Char handling section and related depolymerization process

Abstract

The present disclosure provides a char handling section that includes a series of devices for operating on a char-containing liquid slurry, sequentially depolymerizing the liquid slurry, and finally drying the char, which is collected and handled. The char removal and handling method and apparatus configured in this manner is highly flexible and can be operated in a continuous mode without shutting down the depolymerization reactor.

Description

[Technical field]

[0001] The present disclosure relates to the field of depolymerization of plastic waste into novel products, including hydrocarbon oils, having useful and valuable properties. In one aspect, the present disclosure relates to a method and apparatus for handling the char from the depolymerization process. [Background technology]

[0002] There is a rapidly growing awareness that waste plastic materials have a negative impact on the environment and, consequently, on the health of all forms of life.

[0003] An example of an attempt to reduce the impact of waste plastic materials is the recycling of plastic materials from household and industrial waste, which allows some of these materials to be reintroduced into the production cycle, leading to better outcomes such as a reduction in the use of fossil hydrocarbon sources to manufacture plastic products.

[0004] However, various factors suggest that this solution alone is insufficient to achieve sustainability goals: in practice, mechanical recycling of plastic materials usually produces lower quality materials, is relatively costly and burdensome, and is not applicable to certain municipal waste streams where plastics are mixed with different types of materials.

[0005] As a result, most of the plastic waste is either used as a source of thermal energy in plants such as incinerators, or simply stored in landfills, which, as mentioned above, contribute to the deterioration of the global environment by increasing CO2 emissions and releasing harmful chemicals.

[0006] In view of the above, many attempts have been made in the past to efficiently reprocess waste plastic feedstocks into liquid hydrocarbon products that have useful and valuable properties, particularly as fuels.

[0007] Thermocatalysis is essentially a process in which plastic waste is converted into liquid fuels (pyrolysis products) by thermal decomposition (optionally catalytic decomposition) in the absence of oxygen. The plastic waste is first melted in an inert purge gas, such as nitrogen, typically in a stainless steel chamber. In a first thermal step, this chamber heats the molten material to a gaseous state, and in a subsequent thermocatalytic step, it is decomposed to form hydrocarbon chains of variable length.

[0008] The hot pyrolysis gas is then condensed in one or more condensers to produce a hydrocarbon distillate (pyrolysis oil) containing linear and branched aliphatic, cyclic aliphatic and aromatic hydrocarbons. Depending on the composition, the resulting mixture is used for various applications, but in any case, product consistency and quality requirements must always be met. Also, it is difficult to ensure the consistency of the quality of the recovered oil, considering the unstable composition of the plastic waste feedstock.

[0009] Despite the use of catalysts and stringent conditions, the depolymerization reaction generates large amounts of sticky carbonaceous material as by-products, partly in the form of carbon, but also non-organic materials from the plastic and additives in the depolymerization catalyst. Due to its stickiness, the char adheres to the reactor walls, reducing the heat transfer rate and the productivity and efficiency of the process. For this reason, the char produced must be removed to maintain the operability of the process.

[0010] Industrial pyrolysis or thermocatalytic plants may have two pyrolysis chambers, known as twin-chamber systems, which operate in parallel at approximately equal speeds. When both chambers have completed the pyrolysis of waste materials at the same time, it is necessary to wait for each chamber to cool before removing the char from the internal base of each chamber. In a variant, both chambers may be operated alternately, such that one is in operation while the other is in the cleaning process. However, this method reduces the amount of plastic processed per unit of time.

[0011] In order to avoid the step of cleaning the depolymerization chamber, the technical solution adopted is to extract the contents in the depolymerization chamber while it remains in the form of a slurry rather than a solid sticky material, which allows the char to not adhere to the reactor walls or to adhere to the reactor walls to a limited extent, especially if the char content in the slurry is not highly concentrated.

[0012] However, the relatively dilute slurry extracted from the reactor still has a high content of hydrocarbon chains that require depolymerization to produce pyrolysis products with suitable and acceptable productivity.

[0013] For this reason, the char handling section must be constructed to handle large volumes of effluent and extract the char to complete the depolymerization reactor.

[0014] In view of the above, an object of the present disclosure is to provide a char handling section capable of receiving and handling liquid effluent containing char in slurry form. Summary of the Invention

[0015] Thus, one aspect of the present disclosure is a char handling section, comprising:

[0016] a first jacketed chamber (6a) equipped with an inlet conduit (6a-1) for feeding a char-containing slurry and a stirring system (6b), operable in the temperature range of 350-570°C, and further equipped with a conduit (6b-1) for discharging a gaseous effluent;

[0017] means (6c) for withdrawing the concentrated slurry from said chamber (6a) and conveying it to a second chamber (6d) capable of maintaining said slurry in the same temperature range as said chamber (6a) and equipped with a degassing system for removing gaseous effluents to produce a dry char;

[0018] a second stripping chamber (6d) for receiving the dried char, comprising a stirring system (6d-1), a char outlet (6d-2), a gas inlet (6d-3) located at the bottom of the chamber, and a gas outlet (6d-4) for removing the gaseous effluent stripped from the char;

[0019] a means (6e) for receiving the dried char in the strip chamber (6d) and transporting it to a third collection chamber (6f) and capable of maintaining the char at a temperature in the range of 60°C to 100°C;

[0020] A char handling section is disclosed comprising a third collection chamber (6f) for receiving said dried char, comprising an agitation system (6f-1) and an outlet for handling the char operated by a valve (6f-2). [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of a thermal catalytic process plant.

[0022] [Diagram 2] FIG. 2 is a schematic diagram of a char handling section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] As mentioned above, the char handling section of the present disclosure is intended to separate and handle the solids of the slurry as effluent from the depolymerization reactor. Figure 2 shows a schematic diagram of the process.

[0024] In a preferred embodiment, the hot slurry withdrawn from the depolymerization reactor is sent to a jacketed chamber (6a) operating in the temperature range of 350-570°C, where the depolymerization process can be carried out under stirring by a rotor (6b) by the effect of heat transferred by the high temperature jacket. The generated gaseous effluent leaves the chamber (6a) and is preferably sent to a condensation unit (3) to be treated together with the gaseous effluent of the first reactor (2). A filtering means is preferably installed in the gas outlet conduit to intercept entrained char particles. In a particular embodiment, the gaseous effluent is first condensed in a dedicated unit and then pumped back to the condensation unit (3) by a pump unit.

[0025] A thickened slurry (mud) is formed and is extracted from the bottom of chamber (6a) by a screw (hot) conveyor (6c) and conveyed to chamber (6d). The screw conveyor (6c) is preferably jacketed so that it can operate within the same temperature range as chamber (6a). In a more preferred embodiment, molten solar salt circulates within chamber (6a) and the jacket of the screw conveyor (6c).

[0026] The screw conveyor (6c) is preferably composed of two different conveyors connected to each other. The thickened slurry, preferably in the form of mud, is preferably extracted from the bottom of the chamber (6a) by a first elevating screw conveyor (6c-1), the lower end of which is integrated with the bottom of the chamber (6a) and the upper end of which is higher than the lower end and is connected to one end of a second screw conveyor (6c-2), the other end of which is connected to the top of the stripping chamber (6d) to feed the slurry. Both conveyors are jacketed and operate in the same temperature range as the chamber (6a).

[0027] As the mud is lifted from the bottom of the chamber (6a) and transported by a second conveyor to the stripping chamber (6d), it is gradually discharged as part of the liquid flows back into the chamber (6a) and part is converted into a gaseous effluent that is removed.

[0028] The system described above makes it possible to feed the stripping chamber (6d) with a char material containing a limited amount of liquid and preferably partially dried.

[0029] In the stripping chamber (6d), nitrogen is preferably injected into the bottom of the stripping chamber to remove volatile hydrocarbon products. Gas is withdrawn from the top of the stripping chamber (6d) and sent to a condensation unit (3), and the dried char is discharged from the bottom of the chamber, preferably through a ball valve, and enters another jacketed screw conveyor (6e), maintained at a temperature range of 60-100°C, which conveys the char directly to a third collection chamber (6f), preferably operating at approximately atmospheric pressure and at a temperature range of 60-100°C. In the collection chamber, the circulation of nitrogen gas is more preferably maintained by a gas inlet (6f-3) and a gas outlet (6f-4). Finally, the dried char is discharged through a valve (6f-2), preferably into a transfer vessel (6g) for handling.

[0030] The above disclosed method and apparatus for char removal and handling is very flexible and can be operated in a continuous mode without shutting down the depolymerization reactor. It also allows for a lighter depolymerization plant to be installed since it is no longer necessary to operate reactors in parallel to perform the depolymerization step operating continuously. The slurry, whose char content may range from 10-50%, preferably 20-40% wt, is preferably fed to the char handling section.

[0031] In particular, the entire system for char production, removal and handling is continuous, easily scalable, flexible and has low impact on the operability of the overall depolymerization process.

[0032] The char handling process is also very efficient at discharging dry char with a typical composition including about 20% by weight of discharged catalyst, 50% by weight of inorganics, and about 30% by weight of carbon.

[0033] The char handling section may be associated with any depolymerization plant operating a depolymerization reactor from which a char-containing liquid slurry may be withdrawn.

[0034] Referring to FIG. 1, a preferred method for depolymerizing waste plastic materials to produce pyrolysis products includes: (a) feeding a mixture comprising waste plastic material in an oxygen-free atmosphere into a feeding system comprising at least one screw extruder (1) heated at the melting temperature of said plastic material; (b) feeding the molten plastic material from the extruder to a first depolymerization reactor (2), which is a continuous stirred tank reactor maintained at a temperature range of 280-600°C and operating at a pressure range of 1-10 barg, where depolymerization proceeds in the first depolymerization reactor (2) to form a gaseous effluent and a liquid effluent; (c) directing at least a portion of the liquid effluent produced in the first reactor (2) to a char handling section (6) and feeding the gaseous effluent from the reactor (2) to a condensation unit (3) producing a gas stream and a liquid stream; (d) directing the gas stream from the first condensation unit (3) to a second condensation unit (5) operating at a lower temperature than the first condensation unit and directing the liquid stream from the condensation unit (3) to a second depolymerization reactor (4) which is a continuous stirred tank reactor maintained at a temperature range of 280-600°C and operating at a pressure range of 1-10 barg, in which depolymerization proceeds in the second depolymerization reactor (4) to form a gaseous effluent and a liquid effluent; (e) withdrawing a gaseous effluent from said depolymerization reactor (4) and feeding it to a second condensation unit (5) and recycling at least a portion of the liquid effluent from the depolymerization reactor (4) to the first depolymerization reactor (2). The process is further characterized in that the pyrolysis products are recovered from the condensation unit (5) and that at least one of the depolymerization reactors (2) and (4) operates in the presence of a depolymerization catalyst.

[0035] The method is preferably carried out in a continuous mode.

[0036] In step (a), the loading system allows the loading of the feed waste plastic material into the reactor (2), preferably in a continuous mode. Care must be taken not to introduce an oxygen-containing atmosphere into the system. A barrier against potential oxygen-containing atmospheres can be obtained by various means, such as, for example, a nitrogen blanket or a vacuum system connected to the barrel of the extruder.

[0037] More specifically, the plastic mixed waste is loaded into the feeding system of the depolymerization reactor (2) by means of one or more hoppers connected in parallel, and the oxygen present in the atmosphere of the plastic waste is substantially removed in the hopper(s).

[0038] The disclosed method is very flexible and can feed a variety of plastic waste compositions, such as heterogeneous mixtures of waste plastic materials (called Plasmix in Italy) where polyolefins are the most abundant component, but with additional sorting steps, which are uneconomical. It is preferred to depolymerize mixed plastic waste with a polyolefins (PE and PP) content of 70 wt.% or more, especially when the pyrolysis products are recycled to the cracking / purification unit.

[0039] The waste plastic material preferably undergoes a pretreatment step, in which the waste plastic material is melted by heat and may be mixed with an additive, which may be an alkaline material. By melt pretreatment, a heterogeneous mixture of different types of waste plastics can be converted into a large amount of homogeneous plastic composite. This pretreatment is therefore also suitable for pyrolysis without the use of additives.

[0040] The heating temperature in the pretreatment stage is appropriately set according to the type and content of plastic contained in the waste plastic material so as to suppress thermal decomposition of the plastic material to be treated. Such a temperature is generally in the range of 100°C to 300°C, and preferably in the range of 150°C to 250°C. At temperatures around 300°C or higher, HCl is removed from the PVC resin in which it may be present.

[0041] When waste plastic materials are mixed with alkaline materials during melting / kneading pretreatment, the HCl-forming gas may be removed and neutralized through an exhaust system or may be trapped. To carry out the melting operation, a general kneader, screw extruder, etc. may be used. The plastic waste is preferably fed to the depolymerization reactor by an extruder.

[0042] The extruder melts the plastic waste, holds it at a high temperature (250-350°C) and injects it into the first depolymerization reactor (2). The extruder receives the plastic waste cut into small pieces in a feed hopper and conveys the flow through a melting section, which may heat the polymer by the combined action of the mixing energy and heat provided by a barrel heater.

[0043] Additives may optionally be incorporated into the melt to reduce the corrosiveness of the received plastic waste or to improve the conversion process in the reaction section.

[0044] Upon extrusion, one or more degassing steps can be foreseen to remove any residual moisture present in the product.

[0045] The melt stream may be filtered to remove solid impurities present in the plastic waste before being fed to the reactor (2).

[0046] Depending on the amount and particle size of solid impurities, melt filtration units manufactured in several designs can be applied.

[0047] It is preferable to use a self-cleaning melt filter that can operate for extended periods (days) without manual replacement of the filter element.

[0048] One of the preferred designs of melt filters is based on a circular perforated plate as the melt filtering element, holes (made by laser or by machining depending on the opening) in which solid contaminants accumulate. The accumulation of impurities can increase the differential pressure on the melt filter. To perform in-line cleaning of the filtering element, a rotating scraper removes the accumulated impurities and directs them to an outlet, which is briefly opened to remove contaminants arising in the process.

[0049] This cycle can be repeated several times (up to several days of operating time) without the need for manual intervention or the need to stop production for the time required to replace the filtration elements.

[0050] Another option, self-cleaning melt filters, is based on the application of a continuous filtering metal band through which the polymer stream passes. Impurities accumulate on the metal filter and pressure builds up, which pushes the clogged filter band section out of the polymer flow path, after which a cleaning section is inserted.

[0051] This process is automatic and can be repeated over extended periods of time (up to several days) without the need for manual intervention or the need to stop production for the time required to replace the filtration elements.

[0052] Any extrusion system can be used, such as a single screw extruder, a twin screw extruder, a twin screw extruder with a gear pump, or a combination thereof.

[0053] In step (b), the depolymerization reactor (2) is preferably a stirred vessel operating in the temperature range of 300-550°C, more preferably 350-500°C.

[0054] The operating pressure is preferably maintained in the range of 2.0 to 8 barg, more preferably in the range of 2.5 to 7 barg.

[0055] In order to improve the flowability of the material, a preferred embodiment is configured as follows: the molten material of waste plastic entering the reactor is premixed with a hydrocarbon oil, preferably recycled oil from the first condenser, preferably in a dedicated vessel, to promote dissolution of the molten material in the depolymerization reactor. In this case, the volume ratio of oil / molten material can be in the range of 0.1:1 to 1:1.

[0056] The depolymerization reactor (2) preferably has a cylindrical cross section and a circular bottom.

[0057] The depolymerization reactor (2) preferably has a mixer mounted on its vertical axis. The mixer is equipped with a gear motor that makes it possible to rotate the mixer blades and keep the system in agitated state. The design of the mixer and the power of the motor may vary depending on the content, volume and shape of the reactor. However, as a non-limiting example, it is preferred to operate the reactor with a power input in the range of 0.2-4 kW / m3, preferably 0.2-2 kW / m3, more preferably 0.3 kW / m-1.5 kW / m3.

[0058] The reactor is heated by thermal transfer with a molten salt stream heated to a temperature range of 300°C to 570°C.

[0059] The supply circuit for the molten salt (not shown) is configured to prevent leakage of the molten salt. The molten salt is preferably molten solar salt consisting of a mixture of sodium nitrate and potassium nitrate, more preferably mixed in a weight ratio of 2:3 to 3:2. The solar salt in turn receives heat from a dedicated furnace, which may be electric or fuel-fed. In the latter case, a portion of the recovered oil from the condensation unit (5) may be used to feed the furnace. Alternatively or in combination, the heat may be generated by burning gaseous or liquid hydrocarbons. It is preferable to use gaseous hydrocarbons.

[0060] The heat associated with the molten salt is preferably transferred to the depolymerization reactor by circulating the molten salt through a jacket surrounding the entire reactor and / or by feeding it to an external heat exchanger, as described below.

[0061] In either case, the salt is circulated using a circulation pump. A series of fins ensures even distribution of the molten salt flow within the jacket and maximizes the heat exchange coefficient.

[0062] In the depolymerization process carried out in the reactor, the chain length is shortened to produce molecules with lower boiling points. This continuously progressing chain scission mechanism, especially close to the reactor wall, produces smaller and smaller molecules, some of which are gaseous at the operating temperature and pressure.

[0063] As a result, the composition in the reactor covers a wide range of hydrocarbons, from methane to heavier products, including both saturated hydrocarbons and olefins, with linear or highly branched structures. Some aromatic products and fused ring structures may also be present.

[0064] Materials that remain liquid under operating conditions serve to reduce the viscosity of the liquid material. Depending on the depolymerization process and the composition of the feed, the contents of reactor (2) can be defined as a coexistence of a liquid slurry phase (solids, especially carbonaceous and inorganic materials, dispersed in the liquid hydrocarbon mixture) and a gas phase.

[0065] At least a portion of the liquid slurry phase constitutes a liquid effluent which is withdrawn from the reactor, preferably from the bottom of the reactor, and sent to a char handling section (6) which is described in more detail hereinafter.

[0066] From an operational standpoint, the withdrawal of the slurry phase from the bottom of the reactor is preferably triggered by a density sensor which detects when the density of the liquid slurry reaches a predetermined value.

[0067] In certain preferred embodiments, a portion of the liquid slurry withdrawn from the reactor (2) is recirculated via a circulation pump (7) and, if desired, returned to the top of the reactor by an external heater (8). As mentioned above, the heat transferred to the external heater is preferably provided by a molten salt. This embodiment can improve both the homogeneity of the reactor contents and the reactor heating.

[0068] According to a preferred embodiment, the liquid slurry portion recycled to the reactor is withdrawn at a point different from the point at which the liquid slurry portion sent to the char handling section is withdrawn.

[0069] According to another preferred embodiment, both the liquid slurry portion recycled to the reactor and the liquid slurry portion sent to the char handling section are withdrawn from the same point and then split sequentially.

[0070] The division between the liquid slurry portion sent to the char handling section and the liquid slurry portion recycled to the reactor can be carried out either before or after the recirculation pump (7). In the latter embodiment, the liquid slurry is first fed into a dedicated vessel with a lower and an upper outlet point. The liquid portion sent to the char handling section (6) is withdrawn in concentrated form from the lower outlet point, while the liquid portion recycled to the reactor (2) is withdrawn from the upper outlet point.

[0071] The gas phase of the reactor (2) constitutes the gaseous effluent that is sent to a condensation unit (3) for further processing.

[0072] The gaseous effluent contains a mixture of light hydrocarbons and may further contain some heavy hydrocarbons and entrained char particles. The gaseous effluent is conveyed from the top of the reactor to a condensation unit (3) which preferably operates at a pressure slightly lower than the reactor pressure.

[0073] The condensing unit (3) is more preferably designed as a scrubber column to suppress entrained char. The condenser temperature is selected such that the heavy hydrocarbons are condensed and the light hydrocarbons are released as a gas stream. The gas stream (H2 and light hydrocarbons) is conveyed to another condensing unit (5) operating at a lower temperature than the condensing unit (3) recovering the oil.

[0074] The operating temperature of the condensation unit (3) may vary in a wide range depending on the operating pressure. The temperature, relative to atmospheric pressure, may be between 20 and 200° C., more preferably between 50 and 200° C., particularly preferably between 60 and 180° C. If a higher operating pressure is selected, the temperature range may of course be modified.

[0075] In a particular embodiment, the condenser unit (3) is operated at about 80° C. and the condensed liquid is collected and analyzed by GC analysis.

[0076] The number of compounds is so large that the analytical results are reported by grouping the compounds obtained according to their internal residence time, taking a particular hydrocarbon as the standard. The results indicate that there is more than about 2% by weight of compounds with a residence time equal to or less than that of n-heptane, more than about 25% by weight of compounds with a residence time between that of n-heptane and that of n-dodecane, and a more abundant fraction of compounds (up to 70% by weight) with a residence time higher than that of n-dodecane but lower than that of n-octacosane, with the possibility of a smaller fraction of the higher residence times being present.

[0077] In a preferred configuration of the condensing unit (3), a dephlegmator (partial condenser) is mounted on top of the scrubber and operates at a lower temperature than that in the column. The condensate flows down by gravity as reflux for the scrubber. The dephlegmator may be mounted as a separate device or within the scrubber.

[0078] In another preferred configuration, a pump recirculates liquid collected at the bottom of the scrubber to the top of the column, where it is cooled in a dedicated heat exchanger before being injected into the top of the scrubber as reflux.

[0079] The hydrocarbon condensate, preferably having more than C7 carbon atoms, constitutes the liquid stream that is conveyed by a pump to the second depolymerization reactor (4).

[0080] The second depolymerization reactor (4) is preferably of the same type as the first depolymerization reactor, more preferably a continuous stirred tank reactor.

[0081] The depolymerization is carried out in the same temperature range, but preferably at a higher pressure than in the first reactor in order to limit the volatility of the heavy hydrocarbons, specifically in the range of 2 to 10 barg, preferably 3 to 9 barg, more preferably 3 to 8 barg.

[0082] Reactor (4) is fed with the condensed effluent from reactor (2) and therefore contains less impurities and produces less char. Fresh catalyst is preferably fed to reactor (4) via conduit (15).

[0083] According to the present disclosure, the catalyst may be selected from active catalysts that act as depolymerization / decomposition catalysts in thermal catalytic processes. In particular, the catalyst may be selected from metal oxides, heteropolyacids, mesoporous silica, aluminosilicate catalysts (such as halloysite, kaolinite, etc.), and preferably zeolites. Among them, particularly preferred zeolites are synthetic Y-type zeolite and ZSM-5.

[0084] In a particularly preferred embodiment, the catalyst supply amount is at most 10% by weight, preferably at most 5% by weight, in particular at most 2% by weight, relative to the plastic waste supply amount.

[0085] In a preferred embodiment, the catalyst is injected into the second reactor as a powder dispersed in a hydrocarbon oil, preferably the liquid pyrolysis product (oil) obtained from the condensation unit (3) or (5), preferably the liquid pyrolysis product (oil) obtained from the condensation unit (3).

[0086] The catalyst slurry is preferably prepared in a pot (continuously stirred tank) into which the catalyst is poured from a dedicated silo in order to keep the concentration of catalyst in the slurry constant.

[0087] The pyrolysis oil with dispersed catalyst is preferably withdrawn from the condensation unit (3) in order to keep the level of the slurry in the pot constant. Once ready, the catalyst slurry can preferably be injected into the second reactor, preferably by means of a progressive cavity pump to keep its level constant.

[0088] The liquid effluent from reactor (4) is preferably a concentrated hydrocarbon slurry containing the depolymerization catalyst. This liquid effluent is discharged from the second reactor and returned to the first reactor via conduit (16). The same concentration control exercised in reactor (4) for withdrawing the slurry is preferably also applied to reactor (2).

[0089] The concentration of the slurry can be controlled by available methods such as gamma radiation measurement or Coriolis densitometer. If the operating pressure of the first reactor is lower than that of the second reactor, the light hydrocarbons of the slurry entering the first reactor are expected to vaporize and be extracted with the gaseous effluent produced in reactor (2).

[0090] The amount of the slurry recycled to the first reactor is preferably 5 to 40% by volume, more preferably 10 to 30% by volume, of the content of the second reactor.

[0091] In addition, in the reactor (4), a preferred embodiment is configured as follows: a portion of the liquid slurry withdrawn from the bottom of the reactor (4) is recirculated via a circulation pump (12) and returned to the top of the reactor by an external heater (13).

[0092] The gaseous effluent produced from the reactor (4) is conveyed to a condensation unit (5) for recovery of the pyrolysis products in the form of oil.

[0093] The condensation unit (5) preferably has a similar configuration to the condensation unit (3).

[0094] The operating conditions of the condensing unit (5) are preferably selected such that the condensing unit (5) operates at a lower operating temperature and pressure relative to the condensing unit (3).

[0095] In particular, the temperature may range from 20 to 80° C., preferably from 30 to 70° C. The pressure value is preferably lower than the pressure value of the condensing unit (3) in order to allow the non-condensable gases from the condensing unit (3) to enter the condensing unit (5) without further pressurization. The oil recovered from the condensing unit 5 is usually lighter than the oil recovered from the first condensing unit and may in particular have the following composition (measured by GC): about 10-15% by weight of the portion having a residence time equal to or less than the residence time of n-heptane; about 70-75 wt. % of the portion whose residence time is between the residence time of n-heptane and the residence time of n-dodecane; About 12-20 wt. % of a product having a retention time higher than that of n-dodecane but lower than that of n-octacosane; Trace compounds with longer residence times.

[0096] As mentioned above, the liquid effluent discharged from the pyrolysis reactor (2) and sent to the char handling section is concentrated in the form of a slurry withdrawn from the bottom of the reactor, preferably continuously discharged. By operating the pressurized reactor, the concentrated slurry can be easily discharged to the low pressure unit without the use of additional withdrawal equipment. As mentioned above, the slurry can be discharged from the bottom of the reactor or, if present, from a line or vessel behind the circulation pump (7).

[0097] From the viewpoint of process setting, it is preferable that the flow of the slurry stream is continuous. The char content in the slurry can be in the range of 10 to 50%, preferably 20 to 40% by weight.

Claims

1. 1. A char handling plant for char in a slurry produced by pyrolysis or depolymerization of plastic waste, comprising: a first jacketed chamber (6a) equipped with an inlet conduit (6a-1) for feeding a char-containing slurry and an agitation system (6b), operable in the temperature range of 350-570°C, and further equipped with a conduit (6b-1) for withdrawing a gaseous effluent; means (6c) for withdrawing the concentrated slurry from said chamber (6a) and conveying it to a second chamber (6d) capable of maintaining said slurry in the same temperature range as said chamber (6a) and equipped with a degassing system for removing gaseous effluents to produce a dry char; a second chamber (6d) for receiving the dried char, comprising a stirring system (6d-1), a char outlet (6d-2), a gas inlet (6d-3) located at the bottom of the chamber, and a gas outlet (6d-4) for removing gaseous effluent stripped from the char; a means (6e) capable of receiving the dried char in the second chamber (6d) and conveying it to a third collection chamber (6f) and maintaining said char at a temperature in the range of 60°C to 100°C; a third collection chamber (6f) for receiving said dried char, said third collection chamber (6f) being provided with an agitation system (6f-1) and an outlet for handling char operated by a valve (6f-2).

2. 2. A char handling plant according to claim 1, characterized in that the means (6c) for withdrawing the concentrated slurry from the chamber (6a) and conveying it to a second chamber (6d) is a jacketed screw conveyor (6c) operating in the same temperature range as the chamber (6a).

3. 3. The char handling plant according to claim 2, characterized in that the screw conveyor (6c) is composed of two different conveyors connected to each other, a first lifting screw conveyor (6c-1) having a lower end integrated with the bottom of the chamber (6a) and an upper end located higher than said lower end and connected to one end of a second screw conveyor (6c-2), the other end of which is connected to the top of the second chamber (6d).

4. 2. Char handling plant according to claim 1, characterized in that the second chamber (6d) is provided with a nitrogen inlet which is a gas inlet (6d-3) at the bottom and an outlet at the top as a gas outlet (6d-4) for conveying the stripped gas to a condensation unit.

5. 2. A char handling plant as claimed in claim 1, characterized in that the second chamber (6d) is provided at its bottom with an outlet and a ball valve for discharging the dried char into a jacketed screw conveyor (6e) maintained at a temperature in the range of 60-100°C.

6. A method for treating a char-containing slurry resulting from the pyrolysis or depolymerization of plastic waste, comprising the steps of: introducing the char-containing slurry into a first jacketed chamber (6a) equipped with an agitation system (6b) and operating said chamber at a temperature range of 350-570°C to generate and withdraw a gaseous effluent; removing the gaseous effluent formed by withdrawing the concentrated slurry from said chamber (6a) and conveying it to a second chamber (6d) while maintaining it at the same temperature range as said chamber (6a) to produce a dried char; Introducing the dried char into a second chamber (6d) equipped with a stirring system (6d-1), a char outlet (6d-2), a gas inlet (6d-3) located at the bottom of the chamber, and a gas outlet (6d-4) for removing the gaseous effluent stripped from the char; feeding the dried char obtained in the second chamber (6d) into a third collection chamber (6f) while maintaining the char at a temperature in the range of 60-100°C; and discharging the dried char from the collection chamber through a valve (6-2) for handling.

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