MXPA01001285A - Process and device for aerating dispersions - Google Patents

Abstract

Here is presented a device and process for aerating dispersions, particularly for flotation of pulp suspensions, in a de-inking process where the pulp suspension containing dirt particles is sprayed into a tank together with air. The air is injected at a minimum of two successive points and mixed with the suspension.

Description

PROCESS AND DEVICE TO AIR DISPERSIONS FIELD OF THE INVENTION The invention relates to a process for aerating dispersions, particularly for the flotation of slurries of pulp in the deinking process, where the pulp suspension containing dirty particles is sprayed in a tank together with gas, particularly air. In addition, the invention relates to a device for implementing the process.

BACKGROUND OF THE INVENTION Deinking by flotation is a mechanical process for removing impurities and ink particles from pulp suspensions produced particularly in the treatment of waste paper. This process requires the generation of gas bubbles in the amount and distribution of appropriate size. Hydrophobic substances or substances to which ampholytes were added to make them hydrophobic, such as ink particles or sticky substances, are brought to the liquid surface by the gas bubbles that adhere to them and can be removed from the surface as foam. . This is known as selective flotation because the pulp is already discharged with acceptance due to its hydrophilic nature. Processes of this type are known in numerous geometric modifications, for example from DE 41 16 916 C2 or EP 0 211 834 Bl, and have reached a high technical standard. In addition, it has also proved successful to use self-priming injectors to generate gas bubbles and mix those with the pulp suspension. These injectors basically comprise a propeller jet nozzle, a mixing tube or impulse exchange, and a diffuser. Here, the liquid flow emerging from the jet stream nozzle according to the open jet principle generates a sub-pressure. As a result, the gas is sucked and mixed with the liquid as a result of the impulse exchange between the liquid and the gas in the mixing tube. The diffuser outlet used to recover energy forms a dispersion of pulp and bubbles. The use of known processes and injectors, however, has shown several disadvantages in the selective flowering of pulp suspensions. The suction effect of the known injectors in operation with pulp suspensions is very weak and the bubble size distribution generated by the known injector does not have the optimum design to satisfy the requirements of the selective flotation.

BRIEF DESCRIPTION OF THE INVENTION The invention, therefore, is based on the task of designing an injector with a greater suction effect and an optimal bubble size distribution for use in deinking by flotation. The process according to the invention is thus characterized by the gas, particularly air which is being sucked by the effect of the injector at a minimum of two successive points and mixed with the suspension. Because the suction takes place in stages, the pulp can be loosened by the gas in the first stage, thus achieving a better dispersion of the free jet in the second stage, resulting in a suction effect and the generation of bubbles correspondingly improved, particularly with a reduction in the portion of fine bubbles to avoid loosening solids. In a further advantageous development of the invention, a portion of 20 to 95% of the entire portion of gas, particularly air, sucked is consumed in the first stage. Since the admission of the quantity of gas, particularly air, is divided into several suction points, an even greater mixing of the suspension with the gas is obtained. This allows you to set an appropriate, specific bubble size.

A favorable configuration of the invention is characterized by the flow of gas and liquid obtained by the suction and the mixture being transferred in a free jet after the first stage. As a result, the use of the kinetic energy of the jet, in particular, can be improved for the renewed addition of gas. A further favorable development of the invention is characterized by the gas or air charge of the pulp suspension directly after being surrounded in an amount of about 50-150%. The invention also refers to a device for aerating dispersions, particularly a flotation device for de-indenting slurries of pulp with an injector, characterized by at least two suction points which are arranged in series in the flow direction. Because the suction takes place in stages, the pulp can be loosened by the gas in the first stage, thus achieving a better dispersion of the free jet in the second stage, resulting in a corresponding suction and bubble generation effect improved, particularly with a reduction in the portion of fine bubbles to avoid loosening solids. A further favorable development of the invention is characterized by the injection channel extending after the first suction point. In this way, the kinetic energy of the jet can be object of a better use in a favorable way. A further advantageous development of the invention is characterized by a panel which is mounted at the end of the injector channel through the flow direction.

This panel acts as a radial diffuser to recover energy from the liquid jet. An advantageous configuration of the invention is characterized by the panel which is mounted on a plane inclined towards the direction of flow. A further favorable development of the invention is characterized by the panel containing interiors for directed flow guidance. For better results, the injector can also be mounted in any desired position in the flotation trap. A favorable configuration of the invention is characterized by a minimum of two injectors which are mounted in parallel in the form of a group of injectors.

With this design it is also possible to handle large yields accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention is described in examples and with reference to the drawings, wherein Figure 1 shows an arrangement of a variant of the invention in a flotation cell, Figure 2 is an alternative variant, Figure 3 an additional variant of the invention, Figure 4 a variant with three gas inlet points, Figure 5 a variant with a group of injectors, Figure 6 a diagram of a distribution pattern of the bubble diameter, Figure 7 the air charge for a conventional injector compared to a device according to the invention, and Figure 8 the loss of flotation of a device according to the invention compared with a device of the state of the art.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES OF THE INVENTION Figure 1 shows a diagram of the flotation unit in which the device according to the invention is installed. The flotation cell 9 is filled to a large extent with suspension 8, on the surface of which foam 10 is formed, which contains as large a portion as possible of impurities and ink particles to be removed by flotation. This foam flows through a conduit 11 as an overflow U. The pulp suspension S enters the injector through the jet stream nozzle 1. Due to the open jet principle air is added at the first suction point 2 and mixture in the pulp suspension in a first impulse exchange tube 3. The pulp suspension has thus loosened by the air bubbles sucks more air 4 at a second suction point and thus air is mixed in the the second impulse exchange tube 5 is suspended. The air suction points are connected in this case to a tube projecting out of the suspension and into which air L enters the surface of the suspension. The bubble and pulp dispersion 7 leaves the injector after passing through a radial diffuser 6 for energy recovery purposes. The bubbles formed in this way adhere to the hydrophobic impurities and carry them to the surface. The suspension cleaned by flotation leaves the flotation zone as an acceptable G-pulp. Figure 2 contains an alternative variant of an injector according to the invention, where gas intake devices, for example, are mounted on different sides. A significant difference to Figure 1, however, is that a conically expanded diffuser is installed after the second stage. Figure 3 shows a device according to the invention with a conical first impulse exchange tube 3, where a second propellant jet nozzle analogous to the jet stream nozzle 1 is used, so that a high jet nozzle is also achieved. suction efficiency in the second stage. Figure 4 contains a design according to the invention in which three air intake points 2, 4, 12 are provided, with a diffuser in which after the third impulse exchange tube 13. Figure 5 shows a variant as a group of injectors, where two injectors are mounted here in parallel side by side. This arrangement comprises a top section, in which the propellant jet nozzles 1 are mounted, a common intermediate area to which the intake device 2 conducts, also a block with impulse exchange tubes 3 operating in parallel. This block is connected in turn to a common intermediate area which leads to the gas inlet pipe. This is joined by a common block where the second exchange tubes 5 are mounted. Finally, both impulse exchange tubes 5 lead to a radial diffuser ß. It would also be possible basically to combine the injectors in a group of injectors1 of this type. Figure 6 now shows the distribution pattern of the bubble diameter of a conventional injector compared with that of an injector according to the invention. This shows that the injector according to the invention contains significantly fewer bubbles with a diameter of <0.5 mm than the injector of the state of the art. Here the reduction is approximately 50%. Unlike the conventional injector, however, the distribution spectrum is still retained. In total there are less loose solids (fiber) as a result. The suction effect of an injector is determined by the performance or flow rate of the propeller jet, the diameter of the propeller jet nozzles, the coverage and density of the jet stream liquid. The suction characteristics of this type are illustrated in Figure 7. Here the air charge qc / q is illustrated as a function of the Froude number. The illustration shows that, compared to conventional injectors, this load can be significantly incre with the device according to the invention. Figure 8 contains a diagram of a flotation result in the same air intake compared to that of a conventional injector. The diagram shows that the total fiber loss could be reduced by approximately one third. With the present invention, however, it is possible to inject much more air and in this way, also improve the removal of impurities. It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. A process for aerating dispersions, particularly for the flotation of slurries of pulp in the de-inking process, where the slurry of pulp containing dirty particles is sprayed in a tank together with gas, particularly air, characterized in that gas, particularly air , which is being sucked by the effect of the injector to a minimum of two successive points and mixed with the suspension.
2. 2. The process according to claim 1, characterized in that approximately from 20 to 95% of the entire quantity of gas, particularly air, suctioned is admitted in the first stage.
3. 3. The process according to claim 1 or 2, characterized in that the flow of gas and liquid obtained by suction and mixing is transferred in a free jet after the first stage. .
4. The process according to any of claims 1 to 3, characterized in that the gas or air charge of the pulp suspension directly after spraying accounts for up to about 50-150%.
5. 5. A device for aerating suspensions, particularly a flotation device for de-inking ink suspensions, with an injector, characterized in that at least two suction points are arranged in series in the flow direction. The device according to claim 5, characterized in that the injection channel is enlarged after the first suction point. The device according to claim 5 or 6, characterized by a panel that is mounted at the end of the injector channel through the flow direction and this panel acts as a radial diffuser. The device according to claim 7, characterized in that the panel is mounted in a plane inclined towards the direction of flow. The device according to claim 7, characterized in that the panel contains interiors for the directed guidance of the flow. The device according to one of claims 5 to 9, characterized in that one of two injectors are mounted in parallel in the form of a group of injectors.