WO2005097448A1

WO2005097448A1 - A method and a plant for continuous processing waste plastic materials into a hydrocarbon mixture

Info

Publication number: WO2005097448A1
Application number: PCT/PL2004/000076
Authority: WO
Inventors: Remigiusz Eliasz; Miroslaw Starczewski; Stanislaw Wojtasik; Marek Moczynski; Stanislaw Cwigon
Original assignee: Remigiusz Eliasz; Miroslaw Starczewski; Stanislaw Wojtasik; Marek Moczynski; Stanislaw Cwigon
Priority date: 2004-04-06
Filing date: 2004-10-01
Publication date: 2005-10-20
Also published as: PL367011A1

Abstract

A method for continuous processing waste plastic materials, particularly polyole fins, into the form of hydrocarbon mixture, wherein waste plastic materials are liquefied, subjected to the thermal transformation without a catalyst or to thermocatalytic transformation, and gaseous products are condensed. A method is characterized in that the feed of waste plastic materials is introduced to the exchanger (4), the transformation process is conducted as a continuous process in the exchanger (4) stabilizer (5) assembly, said process of feed melting and optionally the partial evaporation are conducted in the exchanger (4), and the process of the ultimate evaporation of a free-flowing molten feed mass from the exchanger is conducted in the stabilizer (5), while gaseous evaporation products are directed to the separator (6), and optionally a portion of heavy products is recycled to the exchanger (4), and the volatile final products from the separator are condensed. The invention provides also a plant to practice the method of the invention.

Description

A METHOD AND A PLANT FOR CONTINUOUS PROCESSING WASTE PLASTIC MATERIALS INTO A HY DROCARBON MIXTURE

5 The invention provides a method for continuous processing of waste plastic materials, particularly polyolefins, into the form of a high quality liquid hydrocarbon mixture. The method provides an industrial process of continuous thermal or thermocatalytic transformation of waste plastic materials. The invention also provides a plant for continuous processing plastics according to the method of the present invention. 10 Polish Patent Application No P 336773 discloses a method for processing waste plastic materials, comprising a thermal or catalytic cracking of waste plastic materials in the presence of waste catalysts of the fiuidized bed catalytic cracking or natural alumino- silicates in a reactor, while gaseous and liquid cracked products just after the cracking process are directed to the evaporator, where they are mixed with hydrogen gas and evapo- 15 rated, and then the gas- vapour mixture is introduced directly to a hydrogenation reactor. In the reactor, olefins contained in the hydrogen-hydrocarbon feed are hydrogenated, with the use of some typical hydrogenation catalysts, i.e. palladium or platinum on solid supports, tungsten-nickel and molybdenum-nickel on solid supports. Polish Patent Application No P 339821 disclose a method for manufacturing ali- 20 phatic hydrocarbons from a preselected blend of waste plastic materials, particularly disposable plastic containers. A method for manufacturing aliphatic hydrocarbons from a mixture of waste plastic materials in a reaction of thermal decomposition comprises bulk heating a mixture of waste thermoplastic materials, preferably after separating a water- unsinkable fraction and after an optional initial purification, to the temperature of 320 - 25 400°C under the pressure of 0,008-3,5 MPa, followed by distillation under the same conditions, and a product thus obtained is optionally separated and purified by a known method. Polish Patent Application No P 345291 disclose a method for processing waste plastic materials by cracking and a reactor for cracking waste plastic materials. A method comprises directing a waste, comminuted plastic materials with a cracking catalyst from an 30 extruder or other feeder means to the lower part of a reactor, where at 380-500°C the cracking of polymer chains of the plastic material and forming of lower hydrocarbons takes place. From the reactor, the hydrocarbons are directed to an air cooler, than the vapour-gas mixture enters a separator, from where the liquid fraction is recycled to the cracking process in the reactor, and the vapour phase is directed to a water cooler. After condensation, the products are fed to a separator, from where the gaseous phase is directed to a cracking gas tank, whereas the liquid phase is separated in a still into a petrol fraction and a fuel oil. The reactor of the patent application is characterized in that its upper part comprise a pipe exchanger connected to burners supplied with gas or heater oil, and a' device to measure the molten plastic material in the reactor is arranged above the exchanger. In the lower part of the reactor wall, below the heat exchanger, an inspection chamber is placed. Polish Patent No PL 99488 disclose an installation for continuous processing of waste plastic materials, comprising a melting pot, a reactor for thermal decomposition provided with an agitator and a feeding pump, a product vessel provided with a cooler, and a burner, which installation comprises a cooling tank to cool the product before introducing it to the burner. In known methods of processing waste plastic materials the catalytic transformation takes place exclusively in the reactor. The heat exchanger provided in the upper part of the reactor (according to the P 345291 patent) serves to enhance the heat exchange between flue gases and the material being cracked, thus lowering the energy consumption. The main cracking reaction proceeds according to the invention in the upper part of the reactor, in the internal heat exchanger. It is thus necessary to supply the lower part of the reactor with a molten raw material heated to the temperature higher than 250°C. The raw material is prepared in a screw extruder with the multi-section heating. Numerous known methods requires the batch to be initially comminuted, purified, and often also fractionated, supplied with hydrogen gas or blended with depolymerisation enhancers. The object of the present invention is a method for continuous processing of waste plastic materials and a plant to conduct the method, devoid of the above drawbacks, and obtaining hydrocarbons with the specified chain length range. A method for continuous processing waste plastic materials, particularly polyole- fins, into the form of hydrocarbon mixture, wherein waste plastic materials are liquefied, subjected to thermal or thermocatalytic transformation, and gaseous products are condensed, is characterized in that the transformation process is conducted as a continuous process in an exchanger-stabilizer system, wherein the process of melting the feed and optional partial evaporation is conducted in the exchanger, and the main process of evaporation of the molten feed material flowing freely down from the exchanger is carried in the stabilizer. The gaseous evaporation products are fed to the separator, from where a part of heavy fractions is optionally recycled to the exchanger, and volatile final products from the separator are condensed. Preferably the feed of waste plastic materials is fed to the exchanger as a com- pressed unit batch of the plastic material, to assure hermetic conditions of the feeding operation. Preferably the temperature in the exchanger is kept at 300-550°C. Preferably the transformation process is conducted in the presence of a catalyst, preferably metal oxides, and most preferably Al₂O₃ or Al/Al₂O₃. Preferably the catalyst is delivered periodically with the waste feed, preferably at a level of 2 weight percent based on the feed. Preferably, in the stabilizer, a constant level of a liquid mass is maintained, most preferably at a level of about 1/3 of the total volume. Preferably the transformation process is conducted under the atmospheric pressure. Preferably, in the stabilizer, the temperature of the reaction mass is maintained in the range of 300°C to 490°C. Preferably the process in the stabilizer is conducted in an atmosphere of volatile hydrocarbons solely. Preferably the fractions of hydrocarbons are separated in the separator just down- stream the stabilizer's outlet. Preferably, the heavy fractions from the separator are recycled to the exchanger. Preferably, the heavy paraffin fractions from the separator are recycled to the exchanger with hydraulic means. Preferably the temperature in the separator is maintained in a range of 250°C to 280°C to gather the petrol-oil fraction. Preferably the temperature in the separator is maintained at a constant level with simultaneous changes in the amount of gas flow. Preferably the temperature in the separator is maintained by supplying an inert gas, the most preferably nitrogen. Preferably, the volatile final product downstream of the separator is condensed to the temperature not exceeding 50°C. Preferably, the waste solids and impurities are periodically discharged from the stabilizer, the most preferably by means of the outlet system with screw receivers. The method of the invention is mainly designed to process the waste polyoiefins. The feed introduced into the assembly of equipment comprising a processing line can comprise, e.g. the municipal waste without any pretreatment. There is no need to make the waste liquid before entering the processing line of the process of thermal transformation. The products of the process of the invention can be obtained either as a mixture of full-range hydrocarbon fractions, or as a required hydrocarbon fractions - light (petrol-oil) fractions and heavy (paraffin) fractions. Heavy paraffin fractions can be collected as a separate product or recycled to the pyrolysis process to further shorten hydrocarbon chains. The final products of the inventive plant are liquid hydrocarbons after their condensation on the passage through sequential portions of a double jacketed tubing with temperature controlled by means of process water. A plant for continuous processing of waste plastic materials into the form of the hydrocarbon mixture of the invention comprises a feeder system for the feed of waste plastic materials, a heating system, a reaction system, a cooling system, inlet and outlet conduits with an additional function of vapour temperature stabilizing, condensing and liquid product transport, tanks and control system instrumentation. The plant is characterized in that the feeder system is connected to the heat exchanger, the reaction system comprises the exchanger-stabilizer assembly, the separator is arranged directly downstream of the stabilizer and connected with an input conduit to the stabilizer and the product tank and with an output conduit to the exchanger. Preferably, the exchanger of the plant is the shell-and-tube heat exchanger. Preferably, the exchanger comprises a system of horizontal-slant heating tubes. Preferably, the stabilizer has a bottom in a form of at least two multiplicities of a cylinder truncated with a plane parallel to a cylinder's axis. Preferably, the stabilizer's bottom contain at least one allotted pipe to discharge the wastes by means of screw receivers. Preferably, the stabilizer performs simultaneously the function of a feed homo- genizer. Preferably, the stabilizer has at least one revolving agitator, to homogenize the liq- uid contents of the stabilizer and to assist in removing solid wastes. Preferably, the stabilizer has at least one side outlet to discharge the volatile final product into the piping connected to the separator. Preferably as the separator the plant comprise a thermal-mechanical separator. Preferably, the separator has a cuboid shape with a hopper-shaped bottom. Preferably, there is at least one baffle in a perpendicular arrangement against the bottom inside the separator. Preferably the feeder system contains a two-stage pneumatic feeder press. Preferably, the axle of the press assembly initial feed is perpendicular to the axle of the press assembly main feed, to make the system hermetic. Preferably the exchanger and the stabilizer are arranged vertically above a furnace chamber. Preferably, the heating system comprises a source of heat, a mixing chamber to mix air with flue gases, and a furnace chamber. Preferably, the conduits for hydrocarbon vapour transport comprise a double jacketed tubing. For example, the main elements of the heating system are: a source of heat as an oil, gas or solid fuel (e.g. the biomass) burner and a mixing chamber, where air is mixed with flue gases from the burnt fuel to acquire some thermal energy. There is a furnace chamber below the reaction assembly to provide the thermal stabilization of the gas-air mixture. In the shell-and-tube exchanger the state of the feed in between the pipes is altered to the liquid state (melting) and the optional initial gasification of said liquid is conducted.

The stabilizer receives gases and a liquid from the exchanger to conduct the final evapora- tion and to promote permeation of vapors towards the separator. The thermal-mechanical separator carries out a separation of different hydrocarbon vapour fractions. The input and output conduits comprise transport pipelines. The pipelines dedicated for transporting hydrocarbon vapors may be, for example, made as a double jacketed tubing. The pipelines provide also a vapour temperature stabilization, condensation thereof and liquid product transport. A plant may be equipped with an intermediate tank, where the product is homogenized and the liquid hydrocarbon temperature stabilized. Scrubbers, water safety devices and other gas plant elements serve to receive the gaseous fraction (hydrocarbons to C5) eventually returned to the furnace chamber and to protect the stabilizer-exchanger assembly against a pressure build-up. The paraffin is transported through the transport piping for liquid hydrocarbons, from the intermediate tank do the storage tank (pipeline, pump, fittings). The plant contains technological water (heating and cooling) systems and control-measurement and regulation means to control the process. The invention is illustrated in more detail in an embodiment and on attached drawings, wherein Fig. 1 illustrates the arrangement of the plant, Fig. 2 shows a schematic diagram of the process, Fig. 3 shows a view of exchanger piping, Fig. 4 shows a view of the shape of the stabilizer's bottom, and Fig. 5 shows a view of the separator. Fig.l illustrates schematically the arrangement of the plant of the invention. The whole equipment is arranged on a densified surface 1. The heat source comprises the mixing chamber 8, supplied in thermal energy from the conventional burner supplied with any specified kind of fuel. Hot gases from the furnace chamber 3 pass along the conduits 7 to heat the stabilizer 5 and the exchanger 4 arranged above said stabilizer, and then flow out through flue 17. The exchanger 4 and the stabilizer 5 make one complex assembly in a jacket with thermal insulation 18. In the upper part of the exchanger 4 there is the feeder press 10 for the feed, with a loading platform 9. Products of the pyrolysis of the feed converted inside the stabilizer are directed to the hydrocarbon vapour separator 6, from where the heavy paraffin fractions can be returned to the upper part of the exchanger 4. From the separator 6 through the double jacketed tubing with coolers H, and through the volatile vapour condenser 14, the products of pyrolysis are directed to the intermediate tank 12 and through the pipeline 21 , to the storage tank 13 provided with a thermal insulation 19. The stabilizer 5 contains the screw waste outlet 22. The part of the plant comprising the tanks is separated from the reaction part with a refractory wall 2. The volatile but noncondensing hydrocarbons (up to C5) are discharged from the stabilizer 5 and the intermediate tank 12, by means of gas conduits to the gas cooler 15, and then to the scrubber 14, from where the volatile but noncondensing fractions are loaded through the water safety device to the furnace chamber and burnt. Fig. 2 illustrates schematically a simplified process diagram. The feed of waste plastic materials from the press K) is loaded to the exchanger 4, and flows after melting by virtue of gravity to the stabilizer 5. Gaseous products of pyrolysis from the stabilizer 5 are directed to the separator 6, then condensed in the cooler H and directed through the intermediate tank 2J, to the storage tank 13. Heavy paraffin fractions from the separator 6 can be returned to the exchanger 4. In one embodiment, the mixing chamber 8 comprise a cylinder-shaped chamber lined with the ceramic refractory mass and equipped with control elements to adjust the power consumption and inlet temperature. The shell-and-tube exchanger 4 as shown in an embodiment on Fig. 3 is a steel cuboid with the assembly of 30-60 interpenetrating horizontal-slant tubes 25 76-150 mm in diameter, made of boiler steel. The stabilizer 5 as shown in an embodiment on Fig. 4 is a cuboid with a profiled bottom comprising two profiled cylinder-shaped sheets 24 with the radius in the range of 100-700 mm and with allotted pipes to discharge the wastes by means of screw receivers 22. Mechanical agitators are arranged above the cylindrical bottom to homogenize the liquid contents of the stabilizer and to enhance the solid waste removal. Double jacketed casings of the bearings are provided to constantly cool them.0 There is a slot collector on one of the side walls of the stabilizer to receive hydrocarbon vapors. The thermal-mechanical separator 6 as shown in an embodiment on Fig. 5 is a cuboid 26 with the hopper-shaped bottom 27, -with internal steel baffles 28. The separator is connected with gas nozzles 29 to help maintain the temperature by mixing with cold nitro-5 gen, to assure liquefaction of a proper fraction of heavy hydrocarbons. Paraffins recovered from the separator hopper are recycled to the shell-and-tube exchanger. The inventive process of the thermal or thermocatalytic transformation is carried out continuously in a following manner. The pyrolysis process is supplied with thermal energy of hot gases generated by o burning sawdust (sawdust gasification) with the generated power of 150 - 200 kW. An operator of the plant manually charges a batch of feed to the hopper of the press 10 in a quantity of about 3-4 kg with a frequency resulting from the rate of melting the foil in the exchanger 4, i.e. about 60-70 kg per hour. The feed in the exchanger 4 is then melted in a soaked space of the exchanger and through the direct contact with the pipes of the ex-5 changer (of the temperature up to 550°C). The molten polyolefin mass flows by gravity to the stabilizer 5, with partial evaporation. In the stabilizer 5 at 350 - 490°C, the hydrocarbons resulting from the process are ultimately evaporated. In a thermocatalytic process, catalyst is charged simultaneously with the feed through the press 10. There is a possibility to charge catalyst in larger batches each hour, the amount and frequency of charging being0 determined individually depending on the kind of the polyolefin feed. Hydrocarbon vapors at about 350°C are directed through the vapour collector to the thermo-mechanical separator 6, where heavy hydrocarbon fractions are liquefied. In the separator, the effect of condensation of particular vapour fractions at a stable, precisely determined temperature with a simultaneous change in gas flow rate is utilized. The hereinabove described plant should be run at a constant separator temperature of 250 - 280°C. The temperature is stabilized by means of introducing nitrogen gas to the hot hydrocarbon vapors. The isolated heavier paraffin fractions from the separator hopper are pumped again to the space of the upper part of the exchanger 4. The volatile fractions from the separator are transported by pipelines 20, where by virtue of continuous cooling still more and more light hydrocarbon fractions are condensed. The liquid hydrocarbons at the temperature below 50°C are collected in the intermediate tank 12, where a homogenization takes place. The hydrocarbons are periodically pumped by pipelines 21 to the storage tank 13. The final product of the above- described plant is taken away as a liquid by tank-trucks for subsequent processing by refin- eries. The solid residues, either from the carbonization process, or occurring in the impure feed, are periodically removed, e.g. once a day, by means of screw receivers. The purification process takes place during a normal operation of the plant, except of feed charging to the exchanger being temporarily suspended. The method and the plant of the present invention are solutions put into practice on an industrial scale. According to the invention, the process of the thermal or thermocatalytic transformation proceeds without an interruption in the exchanger-stabilizer assembly. The thermal or thermocatalytic transformation in the reaction means needs neither high pressure nor supply of hydrogen.. The feed does not require any purification, fractionation or initial melting. The process utilizes only one ecological heat source to provide heating of all installation in the processing line and multiple use of heat in a closed system. A high quality final product and a potentially useful by-product (a solid mass comprised mostly of carbon of an overall calorific value of about 20 MJ/kg) is obtained.

Claims

What is claimed is:- 1. A method for continuous processing waste plastic materials, particularly polyole- fins, into the form of hydrocarbon mixture, wherein waste plastic materials are liquefied, subjected to thermal transformation without a catalyst or to thermocatalytic transformation, and gaseous products are condensed, characterized in that feed of waste plastic materials is introduced to the exchanger (4), the transformation process is conducted as a continuous process in the exchanger (4) - stabilizer (5) assembly, said process of the feed melting and optionally the partial evaporation is conducted in the exchanger (4), and the process of the ultimate evaporation of a free-flowing molten feed mass from the exchanger is conducted in the stabilizer (5), while gaseous evaporation products are directed to the separator (6), and optionally a portion of heavy products is recycled to the exchanger (4), and the volatile final products from the separator are condensed.

2. A method of claim 1, characterized in that the feed of waste plastic materials is introduced to the exchanger as a compressed unit batch of the plastic material.

3. A method of claim 1, characterized in that the temperature in the exchanger is kept at 300-550°C.

4. A method of claim 1, characterized in that the transformation process is conducted in the presence of catalyst.

5. A method of claim 4, characterized in that metal oxides are used as catalysts.

6. A method of claim 5, characterized in that as a catalyst Al₂O₃ or Al/Al₂O₃ are used.

7. A method of claim 4, characterized in that the catalyst is charged with the waste feed material.

8. A method of claim 4, characterized in that the catalyst is used in an amount up to 2% by weight of the feed.

9. A method of claim 1, characterized in that in the stabilizer, a constant level of a liquid mass is maintained.

10. A method of claim 9, characterized in that in the stabilizer, a constant level of a liquid mass is maintained at the level of about 1/3 of the volume thereof.

11. A method of claim 1, characterized in that the thermal or thermocatalytic transformation process is conducted under the atmospheric pressure.

12. A method of claim 1, characterized in that in the stabilizer the temperature of the reaction mass is maintained in the range of 300°C do 490°C.

13. A method of claim 1, characterized in that the process in the stabilizer is conducted solely in the volatile hydrocarbon atmosphere.

14. A method of claim 1, characterized in that the fractions of hydrocarbons are separated in the separator directly downstream of the stabilizer.

5 15. A method of claim 14, characterized in that the heavy fractions from the separator are recycled to the exchanger.

16. A method of claim 15, characterized in that the heavy paraffin fractions from the separator are recycled to the exchanger by a hydraulic method.

17. A method of claim 1, characterized in that, in the separator, the temperature is o maintained in a range of 250°C do 280°C.

18. A method of claim 1, characterized in that, in the separator, the constant temperature is maintained with the simultaneous change in gas flow rate.

19. A method of claim 1, characterized in that the temperature in the separator is maintained by means of introducing an inert gas.5

20. A method of claim 19, characterized in that the temperature in the separator is maintained by means of introducing nitrogen.

21. A method of claim 1, characterized in that the volatile final product downstream of the separator is condensed to the temperature of at least 50°C.

22. A method of claim 1, characterized in that the residual solid waste products are o periodically removed along with impurities from the stabilizer.

23. A method of claim 22, characterized in that the waste products are removed by means of the outlet system with screw receivers.

24. A plant for continuous processing of the waste plastic materials into the form of hydrocarbon mixture, comprising a feeder system to introduce the feed of the waste plastic5 materials, a heating system, a reaction system, a cooling system, conduits for input and output with an additional function of vapour temperature stabilizing, condensing and liquid product transport, tanks and control system instrumentation, characterized in that the feeder system is connected to the exchanger (4), the reaction system comprises the exchanger (4) - stabilizer (5) assembly, separator (6) is provided directly downstream of the0 _. stabilizer (5) and connected with an input conduit to the stabilizer (5) and product tank, and with an output conduit to the exchanger (4).

25. A plant of claim 24, characterized in that the exchanger (4) comprise the shell- and-tube exchanger.

26. A plant of claim 24, characterized in that the exchanger (4) comprises a system of horizontal-slant heating tubes (25).

27. A plant of claim 24, characterized in that the stabilizer (5) has a bottom in a form of at least two multiplicities of a cylinder (24) truncated with a plane parallel to a cylinder's axis.

28. A plant of claim 24, characterized in that the stabilizer's (5) bottom contain at least one allotted pipe (22) to discharge the wastes by means of screw receivers.

29. A plant of claim 24, characterized in that the stabilizer (5) performs simultaneously the function of a feed homogenizer.

30. A plant of claim 24, characterized in that the stabilizer (5) has at least one revolving agitator, to homogenize the liquid contents of the stabilizer and to assist in removing solid wastes.

31. A plant of claim 24, characterized in that the stabilizer (5) has at least one side outlet to discharge the volatile final product into the receiving pipeline connected to the separator.

32. A plant of claim 24, characterized in that as the separator (6) the plant comprise a thermal-mechanical separator.

33. A plant of claim 24, characterized in that the separator (6) has a cuboid shape (26) with a hopper-shaped bottom (27).

34. A plant of claim 24, characterized in that inside the separator (6) there is at least one baffle (28) in a perpendicular arrangement against the bottom.

35. A plant of claim 24, characterized in that the feeder system contains a two-stage pneumatic feeder press (10).

36. A plant of claim 35, characterized in that the axle of the press assembly initial feed (10) is perpendicular to the axle of the press assembly main feed.

37. A plant of claim 24, characterized in that comprises a source of heat, a mixing chamber to mix air with flue gases (8) and a furnace chamber (3).

38. A plant of claim 24, characterized in that exchanger (4) and the stabilizer (5) are arranged vertically above a furnace chamber (3).

39. A plant of claim 24, characterized in that the conduits for hydrocarbon vapour transport comprise a double jacketed tubing.