Desalination unit and desalination method

Abstract

The present invention provides a technology for stably discharging a desalination gas generated in a desalination device when desalinating waste plastic by using the desalination device. A desalination device 2 provided to a desalination unit 12 for removing chlorine content contained in waste plastic comprises an extruder, thermally decomposes waste plastic supplied from a supply part 4, and discharges, from a discharge part, a mixture of a molten material and a desalination gas containing chlorine. A separation tank 3 separates the mixture discharged from the discharge part into the molten material and the desalination gas. Further, the desalination device 2 is provided with, at a location between the supply part and the discharge part, an outflow prevention mechanism which does not have a vent for drawing out the desalination gas and which prevents the desalination gas inside the desalination device 2 from flowing out toward the upstream of the supply part.

Description

Desalination unit and desalination method

[0001] The present invention relates to a technology for removing chlorine contained in waste plastics.

[0002] Methods for recycling waste plastic include material recycling, in which waste plastic is washed, melted, and regenerated into raw plastic materials such as pellets and flakes; chemical recycling, in which waste plastic is decomposed and converted into monomers or gasified, or used as a reducing agent for blast furnaces or as raw material for coke ovens; and thermal recycling, in which waste plastic is burned as fuel to recover energy.

[0003] Among these methods, the conversion of waste plastics into oil corresponds to chemical recycling, and is a technology in which waste plastics are thermally decomposed to produce pyrolysis oil. The resulting pyrolysis oil can be refined and used as a raw material for various fuel oils and chemical products, or directly combusted for thermal recycling.

[0004] When converting waste plastics into oil, a desalination process is carried out as a pretreatment to remove chlorine from the waste plastics. A known method for this desalination process is to use an extruder as a desalination machine, melting and pyrolyzing the waste plastics by external heating or shear heating, and separating the chlorine as desalination gas. Extruders are broadly divided into single-screw and twin-screw types, but twin-screw extruders have the advantage of being able to process larger amounts than single-screw extruders, and are therefore preferable from an economical perspective.

[0005] On the other hand, twin-screw extruders used as desalters have a tendency for the desalted gas generated within the desalter to flow back upstream. This makes it difficult to adopt a method of discharging the desalted gas together with the molten material only from the rear end of the desalter. Therefore, the desalted gas has traditionally been extracted through a vent installed along the path of the molten waste plastic moving along the screw. The vent from which the desalted gas is extracted is connected to a vacuum exhaust line, and the desalted gas is discharged through this vacuum exhaust line toward the combustion furnace.

[0006] Patent Document 1 describes a technology for detecting vent-up, a phenomenon in which molten plastic rises toward the vent box, in a screw extrusion-type dechlorination device that melts and thermally decomposes waste plastic. Patent Document 1 describes the problem that if the occurrence of vent-up is delayed, it will have a significant impact on the equipment, and the time and amount of work required to restart operation will be extremely serious. However, Patent Document 1 does not disclose a technology for eliminating the occurrence of vent-up itself.

[0007] Furthermore, Patent Document 2 describes a waste plastic feeding device that uses a reciprocating piston to extrude waste plastic supplied from a hopper into a waste plastic preheating chamber, where it is heated to a temperature at which vinyl chloride does not thermally decompose to melt and soften the waste plastic, and then extrudes it through a die into a pyrolysis furnace. In this waste plastic feeding device, the molten and softened waste plastic is always present in the die, forming a material seal that prevents hydrogen chloride gas from inside the pyrolysis furnace from flowing into the waste plastic feeding device and prevents external oxygen from flowing into the pyrolysis furnace through the die.

[0008] Next, Patent Document 3 describes a technology in which an extruder is used to melt raw material made of waste plastic at a temperature at which polyvinyl chloride does not thermally decompose, and when the raw material is supplied to a decomposition tank where the polyvinyl chloride is thermally decomposed, a material seal is formed between the extruder and the decomposition tank using a molten material. However, the technologies described in Patent Documents 2 and 3 only describe technologies for softening and melting waste plastic in a waste plastic preheating chamber or extruder without promoting thermal decomposition, and do not disclose a technology for treating desalted gas when an extruder is used as a desalting machine.

[0009] Japanese Patent No. 4612582 Japanese Patent Application Laid-Open No. 2002-309034 Japanese Patent Application Laid-Open No. 2000-117739

[0010] The present invention has been made against this background, and provides a technology for stably discharging desalted gas generated in a desalting machine composed of an extruder when desalting waste plastics.

[0011] The desalination unit of the present invention is a desalination unit that removes chlorine contained in waste plastics, and comprises: a desalination machine composed of an extruder that thermally decomposes the waste plastics supplied from a supply section and discharges a mixture of desalted gas containing chlorine and a molten material from a discharge section; and a separation tank that is provided downstream of the discharge section and separates the mixture discharged from the discharge section into the molten material and the desalted gas, and is connected to an exhaust line for exhausting the desalted gas and an outlet line for discharging the molten material, wherein the desalting machine does not have a vent for extracting the desalted gas between the supply section and the discharge section, and is equipped with an outflow prevention mechanism for preventing the desalted gas inside the desalting machine from outflowing upstream of the supply section.

[0012] The desalination unit may have the following configuration: (a) The desalination machine is configured with a twin-screw extruder. (b) The outflow prevention mechanism is a region formed upstream of the region where thermal decomposition progresses inside the desalination machine and whose temperature is lower than the thermal decomposition temperature of the waste plastic. In this case, the region lower than the thermal decomposition temperature of the waste plastic is a region heated to a temperature at which the waste plastic plastic is plasticized. Furthermore, the outflow prevention mechanism is a material seal of plasticized plastic formed in a region lower than the thermal decomposition temperature of the waste plastic. (c) The desalination machine is equipped with a temperature adjustment unit that adjusts the temperature inside the desalination machine, and the temperature adjustment unit includes a first temperature control mechanism that maintains the region where thermal decomposition progresses at the thermal decomposition temperature, and a second temperature control mechanism that maintains the region upstream of the region where thermal decomposition progresses inside the desalination machine at a temperature at which the waste plastic is plasticized, in order to form the outflow prevention mechanism. (d) The outflow prevention mechanism comprises a hopper into which the waste plastic is fully supplied to the supply section, or the outflow prevention mechanism comprises a screw-type pushing mechanism into the supply section that pushes the waste plastic into the desalter. In these cases, the outflow prevention mechanism is a material seal for the waste plastic formed in the supply section.

[0013] (e) The desalter is provided with a temperature adjustment unit that adjusts the temperature inside the desalter, a temperature detection unit that detects the temperature inside the desalter, and an interlock control unit that releases the restriction on stopping the supply of the waste plastic from the supply unit on the condition that the temperature inside the desalter detected by the temperature detection unit is lower than the thermal decomposition temperature of the waste plastic.Furthermore, the interlock control unit executes an operation to stop the supply of the waste plastic from the supply unit by releasing the restriction on stopping the supply of the waste plastic.(f) In (e), the interlock control unit determines whether to release the restriction on stopping the supply of the waste plastic based on the temperature detection results of the temperature detection unit provided in the area inside the desalter where the thermal decomposition progresses and / or the temperature detection unit provided in the area inside the desalter upstream of the area where the thermal decomposition progresses.

[0014] (g) In (e), the temperature adjustment unit is configured as a cooling unit that adjusts the temperature inside the desalination machine using a refrigerant. In this case, the temperature adjustment unit is configured to circulate cooling water as the refrigerant through a flow path formed in the wall of the desalination machine. Alternatively, the temperature adjustment unit is configured to supply cooled air as the refrigerant toward the outer wall surface of the desalination machine.

[0015] (h) The outflow prevention mechanism is a lock hopper provided in the supply section and configured to be connectable / disconnectable by an on / off valve to a raw material supply line to which the waste plastic is supplied from upstream. (i) In (h), the lock hopper is provided with a supply mechanism that supplies the waste plastic received from the raw material supply line to the desalter. Alternatively, the lock hopper is provided with a first lock hopper section configured to be connectable / disconnectable to the raw material supply line by a first on / off valve, and a second lock hopper section configured to be connectable / disconnectable to the first lock hopper via an intermediate line provided with a second on / off valve, and provided with a supply mechanism that supplies the waste plastic to the desalter.

[0016] The desalination unit of the present invention does not have a vent in the desalination machine, so problems associated with vent-up can be avoided. Furthermore, the desalination machine is equipped with an outflow prevention mechanism to prevent the desalination gas from leaking upstream, so the desalination gas can be stably discharged toward the separation tank located downstream.

[0017] 1 is a configuration diagram of a waste plastic oil plant equipped with a desalter according to an embodiment. FIG. 1 is a configuration diagram of a desalter according to an embodiment. FIG. 2 is an exterior side view of a conventional desalter equipped with a vent. FIG. 3 is an explanatory diagram of vent-up that occurs in the vent. FIG. 4 is an exterior side view of a desalter according to an embodiment. FIG. 5 is a schematic diagram of a desalter in which a material seal is formed inside. FIG. 6 is a configuration diagram of a desalter in which a material seal is formed by a full supply hopper. FIG. 7 is a configuration diagram of a desalter in which a material seal is formed by a hopper with a screw-type pushing mechanism. FIG. 8 is a configuration diagram of a desalter equipped with an interlock mechanism to prevent the material seal from breaking. FIG. 9 is a configuration diagram of a desalter equipped with a lock hopper. FIG. 10 is a configuration diagram of a desalter equipped with another example of a lock hopper.

[0018] 1 shows an example of the configuration of a waste plastic oil plant (hereinafter simply referred to as an "oil plant") equipped with a demineralization unit 12 according to this embodiment. The waste plastics include chlorine-free waste plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS). Furthermore, the waste plastics often include chlorine-containing waste plastics such as polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), and polyethylene terephthalate (PET).

[0019] The oil-refining plant shown in Figure 1 is equipped with a desalination unit 12 that melts waste plastics and removes chlorine contained in PVC, PVDC, etc., a thermal decomposition furnace 13 that performs thermal decomposition treatment of the molten waste plastics, a cracked oil drum 15 that cools the pyrolysis gas produced by the pyrolysis and then separates it into pyrolysis oil and off-gas, a cracked residue combustion furnace 17 that combusts the pyrolysis residue produced by the pyrolysis furnace 13, and a desalted gas combustion furnace 16 that combusts the desalted gas (gas containing hydrogen chloride, hydrocarbons, organic chlorines, hydrogen, moisture, etc.) generated in the desalting machine 2.

[0020] The desalination unit 12 includes a desalination machine 2, e.g., a twin-screw extruder, and a separation tank 3; its detailed configuration will be described later. Waste plastics that have been pretreated, such as by crushing and granulating, are supplied to the desalination machine 2 as raw material. Before being supplied to the desalination machine 2 (before being melted), an alkaline earth metal, e.g., calcium-containing slaked lime, is added to the waste plastics from the slaked lime adding section 11. The slaked lime reacts with chlorine in the molten waste plastics and organic acids produced by thermal decomposition to produce calcium salts, which serve to prevent corrosive acid components from being mixed into the pyrolysis gas during the subsequent thermal decomposition. The alkaline earth metal added to the waste plastics is not limited to calcium; it may also be magnesium (e.g., magnesium hydroxide) or barium (e.g., barium hydroxide).

[0021] The desalter 2 heats the waste plastics to about 350°C to melt the waste plastics and thermally decomposes the PVC and PVDC, releasing hydrogen chloride, hydrocarbons, organic chlorines, hydrogen, moisture, and the like as desalted gas. The mixture of the molten material and desalted gas discharged from the desalter 2 is separated in a separation tank 3, and the desalted gas is supplied to a desalted gas combustion furnace 16. Meanwhile, the waste plastics are supplied to a pyrolysis furnace 13. The pyrolysis furnace 13 can be, for example, a rotary kiln.

[0022] In the pyrolysis furnace 13, the molten material flowing through the rotating kiln is heated to approximately 450°C, and the molten material is thermally decomposed and separated into pyrolysis gas and pyrolysis residue. The pyrolysis gas flowing out of the pyrolysis furnace 13 is cooled to room temperature in a cooler 14, and high-boiling components are condensed to obtain pyrolysis oil. The mixed fluid of the pyrolysis oil and the off-gas consisting of non-condensable gas components is separated in a cracked oil drum 15, and the pyrolysis oil is sent to, for example, a product tank. This pyrolysis oil may be supplied to, for example, an oil refinery plant and processed together with crude oil to be used as a raw material for chemical products such as plastics or fuel oil. In this case, a distillation column may be added to the oilification plant shown in Figure 1 to distill and separate the cracked oil into light oil, medium oil, and heavy oil, which can then be used for the respective fuel oil applications.

[0023] The off-gas separated from the thermal cracking oil in the cracked oil drum 15 is supplied to a desalinated gas combustion furnace 16 and a cracked residue combustion furnace 17. The desalinated gas combustion furnace 16 is configured as a boiler that burns a mixture of the desalinated gas and the off-gas, recovers heat from the combustion exhaust gas, and generates steam. The desalinated gas generates hydrogen chloride during combustion. For this reason, the desalinated gas combustion furnace 16 is equipped with measures to prevent corrosion by hydrogen chloride and is also equipped with equipment to remove hydrogen chloride from the exhaust gas.

[0024] On the other hand, the cracking residue combustion furnace 17 is a combustion furnace that burns the coke contained in the pyrolysis residue discharged from the pyrolysis furnace 13. The cracking residue combustion furnace 17 is configured, for example, by a fluidized bed furnace, a combustion furnace that burns the pyrolysis residue as pulverized fuel, or a rotary kiln. Note that if the amount of heat generated by the pyrolysis residue alone is insufficient, an auxiliary burner may be provided that burns the off-gas supplied from the off-gas line described above. The pyrolysis residue after the coke has been burned is discharged as ash.

[0025] The decomposition residue combustion furnace 17 is equipped with an air heater, and heated air heated by the air heater is supplied to a jacket-type heater provided in the pyrolysis furnace 13 as a heat medium for thermally decomposing the molten waste plastic. After heat supply in the pyrolysis furnace 13, the air is re-supplied to the air heater as circulating air. Note that the heat medium supplied from the decomposition residue combustion furnace 17 to the pyrolysis furnace 13 as a heat source for pyrolysis is not limited to the example of heated air. Steam or hot oil may also be used as the heat medium.

[0026] The above describes an example of the configuration of an oil refining plant equipped with the demineralization unit 12 according to this embodiment. However, the configuration of a waste plastic oil refining plant is not limited to this example. For example, a burner may be provided in the pyrolysis furnace 13, which is a rotary kiln, and the off-gas may be combusted by the burner to serve as a heat source for the pyrolysis treatment of the molten waste plastic.

[0027] Next, a configuration example of the demineralization unit 12 of this embodiment installed in an oil refining plant will be described in detail with reference to Fig. 2. As described above, the demineralization unit 12 includes the demineralizer 2 and the separation tank 3.

[0028] As shown in Figure 2, the desalting machine 2 is configured, for example, by a known twin-screw extruder, and is equipped with a raw material supply mechanism 4 that supplies waste plastics to the extruder. The extruder is equipped with two screws 22 arranged in parallel, a cylinder 21 that houses the screws 22, and a drive unit 23 that drives each screw 22 to rotate around its axis. Hereinafter, the cylinder 21 portion of the extruder that houses the screws 22 will also be referred to as the main body 20. Note that in Figures 2 and 9, the internal structure of the main body 20 is shown as seen from above to illustrate the two screws 22 arranged in parallel.

[0029] 2, 4, and 9 show examples of a screw 22 in which blades 222 are formed in a spiral shape along the outer circumferential surface of a shaft 221. However, there are no particular limitations on the configuration of the screw 22, and the design conditions such as the number, shape, and pitch of the blades 222 formed on the outer circumferential surface of the shaft 221 may be appropriately selected from a configuration suitable for desalination of waste plastics.

[0030] Furthermore, the screw 22 may be configured by connecting a plurality of elements having shafts 221 of different configurations along the length of the shaft 221 depending on the purpose of the processing. By arranging elements of different configurations along the length of the screw 22 in this way, different processes such as plasticization, kneading, transport, and desalination (pyrolysis) can be performed at different positions within the main body 20 depending on changes in the state of the waste plastic.

[0031] These screws 22 are housed in a cylinder 21. A space having an inner wall surface surrounding the outer periphery of the two screws 22 is formed inside the cylinder 21. By rotating the screws 22 around the central axis within this space, the waste plastic is kneaded and extruded between the screws 22 and between each screw 22 and the inner wall surface of the cylinder 21. The waste plastic is also heated by utilizing the shear heat that occurs during kneading.

[0032] A discharge line 52 leading to the separation tank 3 is connected to the side wall surface of the cylinder 21 facing the tip end of the screw 22. The connection portion with the discharge line 52 corresponds to the discharge portion in this embodiment. Meanwhile, an opening is formed in the surface of the main body 20 on the base end side of the screw 22. The opening is closed by a sealing plate 212.

[0033] The base ends of the screws 22 are connected to the drive unit 23 through the sealing plate 212 described above. The drive unit 23 is equipped with a rotation drive mechanism (not shown) that rotates each screw 22 around its central axis. The rotation drive mechanism may rotate the two screws 22 in the same direction or in opposite directions. The rotation direction of the screws 22 is set according to the configuration of the blades 222 so as to perform an operation of pushing out the waste plastic supplied into the main body 20 toward the discharge unit, which is the connection unit with the discharge line 52 (a process of discharging a mixture of desalted gas and molten material from the discharge unit).

[0034] The outer wall surface of the main body 20 is provided with a heating unit 25, which is a temperature control unit for controlling the temperature of the waste plastic inside. In the examples shown in Figures 2 and 9, heating is performed using electric heaters 251. Each electric heater 251 generates heat when power is supplied from a power supply unit 252, and heats the waste plastic inside via the wall surface of the main body 20 that is provided in contact with the heating unit 25.

[0035] For convenience of illustration, Fig. 2 shows a state in which each electric heater 251 is connected to the power supply unit 252 via a common power supply line. However, for example, the electric heaters 251 may be divided into multiple blocks along the length of the main body 20, and each block may be connected to the power supply unit 252 via a different power supply line. With this configuration, the amount of power supplied to the electric heaters 251 can be changed to perform different temperature control for each block.

[0036] Furthermore, the heating unit 25 is not limited to being configured to perform heating using the electric heater 251. For example, the waste plastic inside the main body 20 may be heated using a heat medium such as the above-mentioned heated air, steam, or hot oil.

[0037] Furthermore, the outer wall surface of the main body 20 is provided with a cooling unit 24, which is a temperature control unit for adjusting the temperature of the waste plastic inside. The cooling unit 24 serves to cool the waste plastic inside to below the thermal decomposition temperature, for example, when shutting down the operating desalination machine 2. For example, as shown in an enlarged view in FIG. 5, the cooling unit 24 is configured as a jacket-type heat exchanger in which flow paths 241 are formed to circumferentially circulate cooling water, which serves as a refrigerant, through each component of the cylinder 21. For example, the flow paths 241 are formed to meander within the side walls of each component, surrounding the cylindrically configured component in the circumferential direction. As shown in FIG. 2, cooling water is supplied to the cooling unit 24 from a cooling water supply unit 241, and the cooling water after heat exchange is discharged toward a drainage unit 242.

[0038] The refrigerant used in cooling unit 24 is not limited to cooling water, and may be other types of cooling liquid. Furthermore, the configuration of cooling unit 24 is not limited to the example in which flow path 241 is formed in a component of cylinder 21. For example, an air-cooled cooling unit may be employed in which cylinder 21 is covered with a casing so as to form a space between the outer wall surface of cylinder 21 and the casing, and cooling air as the refrigerant is supplied into the space using a blower.

[0039] Furthermore, temperature regulation of the waste plastic inside the main body 20 is not limited to using a cooling unit that performs cooling using a refrigerant. For example, the temperature may be lowered below the thermal decomposition temperature by reducing the amount of heat supplied to the waste plastic or by stopping the heat supply. In this case, the heating unit 25 that supplies heat to the waste plastic constitutes a temperature regulation unit that regulates the temperature inside the desalting machine 2.

[0040] Next, the configuration of the raw material supply mechanism 4 will be described. The raw material supply mechanism 4 includes a hopper 44 that supplies waste plastic from the upper surface side of the main body 20, a belt conveyor 42 that is a transport mechanism for transporting the waste plastic, and a hood 41 that covers the belt conveyor 42. The belt conveyor 42 is driven by a drive unit 43 and feeds the waste plastic received from the raw material supply line 51 into the hopper 44 (process of supplying waste plastic). The raw material supply mechanism 4 corresponds to the supply unit in this embodiment. Note that in the raw material supply mechanism 4, the waste plastic transport mechanism is not limited to being configured by the belt conveyor 42. For example, the waste plastic transport mechanism may be configured by a screw conveyor or a table feeder.

[0041] It is known that twin-screw extruders can process waste plastics starved (supplied in an amount below the transport capacity of the screw 22) from the raw material supply mechanism 4. Starved feeding has the advantage that the residence time within the main body 20 can be easily adjusted.

[0042] Meanwhile, a separation tank 3 is provided downstream of the discharge line 52 connected to the discharge part of the main body 20. The separation tank 3 degasses the desalted gas from the mixture received from the desalter 2 and separates it from the molten waste plastic. The separation tank 3 may also have a function of stirring the mixture. The desalted gas separated in the separation tank 3 is discharged to the desalted gas combustion furnace 16 described with reference to FIG. 1 and combusted. Meanwhile, the molten material after separation of the desalted gas is discharged to the pyrolysis furnace 13 and subjected to pyrolysis (a process of discharging the molten material).

[0043] By using the desalination unit 12 having the above-described configuration to desalinate waste plastics, it is possible to prevent corrosion caused by the generation of desalination gas in the downstream pyrolysis furnace 13 and to prevent the desalination gas from flowing into areas other than the desalination gas combustion furnace 16.

[0044] In the desalter 2, the waste plastic supplied from the raw material supply mechanism 4 gradually undergoes plasticization and thermal decomposition as it moves from the hopper 44 side to the discharge line 52 side. As the thermal decomposition progresses, the amount of desalted gas in the main body 20 increases.

[0045] The desalted gas has a lower viscosity than the molten waste plastic, and friction between the desalted gas and the inner wall surfaces of the screw 22 and the cylinder 21 is less likely to occur. For this reason, some of the desalted gas may flow back upstream against the extrusion action caused by the rotation of the screw 22. Because the desalted gas is flammable, it is necessary to prevent the backflowing desalted gas from reaching the hopper 44 and flowing out of the screw 22.

[0046] Therefore, as shown in Figure 3, a conventional desalting machine 2a is provided with a plurality of vents 211 spaced apart from one another downstream of the hopper 44. A vacuum exhaust line 55 is connected to these vents 211 to extract a portion of the desalted gas generated within the main body 20 and prevent backflow due to an increase in the desalted gas. The desalted gas evacuated toward the vacuum exhaust line 55 is discharged to the desalted gas combustion furnace 16 and combusted.

[0047] However, the above-mentioned method of discharging the desalted gas toward the vent 211 may cause problems associated with vent-up. As shown schematically in Figure 4, vent-up is a phenomenon in which molten waste plastic 61, whose viscosity has decreased due to melting and thermal decomposition, is lifted by desalted gas 611 moving toward the vent 211, causing the molten waste plastic 61 to overflow into the vent 211.

[0048] If the molten material overflowing due to venting-up flows further into the vacuum exhaust line 55, the plastic may subsequently cool and solidify, blocking the vacuum exhaust line 55 and making it impossible to extract the desalted gas 611 via the vent 211. As mentioned above, the desalted gas is extracted from the vent 211 to prevent backflow of the desalted gas within the main body 20 and outflow of the desalted gas upstream of the hopper 44. Therefore, a desalting machine 2a that is prone to venting-up does not fundamentally solve the problem of desalted gas outflow.

[0049] Therefore, the desalting machine 2 according to this embodiment does not have a vent 211 for extracting desalted gas between the hopper 44 (raw material supply mechanism 4), which is the supply section for waste plastics, and the connection section of the discharge line 52, which is the discharge section, as shown in the external side view of Figure 5. By not having the vent 211, it is possible to eliminate the occurrence of vent-up, which was described using Figure 4.

[0050] Here, the desalting machine 2 "not having a vent 211 for extracting desalted gas" may be an extruder that is not provided with a vent 211 itself, as shown in Fig. 5. Also, even if a vent 211 is provided, if it is not connected to the vacuum exhaust line 55, or if an open / close valve is provided in the vacuum exhaust line 55 connected to the vent 211 and the open / close valve cannot be closed to perform vacuum exhaust, this can also be said to be in a state where "a vent 211 for extracting desalted gas is not provided."

[0051] On the other hand, if the vent 211 is not provided, the problems of backflow of the desalinated gas and outflow of the desalinated gas upstream of the raw material supply mechanism 4 remain. In this case, a method of preventing backflow and outflow can be considered, for example, by lowering the heating temperature within the temperature range at which the chlorine-containing waste plastics are thermally decomposed, thereby reducing the amount of desalinated gas generated.

[0052] However, in order to reduce the chlorine content in the molten waste plastics to a target value while lowering the reaction temperature, it is necessary to increase the residence time of the waste plastics in the desalter 2. This requires measures such as further increasing the overall length of the main body 20 to ensure a sufficient residence time, which results in a problem of the desalter 2 becoming larger.

[0053] Therefore, the desalting machine 2 of this embodiment is provided with an outflow prevention mechanism for preventing the desalted gas from flowing upstream of the raw material supply mechanism 4. Specific examples of the outflow prevention mechanism for the desalted gas and its associated equipment will be described below with reference to FIGS.

[0054] The desalination machine 2 shown in Figures 6 to 8 uses waste plastics in a plasticized state or waste plastics before being fed into the main body 20 as a material seal to prevent the desalination gas from leaking out.

[0055] FIG. 6 shows an embodiment in which a desalination gas leakage prevention mechanism is configured by forming a material seal 62 within the main body 20 of the desalination machine 2. The temperature of waste plastic supplied from the hopper 44 to the main body 20 rises due to heating using the heating unit 25 and shear heating. Because the temperature of the waste plastic is lower than its thermal decomposition temperature, the waste plastic is supplied to the main body 20 without generating desalination gas due to thermal decomposition. Therefore, the waste plastic can be used as a material seal to block gaps within the main body 20 and prevent the movement of desalination gas. The temperature of the waste plastic further rises and it becomes plasticized, after which it melts and undergoes thermal decomposition. Plasticized waste plastic has a higher viscosity than its molten state. Therefore, plasticized waste plastic (plasticized plastic) before becoming molten can be used as a material seal to block gaps within the main body 20 and prevent the movement of desalination gas.

[0056] Based on the above concept, Fig. 6 shows a schematic diagram of the internal state of a desalting machine 2 in which a plasticized plastic material seal 62 is formed upstream of the region where waste plastics become molten material 61 and thermal decomposition progresses (thermal decomposition region). For ease of illustration, the screw 22 is omitted from Fig. 6.

[0057] The formation of the material seal 62 is performed by controlling the temperature of the heating section 25 and selecting the elements of the screw 22 so that the temperature of the region where the material seal 62 is formed is lower than the temperature of the thermal decomposition region.

[0058] In the desalter 2 of this embodiment, the region where the material seal 62 is formed and the thermal decomposition region are formed by varying the set temperature for temperature control of the waste plastic along the length of the main body 20. The region where the material seal 62 is formed is set to a temperature within a range of 200 to 250°C, for example. The thermal decomposition region is set to a temperature of 350°C, for example, within a range of 300 to 400°C.

[0059] Unlike the schematic diagram shown in Figure 6, it may be difficult to visually monitor the state of the waste plastic in the desalting machine 2 (whether it is plasticized or has become molten material 61 and is undergoing thermal decomposition). Therefore, by checking whether the detected temperatures of the thermometers 26 arranged corresponding to each area have reached their respective set temperatures, it is possible to monitor whether a plasticized plastic material seal 62 has been formed in these areas or whether thermal decomposition of the molten material 61 is progressing.

[0060] The thermometer 26 provided in the area where thermal decomposition is progressing (thermolysis area) and the heating unit 25 that maintains the temperature of the thermal decomposition area at the thermal decomposition temperature based on the temperature detection results of the thermometer 26 constitute a first temperature control mechanism of this embodiment. The thermometer 26 provided in the area where the material seal 62 is formed and the heating unit 25 that maintains the temperature of the area at the temperature at which the waste plastic is plasticized based on the temperature detection results of the thermometer 26 constitute a second temperature control mechanism of this embodiment.

[0061] With the above-described configuration, even if a portion of the desalted gas 611 generated in the pyrolysis region flows backward toward the upstream side, once it reaches the region where the material seal 62 made of plasticized plastic is formed, the desalted gas is prevented from moving further upstream, as shown schematically in Figure 6. As a result, it is possible to prevent the desalted gas 611 from flowing backward further upstream, reaching the hopper 44, and flowing out beyond the raw material supply mechanism 4.

[0062] The gas pool of desalinated gas 611 shown in FIG. 6 is a convenient illustration for explaining the function of the material seal 62 and may not accurately represent the actual state of the desalinated gas 611 contained in the melt 61. For example, the desalinated gas 611 may be in the form of small bubbles dispersed throughout the melt 61. Although FIG. 6 shows the material seal 62 formation region and the pyrolysis region adjacent to each other, the material seal 62 formation region may be located upstream of the pyrolysis region. For example, a region with a different temperature range (e.g., a region lower than the pyrolysis region and higher than the material seal 62 formation region) or a region for performing a different process, such as kneading or transport, may be formed between the material seal 62 formation region and the pyrolysis region. Furthermore, the material seal 62 formation region and the pyrolysis region may be alternately arranged to provide the material seal 62 at multiple locations within the main body 20.

[0063] In the conventional desalination machine 2a, which does not form a material seal 62, the heating temperature is set to 350°C, within the range of 300 to 400°C, throughout the entire region where the heating section 25 is provided. Even in the conventional desalination machine 2a, waste plastic supplied at room temperature may reach a temperature in the range of 200 to 250°C during the process of heating to 350°C, but this is only a temporary temperature state. Therefore, compared to the desalination machine 2 of this embodiment, in which the temperature is set within the range of 200 to 250°C throughout the entire region where the molten material 61 is formed, it is difficult to form a material seal 62 that has an effective function of preventing the backflow of desalination gas.

[0064] In this regard, the desalination machine 2 of this embodiment intentionally forms a low-temperature region (= material seal 62) where plasticized plastic, which has a higher viscosity than the molten material, exists. To form a low-temperature region over the range necessary for the plasticized plastic to act as the material seal 62, the set temperatures of the heating section 25 between the thermal decomposition region and the region upstream of it where the material seal 62 is formed are made different, and screw 22 elements suitable for forming the plasticized plastic in this low-temperature region are employed.

[0065] 7 and 8 show an embodiment in which a mechanism for preventing the outflow of desalted gas is configured by forming a material seal 62a of waste plastic in the full supply hoppers 44a, 44b of the raw material supply mechanism 4. Fig. 7 shows an embodiment in which a material seal 62a made of waste plastic filled in the full supply hopper 44a is formed by performing full supply, in which waste plastic is supplied to the desalter 2 while maintaining a state in which the full supply hopper 44a is filled with waste plastic.

[0066] As mentioned above, twin-screw extruders can process starved-feed waste plastics, making it easy to adjust the residence time. On the other hand, twin-screw extruders can also process fully-fed waste plastics. Therefore, if the need for starved-feed residence time adjustment is compared with the need for forming a material seal 62a in the full-feed hopper 44a, and the latter is more important, full-feeding may be performed.

[0067] Next, the hopper with a pushing mechanism 44b shown in FIG. 8 is equipped with a screw-type pushing mechanism that pushes waste plastic toward the main body 20. FIG. 8 also shows a screw 441 that constitutes this pushing mechanism. The screw 441 rotates in a direction that pushes the waste plastic supplied into the hopper with a pushing mechanism 44b toward the main body 20, for example, by a drive mechanism (not shown) fixedly disposed above the hopper with a pushing mechanism 44b. This pushing action forms a material seal 62a made of compressed waste plastic at the outlet of the hopper with a pushing mechanism 44b. Compressible waste plastics, such as films and flakes, are suitable for forming the material seal 62a using the pushing mechanism. Here, the hopper with a pushing mechanism 44b can also create a starvation supply state when supplying waste plastics that have physical properties that allow them to be compressed near the outlet and gradually fed while being crushed by the screw 411.

[0068] Furthermore, the pushing mechanism is not limited to being provided inside the hopper 44b. For example, a screw-type pushing mechanism may be provided on the underside of the hopper 44b, with the end of the pushing mechanism connected to the side of the main body 20. In this case, waste plastic is supplied from the side of the main body 20, and a material seal 62a is formed inside the pushing mechanism.

[0069] 6 to 8, it is possible to prevent backflow and outflow of desalted gas upstream of the formation position of the material seals 62, 62a (step of preventing outflow of desalted gas). On the other hand, in a system using the material seals 62, 62a, if the supply of waste plastic is stopped while the screw 22 continues to rotate when the operation of the desalting machine 2 is stopped (either normal shutdown operation or emergency shutdown operation), the formation of the material seals 62, 62a cannot be maintained. Furthermore, if the thermal decomposition of the molten material 61 progresses without the formation of the material seals 62, 62a, there is a risk that the desalted gas will backflow and outflow upstream of the raw material supply mechanism 4.

[0070] 9 has a restriction (supply stop restriction) set on the operation of stopping the supply of waste plastic from the raw material supply mechanism 4 when it is detected that a temperature region above the thermal decomposition temperature exists within the main body 20. The desalter 2 is equipped with an interlock mechanism that releases the restriction on stopping the supply of waste plastic, provided that the temperature within the main body 20 is lower than the thermal decomposition temperature. The interlock mechanism includes the cooling unit 24 described above that cools the inside of the main body 20, a thermometer 26 that is a temperature detection unit that detects the temperature of a predetermined region within the main body 20, and an interlock control unit 431 that releases the restriction on stopping the supply of waste plastic from the raw material supply mechanism 4, provided that the temperature within the main body 20 detected by the thermometer 26 is lower than the thermal decomposition temperature.

[0071] The interlock control unit 431 may determine whether to lift the restriction on stopping the supply of waste plastic based solely on the temperature detection result of the thermometer 26 provided in the thermal decomposition area, depending on whether the temperature is lower than the thermal decomposition temperature. Alternatively, the interlock control unit 431 may determine whether to lift the restriction on stopping the supply of waste plastic based solely on the temperature detection result of the thermometer 26 provided in an area upstream of the thermal decomposition area in the main body 20, depending on whether the temperature is lower than the thermal decomposition temperature. Furthermore, when a material seal 62 is formed in the main body 20, the interlock control unit 431 may make a similar determination based on the temperature detection results of both the thermometer 26 provided in the thermal decomposition area and the thermometer 26 provided in the area where the material seal 62 is formed. In this case, whether to lift the restriction on stopping the supply of waste plastic is determined based on whether the temperatures in both the thermal decomposition area and the area where the material seal 62 is formed are lower than the thermal decomposition temperature.

[0072] Next, the specific content of the waste plastic supply stop restriction controlled by the interlock control unit 431 will be described. As a first example, an interlock that prohibits the execution of an operation to stop the supply of waste plastic from the raw material supply mechanism 4 will be described. For example, when an operator inputs a command to stop the supply of waste plastic from the raw material supply mechanism 4 via an operation panel (not shown) attached to the desalter 2, the interlock control unit 431 acquires the detected temperature of the thermometer 26 from the temperature signal output unit 261 at preset intervals (a process of detecting the temperature inside the desalter). If the acquired detected temperature is equal to or higher than the thermal decomposition temperature of the waste plastic, the interlock is activated and the stop command is not accepted. In this case, since the temperature of the waste plastic inside the main body unit 20 is higher than the decomposition temperature, guidance may be displayed on the operation panel indicating that an operation to lower the temperature inside the main body unit 20 using the cooling unit 24 is necessary.

[0073] Thereafter, as a result of stopping heating by the heating unit 5 and cooling by the cooling unit 24 (a process for adjusting the temperature inside the desalting machine), the interlock is released, and it becomes possible to stop the supply of waste plastic from the raw material supply mechanism 4 (a process for releasing the restriction on stopping the supply of waste plastic), provided that the temperature inside the main body 20 is lower than the thermal decomposition temperature of the waste plastic (a process for releasing the restriction on stopping the supply of waste plastic). The fact that the interlock has been released is displayed, for example, via the operation panel described above, and it becomes possible to accept commands to stop the supply of waste plastic thereafter.

[0074] Next, as a second example of a restriction on stopping the supply of waste plastic, we will explain an interlock in the operation of automatically stopping the supply of waste plastic from the raw material supply mechanism 4. When the desalter 2 equipped with the second example interlock mechanism receives, for example, an instruction to stop the supply of waste plastic from an operator or an emergency stop signal for the supply of waste plastic, it executes a stopping operation in the following procedure.

[0075] First, while continuing the supply of waste plastic from the raw material supply mechanism 4 and the rotation of the screw 22, the supply of power to the electric heater 251 is stopped to terminate heating by the heating unit 25. In addition, the supply of cooling water from the cooling water supply unit 241 to the cooling unit 24 is started to cool the inside of the main body unit 20 (a process for adjusting the temperature inside the desalting machine).

[0076] As a result, the temperature of the waste plastic inside the main body 20 gradually drops. The temperature detected by the thermometer 26 is output from the temperature signal output unit 261 to the interlock control unit 431 at preset intervals (a process for detecting the temperature inside the desalting machine). However, if the detected temperature is equal to or higher than the thermal decomposition temperature of the waste plastic, the interlock is activated and no operation is performed to stop the supply of waste plastic.

[0077] The interior of the main body 20 continues to cool, eventually dropping below a temperature in the range of 200-250°C, at which thermal decomposition of chlorine-containing waste plastics does not proceed. The interlock control unit 431 then performs an operation to release the restriction on the supply of waste plastics and outputs an operation stop signal to the drive unit 43 of the belt conveyor 42, provided that the detected temperature is below a preset temperature in the range of 200-250°C and lower than the thermal decomposition temperature of the waste plastics (a process of releasing the restriction on the supply of waste plastics). In the second example, the operation to stop the supply of waste plastics from the raw material supply mechanism 4 is then automatically performed.

[0078] In the first and second examples described above, when the interlock is released and the supply of waste plastic from the raw material supply mechanism 4 is subsequently stopped, the waste plastic remaining inside the main body 20 is pushed out toward the discharge portion. As a result, the state in which the material seal 62 shown in Figure 6 or the material seal 62a shown in Figures 7 and 8 is formed is eliminated, but because the inside of the main body 20 has already been cooled to a temperature at which desalted gas is not generated, there is very little risk of desalted gas flowing out of the main body 20 toward the raw material supply mechanism 4. In other words, the action of the above-mentioned interlock control can be maintained in the state in which the material seals 62 and 62a are formed as long as the waste plastic inside the main body 20 does not generate desalted gas.

[0079] The hopper 44 may also have a level detection mechanism (not shown), such as a level switch, that can detect the height of the waste plastic in the hopper 44. The level detection mechanism may provide an indication that the height of the waste plastic in the hopper 44 is at a preset arbitrary height, and may adjust the amount of waste plastic supplied from the raw material supply mechanism 4 so that the height of the waste plastic in the hopper 44 does not fall below the predetermined height. Because the height of the waste plastic in the hopper 44 can be maintained at the desired height, the waste plastic can be continuously supplied into the main body 20, and the material seals 62, 62a can be maintained in a formed state.

[0080] The level detection mechanism may also issue an emergency stop signal for the waste plastic supply when the height of the waste plastic in the hopper 44 falls below a preset arbitrary height. In this case, a process for adjusting the temperature inside the desalter and a process for detecting the temperature inside the desalter are executed. If the detected temperature is equal to or higher than the thermal decomposition temperature of the waste plastic, an interlock is activated and no operation to stop the supply of waste plastic is executed. In this example, the inside of the main body 20 continues to cool, and the restriction on stopping the supply of waste plastic is lifted when the temperature of the waste plastic is lower than the thermal decomposition temperature. Therefore, when the supply of waste plastic from the raw material supply mechanism 4 is stopped, the inside of the main body 20 has cooled to a temperature at which desalted gas is not generated, so there is very little risk of desalted gas leaking from the main body 20 to the raw material supply mechanism 4 side.

[0081] 10 and 11 show an example in which a desalted gas outflow prevention mechanism is configured using closed lock hoppers 45, 45a, 45b. In the desalting machine 2 shown in Fig. 10, the raw material supply mechanism 4a is equipped with a lock hopper 45 that is configured to be connectable to and disconnectable from a raw material supply line 51 via an on-off valve V1. Connected to the lock hopper 45 are an inert gas supply line that supplies, for example, nitrogen gas to maintain an inert gas atmosphere inside the lock hopper, and an exhaust line 452 that exhausts the atmosphere inside the lock hopper 45.

[0082] Furthermore, the lock hopper 45 is equipped with a supply mechanism that supplies the stored waste plastic to the main body 20. The supply mechanism is constituted, for example, by a belt conveyor 42, which is a transport mechanism housed in a closed hood 41, and this belt conveyor 42 is used to supply waste plastic into the main body 20 via the above-mentioned hopper 44. Note that in this example, the waste plastic transport mechanism may also be constituted by a screw conveyor or a table feeder.

[0083] In this raw material supply mechanism 4a, the on-off valve V1 is opened only during the period when waste plastic is received into the lock hopper 45 from the raw material supply line 51, connecting the lock hopper 45 to the raw material supply line 51. On the other hand, during other periods, the on-off valve V1 is closed, leaving the raw material supply line 51 disconnected from the lock hopper 45. The waste plastic stored in the lock hopper 45 is then fed into the hopper 44 by the belt conveyor 42, thereby supplying the waste plastic to the main body 20.

[0084] According to this embodiment, even if the desalinated gas that has flowed back inside the main body 20 flows into the lock hopper 45 via the hopper 44 and the belt conveyor 42, the lock hopper 45 and the raw material supply line 51 are disconnected except during the period when the waste plastic is being received. This prevents the desalinated gas from flowing upstream of the raw material supply line 51 (step of preventing the outflow of desalinated gas). If the desalinated gas flows into the lock hopper 45 while the raw material supply line 51 and the lock hopper 45 are connected, the occurrence of the inflow can be detected by a gas detector or the like, and the reception of the waste plastic can be stopped and the on-off valve V1 can be closed.

[0085] 11, the lock hopper 45 includes a first lock hopper section 45a and a second lock hopper section 45b. The first lock hopper section 45a is configured to be connectable to and disconnectable from the raw material supply line 51 by a first on-off valve V1. An inert gas supply line 451, which supplies, for example, nitrogen gas to maintain an inert gas atmosphere inside the first lock hopper section 45a, and an exhaust line 452, which exhausts the atmosphere inside the lock hopper 45, are connected to the first lock hopper section 45a.

[0086] The second lock hopper section 45b is configured to be connectable to and disconnectable from the first lock hopper section 45a via an intermediate line 46 provided with a second opening / closing valve V2, and is provided with a supply mechanism that supplies waste plastic to the main body section 20. The supply mechanism is configured, for example, by a belt conveyor 42 housed in a closed hood 41.

[0087] By providing the lock hopper 45 with a two-tiered structure, waste plastic can be received and supplied to the main body 20, for example, as follows: During the period when waste plastic is received from the raw material supply line 51, the second on-off valve of the intermediate line 46 is closed, separating the first lock hopper section 45a from the second lock hopper section 45b. During other periods, the first on-off valve V1 is closed, separating the first lock hopper section 45a from the raw material supply line 51. When transferring waste plastic from the first lock hopper section 45a to the second lock hopper section 45b, the second on-off valve V2 of the intermediate line 46 is opened. Thereafter, the waste plastic stored in the second lock hopper section 45b is fed into the hopper 44 by the belt conveyor 42, thereby supplying the waste plastic to the main body 20.

[0088] According to this embodiment, while the first lock hopper section 45a is receiving waste plastic, the intermediate line 46 on the inlet side of the second lock hopper section 45b is disconnected from the first lock hopper section 45a. During other periods, the first lock hopper section 45a is disconnected from the raw material supply line 51. Therefore, even if the desalinated gas that has flowed back through the main body section 20 flows into the second lock hopper section 45b via the hopper 44 and the belt conveyor 42, the outflow of the desalinated gas upstream of the raw material supply line 51 can be prevented at any time (step of preventing the outflow of desalinated gas).

[0089] The above describes embodiments in which the desalted gas outflow prevention mechanism is configured using material seals 62, 62a (FIGS. 6 to 8), and embodiments in which the outflow prevention mechanism is configured using a lock hopper 45 (FIGS. 10 and 11). These embodiments are not limited to being implemented alone, and outflow prevention mechanisms of multiple types may be combined as appropriate. Furthermore, the desalting machine 2 to which these outflow prevention mechanisms can be applied is not limited to being configured using a twin-screw extruder. For example, the desalting gas outflow prevention mechanism according to each of the above-mentioned embodiments may be applied to a desalting machine 2 configured using a single-screw extruder.

[0090] V1, V2 Opening and closing valve 11 Slaked lime addition section 12 Desalination unit 13 Pyrolysis furnace 14 Cooler 15 Cracked oil drum 16 Desalination gas combustion furnace 17 Cracked residue combustion furnace 2, 2a Desalination machine 20 Main body 21 Cylinder 211 Vent 212 Sealing plate 22 Screw 221 Shaft 222 Blade 23 Drive section 24 Cooling section 241 Cooling water supply section 242 Drainage section 25 Heating section 251 Electric heater 252 Power supply section 26 Thermometer 261 Signal output section 3 Separation tank 4 Raw material supply mechanism 41 Hood 42 Belt conveyor 43 Drive section 431 Interlock control section 44 Hopper 44a Full supply hopper 44b Hopper with pushing mechanism 441 Screw 45 Lock hopper 45a First lock hopper section 45b Second lock hopper section 451 Inert gas supply line 452 Exhaust line 46 Intermediate line 51 Raw material supply line 52 Discharge line 53 Vacuum exhaust line 54 Discharge line 55 Vacuum exhaust line 61 Melt 611 Demineralized gas 62, 62a Material seal

Claims

1. A desalting unit for removing chlorine contained in waste plastics, comprising: a desalting machine composed of an extruder that thermally decomposes the waste plastics supplied from a supply section and discharges a mixture of desalted gas containing the chlorine and a molten material from a discharge section; and a separation tank that is provided downstream of the discharge section and separates the mixture discharged from the discharge section into the molten material and the desalted gas, and is connected to an exhaust line for exhausting the desalted gas and an exhaust line for discharging the molten material, wherein the desalting machine does not have a vent for extracting the desalted gas between the supply section and the discharge section, and is equipped with an outflow prevention mechanism for preventing the desalted gas inside the desalting machine from outflowing upstream of the supply section.

2. The desalting unit according to claim 1, characterized in that the desalting machine is composed of a twin-screw extruder.

3. A desalination unit as described in claim 1, characterized in that the outflow prevention mechanism is an area formed upstream of the area inside the desalter where the thermal decomposition progresses, and whose temperature is lower than the thermal decomposition temperature of the waste plastic.

4. A desalination unit as described in claim 3, characterized in that the region lower than the thermal decomposition temperature of the waste plastic is a region heated to a temperature at which the waste plastic is plasticized.

5. A desalination unit as described in claim 4, characterized in that the leakage prevention mechanism is a material seal made of plasticized plastic formed in an area lower than the thermal decomposition temperature of the waste plastic.

6. The desalting unit of claim 1, characterized in that the desalting machine is equipped with a temperature control unit that controls the temperature inside the desalting machine, and the temperature control unit is equipped with a first temperature control mechanism that maintains the area where the thermal decomposition progresses at the thermal decomposition temperature, and a second temperature control mechanism that maintains the area upstream of the area where the thermal decomposition progresses inside the desalting machine at a temperature at which the waste plastic is plasticized, in order to form the outflow prevention mechanism.

7. The desalination unit according to claim 1, wherein the outflow prevention mechanism comprises a hopper into which the waste plastic is supplied to the supply section until it is fully filled.

8. The desalination unit according to claim 1, characterized in that the outflow prevention mechanism is provided with a screw-type pushing mechanism in the supply section that pushes the waste plastic toward the desalter.

9. A desalination unit as described in claim 7 or 8, characterized in that the outflow prevention mechanism is a material seal for the waste plastic formed in the supply section.

10. A desalination unit as described in claim 1, characterized in that it comprises a temperature adjustment unit that adjusts the temperature inside the desalter, a temperature detection unit that detects the temperature inside the desalter, and an interlock control unit that lifts the restriction on stopping the supply of the waste plastic from the supply unit, on the condition that the temperature inside the desalter detected by the temperature detection unit is lower than the thermal decomposition temperature of the waste plastic.

11. The desalination unit according to claim 10, characterized in that an operation is performed to stop the supply of the waste plastic from the supply section when the restriction on stopping the supply of the waste plastic is lifted.

12. The desalination unit described in claim 10, characterized in that the interlock control unit determines whether or not to lift the restriction on stopping the supply of waste plastic based on the temperature detection results of the temperature detection unit provided in the area inside the desalter where the thermal decomposition progresses and / or the temperature detection unit provided in an area inside the desalter upstream of the area where the thermal decomposition progresses.

13. The desalination unit according to claim 10, wherein the temperature adjustment section includes a cooling section that adjusts the temperature inside the desalination machine using a refrigerant.

14. The desalination unit according to claim 13, characterized in that the temperature adjustment section is configured to circulate cooling water, which is the refrigerant, through a flow path formed in the wall of the desalination machine.

15. The desalination unit according to claim 13, characterized in that the temperature adjustment section is configured to supply cooled air, which is the refrigerant, toward the outer wall surface of the desalination machine.

16. A desalination unit as described in claim 1, characterized in that the outflow prevention mechanism is a lock hopper provided in the supply section and configured to be connected / disconnected by an opening / closing valve to a raw material supply line to which the waste plastic is supplied from the upstream side.

17. The desalination unit according to claim 16, characterized in that the lock hopper is provided with a supply mechanism for supplying the waste plastic received from the raw material supply line to the desalter.

18. The desalination unit described in claim 16, characterized in that the lock hopper comprises: a first lock hopper section configured to be connectable / disconnectable to the raw material supply line by a first opening / closing valve; and a second lock hopper section configured to be connectable / disconnectable to the first lock hopper via an intermediate line provided with a second opening / closing valve, and provided with a supply mechanism for supplying the waste plastic to the desalter.

19. A desalting method for removing chlorine contained in waste plastics, comprising the steps of: supplying the waste plastics from a supply section to a desalting machine constituted by an extruder; pyrolyzing the waste plastics in the desalting machine and discharging a mixture of desalted gas containing the chlorine and a molten material from the discharge section of the desalting machine; separating the mixture discharged from the desalting machine into the molten material and the desalted gas in a separation tank, exhausting the desalted gas from an exhaust line, and discharging the molten material from a discharge line; wherein the desalting machine does not have a vent for extracting the desalted gas between the supply section and the discharge section, and the desalting method includes a step of preventing the desalted gas inside the desalting machine from flowing upstream of the supply section.

20. A desalination method as described in claim 19, characterized in that in the step of preventing the outflow of the desalted gas, a region with a lower temperature than the thermal decomposition temperature of the waste plastic is formed upstream of the region inside the desalter where the thermal decomposition progresses.

21. A desalination method according to claim 19, characterized in that in the step of preventing the outflow of the desalted gas, a hopper provided in the supply section is filled with the waste plastics.

22. A desalination method as described in claim 19, characterized in that in the step of preventing the outflow of the desalted gas, the waste plastic is supplied using a screw-type pushing mechanism provided in the supply section that pushes the waste plastic toward the desalting machine.

23. A desalination method as described in claim 19, comprising the steps of: adjusting the temperature inside the desalter; and detecting the temperature inside the temperature-adjusted desalter, and further comprising the step of lifting the restriction on stopping the supply of the waste plastic from the supply unit, on the condition that the temperature inside the desalter detected in the temperature detection step is lower than the thermal decomposition temperature of the waste plastic.

24. A desalination method as described in claim 19, characterized in that in the process of preventing the outflow of the desalted gas, a lock hopper is provided in the supply section and configured to be connectable / disconnectable to a raw material supply line to which the waste plastic is supplied from the upstream side, and a process of supplying the waste plastic is carried out in a state in which the lock hopper is disconnected from the raw material supply line.

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