CA1095334A - Method and apparatus for treating waste material - Google Patents
Method and apparatus for treating waste materialInfo
- Publication number
- CA1095334A CA1095334A CA344,949A CA344949A CA1095334A CA 1095334 A CA1095334 A CA 1095334A CA 344949 A CA344949 A CA 344949A CA 1095334 A CA1095334 A CA 1095334A
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- Prior art keywords
- furnace
- waste material
- heavy metals
- treatment device
- secondary treatment
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
Method and apparatus for treating waste material in a counter flow furnace wherein the material is introduced at one end thereof and the processed material is discharged from the other end, while air is simultaneously introduced thereto and the gases of combustion are caused to flow in counter-current direction with respect to the material being processed and are exhausted at the first end of the furnace, and wherein the furnace has a natural tendency to form zones of processing including sequentially from the first end of the furnace, a drying zone, a charring and volatile burning zone, a fixed carbon burning zone and an ash cooling zone, the method comprising the steps of bleeding secondary exhaust gases from the middle of the furnace substantially between the fixed carbon burning zone and the charring and volatile burning zone, and adding air to the furnace in the charring and volatile burning zone. According to one aspect of the invention the secondary exhaust gases are passed in heat exchange relation-ship with respect to the air being added to the furnace.
Method and apparatus for treating waste material in a counter flow furnace wherein the material is introduced at one end thereof and the processed material is discharged from the other end, while air is simultaneously introduced thereto and the gases of combustion are caused to flow in counter-current direction with respect to the material being processed and are exhausted at the first end of the furnace, and wherein the furnace has a natural tendency to form zones of processing including sequentially from the first end of the furnace, a drying zone, a charring and volatile burning zone, a fixed carbon burning zone and an ash cooling zone, the method comprising the steps of bleeding secondary exhaust gases from the middle of the furnace substantially between the fixed carbon burning zone and the charring and volatile burning zone, and adding air to the furnace in the charring and volatile burning zone. According to one aspect of the invention the secondary exhaust gases are passed in heat exchange relation-ship with respect to the air being added to the furnace.
Description
3~
; This application is a divlsion oE application Serial No. 28~,7~8 filed ~uly 1~, 1977.
This invelltion relates to method alld a~parcl-tl.ls :Eor -treating waste material and more particu].arly to the -treatment of the exhaus-t yases :Erom ;ncineratiny wast~e material. The inveniion ;.s particularly adapted, among ot:he.r possible uses, ~or use in treating the exhaust gases ~rom incinera-ting municipal, industrial or community garbage, trash or reEuse, and sewage sludge, for example.
The problem of preventing air pollution in our present environment has become a critical matter. The present invention is particularly directed to substantially reducing the particulate matter and other impurities appearing in the .
exhaust gas from furnaces. The seriousness of this problem is such that the National Air Po]lution Control Administration Air Criteria (U.S. Public Health) as well as the Environmental Protection Agency, have constantly been tigh-tening the minimum required standards. In view of the new and higher standards of air emission, it has become more difficult and expensive to remove the solid particles from the furnace exhaust gases. -i ~ -I have substantially reduced this problem in a new and improved manner, as will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
In order to accomplish the desired results, the invention provides, in one form thereof, a new and improved method of treating waste material which includes the steps of continuously introducing the waste material to be processed through an inlet into a primary furnace, while simultaneously adding air to the furnace, heating the waste material in the ~;
furnace until it is in a charred state and thence discharging :
;33~
said mate.rial from the furnace and passing lt to a seco~dary treatmen-t device, whi].e s.irnu]taneously discharging exhaust gas from the furl-lace. The secondary treatment devlce ;.n one forrn thereof comprlses means for adcllng a substantlal amount of S ileat whi.le Inalntaln:ing a lim.ited supply of oxygen -thereln so as -to recove.r or remove the heavy me-tals present ln -the was-te material ~elng processed. In another form of the lnvention the secondary lreaLment device comprises means for chemlcally recovering or removing heavy metal.s from the waste materlal.
Thereafter, the remainder of the waste material in the secondary treatment devlce is passed to a secondary furnace ~ :
to burn the carhonaceous material remaining thereln, and thence separately discharglng the ash and relatively clean exhaust .
gas from thi.s secondary furnace.
The lnventlon, in another form -thereof, provides a new and improved apparatus for the treatment of residual materials, characterized in that it comprises means for continuously introduclng waste material to be processed through a waste material inlet lnto a primary furnace and means for simultaneously adding alr to the furnace, means for heating the waste material ln the furnace until it is in a charred state and means for thence dlscharging the material from the furnace and means for passing it to a secondary treatment device while simultaneously discharging exhaust gas from the furnace, means for chemlcally treating or means for volatilizing the heavy metals to recover or remove the heavy metals present in the waste material in the secondary treatment device, means for thereafter passing the remalnder of the waste material in the secondary treatment device to a secondary furnace to ~urn the carbonaceous material remaining -~
in the waste material and means for separately discharging .
::
; This application is a divlsion oE application Serial No. 28~,7~8 filed ~uly 1~, 1977.
This invelltion relates to method alld a~parcl-tl.ls :Eor -treating waste material and more particu].arly to the -treatment of the exhaus-t yases :Erom ;ncineratiny wast~e material. The inveniion ;.s particularly adapted, among ot:he.r possible uses, ~or use in treating the exhaust gases ~rom incinera-ting municipal, industrial or community garbage, trash or reEuse, and sewage sludge, for example.
The problem of preventing air pollution in our present environment has become a critical matter. The present invention is particularly directed to substantially reducing the particulate matter and other impurities appearing in the .
exhaust gas from furnaces. The seriousness of this problem is such that the National Air Po]lution Control Administration Air Criteria (U.S. Public Health) as well as the Environmental Protection Agency, have constantly been tigh-tening the minimum required standards. In view of the new and higher standards of air emission, it has become more difficult and expensive to remove the solid particles from the furnace exhaust gases. -i ~ -I have substantially reduced this problem in a new and improved manner, as will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
In order to accomplish the desired results, the invention provides, in one form thereof, a new and improved method of treating waste material which includes the steps of continuously introducing the waste material to be processed through an inlet into a primary furnace, while simultaneously adding air to the furnace, heating the waste material in the ~;
furnace until it is in a charred state and thence discharging :
;33~
said mate.rial from the furnace and passing lt to a seco~dary treatmen-t device, whi].e s.irnu]taneously discharging exhaust gas from the furl-lace. The secondary treatment devlce ;.n one forrn thereof comprlses means for adcllng a substantlal amount of S ileat whi.le Inalntaln:ing a lim.ited supply of oxygen -thereln so as -to recove.r or remove the heavy me-tals present ln -the was-te material ~elng processed. In another form of the lnvention the secondary lreaLment device comprises means for chemlcally recovering or removing heavy metal.s from the waste materlal.
Thereafter, the remainder of the waste material in the secondary treatment devlce is passed to a secondary furnace ~ :
to burn the carhonaceous material remaining thereln, and thence separately discharglng the ash and relatively clean exhaust .
gas from thi.s secondary furnace.
The lnventlon, in another form -thereof, provides a new and improved apparatus for the treatment of residual materials, characterized in that it comprises means for continuously introduclng waste material to be processed through a waste material inlet lnto a primary furnace and means for simultaneously adding alr to the furnace, means for heating the waste material ln the furnace until it is in a charred state and means for thence dlscharging the material from the furnace and means for passing it to a secondary treatment device while simultaneously discharging exhaust gas from the furnace, means for chemlcally treating or means for volatilizing the heavy metals to recover or remove the heavy metals present in the waste material in the secondary treatment device, means for thereafter passing the remalnder of the waste material in the secondary treatment device to a secondary furnace to ~urn the carbonaceous material remaining -~
in the waste material and means for separately discharging .
::
- 2 -~9S33~
ash and exhaus-t ~as from ~he secollclary furnace.
There has t:hus been oul~ ecl rat,ller broadlv l:he more lmportan-t Eeal-ures of the i,nvention i,n order that -I,he detailcd descr;ptioll ~hereof that follows may be be-l:-ter understood, and in order -tha-t the present contribution to the ar-t may be be-tt,er appreci,ated. ~rhere are, of course, addi-tional features of the inven~,ion that will be described hereinafter and which will form -the subject of the claims appended here-to'. rrhose skilled i,n the ar-t will appreciate that the conception upon which the disclosure is based may readily be utilized as a basis for the designing of other '~- -methods and appara-tus for carrying out the several purposes of -the inven-tion. It is importan-t, therefore, -tha-t the claims be regarded as including such equivalent methods and appara-tus as do not depart from the spirit and scope of -the invention.
Specific embodiments oE the invention have been ~ ..
chosen for purposes of illustration and descrip-ti,on, and are shown in the accompanying drawings~ forming a part of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic illustration, partially in axial, sec-tional elevation of a system for incinerating waste material, according to my invention; and Figure 2 is a diagrammatic illustration of ano-ther emb'odiment of the invention. ;
DETAILED DESCRIPTION OF THE _EFERRED EMBODIMENTS
In the embodiment of the invention illustrated in Fig. 1 of the drawings, ~here is shown a multiple hearth furnace 10 of generally cylindrical configuration. Such a ~' furnace may be of the type, for example, as described in detail ~9S3~ :
in U.S. pa-tent No. 3,905,757 i.ssued Septernber 16, 1975. The furnace is constructed of a tubular outer s-l-eel shell 12, which is lined witll f.ire brick or o-ther similar heat res:;stant ma-ter~.al 14. Tha :Eurnace is provicled with a plurali-ty ~f burner nozz:Les 16, with one or more being provided on osle or more of the hear-tlls, as necessary, for controlling the temperatures within the different regions of the furnace to carry out the particular processing desiredO ~ny sui-table type of fuel may be provided to the burners The interior of the furnace lO is divided, by mealls of hearth floors 20 and 22, in-to a plurality of vertically aligned hearths, the number of hearths being preselected depending on the particular process being carried out. Each of the hearth floors is made of refractory material and is preferably of slightly arched configura-tion to be self~
supporting within the furnace. Outer peripheral drop holes 24 are provided near -the outer shell 12 of the furnace, and central drop holes 26 are formed in alternate hearth floors 22, near the center of the furnace. Wh;.le Fig. 1 shows the uppermost;
or first, hearth as being an in-flow hearth, it will be appreciated that the concepts of my invention apply equally ~iell to a furnace having an out-flow first hearth.
As illustrated in Fig. 1, a rotatable vertical cen-ter ~ ~-shaft 28 extends axially through the furnace lO and is secured by upper bearing means indicated at 30 and lower bearing means 32. This center drive shaft is rotatably driven by an electric motor and gear drive 34, provided for the purpose.
A plurality of spaced rabble arms 36 are mounted on the center shaft 28, as at 38, and extend outwardly in each hearth over the hearth floor. The rabble arms have rabble teeth 40 formed thereon which extend downwardly nearly to the hearth floor.
9~j33~
The rabble teeth are inclined with respect to the lon~itudinal axis of -their respective rabble arms to that as -lhe rabble arms 36 are carried around by the ro~a-tion of -the cc-~nter shaft 28, the rabble teeth 40 continuously rake -through -the material being processed on tlle associated hearth floor and yradually urge the materlal toward the drop ho]es 24 and 26 in the hearth floors.
The ma-terial -to be processed enters at -the top of the furnace at an inlet 42 and passes downwardly through the furnace in a generally serpentine fashion alternately inwardly and ou-twardly across the hearths and is discharged at the bottom of -the furnace, as indicated at 44.
In effec-t, the furnace ls divided into four zones.
However, -the ~ones are not finely seyregated, but vary lS depending on the characteristics of the material being processed. For example, the first or upper zone 46, consisting of the first several hearths is a drylng zone, and the second zone 48 consisting of the next several hearths ls a charrlng ~;
or volatile burning zone. The third zone 50 is a fixed ;~
~~ carbon burning zone, and the fourth zone 52 is an ash cooling ~`
zone.
Heretofore, in order to support combustion, excess air was added at the bottom of the furnace. It will be ;
appreciated that the hottest part of the furnace is in the central portion thereof, i.e. ln the lower portlon of zone 48 or in the upper portlon of zone 50. Problems were encoun-tered due to the fact that these middle hearths tended to overheat beyond the structural deslgn limits of the furnace. In order to overcome this problem, lt was thought necessary to add more air or oxygen at the bottom of the furnace. Thùs, such a system frequently operated with as much as 100% excess air -9~;33~ .:
(above that required ~or supporting combustion) being added at the bottom of the furnace in order to cool the central portion thereo to workable limits. However, such excess air tended to entrain or carry with it particulate matter into -the exhaust gases, which all exited from the ~op of the furnace.
Further~ in installations such as the one disclosed in a copending application 782,750 filed on July 14, 1977 and entitled "Method and Apparatus for Incinerating Waste Material", the air supply is controlled so that on most hearths there is a deficiency of oxygen as compared to that theoretically required for complete combustion. However, in the furnace described in said applicationr all of the exhaust gases exited at the top of the furnace and, hence, there is still the possibility that in some installations some particu-late matter could be entrained or carried with the exhaustgases, thereby creating a problem for the downstream scrubbers or other cleaning devices.
According to the present invention, there is provided a secondary exhaust outlet 54 at the middle of the furnace, i.e. at about the top of the fixed carbon burning zone 50 or the bottom of the charring or volatile burning zone 48. By manipulation of valves 56, 58 and 60, this exhaust gas may he led via lines 62 and 64 directly to a gas cleaning device, which may be of any suitable conventional type such as a bag collector, hot cyclone, electrostatic precipitator, or mechanical filter, for example. It will be particularly appreciated that this secondary exhaust gas is relatively rich in "heavy metal" particles and/or vapors such as lead, arsenic and antimony just to name a few. Further, the quantity of these secondary exhaust gases is relatively small, as compared to the total quantity of the exhaust gases exiting at the top :~
S3~4 of the furnace in conven-tional designs, and hence, it is economical to -treat tl-le secondary exhaust gases scpara-tely and in a manner particularly sui-table to the character;stlcs thereof. It will be further appreciated that rnost of -this "heavy metal" vapor and/or par-tlculate matter is formed in the lower portion oE the furllace, i.e. in -the Eixed carbon burning zone 50, and hence, according to the invention the upper portions of the furnace will be relatively free of this mat-ter so tha-t the exhaust gases exit;ng from -the furnace at the upper primary exhaust gas outle-t 66 may be cleaned or treated in a different manner/ that is particularly suitable for its characteristics.
Since the secondary exhaust gases are bled from the ~ ;~
furnace in the middle -thereof, as indicated at 54 in Fig. 1, additional air or oxygen is added to the furnace at 68 in order ; -~
to Eacilitate the processing occuring in the upper zones of -the furnace. In some installations, it is desirable to provide -~
a heat exchanger 70 so that by proper manipulation of the ~ `
valves 56, 58 and 60, the secondary exhaust gases serve to heat the air entering the furnace through the inlet 68. This provides added efficiency to the system. ~ ~
Further, according to the invention, it has been "
found desirable to add a minimum quantity of air or oxygen to the furnace at the inlets 72 in the lower portlon of the furnace so that there is a minimum quantity of air in the fixed carbon burning zone 50 and then adding relatively lar~er quan-tities of air in the charring or volatile burning zone 48 where it is needed, as by the inlet 68 or by the upper air inlets 74.
In the embodiment of th~ invention illustrated in Fig. 2 there is provided a primary furnace 76, of any suitable 9~3~
conventional type hav;ng a waste materi.al inlet 78, air or oxygen inlets 80, an e~haust gas outlet 82 ancl a processed material outle-t 84. The was-l-e materi.al in this :Eurnace is heated so that it is discharged there:Erom at 84 in a charred s~ate Erom which i.t is passed ~o a secondary treatment dev.ice 86. It is noted -that the exhallst gases le~aving at the ou-tlet 82 are relatively c].ean, because substant;ally little fixed carbon burning has taken place in this furnace. In the secondary treatment device, i.n one form thereof, heat is added such as by means of an electric arc, and air to a very limited extent may be added, thereby to recover or remove, as indicated at ~8, ~eavy metals which were mixed or compounded in the waste material belng processed. Thus, for example, volatile metals such as lead and chromium can be volatilized by an electric arc and then condensed.
In another form, the secondary treatment is effec-ted in a chemical device wherein heavy metals are recovered or removed chemically such as by di.ssolving the heavy metals in acid and then separating them, for exarnple. Also/ as an example, chromium can be partly extracted chemically by means of leaching with caustic soda, usually in the presence of some air. ..
Thereafter, the remaining material in the secondary treatrnent device 86 is discharged at 90 and passed to a secondary furnace 92, which may be of any conventional type suitable for the purpose. This remaining material is pri.marily of a carbonaceous nature and is substantially all consumed in the secondary furnace, so that only a small amount of ash is discharged as at 94, and the exhaust gases are discharged as at 96 in a relatively clean condition. It is noted that in some installations, the secondary treatment device 86 may be ~9S:~34 by-passed through a line 98, as by rneans of manipul.ation of the valves lOQ, 102 and 104, provicled for -the purpose.
ITaving thus described the invent:ion with particular reference to -the preferred :forms thereof, :it will be obvious to those skilled in the art to which the invention pe:rta:ins, after understallAing -the invelltion that var:ious chanc3es and modificati.ons may be made therein without depa.rting from the t spirit and scope of the invention, as defined by the claims appended hereto.
;'` ''~ ' ~' - ~ ,.
' ,: , '' ~ ~' ' :. 9
ash and exhaus-t ~as from ~he secollclary furnace.
There has t:hus been oul~ ecl rat,ller broadlv l:he more lmportan-t Eeal-ures of the i,nvention i,n order that -I,he detailcd descr;ptioll ~hereof that follows may be be-l:-ter understood, and in order -tha-t the present contribution to the ar-t may be be-tt,er appreci,ated. ~rhere are, of course, addi-tional features of the inven~,ion that will be described hereinafter and which will form -the subject of the claims appended here-to'. rrhose skilled i,n the ar-t will appreciate that the conception upon which the disclosure is based may readily be utilized as a basis for the designing of other '~- -methods and appara-tus for carrying out the several purposes of -the inven-tion. It is importan-t, therefore, -tha-t the claims be regarded as including such equivalent methods and appara-tus as do not depart from the spirit and scope of -the invention.
Specific embodiments oE the invention have been ~ ..
chosen for purposes of illustration and descrip-ti,on, and are shown in the accompanying drawings~ forming a part of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic illustration, partially in axial, sec-tional elevation of a system for incinerating waste material, according to my invention; and Figure 2 is a diagrammatic illustration of ano-ther emb'odiment of the invention. ;
DETAILED DESCRIPTION OF THE _EFERRED EMBODIMENTS
In the embodiment of the invention illustrated in Fig. 1 of the drawings, ~here is shown a multiple hearth furnace 10 of generally cylindrical configuration. Such a ~' furnace may be of the type, for example, as described in detail ~9S3~ :
in U.S. pa-tent No. 3,905,757 i.ssued Septernber 16, 1975. The furnace is constructed of a tubular outer s-l-eel shell 12, which is lined witll f.ire brick or o-ther similar heat res:;stant ma-ter~.al 14. Tha :Eurnace is provicled with a plurali-ty ~f burner nozz:Les 16, with one or more being provided on osle or more of the hear-tlls, as necessary, for controlling the temperatures within the different regions of the furnace to carry out the particular processing desiredO ~ny sui-table type of fuel may be provided to the burners The interior of the furnace lO is divided, by mealls of hearth floors 20 and 22, in-to a plurality of vertically aligned hearths, the number of hearths being preselected depending on the particular process being carried out. Each of the hearth floors is made of refractory material and is preferably of slightly arched configura-tion to be self~
supporting within the furnace. Outer peripheral drop holes 24 are provided near -the outer shell 12 of the furnace, and central drop holes 26 are formed in alternate hearth floors 22, near the center of the furnace. Wh;.le Fig. 1 shows the uppermost;
or first, hearth as being an in-flow hearth, it will be appreciated that the concepts of my invention apply equally ~iell to a furnace having an out-flow first hearth.
As illustrated in Fig. 1, a rotatable vertical cen-ter ~ ~-shaft 28 extends axially through the furnace lO and is secured by upper bearing means indicated at 30 and lower bearing means 32. This center drive shaft is rotatably driven by an electric motor and gear drive 34, provided for the purpose.
A plurality of spaced rabble arms 36 are mounted on the center shaft 28, as at 38, and extend outwardly in each hearth over the hearth floor. The rabble arms have rabble teeth 40 formed thereon which extend downwardly nearly to the hearth floor.
9~j33~
The rabble teeth are inclined with respect to the lon~itudinal axis of -their respective rabble arms to that as -lhe rabble arms 36 are carried around by the ro~a-tion of -the cc-~nter shaft 28, the rabble teeth 40 continuously rake -through -the material being processed on tlle associated hearth floor and yradually urge the materlal toward the drop ho]es 24 and 26 in the hearth floors.
The ma-terial -to be processed enters at -the top of the furnace at an inlet 42 and passes downwardly through the furnace in a generally serpentine fashion alternately inwardly and ou-twardly across the hearths and is discharged at the bottom of -the furnace, as indicated at 44.
In effec-t, the furnace ls divided into four zones.
However, -the ~ones are not finely seyregated, but vary lS depending on the characteristics of the material being processed. For example, the first or upper zone 46, consisting of the first several hearths is a drylng zone, and the second zone 48 consisting of the next several hearths ls a charrlng ~;
or volatile burning zone. The third zone 50 is a fixed ;~
~~ carbon burning zone, and the fourth zone 52 is an ash cooling ~`
zone.
Heretofore, in order to support combustion, excess air was added at the bottom of the furnace. It will be ;
appreciated that the hottest part of the furnace is in the central portion thereof, i.e. ln the lower portlon of zone 48 or in the upper portlon of zone 50. Problems were encoun-tered due to the fact that these middle hearths tended to overheat beyond the structural deslgn limits of the furnace. In order to overcome this problem, lt was thought necessary to add more air or oxygen at the bottom of the furnace. Thùs, such a system frequently operated with as much as 100% excess air -9~;33~ .:
(above that required ~or supporting combustion) being added at the bottom of the furnace in order to cool the central portion thereo to workable limits. However, such excess air tended to entrain or carry with it particulate matter into -the exhaust gases, which all exited from the ~op of the furnace.
Further~ in installations such as the one disclosed in a copending application 782,750 filed on July 14, 1977 and entitled "Method and Apparatus for Incinerating Waste Material", the air supply is controlled so that on most hearths there is a deficiency of oxygen as compared to that theoretically required for complete combustion. However, in the furnace described in said applicationr all of the exhaust gases exited at the top of the furnace and, hence, there is still the possibility that in some installations some particu-late matter could be entrained or carried with the exhaustgases, thereby creating a problem for the downstream scrubbers or other cleaning devices.
According to the present invention, there is provided a secondary exhaust outlet 54 at the middle of the furnace, i.e. at about the top of the fixed carbon burning zone 50 or the bottom of the charring or volatile burning zone 48. By manipulation of valves 56, 58 and 60, this exhaust gas may he led via lines 62 and 64 directly to a gas cleaning device, which may be of any suitable conventional type such as a bag collector, hot cyclone, electrostatic precipitator, or mechanical filter, for example. It will be particularly appreciated that this secondary exhaust gas is relatively rich in "heavy metal" particles and/or vapors such as lead, arsenic and antimony just to name a few. Further, the quantity of these secondary exhaust gases is relatively small, as compared to the total quantity of the exhaust gases exiting at the top :~
S3~4 of the furnace in conven-tional designs, and hence, it is economical to -treat tl-le secondary exhaust gases scpara-tely and in a manner particularly sui-table to the character;stlcs thereof. It will be further appreciated that rnost of -this "heavy metal" vapor and/or par-tlculate matter is formed in the lower portion oE the furllace, i.e. in -the Eixed carbon burning zone 50, and hence, according to the invention the upper portions of the furnace will be relatively free of this mat-ter so tha-t the exhaust gases exit;ng from -the furnace at the upper primary exhaust gas outle-t 66 may be cleaned or treated in a different manner/ that is particularly suitable for its characteristics.
Since the secondary exhaust gases are bled from the ~ ;~
furnace in the middle -thereof, as indicated at 54 in Fig. 1, additional air or oxygen is added to the furnace at 68 in order ; -~
to Eacilitate the processing occuring in the upper zones of -the furnace. In some installations, it is desirable to provide -~
a heat exchanger 70 so that by proper manipulation of the ~ `
valves 56, 58 and 60, the secondary exhaust gases serve to heat the air entering the furnace through the inlet 68. This provides added efficiency to the system. ~ ~
Further, according to the invention, it has been "
found desirable to add a minimum quantity of air or oxygen to the furnace at the inlets 72 in the lower portlon of the furnace so that there is a minimum quantity of air in the fixed carbon burning zone 50 and then adding relatively lar~er quan-tities of air in the charring or volatile burning zone 48 where it is needed, as by the inlet 68 or by the upper air inlets 74.
In the embodiment of th~ invention illustrated in Fig. 2 there is provided a primary furnace 76, of any suitable 9~3~
conventional type hav;ng a waste materi.al inlet 78, air or oxygen inlets 80, an e~haust gas outlet 82 ancl a processed material outle-t 84. The was-l-e materi.al in this :Eurnace is heated so that it is discharged there:Erom at 84 in a charred s~ate Erom which i.t is passed ~o a secondary treatment dev.ice 86. It is noted -that the exhallst gases le~aving at the ou-tlet 82 are relatively c].ean, because substant;ally little fixed carbon burning has taken place in this furnace. In the secondary treatment device, i.n one form thereof, heat is added such as by means of an electric arc, and air to a very limited extent may be added, thereby to recover or remove, as indicated at ~8, ~eavy metals which were mixed or compounded in the waste material belng processed. Thus, for example, volatile metals such as lead and chromium can be volatilized by an electric arc and then condensed.
In another form, the secondary treatment is effec-ted in a chemical device wherein heavy metals are recovered or removed chemically such as by di.ssolving the heavy metals in acid and then separating them, for exarnple. Also/ as an example, chromium can be partly extracted chemically by means of leaching with caustic soda, usually in the presence of some air. ..
Thereafter, the remaining material in the secondary treatrnent device 86 is discharged at 90 and passed to a secondary furnace 92, which may be of any conventional type suitable for the purpose. This remaining material is pri.marily of a carbonaceous nature and is substantially all consumed in the secondary furnace, so that only a small amount of ash is discharged as at 94, and the exhaust gases are discharged as at 96 in a relatively clean condition. It is noted that in some installations, the secondary treatment device 86 may be ~9S:~34 by-passed through a line 98, as by rneans of manipul.ation of the valves lOQ, 102 and 104, provicled for -the purpose.
ITaving thus described the invent:ion with particular reference to -the preferred :forms thereof, :it will be obvious to those skilled in the art to which the invention pe:rta:ins, after understallAing -the invelltion that var:ious chanc3es and modificati.ons may be made therein without depa.rting from the t spirit and scope of the invention, as defined by the claims appended hereto.
;'` ''~ ' ~' - ~ ,.
' ,: , '' ~ ~' ' :. 9
Claims (7)
1. A method of treating waste material containing heavy metal and carbonaceous material comprising the steps of continuously introducing waste material to be processed through a waste material inlet into a primary furnace while simultaneously adding air to said furnace, heating said waste material in said furnace until it is in a charred state and thence discharging said material from the furnace and passing it to a secondary treatment device while simultaneously discharging exhaust gas from the furnace, chemically treating or volatilizing said heavy metals to recover or remove the heavy metals present in the waste material in said secondary treatment device, thereafter passing the remainder of the waste material in the secondary treatment device to a secondary furnace to burn said carbonaceous material remaining in the waste material and separately discharging ash and exhaust gas from said secondary furnace.
2. A method according to Claim 1, characterized in that said step of chemically recovering or removing said heavy metals includes the step of dissolving said heavy metals in acid.
3. A method according to Claim 1, characterized in that said step of volatilizing said heavy metals includes the step of adding a substantial amount of heat to said secondary treatment device while maintaining a limited supply of oxygen therein to volatilize said heavy metals thereby to recover or remove the heavy metals present in the waste material being processed.
4. A method according to any one of Claims 1 to 3, characterized in that said heavy metals are selected from the group consisting of lead, arsenic, antimony and chromium.
5. Apparatus for the treatment of residual materials, characterized in that it comprises means for continuously introducing waste material to be processed through a waste material inlet into a primary furnace and means for simultaneously adding air to said furnace, means for heating the waste material in said furnace until it is in a charred state and means for thence discharging said material from the furnace and means for passing it to a secondary treatment device while simultaneously discharging exhaust gas from the furnace, means for chemically treating or means for volatilizing said heavy metals to recover or remove the heavy metals present in the waste material in said secondary treatment device, means for thereafter passing the remainder of the waste material in the secondary treatment device to a secondary furnace to burn said carbonaceous material remaining in the waste material and means for separately discharging ash and exhaust gas from said secondary furnace.
6. Apparatus according to Claim 5, characterized in that said means for chemically recovering or removing said heavy metal includes means for dissolving said heavy metals in acid.
7. Apparatus according to Claim 5, characterized in that said means for volatilizing said heavy metals includes means for adding a substantial amount of heat to said secondary treatment device while maintaining a limited supply of oxygen therein to volatilize the heavy metals to recover or remove the heavy metals present in the waste material being processed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA344,949A CA1095334A (en) | 1976-07-19 | 1980-02-01 | Method and apparatus for treating waste material |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/706,615 US4118220A (en) | 1976-07-19 | 1976-07-19 | Method for treating waste material |
| US706,615 | 1976-07-19 | ||
| CA282,748A CA1085679A (en) | 1976-07-19 | 1977-07-14 | Method and apparatus for treating waste material |
| CA344,949A CA1095334A (en) | 1976-07-19 | 1980-02-01 | Method and apparatus for treating waste material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1095334A true CA1095334A (en) | 1981-02-10 |
Family
ID=27165181
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA344,949A Expired CA1095334A (en) | 1976-07-19 | 1980-02-01 | Method and apparatus for treating waste material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1095334A (en) |
-
1980
- 1980-02-01 CA CA344,949A patent/CA1095334A/en not_active Expired
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