Nyberg, Ingemar
G�teborg
AKTIEBOLAG
Olausson, Lennart G. K.
Nyberg, Ingemar
| 1. | Method In the purification of liquids, particularly water, by filtering the liquid through a filter consisting of a bed of a particulate filtering mass (54) in a filter vessel (50), which filter is cleaned from collected impurities by introducing highpressure flushing liquid from below through the filtering mass, c h a r a c ¬ t e r i z e d in that the filter bed is brought to expand when the flushing liquid is introduced from below during at least one phase of flushing, so that the filter mass is fluidized and the flushing liquid can pass through all parts of the filter bed and disengage impurities from the filtering mass, which impurities are forced upwardly by the flushing liquid through the filter bed to be collected In the upper part of the vessel, in that the supply of flushing liquid from below is interrupted so that the filter bed during a sedimentation phase is allowed to settle back to its starting level (55) and resume its normal volume, and in that the volume' of liquid above the filter bed containing spent flushing liquid and impurities disengaged from the filter bed are during a draining phase drained off through a plurality of discharge nozzles (62) situated at a level considerably lower than the normal upper liquid level in the vessel but above the upper level of the filter bed, the upper level of the liquid reciding to the level of the discharge nozzles. |
| 2. | Method according to claim 1, c h a r a c t e r i z e d in that the filter bed during the flushing phase is brought to expand by 5 to 25 per cent, preferably to a volume being 10 to 20 per cent greater than its normal volume. |
| 3. | Method according to claim 1, c h a r a c t e r i z e d in that one or more flushing phases of short duration are performed, in that the filter bed after each flushing phase and during a sedimentation phase is allowed to sink back to its normal level, the sedimentation phases being of a shorter duration than the flushing phases, and in that the drainage is performed during a corresponding number of draining phases being of a considerably longer duration than the flushing and sedimentation phases. |
| 4. | Method according to claim 1, c h a r a c t e r i z e d in that each of the draining phases is of a duration at least ten times longer than the duration of each of the flushing phases. |
| 5. | Method according to claim 3, c h a r a c t e r i z e d in that each of the flushing phases is of a duration equal to H x (2to 20 ) seconds, preferably at the most 10 x H seconds, in a filter having a bed height of H meter. |
| 6. | Method according to claim 1, c h a r a c t e r i z e d in the use of an upwardly widening vessel, the wall of the vessel being inclined at least along the main part of the height of the filter bed at an angle of 1 to 8 degrees, preferably 1.5 to 6 degrees and most preferably 2 to 5 degrees, relatively to the vertical. |
| 7. | Method according to claim 1, c h a r a c t e r i z e d in that during the draining phases the surface layer of the filter bed is reflushed by flushing liquid introduced with a low pressure in the surface layer of the filter bed. |
| 8. | Method according to claim 1, c h a r a c t e r i z e d in that as filtering mass there is used a porous mineral product belonging to the group of aqueous alkali and/or earthen alkali silicates known under the name Zeolites, which filtering mass has a particle density of 2 to 3 3 2.5 g/cm and a volume density of 0.5 to 1.0 g/cm . |
| 9. | Method according to claim 8, c h a r a c t e r i z e d in that the filtering mass consists of Clinoptilolite of the following adsorption, ion exchange and preferably also catalytic properties: Adsorption capacity 0.05 to 0.3, perferably 0.10.2 cm? /g Ion exchange capacity max 1.5, preferably max 1.2 to 1.3 mval/g Particle density 2 to 2.5, preferably 2.2 to 2.3 g/cm Volume density 0.5 to 1.0, preferably 0.8 to 0.9 cm /g 2 Active surface 100 to 1000, preferably 300 to 500 m /g 10 Filter for purification of liquids, particularly water, comprising a bed (54) of a particulate filtering mass in a filter vessel (50), means (57) located mainly below the filter bed for the introduction of the liquid to be purified, and first discharge means (60) located 5 above the filtering bed for discharging the filtrate out of the filter vessel, c h a r a c t e r i z e d by one or more discharge nozzles (62) located between the normal upper level (55) of the filtering bed and said first discharge means (60) for draining of spent flushing liquid and therein collected impurities which during a flushing phase Q have been disengaged from the filter by upward flushing. |
| 10. | Filter according to claim 10, c h a r a c t e r i z e d in that the filter vessel (50) widens upwardly along at least the main part (53) of the height of the filter bed (54). 5. |
| 11. | Filter according to claim 11, c h a r a c t e r i z e d in that the main part "(53) of the filter vessel widens upwardly at an angle of 1.5 to 6 degrees, preferably 2 to 5 degrees, between the wall of the vessel and the vertical. 0. |
| 12. | Filter according to claim 10, c h a r a c t e r i z e d by the provision of one or more flushing nozzles (70, 73) at or close to the normal upper level (55) of the filter bed for introduction of flushing liquid of weak pressure during the draining phase or phases. 5. |
| 13. | Filter according to claim 10, c h a r a c t e r i z e d in that the filtering mass mainly consists of a porous mineral product pertaining to the group of aqueous alkali and/or earthen alkali silicates known under the name Zeolites. 0. |
| 14. | Filter according to claim 14, c h a r a c t e r i z e d in that the filtering mass consists of Clinoptilolite, said product having the following adsorption, ion exchange and preferably catalytic properties: 5 Adsorption capacity 0.05 to 0.3, preferably 0.1 to 0.2 cm /g Ion exchange capacity max 1.5, preferably max 2 to 1.3 mval/g 3 Particle density 2 to 2.5, preferably 2.2 to 2.3 g/cm Volume density 0.5 to 1.0, preferably 0.8 to 0.9 cm /g 2 Active surface 100 to 1000, preferably 300 to 500 m /g 16 Filter according to claim 10, c h a r a c t e r i z e d in that the particle size of the filtering mass is less than 0.5 mm. |
The invention relates to a method and an apparatus for purifying liquids, particularly water, by filtering the liquid through a filter consisting of a bed of a particulate filtering mass in a filter vessel, which filter is cleaned from collected impurities by introducing high-pressure flushing liquid from below through the ■ filtering bed. The apparatus according to the invention comprises means located mainly below the filter bed for introduction of the liquid to be purified, and discharge means located above the filter bed for discharging the purified liquid out of the filter vessel.
BAKGROUND OF THE INVENTION Improved apparatuses and systems for purification of water are required, particularly in small or medium-sized plants, for purification of drinking water. The needs are particularly great in many developing countries with inferior infra structure. An other field of demands is in areas threatened by earth quakes, where the plant also should be mobile or at least easy to put in order. Such mobile and easily erected water purifying plants are also required for military purposes. Improved apparatuses and systems for water purification are also in demand in technically highly developed industrial countries, e.g. for purification of drinking water in municipal purification plants, in mobile purification plants for private use in agriculture; for purification of water in fish cultures, in bath establishments, such as municipal baths, bubble pools, therapeutic and medical baths, and for purification of industrial water, including process water and industrial sewage etc. The invention may also be applied to the purification of other liquids than water, e.g. in chemical industries and wood industries.
DISCLOSURE OF THE INVENTION
The object of the invention is to satisfy the above-mentioned demands. According to the invention the filter bed is brought to expand when
SUBSTITUTE SHEET
the flushing liquid is introduced from below during at least one flushing phase, so that the filtering mass is fluidized and the flushing liquid can pass through all parts of the filter bed and disengage impurities from the filtering mass, said impurities being forced by the flushing liquid upwardly through the filtering bed to be collected in the upper part of the vessel. A characteristic feature of the invention is also that the flow of the flushing liquid is interrupted, so that the filtering bed is allowed to settle back to its starting level and due to sedimentation resume its normal volume, and that the liquid volume above the filtering bed, containing spent flushing liquid and impurities disengaged from the filtering bed, is drained off through a plurality of discharge nozzles situated at a level being considerably lower than the normal liquid level in the vessel, the upper level of the liquid receding to the level of the discharge nozzles. Preferably the flushing liquid is pumped up to a number of overflow outlets determining the normal upper liquid level in the filter vessel, be-fore interrupting the supply of flushing liquid. Thus, the invention is perferably characterized in that the volume of flushing liquid and impurities collected therein, which is located between said discharge nozzles and said overflow outlets after a completed flushing phase, is drained off through said discharge nozzles.
The described sequence, consisting of: flushing the filtering bed by means of flushing liquid, whereby the bed is expanded and the filtering material fluidized, interrupting the supply of flushing liquid, sedimentation of the filter material to its starting level and draining of the spent polluted flushing liquid, is preferably repeated several times. By a suitable design of the filter vessel each of the flushing phases can be given a desired short duration, more exactly
H x (2 to 20) seconds and preferably 10 x H seconds at the most, in a filter having a bed height of H meter. As an example, a filter having a bed height H of 1 meter can be flushed during 3 times 10 seconds, i.e. totally 30 seconds, which gives a good guarantee therefor that also polluting particles situated lowermost in the filter bed will
reach so far above the filter bed during the draining phase as to be drained off through the discharge nozzles. During the flushing operation the filter bed expands by 5 to 25 per cent, perferably 10 to 20 per cent. However, by choosing a suitable filtering mass the filter particles will be free to sink back quickly to their normal level during the sedimentation phase interposed between the flushing phase and the draining phase. The time required for said sedimentation of the filtering mass back to its starting level may amount to 5 to 10 percent of the duration of the flushing phase. For instance, a filter bed having a normal height of 1 meter and expanded about 15 cm during a flushing phase will sink back to its starting level in a few seconds. In contrast, the discharge of the spent polluted flushing liquid present above the filtering bed, which follows after completed sedimentation of the filtering mass, will last during a considerably longer time, normally amounting to several minutes, and take place as a gravatational flow. The duration of the drainage depends upon the size of the filter and the number and dimensions of the discharge nozzles. The time required can be deducted from known hydrodynamic laws, but is preferably acertained and/or corrected empirically by practical tests during the trimming of the plant.
According to the invention, several filters are preferably operated in parallel, in which case the supplied water to be purified can be fed and distributed by means of a pump common to said filters. Then the short duration of the flushing phase, or phases, makes it possible and suitable and trouble-free to interrupt the feed of polluted water to those filters as are not being cleaned at the time, and instead to utilize the full capacity of the pump for supplying flushing liquid under high pressure to the filter being cleaned. As soon as the short flushing phase has been interrupted, the feed of the polluted water to the rest of the filters is resumed, i.e. even during the sedimentation and draining phases.
By making use of the pump in the above mentioned manner, in a plant of optimum design there is no need of a pump oversized for its primary
purpose, viz. feeding water to the filters for purification. This is of a great economic significance, because the pump and its pertaining motor are the heaviest cost item of the plant. In a plant containing
3 five filters operating in parallel and feeding 7.5 m polluted water
2 5 pro m filter area and hour in up-flow filtration, the same pump can
3 be used for flushing a filter with maximum 35 m flushing liquid pro
2 m filter area and hour, when the remaining four filters are shut off during the flushing phases. If instead the filters are operated with down-flow filtration, the filtration by use of a pump of the same size
3 _0 can give a capacity of each filter of 20 m water supplied for
2 purification pro m filter area and hour.
As an alternative, a pump can be used for the flushing which in addition to the flushing also is used for distributing the purfied 5 water to the consumer/consumers. As the flushing can be performed during very short sequences, there is no inconvenience in making use of the distributing pump for said first mentioned purpose while the consumer/consumers are shut off.
0 In order to attain the desired rapid expansion and fluidization of the filter bed there is preferably used a filter vessel which widens upwardly, the wall of filter vessel being inclined at least along the major part of the filter bed at an angle of 1 to 8 degrees, preferably 1.5 to 6 degrees and most preferably 2 to 5 degrees, against the 5 vertical. Rupture of the filter bed takes place initially along the wall of the vessel, and then the fluidization of the filter mass follows almost instantaneously, disengaging flocks of chemically precipitated impurities collected in the interspaces between the filtering mass particles. Also in this respect the operating method of 0 the invention differs from the method of operation in conventional filters having straight walls. If in such a filter, flushing liquid under high pressure is introduced from below, the clogged filter forms a piston which can be raised in the filter vessel and forcibly demolish equipment placed in the vessel above the filter bed, provided 5 that the filter is not equipped with special, usually complicated devices for breaking up the filter and thus preventing damage.
As mentioned above, the filter vessel should preferably be of a shape widening upwardly. In other respects the shape as well as the dimensions may vary according to requirements. Thus, in the range of the inclined walls the vessel may take the shape of a truncated cone with its base turned upwardly and with circular cross-section, but also vessels of a rectangular cross-section are possible and in many instances appropriate to use. Normally the inner width does not exceed 2 meter, whereas the length is limited merely by practical conditions. However, in certain cases the width may be greater than 2 meter, if the supply of water into the bottom of the vessel is arranged suitably.
In order to attain that the method of the invention works in the desired manner it is also important to choose a suitable filtering mass material adapted to the method and apparatus of the invention. As filtering mass there is preferably used a porous mineral product pertaining to the group of aqueous alkali and/or earthen alkali silicates known under the name Zeolites. Native zeolites consist of vulcanic minerals and can be found in old vulcanic territories. The special micro crystalline form recommended for water purification according to the invention is known under the name Clinoptilolite. Other zeolite qualities, e.g. Chabasite, Mordenite and Erionite are not equally suitable for water purification. The advantages of zeolites are their adsorption, ion exchange and catalytic properties:
- uniform pore structure
- pore diameter 0.1 to 1.0 nanometer (nm)
- the pores are naturally filled with water. Said pore water is easy to remove by heating without changing the cristal structure. The process is reversible.
- low particle density
- large pore volume
- the cations are movable and can be replaced by anions. '
On account of their structure the zeolites function as molecular screens, i.e. they remove substances from water by adsorption. The Clinoptilolite-zeolite has the following physical properties:
Adsorption capacity 0.05 to 0.3, preferably 0.1 to 0.2 cm /g Ion exchange capacity max 1.5, preferably 1.2 to 1.3 mval/g
3 Particle density 2 to 2.5, preferably 2.2 to 2.3 g/cm Volume density 0.5 to 1.0, preferably 0.8 to 0.9 cm /g
2 Active area 100 to 1000, preferably 300 to 500 m /g
2 Grain hardness 300 to 400 kp/cm
Native, i.e. unactivated, Clinoptilolite an absorb cloroamines, ammonium - ammonium nitrogen, nitrate nitrogen, alkali/hydrogen carbonate, calcium, oil derivatives, etc. Manganese-activated Clinoptilolite with catalytic effect can separate i.a. iron, manganese, calcium and magnesium. The two materials can be used for purification of water in the applications mentioned in the introduction.
In order that the filter mass particles during the fluidization dis¬ engage themselves mutually and substantially instantaneously and in order to avoid their rubbing against each other, they should prefer¬ ably be of a practically uniform grain size, i.e. the variation of the grain size should be small. The difference of the grain sizes should preferably, be less than 0.5 mm, whereas the absolute grain size may be chosen within somewhat wider limits, e.g. between 0.2 and 0.7 mm, or between 0.5 and 1.0 mm.
According to the above-described principles of the invention, precipitations and other macroscopic impurities in the filtering bed can be rapidly driven off the bed and removed by the flushing liquid, whereas microscopic impurities, i.e. impurities of the dust type, may require longer time periods of flushing. Therefore, in order efficiently to remove such impurities, as are collected mainly in the surface layer of the filtering bed, additional nozzles may be arranged in the surface layer. If required, such nozzles are buried in the
surface layer or placed immediately above the surface layer, e.g. 5 cm above the surface. The' best location is determined by the conditions at the plant in question. Through these nozzles a weak reflushing with fresh flushing liquid can take place at the time when the polluted flushing liquid is drained off during the draining phase, i.e. while discharging the spent flushing liquid that has been forced through the filtering bed during the previous flushing phase proper. Said reflushing causes a minor expansion of the filtering bed which may be of the order of 1 per cent. The concomitant stirring of the upper part of the filtering bed is sufficient for whirling up said microscopic impurities, but is not so heavy as to whirl up the filtering mass particles, too, which would involve loss of filtering mass material along with the liquid drained off.
The invention has been developed for up-flow filters, but the principles of the invention are applicable also in down-flow filters, although, of course, in the latter case the flushing should be directed upwardly, as above described.
Further characteristics and aspects of the invention and the advantages gained thereby will appear from the claims and the following description of preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS In the following description of preferred embodiments reference will be made to the following drawing figures, in which
Fig. 1 is a block or flow diagram schematically illustrating a plant adapted to work according to the invention,
Fig. 2 is a side view of an up-flow filter being a first preferred embodiment, the right-hand half of the filter vessel being shown cut off in the drawing,
Fig. 3 is a view taken along the line III-III in Fig. 2 and showing a system of nozzles in the lower part of the filter for introduction of water to be purified,
Fig. 4 is a view taken along the line IV-IV in Fig. 2,
Fig. 5 is an enlarged view of a draining nozzle shown in section along the line V-V in Fig. 4,
Fig. 6 shows a possible embodiment " of a nozzle for reflushing at or near the location of the upper surface of the filter bed,
Fig. 7 shows an other embodiment of such a nozzle, and
Fig. 8 is a perspective view of a second preferred embodiment of an up-flow filter according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to Fig. 1, 2 is a pump arranged for pumping water to be purified and made suitable as drinking water, into equipment placed within a vessel (not shown) . 3 designates a feed conduit leading to the purification equipment in said vessel, and 4 designates a conduit for discharge of clean drinking water. There is also a discharge conduit 5 for impurities collected during the purification. All other apparatuses, machines, etc. for purification and for power supply for the purification ar placed within said vessel.
For pretreatment of the water supplied to the vessel there is provided a coarse filter 6, which may be of a conventional type, e.g. a filter with a rotary scraper. The coarse impurities collected in the coarse filter 6 are carried through a conduit 7 to the discharge conduit 5. The coarsely purified water is lead through a conduit 8 to a first UV-apparatus 8a for ultraviolet irridation of the water. From said first UV-apparatus 8a the water is lead to a flocculating chamber 9 for precipitation and flocculation of dissolved impurities. As precipitating agent there may be used e.g. aluminum sulphate. By a dosing pump 10 the flocculating agent is pumped into the flocculating chamber 9 via a conduit 11.
The flocculating chamber may also be supplied with acid, preferably hydrochloric acid, or alkali, preferably sodium hydroxide, from a second dosing pump 10a via a conduit 11a. The water treated in the flocculating chamber 9 is lead to and distributed between a pair of up-flow filters 13, 14 through a ' conduit 15 via a control valve 16.
The two parallel up-flow filters 13 and 14 are identically alike and may be designed as described more closely herein below with reference to Figs. 2 and 5.
From the conduit 15 the water to be purified can be introduced in the filter 13 via a branch conduit 18 and a pair of valves 19, and the rest of the water can be lead into the filter 14 via a pair of valves 19'. (Details of the filter 14 having counterparts in the filter 13 are given the same reference numbers as there with addition of the suffix • . )
Flushing liquid can be introduced into the up-flow filters 13 and 14 via a conduit 17 and its branch conduits 22 and 22' and valves 23 and 23', respectively. (In case the valves are doubled, one is automatically and the other manually operated.)
Purified water, i.e. filtrate, from the up-flow filters 13 and 14 can be lead either to a posttreatment filter (catch filter) 21 or to a second UV-apparatus 24 via overflow outlets 60, 60', overflow outlet conduits 61 and 61', respectively, discharge conduits 25 and 25', respectively, and other valves 26, 26' pertaining thereto and then via a pair of valves 27 ahead of the catch filter 21 and a pair of valves 27a ahead of the UV-apparatus 24. Water having passed the catch filter 21 can be introduced into said second UV-apparatus 24 via a discharge conduit 21a and a pair of valves 21b. Spent flushing water with impurities collected therein can be discharged from the filters 13, 14 via a drain conduit 28, 28', and from the catch filter 21 via a drain conduit 28'', into the sewer conduit 5 via third valves 29, 29' and 29'', respectively. There are also a conduit 30 for flushing liquid
having passed by the up-flow filter 13, and a conduit 30' for flushing liquid having passed by the up-flow filter 14. Said conduits are connected to the sewer conduit 5 via valves 31 and 31', respectively. Finally there is a conduit 27b which via valves 27c can carry flushing water from the catch filter 21 when the same is flushed in reverse.
The second UV-apparatus 24 sterilizes the filtrated water before it is lead via a conduit 32 and a vlave 33 into a storage tank 35. From the storage tank 35 the water is carried by means of a pump 36 and the distribution conduit 4 to the consumer or consumers. The pump 36 has several functions. It should function partly as a distribution pump, partly as a pump for flushing liquid an also as a pressure—rising pump for pressure tank 37 serving the above-mentioned automatic valves. The storage tank is maintained in a state of equilibrium by having all air pass out and in through a third UV-apparatus. 38 designates an overflow tube in the tank 35. Said tube is provided with a water trap 39 for preventing unsterilized air from entering the tank 35. There is also a check valve 40. (In addition there are a great many check valves in the system, designated by the same symbol as the check valve 40.)
To the entire plant there also belongs a diesel unit 46 which generates all power required in the plant. 48 designates a box containing electrical outfit, timers or other control equipment.
One of the up-flow filters 13, 14 (the filter 13) will now be more closely described with reference to Figs. 2 to 5. 50 designates a filter vessel or container, which is made of glass-fibre reinforced polyester and constitutes a pressure tank having a convexly rounded bottom 51 and a convexly rounded top 52. The main part of the vessel between the convex ends 51 and 52 has the shape of a truncated straight cone turned with the base upwardly and the top downwardly. In other words, the vessel widens upwardly from the bottom part 51 towards the top part 52. The conical wall of the main part of the vessel is inclined in the shown embodiment at an angle of 2.2 degrees
to the vertical plane. Thus, the top angle of the cone is 4.4 degrees. The vessel 50 restes upon a base 54. In a chosen case the total height of the filter vessel was 2.35 m, whereas the diameter at the transition between the bottom part 51 and the main part 53 was 96 cm and the diameter at the transition between the main part 53 and the top part 52 was 110 cm.
The vessel is filled with filtering mass up to a level designated by 55. In the embodiment shown the total height of the filter bed was 155 cm.
In the preferred embodiment the filtering mass consists of crushed and screende Clinoptilolite, which is a zeolite mineral with the following chemical composition:
Percentage by weight
Si0„ 72.87 12.36
A1 2°3 1.14
Fe 2°3 Na 2 0 0.78 κ 2 o 2.49
MgO 1.57 CaO 1.78
Glowing loss (H )• 7.00
The used Clinoptilolite had been screende to a grain size between 0.5 and 1.0 mm.
Buried in the filtering mass 54 in the bottom part 51 of the vessel 50 is a set of nozzles 57 having distribution orifices 58 with a width or diameter of about 1 mm. As the filter operates according to the up-flow principle, greater nozzle apertures essentially independent of the grain size can also be accepted. The inlet conduit 18 is connected to the- nozzles 57.
At a distance of about 40 cm above the upper level 55 of the filter bed there are'four funnel-shaped overflow outlets 60, which are connected by connecting conduits 61 to the conduit 25 letting out the filtrated water. Immediately above the upper level 55 of the filtering bed 54 five discharge nozzles 62 are arranged in the shell of the filter vessel 50. These serve for letting out spent flushing water containing impurities which have been flushed upwardly through the filter during its cleaning. The discharge nozzles 62 are connected to the drain conduit 28, Fig. 1, and are formed as tubular bushings 63 in the shell 53. Said tubes 63 extend horisontally through the vessel shell, as shown in Fig. 5.
In the bottom part of the filter there is a sampling device 64 for measuring of the pH-value in the bed 54, and a discharge outlet for filter material which is normally closed.
The operation of the above-described apparatus will now be more closely explained. The-description will concentrate upon the mode of operation of the up-flow filters 13 and 14, whereas the function of " the more conventional parts in the vessel 21 will not be explained more closely. The water is lead via the conduit 15 from the flocculation chamber 9 and is divided between the two parallel up-flow filters 13 and 14 and is then lead via the nozzles 57 into the filtering mass 54 of the respective filters 13 and 14. The pH-value in the filtering bed is controlled by the sampling device 64. In case the pH-value drops below about 5.7 or rises above about 6.4, an adjustment of the pH-value will preferably take place by supplying an alkali or an acid to the flocculating chamber 9 via the conduit 11a from the dosing pump 10a.
According as the water flows upwardly through the filtering mass 54 impurities are collected upon and between the individual particles of the filtering mass. Above the upper level 55 of the filtering bed 54 there is clean water up to the level of the overflow outlets 60, through which the cleaned water is discharged via the conduit 25 for
13
sterilization in the second UV-apparatus 24, Fig. 1. As an alternative, said water is first lead through the check filter 21, said filter being flushed in the downward direction.
Gradually the filtering bed 54 is saturated with impurities. The flow resistance in the filtering bed 54 rises successively. The cleaning of the filters may take place according to a certain time plan related to the cycle of consumption in the distribution stage. When applying said principal, the filters are cleaned before they are wholly saturated by impurities. As an alternative it is possible to postpone the cleaning until the filters are saturated with impurities, which will be notified by measuring the pressure.
When the filtering bed of one of the filters 13, 14 should be cleaned, as washing liquid there is used clean water from the storage tank 35, which in the described embodiment is fed by the pump 36. A pair of valves 66 in the conduit 17, as well as either of the valves 23 and 23' and either of the valves 31 and 31' are opened, and either of the valves 26 and 26' are closed, dependent upon which filter should be cleaned. If, for example, the up-flow filter 13 should be cleaned, consequently the valves 23 and 31 are opened and the valves 26 closed, whereas the valves 23' and 31' remain closed and the valves 26' remain open. Thus, the supply of water for purification from the flocculation chamber 9 via the valve 16 to the parallel up-flow filter 14 continues, while the filter 13 is being cleaned. However, previously thereto the valves 19 in the conduit 18 are closed, whereas the valves 19' to the filter 14 are maintained open. If instead the filter 14 should be cleaned, the operation takes place in an analogous manner.
By means of the distribution pump 36 (so in this case use is not made of the alternative possibility of taking advantage of the same pump as is normally used for feeding water for purification) water is driven from the storage tank 35 forcibly up through the clogged filter 13, so that the filtering mass of said filter is fluidized, i.e. is lifted upwardly with a simultaneous expansion, stirring washing of the filter
particles, so that collected impurities are set free. The fluidization takes place essentially instantaneously and mainly without rubbing the particle against each other on account of the cross-section of the vessel 50 increasing upwardly over its conically widened part 53. The chosen angle of Inclination - 2.2 degrees - safeguards that the washing water penetrates all parts of the filtering bed 54, including the space close to the vessel shell. Due to the expansion the upper level of the filter bed rises about 12 cm. The heavy upward flushing flow lasts about 15 seconds. Then the flushing is stopped, the valves 23 are closed, and the filtering bed is allowed to settle back to its original level, which takes a few seconds. Thereafter the valves 29 are opened and the spent washing water, which is collected in the upper part of the vessel 50 and which contains the impurities worked loose of the filter, is discharged from the upper part of the vessel 50 by self-draining through the discharge nozzles 62, requiring 2 to 3 seconds. The cleaned filter can then be operated anew for continued purification of water emanating from the flocculation chamber 9.
The check filter 21 may be of the same design as the filters 13 and 14 and can also be washed clear in the same manner as these. In respect of such washing, reference is made to the foregoing description.
As mentioned in the introductory part of the description, it may be favourable to arrange separate nozzles within or near the surface layer of the filtering bed in order, by renewed flushing of liquid during the draining phase, to whirl up such microscopic impurities as have been collected in the surface layer of the filtering bed, too. Said nozzles may be designed in principle equally to the nozzles 57 at the bottom of the filtering bed 54, or be designed as shown in Fig. 6. Such a nozzle 70, Fig. 6, is located in the surface layer 55 or immediately above the same (position 55') or is burled in the surface layer (position 55' '). In the shown embodiment the nozzle 70 comprises a casing placed on end and has a plurality of horizontal nozzle apertures 71. A conduit 72 serves for supplying flushing liquid during the reflushing phase. As earlier mentioned, through said nozzles 70
there an be introduced flushing liquid during the draining phase with so weak a flow that merely microscopic particles of the nature of dust are whirled up in the surface layer, leaving the filter mass material almost unaffected.
Fig. 7 shows an other embodiment of a-reflushing nozzle 73. In this embodiment the nozzle 73 comprises a tube having nozzle apertures 74 placed upon the top side as well as on the bottom side and on the lateral sides. The nozzle 73 may like the nozzle 70 be placed within or near the surface layer 55, 55', 55''.
Fig. 8 illustrates an other embodiment of the filter vessel 80 with pertaining equipment. Like in the filter vessel 50 the walls of said vessel are inclined - the angle of inclination being the same as in the embodiment described in the foregoing - but in this case the cross-section is rectangular. In the bottom part of the vessel 80 there are embedded in the filtering- mass 84 a set of nozzles 87, each having a slit-shaped nozzle aperture 88 with a width of about 1 mm. An inlet conduit is, as earlier, designated by 18. At a distance above the upper level 85 of the filtering bed, which distance is determined by the size of the filter, there are eight funnel-shaped overflow outlets 90 which via connecting conduits 91 communicate with the discharge conduit 25 carrying the filtrated clean water. At a short distance above the upper level 85 of the filtering bed 84 there are provided a number of discharge nozzles 82 inserted in the shell of the filter vessel 80 as well as a number of reflushing nozzles 73 with pertaining connecting conduits 72 extending through the vessel wall. The mode of operation of the equipment in Fig. 8 is the same as has been described with reference to the foregoing embodiment and with reference to Fig. 7. Also in respect of the reflushing through the nozzles 73 it is referred to the foregoing description.
Next Patent: THERMALLY FORMED STACKED DISC FILTER