WO2013110383A1

WO2013110383A1 - Flotation process with foam return

Info

Publication number: WO2013110383A1
Application number: PCT/EP2012/074299
Authority: WO
Inventors: Herbert Britz
Original assignee: Voith Patent Gmbh
Priority date: 2012-01-23
Filing date: 2012-12-04
Publication date: 2013-08-01
Also published as: DE102012200900A1; AT14542U1; DE202012013019U1; CN204276165U

Abstract

The invention relates to a method and a device for removing solids from an aqueous fibrous suspension (1) by means of gas bubbles, wherein a fibrous-suspension gas mixture (2) is supplied to form a flotation foam (3, 4) in at least two flotation chambers (11, 12, 13, 14, 15), wherein said flotation foam collects solids and is discharged from the flotation chamber (11, 12, 13, 14, 15), and wherein the fibrous suspension (1) released from the solids is discharged as a flow (6) from the respective flotation chamber (11, 12, 13, 14, 15). The aim is to improve flotation efficiency, particularly in respect of the de-inking process, such that the flotation foam (4) from at least one flotation chamber (12, 15) is sprayed at least partially into a different flotation chamber (11, 14) below the suspension level in such a way that one or more flotation foam jets (8) are perfused by the fibrous-suspension gas mixture (2).

Description

FLOTATION PROCESS WITH FOAM REFILL

The invention relates to a method for the removal of solids by means of gas bubbles from an aqueous pulp suspension in which in at least two flotation chambers by supplying a pulp suspension gas mixture flotation foam is formed, which collects solids and from the

Flotationskammer is discharged, and in which the freed from the solids pulp suspension is derived as a run from the respective flotation chamber.

The invention also relates to a device for removing solids by means of gas bubbles from an aqueous pulp suspension in at least one flotation chamber, which at least one of a stream of the

Pulp suspension flowed through mixing device for supplying at least one stream of gas and at least one derivative for the formed

Flotationsschaum with the impurities and at least one outlet for the purified pulp suspension has, in particular for carrying out the

Process.

By flotation a foam or scum is formed, which is the

contains and removes excreted substances. A typical application for such processes is the preparation of a recovered from printed waste paper suspension in which the ink particles are already detached from fibers, so that they can be floated.

In this case, a pulp density (amount of fiber based on the total amount) is often set in the pulp suspension, which is between 0.5% and 2%, preferably between 0.8% and 1.2%. The flotation process described here exploits the differences between paper pulp and solids to be separated, in particular from

undesirable particulate matter in the way that the pulp remains in the fiber suspension due to its rather hydrophilic character, while the pulp remains

addressed Störstoffteilchen are hydrophobic and therefore enter together with the air bubbles in the foam.

So not all solids are floated out, but fibers from

Impurities separated. The often used term "flotation deinking" is usually used not only for the removal of ink particles, but also

more generally used for the flotation of fine materials from pulp suspensions. Such substances are in addition to the printing inks more

Impurities, in particular adhesives, fine plastic particles and possibly also resins. Controlled flooding of mineral fillers ("ash") can also be one of the process objectives.

The state of the art regarding flotation processes for pulp suspensions is already very advanced. However, good flotation results are purchased at a relatively high cost, especially in terms of equipment, resources and energy.

The problem is the fulfillment of two requirements, namely the one hand

complete removal of all excreted substances, usually the

Contaminants and on the other hand the avoidance of losses, that is the unwanted excretion of substances that are to be used for the later produced product. In flotation practice, these two goals can only be achieved equally well with complex procedures.

In order to achieve optimal separation of flotable substances as well as a very low loss during flotation, multi-stage systems can be used. The pulp suspension usually flows through several to a flotation belonging Flotationskammern or flotation cells successively until in the run, so the accepts the required substance removal is reached. Since the overflow, so the flotation foam, which is formed in this flotation, still one

contains a considerable proportion of, for example, paper fibers, it is fed as an enema to another stage. Usually one then speaks of a first and second flotation or even of primary and secondary flotation. The pass, so the accept of the second flotation can the inlet of the first

Flotation be added again. There are also cases in which the second stage run is mixed with the pass, that is, the first stage accept. The flotation foam produced in the second stage can then be disposed of or, if it still contains too many fibers, fed to a third stage.

Flotation chambers or cells for the second flotation stage are usually similar or similar to those for the first stage, but their number is significantly smaller. Typical plants have five or six flotation cells in the primary stage and one or two in the secondary stage.

DE 101 25 978 C1 describes a two-stage flotation plant in which

Partial streams are withdrawn and added again at other points of the plant, in particular flotation foam is recycled to the fiber suspension of upstream flotation cells.

The object of the invention is to improve the efficiency of the flotation.

According to the invention, the object is achieved in that the flotation foam at least one flotation at least partially into another

Flotationskammer is injected below the suspension level so that one or more, preferably all flotation foam jets are traversed by the pulp suspension gas mixture.

Since the flotation foam jet with the pulp suspension gas mixture coincides, the impurities, in particular the printing inks can be floated very effectively from the flotation foam jet. This is done by utilizing the turbulence energy of the pulp suspension gas mixture which is introduced into this flotation chamber. Not only the exit energy of the pulp suspension gas mixture but also their gas, especially air bubbles are better utilized.

The reasons for the increase in efficiency are the physical reasons for increasing the probability of collision of the contaminants with and

Accumulation probability of the impurities at the gas bubbles of the

Pulp slurry gas mixture.

This effect can be further enhanced by the number of gas bubbles in the

Collision area is increased by the fact that the flotation foam is mixed with gas before injection into the pulp suspension. A strong turbulence results when the pulp suspension gas mixture is injected into the flotation chamber so that at least one

Flotationsschaumstrahl and cut at least one pulp suspension gas mixture jet in the pulp suspension.

However, in many cases it is sufficient if at least one flotation foam jet flows through the pulp suspension-gas mixture rising in the pulp suspension.

The freed from the solids pulp suspension is usually passed through a drain in the lower region, in particular at the bottom of the flotation of this. In order to avoid that parts of the flotation foam jet are thereby also removed and thus impair the quality of the pulp suspension, the flotation foam jet should enter the pulp suspension via the pulp suspension-gas mixture. According to the nature of the floats and the requirements of the Floated pulp suspension may already be sufficient if several flotation cans are connected in series to form a flotation stage and only the flotation foam of the first flotation chamber is removed as a reject. In this case, the flotation foam of the subsequent flotation chambers of this flotation stage is collected and returned to the first flotation chamber.

With a high degree of contamination or a high required purity, however, it may be advantageous if at least four, preferably at least five flotation chambers are connected in series to form a flotation stage and the flotation foam of the first and second flotation chambers is discharged as reject. The return of the flotation foam can then take place in the first or in the second or in both Flotationskammern.

With regard to the device is essential that at least one nozzle for supplying flotation foam is present in the pulp suspension whose

Nozzle opening is arranged below the suspension level but above the outlet opening of the mixing device. In this way, it is achieved that the flotation foam and the pulp suspension-gas mixture meet and the flotation foam does not reach the outlet for the purified pulp suspension.

To aid mixing, the height difference between the

Nozzle opening of the nozzle and the outlet opening of the mixing device between 1 and 500 mm, preferably between 20 and 300 mm.

Depending on the design, it may be advantageous if the flotation foam jet emanating from the nozzle opening of the nozzle and the pulp suspension / gas mixture jet emanating from the outlet opening of the mixing device are aligned in parallel or intersect.

In this case, the design effort can be reduced when the nozzle on the

Mixing device is attached. In addition, the turbulence on entry into the pulp suspension but also on the encounter with the pulp suspension gas mixture can be increased if the nozzle directs a flotation foam jet on a preferably horizontal baffle plate, which above the outlet opening of the

Mixing device is arranged and so divides the flotation foam jet on all sides. If the flotation foam is to be aerated prior to its injection, then in the direction of flow in front of the nozzle a mixing unit should be present which adds gas to the flotation foam. The invention will be explained in more detail below with reference to several exemplary embodiments.

In the attached drawing shows:

Figure 1: a basic system diagram with two flotation 1 1, 12;

FIG. 2 shows a schematic cross section through a flotation chamber 11, 14;

FIG. 3 shows a cross section through another flotation chamber 11, 14;

Figure 4: a flotation with five flotation 1 1, 12 and

Figure 5: a multi-stage flotation plant.

FIG. 1 shows a simple diagram with a flotation chamber 11, into which the pulp suspension 1 to be floated is fed. Here, the mixing with gas 9 is not shown here. The passage 6 of this chamber 1 1 is guided in a further flotation chamber 12. In both Flotationskammern 1 1 and 12 respectively Flotationsschaum 3 and 4 is formed. The flotation foam 4 of the second flotation chamber 12 is withdrawn as an overflow and guided into the first flotation chamber 1 1, to which purpose a partially degassing foam pump is used.

The passage 6 of the second flotation chamber 12 is either the accept of the flotation plant or it is still further floated. The overflow of the first flotation 1 1 is disposed of as a reject 10. Since the task of the first flotation chamber 1 1 in Figure 1 is slightly different than that the second flotation chamber 21, it may be useful to design the flotation chambers for these different purposes also different.

Usually, more than two flotation chambers 11, 12, 13, 14, 15 will be used, as shown in FIGS. 4 and 5.

FIG. 2 shows a section through a flotation cell having an oval cross-section containing the flotation chamber 11, 14, a shape which has proved to be particularly favorable.

The pulp suspension 1 is pumped into a mixing device 16 and mixed intensively with the gas 9, usually air to form gas bubbles. Advantageously, the mixing device 16 is arranged exmittig in the flotation chamber 1 1, 14 and immersed in the pulp suspension 1 to be ventilated. At the end of the mixing device 16 is a Umlenkdiffusor, which deflects the pulp suspension gas mixture 2 via a baffle body and into the flotation chamber 1 1, 14 passes.

The admixed gas 9 is sucked by means of injection and mixed with the pulp suspension 1. The gas 9 can be removed directly from the flotation chamber 11, 14 above the flotation foam 3.

The ascending flotation foam 3 absorbs the solids to be floated, in particular impurities such as ink particles, plastic particles or resins and flows via a discharge line 17 in the form of a preferably adjustable foam weir into a foam channel. It thus forms the overflow of this flotation chamber and is discharged as a reject 10. The pass 6, so the accept is taken in the lower part of the flotation 1 1, 14 via the outlet 18.

At the mixing device 16, two differently shaped and separately usable nozzles 19 are fixed by way of example, the nozzle openings 23 below the Suspension level but above the outlet opening of the mixing device 16 Flotationsschaum 4 from another flotation chamber 12,15 inject into the pulp suspension 1. It is essential that the flotation foam 4 is injected so that one or more or as here all Flotationsschaumstrahlen 8 are flowed through by the pulp suspension gas mixture 2. For this purpose, the height difference between the outlet opening 24 of the mixing device 16 and the nozzle opening 23 of the nozzles 19 is between 20 and 200 mm.

In the example shown here, the exiting pulp suspension gas mixture 2 flows through the flotation foam jets 8 at least during the ascent within the pulp suspension 1 of the flotation chamber 11, 14. The turbulences occurring in this case increase the efficiency of the flotation considerably.

While the left-hand nozzle 19 injects the flotation foam jets 8 into the pulp suspension 1 approximately horizontally and thus parallel to the pulp suspension gas mixture jet 2 of the deflection diffuser 1, this takes place at the right-hand nozzle 19 via a separate impact plate 20, which is formed by the deflection diffuser itself for the sake of simplicity the flotation foam jets 8 deflects on all sides into the pulp suspension 1. In the case of the right-hand nozzle 19, at least part of the beams 2, 8 can therefore also intersect.

In contrast, the nozzle 19 is not attached to the mixing device 16 in Figure 3, but horizontally spaced therefrom, but here too the height difference between the nozzle opening 23 of the nozzle 19 and the outlet opening 24 of the mixing device 16 is between 100 and 300 mm.

The nozzle opening 23 and the outlet opening 24 are aligned so that the flotation foam jets 8 and the pulp suspension gas mixture jets 2 intersect.

In order to increase the formation of gas bubbles, as in the case of the right-hand nozzle 19 in FIG. 2, a mixing unit 25 may be present in the flow direction in front of the nozzle 19, which mixes gas 9 with the flotation foam 4. As shown in FIG. 4, a flotation plant according to the invention can comprise a first flotation cell with the flotation chamber 11 and four further flotation cells each with a flotation chamber 12.

The pulp suspension 1 to be floated is pumped into the first flotation chamber 11 and gassed with a mixing device, not shown here, so that the flotation foam 3 is formed. The passage 6 of this flotation 1 1 1 is funded with a fuel pump 7 in the next flotation chamber 12, in turn, take place in the first fumigation and then the flotation.

These processes are repeated in the following Flotationskammern 12. The last pass 6 is the Acceptance of the plant.

The overflow of the flotation chambers 12 are collected in a common foam channel and introduced as a flotation foam 4 in the pulp suspension 1 of the first flotation chamber 1 1 as described. It can also z. B. branched off for control purposes, a part of the flotation foam 4 and in particular the feed to the first flotation 1 1 are mixed, which is indicated here by a dashed line with control valve.

The resulting in the first flotation 1 1 overflow is disposed of as a reject 10. Even if it is desired to float with multiple stages, the invention can be used to advantage. Thus, Figure 5 shows a flotation with standard operated five series flotation chambers 13, which serve as a first stage, and wherein the pulp suspension to be floated 1 of the first flotation chamber 13 is pumped.

The flotation foam 5 of the first stage is fed as pulp suspension 1 via a foam destroyer 21 and a foam tank 22 in the inlet of a first flotation chamber 14 of a second flotation. This second flotation stage also contains a second flotation chamber 15, which is charged with the passage 6 of the first flotation chamber 14 of this stage and in which the flotation foam 4 is formed. Again, the flotation foam 4 of the second Flotationskannnner 15 is recycled to the pulp suspension 1 of the first Flotationskannner 14 of this stage. The passage 6 of the second Flotationskannnner 15 enters the inlet to the first flotation and the overflow of the first Flotationskannnner 14 can be disposed of as a reject 10.

Claims

Claims 1. Method for removing solids by means of gas bubbles from an aqueous pulp suspension (1) in at least two

Flotationskammern (1 1, 12,13,14,15) by feeding a pulp suspension gas mixture (2) flotation foam (3,4,5) is formed, which collects solids and from the flotation chamber (1 1, 12,13, 14,15) is discharged, and in which the freed from the solids pulp suspension (1) as a passage (6) from the respective flotation (1 1, 12,13,14,15) is derived, characterized in that the flotation foam (4) at least one

Flotationskammer (12,15) is at least partially injected into another flotation chamber (1 1, 14) below the suspension level so that one or more flotation foam jets (8) from the pulp suspension gas mixture (2) are flowed through.

2. The method according to claim 1, characterized in that the

Flotation foam (4) is injected so that all flotation foam jets (8) from the pulp suspension gas mixture (2) are flowed through.

3. The method according to claim 1 or 2, characterized in that the

Pulp suspension gas mixture (2) is injected into the flotation chamber (1 1, 14), that at least one flotation foam jet (8) and

at least one pulp suspension gas mixture jet (2) in the

Cut pulp suspension (1).

4. The method according to any one of the preceding claims, characterized in that at least one flotation foam jet (8) in the pulp suspension (1) rising fibrous suspension gas mixture (2) is flowed through.

5. The method according to any one of the preceding claims, characterized in that the flotation foam jet (8) via the pulp suspension gas mixture (2) enters the pulp suspension (1).

6. The method according to any one of the preceding claims, characterized in that the flotation foam (4) before the injection into the pulp suspension (1) with gas (9) is mixed.

7. The method according to any one of the preceding claims, characterized in that a plurality of flotation chambers (1 1, 12,13,14,15) one behind the other to a

Flotationsstufe are connected together and the flotation foam (3) of the first flotation chamber (1 1, 14) is discharged as a reject (10).

8. The method according to any one of the preceding claims, characterized in that at least four, preferably at least five flotation chambers (1 1, 12) are interconnected in a row to a flotation and the

Flotationsschaum (3) of the first (1 1) and second flotation as reject (10) is discharged.

9. Apparatus for removing solids by means of gas bubbles from a

aqueous pulp suspension (1) in at least one flotation chamber

(1 1, 14), which at least one, by a stream of pulp suspension (1) flowed through mixing device (16) for supplying at least one stream of gas (9) and at least one derivative (17) for the formed

Flotationsschaum (3) with the impurities and at least one outlet (18) for the purified pulp suspension (1), in particular for carrying out the method according to any one of the preceding claims, characterized

characterized in that at least one nozzle (19) for supplying

Flotationsschaum (3) in the pulp suspension (1) is present, whose Nozzle opening (23) below the suspension level but above the

Outlet opening of the mixing device (16) is arranged.

10. Apparatus according to claim 9, characterized in that the

Height difference between the nozzle opening (23) of the nozzle (19) and the

Outlet opening (24) of the mixing device (16) between 1 and 500 mm, preferably between 20 and 300 mm.

1 1. Apparatus according to claim 9 or 10, characterized in that from the nozzle opening (23) of the nozzle (19) outgoing flotation foam jet (8) and of the outlet opening (24) of the mixing device (16) outgoing

Pulp suspension gas mixture jet (2) are aligned in parallel.

12. The device according to claim 9 or 10, characterized in that of the nozzle opening (23) of the nozzle (19) outgoing flotation foam jet (8) and of the outlet opening (24) of the mixing device (16) outgoing

Pulp suspension gas mixture jet (2) intersect.

13. Device according to one of claims 9 to 12, characterized in that the nozzle (19) is attached to the mixing device (16).

14. Device according to one of claims 9 to 13, characterized in that the nozzle (19) a Flotationsschaumstrahl (8) on a baffle plate (20), which is preferably arranged above the outlet opening of the mixing device (16).

15. Device according to one of claims 9 to 14, characterized in that in the flow direction in front of the nozzle (19) a mixing unit (25) is present, which the flotation foam (4) gas (9) admixed.