NL2033250B1 - Method of heating plastics for the production of oil - Google Patents

Abstract

The disclosure concerns a method of, and apparatus for, heating plastic for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic; passing the stream of molten plastic through at least one heat exchanger, and supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises molten salt.

Description

METHOD OF HEATING PLASTICS FOR THE PRODUCTION OF OIL

TECHNICAL FIELD

[0001] The invention generally concerns a method of heating plastics for the production of hydrocarbon oils or other chemicals derivable, by pyrolysis of plastics, in particular waste plastics. In the invention, plastics materials are heated to achieve pyrolysis by way of a heat exchange system. The invention further relates to a heating oil, a heat-exchange system comprising a heating medium, a molten salt heating medium, and the use of molten salt in the heat exchange system.

BACKGROUND ART

[0002] Used plastics waste has been found to pose problems for the environment e.g. when dumped to landfills, lost into the environment, or when burnt. However, waste plastic may also provide a potential source of hydrocarbons for production of e.g. petrochemicals, and such a source may (partially) replace hydrocarbons that would more usually be recovered from natural gas, crude oil and other fossil fuel sources. That is, plastic materials are made of essentially useful compounds that can be used as is and/or converted for (re)use. 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.

[0003] Industrial plants for the recovery of chemicals, such as oils, from waste plastics, are known. The output of plastic-to-chemical plants typically includes light hydrocarbons (LHC), heavy hydrocarbons (HHC), char, and non-condensables (gases). Currently, LHC, HHC, or mixtures thereof, are the most desirable products, however, this 1s market dependent.

[0004] LHC and HHC fractions are required by industry to meet certain chemical and physical specifications such as vapor pressure, initial boiling point, final boiling point, flash point, viscosity, cloud point and cold filter plugging point. Different qualities may be desired by different customers or end-uses, but it is important that plastic-to-chemical plants produce product of stable quality. The final qualities of the product fractions are controlled by a distillation column such as those well-known and commonly used in the petrochemical industry.

[0005] In plastic-to-chemical plants, feedstock plastics, which may comprise for the most part polyethylene and polypropylene from domestic sources, form the input. These plastics made up of very long chain hydrocarbons are cracked in the plant into shorter chains, forming a wide spectrum of molecules with a variety of chain lengths. These mixtures of cracked materials can be distilled into various temperature-determined fractions as is known.

[0006] 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 the waste plastics in an inert atmosphere (typically nitrogen gas atmosphere). In effect, the long polymer chains of the plastic’s polymers are cracked through heating, resulting in shorter, more generally useable, hydrocarbons.

[0007] Various attempts to provide technically and cost-effective pyrolysis of waste plastics have been attempted previously.

[0008] Technically useful results have been achieved by the technologies discussed in patent publications US2018/0010050 and WO2021053139, the contents of which publications are incorporated herein by reference.

[0009] US2018/0010050A1, discusses a method for recovering hydrocarbons from plastic wastes by pyrolysis without the use of catalysts, in particular polyolefin-rich waste. The process involves melting the plastic waste in two heating devices and admixing a stream derived from a cracking reactor with the incoming molten plastic waste of a first heating device. The heated, molten plastic is passed to a cracking reactor where the plastic materials are cracked. Subsequent thereto the cracked materials are distilled into diesel and low boilers.

[0010] WO 2021/053139 A1, which offers a number of advancements in relation to

US2018/0010050A 1, discusses, among other matters, a method for breaking down long-chain hydrocarbons from plastic-containing waste, comprising providing material containing long- chain hydrocarbons; heating a specific volume of the material containing long-chain hydrocarbons to a cracking temperature, at which cracking temperature the chains of hydrocarbons in the material start cracking into shorter chains; and for the specific volume having a temperature above the cracking temperature, exposing the specific volume to heat which is less than or equal to 50 °C above the temperature of the specific volume.

[0011] Although good results have been achieved based on the above technologies, there remains room for further improvement, for example it would be useful to provide systems and processes that are more versatile than previously attempted methods and systems, and/or with improved efficiency or throughput.

[0012] To make oil from waste plastic through pyrolysis, the plastics must be heated to an appropriate temperature, that is, to a pyrolysis temperature at which cracking of the polymer chains takes place. In some prior art operations, such as those discussed above, heating of the waste plastics to pyrolysis ranges has been achieved through a combination of extruders that impart heat via heating and friction to melt plastic, followed by heat exchanger devices that bring the plastic melt to pyrolysis temperature.

[0013] The pyrolysis temperature for waste plastics may, for example, be at temperatures at or above 350°C, more preferably at temperatures at or above 380°C, still more preferably at or above 400°C. Typically, the higher the temperature to which the treated plastic and partially cracked hydrocarbons is raised, the more quickly pyrolysis will take place and the greater the potential rate of throughput for a plastic-to-chemical plant will be. For example, pyrolysis temperatures in a plastic-to-chemical conversion process may preferably be at least at 400°C, possibly up to 550°C or beyond, more preferably between about 350°C and 550°C, preferably of between about 380°C and 480°C, more preferably of between about 400°C and 420°C.

[0014] Higher temperatures for pyrolysis may, however, be challenging to reach, particularly in a manner that is stable for both the product streams as well as the plastic-to-chemical conversion plant itself. For example, during testing and operation of such prior systems it has been found that although it may be desirable to move to higher temperature pyrolysis with the aim of improved throughput, when the systems are operated at the high end temperatures multiple concerns unexpectedly emerge, which may include excess charring (carbon production, carbon deposition on heat exchanger tubes), reduced end-product quality and/or decreasing yield due to greater production of non-condensable gases, and failure of some mechanical systems, such as pumps for the heat exchange systems, and (electrical) heaters in the heat exchange systems. The possible benefits of higher temperatures in prior art system have thus so far been excessively countered by the disadvantages.

[0015] There thus remains a desire in the field to improve plastic-to-chemical pyrolysis throughput, yet while reducing or avoiding one or more of the aforementioned disadvantages.

For example, there remains a need in the field for methods and devices for heating plastics to produce hydrocarbon oils therefrom, which solves at least one of the abovementioned drawbacks. In particular, there is a need to improve the production of hydrocarbon oils from plastics, while optimizing output rate yet providing high quality products, and robust durability of system and method, such as pumps and heating systems. In a further or alternative aspect it is desirable to ease or improve scale-up of pyrolysis processing to larger streams.

SUMMARY OF THE INVENTION

[0016] The present invention provides a method of heating plastic materials, a method of producing oil or other chemicals from waste plastic by pyrolysis, a heat exchange system, and a pyrolysis plant, as discussed herein.

[0017] In an aspect there is provided a method of heating plastic for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic; passing the stream of molten plastic through at least one heat exchanger, and supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises molten salt.

[0018] In an aspect there is provided a method of producing oil by pyrolysis of plastic, comprising: heating solid plastic to a molten state treating the molten plastic in accordance with the heating method discussed herein to crack the plastic; and obtaining oil by distillation of cracked product from the heated plastic.

[0019] In an aspect there is provided a heat exchange system, the heat exchange system comprising: a molten-salt tank arranged to be filled with molten-salt; a heater arranged to provide heat to the molten-salt tank and melt molten-salt; at least one heat exchanger, fluidly coupled to the molten-salt tank: a pump arranged to pump the molten-salt to the at least one heat exchanger; wherein the at least one heat exchanger comprises a circulation pump arranged to pump the molten-salt through the heat exchanger and a control valve arranged to regulate the temperature of the molten salt in the heat exchanger.

[0020] In an aspect there is provided a heat exchange system, the heat exchange system comprising: a first passage for molten plastic; a second passage for liquid molten-salt heat transfer medium, in heat exchange with the first passage; wherein the heat exchange system contains molten plastic in the first passage and molten salt in the second passage.

[0021] In an aspect there is provided a plastic to chemicals plant comprising: a supply of plastic material, a plastics melter, preferably an extruder, a heat exchange system as discussed herein, and a distillation column.

[0022] Further aspects of the invention are set forth in the dependent claims, the drawings and the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

[0024] Fig. 1 shows an assembly for cracking long chained hydrocarbons; and

[0025] Fig. 2 shows an embodiment of a heat exchanger in greater detail.

DESCRIPTION OF THE INVENTION

[0026] In a first aspect, the invention relates to a method of heating plastic for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic; passing the stream of molten plastic through at least one heat exchanger and supplying a heat- transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises molten salt.

[0027] It has been found that the use of molten salt as a heat transfer medium, higher temperature pyrolysis may be obtained, yet while avoiding (excessively) increased char development in the pyrolyzing plastic stream, substantial maintenance of end-product quality, and/or reduction or avoidance of failure of associated mechanical systems, such as pumps for the heat exchange systems, and (electrical) heaters in the heat exchange systems. This is believed to result from an ability to apply low or lowered pressures in pyrolysis installations, and through reduced plant complexity.

[0028] Through testing and operation of earlier pyrolysis systems carried out by the inventors, it has been identified, without wishing to be bound to theory, that a particular source of impairment when operating previous systems is unexpected, excessive (for the system) degradation of the heat transfer medium, in particular of synthetic oil transfer mediums used in prior pyrolysis systems. Without wishing to be bound by theory, it is believed that an excessively fast degradation of the synthetic oils, when operating at temperatures at or above 400°C, particularly in plastics pyrolysis systems may result poor through flow of heat exchange medium affecting product quality; and changes in flow characteristics, leading to damage of pumps and other equipment.

[0029] Indeed, the inventors have realized that changes to viscosity characteristics and heat transfer characteristics of the oil may then result in pump malfunctioning and possibly also hot spots that damage the heating system or degrade product quality.

[0030] Thus when addressing a desire to increase pyrolysis throughput, yet while maintaining product quality and/or system operation/reliability, the inventors have identified that this can be achieved by use of a molten salt heat exchange liquid. The molten salt is a salt that is liquid at the temperature range of heat-transfer operation, and which is able to heat waste plastics to desired temperatures. Further, the heat transfer medium preferably has good heat transfer properties and is preferably able to be utilised under reasonable or low pressures, without malfunction of pumps, damage to heating systems or, loss of final product quality.

[0031] The use of a molten salt as the heat transfer medium in the at least one heat exchanger may improve the stability of the heat transfer process. The molten salt is preferably able to heat waste plastics up to the required temperature for efficient pyrolysis. Furthermore, the use of molten salt may be advantageous because it may be selected to be a non-toxic salt, which may be contrasted with thermal oils. In addition, the use of molten salt as the heat transfer medium may allow high temperatures to be maintained for long periods of time without degradation. Furthermore, the use of molten salt may be advantageous because it can be used under reasonably low pressures. In preferred embodiments, the molten salt may even be used at atmospheric pressure. This has significant benefits, both in production efficiency and process safety. In particular, the use of molten salt as the heat transfer medium may enable a higher temperature which results in an improved process rate, especially in the final heating stage, where the temperature of the heat transfer medium is increased to maintain a sufficiently high temperature difterential between the stream of molten plastic and the heat transfer medium. The high temperature required by the heat transfer medium to achieve this temperature differential may be attained through the use of molten salt as the heat transfer medium without causing breakdown thereof.

[0032] The method of the present invention may be applied in any heat exchanger. In heat exchangers, a heat transfer medium is used to increase the temperature of the plastic.

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Generally, a heat exchanger is a system used to transfer heat between two or more fluids, such as between gases or liquids. The fluids may be separated by a membrane, such as a wall, or other physical boundaries that prevents intermixing of the fluids. Heat, however, is transferred from the heating medium to the heated material. The heat differential between the heating medium and the heated material influences the rate of heat exchange. Heat exchangers are generally known and are (amongst others) used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. In known systems, the heat transfer medium 1s generally passed internally through or externally over a plurality of tubes, and a material to be heated is passed on the opposite side of the tubes, e.g. tube in shell heat exchangers.

The heat transfer medium is generally in fluid form and is preferably a liquid. Liquids in general have a have a high heat exchange coefficient, resulting in high heat transfer or heat conduction, and have high heat capacities. Gasses have generally lower conductivity than liquids.

[0033] There are three primary classifications of heat exchangers according to their flow arrangement, parallel-flow, counter flow, and cross flow heat exchangers. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is generally the most efficient, in that it can transfer the most heat from the heat transfer medium per unit mass due to the fact that the average temperature difference along any unit length is higher. In a crossflow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.

[0034] In an embodiment, the stream of molten plastic comprises polyethylene. In a preferred embodiment, the stream of molten plastic comprises less than 10 wt% moisture, preferably less than 7 wt% moisture, still more preferably less than 5 wt% moisture. If the moisture content of the stream of molten plastic is too large, the resulting steam may lead to problems in the extruder, related to e.g. pressure increase, changes in viscosity, and increase of put- through speed, leading to a less efficient heat transfer. It is also an economic burden to remove moisture from plastic feed, reducing the efficiency of the overall process.

[0035] Molten salts suitable for use in the present invention may be found the field of concentrated solar power systems.

[0036] In embodiments, the molten salt may comprise NaNO3, KNOs, CaNO: LiF-NaF-KF (FLiNaK), KF-ZrF4, KCI-MgCl, or mixtures thereof.

[0037] Suitable salts may be molten halides composed of LiX, NaX, KX, MgX: or CaX: (where X can be Cl or Br), as individual entities or as mixtures, which are at least partially molten in at or above 300 degrees centigrade.

[0038] Molten chloride salts may be useful candidates. For example MgCl-KC1 molten salts.

Other chloride salts are also considered suitable, including those comprising LiCl, NaCl, KCI,

MgCl; or CaCl:, as individual entities or as binary, ternary, quaternary or quinary mixtures.

Preferably these are at least partially molten at or above 300°C degrees.

[0039] Further halide salts may also be useful, including molten bromide salts comprising

LiBr, NaBr, KBr, MgBr; or CaBra, as individual entities or as binary, ternary, quaternary or quinary mixtures, which are at least partially molten. Floride salts may also be useful, such as salts comprising LiF, NaF, KF or BeF:, as individual entities or as binary, ternary, or quaternary mixtures.

[0040] Further exemplary molten salts may include nitrate molten salts, mixed nitrate salts, mixed ternary nitrate molten salts. Nitrate salts may comprise calcium nitrates, potassium nitrates, sodium nitrates, lithium nitrates or mixtures thereof’

[0041] Nitrate molten salts may comprise binary nitrate molten salt systems, for example

KNO3-NaNO: in weight ratios of 20-40 KNO: to 60-80 NaNOs; more preferably in a ratio of 55:45.

[0042] In an embodiment, the heat transfer medium at entry to the heat exchanger is at a temperature of at least 300°C, preferably at least 350°C, more preferably greater than 400°C, still more preferably of greater than 430°C.

[0043] In a preferred embodiment, the molten salt comprises an eutectic system. An eutectic system is a homogeneous mixture of substances that melts or solidifies at a single temperature that is lower than the melting point of any of the constituents. This temperature is known as the eutectic temperature, and is the lowest possible melting temperature over all of the mixing ratios for the involved component species.

[0044] The molten salt preferably has a melting point that is lower than the pyrolyzing temperatures of a given system such that it is liquid for pumping through heat exchangers.

0.

Preferably the molten salt has an (initial) melting point at below about 350°C, more preferably at or below 300°C, still more preferably at or below 250°C, still more preferably at or below about 200°C and most preferably at or below about 150°C.

[0045] To avoid pressure increase at high temperatures it is preferable that the molten salt does not undergo a phase change to gas in the system. The boiling point of the molten salt is thus preferably at or above about 600°C. This may reduce or remove needs for pressure resistant components and systems.

[0046] In an embodiment, the molten salt 1s heated to a temperature of between about 350°C and about 600°C, preferably between about 350°C and 500°C, preferably of between about 400°C and 480°C, more preferably of between about 440°C and 460°C.

[0047] An increased temperature may lead to an increased heat transfer and pyrolysis rate, which means that the exchanger for a given amount of output can be smaller. The use of a molten salt which is able to reach higher temperatures without rapid degradation is thus advantageous to throughput and/or possibly also overall size of the heat exchanger.

[0048] In an embodiment, the molten plastic is heated by the heat exchanger to a temperature of between about 350°C and 550°C, preferably of between about 380°C and 480°C, more preferably of between about 400°C and 420°C.

[0049] In an embodiment, the molten salt is provided in the heat exchanger at a pressure of less than 10 bar, preferably of less than 5 bar, more preferably of less than 3 bar, still more preferably of less than 2 bar.

[0050] Higher temperatures are possible by using the molten salt, without an associated increase in pressure to maintain the liquid phase. As such, highly pressurized equipment is no longer necessary. In a preferred embodiment, a nitrogen blanket is provided, preferably at less than about 50 mbar. This helps prevent the ingress of ambient moisture into the heat transfer medium. At the start of the process, a low level nitrogen purge is preferably performed to remove most moisture from the system, preferably thereafter a low rate nitrogen purge is continuously provided to prevent ingress of water vapour or air.

[0051] In an embodiment, the input stream is provided through a plurality of heat exchangers, said heat exchangers being coupled in series such that the output stream of a first heat exchanger is the input stream of a second heat exchanger.

[0052] In a preferred embodiment, the heat transfer medium of all heat exchangers comprise a molten salt. In a still more preferred embodiment, the input stream is fed through at least one, two, three, four or more heat exchangers.

[0053] According to a further aspect of the invention, there is provided a method of producing oil by pyrolysis of plastic, comprising: heating solid plastic to a molten state treating the molten plastic in accordance with the method of any preceding claim to crack the plastic; and obtaining oil by distillation of cracked product from the heated plastic.

[0054] According to a still further aspect of the invention, there is provided an oil, obtainable with any of the methods discussed hereinbefore.

[0055] According to an aspect of the invention, there is provided a heat exchange system for use in the method of any of the embodiments discussed hereinbefore, the heat exchange system comprising: a main bulk tank arranged to be filled with salt; a heating arrangement provided in the main bulk tank arranged to heat and melt the salt; at least one heat exchanger, fluidly coupled to the main bulk tank; a pump arranged to pump the molten salt to the at least one heat exchanger; wherein the at least one heat exchanger comprises a circulation pump arranged to pump the molten salt through the heat exchanger and a control valve arranged to regulate the temperature of the molten salt in the heat exchanger.

[0056] In a preferred embodiment, the main bulk tank is arranged below the heat exchanger such that the molten salt can flow downwards to the main bulk tank after shutdown of the system, or in particular in the event of emergency shutdown. In this embodiment, the salt flows out of the heat exchanger prior to solidifying upon cooling down. In an embodiment, the main bulk tank comprises a heating unit to heat the salt and to melt the salt. Once the salt is molten, it may be pumped towards the heat exchanger.

[0057] In a preferred embodiment, a piping system couples the main bulk tank and the heat exchanger, and the piping system is provided under an angle, such that the molten salt flows back to the main bulk tank if the pumps are shut down. In a further preferred embodiment, the piping comprises electrical tracing. This helps prevent solidification of the salt in the system when it is pumped from the main bulk tank to the heat exchanger, in particular at the start up stage when portions of the heat exchange fluid route may be at a temperature below or close to the melting point of the molten salt, which may risk blockages resulting.

[0058] According to an aspect of the invention, there is provided a heat exchange system for use in the method of any of the embodiments described hereinbefore, the heat exchange system comprising: a first passage for molten plastic; a second passage for molten salt heat- transfer medium, in heat exchange with the first passage; wherein the heat exchange system contains molten plastic in the first passage and molten salt in the second passage.

[0059] Referring to Fig. 1 there is shown an apparatus comprising a heating device 11 and a separation vessel 12. The heating device 11 is in communication with the separation vessel 12 to feed fluids (liquids and gases) into the separation vessel 12. More specifically, the heating device 11 feeds fluids containing (partially) cracked hydrocarbons in both gaseous and liquid states into the separation vessel 12 at pyrolysis temperatures.

[0060] In some embodiments a feeding device 7 is arranged to fill material containing long chained hydrocarbons such as waste plastics as discussed, into the heating device 11. In some embodiments the feeding device comprises an effector 8 for heating and/or forwarding the material containing long chained hydrocarbons. In some embodiments the effector is a screw auger 8 arranged to forward, and preferably also heat, the material containing long chained hydrocarbons. In some embodiments the screw auger 8 moves the material, and internal friction in the material causes the material to heat up and to melt. In further embodiments the feeding device 7 comprises a heating device such as an electrical heater or a heat exchanger perfused by a heating medium. The feeding device 7 drives the material containing long chained hydrocarbons to the heating device 11.

[0061] The heating device 11 receives the material containing long chained hydrocarbons. In various embodiments the heating device comprises at least one heating zone 1, 2, 3, 4. The heating zone 1, 2, 3, 4 is arranged to expose the material containing long chained hydrocarbons to a temperature increase, and thereby raise the temperature of the material to a pyrolysis temperature. Pyrolysis temperatures may be 360°C or greater, more preferably 390°C or greater, preferably 395°C or greater, preferably 400°C or greater, more preferably 410°C or greater. A pyrolysis temperature may be in the range of 360-550°C more preferably 390-450°C.

[0062] In the illustrated embodiment, four heating zones are illustrated. Each of the heating zones 1, 2, 3, 4, may be a heat exchanger, preferably a shell and tube heat exchanger. The heating zones 1, 2, 3, 4 provide a flow path for the plastics material containing long chained hydrocarbons. The heating zones 1, 2, 3, 4 continuously or gradually increase the exposure temperature along the flow path. Heating is preferably done gradually to reduce or avoid char formation through excessive temperature differentials.

[0063] The heating device 11 heats and melts plastic material feedstock, raising its temperature to a pyrolysis temperature. Cracking may start in any of the heating zones 1, 2, 3, 4, with most cracking in the heating zones preferably occurring in heating zone 4, zone 4 being the hottest heating zone of the four. The molten, partially pyrolyzed plastic material exits heating zone 4 at a pyrolysis temperature and passes into separation vessel 12 via separation vessel inlet 14.

[0064] In some embodiments the molten salt may be chosen to have a low (initial) melting point, e.g. about 150°C so that it can be supplied to all heat exchangers. A single molten salt heating system may then be provided for a plurality of, or all, heat exchangers 1, 2, 3, 4, 28 in a system. Alternatively, molten salt may be used to heat only those heating zones requiring heating to above about 400°C, for example in heat exchanger 4 and 28 in the illustrated embodiment. Thermal oil may in that case be used as a heat exchange medium in lower temperature heat exchangers such as the heat exchangers 1, 2, 3.

[0065] A recycling loop 26 is provided to remove liquid, partially-pyrolyzed plastic material, and non-pyrolysable material such as sand, coke, metal particles etc., collected in the separation vessel 12 by way of pump 27. The removed liquid is reheated to a pyrolysis temperature by the heat exchanger 28, and then returned to the separation vessel 12, in the illustrated case together with fresh feed. This recycle loop 26 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 5.

[0066] A more detailed illustration of a heat exchanger as may be used as any of the heat exchangers 1, 2, 3, 4, 28 in Fig. 1, is provided in Fig.2. The example of Fig. 1 illustrates the heat exchanger 2, however, the arrangement is similar to each heat exchanger.

[0067] In the illustrated embodiment of figure 2, a bulk tank 50 is provided and 1s filled with molten salt, that is, salt to be melted or salt that is heated to liquid phase. A heater 51 is provided in the bulk tank 50 for heating the molten salt. The heater 51 is preferably an electrical heater or a direct fired heater for heating the molten salt to a temperature of between about 350°C and about 600°C, preferably between about 350°C and 500°C, preferably of between about 400°C and 480°C, more preferably of between about 440°C and 460°C.

[0068] A main pump 40 1s provided to pump molten salts heat exchange liquid to several heat exchangers 1, 2, 3, 4, 28. Line 52 supplies molten salt to heat exchanger 2, while lines 53 supply molten salt to further heat exchangers as may be included. Line 54 returns molten salt to the bulk tank 50 from heat exchanger 2, while lines 55 return molten salt from further heat exchangers as may be included.

[0069] Each heat exchanger 1, 2, 3, 4, 28 is further provided with a circulation pump 41 exclusive to each heat exchanger 1, 2, 3, 4, 28. Circulation pumps 41 may alternatively supply multiple heat exchangers 1, 2, 3, 4, 28, possibly via smaller subpumps with thermostat control to provide each heat exchanger with a desired temperature.

[0070] A control valve 42 is provided, which valve regulates the temperature of the loop.

[0071] Gas accumulation (if any) may be released by a gas release valve 43.

[0072] A pressure control valve 44 provides stable pressure for the main pump 40 and releases excess salts back to the bulk tank 50.

[0073] The bulk tank is preferably at atmospheric pressure or slightly above atmospheric pressure and maintained free of air and moisture by a low level, continuous nitrogen bleed 45 into the bulk tank 50. Nitrogen gas from tank may escape by exhaust line 46.

[0074] Heat exchanger 2 in Fig.2 is illustrated as a shell and tube heat exchanger. The heating section of the heat exchanger is provided with flow tubes 60 running in the direction of the pyrolysis process. Molten waste plastic, possibly partially pyrolyzed, and possibly multi-phase with both gas and liquid, and possibly some remaining solid, is passed through the tubes 60 from left to right in Fig. 2, from tube inlet 61 to tube outlet 62. The tubes 60 are contained within a shell (or bath) to which a fluid heating medium in the form of heated molten salt is supplied. The molten salt is supplied to heat exchanger fluid inlet 63 at a low point in the heat exchanger and fills the shell. Baffles 65 may assist in ensuring good distribution of the molten salt in the heat exchanger 2, and consequently a desired temperature distribution. The molten salt exits the shell at a heat exchanger fluid outlet 64.

[0075] It is preferable for safety reasons that a heating failure valve 47 be provided in the molten salt lines. The heating failure valve 47 can be opened to allow all salts to flow back to the bulk tank 50 in the event of system failure, for example in the event of loss of power.

[0076] Preferably lines carrying molten salt to the heat exchanger are sloped downwardly for gravity driven flow towards the bulk tank 50. Advantageously, in the event of power or other failure, molten salt in the lines will substantially and naturally return to the bulk tank 50. This may assist in preventing solidification of molten salt in the lines and/or heat exchanger 1. In embodiments in which baffles 65 are provided in the heat exchanger 2, the baffles may be provided with draining holes allowing molten salt to drain under gravity to the bulk tank 50, soreducing or minimizing build of solid salt in the heat exchanger 2.

[0077] For start-up or temporary stoppage, the lines carrying molten salt may be provided with local heating, for example heating of the lines may be achieved by provision of insulation 48 and/or electrical tracing on the lines.

[0078] Returning to Fig. 1, at the point of entering the separation vessel 12 via inlet 14 the plastics material is undergoing pyrolysis because it is at a pyrolysis temperature. The cracking of the plastic material results in generation of a wide spectrum of hydrocarbons with a wide range of boiling points. The plastics material exiting the heating device 11 and entering the separation vessel 12 via inlet 14 comprises both gaseous and (partially cracked) liquid components.

[0079] The illustrated separation vessel 12 is elongate and arranged substantially vertically.

Non-vertical arrangements may also be envisioned, such as slanted or horizontal. Pyrolyzed gaseous material rises in the separation vessel 12 and liquid (partially) pyrolyzed material falls under gravity. In this manner, gaseous and liquid materials diverge and so separate in the separation vessel 12. Phase separation of gases and liquids within the separation vessel 12 may be enhanced by provision if a cyclone separator arrangement.

[0080] The gaseous hydrocarbon materials rising in the separation vessel 12 discharge via upper outlet 132 and pass via line 6 to a partial condenser 5. Partial condenser 5 is remote from the separation vessel 12 and is positioned downstream from the separation vessel 12.

[0081] The partial condenser 5 is arranged and/or configured to remove heavy fractions (lower boiling point fractions) from the exiting gas, prior to the exiting gas being further passed to full distillation or condenser sections of the apparatus and process. In the partial condenser 5 the gas is cooled as discussed below. As the gas is cooled, heavier fractions condense and can be collected, while lighter fractions remain gaseous and are passed via line 30 to further processing.

[0082] The partial condenser 5 is preferably provided with a packed column 28 with (optional) random packing material such as rings e.g. raschig rings, which increases the contact surface area between the gas and the liquid which is condensed in the partial condenser. As is known in condensation processes, this may assist in effective condensation by assisting in condensing heavy hydrocarbons and re-evaporating light hydrocarbons by providing a large mass transfer area (e.g. as column packing).

[0083] The partial condenser 5 is also preferably provided with a temperature-controlled cooling element 29, such as a cooling coil supplied with temperature regulated cooling medium. The temperature of the cooling element 8 is controlled to cause condensation of long-chain hydrocarbons (longer than C22, for example), which condensed materials fall under gravity to the lower part of the partial condenser 5. The cooling element 29 is preferably downstream of the packed column 28.

[0084] As alternatives, or additionally, selective condensation may be achieved by a cooling jacket (not shown) acting as a cooling element, or the partial condenser may be an external (full reflux) condenser.

[0085] The gases that do not condense (C1-C20/C22) in the unheated packed column 28 or in the cooling element 29 discharge via a partial condenser upper outlet and pass via line 30 to a downstream distillation unit of a type commonly known for distillation use in the petrochemical arts, for example as used in distillation of crude or mineral oil fractions.

[0086] The downstream distillation section can be designed according to industrial standards as known to those skilled in the art. The gases can be fractionated into gaseous fractions and liquid fractions. A liquid fraction may be stripped off as middle distillate, and a gaseous fraction may be stripped off as light boilers in a distillation unit. Hydrocarbon products from the distillation unit may comprise butane, propane, kerosene, diesel, fuel oil; light distillates, such as LPG, gasoline, naphtha, or mixtures thereof, middle distillates such as kerosene, jet fuel, diesel, or mixtures thereof, heavy distillates and residuum such as fuel oil, lubricating oils, paraffin, wax, asphalt, or mixtures thereof; or any mixtures thereof. Hydrocarbon products may be saturated, unsaturated, straight, cyclic or aromatic. Further products may include non-condensable gases, comprising methane, ethane, ethene and/or other small molecules. The products may be a source of feedstock for steam crackers for the manufacture of plastics.

[0087] The hydrocarbons that condense in the partial condenser 5 (>C22) collect as a liquid 31 at the bottom of the partial condenser 5.

[0088] The liquid level at the bottom of the partial condenser is controlled by one or more level control sensors and may be discharged batchwise or continuously. The level control in the partial condenser 5 can be achieved continuously by way of a flow control valve.

[0089] The condensed liquid 31 in the partial condenser is preferably discharged via a partial condenser lower outlet 32 and is passed to a reboiler 16 via line 33 controlled by optional valve 34. Valve 34 can be any of an open close valve or a control valve.

[0090] The condensed liquid 31 collects in the reboiler 16, where it is reheated by a heater 13, preferably an internal heating element or an internal heat exchanger. The reboiler heater 13 can be heated electrically, with thermal oil or other types of heating medium. The condensed liquid in the reboiler 16 is heated to a temperature higher than the temperature of the partial condenser.

[0091] Light hydrocarbon fractions which may unavoidably be carried along with the partial condenser condensate liquid can in this manner be evaporated or boiled off and sent to the distillation apparatus via a reheater vessel upper outlet 15. These can then be included in the distilled products. This may improve product yields as compared to a system or process in which partially condensed material is directly returned to a pyrolysis zone. This may also be considered preferable to returning light hydrocarbons to a pyrolysis zone, where they may further crack or form a relatively useless heat drain as they are circularly heated to re- evaporate and thereafter recondensed.

[0092] The reboiler 16 is preferably comprised as a component of a distillation section and joined in fluid communication for gases via reheater vessel upper outlet 15.

[0093] Liquid 35 that is collected in the reboiler, and which does not evaporate through reheater vessel upper outlet 15 for distillation, may be pumped back into the separator vessel 12 via line 9 using pump 10, with optional further heating prior to entry into the separator vessel 12. The liquid may in this manner be further pyrolyzed to useful lighter products than those that condense in the partial condenser 5. For example, the liquid is returned to the separating vessel 12 and or pyrolysis zone and cracked until they are reduced to chain lengths of C20 to C22 or less. The product yield may thus be improved, and or the ratio of light to heavy products be more specified to customer requirements.

[0094] Alternatively, the liquid collected in the reboiler, and which does not evaporate through reheater vessel upper outlet 15 for distillation, may be collected as a useful product, for example the product may be paraffin, and be transported to a collecting vessel via valve 21.

[0095] The partial condenser coil 29 is typically operated at temperatures between 220°C and 380°C and the reboiler is typically operated at temperatures between 340°C and 400°C. These temperatures are both lower than the typical crack reactor operating temperature of 390°C and 450°C.

[0096] The liquid pyrolyzed material present in the separator vessel 12 is continuously circulated, preferably by means of an external pump 27. As the liquid is circulated it may be reheated to a pyrolysis temperature for further cracking by a heat exchanger 28.

[0097] A distillation column (not shown) is preferably provided atop reheater vessel upper outlet 15. The distillation column may be provided with a region designed as a packed column, and optionally within this region containing packing or preferably above this region, an intermediate tray on which the liquid fraction (diesel product or HHC) is collected and may be discharged. The HHC, for example diesel, product discharged from the distillation unit is preferably cooled by means of a heat exchanger, and a portion of this cooled diesel product may be recirculated to the distillation unit via a recycle stream line in order to set optimal temperature conditions.

[0098] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “90°” is intended to mean “about 90°”.

[0099] It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein.

Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

Claims (16)

CONCLUSIESCONCLUSIONS 1. Werkwijze voor het verhitten van kunststof voor de productie van olie uit kunststof, waarbij de werkwijze de volgende stappen omvat: - het verschaffen van een stroom gesmolten kunststof; - het leiden van de stroom gesmolten kunststof door ten minste één warmtewisselaar, en - het toevoeren van een warmteoverdrachtsmedium naar de warmtewisselaar om de stroom gesmolten kunststof te verhitten, waarbij het warmteoverdrachtsmedium gesmolten zout omvat.Claims 1. Method for heating plastic for the production of oil from plastic, wherein the method comprises the following steps: - providing a flow of molten plastic; - passing the flow of molten plastic through at least one heat exchanger, and - supplying a heat transfer medium to the heat exchanger to heat the flow of molten plastic, wherein the heat transfer medium comprises molten salt. 2. Werkwijze volgens conclusie 1, waarbij het gesmolten zout NaNOz, KNO3, CaNO: LiF- NaF-KF (FLiNaK), KF-ZrF4 of KCI-MgCl; omvat, waarbij bij voorkeur het gesmolten zout vloeibaar is bij een temperatuur van meer dan ongeveer 350 °C, met meer voorkeur meer dan ongeveer 400 °C, met nog meer voorkeur meer dan ongeveer 450 °C.A method according to claim 1, wherein the molten salt is NaNO 2 , KNO 3 , CaNO: LiF-NaF-KF (FLiNaK), KF-ZrF 4 or KCl-MgCl; wherein preferably the molten salt is liquid at a temperature of greater than about 350°C, more preferably greater than about 400°C, even more preferably greater than about 450°C. 3. Werkwijze volgens een van de voorgaande conclusies, waarbij het warmteover- drachtsmedium bij het binnenkomen bij de warmtewisselaar een temperatuur van ten minste 300 °C, bij voorkeur ten minste 350 °C, met meer voorkeur meer dan 400 °C, met nog meer voorkeur meer dan 430 °C heeft.A method according to any one of the preceding claims, wherein the heat transfer medium, upon entering the heat exchanger, has a temperature of at least 300°C, preferably at least 350°C, more preferably more than 400°C, with even more preferably more than 430 °C. 4. Werkwijze volgens een van de voorgaande conclusies, waarbij het gesmolten zout een smeltpunt van minder dan 300 °C, bij voorkeur minder dan 250 °C, met meer voorkeur minder dan 200 °C, met nog meer voorkeur minder dan 150 °C heeft.Method according to any of the preceding claims, wherein the molten salt has a melting point of less than 300 °C, preferably less than 250 °C, more preferably less than 200 °C, even more preferably less than 150 °C . 5. Werkwijze volgens een van de voorgaande conclusies, waarbij het gesmolten zout verhit wordt tot een temperatuur tussen ongeveer 350 °C en 500 °C, bij voorkeur tussen ongeveer 400 °C en 480 °C, met meer voorkeur tussen ongeveer 440 °C en 460 °C.A method according to any one of the preceding claims, wherein the molten salt is heated to a temperature between approximately 350°C and 500°C, preferably between approximately 400°C and 480°C, more preferably between approximately 440°C and 440°C. 460°C. 6. Werkwijze volgens een van de voorgaande conclusies, waarbij de gesmolten kunststof door de warmtewisselaar verhit wordt tot een temperatuur tussen ongeveer 350 °C en 5506. Method according to any of the preceding claims, wherein the molten plastic is heated by the heat exchanger to a temperature between approximately 350 °C and 550 °C. °C, bij voorkeur tussen ongeveer 380 °C en 480 °C, met meer voorkeur tussen ongeveer 400 °C en 420 °C.°C, preferably between about 380 °C and 480 °C, more preferably between about 400 °C and 420 °C. 7. Werkwijze volgens een van de voorgaande conclusies, waarbij het gesmolten zout in de warmtewisselaar wordt aangeleverd bij een druk van minder dan 10 bar, bij voorkeur minder dan 5 bar, met meer voorkeur minder dan 3 bar, met nog meer voorkeur minder dan 2 bar.7. Method according to any of the preceding claims, wherein the molten salt is supplied to the heat exchanger at a pressure of less than 10 bar, preferably less than 5 bar, more preferably less than 3 bar, even more preferably less than 2 bar. 8. Werkwijze volgens een van de voorgaande conclusies, waarbij de invoerstroom wordt aangeleverd door een veelvoud aan warmtewisselaars, waarbij de warmtewisselaars in serie zijn gekoppeld zodat de uitvoerstroom van een eerste warmtewisselaar de invoerstroom van een tweede warmtewisselaar is.8. Method according to any of the preceding claims, wherein the input stream is supplied by a plurality of heat exchangers, wherein the heat exchangers are coupled in series so that the output stream of a first heat exchanger is the input stream of a second heat exchanger. 9. Werkwijze volgens conclusie 8, waarbij de warmteoverdrachtsvloeistof van alle warmtewisselaars een gesmolten zout omvat.Method according to claim 8, wherein the heat transfer fluid of all heat exchangers comprises a molten salt. 10. Werkwijze volgens een van de conclusies 8 of 9, waarbij de invoerstroom via ten minste vier warmtewisselaars wordt gevoerd.10. Method according to one of claims 8 or 9, wherein the input flow is conducted via at least four heat exchangers. 11. Werkwijze voor het produceren van olie door pyrolyse van kunststof, die het volgende omvat: - het verhitten van vast kunststof tot een gesmolten toestand; - het behandelen van de gesmolten kunststof met de werkwijze volgens een van de voorgaande conclusies om de kunststof te kraken; en het verkrijgen van olie door destillatie van gekraakt product uit de verhitte kunststof.11. A method of producing oil by pyrolysis of plastic, comprising: - heating solid plastic to a molten state; - treating the molten plastic with the method according to any of the preceding claims to crack the plastic; and obtaining oil by distillation of cracked product from the heated plastic. 12. Olie die verkregen kan worden met de werkwijze volgens een van de conclusies 1 tot en met 11.12. Oil obtainable by the method according to any one of claims 1 to 11. 13. Warmtewisselsysteem, waarbij het warmtewisselsysteem omvat: - een tank voor gesmolten zout om met gesmolten zout te worden gevuld;13. Heat exchange system, wherein the heat exchange system comprises: - a molten salt tank for filling with molten salt; - een verhitter die is ingericht om warmte aan de tank voor gesmolten zout te verschaffen en om gesmolten zout te doen smelten; - ten minste één warmtewisselaar, die vloeistof-gekoppeld is aan de tank voor gesmolten zout; - een pomp die is ingericht om het gesmolten zout naar de ten minste één warmtewisselaar te pompen; waarbij de ten minste één warmtewisselaar een circulatiepomp omvat die is ingericht om het gesmolten zout door de warmtewisselaar te pompen en een regelklep die is ingericht om de temperatuur van het gesmolten zout in de warmtewisselaar te reguleren.- a heater arranged to provide heat to the molten salt tank and to melt molten salt; - at least one heat exchanger fluidly coupled to the molten salt tank; - a pump designed to pump the molten salt to the at least one heat exchanger; wherein the at least one heat exchanger comprises a circulation pump designed to pump the molten salt through the heat exchanger and a control valve designed to regulate the temperature of the molten salt in the heat exchanger. 14. Warmtewisselsysteem volgens conclusie 13, waarbij de tank voor gesmolten zout via vloeistofleidingen in vloeistofverbinding staat met de warmtewisselaar en de vloeistofleidingen schuin aflopen om de warmtewisselaar door zwaartekracht te draineren van het gesmolten zout.The heat exchange system of claim 13, wherein the molten salt tank is in fluid communication with the heat exchanger via fluid lines and the fluid lines are sloped to drain the heat exchanger of the molten salt by gravity. 15. Warmtewisselsysteem, waarbij het warmtewisselsysteem het volgende omvat: - een eerste doorgang voor gesmolten kunststof, - een tweede doorgang voor vloeibaar warmteoverdrachtsmedium van gesmolten zout, die in warmte-uitwisseling staat met de eerste doorgang; waarbij het warmtewisselsysteem gesmolten kunststof in de eerste doorgang en gesmolten zout in de tweede doorgang bevat.15. Heat exchange system, wherein the heat exchange system comprises: - a first passage for molten plastic, - a second passage for liquid heat transfer medium of molten salt, which is in heat exchange with the first passage; wherein the heat exchange system contains molten plastic in the first passage and molten salt in the second passage. 16. Installatie voor de omzetting van kunststof naar chemicaliën, omvattende: een aanvoer van kunststofimateriaal, een kunststofsmelter, bij voorkeur een extruder, een warmtewisselsysteem volgens een van de conclusies 13-15, en een destillatiekolom.16. Installation for the conversion of plastic into chemicals, comprising: a supply of plastic material, a plastic melter, preferably an extruder, a heat exchange system according to any one of claims 13-15, and a distillation column.