U.S. patent application number 10/375596 was filed with the patent office on 2003-07-10 for aluminium base alloy of scrap metal and casting alloy produced from this.
Invention is credited to Koch, Hubert, Krug, Peter, Ost, Gerhard, Schramm, Horst.
Application Number | 20030129077 10/375596 |
Document ID | / |
Family ID | 8243217 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030129077 |
Kind Code |
A1 |
Koch, Hubert ; et
al. |
July 10, 2003 |
Aluminium base alloy of scrap metal and casting alloy produced from
this
Abstract
An aluminium base alloy for production of casting alloys with
magnesium as the most essential alloy element contains at least 50%
scrap metal on primary aluminium base and as the remainder primary
aluminium and/or scrap metal on secondary aluminium base of known
composition. For production of the aluminium base alloy mainly
foodstuff and animal feed packings are used, separated with a
pyrolysis process and then the aluminium contained in the packing
recycled by melting. The casting alloys produced from the aluminium
base alloy are suitable in particular for production of
heat-resistant and/or corrosion-resistant parts in the engine area,
in particular for production of engine blocks, cylinder heads and
oil sumps, by means of sand casting, chilled casting, diecasting,
thixocasting or thixoforging.
Inventors: |
Koch, Hubert; (Rheinfelden,
DE) ; Schramm, Horst; (Loerrach, DE) ; Krug,
Peter; (Schopfheim, DE) ; Ost, Gerhard;
(Rheinfelden, DE) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510
US
|
Family ID: |
8243217 |
Appl. No.: |
10/375596 |
Filed: |
February 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10375596 |
Feb 27, 2003 |
|
|
|
09741469 |
Dec 19, 2000 |
|
|
|
Current U.S.
Class: |
420/542 ;
75/687 |
Current CPC
Class: |
Y02P 10/20 20151101;
C22B 21/0092 20130101; C22C 21/08 20130101; Y02P 10/234 20151101;
B21J 5/004 20130101; C22B 21/0069 20130101; Y02P 10/218
20151101 |
Class at
Publication: |
420/542 ;
75/687 |
International
Class: |
C22C 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
EP |
99811210.6 |
Claims
1. Aluminium base alloy for production of casting alloys with
magnesium as the most essential alloy element, characterised in
that it contains at least 50% scrap metal on a primary aluminium
base and as the residue primary aluminium and/or scrap metal on a
secondary aluminium base of known composition.
2. Aluminium base alloy according to claim 1, characterised in that
it consists at least 80%, preferably 100%, of scrap metal on a
primary aluminium base.
3. Aluminium base alloy according to claim 1 or 2, characterised in
that the scrap metal on a primary aluminium base is mainly
recycling metal obtained from foodstuff or animal feed packing.
4. Process for production of an aluminium base alloy according to
any of claims 1 to 3, characterised in that materials on a primary
aluminium base contaminated with organic compounds are prepared
separately according to their thermal value and their aluminium
content, combined in measured quantities to achieve a nominal
value, the organic compounds carbonised by pyrolysis with formation
of pyrolysis gas and pyrolysis coke, the pyrolysis coke separated
off, the materials pretreated in this way are where applicable
bright annealed, and where applicable are sorted to separate out
foil constituents, and then melted.
5. Process according to claim 4, characterised in that aluminium
compound substances are reduced to a unit size and the iron parts
separated out after pyrolysis.
6. Process according to claim 4 or 5, characterised in that the
materials which are prepared separately are combined to achieve a
nominal value by way of a computer-controlled metering system,
where as applicable in addition to the thermal value and aluminium
content of the materials, further parameters of the materials
treated can be taken into account, in particular their moisture,
apparent density and grain size.
7. Casting alloy made from an aluminium base alloy according to any
of claims 1 to 3, characterised in that it also contains 3.0 to 5.0
w. % magnesium and 1.5 to 3.0 w. % silicon.
8. Casting alloy according to claim 7, characterised in that it
also contains 0.5 to 1.2 w. % manganese and/or 0.5 to 1.2 w. %
copper.
9. Casting alloy according to claim 7 or 8, characterised in that
it also contains max 0.2 w. % titanium.
10. Casting alloy according to any of claims 7 to 9, characterised
in that it also contains max 0.4 w. % cobalt, max 0.4 w. % cerium
and max 1.2 w. % zirconium.
11. Process for production of a casting alloy according to any of
claims 7 to 10, characterised in that to a melt of the aluminium
base alloy, including where applicable added further alloy
elements, are added 0.02 to 0.15 w. % vanadium, preferably 0.02 to
0.08 w. % vanadium, in particular 0.02 to 0.05 w. % vanadium and
less than 60 ppm beryllium.
12. Use of a casting alloy according to any of claims 7 to 10
produced from an aluminium base alloy according to any of claims 1
to 3 to produce heat-resistant and/or corrosion-resistant parts in
the engine area, in particular for production of engine blocks,
cylinder heads and oil sumps, by means of sand casting, chilled
casting, diecasting, thixocasting and thixoforging.
Description
[0001] The invention concerns an aluminium base alloy for
production of casting alloys with magnesium as the most essential
alloy element. The scope of the invention also includes a process
for production of the aluminium base alloy, casting alloys produced
from the aluminium base alloy and a process for their
production.
[0002] For the production of heat-resistant and/or
corrosion-resistant parts in the engine area of vehicles, today
largely remelt alloys are used, also known as secondary aluminium
alloys or scrap metal on a secondary aluminium base. Because of the
composition of the standard secondary aluminium alloys, castings
produced from this usually only have a slight elongation of less
than 1%. For certain applications higher elongation values would be
desirable without the alloys needing to be produced from relatively
costly primary or virgin metal.
[0003] DE-C-1483229 discloses AlMgSi alloys made from secondary
aluminium alloys or secondary metals for production of cylinder
heads.
[0004] EP-A-0779371 and EP-A-0780481 disclose a process for
preparation of aluminium-containing waste for recovery of aluminium
from this waste. The essential core of this known process is the
recovery of aluminium from materials contaminated with organic
components, in particular from foodstuff and animal feed packing,
in the form of printed and/or painted aluminium waste or
aluminium/plastic compound material waste.
[0005] The invention is based on the task of preparing a low cost
aluminium base alloy for production of casting alloys. Casting
alloys made from the aluminium base alloy are suitable amongst
others for production of heat-resistant and/or corrosion-resistant
parts in engine areas.
[0006] The task according to the invention is solved by an
aluminium base alloy which contains at least 50% scrap metal on a
primary aluminium base and as the remainder primary aluminium
and/or scrap metal on a secondary aluminium base of known
composition.
[0007] The use of scrap metal on a primary aluminium base, i.e.
primary alloys, leads to a relatively "pure" base material without
high contents of generally undesirable accompanying elements.
[0008] If the content of undesirable accompanying elements is too
high for a particular application, in this case the aluminium base
alloy can be "diluted" with primary aluminium. In general, however,
it should be noted that the scrap composition for production of an
aluminium base alloy with a low content of undesirable accompanying
elements is preselected accordingly before production of the scrap
metal. Secondly, the aluminium base alloy can in principle contain,
as well as the scrap metal on a primary aluminium base, also a
certain proportion of scrap metal on a secondary aluminium base,
but in this case the composition of the scrap metal should be known
so that the quantity of undesirable accompanying elements
introduced into the aluminium base alloy is not too great.
[0009] Preferably the proportion of primary alloys is at least 80%
and ideally 100% of the scrap metal used.
[0010] Suitable scrap metal on a primary aluminium base is mainly
recycling metal obtained from foodstuff and animal feed
packaging.
[0011] For the production of a casting alloy from the aluminium
base alloy according to the invention, magnesium can also be added
up to a total content of 3.0 to 5.0 w. % and silicon up to a total
content of 1.5 to 3.0 w. %. Further additional alloy elements are
0.5 to 1.2 w. % manganese and/or 0.5 to 1.2 w. % copper and max 0.2
w. % titanium, max 0.4 w. % cobalt, max 0.4 w. % cerium and max 1.2
w. % zirconium.
[0012] The casting alloys produced from primary aluminium alloys
according to the invention achieve a higher elongation, which can
be up to 6%, in relation to the casting alloys produced from
secondary aluminium alloys according to the state of the art.
[0013] A process particularly suited for production of the
aluminium base alloy according to the invention is characterised in
that materials on a primary aluminium base contaminated with
organic compounds are prepared separately according to their
thermal value and their aluminium content, combined in measured
quantities to achieve a nominal value, the organic compounds
carbonised by pyrolysis with formation of pyrolysis gas and
pyrolysis coke, the pyrolysis coke separated off, the materials
pretreated in this way are where applicable bright annealed, and
where applicable sorted to separate out foil constituents, and then
melted.
[0014] Here, aluminium compound substances are suitably reduced to
a unit size and after pyrolysis at least the iron parts are
separated out.
[0015] In a suitable version of the process according to the
invention, the separately prepared materials are combined to set
the nominal value by way of a computer-controlled metering system,
where in addition to the thermal value and the aluminium content of
the materials, further parameters of the materials prepared can be
taken into account, in particular their moisture, apparent density
and grain size.
[0016] Depending upon the area of application of the casting alloy
produced from the aluminium base alloy, with the known process by
combining scrap or waste of various types, the composition of the
aluminium base alloy can be set within certain limits i.e. the
process allows in a simple manner the production of different
aluminium base alloys for different applications. Tables 1 to 3
show as examples three mixtures of different scrap metals. The
typical compositions of the individual scrap metals relate to 100%
aluminium alloy. The tables also contain typical further
compositions of aluminium base alloys produced from the three scrap
mixtures. Here:
[0017] DSD material is combined packaging material provided by the
system Duales System Deutschland
[0018] IGORA material is combined packing material produced by the
Swiss collection point IGORA
[0019] mixed aluminium waste is presorted packing and other
aluminium waste of various origins.
1TABLE 1 Mixture I 50% DSD Material 50% bottle Composition in w. %
caps Si Fe Cu Mn Mg Cr Ni Zn DSD material 0.20 0.60 0.10 0.40 0.30
0.01 0.01 0.05 Foreign 0.10 2.00 1.00 -- -- 0.11 0.05 1.70
substances in DSD material Total DSD 0.30 2.60 1.10 0.40 0.30 0.12
0.06 1.75 material Bottle caps 0.20 0.50 0.16 0.52 0.20 0.02 0.01
0.03 Aluminium 0.24 1.20 0.50 0.48 0.25 0.06 0.05 0.30 alloy 1
[0020]
2TABLE 2 Mixture II 40% IGORA material 35% DSD material 25% mixed
Composition in w. % Al waste Si Fe Cu Mn Mg Cr Ni Zn IGORA 0.28
1.00 0.14 0.35 0.18 0.012 0.01 0.05 material Total DSD 0.30 2.60
1.10 0.40 0.30 0.12 0.06 1.75 material Mixed 0.50 0.43 2.90 0.40
0.28 0.03 0.03 2.85 Al waste Aluminium 0.37 1.13 1.10 0.40 0.30
0.03 0.03 0.60 alloy II
[0021]
3TABLE 3 Mixture III 50% DSD Material 25% bottle caps Composition
in w. % 25% cans Si Fe Cu Mn Mg Cr Ni Zn DSD material 0.30 0.54
0.77 0.43 0.07 0.016 0.10 1.80 total Bottle caps 0.20 0.50 0.16
0.52 0.20 0.02 0.01 0.03 Cans 0.20 0.40 0.16 0.77 0.83 0.01 0.01
0.02 Aluminium 0.20 0.49 0.50 0.55 0.32 0.02 0.05 0.45 alloy
III
[0022] The following comments should be made on the composition of
the scrap materials given in the table:
[0023] The relatively high proportion of zinc in the DSD material
including the foreign substances is largely retained in the coke
during pyrolysis so that the aluminium base alloy has a relatively
low Zn content.
[0024] The composition of the aluminium base alloy cannot be
determined theoretically from the compositions of the individual
scrap metals of a mixture because packaging waste in particular
contains a lot of plastic and adhering foreign substances such as
foodstuff residue, and therefore the aluminium proportion in this
scrap material is considerably less than with practically pure
metal scrap such as for example cans or bottle tops.
[0025] In a particularly preferred process for production of a
casting alloy starting from an aluminium base alloy, to a melt of
aluminium base alloy including, where applicable, added further
alloy elements are 0.02 to 0.15 w. % vanadium, preferably 0.02 to
0.08 w. % vanadium, in particular 0.02 to 0.05 w. % vanadium and
less than 60 ppm beryllium.
[0026] The addition of vanadium leads to a higher scabbing
resistance of the casting alloy than is possible with a beryllium
addition according to the state of the art. It has namely been
observed that the beryllium content of an aluminium magnesium alloy
in the melt diminishes with time. When the beryllium concentration
falls below a critical level, evidently scabs rapidly begin to form
on the melt. An increased beryllium addition to the metal melt is
undesirable due to the carcinogenic property of beryllium and
should therefore be avoided as far as possible.
[0027] By the addition of vanadium to the alloy, the scab-reducing
addition of beryllium can take place in substantially lower
quantities than without the addition of vanadium. For a content of
more than 3.5 w. % magnesium, it is sufficient to add 10 to 50 ppm
beryllium, preferably 10 to 35 ppm beryllium. If the content of
magnesium in the melt is less than 3.5 w. %, less than 25 ppm
beryllium is required to achieve a high scabbing resistance. For
lower requirements for the scabbing tendency, the beryllium
addition can even be omitted.
[0028] The preferred area of application of the casting alloys
produced from the aluminium base alloy- according to the invention
is the production of heat-resistant and/or corrosion-resistant
parts in the engine area, in particular engine blocks, cylinder
heads and oil sumps, by means of sand casting, chilled casting,
diecasting, thixocasting or thixoforging.
[0029] Further advantages, features and details of the invention
arise from the following exemplary description of scrap preparation
and the drawings, which show diagrammatically:
[0030] FIG. 1 a diagram of the main structure of a recycling
plant;
[0031] FIG. 2 a basic flow diagram of the plant in FIG. 1;
[0032] FIG. 3 a block circuit diagram of the plant in FIG. 1;
[0033] FIG. 4 a process flow diagram of the plant in FIG. 1;
[0034] FIGS. 5-7 enlarged sections of FIG. 3.
[0035] A plant for recovery of aluminium from aluminium scrap
contaminated with organic compounds according to FIGS. 1 to 7 has
the three operating units:
[0036] BE1 Material preparation
[0037] BE2 Decoating plant
[0038] BE3 Melting plant.
[0039] The material preparation BE1 includes the material delivery,
storage until charging and mechanical preparation and retention
(buffering) of prepared material for the decoating plant BE2.
[0040] Materials to be processed in the plant are usually delivered
by road or rail. The incoming materials are weighed. The nature,
provenance and quantity of the materials supplied are recorded and
documented. A reception test may be performed depending on the
material type.
[0041] The material preparation BE1 in principle serves for
preparation of two fundamentally different material types:
[0042] Chippings S1 from metalwork. These are sieved, the coarse
fraction reduced in size, and ferrous metals separated out.
[0043] Aluminium compound substances S2. These are reduced to a
unit size, for example 30.times.40 mm, and the ferrous metals
removed. Materials used here are therefore e.g. DSD (Duales System
Deutschland) material, painted plates and metal goods, painted
extrusion profiles, painted tubes and aerosol cans, flexible packs
of aluminium combined with plastic or paper, used aluminium cans,
cooling radiator scrap, pipes, fins, cuttings, offset panels,
cables stripped with grease, bottle caps, number plates, road signs
and window profiles.
[0044] Aluminium compound substances S2 are intermediate-stored in
the case of immediately processing in a preparation room before
coarse size reduction. The aluminium compound substances S2 for
coarse size reduction are supplied by way of a delivery conveyor 10
and a subsequent further delivery conveyor 14 into a slow-running
cutter 16. The first delivery conveyor 10 is supplied by way of a
delivery shaft 12 by means of a forklift truck 18. It is also
possible to supply the cutter 16 directly using the forklift truck
18.
[0045] The use of the slow-running cutter 16 for size reduction
generates a specific low proportion of fine grains. Aluminium chips
are mixed into the process later.
[0046] The coarsely reduced material falls from the rotor shears 16
onto a belt conveyor 20 which also has a delivery well 22 for
optimum delivery of batch material. Arranged above the belt
conveyor 20 is a magnetic separator 24 with separating aid. At this
point the coarse iron constituents S3 are removed from the material
flow.
[0047] The belt conveyor 20 is fitted with an integral strong field
magnetic roller or magnetic drum 26. Here further iron constituents
S3 including stainless steel are removed.
[0048] Alternatively the iron constituents S3 can be separated
first after pyrolysis.
[0049] The preferred aluminium compound substances S2 are
transferred by a steep belt conveyor 28 and distribution conveyor
30 into one of for example five buffer containers 32a-e each with a
capacity of for example 40 m.sup.3.
[0050] The buffer containers 32 are designed closed i.e. with
encapsulated input and output and venting to an extraction system.
The material stored is output as required by way of metering
conveyors 34a-e onto a belt conveyor 36; this passes the material
to the distribution conveyor 38 for the decoating plant BE2.
[0051] As an alternative to delivery of the aluminium compound
substances S2 prepared after separation of the iron constituents S3
to the steep belt conveyor 28, these can for example be divided
further in a cross-flow separator 29 according to the aluminium
content or thermal value H.sub.u. Separation into aluminium-rich
constituents with a low thermal value H.sub.u, e.g. profile
sections, and low-aluminium constituents with a high thermal value
H.sub.u, e.g. coated foils, takes place in the cross-flow separator
29 on the basis of the different weight and specific contact
section. The various fractions with different aluminium content or
different thermal value H.sub.u are then intermediate-stored
separately in the buffer containers 32.
[0052] Aluminium chips S1 are taken by wheel loader from chip boxes
in the supplier room and deposited by way of a delivery shaft 40
into a delivery conveyor 42 to a sieve 44. The sieve 44 separates
the coarse and fine chippings.
[0053] The fine chippings travel by way of a belt conveyor 46 and a
subsequent further belt conveyor 48, with an overhead magnetic
separator 50 to separate the iron constituents S3, into a buffer
container 52 with for example a capacity of 20 m.sup.3.
[0054] Any coarse material occurring e.g. bushy chips, are caught
in a collection container 54 and transferred by the forklift truck
18 to the size reduction line for the aluminium compound
substances.
[0055] Before the delivery of the fine chippings to the
distribution conveyor 38, the material flow can pass through a
metal detector 31 for detection and subsequent separation of
undesirable non-ferrous metals.
[0056] Also after separation of the iron constituents, even for a
lumpy part fraction of the cross-flow separator 29, the material
flow can pass through metal detector 31 for detection and
subsequent separation of undesirable non-ferrous metals.
[0057] The fine chippings are passed from the buffer container 52
by way of a metering conveyor 56 onto the belt conveyor 58 and thus
reach the preparation line of the aluminium compound substances on
the distribution conveyor 38 for the decoating system BE2.
[0058] The material from the compound and chip lines first reaches
a buffer container or material store 60 in which the material is
moistened where applicable. From here it reaches the input system
of a pyrolysis drum 70. Instead of moistening in the buffer
container 60, a pyrolysis delivery head can spray water, water
vapour and/or an inert gas, e.g. CO.sub.2.
[0059] At the treatment plant at various points such as the size
reduction unit, transfer points and material buffer, extraction air
is collected in order to prevent a diffuse release of emissions of
foreign particles such as dust. The individual extraction air flows
are combined and passed by way of a cyclone separator 62 and
subsequent fan 64 to a combustion chamber 78 for afterburning.
Solids separated out in the cyclone separator 64 are discharged
into a container 68 by way of a cellular wheel sluice 66 and for
example charged into the delivery well 22.
[0060] The decoating plant BE2 consists of the pyrolysis drum, a
bright annealing machine, a foil separator, a pyrolysis gas
combustion and a flue gas cleaning system with quench, heat
exchanger, two-stage washer etc.
[0061] The material is supplied from the material preparation BE1
by way of the material delivery 60 and a sluice system consisting
of two sealed pushers 72, 74 to the pyrolysis drum 70, which has a
length L of approximately 25 m.
[0062] To avoid the emission of pyrolysis gas from the delivery
area and to minimise undesirable air ingress into the pyrolysis
drum 70, a reduced pressure is applied to the sluice system. Here,
inert gas e.g. CO.sub.2 is flushed into this room and the gas
between the two pushers 72, 74 is simultaneously extracted by means
of a fan 76 and passed to the heating jacket exhaust gas S8 from
the combustion chamber 78.
[0063] The sealed pushers 72, 74 are designed to be tightly closed.
The material is added to the pyrolysis drum 70 in cycles by way of
this pusher system. To avoid undesirable air ingress into the drum,
in each case only one of the two pushers can be opened, which is
guaranteed by means of an end position monitoring. A further seal
is applied by way of the material presentation by way of the first
double pusher 72, between the two sealed pushers 72, 74, and in an
inlet screw 80 which can be liquid-cooled.
[0064] The pyrolysis process takes place at around 550.degree. C.
Because of the conditions of temperature and holding time
conditions, it is guaranteed that on reaching the pyrolysis
discharge head after around 50 minutes, the material is completely
pyrolysed. Extensive degasification of the materials takes place in
the pyrolysis drum 70.
[0065] The energy required for the pyrolysis process is supplied by
way of a heating jacket 82 surrounding the pyrolysis drum 70. The
heating jacket 82 is refractory-lined and designed without burners;
the necessary hot gas S8 is supplied from outside the combustion
chamber 70 to the heating jacket 82 and there evenly distributed
along the pyrolysis drum wall. After flowing through the heating
jacket 82, the hot gas S8, cooled to around 580.degree. C. is
guided by means of the fan in the heating jacket 84 of the
pyrolysis gas lines 86 and then returned to the combustion chamber
78. It is returned to the combustion chamber 78 with a view to a
closed circuit design and consequent emission reduction.
[0066] The heating jacket 82 consists of a boiler plate
construction with refractory lining. To avoid the emission of hot
gas between the heating jacket 82 and the rotary passage through
the pyrolysis drum 70, cable seals are installed. Sealing occurs by
mutually overlapping casting segments which are pressed against the
rotating sealing surface of the rotary furnace by means of a
surrounding cable over locking clamping pins. Because of the
pressure conditions in the heating jacket 82, i.e. the slight
pressure reduction, the fan arrangement on the suction side also
prevents, by design, the emission of hot gas to the
environment.
[0067] To start the pyrolysis drum 70, until sufficient pyrolysis
gas is being produced, natural gas is used as the energy carrier.
It is heated in the same manner i.e. by provision of heating energy
from the combustion chamber 78.
[0068] The pyrolysis drum 70 is driven on the output side by way of
a crown gear by means of a hydraulic drive, the drum also has an
auxiliary drive. The drum rotation speed is for example 5 rotations
per minute and can be varied.
[0069] The pyrolysis drum 70 is sealed on the input and output
sides by means of a rotating mechanical seal and CO.sub.2 barrier
gas supply.
[0070] The pyrolysis gas and the solids are separated at the
pyrolysis discharge head. The pyrolysis gas is extracted under
pressure control. The pressure control and subsequent pyrolysis gas
line 86 are designed redundant for operating security.
[0071] At the pyrolysis discharge head the pyrolysis drum 70
projects with its end part 71 by a dimension a into an outlet
housing 88. This end part 71 is designed as a sieve for separating
the solids discharged from the pyrolysis drum 70 into a sieved fine
fraction and a coarse fraction emerging from the open end part
71.
[0072] The solids discharged from the pyrolysis drum 70 which
consist of aluminium and coke as the residue of organic adhesions
of the materials introduced, are discharged from the outlet housing
88 by means of two sluice systems.
[0073] To separate the pyrolysis coke R1 the material is first
guided on output from the pyrolysis drum 70 by way of a swivelling
sieve 90. Fine material, i.e. pyrolysis coke R1, falls into a well
92 below and from there is discharged downwards in timed cycles by
way of a sealed pusher 94, according to the material
introduction.
[0074] The position of the sieve 90, which is designed as an
adjustable flap, can be used to set the fraction size of discharge
material allocated to the two sluice systems.
[0075] The pyrolysis coke R1 is cooled in a water-cooled cooling
screw 96 with double casing and indirect cooling. From the screw
the cooled coke falls into a cellular wheel sluice 98; this
discharges into a transport container 100. The heat is dissipated
through a cooling water circuit to which the quench water circuit
is also connected, by way of a total of three cooling towers
102a-c.
[0076] The composition of the pyrolysis coke allows a quantitative
use in the production of carbon products e.g. anodes for aluminium
electrolysis.
[0077] The remaining material--as the sieve residue of the sieve 90
--is discharged by way of a sluice system consisting of two sealed
pushers 104, 106, according to the material input. The sealed
pushers 104, 106 are in each case designed to be tightly sealed.
The material is output in cycles by way of these pushers. To avoid
undesirable air ingress into the pyrolysis drum 70, in each case
only one of the two pushers can be opened, which is guaranteed by
means of an end position monitoring.
[0078] The material is discharged from the sluice system onto a
sieve 108 on which the free pyrolysis coke R1 remaining in material
flow is discharged separately as sieve passage (fine goods) from
the aluminium fraction by way of a cellular wheel sluice 110 into
the cooling screw 96; as described above this empties by way of a
cellular wheel sluice 98 into the transport container 100. The
pyrolysis coke can for example be used in production of carbon
anodes for electrolysis for aluminium production.
[0079] The hot aluminium main flow containing the pyrolysis coke R1
is supplied by way of a hot goods conveyor 112 and a cellular wheel
sluice 114 to a bright annealing device 116. In this bright
annealing device 116 the pyrolysis coke residue is burnt in a
targeted fashion on an oscillating bed through which flows
oxygen-regulated hot gas. A proportion of melt furnace extraction
gas S19 is used as a hot gas, to which air is added depending on
the oxygen content, on the extraction gas side of the annealing
device 116. The hot gas is supplied by way of a hot gas fan 118.
The resulting flue gases are supplied to the combustion chamber
78.
[0080] Ash R3, which is contaminated with aluminium particles, is
separated from the aluminium main flow as sieve passage from the
bright annealing device 116 and ejected by way of a cellular wheel
sluice 128 into a collection container 130.
[0081] The annealed material i.e. bright aluminium, is discharged
from the bright annealing device 116 as sieve residue by way of a
cellular wheel sluice and then output, by means of two hot goods
conveyors 122, 124 connected in succession to the foil separator,
into a buffer container 126. Here, the material is supplied to a
sieve 134 by way of a constant conveyor 132. Here, by means of melt
furnace exhaust gases S19 and air at a mixing temperature of
approximately 400.degree. C., foil is removed from the material
flow by air separation, and subsequently precipitated from the
separated air in a hot gas cyclone 136 and discharged by way of a
cellular wheel sluice 138 into a collection container 140. The hot
gas leaves the hot gas cyclone 136 by way of a hot gas fan 137. The
separated foil residue can be passed to separate recycling.
[0082] The heavy goods from the air separation, i.e. the remaining
aluminium fraction, from the separator 134 reaches a hot goods
conveyor 144 by way of a cellular wheel sluice 142. This opens into
an alternating flap 146 which divides the material flow, i.e.
bright aluminium S13, into two lines. One part is output directly
to the buffer container 148, the other part reaches a further
buffer container 154 by way of two hot goods conveyors 150, 152
connected in succession.
[0083] Both buffer containers or silos 148, 154 supply an attached
melting plant BE3 by means of constant conveyors 156, 158.
[0084] The pyrolysis gas S7 is taken from the pyrolysis drum 70 by
way of a redundant pressure control on the outlet housing 88. The
extraction quantity of gas depends on the pressure inside the
drum.
[0085] The separated pyrolysis gas is transported in the shortest
route by means of the, also redundant, double jacket heated
pyrolysis gas line 86 to the combustion chamber 78. The heating
jacket 84 of the pyrolysis gas line 86 here receives the heating
jacket exhaust gas from the pyrolysis drum 70.
[0086] The combustion chamber 78 is a lined, high
temperature-resistant combustion chamber (burner muffle) into which
the pyrolysis gas is discharged by way of a ring line protected
against backfire. As well as pyrolysis gas, into the combustion
chamber 78 are fed the extraction gases from the bright annealing
furnace (S18), the air separator (S20), the remaining flue gas
quantities from the melt plant (S19), extraction air from the
treatment plant (S22) and also fresh air. The combustion air is
supplied, stepped at various levels, to achieve combustion as low
in NO.sub.X as possible.
[0087] The oxygen content and temperature in the combustion chamber
78 are monitored and recorded. A combustion chamber temperature of
1200.degree. C. is maintained and an oxygen content above 6%
ensured in principle. The combustion chamber geometry ensures a
minimum flue gas holding time of 2 seconds. In plant start-up and
shut-down mode, the combustion chamber is operated with natural
gas.
[0088] The combustion chamber extraction gas, where not used as a
part-flow for the pyrolysis drum heating (S8), is passed to the
quench 160. The combustion chamber extraction gas used for heating
is returned to the combustion chamber 78.
[0089] In the quench 160 the flue gas S9 is shock-cooled to below
150.degree. C. This prevents the reformation of polychlorinated
p-dibenzodioxine and dibenzofurane (PCDD/PCDF) (prevention of
de-novo synthesis). In connection with the combustion achievable in
high temperature combustion, the best possible reduction of
PCDD/PCDE emission should be achieved by primary measures.
[0090] The shock-cooling is achieved by spraying a very large
quantity of water into the gas flow. This is recirculated by the
quench sump pump or water circulation pump 162, evaporation losses
are constantly replaced under level control in the quench sump. The
heat extracted from the gas flow by way of the recirculated water
is passed by way of a heat exchanger 164 to a second water circuit
and output to the environment by way of the total of three cooling
towers 102a-c. To ensure a cooling effect, the quench 160 is fitted
with an emergency spraying system; on failure of water circulation
pump 162 water can still be sprayed into the quench 160 by way of
an additional emergency water pump 163. On power failure this
system remains in operation by way of the emergency power
supply.
[0091] After the quench 160 the cooled extraction gas S10 first
reaches a droplet separator 166 and then a two-stage gas washer
168a,b. Liquid occurring at the droplet separator 166 is
recirculated in the quench circuit.
[0092] The hot extraction gas emerging from the combustion chamber
78 can be supplied alternatively for energy use. Here, after
emerging from the combustion chamber 78, the extraction gas enters
a boiler with a cooling spiral. The cooled extraction gas is passed
for cleaning. The water vapour, heated for example to 400.degree.
C. in the cooling spiral, is then passed at a pressure of 38 bar
for example to a generator to generate power.
[0093] As a washing fluid additive in the gas washer, sodium lye
S17 is used; the supply is pH-controlled and takes place by way of
a sodium lye metering pump 170 in the sump or washing lye container
170 of the two washer stages. In addition, level-controlled fresh
water is added. Slurry water with washer slurry (R2) is
continuously centrifuged out from the washer circuit and quench
water circuit, and supplied by means of the washer sump pumps 172,
174 to an evaporation system designed as a thin layer vaporiser
176. The washing circuits of the two washer stages are operated by
redundant circulation pumps 178, 180 (stage 1) and 182, 184 (stage
2).
[0094] The washed exhaust gas S11 leaves the flue gas cleaning
system at a temperature of around 85.degree. C., saturated with
water vapour. To achieve better extraction of the exhaust gas it is
therefore raised to a temperature of approximately 105-110.degree.
C. by the supply of hot melt gases and then discharged by means of
a redundantly designed exhaust gas fan by way of a chimney 189 into
the free air flow.
[0095] After evaporation of the washer slurry, salts such as oxides
(R2) remain. These can be used, where applicable after recipe
correction, as melt salts in the melt plant BE3.
[0096] The melt plant BE3 is a twin-chamber system (open well) and
consists of an open charging chamber 190, 192 with vortex system, a
pump 194, 196, an open hearth furnace as a heating chamber, and a
conduit system.
[0097] From the open hearth furnace 198, 200, liquid metal is
transported by a pump by way of a conduit into a specially designed
charging chamber 190, 192, and there given a rotary movement,
creating a vortex.
[0098] Solid aluminium is continuously added to the vortex in the
rotating liquid metal by way of the metering conveyor system 156,
158. Due to the rotary movement and the delivery point, the solid
aluminium is immediately drawn below the bath surface and
moistened. Oxidation of the aluminium is largely avoided.
[0099] From the charging chambers 190, 192, the metal flow returns
to the open hearth furnace 198, 200. There, the enthalpy applied in
the melting process is compensated by gas heating. For this,
natural gas air burners 202, 204 are used.
[0100] Oxides and salts from the melting process remain on the bath
surface as metal-rich scabs. The scab is moved from the open hearth
furnace 198, 200 in a rhythm determined by operation.
[0101] The melted liquid aluminium is supplied in batches to the
foundry, either with liquid metal crucibles 206, 208 and transport
trolleys, or cast to size by way of a casting device 210, 212.
[0102] The melt power of the system is designed for example so that
in total max 5 t/h can be melted (2.5 t/h per melt device); this
output is achieved only if material with few organic adhesions is
pyrolysed. On average around 3.4 t/h are melted.
[0103] The metal produced is characterised and processed according
to its alloy composition.
* * * * *