METHOD FOR PROCESSING PLASTIC WASTE PYROLYSIS GAS

Abstract

The present disclosure relates to methods for processing plastic waste pyrolysis gas, such as methods wherein clogging of the systems used in the method is avoided or at least alleviated.

Claims

1. A method for processing plastic waste pyrolysis gas, the method comprising: a) providing a plastic waste pyrolysis gas stream wherein a temperature of the plastic waste pyrolysis gas stream is 300-650° C.; b) transferring the plastic waste pyrolysis gas stream to a condensing means, wherein a temperature in the condensing means is 100-300° C. to produce a condensed fraction and a gaseous fraction of the plastic waste pyrolysis gas, c) continuously wiping and/or scraping inner surfaces of the condensing means; d) separating the gaseous fraction and the condensed fraction to yield a first liquid product stream and a gaseous product stream; and e) transferring the first liquid product stream to a collecting means via a line at a temperature above 100° C.

2. The method according to claim 1, comprising: collecting the first liquid product stream.

3. The method according to claim 1, comprising: cooling the gaseous product stream of step d) to 10-50° C. to yield a second liquid product stream and a gaseous stream.

4. The method according to claim 3, comprising: collecting the second liquid product stream.

5. The method according to claim 1, wherein a temperature of the plastic waste pyrolysis gas stream is 450-500° C.

6. The method according to claim 1, wherein temperature in the condensing means is 175-225° C. to produce the condensed fraction and the gaseous fraction of the plastic waste pyrolysis gas.

7. A method according to claim 1, comprising: transferring the first liquid product stream to the collecting means via a line at a temperature of between 150 and 250° C.

8. The method according to claim 3, comprising: cooling the gaseous product stream of step d) to 20-40° C. to yield the second liquid product stream and the gaseous stream.

9. The method according to claim 2, comprising: cooling the gaseous product stream of step d) to 20-40° C. to yield the second liquid product stream and the gaseous stream.

10. The method according to claim 9, comprising: collecting the second liquid product stream.

Description

BRIEF DESCRIPTION OF FIGURES

[0018] The exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying FIGURE, in which

[0019] FIG. 1 shows an exemplary non-limiting system suitable for processing plastic waste pyrolysis gas according to an embodiment of the present invention.

DESCRIPTION

[0020] The present invention is related to processing plastic waste pyrolysis gas such that clogging of a system used in the method is avoided or at least alleviated.

[0021] FIG. 1 shows an exemplary system 100 suitable for use in a method according to an embodiment of the present invention. According to the embodiment shown in the FIGURE, a plastic waste pyrolysis gas stream (A) is transferred a condensing means 101. Temperature of the plastic waste pyrolysis gas stream is typically 300-650° C., preferably 450-500° C. Temperature of the condensing means is below the temperature of the plastic waste pyrolysis gas stream. Exemplary temperature of the condensing means is 100-300° C., preferably 175-225° C.

[0022] According to this embodiment the condensing means comprises wiping means and/or scraping means 102 adapted to wipe and/or scrape mechanically the inner surfaces of the condensing means 101. Exemplary suitable condensing means are wiped film condensers and scraped surface heat exchangers. These condensing means are basically jacketed tanks, with a rotor inside which continuously wipes, and scrapes any solidifying material from the walls of the condensing means. This prevents the formation of thick deposits on the condenser walls and thus prevents clogging of the apparatus.

[0023] The condensing means 101 is operating at temperature which is lower than the temperature of the plastic waste pyrolysis gas stream. Accordingly, the heaviest parts of the pyrolysis gas are condensed, and a heavy component depleted gaseous fraction is produced. Separation of the condensed fraction and the gaseous fraction yields the first liquid product stream (D1) and a gaseous product stream (E1).

[0024] The first liquid product stream (D1) i.e. the heavy fraction may be transferred via line 103 to a collecting means 104 as a heavy product. In order to avoid blockages, the line 203 is preferably kept at temperatures above 100° C. more preferably between 150° C. and 250° C. The desired temperature range can be obtained by insulating the line and/or using one or more heating means.

[0025] According to a preferable embodiment the gaseous product stream is directed via line 105 to a second condensing means 106. This condensing means is typically a traditional heat exchanger. According to an exemplary embodiment, temperature of the gaseous fraction is decreased in the condensing means 106 to 10-50° C., preferably 20-40° C. The cooling produces condensed liquid and non-condensable gases. No fouling or clogging is expected within the line 105 and in the condensing means 106 as the majority of the heavy components have been removed. After cooling, the condensed liquid is separated from the non-condensable gases (E2) to yield a second liquid product stream (D2). It can be transferred in a collecting means such as a tank 107 as a light product. The non-condensable gases may be directed to combustion or to one or more further collecting means. Yield and composition of the light product is dependent mainly on the nature of the waste plastic, the pyrolysis conditions and the condensing temperatures. The non-condensable gases may be directed to combustion or to one or more further collecting means.

Example 1

[0026] The process was simulated with Aspen plus software. The main part of the pyrolysis gas was modelled using pseudo components, and the light ends was modelled using real components. The pseudo components were estimated using experimentally measured distillation curve and density from crude plastics pyrolysis oil. The used density was 809.8 kg/m.sup.3, and true boiling point (TBP) distillation curve is presented in table 1.

TABLE-US-00001 TABLE 1 Recovered mass (%) Temperature (C. °) 2 36.0 5 68.6 10 97.4 30 171.9 50 236.0 70 316.0 90 430.4 95 474.3 100 582.4

[0027] The amount and composition of light ends were estimated from literature (Williams et al., Energy & Fuels, 1999, 13, 188-196; Williams et al., Recources, Concervation and Recycling, 2007, 51, 754-769). Mass ratio of lights and pseudo components was 0.27, and the composition of the lights is presented in Table 2.

TABLE-US-00002 TABLE 2 Component wt-% methane 36.3 ethene 2.2 ethane 28.9 propene 4.7 propane 19.9 butene 1.5 butane 6.7

[0028] The thermodynamic model used in the simulations was Braun K-10, and it was assumed that there was one ideal separation stage in the condensing unit.

[0029] Stream of plastic waste pyrolysis gas, having a pressure of 95 kPa(a), a temperature of 500° C., and average molar weight of 69.2 g/mol and a mass flow of 20 kg/h exited the reactor. It was allowed to enter a scraped film condenser, which was cooled by cooling oil. The scraper kept the heat exchange surfaces clean, and a partial condensation of the gas occurred. The product was collected from the bottom of the vessel. The temperatures of the products from this heat exchanger were adjusted to be 200° C. by adjusting the cooling oil temperature. The heat transfer coefficient for the metallic heat exchanger wall was 176 kW/m.sup.2° C.

[0030] The results from the simulations are presented in Table 3.

TABLE-US-00003 TABLE 3 Heat transfer Product LWP Time Fouling Pressure coefficient temperature condensed (h) (mm) drop (kPa) (kW/m.sup.2C.) (° C.) (wt-%) 0 0 0.09 176 200 41.6 5 0 0.09 176 200 41.6 15 0 0.09 176 200 41.6

Example 2

[0031] The process was simulated with Aspen plus software. The main part of the pyrolysis gas was modelled using pseudo components, and the light ends was modelled using real components. The pseudo components were estimated using experimentally measured distillation curve and density from crude plastics pyrolysis oil. The used density was 809.8 kg/m.sup.3, and true boiling point (TBP) distillation curve is presented in table 4.

TABLE-US-00004 TABLE 4 Recovered mass (%) Temperature (C. °) 2 36.0 5 68.6 10 97.4 30 171.9 50 236.0 70 316.0 90 430.4 95 474.3 100 582.4

[0032] The amount and composition of light ends were estimated from literature (Williams et al., Energy & Fuels, 1999, 13, 188-196; Williams et al., Recources, Concervation and Recycling, 2007, 51, 754-769). Mass ratio of lights and pseudo components was 0.27, and the composition of the lights is presented in Table 5.

TABLE-US-00005 TABLE 5 Component wt-% methane 36.3 ethene 2.2 ethane 28.9 propene 4.7 propane 19.9 butene 1.5 butane 6.7

[0033] The thermodynamic model used in the simulations was Braun K-10, and it was assumed that there was one ideal separation stage in the condensing unit.

[0034] Stream of plastic waste pyrolysis gas, having a pressure of 95 kPa(a), a temperature of 500° C., and average molar weight of 69.2 g/mol and a mass flow of 20 kg/h exited the reactor. It was allowed to enter a cooling oil cooled scraped film condenser, with the scraping turned off. This resulted in partial condensation and the liquid product was collected from the bottom of the vessel. As the condensed products attached to the heat exchanging surfaces were not continuously scraped off, a deposit build-up on the walls resulted.

[0035] The temperatures of the products from this heat exchanger were adjusted by the cooling oil temperature to be initially 200° C. However, as the deposit build up, the heat transfer decreased and less condensation occurred. This decreased the amount of condensed product. Fouling rate of 1 mm/h was assumed and the heat transfer coefficients for the metallic heat exchanger wall and the fouling layer were 176 kW/m.sup.2° C. and 0.083 kW/m.sup.20° C., respectively.

[0036] The results from the simulations are presented in Table 6.

TABLE-US-00006 TABLE 6 Heat transfer Product LWP Time Fouling Pressure coefficient temperature condensed (h) (mm) drop (kPa) (kW/m.sup.2C.) (° C.) (wt-%) 0 0 0.09 176.0 200.0 41.6 0.5 0.5 0.09 85.6 234.3 36.8 1 1 0.09 56.6 272.2 31.6 2.5 2.5 0.10 28.0 347.0 21.2 5 5 0.13 15.2 402.8 13.5 10 10 0.28 8.0 444.1 7.7

[0037] As can be seen from Table 3, the performance of the heat exchanger remains unchanged over time, when the heat exchange surfaces are kept clean using scraping. On the other hand, it can be observed from Table 6 that the fouling has a significant effect on the performance of the heat exchanger if the fouled layer is left untouched.

[0038] The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims.