NL2024261B1 - Belt filter device and method for separating a mixture of solid substance and a liquid - Google Patents
Belt filter device and method for separating a mixture of solid substance and a liquid Download PDFInfo
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- NL2024261B1 NL2024261B1 NL2024261A NL2024261A NL2024261B1 NL 2024261 B1 NL2024261 B1 NL 2024261B1 NL 2024261 A NL2024261 A NL 2024261A NL 2024261 A NL2024261 A NL 2024261A NL 2024261 B1 NL2024261 B1 NL 2024261B1
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- compartment
- filter
- filter belt
- belt
- supply
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- 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
- B01D33/04—Filters with filtering elements which move during the filtering operation with filtering bands or the like supported on cylinders which are impervious for filtering
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D37/00—Processes of filtration
- B01D37/02—Precoating the filter medium; Addition of filter aids to the liquid being filtered
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- Chemical Kinetics & Catalysis (AREA)
- Filtration Of Liquid (AREA)
Abstract
The manner in which a liquid filtration in which a liquid is separated from a solid substance by means of a filter can be best realized generally depends on the 5 specific conditions. The invention relates to a filter device for separating a mixture of solid substance and a liquid. The invention also relates to a method for operating a belt filter device configured to separate a mixture of solid substance and a liquid, in particular a belt filter device according to the invention.
Description
Belt filter device and method for separating a mixture of solid substance and a liquid The invention relates to a belt filter device for separating a mixture of solid substance and a liquid. The invention also relates to a method for operating a belt filter device configured to separate a mixture of solid substance and a liquid, in particular a belt filter device according to the invention. The manner in which a liquid filtration in which a solid substance is separated from aliquid by means of a filter can be best realized generally depends on the specific conditions. If it is wished to at least partially remove solid constituents from relatively large bulk quantities of liquid, it is usually advantageous to carry out (semi-)continuous liquid filtration by applying a filter device which is provided with a filter belt, wherein the filter belt forms an elongate (belt-like or strip-like) filter cloth for separating liquid and solid constituents. The advantage of applying such a filter device is that the filter belt is displaced through the filter device during the filtration process, whereby the part of the filter belt effectively used for filtering is in fact periodically changed, wherein the already used, contaminated part of the filter belt can be removed from the filter device. Transport of the filter cloth through the filter device generally takes place by pulling the cloth by making use of a conveyor belt, such as a chain or rubber belt, or by making use of a wheel, using which the filter cloth can be pushed in forward direction. However, the known belt filter devices frequently lead to cloudy filtrates which still contains quite some solid substance. Moreover, in the known devices the filter cloth is blinded (blocked) relatively swiftly which leads to a relatively high consumption of filter cloth during use of the device, which is undesired from a practical, economical, and environmental point of view. An object of the invention is to provide an improved belt filter device for separating a mixture of a solid substance and a liquid.
The invention provides for this purpose a filter device of the type stated in the preamble, comprising: a first compartment adapted to hold a mixture of solid substance and a liquid, a second compartment connected to, and preferably positioned at least partially under, the first compartment for collecting liquid coming from the first compartment, a stationary open support structure which separates the first compartment and the second compartment, at least one drive element configured to co-act with a filter belt, which may at least partially be formed by a filter cloth, for separating solid substance and liquid, in order to move the filter belt over the support structure and through the first compartment in a transport direction T, at least one first supply for supplying a mixture of solid substance and a liquid to be separated to the first compartment, and at least one second supply for providing at least one filter aid to the filter belt, in particular a substantially unfouled portion of the filter belt.
By adding one or more filter aids, either directly or indirectly, to the filter belt, the permeability and typically also the porosity of a filter cake formed onto the filter belt, can be improved significantly, which leads to an improved filter effect and therefore an improved filtrate clarity, while at the same time the risk of blinding of the filter belt is reduced drastically.
The filter aid is provided, either directly or indirectly, e.g. via the mixture to be separated, to the filter belt, and preferably on an unfouled portion of the filter belt.
This unfouled portion of the filter belt typically constitutes a fresh and substantially unused and uncovered — hence open (permeable) - portion (zone) of the filter belt.
Typically this unfouled portion has not, or merely for a very short period of time (less than 1-2 minutes), been exposed to the mixture to be separated, which prevents the formation of a (thick) filter cake onto this unfouled portion at the initial stage of the filtering process, and which allows the filter aid to form a filter aid layer on top of the filter belt, which improves the filtering effect.
Apart from an improved filter effect, the filter belt can bear more solid substance compared to conventional situations, as a result of which the effective displacement speed of the filter cloth can be reduced drastically leading to a reduced consumption of filter cloth, which is beneficial from a practical,
economical and environmental point of view.
The filter belt can form an endless filter belt, wherein the filter belt (re)circulates continuously through the filter device, wherein the filter belt is typically cleaned.
The filter belt will however generally form a finite strip of filter cloth guided as a batch through the first compartment.
After use of the filter belt, the filter belt will generally be discarded.
The filter device therefore generally comprises at least one supply holder for unused filter belt positioned close to the feed side of the support structure.
The supply holder can for instance be formed by an axially rotatable roll of unused filter cloth.
A collecting vessel for used filter belt is generally positioned on an opposite side of the filter device, close to the discharge side of the support structure. lt is also possible to envisage rolling up the used filter belt.
The mixture of solid substance and liquid to be separated (at least partially) can be of various nature. The mixture may constitute a suspension, a dispersion, and/or a slurry of solid particles in a liquid, e.g. water or oil. The filter belt may or may not be part of the belt filter device according to the invention. The filter belt may be sold as a separate product for use in the belt filter device according to the invention. The support structure takes a stationary form, this meaning that the support structure does not in fact move (significantly) and is thus a static component of the device. However, it is conceivable that the support structure is subjected to slight movement, e.g. a rocking movement, and/or to vibration to improve the efficiency of the device according to the invention. Additionally, the support structure preferably takes a substantially rigid (form-retaining) form and can for instance be manufactured here from metal or plastic. Alternatively, a resilient support structure could be used. The support structure can optionally be received and/or mounted releasably in the filter device.
In a preferred embodiment the support structure is embodied as a substantially rigid perforated plate. Although this plate can take a substantially flat form, optionally oriented horizontally or vertically, the plate preferably takes a curved form and/or bowl-shaped form in order to enable substantially form-fitting connection to the at least one first transport element. The perforated plate is provided with a plurality of perforations, wherein the perforations are preferably arranged such that the belt filter covers the perforations in operational mode so that leakage of liquid around the outer sides of the belt filter from the first compartment to the second compartment can be prevented as far as possible.
The filter aid used is preferably a particulate filter aid. Here, the filter aid is at least partially formed by powder and/or particulate matter, in particular particles and/or loose fibres, which are preferably suspended in liquid. This liquid may be (clean) water and/or may be the liquid in which the to be filter solid particles are dispersed. Preferably, a filter aid is used with a relatively low average particle size. A finer grade of filter aid may be employed to increase the clarity of filtrate. The smaller the filter aid particle size, the smaller the solid particles which can be removed. However, the filtration rate will also be lower, and hence, a balance has to be found between initial filtrate clarity and filtration rate. To this end, it is preferred that the filter aid comprises particles, such as fibres, with a particle size distribution such that at least 95% of the particles have a dimension smaller than 100 micron. More preferably, the filter aid has a particle size distribution being such that at least 95% of the particles have a dimension larger than 10 micron and smaller than 100 micron. Preferably, the filter aid has a density of between 190 and 250 g/l, preferably between 210 and 230 g/l. Preferably, the filter aid comprises at least one material chosen from the group consisting of: diatomaceous earth (DE), perlite, and cellulose. Diatomaceous earth (DE) is the skeleton of fossilized diatoms which are mined from ancient seabed, processed, and classified to make different grade of filter aids. Preferably, an amorphous DE is used, since the crystalline type DE is a suspicious carcinogen and inhalation needs to be avoided during handling. Packed beds of granulated DE have very high porosity; as little as 15% of the total volume of packed DE is solid, while the rest is empty space. Such high porosity facilitates liquid flow around the particles and improves the rate of filtration. Perlite is another suitable mineral filter aid. It is a particular variety of naturally occurring glassy volcanic rock, characterized by onion like, splintery breakage planes. After crushing and heating, this rock will expand in an explosive fashion to about ten times its original volume. Diatomaceous earth and perlite are silica based minerals. There are several other special materials used as filter aids, including asbestos, cellulose, agricultural fibres, saw dust, rice hull ash, paper fibres etc. Cellulose can be used, for example, for filtration systems that cannot tolerate silica. The filterability of cellulose is typically less good than diatomaceous earth or perlite but cellulose can be incinerated as well as providing better filter cake integrity. Calcined rice hull ash and/or fibres from used newspapers may also be used as alternative filter aids, for example in case of wastewater sludge filtering.
The first and second supply may be formed by the same (common or shared) supply. In this case, the filter aid and the mixture to be filtered are mixed prior to dispensing the mixture into the first compartment. Here, the filter aid may be added as dry particulate, e.g. dry powder, to the mixture to be filtered. Alternatively, the filter aid is dispersed in a liquid, e.g. water, prior to mixing the filter aid with the to be filtered mixture. In this latter case, the ratio between the volume content of the filter aid and the volume content of the dispersing liquid is preferably situated between 0,15 and 0,4. In this embodiment, the filter aid is added to the first compartment, and will be urged towards and against the filter belt due to gravitational forces, flow, and preferably also a pressure difference between the (atmospheric) first compartment and the (vacuum) second compartment. In this 5 embodiment, the filter aid is added as body feed to the mixture to be filtered. This typically results in the formation of a filter cake of solid particles onto a top side of the filter cloth (facing away from the support surface), wherein the filter cake typically comprises a more or less homogeneous mixture of filter aid particles and solid particles originating from the mixture to be filtered. The first and second supplies may also be formed by separated supplies. This provides more flexibility in positioning the supplies with respect to the first compartment and with respect to each other. Typically, the first supply is configured to dispense the to be filtered mixture into the first compartment. Here, the mixture can leave the first supply within and/or above the first compartment.
The second supply may be configured to supply at least a fraction of the at least one filter aid, either directly or indirectly, within the first compartment. Here, the filter aid is mixed with the mixture to be filtered within the first compartment. Here, the filter aid is typically mixed with the mixture to be filtered prior to allowing the filter aid to cover the filter belt (as part of the filter cake). It is also conceivable that the second supply is configured to supply at least a fraction of the at least one filter aid to the filter belt at a distance from the first compartment, preferably in a precoat compartment. Here, it is imaginable that a plurality of second supplies is used, wherein one second supply is used to dispense filter aid directly into the first compartment, and wherein one other second supply is used to dispense filter aid into the precoat compartment. In case a precoat compartment is used, it is imaginable that this precoat compartment is situated upstream with respect to the first compartment, as seen in the transport direction T of the filter belt. It is advantageous in case the filter belt is guided through the precoat compartment, such that the, typically wettened, filter aid is applied onto a top surface of (a typically wettened part of) the filter belt. In this manner, the filter aid is applied as precoat to the filter belt. This may not only protect the filter belt during use of the filter belt in the first compartment, but may also further facilitate to prevent blockage or ‘blinding’ of the filter by solids that would otherwise wedge themselves into the pores of the filter cloth. Hence, it could be preferred that the drive element is configured to move the filter belt in a transport direction T, wherein, as seen in the transport direction T, at least one dispensing location of the filter aid is situated upstream with respect to the dispensing location of the to be separated mixture of solid substance and liquid. It is also imaginable that at least one dispensing location of the filter aid is situated downstream with respect to the dispensing location of the to be separated mixture of solid substance and liquid.
Preferably, the filter cloth has an average pore size which is smaller than both the average size of filter aid particles and the average size of the solid to be filtered.
This will typically lead to an improved filtering effect. At the other hand, the average pore size is preferably large to allow water or other liquid to pass through relatively easily. Hence, it is preferred that the average pore size of the filter cloth is situated in between 1 and 3 micron, and is more preferably equal to (substantially) 2 micron. The thickness of the filter cloth is preferably situated between 1.2. and 1.6 mm, and is preferably substantially equal to 1.4 mm. In particular, a needle felt, preferably at least partially made of polyester, would be suitable to act as filter cloth in the device according to the invention.
Preferably, the device comprises at least one axially rotatable first transport element which engages on the support structure and/or on the filter belt, and which is adapted for urging displacement of the filter belt from a feed side of the support structure in the direction of a discharge side of the support structure by means of rotating the first transport element and by clamping the filter belt between the first transport element and the support structure. More preferably, the device comprises at least one axially rotatable second transport element which engages on the first transport element and co-acts with the first transport element, and which is adapted for pulling displacement of the filter belt from the feed side of the support structure in the direction of the discharge side of the support structure by means of rotating the second transport element and by clamping the filter belt between the first transport element and the second transport element. Here, it is favourable in case a drive element is coupled to at least one transport element for causing axial rotation of the first transport element, and, if applied, of the second transport element. Because at least one first transport element and at least one second transport element are applied in the filter device according to the invention which - with interposing of the filter belt - engage each other (under bias) and co-act directly with each other, axial rotation of the first transport element will therefore result in an axial rotation of the second transport element, and vice versa.
This has the advantage that displacement of the filter belt through the filter device takes place by simultaneously pushing the filter belt forward over the support structure by clamping the filter belt between the first transport element, set into rotation by the drive element, and the stationary support structure, and pulling the filter belt by clamping the filter belt between the first transport element, set into rotation by the drive element, and the second transport element set into (counter-)rotation by the first transport element.
As a result of this pulling force the filter belt is pulled through the first compartment, so in fact from the feed side of the support structure, where the filter belt is guided into the first compartment, to the discharge side of the support structure where the filter belt is guided out of the first compartment.
The second transport element will generally be positioned here at or at least close to the discharge side of the support structure.
This simultaneously active but separate push-pull movement realized by the transport elements has the advantage that the filter belt can be displaced in relatively controlled and reliable manner over the support structure of the filter device, this enhancing as such the operation and reliability of the filter device.
In the case of slippage of the filter belt relative to the first transport element, the pulling force realized using the second transport element will be sufficiently great to continue displacing the filter belt relative to the support structure and therefore allow compensation of the slipping effect.
In operational mode the first transport element will in fact engage on the support structure via the filter belt.
This (indirect) engagement will take place under bias, whereby a certain fixation of the filter belt relative to the first transport element is realized, this preventing slippage of the filter belt relative to the first transport element.
Because - generally a longitudinal edge of - the filter belt is pressed against the support structure by the first transport element, particularly from or close to the feed side up to or close to the discharge side of the support structure, liquid present in the first compartment can substantially only be displaced through the filter belt to the second compartment, this generally enhancing the filtering efficiency.
The co-action between the first transport element and the second transport element is a direct and generally mechanical co-action irrespective of the presence or the displacement of the filter belt.
This direct co-action can be realized by having a peripheral side of the first transport element engage on a peripheral side of the second transport element.
In operational mode the second transport element will generally engage under bias on the first transport element via the filter belt, whereby the filter belt is clamped between the first transport element and the second transport element sufficiently tightly to enable a pulling force to be exerted onthe filter belt.
In this embodiment the peripheral speeds of the first transport element and the second transport element will be the same, whereby a smooth push-pull movement can be realized.
It is also possible to envisage co-action of the second transport element with the first transport element via one or more transmission elements.
Examples of transmission elements are toothed wheels,
rollers, chains and belts.
Using these transmission elements the peripheral speed of the second transport element can also be manipulated relative to the first transport element.
It is thus possible to envisage having for instance the second transport element rotate at a (slightly) higher peripheral speed than the first transport element, whereby the pulling force that is realized is greater than the pushing force that is realized, which results in a certain tensioning of the filter belt in the filter device, which can further counteract crease formation in the filter belt in the first compartment. ft is not otherwise necessary to realize the pulling force (only) by clamping the filter belt between the first transport element and the second transport element.
It is for instance also possible to envisage the pulling force being realized by the second transport element as such, for instance by embodying the second transport element with profiled, in particular conical piercing elements, wherein the piercing elements can perforate the filter belt and can in this way pull the filter belt in the direction of the discharge side of the support structure.
It is also possible to envisage the pulling movement being realized by co-action of the second transport element with another transport element, such as at least one first transport element and/or at least one axially rotatable third transport element, between which the filter belt can be clamped.
It is particularly advantageous here for the at least one second transport element to be adapted for co-action with one or more axially rotatable third transport elements, wherein each third transport element engages under bias on the second transport element to enable the filter belt to be pulled forward due to clamping of the filter belt.
The degree of bias can be regulated here, for instance by applying a spring mechanism.
By also having the one or more third transport elements engage on at least one centrally located part of the filter belt, around the centre line of the filter belt, the displacement speed over the width of the filter belt can be kept substantially constant, whereby creasing of the filter belt can be prevented as far as possible.
Itis usually advantageous for the peripheral side of the first transport element to be provided with a substantially flexible liquid-sealing material, such as for instance neoprene. By applying such a peripheral seal a substantially liquid-tight seal can be realized in relatively efficient manner between the first transport element, the filter belt and the support structure, without herein damaging the first transport element, the filter belt and/or the support structure. As already stated, such a substantially liquid-tight seal is desirable for the purpose of preventing as far as possible liquid displacement along the filter belt instead of through the filter belt.
In an advantageous embodiment the filter device comprises a plurality of first transport elements which are oriented co-axially of each other, wherein at least two transport elements are adapted to engage on or close to opposite longitudinal edges of the filter belt. By having different first transport elements engage {close to) the longitudinal edges of the filter belt a relatively good and reliable longitudinal sealing of the part of the filter belt situated in the first compartment can generally be realized, this generally enhancing the filtering action of the filter device. It is advantageous here for the support structure to be adapted to at least support at least the opposite longitudinal edges of the filter belt. The plurality of first transport elements are preferably mutually connected here, particularly by means of a central shaft, whereby the peripheral speeds of the first transport elements are identical, which enhances a homogeneous throughfeed of the filter belt through the first compartment.
The first transport element is preferably formed by an axially rotatable transport wheel with a circular cross-section. The second transport element is generally formed by a guide roller. It is advantageous here for the width of the second transport element to be greater than or equal to the width of the filter belt, this facilitating homogenous guiding of the filter belt. Possible one or more third transport elements are preferably embodied as running wheels which can exert a bias on the guide roller. In an advantageous embodiment the diameter of a part of the guide roller engaging on the first transport element is smaller than the diameter of a part of the guide roller lying at a distance from the first transport element. The narrowed parts of the guide roller are thus adapted here for co-action with the first transport element, and generally also for clamping of the filter belt. By having the diameter vary over the length of the guide roller the local (location-selective) peripheral speed of the guide roller can also be varied and regulated. Increasing the peripheral speed produces a stronger pulling effect. If the peripheral speed of a focation-selective part of the guide roller has a higher peripheral speed than the peripheral speed of the first transport element, the pulling force exerted on the filter belt will be greater than the pushing force exerted on the filter belt, whereby rucking of the filter belt can be prevented to further extent. A centrally located part of the guide roller can optionally be provided with an increased diameter in order to further increase the local peripheral speed, whereby the generally critical central part of the filter belt is also pulled forward smoothly and easily.
The drive element will generally, but not necessarily, be coupled to only a single (type of) transport element. This means that the drive element is coupled to the at least one first transport element or coupled to the at least one second transport element (if applied). Only one transport element is hereby driven directly by the drive element, and the other transport element co-acting with this transport element will be driven indirectly by the drive element. The drive element is preferably coupled (only) to the at least one first transport element, because this first transport element is generally the most difficult to drive because of the relatively great friction forces generally present between the first transport element and the support structure. An electric motor is preferably applied as drive element for rotating the transport elements. The electric motor will generally be directly coupled here to the at least one first transport element, via which first transport element the second transport element and optionally the third (and possible further) transport element will be driven. It is also possible to envisage driving the transport elements manually or hydraulically and/or pneumatically instead of using an electric motor.
Because the one or more first transport elements applied in the filter device according to the invention generally take a substantially round cross-sectional form, it is advantageous when the support structure can connect in substantially form- fitting manner to the peripheral side of the first transport elements. It is therefore advantageous for the support structure to take a curved, in particular semi-circular form.
In an embodiment the second compartment comprises at least one first suction element, in particular a pump, for suctioning filtered water from the second compartment, whereby the second compartment can be prevented as far as possible from being filled with filtered liquid.
It is possible here to envisage the second compartment taking a substantially closed form, except for an upper side directed toward the support structure, such that an underpressure is created in the second compartment by suctioning filtered water out of the second compartment using the suction element.
It will however be generally advantageous here to have a second suction element, in particular a vacuum pump, connected to the second compartment for the purpose of creating an underpressure (subatmospheric pressure) within the second compartment.
Owing to this underpressure liquid situated in the first compartment will be pulled with force through the filter belt, whereby the filtering process can be realized more quickly and with a higher effectivity (amount of filtered solid constituents per surface area of filter belt). Preferably, the device comprises a storage tank for filter aid, and at least one conveyor and/or at least one dosing element for transporting filter aid from the storage tank into the second supply for subsequently providing said filter aid to the filter belt.
The filter device preferably comprises at least one level sensor for detecting the liquid level in the first compartment and/or at least one level sensor for detecting the level in the second compartment.
Alternatively, optionally additionally, the device comprises at least one pressure sensor for measuring the pressure in the second compartment.
In this way information can be obtained about the degree of filling of the first compartment and/or the second compartment, and thereby about the functioning of the filter device and the efficiency of the filtering process.
In a particular embodiment the level sensor in the second compartment is coupled to the suction element via a control unit.
The control unit is preferably programmed here such that the suction element is activated when the liquid level detected by the level sensor exceeds a predefined value.
The control unit is preferably programmed such that a vacuum pump is activated when the level detected by the level sensor in the first compartment exceeds a predefined value and/or when the pressure development detected by the pressure sensor exceed a predefined value.
At least one control unit is typically configured to control at least one drive element. The control unit may be programmed to control the conveyor of the filter aid storage tank dependent on the pressure measured by the pressure sensor and/or the level measured by the level sensor in the first compartment and/or second compartment.
The control unit may be programmed to control the vacuum pump dependent on the pressure measured by the pressure sensor. The control unit may be programmed to control the drive element dependent on the pressure measured by the pressure sensor and/or the level as detected by the level sensor in the first compartment and/or second compartment.
An important advantage of the filter belt device according to the invention is that the device is capable to dose filter aid onto a substantially unfouled portion of the belt filter, such that an additional filter layer, formed by filter aid particles, is formed onto the belt filter to achieve an improved filter effect. In this respect it is in particular advantageous in case the control unit is programmed to execute the following sequence of steps: i) switching off the vacuum pump in case the pressure measured by the pressure sensor exceeds a predefined pressure threshold value and/or in case the level measured by the level sensor in the first compartment exceeds a predefined level threshold value; if) activating the conveyor to dose filter aid into the first compartment, iii) activating the drive element to move the filter belt through the first compartment, such that a substantially unfouled portion of the filter belt is situated within the first compartment, such that the substantially unfouled portion is supported by the open support structure, and iv) switching on the vacuum pump.
During step iv), and typically also during step iii) the filter aid will flow towards the unfouled portion of the belt filter, such that a basic layer of filter aid is formed onto the belt filter prior to forcing the mixture to flow through the filter belt, which forced flow will typically take place in a short period of time after switching on the vacuum pump {step iv)). This forced flow leads to the build-up of filter cake on top of the basic layer of filter aid, wherein the filter cake typically comprises solid substance separated from the liquid, as well as filter aid which was still present in the mixture to be separated after formation of the basic layer of filter aid.
Preferably, the device comprises at least one partition structure, which is at least partially accommodated within the first compartment and which is configured to be positioned in the mixture to be filtered as contained by the first compartment, and which separates a turbulent filter zone created by the supply of filter aid and the mixture to be filtered, from a more quiet filter zone.
The turbulent filter zone is typically formed by the inlet zone, wherein an unfouled filter belt portion, the mixture to be separated and the filter aid are inserted into the first compartment, and the quiet filter zone is the outlet zone, wherein a fouled filter belt portion is removed from the first compartment.
The partition structure may be formed by one or more screens or partitions.
The advantage of such a partition is that at least one filter aid may be added into the turbulent filter zone, which improves and facilitates the formation of the basic layer of filter aid, while the quiet filter zone stabilizes the filter cake formed onto the filter belt.
The invention also relates to a method for operating a belt filter device configured to separate a mixture of solid substance and a liquid, in particular a belt filter device according to one of the foregoing claims, comprising the steps: A) providing a belt filter device, comprising: e a first compartment adapted to hold a mixture of solid substance and a liquid, e a second compartment connected to, and preferably positioned at least partially under, the first compartment for collecting liquid coming from the first compartment, e a stationary open support structure which separates the first compartment and the second compartment, e a filter belt for separating solid substance and liquid, e at least one drive element configured to co-act with said filter belt in order to move the filter belt over the support structure and through the first compartment in a transport direction T, e at least one first supply for supplying a mixture of solid substance and a liquid to be separated to the first compartment, and e at least one second supply for providing at least one filter aid to the filter belt to a substantially unfouled portion of the filter belt, e at least one vacuum pump connected to said second compartment to create a subatmospheric pressure within the second compartment, e a storage tank for filter aid, and at least a conveyor for transporting filter aid from the storage tank into the second supply for subsequently providing said filter aid to the filter belt, e at least one pressure sensor for measuring the pressure in the second compartment and/or at least one level sensor for measuring the level in the first compartment, B) switching off the vacuum pump in case the pressure measured by the pressure sensor exceeds a predefined pressure threshold value and/or in case the level measured by the level sensor exceeds a predefined level threshold value; C) activating the conveyor to dose filter aid into the first compartment, D) activating the drive element to move the filter belt through the first compartment, such that a substantially unfouled portion of the filter belt is situated within the first compartment, such that the substantially unfouled portion is supported by the open support structure, and E) switching on the vacuum pump. Here, it is favourable that the belt filter device comprises a control unit, wherein the control unit is programmed to execute steps B)-E). Advantages and further embodiments of this method have already been described above in an extensive manner.
The invention will be further elucidated below on the basis of the non-limitative exemplary embodiments shown in the following figures. Herein show(s): - figure 1 a basic principle of a belt filter device according to the invention; - figures 2a and 2b a belt filter device according to the present invention; - figure 3 a schematically representation of the filtration process when making use of a belt filter device according the present invention; and - figures 4a-4c schematically representations of the function of the filter aid used in the present invention.
Figure 1 is a schematic side view of a filter device 1 according to the invention.
Filter device 1 comprises a first compartment 2 for holding water 3 contaminated with solid constituents, such as for instance sand or sludge.
The contaminated water 3 is carried into first compartment 2 via a feed 13. An underside of first compartment 2 is bounded by a perforated, semicircular plate 4. Plate 4 is adapted on the one hand to allow through water, and adapted on the other to carry a displaceable belt-like filter cloth 5, also referred to as a filter belt.
Filter cloth 5 is adapted to filter contaminated water 3 while water 3 sinks through filter cloth 5 to a second compartment 6 which is positioned under first compartment 2 and in which the filtered water 7 at least partially separated from the solid constituents will be collected.
In order to improve the filtering effect of the filter cloth 5, in particular to prevent filter cloth blinding during filtering in the first compartment 2, the filter cloth 5 is pretreated by applying a (small layer of) filter aid on top of the filter cloth 5. Typically filter aid materials are diatomaceous earth, perlite, and cellulose.
To prevent the filter aid to be released from the filter cloth, it is preferred that the filter cloth 5 is kept in wet condition.
Here, it is for example imaginable that the filter cloth 5 is wettened and provided with filter aid, preferably a suspension of filter aid dispersed in water, during or prior to winding of the filter cloth 5. The application of the filter aid onto the filter cloth can be realized at another location, although it is also imaginable that the filter aid is applied, e.g. by spraying a filter aid dispersion, to an unwound part of the filter cloth 5 prior to guiding the unwound, with filter aid enriched, part of the filter cloth 5 into the first compartment 2. Displacement of water from first compartment 2 to the second compartment will take place under the influence of gravitational force and can be forced by activating a vacuum pump 8 connecting to second compartment 6. The filtered water 7 collected in second compartment 6 can be discharged from second compartment 6 via a separate pump 9. Filter device 1 also comprises an axially rotatable supply holder 10 for filter cloth 5. By unrolling filter cloth 5 from supply holder 10 and displacing filter cloth 5 through first compartment 2 the effectively used filter cloth 5 can be changed,
whereby relatively large quantities of contaminated liquid 3 can be filtered.
Displacement of filter cloth 5 through first compartment 2 takes place in advantageous manner by simultaneously exerting a forward pushing force as well as a pulling force on filter cloth 5 in a direction of filter device 1 away from supply holder 10. Filter device 1 comprises for this purpose one or more rotatable transport wheels 11 which, with interposing of filter cloth 5, engage in substantially form-fitting manner and under bias on curved plate 4. Because the one or more transport wheels 11 engage under bias on curved plate 4 via filter cloth 5, filter cloth 5 will be clamped between each transport wheel 11 and plate 4, which results during rotation of the one or more transport wheels 11 in a forward pushing force being exerted on filter cloth 5. The pulling force may be realized by mechanical co- action of an axially rotatable guide roller 12 with the one or more transport wheels 11, between which filter cloth 5 is clamped and displaced. The combined forward pushing force and pulling force result in a relatively reliable and controlled displacement of filter cloth 5 through first compartment 2. The used filter cloth 5 guided out of first compartment 2 will be collected and, after filter cloth 5 has been fully fed through first compartment 2, filter cloth 5 will be deemed waste or cleaned and optionally reused. Figures 2a and 2b show a schematic side view of a filter device 100 according to the present invention. The filter device 100 has a number of similar features as seen in the prior art device 1 of figure 1. Similar reference numbers therefore correspond to similar or equivalent technical features. The belt filter device 100 for separating a mixture of solid substance and a liquid according to the present invention comprises a first compartment 2 adapted to hold a mixture of solid substance and a liquid and a second compartment 6 positioned at least partially under the first compartment 2 for collecting liquid 7 coming from the first compartment. The belt filter device 100 further comprises a stationary open support structure 4 which separates the first compartment 2 and the second compartment
6. Further, a filter belt 5 at least partially formed by a filter cloth 5 for separating solid substance and liquid is present and at least one drive element 18 configured to co-act with said filter belt 5 in order to move the filter belt 5 over the support structure 4 and through the first compartment 2. The drive element 18 may be controlled by a control unit (not shown). The drive element 18 is typically configured to move the filter belt 5 in a transport direction T, wherein, as seen in the transport direction T, preferably at least one dispensing location of the filter aid is situated downstream with respect to the dispensing location of the to be separated mixture of solid substance and liquid 3. The filter aid is possibly added batch wise, but it is also conceivable that (small fractions of) filter aid is added continuously. The device 100 further comprises a first supply 13 for supplying a mixture of solid substance and a liquid to be separated to the first compartment 2, and a second supply 14 for providing a (particulate) filter aid to the filter belt 5, in the shown embodiment by applying said filter aid to the first compartment 2. It is, however, also conceivable that the filter aid is supplied to a wettened part of the filter belt 5 (upstream with respect to the dispensing location of the to be separated mixture of solid substance and liquid 3). The device 100 also comprises a vacuum pump 8 which is connected to the second compartment 6 to create a subatmospheric pressure in the second compartment 6. The filtered water 7 collected in second compartment 6 can be discharged from second compartment 6 via a separate pump 9. A transport wheel 11 and an axially rotatable supply holder 10 for filter cloth 5 may be present.
However, this is just exemplary for the present invention, the filter cloth 5 may also be present in the form of an endless belt. Despite not shown, the device 100 may comprise a storage tank for filter aid, and at least one conveyor for transporting filter aid from the storage tank into the second supply for subsequently providing said filter aid (directly or indirectly) to the filter belt.
Figure 2a shows an initial state of the device 100 according to the present invention in use. The second compartment 6 is not subjected to a subatmospheric pressure yet. The vacuum pump 8 is switched off. Both the mixture of solid substance and a liquid to be separated 3 and the filter aid (A) are provided to the first compartment
2. The liquid level in the first compartment 3 is increasing. Figure 2b shows a situation wherein a vacuum is applied to the second compartment 6 via the vacuum pump 8. The supply holder 10 for the filter cloth 5 is rotating such that the filter cloth 5 can be renewed. A layer of filter aid 15, or cake 15, is formed at the filter cloth 5. Said layer of filter aid 15 can protect the basic medium of the system. The filter cloth 5 typically has an average pore size which is smaller than both the average size of filter aid particles and the average size of the solid to be filtered. The layer of filter aid 15, or cake 15, can also be referred to as precoat 15. The filter aid 15 is configured to improve the flow rate though the filter cloth 5 by decreasing cake compressibility and increasing cake permeability.
Figure 3 schematically shows the process of filtration by making use of a belt filter device according the present invention, for example as shown in figures 2a and 2b. The upper region of the figure shows the first compartment 2, and the lower region shows the second compartment 6 of the device. Despite the stationary open support structure 4 shown being curved it is also conceivable that the support structure 4 is at least partially or completely flat. In the shown situation, the second compartment 6 is subjected to a subatmospheric pressure. As described above, a layer of filter aid, or precoat , is formed onto the filter cloth during use of the belt filter device 100. Clean (unfouled) filter cloth 5a is in the shown embodiment supplied from the left hand side, used (filter cake fouled) filter cloth 5b is removed on the right hand side of the schematic figure. The fresh, unfouled portion 5a of the filter cloth is still relatively open, as a result of which the flow-through can take place relatively easily, while during displacement of the filter cloth through the first compartment 2, the filter cloth will be covered more and more by solid particles forming a filter cake 15 onto the filter cloth 5a (depicted by an increasing line thickness), which will decrease the effective permeability of the filter cloth 5a. This decrease of effective permeability of the filter cloth 5a from the inlet side to the outlet side is shown by means of arrows with a decreasing length depicting the (decreasing) amount of flow through the filter cloth 5. The device comprises a supply 19 for combined supplying mixture of liquid and solid substance to be separated, and particulate filter aid to be added to the first compartment 2. The first compartment 2 is provided with a partition structure 20 for separating a turbulent filter zone T (inlet zone) and a more quiet filter zone Q (outlet zone). In the turbulent filter zone T the filter cloth 5a is still relative permeable which allows the filter aid to be deposited relatively quickly and efficiently as a basis layer onto the filter cloth 5a. The flow of filter aid towards the filter cloth 5a is caused by gravitational forces, as well as due to the presence of a vacuum created in the second compartment 6. On top of the basis layer of filter aid, the filter cake will be formed, which is typically a mixture of solid substance and a remaining fraction of the filter aid particulate.
Typically, in the turbulent zone, where the unfouled portion of the filter cloth 5 is present, the more coarse particles (C) flow more rapidly to the filter cloth 5 than the more fine particles (F). This particle distribution is also indicated in the figure via arrows. The device comprises a control unit 21 (schematically shown) configured to operate the device. Preferably, the control unit 18 is configured to execute the following steps: A) switching off a vacuum pump connected to the second compartment, preferably, in case the pressure measured by the pressure sensor exceeds a predefined pressure threshold value and/or in case the level measured by the level sensor in the first compartment exceeds a predefined level threshold value;
B) dosing filter aid into the first compartment, C) activating a drive element to move the filter belt through the first compartment, such that a substantially unfouled portion of the filter belt is situated within the first compartment, and in such a way that the substantially unfouled portion is supported by the open support structure, and D) switching on again the vacuum pump.
By executing these process step, preferably in the order presented above, a filter aid layer can be created on top of a (relatively) unfouled portion of the filter cloth, which will improve the overall filtering effect seriously, and moreover leads to a saving of filter cloth 5 per time unit.
Figures 4a-4c¢ show a schematic representation of the function of the filter aid used in the present invention. Figure 4a shows a situation according to the prior art, wherein no filter aid is used. Figures 4b and 4c show possible situations according to the present invention using filter aid. The figures show each a stationary open support structure 4 in combination with a filter belt 5. The upper compartment holds water 3 contaminated with solid constituents P. The filtered liquid 7 flows into the lower compartment. Figure 4b shows that a precoat layer 15 is formed at the filter belt 5 formed of filter aid A. The precoat layer 15 basically protects the filter belt 5. In the situation as shown in figure 4b a relatively dense precoat layer 15 is present, resulting in that smaller particles P can be removed from the liquid 3. However, this situation has a relatively low filtration rate. Figure 4c shows a situation where both a precoat layer 15b of filter aid is present, and a mixed zone 15a of both filter aid A and particles P. Due to this mixed zone the flow rate is increased due to the decreased cake compressibility and increased cake permeability. ft will be clear that the invention is not limited to the embodiment examples presented and described here, but that numerous variants are possible within the scope of the appended claims, which will be obvious to a person skilled in the art. It is conceivable that various inventive concepts and/or technical measures of the embodiment variants described above may be combined completely or partially without departing from the inventive concepts described in the appended claims.
The verb "comprise" and conjugations thereof used in this patent specification mean not only "comprise", but also the expressions “include”, "consist essentially of", "formed by", and conjugations thereof.
Claims (41)
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2024261A NL2024261B1 (en) | 2019-11-19 | 2019-11-19 | Belt filter device and method for separating a mixture of solid substance and a liquid |
| PCT/NL2020/050728 WO2021101379A1 (en) | 2019-11-19 | 2020-11-19 | Belt filter device and method for separating a mixture of solid substance and a liquid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2024261A NL2024261B1 (en) | 2019-11-19 | 2019-11-19 | Belt filter device and method for separating a mixture of solid substance and a liquid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| NL2024261B1 true NL2024261B1 (en) | 2021-08-18 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| NL2024261A NL2024261B1 (en) | 2019-11-19 | 2019-11-19 | Belt filter device and method for separating a mixture of solid substance and a liquid |
Country Status (2)
| Country | Link |
|---|---|
| NL (1) | NL2024261B1 (en) |
| WO (1) | WO2021101379A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20240029049A (en) * | 2021-07-01 | 2024-03-05 | 레나쉬스 아에스 | Liquid filtration method and liquid filtration device |
| CN115715899B (en) * | 2022-12-23 | 2023-07-18 | 定州市福源食品有限公司 | Live pig slaughtering sewage treatment device |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1255065A (en) * | 1968-06-19 | 1971-11-24 | Friedrich Bilabel | Travelling-band filters |
| US3756411A (en) * | 1971-07-14 | 1973-09-04 | Sparkler Mfg Co | Continuous belt-type gravity filtration apparatus |
| WO2011096802A1 (en) * | 2010-02-05 | 2011-08-11 | Lovasc B.V. | Filter device for separating a mixture of solid substance and a liquid |
-
2019
- 2019-11-19 NL NL2024261A patent/NL2024261B1/en active
-
2020
- 2020-11-19 WO PCT/NL2020/050728 patent/WO2021101379A1/en active Application Filing
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1255065A (en) * | 1968-06-19 | 1971-11-24 | Friedrich Bilabel | Travelling-band filters |
| US3756411A (en) * | 1971-07-14 | 1973-09-04 | Sparkler Mfg Co | Continuous belt-type gravity filtration apparatus |
| WO2011096802A1 (en) * | 2010-02-05 | 2011-08-11 | Lovasc B.V. | Filter device for separating a mixture of solid substance and a liquid |
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| Publication number | Publication date |
|---|---|
| WO2021101379A1 (en) | 2021-05-27 |
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