Fuel filter with organoclay, cleaning cartridge with organoclay, and use

Abstract

A fuel filter has a separating device separating, from a medium flow comprising a first medium and a second medium, the first medium as a separated first medium contaminated with the second medium. The fuel filter has a cleaning device receiving a proportion of the second medium contained in the separated first medium. The cleaning device is arranged upstream of a discharge opening for discharging the first medium from the fuel filter. The cleaning device is provided with an absorbent/adsorbent cleaning material. The cleaning material contains or is made of an organoclay as an active component. The organoclay is a bulk material, wherein at least 50 wt. % of the organoclay has an average particle diameter of greater than 50 Φm and smaller than 1,000 Φm.

Claims

1. A fuel filter comprising: a fuel filtering system comprising: a filter system housing (102) having: a base at a lower end of the filter system housing in a direction of gravity; a detachable cover (104) closing an upper end of the filter system housing; a circumferential outer wall extending from the base to the upper end of the filter system housing; and a connecting part (106) connected to the circumferential outer wall at the base and projecting radially outward away from the circumferential outer wall in a direction transverse to the direction of gravity; and an absorbent cleaning device (10) comprising: a first tubular housing part (14) having: a lower end, relative to the direction of gravity, resting on the connecting part (106) and receiving filtered fluid from the filter system housing (102) through the connecting part (106); an open upper end relative to the direction of gravity, an outer wall extending from the lower end to the upper end of the first tubular housing part (14); an absorbent cleaning cartridge (30) configured to insert into an interior of the first tubular housing part (14) through the open upper end of the first tubular housing part (14) such that the absorbent cleaning cartridge is removable through the open upper end of the first tubular housing part (14) for exchange or service; wherein the absorbent cleaning cartridge (30) comprises: an adsorbent cleaning material (34) having at least 50% organoclay as an active adsorbent/cleaning component, arranged in an interior of the removable absorbent cleaning cartridge (30); wherein the absorbent clearing cartridge includes at least one outlet discharge opening (20,21) arranged at an upper end of the absorbent cleaning cartridge, relative to the direction of gravity, such the fluid flows upwards from the connecting part (106), through the adsorbent cleaning material (34) to discharge from the absorbent cleaning cartridge (30) at the upper end of the absorbent cleaning cartridge; wherein the fuel filtering system is configured to filter fuel having one or more hydrocarbons contaminated with water; wherein the fuel filtering system separates a first portion of the water from the one or more hydrocarbons, to produce a separated mixture having water contaminated with a remaining portion of the one or more hydrocarbons, the separated medium exiting the filter system housing (102) through the connecting part (106) and entering into the lower end of the cleaning device (10) to enter the absorbent cleaning cartridge (30); wherein the adsorbent cleaning device receives the separated mixture having the water contaminated with the remaining portion of the one or more hydrocarbons; wherein the adsorbent cleaning material having the organoclay in the adsorbent cleaning cartridge is configured to adsorb at least a portion of the remaining portion of the one or more hydrocarbons from the separated mixture of the fuel filtering system; wherein the organoclay is a bulk granular material, wherein at least 50 wt. % of the organoclay has an average particle diameter of greater than 50 Φm and smaller than 1,000 Φm.

2. The fuel filter according to claim 1, wherein the fuel is diesel fuel.

3. The fuel filter according to claim 1, wherein an organic component of the organoclay comprises alkyl groups.

4. The fuel filter according to claim 3, wherein the alkyl groups include methyl groups.

5. The fuel filter according to claim 1, wherein the organoclay comprises a layered silicate.

6. The fuel filter according to claim 5, wherein the layered silicate belongs to the smectite-montmorillonite group and is modified chemically such that at least one intermediate layer of the layered silicate comprises at least one organic cation.

7. The fuel filter according to claim 1, wherein the adsorbent cleaning material further comprises at least one additional material and the at least one additional material consists of one or more inert materials, or one or more active materials, or a combination of one or more inert materials and one or more active materials.

8. The fuel filter according to claim 7, wherein the one or more inert materials are selected from the group consisting of a glass, a ceramic, and sand.

9. The fuel filter according to claim 7, wherein the one or more active materials are selected from the group consisting of a zeolite and active carbon.

10. The fuel filter according to claim 7, wherein the at least one additional material is uniformly embedded in the organoclay and/or connected to the organoclay.

11. The fuel filter according to claim 1, wherein the organoclay is characterized by FTIR spectra comprising characteristic hydrocarbon bands in a region of 1,300 cm.sup.−1 to 1,600 cm.sup.−1 and/or in a region of 2,700 cm.sup.−1 to 3,100 cm.sup.−1.

12. The fuel filter according to claim 1, wherein a flow direction of the separated mixture through the cleaning cartridge is opposite to the direction of gravity.

13. A method of separating a water fraction, contaminated with fuel and existing at least partially as a fuel-water emulsion, in a fuel filter according to claim 1, the method comprising using the organoclay to adsorb and/or absorb the fuel.

14. The method according to claim 13, wherein the fuel filter is arranged at a vehicle or at an internal combustion engine.

15. The method according to claim 13, wherein at least a portion of the fuel in the fuel-water emulsion has a drop size smaller than 50 Φm.

16. The method according to claim 15, wherein the drop size is smaller than 10 Φm.

17. The method according to claim 13, comprising reducing by at least 98% a fuel content in the water fraction that comprises a fuel concentration of the fuel of 200 ppm to 2,500 ppm.

18. A method for removing hydrocarbons or hydrocarbon mixtures from water to be purified that accumulates at a fuel filter according to claim 1, the method comprising: providing an average residence time of the water to be purified in the adsorbent cleaning material of 15 minutes to 40 minutes.

19. The method according to claim 18, wherein the residence time is 25 minutes to 35 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in the following in more detail with the aid of several drawings. Further advantages of the invention are explained therein in more detail with the aid of embodiments. A person skilled in the art can consider the combined features of the embodiments expediently also individually or combine or modify them to other meaningful combinations.

(2) FIG. 1 shows a schematic illustration of a fuel filter in a side view with a cleaning module according to a first embodiment of the invention.

(3) FIG. 2 shows the fuel filter with the cleaning module of FIG. 2 in plan view.

(4) FIG. 3 shows the fuel filter with cleaning module of FIG. 1 with a removed cleaning cartridge.

(5) FIG. 4 shows an infrared spectroscopic image of a bentonite embodied as organoclay and of a natural bentonite.

(6) FIG. 5 shows a thermogravimetric diagram.

(7) FIG. 6 shows a solubility diagram of diesel fuel in water.

(8) FIG. 7 shows comparative measurements of the adsorption capabilities between active carbon and organoclay.

(9) FIG. 8a shows an SEM image of a natural clay (bentonite).

(10) FIG. 8b shows an SEM image of an organoclay.

(11) FIG. 9 shows a typical cumulative distribution of the drop sizes of diesel in water after the separation of the water from the diesel by means of an in particular multi-stage fuel filter.

(12) FIG. 10 shows a cumulative distribution of the particle sizes of an organoclay bulk material of a fuel filter according to the invention.

(13) FIG. 11 presents a table which shows a series of preferred surface-active compounds which can be used for organo-functionalization of clay, e.g., smectites.

DESCRIPTION OF PREFERRED EMBODIMENTS

(14) In the Figures, same or same-type components are identified with same reference characters. The Figures show only examples and are not to be understood as limiting.

(15) In the following, the terms diesel and diesel fuel are employed synonymously.

(16) The invention is illustrated in FIGS. 1 to 3 in an exemplary fashion by one embodiment according to which the cleaning device is embodied as an external cleaning device, namely as a cleaning module 10 for a fuel filter for cleaning a media flow of a first medium contaminated with a second medium, wherein the first medium is water and the second medium is diesel fuel, wherein the water is separated from the diesel fuel in the fuel filter 100.

(17) FIG. 1 shows a schematic illustration of a fuel filter 100 in a side view with a cleaning module 10 according to a first embodiment of the invention. The fuel filter 100 for filtering the media flow comprising the first and the second medium comprises a separating device, not illustrated, for the first medium which is arranged in a filter system housing 102 of the fuel filter. The filter housing 102 comprises a preferably detachable media-tight cover 104 in order to service or exchange a filter element, also not illustrated, in the interior of the filter system housing 102. Further, the fuel filter 100 comprises the cleaning module 10, which is connected by a connecting part 106 with the filter system housing 102, for receiving by adsorption and/or absorption a proportion of the second medium contained in the separated first medium. The cleaning module 10 comprises a housing 12 with an inlet 18 and an outlet or discharge opening 20 at the second housing part 16. The first and the second housing parts 14, 16 are embodied for a media-tight connection with each other that is in particular detachable. In this context, the two housing parts 14, 16 can be, for example, screw-connected or connected by a quick-connect device. Moreover, an outlet 21 is illustrated which is arranged at the first housing part 14. Such a solution is also beneficial because then the second housing part 16, for example, for removing the cleaning cartridge 30, can be removed without having to detach a connection from the outlet 21 to continuative components.

(18) The exchangeable cleaning cartridge 30 is detachably arranged in the housing 12. The cleaning cartridge 30 comprises a cleaning material with an organoclay as an absorbent and/or adsorbent material for receiving at least a proportion of the second medium contained in the first medium.

(19) The cleaning material 34 may comprise furthermore inert materials such as at least a glass, a ceramic, a sand and/or an active material, in particular a zeolite and/or active carbon. This inert material and/or an active material can be embedded preferably and advantageously uniformly in the organoclay and/or connected therewith.

(20) However, the main component of the cleaning material 34, i.e., more than 50 wt. %, can be preferably the organoclay. The cleaning material 34 can also consist completely of organoclay.

(21) The organoclay as an active component of the cleaning material 34 can be provided as loose bulk material and/or provided sintered and/or chemically cross-linked and/or foamed.

(22) In this context, the cleaning material 34 and in particular the organoclay can be arranged as a shaped body, e.g., as a hollow cylindrical shaped body, in particular with an open-pore structure, as a coating, or as granules in the fuel filter 100.

(23) The average particle diameter of at least half of the organoclay granular grains can be larger than 50 Φm. In a particularly preferred embodiment variant, the average particle diameter of at least half of the organoclay granular grains is less than 400 Φm.

(24) Particularly preferred, the average particle diameter for a mass-based d50 particle size distribution of the granules can amount to between 50 Φm to 400 Φm, in particular between 100 Φm to 300 Φm.

(25) The flow direction 32 of the media flow is realized from the filter system housing 102 through the connecting part 106 through the inlet 18 into the housing 12 of the cleaning module 10 where the media flow through the cleaning cartridge 30 in the properly mounted state is oriented opposite to the force of gravity and exits from the cleaning module 10 at the top through the outlet 20 or, in the alternative embodiment, through the outlet 21.

(26) In addition, an indicator for indicating loading with the second medium can be arranged at the cleaning module 10 in order to enable need-oriented servicing.

(27) In FIG. 2, the fuel filter 100 with the cleaning module 10 of FIG. 1 is illustrated in plan view. The filter system housing 102 with a cover 104 is illustrated from above. The cleaning module 10 is arranged on the connecting part 106 which is connected with the filter system housing 102. The second housing part 16 arranged on the connecting part 106 can be seen from above. The outlet 20 has been omitted in this illustration.

(28) FIG. 3 shows the fuel filter 100 with the cleaning module 10 of FIG. 1 with removed cleaning cartridge 30 of the cleaning module 10. The cleaning cartridge 30 with the organoclay-containing cleaning material 34 is arranged in this embodiment at the second housing part 16. The cleaning cartridge 30 can be connected in this context non-detachably to the second housing part 16 and can thus be viewed as a unit. However, it is also conceivable that the cleaning cartridge 30 is detachably arranged at the second housing part 16 and can be removed therefrom and separately exchanged. Accordingly, the cleaning cartridge 30 with the second housing part 16 can be removed like a cartridge upwardly out of the first housing part 14 in order to be exchanged and reconditioned, for example. A new cleaning cartridge 30 with a second housing part 16 can then be inserted again and media-tightly connected with the first housing part 14, for example, screwed on or clipped on, in order to return the cleaning module 10 into its operative state again. The advantage of such an embodiment resides in that upon removal of the cleaning cartridge 30 with the second housing part 16 the residual first medium remains in the first housing part 14 and the environment is thus not soiled.

(29) In a further embodiment of the invention, also the entire cleaning module can be embodied to be removable and thus exchangeable.

(30) FIG. 4 shows an infrared spectrograph of an organoclay used as active material according to the invention (curve I) and of an unmodified clay (curve II).

(31) In this context, the extinction is plotted against the wave number. One can see characteristic bands 202 for hydrocarbon compounds at a wave number between 2,800 to 3,000 cm.sup.−1.

(32) In the fingerprint region, one can see bands 203 at a wave number between 1,300 to 1,500 cm.sup.−1 for hydrocarbon compounds. They are not present in natural clay (curve II).

(33) The bands 201 in the region of a wave number of 3,500 cm.sup.−1 characterize embedded water and can be found in the organoclay as well as in the naturally occurring clay.

(34) In the following, providing the organoclay will be explained in more detail:

(35) In a first method step, a clay is provided. In this context, preferably a naturally occurring clay can be provided. Particularly preferred clays are clays which are substantially comprised, i.e., at least to 50 wt. %, of smectite and/or at least one montmorillonite. For example, bentonite is such a clay which is utilized in the following for the concrete embodiment.

(36) Bentonite is dispersed in water, preferably in deionized water. In this context, 4 wt. % of clay are dispersed in deionized water for at least 10 hours by stirring at room temperature.

(37) In a second method step, the exchange or homogenization of metal ions which are contained in the provided clay is carried out. In this context, a replacement of metal ions of the clay by sodium ions can be realized. Preferably, for example, Na.sub.2CO.sub.3 or NaCl in a concentration of 100 meq (milliequivalents) per 100 g clay can be used. After addition of e.g. sodium carbonate, stirring of the emulsion for at least 10 hours at room temperature was carried out.

(38) In a third method step, a slow addition of a quaternary ammonium salt in aqueous solution is carried out. The concentration amounts to 0.2 g of the surface-active substance to 1 g of clay with stirring for at least 10 hrs. at room temperature.

(39) The suspension is then filtered and washed with deionized water in order to wash out an excess of ions. Subsequently, the organoclay is dried in a vacuum oven at 60° C. for 24 hrs.

(40) The afore described method sequence is referred to also as layer expansion or pillarization. Metal ions are located primarily in the intermediate layers of a clay with layered structure. They are first replaced by sodium ions and later on by organic cations, preferably by quaternary alkyl ammonium ions.

(41) Subsequently, the adsorption and/or absorption capacity of the bentonite modified as organoclay, of a natural bentonite, and of bentonite enriched with active carbon was compared.

(42) For this test, 100 ml of an emulsion of diesel fuel and water with 1,000 ppm diesel fuel was contacted with 2 grams of the respective bentonite, respectively. This clay-water-diesel fuel mixture was then stirred for an hour. This was done by a magnetic stirrer. Subsequently, the emulsion was filtered.

(43) The differences of the remaining water solution could be detected visually. The permeate phase, supplied beforehand with the bentonite modified as organoclay, was significantly more clear than the two other permeate phases.

(44) In a second test, the reactivity of the bentonite converted to organoclay was tested. For this purpose, 50 ml of a diesel-water emulsion with 1,000 ppm diesel was contacted with 0.5 grams of the organoclay, stirred for 10 minutes, and subsequently filtered. As a reference, the same emulsion was only filtered.

(45) While the permeate of the pure diesel-water emulsion showed a significant turbidity after filtration, the permeate of the emulsion to which the organoclay was added was substantially clear and without recognizable turbidity.

(46) The composition of fuels, in particular diesel fuels, can vary from region to region. For example, the biodiesel proportion can vary or the proportion as well as the composition of the additives. In particular biodiesel and additives influence the formation and type of diesel-in-water emulsion which then can be separated only with difficulty. Diesel fuels with a high level of additives which lead to very stable emulsions are found in particular in the EU and the USA because here the sulfur contents in the diesel is minimal due to legislative requirements and the natural lubricating action of the diesel is therefore reduced. In order to regain the lubricating action of the fuel, additive packages are added to the diesel in these countries. In particular the use of a cleaning cartridge according to the invention with organoclay and of a fuel filter according to the invention with water discharge is advantageous for diesel fuels with a high level of additives in order to remove hydrocarbons from the water.

(47) Diesel fuels dissolved in water and diesel-in-water emulsions have very different concentrations of diesel fuel.

(48) Typically, only appr. 5 ppm (mg/l) of diesel fuel pass into water. On the other hand, emulsions have a detected proportion of up to 2,500 ppm of diesel fuel, in particular C10-C40 hydrocarbon compounds.

(49) The detection of the proportion of the diesel fuel in water can be realized in both cases by measurement according to DIN EN ISO 9377-2 H53.

(50) In practice, mostly diesel fuels with a high level of additives are encountered. They comprise almost always diesel fuel-in-water emulsions because the additives stabilize the fine diesel drops (they can have a fineness of 5 Φm up to d50 (mass-based)) and no separation of water phase and diesel phase due to the density differences occurs therefore. Diesel with high levels of additives are used in all countries in which a low sulfur diesel is required by law, thus e.g. in the EU (EN 590 fuel) but also in the USA. This means that for these markets a cleaning system with active carbon provides no satisfactory filtration performance; however, the organoclay can even clean the emulsion and the environment can thus be protected.

(51) FIG. 5 shows thermogravimetric measurements of a natural clay with the measured curve 301 and of an organoclay with the measured curve 302 for comparing the two materials in one diagram.

(52) The temperature increase for the gravimetric measurement is illustrated by the inclined straight line 303.

(53) In this context, three phases are characteristic when heating the modified clay. Phase a: First surface water (<100°) evaporates; this can be seen in the natural as well as the modified clay by means of the plateau. Phase b: Subsequently, the measured curve 302 of the modified clay, i.e., of the organoclay, passes into a region with negative incline (appr. 40 min., 300° C.). A degradation/combustion or, more generally, Apassing into the gas phase@ of the organic components takes place; only the modified clay shows this type of curve. Phase c: Beginning at appr. 600° C., this is overlaid with a release of chemically sorbed water. This can be seen well in the region of negative incline also in the natural clay (301) in this region.

(54) Moreover, one can see in this diagram that the proportion of organic components in organoclay amounts to appr. 25 wt. % (y axis begins at 65 wt. %).

(55) FIG. 6 shows concentration of dissolved hydrocarbons in mg/l according to DIN EN ISO 9377-2 H53 under operating conditions: The diagram shows that on average the concentration of dissolved hydrocarbons by use of DIN EN 590 gas station diesel fuel and deionized water with gentle mixing (no emulsion formation) is below 3 mg/l.

(56) The diagram illustrates the difference between diesel fuel which is dissolved in water and a diesel fuel-in-water emulsion. When the value of appr. 5 mg/l is surpassed, the water is saturated, no diesel will dissolve anymore, and an emulsion formation takes place. This type of emulsion cannot be separated or only minimally separated by active carbon. In contrast, the organoclay due to its surface properties is capable of cleaning even a diesel fuel-in-water emulsion.

(57) FIG. 7 provides a comparison between cleaning of a diesel fuel-water mixture with active carbon and organoclay, in particular the cleaning action of different adsorbents, namely of organoclay and active carbon under practice-near conditions (measured values recorded according to DIN EN ISO 9377-2 H53).

(58) While by active carbon only dissolved diesel or other hydrocarbons can be separated from water, the organoclay is capable of purifying also a diesel fuel-in-water emulsion.

(59) FIG. 7 also shows that the concentration of hydrocarbons in water can fluctuate.

(60) At Asample@, a diesel fuel-in-water emulsion is illustrated which is utilized as an initial concentration of hydrocarbons of the mixture prior to contact with an adsorption and/or absorption medium. At Ablind value@, the measured value of the test apparatus when pure water is conveyed through it is illustrated.

(61) Further bars show respectively a diesel fuel-in-water mixture after its treatment with the respective illustrated adsorption and/or absorption medium under analogous conditions. When comparing the final concentration based on logarithmic scale division, one can see that active carbon is hardly capable of separating the emulsion. The organoclay can purify the emulsion better than active carbon by a factor 20 to 80. Inter alia, the surface properties and inner properties can account for this. The determined blind value is by the factor 10 below the determined measured values and shows thus the reliability of the test configuration.

(62) The emulsion of water and diesel due to certain additives is very stable so that a density separation essentially does not occur and the diesel drops essentially do not coalesce. The droplet sizes in the emulsion are very small, typically smaller than 10 Φm. The non-coalescence is caused by the additives while the small droplet diameters are determined by the path of the diesel-water mixture through the fuel filter. The development goes toward the use of fuels that contain even less sulfur and higher levels of additives so that this problem will be aggravated, even worldwide due to environmental laws.

(63) In FIGS. 8a and 8b, the grain sizes of natural clay (FIG. 8a) and of the organoclay (FIG. 8b) are compared under analogous measuring conditions and at identical scale of illustration. Symptomatic for natural clay are very small grain sizes which can lead to a very high flow resistance up to blocking of the cleaning material. In contrast thereto, the organoclay in FIG. 8b shows a more compact form with increased grain size.

(64) FIG. 9 shows a typical cumulative distribution of the drop sizes of diesel in water after the separation of the water from diesel with low sulfur content (ULSD according to EN 590) by means of an in particular multi-stage fuel filter.

(65) Modern diesel fuels contain numerous additives which have become necessary to a great extent only due to the introduction of low sulfur contents (ULSD: ultra low sulfur diesel, 10 ppm). The additives ensure inter alia a satisfactory lubricating action of the fuel because the natural lubrication-improving agents are largely removed due to the process of desulfurization. With higher additive content the water separation becomes more difficult so that increasingly multi-stage water separators are used in order to realize even across the entire service life a functioning water separation. This change affects also the quality of the discharged water: While with a fuel comprising a low level of additives the separated water is still clear and contains for example <10 mg/l of hydrocarbons, in case of modern fuel filters with integrated water separation an emulsion instead of the clear water phase is produced. This emulsion is comprised of finest diesel droplets which are stabilized by the additives and can have a hydrocarbon contents according to EN ISO 9377-2 H53 of 200 mg/l up to >2,500 mg/l.

(66) The average drop diameter in this context is typically below 10 Φm. This is the decisive difference to applications in which hydrocarbons are present as film or only coarsely mixed/emulsified. Examples of this are the separation of oil films or fuel films from water surfaces.

(67) By means of the cleaning device of the fuel filter according to the invention, the fine diesel droplets that occur in case of modern water separators of fuel filters when using USLD can be separated reliably from the water phase.

(68) In FIG. 10, finally an exemplary cumulative distribution of the particle sizes of an organoclay bulk material of a cleaning device of a fuel filter according to the invention is illustrated.

(69) By such an adaptation of the particle sizes, it can be prevented that the aforementioned finest diesel droplets are entrained by a flow through the bulk material in addition to ensuring an acceptable flow resistance. Moreover, in this context the contact time of the medium with the organoclay is an important parameter. The larger the surface of the adsorber, the faster the adsorption. However, even in systems having a high inner porosity such as e.g. active carbon, only a minimal part of the surface is located at the outer side of the adsorber particles. This means that the substance transport of the medium to be removed from the surface of the particle into the inner surface can become a limiting factor with respect to time.

(70) In automotive applications, the installation space as well as the available contact time is very limited. Water that accumulates must be discharged, cleaned, and drained in a few minutes up to hours from the fuel circuit. The installation space in modern vehicles is very limited so that the adsorber must be designed to be as compact as possible. The sensible installation size of the adsorber container is between 200 ml and 400 ml, installation sizes of >600 ml can hardly be accommodated in usual installation spaces at the motor as well as at the vehicle.

(71) Therefore, it is necessary to adjust a defined particle size of the adsorber particles (organoclay) and to match the residence time in the system as well as the volume of the adsorber relative to each other. According to the invention, the adsorber is therefore matched to the special conditions at the fuel supply system of a vehicle and/or motor. The average residence time of the water in the adsorber amounts to appr. 30 minutes in an exemplary automotive application. The residence time in this context can be, for example, adjusted by the control of a valve. Between each discharge cycle, a defined intermission ensures that the required contact time for cleaning is maintained. Across several opening cycles, the water to be purified can be conveyed by means of the pressure of the fuel supply system through the adsorber.

(72) In mobile applications in a motor vehicle but also in stationary applications of the fuel filter according to the invention in which the latter is mounted at an internal combustion engine, furthermore vibrations occur that may not lead to an impermissible change of the particle size distribution, in particular, the vibration effect must not move the particle size distribution to smaller particle sizes.

(73) In FIG. 10, in addition to the particle size distribution of the organoclay starting material, a curve of a particle size distribution after vibration testing in dry state as well as in wet state, i.e., completely wetted with water, is therefore illustrated. In the initial state, the particle diameter is 700 Φm at 50% of the volume-weighted cumulative distribution; it can be seen that this value is essentially constant even after vibration testing.

(74) In this way, it is ensured that the flow through the bulk material, i.e., also the cleaning performance, is available across the service life of the cleaning device.