboutage ;
• un four (5) avec une section de préchauffage (6), une section de maintien à la température de recuit (7), une section de refroidissement rapide (8), une section de plusieurs unités de sur-vieillissement (9) suivies d'une section de refroidissement sous gaz protecteur (10) ;
• une section de sortie avec un accumulateur de sortie (11), un ensemble de laminage de bande de type « Skin-Pass » (12), une cisaille (13) et une ou deux enrouleuses (14) de bande travaillant alternativement.

By way of example, such a continuous annealing line is schematized in figure 1 , and typically comprises:

• an inlet section comprising one or two belt unrollers (1), a guillotine shear (2), a splicing welder (3) for connecting a tail of a belt from one of the unrollers to the head of the machine; next tape from the other unwinder and thus ensuring a continuous operation of the line, a tape accumulator (4) which, on its downstream, restores the previously accumulated tape when the flow upstream of the accumulator is fixed to perform the splicing weld;
• an oven (5) with a preheating section (6), a holding section at the annealing temperature (7), a rapid cooling section (8), a section of several over-aging units (9) followed by a protective gas cooling section (10);
• an output section with an output accumulator (11), a "Skin-Pass" type strip lamination assembly (12), a shear (13), and one or two alternately working strip reels (14).

The furnace must be able to provide, for tape speeds of several hundred meters per minute, heating and cooling rates and holding times adapted to the metallurgy of the treated steel. While the heating and maintenance times essentially involve the length of the furnaces and therefore the investment costs, the cooling rate poses real technological problems.

• les procédés par tubes refroidis à l'eau ou à l'air qui, agissant à l'inverse de tubes de chauffage radiants, absorbent un rayonnement de la bande. Ils n'autorisent que des vitesses de refroidissement faibles de l'ordre de 2 à 10°C/s et ne sont guère utilisés que dans la phase initiale du refroidissement, par exemple entre 800 et 600°C. Ils sont ainsi inadaptés aux fortes vitesses de trempe ;
• les procédés de refroidissement par jets de gaz neutre sur la bande comme de l'azote ou un mélange d'azote et d'hydrogène réducteur dont le pourcentage est voisin ou peu supérieur à 5% (aussi connu sous la terminologie « Gas Jet Cooling »). Ils autorisent des vitesses de refroidissement de 10 à 150°C/s selon les débits et températures de gaz, la vitesse de défilement et l'épaisseur des bandes. Ils présentent l'avantage de ne pas oxyder la surface des bandes et même de réduire les oxydes superficiels qui auraient pu se former en amont dans le four. Ils autorisent cependant des vitesses de refroidissement trop lentes pour certains aciers. De telles installations sont décrites, par exemple, dans les documents EP 1 602 738 et EP 0 182 050 ;
• les procédés de refroidissement de bande sur rouleaux (aussi connu sous la terminologie « Roll Quenching ») qui assurent des allures de refroidissement un peu plus élevés de celles obtenues au moyen de jets de gaz. Ces procédés sont fondés sur l'échange entre la surface de la bande et la surface de rouleaux imbriqués et refroidis par circulation d'eau autour desquels la bande serpente. Pouvant être pratiqués sous atmosphère neutre ou légèrement réductrice, ils présentent les mêmes avantages que les jets de gaz mais aussi certains inconvénients de plissement de la bande, particulièrement pour des bandes larges et fines. D'autre part, l'efficacité de l'échange thermique par conduction diminue avec l'augmentation de l'épaisseur de la bande. De telles installations sont décrites, par exemple, dans le document EP 0 418 166 ;
• les procédés de refroidissement par pulvérisation d'eau ou de brouillards air / eau autorisent des vitesses de refroidissement nettement plus rapide pouvant atteindre plusieurs centaines de degrés par seconde, typiquement, en fonction de la densité de brouillard, entre 50 et 400°C/s. Il est alors possible de traiter des aciers à haute résistance, par exemple à structure finale entièrement ou partiellement martensitique. Ils présentent cependant l'inconvénient d'oxyder superficiellement la bande et de nécessiter un décapage en sortie de four. De telles installations sont décrites, par exemple, dans le document JP 2000 119757 ;
• les procédés par trempe directe de bande dans un bac d'eau (aussi connu sous la terminologie « Water Quenching ») à température régulée voisine de 50°C autorisent des vitesses de refroidissement pouvant atteindre plusieurs milliers de degrés par seconde, typiquement entre 1000 et 4000°C/s. Ils présentent de multiples inconvénients comme celui de refroidir la bande à des températures trop basses pour assurer sans réchauffage un sur-vieillissement, celui d'oxyder la bande et celui de produire de la vapeur qui complique le contrôle d'atmosphère du four. Ils nécessitent un réchauffage jusque vers 350°C avant sur-vieillissement et un décapage en sortie de four. De telles installations sont décrites, par exemple, dans le document JP2005179774 .

There are five types of cooling processes that can be used depending on the required speed:

• water-cooled or air-cooled tube processes which, in contrast to radiant heating tubes, absorb radiation from the strip. They allow only low cooling rates of the order of 2 to 10 ° C / s and are used only in the initial phase of cooling, for example between 800 and 600 ° C. They are thus unsuitable for high tempering speeds;
• the processes of cooling by jet of neutral gas on the strip such as nitrogen or a mixture of nitrogen and reducing hydrogen whose percentage is close to or slightly greater than 5% (also known under the terminology "Gas Jet Cooling" ). They authorize cooling rates of 10 to 150 ° C / s depending on the flow rates and gas temperatures, the speed of travel and the thickness of the strips. They have the advantage of not oxidizing the surface of the strips and even to reduce surface oxides that could have formed upstream in the furnace. However, they allow slow cooling speeds for some steels. Such facilities are described, for example, in the documents EP 1 602 738 and EP 0 182 050 ;
• roll-on-roll cooling processes (also known as "roll quenching") which provide slightly higher cooling rates than those obtained by means of gas jets. These methods are based on the exchange between the surface of the strip and the surface of nested rolls and cooled by circulation of water around which the strip winds. Being able to be practiced under neutral or slightly reducing atmosphere, they have the same advantages as gas jets but also some disadvantages of folding of the band, particularly for wide and thin strips. On the other hand, the efficiency of conductive heat exchange decreases with the increase of the thickness of the strip. Such installations are described, for example, in the document EP 0 418 166 ;
• water spray or air / water mist cooling processes allow much faster cooling rates of up to several hundred degrees per second, typically, depending on the fog density, between 50 and 400 ° C / sec . It is then possible to treat high-strength steels, for example with a final structure that is wholly or partially martensitic. However, they present the disadvantage of superficially oxidizing the strip and requiring stripping out of the oven. Such installations are described, for example, in the document JP 2000 119757 ;
• the processes by direct quenching of tape in a water tank (also known as "Water Quenching") at a controlled temperature of about 50 ° C allow cooling speeds of up to several thousand degrees per second, typically between 1000 and 4000 ° C / s. They have many disadvantages, such as cooling the strip at too low temperatures to ensure, without reheating, an over-aging, that of oxidizing the strip and that of producing steam which complicates the furnace atmosphere control. They require reheating up to 350 ° C before over-aging and stripping at the oven outlet. Such installations are described, for example, in the document JP2005179774 .

All these methods have in common denominator the extraction of heat from the strip and restore it outside the oven via a cooling medium, water in the most general case.

Processes directly implementing this water (such as quench tanks) or indirectly through heat exchanger systems (such as gas jets) are supplied with water at ambient temperature or close to ambient, typically at 30 or 35 ° C. and return water whose temperature does not generally reach more than 40 to 70 ° C. It is obviously difficult to envisage applications of this heated water at a relatively modest temperature except, possibly, for the heating of buildings. Although it is theoretically possible to make the use and distribution of the recovered heat easier by tolerating a higher temperature of the cooling water, this increase in temperature could only be achieved at the expense of the efficiency of the cooling process of the band, which is obviously not desirable.

More commonly, the water is treated according to evaporative cooling techniques such as cooling towers or air-cooling devices. As the temperature of the water thus cooled remains higher than the humid bulb temperature of the ambient air and is also subjected to climatic variations, the efficiency of these cooling processes is limited to minimum temperatures of approximately 30 ° C. at 35 ° C.

Given the constant increase in energy and the impact of its generation on the environment, it is increasingly necessary to recover and use with the greatest efficiency, in the very place where it can be captured. , the energy available in the cooling processes that are numerous in the metallurgical industry.

An object of the present invention is therefore to provide a cooling control method and a device for its implementation, both adapted to a forced cooling of a continuous circulating steel strip in an installation adapted to continuous annealing. or a continuous dipping galvanization allowing an advantageous cooling dynamics for any type of band in various annealing or galvanizing conditions.

• ils assurent une récupération efficace de l'énergie cédée par les bandes d'acier laminé lors de leur refroidissement dans les sections de refroidissement des fours de recuit continu ou de galvanisation et sa réutilisation immédiate de cette énergie avec un maximum d'efficacité ;
• ils permettent d'abaisser la température de l'eau de refroidissement jusqu'à des valeurs inférieures à 10°C ;
• ils permettent d'augmenter la vitesse de refroidissement des procédés utilisés sous atmosphère neutre ou réductrice, ne nécessitant ainsi pas de décapage subséquent ;
• ils peuvent également être mis en oeuvre, dans le domaine de l'industrie métallurgique, partout où il s'agit de récupérer de l'eau de refroidissement, par exemple celle utilisée dans les rouleaux et parois refroidis de coulée continue de l'acier ou dans les murs et voutes refroidies des fours électriques de fusion.

In particular, the method and the device according to the invention should have several advantages over existing methods or devices, in that:

• they ensure an efficient recovery of the energy yielded by the rolled steel strips during their cooling in the cooling sections of continuous annealing or galvanizing furnaces and its immediate reuse of this energy with maximum efficiency;
• they allow to lower the temperature of the cooling water to values lower than 10 ° C;
• they make it possible to increase the cooling rate of the processes used under a neutral or reducing atmosphere, thus not requiring subsequent etching;
• they can also be used, in the field of the metallurgical industry, wherever it is necessary to recover cooling water, for example that used in rolls and cooled walls of continuous casting of steel or in cooled walls and vaults electric melting furnaces.

The invention thus proposes a cooling regulation method and a device for implementing it according to claims 1 and 6.

A set of subclaims also has advantages of the invention as described later in the document.

Figures 2a, 2b, 2c

Schémas liés à différents modes de refroidissement rapide dans un four de recuit continu,

Figure 3a, 3b

Schémas de principe du dispositif selon l'invention,

Figure 4

Schéma général de circulation de fluides concernés par le dispositif selon l'invention dans une installation de recuit continu,

Figure 5

Schéma de principe du dispositif selon l'invention adapté à un refroidissement progressif de la bande par soufflage,

Figure 6

Schéma de principe du dispositif selon l'invention adapté au refroidissement par immersion dans un bac,

Figure 7a, 7b

Mise en série de dispositifs selon l'invention.

Exemplary embodiments and applications for clarifying and aiding in a good interpretation of the invention are provided by means of the figures described:

Figures 2a, 2b, 2c

Schemes related to different modes of rapid cooling in a continuous annealing furnace,

Figure 3a, 3b

Schematic diagrams of the device according to the invention,

Figure 4

General flow diagram of fluids concerned by the device according to the invention in a continuous annealing installation,

Figure 5

Diagram of the device according to the invention adapted to a progressive cooling of the strip by blowing,

Figure 6

Diagram of the device according to the invention adapted to cooling by immersion in a tank,

Figure 7a, 7b

Serialization of devices according to the invention.

The figure 2a schematically discloses rapid cooling by gas jet (or blowing) in a continuous annealing furnace: a steel strip (B) scrolls vertically in an oven (5) passing through at least one blast cell (51). ). Each cell (51) comprises a motor-fan unit (511) supplying a blow box (513) via a sheath (512). Each blow box (513) surrounds the strip and each of its two faces parallel to the strip is equipped with fresh gas diffusers (5131). The heated gas in contact with the strip is cooled in at least one cooling unit (514), each of which comprises a sheath (5141) ensuring the capture of the hot gas in the furnace chamber to bring it into an exchange device constituted by a gas / water exchanger (5142). A circulation of cold water between inlets and outlets (51421, 51422) lowers the temperature of the gas, which, thus cooled, returns to the suction inlet of the motor-fan (511).

The figure 2b schematically describes rapid cooling by cooled rolls: The steel strip (B) winds between a lower layer (RI) and an upper layer (RS) of several rollers arranged side by side and having parallel main axes, said rollers being cooled by circulation of water under low pressure. At least one of the two plies is able to move vertically in order to adjust the nesting of the rollers and, consequently, the arc of contact of the strip with the surface of the rollers in order to regulate the heat exchange. between the two. The greater the arc of contact (by means of a large gap between the layers, that is to say an increase of the consecutive axis deviations of rollers), the more the cooling is intensified, and vice versa for reduce the cooling.

The Figure 2c schematically shows the cooling rate range (V _Ref ), between 1 and 10000 ° C / s, of conventional steel strip cooling processes: a cooled tube process (T), a gas jet process (JG ), a cooled-roller (RR) process, a water-spray or water-gas (PE) mixing process, and finally, for the quickest, a quenching process in a water tank (TE). It should be noted that the cooling regulation according to the invention is advantageously adapted to the dynamics of each of these processes while providing a solution to the problems previously raised.

The figure 3a shows a schematic diagram of the device according to the invention in relation to the figure 2a for example, where a method of cooling by gas jet (blowing) uses a blowing cell (51) on the strip (B) in continuous scrolling. As described in figure 2a , the heated gas is recovered in the furnace enclosure (5) and passes into a gas / water heat exchanger (5142) whose inputs and outputs (51421 and 51422), water side (to be cooled), are connected to a unit vacuum cooling device (52) associated with said exchanger (5142).

• au moins un organe d'échange (51, 5142) assurant un transfert de chaleur de la bande d'acier à une eau de refroidissement et comprenant une sortie (51422) de l'eau de refroidissement ainsi réchauffée,
• au moins une unité de refroidissement (52) constituée d'une enceinte étanche (521) reliée à la sortie (51422) de l'organe d'échange (5142) et équipée d'au moins une sortie (5211) sur un dispositif à effet Venturi tel qu'un éjecteur (522) à vapeur et dans laquelle l'eau de refroidissement est elle-même soumise à un refroidissement par vaporisation sous vide,
• une sortie auxiliaire (5213) de l'enceinte étanche (521) reliée à une entrée (51421) de l'organe d'échange (51, 5142).

More generally, the figure 3a presents the cooling regulator according to the invention, necessary for forced cooling of a steel strip (B) circulating continuously in an installation suitable for continuous annealing or continuous dipping, said device comprising:

• at least one exchange member (51, 5142) providing heat transfer from the steel strip to a cooling water and comprising an outlet (51422) of the thus-heated cooling water,
• at least one cooling unit (52) consisting of a sealed enclosure (521) connected to the outlet (51422) of the exchange member (5142) and equipped with at least one outlet (5211) on a device Venturi effect such as a steam ejector (522) and wherein the cooling water is itself subjected to vacuum vapor cooling,
• an auxiliary output (5213) of the sealed enclosure (521) connected to an inlet (51421) of the exchange member (51, 5142).

In this case of cooling by gas jets, the blowing of the cooling gas is provided by blowing cells consisting of a motor-blower blowing into diffusion chambers placed on either side of the strip in order to cool them. two faces. The gas reheated in contact with the strip up to about 45 ° C. to 180 ° C. is sucked by the fan into the enclosure of the furnace and passes into an exchange member consisting of a gas / water exchanger from which it exits to 30 ° C - 50 ° C before being reinjected by the fan into the diffusion chambers. In general, the cooling is carried out by several cells placed one after the other along the path of the strip. The cooling thereof is progressive between the maximum temperature is 600 to 800 ° C and the usual temperature of over-aging or galvanization is 300 to 500 ° C. Advantageously, the device according to the invention may comprise several cooling units each comprising a cell or a battery of several blowing cells. Each unit can be dimensioned to stagger the temperature of the water returned to the exchange member, for example 30 to 10 ° C in order to stagger the temperature of the cooling gases of the strip in the direction of scrolling of it. The highest water temperature returned upstream of the cooling section and the lowest temperature downstream where the temperature difference between the strip and the cooling gas is the lowest.

In a variant of this first cooling mode, a first cooling unit associated with a first exchange member located upstream of the fan acts as described above and a second cooling unit associated with a second exchange member located in downstream fan ensures very well, with a chilled water whose temperature is between 5 and 10 ° C, the cooling of the gas entering the diffusion chambers.

The same principles can be implemented in a cooling system with cooled rolls in which the contact of the surface of the strip with the surface of the rollers acts as exchange member (51, 5142), being connected to the cooling unit (52). This installation is particularly well suited to an effective staging of the water temperature returned.

The exchange member (51, 5142) between the strip and the cooling water can thus advantageously be, depending on the type of embodiment, a water / water or gas / water exchanger and applies to the progressive cooling processes of the band as cooling by cooled tubes or by gas jets or by cooled rollers.

Finally, the cooling control device according to the invention may comprise at least one vapor condenser (523) being disposed at the outlet of the ejector (522) of the sealed enclosure and adapted to replenish the sealed enclosure ( 521) by booster (5214) of a water level required in and, if necessary, adapted to redirect a surplus of said vaporized water to an external pipe (5233) for reuse or vapor dissipation, ideally for plant-specific or steam rejection purposes.

The cooling device may be of the "barometric" type, that is to say that the partial vacuum chamber is connected to the exchange member by a water column of height, generally equal or greater than eleven meters. This arrangement is particularly well suited to quenching type exchange sources, an example of application of the invention will be presented later.

It can also be of closed type, the sealed enclosure under partial vacuum being connected to the exchange member by a closed circuit comprising a circulation pump. This arrangement is particularly suitable for exchange sources of the heat exchanger type.

Particularly advantageously, the steam supplying the ejector comes from a boiler for producing steam heated with the flue gases in the direct flame heating portion of the furnace or with the flue gases from the radiant tubes (see example according to figure 4 ). In conventional burner furnaces, the amount of steam thus produced is sufficient to meet both the needs of the ejector and a band degreasing section. In the case of so-called "regenerative" burners, the increase in combustion efficiency reduces the amount of gas burned and the steam production capacity may be insufficient to cover the only needs of the degreasing but remains sufficient for the supply of the gases. ejectors.

Thus, a heat of condensation of the steam coming out of the ejector and a heat recovered in the cooling water can be easily recovered in the condensing member (523) supplying hot water at a temperature high, close to the vaporization temperature at a pressure considered.

The condenser member of the steam coming from the ejector may be an exchanger whose steam exchange circuit is supplied with water at a low pressure, more or less hot, recovered from the installation, for example from a degreasing section, and reheated in the exchanger at a temperature equal to or slightly less than the vaporization temperature at the pressure in question.

It can also be constituted by a direct contact exchanger providing a direct exchange between the steam from the ejector and the cooling water to be heated and generally returns a water at a temperature not lower than the vaporization temperature at a pressure considered .

Advantageously, a part of the water leaving the condenser element at a temperature (T _VE3 ) may be used, after optional cooling, as demineralized water in the continuous annealing or galvanizing plant. For example, for high-pressure cleaning of the rolls of a skin-pass mill or to compensate for the loss of demineralised water by evaporation or banding in the degreasing / rinsing tanks.

• l'eau réchauffée (ER) par la bande est captée dans un organe d'échange (5142) à une première pression (P_ER1) voisine de la pression atmosphérique (P₀) et une première température (T_ER1) sensiblement inférieure à la température de vaporisation de l'eau à la pression (P_ER1),
• l'eau réchauffée (ER) depuis l'organe d'échange (5142) est introduite sous forme de jet dans une enceinte étanche (521) équipée d'au moins un éjecteur (522) en tant que dispositif de type venturi, le dit éjecteur étant annexement alimenté en vapeur d'eau (5221) à une pression entrante (P_VE1) supérieure à la pression atmosphérique (P₀),
• l'éjecteur assure dans l'enceinte étariche (521) un vide partiel correspondant à une deuxième pression (P_ER2) inférieure à une pression de vaporisation de l'eau à la première température (T_ER1),
• une eau refroidie est récupérée à une sortie (5213) de l'enceinte étanche (521) à une deuxième température (T_ER2) correspondant à une température de vaporisation de l'eau à la deuxième pression (P_ER2) pour être restituée à l'organe d'échange (5142).

Said device according to the invention is thus advantageously adapted to the implementation of a cooling control method necessary for a forced cooling of a steel strip (B) flowing in continuous scrolling in an installation suitable for continuous annealing or continuous galvanizing with dipping,
characterized in that a cooling energy is transferred to heated water (ER) by the steel strip and then removed by vaporizing said heated water (ER) at a lower pressure (P _ER2 ) at atmospheric pressure (P ₀₎ and finally restored by condensation at a higher temperature (T _VE2) after thermo compression by a venturi type device supplied with steam at a higher pressure (P _VE1 ) at atmospheric pressure (P ₀ ) and comprising the following steps:

• the water heated (ER) by the band is captured in an exchange member (5142) at a first pressure (P _ER1 ) close to the atmospheric pressure (P ₀ ) and a first temperature (T _ER1 ) substantially lower than the water vaporization temperature at pressure (P _ER1 ),
• the heated water (ER) from the exchange member (5142) is introduced in the form of a jet in a sealed chamber (521) equipped with at least one ejector (522) as a venturi type device, the said ejector being attached supplied with water vapor (5221) at an _inlet pressure (P _VE1 ) greater than atmospheric pressure (P ₀ ),
• the ejector provides in the étariche enclosure (521) a partial vacuum corresponding to a second pressure (P _ER2 ) lower than a vaporization pressure of the water at the first temperature (T _ER1 ),
• a cooled water is recovered at an outlet (5213) of the sealed enclosure (521) at a second temperature (T _ER2 ) corresponding to a vaporization temperature of the water at the second pressure (P _ER2 ) to be restored to the exchange agency (5142).

• une vapeur sortant de l'éjecteur (522) et ayant une énergie thermique liée à une énergie cinétique décroissante et augmentée de la fraction de chaleur issue d'eau de refroidissement obtenue par vaporisation, est obtenue à une pression sortante (P_VE2) de l'éjecteur supérieure à la pression atmosphérique (P₀),
• ladite vapeur sort de l'éjecteur à une température sortante (T_VE2) correspondant à une pression de vaporisation de l'eau à la pression sortante (P_VE2) et alimente un organe de condensation (523) dont elle ressort à une température post-condensation (T_VE3) inférieure à la température sortante (T_VE2) de l'éjecteur et sous une pression de vaporisation de l'eau à une pression (P_VE3) avoisinant la pression atmosphérique (P₀),
• l'organe de condensation (523) assure, à travers une paroi (= libre de contact direct), le réchauffage d'un circuit d'eau externe (5231, 5232) à une pression d'entrée externe (P_E1) depuis une température d'entrée externe (T_E1) inférieure à une température sortante (T_E2) de vaporisation à la pression d'entrée externe (P_E1) jusqu'à ladite température de sortie externe (T_E2) correspondant à une température de vaporisation de l'eau à une pression de sortie externe (P_E2), étant quasiment égale à la pression d'entrée externe (P_E1) à des pertes de charge près.

Ideally (but not necessarily), the method provides that a complementary cooling circuit can be used at the ejector outlet, for which:

• a vapor exiting the ejector (522) and having a thermal energy related to a decreasing and increased kinetic energy of the heat fraction obtained from cooling water obtained by vaporization, is obtained at an outgoing pressure (P _VE2 ) of the ejector greater than atmospheric pressure (P ₀ ),
• said vapor exits the ejector at an outgoing temperature (T _VE2 ) corresponding to a vaporization pressure of the water at the outgoing pressure (P _VE2 ) and feeds an organ of condensation (523) from which it emerges at a post-condensation temperature (T _VE3 ) lower than the outgoing temperature (T _VE2 ) of the ejector and under a pressure of vaporization of the water at a pressure (P _VE3 ) close to the atmospheric pressure (P ₀ ),
• the condensing member (523) ensures, through a wall (= free of direct contact), the heating of an external water circuit (5231, 5232) to an external input pressure (P _E1 ) from a external input temperature (T _E1) less than an outgoing temperature (T _E2) of vaporization to the external input pressure (P _E1) to said external outlet temperature (T _E2) corresponding to a vaporization temperature of the water at an external outlet pressure (P _E2 ), being almost equal to the external inlet pressure (P _E1 ) at near pressure drops.

• une vapeur sortant de l'éjecteur (522) et ayant une énergie thermique liée à une énergie cinétique décroissante et augmentée de la fraction de chaleur issue d'eau de refroidissement obtenue par vaporisation, est obtenue à une pression sortante (P_VE2) supérieure à la pression atmosphérique (P₀),
• ladite vapeur sort de l'éjecteur à une température sortante (T_VE2) correspondant à une pression de vaporisation de l'eau à la pression sortante (P_VE2) et est mise en contact direct dans un échangeur (thermique) à contact direct par eau, la dite eau étant à une pression d'entrée externe (P_E1) depuis une température d'entrée externe (T_E1) inférieure à une température sortante (T_E2) jusqu' à ladite température sortante (T_E2) du mélange des deux fluides vapeur-eau apte à atteindre la température de vaporisation de l'eau à la pression d'entrée externe (P_E1).

Alternatively, a complementary cooling circuit is used at the ejector outlet, for which:

• a vapor exiting the ejector (522) and having a thermal energy linked to a decreasing kinetic energy and increased by the heat fraction resulting from cooling water obtained by vaporization, is obtained at an outgoing pressure (P _VE2 ) greater than the atmospheric pressure (P ₀ ),
• said vapor exits the ejector at an outgoing temperature (T _VE2 ) corresponding to a vaporization pressure of the water at the outgoing pressure (P _VE2 ) and is brought into direct contact in a heat exchanger (direct contact) with water said water being at an external inlet pressure (P _E1 ) from an external inlet temperature (T _E1 ) lower than an outgoing temperature (T _E2 ) to said outgoing temperature (T _E2 ) of the mixture of the two steam-water fluids able to reach the vaporization temperature of the water at the external inlet pressure (P _E1 ).

Advantageously, the method according to the invention allows the water leaving the condensing member (523) at the post-condensation temperature (T _VE3 ) to be reintroduced as an addition in the sealed chamber (521) by a sheath (5214) and, if necessary, a surplus of said water is redirected to an external pipe (5233) for reuse (if the condenser is a direct contact exchanger) or vapor dissipation (if the organ condensation is a wall exchanger). Cooling is thus effectively achieved in a circulation loop / dynamic heat transfer and also has a possibility to provide an excess of heat or energy remaining to other applications in need.

Finally, at the outlet of the cooling unit, the cooled water recovered at the outlet (5213) of the sealed enclosure (521) is a so-called ice water at the second temperature (T _ER2 ) of between 5 and 10 ° C. . This is simply led back to the inlet (51421) of the exchange member (5142), for example via a sheath (5215), in order to effectively cool the flow of gas flow in the context of a band blowing cooling.

In summary, the invention figure 3a (and the following figures) in view of the method and the device for its implementation thus very advantageously allows a dynamic recovery of energy stored by the water used for the forced cooling of a continuous circulating steel strip, this same water being reused for cooling purposes of the exchange member (51, 5142).

• Ils assurent une récupération efficace de l'énergie cédée par les bandes d'acier laminé lors de leur refroidissement dans les sections de refroidissement des fours de recuit continu ou de galvanisation et sa réutilisation immédiate avec un maximum d'efficacité. Il est ici à noter que le domaine d'énergie visé se situe au-delà du Mégawatt. Des récupérations d'énergie sont donc majeures et permettent entre autre une redistribution en boucle de refroidissement ou bien de délivrer au moins une part de cette énergie récupérée à d'autres points de consommation, telles que dans l'usine même. La protection de l'environnement est donc considérablement accrue.
• Ils permettent d'abaisser la température de l'eau de refroidissement jusqu'à des valeurs inférieures à 10°C.
• Ils permettent d'augmenter la vitesse de refroidissement des procédés utilisés sous atmosphère neutre ou réductrice et qui ne nécessitent pas de décapage subséquent.

In other words and more specifically, the method according to the invention and the device for its implementation have several advantages over existing methods:

• They provide efficient recovery of the energy given off by the rolled steel strips when they are cooled in the cooling sections continuous annealing or galvanizing furnaces and its immediate re-use with maximum efficiency. It should be noted here that the targeted energy domain is beyond the Megawatt. Energy recoveries are therefore major and allow among other redistribution cooling loop or to deliver at least a portion of this recovered energy to other points of consumption, such as in the plant itself. The protection of the environment is therefore considerably increased.
• They allow the temperature of the cooling water to be lowered to values below 10 ° C.
• They make it possible to increase the cooling rate of the processes used under a neutral or reducing atmosphere and which do not require subsequent etching.

They can also be implemented, in the field of the metallurgical industry, wherever it is a question of recovering cooling water, for example that used in the rollers and cooled walls of continuous casting of the steel or in cooled walls and vaults electric melting furnaces.

• partie jusqu'à totalité d'eau sortant de l'organe de condensation (523) est ré-injectable, après refroidissement éventuel, dans un circuit d'eau déminéralisée utilisable par l'installation de recuit continu ou de galvanisation. L'eau en sortie de l'organe de condensation est ainsi avantageusement réintroduite, pour une part, en tant qu'appoint dans l'enceinte étanche (521) par la tubulure (5214) et, pour la part résiduelle et si besoin, dans une unité de production de vapeur de l'usine via la tubulure (5233) ;
• l'organe de condensation (523) de la vapeur actionnant l'éjecteur peut être un simple échangeur à paroi ;
• l'organe de condensation (523) de la vapeur actionnant l'éjecteur peut alternativement être un simple échangeur à contact direct ;
• l'organe d'échange (51) entre la bande d'acier et l'eau de refroidissement peut être un simple échangeur gaz / eau ;
• entre l'enceinte étanche (521) et l'organe d'échange (51, 5142), un circuit de circulation d'eau comprenant une tubulure de captage (5212) et d'une tubulure de retour (5215) constituant idéalement une colonne d'eau de hauteur égale ou supérieure à onze mètres peut être disposé.
• entre l'enceinte étanche (521) et l'organe d'échange (51, 5142), un circuit de circulation d'eau constitué d'un circuit fermé comportant au moins une pompe de circulation peut être disposé pour y faciliter les transferts d'eau (par exemple en cas de nécessité de relevage) ;

Regarding the device, multiple realization advantages are possible and therefore suitable for a cooling device for any type of a current annealing or galvanizing and de facto for any type of band, in that:

• part until all the water leaving the condensing member (523) is re-injectable, after optional cooling, into a demineralised water circuit that can be used by the continuous annealing or galvanizing installation. The water leaving the condensing member is thus advantageously reintroduced, partly as an addition in the sealed enclosure (521) by the tubing (5214) and, for the residual part and, if necessary, in a steam production unit of the plant via the tubing (5233);
• the condenser (523) of the steam actuating the ejector may be a simple wall exchanger;
• the condenser (523) of the steam actuating the ejector may alternatively be a simple direct contact exchanger;
• the exchange member (51) between the steel strip and the cooling water may be a simple gas / water exchanger;
• between the sealed chamber (521) and the exchange member (51, 5142), a water circulation circuit comprising a collection pipe (5212) and a return pipe (5215) ideally constituting a column of water equal to or greater than eleven meters may be arranged.
• between the impervious enclosure (521) and the exchange member (51, 5142), a water circulation circuit consisting of a closed circuit comprising at least one circulation pump can be arranged to facilitate the transfer of water. water (for example in case of need for lifting);

The figure 3b describes a variant of the device according to the figure 3a wherein a first cooling unit (52a) is associated with a first exchange member (5142a) located upstream of the fan (511) and supplied with cooled water at 30 ° C and a second cooling unit (52b) is associated a second exchange member (5142b) located between the fan (511) and the blow box (513) and supplied with ice water with a temperature of less than or equal to 10 ° C. The cooling is thus more effectively accentuable while having the same energy recovery properties and other advantages related to the device according to figure 3a .

• l'organe d'échange (51) comprend au moins un ventilateur (511) alimentant par l'intermédiaire d'une gaine d'air (512) un caisson de soufflage (513) dans lequel transite la bande d'acier et alimenté par une gaine d'air (5141) captant l'ait chaud dans le caisson (513),
• chacune des gaines d'air. (512, 513) est couplée à un des deux échangeurs de chaleur (5142a, 5142b).

In other words and more generally, the exchange member (51) may comprise at least two heat exchangers (5142a, 5142b) arranged in series on a heat exchange path between the steel strip and cooling water, each of the exchangers being connected to one of two cooling units (51a, 51b), the two ejector outputs (522a, 522b) of the latter cooling units being coupled in parallel.
In the case of a simple blowing unit, the device provides for example that:

• the exchange member (51) comprises at least one fan (511) supplying, by means of an air duct (512), a blower box (513) into which the steel strip passes and is supplied with an air duct (5141) sensing the heat in the casing (513),
• each of the air ducts. (512, 513) is coupled to one of the two heat exchangers (5142a, 5142b).

The figure 4 described by way of example and in relation to the figure 3a and 3b , the general flow diagram of fluids concerned by a cooling control device according to the invention in a continuous annealing system (B). The annealing furnace (5) is equipped with a water cooling unit (52) associated with a rapid cooling unit of the strip according to one of the methods previously described and mentioned in Figure 2c . The device according to the invention also comprises a steam production unit (53) obtained by heating with fumes collected at the entrance of the strip in the oven in the preheating zone by a sheath (531) for collecting the fumes to a boiler (53). The steam thus produced in the boiler feeds the ejector (522) of the cooling unit (52) via the sheath (532). As described in figure 3a and 3b , the water heated by the web heat is sensed at a suction port (51422), cooled in the sealed chamber (521) and returned to a discharge port (51421). The steam coming out of the ejector (522) is, for its part, conducted to the condenser (523) from where it emerges in (5223) in the form of hot water which returns partly in the enclosure (521) in as a supplement, to the tubing (533) for returning the condensates to the boiler (53) and to an output (5333 = 5233 according to figure 3a ) capable of supplying certain devices of the demineralized water treatment line, for example a skin-pass type strip mill or strip degreasing / rinsing tanks. The condenser (523) receives water at (5231) and discharges heated water at (5232). In this figure, the necessary pumping and winnowing accessories have not been shown for the sake of clarity.

In summary, the ejector has an auxiliary input (5221) at its other input output (5211) of the sealed enclosure (521) through which the ejector is efficiently supplied by at least part up to all the required steam by means of a furnace (53) producing steam heated with flue gas (531) in a direct flame heating section of the furnace or with radiant tube section fumes.
In this embodiment, recovery of flue gases or fumes, usually unused, here allows reuse for loop cooling purposes, resulting in considerable energy savings and consequent energy savings.

The figure 5 describes the block diagram of the device according to the invention adapted to a progressive cooling process (as in figure 2a ), for example by gas jet using four blast cells (51a, 51b, 51c, 51d) each having one of four exchangers (or exchange members) assigned (5142a, 5142b, 5142c, 5142d) and being successively placed in the opposite direction of the running of the strip (B) and two cooling units (52a, 52b) each with a sealed enclosure. The cells (51) are connected in parallel pairs, ie the first two cells (51a, 51b) associated with the first cooling unit (52a) and the two second cells (51c, 51d) associated with the second cooling unit (52b). Water cooled by the second cooling unit (52b) is discharged at its output (5213b) at a first outlet temperature (T _ER2b ) sealed chamber partly in the battery of the first two (in the direction of the band) exchangers (5142c, 5142d) by the tubing (51421d) and partly in the first cooling unit (52a) by a booster tubing (5214a). The water cooled by the first cooling unit (52a) is then discharged at its outlet (5213a) at a second outlet temperature (T _ER2a ) lower than the first outlet temperature (T _ER2b ) in the battery of the last two ( according to the direction of the band) exchangers (5142a, 5142b) by a pipe (51421b). In this figure, the necessary pumping and winnowing accessories have not been shown for the sake of clarity.

In summary, it is therefore possible to achieve a high dynamic cooling device such that at least one cooling unit (52a, 52b) is coupled to a plurality of heat exchange members (51a, 51b, 51c, 51d) distributed in the direction of travel of the band (B).
Each exchange member or group of exchange members (5142a, 5142b) mounted in parallel can thus be advantageously equipped with at least two cooling units connected in series.

The figure 6 describes the schematic diagram of the device according to the invention adapted to strip cooling by immersion in a quenching tank. The strip (B) is immersed in a cooling water tank (54) by winding on two guide rollers (541, 542). The cooling unit (52) according to the invention is connected to the tank (54) by two pipes (5214, 5215) of height (H) above the level of the water contained in the tank, thus constituting a column of water at least once the atmospheric pressure and allowing the circulation of water without pumps of the "barometric" type.

According to this embodiment, the exchange member (51) between the steel strip (B) and the cooling water is, for example, a simple quenching cooling tank containing water maintained at a constant temperature. temperature of 30 to 50 ° C which ensures instantaneous cooling of the strip by immersion. This situation exists in the quench tank at the end of maintenance at annealing temperature and before over-aging in the continuous annealing furnaces as well as in the final cooling tanks at the outlet of the furnace of the continuous annealing or final cooling lines at the outlet. of zinc pot in the galvanizing lines.

In a variant of this embodiment, the water of the final quenching tank of a continuous annealing or galvanizing plant is maintained at a temperature of between 5 and 10 ° C. and ensures cooling of the so-called "water" strip. ice cream

In all cases of this embodiment, the partial vacuum allows, among other things, the degassing of the water tanks and removal of dissolved oxygen, which significantly reduces the oxidation of the hot band.

Between the sealed chamber (521) and the exchange member (51) is thus arranged a water circulation circuit consisting of a closed circuit including, if necessary for example for a lifting, at least one circulation pump. .

The figures 7a , 7b illustrate means for serializing devices according to the invention or some of their elements, in order to allow more efficient regulation / dynamic cooling.

The figure 7a describes the series connection of two ejectors adapted to equip a sealed cooling chamber such as that described from figure 3a in that each cooling unit (52) is equipped with at least two ejectors (522a, 522b) connected in series.

A steam outlet of the first ejector (522a) is directly disposed at one of the inputs of the second ejector (522b) connectable to a condensing member. The two ejectors are for example commonly supplied with steam by a boiler (5221). The two final and common inputs (5221) of the ejectors are connected to the partial evacuation output of a sealed enclosure.

The figure 7b described (based on the previous example figure 5 ) placing in series three cooling units (52a, 52b, 52c) capable of ensuring a sharp decrease in the temperature of the cooling water in three successive stages for a single exchange member (51, 5142), side strip to cool. Tubes (514a, 5214b) successively connect a pregnant "water" outlet to a nearby "water" auxiliary inlet. Partial voids are thus formed in the enclosures, for which each of the outputs of their ejectors can be connected to a common condensing member (523).

In summary, several cooling units (52a, 52b, 52c) can be coupled to an exchange member (51) in order to advantageously stagger a decrease in the temperature of the cooling water.
At least one of these cooling units (52a, 52b, 52c) may also be equipped with at least two ejectors connected in series.

Claims (21)

1. Method for adjusting the cooling needed for the forced cooling of a steel strip (B) running continuously in a plant adapted for continuous annealing or continuous hot-dip galvanisation, characterised in that cooling energy is given up to the heated water (ER) by the steel strip and then removed by evaporation of said heated water (ER) at a pressure (P_ER2) below atmospheric pressure (P₀) and finally returned by condensation at a higher temperature (T_VE2) following thermomechanical compression by a Venturi type device supplied with vapour at a pressure (P_VE1) higher than atmospheric pressure (P₀) and comprising the following stages:

   • the water heated (ER) by the strip is collected in an exchange unit (5142) at a first pressure (P_ER1) close to atmospheric pressure (P₀) and a first temperature (T_ER1) appreciably lower than the evaporation temperature of the water at pressure (P_ER1),

   • the heated water (ER) from the exchange unit (5142) is introduced in the form of a jet into a sealed enclosure (521) fitted with at least one ejector (522) as a Venturi type device, said ejector also being supplied with water vapour (5221) at an incoming pressure (P_VE1) higher than atmospheric pressure (P₀),

   • the ejector provides a partial vacuum in the sealed enclosure (521) corresponding to a second pressure (P_ER2) lower than an evaporation pressure of the water at the first temperature (T_Ek1),

   • cooled water is recovered at an outlet (5213) from the sealed enclosure (521) at a second temperature (T_ER2) corresponding to an evaporation temperature of the water at the second pressure (P_ER2) to be returned to the exchange unit (5142).
2. Method according to claim 1, wherein an additional cooling circuit is used at the outlet from the ejector, wherein:

   • a vapour emerging from the ejector (522) and with a thermal energy associated with a decreasing kinetic energy and increased by the fraction of heat originating from the cooling water obtained by evaporation is obtained at an output pressure (P_VE2) from the ejector higher than atmospheric pressure (P₀),

   • said vapour emerges from the ejector at an output temperature (T_VE2) corresponding to an evaporation pressure for the water at the output pressure (P_VE2) and supplies a condensation unit (523) from which it emerges again at a post-condensation temperature (T_VE3) lower than the output temperature (T_VE2) from the ejector and under an evaporation pressure for the water at a pressure adjacent to atmospheric pressure (P_VE3 = P₀),

   • the condensation unit (523) provides, through a wall, for the heating of an external water circuit (5231, 5232) at an external input pressure (P_E1) from an external input temperature (T_E1) lower than an evaporation output temperature (T_E2) at the external input pressure (P_E1) to said external output temperature (T_E2) corresponding to an evaporation temperature for the water at an external output pressure (P_E2).
3. Method according to claim 1, characterised in that an additional cooling circuit is used at the outlet from the ejector, wherein:

   • a vapour emerging from the ejector (522) and with a thermal energy associated with a decreasing kinetic energy and increased by the fraction of heat originating from the cooling water obtained by evaporation is obtained at an output pressure (P_VE2) higher than atmospheric pressure (P₀),

   • said vapour emerges from the ejector at an output temperature (T_VE2) corresponding to an evaporation pressure for the water at the output pressure (P_VE2) and is brought into direct contact in a direct-contact (thermal) water exchanger, said water being at an external input pressure (P_E1) from an external input temperature (T_E1) lower than an output temperature (T_E2) to said output temperature (T_E2) of the mixture of the two vapour-water fluids capable of reaching the evaporation temperature of the water at the external input pressure (P_E1.
4. Method according to one of the preceding claims, characterised in that the water emerging from the condensation unit (523) at the post-condensation temperature (T_VE3) is reintroduced as a supplement into the sealed enclosure (521) through a duct (5214) and, if necessary, a surplus of said water is redirected towards an external pipe (5233) for vapour reuse or dissipation.
5. Method according to one of the preceding claims characterised in that, at the outlet from the cooling unit, the cooled water recovered at the outlet (5213) from the sealed enclosure (521) is water known as icy at the second temperature (T_ER2) between 5 and 10°C.
6. Cooling adjustment device needed for forced cooling of a steel strip (B) running continuously in a plant adapted for continuous annealing or continuous hot-dip galvanisation, characterised in that it comprises:

   • at least one exchange unit (51, 5142) providing for a transfer of heat from the steel strip to a cooling water and comprising an outlet (51422) for the cooling water thus heated,

   • at least one cooling unit (52) comprising a sealed enclosure (521) connected to the outlet (51422) from the exchange unit (5142) and fitted with at least one outlet (5211) on a Venturi effect device such as a vapour ejector (522) and in which the cooling water is itself subjected to cooling by evaporation in a vacuum,

   • an auxiliary outlet (5213) from the sealed enclosure (521) connected to an inlet (51421) to the exchange unit (51, 5142).
7. Device according to claim 6, comprising at least one vapour condensation unit (523) placed at the outlet from the ejector (522) on the sealed enclosure and adapted for re-supplying the sealed enclosure (521) by the addition of a required level of water in and, if necessary, adapted for redirecting a surplus of said vaporised water towards an external pipe (5233) for vapour reuse or dissipation.
8. Device according to one of the preceding claims 6-7, characterised in that the ejector comprises an auxiliary inlet (5221) in addition to its other inlet on the outlet (5211) from the sealed enclosure (521) through which the ejector is supplied by at least part to all of the required vapour by means of a vapour production boiler (53) heated with flue gas (531) in a direct-flame heating part of the furnace or by radiant tube section fumes.
9. Device according to one of the preceding claims 6-8, characterised in that several cooling units (52a, 52b, 52c) are coupled with an exchange unit (51) with a view to staging a reduction in the temperature of the cooling water.
10. Device according to one of the preceding claims 6-11, characterised in that at least one cooling unit (52a, 52b) is coupled with several heat exchange units (51a, 51b, 51c, 51d) arranged in the direction in which the strip (B) is running.
11. Device according to one of the preceding claims 7-10, characterised in that part to all of the water emerging from the condensation unit (523) can be re-injected, following possible re-cooling, into a circuit of demineralised water which can be used by the continuous annealing or galvanisation plant.
12. Device according to one of the preceding claims 7-11, characterised in that the vapour condensation unit (523) actuating the ejector is a wall exchanger.
13. Device according to one of the preceding claims 7-11, characterised in that the vapour condensation unit (523) activating the ejector is a direct-contact exchanger.
14. Device according to one of the preceding claims 6-13, characterised in that each exchange unit or group of exchange units (5142a, 5142b) installed in parallel is fitted with at least two cooling units installed in series.
15. Device according to one of the preceding claims 6-14, characterised in that each cooling unit (52) is fitted with at least two ejectors (522a, 522b) installed in series.
16. Device according to one of the preceding claims 6-15, characterised in that the exchange unit (51) between the steel strip and the cooling water is a gas/water exchanger.
17. Device according to one of the preceding claims 6-16, characterised in that the exchange unit (51) comprises at least two heat exchangers (5142a, 5142b) arranged in series on a heat exchange path between the steel strip and the cooling water, each of the exchangers being connected to one of two cooling units (51a, 51b), the two ejector outlets (522a, 522b) from these cooling units being coupled in parallel.
18. Device according to claim 17, wherein:

    - the exchange unit (51) comprises at least one fan (511) supplying, through an air duct (512), a blowing box (513) through which the steel strip passes and which is supplied by an air duct (5141) collecting the hot air in the box (513),

    - each of the air ducts (512, 513) is coupled to one of the two heat exchangers (5142a, 5142b).
19. Device according to one of the preceding claims 6-18, characterised in that, between the sealed enclosure (521) and the exchange unit (51, 5142), there is a water circulation circuit comprising a collection pipe (5212) and a return pipe (5215) ideally constituting a water column at least 11 metres high.
20. Device according to one of the preceding claims 6-15 and 19, characterised in that the exchange unit (51) between the steel strip and the cooling water is a direct-tempering cooling tank (54).
21. Device according to one of the preceding claims, characterised in that, between the sealed enclosure (521) and the exchange unit (51, 5142), there is a water circulation circuit comprising a closed circuit including at least one circulation pump.

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