FI59028C - OVERFLOWER FOR OVERFLOWER - Google Patents

Description

R3CT ΓΒ1 «« ANNOUNCEMENT ς ΟΠΟΟ

Ma IBJ <11) UTLÄGeNINGSSKRIFT ^ ^ ^ 8 C Patent Ny'jnnctty 10 C6 1921 (4¾ Patent raeddelnt (51) Kv.ik? /Int.ci.3 B 01 D 21/01, C 02 P 1/52 (21 ) P »t * nttlh« Jnmoi - PatcnUnsekning 780U22 (22) Hakamiipltvl - Ansttknlngtdag 09.02.78 * * (23) Alkupllvl — Glhl | h «ttd» g 09.02.78 (41) Tullut | external «Bllvlt offantlig 10.08.79 _ * (44) Date of issue and date of issue - ov np fti ratani- och rasiatarstyralaan 'AniÄkan Utlagd oeh utl.akrlftan publlcarad ^' * u ± (32) (33) (31) Patch requested atuolkaua — Baglrd prlorit (71) Oy Partek Ab, 21600 Pargas, Finland-Finland (FI) (72) Ulf Nylund, Pargas, Finland-Finland (Fl) 7M Berggren Oy Ab (5M Flocculation method and apparatus for performing it - Förfarande för flockning och anordning för dess the embodiment

The invention relates to the method set out in the preamble of claim 1 and to the device according to claim 4 for carrying out this method, and it is an object of the invention to provide a method and apparatus which is considerably accelerated and provides larger and more cohesive flocs than prior flocculation methods.

When separating solid particles from suspensions, the separation is enhanced by the size of the particles to be separated. For this reason, natural agglomeration or artificially induced agglomeration is highly desirable. This is true regardless of the separation method. In separation processes where no natural agglomeration occurs or where it occurs very difficult, agglomeration must be initiated and maintained artificially. Nk. flocculation must be effected in suspension. In most cases, this is achieved by adding suitable chemicals to the process, which, by adhering to the individual particles, bind them together into larger agglomerates. However, the forces holding the flocs together 59028 are relatively weak. For this reason, the addition of chemicals and the mixing of the suspension in order to achieve the greatest possible, uniform contact between the chemicals, the individual particles and the formed flocs must be carried out very carefully and accurately. The addition of chemicals usually occurs in a limited portion of the suspension. Suitable mixers are used for mixing. This usually takes place in a separate container.

If the formed flocs are separated by flotation, air or another suitable gas is also introduced into the suspension already at this stage. Once the suspension is homogenized, the suspension is transferred to the next step, where the actual Flocculation takes place. Also in this case, flocculation is stimulated and maintained by mechanical stirrers. When flotation is used as a separation method, air or gas can also be added to the suspension during the flocculation step. In particular, at this stage, the design of the mixers and the power used are determined by said precaution. Once flocculation has reached the desired degree, final separation takes place. The methods currently used in flocculation result in an unsatisfactorily long waiting time and also a lower degree of separation than desired due to said power limitations and the mechanical design of the mixer.

It is an object of the present invention to provide a method and apparatus for shortening flocculation time and at the same time achieving larger and more cohesive flocs. This is possible if the mechanical stirrers are designed in such a way that they do not affect the flakes formed in a disintegrating manner. Such a method and device are provided according to the invention and their characteristic features are set out in claims 1 and 4.

Methods and devices of this kind have been discussed previously in the following publications: INSKON's handout "Continuing Education Days in Water Supply Technology 1970", Presentation III (M. Tikka), "Publication 23-70", with 3,59028 votes on page 4, discusses the durability of formed flocs. However, it only deals with the breaking effect of water, not the corresponding effect of the wings. On the same page we talk about the details of the structure of the wings, mainly the speed of rotation of the wings and the swirling motion of water caused by it.

U.S. Pat. No. 3,645,346, at the end of column 2 and at the beginning of column 3, discloses that water to be treated, which is generally sewage, can be given a rotational motion of different intensity in two different zones by means of wings with different surface areas. The contact between the wings and the formed flocs is not discussed in said publication.

J AWWA, 65 (1973), page 422, right column, second paragraph, and J AWWA, 59 (1967), page 1258, second column, discuss the need to increase agitation to speed up flocculation, but at the same time state that the increase in rotation has its limits, which depends on the limited shear strength of the flake relative to the velocity gradient. The mechanical effect of the mixing members on the flocs and their durability is not addressed.

No known technique pays attention to the effect of the effective wing size of the mixing members on the formation of flakes and their cohesiveness.

The method and device according to the invention will now be described in more detail with reference to the accompanying figures, in which: Figures 1, 2, 3 and 4 show different embodiments of a flocculation device according to the invention in vertical cross-sections.

In the figures, the corresponding parts are denoted by the same reference numerals. The homogenization and flocculation vessel is denoted by reference numeral 1, the pre-homogenization device feeding the suspension into the vessel is denoted by number 2 and the outlet opening for the flocculated suspension from the vessel is denoted by 3. The mixer is denoted by number 4. 6, which breaks down the flow geometry of the suspension and provides a droplet-like state of the suspension. The upper surface of the suspension in the flocculation vessel is denoted by the number 7 and the flocculated suspension itself is denoted by the number 8. The suspension to be purified to be fed to the vessel is denoted by the number 9 the partition is marked with the number 11.

The method according to the invention and the device for carrying it out are described in more detail below.

The suspension 9 to be cleaned is passed through a pre-homogenizer 2, and chemicals intended to cause flocculation are dispensed into the suspension at the front end thereof. The pre-homogenizer is preferably provided with turbulence, as a result of which the first contact between the added chemicals and the individual particles of the suspension takes place in its pipe part 2 without the event being disturbed by mechanical breaking. The feed of the suspension through the pre-homogenizer 2 can also be laminar. At the outlet end of the pre-homogenization tube 2, the flow geometry of the suspension decomposes under the action of the stopper 6, creating a droplet-like state which enhances homogenization and contact formation in the Kemi-potassium suspension mixture. The stop 6 is preferably in the form of a circular plate arranged transversely to the outlet end of the pre-homogenizer 2. The plate 6 in the embodiments according to Figures 1, 2 and 4 may be either fixed or attached to the end of the mobile mixer 4 to move together with it. The plate 6 may also be provided with vanes formed on the lower surface of the plate to provide effective vortexing. From here, the liquid flow is transferred to the homogenization and flocculation vessel 1 below, which has a motor-driven stirrer 4 below the liquid surface 7 formed in the vessel. In vessel 1, the actual and main flocculation takes place.

5 59028

According to the invention, the design of the mixer 4 is very special. The basic idea is that flocculation must take place in an environment that is as calm as possible, but at the same time so mobile that the flocs that form touch each other and grow into the largest possible flocs. An attempt must be made to preserve the size of the flakes formed as far as possible, i.e. the breaking effect of the mixer must be eliminated as effectively as possible. According to the invention, this can be achieved if the contact surface between the agitator 4 and the flocculant suspension consists of vane members 5 which, when fitted to the agitator shaft, gradually decrease in size in the direction in which the growth of the floc takes place. The part of the mixer 4 which is located in the zone with the lowest flocculant concentration thus has the most active wing members 5, i.e. generally the largest wing members and vice versa. In this connection, it should be noted that this is the effective surface area of the wings, i.e. the area which causes the flakes in the suspension to move. The area bounded by the contours does not have to be the same as the effective area. For example, the surface of the wing may have openings that reduce the effective surface area of the wings.

When the flocs formed have a higher density than the flocs naturally accumulating with the suspension liquid towards the bottom of the flocculation vessel 1. The blades 5 of the mixer then have a gradually decreasing surface area towards the bottom, as shown in Figures 1 and 2. The removal of the fluff-rich suspension from the vessel 1 then takes place from the bottom of the vessel. This embodiment according to the invention is suitable when the separation of the flocs takes place by sedimentation or other separation method based on the gravity of the pulp. The dispersing device 6 at the end of the pre-homogenization tube 2 supplying the suspension can be located above or below the liquid surface 7. In the former case, air enters the flocculation vessel with the suspension stream, whereas instead this is avoided in the latter case.

6 59028

When the flocs formed have a lower density than the flocs which accumulate with the suspension liquid, they naturally accumulate towards the liquid surface 7 due to the lifting effect of the liquid. In this case, the wing members 5 have a decreasing surface area towards the liquid surface, as shown in Figures 3 and 4. The removal of the fluff-rich suspension then takes place from the top of the container. This embodiment of the invention is suitable when the separation of the flocs afterwards takes place by flotation. In this case, additional air is preferably introduced into the flocculation vessel together with the suspension to promote flotation. The suspension is then fed through the bottom of the vessel, as shown in Fig. 4, or through the upper part of the second part of the flocculation vessel, from which the suspension flows downwards and under the partition 11 below the liquid surface of the part; as shown in Fig. 3. In this case, the suspension flow dispersing device 6 can be arranged either above the liquid surface, as shown in Fig. 3, or below the liquid surface, as shown by the dotted liquid surface in Fig. 3. In the former case, more air enters the vessel together with the suspension stream, which in particular in the case of flotation is preferred. When the disperser is located below the liquid surface, no air enters the vessel with the suspension stream. In this case, the gas or air required to effect flotation is supplied separately, preferably via the bottom of the flocculation vessel.

Depending on the type of suspension and processes, the mixer 4 can be arranged in the vessel 1 in a horizontal or oblique position.

The movement of the mixer is mechanically infinitely adjustable and its movement can be either parallel or reciprocating. The speed can be adjusted manually or with the help of a flow rate indicator.

Following the flocculation process, the flocs are separated by previously known methods. When performing experiments

Claims (6)

A method of effecting flocculation in treating a suspension to be purified by sedimentation, flotation or the like, in which the suspension (9), in which flocculant is involved, is directed to a homogenizing and flocculation vessel (1), characterized by the suspension being brought into a flock-promoting movement by means of a mechanical mixer (4), whose mixing means (5) are designed to effect a stronger movement in the zone of the vessel where the flocks are still small and a continuously decreasing movement in the direction towards the zone of the vessel where the flocks are at their greatest, to protect the formed flocks from mechanical disintegration, and to remove the flocculated suspension in a known manner from the latter zone for separating the flocks. 9 59028 Method according to claim 1, characterized in that the continuously changing movement of the suspension is achieved by means of mixing elements (5), the vanes having a large effective surface in the zone where the flocculation is at its initial stage and a small effective area in the zone where the flock is in its final stage, while the effective area of the blades has an intermediate size in intermediate zone r. Method according to Claim 1 or 2, characterized in that by means of a mechanical mixer (4), an adjustable, continuously rotating rectified or forward and eating directed movement of the suspension is achieved. Apparatus for effecting flocculation in treating a suspension (9) to be purified by sedimentation, flotation or the like, comprising a homogenization and flocculation vessel (1), to which the suspension is measured and from which it is removed after the flocculation. in that a mixer (4) is provided in the vessel (1), whose mixing means (5) are provided with blades, the effective area of which is large in the zone where the flock is at its initial stage and small in the zone where the flock is in the its final stage, while the effective surface of the blades has a medium size in intermediate zones, such that the mixing means (5) provide a stronger movement in the zone where the flocks are still small and a - continuously decreasing movement towards the zone where the flocks are greatest. Device according to claim 4, characterized in that the mixer (4) is arranged in a vertical position in the homogenizing and flocculation vessel. 6. Device according to claim 4, characterized in that the mixer (4) is arranged obliquely in the homogenization and flocculation vessel.