CA2148938C - Method for the mechanical removal of moisture from a filter cake and an apparatus for implementing the method - Google Patents
Method for the mechanical removal of moisture from a filter cake and an apparatus for implementing the method Download PDFInfo
- Publication number
- CA2148938C CA2148938C CA002148938A CA2148938A CA2148938C CA 2148938 C CA2148938 C CA 2148938C CA 002148938 A CA002148938 A CA 002148938A CA 2148938 A CA2148938 A CA 2148938A CA 2148938 C CA2148938 C CA 2148938C
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- filter cake
- pressure
- treatment fluid
- filtering surface
- chamber
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- 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.)
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- 239000012065 filter cake Substances 0.000 title claims abstract description 62
- 238000000034 method Methods 0.000 title claims abstract description 37
- 239000012530 fluid Substances 0.000 claims abstract description 49
- 239000007791 liquid phase Substances 0.000 claims abstract 2
- 239000007788 liquid Substances 0.000 claims description 25
- 238000001914 filtration Methods 0.000 claims description 22
- 230000015572 biosynthetic process Effects 0.000 claims description 18
- 238000009833 condensation Methods 0.000 claims description 16
- 230000005494 condensation Effects 0.000 claims description 16
- 239000000126 substance Substances 0.000 claims description 13
- 230000007935 neutral effect Effects 0.000 claims description 4
- 229920006395 saturated elastomer Polymers 0.000 claims description 3
- 238000000605 extraction Methods 0.000 claims description 2
- 239000012071 phase Substances 0.000 claims 2
- 230000001747 exhibiting effect Effects 0.000 claims 1
- 230000016507 interphase Effects 0.000 claims 1
- 239000012466 permeate Substances 0.000 claims 1
- 239000007792 gaseous phase Substances 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 13
- 239000002245 particle Substances 0.000 description 13
- 238000005406 washing Methods 0.000 description 10
- 239000007787 solid Substances 0.000 description 5
- 238000005336 cracking Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000000725 suspension Substances 0.000 description 4
- 238000001816 cooling Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 230000018109 developmental process Effects 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000011148 porous material Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 230000009881 electrostatic interaction Effects 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 238000011085 pressure filtration Methods 0.000 description 2
- 238000003828 vacuum filtration Methods 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000000306 component Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 235000010755 mineral Nutrition 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 230000002028 premature Effects 0.000 description 1
- 235000011121 sodium hydroxide Nutrition 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D35/00—Filtering devices having features not specifically covered by groups B01D24/00 - B01D33/00, or for applications not specifically covered by groups B01D24/00 - B01D33/00; Auxiliary devices for filtration; Filter housing constructions
- B01D35/30—Filter housing constructions
- B01D35/31—Filter housing constructions including arrangements for environmental protection, e.g. pressure resisting features
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
- B01D33/073—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums arranged for inward flow filtration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
- B01D33/60—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for washing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
- B01D33/62—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for drying
- B01D33/66—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for drying by gases or by heating
- B01D33/663—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for drying by gases or by heating by direct contact with a fluid
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2201/00—Details relating to filtering apparatus
- B01D2201/32—Flow characteristics of the filter
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Filtering Materials (AREA)
- Treatment Of Sludge (AREA)
- Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
- Drying Of Solid Materials (AREA)
- Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
Abstract
In a process for mechanically dehumidifying a filter cake, differential pressure causes a treatment fluid to flow through the filter cake. Pressure and temperature on the side of the filter cake which faces the filter surface are set in such a manner that the treatment fluid is present there in its liquid phase, whereas pressure and temperature on the side of the filter cake opposite to the filter surface are set in such a manner that the treatment fluid is present on that side in its gaseous phase.
Description
2I4893~
WO 94/11084 1 PCTlEP93/03148 6Viethod for the mechanical removal of moisture from a filter cake and an apparatus for implementing the method The invention relates to a method for the mechanical removal of moisture from a filter cake, wherein a treatment fluid flows through the filter cake as a result of a difference in pressure, and to an apparatus for implementing the method.
In existing filtration by differential gas-pressure, shrinkage cracks often occur during the moisture-removal phase, thereby considerably impairing the result of filtration. As a result of the physical/chemical composition of solid and liquid, characteristic crack patterns often form on the surface.
These cracks, which in most cases extend through the entire filter cake as far as the filter cloth; mainly occur when processing fine-grain, especially mineral, solid materials, having a complex chemical structure. It is to be assumed that crack formation is governed by capillary forces, by an electrostatic interaction between particles, as well as by the pH vafuo and by the nature and concentration of the ions in the liquid contained in the filter cake. Cracking behaviour is also affected; for example, by the filtration pressure-difference, the height ofi the cake and by the filter cloth.
The occurrence of cracking has a negative effect on further treatment of the filter cake. thus, both in vacuum filtration and in pressure filtration, a bypass f!'ow of ai~'takes'place'~th~rough the cracks produced. Cake washing,deteriorates, drastically, since the washing fluid prefers to pass through the cracks, rather than through the accumulated material being washed.
To prevent crack formation in cake-forming filters, it is known that the filter cake can be compressed by the external application of compressive forces, thereby ~ ~~'~~~~a ----~ 214 8 9 3 8 PCTlEP93/03148 reclosing open cracks. Another known possibility is to carry out further filtration through cracks which have formed, but this causes rewetting of the filter cake which has already formed, and consequently causes fresh cracking.
A further possibility for preventing crack formation consists in adding small quantities of solid substances, such as cellulose or glass fibres, to the suspension being filtered, which, however, because of the cost involved or the negative effect on the purity required in the substance produced, can only rarely be implemented.
It is known from EP 0 179 446 B1 that, in order to prevent crack formation, a filtering medium can be designed, in which, by providing non-filtering bars on the filtering medium, a division into filtration areas is achieved, with an associated division of the filter cake produced into a plurality of small sections.
It is the aim of this invention to create a method of the type mentioned earlier, which permits filtration with moisture removal and washing of the filter cake by a very low consumption of treatment fluid. A further aim is to present an apparatus for the implementation of this method.
Procedurally, the aim is achieved by the characterizing Features presented in claim 1. !n this method, the treatment fluid condenses in the filter cake, wherein the mother liquid originally present in the filter cake is displaced, and wherein at, the same time, further , impurities are washed out raf the filter cake.
25 Replacementlof the mother liquid by the treatment fluid ensures that nocrack formation occurs.
~ ~~~~d ~ _ 214~93~
PCTlEP93/03148 A particular development, in which a piston-flow-like displacement of the mother liquid from the filter cake is executed, is advantageous. Ideally, a sharp displacement front forms between the mother liquid and the treatment fluid.
Repetition of this flow-through process after intermediate cooling of the filter cake increases the efficiency of the method, especially in respect of the wash-out effect.
If the treatment fluid has the properties of a low ionic strength, a low ion concentration and a mild, essentially neutral pH value, the mother liquid between the individual particles of the filter cake is largely replaced by a largely neutral fluid. The electrical interaction between the particles is thereby weakened, and a smaller distance between the solid bodies is made possible.
The cake shrinks as moisture removal progresses. At a degree of saturation of approximately 80°!°; the ensile stresses reach a maximum, and crack formation occurs, if the liquid bridges between two or more particles can no longer absorb the farces, The shrinkage of the filter cake, and thereby the tendency towards cracking during moisture removal, increase with the distance between the particles at the start of or dining moisture removal. The reasons why the particles are not always in mutual contact where the cake is formed include electrostatic interaction betweervthe particles and between the particles and mother liquid.
These interactions incr~ase~ in signi~ic,ance the smaller the particles are.
They . I 4.I
are also affected by the electric charge of the particles, by the ionic strength and the pH value of the liquid contained in the filter cake, so that replacement of mother liquid by a treatment fluid with the properties according to the invention; executed in the method according to the invention, produces a _ ~214~93~
f~ VW2 ~,~e~
--PCTlEP93/03148 greater particle density and thereby a reduction of the tensile stresses between the particles, which reduces the risk of crack formation.
it is also an advantage for the treatment fluid, or the treatment liquid produced S from it by condensation, to have a great capacity to absorb volatile or soluble substances from the filter cake. In this sense, solvents such as alcohol, acetone, sulphuric acid or soda lye can be used as the treatment fluid. In this way, such substances are washed out or extracted, without the need for prior removal of moisture from the filter, with the risk of crack formation.
Further advantageous developments of the method according to the invention are described in the dependent claims.
An alternative apparatus for implementing the method according to the 15 invention is given in the apparatus claim. The filter cake is exposed to treatment fluid under a hood, the rest of the area being exposed to a different gad.
In processes of pressure filtration or enclosed vacuum-filtration, , the entire process area; or more advantageously, within the process area, only the z0 - treatmervt area separated by an internal additional enclosure above the filter cake; is exposed to the treatment fluid: According to a further development, the gas exchange between the two pressure-chambers is minimized, without having to provide expensive seals. The low thermal conductivity of the gas ~contained~ in,th~ first pressure-chamber provides thermal insulation of the filter 25 cake from the external environment of the apparatus, thereby increasing its efficiency:
_214938 I3'0 94lI 1084 5 PCTlEP93/03148 The invention is described below, by reference to an example, referring to the drawing. The drawing shows:
Fig. 1 a cross-section through a first apparatus far the implementation of the method, and Fig. 2 a cross-section through a second apparatus for the implementation of the method.
A first embodiment of an apparatus for implementing the method according to the invention is shown in Fig. 1. There, a drum filter 2 is completely fitted in a pressure-tight housing 3 enclosing a first pressure-chamber 5. During service, pressure chamber 5 is completely filled with the gaseous treatment fluid: The gaseous treatment fluid brings about the steps of cake fiormation, washing and moisture removal in the method.
Fig. ~ shows an alternative embodiment of an apparatus for implementing the method according to the invention; in which a drum filter ~ rotates in a suspension trough 1. Here too, the suspensibn trough 1 aid drum filter 2 are surrounded by a housing 3 enclosing a pressure chamber 5. The pressure chamber 5 is filled with a pressurized gas, which is gaseous under ambient conditions. This gas produces the differential pressure required for bake formation and for moisture removal:
Inan area of; the pe~iph~ry of the filter drum outside the suspension trough, a hood 4 is provided; covering this peripheral section of the drum filter 2 and, together with the peripheral section of the drum filter and the outer area ofi the filter bake lying thereon, encloses a second pressure-chamber 6. This pressure-chamber 6 encloses individual process-areas during cake treatment, _ ~~.4~9~~
WO 94/I r 084 6 PCTlEP93/03148 but also the entire procedural section outside cake formation. In this case, even cake formation can be brought about by the pressure of the treatment fluid.
In the second pressure-chamber 6 is the gaseous treatment fluid, which preferably has the task of washing the cake and of extracting soluble substances from it, while avoiding crack formation. Between the second pressure-chamber 6 and the first pressure-chamber 5, there is almost no difference in pressure, so that overflow of the different gases is kept small.
Besides other advantageous effects, a low thermal conductivity of the gas in la the first pressure-chamber 5 prevents heat losses of the treatment fluid and thereby premature condensation.
Crack formation usually occurring during the removal of moisture from a filter cake causes a deterioration of the result of the process. The moisture-removal air then seeks the path of least resistance, producing a bypass through the cracks formed, instead of through the capillaries of the filter cake from which moisture is to be removed. The capacity limit of the compressor generating the filtration pressure-difference can be quickly reached, followed as a further consequence by a drop in the applied differential-pressure. 'this results in a low mass throughput of the filter, with an increasing residual moisture-content and possible resultant inadequate moisture-removal.
Also; when the filter cake is being washed, a large proportion of the washing liquid then flows unused throug~,the, cracks, as a result of which the desired I
degree of wash-out is not achieved. What is more, the cost of series-connected thermal drying increases with a higher residual moisture-content of the cake.
In addition; with inadequate washing, the washing-liquid requirement of the filter increases, arqd an additional cleaning stage may be necessary.
_214893 WO 94/11084 7 PCTlEP93/03148 in the filtration process according to the invention, the gas phase of a liquid is used for mechanical moisture-removal by means of differential pressure. Under the pressure and temperature conditions prevailing at the underside of the filter cake, this is preferably liquid, but the gas phase in the filter cake condenses as a result of a decay in the differential pressure. The filtered filter cake is still exposed to the treatment fluid prior to pore emptying and the onset of shrinkage. Cake formation can, however, also take place using this treatment fluid.
The temperature of the treatment fluid above the filter cake can be considerably higher than the ambient temperature for the treatment fluid to be in gaseous form. Since a differential pressure is required for the formation of the filter cake and for moisture removal, the pressure of the treatment fluid in its gaseous state can be higher than the normal pressure in the vicinity. The t5 thermodynamic state-paint of the gas should not, however, be all that far from the condensation point. If, after formation of the filter cake from a suspension, whose temperature is below that of the treatment fluid in a gaseous state, the saturated filter cake is brought into contact with the gaseous treatment fluid, then the treatment fluid will penetrate into the filter cake as a result of the applied pressure-difference.
in the filter cake, the gaseous treatment fluid quickly cools on the colder pore-surfaces and at the liquid urfaces. Pores just produced, which were filled with gas, are now filled, wi~h~ thief conde,nsate of the treatment fluid. In this area,, the filter cake remains saturated. Neat is continuously supplied to the filter cake by the oondensatiori enthalpy released, so that its temperature in the condensation zone rises to the gas temperature. During this heating process, the mbther liquid originally present is ejected by continuously produced 21489$
R ~.~ "~I
$ PCTlEP93/03I48 condensate of the treatment fluid, as a result of the filtration pressure-difference.
The processes described initially only take place in the topmost layer of the S filter cake, which is in direct contact with the gaseous treatment fluid.
Immediate further penetration of the gaseous treatment fluid into deeper layers of the filter cake is prevented by cooling and condensation. Thus these processes only take place in a narrow area: a condensation front.
1Q As soon as the filter cake within the condensation front has been heated up to the gas temperature by the condensation enthalpy, the pores remain filled with gas, and the condensation front moves a bit further into the interior of the filter cake. The front gradually passes through the entire filter cake as far as the filter medium.
By e~irtue of a low ionic strength and ion concentration, together with a "mild", essentially neutral pH value, el~ctricai interactions between the particles of the filter cake are reduced. In addition, the pure condensate has a great capacity for washing out or extracting soluble substances from the filter cake.
Whereas, in usual filtration systems, two components, solid and liquid, are separated from etch other, in the case of washing, a further component, the washing liquid or treatment fluid; is also involved in the process. In the method according to this invention, the possibility naw exists of implementing a more ZS complex separating method for systems with even more components. It is thus~~
conceivable that; in addition to solid substance, mother liquid and treatment fluid, a farther Substance or several substances may be in the filter cake, which can of course be extracted with the treatment fluid. In this case, extraction of a _218938 WO 94/1 ! 084 9 PCTlEP93f03148 fourth or further components can take place due to the free through flow of steam/vapour occurring in the method according to the invention.
If, after passage of the candensation front, the desired degree of wash-out has not been achieved; the possibility exists of intermediate cooling of the filter cake by spraying it with a cold liquid, and causing a further condensation front to pass through again.
WO 94/11084 1 PCTlEP93/03148 6Viethod for the mechanical removal of moisture from a filter cake and an apparatus for implementing the method The invention relates to a method for the mechanical removal of moisture from a filter cake, wherein a treatment fluid flows through the filter cake as a result of a difference in pressure, and to an apparatus for implementing the method.
In existing filtration by differential gas-pressure, shrinkage cracks often occur during the moisture-removal phase, thereby considerably impairing the result of filtration. As a result of the physical/chemical composition of solid and liquid, characteristic crack patterns often form on the surface.
These cracks, which in most cases extend through the entire filter cake as far as the filter cloth; mainly occur when processing fine-grain, especially mineral, solid materials, having a complex chemical structure. It is to be assumed that crack formation is governed by capillary forces, by an electrostatic interaction between particles, as well as by the pH vafuo and by the nature and concentration of the ions in the liquid contained in the filter cake. Cracking behaviour is also affected; for example, by the filtration pressure-difference, the height ofi the cake and by the filter cloth.
The occurrence of cracking has a negative effect on further treatment of the filter cake. thus, both in vacuum filtration and in pressure filtration, a bypass f!'ow of ai~'takes'place'~th~rough the cracks produced. Cake washing,deteriorates, drastically, since the washing fluid prefers to pass through the cracks, rather than through the accumulated material being washed.
To prevent crack formation in cake-forming filters, it is known that the filter cake can be compressed by the external application of compressive forces, thereby ~ ~~'~~~~a ----~ 214 8 9 3 8 PCTlEP93/03148 reclosing open cracks. Another known possibility is to carry out further filtration through cracks which have formed, but this causes rewetting of the filter cake which has already formed, and consequently causes fresh cracking.
A further possibility for preventing crack formation consists in adding small quantities of solid substances, such as cellulose or glass fibres, to the suspension being filtered, which, however, because of the cost involved or the negative effect on the purity required in the substance produced, can only rarely be implemented.
It is known from EP 0 179 446 B1 that, in order to prevent crack formation, a filtering medium can be designed, in which, by providing non-filtering bars on the filtering medium, a division into filtration areas is achieved, with an associated division of the filter cake produced into a plurality of small sections.
It is the aim of this invention to create a method of the type mentioned earlier, which permits filtration with moisture removal and washing of the filter cake by a very low consumption of treatment fluid. A further aim is to present an apparatus for the implementation of this method.
Procedurally, the aim is achieved by the characterizing Features presented in claim 1. !n this method, the treatment fluid condenses in the filter cake, wherein the mother liquid originally present in the filter cake is displaced, and wherein at, the same time, further , impurities are washed out raf the filter cake.
25 Replacementlof the mother liquid by the treatment fluid ensures that nocrack formation occurs.
~ ~~~~d ~ _ 214~93~
PCTlEP93/03148 A particular development, in which a piston-flow-like displacement of the mother liquid from the filter cake is executed, is advantageous. Ideally, a sharp displacement front forms between the mother liquid and the treatment fluid.
Repetition of this flow-through process after intermediate cooling of the filter cake increases the efficiency of the method, especially in respect of the wash-out effect.
If the treatment fluid has the properties of a low ionic strength, a low ion concentration and a mild, essentially neutral pH value, the mother liquid between the individual particles of the filter cake is largely replaced by a largely neutral fluid. The electrical interaction between the particles is thereby weakened, and a smaller distance between the solid bodies is made possible.
The cake shrinks as moisture removal progresses. At a degree of saturation of approximately 80°!°; the ensile stresses reach a maximum, and crack formation occurs, if the liquid bridges between two or more particles can no longer absorb the farces, The shrinkage of the filter cake, and thereby the tendency towards cracking during moisture removal, increase with the distance between the particles at the start of or dining moisture removal. The reasons why the particles are not always in mutual contact where the cake is formed include electrostatic interaction betweervthe particles and between the particles and mother liquid.
These interactions incr~ase~ in signi~ic,ance the smaller the particles are.
They . I 4.I
are also affected by the electric charge of the particles, by the ionic strength and the pH value of the liquid contained in the filter cake, so that replacement of mother liquid by a treatment fluid with the properties according to the invention; executed in the method according to the invention, produces a _ ~214~93~
f~ VW2 ~,~e~
--PCTlEP93/03148 greater particle density and thereby a reduction of the tensile stresses between the particles, which reduces the risk of crack formation.
it is also an advantage for the treatment fluid, or the treatment liquid produced S from it by condensation, to have a great capacity to absorb volatile or soluble substances from the filter cake. In this sense, solvents such as alcohol, acetone, sulphuric acid or soda lye can be used as the treatment fluid. In this way, such substances are washed out or extracted, without the need for prior removal of moisture from the filter, with the risk of crack formation.
Further advantageous developments of the method according to the invention are described in the dependent claims.
An alternative apparatus for implementing the method according to the 15 invention is given in the apparatus claim. The filter cake is exposed to treatment fluid under a hood, the rest of the area being exposed to a different gad.
In processes of pressure filtration or enclosed vacuum-filtration, , the entire process area; or more advantageously, within the process area, only the z0 - treatmervt area separated by an internal additional enclosure above the filter cake; is exposed to the treatment fluid: According to a further development, the gas exchange between the two pressure-chambers is minimized, without having to provide expensive seals. The low thermal conductivity of the gas ~contained~ in,th~ first pressure-chamber provides thermal insulation of the filter 25 cake from the external environment of the apparatus, thereby increasing its efficiency:
_214938 I3'0 94lI 1084 5 PCTlEP93/03148 The invention is described below, by reference to an example, referring to the drawing. The drawing shows:
Fig. 1 a cross-section through a first apparatus far the implementation of the method, and Fig. 2 a cross-section through a second apparatus for the implementation of the method.
A first embodiment of an apparatus for implementing the method according to the invention is shown in Fig. 1. There, a drum filter 2 is completely fitted in a pressure-tight housing 3 enclosing a first pressure-chamber 5. During service, pressure chamber 5 is completely filled with the gaseous treatment fluid: The gaseous treatment fluid brings about the steps of cake fiormation, washing and moisture removal in the method.
Fig. ~ shows an alternative embodiment of an apparatus for implementing the method according to the invention; in which a drum filter ~ rotates in a suspension trough 1. Here too, the suspensibn trough 1 aid drum filter 2 are surrounded by a housing 3 enclosing a pressure chamber 5. The pressure chamber 5 is filled with a pressurized gas, which is gaseous under ambient conditions. This gas produces the differential pressure required for bake formation and for moisture removal:
Inan area of; the pe~iph~ry of the filter drum outside the suspension trough, a hood 4 is provided; covering this peripheral section of the drum filter 2 and, together with the peripheral section of the drum filter and the outer area ofi the filter bake lying thereon, encloses a second pressure-chamber 6. This pressure-chamber 6 encloses individual process-areas during cake treatment, _ ~~.4~9~~
WO 94/I r 084 6 PCTlEP93/03148 but also the entire procedural section outside cake formation. In this case, even cake formation can be brought about by the pressure of the treatment fluid.
In the second pressure-chamber 6 is the gaseous treatment fluid, which preferably has the task of washing the cake and of extracting soluble substances from it, while avoiding crack formation. Between the second pressure-chamber 6 and the first pressure-chamber 5, there is almost no difference in pressure, so that overflow of the different gases is kept small.
Besides other advantageous effects, a low thermal conductivity of the gas in la the first pressure-chamber 5 prevents heat losses of the treatment fluid and thereby premature condensation.
Crack formation usually occurring during the removal of moisture from a filter cake causes a deterioration of the result of the process. The moisture-removal air then seeks the path of least resistance, producing a bypass through the cracks formed, instead of through the capillaries of the filter cake from which moisture is to be removed. The capacity limit of the compressor generating the filtration pressure-difference can be quickly reached, followed as a further consequence by a drop in the applied differential-pressure. 'this results in a low mass throughput of the filter, with an increasing residual moisture-content and possible resultant inadequate moisture-removal.
Also; when the filter cake is being washed, a large proportion of the washing liquid then flows unused throug~,the, cracks, as a result of which the desired I
degree of wash-out is not achieved. What is more, the cost of series-connected thermal drying increases with a higher residual moisture-content of the cake.
In addition; with inadequate washing, the washing-liquid requirement of the filter increases, arqd an additional cleaning stage may be necessary.
_214893 WO 94/11084 7 PCTlEP93/03148 in the filtration process according to the invention, the gas phase of a liquid is used for mechanical moisture-removal by means of differential pressure. Under the pressure and temperature conditions prevailing at the underside of the filter cake, this is preferably liquid, but the gas phase in the filter cake condenses as a result of a decay in the differential pressure. The filtered filter cake is still exposed to the treatment fluid prior to pore emptying and the onset of shrinkage. Cake formation can, however, also take place using this treatment fluid.
The temperature of the treatment fluid above the filter cake can be considerably higher than the ambient temperature for the treatment fluid to be in gaseous form. Since a differential pressure is required for the formation of the filter cake and for moisture removal, the pressure of the treatment fluid in its gaseous state can be higher than the normal pressure in the vicinity. The t5 thermodynamic state-paint of the gas should not, however, be all that far from the condensation point. If, after formation of the filter cake from a suspension, whose temperature is below that of the treatment fluid in a gaseous state, the saturated filter cake is brought into contact with the gaseous treatment fluid, then the treatment fluid will penetrate into the filter cake as a result of the applied pressure-difference.
in the filter cake, the gaseous treatment fluid quickly cools on the colder pore-surfaces and at the liquid urfaces. Pores just produced, which were filled with gas, are now filled, wi~h~ thief conde,nsate of the treatment fluid. In this area,, the filter cake remains saturated. Neat is continuously supplied to the filter cake by the oondensatiori enthalpy released, so that its temperature in the condensation zone rises to the gas temperature. During this heating process, the mbther liquid originally present is ejected by continuously produced 21489$
R ~.~ "~I
$ PCTlEP93/03I48 condensate of the treatment fluid, as a result of the filtration pressure-difference.
The processes described initially only take place in the topmost layer of the S filter cake, which is in direct contact with the gaseous treatment fluid.
Immediate further penetration of the gaseous treatment fluid into deeper layers of the filter cake is prevented by cooling and condensation. Thus these processes only take place in a narrow area: a condensation front.
1Q As soon as the filter cake within the condensation front has been heated up to the gas temperature by the condensation enthalpy, the pores remain filled with gas, and the condensation front moves a bit further into the interior of the filter cake. The front gradually passes through the entire filter cake as far as the filter medium.
By e~irtue of a low ionic strength and ion concentration, together with a "mild", essentially neutral pH value, el~ctricai interactions between the particles of the filter cake are reduced. In addition, the pure condensate has a great capacity for washing out or extracting soluble substances from the filter cake.
Whereas, in usual filtration systems, two components, solid and liquid, are separated from etch other, in the case of washing, a further component, the washing liquid or treatment fluid; is also involved in the process. In the method according to this invention, the possibility naw exists of implementing a more ZS complex separating method for systems with even more components. It is thus~~
conceivable that; in addition to solid substance, mother liquid and treatment fluid, a farther Substance or several substances may be in the filter cake, which can of course be extracted with the treatment fluid. In this case, extraction of a _218938 WO 94/1 ! 084 9 PCTlEP93f03148 fourth or further components can take place due to the free through flow of steam/vapour occurring in the method according to the invention.
If, after passage of the candensation front, the desired degree of wash-out has not been achieved; the possibility exists of intermediate cooling of the filter cake by spraying it with a cold liquid, and causing a further condensation front to pass through again.
Claims (8)
1. Method for the mechanical removal of moisture from a filter cake formed on a filtering surface, wherein a treatment fluid, having the capacity to absorb volatile or soluble substances from the filter cake, flows through the filter cake as a result of an applied pressure-difference, characterized in that a) the filter cake is present in a mother liquid saturated state, b) the exposition and the condensation of the liquid phase of the treatment fluid is brought about at an instant prior to the onset of crack formation, c) the pressure and temperature of the treatment fluid are adjusted in such a way that d) the treatment fluid initially condenses in the top layer of the filter cake furthest away from the filtering surface, so that a condensation front forms along this layer, and e) furthermore, by means of condensation enthalpy released, the filter cake is progressively heated up to the gas temperature of the treatment fluid from the top layer towards the filtering surface, so that the condensation front at the interphase between the treatment fluid in its gas phase and the mother liquid is displaced towards the filtering surface thereby also displacing the mother liquid towards the filtering surface.
2. Method as claimed in claim 1, characterized in that the gas phase of the treatment fluid is used as a pressure medium to generate the differential pressure bringing about the pressure difference.
3. Method as claimed in claim 1 or claim 2, characterized in that the treatment fluid permeates through the filter cake in stages.
4. Method as claimed in claim 3, characterized in that after the condensation front has penetrated into the filter cake, the filter cake is cooled, and that gaseous treatment fluid is subsequently again introduced into the filter cake, in order to repeat the process of a condensation front passing through the filter cake.
5. Method as claimed in any of claims 1 - 4, characterized in that formation of the filter cake takes place using the treatment fluid as pressure medium.
6. Method as claimed in any of claims 1 - 5, characterized in that a treatment fluid and also a condensate produced from it with a low ionic strength, a low ion concentration, a "mild", essentially neutral pH value is used, exhibiting a wash-out and extraction character for substances being extracted from the filter cake.
7. Apparatus for implementing a method as claimed in one of claims 1 to 6 with a filtering surface arranged in a housing, in which the filtering surface is surrounded by a pressure-tight housing in the form of a pressure-chamber and the pressure-chamber is filled with a gas at a pressure above atmospheric, characterized in that a hood (4) covering at least a section of the filtering surface (2) is provided, which, together with the filtering surface (2), encloses a second pressure-chamber (6) containing the treatment fluid in a gaseous state.
8. Apparatus as claimed in claim 7, characterized in that the pressure in the first pressure-chamber (5) and in the second pressure-chamber (6) are essentially the same.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP.4238087.1 | 1992-11-11 | ||
| DE4238087A DE4238087C3 (en) | 1992-11-11 | 1992-11-11 | Process for mechanical dehumidification of a filter cake and device for carrying out the process |
| PCT/EP1993/003148 WO1994011084A1 (en) | 1992-11-11 | 1993-11-10 | Mechanical process and device for dehumidifying a filter cake |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2148938A1 CA2148938A1 (en) | 1994-05-26 |
| CA2148938C true CA2148938C (en) | 2002-02-26 |
Family
ID=6472635
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002148938A Expired - Fee Related CA2148938C (en) | 1992-11-11 | 1993-11-10 | Method for the mechanical removal of moisture from a filter cake and an apparatus for implementing the method |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0668791B1 (en) |
| AT (1) | ATE220342T1 (en) |
| AU (1) | AU681611B2 (en) |
| CA (1) | CA2148938C (en) |
| DE (2) | DE4238087C3 (en) |
| WO (1) | WO1994011084A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10050733B4 (en) * | 2000-04-10 | 2009-05-14 | BOKELA Ingenieurgesellschaft für mechanische Verfahrenstechnik mbH | Device and method for dehumidifying a filter cake |
| DE10050072B4 (en) * | 2000-10-10 | 2011-07-07 | BOKELA Ingenieurgesellschaft für mechanische Verfahrenstechnik mbH, 76131 | Process for the chemical and / or thermal conversion of at least one substance and device for carrying out the process |
| DE202012012910U1 (en) | 2012-03-08 | 2014-03-13 | BOKELA Ingenieurgesellschaft für mechanische Verfahrenstechnik mbH | Device for forming and dehumidifying a porous filter cake |
| EP2636436A1 (en) | 2012-03-08 | 2013-09-11 | BOKELA Ingenieurgesellschaft für Mechanische Verfahrenstechnik mbH | Method and device for forming and removing moisture from a porous filter cake |
| DE102012105076A1 (en) * | 2012-06-12 | 2013-12-12 | Andritz Fliessbett Systeme GmbH | Method and plant for the mechanical separation of a solid from a solid-liquid mixture and subsequent thermal treatment of the solid |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1219905B (en) * | 1963-01-26 | 1966-06-30 | Holstein & Kappert Maschf | Pressure filter for continuous filtration |
| DE1177572B (en) * | 1963-05-16 | 1964-09-10 | Harpener Bergbau Ag | Method and device for dewatering coal feasts |
| US3319789A (en) * | 1964-04-09 | 1967-05-16 | United States Steel Corp | Method of filtering liquid from solid particles |
| US4017399A (en) * | 1969-03-11 | 1977-04-12 | Pullman Incorporated | Method and apparatus for filtration of slurries |
| US3592341A (en) * | 1970-01-05 | 1971-07-13 | Envirotech Corp | Method and apparatus for steam drying filter cake |
| DE2423983C3 (en) * | 1974-05-17 | 1978-09-07 | Bayer Antwerpen N.V., Antwerpen (Belgien) | Process for the preparation of aqueous titanium dioxide hydrate suspensions by pressure filtration |
| DE2947329C2 (en) * | 1979-11-23 | 1982-01-28 | Werner Prof. Dr. 6740 Landau Stahl | Filtration arrangement |
| SE451948B (en) * | 1985-05-02 | 1987-11-09 | Hedemora Ab | FILTER FOR CONTINUOUS FILTERING UNDER PRESSURE OF A SUSPENSION |
| US4995972A (en) * | 1988-03-03 | 1991-02-26 | Kramer Timothy A | Method and apparatus for removing liquid from permeable material |
| DE3937952A1 (en) * | 1989-11-15 | 1991-05-16 | Metallgesellschaft Ag | METHOD FOR CLEANING CONTAMINATED SOILS |
| AT398389B (en) * | 1992-11-06 | 1994-11-25 | Andritz Patentverwaltung | METHOD AND SYSTEM FOR SEPARATING SOLID / LIQUID MIXTURES |
-
1992
- 1992-11-11 DE DE4238087A patent/DE4238087C3/en not_active Expired - Lifetime
-
1993
- 1993-11-10 AU AU56239/94A patent/AU681611B2/en not_active Ceased
- 1993-11-10 DE DE59310293T patent/DE59310293D1/en not_active Expired - Lifetime
- 1993-11-10 CA CA002148938A patent/CA2148938C/en not_active Expired - Fee Related
- 1993-11-10 EP EP94901789A patent/EP0668791B1/en not_active Revoked
- 1993-11-10 WO PCT/EP1993/003148 patent/WO1994011084A1/en not_active Application Discontinuation
- 1993-11-10 AT AT94901789T patent/ATE220342T1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| DE4238087A1 (en) | 1994-05-19 |
| EP0668791A1 (en) | 1995-08-30 |
| EP0668791B1 (en) | 2002-07-10 |
| ATE220342T1 (en) | 2002-07-15 |
| DE4238087C3 (en) | 1997-12-04 |
| DE59310293D1 (en) | 2002-08-14 |
| WO1994011084A1 (en) | 1994-05-26 |
| DE4238087C2 (en) | 1994-09-29 |
| AU5623994A (en) | 1994-06-08 |
| AU681611B2 (en) | 1997-09-04 |
| CA2148938A1 (en) | 1994-05-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20131113 |