Heating – With heating gas conveying – agitating – scattering or...
Utility Patent
1999-08-16
2001-01-02
Ferensic, Denise L. (Department: 3749)
Heating
With heating gas conveying, agitating, scattering or...
C048S1970FM, C423S359000
Utility Patent
active
06168425
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for treating solid wastes or fuel derived from solid wastes such as municipal wastes, refuse-derived fuel, solid-water mixture, plastic wastes, FRP wastes, biomass wastes, shredder dust (automobile wastes, electric appliance wastes or the like) by gasification and slagging combustion system.
The refuse-derived fuel is produced by crushing and classifying municipal wastes, adding quicklime to the classified municipal wastes, and compacting them to shape. The solid water mixture (SWM) is produced by crushing municipal wastes, converting them into a slurry by adding water, and converting the slurry under a high pressure into an oily fuel by hydrothermal reaction. The FRP is fiber-reinforced plastics. The biomass wastes include wastes from water works or sewage plants (misplaced materials, sewage sludges), agricultural wastes (rice husk, rice straw), forestry wastes (sawdust, bark, lumber from thinning), industrial wastes (pulp-chip dust), and construction wastes.
BACKGROUND ART
Currently, 75% of municipal wastes is treated by incineration in a fluidized-bed furnace or a Stoker furnace. However, there has long been desired the waste treatment technology suitable for environmental conservation in place of incineration treatment from the following reasons.
1) In order to prolong landfill sites, make ashes harmless, or utilize ashes to materials for civil engineering or construction, needs for ash melting have rapidly been raised.
2) It is necessary to cope with strict restrictions on Dioxins which are expected in the near future.
3) In the conventional method which deals with individually or separately the subject matters of decomposition of Dioxins or ash melting, the rise in construction cost or operation cost of the treatment facilities has been inevitable. On the other hand, it is possible to make scale-down of the gas treatment facilities if the amount of exhaust gas is reduced by a low oxygen-ratio combustion.
4) There has been developing a strong tendency to make use of wastes to generate electric power effectively because waste can be regarded as energy source.
Under these circumstances, new waste treatment systems which incorporate a gasification process have been developed, and some of them which are ahead of others include a system having a vertical shaft furnace as a gasification furnace (hereinafter referred to as a “S system”) and a system having a rotary kiln as a gasification furnace (hereinafter referred to as a “R system”).
FIG. 3
schematically shows the S system. As shown in
FIG. 3
, the S system has a furnace
31
in which a predrying zone
32
, a pyrolyzing zone
33
, and a combusting/melting zone
34
are formed. The S system further comprises a dust collector
35
and a combustion chamber
36
. In
FIG. 3
, the symbols, “a”, “b”, “c” and “d” represent wastes, coke+limestone, oxygen-enriched air, and slag, respectively. Further, the symbols, “e”, “f”, “g”, “h” and “k” represent generated gas, air, dust, exhaust gas, and metal, respectively.
As shown in
FIG. 3
, in the melting furnace
31
, the predrying zone
32
at a temperature ranging from 200 to 300° C., the pyrolyzing zone
33
at a temperature ranging from 300 to 1000° C., and the combusting/melting zone
34
at a temperature of 1500° C. or higher are formed as accumulated layers. Wastes “a” charged into an upper part of the furnace descend in the furnace while exchanging heat with gas which has been generated in the lower zones. The generated gas “e” discharged from the upper part of the melting furnace
31
passes through the dust collector
35
, and is supplied to the combustion furnace
36
and combusted therein at a temperature of about 900° C. Carbonous materials generated in the pyrolyzing zone
33
and the charged (coke+limestone) “b” descend together and reach the combusting/melting zone
34
, and are combusted at a high temperature by oxygen-enriched air “c” supplied from tuyeres. Slag “d” and metal “k” which have been melted because of a high-temperature are discharged from the bottom of the furnace.
FIG. 4
schematically shows the R system. The R system has a pyrolyzing drum
41
. A cooler
42
, a separator
43
, a pulvelizer
44
and a silo
45
are provided adjacent to the pyrolyzing drum
41
. The R system further comprises a swirling-type melting furnace
46
and a high-temperature air heater
47
. In
FIG. 4
, the symbols, “a”, “f”, “i” and “j” represent wastes, air, char, and incombustibles, respectively. Further, the symbols, “e”, “d”, and “h” represent generated gas, slag, and exhaust gas, respectively.
Wastes “a” which have been crushed are supplied into the pyrolyzing drum
41
which is indirectly heated by the high-temperature air “f”, and are pyrolyzed and gasified slowly at a temperature of about 450° C. under a non-oxygen atmosphere in the pyrolyzing drum
41
while they are stirred by rotation of the pyrolyzing drum
41
. The generated gas “e” discharged from the pyrolyzing drum
41
is supplied to the subsequent swirling-type melting furnace
46
.
On the other hand, solid char “i” and incombustibles “j” are taken out from the pyrolyzing drum
41
and cooled in the cooler
42
, and then are classified into large-sized incombustibles “j” and small-sized char “i” by the screen separator
43
. The char “i” pulverized by the pulverizer
44
is stored in the silo
45
, and then supplied to the melting furnace
46
. In the melting furnace
46
, the pulverized char “i” and the generated gas “e” from the pyrolyzing drum
41
are combusted at a high temperature of about 1300° C. Molten slag “d” is discharged from the bottom of the melting furnace
46
.
The S and R systems have various disadvantages of their own as described below. In the shaft furnace of the S system, the operating cost is high and the amount of carbon dioxide discharged from the furnace increases because auxiliary fuel such as coke is required for forming the melting zone at the furnace bottom at a high temperature ranging from 1700 to 1800° C. Since metals contained in the wastes are melted altogether, the recovered metals become alloy-like mixed metal, and hence cannot be recycled as ingot of each kind of metal. It is difficult for the furnace which belongs to fixed-bed type furnaces to allow gas to ascend uniformly through the space among wastes because the wastes, in various different shapes, are stacked in layers in the furnace. This tends to cause the drift of the gas flowing through the layers. Therefore, the furnace cannot be operated stably, and excessive fluctuations of furnace pressure, gas generating rate, or gas composition are unavoidable.
On the other hand, since the rotary furnace of the R system is indirectly heated and has poor thermal conductivity, the furnace size is unavoidably large. This presents a problem in scale-up of the furnace. The generated char is taken out together with other incombustibles from the rotary furnace, and after cooling large-sized incombustibles are separated and removed therefrom. Thereafter, char is pulverized and stored in a hopper, and then a required amount of char is taken out from the hopper, conveyed and supplied to the melting furnace. Thus, the R system needs complicated facilities for handling char, resulting in rise in plant cost as well as obstacle in a stable operation. Further, heat loss caused by cooling of the char or heat radiation from the char is not desirable from the standpoint of effective energy utilization.
It is therefore an object of the present invention to provide a method for treating solid wastes by gasification and slagging combustion system which does not require auxiliary fuel such as coke, can reduce discharge of carbon dioxide, can recover metals such as iron, copper or aluminum in an unoxidized and refined condition, has a furnace which is compact in size and capable of being scaled up easily, and does not require facilities for pulverizing char and handling pulverized char.
DISCLOSURE OF INVENTION
In order to achieve the above object, the R system has been studied care
Fujinami Shosaku
Hirose Tetsuhisa
Irie Masaaki
Oshita Takahiro
Takano Kazuo
Ebara Corporation
Ferensic Denise L.
Wenderoth , Lind & Ponack, L.L.P.
Wilson Gregory A.
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