1. A melting furnace comprising: a furnace chamber where a treatment target containing multiple types of metals is fed from an upstream side and subjected to melt treatment from a surface thereof by a heating mechanism provided on a furnace ceiling, thereby generating molten slag which flows down to a downstream side; and a slag port which discharges the flowed down molten slag, the melting furnace comprising: multi-stage nozzles arranged along the upstream side to the downstream side of the furnace chamber; and an atmosphere control mechanism which controls to vary a type and/or composition of gas supplied from each of the nozzles to adjust an atmosphere near a molten surface to either an oxidizing atmosphere or a reducing atmosphere in each of a plurality of areas from the upstream side to the downstream side, thereby melting a target metal among the multiple types of metals as molten metal which is separable from the molten slag, or capturing the target metal in the molten slag as a metal compound.

2. The melting furnace according to claim 1, wherein the atmosphere control mechanism controls to adjust the atmosphere near the molten surface on the upstream side to a weakly reducing atmosphere to volatilize heavy metals among the multiple types of metals, and adjust the atmosphere near the molten surface on the downstream side to a strongly reducing atmosphere to melt the target metal among the multiple types of metals as the molten metal which is separable from the molten slag.

3. The melting furnace according to claim 1, wherein the atmosphere control 22 mechanism controls to adjust the atmosphere near the molten surface on the upstream side to a weakly reducing atmosphere to volatilize heavy metals among the multiple types of metals, and adjust the atmosphere near the molten surface on the downstream side to the oxidizing atmosphere or the weakly reducing atmosphere to capture the target metal among the multiple types of metals in the molten slag as the metal compound.

4. The melting furnace according to claim 1, wherein the atmosphere control mechanism controls to adjust the atmosphere near the molten surface on the upstream side to a weakly reducing atmosphere to volatilize heavy metals among the multiple types of metals, and adjust the atmosphere near the molten surface on the downstream side to the weakly reducing atmosphere and further adjust temperature of the molten surface to 1400-1600°C, thereby melting the target metal among the multiple types of metals as the molten metal which is separable from the molten slag.

5. The melting furnace according to any one of claims 1 to 4, comprising a rotary surface melting furnace, the rotary surface melting furnace comprising: an inner cylinder dividing the furnace chamber; an outer cylinder arranged around a periphery of the inner cylinder; a storage part for the treatment target formed between the inner cylinder and the outer cylinder; and the furnace chamber in which the treatment target, which is fed out of the storage part into the furnace chamber by relative rotation of the inner cylinder and the outer cylinder, is melt-treated from the surface of the treatment target, and the molten slag flows down to be discharged from the slag port formed at a center of a furnace floor, wherein the multi-stage nozzles arranged along the upstream side to the downstream side of the furnace chamber are disposed on the fumace ceiling or the furnace floor.

6. A method for operating a melting furnace comprising: a fumace chamber where a treatment target containing multiple types of metals is fed from an upstream side and subjected to melt treatment from a surface thereof by a heating mechanism provided on a fumace ceiling, thereby generating molten slag which flows down to a downstream side; a slag port which discharges the flowed down molten slag; and multi-stage nozzles arranged along the upstream side to the downstream side of the furnace chamber, the method comprising: controlling to vary a type and/or composition of gas supplied from each of the nozzles to adjust an atmosphere near a molten surface to either an oxidizing atmosphere or a reducing atmosphere in each of a plurality of areas from the upstream side to the downstream side, thereby melting a target metal among the multiple types of metals as molten metal which is separable from the molten slag, or capturing the target metal in the molten slag as a metal compound.

FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. MELTING FURNACE AND METHOD FOR OPERATING MELTING FURNACE
2.
1. (A) KUBOTA CORPORATION
(B) Japan
(C) 1-2-47, Shikitsuhigashi, Naniwa-ku, Osaka-shi, Osaka 5568601, Japan
The following specification particularly describes the invention and the manner in which it is to
be performed.
2
Technical Field
[0001] The present invention relates to a melting furnace and a method for operating a
melting furnace.
Background Art
[0002] Miscellaneous waste, such as organic sludge such as sewage sludge, livestock
excreta, or methane fermentation residues from food waste; a combustible material such
as plastic, paper, SRF (Solid Recovered Fuel), or recycling residues containing plastic
and metal; and an incombustible material such as incinerated ash, contaminated soil,
waste glass, waste pottery, or asbestos, is melt-treated as a treatment target in a melting
furnace.
[0003] For example, the miscellaneous waste is melt-treated by a surface melting
furnace including a furnace chamber in which a slag port is formed, and a
treatment-target supply mechanism for supplying the treatment target toward the
furnace chamber, the surface melting furnace configured to melt the treatment target
supplied to the furnace chamber by the treatment-target supply mechanism from a
surface thereof, and cause it to flow down to the slag port.
[0004] In such a melting furnace, the inside of the furnace is adjusted to a reducing
atmosphere in order to volatilize heavy metals contained in the treatment target to
remove them from slag.
3
[0005] In addition, Patent Literature 1 proposes a surface melting furnace that
suppresses the volatilization of phosphorus contained in a treatment target during a
melt-treatment. The surface melting furnace is configured to include: a furnace
chamber in which a burner and an air supply mechanism are disposed and a slag port is
formed; and a treatment-target supply mechanism for supplying the treatment target to
the furnace chamber from a treatment-target container provided communicating with the
furnace chamber. The treatment target contains phosphorus and a combustible
material. The surface melting furnace includes an edge portion air-supply mechanism
for supplying air toward a surface of the treatment target in the furnace chamber, the
surface being adjacent to a portion in which the treatment-target container
communicates with the furnace chamber.
[0006] According to the surface melting furnace, the air supplied from the edge
portion air-supply mechanism toward the surface of the treatment target causes a fixed
carbon content remaining on the portion adjacent to the surface of the treatment target
due to the thermal decomposition of the combustible material to combust. The
remainder of oxygen further suppresses reduction reactions of phosphorus compounds
or phosphorus oxides, and thus suppresses the volatilization of phosphorus.
[0007] Patent Literature 2 proposes a method for melt-treating a
phosphorus-containing material, including suppressing the volatilization of a
phosphorus component contained in the phosphorus-containing material to exhaust gas,
and capturing the phosphorus component in slag during the melt-treatment of the
phosphorus-containing material such as sewage sludge. The method for melt-treating
includes the following steps: a pretreatment step for adjusting a moisture content for the
phosphorus-containing material containing 0.04 wt% or more phosphorus in dry
substance equivalent; a melting step for supplying the phosphorus-containing material
4
whose moisture content adjusted in the pretreatment step into a melting furnace to melt;
and a cooling step for cooling and solidifying the slag produced by melting in the
melting step.
[0008] The method for melt-treating further performs an iron compound adding step
for adding divalent or trivalent iron compounds to the phosphorus-containing material
in or before or after the pretreatment step, thereby preventing the volatilization of the
phosphorus component contained in the phosphorus-containing material in the melting
step, and also capturing the phosphorus component in the slag while suppressing the
migration of the phosphorus component into metal phosphorus compounds, for example,
iron phosphide.
[0009] When such a mixture of the divalent or trivalent iron compounds and the
phosphorus-containing material are supplied into the melting furnace, the supplied
ferrous oxide (FeO) or ferrous oxide (FeO) produced from the divalent or trivalent iron
compounds in the melting process causes a melting point lowering effect. Therefore,
for example, at a melting temperature of about 1300°C, a melting flow rate of 60% or
more can be secured over a wider range than the preferred basicity of 0.4-0.8 of the
phosphorus-containing material to iron, and the volatilization of phosphorus component
in the material to be molten is suppressed so that phosphorus is captured in the slag in
the form of non-metallic phosphorus compounds.
Citation List
Patent Literature
[0010] Patent Literature 1: Japanese Unexamined Patent Application Publication No.
2015-190701
Patent Literature 2: Japanese Unexamined Patent Application Publication No.
5
2015-033691
Summary of Invention
Technical Problem
[0011] Thus, a method for operating a melting furnace has been known, the method
including adjusting a furnace atmosphere to an oxidizing atmosphere to suppress
volatilization of metals or the like contained in a treatment target, or adding a melting
auxiliary agent to suppress alloying of the metals or the like contained in the treatment
target to capture them in slag.
[0012] Incidentally, it may be desired to separate and recover a specific metal
contained in a treatment target from slag during melt treatment of the treatment target to
use it as a recycled resource, while it may be desired to capture a specific metal
contained in the treatment target in the slag.
[0013] For example, it may be desired to recover iron and nickel contained in a
treatment target as metal. Conversely, it may be desired to capture iron and nickel in
slag as compounds.
[0014] However, there has been a problem that multiple metals are contained in a
treatment target, and thus the desired object cannot be achieved when uniformly
adjusting an inside of a furnace to a certain oxidizing atmosphere or reducing
atmosphere. For example, adjustment to a weakly reducing atmosphere is required to
volatilize heavy metals contained in the treatment target, while adjustment to a strongly
reducing atmosphere is required to recover nickel as molten metal in a separable state
from molten slag. When not only heavy metals but also nickel are contained in the
treatment target, it is impossible to process the treatment target by a conventional
melting furnace.
[0015] An object of the present invention is to provide a melting furnace and a method
6
for operating a melting furnace that enable each process of volatilization, processing
into slag, and metallization to be appropriately performed depending on a type of a
metal when melting a treatment target containing multiple types of metals in the
furnace.
Solution to Problem
[0016] To achieve the above object, a first feature configuration of a melting furnace
according to the present invention is a melting furnace including: a furnace chamber
where a treatment target containing multiple types of metals is fed from an upstream
side and subjected to melt treatment from a surface thereof by a heating mechanism
provided on a furnace ceiling, thereby generating molten slag which flows down to a
downstream side; and a slag port which discharges the flowed down molten slag, the
melting furnace including: multi-stage nozzles arranged along the upstream side to the
downstream side of the furnace chamber; and an atmosphere control mechanism which
controls to vary a type and/or composition of gas supplied from each of the nozzles to
adjust an atmosphere near a molten surface to either an oxidizing atmosphere or a
reducing atmosphere in each of a plurality of areas from the upstream side to the
downstream side, thereby melting a target metal among the multiple types of metals as
molten metal which is separable from the molten slag, or capturing the target metal in
the molten slag as a metal compound.
[0017] As a result of adjusting the type and/or composition of the gas supplied from
each of the multi-stage nozzles arranged along the upstream side to the downstream side
of the furnace chamber, the atmosphere near the molten surface in each of a plurality of
areas from the upstream side to the downstream side is adjusted to either the oxidizing
atmosphere or the reducing atmosphere. In the area adjusted to the reducing
7
atmosphere, the target metal turns into the molten metal which is separable from the
molten slag, whereas in the area adjusted to the oxidizing atmosphere, the target metal is
captured in the molten slag as the metal compound.
[0018] A second feature configuration of the same is, in addition to the first feature
configuration described above, that the atmosphere control mechanism controls to
adjust the atmosphere near the molten surface on the upstream side to a weakly reducing
atmosphere to volatilize heavy metals among the multiple types of metals, and adjust
the atmosphere near the molten surface on the downstream side to a strongly reducing
atmosphere to melt the target metal among the multiple types of metals as the molten
metal which is separable from the molten slag.
[0019] When the atmosphere near the molten surface on the upstream side of the
treatment target fed into the furnace chamber is adjusted to the weakly reducing
atmosphere, the heavy metals contained in the treatment target are reduced and then
volatilized. Then, once the atmosphere near the molten surface on the downstream
side is adjusted to the strongly reducing atmosphere, the target metal is melted as the
molten metal which is separable from the molten slag. Accordingly, the heavy metals
contained in the treatment target will never be mixed into the slag, and the target metal
will be separated and recovered from the slag after the melt treatment.
[0020] A third feature configuration of the same is, in addition to the first feature
configuration described above, that the atmosphere control mechanism controls to
adjust the atmosphere near the molten surface on the upstream side to a weakly reducing
atmosphere to volatilize heavy metals among the multiple types of metals, and adjust
the atmosphere near the molten surface on the downstream side to the oxidizing
atmosphere or the weakly reducing atmosphere to capture the target metal among the
multiple types of metals in the molten slag as a metal compound.
8
[0021] When the atmosphere near the molten surface on the upstream side of the
treatment target fed into the furnace chamber is adjusted to the weakly reducing
atmosphere, the heavy metals contained in the treatment target are reduced and then
volatilized. Then, once the atmosphere near the molten surface on the downstream
side is adjusted to the oxidizing atmosphere or the weakly reducing atmosphere, the
target metal is captured in the molten slag as the metal compound. Accordingly, the
heavy metals contained in the treatment target will never be mixed into the slag, and the
target metal will be recovered as the metal compound in a captured state in the slag after
the melt treatment.
[0022] A fourth feature configuration of the same is, in addition to the first feature
configuration described above, that the atmosphere control mechanism controls to
adjust the atmosphere near the molten surface on the upstream side to the oxidizing
atmosphere or a weakly reducing atmosphere to volatilize heavy metals among the
multiple types of metals, and adjust the atmosphere near the molten surface on the
downstream side to the weakly reducing atmosphere and further adjust temperature of
the molten surface to 1400-1600°C, thereby melting the target metal among the multiple
types of metals as the molten metal which is separable from the molten slag.
[0023] When the atmosphere near the molten surface on the upstream side of the
treatment target fed into the furnace chamber is adjusted to the weakly reducing
atmosphere, the heavy metals contained in the treatment target are reduced and then
volatilized. Then, once the atmosphere near the molten surface on the downstream
side is adjusted to the weakly reducing atmosphere and the temperature of the molten
surface is adjusted to 1400-1600°C, gold, silver, copper or the like, for example, are
recovered as the molten metal which is separable from the molten slag while
suppressing reduction of iron and nickel.
9
[0024] A fifth feature configuration of the same is, in addition to any of the first to
fourth feature configurations described above, that the melting furnace includes a rotary
surface melting furnace, the rotary surface melting furnace including: an inner cylinder
dividing the furnace chamber; an outer cylinder arranged around a periphery of the
inner cylinder; a storage part for the treatment target formed between the inner cylinder
and the outer cylinder; and the furnace chamber in which the treatment target, which is
fed out of the storage part into the furnace chamber by relative rotation of the inner
cylinder and the outer cylinder, is melt-treated from the surface of the treatment target,
and the molten slag flows down to be discharged from the slag port formed at a center
of a furnace floor, wherein the multi-stage nozzles arranged along the upstream side to
the downstream side of the furnace chamber are disposed on the furnace ceiling or the
furnace floor.
[0025] By arranging the multi-stage nozzles on the furnace ceiling or the furnace floor
of the rotary surface melting furnace along the upstream side to the downstream side of
the furnace chamber, it is possible to supply gas for adjusting the atmosphere to the
molten surface of the treatment target.
[0026] A first feature configuration of a method for operating a melting furnace
according to the present invention is a method for operating a melting furnace
including: a furnace chamber where a treatment target containing multiple types of
metals is fed from an upstream side and subjected to melt treatment from a surface
thereof by a heating mechanism provided on a furnace ceiling, thereby generating
molten slag which flows down to a downstream side; a slag port which discharges the
flowed down molten slag; and multi-stage nozzles arranged along the upstream side to
the downstream side of the furnace chamber, the method including: controlling to vary a
type and/or composition of gas supplied from each of the nozzles to adjust an
10
atmosphere near a molten surface to either an oxidizing atmosphere or a reducing
atmosphere in each of a plurality of areas from the upstream side to the downstream
side, thereby melting a target metal among the multiple types of metals as molten metal
which is separable from the molten slag, or capturing the target metal in the molten slag
as a metal compound.
Advantageous Effects of Invention
[0027] As described above, the present invention can provide a melting furnace and a
method for operating a melting furnace that enable each process of volatilization,
processing into slag, and metallization to be appropriately performed depending on a
type of a metal when melting a treatment target containing multiple types of metals in
the furnace.
Brief Description of Drawings
[0028] Fig. 1 is an illustrative diagram of a rotary surface melting furnace as one
example of a melting furnace to which the present invention is applied.
Fig. 2A is an illustrative diagram of main parts, showing a melting furnace with
nozzles arranged on a furnace ceiling, the nozzles adjusting a combustion atmosphere
near a molten surface; Fig. 2B is an illustrative diagram of the main parts, showing
another aspect in which some of the nozzles in Fig. 2A have a different shape; and Fig.
2C is an illustrative diagram showing the shape of the nozzle in an arrow A direction in
Fig. 2B.
Fig. 3A is an illustrative diagram of main parts, showing a melting furnace with
nozzles arranged on a furnace floor, the nozzles adjusting a combustion atmosphere near
a molten surface, and Fig. 3B is an illustrative diagram of the main parts, showing
11
another aspect of the melting furnace with the nozzles arranged on the furnace ceiling,
the nozzles adjusting the combustion atmosphere near the molten surface.
Fig. 4 is an illustrative diagram of redox properties of metals contained in a
treatment target based on oxygen partial pressure and a CO2/CO ratio.
Figs. 5A and 5B are illustrative diagrams of a surface melting furnace, showing
the other aspects of the melting furnace to which the present invention is applied.
Best Mode for Carrying out the Invention
[0029] Hereinafter, embodiments of a melting furnace and a method for operating a
melting furnace according to the present invention will be described.
Fig. 1 shows a rotary surface melting furnace 1 as one example of a melting
furnace. The surface melting furnace 1 is a furnace for melt-treating miscellaneous
waste, and a treatment target thereof includes: organic sludge such as sewage sludge,
livestock excreta, or methane fermentation residues from food waste; a combustible
material such as plastic, paper, SRF (Solid Recovered Fuel), or recycling residues
containing plastic and metal; an incombustible material such as incinerated ash,
contaminated soil, waste glass, waste pottery, or asbestos; or the like. The metal
includes useful metals such as iron, nickel, copper, silver, and gold, as well as heavy
metals and the like. Although described below is a case in which the treatment target
is a mixture of recycling residues containing plastic and metal and incinerated ash, other
wastes may also be included.
[0030] The rotary surface melting furnace 1 includes an inner cylinder 2 and an outer
cylinder 3 which are concentrically arranged, and a storage part 15 for the treatment
target is formed between the inner cylinder 2 and the outer cylinder 3. A furnace
ceiling 5 is provided inside the inner cylinder 2, and a furnace floor 6 is formed
12
extending in a central direction from a lower part of the outer cylinder 3. A slag port 7
is formed at the center of the furnace floor 6. A furnace chamber 4 is formed in a
space surrounded by the inner cylinder 2, the furnace ceiling 5, and the furnace floor 6,
and the respective inner walls are covered with refractories. The inner cylinder 2 and
the outer cylinder 3 are configured to be airtight with a water-sealing mechanism 13.
[0031] A screw-type conveyor mechanism 11 is provided to convey the treatment
target to the storage part 15, and the treatment target is dropped and supplied into the
storage part 15 via a double damper mechanism 12 to prevent outside air from flowing
into the furnace chamber 4.
[0032] Rotation of the outer cylinder 3 relative to the inner cylinder 2 causes a feeding
blade 9 provided on a lower part of the inner cylinder 2 to feed the treatment target
stored in the storage part 15 into the furnace chamber 4, such that the treatment target is
distributed in a mortar shape toward the slag port 7. The inside of the furnace is
heated to a high temperature of about 1300°C by two combustion burners 8 provided at
a central side of the furnace ceiling 5, such that the treatment target is melted from the
surface thereof and flows down from an upstream side to the slag port 7 on a
downstream side.
[0033] Combustible components, such as waste plastic, of the treatment target fed into
the furnace chamber 4 are first vaporized on the upstream side and burned by gas. On
this occasion, the upstream side has a weakly reducing atmosphere, and heavy metals
contained in the treatment target are reduced and volatilized, and flow down together
with exhaust gas to a secondary combustion chamber. The treatment target heated by
radiant heat from the combustion burners 8 and the furnace ceiling 5 is melted from the
surface thereof and flows down toward the slag port 7. On this occasion, thickness of
a molten layer is several tens of millimeters. The sign A shown in Fig. 1 indicates an
13
un-molten treatment target, the sign B indicates the molten layer, and the sign C
indicates a gasified and burned section.
[0034] Fig. 1 illustrates diagrams indicating waste plastic, incinerated ash, and metal
contained in the treatment target, as well as molten slag and molten metal. The
treatment target is subjected to melt treatment in the furnace chamber 4 and turns into
the molten slag and the molten metal, which drip down from the slag port 7.
[0035] A transport mechanism having a water tank for cooling the molten slag is
arranged below the slag port 7, and the molten slag is discharged outside the furnace as
granulated slag. In addition, combustion gas generated in the furnace chamber 4 is
burned in the secondary combustion chamber provided on a downstream side of the slag
port 7, purified in exhaust gas treatment equipment, and then discharged from a
chimney to the air. The furnace chamber 4 is maintained at a negative pressure by an
induced draft fan arranged on an upstream side of the chimney.
[0036] As shown in Fig. 2A, the furnace ceiling 5 has multi-stage nozzles N1, N2, N3
arranged at different distance along a radius direction of a circle centered at the slag port
7 from the upstream side (i.e. side of the storage part 15) to the downstream side (i.e.
side of the slag port 7) of the furnace chamber 4. Each of the nozzles N1, N2, N3 is
attached at predetermined intervals so as to be concentrically arranged in plan view.
[0037] Each of the nozzles N1, N2, N3 is arranged such that tips thereof are positioned
near the molten surface, and is configured to allow an atmosphere near the molten
surface to be adjusted to either an oxidizing atmosphere or a reducing atmosphere in
each of a plurality of areas from the upstream side to the downstream side.
[0038] Accordingly, an atmosphere control mechanism 16 is provided to adjust a type
and/or composition of gas supplied from each of the nozzles N1, N2, N3. The
atmosphere control mechanism 16 is configured with a control mechanism which
14
controls to supply gas from each of the nozzles N1, N2, N3, the gas having a different
type and/or composition from any of air, oxygen, and combustible gas.
[0039] For example, vicinities of the molten surface on the tip side of the nozzle which
supplies oxygen has an oxidizing atmosphere, whereas vicinities of the molten surface
on the tip side of the nozzle which supplies combustible gas has a reducing atmosphere.
By varying the type and/or composition of the gas, the atmosphere near the molten
surface on the tip side of the nozzle is adjusted to a weakly reducing atmosphere, a
strongly reducing atmosphere, a weakly oxidizing atmosphere, a strongly oxidizing
atmosphere, or the like.
[0040] Since the gas supplied from each of the nozzles N1, N2, N3 is concentrically
supplied to the molten surface as the outer cylinder 3 rotates, the vicinities along the
upstream side to the downstream side can be adjusted to a different atmosphere.
[0041] Although the number of each of the nozzles N1, N2, N3 is not particularly
limited, the number of the nozzle N1 on the most upstream side is greater than those of
the nozzles N2, N3 on the inner side. Therefore, as shown in Figs. 2B-2C, when
arranging an outlet of the nozzle N1 to be aligned with a rotation direction of the outer
cylinder 3, in other words, a circumferential direction of the circle centered at the slag
port 7, it is possible to reduce the installation number thereof.
[0042] As described above, each of the nozzles N1, N2, N3 is attached to the furnace
ceiling 5 so as to be arranged concentrically at predetermined intervals in plan view, and
has the atmosphere control mechanism which controls to adjust the atmosphere near the
molten surface to either an oxidizing atmosphere or a reducing atmosphere in each of a
plurality of areas from the upstream side to the downstream side, thereby melting a
target metal among multiple types of metals as molten metal which is separable from
the molten slag, or capturing the target metal in the molten slag as a metal compound.
15
[0043] As shown in Fig. 3A, each of the nozzles N1, N2, N3 may be installed on the
furnace floor 6 and arranged such that the tips thereof are positioned near the molten
layer B of the treatment target. Note that in this aspect, it is necessary to cover around
each of the nozzles N1, N2, N3 with refractories. If the furnace floor 6 rotates together
with the outer cylinder 3, a configuration of piping for supplying the gas to each of the
nozzles N1, N2, N3 will be complicated; therefore, the furnace floor 6 should be fixed.
[0044] As shown in Fig. 3B, among the three-stage nozzles N1, N2, N3 sequentially
arranged from the upstream side to the downstream side of the furnace chamber 4, the
middle nozzle N2 may be arranged such that the tip thereof is separated above from the
molten surface. Additionally, each tip of the nozzles N1, N2, N3 arranged in a
circumferential direction of the furnace ceiling 5 may be arranged at a different position
between a position separated above from the molten surface and a position near the
molten surface. For example, the position of each tip of the nozzles N1, N2, N3 may
be arranged to alternate between the position separated above from the molten surface
and the position near the molten surface. By employing such configuration, it is
possible to simultaneously adjust control of an entire atmosphere in an inner space of
the furnace chamber 4 and the atmosphere near the molten surface.
[0045] In an area adjusted to a reducing atmosphere by the atmosphere control
mechanism 16, a metal to be treated (hereinafter simply referred to as “target metal”)
turns into molten metal which is separable from the molten slag. In an area adjusted to
an oxidizing atmosphere, the target metal is captured in the molten slag as a metal
compound.
[0046] Fig. 4 shows redox properties regarding multiple types of target metals.
Aluminum, titanium, and chromium belong to a group that is easy to oxidize; iron,
cobalt, nickel, and copper belong to a group that is difficult to oxidize; and silver and
16
gold belong to a group that never oxidizes. The table shows a list of oxygen partial
pressure, a CO2/CO ratio, and oxidizing properties of various metals (theoretical values),
and it is understood that an atmosphere can be adjusted by measuring the oxygen partial
pressure and the CO2/CO ratio in the furnace chamber.
[0047] In this table, it can be seen that when temperature inside the furnace is 1300°C
and the CO2/CO ratio is equal to 100, copper is contained in the metal without being
oxidized while nickel is oxidized and fixed on the slag side. Hereinafter, an
atmosphere no less than the one in which nickel is reduced and melted as molten metal
is referred to as “strongly reducing,” and an atmosphere in which only up to copper is
reduced is referred to as “weakly reducing to oxidizing.”
[0048] When iron, nickel, cobalt, or the like are the target metal, the atmosphere
control mechanism 16 adjusts the atmosphere near the molten surface on the upstream
side to the weakly reducing to oxidizing atmosphere, preferably to the weakly reducing
atmosphere, and volatilizes heavy metals among the multiple types of metals contained
in the treatment target while maintaining other metals in a metal state and metal oxide in
an oxide state.
[0049] When it is required to recover iron, nickel, cobalt, or the like as metal, the
atmosphere control mechanism 16 controls to adjust the atmosphere near the molten
surface on the downstream side to the strongly reducing atmosphere, and melt the target
metal as the molten metal which is separable from the molten slag.
[0050] When it is not required to recover iron, nickel, cobalt, or the like as metal, the
atmosphere control mechanism 16 controls to adjust the atmosphere near the molten
surface on the downstream side to the weakly reducing to oxidizing atmosphere,
preferably to the weakly reducing atmosphere, and capture the target metal in the
molten slag as a metal compound (metal oxide).
17
[0051] When aluminum, chromium or the like are the target metal, the atmosphere
control mechanism 16 adjusts the atmosphere near the molten surface on the upstream
side to the weakly reducing to oxidizing atmosphere, preferably to the weakly reducing
atmosphere, and volatilizes heavy metals among the multiple types of metals contained
in the treatment target while maintaining other metals in a metal state and metal oxide in
an oxide state.
[0052] When it is required to recover aluminum, chromium or the like as metal, the
atmosphere control mechanism 16 controls to adjust the atmosphere near the molten
surface on the downstream side to the strongly reducing atmosphere, and further apply
combustion by the combustion burners at a low air ratio or blow combustible gas to
cause reduction combustion to increase the degree of reduction, thereby melting the
target metal as the molten metal which is separable from the molten slag. On this
occasion, it is preferable to adjust the temperature inside the furnace to 1300°C, and the
CO2/CO ratio to be ≤ 0.0007.
[0053] When it is not required to recover aluminum, chromium or the like as metal,
the atmosphere control mechanism 16 controls to adjust the atmosphere near the molten
surface on the downstream side to the weakly reducing to oxidizing atmosphere,
preferably to the weakly reducing atmosphere, and capture the target metal in the
molten slag as a metal compound (metal oxide). On this occasion, unburned gas and
oxygen for combustion are preferably supplied from the nozzles to maintain the
temperature inside the furnace at 1300°C.
[0054] When gold, silver, copper, or the like are the target metal, the atmosphere
control mechanism 16 adjusts the atmosphere near the molten surface on the upstream
side to the weakly reducing to oxidizing atmosphere, preferably to the weakly reducing
atmosphere, and volatilizes heavy metals among the multiple types of metals contained
18
in the treatment target while maintaining other metals in a metal state and metal oxide in
an oxide state.
[0055] When gold, silver, copper, or the like are to be recovered as metal, the
atmosphere control mechanism 16 maintains the weakly reducing atmosphere near the
molten surface on the downstream side and raises the temperature inside the furnace to
1400-1600°C. It applies combustion by the combustion burners at an adequate air
ratio and blows combustible gas and oxygen gas from the nozzles. In this manner, it is
possible to enhance a recovery rate of the metal by raising the temperature to lower the
viscosity of the slag while suppressing reduction of iron or the like.
[0056] Granulated slag drips down from the slag port 7 as the molten metal together
with the molten slag, is cooled in the water tank, and is discharged outside the furnace.
By specific gravity separation of the granulated slag after pulverization, slag and metal
are separated.
[0057] Although the present invention is described above with regard to the rotary
surface melting furnace, the present invention is applicable to a melting furnace other
than the rotary surface melting furnace.
[0058] For example, as shown in Fig. 5A, the present invention is also applicable to
the surface melting furnace 1 having the slag port 7 formed at the center of the furnace
floor 6 and a plurality of push-in supply mechanisms 30 for supplying the treatment
target disposed around the furnace floor 6. The surface melting furnace 1 is a type of a
surface melting furnace in which both the outer cylinder 3 configured integrally with the
furnace floor 6 and the inner cylinder 2 configured integrally with the furnace ceiling 5
are secured, and the push-in supply mechanisms 30 supply the treatment target into the
furnace chamber.
[0059] Furthermore, as shown in Fig. 5B, the present invention is also applicable to
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the surface melting furnace 1 having the slag port 7 formed at an end of the furnace
floor 6, and a plurality of push-in supply mechanisms 30 for supplying the treatment
target disposed on the opposite side. In any of these surface melting furnaces 1,
multi-stage nozzles are arranged such that the tips thereof are positioned near the molten
surface from an upstream side toward a downstream side of the treatment target which
is pushed into the furnace chamber 4.
[0060] As described above, the method for operating a melting furnace according to
the present invention is a method for operating a melting furnace including: a furnace
chamber where a treatment target containing multiple types of metals is fed from an
upstream side and subjected to melt treatment from a surface thereof by a heating
mechanism provided on a furnace ceiling, thereby generating molten slag which flows
down to a downstream side; a slag port which discharges the flowed down molten slag;
and multi-stage nozzles arranged along the upstream side to the downstream side of the
furnace chamber, the method including: controlling to vary a type and/or composition of
gas supplied from each of the nozzles to adjust an atmosphere near a molten surface to
either an oxidizing atmosphere or a reducing atmosphere in each of a plurality of areas
from the upstream side to the downstream side, thereby melting a target metal among
the multiple types of metals as molten metal which is separable from the molten slag, or
capturing the target metal in the molten slag as a metal compound.
[0061] In the embodiments described above, described is a case where
self-combustible components such as waste plastic are contained in the treatment target.
If suppressing the amount of air supplied from the nozzle N1 during the
self-combustible components contained in the treatment target are being gasified and
burned, suitable adjustment to the reducing atmosphere can be achieved. If no
self-combustible components are contained in the treatment target, adjustment to the
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reducing atmosphere can be achieved by supplying combustible gas from the nozzle N1.
[0062] Each of the embodiments described above are only one example of the present
invention. A specific configuration of each component can be modified and designed
as appropriate to the extent that the operations and effects of the present invention can
be obtained.
Reference Signs List
[0063] 1 Surface melting furnace
2 Inner cylinder
3 Outer cylinder
4 Furnace chamber
5 Furnace ceiling
6 Furnace floor
7 Slag port
8 Combustion burner
9 Feeding blade
15 Storage part
A Un-molten treatment target
B Molten layer on surface of treatment target
C Gasified and burned section
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WE CLAIM:
1. A melting furnace comprising: a furnace chamber where a treatment target
containing multiple types of metals is fed from an upstream side and subjected to melt
treatment from a surface thereof by a heating mechanism provided on a furnace ceiling,
thereby generating molten slag which flows down to a downstream side; and a slag port
which discharges the flowed down molten slag, the melting furnace comprising:
multi-stage nozzles arranged along the upstream side to the downstream side of
the furnace chamber; and
an atmosphere control mechanism which controls to vary a type and/or
composition of gas supplied from each of the nozzles to adjust an atmosphere near a
molten surface to either an oxidizing atmosphere or a reducing atmosphere in each of a
plurality of areas from the upstream side to the downstream side, thereby melting a
target metal among the multiple types of metals as molten metal which is separable
from the molten slag, or capturing the target metal in the molten slag as a metal
compound.
2. The melting furnace according to claim 1, wherein the atmosphere control
mechanism controls to adjust the atmosphere near the molten surface on the upstream
side to a weakly reducing atmosphere to volatilize heavy metals among the multiple
types of metals, and adjust the atmosphere near the molten surface on the downstream
side to a strongly reducing atmosphere to melt the target metal among the multiple types
of metals as the molten metal which is separable from the molten slag.
3. The melting furnace according to claim 1, wherein the atmosphere control
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mechanism controls to adjust the atmosphere near the molten surface on the upstream
side to a weakly reducing atmosphere to volatilize heavy metals among the multiple
types of metals, and adjust the atmosphere near the molten surface on the downstream
side to the oxidizing atmosphere or the weakly reducing atmosphere to capture the
target metal among the multiple types of metals in the molten slag as the metal
compound.
4. The melting furnace according to claim 1, wherein the atmosphere control
mechanism controls to adjust the atmosphere near the molten surface on the upstream
side to a weakly reducing atmosphere to volatilize heavy metals among the multiple
types of metals, and adjust the atmosphere near the molten surface on the downstream
side to the weakly reducing atmosphere and further adjust temperature of the molten
surface to 1400-1600°C, thereby melting the target metal among the multiple types of
metals as the molten metal which is separable from the molten slag.
5. The melting furnace according to any one of claims 1 to 4, comprising a rotary
surface melting furnace, the rotary surface melting furnace comprising:
an inner cylinder dividing the furnace chamber;
an outer cylinder arranged around a periphery of the inner cylinder;
a storage part for the treatment target formed between the inner cylinder and
the outer cylinder; and
the furnace chamber in which the treatment target, which is fed out of the
storage part into the furnace chamber by relative rotation of the inner cylinder and the
outer cylinder, is melt-treated from the surface of the treatment target, and the molten
slag flows down to be discharged from the slag port formed at a center of a furnace
floor,
wherein the multi-stage nozzles arranged along the upstream side to the
downstream side of the furnace chamber are disposed on the fumace ceiling or the
furnace floor.
6. A method for operating a melting furnace comprising: a fumace chamber
where a treatment target containing multiple types of metals is fed from an upstream
side and subjected to melt treatment from a surface thereof by a heating mechanism
provided on a fumace ceiling, thereby generating molten slag which flows down to a
downstream side; a slag port which discharges the flowed down molten slag; and
multi-stage nozzles arranged along the upstream side to the downstream side of the
furnace chamber, the method comprising:
controlling to vary a type and/or composition of gas supplied from each of the
nozzles to adjust an atmosphere near a molten surface to either an oxidizing atmosphere
or a reducing atmosphere in each of a plurality of areas from the upstream side to the
downstream side, thereby melting a target metal among the multiple types of metals as
molten metal which is separable from the molten slag, or capturing the target metal in
the molten slag as a metal compound.