Technical field

In general, present invention relates to processing of recycled textile fibers, especially to processing recycled textile fibers. More especially the present invention relates to a method of processing recycled textile fibers according to preamble part of the independent method claim and to a process system of processing recycled textile fibers according to preamble part of the independent process system claim.

Background

As known from the prior art in processing of recycled textile fibers raw material to textile recycling process includes synthetic fibers in addition to cotton fibers. The content of the synthetic fibers in raw material typically vary from 0 % up to 50 %. Thus, the raw material mixture containing the synthetic fibers is not as valuable as a furnish for recyclable textile products having low and/or steady content of the synthetic fibers. Therefore, there exists a great challenge of how to remove the synthetic fibers from the textile pulp and to ensure that the content of the synthetic fibers in the end product is low. Typically, the synthetic fibers are removed by introducing chemical treatment stage or stages to textile recycling process due to the hydrophobic properties of the synthetic fibers. This need of using of chemicals makes the removal of synthetic fibers from the recycled textile fibers expensive as it needs investments to chemical handling and application technologies and as it will consume the chemicals and further it needs the removal of synthetic fibers from soaking agent. Thus, there exists a great need to find a new manner of how to remove the synthetic fibers from the textile pulp and to ensure that the content of the synthetic fibers in the end product is low with decreased use of chemicals.

Flotation technology is known from prior art to be used in connection with various processes for separation of particles in relation to particle sizes or from separation of particles from other materials. In mining technology the flotation has been used for separation of small particles in relation to particle sizes. In connection with paper recycling the flotation has been used for separation of small particles, such as ink and/or dirt particles, from fibers. In connection with water handling the flotation has been used for separation of small particles from water by using dissolved air flotation in order to remove all solids from the water. In plastic separation the flotation has been used for separation of large particles in relation to particle sizes and in connection of wetting of plastics not intended to be separated.

An object of the invention is to create a process system and method of processing recycled textile fibers, in which the disadvantages and problems of prior art are eliminated or at least minimized.

An object of the invention is to create an improved process system and method of processing recycled textile fibers, in which new, alternative ways of processing recycled textile fibers are provided.

A particular, non-binding, object of the invention is to create a process system and method of processing recycled textile fibers, in which chemical treatment for separating synthetic fibers from the recycled textile fibers, especially from cotton fibers is eliminated or at least minimized.

Summary

In order to achieve the above mentioned objects, the method of processing recycled textile fibers according to the invention is mainly characterized by the features of the characterizing clause of the independent method claim and the process system of processing recycled textile fibers is mainly characterized by the features of the characterizing clause of the independent process system claim. Advantageous embodiments and features are disclosed in the dependent claims. According to the invention in the method of processing recycled textile fiber suspension comprising synthetic fibers and non-synthetic fibers, in particular cotton fibers, is processed, wherein the recycled textile fiber suspension is treated in a flotation stage configured to be executed in at least one flotation cell for removing the synthetic fibers from the recycled textile fiber suspension.

According to an advantageous feature of the invention in the method ultrasonic vibration and/or ultrasonic shock waves is induced to the recycled textile fiber suspension for releasing onto the non-synthetic fibers attached synthetic fibers.

According to an advantageous feature of the invention in the method the recycled fiber suspension is fed to a process system comprising a refiner and/or a screen and/or a cleaning device and/or a thickening device and/or a thickening device, in which method the recycled textile fiber suspension is refined in the refiner in a refining stage and/or the recycled textile fiber suspension is screened in the screen in a screening stage and/or the recycled textile fiber suspension is cleaned in the cleaning device in a cleaning stage and/or the recycled textile fiber suspension is treated in the thickening device for increasing the consistency of the recycled textile fiber suspension in a thickening stage, and the recycled textile fiber suspension has a fiber feed consistency of non-synthetic fibers 0,05-1 ,5%.

According to an advantageous feature of the invention in the method into the recycled textile fiber suspension is fed flotation chemicals, for example soap for controlling foam formation, surfactants for reducing surface tension, collectors for more selective separation, wetting agents for increasing stay of hydrophilic recycled textile in the recycled textile fiber suspension.

According to an advantageous feature of the invention in the method the recycled textile fiber suspension is treated in the flotation cell for flotation time of 1 -30 min, advantageously 2-10 min.

According to an advantageous feature of the invention in the method final reject amount of removed synthetic fibers out from the flotation cell depends on the synthetic fibers amount in the feed of the recycled textile fiber suspension and the amount is 1 - 50% of the total feed mass.

According to the invention the process system of processing recycled textile fibers comprising synthetic fibers and non-synthetic fibers in a recycled textile fiber suspension, in particular cotton fibers, comprises a flotation cell for removing synthetic fibers from the recycled textile fiber suspension having a fiber feed consistency of non-synthetic fibers 0,05-1 ,5%.

The non-synthetic fibers are natural fibers, for example cotton, wool etc. fibers. They can also be plant based fibers or for example man-made cellulose material based fibers. The synthetic fibers typically comprise polyester fibers.

According to an advantageous feature of the invention the process system further comprises a refiner for refining a recycled textile fiber suspension in a refining stage and/or a screen for screening the recycled textile fiber suspension in a screening stage and/or a cleaning device for cleaning the recycled textile fiber suspension in a cleaning stage and/or a thickening device for increasing consistency of the recycled textile fiber suspension in a thickening stage.

According to an advantageous feature of the invention the flotation cell comprises at least one flotation stage.

According to an advantageous feature of the invention the flotation cell comprises at least one recovery stage.

According to an advantageous feature of the invention the at least one recovery stage is configured as a flotation stage.

According to an advantageous feature of the invention the at least one recovery stage is configured as a screen.

According to an advantageous feature of the invention in the process system the flotation cell is located after or before the screen for the screening stage and the cleaning device. According to an advantageous feature of the invention the flotation cell comprises an injector with a feed channel, via which feed channel the recycled textile fiber suspension is configured to be fed to the injector, a dam plate for forming an overflow, a reject space for receiving the overflow with the synthetic fibers, a reject channel for discharging the removed synthetic fibers out from the reject space.

According to an advantageous feature of the invention the flotation cell further comprises at least one ultrasonic device configured to induce ultrasonic vibration and/or ultrasonic shock waves to the recycled textile fiber suspension for releasing onto the non-synthetic fibers attached synthetic fibers.

According to an advantageous feature of the invention ultrasonic devices are located in one or more of the flotation cells.

According to an advantageous aspect of the invention the separation efficiency of separating the synthetic fibers from the recycled textile fibers is increased by using low inlet consistency for separating the synthetic fibers are hydrophobic from the cotton fibers. When the synthetic fibers float towards the surface of the flotation cell, there exists a risk for the synthetic fibers of getting attached onto the cotton fibers are big, which could reduce the separating efficiency. Thus, according to a more advantageous aspect of the invention ultrasonic vibration is induced into the flotation suspension, advantageously in the lower part of the flotation cell, wherein the onto the cotton fibers attached the synthetic fibers are separated by the ultrasonic vibration. In this more advantageous embodiment especially need of chemical treatment for the separation of the synthetic fibers from the recycled textile fibers, in particular from the cotton fibers is substantially decreased or even eliminated. Additionally, by this more advantageous embodiment one extra parameter is provided for adjusting the flotation and for controlling the efficiency of the flotation, and even decreased flotation time in flotation cells and decreased space is needed.

According to an advantageous aspect of the invention in the method separation of the recycled textile fiber the separation is adjusted by usage of flotation chemicals in connection with the flotation, thus no separate chemical treatment stage is needed, and/or controlling bubble size and/or amount and/or controlling retention time in flotation cells and/or varying configuration of flotation cells. Advantageously, the flotation of the recycled textile fibers is performed in a water-based system using flotation chemicals, for example fatty acids and/or silicone derivatives and/or non-ionic surfactants.

According to an advantageous aspect of the invention the flotation cells for the flotation have an elliptical and linear design, which provides an excellent basis for smooth flow velocities and efficient removal of froth.

According to an advantageous aspect of the invention the flotation cell is of the type disclosed in the patent publication EP1891264 (B1 ) of the applicant and the flotation cell is provided with aerating injectors with special shaped jet nozzles of the type disclosed in the patent publication EP2129828 (B1 ) of the applicant.

By the invention and its advantageous features several advantages are achieved: In the process system and the method of processing recycled textile fibers, the chemical treatment for separating synthetic fibers from the recycled textile fibers, especially from cotton fibers is eliminated or at least minimized and the synthetic fibers are removed selectively based on their hydrophobic properties. A furnish for recyclable textile products having low and/or steady content of the synthetic fibers is provided. The separation efficiency of separating synthetic fibers is even more than 95%.

Brief description of the drawings

In the following the invention is explained in detail with reference to the accompanying drawing to which the invention is not to be narrowly limited.

In figure 1 is shown schematically an advantageous example of a process system of processing recycled textile fibers according to the invention. In figure 2 is shown schematically an advantageous example of the flotation cell of the flotation cell of the process system of processing recycled textile fibers according to the invention.

In figure 3 is shown schematically an advantageous example of the flotation cell of the process system of processing recycled textile fibers according to the invention.

Detailed description

During the course of the following description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous examples. In the figure some repetitive reference signs have been omitted for clarity reasons.

In figure 1 is shown schematically an example of a process system 10 of processing recycled textile fibers. The process system 10 comprises a refiner 11 , for example a LC-refiner, a conical refiner or a disc refiner, into which the recycled textile fiber suspension is fed for refining in a refining stage. The process system 10 also comprises a screen 12, for example a pressure screen or a bow screen, for screening the recycled textile fiber suspension in a screening stage. The process system 10 further comprises a cleaning device 13, advantageously a low consistency cleaning device 13, for example a hydrocyclone, for cleaning the recycled textile fiber suspension, advantageously in low consistency. The process system 10 further comprises a flotation cell 14 for removing and recovering the synthetic fibers from the recycled textile fiber suspension. The process system 10 also comprises a thickening device 15, for example a disc filter, for increasing the consistency of the recycled textile fiber suspension. The flotation cell 14 for removing the synthetic fibers is advantageously located after or before the screen 12 and the cleaning device 13, as shown in the example of the figure 1 . This location provides for more secure operation of injectors of flotation cells of the flotation cell 14, as the injectors thus remain cleaner and do not clog. It should be noted that order of the refiner 11 , the screen 12, the cleaning device 13, the flotation cell 14 and the thickening device 15 may have different configurations i.e., these parts of the process system 10 are not necessarily in the numeric order. The flotation cell 14 comprises one or more flotation stages 52, in which flotation stage/-s the synthetic fibers, typically polymeric, are removed from the recycled textile fiber, and one or more recovery stages 53, for example flotation stages or screens, for recovering the synthetic fibers from the recycled textile fibers. The recycled textile fiber suspension has advantageously a fiber feed consistency of 0,05-1 ,5%, even 20%. The recycled textile fiber suspension for feed to the flotation cell 14 may comprise chemicals, for example soap for controlling foam formation, surfactants for reducing surface tension, collectors for more selective separation, wetting agents for increasing stay of hydrophilic recycled textile in the recycled textile fiber suspension. The flotation cell is advantageously of the type disclosed in the patent publication EP1891264 (B1 ) of the applicant.

In figure 2 is shown an example of the flotation cell of the flotation cell of the process system of processing recycled textile fibers. The flotation cell 14 comprises an injector 22 with a feed channel 23, via which feed channel 23 the recycled textile fiber suspension and possible flotation chemicals are fed to the injector 22. The flotation cell 14 comprises a dam plate 24, a reject 26 out from a reject space 28 and a accept channel 27 for accept. Surface of the suspension is denoted by reference sign 25. In the flotation cell 14 synthetic fibers are removed from the recycle textile fiber suspension. The injector 22 is placed with respect to the surface 25 of the recycled textile fiber suspension in the flotation cell 14 such that the lower part of the injector 2f extends below the surface 5 of the fiber suspension. In the flotation cell 14, the synthetic fibers of the recycled textile suspension adhere to bubbles formed by air and possible flotation agent chemical, which rise to the surface 25 of the recycled textile fiber suspension, wherefrom the synthetic fibers are removed for example by overflow. The overflow is formed by means of the dam plate 24 and the foam generated on the surface 25 of the recycled textile fiber suspension and the synthetic fibers therein are transferred over the dam plate 24 to the reject space 28 and forwarded therefrom via the reject channel 26 to further processing. The accept of the flotation cell is removed via the accept channel 27 to a next process phase. The basic structure and mode of operation of the flotation cell 14 is known as such to one skilled in the art, thus they will not be discussed in closer detail herein. In the example of the figure 2 the flotation cell 14 has an elliptical and linear cell design, which provides an excellent basis for smooth flow velocities and efficient removal of foam. The injector 22 is advantageously an aerating injector with special shaped jet nozzles of the type disclosed in the patent publication EP2129828 (B1 ) of the applicant improving even more the efficient removal of the synthetic fibers.

In figure 3 is shown schematically an example of the flotation cell 14 of the process system 10 of processing recycled textile fibers. The flotation cell 14 comprises at least one flotation stage 52 and at least one recovery stage 53, which in this example is a flotation stage. The recycled textile fiber suspension is fed to the flotation cell 14 via a feed channel 56 and pumped by a pump 51 to the first flotation stage 52. The flotation cell 14 comprises pumps 51 for feeding the recycled textile fiber suspension forwards from one flotation/recovery stage 52, 53 to next flotation/recovery stage 52, 53 in feed direction. The flotation cell 14 comprises a tank 59 between the flotation stages 52 and the recovery stages 53 and respectively a feed channel 54 from flotation stages 52 to the tank 59 and a feed channel 55 from the tank 59 to the recovery stages 53. The separated synthetic fibers are removed by a reject channel 57, for example to be recirculated in the flotation cell 14 or to other removal. In one or more flotation cells 14 of the flotation stages 52, 53 ultrasonic vibration and/or ultrasonic shock waves by the ultrasonic device/-s 61 is induced to the flotation suspension in the flotation cell 14, whereby the onto the non-synthetic, in particular cotton, fibers attached the synthetic fibers are released from the non-synthetic fibers and separated by the ultrasonic vibration. The ultrasonic devices 61 are advantageously located in the lower part of the flotation cell 14. By controlling frequency of the ultrasonic vibration and/or ultrasonic shock waves efficiency can be controlled. The flotation cell 14 may also comprise a separate ultrasonic stage with at least one ultrasonic device 61 for treatment of the recycled textile fiber suspension by the ultrasonic vibration and/or ultrasonic shock waves without flotation. This ultrasonic stage may be located at any location within the flotation cell 14. Each flotation cell 14 comprises one or more injectors 22. The flotation time in each flotation cell 14 is 1 -30 min, advantageously 2-10 min. Recycled textile fiber suspension is fed to the flotation cell 14 at the non-synthetic fiber consistency of 0.05 - 1 .5%. The final reject amount of removed synthetic fibers out from flotation cell 14 depends on the synthetic fibers amount in the feed of the recycled textile fiber suspension via the feed channel 56 and the amount can be 1 - 50% of the total feed mass.

In the description in the foregoing, although some functions have been described with reference to certain features and examples, those functions may be performable by other features and examples whether described or not. Although features have been described with reference to the certain examples, those features may also be present in other examples whether described or not.

Above only some advantageous examples of the inventions have been described to which examples the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

Reference sings used in the drawing:

10 process system

11 refiner

12 screen

13 cleaning device

14 flotation cell

15 thickening device

22 injector

23 feed channel

24 dam plate

25 surface

26 accept channel

27 reject channel

28 reject space

51 pump

52 flotation stage

53 recovery stage

54 feed channel from flotation stages to tank

55 feed channel from tank to recovery stages

56 feed channel to flotation cell

57 reject channel

59 tank

61 ultrasonic device