MXPA01001290A - Process and device for aerating dispersions - Google Patents

Abstract

The present discloses a device and process for aerating dispersions, particularly for flotation of pulp suspensions, in a de-inking process. The process includes at least two stages, where each stage has a separate liquid circulating system which sucks in the gas or air and mixes it with the liquid. The device has at least two flotation cells, with each of the cells having a separate injector and a separate circulation system including a pump.

Description

* w PROCESS AND DEVICE TO AIR DISPERSIONS FIELD OF THE INVENTION The invention relates to a process for devise dispersions, particularly for the flotation of, for example, pulp suspensions, in at least two stages. In addition, the invention relates to a device for implementing the process.

BACKGROUND OF THE INVENTION Flotation dispersion is a mechanical process for removing impurities and ink particles, from pulp suspensions produced particularly in the treatment of residual paper. Here the solids Hydrophobes, such as ink particles or sticky substances, are brought into contact with gas bubbles in a suitable flotation cell. Adhered solids are carried to the surface of the liquid along with the bubbles and can be removed as foam. The pulp is downloaded with acceptance due to its hydrophilic nature. To generate the gas bubbles, one of the devices used successfully for this purpose is the self-priming injector. Since the process of selective removal of printing ink from pulp suspensions only operates with low efficiency, multi-stage processes are normally used, as is known, for example, from DE 41 16 916 C2. Here the entire pulp suspension is fed through injectors to create a bubble surface large enough for successful flotation. The acceptance of each stage is used as a feed for the next stage for the admission of the gas flow by the injectors. The foam of all stages is collected and can then be floated once again in a second stage to recycle the fibers. The advantage of the processes of this type is that they are susceptible to fluctuations in production, they have no means to adapt the air content to the specific application and they require a greater treatment of the measuring equipment and process to carry out the secondary flotation stage .

BRIEF DESCRIPTION OF THE INVENTION The invention, therefore, is based on the task of designing an energy-efficient, multi-stage process for the flotation of the pulp suspension which is insensitive to fluctuations in production and can be easily adapted for different applications and compositions of the raw material.

The invention in this way is characterized in that each stage has a separate circulation system or liquid which sucks the gas or air and mixes it with the liquid. Because the feed and jet stream of the injector used to suck the gas do not interact, an additional degree of freedom is formed which makes it possible to set the air content independently of the feed rate. As a result the plant can be adapted very easily to changes in the flows of the feed volume. A further advantageous development 1 of the invention is characterized in that the air content is controlled independently of the feed rate. With this control installation the air content can easily be adapted to changes in the power conditions. A favorable configuration of the invention is characterized in that the speed of air supply is set according to the properties of the pulp suspension. In this way a successful optimal fluctuation can be obtained for each individual application. A further favorable development of the invention is characterized in that different amounts of air are applied to the individual stages. In this way, the special raw materials can also be made to float efficiently without influencing the raw material fed and in this way, the yield. An advantageous configuration of the invention is characterized by the suspension being fed to the next cell / stage in the lower section of the cell / stage. Feeding the suspension in the lower section of the cell / stage prevents the impurities consolidated in the foam from being discharged with the accepted fraction. A further favorable development of the invention is characterized in that at least one secondary stage is provided, which is operated with the overflow of the primary stage whose accepted fraction is fed to the first primary stage. As a result, low losses of fiber can be obtained in the flotation of the pulp suspensions, where the secondary cells can have the same design as the primary cells. The invention also relates to a device for aerating dispersions, particularly a flotation device, for example to de-press pulp suspensions, with at least two flotation cells, characterized in that a separate injector is provided in each stage and that it is connected to an assigned pump to form a liquid circulation system. This provides favorable means to exclude any interaction between the feed and the propellant jet, thereby forming an additional degree of freedom. A further favorable development of the invention is characterized in that openings are provided in the walls dividing the cell at floor level. This arrangement allows the dispersion to flow to the next cell in each case, but prevents the foam from being carried along with this. An advantageous configuration of the invention is characterized in that overflow channels are provided in each cell and because they are connected to a collection tank via a main collection pipe. In this way the foam of each of the primary cells can be collected and discharged or subjected to additional treatment all together. A favorable configuration of the invention is characterized by at least one secondary float cell, operated with the overflow of the primary cells and whose accepted fraction is fed to the first primary cell, being provided and by this secondary float cell having a connection to the collection tank. Using a secondary flotation cell upstream of the primary flotation, fiber losses can be further reduced. A further favorable development of the invention is characterized in that at least two cells are arranged in a tower. Such an arrangement allows an even better separation of the impurities of the accepted fraction. A further advantageous development of the invention is characterized in that at least three cells are combined to form a circular flotation plant. With this arrangement, a good separation of the impurities can be achieved with a low space requirement. A further favorable development of the invention is characterized in that several injectors are provided in each cell. If several injectors are provided, particularly at different points within a cell, this allows a higher performance on the one hand, and on the other allows a better distribution of the suspension and bubbles of the liquid.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention is described in examples and with reference to the drawings, wherein Figure 1 shows a diagram of the process, Figure 2 a further variant of the process according to the invention, Figure 3 a design of a flotation cell according to the invention, Figure 4 a design of a further variant of the invention, and Figure 5 a possible cross-section through the plant illustrated in Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES OF THE INVENTION Figure 1 provides a diagram of a flotation plant with four primary cells Pl, P2, P3, P4 and two secondary cells Si, S2. The feed of the pulp suspension Z enters the first primary cell Pl at a suitable point. The bubbles are generated using the internal circulation system of cell 1, which does not interact with the feed, by the injector 2 which sucks air L and mixes it in the suspension. The entire flotation plant is filled to a large extent with suspension, on whose surface O a foam is formed, which contains as much as possible of the substance and ink particles removed by flotation. After the ink and impurities have been removed from the pulp in the first primary cell Pl, the accepted fraction is moved over, toward the second primary cell P2 through a hole 5 in the dividing wall 10 at floor level. There and in other primary cells, the suspension is treated in the same way with projectors that generate bubbles operated by the internal circulation systems of the cell and is discharged at the end of the plant as the accepted fraction G. The foam collected from all the primary cells Pl a P4 can be drained through a foam channel 3 to a tank 4. From this interim tank 4 the overflow, which the foam has been largely removed in the average time, is fed to the secondary cells S2. The gasification takes place here once again using the internal circulation system of cell ß. The accepted fraction of the secondary cell S2 is transferred to the secondary cell SI in the opening at the level of the floor 7. After gasification by the circulation system 8, the foam of the secondary cells can be discharged as overflow Ü. The accepted fraction of the secondary cell SI is transferred to the first primary cell Pl through the hole in the floor 9 in the dividing wall 11. In Figure 2 there is only one secondary SI cell and the Z feed is partially used as a jet propellant for the injector 3. The remaining partial stream of the feed enters the first primary cell Pl at a suitable point. The accepted fraction of the individual cells passes through the openings of the opening 5 in the partition walls 10 to the next primary cell P2, P3, P, P5 in each case and can then be discharged as the accepted fraction G. To avoid that the air L is sucked with the circulation system of the internal injector of the cell, a safety device 13 is used in each cell and the suspension for the injector propelling jet is not discharged until the safety device has passed. The foam collected from the primary cells Pl to P5 is carried along a foam channel 3 to an intermediate tank 4, from which the overflow - with the foam removed - is brought to the secondary cell SI. The bubbles are generated from a circulation system 8 by means of an injector. The accepted fraction of the secondary cell SI flows through the opening 9 to the primary cell Pl and the foam of the secondary cell SI is discharged as an overflow U. Figure 3 shows an arrangement of two primary cells Pl and P2 in a tower to make partial use of the countercurrent principle also to obtain a better separating effect due to the height of the liquid level. Z feed is carried to the primary cell Pl with the injector, to which air is administered by a compressor 15 if the level of suspension is very high. The accepted fraction is transferred to the second primary cell P2 through the opening 5 in the dividing wall 10 between the two cells. The bubbles in the second primary cell P2 are generated by the circulation system of the suspension 16 using the compressor 17. The accepted fraction G and the overflow U (foam) collected can be discharged. Figure 4 contains a design of the invention with four primary cells, designed as a circular flotation plant. The ink and impurities in the feed Z are floated in the first primary cell Pl with bubbles from the gasification devices (nozzles 2). The flows of accepted fraction through the openings 5 in the lower section of the partition walls 10 to the next primary cell P2, P3 or P4 in each case can be discharged as accepted fraction G of the fourth primary cell P4 after four stages of flotation. The overflow of all the cells is collected in the foam channel 3 and discharged as overflow Ü. Figure 5 shows a possible cross-section through a flotation plant according to Figures 1 and 2, respectively. The disk-shaped flotation cell with the lid 17 filled to a large extent with the suspension. The bubbles are generated by the aeration devices (injector 2) and transport the ink particles and impurities towards the surface O of the liquid, where they can be drained as foam along the foam channel 3. The accepted fraction of this cell enters to the next cell through the opening 5 in the dividing wall 10 and is brought into contact with gas bubbles again there. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (13)

1. CLAIMS 1. A process for aerating dispersions, particularly by flotation of, for example, pulp suspensions in the deinking process in at least two stages, characterized in that each stage has a separate liquid circulation system which sucks the gas or air and mix this with the liquid.
2. 2. The process according to claim 1, characterized in that the air content is controlled independently of the feed rate.
3. 3. The process according to claim 1 or 2, characterized in that the air feed speed is set appropriate according to the properties of the pulp suspension. .
4. The process according to any of claims 1 to 3, characterized in that different amounts of gas or air are applied to the individual stages.
5. 5. The process of compliance with one of the Claims 1 to 4, characterized in that the suspension is fed to the next cell / stage in the lower section of the cell / stage.
6. 6. The process according to one of Claims 1 to 5, characterized in that at least one secondary stage is provided, which is operated with the overflow of the primary stage and whose accepted fraction is fed to the first primary stage. A device for aerating dispersions, particularly a flotation device, for example, for de-inking ink suspensions, with at least two flotation cells, characterized in that a separate injector is provided at each stage (Pl, P2, P3, P4, P5) and that it is connected to an assigned pump to form a liquid circulation system. The device according to claim 7, characterized in that openings are provided in the cell (Pl, P2, P3, P4) that divide the walls at floor level. The device according to one of Claims 7 or 8, characterized in that overflow channels are provided in each cell and that they are connected to a collection tank via a main collection pipe. The device according to Claim 9, characterized in that at least one secondary float cell (SI, S2) operated with the overflow of the primary cells (Pl, P2, P3, P4) and whose accepted fraction is fed to the first primary cell (Pl), which is provided and because this primary flotation cell (SI, S2) has a connection to the collection tank. The device according to Claim 7 or 8, characterized in that at least two cells (Pl, P2) are arranged in a tower. The device according to any of Claims 7 or 9, characterized in that at least three cells (Pl, P2, P3) are combined to form a circular flotation plant. The device according to Claim 12, characterized in that several injectors are provided in each cell (Pl, P2, P3, P4).