DE202012013019U1 - Foam recycling - Google Patents

Abstract

Device for removing solids with the aid of gas bubbles from an aqueous fibrous suspension (1) in at least one flotation chamber (11, 14), which has at least one mixing device (16) through which a stream of fibrous suspension (1) flows to supply at least one stream of gas (9) and has at least one discharge line (17) for the flotation foam (3) formed with the impurities and at least one outlet (18) for the cleaned fiber suspension (1), characterized in that at least one nozzle (19) for supplying Flotation foam (3) is present in the fiber suspension (1), the nozzle opening (23) of which is arranged below the suspension level but above the outlet opening of the mixing device (16).

Description

The invention relates to a method for the removal of solids by means of gas bubbles from an aqueous pulp suspension is formed in at least two flotation by feeding a pulp suspension gas mixture flotation foam, which collects solids and is discharged from the flotation, and in which the the solids freed 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 has at least one mixing device through which a stream of pulp suspension flows to supply at least one stream of gas and at least one discharge for the flotation foam formed has with the impurities and at least one outlet for the purified pulp suspension, in particular for carrying out the method.

By flotation a foam or scum is formed, which contains the excreted substances and dissipates. 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, in the pulp suspension often a pulp density (amount of fiber based on the total amount) is set, which is between 0.5% and 2%, preferably between 0.8% and 1.2%.

The flotation process described here exploits the differences between papermaking pulp and solids to be discharged, in particular unwanted contaminant particles such that the pulp remains in the fiber suspension due to its rather hydrophilic nature, while the impurities mentioned are hydrophobic and therefore enter the foam together with the air bubbles reach. Thus, not all solids are floated, but fibers separated from impurities. The commonly used term "flotation deinking" is typically used not only for the removal of ink particles, but more generally for the flotation of fine pulp suspension solids. Such substances are in addition to the printing inks mentioned further impurities, especially adhesive, 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 on the one hand the complete removal of all substances to be eliminated, usually the impurities and on the other hand the avoidance of losses, so the unwanted excretion of substances 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. In this case, the pulp suspension usually flows through a plurality of flotation chambers belonging to a flotation stage or flotation cells one after the other until they pass through, that is to say the accepts the required substance removal is achieved. Since the overflow, so the flotation foam, which is formed in this flotation, still contains a considerable proportion of, for example, paper fibers, it is passed as an inlet in 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 be added to the feed of the first flotation 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; be 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.

The DE 101 25 978 C1 describes a two-stage flotation plant, subtracted at the sub-streams and re-added at other points of the system, in particular flotation foam is returned 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, this object is achieved in that the flotation foam of at least one flotation chamber is at least partially injected into another flotation chamber below the suspension level such that one or more, preferably all flotation foam jets from Flow through the pulp suspension-gas mixture. Since the flotation foam jet coincides with the pulp suspension-gas mixture, 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 physical reasons for the increase in efficiency are the increase in the probability of collision of the contaminants with and the probability of accumulation of the impurities in the gas bubbles of the pulp suspension / gas mixture. This effect can be increased even further by increasing the number of gas bubbles in the collision area by mixing the flotation foam with gas before it is injected into the pulp suspension.

A strong turbulence results when the pulp suspension gas mixture is injected into the flotation chamber such that at least one flotation foam jet and at least one pulp suspension gas mixture jet intersect 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 floated and the requirements of the floated pulp suspension, it may already be sufficient if several flotation chambers are connected in series to form a flotation stage and only the flotation foam of the first flotation chamber is discharged 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, the 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.

In order to assist the mixing, the height difference between the nozzle opening of the nozzle and the outlet opening of the mixing device should be 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 if the nozzle is attached to the mixing device.

In addition, the turbulence when entering the pulp suspension but also at the meeting with the pulp suspension gas mixture can be increased if the nozzle directs a flotation foam jet on a preferably horizontal baffle plate, which is arranged above the outlet opening of the mixing device and thus 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:

1 : a basic plant scheme with two flotation chambers 11 . 12 ;

2 : a schematic cross section through a flotation chamber 11 . 14 ;

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

4 : a flotation stage with five flotation chambers 11 . 12 and

5 : a multistage flotation plant.

1 shows a simple scheme with a flotation chamber 11 into which the pulp suspension to be floated 1 is fed. Here is the mixing with gas 9 not shown. The pass 6 this chamber 11 gets into another flotation chamber 12 guided. In both flotation chambers 11 and 12 each flotation foam 3 respectively. 4 educated. The flotation foam 4 the second flotation chamber 12 is withdrawn as an overflow and into the first flotation chamber 11 led, which serves here a teilentgasende foam pump. The pass 6 the second flotation chamber 12 is either the acceptor of the flotation plant or it is still further floated. The overflow of the first flotation chamber 11 is called a reject 10 disposed of.

As the task of the first flotation chamber 11 at 1 something different than the second flotation chamber 21 , it may be useful to design the flotation chambers for these different purposes also different.

Usually you will get more than two flotation chambers 11 . 12 . 13 . 14 . 15 use as in 4 and 5 shown.

2 shows a section through a flotation chamber 11 . 14 containing flotation cell with oval cross-section, a form which has proved to be particularly favorable. The pulp suspension 1 gets into a mixing device 16 pumped in and with the gas 9 , usually mixed intensively with the formation of gas bubbles. Advantageously, the mixing device 16 exmittently in the flotation chamber 11 . 14 arranged and immersed in the pulp suspension to be ventilated 1 one. At the end of the mixing device 16 there is a diverting diffuser, which is the pulp suspension gas mixture 2 deflected over an impact body and into the flotation chamber 11 . 14 passes. The gas to be mixed 9 is sucked in by injection and with the pulp suspension 1 mixed. The gas 9 may be from the flotation chamber 11 . 14 above the flotation foam 3 be taken directly. The rising flotation foam 3 absorbs the solids to be floated, especially impurities such as ink particles, plastic particles or resins and flows through a drain 17 in the form of a preferably adjustable foam weir in a foam channel. It thus forms the overflow of this flotation chamber and is considered a reject 10 discharged. The pass 6 So the accept will be in the lower part of the flotation chamber 11 . 14 over the spout 18 decreased.

At the mixing device 16 are exemplary two differently shaped and separately usable nozzles 19 attached, their nozzle openings 23 below the suspension level but above the outlet opening of the mixing device 16 flotation 4 from another flotation chamber 12 . 15 in the pulp suspension 1 inject. It is essential that the flotation foam 4 is injected so that one or more or as here all flotation foam jets 8th from the pulp suspension gas mixture 2 be flowed through. For this purpose, the height difference between the outlet opening 24 the mixing device 16 and the nozzle opening 23 the nozzles 19 between 20 and 200 mm. In the example shown here flows through the exiting pulp suspension gas mixture 2 at least when ascending within the pulp suspension 1 the flotation chamber 11 . 14 the flotation foam jets 8th , The occurring. Turbulence significantly increases the efficiency of the flotation.

While the left nozzle 19 the flotation foam jets 8th approximately horizontally and thus parallel to the pulp suspension gas mixture jet 2 of the deflection diffuser into the pulp suspension 1 dusts, this is done at the right nozzle 19 over a separate baffle plate 20 , which is formed by the Umlenkdiffusor itself for simplicity and the Flotationsschaumstrahlen 8th all sides in the pulp suspension 1 deflects. At the right nozzle 19 Thus, at least a part of the rays can 2 . 8th to cut. In contrast, the nozzle is 19 at 3 not at the mixing device 16 attached, but horizontally spaced therefrom, but here too, the height difference between the nozzle opening 23 the nozzle 19 and the exit opening 24 the mixing device 16 between 100 and 300 mm. The nozzle opening 23 and the exit opening 24 are aligned so that the flotation foam jets 8th and the pulp suspension gas mixture jets 2 to cut. To increase the formation of gas bubbles, as with the right nozzle 19 in 2 indicated, in the flow direction in front of the nozzle 19 a mixing unit 25 be present, which the flotation foam 4 gas 9 is admixed.

A flotation plant according to the invention can, as in 4 shown, a first flotation cell with the flotation chamber 11 and four other flotation cells, each with a flotation chamber 12 include. The fibrous suspension to be floated 1 gets into the first flotation chamber 11 pumped and fumigated with a mixing device, not shown here, so that the flotation foam 3 forms. The pass 6 this flotation chamber 11 is with a fuel pump 7 into the next flotation chamber 12 promoted, in which first the fumigation and then the flotation take place. These processes are repeated at the following Flotators 12 , The last run 6 is the accepter of the plant. The overflow of the flotation chambers 12 are collected in a common foam channel and as flotation foam 4 in the pulp suspension 1 the first flotation chamber 11 introduced as described. It can also z. B. for regulatory purposes, a part of the flotation foam 4 branched off and in particular the inlet to the first flotation chamber 11 be mixed, which is indicated here by a dashed line with control valve. The one in the first flotation chamber 11 accumulating overflow is called a reject 10 disposed of.

Even if it is desired to float with multiple stages, the invention can be used to advantage. That's how it shows 5 a flotation plant with standard five flotation chambers connected in series 13 , which serve as the first stage, and wherein the pulp suspension to be floated 1 the first flotation chamber 13 is pumped. The flotation foam 5 the first stage is called pulp suspension 1 over a foam destroyer 21 and a foam tank 22 into the inlet of a first flotation chamber 14 led a second flotation. This second flotation stage also contains a second flotation chamber 15 which with the pass 6 the first flotation chamber 14 this stage is fed and in which the flotation foam 4 is formed.

Again, the flotation foam 4 the second flotation chamber 15 in the pulp suspension 1 the first flotation chamber 14 attributed to this stage. The pass 6 the second flotation chamber 15 enters the inlet to the first flotation stage and the overflow of the first flotation chamber 14 can as a reject 10 be disposed of.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10125978 C1 [0007]

Claims (7)

Device for removing solids by means of gas bubbles from an aqueous pulp suspension ( 1 ) in at least one flotation chamber ( 11 . 14 ) containing at least one of a stream of pulp suspension ( 1 ) through-flow mixing device ( 16 ) for supplying at least one stream of gas ( 9 ) and at least one derivative ( 17 ) for the formed flotation foam ( 3 ) with the impurities and at least one outlet ( 18 ) for the purified pulp suspension ( 1 ), characterized in that at least one nozzle ( 19 ) for the supply of flotation foam ( 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. Apparatus according to claim 1, characterized in that the height difference between the nozzle opening ( 23 ) of the nozzle ( 19 ) and the outlet ( 24 ) of the mixing device ( 16 ) is between 1 and 500 mm, preferably between 20 and 300 mm. Apparatus according to claim 1 or 2, characterized in that the of the nozzle opening ( 23 ) of the nozzle ( 19 ) outgoing flotation foam jet ( 8th ) and of the outlet ( 24 ) of the mixing device ( 16 ) outgoing pulp suspension gas mixture jet ( 2 ) are aligned in parallel. Apparatus according to claim 1 or 2, characterized in that the of the nozzle opening ( 23 ) of the nozzle ( 19 ) outgoing flotation foam jet ( 8th ) and of the outlet ( 24 ) of the mixing device ( 16 ) outgoing pulp suspension gas mixture jet ( 2 ) intersect. Device according to one of claims 1 to 4, characterized in that the nozzle ( 19 ) at the mixing device ( 16 ) is attached. Device according to one of claims 1 to 5, characterized in that the nozzle ( 19 ) a flotation foam jet ( 8th ) on a baffle plate ( 20 ), which preferably above the outlet opening of the mixing device ( 16 ) is arranged. Device according to one of claims 1 to 6, characterized in that in the flow direction in front of the nozzle ( 19 ) a mixing unit ( 25 ) present to the flotation foam ( 4 ) Gas ( 9 ).

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