EP2655995B1 - Method for operating a furnace in a system for processing metal - Google Patents

Description

The invention relates to a method for operating a furnace for passing a continuously cast slab in a plant for metal processing, in particular in a continuous casting in which exhaust gas from the furnace along a flow path is passed through at least one recuperator, wherein in the recuperator by means of the heat energy contained in the exhaust gas Preheated fresh air for the furnace and the heated air is supplied to the furnace and wherein the exhaust gas is passed in the flow direction behind the recuperator in a fireplace. Furthermore, the invention relates to a plant for metal processing, in particular a continuous casting plant,

The generic method is used in particular in continuous casting, which can be designed as so-called. CSP plants ( C compact S trip P roduction). Such systems require at least one furnace, in which hot air is to be entered, which is heated by burners. Through the oven, the continuously cast slab is passed to be heated to a desired or required temperature.

In order to reduce the energy required for heating the furnace air, it is known to use recuperators, wherein in a preferred embodiment of the plant three recuperators per oven are used. In the recuperator energy recovery takes place from the hot exhaust gas of the furnace, ie in the recuperator the exhaust heat is withdrawn and used to preheat the furnace air.

In the normal case, the combustion air to be supplied to the furnace is heated in the recuperator from the hall temperature (about 30 ° C.) to about 450 ° C. As a result, the exhaust gas is cooled from about 900 ° C to about 700 ° C.

In Fig. 1 such a system is shown. First of all, the furnace 1 of a continuous casting plant (CSP furnace), through which the continuously cast metal strand is passed for the purpose of heating, can be seen. Hot exhaust gas A is discharged from the furnace and fed to a recuperator 2 via a flow path S. A further flow path S "for fresh air F, which is conveyed as burner air by means of a fan 10, also passes through the recuperator 2. Via the further course of the flow path S", the fresh air F enters the oven 1. In this process, the fresh air F becomes known heated by a burner (not shown) to the required temperature. However, in the recuperator 2, a preheating of the fresh air F by a heat transfer between the exhaust A and the fresh air F takes place.

In this case, it is necessary to protect the recuperator 2 and the burner (not shown) from the exhaust gas A at too high a temperature. There are two mechanisms that can be used for this purpose Fig. 1 are sketched.

Through the supply of cooling air K (with ambient temperature), which is promoted by a fan 11, cold air can be added to the exhaust gas A. The control of this process by means of a switchable valve 12. The said cooling takes place, if the exhaust gas A a certain temperature, for. B. 900 ° C exceeds. As a result, the temperature of the recuperator 2 reaching exhaust gas A is reduced and the recuperator 2 so protected or protected.

In order to protect the burners from too high a temperature (the air to be supplied to the burner should not be warmer than approximately 450 ° C.), preheated combustion air can escape into the environment via a hot air outlet 13. This is done by way of a controlled valve 14. By discharging combustion air via the hot air outlet 13, the pressure p in the flow path S "drops, but the pressure p is regulated to a desired value

Level held, which is done by the control of the fan 10. If the pressure p thus decreases, more fresh air F is conveyed by the fan 10 and consequently more cold air is pumped into the recuperator 2. As a result, the temperature drops in the recuperator second

In the prior art, this procedure of heat exchange by means of a recuperator for heating the furnace air are adequately described and corresponding devices known. It is exemplified on the US 2,192,108 A , on the GB 974 836A , on the DE 11 62 391 B , on the WO 2009/018476 A1 , on the EP 0 078 446 A1 and on the DE 697 12 009 T2 pointed. Another solution shows the ZA 200 304 880 A ,

The US 4 528 012 A discloses for a glass melting furnace a solution in which residual heat is used to recover energy by means of the Brayton process. The US 4,340,207 describes a heat recovery process for a cupola furnace.

It has been found that despite the preheating of the furnace air by means of the kiln exhaust gas in the recuperator energy consumption is still too high. For most operating points, the exhaust gas still has a temperature of about 700 ° C even after the recuperator. For a specific example, it was determined that the energy of the exhaust gas before the recuperator is up to 18.5 MW. Of this, 4.2 MW are used to heat the combustion air. The remaining 14.3 MW thermal energy, which has the exhaust after the recuperators still are not used. Furthermore, in some operating points (for example in the simulation with empty CSP furnace) to protect the burner hot combustion air is discharged behind the recuperator (as already explained above). This also causes heat energy to be lost.

The invention is in the light of the task of proposing a method for operating a furnace in a plant for metal processing and such a system, with or with the improved energy efficiency can be achieved. So it should be achieved an improved use of energy.

The solution of this problem by the invention according to the method is characterized in that in the flow path for the exhaust gas from the furnace or parallel to the flow path, a heat exchanger is arranged, fed to the water and in which the water is heated, wherein steam generated in the heat exchanger is used to to operate a power generation plant.

A first preferred embodiment of the invention provides that in the flow path of the exhaust gas, the recuperator and the heat exchanger are arranged in series, wherein the exhaust gas is first passed through the recuperator and then through the heat exchanger.

Alternatively, it is also possible that again in the flow path of the exhaust gas, the recuperator and the heat exchanger are arranged in series, but then the exhaust gas is first passed through the heat exchanger and then through the recuperator.

A further alternative embodiment of the proposed idea is that the heat exchanger is arranged in a second flow path parallel to the flow path, with exhaust gas being conducted at least temporarily through the flow path and through the second flow path at the same time.

In the exhaust gas controlled cooling air can be added in all cases before reaching the recuperator and the heat exchanger.

From the flow path of the preheated air for the furnace can also be controlled or regulated hot air to be discharged to the environment.

The air pressure in the flow path of the preheated air for the furnace can be controlled or maintained at a predetermined value, wherein for controlling or regulating the air pressure, the volume flow of fresh air is influenced, which is supplied to the recuperator.

The proposed plant for metal processing, in particular the continuous casting, is characterized according to the invention in that a heat exchanger is arranged in the flow path or parallel to the flow path, wherein means for supplying water are present in an inlet of the heat exchanger, wherein a plant for generating electricity is present which are connected to a drain of the heat exchanger.

The plant for power generation includes in particular a steam turbine.

Furthermore, it can be provided that a second flow path is arranged parallel to the flow path, wherein the heat exchanger is arranged in the second flow path and wherein at a branch point in which the second flow path branches off from the flow path, a controllable valve is arranged, which is formed, the exhaust gas with a predetermined amount in the two flow paths to guide. The exhaust gas is thus divided by the controllable valve in two flow paths.

With the proposed method and the corresponding device, it is possible to use the residual energy of the furnace exhaust gas much better. This results in an improved energy balance. The waste heat of the kiln exhaust gas can be converted directly into electricity but also provided to the hot water supply of a consumer.

The invention makes it possible to lower the temperature of the combustion air advantageously by passing hot exhaust gases through an additional valve through a second recuperator. As a result, components can be protected and the energy of the hot exhaust gases can still be used. In addition, this can preferably be dispensed with the reduction of the combustion air temperature. The system thus runs more stable overall.

Fig. 1

schematisch ein Anlagenschema für den Betrieb eines Ofens einer Stranggießanlage, das nach dem Stand der Technik ausgeführt ist,

Fig. 2

schematisch ein Anlagenschema für den Ofen, das nach einer ersten Ausführungsform der Erfindung arbeitet,

Fig. 3

schematisch ein Anlagenschema für den Ofen, das nach einer zweiten Ausführungsform der Erfindung arbeitet, und

Fig. 4

schematisch ein Anlagenschema für den Ofen, das nach einer dritten Ausführungsform der Erfindung arbeitet.

In the drawings, embodiments of the invention are shown. Show it:

Fig. 1

1 schematically shows a plant scheme for the operation of a furnace of a continuous casting plant, which is carried out according to the prior art,

Fig. 2

1 schematically shows a plant scheme for the furnace, which operates according to a first embodiment of the invention,

Fig. 3

schematically a plant scheme for the furnace, which operates according to a second embodiment of the invention, and

Fig. 4

schematically a plant scheme for the furnace, which operates according to a third embodiment of the invention.

In the FIGS. 2 to 4 Three different detailed concepts are presented how a furnace 1 of a continuous casting plant can be operated in order to achieve an improved energy balance. They all based on the idea that in addition to at least one recuperator 2, a heat exchanger 4 is available, can be used with the residual heat from the exhaust gas A of the furnace 1 to produce either in a plant 5 for electricity generation electricity (is in the figures shown) or to use the residual heat to provide hot water to a consumer available (is not shown).

The basic structure of the concepts is based first on that according to the state of the art as described in Fig. 1 shown and described above. From the furnace 1, exhaust gas A is then passed along a flow path S into a recuperator 2. The recuperator 2 fresh air F is supplied, along a flow path S "through the recuperator 2 and further into the furnace. 1 is directed. In the recuperator 2, a heat transfer from the exhaust gas A to the fresh air F takes place, so that the fresh furnace air (combustion air) is preheated.

Regarding the recuperators used, reference is made to the state of the art. They each have a separate room for the two media between which heat is to be exchanged. Plate heat exchangers, in particular spiral heat exchangers, tube heat exchangers, jacket tube heat exchangers or countercurrent layer heat exchangers can be used.

According to the in Fig. 2 now shown, a heat exchanger 4 is connected in series with the recuperator 2, that is, the heat exchanger 4 is arranged in the flow path S, which leads from the furnace 1 to the chimney 3. In this case, first the exhaust gas A is passed through the recuperator 2 and then the already cooled to about 700 ° C exhaust gas A through the heat exchanger 4. Also for the heat exchanger, the above mentioned for the recuperator embodiments in question.

The heat exchanger 4 is supplied with water W via an inlet 6. In the heat exchanger 4, the water W is heated and is converted into steam, which is supplied via a drain 7 of a plant 5 for power generation, comprising a steam turbine. The conversion of the energy in the steam into electricity is well known as such and need not be further deepened here.

As in Fig. 2 can be seen, can also be done here - as in the prior art - a temperature of the exhaust gas A behind the furnace 1 by cooling air K via a fan 11 and a switchable valve 12 is mixed. It can also be provided that a hot air outlet 13 is opened via a switchable valve 14 in order to discharge heated fresh air and for the purpose of maintaining it of the pressure p to actuate the fan 10 accordingly, so that more cold fresh air F is conveyed into the flow path S ".

The solution according to Fig. 3 is according to Fig. 2 very similar. The difference here is that the heat exchanger 4 is arranged here for the heating of the water W here first after the furnace 1; the recuperator 2 follows only behind the heat exchanger 4, as seen in the flow direction in the flow path S. Via a valve 15 hot exhaust gas can be routed to the recuperator 2 around the heat exchanger 4, if required. The solution shown is also characterized by the fact that it is possible to first cool the exhaust gas A by heating water and converting it to steam and only then to supply the recuperator 2. Therefore, in Fig. 3 the preferred case outlines that the supply of cooling air K by means of fan 11 and switchable valve 12 is dispensed with; The pre-cooling of the exhaust gas A thus takes place through the heat exchanger 4. However, it should be mentioned that the arrangement in question 11, 12 also in the solution according to Fig. 3 can be provided.

In Fig. 4 a further alternative embodiment of the inventive concept is illustrated. Here it is provided that the heat exchanger 4 is arranged in a flow path S parallel to the second flow path S '. "Parallel" is to be understood here as meaning that the flow paths S and S 'are supplied with exhaust gas A from the furnace and run independently of one another. The exhaust gas A is thereafter at least temporarily passed through the flow path S and through the second flow path S 'simultaneously.

As can be seen, the second flow path S 'is thus arranged parallel to the flow path S, in which the heat exchanger 4 is placed. At a branching point 8, the second flow path S 'branches off. Here is a controllable valve 9 is arranged. With the valve 9 can be specified to what extent exhaust gas is passed to the heat exchanger 4. Is the valve 9 closed, ie exhaust gas A is passed only through the flow path S, is exactly the situation before, as it corresponds to the prior art.

For operating points in which additional heat recovery from the exhaust gas A is not desired, the supply of exhaust gas A to the heat exchanger 4 can thus be prevented via the valve 9, 15 and all exhaust gas A can be guided via the recuperator 2.

In other words, in the prior art, hot air must escape to protect the recuperator and burners if the combustion air is too hot. As a result, energy is lost.

In the procedures as they are in Fig. 3 and 4 illustrated, the combustion air can be reduced by using the valve 15, the hot exhaust gas is passed through the second recuperator. This protects the components and still allows the energy to be used. In addition, the indirect control to lower the combustion temperature by means of the hot air outlet is avoided, making the system more stable.

LIST OF REFERENCE NUMBERS

1

oven

2

recuperator

3

fireplace

4

heat exchangers

5

Plant for power generation

6

Intake

7

procedure

8th

branching point

9

Valve

10

fan

11

fan

12

switchable valve

13

hot air outlet

14

switchable valve

15

Valve

A

exhaust

F

fresh air

W

water

K

cooling air

p

air pressure

S

flow

S '

second flow path

S "

Flow path of preheated air for the oven

Claims (7)

1. Method of operating a furnace (1) for passing through a continuously cast slab in a plant for metal processing, particularly in a continuous casting plant, in which the waste gas (A) is conducted out of the furnace (1) along a flow path (S) through at least one recuperator (2), wherein fresh air (F) for the furnace (1) is preheated in the recuperator (2) by means of the heat energy contained in the waste gas (A) and the heated air is fed to the furnace (1) and wherein the waste gas (A) is conducted into a flue (3) behind the recuperator (2) in flow direction, characterised in that arranged in the flow path (S) or parallel to the flow path is at least one heat exchanger (4) to which water (W) is fed and in which the water is heated, wherein steam generated in the heat exchanger (4) is used in order to operate the plant for power generation (5).
2. Method according to claim 1, characterised in that the recuperator (2) and the heat exchanger (4) are arranged in series in the flow path (S) of the waste gas (A), wherein the waste gas (A) is initially conducted through the recuperator (2) and subsequently through the heat exchanger (4).
3. Method according to claim 1, characterised in that the recuperator (2) and the heat exchanger (4) are arranged in series in the flow path (S) of the waste gas (A), wherein the waste gas (A) is initially conducted through the heat exchanger (4) and subsequently through the recuperator (2).
4. Method according to claim 1, characterised in that the heat exchanger (4) is arranged in a second flow path (S) parallel to the flow path (S), wherein waste gas (A) is conducted at least at times simultaneously through the flow path (S) and through the second flow path (S').
5. Method according to any one of claims 1 to 4, characterised in that cooling air (K) is added to the waste gas (A) under control or regulation before the waste gas reaches the recuperator (2) and the heat exchanger (4).
6. Method according to any one of claims 1 to 5, characterised in that hot air is let off to the environment under control or regulation from the flow path of the preheated air for the furnace (1).
7. Method according to any one of claims 1 to 6, characterised in that the air pressure (p) in the flow path of the preheated air for the furnace (1) is kept, by control or regulation to a predetermined value, wherein for control or regulation of the air pressure (p) the volume flow of fresh air (F) fed to the recupterator (2) is influenced.

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