Apparatus and method for recycling flakes obtained by shredding and washing post-consumer plastic waste.

Abstract

The device for recycling flakes from shredded and washed post-consumer plastic waste comprises, viewed in the direction of processing of the plastic waste, a pre-treatment unit (2) for drying and homogenizing the flakes from the shredded and washed post-consumer plastic waste, a melt extruder (3) for melting the plastic waste dried and homogenized in the pre-treatment unit (2), a degassing extruder (5) with a connection (5a) to a vacuum source for degassing the plastic melt, a granulator (6) for granulating the plastic melt and an odor removal unit (8) for subjecting the granules to odor removal. The odor removal unit (8) has a process gas supply (10) and a gas discharge (11) for discharging an exhaust gas stream, the process gas supply (10) of the odor removal unit (8) being connected to an ozone source (12) or ozone generator (13), whereby the odor removal unit (8) is supplied with a process gas enriched with ozone.

Description

Technical Field

[0001] The present invention relates to an apparatus and a method for recycling flakes from shredded and washed post-consumer plastic waste.

Background Art

[0002] Reuse of plastic materials plays a decisive role from the perspective of a sustainable circular economy. To enable this, it is necessary to remove odorous and infectious contaminants, particularly from post-consumer plastic waste. When recycled plastics are used for food packaging, particularly high purity is required for the recycled plastics. It must also be ensured that the taste, odor and consistency of food are not affected in any way by packaging made from recycled materials.

[0003] Post-consumer plastic waste is typically processed by being shredded into flakes or shredded material in a first step, and then fed into a washing process. The washing step is preferably carried out in high-temperature washing with caustic soda or other cleaning additives added to clean the surface.

[0004] If a certain color purity is required for further use, it is recommended to optically pre-sort the post-consumer plastic waste before shredding, which may be combined with sorting after the washing step if necessary. The flakes produced in this way can then be extruded into recycled granules. These recycled granules are then ventilated for a short time (several hours to several days) using hot air, or for a long time (several days to several weeks) using ambient air, in order to reduce the odor of the recycled granules.

[0005] To make a decisive contribution to a positive eco-balance, the processing of plastic waste and its reuse in new products must be as energy-efficient as possible, protect resources and the environment, and be cost-effective compared to the production of new materials. Conventional degassing systems are particularly energy-intensive and time-consuming for decontamination of post-consumer waste, as contaminated pellets are exposed to hot airflow or kept under vacuum for several hours. A method and apparatus for decontaminating plastic waste is known from European Patent No. 2507022, in which flakes are extruded into pellets, and the resulting pellets are deodorized by blowing hot air into an odor removal unit in which the pellets remain. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] European Patent No. 2507022 [Patent Document 2] Chinese Patent Application Publication No. 108641398 Specification [Patent Document 3] Canadian Patent Application Publication No. 601047 [Patent Document 4] European Patent Application Publication No. 0602505 [Patent Document 5] European Patent Application Publication No. 3705252 [Non-patent literature]

[0007] [Non-Patent Document 1] Resources, Conservation & Recycling 161 (2020) “Development and application of an analytical method to quantify odour removal in plastic waste recycling processes” [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide an efficient and environmentally friendly post-consumer waste recycling process that can provide odorless recycled granules. Ideally, the present invention can improve the washing efficiency in post-consumer plastic recycling to such an extent that the recycling provides food-grade recycled granules.

[0009] It is known from Chinese Patent Application Publication No. 108641398 that plastic bottles are washed in a special cleaning solution, and the ozone is concentrated in a mixer and heated to 180-220°C. The plastic may then be granulated.

[0010] Canadian Patent Application Publication No. 601047 describes ozone treatment of PET short fibers and PET film at room temperature to enable printing. The PET material was found to maintain its flexibility and durability, and a bleaching effect was observed. Ozone treatment was also carried out with a water vapor / ozone mixture. Tests showed that treating PET material at temperatures of 180-230°C had no adverse effects on the material. However, at even higher temperatures, ozone would decompose into oxygen.

[0011] European Patent Application Publication No. 0602505 describes an ozone-forming UV emitter for treating liquids to reduce pollutants.

[0012] European Patent Application Publication No. 3705252 describes a method for producing plastic materials from plastic waste. This method comprises selecting industrial or post-consumer plastic waste, crushing the waste, treating the waste to reduce odors generated by the waste, treating the waste to reduce microbial load, tempering the waste in water, regranulating the waste, and dehumidifying the granules. Ozonation may be used to reduce odor and microbial load, but is not described in further detail.

[0013] A drawback of this known method is that the treatment to reduce odor and microbial load is only carried out on terrestrial waste. However, nonpolar compounds in particular are known to migrate into plastic materials; see, for example, Resources, Conservation & Recycling 161 (2020) “Development and application of an analytical method to quantify odor removal in plastic waste recycling processes”. As with further processing of recycled granules, impurities may be released during regranulation, which in turn causes unpleasant odors, thus hindering the use of regranules in higher-value applications, particularly in the manufacture of food packaging.

[0014] Therefore, there is still a need for an efficient and environmentally friendly post-consumer waste treatment process that can provide odorless recycled granules, and for equipment to implement this process.

[0015] The present invention solves the problem by providing an apparatus for recycling flakes from shredded and washed post-consumer plastic waste having the features of claim 1, and by providing a method for recycling flakes from shredded and washed post-consumer plastic waste having the features of claim 7. Embodiments of the present invention are defined in the dependent claims, description and drawings.

[0016] The present invention provides a method for recycling flakes from shredded and washed post-consumer plastic waste. From shredded and washed post-consumer plastic waste, the flakes are dried and homogenized in a gas stream, particularly a high-temperature gas stream. The process involves melting dried and homogenized plastic waste to form a plastic molten material, If necessary, remove foreign matter from the molten plastic, Degassing the molten plastic, Granulation of molten plastic, If necessary, dry the granules, This includes removing odors from granules using a process gas flow, Here, the process gas stream used to remove odors from the granules is either enriched with ozone, or supplied as an ozone-enriched gas.

[0017] The apparatus according to the present invention for recycling flakes from shredded and washed post-consumer plastic waste is: A pre-processing unit for drying and homogenizing flakes from shredded and washed post-consumer plastic waste, A melt extruder is located downstream of the pre-treatment unit to melt the plastic waste that has been dried and homogenized in the pre-treatment unit. A degassing extruder is located downstream of the melting extruder and has a connection to a vacuum source for degassing the molten plastic, A granulating apparatus disposed downstream of a degassing extruder for granulating a plastic melt, an odor removal unit disposed downstream of the granulating apparatus for removing odor from granules, wherein the odor removal unit has a process gas supply part and a gas discharge part for discharging an exhaust gas flow, the process gas supply part of the odor removal unit is connected to an ozone source or an ozone generator, whereby the ozone-enriched process gas is supplied to the odor removal unit, comprising the odor removal unit.

[0018] That is, on the one hand, an ozone source (for example in the form of a gas cylinder filled with ozone-enriched gas, for example ozone-enriched compressed air) is connected to the odor removal unit. The term "ozone source" does not mean that the source supplies pure ozone. On the other hand, an ozone generator may be connected to the odor removal unit, in which case the ozone generator, to form ozone, either takes in ambient air as the process gas or takes it in from the process gas supply part, and enriches it with ozone by reacting oxygen contained in the air under voltage or UV radiation.

[0019] The method according to the present invention for recycling flakes from shredded and washed post-consumer plastic waste comprises: drying and homogenizing flakes from shredded and washed post-consumer plastic waste in a gas flow, particularly a high-temperature gas flow, melting the dried and homogenized plastic waste to form a plastic melt, removing foreign matter from the plastic melt, if necessary, degassing the plastic melt, granulating the plastic melt, drying the granules, if necessary, removing odor from the granules by means of a process gas flow, This includes enriching a process gas stream used to remove odors from granules with ozone, or supplying a process gas stream as an ozone-enriched gas.

[0020] The present invention makes it possible to remove target odor substances from post-consumer waste. The degree of residual odor remaining in granules manufactured and treated according to the present invention can be determined by various methods. For example, various samples of the granules may be evaluated by a panel of trained testers in diluted or undiluted air. Alternatively, material-specific indices may be defined and evaluated based on the residual amount remaining after the odor removal process is completed. Furthermore, gas chromatography analysis may be used to evaluate the cleaning efficiency of individual substances.

[0021] When recycling post-consumer plastic waste, it is desirable to install a melt filter between the melt extruder and the degassing extruder to remove foreign matter from the molten plastic.

[0022] If the granulation apparatus used to granulate molten plastic is a wet granulation apparatus, it is convenient to install a drying apparatus, such as a drying centrifugal separator, downstream of the granulation apparatus so that the granules are supplied to the odor removal unit in a nearly dry state.

[0023] The process gas enriched with ozone is preferably air, but filtered ambient air may be used if necessary.

[0024] Studies have shown that in order to achieve sufficient odor removal without significantly polluting the environment, the ozone concentration in the enrichment process gas should be at least 0.1 ppm, preferably in the range of 10 ppm to 100 ppm.

[0025] In order to achieve the best odor removal effect while minimizing ozone pollution of the environment, it is preferable to provide an adjustment device for adjusting the amount of ozone supplied to the odor removal unit according to the ozone concentration of the exhaust gas flow from the odor removal unit, according to the present invention. The absolute amount of ozone is crucial for the odor removal effect, that is, the total number of ozone molecules that collide with the granules and the resulting presence of odor molecules (g ozone / kg plastic).

[0026] The amount of ozone supplied is controlled in various ways by the adjustment device. -By changing the ozone concentration of the supplied process gas, or - By shortening / stopping the processing time (processing duration), -By manipulating the flow rate of the process gas, To be influenced.

[0027] To perform this adjustment as accurately, quickly, and automatically as possible, the present invention further provides an in-line measuring device for measuring the ozone concentration in the exhaust gas stream from the odor removal unit, which controls a control device for adjusting the amount of ozone supplied to the odor removal unit as a function of the measured ozone concentration. As a result, sufficient ozone is generated or supplied to the process gas stream to remove odor-forming substances by oxidation, while the in-line measurement and control simultaneously keeps ozone emissions low. The required ozone concentration in the supplied process gas depends on the contamination intensity and odor intensity of the granules. The more contaminated the granules are, the more ozone is consumed during processing (reaction with odor-causing substances). The remaining ozone concentration is measured in the exhaust gas stream. When the ozone concentration in the exhaust gas stream exceeds a certain threshold, the amount of ozone supplied to the process gas or the amount of ozone as process gas is reduced until the ozone concentration in the exhaust gas stream falls below the threshold again.

[0028] This control system solves two problems. a.) On the other hand, excess ozone should not be generated and subsequently released into the environment. b.) On the other hand, the determination should be made when the odor removal treatment is completed, that is, when the odor-causing substances react with ozone.

[0029] Basically, the ongoing chemical process can be described as follows:

[0030] O3 (ozone added) + X → O - X + O2 Here: X... Odor substances OX…Oxidized odor substances

[0031] If there are still enough odorants present to react with ozone, the ozone can react completely and be consumed. The presence of oxidized odorants and oxygen in the exhaust gas stream indicates that the odor removal process is not yet complete.

[0032] However, if more ozone is supplied to the odor removal unit along with the process gas than can react with the odor-causing substances carried by the granules in the odor removal unit, the ozone will leave the odor removal unit through the exhaust gas flow and can be measured there.

[0033] This can also be explained in a simplified way as follows:

[0034] nO3 (ozone input) + X → O - X + O2 + (n-1)O3 (ozone in exhaust gas stream that can be measured using a sensor) Here: n≧2 X... Odor-causing substances OX…Oxidized odor substances

[0035] This occurs when too much ozone is supplied to the mixture removal unit. The following solutions are offered for this problem.

[0036] At the start of the process, a process gas with a low ozone concentration is supplied. If no ozone is detected in the exhaust gas stream, the ozone concentration of the supplied process gas is gradually increased until a certain ozone concentration (e.g., a constant percentage of the supplied amount) is present in the exhaust gas stream. Thereafter, the ozone concentration of the supplied process gas is kept constant until the odor removal process is complete, i.e., until the odor-causing substances have completely reacted with ozone.

[0037] Alternatively or additionally, the flow rate of the process gas stream may be altered to adjust the amount of ozone. This is done by starting with a constant flow rate of process gas and measuring the ozone concentration in the exhaust gas stream. If there is too much ozone, the flow rate is gradually reduced until the ozone in the exhaust gas stream can no longer be measured or falls below a certain threshold. The flow rate is then kept constant until the odor removal process is complete.

[0038] During the odor removal process, the reaction ideally proceeds in such a way that all ozone is consumed. That is,

[0039] O3 (ozone added) + X → O - X + O2 Here: X... Odor substances OX…Oxidized odor substances

[0040] As the odor removal process continues, fewer odor molecules become available as ozone reactants, leaving more ozone behind. The increase in ozone concentration can then be measured in the exhaust gas stream.

[0041] nO3 (ozone input) + X → O - X + O2 + (n-1)O3 (ozone in exhaust gas stream that can be measured using a sensor) Here: n≧2 X... Odor-causing substances OX…Oxidized odor substances

[0042] The completion of the odor removal process may be recognized when a certain increase in the ozone concentration in the exhaust gas stream is measured, or when it exceeds a certain threshold (e.g., a certain percentage of the supplied ozone concentration). As soon as this is detected, the ozone supply is immediately stopped or gradually reduced according to the same principles as described above, by reducing the ozone concentration in the supplied process gas or by gradually reducing the flow rate.

[0043] It should be noted that the above reaction equation is simplified for illustrative purposes, as it only illustrates the case where the odorant is oxidized only once. In reality, most odorants are oxidized several times by ozone; that is, two or more ozone molecules react with one odorant molecule. However, the principle remains the same.

[0044] In-line measuring equipment for measuring the ozone concentration in the exhaust gas flow from an odor removal unit may be provided simply for measuring ozone concentration, for example, to meet official environmental requirements or to comply with national regulatory limits.

[0045] To minimize ozone pollution, in one embodiment of the present invention, at least one device for at least partially decomposing ozone contained in the exhaust gas stream is optionally provided, and the device for decomposing ozone is preferably configured to treat the exhaust gas stream thermally or catalytically, or to irradiate the exhaust gas stream with electromagnetic waves. The electromagnetic waves are preferably UV light having a wavelength of at least 254 nm.

[0046] This apparatus for at least partially decomposing ozone contained in the exhaust gas stream may optionally be controlled or regulated based on the ozone concentration measured in the exhaust gas stream.

[0047] The present invention will be described in more detail below with reference to exemplary embodiments and the drawings. [Brief explanation of the drawing]

[0048] [Figure 1] A schematic diagram of the apparatus according to the present invention for recycling flakes from shredded and washed post-consumer plastic waste is shown. [Figure 2] Figure 1 shows possible embodiments of the apparatus in detail. [Modes for carrying out the invention]

[0049] The apparatus schematically shown in Figure 1 for recycling flakes from shredded and washed post-consumer plastic waste has a pre-treatment unit 2 for drying and homogenizing the flakes from the shredded and washed post-consumer plastic waste, where the supply of flakes to the pre-treatment unit 2 is achieved by a supply unit 1 in the form of a screw conveyor. The pre-treatment unit 2 has a gas supply unit 2a, preferably configured as a high-temperature gas supply unit, and a gas discharge unit 2b. Gas, preferably hot air, is supplied through the gas supply unit 2a to the pre-treatment unit 2, where the flakes are located inside. The flakes are dried and homogenized using the supplied gas stream. The gas stream, containing moisture and contaminants, is discharged from the gas discharge unit 2b. The discharge of the flakes from the pre-treatment unit is carried out by a screw conveyor 2c to a melt extruder 3 located downstream of the pre-treatment unit 2. In the melt extruder 3, the dried and homogenized flakes from the plastic waste are melted. Downstream of the melting extruder 3, a melting filter 4 is positioned to remove foreign matter from the molten plastic.

[0050] Downstream of the melting filter 4 is a degassing extruder 5 having a vacuum connection 5a to a vacuum source (not shown) for degassing the molten plastic, followed by a granulator 6 for granulating the molten plastic. The granules produced in the granulator 6 are dried in a drying centrifuge 7 and then supplied to an odor removal unit 8, where odor removal is performed. After the odor removal treatment, the granules are discharged from the odor removal unit 8 and may be processed directly thereafter or supplied to a storage silo 9.

[0051] The odor removal unit 8 includes a process gas supply unit 10 and a gas discharge unit 11 for discharging exhaust gas flow. The process gas supply unit 10 of the odor removal unit 8 is connected to an ozone source 12, for example, in the form of a container filled with ozone-enriched gas, for example, ozone-enriched compressed air, or an ozone generator 13 which may supply ozone or ozone-enriched process gas to the odor removal unit 8.

[0052] The adjustment device 20 functions to adjust the amount of ozone supplied to the odor removal unit 8 according to the ozone concentration of the exhaust gas flow from the odor removal unit 8. The adjustment of the supplied ozone amount is achieved, for example, by a control valve operated by the adjustment device 20 within the process gas supply unit 10. The adjustment device 20 may be configured as an electronic control unit having a microprocessor, main memory, program memory in which control algorithms are stored, and interfaces for communication and for operating actuators such as the aforementioned control valve. The ozone generator 13 may be configured to apply a voltage to the ambient air so that oxygen in the ambient air reacts to form ozone. The higher the voltage, the more ozone is generated. In this way, the ozone concentration of the gas emitted from the ozone generator 13 can be adjusted by controlling the voltage. Control of the ozone generator 13 to generate and change the voltage can be achieved by the adjustment device 20.

[0053] Alternatively, the ozone generator 13 may operate based on irradiating the drawn-in ambient air with UV light, preferably having a wavelength of less than 240 nm. In such an ozone generator 13, the ozone concentration of the gas discharged from the ozone generator 13 is controlled by changing the wavelength of the UV light. This control may also be performed using a control device 20. Since shorter wavelength UV light has higher energy, more ozone is generated than when longer wavelength UV light is irradiated.

[0054] Preferably, the adjustment device 20 is controlled by an in-line measuring device 30 for measuring the ozone concentration in the exhaust gas flow from the odor removal unit 8, and the control of the adjustment device 20 is performed to adjust the amount of ozone supplied to the odor removal unit 8 according to the measured ozone concentration. With such a configuration, the odor removal process described above may be achieved with little to no impact on the environment from ozone. The in-line measuring device 30 may be located directly in or on the gas exhaust section 11, or alternatively located away from the gas exhaust section 11, but may also include an ozone sensor installed in the gas exhaust section 11.

[0055] Equipment 40 for at least partially decomposing ozone contained in the exhaust gas stream is optionally provided at the gas discharge section of the odor removal unit 8, and the equipment 40 for decomposing ozone is preferably configured to treat the exhaust gas stream thermally or catalytically, or to irradiate the exhaust gas stream with electromagnetic waves. If ozone is decomposed by irradiating the discharged process gas with electromagnetic waves, ultraviolet light having a wavelength of at least 254 nm is preferably used.

[0056] Due to its simple handling, the process gas enriched with ozone is preferably air. The ozone concentration in the enriched process gas should be at least 0.1 ppm, and preferably in the range of 10 ppm to 100 ppm.

[0057] Figure 2 schematically shows one embodiment of an ozone gas generator 13 according to the present invention for recovering ozone from ambient air. This ozone gas generator 13 includes an air filter 14 that comes into contact with the ambient air and filters out dust and other particles from the ambient air. The ambient air thus purified is supplied to an ozone generator 15, which converts a portion of the ambient air into ozone according to a principle known to those skilled in the art, thereby producing ozone-enriched air as a process gas. The output of the ozone generator 15 is connected to the inlet, i.e., intake side, of a blower 16. On one side, the blower 16 causes air to be drawn in through the air filter 14 and the ozone generator 15, and on the other side, it blows the process gas through a heater 17 to a process gas supply unit 10, and through the process gas supply unit 10 to an odor removal unit 8. The process gas containing the ozone portion consumed by odor removal exits the odor removal unit 8 as exhaust gas flow through the gas discharge section 11 and reaches the ozone decomposition equipment 40 for ozone decomposition, where excess ozone is reduced. It should be noted that the term "ozone gas generator" should not be understood to mean that this device generates pure ozone. Rather, the term "ozone gas generator" means that this device produces ozone-enriched gas, in particular ozone-enriched air.

[0058] In a series of tests, the process gas flow into the odor removal unit 8 was enriched with 35 ppm ozone, and within the odor removal unit 8, granules of different types of post-consumer plastic waste were passed through the ozone-enriched process gas for 2 to 2.7 hours each. Ozone concentration: 35 ppm, process gas flow rate: 1600 m³ 3 At a rate of 120 g / h, the ozone delivery rate was 120 g / h. This translates to a supply of 0.24 g of ozone per kilogram of plastic.

[0059] Subsequently, in blind tests, two samples of the same plastic material were subjected to the following treatments: one sample was passed through hot air for 2–2.7 hours using a conventional method, while the other sample was passed through hot air containing 35 ppm ozone as a process gas for the same duration and temperature. These samples were then presented to a trained odor testing committee for evaluation. The results showed that granules produced from HDPE, PP, and LDPE treated with ozone were significantly superior to the control material treated with hot air alone in terms of odor intensity and pleasantness, according to the testers.

Claims

1. An apparatus for recycling flakes obtained by shredding and washing post-consumer plastic waste, A pre-treatment unit (2) for drying and homogenizing the flakes obtained from the shredded and washed post-consumer plastic waste, A melt extruder (3) is located downstream of the pre-treatment unit (2) and is used to melt the flakes obtained by shredding and washing the post-consumer plastic waste that has been dried and homogenized in the pre-treatment unit (2). A degassing extruder (5) is located downstream of the melting extruder (3) and has a connection to a vacuum source (5a) for degassing the molten flakes obtained from the shredded and washed post-consumer plastic waste, A granulator (6) is located downstream of the degassing extruder (5) for granulating the shredded and washed flakes obtained from post-consumer plastic waste, The system includes an odor removal unit (8) located downstream of the granulation apparatus (6) for removing odors from the granules obtained by granulation, The odor removal unit (8) comprises a process gas supply unit (10) and a gas discharge unit (11) for discharging an exhaust gas flow, wherein the process gas supply unit (10) of the odor removal unit (8) is connected to an ozone source (12) or an ozone generator (13), thereby supplying the odor removal unit (8) with ozone-enriched process gas.

2. A melt filter (4) for removing foreign matter from the melted flakes obtained from the shredded and washed post-consumer plastic waste is disposed between the melt extruder (3) and the degassing extruder (5), The apparatus according to claim 1.

3. A drying device (7) for drying the granules is located between the granulation device (6) and the odor removal unit (8), The apparatus according to claim 1 or 2.

4. The system is characterized by comprising an in-line measuring device (30) for measuring the ozone concentration of the exhaust gas flow from the odor removal unit (8), The apparatus according to claim 1.

5. The odor removal unit (8) is supplied with an adjustment device (20) for adjusting the amount of ozone supplied to the odor removal unit (8) according to the ozone concentration of the exhaust gas flow from the odor removal unit, and is characterized by having an adjustment device (20) for adjusting the amount of ozone supplied to the odor removal unit (8) according to the ozone concentration of the exhaust gas flow from the odor removal unit, The apparatus according to claim 1.

6. The apparatus comprises at least one piece of equipment (40) for at least partially decomposing ozone contained in the exhaust gas stream, wherein the equipment (40) is configured to decompose ozone in the exhaust gas stream by heat treatment or catalytic treatment of the exhaust gas stream, or by irradiating the exhaust gas stream with electromagnetic waves. The apparatus according to claim 1.

7. The process gas enriched with ozone is characterized in that it is air. The apparatus according to claim 1.

8. The enriched process gas is characterized in that the ozone concentration is 0.1 ppm or higher. The apparatus according to claim 1.

9. The enriched process gas is characterized in that the ozone concentration is in the range between 10 ppm and 100 ppm. The apparatus according to claim 8.

10. A method for recycling flakes obtained by shredding and washing post-consumer plastic waste, The flakes obtained from the shredded and washed post-consumer plastic waste are dried and homogenized in a gas stream, particularly a high-temperature gas stream. The process involves melting the dried, homogenized, shredded, and washed post-consumer plastic waste flakes to form a plastic molten material. Degassing the aforementioned molten plastic, Granulation of the aforementioned molten plastic, To remove odors from granules obtained by granulation using a process gas flow, A method characterized by comprising enriching the process gas stream used to remove odors from the granules with ozone, or supplying the process gas stream as an ozone-enriched gas.

11. The method is characterized by including removing foreign matter from the plastic molten material before degassing the plastic molten material. The method according to claim 10.

12. The method is characterized by including drying the granules before removing the odor from them. The method according to claim 10 or 11.

13. The amount of ozone supplied to the granules when removing the odor from the granules is adjusted according to the ozone concentration of the process gas discharged after the odor removal treatment of the granules. The method according to claim 10.

14. The ozone concentration of the process gas discharged after odor removal treatment of the granules is measured by in-line measurement, and the amount of ozone supplied to the granules when removing odors from the granules is adjusted according to the measured ozone concentration. The method according to claim 13.

15. The ozone contained in the discharged process gas is at least partially decomposed, and the decomposition of the ozone is carried out by heat treatment or catalytic treatment of the discharged process gas. The method according to claim 10.

16. The ozone contained in the discharged process gas is at least partially decomposed, and the decomposition of the ozone is carried out by irradiating the discharged process gas with electromagnetic waves, wherein the electromagnetic waves are UV light having a wavelength of at least 254 nm. The method according to claim 10.

17. A characteristic feature is that the process gas enriched with ozone is air. The method according to claim 10.

18. The enriched process gas is characterized in that the ozone concentration is 0.1 ppm or higher. The method according to claim 10.

19. The ozone concentration in the enriched process gas is in the range of 10 ppm to 100 ppm. The method according to claim 18.

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