US20010028136A1

US20010028136A1 - Two-chamber furnace for the melt- contact smelting of contaminated aluminum scrap

Info

Publication number: US20010028136A1
Application number: US09/816,789
Authority: US
Inventors: Gunter Hertwich
Original assignee: Hertwich Engineering GmbH
Current assignee: Hertwich Engineering GmbH
Priority date: 2000-03-24
Filing date: 2001-03-23
Publication date: 2001-10-11
Also published as: RU2001107895A; ES2246941T3; ATE304689T1; EP1146304B1; DE10014711A1; CA2342096A1; JP2001324271A; DE50107396D1; EP1146304A1

Abstract

A two-chamber furnace for smelting scrap aluminum which is contaminated, has a distillation chamber above the first furnace chamber functioning as a charging stack and separated from the first chamber by a slider or flap arrangement. Flue gas from the first chamber is forced through the distillation chamber to destructively distill off the contaminants. The hood of the distillation chamber is equipped with a pressing body to compact the charge.

Description

FIELD OF THE INVENTION

The present invention relates to a furnace for the smelting of contaminated aluminum scrap and, more particularly to a two-chamber furnace for the melt-contact smelting of contaminated aluminum scrap.

BACKGROUND OF THE INVENTION

In the smelting of contaminated aluminum scrap, that is aluminum scrap which has oils, paints, lacquers and synthetic resin substances adhering to its surfaces, the scrap is usually melted in a rotary-drum furnace under a salt layer or cover. A drawback of this process is that large amounts of salt slag are produced, e.g. 50 kg of the salt slag per metric ton of the aluminum scrap processed. The system has, therefore, a low yield in terms of the metal and problems with the emission of toxic substances into the environment.

An improvement over this process which has been used for alloy-free scrap primarily carries out the melting in a two-chamber furnace with a destructive distillation bridge in this two-chamber furnace. One advantage of this method is that a salt slag is not produced. A second advantage is that higher metal yields are obtained since a contact melting process is used. In the contact melting process scrap is melted or dissolved by contact with hot metal melt. The oxidation losses which result from this process are small.

A drawback of this process is found in the charging of the aluminum scrap into the furnace and the manner in which the nonmetallic adhesives are destroyed. In spite of efforts to expand the destructive distillation bridge, the scrap tends to settle. Depending upon the type of scrap used, the settling can result in substantial amounts of scrap falling out of the furnace without preheating and destructive distillation of the contaminants or falling directly into the melt bed before the contaminants have been destroyed.

These problems, in turn, have collateral difficulties. For example, if the scrap is moist and comes into direct contact with the metal melt, explosions can occur. In addition, if the contaminants which adhere to the scrap enter the melt without destructive distillation, there can be a sudden liberation of large quantities of gases from the contaminants which cannot be fully burned off in the furnace and can overwhelm any gas scrap or cleaning equipment attached to the furnace. Furthermore, some contaminants can react with aluminum and increase the metal losses.

In earlier systems, moreover, the full charge of scrap may not be uniformly heated and treated for contaminant removal. For example, the heating of the charge by radiation and even blowing of flue gasses to the charge may heat the charge effectively only in surface regions and not in the interior or portions of the charge at the bottom thereof.

When there are parts of the charge which are not fully heated and thus also may retain organic adhesions, there can be sudden liberation of gases when the charge is pushed into the melt and which cannot be fully burned up. Here again the gas processing equipment can be overwhelmed.

When attempts are made to heat the charge more thoroughly by increasing the heating time, losses in aluminum can be encountered. If one resets the furnace temperature in the scrap chamber for this purpose, i.e. to increase the heat transferred to the charge, some melting of aluminum may occur in the surface portions of the charge which can result in higher oxidation losses.

In practice it has been found that such two-chamber furnaces can be operated effectively only with certain limitations. For example, only a maximum of 35% of the metal introduced into the furnace can be contaminated scrap. The remainder must be clean scrap or crude metal billets.

The charge must be so assembled that clean scrap must lie at the bottom of the charge and the contaminated scrap only at the top of the charge.

Large shaped scrap, such as bars of a variety of cross section, as are generally produced by extruding systems and which arise in large volumes, must be chopped into smaller pieces before use.

OBJECTS OF THE INVENTION

It is, therefore, the principal object of the present invention to provide a melting furnace which can be charged with up to 100% contaminated aluminum scrap but which nevertheless can be operated economically and in an environmentally-sound manner.

Another object of this invention is to provide a two-chamber furnace for the smelting of contaminated aluminum scrap by the immersion process, i.e. direct contact of the scrap with the melt, whereby drawbacks of earlier systems are avoided.

SUMMARY OF THE INVENTION

These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a furnace for the smelting of contaminated aluminum scrap which comprises:

a first furnace chamber adapted to receive a contaminated aluminum scrap for contacting the contaminated aluminum scrap with an aluminum melt, thereby dissolving aluminum from the scrap in the melt;

a second chamber connected to the first chamber for receiving the aluminum melt;

gas-fired burners in the chamber for heating same while producing flue gases in the chambers;

a flue-gas recirculation system connected to as least one of the chambers for withdrawing flue gas therefrom and recirculating withdrawn flue gas to the furnace;

a destructive-distillation chamber receiving a charge of the contaminated scrap for decontaminating the charge and connectable to the first chamber; and

means connected with the flue-gas recirculation system for forcing hot flue gas through the destructive-distillation chamber to destroy contaminants on the charge.

In particular, the two-chamber furnace for the immersion smelting of contaminated aluminum scrap can have a first and a second furnace chamber, a gas-firing heating arrangement for the furnace and a flue gas recirculation system as well as a device for the thermal decontamination of the charge.

According to the invention, the device for the thermal decontamination of the charge comprises a destructive distillation compartment or chamber which is separated from or separable from the chambers of the furnace but yet is connectable with the first chamber thereof and which is traversed by a forced flow of hot flue gas from the first furnace chamber.

With the system of the invention, a closed distillation chamber is provided to receive the charge by contract with the open destructive distillation bridge hitherto used. The danger of the charge falling out is thus minimal and contaminated or wet pieces of the charge cannot be supplied to the melt to give rise to explosions or gas-emission leaks of unburned distillation gases. A layering or comminution of the charge is not required if the destructive distillation chamber is appropriately dimensioned and the use of a charge consisting of 100% of contaminated scrap is not a problem.

While in the conventional two-chamber furnace having the distillation bridge, the scrap pile can only be contacted from the exterior with flue gases, with the system of the invention, wherein a closed destructive distillation chamber is separated from the two-furnace chambers, a forced flow of the hot flue gases from the first chamber through the body of the charge in the distillation chamber is possible over the entire free cross section of the charge. The heat transfer surface of the charge is thereby increased by at least ten times which ensures a rapid and uniform heating and complete decontamination. The furnace throughput is thereby increased and the efficiency of the furnace greatly enhanced.

Since the flue gas temperature need not be excessive with the system of the invention, overheating of the charge, melting within the charge and oxidation of the charge can be avoided.

It is also possible to provide the two-chamber furnace in two separate furnace units which are connected by a recycle pipe for the melt and with a flue gas line.

This approach however creates sealing problems and heat losses and increases the spatial requirements.

In another modification the smelting furnace has only one furnace chamber whose melt is maintained at a uniform temperature by recirculation effected by a recirculation pump. The flue gases which are fed to the destructive distillation chamber are then drawn from a recycling duct located outside the smelting furnace. This is generated by a gas burner system which supplies the required energy for preheating the charge and for combustion of the distillation gases.

This latter approach has the drawback that it provides a higher temperature loading of the closing elements (1000° C. as opposed to 600° C.) for a two-chamber furnace and a heating loss from the recycle duct which both contribute to higher construction costs of the apparatus.

It has been found to be advantageous to provide the distillation chamber with at least one inlet opening and at least one outlet opening for the flue gas, the inlet and outlet openings preferably being located opposite one another. The inlet and outlet openings should be positioned to ensure that the hot flue gas has a forced flow through the entire distillation chamber and the charge therein.

It is also advantageous to form the destructive distillation chamber as a filling shaft for the first furnace chamber and which is preferably vertical and is connected to the first furnace chamber by a closing element. The result is an integrated two-chamber furnace in which the filling shaft or the destructive distillation chamber is an integral part of the two-chamber furnace. Its configuration as a filling shaft for the first furnace chamber simplifies the construction and operation of the two-chamber furnace. The vertical orientation of the distillation chamber simplifies rapid and complete emptying. The closure element enables connection between the distillation chamber and the first furnace chamber.

When the closure element is comprised of two flaps which swing relative to one another, or by a slider which can open the passage between the distillation chamber and the first furnace chamber, i.e. the melting chamber, over the entire cross section of the shaft or the distillation chamber, the charge can be metered into the melting chamber by the opening speed of the flaps or slider and, with full opening, can be rapidly and completely emptied.

It has been found to be advantageous to provide the distillation chamber or shaft with a rectangular cross section in which a pressing body of corresponding shape is exactly movable. The pressing body can be displaceable with play in the shaft. The pressing body can fill the space above the charge in the distillation chamber and can press portions of the charge which may stick out of the latter downwardly and into the charge. In this manner short-circuiting or bypass flow of gas above the charge can be precluded entirely. Flue gas is thus forced to pass substantially uniformly through the charge and ensure uniform heating and destructive distillation of the contaminants from the surface of the scrap.

According to a feature of the invention, moreover, the distortion chamber is closed toward the exterior by a hood which is provided with a recess into which the pressing body can fit and which can support and receive a guide structure for the pressing body. The guide prevents horizontal migration of the pressing body and limits its penetration into the distortion chamber. When the pressing body is lifted into its uppermost position, its bottom can be flush with the bottom or sealing surface of the hood. With slight elevation of the hood in an upper position of the pressing body, the hood can be displaced laterally to provide an opening in the shaft and distillation chamber for a new charge.

According to another feature of the invention, in the furnace chambers, gas burners are provided. The gas burner systems in the two furnace chambers can include an oxygen sensor in one or both chambers to monitor residual oxygen in the combustion gases following the combustion process. It has been found that it is advantageous to operate the furnace with a constant oxygen excess in the flue gases. The O ₂sensors can thus be connected in a feedback arrangement with the gas burner system to provide a predetermined air excess in the combustion gases, for example 2%, thereby ensuring for a constant heat value of the combustion gases, a certain flue gas temperature. When the distillation-produced gases are then additionally burned, because they have heat values other than the full gas, in spite of the air excess, the temperature may vary. In that case, additional control can be effected based upon the flue gas temperature utilizing temperature sensors.

Advantageously, the first gas burner system, i.e. the gas burner system effective in the first or melting chamber, is operated to provide a flue gas temperature of about 600° C. in the first furnace chamber. In the second furnace chamber the flue gas temperature is controlled at preferably 1000° C.

The gas burner system in the first furnace chamber supplies the heat required to heat up the aluminum scrap to a temperature which is below the melting point of the scrap but at which rapid decontamination is effected by destructive distillation of the contaminants to produce a distortion gas. The distortion gas is largely burned in the furnace chamber. The second gas burner system in the second furnace chamber supplies the heat required to maintain the charge in a molten state and to melt any of the solid charge which may pass with the liquid metal into the second chamber. This temperature should be sufficient to crack toxic distillation gas residues which may remain from the first furnace chamber.

The intensity of the distortion gas formation can be varied by the control of the temperature prevalent in the distortion chamber and the speed of the flue gas therein. Rapid decontamination can be effected without gas-emission peaks. The temperature of the flue gas can be controlled by the first burner system, its velocity as determined by the seed of the circulating blowers for the flue gas, and the pressure with which the gas is forced through the charge within a wide range.

Advantageously a particular flue gas temperature is achieved in the first furnace chamber by the first gas burner system utilizing a fuel pass flow which is inversely proportional to the respective distillation gas flow during the distillation step. The control of the first burner system to a constant air excess requires a reduction in the fuel gas flow with increasing distillation gas flow. The level of the fuel gas flow can thus serve as a measure of the distillation progress and the conclusion of decontamination. In the system of the invention the distillation gases resulting from the thermal decontamination supply a significant proportion of the required energy.

According to another feature of the invention, the second furnace chamber is connected with the first furnace chamber by a flue gas duct. Through this duct the flue gases from the first furnace chamber can pass into the heating region of the second furnace chamber. If the flue gases from the first furnace chamber which are supplied to the second furnace chamber contain unburned distillation gas components, these components are subject to after-burning in the second furnace chamber. A monitoring of the flue gas in the second furnace chamber ensures that there will always be sufficient oxygen for this after-burning step. All of the flue gases produced in the furnace are discharged from the second furnace chamber through a combustion air preheater. This preheater serves on the one hand to effect rapid cooling of the flue gases and on the other hand to recover the heat of these flue gases. The preheating of the combustion air reduces the energy consumption of the two chamber furnace and thus increases the efficiency thereof. The rapid cooling of the flue gas reduces the tendency toward recombination of cracked toxic substances in the second furnace chamber and thus also reduces any environmental contamination by the furnace.

The bottom of the first furnace chamber has in the region below the distillation chamber an elevated smelting platform which projects out of the melt at low melt levels. This is the case during the initial charging of the first furnace chamber. The charge can then cascade onto the melt-free melting platform and not directly into the melt where an uncontrolled smelting can occur.

It has been found to be advantageous further to provide a melt pump for displacing the melt in the first furnace chamber and to also provide a throttled melt return line between the furnace chambers with the melt pump having a rate of displacement adjustable between at least two steps. At standstill of the melt pump, a uniform, low melt level prevails in both furnace chambers. This is the case during the charging of the first furnace chamber. However, upon operation of the melt pump, the melt level in the first furnace chamber rises since the return of the melt to the second furnace chamber is throttled. The melt platform is then flooded by melt which overflows onto this platform and enables a controlled smelting by direct contact of the charge with the molten metal. When a level measurement device for limiting the maximum melt level in the first chamber is provided, undesired increases above this level are avoided.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: [0043]
FIG. 1 is a vertical section through a two-chamber furnace according to the invention showing its separate distillation chamber shut off from the first furnace chamber; [0044]
FIG. 2 is a horizontal section through a two-chamber furnace diagrammatically illustrating the operation thereof; [0045]
FIG. 3[0046] a is a fragmentary vertical sectional view of a two-chamber furnace with its distillation chamber open to the exterior and with a charging carriage aligned therewith for filling the distillation chamber;
FIG. 3[0047] b is a diagram similar to that of FIG. 3a showing the charged state of the distillation chamber;
FIG. 3[0048] c is a view similar to FIG. 3a and 3 b but with the hood replaced on the distillation chamber and showing the compaction of the charge; and
FIG. 3[0049] d is a view similar to FIGS. 3a-3 c after the distillation chamber has deposited the charge on the aforementioned platform.

SPECIFIC DESCRIPTION

The two-chamber furnace [0050] 1 shown in FIG. 1 has a first furnace chamber 3 separated from a second furnace chamber 4 by a partition positioned at a short distance above the bottom of the furnace 1 so that a molten metal flow path is provided beneath the partition 2.
Above the [0051] first furnace chamber 3, a distillation chamber 5 of rectangular cross section is provided as a filling shaft for the first furnace chamber 3. It, in turn, is covered by a hood 7 toward the exterior and is closed off from the first furnace chamber by a slider 6.
The [0052] cover hood 7 is provided with a guide 8 for a pressing body 9 which is received with play within the hood and the distillation chamber 5. It can be accommodated within a space 10 matched in shape to the pressing body 9 when the pressing body is lifted. In the lifted position, the lower surface 9 a of the pressing body lies flush with the sealing surface 7 a of the hood 7.
The [0053] pressing body 9 is thus axially movable within the distillation chamber 5 and can serve to compact and thus homogenize the charge therein. This is important for a uniform passage of the gases through the charge and thus to uniform heating and decontamination thereof.
The [0054] pressing body 9 is retractable via the guide 8 into the recess 10, whereupon the hood 7, with slight lifting by the guide rail 11 can be swung to a side to thereby open the distillation chamber 5 to receive a charge. This is done after a pair of funnel members 12 have been swung into position to guide the charge. The charge is delivered by a tilting charging carriage 13 on an inclined conveyor 14.
FIG. 2 shows a horizontal section through the two-chamber furnace [0055] 1 and from this Figure it is possible to see the partition 2 which separates the first and second furnace chambers 3 and 4, the distillation chamber 5 and the slider 6. The distillation chamber 5 is connected by a first flue gas passage 15 and a second flue gas passage 16 with the furnace chamber 3 so that a circulating blower 17 with a controlled speed, can force the flue gas from the first furnace chamber 3 into the chamber 5 through an inlet opening 18. After passing through the charge in chamber 15, the flue gas is discharged via outlet opening 19 which can be directly opposite the opening 18 and is returned by the second flue gas passage 16 to the first furnace chamber 3. The resulting closed circulation ensures a forced flow through the distillation chamber 5 and its charge.
The [0056] first furnace chamber 3 is also provided with a first gas burner system 20 while the second furnace chamber 4 has a second gas burner system 21. The burner systems are supplied with air by the blower 22 which passes the air through a combustion air preheater 23 which is traversed in counterflow to the air by the flue gases discharged from the furnace via the duct 25. Flue gas from the first chamber 3 is admitted to the second chamber 4 via a passage 24 in the partition 2. The preheater 23 ensures a recovery of a sensible part of the waste heat. The melt duct 26 is provided with a melt pump 27 of the electromagnetic circulation type and recirculates the melt from the second chamber 4 of the first chamber 3. The passage below the partition 2 is shown at 28 in FIG. 2.
The energy required for preheating the charge is supplied by the first [0057] gas burner system 20. The hot flue gas circulated by the blower 17 between the first furnace chamber 3 and the distillation chamber 5 serves for the rapid and uniform heating of the charge in the chamber 5 and a decontamination thereof by destructive distillation of the contaminants. The result is a generation of distillation gases which are carried along with the circulating flue gases and are burned at least in part in the chamber 3. Because of the large surface area of the charge and the fact that the hot combustion gases forced through the charge, the decontamination and heating are especially rapid.
By varying the flue gas temperature in the [0058] first furnace chamber 3 and the speed of the circulating blower 17, the amount of heat introduced into the charge can be varied over a wide range so that peaks in the liberation of distillation gas are avoided.
The hot gas temperature is used which avoids partial melting of exposed parts of the charge. The air excess in the flue gas in the [0059] first furnace chamber 3 is detected by an O₂sensor 40 of an oxygen-measuring unit which can control the blower 22 as shown at 41. If the oxygen content drops because of the combustion of distillation gases below the setpoint value of about 2% O₂, the fuel gas supplied to the burner can be reduced by a gas control 42 responsive to the oxygen-measuring unit with a constant air supply. In this manner sufficient atmospheric oxygen is ensured for complete combustion of the distillation gases. Since the fuel gas supply is inversely proportional to the distillation gas quantity, a monitoring of the fuel gas supply can be used to indicate the progress and conclusion of decontamination.
With highly contaminated scrap (significantly more than 2% hydrocarbons) not all of the distillation gases can be burned in the [0060] first furnace chamber 3 since the heat produced by such combustion may not be required to heat the scrap. The temperature in the first furnace chamber 3 (about 600° C.) sets an upper limit for the amount of combusted distillation gas. There are phases in the distillation process in which the O₂content of the flue gas cannot be held at 2% and in which unburned distillation gas circulates between the first furnace chamber and the distillation chamber 5. The unburned distillation gas can, in that case, also pass into the second furnace chamber 4 where it is after-burned. In the second furnace chamber, to the extent that a distillation gas combustion occurs, the fuel gas supply is correspondingly reduced. By reducing the preheating of the combustion air, the heat requirement of the melting furnace and thus the permissible hydrocarbon content of the aluminum scrap can be increased.
The flue gas from the first furnace chamber passes through the [0061] opening 24 into the second furnace chamber 4 which is maintained at a constant temperature between 900 and 1100° C. by the second gas burner system 21 and in which, via another O₂sensor 43, an O₂excess is maintained.
Residual unburned hydrocarbons and toxic gases resulting from the destructive distillation, like dioxin and furanes are completely cracked or burned up because of the conditions in the [0062] second furnace chamber 4. Because of the rapid cooling of the flue gas in the combustion air preheater 23, a reformation of toxic compounds is precluded.
The second gas-burner system [0063] 21 also serves for the heating of the melt bath in the first and second chambers 3 and 4 which are connected by the melt pipe 26 and the electromagnetic melt recirculating pump 27 and via the opening 28 for the melt circulation.
The heat which is introduced into the melt bath in the [0064] second furnace chamber 4 serves to melt the charge which has been preheated to about 600° C. After decontamination is completed, by retraction of the slider 6, the charge is dropped into the melt in the first furnace chamber 3 where it is melted by contact with the molten metal in a matter of minutes. FIGS. 3a-3 d illustrate a variant of the two-chamber furnace shown in FIGS. 1 and 2.
The [0065] distillation chamber 5 here has two bottom flaps 29 instead of a slider for closing the bottom of the distillation chamber and which can be opened to allow controlled charging of the first furnace chamber 3′.
Below the [0066] distillation chamber 5 on the bottom 30 of the first furnace chamber 3 there is an elevated smelting platform 31. The melt level is variable in this embodiment. A melt pump displaces the melt into the first furnace chamber 3′ from which it flows via a throttled return duct 32 back into the second furnace chamber 4. When the melt pump is at standstill, the melt levels in the two furnace chambers is the same and low so that the smelting platform 31 is above the melt and free from the melt. When the melt pump runs, the melt level in first chamber 3′ and the throttled return flow higher and can overflow the platform 31. The height of the melt level can be limited by a level measuring device 50 shown only diagrammatically in FIG. 3b. This level measuring device can be used to control the displacement of the melt pump.
For the charging of the [0067] distillation chamber 5 an inclined conveyor 14′ is provided with a charging carriage 13′. The charging carriage 13′ is not tiltable but has two flaps 33 closing the bottom thereof and w3hich can be opened (compare FIGS. 3a and 3 b) to empty the charge into the distortion chamber. The outwardly swung flaps 33 also serve to guide the charge into the distillation chamber. The result is a uniform filling of chamber 5 with the charge which can have a variety of different slag consistencies. For charging, the hood 7 with its guide 8 and pressing member 9 is moved away from the shaft 5. The movement of the hood 7 can be effected in the manner previously described.
As can be seen from FIG. 3[0068] a, therefore, the hood 7 is initially shifted laterally with the body 9 (FIG. 3a) while the charging carriage 13′ is brought into its discharging position above the shaft 5. The melt pump is turned on and the liquid level in chamber 13′ is in its raised position in which the previous charge in in contact with the melt and the scrap thereof is in the process of melting. With the flaps 29 closed (FIG. 3b), the flaps 33 are opened and the charge in carriage 13′ is dumped into the empty distortion chamber 5. The melting of the previous charge continues on the melting platform 31. The charging carriage 13 is then shifted to receive a new charge and the hood 7 is replaced upon the distortion chamber 5 (FIG. 3c). The charge 5 is then compacted by the pressing body 9 and the charge is then heated and decontaminated. The contact melting of the previous charge is completed during this period.
As can be seen from FIG. 3[0069] d, the melt pump is turned off so that the platform 31 is free form the melt. The flaps 29 are opened and the heated and decontaminated charge is dumped upon the melt platform 31. The process can then be repeated.
The two chamber furnace of the invention has a substantially higher throughput with reduced specific energy demand by comparison with bridge systems, it provides improved melting without environmental contamination, simplified charging and better control of complete distortion. [0070]

Claims

I claim:

1. A furnace for the smelting of contaminated aluminum scrap, comprising:

a first furnace chamber adapted to receive a contaminated aluminum scrap for contacting said contaminated aluminum scrap with an aluminum melt, thereby dissolving aluminum from said scrap in said melt;

a second chamber connected to said first chamber for receiving said aluminum melt;

gas-fired burners in said chamber for heating same while producing flue gases in said chambers;

a flue-gas recirculation system connected to as least one of said chambers for withdrawing flue gas therefrom and recirculating withdrawn flue gas to the furnace;

a destructive-distillation chamber receiving a charge of said contaminated scrap for decontaminating said charge and connectable to said first chamber; and

means connected with said flue-gas recirculation system for forcing hot flue gas through said destructive-distillation chamber to destroy contaminants on said charge.

2. The furnace defined in

claim 1

wherein said means connected with said flue gas recirculation system comprises at least one inlet into said destructive-distillation chamber for hot flue gas and at least one outlet opposite said inlet for discharging said hot flue gas.

3. The furnace defined in

claim 2

wherein said destructive-distillation chamber is formed as a filling shaft for said first furnace chamber and is separated from said first furnace chamber by a closure element.

4. The furnace defined in

claim 3

wherein said shaft is generally upright and said closure element is comprised of a pair of bottom flaps or a slider which opens over the entire cross section of said destructive-distortion chamber.

5. The furnace defined in

claim 4

wherein said destructive-distillation chamber has a rectangular cross section, said furnace further comprising a pressing body displaceable with play in said destructive-distillation chamber and adapted to compact a charge therein.

6. The furnace defined in

claim 5

, further comprising a hood adapted to cover said destructive-distillation chamber and removable therefrom to enable filling of said charge into said destructive-distillation chamber, said hood being provided with a guide for said pressing body.

7. The furnace defined in

claim 6

wherein each of said furnace chambers comprises a respective gas burner system, each of said gas burner systems having an O₂sensor for controlling conbustion in the respective chamber to maintain a constant air excess therein.

8. The furnace defined in

claim 7

wherein the gas burner system of said first furnace chamber maintains a flue gas temperature of substantially 600° C. therein and the gas pressing system of said second chamber maintains a flue gas temperature of about 1000° C. therein.

9. The furnace defined in

claim 8

, further comprising means for controlling inensity of distortion gas formation in the destructive-distillation chamber by controlling temperature and velocity of flue gas through said destructive-distillation chamber.

10. The furnace defined in

claim 9

, further comprising means for controlling fuel gas flow to said burner system in inverse proportion to generation of distillation gases in said dstructive-distillation chamber.

11. The furnace defined in

claim 10

, further comprising a flue gas outlet in said second chamber connected with a combustion air preheater.

12. The furnace defined in

claim 11

, further comprising a flue gas passage connecting said first and second chambers.

13. The furnace defined in

claim 12

wherein said first chamber is provided with an elevated smelting platform above a level of melt in said first and second chambers when said level of said melt in said first and second chambers is equal.

14. The furnace defined in

claim 12

, further comprising a melt pump for pumping molten metal from said second chamber into said first chamber and a throttled return passage connecting said first chamber to said second chamber, said pump having at least two speed settings.

15. The furnace defined in

claim 14

, further comprising a level measuring device for establishing a maximum liquid level in said first chamber.