EP3322953A1

EP3322953A1 - Device and method for reheating metallic products

Info

Publication number: EP3322953A1
Application number: EP16733910.0A
Authority: EP
Inventors: Michael Potesser; Johannes Rauch; Mathias SWOBODA
Original assignee: Messer Austria GmbH
Current assignee: Messer Austria GmbH
Priority date: 2015-07-16
Filing date: 2016-06-23
Publication date: 2018-05-23
Also published as: MA43067A; CN107923709A; DE102015009194A1; WO2017009020A1

Abstract

In prior art reheating furnaces, the products that are to be heated pass through, in sequence, a preheating zone and one or more heating or equalizing zones, in which the products are brought step-by-step to their end temperature that is determined for further processing. In order to reduce the residence time of the products in the furnace space, and thus minimize the risk of scale forming on the product surface, the preheating zone is, according to the invention, equipped at least in certain sections with oxygen-fuel burners which are designed such that the combustion gases issuing therefrom form a flame that, in operation of the device, reaches the surface of the products. Direct flame impingement increases the effectiveness of the heat transfer, and thus reduces the residence time of the products.

Description

Apparatus and method for reheating metallic products

The invention relates to a device for reheating metallic products for subsequent mechanical forming, comprising a furnace chamber having a preheating zone and at least one subsequent zone, a transport device for transporting the products to be heated from the preheating zone into the subsequent zone and one in the region of the preheating zone

Discharge device for discharging generated in the subsequent zone

Has flue gases, and installed in the subsequent zone fuel-air burners, which are designed such that a flame emanating from them does not touch the surface of the products. The invention further relates to a method for operating a reheating furnace.

Such furnaces are also known as "reheating furnaces" or "second-heat furnaces" and are described, for example, in WO 02/097348 A1, US 2004/0259047 A1 or US Pat. No. 6,290,492 B1. They serve for reheating a metallic blank obtained by continuous casting, for example (hereinafter referred to as "product" or "thermal material") after solidification from the melt and before a subsequent mechanical deformation, such as forging or rolling; In the reheating furnaces no heat treatment of the products takes place. The thermal material which is usually present at a temperature of less than 400 ° C. passes successively through several zones in which it is brought to its final temperature of, for example, 750.degree. C. to 1500.degree. C. required for forming. From a furnace entrance from the Wärmgut is thereby first transported through a so-called preheating or convection zone in which it comes into hot contact with hot flue gas in the, from

Combustion processes in one or more subsequent zones.

These subsequent zones are designated according to their task as a "heating zone" or as a "compensation zone", wherein in each case a plurality of heating zones and / or

Balancing zones can be present. In the heating zone (or heating zones), in the known reheating furnaces, the greatest energy input is used to heat the products, while in the preheating zone the high temperature of the flue gases generated in the heating zone is used to preheat the products. The compensation zone is used in particular to ensure that the heat from the surface The products are evenly and homogeneously distributed inside the products before the products leave the kiln at the exit of the kiln for subsequent forming.

Both heating and compensation zones are equipped with a number of burners, which are usually operated with air as the oxidant and as

Ceiling burners are installed in the loft or as front burners in the side walls of the furnace. These burners are designed in such a way that the flames they emit do not touch the surface of the products to be heated, because if the heat is too high, there is a risk that the surface of the material will be oxidised, thereby reducing the quality of the products. Instead, these burners fuel the furnace atmosphere above the Wärmguts with a in the

Substantially parallel to the transport plane of the Wärmguts extending flame or have a short and wide flame, which ends well in front of the product surface. The heating of the products in the heating zone thus takes place by convection of the flue gases produced by the burners and by the radiation emitted by the flames of the burner. The predominantly CO ₂ , H ₂ O, N ₂ and O ₂

Existing flue gases are then passed through the furnace chamber in countercurrent to the Wärmgut and deducted via an exhaust system, which in the

Preheating zone is installed in the area of the furnace inlet and at the same time controls the furnace pressure.

Reheating furnaces have a high energy consumption and sometimes significant emissions of pollutants, especially nitrogen oxides on. In order to reduce the accumulation of nitrogen oxides, it is proposed in WO 02/097348 A1 to install several burners in the region of the preheating zone of a reheating furnace which use an oxidizing agent with a higher oxygen content than air. It is also proposed in WO 2002/021061 A1 to install at least one additional burner, which is operated with an oxygen-rich oxidizing agent, to increase the thermal output. This burner can be mounted in a zone in which no burner was previously available, so for example, the preheating zone, or it replaces a fuel-air burner in the heating zone.

A disadvantage of the prior art ovens is that it often increases during the run Quality loss due to scaling on the surface of the thermal material comes. A major cause of scaling is especially in the long

Seen duration of residence, in which the heated Wärmgut the flue gases are exposed when passing through the furnace chamber.

The invention is therefore based on the object, a furnace for the

To re-heat metallic products that provide high thermal performance and reduce the risk of scaling during warm-up.

This problem is solved in a furnace of the type mentioned and

Purpose by the fact that the preheating zone is at least partially equipped with fuel-oxygen burners, which are designed so that during operation of the device, the fuel gases flowing out of them form a flame that reaches the surface of the products.

According to the invention, so-called "direct flame impingement" are thus installed in at least one section of the preheating zone, by means of which the products passing through this region are directly exposed to the burner flame. By the direct application of flame there is a high efficiency in the heat transfer, which makes it possible to supply a large part of the total heat to be supplied to the heat already in the preheating area. Correspondingly lower, the performance of the burners in the subsequent zone or the subsequent zones can be set, so that a total of

Savings in heating energy can be achieved. As "subsequent zones" here the preheating zone in the transport direction of the products downstream zones are considered, in particular one or more heating and / or one or more balancing zone / n. Since the installed in the preheating zone burners are designed as oxyfuel burner, which with a oxygen-rich oxidant with, for example, 40% by volume of oxygen, preferably greater than 90% by volume of oxygen and more are operated, there is only a small amount of additional

Flue gas, which is then withdrawn together with the flue gas from the following zones on the trigger device. The very early and intensive heating of the heat in the preheating zone further leads to the task of the subsequent zone (s) consists primarily of producing a very homogeneous temperature distribution in the products. Consequently, the burners of the subsequent zones are designed as a fuel-air burner, the hot flue gas with his due to his

Nitrogen content of comparatively large mass flow a good convective

Heating of the Wärmguts and thereby favors in particular a uniform heating of the surface of the products.

The rapid heating of the products already in the preheating zone and the early onset of the temperature equalization phase also allows faster passage of the products through the oven compared to prior art furnaces, thereby reducing the risk of scaling of the product surface.

An installation of oxyfuel burners in the area of the preheating zone of a

Although rewarming furnace has already been proposed in WO 2002/021061 A1 and WO 02/097348 A1; However, the burners described therein serve only to heat the guided through the preheating flue gases and thereby optimize the conditions in the convective heating of the furnace chamber passing through products. Direct flame exposure of the products is not described in these documents.

A particularly advantageous embodiment of the invention provides that the installed in the preheating, directly acting oxygen-fuel burner are designed as flameless burner. Flameless burners are to be understood here as meaning those burners in which flameless operation, ie conversion of the fuel gases, is possible without the formation of a visible flame front Flameless operation of the burners in the preheating zone leads to a uniform application of thermal energy to the surface of the thermal material Surprisingly, it has also been found, surprisingly, that due to the strong current of the combustion gases leaving the burner in flameless operation, the flow of fuel passed through the preheating zone, from combustion to subsequent combustion Zone-derived flue gases is strongly deflected towards the products. In addition to the supply of heat energy through the direct

Due to the flameless operation of the burners in the preheating zone, flame exposure is subject to intense convective heating of the products, which goes well beyond the warm-up power that is available in conventional heating systems

Reheating ovens due to the thermal contact of the products with the flue gases in the preheating zone is recorded. Flameless operation, in particular, allows heat transfer to the products that is so efficient that the temperature of the flue gases as the preheat zone passes during flameless operation of the burners decreases, thus giving the flue gases more heat to the products than they do from the flame of the burners receive.

A preferred development of the invention provides that the burners of at least the preheating zone are at least partially installed in the area of the furnace roof and substantially perpendicular, ie between 80 ° and 100 °, preferably 90 ° to

Direction of transport of the products to which the surface of the products in transit is directed. The burners preferably recessed in the furnace roof are designed in such a way that the flame generated by them overcomes the distance between the furnace roof and the surface of the material to be heated, which in some furnaces may well be between 1 m and 2 m, and the products directly

applied. In addition to the ceiling burners, oxygen-fuel burners may also be installed in the sidewalls and / or in the floor area of the preheat zone, which directly apply the heat.

In an advantageous embodiment of the invention, the burners installed in the preheating zone form a field of a plurality of burners distributed uniformly over the furnace roof. The burners arranged in this way allow very uniform heating of the thermal material, especially in flameless operation.

In particular, with lumpy products, it is also advantageous that the burner can be controlled individually to allow a targeted exposure of the Wärmguts.

Conveniently, the burners are in the preheating zone and / or in the

subsequent zones of the device according to the invention individually or In groups controlled by a control unit. The burners can be switched on or off as required individually or in groups, or their performance can be regulated. The control unit regulates in particular the heat input via the individual burners after one

pre-installed program and / or depending on measured values, for example, the temperature of the Wärmguts and / or a

Pollutant concentration in the flue gas and / or the path of a product to be heated through the furnace chamber. By means of a control unit and the process temperature, for example, regulated between 750 ° C and 1500 ° C and the combustion ratio of the burner in the preheating zone and / or in the

subsequent zones are adapted to the specific furnace data.

The object of the invention is also achieved by a method having the features of patent claim 6.

The inventive method for heating products in one

Reheating furnace in which products to be heated successively pass through a preheating zone and at least one subsequent zone of a furnace chamber of the reheating furnace and thereby in thermal contact with in the

Countercurrent to the products guided, produced by burners in the subsequent zone flue gases are brought, is characterized in that the products in the preheating zone by means of burners installed there by direct

Flame impingement and convective in at least one of the following zones, by heating of subsequently flowing the products

Flue gases are heated.

Due to the direct application of flame, a substantial part of the total heat to be transferred is already transferred to the products in the pre-heat zone. In the following zones, an indirect heating of the products takes place by heating the furnace chamber in the region above the products passing through these zones by means of burners and subsequent contacting of the thermal material with the flue gases generated thereby or the atmosphere thereby heated. This convective heating favors in particular the production of a homogeneous temperature profile in the products. The products leave the Thus, the reheating furnace according to the invention with a very homogeneous temperature profile and have no or only a slight scaling on the surface.

Preferably, the burners are operated flameless in the preheating zone. As a result, the surface of the heat is heated evenly and without the risk of local overheating. In the context of the invention, however, it is also possible to operate the burners in the preheating zone at least temporarily with a visible flame.

In order to ensure efficient heat transfer and the shortest possible duration of the products in reheating furnace provides an advantageous embodiment of the invention that at least 25%, preferably more than 50% of the products in the oven room to be supplied total heating energy products already on the directly impinging and preferably flameless operated oxygen-fuel burners in the preheating zone is supplied.

Reference to the drawings, an embodiment of the invention will be explained in more detail.

In schematic views show:

Fig. 1: A reheating furnace according to the invention in longitudinal section

2: The heat zones of the furnace of FIG. 1

The furnace 1 shown in Fig. 1 comprises a furnace chamber 2, in which metallic

Products, such as billets or slabs of steel or copper, for the purpose of subsequent mechanical forming by, for example, forging, rolling or bending to a predetermined processing temperature, for example, between 1000 ° C and 1500 ° C are brought. The furnace chamber 2 comprises an inlet 3, through which the products 4 to be heated are transported into the interior of the furnace chamber 2, and an outlet 5, through which the heated products 4 leave the furnace chamber 2. The products 4 are transported by means of a transport device 6 through the furnace chamber 2 and pass through several zones 8, 9, 10, 1 1, namely a preheating zone 8, a first heating zone 9, a second heating zone 10 and a balancing zone 1 1. The zoning of a

Reheating furnace is to be understood merely as an example, in particular, only one or three or more heating zones can be provided. The

Transport direction 12 of the products 4 through the furnace chamber 2 is indicated in Fig. 1 by an arrow.

The two heating zones 9, 10 and the balancing zone 1 1 are with - in

Embodiment designed as ceiling burner - equipped burners 14, of which in Fig. 2 for reasons of clarity, only one burner is provided with a reference numeral. In each of the zones 9, 10, 1 1 is a field of a plurality of in the respective ceiling region of the zone 9, 10, 1 1 uniformly, ie at equal distances from each other, distributed burners 14 are provided. The number and spacing of the burners can be the same or different in all zones. The resulting in the combustion processes described in more detail below in the furnace chamber 2 flue gases are withdrawn at a discharge device 15 in the preheating zone 8, as indicated by the dashed arrow 1 6. About the here not explained triggering device 15 is also the pressure in

Furnace room 2 regulated.

The burners 14, which are preferably constructed substantially identically in the heating zones 9, 10 and in the equalization zone 11, are preferably burners, by means of which a gaseous, liquid or solid fuel,

For example, coal dust, oil or natural gas, is burned with air as the oxidant. They are built so that the flames emanating from them are so wide and short shaped that the area of the furnace chamber 2 before the respective

Outlet of the burner 14 and evenly heated above the products 4, the surface of the products 4 but is not touched by the flame. Burners of this type are described, for example, in WO 02/0973348 A1.

In the area of the preheating zone 8, a field of a plurality of burners 18 arranged in the region of the furnace roof 17 of the preheating zone 8 is installed. in the

In contrast to the burners 14, the burners 18 are oxy-fuel burners in which a liquid or gaseous fuel with oxygen or an oxygen-rich gas with at least 40 vol .-% oxygen, preferably greater than 90 vol .-% oxygen is burned. The burner 18 are directed with their outlets 19 vertically downwards, ie at an angle of approximately 90 ° to the transport direction 6 of the products 4. The burners 18 are designed so that the flame emanating from them is sufficiently long to touch the surface of the products, so they are so-called "DFI burners", and they are also suitable for flameless operation are described, for example, in WO 2008/092763 Al.Other burners 18 of the type mentioned can-not shown here-be arranged in the side walls of the preheating zone 8 and permit lateral direct application of the products 4. Also, burners 18 below the transport level of the products 4 are arranged, and heat the products 4 from below, are conceivable within the scope of the invention, as long as the products 4 can be heated directly with them.

During operation of the device 1, the products 4 are transported by means of the transport device 6 from the inlet 3 of the furnace chamber 2 to the outlet 5. In the burners 14 of the zones 9, 10, 11, a solid, gaseous or liquid fuel is burned with air, without the flame generated thereby touching the surface of the products. The resulting from combustion mainly of carbon dioxide, water vapor and nitrogen hot flue gases are in the

Counterflow to the products 4 through the furnace chamber 2 in the direction of

Preheating zone 8 out come here with the respective zone passing through products in contact and heat them on. Subsequently, the flue gases are deducted from the discharge device 1 6. In particular, the nitrogen serves the air supplied to the burners 14 as the oxidant as

Heat transfer medium to achieve the most intense, convective heating of the products 4.

In the preheating zone 8, the products 4 are additionally by direct

Flame applied from the oxyfuel burners 18 heated. The burners 18 are thereby operated in the flameless mode, that is to say in the preheating zone 8 a reaction zone 20 is formed, which extends from the outlets 19 of the burners 18 to the surface of the products 4 and within which the combustion reaction takes place. Due to the strong flow of ejected from the burners 18 Fuel gases during flameless operation, the flowing out of the zones 9, 10, 1 1 flue gases are deflected towards the products 4, as indicated by the arrow 22, resulting in improved heat transfer from these flue gases to the products 4.

By the direct admission of the products 4 and the flameless operation of the burner 18 in the preheating a particularly efficient heat transfer is achieved. As a result, more than 25%, preferably more than 50%, of the heat energy to be transferred to the products 4 as a whole is provided by the burners 18.

During the passage through the zones 9, 10, 1 1, therefore, there is already an intense temperature balance within the products 4, so that the

Length of stay of the products 4 in these zones

Reheating furnace according to the prior art can be shortened.

This reduces the risk of scaling of the products 4.

The operation of the burners 14, 18 is monitored by a control unit, not shown here, which in particular the supply of fuel and oxidizing agent to each burner 14, 18 in response to a predetermined

Program and / or measured values. In particular, you can

Burner 18 are switched on or off individually or in groups, depending on whether there is a product below them or not. Likewise, the power of the burners 14, 18 and the distribution of the heat energy to be transmitted to the burners 14, 18 can be controlled, for example, as a function of a measured temperature, and / or material parameters that are downstream of the furnace 1, for example before or during a mechanical deformation process of the products heated in the furnace 1 4 measured and used as a control parameter for controlling the burner 14, 18.

Incidentally, it is also possible to retrofit existing furnaces according to the invention. For this purpose it is necessary to install DFI burners in the ceiling area or in the side walls of the respective preheating zone, whose flames are capable of increasing the distance between the ceiling / side wall and the product surface

bridge, which can have up to 1 m and more. LIST OF REFERENCE NUMBERS

1 oven

2 ovens room

3 entrance

4 product

5 output

6 transport device

7 -

8 preheating zone

9 first heating zone

10 second heating zone

1 1 equalization zone

12 transport direction

13 -

14 burners

15 fume cupboard

16 arrow

17 oven ceiling

18 burners

19 outflow

20 reaction zone

21 -

22 arrow

Claims

claims

1 . Apparatus for reheating metallic products for subsequent mechanical forming, comprising a furnace chamber (2) having a preheating zone (8) and at least one subsequent zone (9, 10, 11), a transporting device for transporting the products (4) to be heated the preheating zone (8) in the subsequent zone (9, 10, 1 1) and in the preheating zone (8) arranged withdrawal means (15) for discharging in the

downstream zone (9, 10, 1 1) produced flue gases, and with in the subsequent zone (9, 10, 1 1) installed fuel-air burners (14) which are designed such that a flame emanating from them the

Surface of the products (4) not touched,

characterized,

the preheating zone (8) is equipped, at least in sections, with oxygen-air burners (18) which are designed in such a way that, during operation of the device, the combustion gases emanating from them form a flame which reaches the surface of the products (4).

2. Device according to claim 1, characterized in that in the

Preheater installed burners (18) are designed as flameless or non-flameless burner.

3. Apparatus according to claim 1 or 2, characterized in that the

Burner (14, 18) at least the preheating zone (8) at least partially in the region of the furnace roof (17) are installed and directed substantially perpendicular to the surface of the continuous products (4).

4. Device according to one of the preceding claims, characterized

characterized in that in the preheating zone (8) a field of a plurality of uniformly over the furnace roof (17) distributed burners (18) is provided.

5. Device according to one of the preceding claims, characterized by a control and regulating unit, with which the burner (18) in the preheating zone (8). and / or the burner (14) in the subsequent zone (9, 10, 1 1) individually or in groups can be controlled.

6. A method for heating products in a reheating furnace, in the products to be heated (4) successively through a preheating zone (8) and at least one subsequent zone (9, 10, 1 1) of a furnace chamber (2) of the reheating furnace (1) and doing so in thermal contact with countercurrent to the products (4) guided by burners in the

subsequent zone (9, 10, 1 1) generated flue gases are brought, characterized

that the products (4) in the preheating zone (8) by direct

Flame impingement by means installed in the preheating zone oxygen-fuel burner (18) and in the subsequent zone (9, 10, 1 1) convectively, by heating then the products (4) inflowing

Flue gases to be heated.

7. The method according to claim 6, characterized in that the burners (18) in the preheating zone (8) are operated flameless or not flameless.

8. The method according to claim 1 or 2, characterized in that at least 25%, preferably more than 50% of the products (4) in the furnace chamber (2) supplied heat energy to the products (4) in the preheating zone (8) is supplied.