Method and burner for heating a furnace for metal processing

Abstract

A method for heating a furnace (40) used for metal processing by combusting a fuel in the furnace (40) by supplying an oxidizing gas through an oxidizing gas supply line (20) into the furnace (40) and by supplying a fuel through a fuel supply line (30) into the furnace (40), wherein the oxidizing gas is supplied in form of a central oxidizing gas flow (24) together with a first shroud gas flow (25), and/or the fuel is supplied in form of a central fuel flow (34) together with a second shroud gas flow (35), and to a corresponding burner (10).

Claims

1. A method for heating a furnace (40) used for metal processing, comprising: supplying an oxidizing gas through an oxidizing gas supply line (20) into the furnace (40), the oxidizing gas supplied as a central oxidizing gas flow (24) together with a first shroud gas flow (25) for the central oxidizing gas flow (24), supplying a fuel through a fuel supply line (30) into the furnace (40), the fuel supplied as a central fuel flow (34) together with a second shroud gas flow (35) for the central fuel flow (34), initially sucking the first shroud gas flow (25) into itself, and subsequently sucking an atmosphere of the furnace (40) into itself for moving a point of recirculation of the atmosphere away from a refractory wall of the furnace, and reducing particles in the atmosphere of the furnace (40) where the first shroud gas flow (25) is occurring in the furnace atmosphere.

2. The method of claim 1, further comprising supplying the central oxidizing gas flow (24) at a velocity higher than a velocity of the first shroud gas flow (25).

3. The method of claim 1, further comprising supplying the central fuel flow (34) at a velocity higher than a velocity of the second shroud gas flow (35).

4. The method of claim 1, further comprising supplying the central oxidizing gas flow (24) at a velocity at least equal to or higher than a sonic velocity of the oxidizing gas.

5. The method of claim 1, further comprising supplying the central fuel flow (34) at a velocity at least equal to or higher than a sonic velocity of the fuel.

6. The method of claim 1, further comprising adjusting a ratio of a flow rate of the first shroud gas flow (25) and a flow rate of the central oxidizing gas flow (24).

7. The method of claim 1, further comprising adjusting a ratio of a flow rate of the second shroud gas flow (35) and a flow rate of the central fuel flow (34).

8. The method of claim 1, wherein the first shroud gas flow (25) comprises the oxidizing gas.

9. The method of claim 1, wherein the second shroud gas flow (35) comprises the fuel.

10. The method of claim 1, wherein the first shroud gas flow (25) comprises a gas selected from the group consisting of air, steam, an inert gas, flue gases, and a combination thereof.

11. The method of claim 1, wherein the second shroud gas flow (35) comprises a gas selected from the group consisting of air, steam, inert gas, and a combination thereof.

12. The method of claim 1, wherein the fuel is selected from the group consisting of a gaseous fuel, and a liquid fuel.

13. The method of claim 1, wherein the oxidizing gas is selected from the group consisting of oxygen, and air.

Description

DESCRIPTION OF THE FIGURES

(1) The invention is schematically depicted in the drawings on the basis of exemplifying embodiments, and will be described in detailed below with reference to the drawings.

(2) FIG. 1 schematically shows an oxidizing gas supply line or a fuel supply line of a burner according to an embodiment of the present invention, and

(3) FIG. 2 shows the supply line of FIG. 1 in combination with a furnace used for metal processing implementing a method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 schematically shows one of the oxidizing gas supply lines 20 of a burner 10 for heating an aluminum recycling furnace 40. Hitherto, in such furnace accretions were deposited around the burner oxygen nozzles/supply lines (this could also apply to the fuel supply, although it is more common on oxygen lines because of the much higher jet velocity), usually the deposited material being fine dross dust and/or coarse solid particlesthey could also be recirculated liquid metal droplets that deposit and then potentially solidify around the nozzle outlet. The invention came about in trying to prevent the recirculation of liquid copper and slag droplets in a Peirce Smith converter that occurs during the air blowing phase. Such accretions build up around the oxygen supply line 20 on the wall of the refractory 50. With a burner 10 comprising supply lines as shown in FIG. 1 such accretions are largely reduced.

(5) The example of FIG. 1 shows one of the two oxygen supply lines 20 in a flameless oxy-fuel burner, e. g. of 1500 kW. The oxygen supply lines or lances would normally (but must not) be identical in layout. The burner 10 would typically require one fuel, e. g. natural gas, and two oxygen supply lines, with the oxygen supply lines typically installed in a single plane on either side of the central fuel supply line, the oxygen supply lines being around 50 mm away from the fuel supply line (outer wall to outer wall). This geometry is only exemplary and not relevant to the present invention. The fuel supply line (30) may look similar to the oxygen supply line 20, but typically would have larger dimensions. For illustration purposes, however, FIG. 1 shows either an oxidizing gas supply line 20 or a fuel supply line 30. The fuel supply line 30 would also have a central fuel supply line 31 and a second annular supply line 32. The corresponding gas flows are labeled 34 and 35, respectively. It should be noted, however, that since the fuel is typically injected at lower velocities, either a reduced shroud flow 35 or no shroud flow 35 could be used. Therefore, in the following, for easy of illustration, only the oxidizing gas supply line 20 is described in further detail.

(6) The sizing of this oxygen supply line 20 is for approximately 160 Nm3/h of oxygen at a 2 barg supply pressure, by using 33 mm nozzles 23 opening up into the outer annular supply line 25, an oxygen flow/first shroud gas flow 25 of around 35 Nm3/h will pass through into the annulus 25 exiting the outer annulus at around 25 m/s. The balance of the oxygen flow 24 (around 125 Nm3/h) exits through the central supply line 21 preferably at the sonic velocity of oxygen. In this example, between 20 and 25% of the oxygen exits through the annulus 22. The dirtier the furnace environment, the higher this ratio would be.

(7) The total fuel (NG) and oxygen flow must always correspond to what is required for the combustion process stoichiometry calculations.

(8) As already mentioned above, typically the fuel gas is not injected at sonic velocity, although this is an option if sufficient pressure is available and if all safety standards and norms are complied with. If the fuel outlet velocity is low enough, then either a reduced shroud flow or no shroud flow could be used.

(9) By adjusting the diameter and number of the small nozzles (23 for the oxidizing gas and 33 for the fuel) feeding the annulus 22, 32, the ratio of shroud gas 25,35 and central gas 24, 25 can be varied, according to the needs of the process. As already mentioned above, a large number of smaller nozzles, especially in case of oxidizing gas supplying nozzles 23, are preferable to a single or fewer slightly larger nozzles.

(10) The supply pipe feeding the oxidizing gas supply line 20 or the fuel supply line 30 is labeled 60.

(11) FIG. 2 shows schematically the part of the burner 10 of FIG. 1 in e. g. an aluminum recycling furnace 40. Oxygen is used as the oxidizing gas which is supplied with high pressure through the central oxygen supply line 21 and exits the supply line 21 in form of a high velocity jet 24. In this embodiment, oxygen is also used as the shroud gas. This simplifies the installation since less piping and controlling equipment is required. The shroud gas proportion is a mechanical function depending on the pressure and the geometry and number of nozzles 23. Oxygen exits the annulus 22 in form of an annular oxygen flow 25 as shown in FIG. 2.

(12) The high velocity central oxygen jet 24 sucks parts of the furnace atmosphere back into itself resulting in a recirculation of furnace gases 41. The high velocity central jet 24 initially sucks the shrouding oxygen gas flow 25 into itself rather then the surrounding furnace atmosphere. Only once the shroud gas 25 has been aspired into the jet 24, the jet 24 will start sucking the furnace gases 41 into itself. The point of recirculation is thus moved away from the wall of the refractory 50 and away from the supply line tip. This reduces or even eliminates the deposition of solid or liquid particles in the recirculated furnace atmosphere around the supply line outlet on to the wall of the refractory 50.

(13) As already mentioned in the general part of the description, the shroud gas must not necessarily be the same as the central gas. The system is not limited to a single fuel and two to or four oxygen supply lines configuration. A single oxygen supply line as well multiple oxygen supply lines (3, 5, 6 even 8) are also conceivable. The system can also be implemented in air-fuel burners especially when a high enough air pressure is available.

LIST OF REFERENCE SIGNS

(14) 10 Burner 20 Oxidizing gas supply line 21 Central oxidizing supply line 22 First annular supply line 23 Nozzle 24 Central oxidizing gas jet/flow 25 Annular oxidizing gas flow, first shroud gas flow 30 Fuel supply line 31 Central fuel supply line 32 Second annular supply line 33 Nozzle 34 Central fuel flow 35 Second shroud gas flow 40 Furnace 41 Recirculated furnace gases 50 Refractory 60 Supply pipe