EP2318761A1

EP2318761A1 - Device for controlling regenerative burners

Info

Publication number: EP2318761A1
Application number: EP09797609A
Authority: EP
Inventors: Patrice Sedmak
Original assignee: Fives Stein SA
Current assignee: Fives Stein SA
Priority date: 2008-07-15
Filing date: 2009-06-25
Publication date: 2011-05-11
Also published as: CN102099624B; US20110111355A1; FR2934033B1; WO2010007547A1; CN102099624A; BRPI0915554A2; FR2934033A1; US8845324B2

Abstract

The invention relates to a device for controlling regenerative burners used as a firing device, particularly for iron and steel product heating furnaces or for radiating tubes for continuous strip steel processing lines, according to which the supply of at least one of the fluids involved in the combustion (fuel and comburent) is carried out through a rotary injector (12) rotating by means of a rotatable actuator (M) so as to supply fluid alternately to one and then the other of the burners (B1, B2), the rotary injector (12) being placed on the comburent inlet duct (6), particularly air, and is provided to partially obstruct the supply pipe (19.1; 19.2) to the burner (B1; B2) such that one portion of the fumes from a regenerator (2.2; 2.1) for the non-operating burner (B2; B1) is led to the operating burner (B1; B2) and such that the other portion of the fumes is discharged to the stack.

Description

DEVICE FOR CONTROLLING REGENERATIVE BURNERS.

The invention relates to a device for controlling regenerative burners, which are used as heating equipment, for example for reheating furnaces, in particular reheating furnaces for steel products, in particular slabs, blooms and blanks. or biliettes, for carrying the product to be heated to the desired temperature for rolling, and the radiant tubes for continuous treatment lines of steel strips, for example annealing lines and galvanizing lines. Regenerative burners are systems with high combustion efficiency because of the high temperature preheating of one of the two fluids involved in the combustion, generally air, through the regenerative matrices of the burners. Their operation in pairs alternately as a burner and chimney imposes a particular winnowing system. FR 2 905 753 relates to a heating furnace equipped with such burners.

In the accompanying drawings, Fig.1 shows in schematic vertical section a pair of regenerative burners B1, B2 mounted vis-à-vis opposite longitudinal walls of a furnace. Each burner comprises a fuel injection tube 1.1, 1.2 and a regenerative matrix 2.1, 2.2 formed by a compact mass of heat storage materials. On the side of each matrix opposite to the combustion zone, there are respectively a 3.1, 3.2 inlet pipe of oxidant, generally air, and an outlet pipe 4.1, 4.2 for the fumes.

A solenoid valve 5.1, 5.2 is provided respectively on the air pipes 3.1, 3.2 fed by a common inlet pipe 6. A solenoid valve 7.1, 7.2 is provided respectively on the outlet pipes 4.1, 4.2 which join a common flue gas duct. 8, connected to a fireplace. The supply of fuel is ensured, from a common pipe 9, by means of connections with respective solenoid valves 10.1, 10.2 for the tubes 1.1 and 1.2.

When the burner B2 is heated, the valves 10.2 for the arrival of fuel, 5.2 for the air inlet and 7.1 for the flue gas discharge are open. The other valves are closed. The burner B1 is stopped and acts as a chimney and the combustion gases pass through the die 2.1 to escape through the pipe 4.1, the valve 7.1 and the pipe 8. When the burner B1 heats up, the burner B2 is stopped and acts as a chimney. The position of the solenoid valves is reversed and the combustion air passes through the regenerative matrix 2.1, where it heats up, before being mixed with the fuel to be burned. Thus, where a single air solenoid valve is useful on a conventional burner, it will require four solenoid valves 5.1, 5.2, 7.1, 7.2 on a pair of regeneratives including two hot 7.1, 7.2.

In addition to the additional cost imposed by this system during the purchase, the maintenance cost of the winnowing is also high because the valves are very solicited because of the high number of cycles of opening and closing, typically every 30 seconds.

In particular, hot flue gas evacuation valves pose a technical problem when they leak after a large number of opening and closing cycles, which eventually occurs on these hot valves. The lack of tightness of the valve on the fumes leads to the leakage of some of the combustion air to the chimney. This results in a lack of air at the burner. Soot produced by poor combustion foul the regenerators, further limiting the flow of combustion air. The burners eventually become completely clogged. In addition, the fumes loaded with unburnt find the air leak in the downstream pipes from where a risk of afterburner in the pipes.

The maintenance of these valves with heat becomes quickly binding which often forces to regulate the combustion in large excess of air. But these burners already tend to produce a lot of nitrogen oxide. Mismanagement of the excess air worsens the phenomenon.

In multi-burner furnaces of the high capacity type, the problem is slow enough to settle, which makes it possible to act before the failure.

On systems with radiant tubes, the problem would quickly become unmanageable, each unit being likely to be disrupted without warning. Finally, the use of small powers does not simplify the regulation of the flows.

The supply of fuel burners requires two solenoid valves 10.1, 10.2 also very stressed by a large number of opening and closing cycles. The object of the invention is, above all, to reduce, if not to eliminate, the operating faults mentioned above despite the high frequency of the openings and closures of the circuits. US 3 170 680 discloses a glass furnace comprising regenerators. Each regenerator feeds several fuel injectors. In this type of furnace there are not strictly speaking burners but fuel injectors knowing that the temperature level is such that there is self-ignition fuel. This document does not describe an air injector, but pipes or supply ducts. The field of application is different from that of the invention which relates to regenerative burners, each being equipped with an individual regenerative matrix and an injector. The proposed invention, particularly well suited to small power units, avoids the problems mentioned by allowing:

the elimination of valves and in particular of hot valves, thereby avoiding any deterioration of these over time, leading to a reduction in installation costs, better management of the excess air,

- The reduction of nitrogen oxides produced during combustion by a flue gas recirculation device.

According to the invention, a device for controlling regenerative burners used as heating equipment, in particular for furnaces for reheating steel products or for radiant tubes for continuous treatment lines of steel strips, is characterized in that:

- The supply of at least one of the fluids involved in the combustion (fuel and oxidant) is performed using a rotating injector by means of a rotary actuator so alternately feed one and then the other burners,

the air inlet and the flue gas outlet for a burner are provided by the same supply pipe,

the rotating injector is arranged on the oxidizer inlet pipe, in particular with air, and is designed to partially obstruct the supply pipework towards the burner, so that a portion of the fumes coming from a Burner regenerator at shutdown is induced towards the burner in operation and that the other part of the fumes is evacuated towards the chimney.

Regenerative burners are combined in pairs and work alternately. The same supply pipe of a burner ensures, when this burner is running, the air inlet and when this burner is at stopping the smoke outlet of the other burner running the pair, and vice versa for this other burner of the pair.

Advantageously, the recirculation of a portion of the combustion fumes to the burner in operation is ensured by a driving effect related to the speed of the fluid at the outlet of the injector.

The injector may comprise a cylindrical hollow body having, at one end, a frustoconical nozzle which opens radially through an outlet orifice of reduced diameter, the nozzle being able to be placed facing the inlet of an air duct towards a burner, so that smoke entrainment areas are created by the ejection of air through the outlet port.

The injector may include, towards its end remote from the nozzle, a portion disposed in a cylindrical housing formed as a cold air valve with two diametrically opposite orifices provided in the part, and an orifice provided in the wall of the housing, at the openings. In general, a ring of low friction material is disposed between the body of the injector and the wall of the housing. The ring can be bronze.

The rotary actuator can be constituted by an electric motor.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with reference to an embodiment described with reference to the accompanying drawings, but which is in no way limiting. On these drawings:

Fig.1 shows, in schematic vertical section, a pair of regenerative burners according to the state of the art.

Fig.2 shows, in schematic vertical section, a pair of regenerative burners with a control device according to the invention.

Fig.3 shows in vertical axial section, on a large scale, the injector rotating in the closed position, and Fig.4 shows in vertical section, on a larger scale, the nozzle of the injector and a pipe inlet.

The description of the invention is made with reference to FIGS. 2 to 4 of the accompanying drawings. The description is made for an application in U-shaped radiant tubes 11 of which only the ends of the parallel branches are shown. The description is fully applicable to other applications of regenerative burners such as preheating furnaces before rolling. The elements of FIG. 2 similar to elements described with reference to FIG. 1 are designated by the same reference numerals, without their description being repeated.

According to the representation of FIG. 2, the burner B1 heats, while the burner B2 is stopped and operates in a fireplace.

The air supply and flue gas solenoid valves have been removed.

According to the invention, the supply of combustion air is carried out by an injector 12 rotating by means of a three-position rotary actuator M 180 ° which sways the air inlet to the top burner B1 and then reverses the combustion. to the bottom burner B2. The third position is intermediate and corresponds to the burners stopped. The actuator M, generally constituted by an electric motor, may be equipped with end-of-travel contacts for controlling the positioning. The rotary injector 12 comprises a cylindrical hollow body 13 coaxially disposed in a cylindrical housing 14 for supporting and guiding in rotation. Advantageously, a ring 15 (FIG. 3) made of a material with a reduced coefficient of friction, in particular made of bronze, is disposed between the body 13 and the housing 14. According to the example illustrated in FIG. 2, the geometric axis of the body 13 is horizontal, but a different orientation is possible, in particular vertical.

The body 13 is closed at its axial end facing the actuator M. This end is connected by a shaft 16 to the actuator. At its other end, the body 13 comprises an injection nozzle 17 which opens radially in a space 18.

The air inlet 3.1 and the outlet 4.1 of the burner fumes B1 are provided by a single conduit 19.1, also called supply piping. It is the same for the burner B2 and the conduit 19.2. More specifically, when the burner B1 is running, the conduit 19.1 ensures the supply of air to the burner B1, while the flue gas output from the burner B1 is provided by the conduit 19.2 of the burner B2 stopped. When the burner B1 is stopped while the burner B2 is running, the duct 19.1 ensures the exit of the fumes from the burner B2, and the duct 19.2 ensures the supply of air to the burner B2. The geometric axes of the ducts 19.1, 19.2 are aligned and orthogonal to the geometric axis of rotation of the body 13. The pipes 19.1, 19.2 open into the space 18. The outlet of the nozzle 17 can be placed either 19.1 facing the tubing, either by a rotation of 180 ° facing the tubing 19.2, or in an intermediate stopping position.

The portion 13a of the body 13 disposed in the housing 14 is formed as a "cold air valve" V, and has in its cylindrical wall two orifices 20a, 20b diametrically opposed. The air inlet duct 6 opens into the cylindrical wall of the housing 14 through an orifice 21 located in the direction of the axis of the body 13, at the orifices 20a, 20b. In the case where a bronze ring 15 is provided (FIG. 3), it comprises an orifice 15a placed at the right of the orifice 21. The smoke duct 8 opens in the space 18 and a sufficient passage 22 exists , on the side opposite the nozzle 17, between the body 13 and the inlet of the pipe 8 for the passage of fumes, according to the arrow F, to the chimney not shown.

The nozzle 17 has a frustoconical outer wall whose diameter decreases to the outlet 17a. As clearly visible in FIG. 4, when the nozzle 17 is placed facing the inlet of a duct 19.1 or 19.2, a configuration close to a venturi is obtained, and smoke entrainment zones are created around the frustoconical outer wall, by ejection of the air through the orifice 17a. The cold air valve V located at the end of the rotating injector is of the 180 ° cylindrical type. Its role is to shut off the air supply to the intermediate position and ensure the air supply in the two operating positions corresponding to the two burners. It remains of simple construction to the extent that it has no obligation to be strictly sealed in the closed position.

The injector 12, through its frustoconical nozzle 17 reduced outlet orifice 17a, allows the setting of the cold air speed. The combustion air supply is generally performed at a high pressure, of the order of 1000daPa (0.1 bar), which prevents the air goes directly to the fumes. The air velocity causes a portion of the flue gas locally to the burner, the other part being discharged to the outside of the system. The fumes are at a moderate temperature, typically around 200 ^° C., since they have previously been cooled during their passage through the regenerative matrix 2.2 of the burner in the stacked position. The rotary injector 12 equipped with its cold air valve V is particularly suitable for operation in all or nothing of the burners. In this case, it is not necessary to provide for an additional body of control of the air flow upstream of the cold air valve V. For operation of the burners in proportional mode, the variation of the air flow is carried out upstream of the cold air valve of the injector, by example by means of a flow control valve. The operation of the regenerative burner control device

1.1, 1.2, with the rotating injector 12 is as follows.

In the position illustrated in FIG. 2, the burner B1 is on, and the burner B2 is stopped. The injector 12 occupies the position for which the orifice 20b of the body 13 communicates with the cold air supply line 6, while the nozzle 17 faces the inlet of the pipe 19.1. the cold combustion air arriving via the pipe 6 is directed by the nozzle 17 in the pipe 19.1. The narrowing of the section of the nozzle 17 causes an increase in the speed of the air at the outlet 17a and the entrainment of a part of the hot fumes that arrive via the pipe 19.2 to be evacuated via the pipe 8.

The air / smoke mixture obtained passes through the regenerative matrix 2.1, which has accumulated heat during the previous cycle. Significantly warmed up at the exit of matrix 2.1, i! is used to burn in good conditions the fuel that arrives through the tube 1.1. The hot fumes circulate in the radiant tube 11 and return, after losing some of their heat, to the burner B2 which is stopped. The still hot fumes pass through the matrix 2.2 where they give up part of their heat, then are directed by the pipe 19.2 to the outlet pipe 8.

In the following cycle, the fuel supply to the burner B1 is stopped while the fuel supply in the tube 1.2 of the burner B2 is open. The injector 12 is rotated 180 degrees so that the nozzle 17 opens into the pipe 19.2. Operation is reversed from that described above.

The rotary injector 12 thus acts as a distributor and performs the role of air / fumes separation by partially blocking the supply pipe 19.1 (or 19.2) to the burner B1 (or B2) so that the evacuation of fumes takes place. proceeds to the stack after passing through the burner regenerator 2.2 (or 2.1) at stop B2 (or B1) without being driven to the burner running B1 (or B2). It is known to those skilled in the art that the recirculation of a portion of the fumes in the combustion air has the effect of reducing the nitrogen oxides formed during combustion. By only partially blocking the supply piping 19.1 (or 19.2) to the burner B1 (or B2), the speed given to the combustion air by the injector makes it possible to drive part of the fumes, which contributes to the reduction of nitrogen oxides. Finally, no longer dependent on the life of the solenoid valves, it becomes possible to reduce the duration of the inversion cycle of the burners which allows to build regenerators 2.1, 2.2 of small dimensions.

A rotating injector, similar to that described above for the combustion air, can also be implemented for the fuel, in order to replace the solenoid valves 10.1 and 10.2 of Fig.1. Such a rotating injector for the fuel would not include a nozzle 17, but a single orifice at the nozzle. This would benefit from a double recirculation of flue gases by combustion air and fuel in order to reduce the level of NOx produced.

Claims

1. Device for controlling regenerative burners used as heating equipment, in particular for furnaces for reheating steel products or radiant tubes for continuous treatment lines of steel strips, characterized in that the feed of least one of the fluids participating in the combustion (fuel and oxidant) is produced using a rotary injector (12) by means of a rotary actuator (M) so as to alternately feed one then the other burners (81, B2), the air inlet and the flue gas outlet for a burner are provided by the same supply pipe (19 .1, 19.2), the rotary injector (12) is arranged on the supply line (6) of oxidant, in particular air, and is provided to partially block the supply piping (19.1; 19.2) to the burner (B1; B2), so that part of the fumes from a regenerator (2.2; 2.1) of the stationary burner (B2; B1) is induced towards the burner in operation (B1; B2) and that the other part of the fumes is evacuated towards the chimney.

2. Device according to claim 1, characterized in that the recirculation of a portion of the combustion fumes to the burner in operation (B 1; B2) is ensured by a driving effect related to the speed of the fluid at the exhaust of the injector (12).

3. Device according to claim 1 or 2, characterized in that the injector (12) comprises a cylindrical hollow body (13) having, at one end, a frustoconical nozzle (17) which opens radially by an outlet orifice (17a) of reduced diameter, the nozzle can be placed facing the inlet of an air duct (19.1, 19.2) to a burner (B1, B2), so that smoke entrainment zones are created by ejecting air through the outlet (17a).

4. Device according to claim 3, characterized in that the injector (12) comprises, towards its end remote from the nozzle, a portion (13a) disposed in a cylindrical housing (14) formed as a cold air valve. (V) with two orifices (20a, 20b) diametrically opposite provided in the portion (13a), and an orifice (21) provided in the wall of the housing (14), at the orifices (20a, 20b).

5. Device according to claim 4, characterized in that a ring (15) of reduced friction material material is disposed between the body (13) of the injector and the housing wall (14).

6. Device according to claim 5, characterized in that the ring (15) is bronze.

7. Device according to any one of the preceding claims, characterized in that the rotary actuator (M) is constituted by an electric motor.