DE102013012831A1 - Process for melting contaminated aluminum - Google Patents

Abstract

The present invention relates to a method for melting contaminated aluminum (101) in a rotary drum furnace (100), a rotary drum furnace (100), and a use of a mixed gas (111). The rotary drum furnace (100) is heated by means of a burner (110), wherein the burner (110) is fired with a gas mixture (111) of fuel, oxygen and air, wherein the burner (110) with the gas mixture (111) in a mixing ratio of fuel, oxygen and air is fired so that the burner (110) is fired in a superstoichiometric combustion ratio with a lambda value greater than 1.

Description

The invention relates to a method for melting contaminated aluminum in a rotary drum furnace and a rotary drum furnace, wherein the rotary drum furnace is heated by a burner and the burner is fired with a gas mixture of fuel, oxygen and air. The invention further relates to a use of a gas mixture of fuel, oxygen and air for a burner of a rotary drum furnace for melting contaminated aluminum.

State of the art

Kleinstückeliger aluminum scrap, especially aluminum shavings, but also cans and scrap film, generally have organic impurities in the form of cutting agents, oils, paints, plastics and the like. Melting of such contaminated aluminum takes place today especially in rotary drum furnace. By means of such rotary drum furnaces, a melt refining or a working up of the contaminated aluminum is made possible. In order to produce the necessary temperatures for this, the rotary drum furnace in question is heated from the inside via a burner, wherein a uniform drum rotation ensures the switching and mixing of the material introduced into the rotary drum furnace and to be melted.

Such a rotary drum furnace is for example from the DE 10 2008 029 512 A1 known. A rotary drum furnace is heated with a burner. The burner burns fuel and a primary oxidizer in a flame. A lance is used to direct a secondary oxidant to the flame. The secondary oxidant has a high oxygen content of advantageously more than 95%.

From the DE 100 46 569 A1 a special burner is known for furnaces for smelting aluminum. The burner is operated by means of a gas mixture of a fuel, in particular natural gas, air and oxygen.

Aluminum reacts very quickly with oxygen to form alumina. In rotary drum furnaces, oxidation of the aluminum can thus occur, which leads to metal loss. Burners of a rotary drum furnace, which are operated with a fuel-air-oxygen mixture, are always operated in a substoichiometric combustion ratio with a lambda value less than 1. Oxygen deficiency of the stoichiometric ratio can limit unwanted oxidation of the aluminum.

Due to the substoichiometric operation of a burner, however, there are considerable disadvantages and problems of a corresponding rotary drum furnace for melting contaminated aluminum. On the one hand, only a low degree of efficiency can be generated and high metal losses or high aluminum burnup occur at high temperatures. On the other hand, large quantities of carbon monoxide and unburned hydrocarbons are produced. This results in a high safety and health risk. In particular, a permissible maximum workplace concentration (MAK) by the resulting carbon monoxide hardly or not at all be respected. Furthermore, a maximum permissible limit of carbon in the half-hourly average of 50 mg / nm ^{3 is} exceeded. Typically occurring values of carbon in the half-hourly average may be from ³ to 1000 mg / nm ³ for rotary drum furnaces at 450 mg / nm.

It is therefore desirable to provide a means for smelting contaminated aluminum which reduces safety and health hazards, increases efficiency, and reduces aluminum burn-up.

Disclosure of the invention

This object is achieved by a method for melting contaminated aluminum in a rotary drum furnace, a rotary drum furnace and a use of a gas mixture of fuel, oxygen and air for a burner of a rotary drum furnace according to the independent claims. The rotary drum furnace is heated by means of a burner. The burner is fired with a gas mixture of fuel, oxygen and air. The burner is fired with the gas mixture in a mixing ratio of fuel, oxygen and air so that the burner is fired in a superstoichiometric combustion ratio with a lambda value greater than 1. Advantageous embodiments will become apparent from the dependent claims and the description below.

Under contaminated aluminum is to be understood that the aluminum has organic impurities in the form of, for example, cutting agents, oils, paints and / or plastics. Such contaminated aluminum or contaminated aluminum scrap in particular has aluminum in the form of aluminum chips.

In particular, natural gas is used as fuel for the gas mixture of fuel, oxygen and air. Oxygen or air serve in particular as an oxidizing agent.

Advantages of the invention

The invention is based on the finding that there are considerable advantages when a burner of a rotary drum furnace for melting contaminated aluminum in a superstoichiometric combustion ratio with the lambda value greater than 1 is fired with excess oxygen. Conventional burners for such rotary drum furnaces are always operated stoichiometrically, with lambda values of typically between 0.7 and 0.8.

According to the invention, such a burner is now operated with a lambda value of far more than 1. Since aluminum reacts very quickly with oxygen and as a result unwanted aluminum burn-up, it is per se counter-intuitive to operate the burner more than stoichiometrically and thus to provide more oxygen for the oxidation of the aluminum. Preferably, the burner is fired in a superstoichiometric combustion ratio with a lambda value of 1.5 to 10, more preferably 5.

In the context of the invention, however, it has been shown that effects are associated with a superstoichiometric operation of a burner, which prevent unwanted oxidation of the aluminum. Due to the superstoichiometric combustion ratio with the lambda value greater than 1, a flame of the burner to relatively lower temperatures - compared to burners in a substoichiometric combustion ratio with a lambda value less than 1 - set. In particular, the burner is operated with a minimum burner power. The aluminum is not yet melted down, but abgeschwwelt. As a result of this comparatively low flame temperature and the superstoichiometric combustion ratio with the lambda value greater than 1, the contaminated aluminum in the rotary drum furnace is only heated to such an extent that organic constituents are exhausted. In this case, a carbon layer or soot layer forms on the aluminum. This carbon layer serves as a protective layer and protects the aluminum from reaction with oxygen and thus from oxidation. Thus, metallic spreading can be increased and aluminum burning can be reduced.

By a high exit pulse, with which the fuel and the oxidant leaves the burner at a burner mouth, in conjunction with a comparatively low flame temperature and with the superstoichiometric combustion ratio with the lambda value greater than 1, it is further ensured that exhaust gases are sucked into the rotary drum furnace, mixed and returned to the rotary drum furnace. By a sufficient, suitable pulse or a pulse current density of the fuel and the oxidant, which are supplied to the burner and the rotary drum furnace, exhaust gases are sucked in the rotary drum furnace from the burner. This suction prevents the corresponding exhaust gases from leaving the rotary drum furnace. Instead, the exhaust gases together with the gas mixture or the flame of the burner are returned to the rotary drum furnace. Recirculation of the exhaust gases is understood to mean that the exhaust gases are prevented from leaving the rotary drum furnace and instead move back to the interior of the rotary kiln or toward a center of the rotary kiln. Thus, a circulation of the exhaust gases is effected. The exhaust gases are sucked in the form of an additional fuel into the flame, mixed and oxidized. These chemical reactions or burns generate heat, which is fed to the melting process in the rotary drum furnace and is available for the further smelting process. The heat is transferred to a large extent to a wall or walls of the rotary drum furnace. The wall or walls of the rotary drum furnace transmits or transmit the heat to the melt.

By this suction and return of the exhaust gases, the temperature of the flame of the burner is further reduced and maintained at a relatively low value. In particular, the burner is fired so that a pulse current density of the burner and / or the exhaust gases is maintained above a lower limit. This lower limit of the pulse current density is in particular 5400 N / m ² . By controlled and stable burning of the flame of the burner, the suction and return of the exhaust gas is maintained and it is prevented that the unburned exhaust gas is sucked, for example, into an exhaust pipe and an exhaust hood and leaves the rotary drum furnace. Suction and return of the exhaust gases through the burner are ensured and an appropriate penetration depth of the burner and / or the exhaust gases in the rotary drum furnace is achieved. The depth of penetration is to be understood in particular as the extent to which the gas mixture of the burner or the exhaust gases move into the interior of the rotary drum furnace or in the direction of a center of the rotary drum furnace. A resulting pulse stream from the burner and the exhaust gas is very uniform in temperature and in an oxygen distribution. Thus, it is achieved that there are no locations in the rotary drum oven with localized overheating associated with a high concentration of oxygen.

The fuming of the aluminum is controlled by the invention, controlled and stable. By the invention, the Abschwelen of Aluminum scrap can be significantly accelerated. Whereas according to the prior art values of 15 to 30 minutes are typical for the defluxing of the aluminum, in the context of the invention this can take place in substantially shorter time periods, in particular in only two minutes. The energy consumption and thus the cost of the rotary drum furnace or the melting process can thus be reduced.

Furthermore, temperatures of exhaust gases are reduced, for example to 270 ° C compared to, for example, 500 ° C according to the prior art. Thus, the (firing) energy consumption of the rotary drum furnace or the melting process are reduced and increases the efficiency.

In the course of the invention in particular carbon monoxide is burned in the rotary drum furnace itself, which brings a reduction in energy costs. An amount of carbon monoxide in the breathing air is thus reduced. A permissible maximum workplace concentration (MAK) for carbon monoxide can thus be maintained. Furthermore, a maximum permissible limit of carbon in the half-hourly average of 50 mg / nm ^{3 is} not exceeded. Safety and health risks are considerably reduced by the invention.

In addition, the invention achieves further significant advantages over the prior art. Flashbacks in an exhaust system as well as overheating of, in particular, exhaust pipes and / or an exhaust hood are reduced. A thermal load on a lining or walls of the rotary drum furnace is reduced. Thus, only a small amount of refractory wear occurs in the course of the invention.

Advantageously, by means of the mixing ratio of fuel, oxygen and air, the temperature of the flame of the burner is set to a value above a lower limit and / or below an upper limit. The upper limit is preferably 1400 ° C, more preferably 1250 ° C to 1200 ° C. The lower limit is chosen in particular such that the aluminum does not burn, but nevertheless a safe combustion is guaranteed. Preferably, the lower limit of the temperature of the flame is 800 ° C. When smelting contaminated aluminum at temperatures below 800 ° C, the flame of the burner would burn unstably and the melting process take too long.

Preferably, the benner is fired with the gas mixture in a mixing ratio of 55% to 59% oxygen, 5% to 6% fuel and 35% to 39% nitrogen. In order to obtain a stable combustion and to ensure that the flame of the burner does not go out, a proportion of natural gas in the mixing ratio is chosen such that an ignition limit of natural gas in air is not undershot. The proportion of natural gas in the mixing ratio is therefore in particular at least 5%. Unless otherwise stated, "%" means "% by volume".

Advantageously, the burner is fired with the gas mixture in the mixing ratio such that the rotary drum furnace is operated in a substoichiometric combustion ratio with a lambda value less than 1. The lambda value of the rotary drum furnace is given by the fuel of the burner and exhaust gases or carbonization in the rotary drum furnace. The burner is thereby still fired in a superstoichiometric combustion ratio with the lambda value greater than 1. This ensures that as little aluminum burns as possible. The rotary drum furnace is preferably operated in a combustion ratio with a lambda value between 0.7 and 0.95, more preferably in a combustion ratio with a lambda value of 0.9. In particular, the lambda value in the rotary drum furnace is adjusted by means of an exhaust gas temperature. The exhaust gas temperature can be determined, for example, by means of measuring probes, in particular infrared measuring probes. Such measuring probes can be arranged inside the rotary drum furnace, in an exhaust pipe or an exhaust system or an exhaust hood. The exhaust gas temperature can also be determined by means of an exhaust gas analysis. Alternatively or additionally, the lambda value in the rotary drum furnace can be adjusted by means of an observation or analysis of the flameout of the burner.

The invention relates to a further second method for melting contaminated aluminum scrap in a rotary drum furnace, which takes place in two phases. In a first phase, a desulphurisation phase, the burner of the rotary drum furnace is operated in accordance with one embodiment of the above-described first method according to the invention. In a subsequent second phase, a melting phase, the burner is fired with the gas mixture in a second mixing ratio of fuel, oxygen and air such that the burner is fired in a substoichiometric combustion ratio with a lambda value less than 1. Embodiments of this second method of the invention will become apparent from the above description of the method according to the invention in an analogous manner.

Due to the fact that, in the first phase, the burner is initially operated according to the invention in a superstoichiometric combustion ratio with the lambda value greater than 1, it is initially the protective carbon layer of aluminum is formed. The interior of the rotary kiln has a black to dark red color after the first phase and is evenly heated. After the first phase of the burner is fired in the meltdown phase in a substoichiometric combustion ratio with a lambda value less than 1. The burner is operated with a small amount of oxygen and a lack of oxygen at high power.

Although the burner is operated according to the prior art in the melting phase, the combination of the first phase according to the invention and the second phase achieves considerable advantages over the prior art. The protective carbon layer protects the aluminum from oxidation and reaction with oxygen. The aluminum can be melted in the second phase, without any unwanted oxidation of the aluminum takes place. The metallic spreading is increased and aluminum burning is reduced. Since carbon monoxide is burned in the rotary drum furnace itself in the course of the first phase in the first phase and an amount of carbon in the half hourly means is reduced, the permissible maximum workplace concentration (MAK) for carbon monoxide and the maximum permissible limit of Carbon in half-hourly means not exceeded. Safety and health risks of the entire smelting process of contaminated aluminum are thereby reduced.

The invention further relates to a rotary drum furnace and a use of a gas mixture of fuel, oxygen and air for a burner of a rotary drum furnace. Embodiments of the rotary drum furnace according to the invention and the use according to the invention will become apparent from the above description of the inventive method in an analogous manner.

In an advantageous embodiment of a rotary drum furnace according to the invention, the burner is arranged in the rotary drum furnace such that the flame of the burner is directed between the contaminated aluminum and a wall or walls of the rotary drum furnace. The flame of the burner is directed in particular into a free space between the melt and wall of the rotary kiln in the furnace chamber. In particular, the flame is directed closer to the wall of the rotary kiln than to the melt. Under the furnace chamber is to be understood in particular the interior of the rotary drum furnace. Under the melt is in particular the melted or abgeschwelte aluminum to understand.

Rotary drum furnaces are usually designed such that hot gases leave the same above a door of the rotary drum furnace, for example through an exhaust gas opening. The burner or a nozzle of the burner is therefore arranged in particular within this door of the rotary drum furnace. In particular, the burner is arranged such that the flame of the burner, or the pulse stream of the burner above the door of the rotary drum furnace enters the same.

The flame of the burner comes close to a wall of the rotary kiln, but does not touch it. Energy from pyrolysis gas oxidations, which take place in the course of the melting process of the aluminum scrap in the rotary drum furnace, is largely transferred to the wall or walls of the rotary drum furnace. The wall or walls of the rotary drum furnace in turn transmit this energy to the aluminum. A rotational speed of the rotary drum furnace is chosen such that the wall or walls of the rotary drum furnace can absorb and transmit a lot of energy. In particular, the speed of the rotary drum furnace is 1 to 6 revolutions per minute. In a horizontal rotary drum furnace, the burner is arranged in particular such that the flame of the burner is opposite to the flow of exhaust gas (through suction and return) and burns close to the wall or walls of the rotary drum furnace.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

1 schematically shows a preferred embodiment of a rotary drum furnace according to the invention, which is adapted to carry out a preferred embodiment of a method according to the invention.

In the only one 1 is designed as a rotary drum furnace furnace shown schematically and with 100 designated. The rotary drum oven 100 is designed to contain contaminated aluminum 101 melt and perform a preferred embodiment of a method according to the invention.

By means of a door 102 Can the still solid aluminum 101 in the rotary drum oven 100 be introduced. Furthermore, the rotary drum furnace 100 by means of the door 102 locked. The door 102 is fixed and not rotatable.

The rotary drum oven 100 also has a burner 110 on. The burner 110 is in the door 102 arranged. The burner 110 has three lines 110a . 110b and 110c on. By means of each of these three lines, a gas is supplied to the burner. For example, the burner 110 over the line 110a a fuel in the form of natural gas, via the pipe 110b high purity oxygen and over the line 110c Supplied with air. At an outlet of the burner 110 The natural gas, the oxygen and the air are mixed to a gas mixture. A control unit 150 , For example, a suitably ausgestaltetes control unit, it sets a mixing ratio of this gas mixture of natural gas, oxygen and air. The control unit 150 controls in particular control valves of the lines 110a . 110b and 110c such that adjusts the corresponding mixing ratio. The burner burns this gas mixture 111 causing a burner flame 112 arises.

Via an exhaust duct 103 , above the door 102 is arranged, exhaust gas from the rotary drum furnace 100 dissipated. An exhaust hood 104 sucks in the exhaust gases which pass through the exhaust duct 103 leave the rotary drum oven, indicated by the reference numeral 104a ,

Via an electric drive (motor) 105 becomes the rotary drum furnace 100 rotated at a certain speed. In particular, we use this speed through the control unit 150 set.

The burner 110 is in particular arranged such that the flame 112 the burner of a wall 102 of the rotary drum furnace 100 comes close, but this does not touch. The wall 102 of the rotary drum furnace 100 is in particular made of a refractory steel shell.

The three lines 110a . 110b and 110c of the burner 110 are arranged coaxially and formed such that the respective gas burner 110 leaves in the axial direction. For a detailed description of such a burner is on the DE 100 46 569 A1 referred to the same applicant.

The control unit 150 is further adapted to perform a preferred embodiment of a method according to the invention. At the same time, the control unit 150 the mixing ratio of natural gas, oxygen and air such that the burner 110 is fired in a superstoichiometric operation. The control unit 150 sets the mixing ratio in such a way that the burner 110 in a superstoichiometric combustion ratio with a lambda value of 5, thereby ensuring that the rotary drum furnace 100 is fired in a substoichiometric combustion ratio with a lambda value of 0.9 and the flame 112 of the burner 110 a temperature above a lower limit of 800 ° C and below an upper limit of preferably 1400 ° C, more preferably 1250 ° C. Preferably, the mixing ratio is about 57% oxygen, about 5-6% fuel and about 37% nitrogen.

A volume flow of oxygen and air or an amount of oxygen and air supplied through the lines 110b and 110c is chosen to be identical in particular.

By the pulse or the pulse current density with which the gas mixture 111 the burner 110 leaves exhaust gases in the rotary drum furnace 100 from the burner 110 sucked and the rotary drum furnace 100 again returned or supplied, indicated by the reference numeral 130 , The exhaust gases are thus from the burner 110 out again into the interior of the rotary kiln 100 or in the direction of a center of the rotary drum furnace 100 emotional. The burner 110 is in the door 102 arranged such that this sucking and returning 130 be enabled. This will prevent exhaust gases through the exhaust duct 103 the rotary drum furnace 100 leave, whereby they are mostly burned in the same. A theoretical pulse current density without ignition of the burner is due to an exit of the burner at 5400 N / m ² .

The control unit 150 is still set to the burner 110 to fire in a second phase according to a preferred embodiment of a method according to the invention. At the same time, the control unit 150 the mixing ratio of the gas mixture 111 such a thing that the burner 110 is now fired in a substoichiometric combustion ratio with a lambda value less than 1.

LIST OF REFERENCE NUMBERS

100

Rotary furnace

101

contaminated aluminum

102

door

102

wall

103

exhaust duct

104

exhaust hood

104a

extracted exhaust gas

105

electric drive

110

burner

110a

Pipe for natural gas

110b

Pipe for oxygen

110c

Lead for air

111

mixture of gases

112

flame

130

Aspiration and recirculation of exhaust gas

150

control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008029512 A1 [0003]
• DE 10046569 A1 [0004, 0039]

Claims (13)

Process for melting contaminated aluminum ( 101 ) in a rotary drum oven ( 100 ), which by means of a burner ( 110 ) is heated, - wherein the burner ( 110 ) with a gas mixture ( 111 ) is fired from fuel, oxygen and air, characterized in that - the burner ( 110 ) with the gas mixture ( 111 ) is fired in a mixing ratio of fuel, oxygen and air such that the burner ( 110 ) is fired in a superstoichiometric combustion ratio with a lambda value greater than 1. Method according to claim 1, wherein a temperature of a flame (by means of the mixing ratio of fuel, oxygen and air ( 112 ) of the burner ( 110 ) is set to a value above a lower limit. Method according to claim 2, wherein the lower limit of the temperature of the flame ( 112 ) Is 800 ° C. Method according to one of the preceding claims, wherein by means of the ratio of fuel, oxygen and air, the temperature of the flame ( 112 ) of the burner ( 110 ) is set to a value below an upper limit. Method according to claim 4, wherein the upper limit of the temperature of the flame ( 112 ) 1400 ° C, in particular 1200 ° C to 1250 ° C, is. Method according to one of the preceding claims, wherein the Benner ( 110 ) with the gas mixture ( 111 ) in a mixing ratio of 55% to 59% oxygen, 5% to 6% fuel and 35% to 39% nitrogen. Method according to one of the preceding claims, wherein the burner ( 110 ) with the gas mixture ( 111 ) is fired in the mixing ratio such that the rotary drum furnace ( 100 ) is operated in a substoichiometric combustion ratio with a lambda value less than 1. Method according to claim 7, wherein the burner ( 110 ) with the gas mixture ( 111 ) is fired in the mixing ratio such that the rotary drum furnace ( 100 ) is operated in a substoichiometric combustion ratio with a lambda value between 0.7 and 0.95, in particular 0.9. Method according to one of the preceding claims, wherein the burner ( 110 ) with the gas mixture ( 111 ) in the mixing ratio in a superstoichiometric combustion ratio with a lambda value between 1.5 and 10, in particular 5, is fired. Process for melting contaminated aluminum ( 101 ) in a rotary drum oven ( 100 ), which by means of a burner ( 110 ) is heated, - wherein the burner ( 110 ) with a gas mixture ( 111 ) is fired from fuel, oxygen and air, characterized in that - the burner ( 110 ) is first fired in a first phase according to a method according to one of the preceding claims and - the burner ( 110 ) in a second phase with the gas mixture ( 111 ) is fired in a second mixing ratio of fuel, oxygen and air such that the burner ( 110 ) is fired in a substoichiometric combustion ratio with a lambda value less than 1. Rotary drum furnace ( 100 ) comprising a burner ( 110 ), - the burner ( 110 ) a feeder ( 110a . 110b . 110c ) of a gas mixture ( 111 ) of fuel, oxygen and air, characterized in that - a control unit ( 150 ) is adapted to the burner with the gas mixture ( 111 ) supply of fuel, oxygen and air in a mixing ratio of fuel, oxygen and air in such a way that the burner ( 110 ) is fired in a superstoichiometric combustion ratio with a lambda value greater than 1. Rotary drum furnace ( 100 ) according to claim 11, wherein the burner ( 110 ) in the rotary drum furnace ( 100 ) is arranged such that a flame ( 112 ) of the burner ( 110 ) between the contaminated aluminum ( 101 ) and a wall ( 102 ) of the rotary drum furnace ( 100 ). Use of a gas mixture ( 111 ) of fuel, oxygen and air for a burner ( 110 ) of a rotary drum furnace ( 100 ) for melting contaminated aluminum ( 101 ) in such a mixing ratio of fuel, oxygen and air that the burner ( 110 ) is fired in a superstoichiometric combustion ratio with a lambda value greater than 1.

Images