CA1126504A - Process for thermal treatment, especially drying - Google Patents
Process for thermal treatment, especially dryingInfo
- Publication number
- CA1126504A CA1126504A CA352,702A CA352702A CA1126504A CA 1126504 A CA1126504 A CA 1126504A CA 352702 A CA352702 A CA 352702A CA 1126504 A CA1126504 A CA 1126504A
- Authority
- CA
- Canada
- Prior art keywords
- bed
- fluidized bed
- gases
- inert gases
- contact surfaces
- 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
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B15/00—Fluidised-bed furnaces; Other furnaces using or treating finely-divided materials in dispersion
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
- C05F7/00—Fertilisers from waste water, sewage sludge, sea slime, ooze or similar masses
-
- 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
- F26B3/02—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air
- F26B3/06—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried
- F26B3/08—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed
- F26B3/084—Drying solid materials or objects by processes involving the application of heat by convection, i.e. heat being conveyed from a heat source to the materials or objects to be dried by a gas or vapour, e.g. air the gas or vapour flowing through the materials or objects to be dried so as to loosen them, e.g. to form a fluidised bed with heat exchange taking place in the fluidised bed, e.g. combined direct and indirect heat exchange
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
- Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
- Y02A40/20—Fertilizers of biological origin, e.g. guano or fertilizers made from animal corpses
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Hydrology & Water Resources (AREA)
- Water Supply & Treatment (AREA)
- Dispersion Chemistry (AREA)
- Microbiology (AREA)
- Drying Of Solid Materials (AREA)
- Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
- Crucibles And Fluidized-Bed Furnaces (AREA)
- Gasification And Melting Of Waste (AREA)
Abstract
ABSTRACT
The invention relates to the thermal treatment of flowable material using heated contact surfaces in a fluidised bed. Known processes use a gas, often air, to fluidise the bed. This imposes limits on the tempera-tures that can be allowed to be reached as higher temperatures can cause the material to be treated to burn. It also often produces sterilization of the material. Further there is the problem of disposal of the gases generated in the treatment process. In an attempt to alleviate these problems, the present invention proposes a process generally of the abo-ve kind but in which the fluidising gas comprises gases generated in the bed itself. This is economical as it reduces the heat losses, environ-mentally desirable as it reduces the amount of gas discharge and more efficient as these gases are generally inert, thus enabling higher tempe-ratures to be generated in the bed without risk of the material burning, thus also facilitating sterilization of the material.
The invention relates to the thermal treatment of flowable material using heated contact surfaces in a fluidised bed. Known processes use a gas, often air, to fluidise the bed. This imposes limits on the tempera-tures that can be allowed to be reached as higher temperatures can cause the material to be treated to burn. It also often produces sterilization of the material. Further there is the problem of disposal of the gases generated in the treatment process. In an attempt to alleviate these problems, the present invention proposes a process generally of the abo-ve kind but in which the fluidising gas comprises gases generated in the bed itself. This is economical as it reduces the heat losses, environ-mentally desirable as it reduces the amount of gas discharge and more efficient as these gases are generally inert, thus enabling higher tempe-ratures to be generated in the bed without risk of the material burning, thus also facilitating sterilization of the material.
Description
! --`` il~65~4 The invention relates to a process for themally tr~ating 2 ~1O~
ble material in a ~luidised bed. It has particular application to the drying or calcining of a granular, compacted or granulated substance using heated contact surfaces in a fluidised bed.
To such processes, the material to be treated cones into contact with heated contact surfaces, thus transmitting heat to the particles of ~aterial. The contact surfaces are incorporated in the layer of material which ;s to be treated. The introduction of gas causes movement of the layer in order to intensify the heat transfer. A known apparatus for carrying out such treatment is a fluidised bed contact drier, for exam-ple. It isknown to use hot air for the gas treatment of the fluidised layer. However, this process imposes limits on the temperatures which can prevail in the layer. Temperatures in the fluidised bed which are a-bove the burning point of the material which is to be treated should not be permitted, as the material would start to burn. This means that the temperatures are kept relatively low so as not to damage the product, with the result that the process to be carried out lasts longer than might be the case if higher temperatures were used.
, . . .
In other cases, it can be desirable to use higher temperatures for the purpose of sterilizing of disinfecting the product by treating it at a correspondingly high temperature. This is the case, for example, with thermal treatment, particularly when drying sewage sludge, wherein the product has to be hygienically satisfactory so that it can be used, for example, in agriculture for improving the soil. In each of these proces-ses, there is the problem of disposal of the gases discharged from the fluidised bed.
It is the aim of the present invention to increase the economic viability of such thermal treatment processes of, more particularly, drying processes, or to make it possible to use higher temperatures than we~e hitherto permissible in the fluidised bed, and thus obtain better guality products, e.g. sterilized. Another aim is to make these proces-,~
ble material in a ~luidised bed. It has particular application to the drying or calcining of a granular, compacted or granulated substance using heated contact surfaces in a fluidised bed.
To such processes, the material to be treated cones into contact with heated contact surfaces, thus transmitting heat to the particles of ~aterial. The contact surfaces are incorporated in the layer of material which ;s to be treated. The introduction of gas causes movement of the layer in order to intensify the heat transfer. A known apparatus for carrying out such treatment is a fluidised bed contact drier, for exam-ple. It isknown to use hot air for the gas treatment of the fluidised layer. However, this process imposes limits on the temperatures which can prevail in the layer. Temperatures in the fluidised bed which are a-bove the burning point of the material which is to be treated should not be permitted, as the material would start to burn. This means that the temperatures are kept relatively low so as not to damage the product, with the result that the process to be carried out lasts longer than might be the case if higher temperatures were used.
, . . .
In other cases, it can be desirable to use higher temperatures for the purpose of sterilizing of disinfecting the product by treating it at a correspondingly high temperature. This is the case, for example, with thermal treatment, particularly when drying sewage sludge, wherein the product has to be hygienically satisfactory so that it can be used, for example, in agriculture for improving the soil. In each of these proces-ses, there is the problem of disposal of the gases discharged from the fluidised bed.
It is the aim of the present invention to increase the economic viability of such thermal treatment processes of, more particularly, drying processes, or to make it possible to use higher temperatures than we~e hitherto permissible in the fluidised bed, and thus obtain better guality products, e.g. sterilized. Another aim is to make these proces-,~
- 2 -,', ~
j?. ~ :
11~65~
ses more acceptable, by ensuring that exhaust gases from the process do not pollute the environment. Ib these ends, the invention provides a process for continuously thenmally treating an at least partially water-logged, moist material ccmprising the steps of feeding the material to the bed of a closed fluidized bed apparatus; heating the bed by means of heated contact surfa oes, thereby producing inert gases containing mainly water vapor; fluidizing said bed exclusively by said inert gases, which are recirculated through the bed, the recirculated gas constituting only a portion of the gases produoed in the apparatus, having essentially the same gas composition as when produced, and containing at the most a negligible amDunt of oxygen; and discharging the remainder of the inert gases produced in said apparatus. Not all the gases generated in the treatment need be recirculated; some may be separated and discharged, or for other purposes as will be described.
~hus, in processes of the invention, normally, inert gases, e.g.
mainly water vapour when drying sewage sludge, and used to fluidise the bed, which will prevent the dried material from burning. Therefore it is ~;; possible to generate higher temperatur~sin the bed than hitherto. It is also possible to generate temperatures which ensure sterilization of the product again, for exa~ple, sewage sludge.
In preferred embodiments of the invention, it is reoommended to use a fluidised bed oontact apparatus wherein, during the treatment, the ; depth of the fluidised bed is such as to cover the heated contact surfaoes, the gases keing oollected above the bed, and untreated material being fed to the surface of the bed.
Okher preferred features of the invention will be apparent from the following description of a preferred embodiment in which reference will be made to the aocowpanying drawing which diagrammatically shows apparatus - for performing the process acoording to the invention.
The apparatus shc~n is used for drying a liquid-containing material, e.g. sewage sludge, which has previously been mechanically dewatered and .~ ,, .
-~ , ~1265~
processed to form a granulate.
The apparatus comprises a sealed fluidized bed contact drier 1 which is provided with a gas distributor 2 kelow a perforated base 3. Above the base 3p there are provided contact surfaces 4 and 5 which are regulably connected to a heat source, e.g. a steam boiler, via ducts 6 and 7, res-pectively. In this case, condensate ducts for removing the oondensate are f '''' s ~ - 3a -. ' ' ' ' ' ' ~' , .
provided on the other sides of the contact ~urfaces Tlle bed of the ~ate-rial which is to be treated is held at a height H ~ith a surface 8 in the chamber in the drier formed by the contact surfaces. Thus the layer is heated by the contact surfaces, i.e. the heat which is ;ntroduced through the ducts 6 and 7 is trans~itted via the contact surfaces 4 and 5 to the particles of Q~terial when they come into contact with the surfaces.
To improve the heat exchange, gas is passed through the bed of mate-ria7, but only the inert gases fonmed during drying are used. These are cc~lected above the bed after they leave the material and, uniformly dis-t,.buted by the gas distributor, they are driven in a circuit through a duct g and through the base 3 to the bed. For this purpose, a blower 10 is provided in the duct 9 in the circuit. A cyclone or filter 11 with a `
sluice 111 is used to remove the dust from the inert circulating gases.
lhe gases are passed through the material in an amount and at a velocity such that the bed is ~luidised. When the layer of material is in the fluidised state, very good heat exchange is obtained between the contact surfaces and the material.
The inert gases are essentially the steam of the liquid evaporated froo the material to be dried during the drying process. The gases are auto~atically rendered inert during the circulation of the gases, as a result of the gradual uptake of vapours from the material, or else they can be rendered inert when the apparatus is started up, by spraying the contact surfaces by means of a spray 12.
5asically, all the heat which is to be supplied for vaporising the liquid which is to be vaporised is passed into the fluidised bed via the contact surfaces 4 and 5 incorporated in the bed. Obviously, the height of the bed is detenmined by the height of the chamber in the drier defi-ned by the contact surfaces. In other words, the area of contact surface which is required for the transfer of the heat supplied must be incorpo-rated.
If necessary, the circulating gases can be heated, for example, by i,~ , .
.:
,. ' ' ~ ~
.
11;~65V4 means of a heat exchager 13 connected to a heat source, so as to avoid condensation of the circulating gases in the bed, for example. In other cases, this heat exchager could also be connected to the condensate duct of the contact surfaces.
The residual exhaust gases which are surplus to requirements for the gas treatment of the bed are removed from the fluidised bed contact drier along a path branching off the circuit, i.e. through the duct 14.
A cyclone or a filter 15 with a sluice 1S1 for dusting the exhaust gases, or a condenser 16, for example, for recovering heat is provided in this path.
Thè fresh material to be dried is fed into the contact drier by means of a conveying apparatus 17. This may consist, for example, of a ~ decanter with a screw conveyor. The mater~al is fed in on to the surfa-f ce 8 of the bed of material, at a distance E from the site of the dis-charge 18 of the product. This is in the first half of the bed of mate-- rial, viewed towards the discharge point for the product.
This feed point is situated at a space O in the bed of material f which is kept free, i.e. which does not conta;n any contact surfaces.
The contact surfaces are incorporated in the chamber in the bed in two systems 4 and S and a space O is kept free between them, The two sys-~ " ~ , .
" tems may convey different amounts of heat. Thus, the bed may be at a - ,;
'f~' ~ different temperature in each of-the systems. It is advantageous for the fresh material to be fed into this unoccupied space 0. There, it can be very intensively mixed with the dry materials present under the , ~
i ~ conditions of fluidisation. This space O "sucks" the heat out of the ;~ two chambers heated by the contact surfaces. This measure is a consi-$~ ' derable help in~maintaining the fluidised bed, as the moist fresh ma-f~::
terial is constantly mixed with a sufficient quantity of material which ~' is already dry. However, the average moisture content of the layer must
j?. ~ :
11~65~
ses more acceptable, by ensuring that exhaust gases from the process do not pollute the environment. Ib these ends, the invention provides a process for continuously thenmally treating an at least partially water-logged, moist material ccmprising the steps of feeding the material to the bed of a closed fluidized bed apparatus; heating the bed by means of heated contact surfa oes, thereby producing inert gases containing mainly water vapor; fluidizing said bed exclusively by said inert gases, which are recirculated through the bed, the recirculated gas constituting only a portion of the gases produoed in the apparatus, having essentially the same gas composition as when produced, and containing at the most a negligible amDunt of oxygen; and discharging the remainder of the inert gases produced in said apparatus. Not all the gases generated in the treatment need be recirculated; some may be separated and discharged, or for other purposes as will be described.
~hus, in processes of the invention, normally, inert gases, e.g.
mainly water vapour when drying sewage sludge, and used to fluidise the bed, which will prevent the dried material from burning. Therefore it is ~;; possible to generate higher temperatur~sin the bed than hitherto. It is also possible to generate temperatures which ensure sterilization of the product again, for exa~ple, sewage sludge.
In preferred embodiments of the invention, it is reoommended to use a fluidised bed oontact apparatus wherein, during the treatment, the ; depth of the fluidised bed is such as to cover the heated contact surfaoes, the gases keing oollected above the bed, and untreated material being fed to the surface of the bed.
Okher preferred features of the invention will be apparent from the following description of a preferred embodiment in which reference will be made to the aocowpanying drawing which diagrammatically shows apparatus - for performing the process acoording to the invention.
The apparatus shc~n is used for drying a liquid-containing material, e.g. sewage sludge, which has previously been mechanically dewatered and .~ ,, .
-~ , ~1265~
processed to form a granulate.
The apparatus comprises a sealed fluidized bed contact drier 1 which is provided with a gas distributor 2 kelow a perforated base 3. Above the base 3p there are provided contact surfaces 4 and 5 which are regulably connected to a heat source, e.g. a steam boiler, via ducts 6 and 7, res-pectively. In this case, condensate ducts for removing the oondensate are f '''' s ~ - 3a -. ' ' ' ' ' ' ~' , .
provided on the other sides of the contact ~urfaces Tlle bed of the ~ate-rial which is to be treated is held at a height H ~ith a surface 8 in the chamber in the drier formed by the contact surfaces. Thus the layer is heated by the contact surfaces, i.e. the heat which is ;ntroduced through the ducts 6 and 7 is trans~itted via the contact surfaces 4 and 5 to the particles of Q~terial when they come into contact with the surfaces.
To improve the heat exchange, gas is passed through the bed of mate-ria7, but only the inert gases fonmed during drying are used. These are cc~lected above the bed after they leave the material and, uniformly dis-t,.buted by the gas distributor, they are driven in a circuit through a duct g and through the base 3 to the bed. For this purpose, a blower 10 is provided in the duct 9 in the circuit. A cyclone or filter 11 with a `
sluice 111 is used to remove the dust from the inert circulating gases.
lhe gases are passed through the material in an amount and at a velocity such that the bed is ~luidised. When the layer of material is in the fluidised state, very good heat exchange is obtained between the contact surfaces and the material.
The inert gases are essentially the steam of the liquid evaporated froo the material to be dried during the drying process. The gases are auto~atically rendered inert during the circulation of the gases, as a result of the gradual uptake of vapours from the material, or else they can be rendered inert when the apparatus is started up, by spraying the contact surfaces by means of a spray 12.
5asically, all the heat which is to be supplied for vaporising the liquid which is to be vaporised is passed into the fluidised bed via the contact surfaces 4 and 5 incorporated in the bed. Obviously, the height of the bed is detenmined by the height of the chamber in the drier defi-ned by the contact surfaces. In other words, the area of contact surface which is required for the transfer of the heat supplied must be incorpo-rated.
If necessary, the circulating gases can be heated, for example, by i,~ , .
.:
,. ' ' ~ ~
.
11;~65V4 means of a heat exchager 13 connected to a heat source, so as to avoid condensation of the circulating gases in the bed, for example. In other cases, this heat exchager could also be connected to the condensate duct of the contact surfaces.
The residual exhaust gases which are surplus to requirements for the gas treatment of the bed are removed from the fluidised bed contact drier along a path branching off the circuit, i.e. through the duct 14.
A cyclone or a filter 15 with a sluice 1S1 for dusting the exhaust gases, or a condenser 16, for example, for recovering heat is provided in this path.
Thè fresh material to be dried is fed into the contact drier by means of a conveying apparatus 17. This may consist, for example, of a ~ decanter with a screw conveyor. The mater~al is fed in on to the surfa-f ce 8 of the bed of material, at a distance E from the site of the dis-charge 18 of the product. This is in the first half of the bed of mate-- rial, viewed towards the discharge point for the product.
This feed point is situated at a space O in the bed of material f which is kept free, i.e. which does not conta;n any contact surfaces.
The contact surfaces are incorporated in the chamber in the bed in two systems 4 and S and a space O is kept free between them, The two sys-~ " ~ , .
" tems may convey different amounts of heat. Thus, the bed may be at a - ,;
'f~' ~ different temperature in each of-the systems. It is advantageous for the fresh material to be fed into this unoccupied space 0. There, it can be very intensively mixed with the dry materials present under the , ~
i ~ conditions of fluidisation. This space O "sucks" the heat out of the ;~ two chambers heated by the contact surfaces. This measure is a consi-$~ ' derable help in~maintaining the fluidised bed, as the moist fresh ma-f~::
terial is constantly mixed with a sufficient quantity of material which ~' is already dry. However, the average moisture content of the layer must
3~
be kept low by regulating the supply of heat and/or fresh material into the layer. It then remains fluidisable and does not break down, since z (. ~
.. ,. ~ . . , 1126~
the circulating gases, i.e. the vapours, would condense if the moisture level of the layer were higher.
The geometric form of the bed of material is very i~portant in or-der to keep this layer in the fluidised state. The layer is relatively high, owing to the height of the contact surfaces which have to be incorporated, as mentioned hereinbefore. It has also been found that for the same reason it is important that the ratio:
distanoe E/height H
be within the range 0.1 to 5Ø
The fresh material to be treated may also be introduced to the fluidized bed at a plurality of locations which are so chosen that the ratio of the distance between any two locations to-~the hèight of~the~bed is in-the range of 0.5 to 2.5.
The product discharge point 18, and henoe the contact drier 1, is sealed off from the atmosphere b~y a sluice 19. Thus, a slight over-pressure is maintained in the drier, to prevent air from be m g sucked in from the atmDsphere. Tb prevent air from ccming in with the fresh material via the sonveying apparatus 17, the path for the exhaust gases which are to be re-moved from the drier may be directed at least partially counter to the stream of fresh material being fed in, so as to expel the air from the stream of fresh material with the opposing stream of exhaust gases. An exhaust gas duct suitable for this purpose is shown by broken lines in the drawing and is designated 20.
~ On the ot~er hand, it may be advantageous to suck air into the ! drier, for example in the case of a malodorous material. This air can then, for example, be separated when the exhaust gases are condensed, and can be deodorised by burning, for example. In this case, a slight underpressure may be established in the drier.
The process described is not only useful for drying, as in the i 30 exemplary embodiment described. The same technique can also be used in other thermal processee, e.g. the calcining of sodium bicarbonate to form light soda by a corresponding thermal treatment.
.. ..
:, , 6~4 The following example sets forth technical data of a process according to the invention.
Drying of clarified sludge:
, ! - 6 a -Fonm of product: granulate prepared by recycling dry material by mixing with fresh slurry, particle size 0.1 - 8.0 mm.
Amount of dry material: 12000 kg Quantity of water: 3000 kg (corresponding to 20%) Evaporation of water: 3000 kg Dimensions of fluidised bed contact drier:
Flow-in base: length x width 2.5 x 2 = 5 m2 Contact surfaces: 1st system (5) 30 m2 2nd system (4) 60 m2 total 90 m2 Height of bed (H): H = 1.5 m Lengths: contact surfaces 50.75 m contact surfaces 41.35 m Feed spaces between them (O) 0.4 m E = 1.35 + 1/2 (0.4) =1.55 m E/H = 1.55 / 1.5 = 1.033 Hedting ~edium for contact surfaces: saturated steam at 30 bart230C
Heating medium for heat exchanger (13) in circuit:
~- saturated steam at 30 bar/230C
Amount of circulating gas:14.000 kg/h at 170C28.600 m3/h Speed gas flow: 1.6 m/sec Startinq up the apparatus:
a) When spraying in water to exchange the volume of gas in the heated apparatus: ~ -quantity of water: approx. 150 litres ~ b) adding 5 m3 of dry granulate and heating the dry granulate to -, above 130C, then supplying wet material.
' Operating conditions:
.
h, Input of product: 7.500 kg per 1 m of width of bed .i,, .
.
' :.,.,, . , -~1~65Q4 Average exhaust gas temperature: 120C (above the layer)Temperature in input zone (0): 103C
Final temperature of product: 125C
Temperature in the region of the systems of contact surfaces (4, 5):
approx. 120 C
Temperature of fluidising gases: 170 C
Exhaust gas: 3000 kg/h at 120C out of the apparatus.
Possibility of heat recovery:
Condensation of 3.000 kg at 1 bar = approx. 1.618 x 106 kcal/h.
The dust port;on from the cyclone 11 and 15 is recycled into the pre-paration of the granulate.
be kept low by regulating the supply of heat and/or fresh material into the layer. It then remains fluidisable and does not break down, since z (. ~
.. ,. ~ . . , 1126~
the circulating gases, i.e. the vapours, would condense if the moisture level of the layer were higher.
The geometric form of the bed of material is very i~portant in or-der to keep this layer in the fluidised state. The layer is relatively high, owing to the height of the contact surfaces which have to be incorporated, as mentioned hereinbefore. It has also been found that for the same reason it is important that the ratio:
distanoe E/height H
be within the range 0.1 to 5Ø
The fresh material to be treated may also be introduced to the fluidized bed at a plurality of locations which are so chosen that the ratio of the distance between any two locations to-~the hèight of~the~bed is in-the range of 0.5 to 2.5.
The product discharge point 18, and henoe the contact drier 1, is sealed off from the atmosphere b~y a sluice 19. Thus, a slight over-pressure is maintained in the drier, to prevent air from be m g sucked in from the atmDsphere. Tb prevent air from ccming in with the fresh material via the sonveying apparatus 17, the path for the exhaust gases which are to be re-moved from the drier may be directed at least partially counter to the stream of fresh material being fed in, so as to expel the air from the stream of fresh material with the opposing stream of exhaust gases. An exhaust gas duct suitable for this purpose is shown by broken lines in the drawing and is designated 20.
~ On the ot~er hand, it may be advantageous to suck air into the ! drier, for example in the case of a malodorous material. This air can then, for example, be separated when the exhaust gases are condensed, and can be deodorised by burning, for example. In this case, a slight underpressure may be established in the drier.
The process described is not only useful for drying, as in the i 30 exemplary embodiment described. The same technique can also be used in other thermal processee, e.g. the calcining of sodium bicarbonate to form light soda by a corresponding thermal treatment.
.. ..
:, , 6~4 The following example sets forth technical data of a process according to the invention.
Drying of clarified sludge:
, ! - 6 a -Fonm of product: granulate prepared by recycling dry material by mixing with fresh slurry, particle size 0.1 - 8.0 mm.
Amount of dry material: 12000 kg Quantity of water: 3000 kg (corresponding to 20%) Evaporation of water: 3000 kg Dimensions of fluidised bed contact drier:
Flow-in base: length x width 2.5 x 2 = 5 m2 Contact surfaces: 1st system (5) 30 m2 2nd system (4) 60 m2 total 90 m2 Height of bed (H): H = 1.5 m Lengths: contact surfaces 50.75 m contact surfaces 41.35 m Feed spaces between them (O) 0.4 m E = 1.35 + 1/2 (0.4) =1.55 m E/H = 1.55 / 1.5 = 1.033 Hedting ~edium for contact surfaces: saturated steam at 30 bart230C
Heating medium for heat exchanger (13) in circuit:
~- saturated steam at 30 bar/230C
Amount of circulating gas:14.000 kg/h at 170C28.600 m3/h Speed gas flow: 1.6 m/sec Startinq up the apparatus:
a) When spraying in water to exchange the volume of gas in the heated apparatus: ~ -quantity of water: approx. 150 litres ~ b) adding 5 m3 of dry granulate and heating the dry granulate to -, above 130C, then supplying wet material.
' Operating conditions:
.
h, Input of product: 7.500 kg per 1 m of width of bed .i,, .
.
' :.,.,, . , -~1~65Q4 Average exhaust gas temperature: 120C (above the layer)Temperature in input zone (0): 103C
Final temperature of product: 125C
Temperature in the region of the systems of contact surfaces (4, 5):
approx. 120 C
Temperature of fluidising gases: 170 C
Exhaust gas: 3000 kg/h at 120C out of the apparatus.
Possibility of heat recovery:
Condensation of 3.000 kg at 1 bar = approx. 1.618 x 106 kcal/h.
The dust port;on from the cyclone 11 and 15 is recycled into the pre-paration of the granulate.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for continuously thermally treating an at least part-ially waterlogged, moist material comprising the steps of feeding the material to the bed of a closed fluidized bed apparatus; heating the bed by means of heated contact surfaces, thereby producing inert gases contain-ing mainly water vapor; fluidizing said bed exclusively by said inert gases, which are recirculated through the bed, the recirculated gases constituting only a portion of the gases produced in the apparatus, having essentially the same gas composition as when produced, and containing at the most a negligible amount of oxygen; and discharging the remainder of the inert gases produced in said apparatus.
2. A process as defined in claim 1 including the steps of maintaining a superatmospheric pressure in the fluidized bed apparatus; and directing at least a portion of said remainder of inert gases along a path through which said material is fad to the fluidized bed apparatus and in counter-flow to said material, whereby entrained air in said material is removed and kept from mixing with the inert gases which are to be recirculated.
3. A process as defined in claim 1 wherein, prior to discharge, said remainder of the inert gases is subjected to at least one of the following treatments: recovery of heat by condensation, removal of entrained particles of said material, and deodorizing.
4. A process as defined in claim 1 including the step of filtering the recirculated inert gases to remove entrained particles of said material before the gases are reintroduced to the fluidized bed.
5. A process as defined in claim 1 including the step of adjusting the temperature of the recirculated inert gases before those gases are reintroduced to the fluidized bed.
6. A process as defined in claim 1 including the step of feeding fresh material to and withdrawing treated material from the fluidized bed at rates correlated to maintain a bed surface at least at the level of said heated contact surfaces, whereby those surfaces are located wholly within the fluidized bed.
7. A process as defined in claim 6 wherein the heated contact surfaces are divided into two systems spaced apart by a contact surface-free bed region; and the fresh material fed to the bed is introduced to said region, whereby different temperatures may be maintained in the spaced bed portions containing said systems of contact surfaces.
8. A process as defined in claim 1 including the step of maintaining the moisture level in the fluidized bed low enough to prevent condensation of vapors in the recirculated inert gases by at least one of the following measures: regulating the rates at which material is fed to and withdrawn from the fluidized bed, and controlling heating of the contact surfaces.
9. A process as defined in claim 1 wherein the fluidized bed has opposite ends, and which includes the steps of withdrawing treated material from one of said ends, and introducing fresh material to the bed at a location which is closer to the other of said ends than to said one end.
10. A process as defined in claim 1 wherein material is introduced to and withdrawn from the fluidized bed at locations spaced apart horizon-tally by a predetermined distance; and wherein the ratio of said distance to the height of the fluidized bed is in the range of 0.1 to 5Ø
11. A process as defined in claim 1 including the step of introducing said material to the fluidized bed at a plurality of locations so chosen that the ratio of the distance between any two locations to the height of the bed is in the range of 0.5 to 2.5.
12. A process as defined in claim 1 including the step of maintaining the temperature of the fluidized bed at a level which is above that required to vaporize liquid in the material and is sufficient to sterilize the material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH494079A CH644683A5 (en) | 1979-05-28 | 1979-05-28 | METHOD FOR THERMALLY TREATING A MATERIAL LAYER. |
| CH4940/79-2 | 1979-05-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1126504A true CA1126504A (en) | 1982-06-29 |
Family
ID=4285160
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA352,702A Expired CA1126504A (en) | 1979-05-28 | 1980-05-26 | Process for thermal treatment, especially drying |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS55157323A (en) |
| AT (1) | AT393379B (en) |
| BR (1) | BR8003119A (en) |
| CA (1) | CA1126504A (en) |
| CH (1) | CH644683A5 (en) |
| DE (1) | DE2943528C2 (en) |
| ES (1) | ES8103987A1 (en) |
| FR (1) | FR2458037A1 (en) |
| GB (1) | GB2053715B (en) |
| IT (1) | IT1130765B (en) |
| ZA (1) | ZA803005B (en) |
Families Citing this family (24)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH655782A5 (en) * | 1981-07-03 | 1986-05-15 | Escher Wyss Ag | METHOD FOR DRYING A SOLID PARTICLE WET, MEANS FOR IMPLEMENTING AND APPLYING THE METHOD. |
| AT386551B (en) * | 1985-11-25 | 1988-09-12 | Waagner Biro Ag | METHOD AND DEVICE FOR THERMAL TREATMENT |
| FR2618539B1 (en) * | 1987-07-21 | 1989-09-22 | Electricite De France | ELECTRIC HEATER DEHYDRATION PROCESS AND DEVICE |
| DE3902446C1 (en) * | 1989-01-27 | 1990-07-05 | Sulzer-Escher Wyss Gmbh, 7980 Ravensburg, De | |
| DE4235422C2 (en) * | 1992-10-21 | 1997-01-23 | Dornier Gmbh Lindauer | Process for drying pasty material, in particular sewage sludge, preferably in pellet form, and device for carrying out the process |
| DE19614058A1 (en) * | 1996-04-09 | 1997-10-16 | Alexander Czetsch | Contaminated soil heated and agitated within low-pressure chamber |
| DE19739864A1 (en) * | 1997-09-11 | 1999-03-18 | Dornier Gmbh Lindauer | Process for treating the exhaust air from thermal drying processes, in particular from processes during the drying of sewage sludge in sewage sludge dryers and plant for carrying out the process |
| AU2001293831A1 (en) * | 2000-09-25 | 2002-04-02 | Seghers Better Technology Group | Method and apparatus for sludge drying and simultaneous pelletization |
| DE10048516B4 (en) * | 2000-09-29 | 2006-01-05 | Fritz Curtius | Device for heat and mass exchanges |
| EP1319632A1 (en) * | 2001-12-13 | 2003-06-18 | Klimapol Sp.Z O.O.J.V. | Process and device for drying of sludge, in particular sewage sludge |
| AT504996B1 (en) * | 2007-03-02 | 2009-03-15 | Andritz Tech & Asset Man Gmbh | METHOD AND DEVICE FOR DRYING CRYSTALLINE CARBOXYLIC ACIDS |
| JP5535731B2 (en) * | 2010-04-02 | 2014-07-02 | 三菱重工業株式会社 | Fluidized bed drying apparatus and fluidized bed drying equipment |
| DE102015013570A1 (en) | 2015-10-20 | 2017-04-20 | Fritz Curtius | Heat pump dryer for laundry |
| DE202017005283U1 (en) | 2017-08-30 | 2017-11-24 | Fritz Curtius | Quench cooler |
| DE102018004741A1 (en) | 2018-06-14 | 2019-12-19 | Fritz Curtius | Quench cooler for phosphorus-containing gases |
| DE202018004168U1 (en) | 2018-09-07 | 2018-12-12 | Fritz Curtius | Phosphor plant in air-technical construction |
| DE202018004398U1 (en) | 2018-09-21 | 2018-12-11 | Fritz Curtius | Heating device for flowable solids |
| DE202019000127U1 (en) | 2019-01-10 | 2019-04-11 | Fritz Curtius | Super Steam Producer for distillates made of moist material |
| DE102019000162A1 (en) | 2019-01-10 | 2020-07-16 | Fritz Curtius | Superheated steam generator for distillates made of moist material |
| DE102019000741A1 (en) | 2019-02-01 | 2020-08-06 | Fritz Curtius | Torre ficator for wet material |
| DE202019000496U1 (en) | 2019-02-01 | 2019-04-09 | Fritz Curtius | Torrefikator for damp material |
| DE202020001235U1 (en) | 2020-03-28 | 2020-06-12 | Fritz Curtius | Tumble dryer in a closed atmosphere |
| DE102021001543A1 (en) | 2020-03-28 | 2021-09-30 | Fritz Curtius | Closed atmosphere dryer |
| DE202022000456U1 (en) | 2022-02-23 | 2022-06-01 | Fritz Curtius | Container parking spaces for drying containers for sewage sludge. |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH17225A (en) * | 1898-06-13 | 1899-05-15 | Moeller & Pfeifer | Drying device |
| BE523139A (en) * | 1952-01-23 | |||
| FR1128086A (en) * | 1955-06-23 | 1957-01-02 | Grain processing process | |
| US3585732A (en) * | 1968-05-15 | 1971-06-22 | Gen Am Transport | Apparatus for drying solids |
| JPS4827266B1 (en) * | 1968-07-13 | 1973-08-21 | ||
| US3861058A (en) * | 1972-12-18 | 1975-01-21 | California Pellet Mill Co | Fluidized bed grain processor |
| US3954069A (en) * | 1975-03-10 | 1976-05-04 | Myrens Verksted A/S | Process and apparatus for the incineration of aqueous sewage sludge |
| CH612003A5 (en) * | 1976-03-02 | 1979-06-29 | Kuelling Hans Peter |
-
1979
- 1979-05-28 CH CH494079A patent/CH644683A5/en not_active IP Right Cessation
- 1979-10-27 DE DE2943528A patent/DE2943528C2/en not_active Expired
-
1980
- 1980-05-19 BR BR8003119A patent/BR8003119A/en not_active IP Right Cessation
- 1980-05-20 ZA ZA00803005A patent/ZA803005B/en unknown
- 1980-05-23 FR FR8011537A patent/FR2458037A1/en active Granted
- 1980-05-26 JP JP6908080A patent/JPS55157323A/en active Granted
- 1980-05-26 IT IT22331/80A patent/IT1130765B/en active
- 1980-05-26 CA CA352,702A patent/CA1126504A/en not_active Expired
- 1980-05-27 AT AT2797/80A patent/AT393379B/en not_active IP Right Cessation
- 1980-05-27 GB GB8017256A patent/GB2053715B/en not_active Expired
- 1980-05-27 ES ES491872A patent/ES8103987A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ES491872A0 (en) | 1981-04-01 |
| DE2943528C2 (en) | 1985-06-27 |
| ZA803005B (en) | 1981-05-27 |
| JPS55157323A (en) | 1980-12-08 |
| GB2053715B (en) | 1984-02-29 |
| DE2943528A1 (en) | 1980-12-11 |
| ES8103987A1 (en) | 1981-04-01 |
| IT8022331A0 (en) | 1980-05-26 |
| AT393379B (en) | 1991-10-10 |
| JPS6328658B2 (en) | 1988-06-09 |
| FR2458037B1 (en) | 1985-02-01 |
| ATA279780A (en) | 1988-09-15 |
| CH644683A5 (en) | 1984-08-15 |
| FR2458037A1 (en) | 1980-12-26 |
| IT1130765B (en) | 1986-06-18 |
| BR8003119A (en) | 1980-12-23 |
| GB2053715A (en) | 1981-02-11 |
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