CA2068228C - Process and apparatus for drying material to be dried - Google Patents
Process and apparatus for drying material to be driedInfo
- Publication number
- CA2068228C CA2068228C CA002068228A CA2068228A CA2068228C CA 2068228 C CA2068228 C CA 2068228C CA 002068228 A CA002068228 A CA 002068228A CA 2068228 A CA2068228 A CA 2068228A CA 2068228 C CA2068228 C CA 2068228C
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- Prior art keywords
- dried
- heating
- pressurized vessel
- vessel
- process according
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/30—Treatment of water, waste water, or sewage by irradiation
- C02F1/302—Treatment of water, waste water, or sewage by irradiation with microwaves
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/48—Treatment of water, waste water, or sewage with magnetic or electric fields
-
- 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
- C02F11/131—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating using electromagnetic or ultrasonic waves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F26—DRYING
- F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
- F26B7/00—Drying solid materials or objects by processes using a combination of processes not covered by a single one of groups F26B3/00 and F26B5/00
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Water Supply & Treatment (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Environmental & Geological Engineering (AREA)
- Mechanical Engineering (AREA)
- Electromagnetism (AREA)
- Physics & Mathematics (AREA)
- General Engineering & Computer Science (AREA)
- Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Treatment Of Sludge (AREA)
- Drying Of Solid Materials (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
Abstract
The invention relates to a process and an apparatus for drying sludge, in particular sewage sludge, or moist bulk material, wherein the material to be dried is heated by supplying energy by means of an electromagnetic alternating field generated between electrodes in a sealed pressurized vessel at an overpressure and the material moisture evaporated by the heating is used as heat transfer medium for heating the material to be dried in a step which is separate from the heating in the electromagnetic alternating field. In this process, the material to be dried is received with electrically insulated contiguous contact with the electrodes located in the pressurized vessel at least for a dwell time which is necessary for the heating and is then subjected to a flash drying.
Description
Process and apparatus for drying materlal to be drled Technlcal fleld The lnventlon relates to a process and an apparatus for drylng materlal, such as sludge, ln partlcular sewage sludge, or molst bulk materlal, to be drled.
Prlor Art Sewage sludge orlglnatlng from a mechanlcal prellmlnary dehydratlon ls normally drled convectlvely ln a contact, dlsk, clrculatlng-alr or fluldlzed-bed dryer or the llke, the vapors produced ln thls process belng dlscharged lnto the envlronment, and thls results not only ln the large energy loss assoclated therewlth but ln envlronmental pollutlon and odor nulsance.
DE-A-3 734 281 dlscloses the drylng of sludge or molst bulk materlal by heatlng lt ln a reactor houslng by means of an electromagnetlc alternatlng fleld ln whlch drylng the materlal molsture evaporated by the heatlng ls used as heat transfer medlum for heatlng the materlal to be drled ln an upstream step separate from the heatlng ln an electromagnetlc alternatlng fleld. In thls process, the material to be dehydrated and havlng a relatlvely hlgh lnltlal molsture content ls transported ln the reactor houslng on a conveyor device through at least one hlgh-frequency fleld and is dehydrated under these clrcumstances substantlally to a resldual molsture content, the dehydrated materlal ls dlscharged, and the evaporated vapors obtalned are used for preheatlng the materlal to be drled and then aftertreated.
~ 23448-184 The conveyance of the material to be drled past and between the capacltor plates results ln a very unfavorable energy utlllzatlon because of the large alr gap located between the capacltor plates and the materlal to be drled and, ln addltlon, it requlres a hlgh equlpment cost for the vessel.
In addltlon, the evaporatlon vapors condensed after thls process result, as a rule, in a nurnber of - la -2068228 23448-l84 pollutants.
Disclosure of the invention One object of the invention is to provide a process and an apparatus for drying material to be dried which function very favorably from the point of view of energy.
Accordingly, one aspect of the invention provides process for drying sludge, in particular sewage sludge or moist bulk material, in which the material to be dried is heated by supplying energy by means of an electromagnetic alternating field generated between electrodes in a sealed vessel and the material moisture evaporated by the heating is used as heat transfer medium for heating the material to be dried in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the material to be dried is received at an overpressure by the vessel constructed as a pressurized vessel with electrically insulated contiguous contact with the electrodes located in the pressurized vessel at least for a residence time which is necessary for the heating and is then subjected to flash drying.
According to another aspect of the invention, there is provided apparatus for drying sludge, in particular sewage sludge or moist bulk material, having a sealed vessel for receiving the material to be dried, with an apparatus having electrodes disposed in the vessel for heating the material to be dried by means of an electromagnetic alternating field and an apparatus for heating the material to be dried by means of the material moisture generated by the heating in the electromagnetic alternating field in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the vessel is constructed as a through-type pressurized vessel optionally vented on the inlet and outlet side, with electrodes therein, which are in electrically insulated contiguous contact with the material to be dried, and there is a flash tank downstream of the pressurized vessel.
The contlguous contact o~ the material to be dried with electrodes insulated agalnst electrlcal contact and the alr space lacklng in between achieves an lmproved utllizatlon of the energy used ln the heating, whlch utlllzatlon ls further lncreased by the downstream flash drylng whlch results ln an addltlonal lncrease ln the dry matter content of the materlal. The flash drying is only possible because of the overpressure procedure lnvolvlng appreclable overpressure ln the pressurlzed vessel.
In thls way, environmentally friendly electrlcal energy is used in order to heat the materlal to be drled lnductlvely, or preferably dlelectrlcally, ln the (low- to hlgh-frequency) electromagnetlc alternatlng fleld. Under theses clrcumstances, mlcrowave drylng, or in particular, drylng ln a hlgh-frequency fleld, for example wlth frequencles of 13.56, 27.12 or 40.58 MHz can be carrled out. The evaporated materlal moisture is used for convective and/or contact heating either for the purpose of predrylng or for the purpose of afterdrylng, ln whlch connectlon two or more drylng steps may optlonally be arranged ln a serles, or for drylng ln a contact or convectlon dryer arranged ln parallel, thereby resultlng ln an energetlcally very favorable procedure.
The material to be dried passes through the through-type pressurlzed vessel ln batches, quasl-contlnuously or continuously from bottom to top or from top to bottom wlth approprlate heatlng. Generally, an appreclable overpressure substantlally greater than or equal to 2 bar, ln partlcular a pressure of between 2 and 3 bar, ls malntalned ln the pressurlzed vessel.
The temperature of the materlal to be drled ls expedlently kept below 150C at least durlng the convectlve heatlng ln order that essentlally only steam ls produced durlng sald heatlng and essentlally no degasslng of the materlal to be heated occurs, wlth the result that, ultlmately, as small amounts as posslble of envlronmentally pollutant exhaust gases are dlscharged. Preferably, the materlal to be drled ls kept below 150C durlng the entlre drylng operatlon, but heatlng can also be carrled out to over 150C durlng the heatlng ln the electromagnetlc alternatlng fleld, the evaporated materlal molsture can be condensed durlng or after the further use and the condensate can be dlscharged lnto the waste water, wlth the result that even then essentlally no envlronmentally pollutant emlsslons to the envlronmental alr take place.
Between the stage of heatlng ln the electromagnetlc alternatlng fleld and the further stage of heatlng operated wlth the vapors from the latter, a sludge temperature dlfference of greater than or equal to 25C ls expedlently employed, l.e. the materlal to be drled ln the electromagnetlc alternatlng fleld ls at a temperature at least 25C hlgher than ln the vapor-heated drylng stage.
Further ob~ects and developments of the lnventlon are to be found ln the subclalms and the descrlptlon below.
Brlef descrlptlon of the drawlngs The lnventlon is explalned ln greater detall below - 206i8228 by reference to exemplary embodlments shown ln the accompanylng flgures.
Flgures 1 to 4 dlagrammatlcally show apparatuses for drylng sewage sludge.
Exemplary embodlments of the lnventlon In the embodlment shown in Flgure 1, sewage sludge orlglnatlng from a mechanlcal prellmlnary dehydratlon ls fed vla a plpe 1, for lnstance by means of a sludge pump 2, to a clrculatlng-alr predryer 3 and from there lt passes, also for example vla a sludge pump 4 and a plpe 5, wlthout entralned alr lnto a sealed pressurlzed vessel between two electrodes 8 whlch are lmmersed ln the sewage sludge and act as capacltor plates electrlcally lnsulated from the sewage sludge and from each other and whlch are connected to a hlgh-frequency generator 9 operated wlth electrlcal prlmary energy ln order to be dlelectrlcally heated thereln.
In the pressurlzed vessel 6, the sewage sludge, preheated ln the clrculatlng-alr dryer 3, ls heated under pressure to a temperature preferably below 150C. The vapors produced ln thls process are fed to a vapor turbo-compressor 10 whlch compresses the vapors and dellvers them to an ln~ectlon cooler 11 to whlch coollng water ls fed to reduce the superheat temperature of the compressed vapors and at the same tlme to generate further steam vla a plpe 12. From the ln~ectlon cooler 11, the steam passes to a heat exchanger 13 for heatlng clrculatlng alr fed to the heat exchanger 13 by means of a clrculatlng-alr fan 14.
In addltion, the heat generated by the hlgh-frequency generator 9 ls fed via a coollng clrcult (water heated to about 60 to 70C on the feed slde) to a heat exchanger 15 to preheat clrculatlng alr ln order also to utlllze this waste heat for heatlng circulatlng air.
The alr heated by the heat exchanger 13 is fed to the circulating-alr predryer 3, while the vapor condensate generated ln the heat exchanger 13 is dlscharged lnto the waste water via an lnterceptor 16.
Cooled clrculatlng alr from the clrculatlng-air predryer 3 ls at least partlally fed to a premlxer 17 to which preheated cold alr can, ln addltlon, be fed vla a pipe 18.
Furthermore, a waste-air fan 19 ls provlded for partlally dlscharglng circulating air into the envlronment. Slnce the temperature of the clrculating air used for predrying is kept commensurately low, l.e. ln the reglon of, for example, approxlmately 110C, only vapors whlch essentlally contaln steam and whlch can be dlscharged lnto the envlronment wlthout further ado are thereby generated.
Slnce the vapors from the pressurlzed vessel 6 cannot be discharged into the envlronment but are encountered as condensate on leaving the heat exchanger 13 (and optionally after further coollng), the heatlng ln the pressurlzed vessel 6 may also be carrled out at above 150C.
In the embodlrnent shown ln Flgure 2 the preheated sewage sludge comlng from the clrculatlng-alr dryer 3 ls pumped lnto the pressurlzed vessel 6 and ls heated dlelectrlcally in a hlgh-frequency fleld by means of electrodes 8 lmmersed ln the sewage sludge and electrlcally lnsulated from the latter. The vapors produced ln thls process have a pressure of, for example, 2 to 3 bar, wlth the result that they are essentlally composed of pure steam (slnce the vapors are later condensed higher pressures, and consequently temperatures hlgher than 150C, can also be used). In thls case, the vapors are fed to the heat exchanger 13 vla a water trap 20.
The heated sewage sludge from the pressurlzed vessel 6 ls fed ln the two embodlments descrlbed above vla a plpe 21 havlng a valve 22, whlch serves as pressure seal on the dlscharge slde ~the pressure seal on the inlet slde ls the sludge pump 4), to a flash tank 23. As a consequence of the flash on enterlng the flash tank 23, flash drylng takes place, as a result of whlch the water content of the sewage sludge ls agaln reduced substantlally. In addltlon, the flashlng ln the flash tank 23 advantageously effects a formatlon of powdered or granular materlal, or at least a dlslntegratlon of the materlal to be drled. The dlscharge from the flash tank 23 ls carrled out, for example, by means of a conveyor screw.
Water vapor produced ln thls process may optlonally also be used to preheat the sewage sludge before lt enters the clrculatlng-alr predryer 3.
The upwardly dlrectly vapor outlet of the pressurlzed vessel 6 causes contlnuously heated and drled sewage sludge to be produced ln the pressurlzed vessel 6, whlch sewage sludge bullds up from the bottom to the top. A
batchwlse dlscharge of the drled sewage sludge from the pressurlzed vessel 6 to the flash tank 23 can be carried out by sultably controlled opening of the valve 22 by means of two level sensors SL and Su, which are disposed above the electrodes 8 by opening the valve 22 when the level of the sewage sludge reaches the upper level sensor Su and closlng the valve 22 again when the level of the sewage sludge reaches the lower level sensor SL which is essentlally ad~acent to the level of the outlet openlng to the pipe 21. When the valve 22 ls open, the pressure ln the pressurlzed vessel 6 forces the sewage sludge out. Under these clrcumstances, the sewage sludge can be contlnuously fed lnto the pressurlzed vessel 6.
(Alternatlvely, however, the sewage sludge can also be fed ln and dlscharged dlscontlnuously). If an energy transfer whlch ls sufflclent for the heatlng envisaged ln the pressurlzed vessel 6 ls achleved, a contlnuous feedlng-ln and dlscharge of the material to be drled ls also possible with the result that no level sensors are necessary and the valve 22 essentlally fulflls a safety role.
In the embodlment shown in Flgure 3, the steam generated ln the pressurlzed vessel 6 ls fed dlrectly, l.e.
wlthout a gaseous lntermedlate clrcult, lnto a sludge predryer 24 (a contact or convectlon predryer) to preheat the sewage sludge. The condensate produced by coollng the steam ls dlscharged lnto the waste water. Vapors produced ln the sludge predryer 24 by the preheatlng are cooled ln the vapor condenser 25 by means of coollng water and dlscharged, together wlth the latter, as condensate lnto the waste water, resultlng ln a gas emlsslon whlch ls at most sllght. The high-frequency generator 9 is cooled by clrculated coolant whlch ls ln turn cooled by fresh coollng water ln a heat exchanger 26.
In the embodlment shown ln Flgure 4, the sewage sludge ls conveyed vla the pump 2 lnto a preheater 27, whlch ls, for example, a double-caslng plpe or the llke, optionally havlng a conveyor screw for the sewage sludge and ls disposed, ln partlcular, vertlcally, wlth the result that the sewage sludge is conveyed upwards through the preheater 27 via a plpe havlng a shutoff valve into the pressurlzed vessel 6 ln order to be heated further thereln, for example, to somewhat below 150C by means of electrlcal prlmary energy. From the pressurlzed vessel 6, the sewage sludge passes into the flash tank 23, the steam released ln the latter belng fed to the preheater 27 to preheat the sewage sludge. The steam formed ln the pressurlzed vessel 6 ls fed to a convectlve or contact afterdryer 28, for example a dlsk or contact dryer, to whlch the sewage sludge, predrled to thls extent, ls fed from the flash tank 23 and the vapors generated ln sald afterdryer 28 are fed to the preheater 27, together wlth those from the flash tank 23. (The waste heat of the hlgh-frequency generator 9 and the condensate waste heat can be used for lnltlally preheatlng the sewage sludge by means of heat exchangers 29, 30 dlsposed upstream of the preheater 27).
The pressure lnslde the pressure vessel 6 can be monltored in all the embodlments described above by means of a pressure sensor 31 whlch controls a valve 32 ln the plpe from the pressurized vessel 6 to the afterdryer 28, wlth the result g that the pressure ln the pressurlzed vessel 6 is kept constant. The flow rate of the drylng vapor from the pressurlzed vessel 6 to the afterdryer 28 may furthermore be measured by a sensor 33 and an overall regulatlon of the mass flow (whlch ls ad~usted by a motor 35, controlled by a control element 34 for the pump 2) and the output of the hlgh-frequency generator 9 (controlled by means of an adapter 36) can thus be carrled out ln such a way as to result ln a constant drylng rate and, consequently, lf the dry matter content of the sewage sludge fed ln ls constant, also ln a constant dry matter content after drylng. In addltlon, a maxlmum level sensor 37 whose response results ln the motor 35 of the pump 2 belng swltched off may be provlded.
The hlgh-frequency voltage may be fed ln, preferably, ln a balanced manner wlth respect to ground potentlal or, alternatlvely, ln an unbalanced manner.
In the pressurlzed vessel 6, the electrodes 8 lmmersed ln the sewage sludge are completely encapsulated and arranged, for example, ln a sheath of electrlcally lnsulatlng ceramlc materlal such as Al2O3 and are supported, for example, by ceramlc bodles.
One electrode 8 may be formed by the wall of the pressurlzed vessel 6, ln whlch there ls a centrally dlsposed, rod-type electrode 8 ln order to form an annular capacltor.
The annular electrode 8 may, however, also be dlsposed at a dlstance from the wall of the pressurlzed vessel 6, ln whlch case the sewage sludge ls pumped from below lnto the reglon of the annular electrode and overflows at lts top rlm lnto the - 9a -annular space between the wall of the pressurlzed vessel and the outslde of the annular electrode 8 ln order to be contlnuously dlscharged from that point. Alternatlvely, the sewage sludge can be discharged in batches by means of a level regulator.
Incidentally, the pressurlzed vessel 6 can be dlsposed in a space-saving manner above the predryer 3 or preheater 27 or the afterdryer 28 wlth the flash tank 23 belng arranged ln between.
- 9b -
Prlor Art Sewage sludge orlglnatlng from a mechanlcal prellmlnary dehydratlon ls normally drled convectlvely ln a contact, dlsk, clrculatlng-alr or fluldlzed-bed dryer or the llke, the vapors produced ln thls process belng dlscharged lnto the envlronment, and thls results not only ln the large energy loss assoclated therewlth but ln envlronmental pollutlon and odor nulsance.
DE-A-3 734 281 dlscloses the drylng of sludge or molst bulk materlal by heatlng lt ln a reactor houslng by means of an electromagnetlc alternatlng fleld ln whlch drylng the materlal molsture evaporated by the heatlng ls used as heat transfer medlum for heatlng the materlal to be drled ln an upstream step separate from the heatlng ln an electromagnetlc alternatlng fleld. In thls process, the material to be dehydrated and havlng a relatlvely hlgh lnltlal molsture content ls transported ln the reactor houslng on a conveyor device through at least one hlgh-frequency fleld and is dehydrated under these clrcumstances substantlally to a resldual molsture content, the dehydrated materlal ls dlscharged, and the evaporated vapors obtalned are used for preheatlng the materlal to be drled and then aftertreated.
~ 23448-184 The conveyance of the material to be drled past and between the capacltor plates results ln a very unfavorable energy utlllzatlon because of the large alr gap located between the capacltor plates and the materlal to be drled and, ln addltlon, it requlres a hlgh equlpment cost for the vessel.
In addltlon, the evaporatlon vapors condensed after thls process result, as a rule, in a nurnber of - la -2068228 23448-l84 pollutants.
Disclosure of the invention One object of the invention is to provide a process and an apparatus for drying material to be dried which function very favorably from the point of view of energy.
Accordingly, one aspect of the invention provides process for drying sludge, in particular sewage sludge or moist bulk material, in which the material to be dried is heated by supplying energy by means of an electromagnetic alternating field generated between electrodes in a sealed vessel and the material moisture evaporated by the heating is used as heat transfer medium for heating the material to be dried in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the material to be dried is received at an overpressure by the vessel constructed as a pressurized vessel with electrically insulated contiguous contact with the electrodes located in the pressurized vessel at least for a residence time which is necessary for the heating and is then subjected to flash drying.
According to another aspect of the invention, there is provided apparatus for drying sludge, in particular sewage sludge or moist bulk material, having a sealed vessel for receiving the material to be dried, with an apparatus having electrodes disposed in the vessel for heating the material to be dried by means of an electromagnetic alternating field and an apparatus for heating the material to be dried by means of the material moisture generated by the heating in the electromagnetic alternating field in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the vessel is constructed as a through-type pressurized vessel optionally vented on the inlet and outlet side, with electrodes therein, which are in electrically insulated contiguous contact with the material to be dried, and there is a flash tank downstream of the pressurized vessel.
The contlguous contact o~ the material to be dried with electrodes insulated agalnst electrlcal contact and the alr space lacklng in between achieves an lmproved utllizatlon of the energy used ln the heating, whlch utlllzatlon ls further lncreased by the downstream flash drylng whlch results ln an addltlonal lncrease ln the dry matter content of the materlal. The flash drying is only possible because of the overpressure procedure lnvolvlng appreclable overpressure ln the pressurlzed vessel.
In thls way, environmentally friendly electrlcal energy is used in order to heat the materlal to be drled lnductlvely, or preferably dlelectrlcally, ln the (low- to hlgh-frequency) electromagnetlc alternatlng fleld. Under theses clrcumstances, mlcrowave drylng, or in particular, drylng ln a hlgh-frequency fleld, for example wlth frequencles of 13.56, 27.12 or 40.58 MHz can be carrled out. The evaporated materlal moisture is used for convective and/or contact heating either for the purpose of predrylng or for the purpose of afterdrylng, ln whlch connectlon two or more drylng steps may optlonally be arranged ln a serles, or for drylng ln a contact or convectlon dryer arranged ln parallel, thereby resultlng ln an energetlcally very favorable procedure.
The material to be dried passes through the through-type pressurlzed vessel ln batches, quasl-contlnuously or continuously from bottom to top or from top to bottom wlth approprlate heatlng. Generally, an appreclable overpressure substantlally greater than or equal to 2 bar, ln partlcular a pressure of between 2 and 3 bar, ls malntalned ln the pressurlzed vessel.
The temperature of the materlal to be drled ls expedlently kept below 150C at least durlng the convectlve heatlng ln order that essentlally only steam ls produced durlng sald heatlng and essentlally no degasslng of the materlal to be heated occurs, wlth the result that, ultlmately, as small amounts as posslble of envlronmentally pollutant exhaust gases are dlscharged. Preferably, the materlal to be drled ls kept below 150C durlng the entlre drylng operatlon, but heatlng can also be carrled out to over 150C durlng the heatlng ln the electromagnetlc alternatlng fleld, the evaporated materlal molsture can be condensed durlng or after the further use and the condensate can be dlscharged lnto the waste water, wlth the result that even then essentlally no envlronmentally pollutant emlsslons to the envlronmental alr take place.
Between the stage of heatlng ln the electromagnetlc alternatlng fleld and the further stage of heatlng operated wlth the vapors from the latter, a sludge temperature dlfference of greater than or equal to 25C ls expedlently employed, l.e. the materlal to be drled ln the electromagnetlc alternatlng fleld ls at a temperature at least 25C hlgher than ln the vapor-heated drylng stage.
Further ob~ects and developments of the lnventlon are to be found ln the subclalms and the descrlptlon below.
Brlef descrlptlon of the drawlngs The lnventlon is explalned ln greater detall below - 206i8228 by reference to exemplary embodlments shown ln the accompanylng flgures.
Flgures 1 to 4 dlagrammatlcally show apparatuses for drylng sewage sludge.
Exemplary embodlments of the lnventlon In the embodlment shown in Flgure 1, sewage sludge orlglnatlng from a mechanlcal prellmlnary dehydratlon ls fed vla a plpe 1, for lnstance by means of a sludge pump 2, to a clrculatlng-alr predryer 3 and from there lt passes, also for example vla a sludge pump 4 and a plpe 5, wlthout entralned alr lnto a sealed pressurlzed vessel between two electrodes 8 whlch are lmmersed ln the sewage sludge and act as capacltor plates electrlcally lnsulated from the sewage sludge and from each other and whlch are connected to a hlgh-frequency generator 9 operated wlth electrlcal prlmary energy ln order to be dlelectrlcally heated thereln.
In the pressurlzed vessel 6, the sewage sludge, preheated ln the clrculatlng-alr dryer 3, ls heated under pressure to a temperature preferably below 150C. The vapors produced ln thls process are fed to a vapor turbo-compressor 10 whlch compresses the vapors and dellvers them to an ln~ectlon cooler 11 to whlch coollng water ls fed to reduce the superheat temperature of the compressed vapors and at the same tlme to generate further steam vla a plpe 12. From the ln~ectlon cooler 11, the steam passes to a heat exchanger 13 for heatlng clrculatlng alr fed to the heat exchanger 13 by means of a clrculatlng-alr fan 14.
In addltion, the heat generated by the hlgh-frequency generator 9 ls fed via a coollng clrcult (water heated to about 60 to 70C on the feed slde) to a heat exchanger 15 to preheat clrculatlng alr ln order also to utlllze this waste heat for heatlng circulatlng air.
The alr heated by the heat exchanger 13 is fed to the circulating-alr predryer 3, while the vapor condensate generated ln the heat exchanger 13 is dlscharged lnto the waste water via an lnterceptor 16.
Cooled clrculatlng alr from the clrculatlng-air predryer 3 ls at least partlally fed to a premlxer 17 to which preheated cold alr can, ln addltlon, be fed vla a pipe 18.
Furthermore, a waste-air fan 19 ls provlded for partlally dlscharglng circulating air into the envlronment. Slnce the temperature of the clrculating air used for predrying is kept commensurately low, l.e. ln the reglon of, for example, approxlmately 110C, only vapors whlch essentlally contaln steam and whlch can be dlscharged lnto the envlronment wlthout further ado are thereby generated.
Slnce the vapors from the pressurlzed vessel 6 cannot be discharged into the envlronment but are encountered as condensate on leaving the heat exchanger 13 (and optionally after further coollng), the heatlng ln the pressurlzed vessel 6 may also be carrled out at above 150C.
In the embodlrnent shown ln Flgure 2 the preheated sewage sludge comlng from the clrculatlng-alr dryer 3 ls pumped lnto the pressurlzed vessel 6 and ls heated dlelectrlcally in a hlgh-frequency fleld by means of electrodes 8 lmmersed ln the sewage sludge and electrlcally lnsulated from the latter. The vapors produced ln thls process have a pressure of, for example, 2 to 3 bar, wlth the result that they are essentlally composed of pure steam (slnce the vapors are later condensed higher pressures, and consequently temperatures hlgher than 150C, can also be used). In thls case, the vapors are fed to the heat exchanger 13 vla a water trap 20.
The heated sewage sludge from the pressurlzed vessel 6 ls fed ln the two embodlments descrlbed above vla a plpe 21 havlng a valve 22, whlch serves as pressure seal on the dlscharge slde ~the pressure seal on the inlet slde ls the sludge pump 4), to a flash tank 23. As a consequence of the flash on enterlng the flash tank 23, flash drylng takes place, as a result of whlch the water content of the sewage sludge ls agaln reduced substantlally. In addltlon, the flashlng ln the flash tank 23 advantageously effects a formatlon of powdered or granular materlal, or at least a dlslntegratlon of the materlal to be drled. The dlscharge from the flash tank 23 ls carrled out, for example, by means of a conveyor screw.
Water vapor produced ln thls process may optlonally also be used to preheat the sewage sludge before lt enters the clrculatlng-alr predryer 3.
The upwardly dlrectly vapor outlet of the pressurlzed vessel 6 causes contlnuously heated and drled sewage sludge to be produced ln the pressurlzed vessel 6, whlch sewage sludge bullds up from the bottom to the top. A
batchwlse dlscharge of the drled sewage sludge from the pressurlzed vessel 6 to the flash tank 23 can be carried out by sultably controlled opening of the valve 22 by means of two level sensors SL and Su, which are disposed above the electrodes 8 by opening the valve 22 when the level of the sewage sludge reaches the upper level sensor Su and closlng the valve 22 again when the level of the sewage sludge reaches the lower level sensor SL which is essentlally ad~acent to the level of the outlet openlng to the pipe 21. When the valve 22 ls open, the pressure ln the pressurlzed vessel 6 forces the sewage sludge out. Under these clrcumstances, the sewage sludge can be contlnuously fed lnto the pressurlzed vessel 6.
(Alternatlvely, however, the sewage sludge can also be fed ln and dlscharged dlscontlnuously). If an energy transfer whlch ls sufflclent for the heatlng envisaged ln the pressurlzed vessel 6 ls achleved, a contlnuous feedlng-ln and dlscharge of the material to be drled ls also possible with the result that no level sensors are necessary and the valve 22 essentlally fulflls a safety role.
In the embodlment shown in Flgure 3, the steam generated ln the pressurlzed vessel 6 ls fed dlrectly, l.e.
wlthout a gaseous lntermedlate clrcult, lnto a sludge predryer 24 (a contact or convectlon predryer) to preheat the sewage sludge. The condensate produced by coollng the steam ls dlscharged lnto the waste water. Vapors produced ln the sludge predryer 24 by the preheatlng are cooled ln the vapor condenser 25 by means of coollng water and dlscharged, together wlth the latter, as condensate lnto the waste water, resultlng ln a gas emlsslon whlch ls at most sllght. The high-frequency generator 9 is cooled by clrculated coolant whlch ls ln turn cooled by fresh coollng water ln a heat exchanger 26.
In the embodlment shown ln Flgure 4, the sewage sludge ls conveyed vla the pump 2 lnto a preheater 27, whlch ls, for example, a double-caslng plpe or the llke, optionally havlng a conveyor screw for the sewage sludge and ls disposed, ln partlcular, vertlcally, wlth the result that the sewage sludge is conveyed upwards through the preheater 27 via a plpe havlng a shutoff valve into the pressurlzed vessel 6 ln order to be heated further thereln, for example, to somewhat below 150C by means of electrlcal prlmary energy. From the pressurlzed vessel 6, the sewage sludge passes into the flash tank 23, the steam released ln the latter belng fed to the preheater 27 to preheat the sewage sludge. The steam formed ln the pressurlzed vessel 6 ls fed to a convectlve or contact afterdryer 28, for example a dlsk or contact dryer, to whlch the sewage sludge, predrled to thls extent, ls fed from the flash tank 23 and the vapors generated ln sald afterdryer 28 are fed to the preheater 27, together wlth those from the flash tank 23. (The waste heat of the hlgh-frequency generator 9 and the condensate waste heat can be used for lnltlally preheatlng the sewage sludge by means of heat exchangers 29, 30 dlsposed upstream of the preheater 27).
The pressure lnslde the pressure vessel 6 can be monltored in all the embodlments described above by means of a pressure sensor 31 whlch controls a valve 32 ln the plpe from the pressurized vessel 6 to the afterdryer 28, wlth the result g that the pressure ln the pressurlzed vessel 6 is kept constant. The flow rate of the drylng vapor from the pressurlzed vessel 6 to the afterdryer 28 may furthermore be measured by a sensor 33 and an overall regulatlon of the mass flow (whlch ls ad~usted by a motor 35, controlled by a control element 34 for the pump 2) and the output of the hlgh-frequency generator 9 (controlled by means of an adapter 36) can thus be carrled out ln such a way as to result ln a constant drylng rate and, consequently, lf the dry matter content of the sewage sludge fed ln ls constant, also ln a constant dry matter content after drylng. In addltlon, a maxlmum level sensor 37 whose response results ln the motor 35 of the pump 2 belng swltched off may be provlded.
The hlgh-frequency voltage may be fed ln, preferably, ln a balanced manner wlth respect to ground potentlal or, alternatlvely, ln an unbalanced manner.
In the pressurlzed vessel 6, the electrodes 8 lmmersed ln the sewage sludge are completely encapsulated and arranged, for example, ln a sheath of electrlcally lnsulatlng ceramlc materlal such as Al2O3 and are supported, for example, by ceramlc bodles.
One electrode 8 may be formed by the wall of the pressurlzed vessel 6, ln whlch there ls a centrally dlsposed, rod-type electrode 8 ln order to form an annular capacltor.
The annular electrode 8 may, however, also be dlsposed at a dlstance from the wall of the pressurlzed vessel 6, ln whlch case the sewage sludge ls pumped from below lnto the reglon of the annular electrode and overflows at lts top rlm lnto the - 9a -annular space between the wall of the pressurlzed vessel and the outslde of the annular electrode 8 ln order to be contlnuously dlscharged from that point. Alternatlvely, the sewage sludge can be discharged in batches by means of a level regulator.
Incidentally, the pressurlzed vessel 6 can be dlsposed in a space-saving manner above the predryer 3 or preheater 27 or the afterdryer 28 wlth the flash tank 23 belng arranged ln between.
- 9b -
Claims (22)
1. Process for drying sludge, in particular sewage sludge or moist bulk material, in which the material to be dried is heated by supplying energy by means of an electromagnetic alternating field generated between electrodes in a sealed vessel and the material moisture evaporated by the heating is used as heat transfer medium for heating the material to be dried in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the material to be dried is received at an overpressure by the vessel constructed as a pressurized vessel with electrically insulated contiguous contact with the electrodes located in the pressurized vessel at least for a residence time which is necessary for the heating and is then subjected to flash drying.
2. Process according to claim 1, characterized in that the temperature of the material to be dried is kept below 150°C at least during heating.
3. Process according to claim 1 or 2, characterized in that the heating is carried out convectively or by contact.
4. Process according to claim 1 or 2, characterized in that the material to be dried is heated to at least about 25°C
higher in the electromagnetic alternating field than in a preceding or subsequent heating stage employing the evaporated material moisture.
higher in the electromagnetic alternating field than in a preceding or subsequent heating stage employing the evaporated material moisture.
5. Process according to claim 1 or 2, characterized in that the heating in the pressurized vessel is carried out under a pressure of 2 to 3 bar.
6. Process according to claim 1 or 2, characterized in that the steam produced during the flashing of the material to be dried after discharge from the pressurized vessel is further used to heat the material to be dried.
7. Process according to claim 1 or 2, characterized in that the heating in the pressurized vessel is carried out dielectrically by means of a high-frequency field.
8. Process according to claim 7, characterized in that the heat generated during the generation of the high-frequency field is used to preheat circulating air which is used to heat the material to be dried.
9. Process according to claim 1, 2, or 8, characterized in that the evaporated material moisture is brought into heat exchange with the heated material discharged from the sealed pressurized vessel.
10. Process according to claim 1, 2 or 8, characterized in that the evaporated material moisture is used to heat air which in turn convectively heats the material to be dried.
11. Process according to claim 1, 2 or 8, characterized in that the flash drying is controlled by a level measurement of the material to be dried in the pressurized vessel.
12. Process according to claim 1, 2 or 8, characterized in that the flow rate of the vapours from the pressurized vessel is measured and used to control the mass flow of the material to be dried into the pressurized vessel and the power to generate the electromagnetic alternating field.
13. Apparatus for drying sludge, in particular sewage sludge or moist bulk material, having a sealed vessel for receiving the material to be dried, with an apparatus having electrodes disposed in the vessel for heating the material to be dried by means of an electromagnetic alternating field and an apparatus for heating the material to be dried by means of the material moisture generated by the heating in the electromagnetic alternating field in a step which is separate from the heating in the electromagnetic alternating field, characterized in that the vessel is constructed as a through-type pressurized vessel with electrodes therein, which are in electrically insulated contiguous contact with the material to be dried, and there is a flash tank downstream of the pressurized vessel.
14. The apparatus according to claim 13, wherein the through-type pressurized vessel is vented on the inlet and outlet side.
15. Apparatus according to claim 13, characterized in that at least one dryer is provided which can be operated using the vapours produced in the pressurized vessel as heat transfer medium in such a way that the material to be dried does not exceed a temperature of 150°C in said dryer.
16. The apparatus according to claim 15, wherein the dryer is operated with a gaseous intermediate circuit.
17. Apparatus according to claim 13, 14, 15, or 16 characterized in that the apparatus for heating in the electromagnetic alternating field comprises two capacitor plates which are outwardly insulated and are connected to a high-frequency generator.
18. Apparatus according to claim 17, characterized in that the electrodes form a vertical coaxial capacitor.
19. Apparatus according to claim 18, characterized in that the feed pipe for the pressurized vessel discharges at the bottom inside the region of the vertical coaxial capacitor.
20. Apparatus according to claim 17, characterized in that the high-frequency voltage of the high-frequency generator can be applied to the electrodes in a balanced manner with respect to ground potential.
21. Apparatus according to claim 15 or 16 characterized in that the pressurized vessel with flash tank disposed underneath is disposed above the dryer.
22. Apparatus according to claims 15, 16, 18, 19 or 20, characterized in that a preheater for the material to be dried is arranged upstream of the pressurized vessel and is fed with vapours from dryers arranged downstream of the pressurized vessel as heat transfer medium.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4115408A DE4115408A1 (en) | 1991-05-10 | 1991-05-10 | METHOD AND DEVICE FOR DRYING SLUDGE OR DAMP DUMP |
| DEP4115408.8 | 1991-05-10 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2068228A1 CA2068228A1 (en) | 1992-11-11 |
| CA2068228C true CA2068228C (en) | 1996-05-28 |
Family
ID=6431464
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002068228A Expired - Fee Related CA2068228C (en) | 1991-05-10 | 1992-05-08 | Process and apparatus for drying material to be dried |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5373646A (en) |
| EP (1) | EP0512481B1 (en) |
| AT (1) | ATE105834T1 (en) |
| CA (1) | CA2068228C (en) |
| DE (2) | DE4115408A1 (en) |
| DK (1) | DK0512481T3 (en) |
| ES (1) | ES2056677T3 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4323811A1 (en) * | 1993-07-15 | 1995-01-19 | Andritz Tcw Eng Gmbh | Method and arrangement for removing liquid from a solid/liquid mixture |
| AU667021B1 (en) * | 1994-10-28 | 1996-02-29 | Ecocover Holdings Limited | Mulch or seed mat |
| US6316518B1 (en) | 1999-02-05 | 2001-11-13 | Advanced Polymer Technology, Inc. | Methods of treating polymeric materials, methods of forming nylon, and apparatuses |
| CA2418431C (en) * | 2000-08-16 | 2010-02-09 | John F. Novak | Method and apparatus for microwave utilization |
| SE527166C2 (en) * | 2003-08-21 | 2006-01-10 | Kerttu Eriksson | Method and apparatus for dehumidification |
| US20070234589A1 (en) * | 2006-04-05 | 2007-10-11 | Peter Bernegger | Pressurized Drying/Dehydration Apparatus and Method |
| US9951281B2 (en) | 2006-12-14 | 2018-04-24 | John Otis Farneman | Microwave based systems and methods for obtaining carbonaceous compounds from polypropylene-containing products |
| US8382957B2 (en) * | 2006-12-14 | 2013-02-26 | Micro Recovery Solutions, LLC | Recycling and material recovery system |
| FR2966818B1 (en) * | 2010-10-29 | 2014-02-14 | Orege | METHOD FOR SEPARATION BETWEEN LIQUID AND SUSPENDED MATERIAL OF A SLURRY AND DEVICE USING SUCH A METHOD |
| EP4339167A1 (en) * | 2021-08-05 | 2024-03-20 | Gestion Y Tratamientos Medioambientales Sl | Microwaved-induced wastewater recycling system |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2555450A (en) * | 1943-11-29 | 1951-06-05 | Lee Foundation For Nutritional | High-frequency dehydrating method and apparatus |
| US3235971A (en) * | 1963-03-01 | 1966-02-22 | Hammtronic S Systems Inc | Method and apparatus for drying |
| US4222176A (en) * | 1978-10-23 | 1980-09-16 | Tjurin Nikolai A | Method and apparatus for drying granulated dielectric materials |
| DE3138706C2 (en) * | 1981-09-29 | 1987-01-02 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Capacitive high frequency dryer |
| DE3142172A1 (en) * | 1981-10-23 | 1983-05-05 | Siemens AG, 1000 Berlin und 8000 München | DRYING SYSTEM FOR COLORED REELS IN THE TEXTILE INDUSTRY |
| DE3233069A1 (en) * | 1982-09-06 | 1984-03-08 | Siemens AG, 1000 Berlin und 8000 München | CAPACITIVE HIGH-FREQUENCY CONTINUOUS |
| FI81141B (en) * | 1986-09-22 | 1990-05-31 | Ahlstroem Oy | FOERFARANDE FOER KONCENTRERING AV UPPSLAMNINGAR. |
| DE3734281C2 (en) * | 1987-10-09 | 1994-10-06 | Kurt Von Dr Rer Nat Beckerath | Process for dewatering water-containing and in particular contaminated water-containing sludge and solid aggregates and device suitable therefor |
| DK159488A (en) * | 1988-03-23 | 1989-09-24 | Danske Sukkerfab | Apparatus for stretching of reinforcement lock strips |
| DE3923841C2 (en) * | 1989-07-19 | 1997-04-24 | Satow Kurt Dipl Ing | Sterilization method and apparatus |
-
1991
- 1991-05-10 DE DE4115408A patent/DE4115408A1/en not_active Ceased
-
1992
- 1992-05-05 ES ES92107586T patent/ES2056677T3/en not_active Expired - Lifetime
- 1992-05-05 AT AT92107586T patent/ATE105834T1/en not_active IP Right Cessation
- 1992-05-05 DE DE59200169T patent/DE59200169D1/en not_active Expired - Fee Related
- 1992-05-05 EP EP92107586A patent/EP0512481B1/en not_active Expired - Lifetime
- 1992-05-05 DK DK92107586.7T patent/DK0512481T3/en active
- 1992-05-07 US US07/879,641 patent/US5373646A/en not_active Expired - Fee Related
- 1992-05-08 CA CA002068228A patent/CA2068228C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2068228A1 (en) | 1992-11-11 |
| DK0512481T3 (en) | 1994-09-26 |
| US5373646A (en) | 1994-12-20 |
| EP0512481B1 (en) | 1994-05-18 |
| DE4115408A1 (en) | 1992-11-12 |
| ATE105834T1 (en) | 1994-06-15 |
| ES2056677T3 (en) | 1994-10-01 |
| EP0512481A1 (en) | 1992-11-11 |
| DE59200169D1 (en) | 1994-06-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |