Pyrolysis device and method for pyrolysis of plastic materials

Abstract

Pyrolysis device comprising a pyrolysis reactor with a first inlet opening for charge, a second inlet opening for carrier gas, a first discharge opening for pyrolysis gas and a second discharge opening for solid residue, wherein the device comprising a combined quenching, cooling and fractionating unit arranged downstream of the pyrolysis reactor and fluidly connected to the first discharge opening thereof, the combined quenching, cooling and fractionating unit being arranged to fractionate the pyrolysis gas into at least two fractions of pyrolysis oil.

Description

[0001] Pyrolysis device and method for pyrolysis of plastic materials

[0002] The present invention relates to a pyrolysis device as indicated by the preamble of claim 1 and a method for pyrolysis of plastic materials as indicated by the preamble of claim 11.

[0003] Background

[0004] Pyrolysis of mixed waste plastics has proven to be very challenging due to fouling of heat transfer equipment and flow assurance issues caused by partly, or complete, plugging of piping and cooling surfaces. The purpose of this invention is to use certain design principles, which is not practiced in the pyrolysis of waste plastics, to obtain improved process control, manage fouling and clogging of piping and equipment and obtain significantly improved operations regularity and an optimized product profile.

[0005] Pyrolysis is a type of process which belongs to the category thermal cracking processing. Slow cracking, at lower temperatures, to produce tar, charcoal and gases is an example of a very traditional pyrolysis process. The process is characterized by heating up the feedstock in absence of air and the main variation in processing conditions are temperature and residence time. Until recent times the feedstock has consisted of biomass and mineral oil. For some time, pyrolysis has been practiced converting tires to oil and carbon black. And during the last 8-10 years attempts to commercialize pyrolysis of waste plastics have been made.

[0006] The motivation for using waste plastics as feedstock is established by acknowledging the accumulating problem of uncontrolled pollution, and degradation to micro-plastics, in the environment. Legislations are being enforced to require new plastics to have an increasing content of recirculated material.

[0007] Conventional production of plastics (i.e. the polymer) starts with the monomer (the repeating unit in the polymer) which today is almost entirely based on fossil feedstock. The main route to the monomer is lighter fractions from the refineries (i.e. naphtha and mixed olefins) or natural gas condensate. These fractions are then cracked catalytically with steam to obtain the monomers (ethene, propene, butene etc) which is then polymerized to plastics. Some specialized monomers are also synthesized by adding functional groups to the monomer which is then polymerized.

[0008] Light distillation cuts or upgrading of heavy feedstocks by catalytic cracking is today the most applied route in refineries for feedstock to olefins. Catalytic cracking is developed specifically for heavy oil fractions from distillation of crude oil. The catalyst requires strict control on certain trace components and physical characteristics of the feedstock, and it is significantly more complex than the process of thermal pyrolysis. Pyrolysis oilmade from pyrolysis of waste plastics can however be used as feedstock for the catalytic cracking process and can then take the conventional route back to virgin polymer.

[0009] Waste plastics are today commonly used for energy (fired in heat plants) or deposited in landfills. Sorting plants for waste plastics are increasingly installed and some plastic materials can be circulated by sorting. This recirculated plastic is not of the original quality and can only be used to lower quality products in its second life and end up being rejected on the next cycle. Around 50% of the plastics from the first sorting also ends up in the reject fraction and have the energy plants or the landfill as their endpoint. Pyrolysis of this rejected part can change this to a true circular plastics economy by rerouting rejected plastics back into the route of virgin polymers.

[0010] Existing and forthcoming EU legislations require the recirculated content to increase in all plastics to be distributed within this economic area. It is expected that this will also be the trend worldwide. This is causing the plastic value chain to increasingly demand recirculated material from the petrochemical value chain. And the increased demand causes this feedstock to sell at a premium. This premium is what motivates the development of the pyrolysis process and the commercial business which can be established from its use.

[0011] The chemistry of pyrolysis of waste plastics has been tested at laboratory scale and in pilot or demonstration type of plants. It is concluded that the feedstock can be converted to a pyrolysis oil and become a feedstock, after upgrading, to the petrochemicals value chain to produce new plastics. It has been found that the process can be optimized for a maximum liquid oil fraction of some 45 - 80 %(w) depending on type of plastics and process parameters. The remaining part of the feedstock is converted to lighter noncondensable gases (used for energy or integrated into other chemical synthesis) and a dry fraction consisting of ash and soot.

[0012] In demonstration / pilot plants it is experienced that, downstream the pyrolysis reactor, there is a tendency of fouling due to deposition of particles, gumming, re-polymerization which severely limits the on-stream time for the plants before they need to be stopped and go through some serious cleaning and maintenance. Typically, the plants run for a maximum of days to 1 - 3 weeks before they need this kind of service. The production efficiency is severely affected, and the maintenance costs are high, which creates a barrier for the development of this new value chain.

[0013] One origin of this problem is the particles entrained in pyrolysis gas which are managed by particle separation downstream the reactor in the transfer line. The efficiency of such separators is dependent on gas velocity which takes on large variations. A second origin isrepolymerisation on colder surfaces and a third is gumming deposits due to traces of oxygen.. The gas velocity reflects the wide operating range (velocity) during start-up, heat up, feed and feedstock variation and mechanical stops in the feed-in arrangement of plastics. Gumming is a known consequence of oxygen / air in the feedstock caused by traces of air not properly stripped out of the feedstock voids or as air leaks when the reactor is operated under vacuum. Re-polymerization is a reaction which is favoured at temperatures below the ceiling point temperature of the relevant polymers. This temperature corresponds to the point where the reaction rate for the polymerization is equal to the reverse reaction back to the monomer.

[0014] Attempts have been made to resolve these problems. Sorting of the feedstock has been tested out but is in conflict with the basic idea of solving the problem of low-quality plastics recycling. Different particles separation principles have been applied. A variation of condensers and spray cooling systems has been tried. Some improvements have been experienced, but none of these methods have resolved the problems. The three causes materialize in different parts of the process as a flow assurance problem and severely affect the condensing part where the pyrolysis liquids in loss of heat transfer.

[0015] Prior art technology in this technical field is described e.g. in the following publications: US2024 / 0368479 Al, US2024 / 0359368 Al, US2024 / 0352324 Al, US2024 / 0308937 Al, and US7951289 B2.

[0016] US6011187A concerns a device and method for pyrolysis of plastic material, where plastic is mixed with heated sand (500-950 °C, sand at pyrolysis zone heated to 400-480 °C), and plastic is converted into low molecular-weight gas, gaseous and liquid oils with low and high boiling points, and solid carbonaceous residue.

[0017] Objectives

[0018] An objective of the present invention is to provide an improved device for pyrolysis of plastic materials, hereunder to obtain improved process control, manage fouling and clogging of piping and equipment and obtain significantly improved operations regularity and an optimized product profile. Another objective is to provide a method with same inherent benefits.

[0019] The present invention

[0020] The above objectives are achieved by the device defined by claim 1 which constitutes a first aspect of the present invention.The objectives are also achieved by the method defined by claim 11, which constitutes a second aspect of the present invention.

[0021] Preferred embodiments of the invention are disclosed by the dependent claims.

[0022] The pyrolysis reactor of the present invention may be arranged for batch operation or for continuous operation, the latter being preferred. A reactor for continuous operation typically comprises an auger or a screw for transportation of charged material from an inlet end to a discharge end of the reactor.

[0023] The reactor is typically provided with a recirculation loop arranged between the gas discharge opening of the combined quenching, cooling and fractionating unit and the second inlet opening of the pyrolysis reactor. The reactor is preferably horizontally arranged. The term “quenching” as used herein refers to a sudden cooling in which hot gas is immediately cooled and partly condensed in a pool of liquid, typically a liquid fraction of already condensed pyrolysis gas.

[0024] The reactor may also be arranged for internal circulation of a heat transfer material in the form of a solid, particulate material.

[0025] The pyrolysis reactor is arranged to be heated by electrical heating or heating by combustion gases.

[0026] The inlet opening for charge into the reactor is preferably provided with a gas-tight charge valve to prevent air from entering the reactor during operation. This feature has the dual functionality of preventing air to enter the reactor and to allow operation under pressures above or below the ambient pressure.

[0027] The combined quenching, cooling and fractionating unit is typically arranged to quench and cool the pyrolysis gas in a bath of pyrolysis oil, thereby causing condensation of high-boiling constituents of the pyrolysis gas. It is further (preferably) arranged for cooling and mass transfer in a stepwise manner, to allow condensation of two or more fractions of pyrolysis oil.

[0028] In a second aspect of the invention, the step of particle removal is preferably conducted within the pyrolysis reactor, applying inertia principles such as cyclone separators arranged at the outlet.

[0029] The step or steps of fractionating comprise(s) fractionating into at least two fractions and more preferred into at least three fractions using successively lower temperatures.

[0030] The method is typically and preferably conducted using a continuous type of pyrolysis reactor.The heating is preferably conducted using at least one heat source selected from the group consisting of hot gas and electrical heating means. Heating is typically performed to a temperature in the range from 450 °C to 650 °C.

[0031] Upstream of the two steps the preparation for pyrolysis of waste plastics starts with preparing the feedstock for efficient feed-in and heat transfer. This is achieved by taking dry waste plastics and perform shredding to a typical size of 20 - 50 mm particles / flakes. This will assure that the feedstock can be handled as an approximative homogenous material for a mechanical feed-in system of augers, hoppers and extruder. For the batch reactor this can be simplified by a manual mechanical feeding through an exposed reactor opening.

[0032] In the description, to follow, all the specific technical solutions elements and operations proposed in this invention is included at its proper functional location in the process. Each solution element is discussed in relation to the contribution it makes in resolving the technical and operational issues. The solution elements form the basis for the patent claims as a whole and as individual elements. The description is supported by three figures which are referred to where relevant.

[0033] The process according to the present invention includes the steps of a pyrolysis, quenching, cooling and fractionating. It also includes transfer of the pyrolysis gas between a pyrolysis reactor and a subsequent quenching, cooling and fractionating unit and a recirculation loop for non-condensable gas as carrier-gas back to the reactor.

[0034] The process can be a batch type of reactor or a continuous reactor. These two types of reactors display similar characteristics in the vapour phase as this product is continuously displaced out of the reactor in both variants. The difference in the vapour phase is that the composition and flow rate gradually change during the batch processing due to the gradual change in composition of the plastic batch in the reactor. The continuous type reactor typically operates in a steady state as new feedstock is supplied to the reactor as the cracking process is running.

[0035] The two different types of reactors are discussed separately only with respect to the feedin point for the elements proposed in this invention. All the remaining elements are applicable to both type of reactors and in the downstream processing of the product gases. The removal of the solid-state materials (ash) from the two reactors is principally similar or, in the batch reactor, it may be emptied while the reactor is opened for recharging. There are however no elements in this invention which take effect on this stream as the particles separated out from the vapour stream will join the solid state inside the reactor and follow the selected procedure for removal.The continuous reactor will typically be a horizontal oriented device which take in the feedstock in one end and transport it through the reaction chamber with the help of an auger or a conveyor screw. As the feedstock is moved through the reactor it is heated by applying a heating medium to the reactor inner wall and, sometimes, aided by an internally circulated heat carrier (sand, ceramics, etc) which is mixed with the plastics itself. The heating medium working on the reactor inner walls may be hot flue gas from the combustion of light non-condensable off gases, from the pyrolysis process itself or natural gas (during start-up typically). It may also be by electrical heaters (resistance, induction or microwave).

[0036] A proper thermal insulation of the pyrolysis reactor, whether continuous or batch type, is typically employed while not as such involving anything inventive.

[0037] Below, the present invention is described in further details in the form of non-limiting embodiments illustrated by drawings, where:

[0038] Fig. l is a side sectional simplified view of a reactor according to the present invention. Fig. 2 is a side sectional, simplified view of a quenching, cooling and fractionating unit according to the present invention.

[0039] Fig. 3 is a side sectional enlarged view of the lower part of the quenching, cooling and fractionating unit with emphasize on the inlet pyrolysis gas arrangement and gas dispersion into the quenching liquid.

[0040] Fig. 4 is a side sectional, simplified view of a quenching, cooling and fractionating unit according to the present invention.

[0041] Figure 1 is a simplified and schematic side sectional view of a pyrolysis reactor according to an embodiment of the present invention, the reactor being arranged for continuous operation. The reactor has an inlet opening 11 for plastic material (charge), an inlet opening 12 for carrier gas, a first discharge opening 13 for pyrolysis gas and a second discharge opening 14 for solid residue. The space between the inlet and discharge openings constitute the reaction zone or the reaction chamber 15, which also includes an auger 16 powered by a motor 17. A “battery” of cyclone separators 18 are optionally arranged between the reaction zone 15 and the discharge opening 13 for the pyrolysis gas. At the bottom of the reactor, a transportation screw 19 is arranged to bring solid residues to the discharge opening 14 therefore.

[0042] In operation, the carrier gas is initially an inert gas, such as nitrogen, which at least in the case of embodiments of continuous operation is typically compressed, preheated and is circulated through the reactor system before start-up, to ensure that all surfaces withwhich the charged material and the pyrolysis gas will contact are hot. During continuous operation, the content of nitrogen is gradually reduced and replaced by non-condensed part of the pyrolysis gas recycled from the combined quenching, cooling and fractionating unit.

[0043] Figure 2 and figure 4 show a quenching, cooling and fractionating unit 20 arranged to receive the hot pyrolysis gas 13 from the reactor 10. In the quenching, cooling and fractionating unit the gas is quenched in a pool of temperature-controlled pyrolysis oil, i.e. already liquefied pyrolysis gas at the lower end thereof. To maintain a steady temperature of the pyrolysis oil at this level within the quenching, cooling and fractionating unit,, pyrolysis oil 21 is continuously withdrawn from the lower end thereof, pumped 22b through a heat exchanger 22a, which may be cooled with water, and recycled at one or several levels of the quenching, cooling and fractionating unit as flows 23 and 25. To maintain a steady level of pyrolysis oil at the lower end of the quenching, cooling and fractionating unit, a portion of the pyrolysis oil is continuously withdrawn as product flow 24, that being the pyrolysis oil having the highest boiling point temperature of the pyrolysis oils being produced.

[0044] The quenching, cooling and fractionating unit 20 of Fig. 2 and Fig. 4 shows two additional stages at which pyrolysis oil is discharged from the quenching, cooling and fractionating unit, using additional cooling, recycling and discharge of same kind as shown at the lower end of the quenching, cooling and fractionating unit. Condensed pyrolysis oil 26 of a lower boiling point than the pyrolysis oil of flow 24 is withdrawn at a vertical level above the latter. A part of this flow leaves the quenching, cooling and fractionating unit as product flow 27 while another flow 28 is returned to the quenching, cooling and fractionating unit. Thus, the pyrolysis oil leaving the quenching, cooling and fractionating unit as flow 27 has a lower boiling point than the one of flow 24 and the pyrolysis oil leaving the quenching, cooling and fractionating unit as flow 32 / 34 has a lower boiling point than the flow 24 and flow 27.

[0045] Accordingly, the number and location at which pyrolysis oil is discharged from the quenching, cooling and fractionating unit decides the number of oil fractions to be produced, Typically, the number of fractions discharged is at least two, and more typically three.

[0046] At its top, highly volatile pyrolysis gas and non-condensable gaseous elements, such as e.g. nitrogen used during start-up, leaves the quenching, cooling and fractionating unit as flow 29. After cooling of this gas, shown as flow 30, is returned to the pyrolysis reactor 10 to become carrier gas after being compressed to desired pressure and heated to desired temperature.In the embodiment on Fig.4 any condensed liquids from this gas 31 is collected in the reflux drum 41 into which the fractionator lowest boiling side stream 40 is cooled and then pumped. From the reflux drum 41 a stream is discharged as a product flow 32 while another part is redirected as reflux to the combined quenching, cooling and fractionating unit as flow 33. Stream 36 is a balance flow outlet to further regulate the return flow 30.

[0047] A nitrogen make-up supply (not shown) is typically arranged upstream the compressor for start-up / heat-up purposes. If steam is to be used a steam supply is added in this loop depending on the supplied steam conditions (pressure and temperature).

[0048] Figure 3 is an enlarged side sectional view of an embodiment of the lower part of the quenching, cooling and fractionating unit, showing that the hot pyrolysis gas flow 13 enters the quenching, cooling and fractionating and is directed down, by an inner wall 41 which is slightly immersed in the liquid pool (before gas dispersion), and then forced through a flow dispersion unit 42 to be entrained in the liquid pool 43. The dispersion unit 42 is typically in the form of a perforated cylinder and made replaceable. At the bottom of the quenching, cooling and fractionating unit, pyrolysis oil 21 is discharged as shown and already commented in relation to Figure 2.

[0049] In a batch reactor the feedstock melt will typically be moved around in the reactor by an agitator / impeller during the batch processing. Other than affecting the heat transfer mechanism in the reactor this difference in design will not affect the general principles of the invention.

[0050] The feeding of the reactors is the main difference. The batch reactor is cooled down and opened between each new load of dried plastic materials. This will allow air to ingress into the system. Air is one of the constituents which will impact gumming in the vapour phase condensing parts even if its partial volume consists of traces well below any internal combustible risk to the reaction. Hence the proper sweeping and displacement of all air traces, throughout the batch before the next heat-up, is vital.

[0051] It is considered that a continuous operation is preferred over a batch-wise operation for at least a couple of reasons, the main reasons being a better control of the end products due to steady state operation and a better cost-efficiency of the overall process due to less stand-still time for filling and emptying the reactor. It is also much more energy efficient (less cooling down and heating up)

[0052] The continuous reactor, when the feed is dry plastics particles (20-50 mm), pose a similar type of challenge with respect to complete purging of all traces of air. In the conventional feed-in arrangement this is usually done by operating two individual hoppers which feedthe inlet extruder to the reactor. The two hoppers operate in complementary cycles, and each is purged (with nitrogen), to displace the air, before the extruder compress it to the reactor. The efficient displacement of air by this purging is important to reduce the potential for gumming formation in the reactor vapour transfer and condensing system. The present invention is not dependent on the number of hoppers involved in charging the reactor.

[0053] The first step pyrolysis reactor can be operated at a pressure below or above atmospheric. A modest vacuum is the conventional operating mode for the continuous type of reactor. This is usually preferred to avoid pressure protection systems of the upstream elements and to avoid any leaking flanges or connections to release hydrocarbons to the environment. For the batch reactors pressurized design and operation is easier to accomplish as there is no plastic mix feed to the reactor during the operating cycle. The large opening flange packing do however represent a potential for leakage.

[0054] Pressurized operation comes with significant operating improvements and flexibility due to its inherent capability to provide and maintain a higher driving force through to the process, hereunder and specifically the operation of and condition within the combined quenching, cooling and fractionating unit. It facilitates better control and flexibility in keeping the beneficial vapour velocities in the system. Pressurized operation is thus preferred, but it is not a prerequisite for application of the invention.

[0055] To prevent gas leakage from the pyrolysis reactor, into the upstream system during operations, a rotary valve may be applied at the reactor inlet. To obtain proper pressure protection of the extruder upstream of the first step continuous reactor, automatic closure of the pressure supplying sources is should typically be used as the first pressure protection level and to protect the extruder itself with a pressure relief safety device as a second barrier. The pressure supply from the carrier gas connected to the reactor and the reactor heating system needs to be shut in. The residual heat from the reactor may cause melting of the plastics at or near the reactor inlet during shut down. This melted plastic will solidify during longer shut-ins and can pose problems during start-up. Hence, heating of this part of the extruder should be designed for and applied in such events. Operating with a pre-melt extruder will facilitate melting of the plastics before the reactor as the normal feed modus and should be considered. Such pre-melting is already practiced by some actors motivated by its ability to evaporate some halogens (like chlorine) components.

[0056] In batch reactors, the plastic feedstock is loaded into the reactor and all air is purged out of the system before the heating medium is applied. In the continuous reactor the plastic feedstock is fed to the reactor in any of the two modes described (solid or melted) andheating medium is applied while the reactor internal auger(s) move the feed slowly forward as it heats up. In both reactors the ultimate temperature will be some 450 - 650r<°C. The phase change of the plastic material in the batch reactor will be a function of time while in the continuous reactor it will be a function of time (auger speed) and position. Both depend on the applied heating profile. The feedstock will melt, vaporize and crack over a range of temperatures depending on the different plastic materials in the mix. In both reactors the vapour formed is continuously discharged from the reactor.

[0057] Heated carrier gas is applied to facilitate constant gas velocity during all operations modus and reactor duties and better control of the residence time in the continuous vapour phase of the reactor. To some extent it will allow an independent (from the plastic melt) control of the reactor vapour head temperature (to control further gas phase cracking outside the plastic melt). In both type of reactors this carrier gas is injected at the opposite (upstream) end in relation to the vapour outlet. The carrier gas is recirculating noncondensed gas from the combined condensing, cooling and fractionating unit supplemented with an inert gas such as nitrogen for make-up and start-up. Superheated steam can also be used with nitrogen back us as described. Using superheated steam will require steam condensate treatment facilities to be installed downstream step 2. The use of a carrier gas allows the operation of the reactor internal cyclones at their optimum efficiency independent of the vapour formation load from the plastic melt. And, by keeping gas velocity steady during different feedstock loadings, all parts of the process are maintained at a steady temperature minimizing risk of pyrolysis oil droplets condensation and re-polymerization in the pyrolysis gas. The carrier gas will also be used as the pressurizing agent when the process is designed to run pressurized.

[0058] At the reactor vapour exit internal cyclones 18 are optionally incorporated to remove particles (ash, sot, ceramics, fines etc.) which is commonly entrained in the vapour. The internal location in the reactor and arrangement of the cyclones is important in eliminating any possibility of particles meeting colder surfaces causing deposition of gumming and / or particles. The application of a carrier gas will assure the most efficient separation of these particles independent from the reaction vapour load. The separated particles will join the ash / soot fraction at the bottom of the reactor and be transported out of the reactor at discharge opening 14 without the need for additional external equipment (separators, accumulator and solid state feed-out arrangement)..

[0059] A short transfer line fluidly connects the reactor 10 and the combined quenching, cooling and fractionating unit 20. The use of reactor internal cyclones, operated at maximum efficiency with the aid of a carrier gas, and a proper heat insulation of the short transfer line resolve the problem of particles deposition in this line. The transfer line typicallydoes not include any in-line components before the gas injection system on the combined quenching, cooling and fractionating unit.

[0060] The combined quenching, cooling and fractionating unit requires a special design to prevent the inherent tendency of the pyrolysis gas to re-polymerize and deposit polymerized matter on the inside processing surfaces. The basic approach of this unit is to quench the pyrolysis gas in a continuous and temperature controlled, pool of condensate accumulating in the unit during operation. The combined quenching, cooling and fractionating unit facilitates rapid further cooling of the remaining vapour part in a counter current reflux flow above the pool. In this manner, the pyrolysis gas is liquified, preferably in at least two steps, through partly condensation and cooling into a temperature range of very slow re-polymerization kinetics without contact with cold cooling surfaces.

[0061] Typically, the quenching pool cools the vapour from its reactor outlet temperature of approx. 500 °C to some 250-350 °C or 200-250°C and causes condensation of high boiling constituents while the non-condensed vapour flows vertically upwards into a counter current cooling section immediately above the pool with down flowing reflux from cooled condensate liquids from any extracted side streams from the unit. The combined quenching, cooling and fractionating unit condenses and cools the pyrolysis gas down to a temperature set by the cooling medium applied at the top of the unit.

[0062] The pyrolysis gas injection and entrainment into the liquid pool is designed with careful considerations to facilitate direct and well distributed dispersion of the pyrolysis gas directly into the quenching liquid pool. The pyrolysis gas may enter the combined quenching, cooling and fractionating unit through several nozzles and / or via a manifold comprising any number of openings into the combined quenching, cooling and fractionating unit as explained in relation to Figure 3. All external parts of the manifold and / or nozzles are heat insulated to maintain the pyrolysis gas temperature and avoid condensation therein. The nozzles and / or manifold is / are free draining into the liquids with no other low points to accumulate any condensate formed during shut down and other causes of cool-down. The piping, manifold and nozzles are operated at a gas velocity which assures efficient sweeping of any particles or liquids. The application and control of the carrier-gas facilitate this requirement independent of the pyrolysis reactor operating duty.

[0063] The gas flows downwards by the inner wall 41 and is distributed into the liquid pool, by a perforated cylinder which span the liquid pool 42 and force the gas to entrain the liquid level during injection. Both the still liquid level and the entrained liquid level are indicated on fig.3. The cylinder shall be retrievable and the perforations in the cylindercan preferably be by vertical slits. The bottom part will hold the non-entrained liquid part of the pool which will be cooled and pumped (or by gravity) out of the unit at flow 21 and part recycling to the pool at flow 23, for temperature control, and to the cooling section above the pool at flow 25. The vapour from the pool will flow vertically up to a first bubble cap tray, or similar trays for condensation of gas at a zone 43 in the cooling section of the quenching, cooling and fractionating unit.

[0064] Vapour from the cooling section is further cooled against counter-current liquids from the top of the unit and from any side streams cooling and reflux arrangements. The top outlet of the unit at flow 29 is cooled and may condenses out some liquids. A separator accumulates the liquids together with the top side stream withdrawal and route part of it back to the fractionation as reflux in flow 33 while extracting the balance as the low boil pyrolysis oil product at flow 32. Part of the non-condensable vapour is extracted as flow 30and routed via compression and heating (not shown) as carrier-gas to the inlet 12 of the pyrolysis reactor. The balance at flow 36 is used for energy or integrated into any downstream plants which may make use of the stream. Any unit side stream arrangements are established by extracting reflux liquids, perform sub cooling and return a fraction of the liquids as reflux and an intermediate boiling cut pyrolysis oil product.

[0065] If using superheated steam as a carrier gas, the product streams will contain some dissolved water which will condense out during cooling of the liquid products. Hence liquid / liquid separation of the hydrocarbons / water phases needs to be applied. This will normally be achieved by conventional separation applying residence time to break any emulsions / dispersions. Some water may also be extracted from the bottom of the product storage tanks at regular intervals. The exact water profile, in the combined quenching and fractionation unit, will need to be established by simulation and / or testing and depend on the selected products profile.

[0066] The quenching of the reactor vapour being the first process step of the combined quenching, cooling and fractionating unit brings down the temperature to a level where re-polymerization is very slow if at all. Quenching is performed in a continuous liquids phase which is not affected by any fouling exposed heat transfer surface. The combined quench and fractionation achieve a very efficient use of part of the reactor product latent heat by using It directly for the purpose of separating and optimizing the pyrolysis oil products profile. Hence there is no need for intermediate storage of crude pyrolysis oils and any subsequent distillation.

[0067] The elements and features of the described device and method represent inventive steps to resolve latent experienced problems in the pyrolysis processing of the novel feedstock of waste plastics.The principles and elements are specifically adapted to the issues which prevents today’s technology to perform in a commercially viable way. Present status of the application of pyrolysis to this feedstock is that these steps are not practiced or not adapted sufficiently for the characteristics of the feedstock.

Claims

Claims1. Pyrolysis device comprising a pyrolysis reactor (10) with a first inlet opening (11) for charge, a second inlet opening (12) for carrier gas, a first discharge opening (13) for pyrolysis gas and a second discharge opening (14) for solid residue, characterized in that the device comprising a combined quenching, cooling and fractionating unit (20) arranged downstream of the pyrolysis reactor and fluidly connected to the first discharge opening thereof, the combined quenching, cooling and fractionating unit (20) being arranged to fractionate the pyrolysis gas into at least two fractions of pyrolysis oil.

2. Pyrolysis device as claimed in claim 1, wherein a plurality of cyclone separators (18) are arranged within the pyrolysis reactor through which the pyrolysis gas have to pass to reach the first discharge opening (13).

3. Pyrolysis device as claimed in claim 1 or 2, wherein the pyrolysis reactor (10) is arranged for continuous operation and comprises an auger or a screw (16) for transportation of charged material from an inlet end to a discharge end of the pyrolysis reactor.

4. Pyrolysis device as claimed in any one of the preceding claims, wherein a recirculation loop is arranged between a gas discharge opening of the combined quenching, cooling and fractionating unit (20) and the second inlet opening (12) of the pyrolysis reactor.

5. Pyrolysis device as claimed in any one of the preceding claims, wherein the pyrolysis reactor (10) is arranged for circulation of a heating material in the form of a solid, particulate material.

6. Pyrolysis device as claimed in any one of the preceding claims, wherein the pyrolysis reactor (10) is arranged for electrical heating and / or heating by a gaseous medium such as pyrolysis gas.

7. Pyrolysis device as claimed in any one of the preceding claims, wherein the inlet opening (11) for the charge is provided a gas-tight charge valve to prevent air from entering the reactor during operation.

8. Pyrolysis device as claimed in any one of the preceding claims, wherein the pyrolysis reactor (10) is horizontally arranged.

9. Pyrolysis device as claimed in any one of the preceding claims, wherein the combined quenching, cooling and fractionating unit (20) is arranged to quench and cool the pyrolysis gas in a bath (43) of pyrolysis oil, thereby causing condensation of high-boiling constituents of the pyrolysis gas.

10. Pyrolysis device as claimed in any one of the preceding claims, wherein the combined quenching, cooling and fractionating unit (20) is arranged for cooling in a stepwise manner, to provide at least three fractions of pyrolysis oil.

11. Method for pyrolysis of plastic material, comprising:- charging plastic material to a pyrolysis reactor,- heating the pyrolysis reactor,- discharging pyrolysis gas from the pyrolysis reactor,- discharging solid residuals from the pyrolysis reactor,wherein- charging also a carrier gas to the pyrolysis reactor,subjecting the pyrolysis gas discharged from the pyrolysis reactor to quenching, cooling and fractionating,after the step of fractionating, recycling carrier gas to the pyrolysis reactor.

12. Method as claimed in claim 11, further comprising the step of particle removal is conducted within the pyrolysis reactor.

13. Method as claimed in claim 11 or 12, using cyclone separators arranged within the pyrolysis reactor to facilitate the particle removal.

14. Method as claimed in any one of claims 11 to 13, wherein the steps of fractionating comprise fractionating into at least three fractions using successively lower temperatures.

15. Method as claimed in any one of claims 11 to 14, using a continuous pyrolysis reactor.

16. Method as claimed in any one of claims 11 to 15, wherein the heating is conducted using at least one heat source selected from the group consisting of hot gas and electrical heating means.

17. Method as claimed on any one of claims 11 to 16, wherein the plastic material is charged as pieces with a particle size in the range from 20 mm 50 mm.

18. Method as claimed on any one of claims 11 to 17, wherein the step of heating the pyrolysis reactor involves heating to a steady state temperature in the region from 450 °C to 650 °C.

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