PRESSURIZED WATER FLOTATION APPARATUS

Abstract: The present invention relates to an apparatus based on a pressurized water flotation method (DAF), in which dispersion water and the water to be treated, e.g. flocculated water, are supplied to a reaction space (1), in which they encounter and react with each other. The inlet conduit (8) for the water to be treated is constructed in connection with a reaction space (1) in such a way that the distance of the orifice (11) of the inlet conduit (8) from the bottom (2) of the orifice (11) can be controlled by moving the inlet conduit (8) in the direction b of the mid-axis (13) of the reaction space, whereby the encountering location and manner (turbulent, gentle) of the dispersion water and the water to be treated, e.g. flocculated water, inside the reaction space can be adjusted appropriate for the process conditions in question.

Description: PRESSURIZED WATER FLOTATION APPARATUS The present invention relates to an apparatus according to the preamble of claim 1. In accordance with the present flotation method, the water to be treated, e.g. flocculated waste water or raw water, is made react with so called dispersion water. Dispersion water is pressurized water, often for example clarified waste water, into which gas, such as air, has been dissolved. This pressurized water flotation method, in which the dispersion water and the water to be purified/treated are made react with each other, is generally known as DAF (dissolved air flotation). It is known that in waste water treatment of paper and chemical pulp industry, for example, the dispersion water and the flocculated water to be purified are brought into contact with each other directly in a flotation basin. Hereby, the flocculated water to be purified is brought into the vicinity of the dispersion water nozzles. After the reaction of the dispersion water and flocculated water, the floes, to which a great number of micro bubbles from the dispersion water have been adhered, begin to rise towards the surface. In connection with the reaction space of the flocculated water and the dispersion water there are usually various baffles intensifying the flotation. Depending on the construction of the flotation apparatus, there may be even several dozens of dispersion water nozzles in the proximity of the bottom of the flotation basin. As regards to an individual dispersion water nozzle, the substantial thing is how much dispersion water (1/min) it is capable of producing and what the distribution of the micro bubbles formed by it, i.e. the quality of the bubbles, is. In paper and chemical pulp industry, the diameter of the micro bubbles is ideally about 100 urn, as a rule, the tendency being to avoid large bubbles. Also, an arrangement is known in which the dispersion water is mixed into the horizontal inlet tube for the flocculated water. The inlet tube is hereby arranged to open inclined to this horizontal tube for the flocculated water. The mixture of the flocculated water and the dispersion water will thus continue flowing horizontally until the tube turns upwards, opening to the bottom of the flotation basin. There are, however, some disadvantages relating to such reaction in a horizontal inlet tube. The dispersion water having reacted with the flocculated water, the air bubbles tend to rise upwards. Thus, the distribution of the air bubbles in the tube is no longer even but the concentration thereof is greater in the top portion of the tube. Also, one disadvantage is that air bubbles have a tendency to stick to the top surface of the tube. Small air bubbles already stuck to the top surface of the tube tend to combine with new air bubbles, whereby larger bubbles are formed. As regards to the flotation process, these large air bubbles are inefficient. It is known from the patent publication EP 0 406 048 to arrange the reaction location of the dispersion water and the flocculated water, i.e. the reaction vessel, in the flotation basin. According to the arrangement of this patent, the dispersion water is led into the reaction vessel located in the flotation basin in such a way that prior to mixing with the flocculated water, it will bump against a collision plate which is positioned at the end of the inlet tube, vertically relative to the inlet tube. A first pressure reduction of the dispersion water has occurred earlier in the valve located in the inlet tube. In the patent publication US 3,809,240, an arrangement rather similar to that in the above-mentioned patent publication EP 0 406 048 is disclosed. In this arrangement, the dispersion water is brought into the reaction vessel of the flotation basin in the radial direction. In both cases, the only factor that can affect the quality of the reaction between the dispersion water and the water to be treated is the pressure of the dispersion water. An object of this invention is to avoid disadvantages relating to the prior art and to achieve an improved reaction between the water to be treated and the dispersion water. These objects are achieved by means of the characterizing features of the invention that become apparent primarily in the characterizing part of the independent claim relating to a flotation apparatus. Also, the invention relates to use of the apparatus in connection with waste water treatment in paper and chemical pulp industry, in particular. The other characterizing features of an apparatus according to the invention become apparent in the characterizing parts of the dependent claims. In an apparatus according to the invention, using a pressurized water flotation method (DAF), the idea is applied that the reaction between the dispersion water and the water to be treated, e.g. flocculated water, is achieved in a special reaction space, in which factors affecting the reaction can be adjusted optimal according to the properties of the water to be treated. This reaction space is arranged substantially around the orifice of the inlet conduit for the water to be treated. In order to control and adjust the conditions in the reaction space, the apparatus according to the invention is constructed in the following way. An inlet conduit for the water to be treated is constructed to be in connection with the reaction space in such a way that the distance of the orifice of the inlet conduit from the bottom of the reaction space can be adjusted by moving the inlet conduit in the direction b of the mid-axis of the reaction space, whereby it is possible to adjust the encountering location and manner (turbulent, gentle) of the dispersion water and the water to be treated, e.g. flocculated water, inside the reaction space to be appropriate for the process conditions in question. The diameter of the casing of the reaction space is substantially greater than the diameter of the concentrical orifice opening to the reaction space of the water to be treated. This is not only because in this way the velocities of both these water fractions can be adjusted as high as desired, but also because the velocity of the combination of the waters reacting with each other can be adjusted as high as desired, too. Also, positioning of the dispersion water orifices in such a way that they open to the casing of the reaction space affects the dimensioning of the casing of the reaction space. The reaction in the reaction space between the dispersion water and the water to be treated is made optimal by positioning the orifice for the water to be treated, which orifice opens to the reaction space, in such a way that, relative to the location and angular setting of the orifices of the dispersion water opening to the casing of the reaction space, the intersecting angles and velocities of the reacting waters relative to each other are appropriate for the properties of the water to be treated. In the arrangement according to the invention, prior to the contact with the water to be treated, the velocity of the dispersion water may be adjusted as desired by appropriate dimensioning of the pass for the dispersion water between the reaction space and the inlet conduit for the water to be treated. Thus, the desired velocity may be achieved for the dispersion water. The encountering location and manner (turbulent, gentle) of the dispersion water and flocculated water inside the reaction space may be adjusted suitable in a construction according to the invention by changing, relative to each other, the location and/or direction of the orifice of the inlet conduit for the water to be treated opening to the reaction space, and that of the orifice of the inlet conduit for the dispersion water opening to the reaction space. Depending on the properties of the reacting waters, it may also be preferable for the dispersion water (at a certain suitable intersecting angle) to react immediately with the water to be treated. Hereby, the orifice of the inlet conduit for the water to be treated, positioned inside the reaction space, is arranged within such a distance from the bottom of the reaction space that the casing of the inlet conduit for the water to be treated does not prevent the waters from reacting with each other immediately. An apparatus according to the invention is explained in detail with reference to the appended figures describing an embodiment according to the invention, the intention being, however, not to limit the scope of the invention to said embodiment. This embodiment may be preferably used for treatment of for example various waters in connection with processes in paper and chemical pulp industry, e.g. raw water, various process waters and waste waters. The water to be treated is thus water that contains solid or colloidal floes. The floes are controllably made react with fine micro bubbles contained in the dispersion water, these combinations (floe + micro bubbles) being then controllably and freely raised to the surface of the flotation basin, wherefrom they are collected by means of a suitable apparatus. In other words, the reaction space opens hereby directly to the flotation basin, and, due to gravity and flowing of water, the floes having reacted rise freely and gently to the surface of the flotation basin. In connection with this invention, reaction between floes and micro bubbles means the physical phenomenon in which floes and micro bubbles stick to each other. Fig. 1 illustrates a partial section view from one side of an apparatus for pressurized water flotation; Fig. 2 illustrates a top view of the same apparatus, taken along the line A-A shown in Fig. 1; and Fig. 3 illustrates an apparatus according to Fig. 1, the apparatus being provided with a guiding device. In the figures, a reaction space is denoted by the reference number 1. The reaction space is limited by a bottom flange 2 and a casing 3. In the lower part of the casing 3, there is a flange 9. The flanges 2 and 9 are attached to each other in such a way that they can be detached. In the upper part of the casing 3, there is a flange 7, in connection of which a closing apparatus may be arranged (not shown). By closing this closing apparatus, it is possible to separate the whole apparatus for pressurized water flotation from the flotation basin. Between the reaction space and the flotation basin, there is a conduit 14 connected to the upper part of the casing 3 by means of the flange 7. As illustrated in Fig. 1. this conduit may extend through the bottom 16 of the flotation basin as far as to the inside of the flotation basin. The upper part 15 of the conduit 14, extending to the flotation basin, may be shaped for example conic, as illustrated in Fig. 1. The dispersion water is led to the apparatus for pressurized water flotation by means of a delivery pipe 4, from which it divides into one or more inlet conduits 5. The dispersion water is led to the reaction space 1 through these inlet conduits 5 and orifices 6 opening to the reaction space. In connection with the inlet conduits 5, dispersion water nozzles 12 for the dispersion water are arranged. The flocculated water is led into the reaction space 1 through an inlet conduit 8 for the flocculated water. As to the flocculated water, it is led to the reaction space through an inlet conduit 8 for the flocculated water. The dispersion water is in this arrangement led to the space 17 between the casing 3 and the inlet conduit 8 for the flocculated water in the reaction space 1, the width of which space 17 is marked by the letter a. The bottom 2 is arranged in the flange 9 positioned in the bottom part of the casing 3, the interior surface of the bottom 2 being firmly attached to the exterior surface of the inlet conduit 8 for the flocculated water. In the bottom part of the inlet conduit 8 for the flocculated water, there is a lower flange 10. The location of the orifice 11 of the inlet conduit for the flocculated water, opening to the reaction space 1, and thus the relation of said location to the location of orifices 6 of the inlet conduits 5 for the dispersion water can be adjusted by changing the distance between the bottom 2 of the reaction space and the lower flange 10 of the inlet conduit for the flocculated water, as indicated by arrow b in Fig. 2. The surface of the inlet conduit 8 for the flocculated water has to be of extremely high quality, e.g. polished. The requirement of a high-quality surface is based on the fact that the surface acts as a sealing surface together with the inner edge of the bottom 2. On the other hand, in order to ensure undisturbed flowing of the dispersion water in the space 17, micro bubbles must not stick to each other while flowing in this space 17 and/or bumping against the surface 8 of the inlet conduit 8, nor must they stick to the surface of the inlet conduit 8. This also imposes a requirement for an even, e.g. polished surface of the inlet conduit 8. In this arrangement, the inlet conduits 12 are attached immovably to their locations, whereby the encountering location and manner (turbulent, gentle) of the dispersion water and the flocculated water inside the reaction space can be adjusted by changing the location of the orifice 11 of the inlet conduit for the flocculated water relative to the orifices 6 of the inlet conduits for the dispersion water in the direction of the mid-axis 13 of the reaction space, i.e. in the direction b. The distance a of the flocculated water inlet conduit 8 from the casing 3, shown in the figures, is adjusted such that the velocity of the dispersion water in the reaction space prior to the contact between the dispersion water and flocculated water is as high as desired. This distance a is thus dependent on the volume flow rate of the dispersion water, properties of the water to be treated, and other measures relating to an apparatus for the pressurized water flotation, which for their part are dependent on the capacity of an individual apparatus for pressurized water flotation. There may be several apparatuses according to the invention in the same flotation basin, depending on for example the shape and size of the basin. The angle α between the inlet direction of the dispersion water (arrow c) and the inlet direction of the water to be treated, e.g. flocculated water, and the angle β between the inlet direction of the dispersion water (arrow c) and the direction being vertical relative to the inlet direction of the water to be treated, e.g. flocculated water, (arrow d) are adjusted in each individual case according to the operating conditions, i.e. depending on the pressure and volume flow rate of the dispersion water as well as on properties of the water to be treated, so that desired encountering velocity and manner (turbulent, gentle) of the dispersion water and flocculated water are achieved. This adjustment of the inlet angles α and β of the dispersion water is performed at the same time as the adjustment of the distance of the orifice of the inlet tube for the flocculated water from the orifices of the inlet conduits for the dispersion water. Thus, adjustment of both factors has a substantial effect on how the flotation works out. The parameters affecting the operation of an apparatus for pressurized water flotation under given conditions having been determined, it is possible to partly use fixed settings under corresponding conditions, e.g. in determining directions of the inlet conduits for the dispersion water. Reacting of the flocculated water, i.e. controllable mixing with the dispersion water may be adjusted and/or intensified, for example, as illustrated in Fig. 3, by means of (a) guiding device(s) 19, such as (a) baffle(s), a deflection spiral, a separate mixing device or the like, positioned in the proximity of the orifice 11 of the inlet conduit for the water to be treated. The invention disclosed above has been described in more detail with reference to what is regarded as a preferred embodiment, used in connection with purification of waste waters, especially in treatment of waste waters in paper and chemical pulp industry. Thus, the invention is described above by means of one preferred embodiment only. Naturally, the intention is by no means to limit the scope of the invention. There are several other areas of application, e.g. purification of raw water and dressing of ore, and as is clear to a person skilled in the art, many alternative and optional constructions and modifications are possible within the inventive step defined in the appended claims.

Claims: CLAIMS 1. An apparatus for pressurized water flotation, in which the dispersion water and the water to be treated, e.g. flocculated water, are led into a reaction space (1), in which they encounter and react with each other, and which reaction space (1) is positioned substantially around an orifice (11) of the inlet conduit for the water to be treated, which orifice opens to the reaction space, said apparatus comprising a reaction space (1), in which the dispersion water and the water to be treated, e.g. flocculated water, encounter and react with each other, said reaction space being limited by the bottom (2) and casing (3) thereof, at least one inlet conduit (12) for the dispersion water, leading into the reaction space, at least one inlet conduit (8) for the water to be treated, e.g. flocculated water, leading into the reaction space, characterized in that the inlet conduit (8) for the water to be treated is constructed to be in connection with the reaction space (1) in such a way that the distance of the orifice (11) of the inlet conduit (8) from the bottom (2) of the reaction space can be adjusted by moving the inlet conduit (8) in the direction b of the mid-axis (13) of the reaction space, whereby the encountering location and manner (turbulent, gentle) of the dispersion water and the water to be treated, e.g. flocculated water, inside the reaction space may be made suitable for the process conditions in question. 2. An apparatus as recited in claim 1, characterized in that the reaction space (1) is located at least primarily below the actual flotation basin. 3. An apparatus as recited in claim 1 or claim 2, characterized in that the reaction space (1) is arranged to open directly to the flotation basin in such a way that the floes, which were formed by the reaction between the dispersion water and the water to be treated, e.g. flocculated water, and to which micro bubbles have been adhered (= combination dispersion water + flocculated water), rise freely and gently towards the surface of the flotation basin. 4. An apparatus as recited in claim 1, 2 or 3, characterized in that an apparatus for pressurized water flotation comprises at least two inlet conduits (8) for the dispersion water, the inlet conduit orifices (6), which open to the reaction space, being arranged in the casing (3). 5. An apparatus as recited in any of the claims 1 - 4, characterized in that a flotation apparatus further comprises - at least one conduit (14) leading from the reaction space (1) into the flotation basin, along which conduit the water to be treated, e.g. flocculated water, can be led into the actual flotation basin. 6. An apparatus as recited in claim 5, characterized in that the conduit (14) leading from the reaction space (1) into the flotation basin is a combination of (a) tubular and/or conic part(s) (15). 7. An apparatus as recited in any of the claims 5 or 6, characterized in that the apparatus for the pressurized water flotation is located below the actual flotation basin, and that a closing device is arranged in connection of the flange (7) in the conduit (14) leading from the reaction space (1) to the flotation basin, closing of which closing device prevents the liquid flow between the reaction space and flotation basin, whereby maintenance etc. is easily effected without the necessity to empty the flotation basin. 8. An apparatus as recited in any of the claims 1 - 7, characterized in that the angle α between the inlet direction of the dispersion water (arrow c) and the inlet direction of the water to be treated, e.g. flocculated water, (arrow d) is adjusted appropriately according to properties of the water to be treated and/or those of the dispersion water, being thus between 0 - 180°, preferably between 0 - 90° . 9. An apparatus as recited in claim 8, characterized in that the angle α is especially preferably about 70° - 90°. 10. An apparatus as recited in any of the claims 1 - 9, characterized in that the angle β between the inlet direction of the dispersion water (arrow c) and the direction being vertical relative to the inlet direction of the water to be treated, e.g. flocculated water, (arrow d) is adjusted appropriately according to properties of the water to be treated and/or those of the dispersion water, being thus 90° - 180°. 11. An apparatus as recited in claim 10, characterized in that the angle β is preferably about 90° - 135°. 12. An apparatus as recited in claim 11, characterized in that the angle β is especially preferably about 90° - 100°. 13. An apparatus as recited in any of the preceding claims, characterized in that (a) guiding device(s) (19), such as (a) baffle(s), a deflection spiral, a separate mixing device or the like has/have been arranged in the proximity of the orifice (11) of the inlet conduit for the water to be treated, by means of which member(s) the reaction between the water to be treated, e.g. flocculated water, with dispersion water is controlled and/or intensified. 14. An apparatus as recited in any of the preceding claims, characterized in that the reaction space is within a distance from the liquid surface of the flotation basin. 15. Use of an apparatus as recited in any of the preceding claims, especially for treatment of various waters, such as raw water, various process waters and waste waters in processes of paper and chemical pulp industry.

Inventors: RISSANEN SEPPO, WASENIUS CLAS-OTTO, RISSANEN, SEPPO, WASENIUS, CLAS-OTTO
Applicants: AHLSTROM AQUAFLOW OY, RISSANEN SEPPO, WASENIUS CLAS OTTO, RISSANEN, SEPPO, WASENIUS, CLAS-OTTO
Application year: 1996
Main classification: C02F1
IPC codes: B03D1, C02F1