WO2012168141A1

WO2012168141A1 - Method and device for pretreating a rolled good before hot rolling

Info

Publication number: WO2012168141A1
Application number: PCT/EP2012/060327
Authority: WO
Inventors: Gerald Hohenbichler; Bernd Linzer
Original assignee: Siemens Vai Metals Technologies Gmbh
Priority date: 2011-06-10
Filing date: 2012-06-01
Publication date: 2012-12-13
Also published as: EP2718470A1; CN103582708B; RU2013158326A; CN103582708A; EP2718470B1; RU2605733C2; AT511429B1; AT511429A4

Abstract

The invention relates to a method and a device for pretreating a rolled good (3). The aim of the invention is to find a method and a device with which the rolled good (3) can be both energy-efficiently heated and thoroughly descaled before hot rolling. Said problem is solved by the following method steps: preheating the rolled good (3) in a preheating furnace (4) by a plurality of burners (11); descaling the preheated rolled good (3) in a descaling device (5); heating the descaled rolled good (3) in a heating furnace by means of a plurality of burners (11), wherein the burners substoichiometrically burn a carbon carrier so that the rolled good (3) is held in a reducing atmosphere in the heating furnace (7) by the exhaust (12, 13) created during combustion; introducing a first part of the exhaust (12) and oxygen (15) into the preheating furnace (4); post-combusting the first part of the exhaust (12) in the preheating furnace (4), wherein the volume of oxygen (15) is chosen so that the rolled good (3) is held in an oxidizing atmosphere in the preheating furnace (4).

Description

description

Method and device for pretreatment of a rolling stock before hot rolling

Field of engineering

The invention relates to a method and a device for the pretreatment of a rolled steel material before hot rolling.

State of the art

From JP 63-262417 A a method of heating a slab in a multi-part furnace is known wherein the slab is preheated in a preheating zone of the furnace by a burner and then heated in a reducing atmosphere of a heating zone of the furnace. The exhaust gas of the heating zone is supplied to the burner in the preheating zone of the furnace, where the unburned CO of the exhaust gas is burned by a burner. A disadvantage of this method is that the slab must be descaled either before or after heating. A disadvantage of descaling prior to heating is that the scale is difficult to remove due to its slow growth; A disadvantage of the descaling after heating is that the rolling stock is at a higher temperature than the

Rolling temperature must be heated, causing the

Energy efficiency of the process suffers. From JP 63-262417 A no approaches are known how these disadvantages can be overcome.

Summary of the invention

The object of the invention is to find a method and a device with which the rolling stock can be both energy-efficiently heated and thoroughly descaled before hot-rolling. This object is achieved by a method according to claim 1, comprising the following method steps:

- Preheating of the rolling stock in a preheating furnace by a plurality of burners;

- Descaling of the preheated rolling stock in one

Entzünderungseinrichtung;

- Heating the descaled rolling stock in a heating furnace through a plurality of burners, wherein the burners

Stoichiometric burn carbon support so that the rolling in the heating furnace by the combustion

resulting exhaust gas is kept in a reducing atmosphere;

- Introducing a first part of the exhaust gas and from

Oxygen in the preheating furnace;

Post-combustion of the first part of the exhaust gas in the

Vorwärmofen, wherein the amount of oxygen is chosen so that the rolling stock in the preheating in an oxidizing

Atmosphere is maintained.

In this case, the rolling stock, for example a slab, a so-called intermediate strip or an intermediate strip, in a preheating oven by a plurality of burners to a temperature of typically more than 1000 ° C, preferably more than 1050 ° C preheated. At these temperatures, the rolling stock is particularly descaled. After descaling, the rolling stock is heated in a heating furnace through several burners to rolling temperature, the burners a

Carbon carriers (for example, a heating gas such as methane, ethane, propane or butane, or even a liquid fuel such as fuel oil) with the addition of oxygen stoichiometrically burn. The substoichiometric combustion of the carbon carrier produces an exhaust gas which keeps the rolling stock in the heating furnace in a reducing atmosphere. This reducing atmosphere ensures that the descaled stock is faced with another substantial - i. the

subsequent hot rolling disturbing - scaling is protected. Due to the stoichiometric combustion in the heating furnace, the exhaust gas of the heating furnace still has flammable Shares of CO and typically also H2. Subsequently, at least a portion of the exhaust gas with the addition of

Oxygen is introduced into the preheat furnace, where the

introduced exhaust gas is burned. In the

Afterburning, the amount of oxygen in the preheating furnace is now chosen so that sets an oxidizing atmosphere in the preheating furnace. The oxidizing atmosphere in the

Preheating furnace provides a rapid scale growth on the

Good to be rolled, whereby the scale in the subsequent descaling particularly light (i.e., at low water pressure or a low amount of water) and can be removed thoroughly. It is basically possible that

either to be recirculated exhaust gas directly into the furnace chamber or burn by means of burners that heat the furnace chamber.

In an advantageous embodiment, the burners in the preheating furnace and the burners in the heating furnace are designed as gas-fired oxygen burners, which are a heating gas - typically a saturated hydrocarbon, such as

Methane, ethane, propane or butane - with the addition of

Burn oxygen. By the oxygen burner, on the one hand, the heating power is increased, on the other hand is reduced by the combustion of technically pure oxygen and the nitrogen oxide load in the exhaust gases of the furnaces.

Of course it would also be possible to use only the burners of a furnace or even just single burners of a furnace

Form oxygen burner. In a high-performance embodiment, a heating gas is additionally introduced into the preheating furnace and burned. As a result, the power supply is increased in the preheating furnace, but also with the addition of a hot gas the

Quantity of oxygen in the preheating furnace is chosen so that the rolling stock is kept in an oxidizing atmosphere.

According to another high-performance embodiment, the descaled rolling stock is immediately after the descaling in an induction furnace is heated, wherein the rolling stock is kept in the induction furnace by a second part of the exhaust gas of the heating furnace in a reducing atmosphere. The use of the induction furnace ensures a highly dynamic heating of the rolling stock, so in particular

Temperature changes caused by changes in the

Transport speed of the rolling stock can be compensated very well. According to one embodiment, the exhaust gas of the heating furnace is divided into a first part and a second part of the exhaust gas at the inlet end of the heating furnace in the transporting direction of the rolling stock. It is advantageous to also the second part of the exhaust gas after flowing through the induction furnace, preferably against the transport direction of the rolling stock, in the

To initiate the preheating oven. As a result, the energy content of the exhaust gas of the heating furnace is utilized as best as possible, in which the temperature of the second exhaust gas heats the rolling stock in the induction furnace and contributes to the heating of the preheating furnace by means of the afterburning. The passing of the second part of the exhaust gas against the transport direction of the rolling stock ensures that the hot exhaust gas for heating the hot

Walzguts contributes.

It is advantageous to measure an actual gas concentration, in particular the actual gas concentration of CO and / or H ₂ , in the heating oven and feed it to a controller, wherein the controller determines a manipulated variable with the aid of a desired gas concentration and at least one actuator (eg Valve that changes the oxygen supply to the burners) provides, so that the actual gas concentration of the desired gas concentration corresponds as possible. As a result, the degree of reduction of the reducing atmosphere in the preheating oven can be set very precisely. It is also advantageous to measure an actual oxygen concentration in the preheating furnace and feed it to a controller, wherein the controller determines a manipulated variable with the aid of a desired oxygen concentration and

at least one actuator (e.g., a valve incorporating the

Oxygen supply to the burners changed), so that the actual oxygen concentration corresponds to the desired oxygen concentration as far as possible. As a result, the growth of scale in the preheating furnace can be controlled in a controlled manner, so that the descaling can be carried out as thoroughly as possible and, moreover, the rolling stock is cooled as little as possible.

The temperature of the rolled product can be set with high precision when an actual temperature of the rolling stock is measured immediately before descaling or immediately before hot rolling and fed to a regulator, the regulator under

With the aid of a desired temperature determines a manipulated variable and at least one actuator provides, so that the actual temperature of the target temperature corresponds as possible.

The object of the invention is also by a

Device according to claim 9, comprising:

a preheating furnace for preheating the rolling stock, wherein the preheating furnace has a plurality of burners for burning a

Carbon carrier has;

a descaling device for descaling the

preheated rolling stock, wherein the descaling device is downstream of the preheating furnace;

a heating furnace for heating the descaled rolling stock to rolling temperature, the heating furnace having a plurality of burners for burning a carbon carrier, and the

Heating furnace downstream of the descaling;

an exhaust gas recirculation line for returning an exhaust gas of the heating furnace into the preheating furnace, wherein the

Exhaust gas recirculation line leads from the heating to the preheating furnace; and - An oxygen line for introducing oxygen into the preheating furnace, wherein the oxygen line in the

Preheating furnace opens. In a compact embodiment, the burners are as

Oxygen burner for burning a hot gas with the addition of oxygen formed. This allows the

inventive system with a particularly short length

will be realized.

In an advantageous embodiment opens a

Heizgasleitung for introducing a heating gas in the

Preheating oven. In a powerful embodiment is a

Induction oven disposed immediately after the descaling, wherein the heating oven is connected via an exhaust duct to the induction furnace. It is advantageous that in the transport direction

Input end of the induction furnace by means of a

Exhaust gas recirculation line is connected to the preheating furnace.

It is advantageous if a controller on the one hand with a gas concentration meter for determining the

Gas concentration in an oven and on the other hand connected to an actuator for influencing the gas concentration in the furnace. This can reduce the concentration of CO in the

Heating oven or the oxygen concentration in the preheating oven are set very accurately.

Brief description of the drawings

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following schematic figures, which show the following: 1 shows an illustration of a device according to the invention with an induction furnace. FIG. 2 shows a control diagram for the preheating furnace

3 shows a control scheme for the heating furnace

Description of the embodiments

1 shows a plant for the preparation of a rolling stock is shown. The rolling stock designed as intermediate strip 3 is fed to a preheating furnace 4 after rough rolling in a two-stand rolling mill 1 in the transporting direction 10, where it is preheated by a plurality of oxygen burners 11 to a temperature of 1050 ° C. This burn the

Oxygen burner 11 the heating gas methane with the addition of technically pure oxygen. Moreover, in the preheating furnace 4, a first part 12 and a second part 13 of an exhaust gas of a downstream heating furnace 7 are post-combusted. After preheating, the rolling stock 3 is in a descaling device 5, which serves as a rotary descaling device

is formed, descaled, wherein the rolling stock is cooled to 980 ° C. Immediately thereafter, the rolling stock is fed to an induction furnace 6 and there by 5

Heated inductor modules. Subsequently, the rolling stock 4 is heated in a heating furnace 7 to a rolling temperature of 1150 ° C, so that the rolling stock in the last rolling pass in the frame 9b still has an austenitic structure. In the heating furnace 7, the rolling stock is heated by 9 rows of oxygen burners in the lower part of the furnace and 9 rows of oxygen burners in the upper part of the furnace, again burning methane with the addition of technically pure oxygen. The amount of oxygen supplied to the oxygen burners 11 is adjusted so that the methane in the heating furnace 7 is burned substoichiometrically. The resulting at the assumed bandwidth amount of exhaust gas 12 of a total of 10,000 m ³ iN / h is in each case in the upper part of the furnace and in the collected at the bottom of the furnace, has about 10% vol CO and 2% vol H2 and a temperature of about 1000 ° C, and is introduced by means of an exhaust gas recirculation line 14 in the preheating furnace 4. Since the input side end of the heating furnace 7 is connected to the output side end of the induction furnace 6 via an exhaust gas guide 17, a second part of the exhaust gas 13, which constitutes about 5000 m ³ iN / h, flows counter to the transporting direction 10 of the rolling stock through the induction furnace 6 After flowing through the induction furnace, the second part of the exhaust gas 13 still has a temperature of near 1000 ° C. and is likewise introduced into the preheating furnace 4 via a further exhaust gas recirculation line 14. In the preheating furnace 4, the first part 12 and the second part 13 of the exhaust gas, a total of 15000 m ³ iN / h afterburning, wherein the preheating furnace additionally methane as heating gas, specifically about 1000 m ³ iN / h, and oxygen, specifically approx. 2000 m ³ iN / h, are supplied. The actually supplied amount of oxygen is regulated so adjusted that the rolling stock 3 is exposed in the preheating furnace 4 an oxidizing atmosphere. By the

Preheating of the rolling stock 3 in the preheating furnace 4 to a temperature of 1050 ° C in an oxidizing atmosphere, the

Scale growth accelerates on the intermediate belt 3. In practical experiments, it has been found that a rapidly growing scale in a descaling device 5 can be removed thoroughly and with a small temperature drop of the rolling stock. Overall, the generate

Oxygen burner 11 in the preheating furnace 4 and in the heating furnace 7 each approximately 10 MW of thermal energy. In addition, by the post-combustion of the exhaust gas 13,14 in

Preheating furnace 4 heats the rolling stock with a thermal power of an additional nearly 2 MW. Finally, the rolling stock in the induction furnace 6 is heated very dynamically with an adjustable heating power of about 5 to 10 MW. Of course, the gas quantities given are specific to the embodiment of Figure 1 and therefore can vary widely.

FIG. 2 shows a control scheme for carrying out the

Method according to the invention for a preheating furnace 4. As well 1, the rolling stock 3 is preheated in a preheating furnace 4 by a plurality of burners 11, then descaled in a descaling device 5, and by means of a heating furnace, not shown in a reducing

Atmosphere brought to rolling temperature. That at the

stoichiometric combustion in the heating furnace 7

Resulting exhaust gas is introduced by means of an exhaust gas recirculation line 14 in the preheating furnace 4 and post-combusted therein with supply of oxygen and a heating gas, which is methane according to FIG. The actual temperature 23 of the rolling stock after preheating and before the descaling is continuously measured by means of a temperature measuring device 23 and fed to a controller 19. In addition, the actual oxygen concentration 22 in the heating oven 4 is continuously measured by an oxygen concentration meter 20 and also supplied to the controller 19. Taking into account a desired oxygen concentration 21 and a desired temperature 24, the controller now determines two manipulated variables 26a, 26b, which are each supplied to a control valve 18a, 18b. The control valve 18 a changes the amount of oxygen supplied to the preheating furnace 4 via an oxygen pipe 15. Similarly, the control valve 18b changes the amount of heating gas, the

Preheating 4 is supplied via a heating gas 16. This regulation ensures that the rolling stock 3 is descaled at a suitable temperature, typically> 1000 ° C. or preferably around 1050 ° C., and that the scale growth of the rolling stock 3 in the oxidizing

Atmosphere of the preheating furnace 4 can be controlled specifically, so that a rapidly grown scale arises in the descaling 5 thoroughly and at low

Temperature drop can be removed. Of course, it would also be possible to apply the control to several regulators, e.g. a temperature controller and a controller for controlling the oxygen concentration in the preheating furnace, split.

3 shows a control scheme for carrying out the

process according to the invention for a heating furnace 7. In this case, the descaled rolling stock 3 immediately after Descaling device 5 introduced into the heating furnace 7. In the heating furnace 7, the rolling stock 3 by several

Oxygen burner 11 is heated, wherein each burner technically pure oxygen via an oxygen line 15 and the heating gas methane is supplied via a Heizgasleitung 16. For reasons of clarity, only the first burner 11 has been shown somewhat more accurately. On the one hand to bring the rolling stock 3 to the rolling temperature and on the other hand, the rolling stock 3 in the heating furnace 7 in a defined

To keep reducing atmosphere, on the one hand, the actual temperature 25 of the rolling stock 3 directly from the hot rolling in the finishing train 8 by means of a

Temperature measuring device 23 is determined and fed to a controller 19. On the other hand, the actual carbon monoxide concentration 29 in the heating furnace 7 is determined by means of a carbon monoxide concentration measuring device 27 and also supplied to the regulator 19. Regulating the setpoint temperature 24 and the desired carbon monoxide concentration 28, the controller 19 determines two manipulated variables 26a and 26b which respectively change the supply of oxygen or of heating gas to the burners 11 in the heating oven 7 via control valves 18a, 18b.

Of course, it would also be possible to connect the separate control circuits of FIGS. 2 and 3 with each other and to realize them by a single digital controller, for example.

Reference sign list

1 roughing line

2a, 2b stands of the rough rolling mill

3 intermediate band

4 preheating oven

5 descaling device

6 induction furnace

7 heating oven

8 finishing mill

9a, 9b stands of the finishing train

10 transport direction

11 oxygen burner

12 first part of the exhaust gas

13 second part of the exhaust gas

14 exhaust gas recirculation line

15 oxygen line

16 heating gas line

17 exhaust system

18a, 18b control valve

19 controllers

20 oxygen concentration meter

21 target oxygen concentration

22 actual oxygen concentration

23 temperature measuring device

24 set temperature

25 actual temperature

26a, 26b manipulated variable

27 carbon monoxide concentration meter

28 Target carbon monoxide concentration

29 actual carbon monoxide concentration

Claims

claims

1. A method for pretreating a rolled stock (3) from steel before hot rolling, comprising the following method steps:

- Preheating of the rolling stock (3) in a preheating furnace (4) by a plurality of burners (11);

- Descaling of the preheated rolling stock (3) in one

Descaling device (5);

- Heating the descaled rolled stock (3) in one

Heating furnace (7) by a plurality of burners (11), wherein the burners (11) burn a carbon carrier substoichiometrically, so that the rolling stock (3) in the heating furnace (7) by the resulting combustion exhaust gas (12,13) held in a reducing atmosphere becomes;

- Introducing a first part of the exhaust gas (12) and of

Oxygen (15) in the preheating furnace (4);

Post-combustion of the first part of the exhaust gas (12) in the preheating furnace (4), wherein the amount of oxygen (15) is selected so that the rolling stock (3) is maintained in the preheating furnace (4) in an oxidizing atmosphere.

2. Method according to claim 1, characterized in that the burners (11) in the preheating furnace (4) and the burners (11) in the heating furnace (7) are designed as gas-fired oxygen burners which burn a heating gas (16) with the addition of oxygen.

3. The method according to claim 1, characterized in that in addition a heating gas (16) in the preheating furnace (4)

is initiated and burned.

4. The method according to claim 1, characterized in that the descaled rolling stock (3) is heated immediately after the descaling in an induction furnace (6), wherein the rolling stock (3) in the induction furnace (6) through a second part of the

Exhaust gas (13) of the heating furnace (7) in a reducing

Atmosphere is maintained.

5. The method according to claim 4, characterized in that the second part of the exhaust gas (13) after flowing through, preferably counter to the transport direction (10) of the rolling stock (3), the induction furnace (6) in the preheating furnace (4)

is initiated.

6. The method according to claim 1, characterized in that an actual gas concentration, in particular the actual gas concentration of CO and / or H ₂ , measured in the heating furnace (7) and fed to a controller (19), wherein the

Controller (19) determined with the aid of a target gas concentration, a control variable and at least one actuator, so that the actual gas concentration of the target gas concentration corresponds as possible.

7. The method according to claim 1, characterized in that an actual oxygen concentration (22) in the preheating furnace (4) is measured and fed to a controller (19), wherein the controller (19) with the aid of a desired oxygen concentration (21) is a manipulated variable (26a) determined and at least one actuator (18a) provides, so that the actual oxygen concentration (22) of the desired oxygen concentration (21) corresponds as possible.

8. The method according to claim 1, characterized in that an actual temperature (25) of the rolling stock (3) measured immediately before descaling or immediately before hot rolling and a controller (19) is fed, wherein the controller (19) with the aid a target temperature (24) determines a control variable (26b) and at least one actuator (18b) provides, so that the actual temperature (25) of the target temperature (24) corresponds as possible.

9. A device for pretreating a rolling stock (3) made of steel before hot rolling, comprising:

- A preheating furnace (4) for preheating the rolling stock (3), wherein the preheating furnace (4) a plurality of burners (11) for

Burning a carbon carrier has; a descaling device (5) for descaling the preheated rolling stock (3), wherein the

Descaling device (5) the preheating furnace (4)

is downstream;

- A heating furnace (7) for heating the descaled

Rolling stock (3) at rolling temperature, the heating furnace (7) having a plurality of burners (11) for burning a carbon carrier and the heating furnace (7) downstream of the descaling device (5);

- An exhaust gas recirculation line (14) for introducing a

Exhaust gas (12) of the heating furnace (7) into the preheating furnace (4), the exhaust gas recirculation pipe (14) leading from the heating furnace (7) to the preheating furnace (4); and

- An oxygen line (15) for introducing oxygen into the preheating furnace (4), wherein the oxygen line (15) opens into the preheating furnace (4).

10. The device according to claim 9, characterized in that the burners (11) are designed as oxygen burners for burning a hot gas with the addition of oxygen.

11. The device according to claim 9, characterized in that a heating gas line (16) for introducing a heating gas in the preheating furnace (4) opens.

12. The device according to claim 9, characterized in that an induction furnace (6) immediately after the

Descaling device (5) is arranged, wherein the

Heating furnace (7) via an exhaust gas duct (17) with the

Induction furnace (6) is connected.

13. The apparatus according to claim 12, characterized in that in the transport direction (10) input end of the induction furnace (6) via an exhaust gas recirculation line (14) to the preheating furnace (4) is connected.

14. The apparatus according to claim 9, characterized in that a controller (19) on the one hand with a Gas concentration meter (20) for the determination of

Gas concentration (22) in a furnace (4) and on the other hand with an actuator (18 a, 18 b) for influencing the

Gas concentration is connected.