APPARATUS FOR DISTRIBUTION AND DISPERSION OF AIR SATURATED WATER

Abstract: The invention refers to an apparatus for distribution and dispersion of water, saturated with air under high pressure, which apparatus is preferably intended for use in a flotation basin (1) in a water treatment plant in which it is positioned at the inlet openings (2) for the water to be treated in the flotation basin (1). The apparatus comprises a predispersion unit (27, 28) arranged in a distribution tube (22) or its connection piece (24) comprising a perforated tube arranged preferably co-axially in the respective tube through the perforations or reducing holes (26) of which the air saturated water during a first decrease of the pressure and corresponding dispersion passes on its way to the distribution tube (22) from which the water during a second decrease of the pressure and dispersion is pressed out into the flotation basin (1) through one or several openings (23) in the wall of the distribution tube (22).

Description: APPARATUS FOR DISTRIBUTION AND DISPERSION OF AIR SATURATED WATER TECHNICAL FIELD An apparatus for distribution and dispersion of water, saturated with air under high pressure, which apparatus is preferably intended for use in a flotation basin in a water treatment plant, whereby the apparatus which comprises a distribution tube provided with orifices along one of its sides is positioned at the inlet openings for the water to be treated in the flotation basin. PRIOR ART When treating water, drinking water as well as sewage wa¬ ter, flotation plants are used to an increasing extent in order to increase the rate of flow of the water through the treatment plants and as a consequence of this also making it possible to decrease the size of the necessary basins and thereby the size of the complete treatment plants. When it comes to drinking water the requirements on the finished product are mainly uniform and the design of a treatment plant is mainly decided by the character of the source of water supply. If the source is a lake or a water course usually separation of larger particles is taking place in a filter chamber whereafter the water is subjected to a chemical and biological treatment carried out by means of the addition of precipitation- and flocculation- agents in a flocculation chamber. The particles which are precipi¬ tated are then to be separated from the water which can be done by means of sedimentation which means that the parti¬ cles through the influence from gravity sink to the bottom in a sedimentation basin. Different types of particles have different density and therefore different sinking velocity. In order to make it possible for particles having low den¬ sity, "light particles", to sediment while the water passes a sedimentation basin a long time is required which means that the surface of the sedimentation basin must be large. The time for the particle separation could be considerably reduced by means of flotation which means that microscopic air bubbles are added to the water which adhere to parti¬ cles or particle flocculations in the water and also con- tribute in the process of creating particle flocculations and keeping them together. Air bubbles raise fast towards the water surface bringing adhered particles and particle flocculations to the water surface where they create a sta¬ ble sludge cover which can be removed by means of scrapers or by intermittently raising the water level in the flota¬ tion basin so that the sludge cover transfers to a sludge channel arranged at one of the edges of the basin. The microscopic air bubbles which are used in the flotation procedure have a diameter of 30-80 micrometer and can not be generated for instance by means of the injection of air directly in the water. Microscopic air bubbles for flota¬ tion of drinking water are usually generated by means of dissolving air in clean water in a pressured vessel under overpressure whereby the biggest possible saturation level is aimed at. This water which usually is called dispersion water is fed with maintained high pressure to the inlet for the flocculated water in the flotation basin positioned at its bottom where it is added to said water via special noz- zles or sprayers which are designed to give an instantane¬ ous decrease in the pressure at which the air dissolved in the water is released in the form of microscopic bubbles creating a dispersion of air in the water. The pressure vessels which are used for the generation of high pressure dispersion water, saturated with air to the greatest possible extent, are usually kept half filled with water by means of a control unit including sensors. The supply of compressed air takes place in the space filled with air above the water surface and the water is often supplied through a nozzle arranged in the side wall of the vessel in the air filled space through which nozzle the wa¬ ter is spraying against the opposite wall of the vessel where the water jet to some extent is split up. The flotation method has considerably decreased the time for water treatment and the decreased time of flow means that water treatment plants could be made smaller keeping the same capacity. When the space requirement of the treat¬ ment plants decreases new application fields are opened. The method has however not only implied advantages. It has thus at the same time implied an increase of the cost for the treatment due to the fact that already cleaned water is recirculated and is being used for producing dispersion wa¬ ter. In order to get economy in the procedure it is neces- sary, by means of sophisticated methods, to keep the con¬ sumption of dispersion watered low, on one hand by increas¬ ing the level of air saturation in the dispersion water and on the other hand by achieving an ameliorated dispersion at the inlet of the dispersion water in the flotation basin. As earlier mentioned the dispersion water is supplied to the flotation basin through a number of nozzles each one of which is provided with a valve which creates the instanta¬ neous pressure decrease for the dispersion water which is required in order to release the air in the same creating microscopic bubbles. The nozzles are often positioned in a rake-formed arrangement on one side of a distribution tube having a length of several meters, to which tube the feed¬ ing is taking place through a feeding tube arranged at the middle of the distribution tube essentially perpendicular relative to the nozzles, which position, if we revert to the comparison with a rake, corresponds to the hole for the handle of the rake. A "rake" can comprise about 25 nozzles which are screwed into sockets welded on to the distribu¬ tion tube. Complete distribution tubes provided with noz¬ zles are comparatively expensive and if the nozzles are made of plastic they will easily be damaged e.g. when cleaning the basin. DESCRIPTION OF THE INVENTION One object of the present invention is to propose an appa¬ ratus with high efficiency for distribution and dispersion of water, saturated with air under high pressure. Another object is to propose an apparatus which is rugged and has a low manufacturing cost. This is achieved by means of an ap¬ paratus having the characteristics according to the ap¬ pended claims. DESCRIPTION OF THE DRAWINGS One embodiment of the invention will be described more in detail with reference to the enclosed drawing on which fig¬ ure 1 in a side view and schematically shows a convention¬ ally equipped flotation basin in section, figure 2 shows in a front view and partly in section an apparatus according to the invention for distribution and dispersion of air saturated water and figure 3 shows the same apparatus in a side view and partly in section. PREFERRED EMBODIMENT In figure 1 which schematically and in a side view shows a conventionally equipped flotation basin in section the ba¬ sin is generally designated 1. The basin has an inlet 2 to which water is fed from a flocculation chamber, not shown. By means of an inclined barrier 3 arranged in front of the inlet 2 in the basin 1 the water is caused to flow upwards in the basin 1. At the bottom of the pocket which is cre¬ ated between the wall 4 of the basin and the barrier 3 a set of nozzles or sprayers 5 debouch arranged on a horizon- tal distribution tube. The tube 6 feed air saturated water, dispersion water, to the flocculated water supplied to the basin through the inlet 2 which water is given an increased movement by the dispersion water injected under pressure. The nozzles or sprayers 5 are so designed that the disper- sion water is subjected to an instantaneous pressure de¬ crease which releases the air in that water in the form of microscopic bubbles which in their movement towards the wa¬ ter surface adhere particles and particle flocculations and relatively fast carry most of these particles to the water surface where a sludge cover is created which by means of some kind of sludge scraper 7 or in another way is trans¬ ferred to the sludge channel 8 at the wall 9 of the basin. Heavy particles which the Micro bubbles are not able to lift are collected by the filter 10 which is arranged be- tween the back side of the barrier 3 and the wall 9 of the basin and through which filter the treated water passes on its way via the outlet 11 to a clear water basin, not shown. From this basin part of the treated water is pumped, under high pressure, to the water inlet 13 of the pressure vessel 12. The vessel 12 in which the dispersion water is produced is supplied with compressed air via the air inlet 14 from a compressor, not shown, and the air saturated wa¬ ter is fed back via the outlet 15 and the distribution tube 6 to the nozzles 5 arranged on the same in the flotation basin 1. In figure 2 which schematically, in a front view and partly in section shows an apparatus according to the invention for distribution and dispersion of air saturated water the apparatus is generally designated 21. The apparatus com¬ prises a housing including on one hand a horizontally posi- tioned distribution tube having outlet openings 23 arranged along one of its sides (the back side in the figure) for dispersion water, on the other hand a tube connection piece 24 arranged at the middle portion of the distribution tube to which a feeding tube 25 for the supply of dispersion wa¬ ter is connected. Inside the housing a predispersion unit is positioned through the reducing holes 26 of which the supplied dispersion water has to pass while the pressure is decreased and a certain dispersion, predispersion, takes place, before it reaches the distribution tube 22. In fig¬ ure 2 two embodiments for predispersion are shown, one in each half of the figure. The predispersion unit 27 to the left of the symmetry line is mainly arranged in the tube connection piece 24 and comprises a container provided with reducing holes 26 into which container the feeding tube 25 debouch. The fact that there is only a certain dispersion of the air in the dispersion water at its passage through the holes 26 is due to the fact that the pressure decrease is not com¬ plete as part of the pressure is still present in the dis¬ tribution tube 22. The final pressure equalization and dis¬ persion is only taking place at the passage of the predis- persed water through the outlet openings 23. The dispersion which is taking place in two steps will be much more effi¬ cient than dispersion by means of nozzles 5, between which there will be created a certain back-water or smooth water, partly due to the fact that the openings 23 are arranged close to each other and are evenly distributed. The predispersion unit 28 which is shown to the right of the symmetry line in figure 2 has the form of a tube, hav¬ ing reducing holes 23 arranged along one side, being posi¬ tioned co-axially inside the distribution tube 22, through which holes the dispersion water which is supplied to the dispersion unit 28 through the extension of the feeding tube 25 is pressed out, whereby as described above a cer¬ tain dispersion takes place before the final dispersion at the passage of the openings 23. The openings 23 could be replaced by narrow horizontal slots. The apparatus as it is shown in the right portion of figure 2 is also shown in a side view and partly in section in figure 3. The designations of the different parts are the same as in figure 2. The flow of the dispersion water in and between the two tubes has been illustrated by means of arrows. The embodiment of the predispersion unit 28 shown in figure 3 and the right portion of figure 2 is in par¬ ticular suited for long distribution tubes, while the pre¬ dispersion unit 27 shown in the left portion of figure 2 is preferably suited for short distribution tubes.

Claims: CLAIMS 1. Apparatus for distribution and dispersion of water, saturated with air under high pressure, which apparatus is preferably intended for use in a flotation basin (1) in a water treatment plant, whereby the apparatus which com¬ prises a distribution tube provided with orifices along one of its sides is positioned at the inlet openings (2) for the water to be treated in the flotation basin (1), charac¬ terised in that a predispersion unit (27, 28) is arranged in the distribution tube (22) or its connection piece (24) comprising a perforated tube arranged preferably co-axially in the respective tube through the perforations or reducing holes (26) of which the air saturated water during a first decrease of the pressure and corresponding dispersion passes on its way to the distribution tube (22) from which the water during a second decrease of the pressure and dis¬ persion is pressed out into the flotation basin (1) through one or several openings (23) in the wall of the distribu¬ tion tube (22).

Inventors: ERIKSSON HANS, ISAKSSON KENT, ERIKSSON, HANS, ISAKSSON, KENT
Applicants: ERIKSSON HANS, ISAKSSON KENT, ERIKSSON, HANS, ISAKSSON, KENT
Application year: 1996
Main classification: C02F1
IPC codes: B01F3, B01F5, B01F13, B03D1, C02F1