METHOD AND BURNER FOR HEATING A FURNACE FOR METAL PROCESSING

Abstract

A burner (10) for heating a furnace (40) includes at least one oxidizing gas supply line (20) for supplying an oxidizing gas into the furnace, the at least one oxidizing gas supply line having a central oxidizing gas supply line (21) for supplying the oxidizing gas together with a first annular supply line (22) surrounding the central oxidizing gas supply line for supplying a first shroud gas flow (25) for the oxidizing gas, at least one fuel supply line (30) for supplying a fuel into the furnace, the at least one fuel supply line including a central fuel supply line (31) for supplying the fuel together with a second annular supply line (32) surrounding the central fuel supply line for supplying a second shroud gas flow (35) for the fuel, wherein the first shroud gas flow is initially sucked into itself and subsequently an atmosphere of the furnace is sucked into itself for a point of recirculation of the atmosphere to be away from a refractory wall of the furnace such that particles are reduced in the atmosphere at where the first shroud gas flow occurs in the furnace atmosphere.

Claims

1. A burner (10) for heating a furnace (40) used for metal processing, the burner (10) comprising: at least one oxidizing gas supply line (20) for supplying an oxidizing gas into the furnace (40), the at least one oxidizing gas supply line (20) comprising a central oxidizing gas supply line (21) for supplying the oxidizing gas together with a first annular supply line (22) surrounding the central oxidizing gas supply line (21) for supplying a first shroud gas flow (25) for the oxidizing gas; and at least one fuel supply line (30) for supplying a fuel into the furnace, the at least one fuel supply line (30) comprising a central fuel supply line (31) for supplying the fuel together with a second annular supply line (32) surrounding the central fuel supply line (31) for supplying a second shroud gas flow (35) for the fuel; wherein the first shroud gas flow (25) is initially sucked into itself and subsequently an atmosphere of the furnace (40) is sucked into itself for a point of recirculation of the atmosphere to be away from a refractory wall of the furnace such that particles are reduced in the atmosphere at where the first shroud gas flow (25) occurs in the furnace atmosphere.

2. The burner (10) of claim 1, further comprising: at least two first nozzles (23) in fluid connection with and opening up into the first annular supply line (22); and/or at least two second nozzles (33) in fluid connection with and opening up into the second annular supply line (32).

3. The burner 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.

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

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

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] 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

[0024] 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

[0025] 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.

[0026] 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.

[0027] 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 mis. 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.

[0028] The total fuel (NG) and oxygen flow must always correspond to what is required for the combustion process stoichiometry calculations.

[0029] 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 ail 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.

[0030] 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.

[0031] The supply pipe feeding the oxidizing gas supply line 20 or the fuel supply line 30 is labeled 60.

[0032] 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.

[0033] 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.

[0034] 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

[0035] 10 Burner [0036] 20 Oxidizing gas supply line [0037] 21 Central oxidizing supply line [0038] 22 First annular supply line [0039] 23 Nozzle [0040] 24 Central oxidizing gas jet/flow [0041] 25 Annular oxidizing gas flow, first shroud [0042] gas flow [0043] 30 Fuel supply line [0044] 31 Central fuel supply line [0045] 32 Second annular supply line [0046] 33 Nozzle [0047] 34 Central fuel flow [0048] 35 Second shroud gas flow [0049] 40 Furnace [0050] 41 Recirculated furnace gases [0051] 50 Refractory [0052] 60 Supply pipe