CA1217051A - Melting apparatus for melting and slagging particulate waste material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A melting apparatus comprising a low temperature melting portion (29), an exhaust gas cooling portion (26), a dust collecting portion (B27) which are arranged, in succession, in an exhaust gas duct (54) of a melting furnace (22), a low boiling point dust collected in the dust collecting portion (B27) being returned to the low temperature melting portion (29) and being melted therein by retention heat of an exhaust gas flowing into the exhaust gas duct (54).

Description

~z~

The present invention relates to a melting apparatus for melting and slagging a waste water treatment sludge, an ash or dust discharged from an incinerating apparatus, or the like and, more particularly, relates to a melting appara-tus comprising a structure for effectively collecting low boiling point dust apt to circula-ting in the dus-t collec-ting path.
In arrangements for incinerating and treating a waste to be treated, it is widely practiced, for the purpose of 10 solidifying an incinerated residue and collected dust, that a melting furnace is provided in the post process of an incinerating furnace, wherein the incinerated residue and the collected dust are melted and slagged, and then the melt-ed slag is cooled and solidified to be discharged. A waste water treatment sludge is directly melted in a melting furnace to form a melting slag and then is cooled and soli-dified to be discharged.
However, the chloride or dust genera-ted or collected in the conventional type of melting furnace con-tains components 20 such as ZnC12, PbC12, CdC12, KCl, NaCl and FeC12, having a lower boiling point than the temperature within the melting furnace. These low boiling point dusts are gasified in -the melting furnace and thus discharged with the exhaust gas and the like. Therefore, such dust can not be solidified. If such gasified componen-t having a low boiling point is cooled in a heat exchanger, the component is again solidified -to become dust and is collected. Thus, the collected dust is again introduced into the melting furnace. However, since 7~

the internal temperature in the melting furnace is higher the low boiling point of -the low boiling point component, the low boiling point components are again gasified to cir-culate in the system. Thus, such low boiling point compo-nents always continue to circulate in the collecting system and hence are not discharged to the exterior of the sys-tem.
Therefore, while this type of melting apparatus con-tinues to be driven for a longer time period, such low boiling point dust is stored in the collecting system and a con-lO siderable amount thereof tends to be deposited on inner surfaces of tubes and heat exchangers through which the ex-haust gas from the melting furnace flows, which causes a problem of blockade or failure of the tube and heat ex-changer.

The present inventor has proposed a structure for over-coming such a problem, wherein a separate dust collecting portion is provided in an exhaust gas line of -the melting furnace, in which dust collecting portion the low boiling point dust is collected and is introduced into a separately designed melting furnace having a lower furnace temperature in which the low boiling point dust is melted and slagged and is discharged to the exterior of the system.

5~

However, even in such an improved melting apparatus, there are some problems in tha-t the struc-ture is rela-tively complicated and the operation of the re-melting furnace newly provided is costly.
Accordingly, a principal object of the present inven-tion is to provide a melting apparatus capable of effect-ively discharging a low boiling point dust to an exterior of the system, the struc-ture thereof being relatively simple and the operating cost being small.
sriefly stated, the présent invention is directed to a melting apparatus comprising a melting furnace for melt-ing a waste and for discharging a slag from a slag dis-charging port, an exhaust gas duct diverged from the slag discharging port of the melting furnace for discharging an exhaust gas generated in the melting furnace, a low tempera-ture melting portion provided in the exhaust gas duct and for melting dust con-tained in the exhaust gas, an exhaust gas cooling portion provided on a farther downstream side than the lower temperature melting portion in -the exhaust gas duct and for cooling the exhaust gas, a dust collecting portion provided on a farther downstream side of said exhaus-t gas duct than the exhaust gas cooling portion and for collect-ing dust contained in the exhaus-t gas, a first dust supply line for introducing the low boiling point dus-t collected in the dust collecting portion to the low temperature melting portion, and cooling means for cooling the melted subs-tance discharged from the low tempera-ture melting portion.

" 5~

In accordance wi-th -the present invention, with the above described s-tructure of the presen-t invention, it be-comes possible to economically slag relatively low boiling point dust and also becomes possible to surely prevent an accident such as blockage in a duct or a dus-t collector, since no dust is stored in a system.
In the accompanying drawings:
Fig. 1 is a flow diagram of a conventional waste melt-ing apparatus system;
Fig. 2 is a flow diagram of a system in which a melting apparatus of one embodiment of the present invention is incorporated;
Fig. 3 is a schematic cross-sectional view showing a structure of a mel-ting apparatus of the present inven-tion shown in Fig. 2; and Fig. 4 is a graph showing a relation between a compound-ing ratio of dust supplied to a low temperature melting portion from a first dust supplying line tc dust supplied to the low temperature melting portion from a third dust supplying line and a melting point of the dust supplied -to the low temperature melting portion.
Fig. 1 shows a flow diagram of a conventional melting appara-tus for waste wa-ter treatment sludge. After collect-ed waste 1 is temporarily stored in a reservoir pit, the waste 1 is incinerated in an incinerating furnace. An in-cinerated residue 2 such as ash or non-combustible material, and exhaust gas 3 are discharged from the incinerating 7~

furnace. Of -these, the incinerating residue 2 is introduc-ed into a melting furnace, the temperature of which is raised to predetermined kemperature, and is melted and slagged, and then the melted slag is cooled and solidified to be discharged as a solid slag 7 to the ex-terior of the system. On the other hand, the exhaust gas 3 is passed -to an exhaust gas cooling portion A (for example, water sprinkling cooler apparatus) so that the gas 3 is cooled, and then, after the dust included in -the exhaust gas is removed in a dust collecting portion A, the gas is dis-charged to the exterior. The dust 4 collected in the dust collecting portion A is introduced into the melting furnace wherein the dust 4 is melted and slagged together with the incinerated residue 2. In addition, an exhaust gas 5 generated when the incinerated residue 2 and the collected dust 4 are melted in the melting furnace, is introduced in-to a heat exchanger and cooled therein, and then, is through a line 6 to be joined with the exhaust gas 3 from said incinerating furnace through a line 6 -to be supplied to the dust collecting portion A in which the dust is again collected.
Fig. 2 is a diagram for explaining a flow of a melting apparatus of an embodiment of the present invention. As seen from ~ig. 2, a melting apparatus of the embodiment comprises an incinerating and treating portion encircled by a chain line X and a melting and treating portion encircled in a chain line Y. A reference character A in the following description indicates a structure included in a conventional apparatus shown in Fig. 1 and a reference character B indicates apparatuses provided at the first time in this embodiment.
A waste 11 to be incinerated and treated is stored in a reservoir pit 12, arJd then is introduced into an incinerating furnace 13. In the incinerating furnace 13, the waste 11 is incinerated and treatedl so that an incinerated residue 14 and an exhaust gas 15 are generated. The incinerated residue 14 is supplied to a melting and treating portion Y described subsequently. On the other hand, the exhaust gas 15 generated in the incinerating furr.ace 13 is cooled in an exhaust gas cooling portion A16, and then is introduced into an exhaust gas treating portion 17. The exhaust gas treating portion 17 comprises an HCl absorbing portion 18 and a dust collecting portion A19. HCl generated in the incinerating furnace, for example, by combustion of PVC
products and the like, is removed by absorption or adsorption thereof in the HCl absorbing portion 18. When HCl is absorbed, CaCC~, Ca(OH)2, CaO, NaOH or the like is used in a dry method or a wet method. As a result of absorbing action, CaC12, ~aCl or the like (referred as ~2~7~S~

"chloride" hereinafter) is formed. On the other hand, the dust in the exhaust gas ls collected in the dust collecting portion A19.
The chloride formed in -he ~ICl absorbing portion 18 and the dust collected in the dust collecting portion A19 are gathered together to be ,upplied to a melting furnace 22 through a second dust supplying line 21. A separate dust supplying line 23 is diverged from the dust supplying line 21. The dust supplying line 23 is introcuced into a lo~ temperature melting furnace 29 of the melting ar.d treating portion Y described subsequently.
The incinerated residue 14 and the chloride, dust and the like in the exhaust gas are applied to the melting furnace 22 and are melted and slagged therein, and~
thereafter, the melted slag is cooled and solidified in a slag cooling portion ~25 to be discharged as a solid slag to an ext~rior of the system.
The melting furnace 22 is usually maintained to be relatively high temperature such as 1300C - 1500DC.
Thus, the exhaust gas generated in the melting furnace 22 contains a large aamount of gasification substances of th~
above described low boiling pGint dust component. ~he gasification substance is cooled and solidified in ar, exhaust gas cooling portion B26 provided in the exhaust gas duct, and thereafter, is collectec ir. a dust ~Z~7~

co]lecting portion B27. The low boiling point dust collected in the dust colle,~ting portion B27 is applied to the low temperature melting portion 29 through â first dust supplying line 28. As apparent from Fig. 2, the low temperature melting portion 29 is disposed on the upstream side as compared with the exhaust gas cooling portion B26.
Accoràingly, an exhaust gas with heat quantity discharged from the melting furnace 22 is suppliea to the low temperature melting portion 29 and thus the lcw boiling point dust is melted and treated by the heat quantity of the exhaust gas. As a result, the low boiling point component becomes a melted slag 30 so that it is discharged as a solid slag to an e~terior of the system from the slag cooling portion s31.
lS In the above describec apparatus shown in Fig. 2, the incinerating furnace 13 was disposed in the front stage of the melting furnace 22. Hc,wever, in case where a waste to be treated is a waste water treatment sludge, as shown in a phantom line in Fig. 2, it is possible to treat the waste water treatment sludge 41 by directly supplying the sludge 41 to the melting furnace 22, without using an incinerated furnace 13 and the like. In such a case, the dust supplied to the low temperature meltirg portion 29 is only a dust collected in the dust collecting portion ~G7.

However, as an alternative means, a portion of solid slag discharged from the sl~g cooling portion A25 may be supplied to the low temperature mel-ting portion 29 through a slag supplying line 49 ~shown in a phantcm line in Fig.

2), together with the dust from the dust collecting portions B27.
Now, a specific structure of a melting apparatus of the embodiment will be described together with Fig. 3. The most significant feature of the apparatus resides in a point that there is provided a low temperature melting portion in which sensible heat of an exhaust gas generated in the n-,elting furnace is directl~ utilized, without comprising a low temperature melting portion requiring a separate heat source such as the above described invertion in the prior filecd application.
Referring to Fig. 3, the melting apparatus of the present embodiment comprises a melting furnace 22, a low temperature melting portion 29, a coGling water reservoir 25 for slag from the melting furnace, a coolina water reservoir 31 for slag from the low temperature meltirlg portion (corresponding to the slag cooling poxtion B31 in Fig. 2), an exhaust gas cooling portion B26, a dust collecting portion B27 and the like. A hopper H is provided in an upper portion of the melting fu~nace 22.
The wastes, such as shred~ed waste from the reservoir pit ~7C~

12, the incinerated ash from the ir.cinerating furnace 13, the chloride collected in the ~Cl absorbing portion 18) the collected dust from tile dust collecting portion Al9 ar.d the like are collecti~ely supplied to the hopper ~l.
As described in the foregoing, in the treatment of a waste such as a waste water treatment sludge, such waste water treatment sludge is directly supplied to the hopper H and is meited and treated as described subsequentl~.
The waste to be treated supplied through the hopper H
is melted by flame heat from burners 34, 34 provided in an approximately mid portion of an upper refractory wall 33 in a flame chamber 32 in the melting furnace 22. An afterburning chamber is formed in the bottom of the melting furnace 22. The afterburning chamber 35 serves as a dropping path and afterburning of exhaust gas (incomplete combustion exhaust gas containing H2, C0 and the like) generated in the melting furnace. The melted slag 36 drops onto an inclined bottom portion 37 of the afterburning chamber 35.
In the present embociment, an inclined slag chute 38 is provided in such a manner that the surface of the inclined bottom portion 87 is covered with the chute 38.
The inclined slag chute ^8 is made of, for example, a stainless steel plate having a good corrosion-resistance and a good heat-resistance. A cooliny water supplying port 39 is provided in a s.ide wall of the afterburning chamber 35 in the upper portion of the inclined slag chute 38 and a cooling water is :,upplied to the inclined slag chute 38 from the cooling water supplying pcrt 39. Thus, the melted slag 36 dropping to the afterburning chamber 35 does not contact directly with the inclined bottom portion 37, but drops onto the inclined slag chute 38. Therefore, the damage of the inclined bottom portion 37 caused by the heat of the melted slag 36 can be effectively prevented.
In addition, the damage of the inclined botto~. portion 37 caused by dropping of the melted slag 36 can be also avoided, since the shoc~ at the time of dropping of the melted slag 36 i.s softened by the inclined slag chute 38 The melted slag dropping together with the cooling water from Ihe inclined slag chute 38 is solidified in the cooling water reservoir 25 and discharged to the-exterior of the system by a conveyGr 42.
A surplus cooling wat.er circulating paths Aa, Ab are provided between the cooli.ng water supplying port 39 and a cooling water collecting path 43a, which paths Aa, Ab serve as a circulating pat.h of a cooling water supplied onto the inclined slag chute 38 from the cooling water supplying port 39. In thi.s case, a portion of -the cooling water in the cooling water reservoir 25 is utilized as a cooling water. ~ore part:icularly, the water circulated ~7~

as a coolin~ water is the water flowir.g into the surplus cooling water collecting path 43a prcvided in the upper pGrtion of the cooling water reservoir 25, in which case the surplus cooling water flowing into the ccllecting path 43a is pumped by a p~mp 44 and is fed to a heat exchanger 45 from the cooling water circulating path Aa. After the water is cooled in the heat exchar.ger 45, the water is introduced into the cooling water supplying port 39 through the cooling water cjrculating path Ab. Then, the cooling water discharged from the cooling water supplying port 39 flows into the cool:Lng water reservoir 25 through the inclined slag chute 38 and again overflows to the surplus cooling water collecting path 43a. Thus, the cooling water is circulated and is always supplied onto the inclined slag chute 38, so that the dropping melted slag 36 is smoothly carried down the cooling water reser~oir 25 and is cooled ~herein. Accordingly, the above described problem that the inclined bottom portion 37 is heated can be effectively overccme.
The melted slag 36 is cooled on the inclined slag chute 38 by the cooling wa~er, and hence water vapor is generated. However, it can be understood that the place where the water vapor is actually generated is a lower portion of a communicating path 46, since the cooling water always flows over the inclined slag chute 38. The ~L2~

cooling water flowing down through the inclined slag chute 38 forms an inclined water film, that is a water curtain in the pcrtion of the commu.nicating path 46. Accordingly, the water vapor generated i.n the cooling wa-ter reservoir 25 is prevented from risinci by the water curtain.
Therefore, there is no fear that the water vapor flows into an interior of the aft:erburning chamber 35 and hence the temperature in the afterburning chamber 35 can be maintained constant.
On the other hand, a cooling meaium, such as water, cGntinues to be supplied fr.om the tubes Ba, Bb to the heat exchanger 45, for the purpose of cooling the cooling water fed from the pump 44. More particularly, the cooling medium is supplied to the heat exchanger 45 from the lS reservoir tank S1 by a pump 52 and is heat exchanged in the heat exchanger 45, and then, is discharged from the tube Bb. The cooling medium fed out from the tube Bb, that is, the heated cooling medium is appropriately supplied to a terminal apparatus for utilizing remaining 2n heat, so that the exhaust .heat can be effectively utilized.
Now, the treatment of the dust in the exhaust gas, which is a characterized structure of the present invention, will be describ_a. An incomplete co~ustion exhaust gas generated in the melting furnace 22 is completely burnt out by an a:Eterburning burner 53 provided in the afterburning chamber :35. The exhaust gas completely burnt out is introduced into the exhaust gas cooling porticn B26 through an exhaust gas duct 54 diverged from the afterburnig chamber 35. In the exhaust gas cooling portion B26, the gasification substar,ce of the low boiling point dust in the exhaust gas is cooled and solidified. Therefore, these solidified dusts are collected in the dust collecting portion B27 and purified 10 exhaust gas is discharged to the exterior of the system.
On the other hand, a low temperature melting portion 29 is interposed on the upstream side of the exhaust gas cooling pcrtion B26 of the exhaust gas duct 54. The low temperature melting portion 29 has a silo-like charging tube 55 the outer surface of which is covered with refractory material, and a pan 56 depending from a lower portion of the silo~like charging tube 55. A water seal type of cooling water reservoir 31 for slag from the low temperature melting portion is disposed in a lower portion of the low temperature melting portion 29. The dust collected in the dust collecting portion B27 as described in the foregoing is applied to the low temperature melting portion 29 thrcugh the first dust supplying line 28. A
mixer 58 is provided in midway of the aust supplying line 28. To the mixer 58 is connected a third dust supplying lL2~

line 23 di~erged from the second dust supplying line 21 which is directed to the me:Lting furnace 22 from the HCl absorbing portion 18 and the dust collecting portion Al9 of the incinerating and treating portion 17. In addition, an introduction line 60 for adding FeSO4 is connected to the mixer 58. Accordingly, these dust and FeSO4 are altogether applied to the low temperature melting portion 29. The mixer 58 includes a structure adapted such that a compounding ratio of the dusts supplied from the dust supplying lines 28 and 23 can be~ made to be a predetermir,ed value, so that the dust compounding ratio can be made to be a preferable value as described subsequently. In addition, it is desirable to uniformly mix each of dusts in the mixer 58, in supplying the dust to the low temperature melting portion 29. For this reason, warm water supplied from the tube path Bb utilizing the above described remaining heat is introduced into the mixer 58 in which each dust and FeSO4 may be mixed by any agitating means. As a matter of course, water may be mixed insteaâ of warm water. As the agitating means, a well-kncwn mechanical agitator, an air bubbling or the like can be employed. In addition, if the gas discharged from the dust collecting portion B27 is used for the air bubbling, the apparatus can be simplified. ~he reason why the mixer 58 is provided in - \

~2~L7~

which the dust supplied from the dust supplying line 23 from an incineratin~ and treating portion is mixed will be subsequently described in detail.
The dust applied to the low temperature melting porticn 29 is just like past:e, and thus flows down to the silo-like charging tube 55. Since the tip of the silo-like charsing tube 55 is inserted into the exhaust gas duct 54, the paste-like dust is heated by high temperature exhaust gas flo~Jing into the exhaust gas duct 54 and hence the temperature thereof is gradually raised.
Since the temperature of the exhaust gas flowing into the exhaust gas duct is lower than the temperature in the melting furr.ace 22 and the afterburning chamber 35, the low boiling point dust is not gasified. Accordingly, the low boiling point dust is surely melted in the low temperature melting portion 29 and stored in the pan 56 and overflGws from the edge of the pan 56 and drops into the cooling water reservoir 31. The melted slag is cooled anZ solidified in the cooling water reservoir 31, ~r.d then, discharge~ tc the exterior by a conveyor 61. In the above described melting apparatus, the temperature in the melting furnace 22 is raised to about 1350C for the purpose of melting and slagging high boiling point dust such as incinerated ash. However, the temperature of the exhaust gas arri~7ing at the low temperature meltir.g ~2~

portion 29 from the melting furnace 22 through the afterburning chamber 35 and the exhaust gas duct 54 ranges in 1000C - 1200C. Thus, the -temperature of the dust in the charging tube 55, which is heated by the exhaust gas, is raised to at most 900C - ~50C, and hence, the low boiling point dust ln the charginy tube 55 is merely melted and is not gasified. Hence, the low boiling point dust becomes a melted slag and drops into the cooling water reservoir 31.
The feature of the melting apparatus of the present embodiment resides in the point that a low boiling point dust is selectively extract:ed and is melted and slagged in the range of temperature higher than the melting point and lower than the boiling point by utilizing, as heat source, retention heat of exhaust ~fas. Therefore, it can be understood that the low bo:ling point dust can be economically slagged.
Now, the mixture in the above described a~itator 58, of the dust supplied from l-he dust supplying line 28 with the dust supplied from the dust supplying line 23 will be described. It is first pointed out that the mixer 58 is not an indispensable const:ituent element of the present invention. More particulacly, without the mixer 58 and the dust supplying line 23, only the dust generated in the dust collecting portion BZ7 may be supplied to the low ~2~ 5~

temperature melting portion 25 through the dust supplying line 28. Everl in such a case, it can be understood that the low boiling point dust is melted and slagged by retention heat of the exhaust gas ~lowing into the exhaust gas duct 54 and hence can be surely discharged to the exterior of the system. However, preferably, as described in the foregoing, there is provided the agitator 58 to which the dust supplying line 23 from the incinerating and treating portion and the FeSO2 introduction line 60 are connected, and as a result, a mixed dust is supplieci to the low temperature melting portion 29. The reason will be described based on the following examples of experimer.t.
Fig. 4 is a graph shcwing a variation of melting point of the mlxed dust in case ~7here a mixing ratio o~
the dust supplied from the dust supplying line 28 to the dust supplied from the dust supplying line 23 is changed.
As seen from Fig. 4, it will be understood that the melting point of the mixeci dust exceeds 900C if and when the compounding ratio of t:he dust supplied from the dust supplying line 28 to the clust supplied from the dust supplying line 58 exceeds 1:2. Accordinglv, if and ~-hen the compounding ratio exceeds 1:2, the low ~oiling point dust such as a chloride is gasified and hence can not be melted and slagged. Therefore, it is required that the ~L2~7~

compounding ratio of the dust supplied from the dust supplying line 28 to the dust supplied from the dust supplying line 50 is less than 1:2. Preferably, it is desirable that the ratio is less than 1:0.9. As a result, the melting ~oint of the mixed dust can be made to be less than 800C and gasification of the low boiling point dust can be surely preventecl.
The essential reason for treating as the mixed dust is that elution of heavy metals such as Cd, Pb or the like from the slag cooled and solidified in the low temperature rnelting portion 29 and the slag cooling water reservoir 31 is prevented. More particularly, the elution of heavy metals such as Cd, ~b and the like from the slag which is obtained by applying on]y the low boiling point dust collected in khe dust collectir,s portion 27 to the low temperature melting portion 29 throu~h the dust supplying line 28, is confirmed throuch experiment. In order to prevent such elution, the dust from the dust supplying line 23 is mixed by the agitator 58, as described in the foregoing. As a result of repetition of experiment with various kinds of conditions in the melting apparatus of the present embodiment, following results were obtained.
Table l indicates the result: of elution of heavy metals f~om the obtained slag.

-- ~0 ~2~

TA:3LE l MELTING AMDUNT CF ELUTION
No. CoMPOUND ~ATIO l~PERATURE OF HEAVY METALS mg/l Cd Pb 1 1 :0 900C 59 18 2 1 :0.6 900C Ø33 0.5

3 1 :0.7 900C C.02 0.5

4 1 :0.8 900C 0.3 0.4 1 :0.85 900C 0.29 0.4 6 1 :0.9 900C 0.12 0.4 7 1 :1 900C <0.01 9.6 8 0.5:1 900C ~ 0.01 24 As seen from Table 1, it will be understood that an elution amount of Pb and Cd can be controlled to be sc small on condition that the compounding ratio of the melted dust supplied from the dust supplying line 28 to the incinerated dust supplied from the dust supplying line 23 is 1:0.7 - 1:0.9. However, it will be also understood that the compounding ratio may range in 1:0.5 - 1:0.9 if elution of Cd is neglected and the elution amount of Pb is controlled to be less than ..0 PPM.
Conversely, in case where it is possible to neglect the elution of Pb and it .is required that the elution ~L2~

amount of Cd is controlled to be less than 0.3 PPM, the compounding ratio may be ove~r 1:0.6. As apparently seen from the above described result of Table 1, elution of heavy metals from the slag i.ormed in the low temperature melting portion 29 and the slag cooling water reservoir 31 can be effectively pxeventecl by mixing the ~ust of the incinerating and treating portion from the dust supplying line 23 in the mixer 58.
Now, an advantage that the FeS04 introduction line 60 is connected to the ~ixer 5~3 will be described. Table 2 indicates the result of experiment in case where FeS04 is mixed.

~ ~ . , AMOUNT OF ELUTION
AMOUNT OF OF ~EAVY METALS*
No. COMPOUND RATIO FeSO4 Cd Pb 1 1:0.85 1 % 0.30 0.2 2 1:0.90 1 % 0.10 0.2 3 1:1.0 1 % 0.01 0.2 4 1:0.85 0 0.80 0.5 1:0.g0 0 0.13 0.3 6 1:1.0 0 0~01 0.3 *:mg/l As seen from Table 2, it will be understood that elu-tion amount of Cd and Pb can be effectively reduced if 1 %
of FeSO4 is added as compared with the case where such is not added. In addition, it was confirmed that if FeSO4 is added, the mixed dust agitated in the agitator 58 is made more uniform and hence the mixed dust of stabilized composition can be obtained and thus elution amount of heavy metals from the slag can be surely reduced -to less than a predetermined value.
Al-though the present invention has been described and illustrated in detail, it is clearly unders-tood that the same is by way of illustration and example only and is not ~LZ~7~

to be taken by way of 1imitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims (7)

In the embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A melting apparatus comprising:
a melting furnace for melting a waste and discharging a slag from a discharging port thereof, an exhaust gas duct diverged from -the slag discharging port of said melting furnace for discharging an exhaust gas generated in said melting furnace, a low temperature melting portion provided in said exhaust gas duct and for melting low boiling point dust contained in the exhaust gas, an exhaust gas cooling portion provided on a farther downstream side of said exhaust gas duct than said low temperature melting portion and for cooling the exhaust gas, a dust collecting portion provided on a farther down-stream side of said exhaust gas duct than said exhaust gas cooling portion and for collecting dust contained in the exhaust gas, a first dust supply line for introducing the low boiling point dust collected in said dust collecting por-tion into said low temperature melting portion, and cooling means for cooling melted material discharged from said low temperature melting portion.

2. A melting apparatus in accordance with claim 1, which further comprises an incinerating furnace disposed in the front stage of said melting furnace, said incinerating furnace being provided with an exhaust gas cooling portion for cooling an exhaust gas generated in incinerating, and a dust collecting portion for the incinerating furnace for collecting dust from said exhaust gas, a second dust supplying line for supplying to said melting furnace the dust collected in said dust collecting portion for said incinerating furnace, and a third dust supplying line diverged from said second dust supplying line and connected to said first dust supplying line.

3. A melting apparatus in accordance with claim 2, wherein said dust supplying lines are connected to each other such that the dust supplied to said low temperature melt-ing portion through said third dust supplying line is at most 0.9 times of the dust supplied through said first dust supplying line.

4. A melting apparatus in accordance with claim 3, wherein the ratio of the dust supplied to said low temperature melting portion through said first dust supply-ing line to the dust supplied to said low temperature melt-ing portion through said third dust supplying line ranges in 1:0.85 - 1:0.90.

5. A melting apparatus in accordance with claim 2, which further comprises an agitating and mixing apparatus is provided in the portion where the first dust supplying line and said third dust supplying line are connected, an Fe2SO4 introduction line being connected to said agitating and mixing apparatus, other -than said first and third dust supplying lines.

6. A melting apparatus in accordance with claim 1, wherein said cooling means comprises a cooling water reservoir for cooling melted material of the low boiling point dust.

7. A melting apparatus in accordance with claim 1, which further comprises a solid slag discharging conveyor disposed in a lower portion of a melted slag dropping port of said melting furnace, an inclined slag chute provided in said melted slag dropping port, a cooling water supplying port being provided on an upper portion of said inclined slag chute and for flowing a cooling water to an inclined surface of the slag chute, a cooling water collecting path provided in said solid slag discharging conveyor in a low in the lower portion of said inclined slag chute, and said cooling water supplying port and said cooling water collecting path are connected by tube paths so that a circulating water path is formed, a heat exchanger for cooling circulating water being disposed in the circulating water path.