Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Reexamination Certificate
2001-03-29
2002-11-12
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
C373S141000
Reexamination Certificate
active
06478839
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method of induction-heat melting treatment of powders and a device for this method, and to be more specific, concerns a method of induction-heat melting treatment of powders and a device for this method by which metals, contained in incineration ash, fly ash, and other forms of ash treated as general waste, can be recovered at high purity and high recovery and by which the incineration ash, fly ash, etc. can be rendered harmless.
BACKGROUND ARTS
Combustibles that have been separated from among industrial waste and domestic waste are incinerated in an incinerator after collection and subject to dumping, landfill treatment, etc. in the form of incineration ash. Meanwhile, when such wastes are combusted, they become so-called fly ash upon vaporization of various low-boiling-point components. Since this fly ash contains large amounts of metals, such as lead, cadmium, chromium, zinc, arsenic, mercury, etc., in comparison to the abovementioned incineration ash, it is collected by means of a bag filter, etc. equipped with slaked lime, etc. and thereby prevented from becoming dispersed into the external environment as exhaust combustion gas.
Since the fly ash that has thus been collected contains large amounts of metals as has been mentioned above, it not only cannot be subject to landfill disposal directly as general waste but also requires strict control in terms of environmental sanitation. Fly ash is thus subject to treatment, such as adjustment of the pH to 11 to 14, for making the metals insoluble in water and thereby preventing elution of the metals, and subsequent mixing with concrete and dumping at a disposal site as concrete-sealed matter.
However, large amounts of unreacted slake lime remain in fly ash, and when the pH of fly ash becomes high, lead and zinc, which are the amphoteric metals among the metals contained in fly ash, become more readily eluted in water. This has thus been a problem especially for landfill disposal.
Thus presently in order to prevent elution and render the fly ash harmless, fly ash is treated with organic chelates or inorganic chemicals, etc., which make use of crystallization reactions. However, such treatment methods have the following problems.
(1) Organic chelate products are decomposed by soil microbes, resulting in the elution of zinc and lead.
(2) Organic treatment products are dissolved by the humic acid in the soil, resulting in the elution of zinc and lead.
(3) Though products of treatment by inorganic chemicals are excellent in long term stability, the amount of treatment product increases, thus resulting in the shortening of the lifetimes of landfill disposal sites.
Also, since metals that have been sealed in concrete become readily eluted when the pH is lowered by acid rain, etc., methods for removing metals without fail from within fly ash have been demanded.
On the other hand, ash melting methods have been noted by various municipalities not only in terms of volume-reduction effects but also in that large merits are provided in terms of enabling the ash to be rendered into harmless matter with which there is no elution of metals, etc. and improving the recycling rate. However, ash melting furnaces, such as plasma melting furnaces, reverberatory melting furnaces, electric resistance melting furnaces, etc., which can be erected adjacent existing incineration furnaces, are all high in construction cost and running cost, etc. and this has been an impeding factor in the introduction and spreading of ash melting methods among municipalities.
As an example of application of an induction-heat melting treatment device to the melting of the abovementioned incineration ash and fly ash, the device of
FIG. 8
has been proposed. As shown in
FIG. 8
, this induction-heat melting treatment device
100
is comprised of a ceramic shell part
102
a
of a large diameter (approximately 2 meters) and a ceramic lower part
102
b
, formed to have the shape of an inverted cone, and is equipped with a hopper
102
, which is connected to a powder supplying pipe
101
at the upper end, and an induction heating coil
103
, which surrounds the outer periphery of the cylindrical shell part
102
a
of the abovementioned hopper
102
. The melt resulting from the melting of ash inside the abovementioned hopper
102
is supplied to a melt storage tank
105
via a conical liquid distributor
104
, provided at the exit at the lower end of the abovementioned hopper.
However, the above-described induction-heat melting treatment device
100
shown in
FIG. 8
had the following problems.
(1) Due to the poor heat conduction of ash, a large amount of time is required for all of the ash stored in the large-diameter hopper
102
to melt. The amount treated per unit time was thus low, the thermal efficiency was also low, and as a result, the running cost was high.
(2) Since the interiors of hopper
102
and melt storage tank
105
are at atmospheric pressure and since the area for vaporization of the metals in the melt after the melting of ash is not large, it was difficult to render the ash slag completely harmless by vaporization of the metals in the melt. The metals also could not be recovered at high purity and high recovery.
(3) Due to the poor heat conduction of ash, when attempts were made to increase the treatment rate of ash, hopper
102
, etc. and other parts of the device had to be made large, leading to increased equipment cost.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method of induction-heat melting treatment of powders and a device for this method, which solve the abovementioned problems of the prior art, enable the rendering of incineration ash, fly ash, and other ash harmless by favorable removal of the metals contained in the ash, enable the metals to be recovered at high purity and high recovery, are high in equipment productivity, and are low in running cost.
(First Aspect: Method of Induction-heat Melting Treatment)
The first aspect of this invention is a method of induction-heat melting treatment of metal-oxide-containing powders, which comprises
a process in which a metal-oxide-containing powder is stored in a closed hopper,
a process in which the abovementioned metal-oxide-containing powder that has been stored in the abovementioned closed hopper is supplied at a prescribed flow rate to an induction heating pipe, which is comprised of dielectric material and has been induction heated to or higher than a prescribed temperature, and the abovementioned metal-oxide-containing powder that falls through the abovementioned induction heating pipe is heated to be melted while at least a part of the metal oxides are reduced,
a process in which the melt that has been obtained by melting is heated while being stored in a receiving container, made of dielectric material, to reduce the remaining metal oxides,
a process in which the liquid-film-like melt flow that overflows and flows down from the abovementioned receiving container is exposed to a vacuum atmosphere to cause the metals in the melt to vaporize and thereby convey the metals along with the ascending evacuation flow,
a process in which the metal vapor particles and/or the condensed metal particles in the abovementioned ascending evacuation flow are collected by means of an electric precipitation means,
a process in which the melt flow that overflows and flows down from the abovementioned receiving container is received and stored in a melt storage tank, and
a process in which the metal that has been collected by and has accumulated on the abovementioned electrostatic precipitation means is removed and recovered from the abovementioned precipitation means, and
with which at least one of either the abovementioned induction heating pipe and the abovementioned receiving container is formed from carbon material or graphite material.
With this invention's method of induction-heat melting treatment of powders arranged as described above, incineration ash, fly ash, or other metal-oxide-containing powder, which has been vacuum dried in adva
Kansa Ken
Mukouyama Yoshihide
King Roy
McGurthry-Banks Tima
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