Freeze grinding apparatus and method for waste plastic recycling

Abstract

The present invention relates to a waste plastic freeze-crushing device and method capable of preventing the generation of harmful volatile organic compounds (VOCs) generated during the crushing process for plastic recycling by controlling the heat generated during the crushing process by injecting cooling air into the inside of the crusher while operating the waste plastic crushing process in a sealed environment. The waste plastic freeze-crushing device according to the present invention comprises: a crushing section having a crushing chamber into which waste plastic is introduced and a crusher that crushes the waste plastic inside the crushing chamber; a sealed discharge pipe whose upper part is connected to the lower part of the crushing section to discharge waste plastic particles crushed in the crushing section; a collection section for collecting waste plastic particles that have passed through the sealed discharge pipe; and a cooling cycle including a compressor that compresses a refrigerant to a high temperature and high pressure, a condenser that releases heat from the high temperature and high pressure refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has passed through the condenser to a low pressure, and an evaporator in which heat exchange occurs between the low temperature and low pressure refrigerant that has passed through the expansion valve and air. It may include a cold air injection unit that injects cooling air cooled by the cooling cycle into the interior of the grinding chamber; and a control unit that controls the operation of the grinding unit, the cooling cycle, and the cold air injection unit.

Description

Technology Field

[0001] The present invention relates to an apparatus and method for crushing waste plastic for recycling waste plastic, and more specifically, to an apparatus and method for freezing and crushing waste plastic for recycling that controls heat generated during the crushing process by injecting cooling air into the interior of a crusher for crushing waste plastic and prevents the generation of harmful volatile organic compounds (VOCs). Background Technology

[0002] Plastics are widely used in various fields, ranging from household goods to electrical and electronic products and automobiles, due to their excellent mechanical strength and ease of product molding. However, the amount of waste plastic being disposed of is increasing significantly due to the difficulties in post-processing and sorting.

[0003] Waste plastics are emerging as a major cause of environmental pollution because they do not decompose naturally in nature. Recognizing this problem, various studies and technologies for recycling and processing waste plastics are currently underway. Furthermore, there is a growing trend among existing plastic injection molding factories to increase recycling rates by crushing surplus plastics rather than disposing of them as waste. Regarding disposed waste plastics, new technological developments are being carried out in the fields of recycling methods and processing techniques, and they are being treated in various ways to prevent environmental exposure and ecosystem invasion.

[0004] Recycling waste plastics requires several processes. It must undergo a step-by-step recycling process including sorting, classification, washing, and crushing. First, waste plastics are classified by type through the sorting process, and then compressed, washed, and crushed to form small flakes. It is crucial that the physical properties of the plastic are preserved during this stage. However, thermal degradation can occur due to frictional heat during the crushing process, which is pointed out as a problem. In particular, for plastics recycled in the injection molding process, abnormalities in physical properties occur as the number of recycling cycles increases. In the short term, this leads to issues with the low mechanical strength of injection-molded products, and in the long term, the degradation of thermal properties causes the melting point of the plastic to change. Consequently, the plastic fails to burn or melt during the injection process, resulting in problems such as clogging of the injection port. As a result, the recycling rate of waste plastics typically remains at around 30–40%, and the majority is currently incinerated or landfilled.

[0005] Furthermore, a crushing process is essential in existing plastic injection molding factories and in the production of plastic pellets or beads for resource recycling. During this process, the heat generated causes the plastic to instantaneously reach a molten state, releasing VOCs (Volatile Organic Compounds). These VOCs are harmful gaseous components that can cause harm to the human body upon exposure, particularly through inhalation via the bronchi. While the composition of these VOCs varies depending on the type of plastic being crushed, ABS (Acrylonitrile Butadiene Styrene), the most commonly used plastic, releases a large amount of styrene gas, which can cause cancer upon long-term exposure.

[0006] Generally, large amounts of VOC gases are released during the plastic melting process; however, since most plastic production processes are carried out in enclosed environments and cooled with water immediately after injection, large quantities of harmful gases are not generated within the actual production plant. In the case of the grinding process, although heat generation is acknowledged, it is not operated in an enclosed environment like the injection molding process and does not significantly contribute to this heat generation phenomenon.

[0007] One of the technologies to solve these problems is freeze-crushing technology. Freeze-crushing technology eliminates the risk of thermal deformation during the crushing process and crystallizes the plastic to minimize deformation of the chain structure, thereby minimizing factors that impair physical properties and increasing the recycling rate. Through this, it can significantly contribute to the recycling rate of waste plastics and sustainable resource utilization.

[0008] Exposing plastic to extremely low temperatures makes it brittle and fragile, resulting in reduced energy consumption compared to grinding at room temperature. Additionally, frozen plastic suppresses heat generation during grinding, thereby reducing the risk of thermal melting, which can negatively impact the quality of the final plastic particles. Furthermore, freeze grinding reduces grinding time and power consumption regardless of the grinding method, significantly improving grinding efficiency compared to room temperature grinding.

[0009] Conventional freeze-crushing processes for plastic waste involve rapid cooling by impregnating or spraying with liquid nitrogen, after which the plastic passes through a grinding or milling machine. The crusher applies physical force to the frozen plastic to break it down into small particles, which can then be further processed or recycled.

[0010] The optimal freezing temperature for waste plastics varies depending on the type; typically, PVC (Polyvinyl Chloride) and PP (Polypropylene) require around -20°C, while PE (Polyethylene) and others require around -100°C. Conventional waste plastic freezing technology utilizes the ultra-low temperature of -196°C of liquid nitrogen and phase change energy for processing.

[0011] However, while this freeze-grinding method enables rapid freezing due to the cryogenic temperature of liquid nitrogen, there is a problem in that the freezing process costs are high due to the consumption of a large amount of liquid nitrogen.

[0012] In addition, there exists a waste plastic freezing technology that utilizes the gaseous phase change coldness of LNG at -162°C. However, this method is difficult to apply in practice due to concerns regarding the explosiveness and leakage of natural gas caused by the vaporization of LNG. Accordingly, new technologies capable of resolving these issues are required.

[0013] Therefore, new technologies are being developed to simultaneously achieve cost reduction and safety improvement by using LNG cold energy instead of conventional liquid nitrogen for freezing waste plastics.

[0014] However, even with the use of cryogenic cooling, heat generation still occurs due to impact and friction during the grinding process, which can potentially generate large amounts of harmful gases in materials such as ABS.

[0015] In particular, the generation of such hazardous gases can cause serious problems in non-enclosed grinding environments. Methods to address this include the use of filters, ventilation systems, activated carbon adsorption, and scrubbers to capture and remove hazardous gases. However, these methods are currently difficult to implement due to high installation and maintenance costs. Therefore, to minimize the release of hazardous gases during the grinding process, it is essential to maintain cryogenic cooling at the lowest possible temperature and optimize parameters to reduce frictional heat generation.

[0016] Furthermore, the emission of harmful gases, particularly VOCs, during the melting and grinding processes of ABS is a significant issue in various melt injection applications, such as 3D printers. In 3D printers, the approach to addressing this problem involves using specialized equipment designed to mitigate VOC emissions and preventing VOC exposure through indoor ventilation. This includes the use of filters, ventilation systems, activated carbon adsorption, and scrubbers to capture and remove VOCs from the air. However, unlike 3D printers, which have relatively small capacities and low overall VOC emissions, the use of such equipment is inefficient and capacity expansion is impossible in industries where high-volume operations are performed. Therefore, the conventional method used to reduce VOC emissions during the grinding of ABS materials involves freezing the ABS. Prior art literature

[0017] Japanese Published Patent No. JP 2006-7188, Korean Registered Patent No. 10-2555690, Korean Registered Patent No. 10-1931252 The problem to be solved

[0018] The objective of the present invention is to provide a waste plastic freezing crushing device and method capable of preventing the generation of harmful volatile organic compounds (VOCs) during the crushing process for plastic recycling by operating the waste plastic crushing process in a closed environment and controlling the heat generated during the crushing process by injecting cooling air into the crusher.

[0019] Furthermore, another objective of the present invention is to provide an economical and practical cryogenic crushing apparatus and method for waste plastics by controlling the heat generated during the crushing process without using cryogenic fluids, such as LNG (Liquefied Natural Gas) or LN2 (Liquid Nitrogen), which are required in conventional cryogenic crushing technologies and have low accessibility and supply constraints. means of solving the problem

[0020] A waste plastic freezing and crushing device according to the present invention for achieving the above-mentioned purpose may include: a crushing chamber into which waste plastic is introduced and a crushing unit equipped with a crusher that crushes the waste plastic inside the crushing chamber; a sealed discharge pipe, the upper part of which is connected to the lower part of the crushing unit and through which waste plastic particles crushed in the crushing unit are discharged; a collection unit that collects waste plastic particles that have passed through the sealed discharge pipe; a cooling cycle comprising a compressor that compresses a refrigerant to a high temperature and high pressure, a condenser that releases heat from the high temperature and high pressure refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has passed through the condenser to a low pressure, and an evaporator in which heat exchange occurs between the low temperature and low pressure refrigerant that has passed through the expansion valve and air; a cold air injection unit that sprays cooling air cooled by the cooling cycle into the crushing chamber; and a control unit that controls the operation of the crushing unit, the cooling cycle, and the cold air injection unit.

[0021] A waste plastic freezing and crushing device according to another embodiment of the present invention may further include: an air intake pipe, one end of which is connected to the sealed discharge pipe and sucks in air discharged from the crushing chamber into the sealed discharge pipe; an air pump connected to the other end of the air intake pipe and sucking in air through the air intake pipe; and a cold air circulation pipe, one end of which is connected to the discharge port of the air pump and the other end of which is connected to the cold air injection unit via the evaporator of the cooling cycle.

[0022] A dehumidifier that removes moisture from the air discharged from the air pump may be installed between the discharge port of the air pump and the cold air circulation pipe.

[0023] A waste plastic freezing and crushing device according to another embodiment of the present invention further includes a temperature sensor installed in the crushing chamber to measure the temperature, and the control unit can control the operation of the cooling cycle according to the temperature measured by the temperature sensor to adjust the temperature of the cooling air sprayed into the crushing chamber.

[0024] A waste plastic freezing and crushing device according to another embodiment of the present invention further includes a VOC sensor installed in the sealed discharge pipe to measure the concentration of volatile organic compounds (VOCs) in the air, and the control unit can control the operation of the cooling cycle according to the concentration of volatile organic compounds (VOCs) measured by the VOC sensor to adjust the temperature of the cooling air sprayed into the crushing chamber.

[0025] A heating corrugated pipe made of a thermally conductive metal material is installed at the bottom of the above-mentioned sealed discharge pipe to perform heat exchange between the air passing through the sealed discharge pipe and the outside air to raise the temperature of the air passing through the sealed discharge pipe, and the VOC sensor may be installed on the lower side of the heating corrugated pipe.

[0026] A mesh-type filter may be installed at the top of the above-mentioned sealed discharge pipe to allow waste plastic particles of a predetermined size or smaller, crushed in the crushing chamber, to pass through.

[0027] A waste plastic freezing and crushing device according to another embodiment of the present invention may further include a waste plastic supply unit that supplies and feeds waste plastic into the crushing chamber of the crushing unit.

[0028] A method for freeze-crushing waste plastic using a waste plastic freeze-crushing device according to the present invention is,

[0029] (S1) A step of introducing waste plastic into a crushing chamber and operating a crusher to crush the waste plastic;

[0030] (S2) A step of crushing waste plastic while controlling the heat generated during crushing by injecting cooling air cooled through a cooling cycle into the crushing chamber while proceeding with the above step (S1);

[0031] (S3) A step of discharging waste plastic particles crushed by a crusher through a sealed discharge pipe; and,

[0032] (S4) A step of collecting waste plastic particles that have passed through the above sealed discharge pipe in a collection unit;

[0033] It may include.

[0034] According to the waste plastic freezing and crushing method of the present invention, when proceeding with steps (S1) to (S4), air discharged into the sealed discharge pipe can be sucked in by an air pump, cooled by passing through the evaporator of the cooling cycle, and then injected into the crushing chamber to circulate.

[0035] According to the waste plastic freezing and crushing method of the present invention, moisture can be removed from the air in the sealed discharge pipe sucked in by the air pump and then transferred to an evaporator.

[0036] In addition, the operation of the cooling cycle can be controlled according to the temperature measured by the temperature sensor installed in the grinding chamber, thereby adjusting the temperature of the cooling air sprayed into the grinding chamber.

[0037] According to a method for freezing and crushing waste plastic according to another embodiment of the present invention, the concentration of volatile organic compounds (VOCs) in the air discharged through the sealed discharge pipe is measured by a VOC sensor installed in the sealed discharge pipe, and the temperature of the cooling air sprayed into the crushing chamber can be adjusted by controlling the operation of the cooling cycle according to the concentration of volatile organic compounds (VOCs) measured by the VOC sensor.

[0038] The air discharged through the above-mentioned sealed exhaust pipe can be heat-exchanged with outside air at room temperature to raise the temperature of the air discharged through the sealed exhaust pipe, and then the concentration of volatile organic compounds (VOCs) can be measured using a VOC sensor. Effects of the invention

[0039] According to the present invention, when a crushing process is carried out in a crushing section, cooling air cooled through a cooling cycle is supplied to a cold air injection section and injected into the crushing chamber, thereby suppressing heat generation during the crushing process of waste plastics and suppressing the generation of harmful gases, including volatile organic compounds (VOCs), during the crushing process of waste plastics.

[0040] In addition, instead of using cryogenic fluids such as liquid nitrogen, air discharged from a sealed discharge pipe and circulating is cooled using a cooling cycle and supplied to the grinding section, thereby resolving the handling difficulties, practical application problems, and economic issues associated with the use of cryogenic fluids.

[0041] In addition, since the air discharged from the grinding chamber circulates through a closed system connected to the air intake pipe, air pump, dehumidifier, cold air circulation pipe, cold air injection unit, and grinding chamber connected to the closed exhaust pipe, harmful gases generated during the grinding process can be prevented from being discharged to the outside.

[0042] In addition, since it is possible to obtain temperature information inside the grinding chamber and information on the concentration of VOCs and harmful gases in the air discharged through the sealed exhaust pipe, and to appropriately adjust the temperature of the cooling air by adjusting the opening of the expansion valve of the cooling cycle, there is also the advantage of efficiently utilizing the power consumption of the cooling cycle and effectively suppressing VOC generation in the grinding section. Brief explanation of the drawing

[0043] FIG. 1 is a schematic diagram showing the overall configuration of a waste plastic freeze-crushing device according to one embodiment of the present invention. FIG. 2 is a drawing showing some components constituting a waste plastic freeze-crushing device according to one embodiment of the present invention. FIG. 3 is a drawing showing other parts of a waste plastic freeze-crushing device according to one embodiment of the present invention. FIG. 4 is a configuration diagram showing the configuration for controlling a waste plastic freezing and crushing device according to one embodiment of the present invention. FIG. 5 is a drawing showing another part of the configuration constituting a waste plastic freeze crushing device according to one embodiment of the present invention. Specific details for implementing the invention

[0044] The embodiments described in this specification and the configurations illustrated in the drawings are merely preferred examples of the disclosed invention, and various modifications that may replace the embodiments and drawings of this specification may exist at the time of filing this application.

[0045] Hereinafter, a waste plastic freeze-crushing apparatus and method for waste plastic recycling will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals indicate the same components.

[0046] FIGS. 1 to 5 show a waste plastic freeze-crushing device for waste plastic recycling according to one embodiment of the present invention.

[0047] First, referring to FIG. 1, a waste plastic freezing and crushing device according to one embodiment of the present invention comprises: a waste plastic supply unit (100) for supplying and feeding waste plastic; a crushing unit (200) for crushing waste plastic; a sealed discharge pipe (300) connected to the lower part of the crushing unit (200) through which waste plastic particles crushed in the crushing unit (200) are discharged; a collecting unit (500) for collecting waste plastic particles that have passed through the sealed discharge pipe (300); a cooling cycle (400) for cooling air to generate cooling air; a cold air injection unit (600) for injecting the cooling air cooled by the cooling cycle (400) into the crushing chamber (210) of the crushing unit (200); an air intake pipe (610) and an air pump (620) for sucking in air discharged from the crushing unit (200) to the sealed discharge pipe (300), circulating it through the cooling cycle (400), and then supplying it to the cold air injection unit (600); It may include a control unit (700) that controls the operation of a cold air circulation pipe (630), a waste plastic supply unit (100), a crushing unit (200), a cooling cycle (400), and an air pump (620).

[0048] The waste plastic supply unit (100) is configured to supply waste plastic to be crushed to the crushing unit (200), and may include a waste plastic transfer pipe (120) equipped with a screw conveyor (121) that transfers the waste plastic fed through the hopper (110) to the crushing chamber (210) of the crushing unit (200). The discharge port of the waste plastic transfer pipe (120) is connected to an input port (211) formed at the top of the crushing chamber (210) and supplies the waste plastic transferred by the screw conveyor (121) into the crushing chamber (210) through the input port (211) of the crushing chamber (210).

[0049] Referring to FIG. 2, the crushing unit (200) may include a crushing chamber (210) having an input port (211) formed at the top, and a crusher (220) that crushes waste plastic inside the crushing chamber (210). A sealed discharge pipe (300) is installed to communicate with the bottom of the crushing chamber (210) to discharge waste plastic particles crushed by the crusher (220). A mesh-type filter (310) may be installed at the top of the sealed discharge pipe (300) communicating with the bottom of the crushing chamber (210) to allow waste plastic particles of a predetermined size or smaller, crushed inside the crushing chamber (210), to pass through.

[0050] The crusher (220) may be equipped with a plurality of crushing blades (221) that finely crush waste plastic while rotating by a motor (not shown).

[0051] The lower part of the crushing chamber (210) is connected to a sealed discharge pipe (300) that is sealed so that the gas generated inside cannot escape directly to the outside.

[0052] Referring to FIG. 3, the sealed discharge pipe (300) communicates with the lower surface of the crushing chamber (210) and serves to guide waste plastic particles crushed to a size smaller than a predetermined size by the crusher (220) to the lower collection section (500) (see FIG. 1). In addition, it forms a sealed system connected to an air pump (620) through the air intake pipe (610) to circulate air discharged from the crushing chamber (210) to the sealed discharge pipe (300) through the air intake pipe (610), the air pump (620), and the cold air circulation pipe (630), thereby ensuring that air containing harmful gases generated during the crushing process is not discharged to the outside and circulates through the waste plastic freezing crushing device.

[0053] The cooling cycle (400) is configured to control the heat generated during the crushing process of waste plastic by supplying cooling air into the crushing chamber (210) through a cold air injection unit (600). The cooling cycle (400) may include a compressor (410) that compresses a refrigerant to a high temperature and high pressure, a condenser (420) that releases heat from the high temperature and high pressure refrigerant compressed by the compressor (410), an expansion valve (430) that expands the refrigerant passing through the condenser (420) to a low pressure, and an evaporator (440) in which heat exchange occurs between the low temperature and low pressure refrigerant passing through the expansion valve (430) and air.

[0054] The evaporator (440) is installed to be in contact with the pipe connected to the discharge side of the air pump (620), namely the cold air circulation pipe (630), and cools the air flowing through the cold air circulation pipe (630).

[0055] The refrigerant used in the cooling cycle (400) can be varied according to the calorific value of the waste plastic to be crushed. For example, since low-temperature embrittlement occurs at around -20°C for PVC (Polyvinyl Chloride) and PP (Polypropylene), single or mixed refrigerants such as R134A, R401A, and R407C, which have a boiling point of -25 to -45°C, can be applied as appropriate refrigerants.

[0056] The air pump (620) sucks in air from the sealed discharge pipe (300) through the air intake pipe (610) and discharges it to the cold air circulation pipe (630). At this time, since the air inside the sealed discharge pipe (300) contains air containing moisture that has flowed into the crushing chamber (210) from the waste plastic supply unit (100), it is desirable to remove moisture from the air sucked in by the air pump (620) and transfer it to the cold air circulation pipe (630). When air containing moisture is cooled by the cooling cycle (400) and sprayed into the crushing chamber (210), frost may form on the mesh-type filter screen (310) at the top of the sealed discharge pipe (300), causing a blockage problem. Therefore, it is desirable to install a dehumidifier (640) that removes moisture between the discharge port of the air pump (620) and the cold air circulation pipe (630) so that dry air is transported to the cold air circulation pipe (630).

[0057] The dehumidifier (640) can be configured to absorb and remove moisture from the air using silica gel or alumina gel as a desiccant. At this time, to desorb moisture adsorbed on the silica gel or alumina gel, a pair of known rotary heating dryers or dehumidifiers (640) can be configured and operated alternately to regenerate the internal desiccant.

[0058] The cold air injection unit (600) may include a nozzle connected to one end of the cold air circulation pipe (630) that injects air cooled through the evaporator (440) of the cooling cycle (400) into the crushing chamber (210).

[0059] The collection unit (500) is in the form of a tank or container connected to the lower part of the sealed discharge pipe (300) and collects and stores waste plastic particles that have passed through the sealed discharge pipe (300).

[0060] Meanwhile, referring to FIGS. 3 and 4, the control unit (700) can appropriately adjust the temperature of the cooling air injected into the grinding chamber (210) by controlling the opening of the expansion valve (430) of the cooling cycle (400). In order to efficiently utilize the power consumption of the cooling cycle (400) and effectively suppress the generation of VOCs in the grinding unit (200), a temperature sensor (710) for measuring the temperature inside the grinding chamber (210) may be installed on one side of the grinding chamber (210). Additionally, a VOC sensor (720) for measuring the concentration of volatile organic compounds (VOCs) in the air discharged through the sealed discharge pipe (300) may be installed in the sealed discharge pipe (300).

[0061] The temperature sensor (710) and the VOC sensor (720) are electrically connected to the control unit (700) and transmit measurement signals to the control unit (700). The control unit (700) can adjust the temperature of the cooling air sprayed into the grinding chamber (210) by PID controlling the operation of the expansion valve (430) of the cooling cycle (400) according to the temperature information measured by the temperature sensor (710) and the concentration information of volatile organic compounds (VOC) measured by the VOC sensor (720). For example, if the control unit (700) observes that the internal temperature of the grinding chamber (210) is rising and the amount of VOC generated is increasing, it can increase the supply of cooling energy by increasing the inlet of the expansion valve (430), thereby further suppressing the heat generation phenomenon inside the grinding chamber (210) to prevent VOC generation and efficiently manage cooling energy in terms of device operation.

[0062] The VOC sensor (720) measures the resistance value of an internal detection sensor that changes according to the amount of VOC or special gas components generated. If this value is denoted as Ro, the resistance value in a normal atmospheric composition without pollutants decreases when exposed to special gases, and if this is expressed as Rs, the ratio of the resistance values ​​is It is represented as follows. In the case of normal air, this value is the same at 1, but when contaminants are introduced, the ratio of this resistance value becomes less than 1. The amount of this decrease in the ratio of resistance values ​​varies depending on the type and density of the exposed material, and these values ​​are retrieved into a database to define the measurement values. However, since these calibration values ​​are measured in an experimental environment of 20°C and 65% relative humidity, the temperature and relative humidity of the sensor measurement unit must be maintained at a state similar to the calibration values ​​to ensure the reliability of the calibration values. In particular, because it is measured based on resistance values, it is sensitive to temperature changes; if the internal temperature rises, the resistance value decreases, causing the Rs value to decrease even in normal air conditions, so this must be taken into consideration.

[0063] Accordingly, in order to raise the temperature of the low-temperature air discharged through the sealed discharge pipe (300), as shown in FIG. 5, a heating corrugated pipe (320) made of a thermally conductive metal material is installed at the bottom of the sealed discharge pipe (300) to perform heat exchange between the air passing through the sealed discharge pipe (300) and the outside air to raise the temperature of the air passing through the sealed discharge pipe (300), and the VOC sensor (720) can be installed at the bottom of the heating corrugated pipe (320).

[0064] The heating corrugated pipe (320) may be made of a corrugated pipe made of a metal material with excellent thermal conductivity, such as aluminum. The heating corrugated pipe (320) is installed in the lower region of the part connected to the air intake pipe (610), and after the air cooled to 0°C or lower is drawn in as much as possible from the air intake pipe (610), it passes through the heating corrugated pipe (320) region to minimize the amount of heat required for heating the air. The low-temperature air passing through the heating corrugated pipe (320) exchanges heat with the warm outside air through the thin surface of the heating corrugated pipe (320), which has excellent thermal conductivity, and is heated to a state similar to room temperature, and the heated air is allowed to flow to the VOC sensor (720) so as not to affect the resistance value of the VOC sensor (720).

[0065] Hereinafter, a method for freeze-crushing waste plastic using a waste plastic freeze-crushing device having the configuration described above will be explained in detail.

[0066] First, waste plastic to be crushed is fed through the hopper (110) of the waste plastic supply unit (100), and the waste plastic is transported to the crushing unit (200) using a screw conveyor (121) and supplied into the crushing chamber (210) through the input port (211) at the top of the crushing chamber (210).

[0067] Waste plastic introduced into the crushing chamber (210) is crushed into waste plastic particles by a rotating crusher (220), then passes through a mesh-type filter (310) at the top of the sealed discharge pipe (300) and is discharged into the sealed discharge pipe (300), after which it is collected and stored in the collection unit (500).

[0068] In this way, when the crushing process is carried out in the crushing section (200), cooling air cooled through the cooling cycle (400) is supplied to the cold air injection section (600) and injected into the crushing chamber (210), thereby suppressing the heat generated during the crushing process of waste plastic and suppressing the generation of harmful gases, including VOCs, during the crushing process of waste plastic.

[0069] At this time, the cooling cycle (400) cools the air discharged from the sealed discharge pipe (300) by circulating it and supplies it to the cold air injection unit (600). That is, the air discharged from the crushing chamber (210) into the sealed discharge pipe (300) is sucked in by the air pump (620) through the air intake pipe (610), moisture is removed by the dehumidifier (640), and then cooled by passing it through the evaporator (440) of the cooling cycle (400) via the cold air circulation pipe (630), and then supplied to the cold air injection unit (600) to be injected into the crushing chamber (210).

[0070] In this way, the air discharged from the crushing chamber (210) circulates through the air intake pipe (610), air pump (620), dehumidifier (640), cold air circulation pipe (630), cold air injection unit (600), and the closed system of the crushing chamber (210) connected to the closed discharge pipe (300), thereby preventing harmful gases generated during the crushing process from being discharged to the outside.

[0071] When the crushing process of waste plastic is carried out while controlling heat generation by injecting cooling air into the crushing chamber (210) during the crushing process, the temperature inside the crushing chamber (210) is measured in real time by a temperature sensor (710) installed in the crushing chamber (210) and transmitted to the control unit (700), and the VOC sensor (720) measures the concentration of VOC in the air discharged through the sealed discharge pipe (300) and transmits to the control unit (700).

[0072] And, as described above, the control unit (700) adjusts the opening of the expansion valve (430) of the cooling cycle (400) based on the measurement value of the temperature sensor (710) and the measurement value of the VOC sensor (720) to adjust the temperature of the cooling air sprayed into the grinding chamber (210).

[0073] Although the present invention has been described in detail above with reference to embodiments, it is obvious to those skilled in the art that various substitutions, additions, and modifications are possible within the scope of the technical concept described above without departing from the spirit of the invention, and such modified embodiments should also be understood to fall within the scope of protection of the present invention as defined by the claims appended below. Explanation of the symbols

[0074] 100 : Waste plastic supply unit 200 : Crushing unit 210 : Grinding Chamber 220 : Grinder 300 : Sealed discharge pipe 310 : Mesh type strainer 320 : Heating corrugated tube 400 : Cooling cycle 410: Compressor 420: Condenser 430 : Expansion valve 440 : Evaporator 500 : Collection unit 600 : Cold air injection unit 610 : Air intake pipe 620 : Air pump 630 : Cold air circulation pipe 640 : Dehumidifier 700 : Control unit 710 : Temperature sensor 720: VOC sensor

Claims

Claim 1 A crushing unit equipped with a crushing chamber into which waste plastic is fed and a crusher that crushes the waste plastic inside the crushing chamber; a sealed discharge pipe, the upper part of which is connected to the lower part of the crushing unit and through which waste plastic particles crushed in the crushing unit are discharged; a collection unit that collects waste plastic particles that have passed through the sealed discharge pipe; a cooling cycle comprising a compressor that compresses a refrigerant to a high temperature and high pressure, a condenser that releases heat from the high temperature and high pressure refrigerant compressed by the compressor, an expansion valve that expands the refrigerant that has passed through the condenser to a low pressure, and an evaporator in which heat exchange occurs between the low temperature and low pressure refrigerant that has passed through the expansion valve and air; and a cold air injection unit that injects cooling air cooled by the cooling cycle into the crushing chamber. A waste plastic freezing and crushing device comprising: a control unit for controlling the operation of the crushing unit, the cooling cycle, and the cold air injection unit; an air intake pipe, one end of which is connected to the sealed discharge pipe and sucks in air discharged from the crushing chamber into the sealed discharge pipe; an air pump connected to the other end of the air intake pipe and sucks in air through the air intake pipe; and a cold air circulation pipe, one end of which is connected to the discharge port of the air pump and the other end of which is connected to the cold air injection unit via the evaporator of the cooling cycle. Claim 2 delete Claim 3 A waste plastic freezing and crushing device according to claim 1, wherein a dehumidifier for removing moisture from the air discharged from the air pump is installed between the discharge port of the air pump and the cold air circulation pipe. Claim 4 A waste plastic freezing and crushing device according to claim 1, further comprising a temperature sensor installed in the crushing chamber to measure the temperature, wherein the control unit controls the operation of the cooling cycle according to the temperature measured by the temperature sensor to adjust the temperature of the cooling air sprayed into the crushing chamber. Claim 5 A waste plastic freezing and crushing device according to claim 1, further comprising a VOC sensor installed in the sealed discharge pipe to measure the concentration of volatile organic compounds (VOCs) in the air, wherein the control unit controls the operation of the cooling cycle according to the concentration of volatile organic compounds (VOCs) measured by the VOC sensor to adjust the temperature of the cooling air sprayed into the crushing chamber. Claim 6 In claim 5, a heat-conducting metal-based heating corrugated pipe is installed at the bottom of the sealed discharge pipe to perform heat exchange between the air passing through the sealed discharge pipe and the outside air to raise the temperature of the air passing through the sealed discharge pipe, and the VOC sensor is installed at the bottom of the heating corrugated pipe in a waste plastic freezing and crushing device. Claim 7 A waste plastic freezing and crushing device according to claim 1, wherein a mesh-type filter is installed at the top of the sealed discharge pipe to allow waste plastic particles of a predetermined size or smaller, crushed in the crushing chamber, to pass through. Claim 8 A waste plastic freezing and crushing device according to claim 1, further comprising a waste plastic supply unit that supplies and feeds waste plastic into the crushing chamber of the crushing unit. Claim 9 A method for freeze-crushing waste plastic using a waste plastic freeze-crushing device according to any one of claims 1 and 3 to 8, comprising: (S1) a step of introducing waste plastic into a crushing chamber and operating a crusher to crush the waste plastic; (S2) a step of crushing waste plastic while controlling the heat generated during crushing by injecting cooling air cooled through a cooling cycle into the crushing chamber while performing step (S1); and (S3) a step of discharging waste plastic particles crushed by the crusher through a sealed discharge pipe; and (S4) a step of collecting waste plastic particles that have passed through the sealed discharge pipe in a collection unit; wherein, when performing steps (S1) to (S4), the air discharged into the sealed discharge pipe is sucked in by an air pump, cooled by passing through the evaporator of the cooling cycle, and then injected into the crushing chamber to circulate it. Claim 10 delete Claim 11 A method for freezing and crushing waste plastic according to claim 9, characterized by removing moisture from the air in a sealed discharge pipe sucked in by the air pump and then transferring it to an evaporator. Claim 12 A method for freezing and crushing waste plastic according to claim 9, characterized by controlling the operation of the cooling cycle according to the temperature measured by a temperature sensor installed in the crushing chamber to adjust the temperature of the cooling air sprayed into the crushing chamber. Claim 13 A method for freezing and crushing waste plastic according to claim 9, characterized by measuring the concentration of volatile organic compounds (VOCs) in the air discharged into the sealed discharge pipe using a VOC sensor installed in the sealed discharge pipe, and controlling the operation of the cooling cycle according to the concentration of volatile organic compounds (VOCs) measured by the VOC sensor to adjust the temperature of the cooling air sprayed into the crushing chamber. Claim 14 A method for freezing and crushing waste plastic according to claim 13, characterized by heat-exchanging the air discharged through the sealed discharge pipe with outside air at room temperature to raise the temperature of the air discharged through the sealed discharge pipe, and then measuring the concentration of volatile organic compounds (VOCs) using a VOC sensor.

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