AU2020256352A1

AU2020256352A1 - Vent for an anode furnace

Info

Publication number: AU2020256352A1
Application number: AU2020256352A
Authority: AU
Inventors: Julien Maugain
Original assignee: Rio Tinto Alcan International Ltd
Current assignee: Rio Tinto Alcan International Ltd
Priority date: 2019-10-31
Filing date: 2020-10-14
Publication date: 2021-05-20
Also published as: FR3102839A1; CA3096940A1; FR3102839B1

Abstract

VENTFORANANODEFURNACE ABSTRACT Vent (100, 200, 300) provided to serve as an opening in an anode baking furnace (1), having: a frame (102); at least one flap (104, 204) movable relative to the frame from a closed position in which communication between the environment and the hollow partition (4) is limited to an open position in which the vent allows communication between the hollow partition and the environment (E); and a stress mechanism (110, 210, 310)attached to the at least one flap and exerting a stress force nudging the at least one flap into the open position, the stress force (FS) being less than a pressure force resulting from a difference between a nominal pressure of the hollow partition and pressure from the environment, the biasing force being such that the at least one flap moves from the closed position to the open position by means of the stress force when the pressure force decreases to below a determined threshold. 1/5 Fig. 1 L L L L L 18 12 13 10 171 x8 9 Fig. 2 1 5 4 C F )F 16 4a 4b"" 4c-- L 4d 4f L 49L L 4h7 ~-5 L -19 25 2 2 26 26 27 1

Description

1/5

Fig. 1

L L L L L

18 12 13

171

x8 9

Fig. 2

1 5 4 C F )F

16

4a 4b"" 4c-- L 4d 4f L 49L L 4h7 ~-5

-19 25 2 2 26 26 27 1 L

VENTFORANANODEFURNACE TECHNICAL AREA

[0001] This disclosure relates to a so-called "ring furnace" of carbonaceous blocks, more particularly carbon anodes used for the production of aluminum by electrolysis.

BACKGROUND OF THE TECHNIQUE

[0002] Anode furnaces have a plurality of chambers containing anodes. A preheating, heating, and cooling system moves relative to the chambers so that each chamber goes through a cycle of preheating, heating, and cooling successively. Each chamber comprises openings allowing fluid communication between the interior thereof and the exterior environment.

[0003] Some of the chambers are located in a negative-pressure zone while the rest of the chambers are in over-pressure. A ventilation system circulates the gases and is responsible for maintaining the vacuum which ensures adequate circulation of the gases.

[0004] However, in some cases a shutdown of the ventilation system, and thus of the negative pressure, occurs. One or more employees must then quickly open certain openings in order to allow the gases generated by the anodes to escape.

[0005] It is an object of the present invention to overcome or ameliorate some of the disadvantages of the prior art, or at least to provide a useful alternative.

SUMMARY

[0006] In one aspect, A vent is provided to serve as an opening in an anode baking furnace allowing communication between a hollow partition wall of the furnace and an environment external to the hollow partition, comprising: a frame; at least one flap movable relative to the frame from a closed position in which communication between the environment and the hollow partition is limited by said at least one flap to an open position in which the vent allows communication between the hollow partition and the environment; and a stress mechanism attached to the at least one flap and exerting a stress force nudging the at least one flap into the open position, the stress force being less than a pressure force resulting from a difference between a nominal pressure of the hollow partition and pressure from the environment, the stress force being such that the at least one flap moves from the closed position to the open position by means of the stress force when the pressure force decreases to below a determined threshold.

[0007] In one embodiment, the at least one flap is pivotably mounted on the frame with respect to at least one pivot axis, the stress force generating a moment of stress around the at least one pivot axis and the difference between the pressures of the hollow partition and of the environment generating a moment of pressure around the at least one pivot axis and in the direction opposite to the moment of stress.

[0008] In one embodiment, the stress mechanism includes at least one counterweight attached to the at least one flap, the at least one counterweight and the at least one flap being disposed on either side of at least one hinge connecting the at least one flap to the frame.

[0009] In one embodiment, the at least one counterweight is movable in a radial direction relative to the at least one pivot axis so as to approach or move away from the at least one hinge in order to vary the moment of stress.

[0010] In one embodiment, a spring is placed around the at least one pivot axis and engages with the frame and with the at least one flap to create the moment of stress.

[0011] In one embodiment, the at least one flap includes two flaps each being placed respectively on the opposite sides of the opening.

[0012] In one embodiment, the vent further comprises a layer of high temperature refractory fiber attached to a peripheral edge of the at least one flap and creating an airtight connection between the frame and the at least one flap when the vent is in the closed position.

[0013] In one embodiment, the frame is removably securable to the furnace.

[0014] In one embodiment, the vent further comprises at least one handle attached to the frame to allow manipulation of the vent.

[0015] In one embodiment, the frame defines aside wall extending circumferentially around the opening and extending vertically between the opening and an upper edge of said side wall, the at least one flap being in abutment against the top edge in the closed position.

[0016] In another aspect, a carbon anode baking furnace is presented for the production of aluminum by electrolysis, comprising: longitudinal hollow partitions in each of which a flow of hot baking gases at a certain temperature may circulate with a certain flow rate, the hollow partitions defining between them recesses for receiving the anodes to be fired and comprising a plurality of openings; a heating system rotating with respect to the hollow partitions, which has an upstream ramp with several air blowing legs in the various hollow partitions, a downstream ramp with several gas suction legs from the various hollow partitions and, between said upstream and downstream ramps, at least one heating ramp fitted with at least one burner or at least one fuel injector per hollow partition; lines for the circulation of gas streams in the hollow partitions being formed in the hollow partitions between the blowing legs and corresponding suction legs; and a natural preheating zone of the furnace being defined between the downstream ramp and the heating ramp and in which a natural degassing of the anodes occurs, wherein, for each of the lines, at least one vent as described above is placed above at least one opening, the at least one opening being located in the natural preheating zone of the furnace.

[0017] In one embodiment, the at least one opening includes two openings located upstream and downstream of one of the chambers of the preheating zone.

[0018] In another aspect, a method to use a vent which maybe placed over an opening of an anode baking furnace is provided, comprising: limiting fluid communication between the hollow partition and an environment outside the hollow partition when a difference between a hollow partition pressure and an environmental pressure is above a nominal value; and biasing the at least one flap of the vent from a closed position to an open position allowing fluid communication between the hollow partition and the environment when the difference between the pressure of the hollow partition and that of the environment falls below the nominal value and below a determined threshold.

[0019] In one embodiment, biasing the at least one flap of the vent comprises exerting a moment relative to a pivot axis of the at least one upper and opposite flap at a moment relative to the pivot axis created by the weight of the at least one flap.

[0020] In one embodiment, exerting the moment includes exerting the moment with at least one counterweight, the at least one counterweight and the at least one flap each being provided with at least one hinge on one of the respective opposite sides.

[0021] Several aspects and combinations of said aspects relating to these improvements will be apparent to those skilled in the art upon reading this disclosure.

DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is a partial schematic view, in perspective, of a typical anode baking furnace;

[0023] Fig. 2 is a schematic top view of the furnace of Figure 1;

[0024] Fig. 3 is a schematic side view representation of the partitions of the furnace of Figures l and 2;

[0025] Fig. 4 is a partial schematic view, in perspective, and from above of the furnace of Figure 1 using vents according to one embodiment coupled to certain openings of the furnace;

[0026] Fig. 5 is a schematic perspective view of one of the vents of Figure 4 shown in the closed position;

[0027] Fig. 6 is a schematic perspective view of the vent of Figure 5 shown in the open position;

[0028] Fig. 7 is a schematic view illustrating the forces and moments perceived by a flap of the vent of the Figure 5;

[0029] Fig. 8 is a schematic top view of a vent according to another embodiment illustrated in the closed position;

[0030] Fig. 9 is a schematic top view of the vent of Figure 8 in the open position; and

[0031] Fig. 10 is a schematic top view of a vent according to another embodiment illustrated in the closed position.

DETAILED DESCRIPTION

[0032] An anode furnace, also called an "open chamber" furnace, comprises, in the longitudinal direction, a plurality of natural preheating, baking, blowing, forced cooling and unloading chambers, and non-active chambers, each chamber being made up, in the transverse direction, by the juxtaposition, alternately, of hollow heating partitions in which the gases circulate, and cells in which the carbonaceous blocks to be fired are stacked, the blocks being embedded in a carbonaceous dust called "dust" . The hot gases or combustion fumes ensuring the baking circulate in a flow in the hollow partitions, with thin walls, extending in the longitudinal direction of the furnace. The hollow partitions are provided, at their upper part, with closable openings called "openings". They may further include baffles or spacers to lengthen and more evenly distribute the path of the flow of combustion gases or fumes. The cells are open at their upper part to allow loading, by stacking, the raw blocks and the unloading the cooled baked blocks.

[0033] This type of furnace generally comprises two longitudinal bays the total length of which can reach more than a hundred meters and comprising a succession of chambers separated by transverse walls. The two bays are placed in communication at their longitudinal ends by swiveling flues which allow gas to be transferred from one bay to the other.

[0034] The heating of the furnace is ensured by the heating ramps having a length equal to the width of the chambers and comprising one or more burners, or one or more injectors per hollow partition. The injectors or burners are introduced, via the openings, into the hollow partitions of the chambers concerned. Upstream of the burners or injectors (in relation to the direction of advance of the rotating fire also corresponding to the direction of gas circulation in the hollow partitions), there are combustion air blowing legs mounted on an upstream blowing ramp fitted with fans, these blowing legs being connected, via the openings, to said partitions. Downstream of the burners or injectors, there are suction legs for combustion fumes, mounted on a downstream suction ramp supplying fume collection and treatment centers, and fitted with flaps to make it possible to keep the suction flow rates of the suction legs at the desired levels. Heating is provided both by the combustion of said primary fuel injected into the baking chambers, and by the combustion of said secondary fuel consisting of the volatile combustible materials (such as, for example polycyclic aromatic hydrocarbons) emitted by the blocks. These volatile combustible materials are more particularly emitted by the coal pitch of the blocks, during the rise in temperature of the blocks in the natural preheating chambers. The partitions being in negative pressure in the natural preheating chambers, the combustible volatile materials leave the cells by crossing the hollow partition through openings provided for this purpose and burn with the oxygen remaining in the combustion fumes which circulate in the hollow partitions of these chambers.

[0035] Typically, around ten chambers are simultaneously "active": four in a blowing zone, three in a heating zone, and three in a natural preheating zone.

[0036] As the baking takes place, for example in cycles of 28 hours, the assembly "upstream blowing ramp/heating ramp/downstream suction ramp" is moved forward (rotated) by one chamber, thus ensuring different functions of each chamber successively: downstream of the natural preheating zone (non "active" chamber or loading chamber), a function of loading the raw carbonaceous blocks, then; in the natural preheating zone, a function of natural preheating of the partitions, carbon blocks, etc. by the combustion fumes circulating in the partitions and the combustion of the secondary fuel, then; in the baking zone, a function of heating the carbon blocks to 1100-1200°C; and finally, in the blowing zone, a function of cooling the carbon blocks by cold outside air blown into the hollow partitions and, correlatively, preheating this air circulating in the hollow partitions constituting the oxidizer of the furnace by the heat restored by the partitions, carbon blocks etc., the blowing zone being followed, downstream, by a forced cooling zone and unloading of the cooled carbon blocks.

[0037] The detailed description relates to a rotary chamber furnace, as illustrated in Figures 1 to 3. This disclosure is not, however, limited to this type of furnace. In particular, it is also applicable to installations comprising a furnace without intermediate transverse walls.

[0038] Referring to Figure 1, the furnace 1 comprises a heat-insulated enclosure 2 of a substantially parallelepiped shape, with respect to which a longitudinal direction X and a transverse direction Y are defined. In the enclosure 2 transverse walls 3 are placed defining the successive chambers C in the direction X. In each chamber C are provided hollow partitions 4 arranged in the longitudinal direction, forming between them elongated cells 5. Each chamber C thus comprises several partitions 4a to 4i, as illustrated in Figure 2. In each chamber C, each of the partitions 4a to 4i is fluidly independent of the other partitions 4a to 4i.

[0039] The partitions 4 comprise thin side walls 6 generally separated by spacers 7 and baffles 8. The ends of the hollow partitions have openings 10 and are embedded in the notches 9 of the transverse walls 3. These notches 9 are themselves provided with openings 10' located opposite the openings 10 of the partitions 4, in order to allow the passage of the gases circulating in the partitions 4 from one chamber C to the next chamber. The partitions 4 further include openings 11 or orifices which serve in particular to introduce heating means (such as injectors or fuel burners), suction legs 12 of a downstream suction ramp 13 connected to a main duct 14 along the furnace 1, air blowing legs, sensors of measuring devices (such as thermocouples, opacimeters), devices for maintenance, and so on.

[0040] As may be seen more particularly in Figure 2, the chambers C form a long bay 15 in the longitudinal direction X, and the furnace 1 typically comprises two parallel bays, each of which may have a length on the order of a hundred meters, delimited by a central wall 16. In each bay 15, there are therefore longitudinal lines L of hollow partitions 4. Each longitudinal line L is fluidly independent of the other longitudinal lines L.

[0041] Raw carbonaceous blocks 17 are stacked in the cells 5, that is to say, the anodes to be fired, and the cells 5 are then filled with a granular or pulverulent material (typically coke based), called "dust" 18, which surrounds these blocks 17 and protects them when they are baking.

[0042] The anode baking furnace also includes a heating system, which typically includes: an upstream blowing ramp 19 of several air blowing legs 20 in the different partitions 4 of a chamber C (through the openings 11), two or three heating ramps 21, 22, 23 each composed of one or two burners or fuel injectors per partition, and a downstream suction ramp 13 of several gas suction legs 12 from the various partitions 4 of a chamber C (from the orifices 11).

[0043] As seen in Figure 3, and according to the illustrated embodiment, the various elements of the heating system are placed at a distance from each other according to the following typical fixed configuration: the air blowing ramp 19 is located at the inlet of a given chamber C1; the first ramp 21 of bumers/injectors is placed above the fifth chamber C5 downstream of the air blowing ramp 19, the second ramp 22 of bumers/injectors is placed above the chamber C6 located immediately downstream of the first ramp 21; the third ramp 23 of burners/injectors is placed above the chamber C7 located immediately downstream of the second ramp 22; and the suction ramp 13 is located at the outlet of the third chamber C10 downstream of the third ramp 23.

[0044] More generally, and according to the illustrated embodiment, the relative position of the various elements is always the same (namely, in the direction of the fire, the blowing ramp 19, the ramps of burners/injectors 21, 22, 23 and the suction manifold 13). However, the spacing (in number of chambers) between elements may vary from furnace to furnace. This is how the first ramp 21 of bumers/injectors might be positioned above chamber C4 or C3. Furthermore, the suction ramp 13 could be located at the outlet of the second chamber downstream of the third ramp 23. Also, the number of ramps burners/injectors can typically vary from 2 to 4.

[0045] The air may be blown by the blower legs 20. This air, mixed with the primary fuel injected by the bumers/injectors 21, 22, 23 and the secondary fuel produced by the baking of the anodes, circulates in the longitudinal lines of partitions 4, from chamber to chamber, following the path, or line of circulation, formed by the baffles 8 and passing from one partition to another through the openings 10, until it is suctioned in by the suction legs 12. The suction legs have suction flaps, the opening percentage of which allows regulation of the negative-pressure in the furnace partitions. The furnace, and more particularly the partitions and the cells, are closed as hermetically as possible in order to limit as much as possible the infiltration of cold air or the exfiltration of hot air.

[0046] Between a blowing leg 20 and a corresponding suction leg 12, there is therefore a generally longitudinal gas flow line 24 along the successive partitions 4. The term, "generally longitudinal" is understood to mean that the gas circulates from a blower leg to the corresponding suction leg, in the direction X overall, while locally performing vertical movements, typically in undulations, as illustrated in Figure 3. As indicated above, the gas flow consists of air, gas resulting from the combustion of the injected liquid or gaseous primary fuel, and the volatile materials released by the carbonaceous blocks 17 (secondary fuel). The heat produced by the combustion of the primary and secondary fuels is transmitted to the carbonaceous blocks 17 contained in the cells 5, which causes their baking.

[0047] A carbon block firing operation, for a given chamber C, typically comprises loading the cells 5 of this chamber C with raw carbon blocks 17, heating this chamber C to the temperature of baking the carbon blocks 17 (typically from 1100 to 1200 C), cooling chamber C to a temperature which removes the baked carbon blocks and cooling chamber C to room temperature.

[0048] The principle of the rotating fire consists of successively carrying out the heating cycle on the furnace chambers by moving the heating system. Thus, a given chamber passes successively through phases of natural preheating (by the hot gases circulating in the partitions), forced heating and blowing. The baking zone is formed by all the chambers located between the blowing ramp and the suction ramp. In Figures 2 and 3, the direction of the fire is represented by the arrow F.

[0049] The conditions prevailing in the various chambers C of the furnace 1 at which the heating system is placed at a given moment are now described, with reference to Figures 2 and 3.

[0050] The first four chambers C1 to C4 along the blowing ramp 19 are so-called blowing zones BL, respectively BL4, BL3, BL2 and BLI. There is an overpressure. The anodes which are placed there are already baked, and undergo cooling by blowing, which has the effect of increasing the temperature of the blown air, which will be used for combustion. The next six chambers C5 to C10, up to the suction manifold 13, are negative-pressure zones. Substantially, the "zero point" PO, that is to say a point where the pressure in furnace 1 is substantially equal to atmospheric pressure, is at the junction between these two blocks of chambers. The zero point is located upstream of the first heating ramp 21 in order to avoid the rejection of combustion products into the ambient environment by exfiltration.

[0051] Typically, a pressure take-off ramp 25- called the zero point ramp 25 (PZR)- is provided and positioned in a fixed manner with respect to the heating system in order to regulate the pressure at the zero point. In the embodiment shown, the zero point ramp 25 is located at the level of the openings 11 of the partition 4 located most downstream from the last chamber C4, BL Located in the blowing zone. However, this zero point ramp 25 may be placed at another point in the blast zone BL.

[0052] In the negative-pressure zone, successively from upstream to downstream, we find: a HR heating zone at the level of the chambers C5, C6 and C7 located under the three heating ramps 21, 22, 23, comprising in the first two chambers C5, C6 a forced heating zone, respectively HR3, HR2, then in the next chamber C7 a forced preheating zone HR1. The temperature of the preheated air in the BL blowing zones is sufficient to create ignition and combustion of the fuel; a natural preheating zone PN at the level of the chambers C8, C9 and C10, respectively PN3, PN2 and PN1. The hot gases coming from the heating zone allow the ignition of the combustible volatile materials released by the carbonaceous blocks during their preheating in the preheating zone.

[0053] Chamber C, locatedjust after the suction ramp 13 (completely to the right in Figure 3), called the dead chamber, is a chamber ready to receive raw carbonaceous blocks 17 when the heating system is moved in the direction of fire F, which will thus successively undergo: natural preheating (PN1, PN2 then PN3), forced preheating (HR1), forced heating (HR2 then HR3), then blowing (BLI, BL2, BL3 then BL4), before unloading the baked and cooled anodes.

[0054] The gas flows circulating inside the partitions allow the heat exchanges necessary for baking the anodes. As previously described, the fans circulate the flow creating a negative pressure in chambers C5 to C10 inside all the ducts.

[0055] During natural preheating, the temperature inside at least one of the chambers of the preheating zone PN (e.g., chambers C8, C9, C1O) may be between 250 and 650 degrees Celsius. At this temperature, a natural degassing of the anodes occurs. The volatile materials thus generated by the natural degassing of the anodes are drawn in by the suction legs 12 located downstream of the last natural preheating chamber (e.g., chamber C10).

[0056] However, there is the possibility that gas circulation may go down. This means that the combustion gases present inside the partitions and the manifold surrounding the furnace are no longer drawn in. This situation then leads to the formation of gas pockets in the partitions, suction ramp, manifold and capture.

[0057] The closing of the main flap on the flue; a partition blocked by dust; a total loss of energy (e.g., electrical, air); an uncontrolled restart of the fires; a heavily pinched partition; fans stopping in the collection center; a loss of negative-pressure when changing the fires (manipulation of the dampers at the front of the suction ramp); forgetting to remove a damper when moving the fires; a damper in place but not open or a lack of tightness; and/or unstopped energy injection at the loss of negative-pressure are just a few possible events that can lead to a total or partial loss of negative-pressure in chambers C5 to C10.

[0058] Such loss of negative-pressure is unwanted as it may result in gas build-up. The combination of this gas build-up, heat from the high temperature of the unburnt gases coming from the preheating zone, and an oxygen supply coming from fans (when the latter are restarted, for example) or else coming from a parasitic air inlet at the flanges or other leaks on the manifold, may have harmful consequences.

[0059] In reference to Figures 3 and 4, a safety vent 100 maybe placed in the PN preheating zone, either upstream of the suction leg 12 and downstream of the heating ramps 21, 22, 23 relative to the line of gas circulation 24 which extends from the blowing leg 20 to the suction leg 12. The vent 100 may have the same total weight as a cover normally used to close the openings 11. According to the illustrated embodiment, the vent 100 is located downstream of the chamber where preheating is most active. Alternatively, the vent may be located upstream of the chamber where preheating is most active. Vents may be placed upstream and downstream of the chamber where preheating is most active. In this case, the chamber where preheating is most active is chamber C9. The safety vent 100 may be located either upstream, or downstream, or upstream and downstream from the place where the natural degassing of the anodes occurs. This place is typically where the temperature reaches between 250 and 650 degrees Celsius. According to one embodiment, the vent 100 is located vis-d-vis the chamber in which the temperature is the highest.

[0060] As previously mentioned, the furnace 1 includes a plurality of longitudinal lines L arranged parallel to each other (Figure 2) and each running through all the chambers C1 ... C10 and including a plurality of partitions 4. Each of the longitudinal lines L is fluidly independent from the others. According to the embodiment described here, each of the longitudinal lines L comprises at least one safety vent 100 which may be positioned as described above.

[0061] With reference to Figures 4 to 6, the safety vent 100 is described in detail below. The vent 100 includes a frame 102 and a flap 104 being movable relative to the frame 102. The flap 104 can move relative to the frame 102 from a closed position in which the communication between an environment E outside the furnace and the partition 4 (Figure 2) is limited by the at least one flap 104 to an open position in which the vent 100 allows communication between the partition 4 and the environment E.

[0062] According to the illustrated embodiment, the vent 100 includes a handle 106 attached to the frame 102 to allow manipulation of the vent 100 by an employee to move the vent 100 from one partition to the other to follow the progress of the fire, and thus follow the progress of the preheating zone where the natural degassing of the anodes. Consequently, and according to the illustrated embodiment, the frame 102 can be removably secured upon the furnace in order to allow it to move in the direction of the fire.

[0063] The frame 102 of the vent 100 may include a portion 102a making it possible to engage one of the apertures 11 in a sealed manner. The portion 102a of the frame can therefore have any shape allowing it to be coupled to the openings 11. The vent 100 can be moved from one opening 11 to another in the case of the furnace described above with reference to Figures 1-3. Alternatively, the vent 100 can be secured on movable ramps (not shown) which move integrally with the direction of the fire.

[0064] As shown in Figure 5, the frame 102 includes a side wall 102b extending circumferentially around the opening 11 and vertically between the opening 11 and an upper edge 102c of the side wall 102b. In the closed position as illustrated in Figure 5, the flap 104 is in abutment against the upper edge 102c of the side wall 102b of the frame 102. The engagement between the flap 104 and the frame 102 is preferably airtight. It is understood that, despite the fact that the side wall 102b has a rectangular shape, it may alternatively have a cylindrical shape, or any other suitable shape, without deviating from the scope of this disclosure.

[0065] Referring more particularly to Figure 6, the flap 104 has a layer of high temperature refractory fiber 104c which can help prevent metal/metal contact between the frame and the flap and which can create an airtight connection between the frame and the flap. According to the illustrated embodiment, the fiber layer 104c is placed all around a peripheral edge of the flap 104 so as to be in contact with the upper edge 102c of the side wall 102b of the frame when the vent 100 is in the closed position.

[0066] Note that the hole at the bottom of the vent may be round as shown. Alternatively, the hole may be square so as to increase its area in order to maximize the flow of gas that can be discharged through the vent. The position and/or the weight of the counterweight can be adjusted accordingly.

[0067] With particular reference to Figures 5 and 7, the vent 100 has a stress mechanism 110 being joined with the flap 104. The stress mechanism 110 is configured to exert a stress force FS in order to bias the flap 104 in the open position. In other words, the stress mechanism 110 exerts a force which, in the absence of another force on the flap 104, pushes and maintains said flap 104 in the open position. According to the illustrated embodiment, the stress force FS generated by the stress mechanism 110 is sufficient to counterbalance a weight W of the flap 104.

[0068] As previously discussed, the vent 100 is designed to be coupled to one of the openings 11 of the furnace and in this way, maintain a pressure differential between the respective partition of the opening 11 and the environment E outside partition 4. When the flap 104 is in the closed position and the furnace is operating normally, a nominal pressure inside the partition 4 is established and is lower than the pressure of the environment E. Therefore, this nominal pressure differential exerts a pressure force FP on the flap 104 which maintains the flap 104 in the closed position. This pressure force FP, resulting from the nominal pressure differential, is greater than the stress force FS exerted by the stress mechanism 110 when the furnace is operating normally (i.e., pressure inside the partition 4 corresponding to the nominal pressure). The pressure force FP is exerted on a center of pressure of the flap 104, the position of which varies depending on the shape of the flap 104.

[0069] The stress force FS generated by the stress mechanism 110 is less than the pressure force FP resulting from a difference between a nominal pressure of the partition and a pressure of the environment. The stress force FS is such that the flap 104 moves from the closed position to the open position by means of the stress force FS when the pressure force FP decreases to below a determined threshold. Typically, the pressure force FP can drop below the determined threshold when there is a loss of suction as previously explained.

[0070] Following such a loss of suction, the pressure of the partition 4 increases and approaches the pressure of the environment E, possibly even going so far as to exceed it. The pressure force FP exerted on the flap 104 being directly proportional to the difference between the pressure of the partition and the environment, an increase in the pressure of the partition generates a decrease in the pressure force FP exerted on the flap 104. When the pressure of the partition 4 reaches a determined threshold, in other words, when the pressure force FP decreases to below a determined threshold, the stress force FS generated by the stress mechanism 110 becomes greater than the pressure force FP and moves the flap 104 from the closed position to the open position.

[0071] According to the illustrated embodiment, the flap 104 is pivotably mounted on the frame 102 relative to a pivot axis 104a defined by a hinge 104b. In this case, the stress and pressure forces FS, FP translate into the stress moment and pressure moment MS, MP around the pivot axis 104a. Like the stress and pressure forces, stress and pressure moments are in opposite directions. The moment of stress MS configured to be greater than a moment of weight MW generated by the weight W of the flap 104 when no other force is exerted on said flap 104.

[0072] According to the illustrated embodiment, the stress mechanism 110 includes a counterweight 1Oa attached to the flap 104. The counterweight 1Oa and the flap 104 are placed on either side of the hinge 104b so that the moments of weight MW and stress MS are in the opposite direction around the pivot axis 104a.

[0073] In reference to Figures 8 and 9, a safety vent 200 according to another embodiment is illustrated. For simplicity, only the elements distinguishing the vent 200 from the vent 100 of Figures 4 to 6 are described below.

[0074] The vent 200 includes two flaps 204, each covering a respective portion of the opening defined by the frame 102. Each of the two flaps 204 is pivotable relative to one of the respective pivot axes 204a. The description of the flap 104 presented above in connection with the vent 100 of Figures 4 to 6 can be applied similarly to each of the two flaps 204 of this vent 200.

[0075] The stress mechanism 210 includes two counterweights 210a each being attached respectively to one of the two flaps 204. Each of the two counterweights 210a may be moved radially relative to one of the respective pivot axes 204a so as to allow the approximation and removal of the counterweights 21Oa from the pivot axes 204a in order to calibrate the moment of stress MS (Figure 6) generated by the counterweights 21Oa.

[0076] According to this embodiment, the counterweights 210a are connected to the flaps 204 by threaded rods 21Ob each having a first end in sliding attachment with one of the flaps 204 and an opposite second end attached to a one of the corresponding counterweights 21Oa. In this case, each of the counterweights 210a is connected to one of the respective flaps 204 by two threaded rods 21Ob. It is understood, however, that more or less two rods may be used without departing from the scope of this disclosure.

[0077] According to the illustrated embodiment, each of the second ends of the threaded rods 21Ob passes through an opening 21Oc defined by the counterweight 210a and is secured by bolts 210d arranged on either side of the opening 210c. Each of the first ends of the threaded rods 21Ob is received through an opening 204c defined by a portion of one of the respective flaps 204 so as to be able to move relative to the opening 204c and thus relative to one of the respective flaps 204. A bolt 210e is attached to the rod 210b so as to maintain a desired position of the counterweight 210 relative to the pivot axis 204a of said flap 204.

[0078] Consequently, the increase in the radial distance between the counterweight 210a and the pivot axes 204a of the flaps 204 makes it possible to increase the stressing moments MS. Similarly, reducing the radial distance between the counterweight 210a and the pivot axes 204a of the flaps 204 makes it possible to reduce the moment of stress MS.

[0079] The possibility of moving the counterweights 210a makes it possible to modify the moment of stress MS in order to calibrate the vent 200 in the furnace and at the nominal pressure differential of said furnace. In other words, each furnace can express a specific value of this pressure differential, and the stress mechanism described here can allow adjustment to each furnace.

[0080] It is understood that this same mechanism for moving the counterweights can be applied to the vent 100 of Figures 4 and 5. Other modifications to this stress mechanism may appear obvious to a person skilled in the art and are included within the scope of this disclosure. For example, the counterweight may be replaced by a spring placed around the pivot axis of the flap and configured to create the moment of stress. The counterweight may move in the radial direction with respect to the pivot axis through the slide. Any other mechanism that enables creating the moment of stress and allowing the radial movement of the counterweight may be used, and are within the scope of this disclosure.

[0081] The adjustment of the counterweights as previously discussed can make it possible, if necessary, to adjust the sensitivity of the flaps to open in order to keep them in the closed position. When the suction is completely stopped, the gas pressure raises at least one of the flaps 204, which can automatically release the gases contained in the partition 4.

[0082] More particularly, in reference to Figure 8, and according to the illustrated embodiment, a transverse plate 204d is attached to the frame 102 and extends diametrically from one side of the frame 102 to an opposite side of the frame 102. Each of the two flaps 204 has a distal free edge 204e in abutment against the transverse plate 204d when the two flaps 204 are in the closed position. The contact between the free distal edges 204e and the transverse plate 204d can help to increase the tightness of the vent 200 in the closed position compared to a configuration without a transverse plate 204d. Alternatively, the distal edges of the flaps may include male and female connectors, the coupling of which may be airtight or substantially airtight.

[0083] To use the vent, fluid communication between the partition and the environment outside the partition is limited when the difference between a partition pressure and an environment pressure is above a nominal value; and the at least one flap of the vent is biased into an open position allowing fluid communication between the partition and the environment when the difference between the pressure of the partition and that of the environment falls below the nominal value and below a determined threshold.

[0084] In the illustrated embodiments, biasing the at least one flap of the vent comprises exerting a moment relative to the pivot axis of the at least one upper and opposite flap at a moment relative to the pivot axis created by the weight of at least one flap. In the illustrated embodiments, exerting the moment includes exerting the moment with the at least one counterweight, the at least one counterweight and the at least one flap each being provided with at least one hinge on one of the respective opposite sides.

[0085] In reference to Figure 10, a safety vent 300 is illustrated according to another embodiment. For simplicity, only the elements distinguishing the vent 300 from the vent 100 of Figures 4 to 6 are described below.

[0086] According to the illustrated embodiment, the stress mechanism 310 includes a counterweight 31Oa having three openings 31b, each receiving one of the three respective rods. The three rods include a central rod 310c and two side rods 310d. A locking element 310e is fixed on the central rod 31Oc. The position of the blocking element 31Oe along the central rod 31Oc is predetermined and defines a calibrated base position for the vent 300 to open when the suction stops. Predetermining the position of the blocking member 31Oe, can facilitate installation of the vent 300, as an employee will not need to experiment with where to position the counterweight 310a. The locking element 310e may be a nut permanently attached to the central rod 31Oc, which may be threaded. The counterweight 310a can be locked on the central rod 310c by a nut 310f located on the other side of the counterweight 310a.

[0087] In some cases, small adjustments to the position of the counterweight 310a maybe required. In these cases, spacers may be slid between the counterweight 310a and the locking element 310e in order to precisely position the counterweight 310a along the central rod 31c.

[0088] It is also possible to place visual cues on one or more of the rods in order to assist the employee in positioning the counterweight 310a. These marks may be, for example, a notch in one of the rods.

[0089] The vent 100 of Figures 4 to 6 maybe modified so that the counterweight is semi stationary so that it is basically set at a predetermined position and its position may be adjusted by spacers. For example, each of the two rods may define a shoulder located at a base distance from the cover. Washers may be slid over the rods until they are in contact with the shoulders. The counterweight can then be slid so that the washers are placed between the shoulders and the counterweight. The use of washers can then vary the distance between the counterweight and the cover. For example, this distance can therefore go from 22 to 24 millimeters.

[0090] In reference to Figures 1 to 10, to use the furnace 1, and as previously described, the upstream blowing ramp 19, at least one heating ramp 21, 22, 23, and the suction ramp 13 are successively moved in the longitudinal direction X with respect to the chambers C so that each chamber C successively goes through a cycle of preheating, heating, and cooling.

[0091] In this embodiment, each of the lines L comprises at least one vent 100, 200, 300 as described above; each of the vents 100, 200, 300 is moved successively from chamber to chamber so that the vents are always located in the natural preheating zone where the natural degassing of the anodes occurs.

[0092] By removing the vents 100, 200, 300, the openings 11 upon which the vents were located are plugged by lids and the following apertures 11 are opened and the vents 100, 200, 300 are placed upon the latter. Since the movement of the vents zeroes the pressure force FP (the pressure on either side of the flap corresponding to the pressure of the environment E), the flaps move from their closed position to their open position due to the stress force FS becoming greater than the pressure force FP. Consequently, and in this embodiment, once the vents are connected to the successive openings 11, the flaps are manually closed thus allowing the pressure differential to hold them in the closed position and to counterbalance the stress force FS generated by the stress mechanism.

[0093] In the event of a loss of suction, and in the illustrated embodiments, the flaps will open and allow the gases generated by the anodes to be emitted. Once the suction is restored, the flaps may be manually moved from their open position to their closed position in order to resume baking the anodes.

[0094] The vents as described above may make the automatic safety of the furnace possible in the event of a loss in the negative-pressure without an immediate intervention by the operator. The evacuation of the gases contained in the partitions may then be immediate or almost immediate. The sizing is calculated so as to be sufficient to guarantee sufficient evacuation of the gases.

[0095] The embodiments described herein include:

[0096] A. A vent is provided to serve as an opening in an anode baking furnace allowing communication between a hollow partition of the furnace and an environment external to the hollow partition, comprising: a frame; at least one flap movable relative to the frame from a closed position in which communication between the environment and the hollow partition is limited by said at least one flap to an open position in which the vent allows communication between the hollow partition and the environment; and a stress mechanism attached to the at least one flap and exerting a stress force nudging the at least one flap into the open position, the stress force being less than a pressure force resulting from a difference between a nominal pressure of the hollow partition and pressure from the environment, the stress force being such that the at least one flap moves from the closed position to the open position by means of the stress force when the pressure force decreases to below a determined threshold.

[0097] B. Carbon anode baking furnace for the production of aluminum by electrolysis, comprising: longitudinal hollow partitions in each of which a flow of hot baking gases at a certain temperature may circulate with a certain flow rate, the hollow partitions defining between them recesses for receiving the anodes to be fired and comprising a plurality of openings; a heating system rotating with respect to the hollow partitions, which has an upstream ramp with several air blowing legs in the various hollow partitions, a downstream ramp with several gas suction legs from the various hollow partitions and, between said upstream and downstream ramps, at least one heating ramp fitted with at least one burner or at least one fuel injector per hollow partition; lines for the circulation of gas streams in the hollow partitions being formed in the hollow partitions between the blowing legs and corresponding suction legs; and a natural preheating zone of the furnace being defined between the downstream ramp and the heating ramp and in which a natural degassing of the anodes occurs, for each of the lines, at least one vent as described above is placed above at least one opening, the at least one opening being located in the natural preheating zone of the furnace.

[0098] Embodiments A and B can include any of the elements below, in any combination.

[0099] Element 1: the at least one flap is mounted on the frame in a pivotable manner relative to at least one pivot axis, the stress force generating a moment of stress around the at least one pivot axis and the difference between the pressures of the hollow partition and of the environment generating a moment of pressure around the at least one pivot axis and in the direction opposite to the moment of stress.

[00100] Element 2: the stress mechanism includes at least one counterweight attached to the at least one flap, the at least one counterweight and the at least one flap being placed on either side of at least one hinge connecting the at least one flap to the frame.

[00101] Element 3: the at least one counterweight can move in a radial direction relative to the at least one pivot axis so as to approach or move away from the at least one hinge in order to vary the moment of stress.

[00102] Element 4: a spring is placed around the at least one pivot axis and is attached to the frame and to the at least one flap to create the moment of stress.

[00103] Element 5: the at least one flap includes two flaps each being placed on one of the respective opposite sides of the opening.

[00104] Element 6: the vent further comprises a layer of high temperature refractory fiber attached to a peripheral edge of the at least one flap and creating an airtight connection between the frame and the at least one flap when the vent is in the closed position.

[00105] Element 7: the frame may be secured to the furnace in a removable manner.

[00106] Element 8: the vent further comprises at least one handle attached to the frame to allow manipulation of the vent.

[00107] Element 9: the frame defines a side wall extending circumferentially around the opening and extending vertically between the opening and an upper edge of said side wall, the at least one flap abutting the upper edge in the closed position.

[00108] Element 10: the at least one opening includes two openings located upstream or downstream of one of the chambers of the preheating zone.

[00109] C. Method to use a vent which may be placed over an opening of an anode baking furnace is provided, comprising: limiting fluid communication between the hollow partition and an environment outside the hollow partition when a difference between a hollow partition pressure and an environmental pressure is above a nominal value; and biasing the at least one flap of the vent from a closed position to an open position allowing fluid communication between the hollow partition and the environment when the difference between the pressure of the hollow partition and that of the environment falls below the nominal value and below a determined threshold.

[00110] Embodiment C may include any of the items below, in any combination.

[00111] Element 11: Biasing the at least one flap of the vent comprises exerting a moment with respect to a pivot axis of the at least one upper and opposite flap at a moment with respect to the pivot axis created by a weight of the at least one flap.

[00112] Element 12: Exerting the moment includes exerting the moment with at least one counterweight, the at least one counterweight and the at least one flap each being provided with at least one hinge on one of the respective opposite sides.

Claims

CLAIMS:

1. Vent for an opening in an anode baking furnace allowing communication between a hollow partition of the furnace and an environment external to the hollow partition, comprising: a frame; at least one flap movable relative to the frame from a closed position in which communication between the environment and the hollow partition is limited by said at least one flap to an open position in which the vent allows communication between the hollow partition and the environment; and a stress mechanism attached to the at least one flap and exerting a stress force nudging the at least one flap into the open position, the stress force being less than a pressure force resulting from a difference between a nominal pressure of the hollow partition and an environmental pressure, the stress force being such that the at least one flap moves from the closed position to the open position through the stress force as the pressure force decreases to below a determined threshold.

2. The vent according to claim 1, wherein the at least one flap is mounted on the frame pivotably relative to at least one pivot axis, the stress force generating a moment of stress around the at least one pivot axis and the difference between the pressures of the hollow partition and the environment generate a moment of pressure around the at least one pivot axis and in the opposite direction at the moment of stress.

3. The vent according to claim 2, wherein the stress mechanism includes at least one counterweight attached to the at least one flap, the at least one counterweight and the at least one flap being placed on either side of at least one hinge connecting the at least one flap to the frame.

4. The vent according to claim 3, wherein the at least one counterweight can move in a radial direction relative to the at least one pivot axis so as to approach or move away from the at least one hinge in order to vary the biasing moment.

5. The vent according to claim 2, wherein a spring is placed around the at least one pivot axis and is attached to the frame and to the at least one flap to create the stress moment.

6. The vent according to any one of claims I to 5, wherein the at least one flap includes two flaps each placed on one of the respective opposite sides of the opening.

7. The vent according to any one of claims I to 5, further comprising a layer of high temperature refractory fiber attached to a peripheral edge of the at least one flap and creating an airtight connection between the frame and the at least one flap when the vent is in the closed position.

8. The vent according to any one of claims I to 7, wherein the frame may be secured to the furnace in a removable manner.

9. The vent according to any one of claims 1 to 8, further comprising at least one handle attached to the frame to allow manipulation of the vent.

10. The vent according to anyone of claims Ito 9, wherein the frame defines aside wall extending circumferentially around the opening and extending vertically between the opening and an upper edge of said side wall, the at least one flap abutting the upper edge in the closed position.

11. Carbon anode baking furnace for the production of aluminum by electrolysis, comprising: longitudinal hollow partitions in each of which can circulate a flow of hot cooking gases at a certain temperature with a certain flow rate, the hollow partitions defining between them cells for receiving the anodes to be baked and comprising a plurality of openings; a heating system rotating with respect to the hollow partitions, which comprises an upstream ramp of several air blowing legs in the different hollow partitions, a downstream ramp of several suction legs for gas from the various hollow partitions and, between said upstream and downstream ramps, at least one heating ramp provided with at least one burner or at least one fuel injector per hollow partition; lines for the circulation of gas flows in the hollow partitions being formed in the hollow partitions between blowing legs and corresponding suction legs; and a natural preheating zone of the furnace being defined between the downstream ramp and the heating ramp and in which a natural degassing of the anodes occurs, wherein, for each of the lines, at least one vent as described in any one of claims 1 to 10 is placed above at least one opening, the at least one opening being located in the natural preheating zone of the furnace.

12. The furnace according to claim 11, wherein the at least one opening includes two openings located upstream or downstream of one of the chambers of the preheating zone.

13. A method to use a vent which may be placed over an opening of an anode baking furnace is provided, comprising: limiting fluid communication between the hollow partition and an environment outside the hollow partition when a difference between the hollow partition pressure and the environment pressure is above nominal value; and and biasing the at least one flap of the vent from a closed position to an open position allowing fluid communication between the hollow partition and the environment when the difference between the pressure of the hollow partition and that of the environment falls below the nominal value and below a determined threshold.

14. The method according to claim 13, wherein biasing the at least one flap of the vent comprises exerting a moment relative to a pivot axis of the at least one upper and opposite flap at a moment relative to the pivot axis created by the weight of the at least one flap.

15. The method according to claim 14, wherein exerting the moment includes exerting the moment with at least one counterweight, the at least one counterweight and the at least one flap each being provided with at least one hinge on one of the respective opposite sides.

Rio Tinto Alcan International Limited

Patent Attorneys for the Applicant/Nominated Person

SPRUSON&FERGUSON

Fig. 2 Fig. 1 1/5

Fig. 4 Fig. 3 2/5

Fig. 6 Fig. 5 3/5

Fig. 8 Fig. 7 4/5

Fig. 9

Fig. 10 5/5