WO2011151162A1 - Method and device for generating hot steam in a continuous casting machine - Google Patents

Abstract

The present invention relates to a method and a device for generating hot steam in a continuous casting machine and to the use of the device in a continuous casting installation for producing a strand of steel. The object of the invention is to provide a method and a device for generating hot steam with which great amounts of heat can be removed from the mould even at relatively low temperatures and, nevertheless, the hot steam has a high energy content, allowing it to be fed to a steam turbine for heat recovery. This object is achieved by a method in which an organic cooling medium, in particular an alcohol or a thermal oil, is used and the hot steam has before expansion a temperature of 180 to 400°C.

Description

description

Method and device for producing superheated steam in a continuous casting machine

The present invention relates to a method and apparatus for generating superheated steam in a

Continuous casting machine and the use of the device in a continuous casting plant for producing a strand of steel.

Specifically, the invention relates to a method for producing superheated steam in a continuous casting machine, comprising

the following process steps:

 - introducing a metallic melt into a mold; - Cooling of the melt in the mold to form a solid strand shell, wherein the cooling of the melt, a cooling medium in at least one

 Evaporation chamber of the mold is evaporated by means of nucleate boiling to saturated steam;

 - Extracting an at least partially solid strand from the

mold;

 Guiding, supporting and cooling the drawn strand in a strand support device;

 - overheating the saturated steam to a superheated steam;

 - Relaxing of the superheated steam in a steam turbine, wherein the method for generating superheated steam as

 Circular process is formed, in particular that the cooling medium after the relaxation, and optionally a subsequent condensation, is fed back to the mold.

Furthermore, the invention relates to a device for generating superheated steam in a continuous casting machine, comprising

- A cooled mold for casting a metallic

 Melt to an at least partially solidified strand, wherein the mold with at least one evaporation space for

Generation of saturated steam is formed; - One of the mold subordinate strand support means for supporting, guiding and further cooling of the strand;

 - a superheater to overheat the saturated steam

 Superheated steam connected to a steam turbine for releasing the superheated steam;

 at least one capacitor, wherein the steam turbine with the capacitor and the capacitor via at least one

 Feed pump is connected to the mold. In the continuous casting of a metallic melt into a strand, for example, liquid steel is poured into a downwardly open mold, the so-called mold, wherein the

Molten metal is cooled mainly on the mold walls, so that forms a stable strand shell in the mold. The at least partially solid strand becomes

then pulled out of the mold and out in a mold downstream strand support means, supported and further cooled. Often, the cooling of the molten metal in the mold is also referred to as primary cooling and the cooling of the drawn strand in the strand support means as secondary cooling. It is known to form the mold walls of copper plates, wherein the

Mold walls on the back, i. on the

Molten metal side facing away, to be cooled by cooling water. Typically, the flow rate of the

Cooling water through the mold chosen so that the cooling water by max. 10 ° C is heated. Although the heat dissipated by the cooling water with up to 2 MW / m ² Kokillenoberfläche is high, this amount of heat due to the low

Temperaturhubs not a conventional heat recovery (such as a steam turbine) are supplied. Due to the high flow rates of the cooling water through the mold, there are also high pressure losses, which results in high overall temperatures

Services are required for the circulation pumps of the primary cooling circuit.

From the document JP 1143743 A2 it is known several

Heat pipes (English, heat pipes) in the shell of a mold to integrate, so that the overall thermal conductivity of the mold is increased. Although heat pipes can be beneficial, direct use of it is inside the heat pipes

evaporated cooling medium not possible.

From CN 2379234 Y it is known to supply the heat of vaporization of a casting process of heat recovery; from the disclosure, however, there are no starting points, such as the proposed device in a conventional continuous casting machine (for example, a bow or

 Vertical plant) for iron or steel materials would be applicable. Furthermore, the generated steam has only one

low energy content.

From EP 1 785 206 AI, the cooling of a

Continuous casting mold known,

 - Where a metallic melt in a mold

is introduced;

 - The melt is cooled in the mold to form a solid strand shell, wherein by cooling the

Melt the cooling medium water in at least one

Evaporation chamber of the mold by means of nucleate boiling too

Saturated steam is evaporated;

 - The saturated steam is overheated to a superheated saturated steam or a superheated steam; and

 - The superheated steam is expanded in a steam turbine, wherein the method for generating superheated steam is designed as a cyclic process. A disadvantage of this method is that the mold - due to the high temperature of the superheated steam - is also exposed to very high temperatures, so that the mold must be made on the one hand of highly heat-resistant materials, but on the other hand the

Thermal conductivity of the mold suffers. The object of the invention is a method and apparatus for generating superheated steam in a

To specify continuous casting, with which even at relatively low surface temperatures in the mold high Amounts of heat can be removed from the mold and still the hot steam has a high energy content, so that it can be fed to a steam turbine for heat recovery.

This object is achieved by a method of the type mentioned, in which as an organic cooling medium

Cooling medium, in particular an alcohol or a thermal oil, is used and the superheated steam before relaxation has a temperature of 180 to 400 ° C.

By evaporating the organic cooling medium in at least one evaporation space (for example, the space between a copper plate and the water box) of the mold by means of nucleate boiling to saturated steam, a very good heat transfer, i.e., boiling, is achieved. ensures a high heat transfer coefficient, between the mold and the cooling medium, so that in particular overheating of the copper plates of the mold is reliably prevented. Under bladder boiling (engl.

nucleate boiling, cf. e.g. Fig. 9.2 in John H. Lienhard. The heat transfer textbook, Third edition, Phlogiston Press, 2003 or the curve range between the points A and C (partial nucleate boiling and fully developed nucleate boiling) in the "typical boiling curve" on

http://encyclopedia2.thefreedictionary.com/boiling is understood to mean boiling in an area between the

natural convection and the point with the maximum

Heat flux density is. Since the evaporation of the cooling medium in the evaporation space directly, i. can be done without a DC link, the process is very simple and

inexpensive feasible.

Due to the subsequent overheating of the saturated steam

Superheated steam (also referred to as superheated saturated steam) directly achieves a higher and, at least for conventional heat recovery processes, a usable temperature level of the cooling medium, so that superheated steam can be fed directly to a steam turbine. In addition, by the Overheat the Carnot's efficiency (see, eg

http: // en. wikipedia. org / wiki / Carnot efficiency).

Subsequently, the superheated steam in a steam turbine

relaxed. Steam turbines are available for different capacities and have a high efficiency, the method is designed as a cyclic process, so that

in particular the cooling medium after relaxation, and

optionally a subsequent condensation, the mold is fed again.

As the cooling medium, an organic cooling medium, e.g. an alcohol or a thermal oil, wherein the hot steam before the relaxation has a temperature of 180 to 400 ° C. Because organic cooling media available in conventional

 Steam turbines can be relaxed, it is generally not necessary, two different circuits (a first cycle, also called primary circuit, which is operated with the organic cooling medium and a second

Cycle, the so-called secondary circuit, e.g. operated with water).

Of course, it would be possible in principle to divide the cooling in two separate circuits, the first

Circuit comprises at least the mold and the superheater, and the second circuit comprises at least the steam turbine and a condenser. In this case, both circuits would be e.g. via at least one heat exchanger with each other

coupled, the first with the second cycle

combines. Of course, in the two loop embodiment, it would also be possible to use inorganic cooling media, e.g.

molten salts, to be used for secondary circulation; It is advantageous, in turn, to use the organic cooling media described above for the primary circuit.

According to an embodiment not claimed, water could also be used as the cooling medium, wherein the superheated steam before relaxation has a temperature of 200 to 400 ° C.

It is advantageous that the saturated steam is overheated by cooling the strand, wherein the saturated steam is guided in at least one line along at least one surface of the strand. In this case, the saturated steam, e.g. passed over partially or solidified steel slabs. For the setting of a defined vapor pressure or a defined steam temperature in the evaporation space of the mold, it is advantageous that the pressure of the saturated steam in

Evaporation chamber of the mold by means of a

Vapor pressure adjusting device is set to a predetermined pressure. This measure has a favorable effect especially when starting the continuous casting.

The object of the invention is also by a

Device of the type mentioned above, wherein the mold is connected to at least one superheater to overheat the saturated steam and the superheater as a

Secondary cooler or a secondary cooling line of

Continuous casting machine is formed. As a result, the amount of heat dissipated by the secondary cooling of the partially solidified or continuously solidified strand is also absorbed by the saturated steam.

When connecting the superheater with a steam turbine to relax the superheated steam, it is of course possible to arrange several steam turbines in parallel and / or in series. A parallel arrangement is advantageous for realizing higher power with several smaller steam turbines; a serial arrangement is advantageous for making better use of the pressure level of the superheated steam, for example by means of a high-pressure and a subsequent low-pressure steam turbine. Of course it is also possible, for example several

High-pressure steam turbine to arrange parallel and then, ie in a serial arrangement, to arrange one or more low-pressure steam turbines. Advantageously, at least one line in the superheater is meandering for uniform cooling of the strand

educated .

Advantageously, a condenser in a cooling section, preferably in a cooling section in the outlet region of

Continuous casting or in a cooling section in the outlet region of a rolling mill downstream rolling mill, arranged.

To a high thermal conductivity of the mold at a

At the same time to achieve high thermal shock resistance of the mold, it is advantageous that the mold at least in the region of the meniscus in a direction transverse to

Casting a ceramic or ceramic-metallic

Layer, a plate made of copper or a copper alloy, a ribbed plate for evaporating the cooling medium and a holding plate.

It is advantageous to use the device according to the invention in a continuous casting plant for producing a strand of steel, which very quickly a high amount of heat from

Gießstrang removed and the continuous casting machine compact, in particular with a smaller metallurgical length, can be formed.

Further advantages and features of the present invention will not become apparent from the following description

limiting embodiments, reference being made to the following figures, which show the following:

Fig. 1 is a schematic representation of a continuous casting machine with heat recovery

 Fig. 2 is a schematic diagram of the thermodynamic

State variables of the continuous casting machine with heat recovery for the cooling medium water Fig. 3 is a schematic diagram of the thermodynamic

State variables of the continuous casting machine with heat recovery for the cooling medium methanol

 4 shows a schematic representation of a superheater which is integrated into the secondary cooling of the continuous casting machine FIG. 5 shows a schematic representation of a condenser which is integrated into a cooling section

 Fig. 6 is a schematic representation of the structure of a

mold

Fig. 1 shows a continuous casting machine for the production of steel ^¬ slabs, by means of the continuous casting

accumulating waste heat produces superheated steam. There will be a

Molten steel melt introduced by means of a pan, not shown, via a distributor in a mold 2, in which the melt is cooled by means of the primary cooling 3, wherein a solid strand shell is formed. That's how it is

forming partially solid strand 12 is pulled out of the mold 2 and downstream in one of the mold 2

Strand support device 5 out, supported and by means of

Secondary cooling further cooled. The strand support device 5 has a plurality of strand guide segments ^¬ not shown in detail, each having a plurality of both sides of the strand 12 arranged strand guide rollers 5a. By means of the mold 2, the initially liquid cooling medium water of about 35 ° C (point II) is heated to about 200 ° C (point III) and then evaporated in several evaporation chambers of the mold by means of nucleate boiling to saturated steam (point IV). A large part of the molten steel or the partially solidified strand 12 extracted heat is absorbed by the cooling medium and thus increases the entropy of the cooling medium (see Fig. 2). The saturated steam is supplied via a steam line to a superheater 4, in which the saturated steam is passed over at least one meandering line over the approximately 900 ° C hot slab and thereby absorbs energy; In this case, the saturated steam of about 200 ° C (point IV) is heated to about 330 ° C (point V) to superheated steam. Subsequently, the superheated saturated steam (the superheated steam) by means of a Steam line fed to a steam turbine 7, in which the steam from point V to point VI relaxed and thereby free

expectant energy by means of a wave between the

Steam turbine and a generator 8 is converted into electrical energy. Subsequently, the cooling medium is first fed to a first condenser 9 and then to a second condenser 9a in which the entropy of the cooling medium is further reduced. The first capacitor 9 is part of the cooling section 10 in the outlet region of the

Continuous casting machine arranged in the solidified

Strand 12 is cooled by means not shown spray nozzles to near room temperature (point I). At least one circulating pump 11 increases the pressure of the cooling medium, so that this again the steam generator 1, i. the primary cooling 3 of the mold 2, is supplied.

The thermodynamic state variables assumed in the process according to FIG. 1 are again shown in FIG. 2 in an entropy-temperature diagram for the cooling medium water

summarized .

FIG. 3 shows the thermodynamic state variables in an entropy-temperature diagram for the process according to FIG. 1 for the cooling medium methanol. Compared to Fig. 2, the cooling medium methanol, the temperature in the

Mold to keep much lower than this

Cooling medium water would be possible. Specifically, the cooling medium is heated in the evaporation space of the mold from about 35 ° C (point II) to a temperature of only about 100 ° C (point III), before the evaporation of methanol begins. In point IV, the methanol is then completely evaporated. In the superheater 4, the methanol is superheated to about 180 ° C (point V) before it is expanded in the steam engine 7. After relaxation in the steam engine 7 (point IV), the cooling medium

condenses before it is again supplied by means of a feed pump 11 to the evaporation chamber 23 of the mold. Of course, the invention is by no means limited to methanol; much more Other organic cooling media such as ethanol or thermal oils can also be used.

In Fig. 4, a superheater 4 is shown schematically. In this case, the saturated steam is guided in at least one meandering line 13 at a small distance over the surface of the partially or durcherstarrten strand 12, wherein the strand is cooled further and thereby a large part of the thereby dissipated amount of heat is used to overheat the saturated steam. Preferably, the meandering line 13 is counter-flowed against the casting direction 15, so that while the saturated steam initially absorbs energy from a colder strand and later energy from a warmer strand. In Fig. 5, a capacitor is shown schematically. At the top of the strand 12, the strand of several

Spray nozzles 14 cooled, with the resulting

Cooling water is used for condensation of the cooling medium within a meandering line 13. In contrast to the superheater shown in FIG. 4, the

 Condenser 9 flows in the casting direction 15, so that the

Cooling medium is initially cooled by a warmer cooling water and later by a colder cooling water. Should the

Temperature of the cooling medium through this process is not

Of course, it is also possible, instead of the capacitor shown in Fig. 4 or in addition thereto, a capacitor according to the prior art (see capacitor 9a of Fig. 1, embodiments of

Capacitors e.g. Dubbel. Paperback for Mechanical Engineering, 17th Edition, Chapter K22 "Components of the thermal

 Apparatus construction - 4 condensation and recooling ").

In Fig. 6, the structure of a mold 2 in a direction transverse to the casting direction 15 is shown schematically, wherein the representation of the dip tube for reasons of

Clarity was waived. Between the steel 16, which forms a partially solidified strand in the mold, and the mold 2, there is a layer of casting powder 17 to the friction between the strand and the mold to

to reduce. Since the mold 2 becomes hotter than a prior art mold due to evaporative cooling, the copper plate 19 of the mold has a highly abrasion-resistant, wear-resistant layer of a ceramic 18 or a ceramic

Composite materials of ceramic materials in a metallic matrix (a so-called cermet material, see eg http://de.v7ikipedia.org/wiki/Cermet). Following the copper plate of Cu or a Cu alloy is a ribbed plate 20 having a plurality of extending in the casting direction and / or in a direction transverse to the casting direction ribs 21. By means of this construction, the effective surface of the mold is increased, so that particularly high amounts of heat can be removed through the mold (for example 3 MW / m ² , this value being based on the wetted by the steel mold surface), without it a movie boiling comes. Between the ribs 21 of the ribbed plate 20, there is the evaporation space 23 of the mold, in which an organic cooling medium is evaporated to saturated steam. Following the ribbed plate 21 is a holding plate 22 which is connected by means of several designed as screws fasteners with the ribbed plate.

List of reference numbers

1 steam generator

 2 mold

 3 primary cooling

 4 superheaters

 5 strand support device

 5a strand guide roller

 6 secondary cooling

 7 steam turbine

 8 generator

 9, 9a capacitor

 10 cooling section

 11 pump

 12 strand

 13 Meandering line

 14 spray nozzles

 15 casting direction

 16 steel

 17 casting powder

 18 ceramics

 19 copper plate

 20 Ribbed plate

 21 rib

 22 retaining plate

 23 Evaporation room

I-II pressure increase

 II-III heating to the evaporation temperature

III-IV evaporation

 IV-V overheat

 V-VI relaxation

 VI-I condensation

Claims

claims 1. A process for the production of superheated steam in one Continuous casting machine, comprising the following process steps: - introducing a metallic melt into a mold  (2);  - Cooling of the melt in the mold (2) to form a solid strand shell, wherein the cooling of the melt, a cooling medium in at least one  Evaporation chamber (23) of the mold (2) is evaporated by means of nucleate boiling to saturated steam;  - Extracting an at least partially solidified strand (12) from the mold (2);  - guiding, supporting and cooling the extended strand (12) in a strand support device (5);  - overheating the saturated steam to a superheated steam;  - Relaxing of the superheated steam in a steam turbine (7), wherein the method for generating superheated steam is designed as a cyclic process, in particular that the cooling medium after the expansion, and optionally a subsequent  Condensation, the mold (2) is fed back; characterized, that an organic cooling medium, in particular an alcohol or a thermal oil, is used and the superheated steam has a temperature of 180 to 400 ° C before the expansion. 2. The method according to claim 1, characterized in that the saturated steam is overheated by cooling the strand (12), wherein the saturated steam is guided in at least one line along at least one surface of the strand. 3. The method according to any one of the preceding claims, characterized in that the pressure of the saturated steam in Evaporation space (23) of the mold (2) by means of a Vapor pressure adjusting device is set to a predetermined pressure. 4. A device for generating superheated steam in a continuous casting machine, comprising  - A cooled mold (2) for casting a metallic melt to an at least partially solidified strand (12), wherein the mold (2) with at least one evaporation space (23) is designed to generate saturated steam;  - One of the mold (2) downstream strand support means (5) for supporting, guiding and further cooling of the strand (12); - A superheater (4) for overheating the saturated steam  Superheated steam connected to a steam turbine (7) for releasing the superheated steam;  at least one condenser (9), wherein the steam turbine (7) with the condenser (9) and the condenser (9) via at least one feed pump to the mold (2) is connected; characterized, that the mold (2) with at least one superheater to Overheating of the saturated steam is connected, wherein the superheater (4) as a secondary cooler (6) or a secondary cooling section (6) of the continuous casting machine is formed. 5. Apparatus according to claim 4, characterized in that at least one line in the superheater (4) is meander-shaped for uniform cooling of the strand (12) is formed. 6. Apparatus according to claim 4, characterized in that a capacitor (9) in a cooling section (10) is arranged. 7. Device according to one of claims 4 to 6, characterized in that the mold (2) at least in the region of the meniscus in a direction transverse to the casting direction (15) has a ceramic or ceramic-metallic layer, a plate made of copper or a copper alloy, a ribbed plate for evaporating the cooling medium and a holding plate. 8. Device according to one of claims 4 to 7, characterized in that an evaporation space (23) in the interior of the Mold (2) with one, optionally adjustable, Pressure limiting device is connected so that the pressure of the saturated steam is adjustable. 9. Use of the device according to one of claims 4 to 8 in a continuous casting plant for producing a strand of steel.