Plastic pyrolysis system and method with degassing reactor

Abstract

The present invention concerns a pyrolysis process comprising the steps of: providing first (1) and second (2) pyrolysis reactors; feeding plastic waste material to the first pyrolysis reactor (1) and subjecting it to pyrolysis; discharging a first fraction of the first pyrolysis composition, which is enriched in char particles, discharging a second fraction of gaseous hydrocarbon material and discharging a third fraction, which is enriched in liquid hydrocarbon material, to the second pyrolysis reactor (2); subjecting the third fraction in the second pyrolysis reactor (2) to pyrolysis; discharging a first fraction of the second pyrolysis composition of gaseous hydrocarbon material and a second fraction comprising liquid hydrocarbon material and char particles; and heating the second fraction of the second pyrolysis composition downstream of the second pyrolysis reactor (2) and feeding the heated second fraction to the first pyrolysis reactor (1). The present invention further concerns a corresponding pyrolysis system.

Description

[0001] PYROLYSIS SYSTEM WITH DEGASSING REACTOR

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for the pyrolysis of plastic waste material and to a pyrolysis system configured to convert plastic waste material into pyrolysis products.

[0004] BACKGROUND OF THE INVENTION

[0005] Large quantities of waste plastics are generated in the present society. While recycling of plastics is becoming ever more efficient and effective, much of the waste plastic still cannot be effectively or efficiently recycled and is disposed to landfill sites where it takes many years to degrade, or it is incinerated. Even worse, it may be lost to the environment where it can be damaging to ecosystems.

[0006] Plastic materials can however be converted for reuse. For example, fuels such as diesel may be derived from waste plastics, or waste plastics may be converted to raw materials suitable for synthesis of new materials, such as new plastics, other hydrocarbon materials, or similar. Materials recovered from waste plastics may be useful to at least partially replace hydrocarbons obtained from fossil sources.

[0007] A known process in the art for converting waste plastic to, among other things, diesel, is the thermochemical breakdown process of pyrolysis. Pyrolysis is the thermal decomposition of material in an inert atmosphere, i.e. in the absence of oxygen. In plastic-to-chemical pyrolysis plants, waste plastics, typically mostly comprising polyethylene and polypropylene from domestic sources, form the input. These waste plastics that are made up of very long chain hydrocarbons are then cracked into shorter chains forming a wide spectrum of molecules with a variety of chain lengths. The resulting mixtures can be distilled into various fractions, typically including light hydrocarbons (LHC), heavy hydrocarbons (HHC) and noncondensables (gases). During pyrolysis of waste plastics, also char particles are formed. As used herein, the term ‘char particles' refers to the solid carbonaceous material remaining after a plastic feed stream has been pyrolyzed. It is known that certain plastic compositions yield char in higher amounts than others. Rigid plastics and aromatic-molecule-containing plastics, such as PVC, PET, PS and acrylonitrile butadiene styrene for example, tend to result in more char than polyethylene and polypropylene at comparable processing conditions. Moreover, non-plastic contaminants that may be present in plastic waste streams, such as food, wood and paper, and additives typically present in plastics, such as fillers, flame retardants and colorants, all have an influence on the amount of the char formed during pyrolysis and can be part of this char. As is generally known to the skilled person, no matter how efficient the pyrolysis process is performed and irrespective of the composition of the feedstock, always some char particles are formed. As will be appreciated by those skilled in the art, inorganic particles present in the waste plastic to be pyrolyzed will remain substantially unaffected during the pyrolysis process and will also be present in the pyrolysis reaction mixture.

[0008] In continuous pyrolysis processes of plastic waste materials, plastic waste to be pyrolyzed is continuously supplied to the pyrolysis reactor and pyrolysis products, including condensable and non-condensable gases and char particles, are continuously removed from the pyrolysis reactor. This means that during a continuous pyrolysis process, materials which are cracked to a variety of degrees and char particles with a variety of sizes are simultaneously present. During the pyrolysis reaction, pyrolysis gases are formed from and within liquid hydrocarbon material. Char particles are also formed within liquid hydrocarbon material. This means that during pyrolysis, a fluid phase is present in the pyrolysis reactor with char particles and optionally with inorganic particles suspended therein. The fluid phase comprises a mixture of liquid hydrocarbon material and gaseous hydrocarbon material. Gaseous hydrocarbon material forms gas bubbles that escape the fluid phase and form a separate gaseous hydrocarbon above the fluid phase which can be removed from the fluid phase via a top outlet of a pyrolysis reactor. The liquid, partially pyrolyzed, part of the fluid phase typically needs to be (re)heated to provide sufficient heat for further pyrolysis.

[0009] Accordingly, pyrolysis systems and reactor geometries have been developed to efficiently and continuously remove gaseous hydrocarbon material, char particles and optionally inorganic particles, from the liquid hydrocarbon material that needs to be subjected to further pyrolysis. Examples of such pyrolysis systems comprise pyrolysis reactors that apply internal physical mixers and / or internal heat exchanger elements and / or internal scrapers to remove char particles from the reactor walls.

[0010] EP3186556B 1 , for example, discloses a pyrolysis reactor comprising agitation blades for rotating on a central shaft in close proximity to a reactor vessel inner surface at the lower end of the reactor.

[0011] JP3246748U, for example, discloses a pyrolysis reactor having a rotary kiln and a rotary screw, the rotary kiln having a cylindrical kiln shell equipped with a heating device capable of heating the internal space, wherein the rotary screw is disposed within the kiln shell. The rotary screw has spiral ribbon- shaped blades on the outer periphery, and the inner periphery of the rotary screw has screw blades. Other pyrolysis systems comprise pyrolysis reactors that neither apply internal physical mixers and scrapers nor internal heat exchanger elements, to reduce fouling of internal structural elements with char particles and / or to reduce local overheating of the plastic waste.

[0012] US2022 / 0204861A1, for example, discloses a process and a reactor system for pyrolysis of a mixed plastic stream that contains PVC. The reactor system comprises a melting reactor and a pyrolysis reactor having a cylindrical geometry and comprising an internal cylinder, such that an annular space is formed between the reactor wall and the internal cylinder. The pyrolysis reactor has a conical bottom part. It is described that the process using the reactor system provides a continuous pyrolysis operation and solid separation. The melting reactor melts the waste plastics and produces a first vapor stream and a first liquid stream. The first liquid stream is fed to the pyrolysis reactor where it is cracked, resulting in a second vapor, a second liquid and solid particles. It is described that a portion of the pyrolysis reactor liquid is circulated and that part of it is heated in an external heater system where all heat needed to sustain the main cracking reaction is provided and that the remaining part is directly sent to the melting reactor to sustain melting reaction needs. Heated recirculated stream is fed back into the pyrolysis reactor in a tangential direction in the annular space resulting in a swirl-like movement of the reactor contents along the cylindrical reactor wall. The reactor system does not apply a physical mixer. During the pyrolysis reaction, char particles are produced that settle along the circular wall area down to the bottom of the pyrolysis reactor together with metal particles. Metal and large char particles are collected and discharged as a residue.

[0013] WO2021 / 053139A1 discloses a method for breaking down long-chain hydrocarbons from plastic-containing waste with limited carbonization of the hydrocarbons, said method comprising providing material containing long-chain hydrocarbons, subjecting the material to heating in a heating structure followed by separation in a separation structure. The heating structure typically comprises more than one serial heating zones with increasing temperatures in the downstream direction. The material leaving the last heating zone and entering the separation structure contains both long-chain hydrocarbons and cracked hydrocarbons. The separation structure comprises a cylinder- shaped intermediate portion containing a separation zone, and a funnel shaped bottom portion containing a settling zone with the funnel ending in an outlet for heavy hydrocarbons and / or solid carbons. Part of the hydrocarbon liquid formed in the separation structure is discharged from and recycled to the separation structure via a reheating zone. The heavy hydrocarbons and / or solid carbons are released via a valve structure.

[0014] WO2024 / 046896A1 discloses a process and a reactor system for pyrolysis of plastic material. The process comprises heating and melting plastic material in a heating structure to a pyrolysis temperature resulting in cracking, followed by separation of cracked gases and liquid in a separation vessel. Gases rise and exit to a partial condenser and liquids fall to the bottom of the separation vessel. A recycling loop is provided to remove liquid, partially pyrolyzed, plastic material collected in the separation vessel by way of a pump. The removed liquid is reheated to a pyrolysis temperature by a heat exchanger, and then returned to the separation vessel. This recycle loop increases the residence time for long-chain hydrocarbons at pyrolysis temperature so that they are subjected to further pyrolysis and broken down to shorter-chain hydrocarbons, eventually exiting via the partial condenser. The separation vessel is not heated by any source other than heat carried by incoming heated material and does not comprise an internal agitator. The reactor contents are subjected to a swirling or cyclonic flow pattern by using tangential feed inlets. This swirling flow pattern is said to assist in efficient phase separation with the denser liquid and entrained solids being centrifugally driven to the periphery and to the bottom and the gas rising upwardly. WO2024 / 046896A1 further teaches the use of a radially centered internal structural element and a radially centered internal liquid outlet that are both intended to reduce entrainment of gas bubbles and solids particles in the liquid to be reheated and recycled. This is described to be advantageous to reduce cavitation effects in the pump and reduce blockage of the pump and heat exchanger. The heat exchanger heats the liquid in the recycle loop to pyrolysis temperatures resulting in gas formation in the heat exchanger. Moreover, according to WO2024 / 046896A1, to reduce cavitation effects in the pump, it is preferred that the pump is upstream of the heat exchanger, so that the pump is presented predominantly with liquid phase.

[0015] As will be appreciated by those skilled in the art, the swirl-like flow pattern that is imposed in some of the pyrolysis reactors of the prior art helps to separate solid particles from the fluid reaction mixture, but it is not necessarily helpful in degassing of the fluid reaction mixture, because the swirl-like flow pattern stimulates entrainment of gas bubbles in the fluid phase. Accordingly, the solutions suggested in the prior art provide suboptimal solutions for simultaneously separating solid particles and gas bubbles from the partially-pyrolyzed fluid pyrolysis phase in a pyrolysis reactor.

[0016] It is therefore an object of the invention to provide a continuous process for the pyrolysis of plastic waste material and a corresponding pyrolysis system with improved separation characteristics of solid particles and gas bubbles from the partially-pyrolyzed fluid.

[0017] It is a further object of the invention to provide a continuous process for the pyrolysis of plastic waste material and a corresponding pyrolysis system with improved process stability and / or with less downtime and / or with less operating expenses (OpEx) and / or with higher throughput.

[0018] SUMMARY OF THE INVENTION

[0019] The inventors have unexpectedly found that one or more of the objects can be met by heating and recycling pyrolysis liquid over a reactor system comprising two serial pyrolysis reactors, wherein a first pyrolysis reactor is operating at a first pyrolysis temperature and is optimized to remove char particles and optionally inorganic particles from the pyrolysis reaction mixture, and wherein a downstream second pyrolysis reactor, which is operating at a second and lower pyrolysis temperature, is optimized to separate process gases from the pyrolysis reaction mixture.

[0020] The inventors have found that the pyrolysis reaction heavily depends on temperature. A temperature difference of only 2 degrees Celsius, wherein both temperatures are sufficiently high to allow pyrolysis of the feedstock, can already differentiate between a violent and rather quiet pyrolysis reaction. The first pyrolysis reactor is operating at a first (higher) pyrolysis temperature and thus results in the more violent pyrolysis reaction and in the formation of char particles. This first pyrolysis reactor is configured to efficiently remove char particles and optionally inorganic particles from the pyrolysis reaction mixture, allowing or forcing them to sediment to the bottom part. Although degassing also takes place in the first pyrolysis reactor, in addition to separation of char particles, a sufficient gas-liquid separation is not achieved at this stage. Hence, a fluid phase comprising a substantial gas content but only a limited amount of char particles is withdrawn from the first pyrolysis reactor and is then subjected to pyrolysis in the second downstream pyrolysis reactor. The second pyrolysis reactor is operating at a second (lower) pyrolysis temperature and thus results in a quieter pyrolysis reaction and in less formation of char particles. This second pyrolysis reactor allows, due to the quieter pyrolysis reaction and flow conditions, for efficient degassing of both the gaseous hydrocarbons in the feed and the gaseous hydrocarbons formed during the pyrolysis reaction. Although no complete degassing will take place in the second pyrolysis reactor, the efficient degassing nevertheless allows to transport the resulting fluid phase to a heat exchanger using a pump with reduced cavitation. Because of the limited amount of char particles in the fluid phase withdrawn from the first pyrolysis reactor and the limited formation of char particles in the second pyrolysis reactor, the risk of blockage of the downstream pump and heat exchanger is considerably reduced, and the efficiency of the heat exchanger and pump is considerably improved. Accordingly, in a first aspect, the invention provides a process for the pyrolysis of plastic waste material, comprising the steps of:

[0021] (a) providing a first pyrolysis reactor (1) having at least one inlet and having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf) and further providing a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having at least one inlet (2d), wherein the top part (2a) and bottom part (2c) of the second pyrolysis reactor (2) comprise at least one outlet (2e,2f);

[0022] (b) continuously feeding plastic waste material (1g) to the first pyrolysis reactor (1) via an inlet (Ih) and subjecting the plastic waste material (1g) to pyrolysis, resulting in a first pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the char particles and optionally present inorganic particles sediment to the bottom part (1c) of the first pyrolysis reactor (1);

[0023] (c) continuously or semi-continuously discharging a first fraction (li) of the first pyrolysis composition, which is enriched in char particles compared to the first pyrolysis composition, via outlet (If) in the bottom part (1c) of the first pyrolysis reactor (1), continuously discharging a second fraction (Ij) of gaseous hydrocarbon material via outlet (Id) in the top part (la) of the first pyrolysis reactor (1) and continuously discharging a third fraction (Ik), which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, via outlet (le) in the middle part (lb) of the first pyrolysis reactor (1) to an inlet (2d) of the second pyrolysis reactor (2);

[0024] (d) subjecting the third fraction (Ik) of the first pyrolysis composition in the second pyrolysis reactor (2) to pyrolysis, resulting in a second pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the net flow of gaseous hydrocarbon material is to the top part (2a) and the net flow of the liquid hydrocarbon material and the char particles is to the bottom part (2c);

[0025] (e) continuously discharging a first fraction (2g) of the second pyrolysis composition of gaseous hydrocarbon material via outlet (2e) in the top part (2a) of the second pyrolysis reactor (2) and a second fraction (2h) comprising liquid hydrocarbon material and char particles via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2); and

[0026] (f) heating the second fraction (2h) of the second pyrolysis composition downstream of the second pyrolysis reactor (2) in a heating section (3) comprising a heat exchanger (5) and a pump (4) and continuously feeding the heated second fraction (3a) to the first pyrolysis reactor (1) via an inlet in the first pyrolysis reactor (1), wherein the highest temperature in the first pyrolysis reactor (1) is higher than the temperature anywhere in the second pyrolysis reactor (2), and wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1).

[0027] In a second aspect, the invention provides a pyrolysis system configured to convert plastic waste material into pyrolysis products, said system comprising:

[0028] (1) a first pyrolysis reactor (1) having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf), said first pyrolysis reactor (1) further having at least one inlet (Ih) configured to receive plastic waste material, and wherein said first pyrolysis reactor (1) is configured to separate solid particles from a fluid phase via sedimentation;

[0029] (ii) a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having an inlet (2d) in fluid connection with outlet (le) in the middle part (lb) of the first pyrolysis reactor (1), an outlet (2f) in the bottom part (2c) and an outlet (2e) in the top part (2a); and

[0030] (iii) a heating section (3) comprising a pump (4) and a heat exchanger (5) in fluid connection with the outlet (2f) of the second pyrolysis reactor (2) and in fluid connection with an inlet of the first pyrolysis reactor (1), wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1).

[0031] DEFINITIONS

[0032] The terms ‘horizontal' , ‘horizontal direction' , ‘vertical' and ‘vertical direction' as used herein as regards the spatial arrangement of the pyrolysis reactors (1) and (2) in use in the process of the invention have their common meaning in the art. Hence, a horizontal arrangement concerns an arrangement substantially parallel to the floor or bottom and a vertical arrangement concerns an arrangement substantially perpendicular to the floor or bottom.

[0033] The term ‘axial direction' as used herein in the context of the pyrolysis reactors (1) and

[0034] (2) refers to a direction parallel to the central axis of the pyrolysis reactors (1) and (2). When in use in the process of the invention, the ‘axial direction' substantially coincides with the ‘vertical direction' .

[0035] The term ‘radial direction' as used herein in the context of the pyrolysis reactors (1) and (2) refers to a direction perpendicular to the ‘axial direction' of the pyrolysis reactors (1) and (2). When in use in the process of the invention, the ‘radial direction' substantially coincides with the ‘horizontal direction' .

[0036] The terms ‘bottom part (lc)', ‘middle part (lb)' and ‘top part (la)' as used in the context of the pyrolysis reactors (1) and (2) refer to subsequent sections of the pyrolysis reactors (1) and (2) when moving in the axial direction.

[0037] The terms ‘tangential’ or ‘tangential direction' as used herein refers to a direction substantially in the horizontal plane and parallel to the tangent to the wall of the pyrolysis reactor (1).

[0038] BRIEF DESCRIPTION OF THE FIGURES

[0039] Figure 1 depicts a flow scheme of the pyrolysis process and a pyrolysis system according to the invention.

[0040] Figures 2 and 3 depict flow schemes of the pyrolysis process and a pyrolysis system according to embodiments of the invention.

[0041] Figure 4 depicts a flow scheme of a comparative pyrolysis process and pyrolysis system.

[0042] Figure 5 graphically shows heat transfer coefficients in a heat exchanger versus the number of days of operation since the last cleaning of the heat exchanger in a system / process according to the invention and in a comparative system / process.

[0043] DETAILED DESCRIPTION

[0044] Process

[0045] In a first aspect, the invention concerns a process for the pyrolysis of plastic waste material, comprising the steps of:

[0046] (a) providing a first pyrolysis reactor (1) having at least one inlet and having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf) and further providing a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having at least one inlet (2d), wherein the top part (2a) and bottom part (2c) of the second pyrolysis reactor (2) comprise at least one outlet (2e,2f);

[0047] (b) continuously feeding plastic waste material (1g) to the first pyrolysis reactor (1) via an inlet (Ih) and subjecting the plastic waste material (1g) to pyrolysis, resulting in a first pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the char particles and optionally present inorganic particles sediment to the bottom part (1c) of the first pyrolysis reactor (1);

[0048] (c) continuously or semi-continuously discharging a first fraction (li) of the first pyrolysis composition, which is enriched in char particles compared to the first pyrolysis composition, via outlet (If) in the bottom part (1c) of the first pyrolysis reactor (1), continuously discharging a second fraction (Ij) of gaseous hydrocarbon material via outlet (Id) in the top part (la) of the first pyrolysis reactor (1) and continuously discharging a third fraction (Ik), which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, via outlet (le) in the middle part (lb) of the first pyrolysis reactor (1) to an inlet (2d) of the second pyrolysis reactor (2);

[0049] (d) subjecting the third fraction (Ik) of the first pyrolysis composition in the second pyrolysis reactor (2) to pyrolysis, resulting in a second pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the net flow of gaseous hydrocarbon material is to the top part (2a) and the net flow of the liquid hydrocarbon material and the char particles is to the bottom part (2c);

[0050] (e) continuously discharging a first fraction (2g) of the second pyrolysis composition of gaseous hydrocarbon material via outlet (2e) in the top part (2a) of the second pyrolysis reactor (2) and a second fraction (2h) comprising liquid hydrocarbon material and char particles via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2); and

[0051] (f) heating the second fraction (2h) of the second pyrolysis composition downstream of the second pyrolysis reactor (2) in a heating section (3) comprising a heat exchanger (5) and a pump (4) and continuously feeding the heated second fraction (3a) to the first pyrolysis reactor (1) via an inlet in the first pyrolysis reactor (1), wherein the highest temperature in the first pyrolysis reactor (1) is higher than the temperature anywhere in the second pyrolysis reactor (2), and wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1).

[0052] The verb ‘to comprise' and its conjugations are used in their non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. Hence, the wording ‘a heating section (3) comprising a heat exchanger (5) and a pump (4)' does not exclude the presence of more than one heat exchanger (5) and pump (4). The wording "each part comprising at least one outlet ( ld,le,lf)' means that the top part (la) comprises at least one outlet (Id), that the middle part (lb) comprises at least one outlet (le) and that the bottom part (1c) comprises at least one outlet (If). Likewise, the wording ‘the top part (2a) and bottom part (2c) comprise at least one outlet (2e,2f)' means that the top part (2a) comprises at least one outlet (2e) and that the bottom part (2c) comprises at least one outlet (2f).

[0053] The volume of the first (1) and second (2) pyrolysis reactors as defined in the first and second aspects concerns the total internal volume inside the reactor walls.

[0054] Typically, part (la) of the first pyrolysis reactor (1) and part (2a) of the second pyrolysis reactor (2) are the parts where the gaseous components are present. Typically, parts (lb) and (1c) of the first pyrolysis reactor (1) and parts (2b) and (2c) of the second pyrolysis reactor (2) are the parts where the liquid components, char particles and any inorganic particles are present.

[0055] In an embodiment, the first fraction (li) of the first pyrolysis composition, which is enriched in char particles compared to the overall first pyrolysis composition, is continuously discharged from the first pyrolysis reactor (1) via bottom outlet (If). However, continuous discharge of the first fraction (li) may result in disposal of too much partially -pyrolyzed pyrolysis liquid, with a corresponding decreased yield of the pyrolysis reaction. Hence, in another embodiment, the first fraction (li) is discharged semi-continuously, such as every 10 minutes or every 20 minutes or every time a minimum density of the first fraction (li) has been obtained.

[0056] Outlet (le) can be configured to discharge reactor contents from close to the wall of the first pyrolysis reactor (1), can be configured to discharge reactor contents from close to the central axis of the first pyrolysis reactor (1) via a pipe in the radial direction of the first pyrolysis reactor (1) reaching inside the first pyrolysis reactor (1), or can be configured to discharge reactor contents from somewhere in between. In order to reduce the risk of fouling of internal structures by char particles, the reactor contents are preferably discharged from close to the wall of the first pyrolysis reactor (1).

[0057] In an embodiment, the pump (4) is a positive displacement pump or a centrifugal pump, preferably a centrifugal pump. In a preferred embodiment, the volume of the second pyrolysis reactor (2) is between 7 and 200% of the volume of the first pyrolysis reactor (1), more preferably between 10 and 150%, even more preferably between 15 and 80%.

[0058] The second pyrolysis reactor (2) typically has a temperature gradient in the axial direction, wherein the temperature is highest where the third fraction (Ik) enters the second pyrolysis reactor (2), i.e. where inlet (2d) is located.

[0059] In a preferred embodiment, the highest value for the temperature in the first pyrolysis reactor (1) is between 0.1 and 10 °C higher than the lowest value for the temperature in bottom part (2c) in the second pyrolysis reactor (2), more preferably between 0.15 and 5 °C higher, even more preferably between 0.2 and 2 °C higher.

[0060] As will be appreciated by those skilled in the art, the temperatures are determined during operation and concern time-averaged measurements, such as measurements time-averaged over a period of at least one minute. The temperatures are preferably measured at least 10 cm from the reactor walls of the first pyrolysis reactor (1) and from the reactor walls of the second pyrolysis reactor (2).

[0061] The highest temperature in the first pyrolysis reactor (1), the temperature throughout the second pyrolysis reactor (2) and the lowest value for the temperature in bottom part (2c) in the second pyrolysis reactor (2) can be determined using multipoint temperature sensors that simultaneously measure the temperature at several points over the length of the probe. Such multipoint temperature sensors can thus be used to determine a (time- averaged) temperature profile along a length in the vertical and horizontal direction of the first (1) and the second pyrolysis reactor (2), including a length in the vertical and horizontal direction of the bottom part (2c) in the second pyrolysis reactor (2). Examples of such multipoint temperature sensors are provided by Thermo-Electra, Pijnacker, The Netherlands.

[0062] The highest temperature in the first pyrolysis reactor (1) is typically found in the middle part (lb). The highest temperature in the second pyrolysis reactor (2) is typically found where the third fraction (Ik) of the first pyrolysis composition enters the second pyrolysis reactor (2). In a preferred embodiment, the highest value for the temperature in the first pyrolysis reactor (1) is between 400 and 430 °C, more preferably between 405 and 425 °C, even more preferably between 407 and 423 °C.

[0063] In a preferred embodiment, the lowest value for the temperature in bottom part (2c) in the second pyrolysis reactor (2) is between 390 and less than 429.9 °C, more preferably between 400 and 424.85 °C, even more preferably between 405 and 422.8 °C.

[0064] In a preferred embodiment, the plastic waste material (1g) and the heated second fraction (3a) are fed to the first pyrolysis reactor (1) via different inlets. In another embodiment, the plastic waste material (1g) and the heated second fraction (3a) are first combined and then fed to the first pyrolysis reactor (1) via a single inlet.

[0065] In a preferred embodiment, the plastic waste material (1g) is fed to an inlet (Ih) of the first pyrolysis reactor (1) in the top part (la) or in the middle part (lb). Most preferably, the plastic waste material (1g) is fed to an inlet (Ih) below the level of the first pyrolysis mixture in the first pyrolysis reactor (1).

[0066] In a preferred embodiment, the heated second fraction (3a) is fed to the first pyrolysis reactor (1) via an inlet (11) in the top part (la) or in the middle part (lb). Most preferably, the heated second fraction (3a) is fed to an inlet (11) below the level of the first pyrolysis mixture in the first pyrolysis reactor (1).

[0067] In a preferred embodiment, the plastic waste material (1g) and / or the heated second fraction (3a) are fed to the first pyrolysis reactor (1) via one or more tangential inlets.

[0068] In a preferred embodiment, the plastic waste material (1g) is subjected in step (b) to a pyrolysis reaction in the first pyrolysis reactor (1) under a swirl-like movement of the reactor contents along the vertical reactor wall.

[0069] Such a swirl-like movement of the reactor contents along the vertical reactor wall can for example be established by feeding the plastic waste material (1g) and / or the heated second fraction (3a) via one or more tangential inlets to the first pyrolysis reactor (1).

[0070] As indicated hereinbefore, char particles and optionally present inorganic particles sediment to the bottom part (1c) of the first pyrolysis reactor (1), where fraction (li) can be removed via outlet (If). Sedimentation of char particles and optionally present inorganic particles takes place because these particles have a higher density than the surrounding fluid phase. A swirl-like movement of the reactor contents along the vertical reactor wall further helps to direct the char particles and optionally present inorganic particles towards the bottom part (1c) of the first pyrolysis reactor (1).

[0071] In a very preferred embodiment, neither the first pyrolysis reactor (1) nor the second pyrolysis reactor (2) comprises an internal physical mixer, internal heat exchanger element and internal scraper. Hence, in this embodiment mixing and heating of the first pyrolysis composition in the first pyrolysis reactor (1) takes place by feeding the heated second fraction (3a), and (heated) plastic waste material (1g), into the first pyrolysis reactor (1), for example via one or more tangential inlets, and by gas bubbles and solid particles moving into opposite directions. In this embodiment, all heat provided to the second pyrolysis reactor (2) is contained in the third fraction (Ik) of the first pyrolysis composition that is discharged from the first pyrolysis reactor (1). Any mixing in the second pyrolysis reactor (2) takes place by feeding the third fraction (Ik) of the first pyrolysis composition into the second pyrolysis reactor (2) and by gas bubbles moving upwards.

[0072] In a preferred embodiment, the top part (la) and the middle part (lb) of the first pyrolysis reactor (1) have a cylindrical shape and the bottom part (1c) of the first pyrolysis reactor (1) has the form of a cone. The cone-shape of the bottom part (1c) of the first pyrolysis reactor (1) helps to direct sedimenting char particles and optional inorganic particles to the tip of the cone where they can be removed via outlet (If) of the first pyrolysis reactor (1). Such a shape is particularly advantageous when combined with a swirl-like movement of the reactor contents along the vertical reactor wall.

[0073] In a preferred embodiment, the top part (2a) and the middle part (2b) of the second pyrolysis reactor (2) have a cylindrical shape and the bottom part (2c) of the second pyrolysis reactor (2) has the form of cone. The cone-shape of the bottom part (2c) of the second pyrolysis reactor (2) locally increases the superficial velocity and helps to keep any char particles and optional inorganic particles in suspension.

[0074] In a preferred embodiment, the average residence time of the first pyrolysis composition during one cycle in the first pyrolysis reactor (1) is between 1 and 60 minutes, wherein the average residence time during one cycle is determined by the average volume, confined by the reactor walls and the liquid level, in m3, of the first pyrolysis composition in the first pyrolysis reactor (1), divided by the combined volumetric flow rate, in m3 / min., of the plastic waste material (1g) and the heated second fraction (3a) supplied to the first pyrolysis reactor (1).

[0075] The residence time is defined ‘per cycle' because partially-pyrolyzed liquid may be recycled multiple times over the reactor system.

[0076] In a preferred embodiment, the average residence time of the second pyrolysis composition during one cycle in the second pyrolysis reactor (2) is between 0.5 and 15 minutes, wherein the average residence time during one cycle is determined by the average volume, confined by the reactor walls and the liquid level, in m3, of the second pyrolysis composition in the second pyrolysis reactor (2), divided by the volumetric flow rate, in m3 / min., of the third fraction (Ik) of the first pyrolysis composition supplied to the second pyrolysis reactor (2).

[0077] In a preferred embodiment, the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 8 and 40 vol.%, more preferably between more than 8 and 30 vol.%, even more preferably between more than 8 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 8 vol.%, more preferably less than 6 vol.%, even more preferably less than 4 vol.%.

[0078] In another embodiment, the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 10 and 40 vol.%, preferably between more than 10 and 30 vol.%, more preferably between more than 10 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 10 vol.%, preferably less than 8 vol.%, more preferably less than 5 vol.%.

[0079] In another embodiment, the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 15 and 40 vol.%, preferably between more than 15 and 30 vol.%, more preferably between more than 15 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 15 vol.%, preferably less than 10 vol.%, more preferably less than 8 vol.%.

[0080] Since the heat exchanger (5) increases the temperature of the liquid to be returned to the first pyrolysis reactor (1) to a pyrolysis temperature that is generally higher than the highest temperature in the first pyrolysis reactor (1), gaseous hydrocarbon materials are formed in the heat exchanger (5) due to pyrolysis. As explained hereinbefore, too high a volume fraction of gas contents in the material to be pumped may lead to increased cavitation in pump (4). Hence, in a preferred embodiment, the pump (4) is positioned upstream of the heat exchanger (5) in the heating section (3). Formation of pyrolysis gas in a heat exchanger (5) downstream of pump (4) does not necessarily pose a problem, because heated stream (3a) is fed to the first pyrolysis reactor (1) where at least part of the gaseous hydrocarbon material is separated off.

[0081] Pyrolysis system

[0082] In a second aspect, the invention concerns a pyrolysis system configured to convert plastic waste material into pyrolysis products, said system comprising:

[0083] (i) a first pyrolysis reactor (1) having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf), said first pyrolysis reactor (1) further having at least one inlet (Ih) configured to receive plastic waste material, and wherein said first pyrolysis reactor (1) is configured to separate solid particles from a fluid phase via sedimentation;

[0084] (ii) a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having an inlet (2d) in fluid connection with outlet (le) in the middle part (lb) of the first pyrolysis reactor (1), an outlet (2f) in the bottom part (2c) and an outlet (2e) in the top part (2a); and

[0085] (iii) a heating section (3) comprising a pump (4) and a heat exchanger (5) in fluid connection with the outlet (2f) of the second pyrolysis reactor (2) and in fluid connection with an inlet of the first pyrolysis reactor (1), wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1). In a preferred embodiment, the volume of the second pyrolysis reactor (2) is between 7 and 200% of the volume of the first pyrolysis reactor (1), more preferably between 10 and 150%, even more preferably between 15 and 80%.

[0086] In a preferred embodiment, the pump (4) is positioned upstream of the heat exchanger (5). See Figure 1 for an embodiment of a pyrolysis system according to the second aspect wherein the pump (4) is positioned upstream of the heat exchanger (5) in the heating section (3).

[0087] In an embodiment, the second pyrolysis reactor (2) has two bottom outlets (2f) in the bottom part (2c) and each bottom outlet (2f) is in fluid connection with a heating section (3) comprising a pump (4) and a heat exchanger (5), each heating section further being in fluid connection with the first pyrolysis reactor (1). Preferably, the two bottom outlets (2f) of the second pyrolysis reactor (2) are placed on opposing sides of a conical bottom part (2c) of the second pyrolysis reactor (2).

[0088] See Figure 2 for an embodiment of a pyrolysis system according to the second aspect wherein the second pyrolysis reactor (2) has two bottom outlets (2f) placed on opposing sides of a conical bottom part (2c) of the second pyrolysis reactor (2) and wherein each bottom outlet is in fluid connection with a separate heating section (3).

[0089] In an embodiment, the pyrolysis system comprises more than one parallel second pyrolysis reactor (2), wherein each second pyrolysis reactor (2) has a top part (2a), a middle part (2b) and a bottom part (2c), and further has an inlet (2d) in fluid connection with outlet (le) in the middle part (lb) of the first pyrolysis reactor (1), one or two bottom outlets (2f) in the bottom part (2c) and a top outlet (2g) in the top part (2a), wherein each bottom outlet (2f) of each second pyrolysis reactor (2) is in fluid connection with a common heating section (3) comprising a pump (4) and a heat exchanger (5) or with individual heating sections (3) comprising a pump (4) and a heat exchanger (5), each heating section further being in fluid connection with the first pyrolysis reactor (1). In this embodiment, the combined volume of the more than one second pyrolysis reactors (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1). As an example, the pyrolysis system comprises four second pyrolysis reactors (2) of equal volume, wherein the combined volume of the four second pyrolysis reactors (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1). In an embodiment wherein the pyrolysis system comprises more than one second pyrolysis reactor (2), a single outlet (le) of the first pyrolysis reactor (1) is, via a split in the piping, in fluid connection with each inlet (2d) of each second pyrolysis reactor (2). In another embodiment wherein the pyrolysis system comprises more than one second pyrolysis reactor

[0090] (2), each inlet (2d) of each second pyrolysis reactor (2) is in fluid connection with a unique outlet (le) of the first pyrolysis reactor (1).

[0091] Outlet (le) of the first pyrolysis reactor (1) can be configured to discharge reactor contents from close to the wall of the first pyrolysis reactor (1), can be configured to discharge reactor contents from close to the central axis of the first pyrolysis reactor (1) via a pipe in the radial direction of the first pyrolysis reactor (1) reaching inside first pyrolysis reactor (1), or can be configured to discharge reactor contents from somewhere in between. In order to reduce the risk of fouling of internal structures by char particles, the reactor contents are preferably discharged from close to the wall of the first pyrolysis reactor (1).

[0092] In embodiments wherein the pyrolysis system comprises more than one heating system

[0093] (3), the heating systems (3) are preferably in fluid connection with a single inlet of the first pyrolysis reactor (1). See for example Figure 2. In other embodiments, each heating system (3) is in fluid connection with the first pyrolysis reactor (1) via its own inlet.

[0094] In an embodiment, the first pyrolysis reactor (1) of the pyrolysis system has one or more inlets, such as two inlets (Ih, 11). In an embodiment, the first pyrolysis reactor (1) of the pyrolysis system has at least one inlet (Ih), configured to receive plastic waste material (1g) and at least one inlet (11) in fluid communication with the or with each heating section (3).

[0095] In an embodiment, the first pyrolysis reactor (1) of the pyrolysis system has one or more tangential inlets. In a preferred embodiment, the first pyrolysis reactor (1) has one or more first tangential inlets (Ih) configured to receive plastic waste material (1g) and one or more second tangential inlets (11) in fluid communication with the or with each heating section (3).

[0096] In another embodiment, the first pyrolysis reactor (1) has one inlet (Ih), preferably a tangential inlet (Ih), that is configured to receive plastic waste material (1g) and is in fluid communication with the or with each heating section (3).

[0097] In another embodiment, the first pyrolysis reactor (1) is configured to apply a swirl-like movement to the reactor contents along the vertical reactor wall during operation. Such a swirl- like movement of the reactor contents along the vertical reactor wall can for example be realized by using tangential inlets.

[0098] In a preferred embodiment, the top part (la) and the middle part (lb) of the first pyrolysis reactor (1) have a cylindrical shape and the bottom part (1c) of the first pyrolysis reactor (1) has the form of a cone.

[0099] In a preferred embodiment, the top part (2a) and the middle part (2b) of the second pyrolysis reactor (2) have a cylindrical shape and the bottom part (2c) of the second pyrolysis reactor (2) has the form of a cone.

[0100] In a preferred embodiment, the pyrolysis system according to the second aspect is configured to perform the process according to the first aspect.

[0101] Preferred embodiments disclosed in the context of the first aspect are equally applicable to the second aspect, and vice versa, unless explicitly indicated otherwise.

[0102] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0103] Furthermore, for a proper understanding of this document and its claims, it is to be understood that the verb ‘to comprise' and its conjugations are used in their non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article ‘a’ or 'an' does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article 'a' or 'an' thus usually means 'at least one' . EXPERIMENTAL SECTION

[0104] Example 1: Reaction kinetics

[0105] The reaction kinetics of the pyrolysis of plastic was assessed in a labscale pyrolysis unit. The pyrolysis unit consisted of a reactor that was placed in an oven (Genlab High Temperature Oven HT / 64 / 500 / F / DIG). The weight of the reactor, and thus also of its contents, can be constantly measured such that it can be assessed how fast the plastic in the reactor reacts into gaseous components. The temperature was controlled with a Eurotherm Nanodac EPC3016 Profile Controller in combination with a Eurotherm Pl 16 Overheat Controller. The reaction was carried out with a nitrogen gas blanket in the reactor by continuously feeding 150 ml / min N2 into the reactor. The gas from the reactor was first condensed in a graham condenser, making use of tap water as a cooling medium. The non-condensed gas was then flared in a gas flare system. During the experiments, about 800 g of virgin plastic, being either LDPE or PP, was placed in the reactor. The oven was then heated to a temperature in the range of 405 - 440°C. The temperature of the reactant was constantly measured. As soon as it reached its maximum temperature, it was kept at that temperature for about 6 h. From the weight loss as a function of time, the reaction constant was assessed, assuming that the reaction order of the reaction was equal to one. It was found that PP pyrolyzed at a much higher rate than LDPE, making the conversion of LDPE the time-limiting step in the total reaction. From the dependence of the reaction constant of the temperature for LDPE, the activation energy was assessed with the Arrhenius equation. From this, it followed that the pyrolysis reaction rate of LDPE increased with a factor of 2.5 with an increase of the reaction temperature from 390 to 400°C. At higher temperatures, this factor decreased a bit, up to a factor of 2.3 with an increase of the reaction temperature from 420 to 430°C.

[0106] Example 2: pyrolysis process

[0107] A continuous pyrolysis process of plastic waste was performed in a pyrolysis system as indicated in Figure 3, wherein outlet (le) of the first pyrolysis reactor (1) is in fluid connection with two parallel second pyrolysis reactors (2) via their respective inlets (2d). Each bottom outlet (2f) of each second pyrolysis reactor (2) is in fluid connection with a single heating section (3) comprising a pump (4) and a heat exchanger (5), and the heating section (3) is in fluid connection with the first pyrolysis reactor (1) via one single tangential inlet (11) in the middle part (lb). The combined volume of the two second pyrolysis reactors (2) was 46 % of the volume of the first pyrolysis reactor (1). The top part (la) and the middle part (lb) of the first pyrolysis reactor (1) had a cylindrical shape and the bottom part (1c) had the form of cone. Likewise, the top part (2a) and the middle part (2b) of both second pyrolysis reactors (2) had a cylindrical shape and the bottom part (2c) had the form of a cone.

[0108] Neither the first pyrolysis reactor (1) nor the second pyrolysis reactors (2) comprised an internal physical mixer, internal heat exchanger element or internal scraper.

[0109] Plastic waste material (1g), consisting of post-consumer waste comprising at least 80% polyolefins, was continuously fed to the first pyrolysis reactor (1) via a tangential inlet (Ih) in the middle part (lb) and was subjected to pyrolysis, resulting in a first pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles. The highest time-averaged temperature measured in part (lb) was about 413.5° C, which was also the highest temperature measured in the first pyrolysis reactor (1).

[0110] A first fraction (li) of the first pyrolysis composition, which was enriched in char particles compared to the overall first pyrolysis composition, was semi-continuously discharged via outlet (If) in the bottom part (1c) at regular time intervals. A second fraction (Ij) of the first pyrolysis composition, of gaseous hydrocarbon material, was continuously discharged via outlet (Id) in the top part (la). A third fraction (Ik), which was enriched in liquid hydrocarbon material compared to the first pyrolysis composition, was continuously discharged via outlet (le) in the middle part (lb) and fed to inlets (2d) of the second pyrolysis reactors (2) in their respective middle parts (2b). Equal parts of the third fraction (Ik) were fed to the individual second pyrolysis reactors (2).

[0111] The third fraction (Ik) of the first pyrolysis composition was subjected in the second pyrolysis reactors (2) to pyrolysis at a temperature that was lower than the highest temperature measured in the first pyrolysis reactor (1), resulting in a second pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles. The lowest time-averaged temperature measured in part (2c) was about 411.5 °C. There was a temperature gradient in the second pyrolysis reactors (2) in the axial direction. The temperature was highest where the third fraction (Ik) entered the second pyrolysis reactors (2).

[0112] The net flow of gaseous hydrocarbon material was to the top part (2a) and the net flow of the liquid hydrocarbon material and the char particles was to the bottom part (2c). A first fraction (2g) of the second pyrolysis composition of gaseous hydrocarbon material was continuously discharged via outlet (2e) in the top part (2a) and a second fraction (2h) comprising liquid hydrocarbon material and char particles was continuously discharged via outlet (2f) in the bottom part (2c) of each second pyrolysis reactor (2). The second fractions (2h) of the second pyrolysis composition of both second pyrolysis reactors (2) were combined and heated in a heating section (3) comprising a pump (4) and a heat exchanger (5) downstream thereof to provide a heated second fraction (3a). The heated second fraction (3a) was continuously fed to the first pyrolysis reactor (1) via tangential inlet (11).

[0113] Feeding the plastic waste material (1g) and the heated second fraction (3a) to the first pyrolysis reactor (1) via tangential inlets resulted in a swirl-like movement of the reactor contents along the vertical reactor wall during operation. Char particles and inorganic particles present in the plastic waste material (1g) sedimented to the bottom part (1c) of the first pyrolysis reactor (1) because of a density difference with the surrounding fluid phase. Moreover, the swirl-like movement of the reactor contents along the vertical reactor wall further helped to direct the char particles and inorganic particles towards the bottom part (1c).

[0114] Mixing and heating of the first pyrolysis composition in the first pyrolysis reactor (1) took place by feeding the heated second fraction (3 a) and heated plastic waste material (1g) to the first pyrolysis reactor (1) via the tangential inlets (Ih) and (11) and by gas bubbles and solid particles moving into opposite directions.

[0115] All heat provided to the second pyrolysis reactors (2) was contained in the third fraction (Ik) that was discharged from the first pyrolysis reactor (1). The only mixing that took place in the second pyrolysis reactors (2) was caused by feeding the third fraction (Ik) into the fluid phase already present in the second pyrolysis reactors (2) and by gas bubbles moving upwards in the fluid phase. Under these conditions, efficient degassing could be performed. The gas content of the third fraction (Ik) fed to the second pyrolysis reactors (2) was higher than 8 vol.% and the gas content of the second fractions (2h) discharged from the second pyrolysis reactors (2) was lower than 8 vol.%.

[0116] A volumetric flow rate of 60 m3 / h of fluid, i.e. heated second fraction (3a), was thus recirculated from the second pyrolysis reactors (2) back to the first pyrolysis reactor (1).

[0117] A graph of the heat transfer coefficient in the heat exchanger (5) versus the number of days of operation since the last cleaning of the heat exchanger (5) is provided in Figure 5 (refer to two different runs for Example 2). Figure 5 further indicates a lower limit for the heat transfer coefficient. If the heat transfer coefficient drops below this limit, cleaning is necessary. The longer the heat transfer coefficient stays above the lower limit, the more stable the operation is. Comparative Example 1: pyrolysis process

[0118] Example 2 was repeated in a pyrolysis system as indicated in Figure 4, i.e. in a system without the second pyrolysis reactors (2). Three different runs were performed. A graph of the heat transfer coefficient in the heat exchanger (5) versus the number of days of operation since the last cleaning of the heat exchanger (5) is provided in Figure 5 for the three different runs (refer to Comparative Example 1). Figure 5 further indicates a lower limit for the heat transfer coefficient. If the heat transfer coefficient drops below this limit, cleaning is necessary. The longer the heat transfer coefficient stays above the lower limit, the more stable the operation is.

[0119] Conclusions

[0120] It was found that the pump (4) ran much more stable and that the fouling in the heat exchanger (5) was much less in the pyrolysis system applied in Example 2 than when the system was operated without the second pyrolysis reactors (2) such as in Comparative Example 1 (see Figure 5). The pyrolysis system applied in Example 2 could be operated in a continuous mode for a longer time and at a plastic waste throughput rate of at least 85% higher.

Claims

1. 23CLAIMS1. A process for the pyrolysis of plastic waste material, comprising the steps of:(a) providing a first pyrolysis reactor (1) having at least one inlet and having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf) and further providing a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having at least one inlet (2d), wherein the top part (2a) and bottom part (2c) of the second pyrolysis reactor (2) comprise at least one outlet (2e,2f);(b) continuously feeding plastic waste material (1g) to the first pyrolysis reactor (1) via an inlet (Ih) and subjecting the plastic waste material (1g) to pyrolysis, resulting in a first pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the char particles and optionally present inorganic particles sediment to the bottom part (1c) of the first pyrolysis reactor (1);(c) continuously or semi-continuously discharging a first fraction (li) of the first pyrolysis composition, which is enriched in char particles compared to the first pyrolysis composition, via outlet (If) in the bottom part (1c) of the first pyrolysis reactor (1), continuously discharging a second fraction (Ij) of gaseous hydrocarbon material via outlet (Id) in the top part (la) of the first pyrolysis reactor (1) and continuously discharging a third fraction (Ik), which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, via outlet (le) in the middle part (lb) of the first pyrolysis reactor (1) to an inlet (2d) of the second pyrolysis reactor (2);(d) subjecting the third fraction (Ik) of the first pyrolysis composition in the second pyrolysis reactor (2) to pyrolysis, resulting in a second pyrolysis composition comprising gaseous hydrocarbon material, liquid hydrocarbon material and char particles, wherein the net flow of gaseous hydrocarbon material is to the top part (2a) and the net flow of the liquid hydrocarbon material and the char particles is to the bottom part (2c);(e) continuously discharging a first fraction (2g) of the second pyrolysis composition of gaseous hydrocarbon material via outlet (2e) in the top part (2a) of the second pyrolysis reactor (2) and a second fraction (2h) comprising liquid hydrocarbonmaterial and char particles via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2); and(f) heating the second fraction (2h) of the second pyrolysis composition downstream of the second pyrolysis reactor (2) in a heating section (3) comprising a heat exchanger (5) and a pump (4) and continuously feeding the heated second fraction (3a) to the first pyrolysis reactor (1) via an inlet in the first pyrolysis reactor (1), wherein the highest temperature in the first pyrolysis reactor (1) is higher than the temperature anywhere in the second pyrolysis reactor (2), and wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1).

2. Process according to claim 1, wherein the volume of the second pyrolysis reactor (2) is between 7 and 200% of the volume of the first pyrolysis reactor (1), preferably between 10 and 150%, more preferably between 15 and 80%.

3. Process according to claim 1 or 2, wherein the highest value for the temperature in the first pyrolysis reactor (1), is between 0.1 and 10 °C higher than the lowest value for the temperature in the second pyrolysis reactor (2) measured in bottom part (2c), preferably between 0.15 and 5 °C higher, more preferably between 0.2 and 2 °C higher.

4. Process according to any one of claims 1 to 3, wherein the highest value for the temperature in the first pyrolysis reactor (1) is between 400 and 430 °C, preferably between 405 and 425 °C, more preferably between 407 and 423 °C.

5. Process according to any one of claims 1 to 4, wherein the lowest value for the temperature in bottom part (2c) in the second pyrolysis reactor (2) is between 390 and less than 429.9 °C, preferably between 400 and 424.85 °C, more preferably between 405 and 422.8 °C.

6. Process according to any one of claims 1 to 5, wherein the plastic waste material (1g) and the heated second fraction (3a) are fed to the first pyrolysis reactor (1) via different inlets.

7. Process according to any one of claims 1 to 6, wherein the plastic waste material (1g) is fed to an inlet (Ih) of the first pyrolysis reactor (1) in the middle part (lb).

8. Process according to any one of claims 1 to 7, wherein the heated second fraction (3a) is fed to the first pyrolysis reactor (1) via an inlet (11) in the middle part (lb).

9. Process according to any one of claims 1 to 8, wherein the plastic waste material (1g) and / or the heated second fraction (3 a) are fed to the first pyrolysis reactor (1) via one or more tangential inlets.

10. Process according to any one of claims 1 to 9, wherein the plastic waste material (1g) is subjected in step (b) to a pyrolysis reaction in the first pyrolysis reactor (1) under a swirllike movement of the reactor contents along the vertical reactor wall.

11. Process according to any one of claims 1 to 10, wherein the top part (la) and the middle part (lb) of the first pyrolysis reactor (1) have a cylindrical shape and wherein the bottom part (1c) of the first pyrolysis reactor (1) has the form of a cone.

12. Process according to any one of claims 1 to 11, wherein the top part (2a) and the middle part (2b) of the second pyrolysis reactor (2) have a cylindrical shape and wherein the bottom part (2c) of the second pyrolysis reactor (2) has the form of a cone.

13. Process according to any one of claims 1 to 12, wherein the average residence time of the first pyrolysis composition during one cycle in the first pyrolysis reactor (1) is between 1 and 60 minutes, wherein the average residence time during one cycle is determined by the average volume, confined by the reactor walls and the liquid level, in m3, of the first pyrolysis composition in the first pyrolysis reactor (1), divided by the combined volumetric flow rate, in m3 / min., of the plastic waste material (1g) and the heated second fraction (3a) supplied to the first pyrolysis reactor (1).

14. Process according to any one of claims 1 to 13, wherein the average residence time of the second pyrolysis composition during one cycle in the second pyrolysis reactor (2) is between 0.5 and 15 minutes, wherein the average residence time during one cycle is determined by the average volume, confined by the reactor walls and the liquid level, in26 m3, of the second pyrolysis composition in the second pyrolysis reactor (2), divided by the volumetric flow rate, in m3 / min., of the third fraction (Ik) supplied to the second pyrolysis reactor (2).

15. Process according to any one of claims 1 to 14, wherein the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 8 and 40 vol.%, preferably between more than 8 and 30 vol.%, more preferably between more than 8 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 8 vol.%, preferably less than 6 vol.%, more preferably less than 4 vol.%.

16. Process according to any one of claims 1 to 14, wherein the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 10 and 40 vol.%, preferably between more than 10 and 30 vol.%, more preferably between more than 10 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 10 vol.%, preferably less than 8 vol.%, more preferably less than 5 vol.%.

17. Process according to any one of claims 1 to 14, wherein the third fraction (Ik) of the first pyrolysis composition, which is enriched in liquid hydrocarbon material compared to the first pyrolysis composition, that is fed to the second pyrolysis reactor (2), has a gas content of between more than 15 and 40 vol.%, preferably between more than 15 and 30 vol.%, more preferably between more than 15 and 20 vol.%, and the second fraction (2h) of the second pyrolysis composition comprising liquid hydrocarbon material and char particles that is discharged via outlet (2f) in the bottom part (2c) of the second pyrolysis reactor (2) has a gas content of less than 15 vol.%, preferably less than 10 vol.%, more preferably less than 8 vol.%.2718. Process according to any one of claims 1 to 17, wherein the pump (4) is positioned upstream of the heat exchanger (5).

19. A pyrolysis system configured to convert plastic waste material into pyrolysis products, said system comprising:(i) a first pyrolysis reactor (1) having a top part (la), a middle part (lb) and a bottom part (1c), each part comprising at least one outlet (ld,le,lf), said first pyrolysis reactor (1) further having at least one inlet (Ih) configured to receive plastic waste material, and wherein said first pyrolysis reactor (1) is configured to separate solid particles from a fluid phase via sedimentation;(ii) a second pyrolysis reactor (2) having a top part (2a), a middle part (2b) and a bottom part (2c), and further having an inlet (2d) in fluid connection with outlet (le) in the middle part (lb) of the first pyrolysis reactor (1), an outlet (2f) in the bottom part (2c) and an outlet (2e) in the top part (2a); and(iii) a heating section (3) comprising a pump (4) and a heat exchanger (5) in fluid connection with the outlet (2f) of the second pyrolysis reactor (2) and in fluid connection with an inlet of the first pyrolysis reactor (1), wherein the volume of the second pyrolysis reactor (2) is between 5 and 250% of the volume of the first pyrolysis reactor (1).

20. Pyrolysis system according to claim 19, wherein the volume of the second pyrolysis reactor (2) is between 7 and 200% of the volume of the first pyrolysis reactor (1), preferably between 10 and 150%, more preferably between 15 and 80%.

21. Pyrolysis system according to claim 19 or 20, wherein the pump (4) is positioned upstream of the heat exchanger (5) in the heating section (3).

22. Pyrolysis system according to any one of claims 19 to 21, wherein the second pyrolysis reactor (2) comprises two or more parallel second pyrolysis reactors (2).

23. Pyrolysis system according to any one of claims 19 to 22, wherein the first pyrolysis reactor (1) has one or more tangential inlets, preferably one or more first tangential inlets (Ih) configured to receive plastic waste material (1g) and one or more second tangential inlets (11) in fluid communication with the heating section (3).2824. Pyrolysis system according to any one of claims 19 to 23, wherein the first pyrolysis reactor (1) is configured to apply a swirl-like movement to the reactor contents along the vertical reactor wall during operation.

25. Pyrolysis system according to any one of claims 19 to 24, wherein the top part (la) and the middle part (lb) of the first pyrolysis reactor (1) have a cylindrical shape and wherein the bottom part (1c) of the first pyrolysis reactor (1) has the form of a cone.

26. Pyrolysis system according to any one of claims 19 to 25, wherein the top part (2a) and the middle part (2b) of the second pyrolysis reactor (2) have a cylindrical shape and wherein the bottom part (2c) of the second pyrolysis reactor (2) has the form of a cone.

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