FR2767580A1 - Quenching and cooling of hot metal dross treatment residues - Google Patents

Abstract

Hot residues from a dross treatment furnace are quenched and cooled by mixing with cold fines of the same type as those contained within the residue. A method of quenching and cooling hot residues, discharged from a dross treatment furnace and containing unrecovered metal droplets and inert oxide fines, comprises (a) mixing the hot residue with cold fines of the same type to achieve the desired rapid quenching and cooling and to coagulate the metal droplets without the need for prolonged storage and/or water cooling; and (b) screening the resulting mixture to recover a metal-rich concentrate and the fines. An Independent claim is also included for a mixer-quencher for use in the above method.

Description

METHOD AND APPARATUS FOR EXTINGUISHING AND COOLING A RESIDUE
HOT OUT OF A CREST PROCESSING OVEN
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method using residue fines for extinguishing and cooling the hot residue leaving a furnace for recovering the metal contained in dross without the use of salt flux.

 This invention has been developed primarily for quenching and cooling the hot residue of aluminum slag. However, it can also be used for extinguishing residues of other types of dirt, such as zinc or magnesium scum. The residue fines are mainly composed of metal oxide and the zinc oxide and magnesium oxide powders as well as the alumina powder are refractory powders and are easily separable after cooling the frozen metal droplets initially contained in the residue. by sieving.

 The present invention is therefore of general application in that it is usable where residue fines are available and where it is necessary to cool or extinguish the residue leaving an oven for the purpose of preserving and recovering the metal. that it contains. After mixing and cooling, a metal-rich concentrate is separated from the residue fines. Recycling the concentrate increases the production of metal in the plant.

BRIEF DESCRIPTION OF THE STATE OF BA TEHNIC
The techniques of metal recovery from their dross, and this mainly in the field of aluminum, use less and less salt flow. Indeed, the flows used are expensive, they pollute and their recycling is often too expensive to be profitable.

 To solve the environmental and financial problems of traditional methods, many collectors have modified their technology by decreasing or eliminating the use of salt flows. However, this elimination leads to the production of a hot residue containing fine droplets of metal that can ignite when they are placed in the presence of ambient air at the outlet of the oven.

 There are already systems for extinguishing and cooling the dirt coming out of the holding baths of the liquid aluminum.

 One of these systems known under the acronym STAS, uses bells under argon to store the dross during their cooling. This method is very long and a large floor space is needed.

 Another system known under the acronyms MFS and ARCOS, uses coolers in the form of rotary drums cooled with water for the extinction of dross. The dross cooling is very fast and makes the system very attractive to recyclers but the cost of these drums is prohibitive. In addition, the use of water presents a certain danger of explosion and the cost of maintenance and operation is high.

 In all cases, these systems have essentially been designed to cool the dirt coming out of the holding baths of liquid aluminum.

In such a case, the amount of aluminum in the product to be cooled is greater than in the case of the present invention where it is the residue obtained after the treatment of dross. In fact, the initial dross contains 30 to 80% of the aluminum while the residue obtained after treatment contains hardly more than 20% of metal.

 Currently, the recyclers use the same equipment to extinguish and cool the hot residue coming out of the aluminum sludge treatment furnaces.

 In the MFS and ARCOS systems, the hot residue is discharged into one or more bins as means of transport between the recovery oven and a rotary cooler. A transfer system is then required to load the rotary cooler. A hood is also necessary at the entrance of the chiller to capture fumes and dust during this transfer. The mass of the residue charge and the temperature are limited.

The rotary cooler thus used in MFS systems and
ARCOS consists of a special steel tank, whose interior is equipped with a propeller similar to that of a cement mixer and whose outside of the tank has fins. This tank dipped in a water bath to achieve rapid cooling. Sprinklers sprinkle the outside of the tank, which makes it necessary to provide an exhaust for the steam. The rotation is carried out in one direction during cooling. The material remains in the cooled part by the water of the apparatus until its complete cooling.

When the cooling is completed, the rotation of the tank is reversed and the material pushed by the movement of the propeller is routed to an outlet formed of a cylinder pierced with a multitude of holes. The fines of residue then pass through the holes of the cylinder while the coarse fraction of the residue leaves at the end of the apparatus. Again, a hood is required to capture the dust in this part of the apparatus where is sieved the cooled product.

 In the MFS system, the ends of the apparatus are open, so that the surrounding air can very well enter with the possibility of supplying oxygen with localized combustion points in the load.

 In the ARCOS system, the residue tank, instead of being emptied in the open air, adapts to the device in a sealed way. A rotating shovel takes a part of the residue and sends it into the cylinder cooled with water. This system is more waterproof but also more complex than the MFS.

In addition to either of the systems described above, some recyclers use a ball crusher to process the coarse fraction of the residue leaving the apparatus. In this coarse fraction, there are pieces of friable alumina and non-friable aluminum granules. The output of the ball crusher consists of a cylinder pierced with holes (as is the case of the MFS cooler), which ensures the separation between, on the one hand, the concentrate of the coarse fraction and on the other hand , the residue fines. Only the concentrate coming out of the crusher is recycled to the kiln, while the fines of residue coming out of the crusher and the cooler are united to be buried or bagged.
In all cases, the devices used for extinguishing and cooling the residue are cooled with water. The risk that the cell pierces and that water comes into contact with the product always exists. The presence of water also creates significant thermal stresses and the risks of corrosion require the use of special steel.

 Another disadvantage of these devices is their prohibitive purchase and maintenance costs and the additional costs of the ancillary equipment necessary for their operation (large suction flow, large size, water inlet, steam evacuation, etc.). water, etc ...).

OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is essentially to provide a new method as well as a new apparatus for extinguishing and cooling the hot residue coming out of a dirt treatment furnace.

The method according to the invention offers the following advantages over known methods previously mentioned:
it ensures a very rapid extinction of the hot residue; it therefore very effectively stops the burning of the metal and ensures its preservation;
- it avoids fumes of smoke during the cooling of the residue;
it eliminates the hazardous storage of the hot and smoking residue in tanks;
it preserves the metal contained in the residue much better;
it limits the space necessary for the treatment of the residue;
- it increases the metal recovery rate of the plant by allowing recycling of the concentrate;
it produces a residue of well-defined particle size, the quality of the residue of which depends on the starting material;
- it implies minimum costs for the purchase, operation and maintenance of the equipment in relation to the competition;
it does not cause any contamination of the residue since the cooling agent is a part of the residue itself;
- it ensures a total conservation of the mass of the inputs (hot residue and fines of residue) and the outputs (concentrated and fines of residue);
it is universal and can therefore be used to extinguish and cool droplets of metal dispersed in a mass of residue by the powder of its oxide whatever the metal in question, which makes it applicable to aluminum, zinc, magnesium, etc .; and
- it does not use salt, water, gas or foreign matter to extinguish and cool the residue.

 In other words, the invention provides a method which is both simple and effective for extinguishing and cooling the hot residue from a slag treatment furnace in order to preserve the metal that this residue contains and which does not use no salt, no water, no gas, or other foreign agents.

 The invention also relates to an apparatus for implementing this method.

 The method according to the invention for extinguishing and cooling the hot residue leaving a furnace slag treatment consists essentially of using a quantity of fines of the same type as those contained in the residue that is to extinguish and cool. These fines are at room temperature and available in large quantities. They are placed in the tank for receiving the hot residue before it is poured therein. They thus serve to protect the bottom of the tank against possible spills of aluminum and against the heat of the residue. After pouring, these fines are mixed with the hot residue. They then serve as heat capacity to absorb the heat of the hot residue and, from there, "choke" and cool it.

 According to the invention, therefore, the hot residue leaving the waste treatment furnace is mixed with a large mass of cold fines extracted from the same kind of residue. This mixture allows to quickly cool the hot residue and freeze the metal droplets contained therein.

 The mixture obtained, which is then at an intermediate temperature, can then be subjected to crushing. The crushing is preferably carried out in a toothed roller crusher. Its main purpose is to break the large friable pieces present in the mixture. The fines from the hot residue and those mixed with this residue pass through the crusher without being altered.

 It should be understood that crushing of the mixture is not essential to achieve the extinguishing and cooling method described herein, since the residue fines used (and those from the hot residue) are easily separated by simple sieving.

 In practice, this crushing phase makes it possible to enrich the metal obtained in the following sieving phase with metal and to reduce the amount of material to be recycled in the oven. This saves time (productivity), saving energy (expenses) and a gain in metal recovery (income).

 The fines used for extinguishing contained in the crushed mixture pass entirely through the sieve grid since they do not tend to agglomerate during the mixing operation. It will be understood in this regard that the fines from the hot residue are added to those used for cooling. Some of the collected fines can be recycled for further quenching and cooling, while the surplus can be bagged for shipment to customers or landfilled. The fraction of the mixture remaining on the grid of the sieve is rich in metal. This fraction is hereinafter referred to as "concentrate". This fraction is recycled into the dross treatment furnace, so as to recover the surplus of metal it contains and make the waste treatment equipment profitable.

The invention as hereinafter claimed can therefore be defined as a method for extinguishing and cooling a hot residue leaving a waste treatment furnace, this hot residue containing droplets of the metal originally present in the dross but not recovered in the oven and fines mainly consisting of inert oxide (s), characterized in that:
the hot residue is mixed with a sufficient quantity of cold fines of the same kind as those contained in the hot residue to rapidly obtain the desired quenching and cooling and freeze the droplets of metal without the need for prolonged storage and / or cooling with water; and
the resulting mixture is crushed or not at an intermediate temperature; and
the mixture thus obtained is sieved to collect, on the one hand, a metal-rich concentrate and, on the other hand, the fines from the hot residue and those mixed with this residue.

According to a particularly advantageous embodiment,
the metal-rich concentrate collected during the sieving is recycled to the slag treatment furnace; and
- Some of the fines collected during sieving are recycled to mix them cold with another hot residue to be extinguished and cooled.

 The method according to the invention is particularly well suited for extinguishing and cooling residues from aluminum slag processing furnaces not using a salt stream, where there are residue quenching problems. This method can also be used in any other case where it is necessary to cool a product generating fumes and likely to catch fire in contact with the air, this at the same time eliminating problems of hazardous storage of smoking and very hot residue.

 The method according to the invention uses the residue fines from the metal recovery treatment, the major part of which consists of inert oxide. These fines are recoverable by sieving after cooling and reused for a new treatment. In fact, some of the fines generated by the plant will be used for extinction. The fact that these fines have a well-defined particle size and do not contain salt, gives the opportunity to find markets for them.

 From a practical point of view, the step of mixing the method according to the invention can be implemented by means of a new apparatus specially designed for this purpose, which constitutes another object of the invention.

This apparatus, hereinafter called extinguisher-mixer, is characterized in that it comprises:
a tank consisting of two parts hereinafter abacff and "lid" respectively, the lid being fixed rigidly to a rotary frame supported by two coaxial and horizontal shafts, the tray being removably attached to the frame and having a base provided with gripping means, this tray being intended to receive the hot residue and the fines;
- A sliding door for emptying the device, this door being fixed on the lid or on the tray according to the chosen emptying option;
a frame on which the tank is rotatably mounted by means of rolling bearings engaging the shafts of the frame; and
means for rotating the tank on said chassis.

Preferably:
- The removable tray comprises a flange which fits in the rotary frame of the mixer by a system of wedge grooves for locking in rotation from the front when the tray is filled;
- A lock device is provided to maintain the tray in position after its contents has tumbled; and
- The sliding door is moved by a worm gear mechanism, in which the screw can be driven manually by a removable wheel or automatically using a motor;
The extinguisher mixer according to the invention is of interest insofar as it makes it possible to carry out, in the absence of the ambient atmosphere, a homogeneous mixture between a hot residue containing fine droplets of an oxidation-sensitive metal and fines. cold residue initially at room temperature
The invention as well as its various advantages will become more apparent from the general and nonlimiting description which follows, with reference to the appended drawings.

BRIEF PRESENTATION OF THE DRAWINGS
Figure 1 is a front view of a mixer used for the implementation of the invention; and
Figure 2 is a side view of the mixer vessel illustrated in Figure 1.
Figure 3 is a side view of the vessel shown in Figure 2, showing the tray thereof in disassembled position;
FIG. 4 is a schematic view of an automated set of apparatuses usable for implementing the method according to the invention;
Figure 5 is a schematic view of a plant for separation of fines according to the invention;
Fig. 6 is a diagram showing the cooling kinetics of 4.94 kg of a hot residue of aluminum slag at 834 ° C, when this residue is mixed with 15 kg of fines at 25 ° C in a mixer rotating at 20 rpm; and
Fig. 7 is a diagram showing the cooling kinetics of 10.01 kg of hot residue of aluminum slag at 783 ° C, when this residue is mixed with 15 kg of fines at 25 ° C in a mixer rotating at 20 rpm /minutes.

GENERAL DESCRIPTION OF THE INVENTION
As previously stated, the idea underlying the present invention is a use of the available residue fines in large quantities for extinguishing and preserving the unrecovered metal upon emptying the solid residue from a treatment furnace. or dirt recovery.

The invention allows this metal or a rich fraction of this metal to be separated from the mixture by simple sieving. The fines that do not tend to agglomerate hot, since they do not contain aluminum, are also recovered during this sieving. After complete cooling, some of these fines are recycled to be mixed with another amount of residue in a new quench and quench cycle.

 The recycled fines used to extinguish a new quantity of residue leaving the recovery oven have by their nature already undergone a heating cycle in the oven. These fines are thus free of moisture or other volatiles and should in practice be carefully stored away from moisture. Complete cooling of these fines before use is preferably carried out by spreading in a storage site or by storage in bins or silos. These fines consist largely of the metal oxide to be recovered and their metal content is very poor. The more the metal is reactive with oxygen, the more its oxide is stable and inert and has the properties of a refractory (high melting point and high specific heat). This is actually the case for aluminum, zinc and magnesium. The oxide powder of a metal as cooler and coating agent is therefore an ideal extinguisher for a fire of this metal in the presence of oxygen in the air.

 Tests carried out by the Applicant for the extinction of hot residue coming out of the aluminum sludge treatment furnace have shown that the mass balance of the inputs (mass of cold fines + mass of the hot residue) is equal to the mass of the mixture. cooled. This demonstrates that the fine aluminum droplets contained in the residue were not oxidized, because if this had been the case, the mass of the mixture would have been greater than that of the inputs. The method according to the invention thus makes it possible to preserve the metal contained in the residue and to recover it largely in the form of concentrate by a simple operation of crushing and sieving the cooled mixture.

The method according to the invention is perfectly suited to be combined with the aluminum scum treatment method marketed under the brand name DROSCARs (see US Pat. No. 5,245,627 in the name of the Applicant). This method DROSCARe is the only one in which the heating of the dross can be carried out easily under controlled atmosphere. By integrating the latter with the method according to the invention, it is then possible to obtain a preservation of the mass according to the equation: mass of dirt = mass of aluminum + masses of residue fines + dust mass collected
Indeed, this equation will be respected only if the treatment of the dross is carried out without oxidation of the metal. This can be achieved with the method DROSCAR @. Similarly, this equation will be respected only if the residue leaving the oven is as little as possible handled in the presence of air. Here again, this is possible with the method according to the invention. The combination of these two technologies therefore maximizes the treatment of aluminum slag.

The mixture of cold residue residues with the hot residue to be quenched and cooled can be made in a mixer-extinguisher 1 as illustrated in Figures 1 to 5 of the accompanying drawings. This mixer-extinguisher
1 was designed for a hot residue load of 600 kg, the emptying temperature of the aluminum recovery furnace 3 (see Figure 4) can be between 700 ° C and 1 000C and whose aluminum content can be understood between 5% and 20% The purpose of this mixer-extinguisher is to homogeneously mix cold fines (about 1400 kg) with the hot residue (maximum 600 kg) In this mixing process, the temperature of the hot residue decreases quickly and the droplets of metal contained in this residue are frozen in solid form.

 The extinguisher mixer 1 comprises a steel tank 5a, 5b having an average diameter of 2.2 m and whose width and length are approximately identical. This tank 5a, 5b is driven by a 15 HP motor and rotates at an adjustable speed which can be, for example, 4 rpm.

In the case of aluminum, the target maximum target temperature after homogeneous mixing and cooling is less than 300 ° C. In practice, this can be obtained after 25 minutes of stirring (100 tank revolutions). will then be set at 45 minutes to allow optimal homogenization and cooling The outer surface of the steel tank can be painted black to promote its cooling by radiation and fans or hood (not shown) can be placed above to evacuate the heat by forced convection.

 The mixer-extinguisher 1 also comprises a rotating frame 7 supported by two coaxial and horizontal shafts 9 rotatably mounted on a frame with rolling bearings 11. According to this design, the vital mechanical parts such as the shafts and bearings are not not in contact with hot spots. The rotation of the frame and the tank is ensured by a motor 13 connected to a shaft 9 by means of gears 1 5.

 As best illustrated in FIG. 3, the tank is made up of two parts 5a, 5b which match the frame 7. The one 5a called "lid" is bolted rigidly to the frame 7 and comprises a bolted plate 17. 5b another consists of a removable tray provided with a collar-shaped collar 19 engaging in grooves 21 also wedge provided for this purpose in the frame 7 (see Figure 3). Two locking locks 23 hold the tray in these grooves.

 At the bottom of the removable tray is fixed a sliding door moved by a worm mechanism. The sliding door 17 can be fixed on the lid or the tray according to the preferences of the user.

 The direction of rotation 'A' of the tank is imposed such that the load in the removable tray 5b force the flange 19 thereof to lock in the grooves 21. When the load has tumbled after half a turn, the two locking locks hold the removable tray 5b in position A safety device prevents the start of the rotation if the locking pins of the locks are not engaged to hold the removable tray.

The door 17 of the lid or tray can be actuated by a wheel or a motor.

 The removable tray 5b has at its base two tubes 25 to allow its transport, positioning and removal from the mixer using a forklift truck. The elongated shape of the tank is imposed by the geometric characteristics of the removable tray 5b which is deeper than wide for reasons of capacity and must also adapt to the receipt of hot residue under the oven mouth.

 The mixing movement exerted in the tank 5a, 5b at each half-turn corresponds to a spreading and gathering phase. One or two pallets (not shown) may be placed inside the rotating frame 7 to break the blocks in the mixture as the bowl rotates. The rotation of the tank makes it possible to put new parts of the mixture in contact with the surface of the colder mixer. A forced air flow around the rotating mixer-extinguisher may be provided to improve its cooling and that of the mixture.

 Gases can be formed during the stirring and are evacuated by two tubes 27 extending in the shafts 9, along the axis of rotation.

The exhaust is free on one side while on the other a disc with spring acts as a valve.

In the case of the mixer-extinguisher 1 described above, the removable tray 5b has a capacity of 2 m 3, or 2 metric tons of residue assuming for the aluminum dross a bulk density of 1. In use, the entire SF fines required for the mixture can be previously arranged in the bottom of the tray 5b before receiving the incandescent residue gR from the oven 3 (see Figure 4). This base layer allows the protection of the metal of the tray 5b against the heat of the residue and against a possible spill of metal. However, in practice, only half of the fines' F 'will preferably be placed in the bottom of the tank 5b After pouring the hot residue on the fines' F * thus disposed in the tank, the other half of the fines will then be extend over the hot residue "R" after careful raking of the top of the hot residue layer and that of the coating fines in order to effectively cover the hot residue against oxidation. This precaution is useful in the case where trays 5b containing the hot residue are placed on hold as shown in Figure 4. In fact, it ensures good control of smoke during storage, it decreases by a factor of 5
The oxidation of the residual metal (a mass increase of about 6 kg instead of 30 kg over a period of 24 hours) and gives the tank a good protection against heat. However, the residue even covered tends to agglomerate, because the oxidation is not completely stopped and the extinction time is very long. If the amount of hot residue to extract from the furnace is greater than 600 kg (capacity of a tank), the mixer-fire extinguisher 1 will be mainly used as fire extinguisher.

 As illustrated in Figure 4, the fines can be placed in a silo 29 to facilitate the spreading operations thereof in the bins.

 It will be understood that it is necessary to have in the tray 5b the amount of cold residue fines required for extinguishing and cooling the poured residue. It will also be understood that the fines thus poured into the tank 5b serve not only the desired cooling but also as protection for the metal tray. In practice, the mass of fines used may represent up to three times the mass of residue to be extinguished.

 As previously mentioned, in order to use the maximum available time within the cycle time of the oven 1, in order to achieve maximum cooling, it may be necessary to use several bins 5b as illustrated on the Figure 4. It is also possible to provide several mixer-extinguishers 1 operating in parallel.

 After obtaining the desired extinction and cooling, the tank is stopped in vertical position and the sliding door is opened for emptying the tank. The mixture contained in the tank discharges into a hopper whose inlet is equipped with a grid 33 intended to retain the large pieces or any other object that may block the operation of the assembly consisting of a crusher 35 and a screen 37 disposed downstream. This grid preferably has meshs of 100 mm. After emptying, the door of the mixer extinguisher 1 is closed. The emptying can be assisted by the rotation of the tank which stops automatically in the vertical position to allow removal of the removable tray 5b with the forklift. Depending on their equipment and that the size of the mesh of the grid can be modified giving more flexibility to the set according to the type of product treated.

 The crusher 35 plays an important role in that in the mixture are large pieces or blocks that are low in metal. These blocks will disintegrate into smaller pieces and, in this process, a good fraction of the blocks will be reduced to powder passing through the sieve grid. This action also releases metal granules found "trapper" in the blocks that will be retained on the grid of the sieve. Thus, the crusher 35 makes it possible to reduce the mass of concentrate and to enrich it with metal, which is reflected during its recycling in the oven, by a gain in time and energy. The spacing between the toothed rollers of this crusher must of course be greater than the diameter of the fines so that they pass through the crusher without being altered.

 The mesh of the sieve 37 preferably consists of circular holes 3.2 mm (1/8 ") in diameter, this size seems adequate for a good separation of the fines and the concentrate.The separated fines can be stored in a silo to allow a complete cooling and facilitate their pouring into the removable tray of the mixer The silo storage also facilitates the bagging operation of the fines.

 The sieve 37 thus serves to separate the concentrate from the fines. From a practical point of view, the sieving is carried out to obtain two fractions, namely a first fraction whose particle diameter is greater than or equal to 3.2 mm, this first fraction consisting essentially of the concentrate to be collected; a second fraction having a particle diameter of less than 3.2 mm, this second fraction consisting essentially of residue fines, part of which is recycled for extinguishing and cooling another residue feed.

 The first fraction Sgrossièren consists of the concentrate.

This coarse fraction can be recycled to the dross treatment furnace 3 to increase metal recovery. Part of the fines constituting the second fraction is reused for the extinction of the residue.

 As previously indicated, the method according to the invention can be used for all applications for treating metal scum. It has been developed especially for extinguishing the residue of aluminum recovery furnaces but is also applicable for all types of metals such as zinc or magnesium. The residue to be cooled contains fine droplets of metal which, when exposed to air, can ignite with a strong release of heat and smoke. The method according to the invention makes it possible to avoid the hazardous storage of hot and smoking residue for a long time. In addition to this advantage, the metal in the residue is preserved and recoverable. The method according to the invention therefore makes it possible to increase the production of the metal of the plant and creates a by-product (residue fines) of well-defined particle size with potential applications.

 The techniques of recovering metals from their dross without the use of a salty stream are in full expansion. The method according to the invention therefore represents a solution not only effective but the most economical to the problem of extinguishing the residue and preservation of the metal it contains.

 This method is perfectly suitable for the extinction of the residue and is less costly in investment and operating cost than known methods. The main advantages of this method are that it does not use salt, water or gas, and that quenching is very effective. In addition, the fines used for extinction are recovered by simple sieving and reused later after their complete cooling. The operating cost of such a method is minimal. Risks related to the use of water such as the danger of explosion or the presence of strong thermal stresses are absent. The absence of moisture also minimizes the risk of corrosion. The rotary drum of the mixer can therefore be made of ordinary steel while the drum of a MFS must necessarily be made of special steel.

The maintenance of the mixer tank is minimal since in fact the heat constraints are minimized by the presence of a large amount of fines.

On the other hand, the mixing cooling technique does not tend to disperse the fine droplets of metal contained in the residue. This quenching technique is more of a quenching by cutting off available oxygen by covering the hot residue. The moderate stirring makes it possible to avoid agglomeration of the hot residue while participating in the cooling of the hot residue and homogenization of the temperature of the mixture. The tank of the mixer and sealed which limits the exposure of the residue to the oxygen of the air and allows to obtain a rapid extinction of the residue.

EXAMPLE
aluminum recovery from dirt
HYDRO-QUÉBEC's electrochemical technologies and electrotechnologies laboratory has two DR0SCARoe furnaces, one of 30 kW and the other of 600 kW, with respective capacities for treating aluminum slag and 15 1000 kg. The DROSCAR method is described in US Patent 5,245,627. It uses the radiation of an electric arc to heat the aluminum scum at a temperature of about 800 ° C. After stirring, the metal droplets form a bath that is poured.

The recovered metal is weighed. The oven door is opened and the hot residue is scraped off with a shovel or tilt and rotation of the tank.

On average, on 1000 kg of treated slag, 500 kg of aluminum is poured and 500 kg of hot residue is produced and stored in a steel tank covered with a lid for cooling. Without a rapid quenching technique, the complete cooling of the residue takes more than 24 hours and the mass increase of the hot residue is on average 30 kg, correspondingly a loss of aluminum of about 30 kg.
(b) summary of the tests carried out on the residue of
DROSCAR oven! 30 kW
A first series of experimental tests has demonstrated that the method according to the invention of mixing the hot residue with the cold fines is the best method of extinguishing and protecting against the oxidation of the metal contained in the residue relative to to other techniques such as overlay storage with fines or under argon atmosphere.

 The criterion used to determine if this is the best method was to ensure that the minimum amount of mass increase of the hot residue or mixture after full cooling is achieved. For a mass of hot residue of 11 kg, it was found that the mass balance during complete cooling is +0.23 kg without addition, +0.13 kg with argon, +0.03 kg with fine residue coverage and -0.02 kg by mixing with fines. The advantage of the mixture over the other methods is that the incandescent parts of the hot residue disappear rapidly, thus annihilating the sensitivity of this residue to the subsequent oxidation by virtue of this rapid cooling and the covering effect with the fines. In addition, the risk of agglomeration of the residue by thermitage is zero since the residue is dispersed in cold fines.

In a second series of experimental tests, a cement mixer was used to perform the mixing. The average diameter of the mixer was 0.5 m and its rotational speed was 20 rpm. 1 5 kg of cold fines were previously placed in the mixer. The hot weighed residue, whose temperature was initially taken as being equal to the casting temperature of the metal, was introduced into the mixer. A cover was placed on the mixer mouth to prevent the loss of dust and the rotation is engaged. Two thermocouples were placed on the apparatus: one junction on the inside to measure the temperature of the mixture and the other on the surface of the mixer. The rotation was stopped at intervals to acquire the temperatures. After 15 minutes of stirring, the mixture was screened on a 3.2 mm circular grid to obtain two fractions corresponding respectively to the concentrate (> 3.2 mm) and the residue fines (<3, 2 mm). After complete cooling, some of these fines after complete cooling was recycled for a new extinguishing cycle.
c) analysis of the results obtained
The table below gives the average results obtained by treating samples of 15 kg of aluminum slag from different sieving fractions of a batch of aluminum slag from a holding furnace in the primary industry. In these tests, the hot residue leaving the oven was mixed with 15 kg of cold fines. In this table:
m ,,, is the mass of aluminum recovered during the treatment of baked dirt;
mc is the mass of concentrate obtained after sieving the mixture;
m ,,, is the average additional aluminum mass recovered by recycling the concentrate and;
the last column of the table gives the relative increase in metal recovery according to the different sizes of dirt.

TABLE 1

<tb> Type <SEP> of <SEP> Aluminum <SEP> Increase
<tb> dross <SEP> of <SEP> Aluminum <SEP> Report <SEP> of <SEP> mass <SEP> concentrated <SEP> in <SEP> more <SEP> by <SEP> relative <SEP> in
<tb> departure <SEP> recovered <SEP> when <SEP> of <SEP> obtained <SEP> recycling <SEP> recovery
<tb> sample <SEP> in <SEP> one <SEP> cooling <SEP>(> 3,2 <SEP> of
<tb> of <SEP> pass <SEP> mm) <SEP> concentrate
<tb><SEP> 15 <SEP> kg <SEP> mc <SEP> sn <SEP> me
<tb> granulometry <SEP> kg <SEP> kg <SEP> kg <SEP> kg
<tb><SEP><3.2<SEP> mm <SEP> 3.67 <SEP> -0.18 <SEP> 1.00 <SEP> 0.90 <SEP> 25
<tb><SEP><10mm<SEP> 4.35 <SEP> 4.02 <SEP> 2.30 <SEP> 0.50 <SEP> 11
<tb><SEP>> 16 <SEP> mm <SEP> 9.98 <SEP> -0.05 <SEP> 3.76 <SEP> 0.11 <SEP> 1
<tb><SEP><102<SEP> mm
<Tb>
An analysis of the results reported in this table shows that, under the experimental conditions mentioned, the recycling of the concentrate is very beneficial for fine grained dross. In the case of dross with particle size less than <3.2 mm (passing completely through the screen of the sieve before treatment), their baking allowed the fine aluminum droplets to coalesce in a bath, but a strong percentage of these droplets remained dispersed in the residue and was therefore not recovered. By mixing with the cold fines, these metal droplets were frozen and were recovered on the 3.2 mm sieve forming the concentrate whose aluminum content was 91%.

 The oxide fines that did not tend to agglomerate were passed through the sieve grid and the resulting concentrate was substantially pure metal, the recycle of which in the oven allowed a relative 25% increase in the recovery rate.

 Larger dirt gave more aluminum but also a larger mass of concentrate containing larger pieces and less aluminum content. The large pieces obtained on the sieve were not rich in aluminum and it became imperative to break these blocks or granules of oxide to reduce the mass of concentrate and enrich the metal.

 The metal oxide is friable while the metal is ductile and this difference in properties allows mechanical separation of the metal from its oxide by crushing. The fact of passing the mixture in a crusher and then sieving it results in a significant reduction in energy and time for the recycling of the concentrate with a bonus bonus more appreciable metal recovery.

 Crushing tests of the concentrate in a jaw crusher were unsuccessful because this apparatus mechanically blocked due to metal pellets that remained stuck between the jaws. In addition, the aluminum granules tended to stick on the serrations of the jaws under the effect of crushing. Crushers suitable for this type of application are therefore preferably ball mills or horizontal toothed roller crushers.

 Visual observation during the mixing process with cold fines showed that the incandescent parts of the hot residue disappear after 5 tank revolutions.

 Figures 6 and 7 attached show the cooling kinetics of the hot residue mixed with the residue fines. It should be noted immediately that the measured temperatures of the mixture after one minute are well below 600 ° C, the estimated temperature at which incandescence occurs and above which the oxidation of the metal would be significant. Figure 6, the hot / cold ratio of 2/3 corresponding to the residue of dross <16 mm In the measurements reported in Figure 7, this ratio hot / cold was 1/3, this corresponding to the residue of dross - 102 mm For a ratio 2/3, the temperatures were higher and the surface temperature of the mixer reached a maximum of 250au after 5 minutes.

However, the mass balances during cooling were zero or very slightly negative in both cases, which shows that there is no oxidation of the metal. Thus, the ratio of the masses of the hot residue on cold fines can be between these two values without loss of efficiency of the method.

Examination of the two kinetic curves illustrated in Figures 6 and 7 attached, we see that the surface temperature of the mixer reaches its maximum after five minutes of stirring. It can be deduced that the temperature of the mixture is then homogeneous and that there is no hot spot in the mixture. After five minutes, the mixture coming into contact with the surface of the device no longer causes an increase in temperature of its surface and the ambient air then participates in cooling the assembly. The cooling curves of the mixture and the apparatus become straight, meaning that the temperature decrease is then proportional to the time.
d) interpretation of the kinetics of cooling curves
In view of the kinetic curves described above and the observations made by the invention, the mixer-extinguisher according to the invention can be emptied after a stirring time of between 1 and 15 minutes (at 20 rpm) in the extent to which the objective of extinguishing the hot residue in order to preserve the metal it contains is achieved within this period of time. These modes of operation will be extrapolable for a larger device and will depend on the requirements of the user. In what follows, we will assume the number of tank revolutions as a mixing parameter. However, time could be used as a mixing parameter.

(i) extinguisher mode
20 tank revolutions or a stirring time of 1 minute at 20 rpm allow rapid quenching. After emptying the tank, the mixture can be stored for cooling before grinding and sieving.

In this mode of operation, the extinguishing capacity of the apparatus will be very important since several successive charges must be processed.

 There is, however, a risk of handling the mixture immediately because some hot spots in the mixture can coexist.

(II) extinguisher-melaneur mode
100 tank revolutions or a stirring time of 5 minutes at 20 rpm are obviously safer (for the handling of the mixture either grinding and sieving) insofar as the temperature of the mixture is homogeneous and there is no more hot spots that could ignite by exposure to the ambient air. However, the temperature reached by the device is higher than in the previous case.

(III) extinguisher-melaneur cooler mode
For more than 100 tank runs or a stirring time of more than 5 minutes at 20 rpm, the mixing and machine temperatures decrease in proportion to the time. The maximum time constraint for cooling is the furnace operating cycle time, the total time for charging, heating, casting and emptying.

 In the example used, the cycle time of the oven DROSCARs 30 kW is 21 minutes (the cycle time for the oven DROSCARs 600 kW is 69 minutes). It will thus be understood that the cycle time of the mixer-extinguisher of the hot residue, including the setting of the cold fines, the pouring of the hot residue, the stirring and the emptying of the mixer, should be less than the cycle time of the oven is less than < 21 minutes. The crusher-sieve cycle time must also be shorter than that of the oven in order to avoid build-up of the mixture. In the case where the residual charge corresponds to the capacity of the mixer, it is preferable to favor the operating mode of the mixer according to a maximum stirring time in order to achieve optimum homogenization and cooling.

 In fact, the mode of operation of the apparatus will depend on its capacity, the volume of residue to be treated and the cycle time of the oven. In Figure 4, the volume of residue to be treated corresponds to four bins and one has a single mixer. The maximum stirring time will therefore be equal to the cycle time of the oven divided by four. If a longer stirring is desired, the solutions will be either to increase the capacity of the mixer, or to add other mixer (s) in parallel.

The automation of all operations on the residue (stirring, emptying, grinding, sieving and storage of fines) is easily achievable as shown in Figure 4.
e) Estimation of the metal gain according to the invention
In view of the above results, it will be understood that in a plant incorporating a DROSCARs furnace of 600 kW with the apparatus and the extinction method according to the invention, the metal will be preserved from oxidation and mass balances (inputs c) Outputs) will be respected during processing. The rate of dust to the dust collector will be less than 0.4% of the mass of dirt.

 The load of dirt containing 50% aluminum will be 1000 kg and will include a mixture of blocks, granules and powder. The amount of aluminum recovered will be 450 kg and 550 kg of residue will be produced containing 50 kg of aluminum. After extinction, crushing and sieving of the residue, 100 kg of concentrate containing 50% of aluminum and 450 kg of additional residue fines will be obtained. The concentration of aluminum in these fines is estimated at 1%.

 After 10 kiln charges, or 10 tons of treated slag, we will obtain 4500 kg of aluminum and 1 ton of concentrate containing 50% aluminum.

The baking of the concentrate will recover 450 kg of additional aluminum, a relative increase in aluminum recovery of 10%. This increase in recovery will result in a 10% time and energy consumption since it was assumed that for the type of treated slag, 10% concentrate was produced.

 According to this estimate, the recovery rate in the oven will be 90% while that of the integrated plant will be almost 100%. In fact, the residue fines produced will titrate 1% aluminum, which for this example corresponds to an aluminum recovery rate for an integrated plant of 99%.

Claims (13)

 1. A method for extinguishing and cooling a hot residue leaving a waste treatment furnace, this hot residue containing droplets of the metal originally present in the dross but not recovered in the furnace and fines mainly consisting of oxide (s) inert (s), characterized in that:  the hot residue is mixed with a sufficient quantity of cold fines of the same kind as those contained in the hot residue to rapidly obtain the desired quenching and cooling and freeze the droplets of metal without the need for prolonged storage and / or cooling with water; and  the mixture thus obtained is sieved to collect, on the one hand, a metal-rich concentrate and, on the other hand, the fines from the hot residue and those mixed with this residue.  2. Method according to claim 1, characterized in that before sieving, the mixture is crushed to break any blocks or granules of oxide (s) contained in the hot residue and that could not be disintegrated during treatment in the oven or when mixing.  3. Method according to claim 1 or 2, characterized in that:  the metal-rich concentrate collected after sieving is recycled to the dross treatment furnace; and  - Some of the fines collected during sieving are recycled to mix them cold with another hot residue to be extinguished and cooled.  4. Method according to claim 3, characterized in that the mixture of the hot residue with the cold fines is carried out in a rotary mixer with horizontal axis and in that the crushing is carried out in a crusher type toothed roller or ball.  5. Method according to claim 4, characterized in that the mixer-extinguisher includes a removable tray and in that, prior to mixing, is introduced a layer of cold fines and the hot residue in this order in the tray.  6. Method according to claim 5, characterized in that there is another layer of cold fines on the hot residue introduced into the tray to provide a cover against the oxidation of the metal contained in said residue during the transfer of the oven with mixer-fire extinguisher or when the tank is placed on hold.  7. Method according to any one of claims 1 to 6, characterized in that the ratio by weight of the amount of cold fines mixed with the hot residue is of the order of 3: 1 or less.  8. Method according to any one of claims 1 to 7, characterized in that the sieving is performed in a sieve for separating the mixture into two distinct fractions including:  a first so-called "grnssière" fraction whose particle diameter is greater than or equal to 3.2 mm, this first fraction consisting essentially of the concentrate to be collected;  a second fraction called "fines" whose particle diameter is less than 3.2 mm, part of which is recycled.  9. Method according to any one of claims 1 to 8, characterized in that the dross whose hot residue is extinguish and cool, are slag of aluminum, zinc or magnesium.  10. Method according to claim 9, characterized in that the dirt whose hot residue is to be extinguished and cool, are aluminum scum.  11. A mixer-extinguisher for carrying out the step of mixing the method according to any one of claims 1 to 10, characterized in that it comprises:  - A tank consisting of two parts hereinafter called "tray" and "lid", the lid being fixed rigidly to a rotary frame supported by two coaxial and horizontal shafts, the tray being removably attached to the frame and having a base provided with gripping means, this tray being intended to receive the hot residue and the fines;  - a dump door fixed on the lid or the removable tray to perform the emptying;  a frame on which the tank is rotatably mounted by means of rolling bearings engaging the shafts of the frame; and  means for rotating the tank on said chassis.  Mixer-extinguisher according to Claim 11, characterized in that:  - The removable tray comprises a flange which fits in the rotary frame of the mixer by a system of wedge grooves for locking in rotation from the front when the tray is filled;  - A lock device is provided to maintain the tray in position after its contents has tumbled; and  - The emptying door is sliding type and is moved by a worm.  13. mixer-fire extinguisher according to claim 12, characterized in that the shafts of the tank each comprise an opening for the escape of gases that may be formed during mixing and to prevent pressurization of the tank, one of said openings being directly connected to the outside atmosphere, the other being closed by a spring disk acting as a valve.