CA1110498A - Sludge drying system with sand recycle - Google Patents
Sludge drying system with sand recycleInfo
- Publication number
- CA1110498A CA1110498A CA325,255A CA325255A CA1110498A CA 1110498 A CA1110498 A CA 1110498A CA 325255 A CA325255 A CA 325255A CA 1110498 A CA1110498 A CA 1110498A
- Authority
- CA
- Canada
- Prior art keywords
- sludge
- granular material
- dry
- classifier
- hot
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/18—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact
- F26B3/22—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact the heat source and the materials or objects to be dried being in relative motion, e.g. of vibration
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/13—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
- F23G7/001—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals for sludges or waste products from water treatment installations
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B23/00—Heating arrangements
- F26B23/02—Heating arrangements using combustion heating
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B3/00—Drying solid materials or objects by processes involving the application of heat
- F26B3/18—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact
- F26B3/20—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact the heat source being a heated surface, e.g. a moving belt or conveyor
- F26B3/205—Drying solid materials or objects by processes involving the application of heat by conduction, i.e. the heat is conveyed from the heat source, e.g. gas flame, to the materials or objects to be dried by direct contact the heat source being a heated surface, e.g. a moving belt or conveyor the materials to be dried covering or being mixed with heated inert particles which may be recycled
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G2203/00—Furnace arrangements
- F23G2203/50—Fluidised bed furnace
- F23G2203/503—Fluidised bed furnace with two or more fluidised beds
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B2200/00—Drying processes and machines for solid materials characterised by the specific requirements of the drying good
- F26B2200/18—Sludges, e.g. sewage, waste, industrial processes, cooling towers
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Microbiology (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Organic Chemistry (AREA)
- Combustion & Propulsion (AREA)
- Sustainable Development (AREA)
- Treatment Of Sludge (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process and system to dry wet sewage sludge with hot sand and to burn the dried sludge. The sand is heated in a heating device by burning dried sludge, and the hot sand is mixed with wet sludge in a drying device. Thereby moisture is driven from the wet sludge to dry it. The dried sludge and sand are separated, and the sand returned to the heating device while the dried sludge is burned to heat the sand.
A process and system to dry wet sewage sludge with hot sand and to burn the dried sludge. The sand is heated in a heating device by burning dried sludge, and the hot sand is mixed with wet sludge in a drying device. Thereby moisture is driven from the wet sludge to dry it. The dried sludge and sand are separated, and the sand returned to the heating device while the dried sludge is burned to heat the sand.
Description
I S~UDGE DRYING SYSTEM WITH SAND RECYCLE
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BACKGROUND OF I~IE INVENTION
1.
, 1. Field of the Invention -- .
This invention relates to the drying and burning of waste materials such as sewage sludge.
. State of the_Art Conventlonal wastewater ~rea~ment processes remove ¦ pollutants from the wastewat~!r and generate slurr:ies of the removed pollutants. These slurries are generally known as sludge, which contains organic materials as well ~1 as a high percentage of water. Disposal of the sludge is accomplished by known methods, and one such method includes dewatering the sludge by fi:Ltration and incineration of the dewatered sludge.
I 15 It is generally recogn:ized that filtration of sludge I removes only a fraction of the water, and substantial ¦ cluantities of water remain with the sludge even after ! filtration. Therefore, it is desirable to remove I additional water from the sludge prior to incineration so j 20 that it is not necessary to heat substantial quantities of ! water in the incineration step.
One conventional process for removing additional water from filtered sludge includes heating the sludge prior to incineration. In a dryer, the sludge is contacted with hot combustion gases from the incineration step so that the sludge is heated and water is driven off 884a , .. .: .. . . . : ~ . . . . . .
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~8 as vapor. When the sludye is heated, malodorous gases as well as water evolve from the drying sludge and they are carried from the dryer by the comhustion yases. These gases are then passed through a condenser wherein the water vapor condenses and is disposed of, and the dry, malodorous gas is returned to the incinerator to be burned.
It should be ~ppreciated that a gas has a relatively low heat capacity, and therefore large quantities of the combustion gas must be contacted with the-sludge in orcler to effectively heat and dry it. Moreover, a large dryer and condenser are also necessary to handle the large v~lumes of gas.
SUMMARY OF THE INVENTION
-The problems of the prior art are overcome by the pr~sent invention which broadly provides a process Eor drying we~ sludge with granular material and burning dr~ sludge comprising: introducing the granular material into a heating means; burning dry sludge in a burning means to produce hot gases; transferring the hot gases from the burning means to the heating means to heat the granular material; transferring the hot granular material and wet sludge to a drying means~and mixing the hot granular material and wet sludge to substantially dry the wet sludge; transferring the mixture of granular material and substantially dry sludge to a classifier; in the classifier substantially separating the dry sludge from the granular material; transferring the dry sludge from the classifier to the burning means to be burned; and, transferring the granular material fr~m the classifier to the heating means to be heated.
The above process may be effected by way of a system to dry wet sludge with hot granular material and to burn the dry .~ .
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sludge comprising: heating means to heat the granular material;
burniny means coupled in gas flow communication with the heating means to burn dry sludge and to produce hot gases which are transferred to the heating means; drying means coupled in communication with the heating means to receive hot granular material from the heating means and to receive wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge; classifier means coupled to receive granular material and dry sludge from the drying means and to substan-tially separate the granular material from the dry sludge;transfer means coupled to the classifier means to convey the dry sludge to the burning means; and second transfer means coupled to the classifier means to convey the granular material ~rom khe classifier means to the heating mean~.
Further ~eatures and advantages of the present .inventi~n can be readily ascertained by reference to the following des~
cription and drawings, which are offered by way of example only : and not in limitation of the invention, the scope of which is defined by the appended claims and be equivalents to the structure, materials, and acts set forth hereinafter, BRIEF DESCRIPTION OF THE DRAWINGS
:
In the drawings:
Figure 1 is a schematic representation o~ one embodiment of the present system~
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': ' .' . ' . : ' :. . : ' , : . ' Figure 2 is a schematic represen~ation of another em-bodiment of the present system.
Figure 3 is a schematic representation of still another embodiment of the present system.
Figure 4 is a schematic representation of still another embodiment of the present system.
I DETAILED DESCRIPTION C)F
: THE PREFERRED EMBODIMENT
The presentl~ preferred embodiment shown in Figure 1 includes a conventional multiple hearth furnace 10. This multiple hearth furnace includes a substantially vertically disposed~ cylindrical vessel having an inlet 12 at its upper end and an outlet 14 at the lower end. A plurality of hearths 16 are located within the vessel perpendi.cular to its axis, and spaced apart from one another. A center column 18 is rotatably disposed in the center of the furnace 10 parallel to ~he axis of the furnace, and a plurality oE rabble arms 19 are affixed to the center column parallel to the hearths 16. Drive means 20 is coupled to the lower end of the center column 18 to cause the center column to rotate so that the rabble arms 19 urge material to travel across the hearths 16. The hearths 16 are constructed so that material flows downward through the furnace in a generally serpentine path.
A plurality of burners 21 are connected through the sides o~ the furnace 10. Th~ burners 21 are coupled to sources of pressurized air and of fuel, not shown, to provide heat to the furnace. ~n inlet conduit 23 is coupled to the lower part of the furnace to introduce wet sludge thereinto.
For the purpose of this description the furnace 10 should be understood to include an upper æone 22 wherein sand is heated, a middle zone 24 wherein dry sludge is burned, and a lower zone 26 wherein wet sludge is dried.
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Each of these zones comprises one or more hearth spaces.
Although each oE the zones is illustrated to encompass a particular number of hearth spaces, various operating conditions can dictate the use of different numbers of hearth spaces for a particular zone. I'he upper zone 22 and middle zone 24 are in gas flow communication, in that rising gases flow upward around the hearths 16. However, the hearth 27 separating the middle zone 24 from the lower zone 26 extends across the furnace to prevent the upward flow of gas. A conduit 29 is connected between the hearth 27 to extend downward almost to the next lower hearth 16 thereby providing a means for sludge to flow downward.
I The conduit 29 is arranged so that the sludge normally I blocks the lower end of the conduit but is periodically raked away by the rabble arms 19 to permit more sludge to flow downward. Thereby no substantial upward Elow of gas is permitted through conduit 29. This construc~:Lon of conduit 29 is conventional, and o~her conventional means can also be utilized to permit downward flow of sludge while preventlng upward flow of substantial quantities of I gas.
It should be understood that in operation the sand and wet sludge are mixed in the multiple hearth furnace 10 and the sludge is dried. This will be discussed below.
¦ 25 After the sludge is dried in the furllace 10, the mixture ~¦ of sand and sludge is removed via line 28 and transferred to classifer 30. The classifier 30 is a known device such as a screening device, an air classifier or a cyclone centrifuge, which utili~e the dif~erence in particle sizes 30 or in specific gravity between two materials to accomplish separation of the materials. From the classifier 30 the sludge is transferred to a sludge storage container 31 via line 32, and the sand is returned to the furnace 10 via line 34. From the storage container 31 dry sludge i5`
conveyed to the furnace by line 33.
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Coupled to the lower zone 26 is a cyclone 36 for receiving gas and water vapor evolved from the wet sludge along with some light sludge particles carried by the gas.
~ The sludge par~icles removed from the gas stream by the 1 5 cyclone 36 can be transferred to the sludge storage I container 31 or disposed of. The gas from the cyclone 36 ; is transferred to a condenser 38 wherein a substantial part of the water vapor is removed from the gas, for example, by spraying cold water through the condenser to cause condensation of the water vapor. After the water vapor has been removed, the substantially dry gas is conveyed via blower 40 and line 41 to the middle zone 24 to be burned therein.
A line 42 is coupled to the upper end of the furnace to receive the products of combustion generated in the furnace 10 along with some light particles, and convey them to a cyclone 43 wherein the particles are removed ancl dLsposed o~. The gases leaving the cyclone ~3 are transferred to a conventivnal scrubber ~ n ~he scrubber 44 a spray of water or other scrubblng liquld is directed into the gas stream to collect particles which ~iwere not removed by the cyclone 43. Alternatively a conventional dry-type particle collection means such as a bag house can be employed. A blower 46 or the like is 125 connected to the gas outlet of the scrubber 44 to pull the Igas through the system.
IIn operat-Lon of the present system sand is con-!tinuously fed into the upper zone 22, and fuel such as oil !or gas is burned in the burners 21. The rabble arms .l9 are rotated so that the sand is raked over the hearths 16 and cascades through the hot gas rising in the ~urnace.
Thus the sand :Ls heated as it travels to the middle zone 24. In practice the sand is heated to about 427 - 650 C
before it reaches the middle zone 24.
Dry sludge is introduced into the middle zone 24 via `
line 33 to burn thereb~ heating the sand. Thereafter a '~
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-` ~$3L~498 mixture of hot sand and the ash from the burned sludge flows to the lower zone 26 via conduit 29.
While the hot sand and sludge flow into the lower zone 26, wet sludge is introduced via line 23. The rabble arms 19 mix the sludge and sand, and the sand gives up its heat to evapo;rate a substantial part of the water from the sludge. In practice the wet sludge introduced into the furnace has a high moisture content, for example, about 75% water. However, wet sludge having more or less water by weight can also be treated. The sludge leaving the furnace via port 14 has a low moisture content, for example, about 5% water and has a temperature of, say 93C.
However, it should be recognized that the moisture content and temperature of the dried sludge can be varied lS depending upon various parameters such as the time of contact between the sand and sludge and the ratio oE sand to sludge.
A small amownt of ambient, purge air is drawn by blower 40 through the furnace 10 to convey the gases from 20' the drying sludge to the middle zone 24. It should be appreciated that these gases contain a substantial quantity of water vapor and also malodrous gases from the sludge. In the condenser 38 a substantial part of the water vapor is condensed so that it can be disposed of, and the malodorous gases, which are combustible, are transferred to the middle zone 24 where they are burned.
The dry sludge and sand mixt~re is removed from the furnace 10 and conveyed to the classifier 30. The sand used in the present process preferably has a grain size substantiall~ different from the dry sludge particles, and the classifier can separate particles on the basis of si~e or specific gravity to efEect a substantially complete separation of the sludge from the sand. The sand from the classifer 30 is transferred to the furnace 10 and the - 35 sludge is transferred to the storage container 31.
884a 4~8 From the storage container 31 the sludge is sent ~o the furnace 10 to be burned. It should be understood that the sludge can be mixed with a fluid fuel for burning.
ll For example, it can be mixed with oil or gas or waste 1 5 grease. Alternatively, the sludge can be burned uncombined with any fluid fuel.
If all of the sludge is not burned in the middle zone 24, any remaining sludge can be used as humus or fertlizer. For example~ my calcula~ions show that when sludge which is about 78% water, with the non-water constituents being about 65% volatile material, is introduced into the upper zone 22 for drying and all the dry sludge is burned in the furnace~ it is not necessary I to burn additional fuel to heat the sand. In this ¦ 15 circumstance the combustion of the sludge is termed autogenous. Furthermore, if the sludge contains le~s than about 78% moisture, all the dry sludge need not be burned, and dry sludge is ava:llable to be used as humus or ;fertilizer. If :fluld Euel is burned with the sludge, larger quantities of the dry sludge will be available as humus or fertilizer.
Generally, unless the temperature is in excess of about 538~C the the malodorous gases introduced through line 41 are not substantially burned and deodorized.
Therefore, the temperature in the middle zone 24 is generally maintained above 538C. The system i5 preferably designed so that the temperature near line 42 ~s substantially lower than 538C, and the gas leaving the furnace 10 via line 42 is at a relatively low temperature, say about 93C. Thus it can be appreciated that the sand and malodorous gases can be heated to relatively high temperaute while insuring that the gas discharged from the furnace lO need not be a high temperature. In other words, the majority of the heat from the burning sludge is usefully transferred to the sand and combustion of the malodorous gases. -. 884a ., ..
Referring now to Figure 2, there is illustrated another embodiment of the present system. In this embodiment, many of the elements are the same as those in the Figure 1 system, and like elements are numbered the same. The system shown in Figure 2 differs from that shown in ~igure 1 in several respects. In particular the Figure 2 system does not include a sludge storage container 31 but rather includes a screw conveyor 49. The screw conveyor 49 is a conventional device to con-tain material and transport the material at a controllable rate via a rotating helical member. Moreover, the Figure 2 system includes a screw conveyor 50 coupled to the furnace to feed wet sludge into the lower zone 26. A conduit 52 is connected to the upper part of the screw conveyor 50 and to the hearth 54 which is lowest in the upper zone 22.
The hearth 54 has a raised portion on its edge so that sand can exit the hearth 5~ only via conduit 52. In operatlon wet sludge is introduced into the leEt end oE
the screw conveyor 50, hot sand from conduit 52 :is mi~ed with the sludge near the middle of the screw conveyor, and the mixture is introduced into the lower zone 26.
Referring now to Figure 3, there is illustra~ed another embodiment of the present system. In this embodiment many elements are the same as in the Figure 2 system, and like elements are numbered the same.
According to the Figure 3 system the multiple-hearth furnace 10 includes a middle zone 24 and lower zone 26 but no zone equivalent ~o ~he upper zone 22 of the Figure 2 system. A collar 60 is aEixed to the center column 18 above the lowest hearth of the middle zone 24. The collar 60 is spaced apart from the hearth 16 to permit hot gases to rise from the lower zone 26 to the middle zone 24 and prevent ash from the burned sludge from falling between those two zones. The ash from the burned sludge is removed from the furnace 10 via conduit 62 and transferred to disposal.
884a 34~i 3 A conventional rotary kiln 64 is coupled to receive hot gases exiting from the furnace via conduit 66. The rotary kiln 64 includes a substantially horizontally disposed~ rotatable cylindrical vessel having an inlet at one end and an outlet at the other. A plurality of baffles are located within the vessel parallel to its axis, and the vessel is inclined slightly with its lower end at the outlet so that when the vessel is ro~ated, the sand cascades as it moves from the inlet to the outlet. A
discharge breaching 68 is coupled to the outlet end of the kiln 64 so that hot sand leaving the kiln is transferred to conduit 69~ and hot gases are conveyed into the kiln via conduit 66. The hot gases pass through the cascading sand thereby heating the sand. The condui~ 69 is coupled to the lower zone 26 to convey the hot sand thereinto.
Referring now to Figure 4 there is illustrated another embodiment of the present system wherein elements which are common to the Figure 2 system are numbered the same.
The Figure 4 system includes two fluidized bed reactors 70 and 72. The lower reactor 72 includes a container 74 for containing a bed of solid particles 75 on a porous floor 76. The porous floor 76 contains a pluralit~ of ports 79 which are large enough to permit the passage of gas but not the passage of the solid particles 75. A plenum chamber 78 is disposed below the floor 76 so that pressurized air introduced into the plenum chamber by blower 80 flows upward thereby fluidizing the particles.
That is, the particles are separated frorn one another and agitated by the rising air thereby forming a so-called fluidized bed. The upper reactor 70 is disposed atop the lower reactor 72 so that the plenum chamber of the upper reactor 70 is, in effect, the upper part of the lower reactor 72. A second bed of particles 82 is maintained in the upper reactor 70 atop a porous floor 84 having ports 884a -, .
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85. A wall 87 is affixed to the floor 76 and extends across the lower reactor 72 to separate the bed of particles 75 into two parts. The wall 87 extends a predetermined distance above the bed of particles 75 when the bed is not fluidized so that when the bed is fluidized a controllable quantity of particles flows from the right side to the left side of the wall 87. The sludge is introduced into the right part of the bed 75 so that it is substantially completely burned before leaving the reactor 72, The construction of two fluidized bed reactors disposed one atop the other is conventional and, for example, the principle is taugh~ in U.S. patent 2,638,684 to Jukkola. It should be understood that if the single upper reactor 70 does not heat the sand efficiently, one or more additional reactors can be disposed atop reactor 70 to heat the sand in stages.
j In accordance wLth ~he Figure 4 systenl a condu:it 86 ls coupled to tran~fer hot sand Erom the upper rcclctor 70 to the lower reactor 72, and a conventional rotary feeder 88 is interposed in the conduit 86 to allow sand to flow downward but prevent gas from traveling upward. The conduit 86 is affixed to the upper reactor 70 at a predetermined height relative to the bed of particles 82 so that only particles at a certain height above the porous floor 84 are conveyecl by the conduit 86.
A burner 89 is coupled to the lower reactor 72 to burn fuel and the dry sludge in the fluidized bed of sand.
A condu:lt 90 ls coupled to the lower reactor 72 to convey hot sand to rotary kiln 92, and an air lock 9S is interposed in the conduit 90 to permit sand and ash to ! flow downward but to prevent the upward flow of gas. The rotary kiln 92 is substantially the same as the rotary kiln 64 illustrated in Figure 3. A conduit 94 is coupled to the inlet end of the rotary kiln 92 for introducing wet sludge for mixing with the hot sand.
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In operation sand is heated in the upper reactor 70 by hot gases rising from the lower reactor. The hot sand flows to the lower bed to mix with dry sludge on the right side of the wall 87 and the sludge is burned. The sludge is substantially burned on the right side of the wall 87, and primarily ash and sand flow over the wall and thence through the conduit 90. The hot sand then flows into the rotary kiln 92 to dry wet sludge, and the mixture of dry sludge and sand is transferred to the classifier 30 for separation.
It should be appreciated that although specific devices have been discussed above, other similar devices can be substituted therefor in accordance with conventional practice. It should also be appreciated that granular materials other than sand could also be utilized as a heat-transfer medium.
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BACKGROUND OF I~IE INVENTION
1.
, 1. Field of the Invention -- .
This invention relates to the drying and burning of waste materials such as sewage sludge.
. State of the_Art Conventlonal wastewater ~rea~ment processes remove ¦ pollutants from the wastewat~!r and generate slurr:ies of the removed pollutants. These slurries are generally known as sludge, which contains organic materials as well ~1 as a high percentage of water. Disposal of the sludge is accomplished by known methods, and one such method includes dewatering the sludge by fi:Ltration and incineration of the dewatered sludge.
I 15 It is generally recogn:ized that filtration of sludge I removes only a fraction of the water, and substantial ¦ cluantities of water remain with the sludge even after ! filtration. Therefore, it is desirable to remove I additional water from the sludge prior to incineration so j 20 that it is not necessary to heat substantial quantities of ! water in the incineration step.
One conventional process for removing additional water from filtered sludge includes heating the sludge prior to incineration. In a dryer, the sludge is contacted with hot combustion gases from the incineration step so that the sludge is heated and water is driven off 884a , .. .: .. . . . : ~ . . . . . .
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.
: . . .. .: . :
~8 as vapor. When the sludye is heated, malodorous gases as well as water evolve from the drying sludge and they are carried from the dryer by the comhustion yases. These gases are then passed through a condenser wherein the water vapor condenses and is disposed of, and the dry, malodorous gas is returned to the incinerator to be burned.
It should be ~ppreciated that a gas has a relatively low heat capacity, and therefore large quantities of the combustion gas must be contacted with the-sludge in orcler to effectively heat and dry it. Moreover, a large dryer and condenser are also necessary to handle the large v~lumes of gas.
SUMMARY OF THE INVENTION
-The problems of the prior art are overcome by the pr~sent invention which broadly provides a process Eor drying we~ sludge with granular material and burning dr~ sludge comprising: introducing the granular material into a heating means; burning dry sludge in a burning means to produce hot gases; transferring the hot gases from the burning means to the heating means to heat the granular material; transferring the hot granular material and wet sludge to a drying means~and mixing the hot granular material and wet sludge to substantially dry the wet sludge; transferring the mixture of granular material and substantially dry sludge to a classifier; in the classifier substantially separating the dry sludge from the granular material; transferring the dry sludge from the classifier to the burning means to be burned; and, transferring the granular material fr~m the classifier to the heating means to be heated.
The above process may be effected by way of a system to dry wet sludge with hot granular material and to burn the dry .~ .
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sludge comprising: heating means to heat the granular material;
burniny means coupled in gas flow communication with the heating means to burn dry sludge and to produce hot gases which are transferred to the heating means; drying means coupled in communication with the heating means to receive hot granular material from the heating means and to receive wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge; classifier means coupled to receive granular material and dry sludge from the drying means and to substan-tially separate the granular material from the dry sludge;transfer means coupled to the classifier means to convey the dry sludge to the burning means; and second transfer means coupled to the classifier means to convey the granular material ~rom khe classifier means to the heating mean~.
Further ~eatures and advantages of the present .inventi~n can be readily ascertained by reference to the following des~
cription and drawings, which are offered by way of example only : and not in limitation of the invention, the scope of which is defined by the appended claims and be equivalents to the structure, materials, and acts set forth hereinafter, BRIEF DESCRIPTION OF THE DRAWINGS
:
In the drawings:
Figure 1 is a schematic representation o~ one embodiment of the present system~
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': ' .' . ' . : ' :. . : ' , : . ' Figure 2 is a schematic represen~ation of another em-bodiment of the present system.
Figure 3 is a schematic representation of still another embodiment of the present system.
Figure 4 is a schematic representation of still another embodiment of the present system.
I DETAILED DESCRIPTION C)F
: THE PREFERRED EMBODIMENT
The presentl~ preferred embodiment shown in Figure 1 includes a conventional multiple hearth furnace 10. This multiple hearth furnace includes a substantially vertically disposed~ cylindrical vessel having an inlet 12 at its upper end and an outlet 14 at the lower end. A plurality of hearths 16 are located within the vessel perpendi.cular to its axis, and spaced apart from one another. A center column 18 is rotatably disposed in the center of the furnace 10 parallel to ~he axis of the furnace, and a plurality oE rabble arms 19 are affixed to the center column parallel to the hearths 16. Drive means 20 is coupled to the lower end of the center column 18 to cause the center column to rotate so that the rabble arms 19 urge material to travel across the hearths 16. The hearths 16 are constructed so that material flows downward through the furnace in a generally serpentine path.
A plurality of burners 21 are connected through the sides o~ the furnace 10. Th~ burners 21 are coupled to sources of pressurized air and of fuel, not shown, to provide heat to the furnace. ~n inlet conduit 23 is coupled to the lower part of the furnace to introduce wet sludge thereinto.
For the purpose of this description the furnace 10 should be understood to include an upper æone 22 wherein sand is heated, a middle zone 24 wherein dry sludge is burned, and a lower zone 26 wherein wet sludge is dried.
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Each of these zones comprises one or more hearth spaces.
Although each oE the zones is illustrated to encompass a particular number of hearth spaces, various operating conditions can dictate the use of different numbers of hearth spaces for a particular zone. I'he upper zone 22 and middle zone 24 are in gas flow communication, in that rising gases flow upward around the hearths 16. However, the hearth 27 separating the middle zone 24 from the lower zone 26 extends across the furnace to prevent the upward flow of gas. A conduit 29 is connected between the hearth 27 to extend downward almost to the next lower hearth 16 thereby providing a means for sludge to flow downward.
I The conduit 29 is arranged so that the sludge normally I blocks the lower end of the conduit but is periodically raked away by the rabble arms 19 to permit more sludge to flow downward. Thereby no substantial upward Elow of gas is permitted through conduit 29. This construc~:Lon of conduit 29 is conventional, and o~her conventional means can also be utilized to permit downward flow of sludge while preventlng upward flow of substantial quantities of I gas.
It should be understood that in operation the sand and wet sludge are mixed in the multiple hearth furnace 10 and the sludge is dried. This will be discussed below.
¦ 25 After the sludge is dried in the furllace 10, the mixture ~¦ of sand and sludge is removed via line 28 and transferred to classifer 30. The classifier 30 is a known device such as a screening device, an air classifier or a cyclone centrifuge, which utili~e the dif~erence in particle sizes 30 or in specific gravity between two materials to accomplish separation of the materials. From the classifier 30 the sludge is transferred to a sludge storage container 31 via line 32, and the sand is returned to the furnace 10 via line 34. From the storage container 31 dry sludge i5`
conveyed to the furnace by line 33.
~84a . ::
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Coupled to the lower zone 26 is a cyclone 36 for receiving gas and water vapor evolved from the wet sludge along with some light sludge particles carried by the gas.
~ The sludge par~icles removed from the gas stream by the 1 5 cyclone 36 can be transferred to the sludge storage I container 31 or disposed of. The gas from the cyclone 36 ; is transferred to a condenser 38 wherein a substantial part of the water vapor is removed from the gas, for example, by spraying cold water through the condenser to cause condensation of the water vapor. After the water vapor has been removed, the substantially dry gas is conveyed via blower 40 and line 41 to the middle zone 24 to be burned therein.
A line 42 is coupled to the upper end of the furnace to receive the products of combustion generated in the furnace 10 along with some light particles, and convey them to a cyclone 43 wherein the particles are removed ancl dLsposed o~. The gases leaving the cyclone ~3 are transferred to a conventivnal scrubber ~ n ~he scrubber 44 a spray of water or other scrubblng liquld is directed into the gas stream to collect particles which ~iwere not removed by the cyclone 43. Alternatively a conventional dry-type particle collection means such as a bag house can be employed. A blower 46 or the like is 125 connected to the gas outlet of the scrubber 44 to pull the Igas through the system.
IIn operat-Lon of the present system sand is con-!tinuously fed into the upper zone 22, and fuel such as oil !or gas is burned in the burners 21. The rabble arms .l9 are rotated so that the sand is raked over the hearths 16 and cascades through the hot gas rising in the ~urnace.
Thus the sand :Ls heated as it travels to the middle zone 24. In practice the sand is heated to about 427 - 650 C
before it reaches the middle zone 24.
Dry sludge is introduced into the middle zone 24 via `
line 33 to burn thereb~ heating the sand. Thereafter a '~
884a . .
;
, . . , . : , , . . : .
- . ,, . .
' ': . . " ' ' :
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-` ~$3L~498 mixture of hot sand and the ash from the burned sludge flows to the lower zone 26 via conduit 29.
While the hot sand and sludge flow into the lower zone 26, wet sludge is introduced via line 23. The rabble arms 19 mix the sludge and sand, and the sand gives up its heat to evapo;rate a substantial part of the water from the sludge. In practice the wet sludge introduced into the furnace has a high moisture content, for example, about 75% water. However, wet sludge having more or less water by weight can also be treated. The sludge leaving the furnace via port 14 has a low moisture content, for example, about 5% water and has a temperature of, say 93C.
However, it should be recognized that the moisture content and temperature of the dried sludge can be varied lS depending upon various parameters such as the time of contact between the sand and sludge and the ratio oE sand to sludge.
A small amownt of ambient, purge air is drawn by blower 40 through the furnace 10 to convey the gases from 20' the drying sludge to the middle zone 24. It should be appreciated that these gases contain a substantial quantity of water vapor and also malodrous gases from the sludge. In the condenser 38 a substantial part of the water vapor is condensed so that it can be disposed of, and the malodorous gases, which are combustible, are transferred to the middle zone 24 where they are burned.
The dry sludge and sand mixt~re is removed from the furnace 10 and conveyed to the classifier 30. The sand used in the present process preferably has a grain size substantiall~ different from the dry sludge particles, and the classifier can separate particles on the basis of si~e or specific gravity to efEect a substantially complete separation of the sludge from the sand. The sand from the classifer 30 is transferred to the furnace 10 and the - 35 sludge is transferred to the storage container 31.
884a 4~8 From the storage container 31 the sludge is sent ~o the furnace 10 to be burned. It should be understood that the sludge can be mixed with a fluid fuel for burning.
ll For example, it can be mixed with oil or gas or waste 1 5 grease. Alternatively, the sludge can be burned uncombined with any fluid fuel.
If all of the sludge is not burned in the middle zone 24, any remaining sludge can be used as humus or fertlizer. For example~ my calcula~ions show that when sludge which is about 78% water, with the non-water constituents being about 65% volatile material, is introduced into the upper zone 22 for drying and all the dry sludge is burned in the furnace~ it is not necessary I to burn additional fuel to heat the sand. In this ¦ 15 circumstance the combustion of the sludge is termed autogenous. Furthermore, if the sludge contains le~s than about 78% moisture, all the dry sludge need not be burned, and dry sludge is ava:llable to be used as humus or ;fertilizer. If :fluld Euel is burned with the sludge, larger quantities of the dry sludge will be available as humus or fertilizer.
Generally, unless the temperature is in excess of about 538~C the the malodorous gases introduced through line 41 are not substantially burned and deodorized.
Therefore, the temperature in the middle zone 24 is generally maintained above 538C. The system i5 preferably designed so that the temperature near line 42 ~s substantially lower than 538C, and the gas leaving the furnace 10 via line 42 is at a relatively low temperature, say about 93C. Thus it can be appreciated that the sand and malodorous gases can be heated to relatively high temperaute while insuring that the gas discharged from the furnace lO need not be a high temperature. In other words, the majority of the heat from the burning sludge is usefully transferred to the sand and combustion of the malodorous gases. -. 884a ., ..
Referring now to Figure 2, there is illustrated another embodiment of the present system. In this embodiment, many of the elements are the same as those in the Figure 1 system, and like elements are numbered the same. The system shown in Figure 2 differs from that shown in ~igure 1 in several respects. In particular the Figure 2 system does not include a sludge storage container 31 but rather includes a screw conveyor 49. The screw conveyor 49 is a conventional device to con-tain material and transport the material at a controllable rate via a rotating helical member. Moreover, the Figure 2 system includes a screw conveyor 50 coupled to the furnace to feed wet sludge into the lower zone 26. A conduit 52 is connected to the upper part of the screw conveyor 50 and to the hearth 54 which is lowest in the upper zone 22.
The hearth 54 has a raised portion on its edge so that sand can exit the hearth 5~ only via conduit 52. In operatlon wet sludge is introduced into the leEt end oE
the screw conveyor 50, hot sand from conduit 52 :is mi~ed with the sludge near the middle of the screw conveyor, and the mixture is introduced into the lower zone 26.
Referring now to Figure 3, there is illustra~ed another embodiment of the present system. In this embodiment many elements are the same as in the Figure 2 system, and like elements are numbered the same.
According to the Figure 3 system the multiple-hearth furnace 10 includes a middle zone 24 and lower zone 26 but no zone equivalent ~o ~he upper zone 22 of the Figure 2 system. A collar 60 is aEixed to the center column 18 above the lowest hearth of the middle zone 24. The collar 60 is spaced apart from the hearth 16 to permit hot gases to rise from the lower zone 26 to the middle zone 24 and prevent ash from the burned sludge from falling between those two zones. The ash from the burned sludge is removed from the furnace 10 via conduit 62 and transferred to disposal.
884a 34~i 3 A conventional rotary kiln 64 is coupled to receive hot gases exiting from the furnace via conduit 66. The rotary kiln 64 includes a substantially horizontally disposed~ rotatable cylindrical vessel having an inlet at one end and an outlet at the other. A plurality of baffles are located within the vessel parallel to its axis, and the vessel is inclined slightly with its lower end at the outlet so that when the vessel is ro~ated, the sand cascades as it moves from the inlet to the outlet. A
discharge breaching 68 is coupled to the outlet end of the kiln 64 so that hot sand leaving the kiln is transferred to conduit 69~ and hot gases are conveyed into the kiln via conduit 66. The hot gases pass through the cascading sand thereby heating the sand. The condui~ 69 is coupled to the lower zone 26 to convey the hot sand thereinto.
Referring now to Figure 4 there is illustrated another embodiment of the present system wherein elements which are common to the Figure 2 system are numbered the same.
The Figure 4 system includes two fluidized bed reactors 70 and 72. The lower reactor 72 includes a container 74 for containing a bed of solid particles 75 on a porous floor 76. The porous floor 76 contains a pluralit~ of ports 79 which are large enough to permit the passage of gas but not the passage of the solid particles 75. A plenum chamber 78 is disposed below the floor 76 so that pressurized air introduced into the plenum chamber by blower 80 flows upward thereby fluidizing the particles.
That is, the particles are separated frorn one another and agitated by the rising air thereby forming a so-called fluidized bed. The upper reactor 70 is disposed atop the lower reactor 72 so that the plenum chamber of the upper reactor 70 is, in effect, the upper part of the lower reactor 72. A second bed of particles 82 is maintained in the upper reactor 70 atop a porous floor 84 having ports 884a -, .
. , ~
' .
', .
4~
85. A wall 87 is affixed to the floor 76 and extends across the lower reactor 72 to separate the bed of particles 75 into two parts. The wall 87 extends a predetermined distance above the bed of particles 75 when the bed is not fluidized so that when the bed is fluidized a controllable quantity of particles flows from the right side to the left side of the wall 87. The sludge is introduced into the right part of the bed 75 so that it is substantially completely burned before leaving the reactor 72, The construction of two fluidized bed reactors disposed one atop the other is conventional and, for example, the principle is taugh~ in U.S. patent 2,638,684 to Jukkola. It should be understood that if the single upper reactor 70 does not heat the sand efficiently, one or more additional reactors can be disposed atop reactor 70 to heat the sand in stages.
j In accordance wLth ~he Figure 4 systenl a condu:it 86 ls coupled to tran~fer hot sand Erom the upper rcclctor 70 to the lower reactor 72, and a conventional rotary feeder 88 is interposed in the conduit 86 to allow sand to flow downward but prevent gas from traveling upward. The conduit 86 is affixed to the upper reactor 70 at a predetermined height relative to the bed of particles 82 so that only particles at a certain height above the porous floor 84 are conveyecl by the conduit 86.
A burner 89 is coupled to the lower reactor 72 to burn fuel and the dry sludge in the fluidized bed of sand.
A condu:lt 90 ls coupled to the lower reactor 72 to convey hot sand to rotary kiln 92, and an air lock 9S is interposed in the conduit 90 to permit sand and ash to ! flow downward but to prevent the upward flow of gas. The rotary kiln 92 is substantially the same as the rotary kiln 64 illustrated in Figure 3. A conduit 94 is coupled to the inlet end of the rotary kiln 92 for introducing wet sludge for mixing with the hot sand.
884a ', ' : ' ., ' '.:
49~3 .
In operation sand is heated in the upper reactor 70 by hot gases rising from the lower reactor. The hot sand flows to the lower bed to mix with dry sludge on the right side of the wall 87 and the sludge is burned. The sludge is substantially burned on the right side of the wall 87, and primarily ash and sand flow over the wall and thence through the conduit 90. The hot sand then flows into the rotary kiln 92 to dry wet sludge, and the mixture of dry sludge and sand is transferred to the classifier 30 for separation.
It should be appreciated that although specific devices have been discussed above, other similar devices can be substituted therefor in accordance with conventional practice. It should also be appreciated that granular materials other than sand could also be utilized as a heat-transfer medium.
884a - : . -.
. .
.
,
Claims (9)
1. A system to dry wet sludge with hot granular material and to burn the dry sludge comprising:
a. heating means 22 to heat the granular material;
b. burning means 24 coupled in gas flow communication with said heating means to burn dry sludge and to produce hot gases which are transferred to said heating means;
c. drying means 26 coupled in communication with said heating means to receive hot granular material from said heating means and to receive wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge;
d. classifier means 30 coupled to receive granular material and dry sludge from said drying means and to substantially separate the granular material from the dry sludge;
e. transfer means 33 coupled to said classifier means to convey the dry sludge to said burning means; and, f. second transfer means 34 coupled to said classifier means to convey the granular material from said classifier means to said heating means.
a. heating means 22 to heat the granular material;
b. burning means 24 coupled in gas flow communication with said heating means to burn dry sludge and to produce hot gases which are transferred to said heating means;
c. drying means 26 coupled in communication with said heating means to receive hot granular material from said heating means and to receive wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge;
d. classifier means 30 coupled to receive granular material and dry sludge from said drying means and to substantially separate the granular material from the dry sludge;
e. transfer means 33 coupled to said classifier means to convey the dry sludge to said burning means; and, f. second transfer means 34 coupled to said classifier means to convey the granular material from said classifier means to said heating means.
2. A system according to claim 1 further including:
a. purge air introduction means 23 coupled to said drying means to introduce ambient air into said drying means; and, b. gas transfer means 40 to convey gas from said drying means 26 to said burning means 24.
a. purge air introduction means 23 coupled to said drying means to introduce ambient air into said drying means; and, b. gas transfer means 40 to convey gas from said drying means 26 to said burning means 24.
3. A system according to claim 2 wherein said gas transfer means includes a condenser 38.
4. A system according to claim 1 wherein said heating means 22 includes a first fluidized bed reactor 70, and said burning means 24 includes a second fluidized bed reactor 72.
5. A system according to claim 4 further including first means 86 to transfer the hot granular material form said first fluidized bed reactor 70 to said second fluidized bed reactor 72 and second means 90 to transfer the hot granular material from said second fluidized bed reactor 72 to said drying means 92.
6. A system to dry wet sludge with granular material and to burn dry sludge comprising:
a. multiple hearth furnace means 10 including, i. an upper zone 22 to heat the granular material;
ii. a middle zone 24 to burn dry sludge to heat the granular material;
iii. a lower zone 26 to receive hot granular material and the wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge;
b. classifier means 30 coupled to receive granular material and dry sludge from said multiple hearth furnace means 10 and to substantially separate the granular material form the dry sludge;
c. transfer means 33 coupled to said classifier means 30 to convey the dry sludge to said middle zone means 24; and, d. second transfer means 34 coupled to said classifier means 30 to convey the granular material from said classifier means 30 to said upper zone means 22.
a. multiple hearth furnace means 10 including, i. an upper zone 22 to heat the granular material;
ii. a middle zone 24 to burn dry sludge to heat the granular material;
iii. a lower zone 26 to receive hot granular material and the wet sludge and to mix the hot granular material with the wet sludge to dry the wet sludge;
b. classifier means 30 coupled to receive granular material and dry sludge from said multiple hearth furnace means 10 and to substantially separate the granular material form the dry sludge;
c. transfer means 33 coupled to said classifier means 30 to convey the dry sludge to said middle zone means 24; and, d. second transfer means 34 coupled to said classifier means 30 to convey the granular material from said classifier means 30 to said upper zone means 22.
7. A system according to claim 6 further including means 52 to convey the hot granular material directly from said upper zone to said lower zone without passing through said middle zone.
8. A process for drying wet sludge with granular material and burning dry sludge comprising:
a. introducing the granular material into a heating means 22;
b. burning dry sludge in a burning means 24 to produce hot gases;
c. transferring the hot gases from the burning means 24 to the heating means 22 to heat the granular material;
d. transferring the hot granular material and wet sludge to a drying means 26 and mixing the hot granular material and wet sludge to substantially dry the wet sludge;
e. transferring the mixture of granular material and substantially dry sludge to a classifier 30;
f. in the classifier 30 substantially separating the dry sludge from the granular material;
g. transferring the dry sludge from the classifier 30 to the burning means 24 to be burned; and, h. transferring the granular material from the classifier 30 to the heating means 22 to be heated.
a. introducing the granular material into a heating means 22;
b. burning dry sludge in a burning means 24 to produce hot gases;
c. transferring the hot gases from the burning means 24 to the heating means 22 to heat the granular material;
d. transferring the hot granular material and wet sludge to a drying means 26 and mixing the hot granular material and wet sludge to substantially dry the wet sludge;
e. transferring the mixture of granular material and substantially dry sludge to a classifier 30;
f. in the classifier 30 substantially separating the dry sludge from the granular material;
g. transferring the dry sludge from the classifier 30 to the burning means 24 to be burned; and, h. transferring the granular material from the classifier 30 to the heating means 22 to be heated.
9. The process of claim 8 wherein the granular material is sand.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/895,684 US4153411A (en) | 1978-04-12 | 1978-04-12 | Rotary sludge drying system with sand recycle |
| US895,684 | 1978-04-12 | ||
| US18,389 | 1979-03-09 | ||
| US06/018,389 US4248164A (en) | 1979-03-09 | 1979-03-09 | Sludge drying system with sand recycle |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110498A true CA1110498A (en) | 1981-10-13 |
Family
ID=26691065
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA325,255A Expired CA1110498A (en) | 1978-04-12 | 1979-04-10 | Sludge drying system with sand recycle |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1110498A (en) |
| GB (1) | GB2019541A (en) |
| IT (1) | IT1115184B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2963616B1 (en) * | 2010-08-06 | 2012-09-21 | Commissariat Energie Atomique | METHOD AND INSTALLATION FOR DRYING SLUDGE |
-
1979
- 1979-04-06 GB GB7912235A patent/GB2019541A/en not_active Withdrawn
- 1979-04-10 CA CA325,255A patent/CA1110498A/en not_active Expired
- 1979-04-12 IT IT21821/79A patent/IT1115184B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| IT7921821A0 (en) | 1979-04-12 |
| GB2019541A (en) | 1979-10-31 |
| IT1115184B (en) | 1986-02-03 |
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