METHOD FOR INCINERATING CARBON-CONTAINING DRY METALLIC ASH

PROCEDE POUR INCINERER DES CENDRES METALLIQUES SECHES CARBONEES

English Abstract

The invention is directed to a device for incinerating carbon-containing dry
metallic ash. The
device comprises a trough (a1 ) which comprises a first level hearth (b2),
which comprises first
openings (c3), metal fibres (d4) arranged below the first level hearth (b2)
and above a second
level hearth (e5) which form a space (d4a) between the first level hearth (2b)
and the second
level hearth (e5). The second level hearth (e5) is arranged parallel to the
first level hearth (b2)
and has second openings (f6) that are arranged at an offset from said first
openings (c3). The
first level hearth (b2) and the second level hearth (e5) are connected by a
connecting means
(g7) in such manner that metal fibres (d4) are held firmly between the first
level hearth (2b) and
the second level hearth (e5). A space (h8) is provided below the second level
hearth (e5) to
which means (i9) for supplying air or/and oxygen are provided.

French Abstract

Linvention concerne un dispositif permettant dincinérer des cendres métalliques sèches carbonées. Le dispositif comprend un creux (a1) qui comporte un âtre de premier niveau (b2), lui-même doté de premières ouvertures (c3) et de fibres métalliques (d4) disposées sous lâtre de premier niveau (b2) et au-dessus de lâtre de deuxième niveau (e5) qui forme un espace (d4a) entre lâtre de premier niveau (2b) et lâtre de deuxième niveau (e5). Lâtre de deuxième niveau (e5) est parallèle à lâtre de premier niveau (b2) et comporte des deuxièmes ouvertures (f6) décalées par rapport aux premières ouvertures (c3). Lâtre de premier niveau (b2) et lâtre de deuxième niveau (e5) sont raccordés par un lien (g7) de façon à ce que les fibres métalliques (d4) soient maintenues fermement entre lâtre de premier niveau (2b) et lâtre de deuxième niveau (e5). Un espace (h8) est prévu sous lâtre de deuxième niveau (e5) et comporte des éléments (i9) qui permettent dy acheminer de lair ou de loxygène.

Claims

5
claims
1. A device for incinerating carbon-containing dry metallic ash comprising:
a trough (a1) comprising:
i) a first level hearth (b2), which comprises first openings (c3);
ii) metal fibres (d4) arranged below the first level hearth (b2) and above
a
second level hearth (e5) which form a space (d4a) between the first level
hearth (2b) and
the second level hearth (e5);
iii) the second level hearth (e5) being arranged parallel to the first
level
hearth (b2); and
iv) the second level hearth (e5) having second openings (f6) that are ar-
ranged at an offset from said first openings (c3);
wherein
the first level hearth (b2) and the second level hearth (e5) are connected by
means of connecting means (g7) in such manner that metal fibres (d4) are held
firmly be-
tween the first level hearth (2b) and the second level hearth (e5); and
a space (h8) is provided below the second level hearth (e5) to which means
(i9)
for supplying air or/and oxygen are provided.
2. The device according to claim 1, wherein flow guides (j) for optimising the
air circulation
are provided in the space (h8).
3. The device according to claim 1 or 2, wherein the metal fibres (d4) are in
a form selected
from the group consisting of a woven material, a fabric, a fleece and a
knitted material.

Description

CA 02796899 2012-11-27
Method for incinerating carbon-containing dry metallic ash
The invention relates to a method for incinerating carbon-containing dry
metallic ash and a de-
vice for implementing said method.
Metallic ash is understood to be the product of primary incineration of
recycling material that
contains plastic materials and solvents and is to be reprocessed for its noble
metal content. No-
ble metals can be present in recycling material of this type either in
elemental or chemically
bound form, e.g. as salts or oxides. The metallic ash can therefore also
contain these substanc-
es.
Following primary incineration/carbonisation, said ashes still contain
substantial fractions of car-
bon that should be removed before further recycling steps and/or should be
reduced to a frac-
tion of less than 3 %.
US4360380/DE3134733A1 specifies a metal recycling method, in which the
incineration of or-
ganic fractions is carried out at temperatures below the slag formation
temperature of the sili-
cate fractions. This is aimed at preventing valuable metals from being
included in glass:
"The slag formation temperature of quartz is approx. 760 C. Accordingly, if
the incineration pro-
ceeds at a temperature between 315 and 480 C and in the presence of sufficient
oxygen or of
an excess of oxygen with adequate stirring, it has been found that the organic
fraction is incin-
erated without undesirable silicates being formed."
Accordingly, DE3134733A1 describes a method having the following features:
"Method for recycling selected metal fractions from quartz-containing sludges
by incinerating the
sludge in order to disintegrate organic fractions followed by acidic leaching
of the ash and hy-
drometallurgical recovery of the metal fractions from the remaining solid and
liquid residues,
whereby the incineration is carried out at a temperature below the slag
formation temperature of
silicates in order to prevent metal fractions from being occluded in glass
matrices that are not
attacked by the subsequent acidic leaching and the hydrometallurgical
procedural steps."
According to DE3134733A1, the process is carried out in a furnace. The
efficiency of the pro-
cess is said to be increased through stirring and supplying air: "Moreover, it
has been evident

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that stirring of the sludge aimed at keeping the temperature at an even level
throughout and
increasing the access of oxygen to the organic material, improved the method
significantly. Ob-
viously, stirring or forced aeration are used in one way or another in many
sludge incineration
facilities and are not considered to be novel features as such".
In contrast, the present invention provides a method for incinerating carbon-
containing slags in
open troughs through overturning on air and includes additional aeration from
below. Consistent
with DE3134733A1, the prior art is the incineration in open troughs with
frequent overturning by
means of rakes. Additional aeration from below according to the invention
surprisingly reduces
the duration of the incineration process by 50 to 80%. This is more than an
additive effect and
rather represents a surprising synergism. Additional aeration from below
according to the inven-
tion surprisingly reduces the duration of the incineration process by 50 to
80%. This is more
than an additive effect and rather represents a surprising synergism. It also
needs to be noted
that the material burns more rapidly after ignition. The overturning by means
of rakes is kept for
expedient reasons to ensure that no crusts are formed at the hearth region of
the troughs or on
the surface of the incinerated goods. The carbon content is reduced to less
than 3%.
The overturning by means of rakes is kept for expedient reasons to ensure that
no crusts are
formed at the hearth region of the troughs or on the surface of the
incinerated goods. The car-
bon content is reduced to less than 3%.
Another option is to enrich the air, which is blown-in from below, with oxygen
in order to improve
the efficiency of incineration.
According to an essential feature of the method according to the invention,
any reverse
transport of ash is prevented whereas the supply of air and/or oxygen is
maintained.
In detail, the method comprises the steps of:
a) adding metallic ash into a trough;
b) aerating from above with ambient air;
c) injecting air and/or oxygen through the trough hearth;
d) establishing the ignition temperature;
e) stirring of the metallic ash by means of a suitable tool;
f) whereby the carbon content is reduced to less than 3%;

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whereby steps b), c), and d) can proceed concurrently or in alternating order
or pairs or all of
these steps can proceed concurrently;
step d) can just as well proceed selectively in partial quantities of the
metallic ash;
and the reverse transport of ash through the trough hearth is prevented,
whereas the supply of
air and/or oxygen is maintained.
In a convenient embodiment, the incineration process is carried out in a
multiple hearth incinera-
tor at the open top of the trough exposed to ambient air and by means of
injecting air from be-
low. The time for the carbon fraction to reach a level below 3% is 2 hours.
The invention also relates to a device for incinerating carbon containing dry
metallic ash in the
form of a container, preferably a trough, that comprises a hearth that is
aerated from below.
The hearth comprises means preventing the ash from dropping through the grate,
whereas the
supply of air and/or oxygen from below is not obstructed.
Preferably, the invention provides a hollow double-hearth trough having an
upper hearth and a
lower hearth. Openings, such as, e.g., holes or slits, in the upper and lower
hearth ensure the
supply of air from below, whereas metal fibres, such as a wire mesh or similar
material, in the
space between the hearths ensures that the ash cannot fully drop through the
two hearths. In
addition, it is expedient for the openings to be situated not directly across
from each other,
which results in favourable flow conditions from the start.
Overall, the feature of having a metal fibre-containing double-hearth trough
provides a surpris-
ingly simple solution allowing the desired substance transport from below to
proceed while suffi-
ciently impeding the undesired substance transport from above.
Flow guides are another expedient feature that further optimises the flow
conditions provided
they are situated properly.
The fibres can be present as woven material, fabric, non-woven fabric or
knitted material. Pref-
erably, they are knitted.

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4
Fig. 1 shows a preferred embodiment of the device.
This comprises
a) a trough al
b) having a level hearth b2,
c) whereby hearth b2 comprises openings c3,
d) with metal fibres d4 being arranged below hearth b2 and forming a space
d4a, which is
closed in downward direction through
e) another trough hearth e5 that is arranged parallel to hearth b2
f) having further openings f6 that are arranged at an offset from said
openings c3, whereby
g) hearth e5 and hearth b2 are connected by means of connecting means g7 in
such man-
ner that metal fibres d4 are firmly occluded, and
h) a space h8 is provided below hearth e5 to which
i) means i9 for supplying air or/and oxygen are provided.
Flow guides for optimising the air circulation can be provided in space (h8).
The metal fibres (d4) can be present as woven material, fabric, fleece or
knitted material.
Preferably, they are knitted.

Representative Drawing