DE102022116573B4 - Reactor unit for plastic thermolysis, plastic thermolysis plant and methods for its operation - Google Patents

Abstract

Reactor unit for plastic thermolysis, comprising
- a melting reactor (1) for melting plastic waste (4) introduced into the melting reactor (1) and for receiving the plastic melt (5) formed from the plastic waste (4),
- a pre-evaporator (2) for receiving and partially evaporating a pre-evaporator liquid (7), as well as
- a post-evaporator (3) for receiving and residual evaporation of a post-evaporator liquid (8), wherein
- the melting reactor (1) has a melting agitator (13) driven by a melting agitator drive (12) for circulating and mixing the polymer melt (5),
- the melting reactor (1) is connected to the pre-evaporator (2) via a pre-evaporator supply line (20), through which the pre-evaporator liquid (7) forming in the melting reactor (1) in the area of the liquid level of the plastic melt (5) passes into the pre-evaporator (2),
- the pre-evaporator (2) is connected to the post-evaporator (3) via a post-evaporator supply line (21), through which the post-evaporator liquid (7) forming in the pre-evaporator (2) in the region of the liquid level of the pre-evaporator liquid (7) passes into the post-evaporator (2), and
- the pre-evaporator (2) has a pre-evaporator exhaust (28) and the post-evaporator (3) has a post-evaporator exhaust (29) through which gases and/or vapors (9) generated in the melting reactor (1), in the pre-evaporator (2) or in the post-evaporator (3) can be discharged from the reactor unit as valuable materials, characterized in that the reactor unit further comprises:
- a viscometer for determining the viscosity of the polymer melt (5) in the melting reactor (1), a controllable recirculation pump (15) and a controller (14) coupled to the viscometer and the recirculation pump (15) via signal lines (16), wherein the controller (14) is configured to control the delivery rate of the recirculation pump (15) as a function of the viscosity of the polymer melt (5), by means of the control provided by the controller (14) controlled return feed pump (15) to discharge a predetermined quantity of the pre-evaporator liquid (7) from the pre-evaporator sump (30) of the pre-evaporator (2) and/or the post-evaporator liquid (8) from the post-evaporator sump (31) of the post-evaporator (3) and introduce it into the polymer melt (5) in the melting reactor (1) as soon as the measured viscosity of the polymer melt (5) exceeds a predetermined maximum viscosity;
- a return line (38) connected to the return feed pump (15), wherein the return line (38) is connected to the pre-evaporator (2) for the discharge of pre-evaporator liquid (7) from the pre-evaporator sump (30) of the pre-evaporator (2) and/or to the post-evaporator (3) for the discharge of post-evaporator liquid (8) from the post-evaporator sump (31) of the post-evaporator (3);
- a return feed line (39) connected to the return feed pump (15) and extending into the melting reactor (1) for the quantity-controlled introduction of the pre-evaporator liquid (7) and/or post-evaporator liquid (8) conveyed via the return line (38) to the return feed pump (15) from an outlet opening of the return feed line (39) into the plastic melt (5).

Description

The invention relates to a reactor unit for plastic thermolysis, a plastic thermolysis plant containing the reactor unit, and a method for operating the reactor unit or the plastic thermolysis plant. These serve to obtain fractionated hydrocarbons from plastic waste.

Due to the ever-increasing amount of plastic waste worldwide, processes for converting plastic residues into industrially usable, recycled raw materials are rapidly gaining importance. These processes include those for obtaining fractionated, short-chain hydrocarbons from plastic residues through thermolysis. Such processes are used, among other things, in... JP H 08034978 A , CN 1284537 A or US 4 584 421 A described.

To carry out plastic thermolysis, the plastic waste is fed into a reactor where it is melted under anaerobic conditions, broken down into short-chain hydrocarbons, and vaporized. The short-chain hydrocarbons escaping as gas are removed from the reactor and condensed. These condensed hydrocarbons ultimately constitute the majority of the recyclable materials produced by this process.

A process-engineered and energy-efficient multi-stage process, in which the melting and evaporation processes take place in several reactors, is described. DE 10 2004 003 667 A1 or WO 2005/071043 A1 In the first reactor, the melting vessel or melting reactor, the plastic waste is introduced and melted, as in single-reactor processes. Unlike single-stage processes, a liquid phase is transferred to an evaporation vessel, the second reactor, where the majority of the evaporation takes place. A reheater, the third reactor, is connected to the evaporation vessel in the same manner and serves to evaporate any remaining liquid.

Out of DE 10 2013 205 996 A1 A similar three-stage process for the production of product oils is known, wherein a mixing vessel is connected to the second reactor, in which bottoms products from the second reactor and bottoms products from the third reactor are mixed and pumped back into the second reactor. This recirculation of the mixture makes it possible to subject the degradable bottoms products to the cracking process again in the second reactor, thus increasing the yield of product oil.

For homogenization, the process is carried out in the melting reactor according to the procedure according to WO 2005/071043 A1 The forming plastic melt is continuously circulated by means of a stirrer and thus homogenized. This stirring promotes the liquefaction and evaporation of the added plastic residues.

However, the power consumption of the agitator drive required to homogenize the polymer melt can vary considerably depending on the composition of the polymer residues used as starting material. Due to the in WO 2005/071043 A1 The multi-stage process described, i.e., by branching off the liquid phase, does achieve a more uniform power consumption; however, it results in an increase in the viscosity of the polymer melt.

Viscous polymer melts, in turn, require a particularly high-performance agitator drive. Another disadvantage of highly viscous polymer melts is that the reactions in the melting reactor proceed more slowly, ultimately impairing the efficiency of the overall process.

The object of the invention is to provide a reactor unit for a multi-stage process for plastic thermolysis, a plastic thermolysis plant containing the reactor unit, and a method for operating the reactor unit or the plastic thermolysis plant, which enable the fastest possible homogenization of the plastic melt in the melting reactor by means of stirring, wherein the agitator used for stirring the plastic melt can be operated with low and as uniform a power consumption as possible, regardless of the composition of the starting material consisting of plastic residues.

This problem is solved by a reactor unit for plastic thermolysis according to claim 1, a plastic thermolysis plant according to claim 5, and a method for operating them according to claim 9. Advantageous embodiments of the invention are described in the dependent claims.

According to the invention, the reactor unit comprises a melting reactor, a pre-evaporator, and a post-evaporator. In the melting reactor, also referred to as the first reactor, plastic waste is introduced during normal operation and melted in the absence of air in a generally known manner. The molten plastic in the melting reactor is circulated and mixed by means of a melting agitator within the melting reactor. The melting agitator has a melt stirrer drive, by means of which the stirrer of the stirrer is set into rotational motion.

Furthermore, the reactor unit comprises a pre-evaporator for receiving and partially evaporating a pre-evaporator liquid, and a post-evaporator for receiving and completely evaporating a post-evaporator liquid. The melting reactor is connected to the pre-evaporator via a pre-evaporator feed line, through which the pre-evaporator liquid forming at the liquid level of the polymer melt in the melting reactor flows into the pre-evaporator. The pre-evaporator is in turn connected to the post-evaporator via a post-evaporator feed line, through which the post-evaporator liquid forming at the liquid level of the pre-evaporator liquid in the pre-evaporator flows into the post-evaporator.

The pre-evaporator and the post-evaporator each have a pre-evaporator exhaust and a post-evaporator exhaust, respectively, through which gases and/or vapors generated in the melting reactor, the pre-evaporator, or the post-evaporator can be removed from the reactor unit as valuable materials. The bottom section of the pre-evaporator and the bottom section of the post-evaporator are referred to in the usual manner as the pre-evaporator sump and the post-evaporator sump, respectively.

According to the invention, the reactor unit comprises a viscometer for determining the viscosity of the polymer melt in the melting reactor, a controllable recirculation pump, and a controller coupled to the viscometer and the recirculation pump via signal lines. The controller is configured to control the flow rate of the recirculation pump as a function of the viscosity of the polymer melt.

To drain pre-evaporator fluid from the pre-evaporator sump and/or to drain post-evaporator fluid from the post-evaporator sump of the post-evaporator, a return line connected to the return feed pump is connected to the pre-evaporator and/or to the post-evaporator.

Furthermore, the reactor unit has a return feed line connected to the return pump and extending into the melting reactor. The pre-evaporator liquid and/or post-evaporator liquid, conveyed via the return line to the return pump, enters the return feed line after passing through the return pump and then flows into the melting reactor.

Within the melting reactor, the return feed line has an outlet opening through which the pre-evaporation liquid and/or the post-evaporation liquid from the return feed line enters the polymer melt and mixes with it. The introduction of the pre-evaporation liquid and/or the post-evaporation liquid into the polymer melt via the return feed line is volume-controlled by the dedicated return feed pump.

According to the inventive method for operating the reactor unit described above, the viscosity of the polymer melt is continuously measured during operation using a viscometer. The measured viscosity is then transmitted to the controller. Depending on the measured or transmitted viscosity, the controller regulates the feed pump such that a predetermined quantity of pre-evaporator liquid from the pre-evaporator sump and/or post-evaporator liquid from the post-evaporator sump is drawn off or diverted into the polymer melt in the melting reactor by means of the return feed pump as soon as the measured viscosity of the polymer melt exceeds a predetermined maximum viscosity.

The direct, volume-controlled introduction of the post-evaporation liquid and/or the pre-evaporation liquid into the polymer melt reduces the viscosity of the polymer melt by a limited amount. Consequently, the polymer melt is easier to mix and homogenize using the melt agitator. The resulting limitation of the power consumption of the melt agitator drive, in addition to reducing energy consumption, helps to prevent mechanical overloads or blockages of the melt agitator.

By selectively controlling the amount of post-evaporation liquid and/or pre-evaporation liquid added to the polymer melt, the viscosity can be maintained at an optimal level suitable for thermolysis. This explains the higher efficiency of polymer thermolysis when using the reactor unit or the viscosity-controlled operating process according to the invention.

Since the post-evaporator and/or pre-evaporator liquid produced for viscosity control in the multi-stage thermolysis process is specifically fed back into the polymer melt or metered in, the process remains free of contamination. The post-evaporator or pre-evaporator liquid thus serves as a process-integrated viscosity adjusting agent, which ultimately returns from the melting reactor to the pre- or post-evaporator.

Regularly adding small amounts of the post-evaporator liquid and/or the pre-evaporator liquid to the polymer melt is sufficient to reduce the viscosity to the desired level. Preferably, the post-evaporator liquid is used for viscosity control in the melting reactor.

To control the process based on viscosity, it can additionally be provided that additional plastic residues are introduced into the plastic melt as soon as the measured viscosity of the plastic melt falls below a predetermined minimum viscosity.

Preferably, the viscometer is the melt agitator itself, driven by the melt agitator drive. The melt agitator simultaneously functions as a measuring agitator; that is, the torque and/or rotational speed of the melt agitator drive are the measured variables for determining or characterizing the viscosity of the polymer melt.

The melting reactor can have a sedimentation chamber near the bottom for settling non-melting or difficult-to-melt residues. The sedimentation chamber can be emptied via a closable residue discharge channel.

According to one embodiment of the melting reactor, the melt agitator is arranged vertically within the melting reactor, above the sedimentation compartment. The outlet of the return feed line, which extends into the melting reactor, faces the melt agitator and is located between the sedimentation compartment and the melt agitator, with the outlet end of the return feed line aligned axially with the melt agitator. Introducing the pre-evaporator liquid and/or the post-evaporator liquid close to the agitator contributes to the rapid mixing of the pre-evaporator liquid and/or the post-evaporator liquid with the polymer melt.

Furthermore, the melt agitator may be designed to have a vertically oriented hollow shaft. The internal channel of the hollow shaft forms part of the return feed line; the outlet of the return feed line is located at the bottom end of the hollow shaft. In addition to the resulting close introduction of the pre-evaporator liquid and/or post-evaporator liquid into the polymer melt, this design of the melt agitator with the hollow shaft offers the advantage that no additional piping is required in the melt reactor.

The plastic thermolysis plant according to the invention comprises the described reactor unit. It is operated according to the viscosity-controlled process. In addition to the reactor unit, the plastic thermolysis plant also has a plastic feed unit connected to the melting reactor for feeding the plastic residues, as well as a fractionation unit with quench connected to the pre-evaporator exhaust and the post-evaporator exhaust for liquefying and fractionating the gases and vapors discharged from the reactor unit.

The plastic feed unit is preferably designed as a conveying and airlock system for pre-compacting the plastic residues and for introducing gas-free or low-gas plastic residues into the melting reactor. Such a conveying and airlock system is, for example, used in WO 2007/076744 A1 described.

Furthermore, the plastics thermolysis plant can include a separation stage connected to the melting reactor for separating substances that interfere with thermolysis from the reactor unit. A suitable separation stage is found in WO 2009/087080 A2 revealed.

• 1: eine schematische Schnittdarstellung einer ersten Ausführung der Reaktoreneinheit bzw. Kunststoffthermolyseanlage; und
• 2: eine schematische Schnittdarstellung einer zweiten Ausführung der Reaktoreneinheit bzw. Kunststoffthermolyseanlage.

The invention is explained in more detail below with reference to exemplary embodiments and the schematic drawings, wherein identical or similar features are designated with the same reference numerals. The drawings show:

• 1 : a schematic sectional view of a first version of the reactor unit or plastic thermolysis plant; and
• 2 : a schematic sectional view of a second version of the reactor unit or plastic thermolysis plant.

The one in 1 and the 2 The depicted reactor unit or plastic thermolysis plant comprises three reactors, namely the melting reactor 1, the pre-evaporator 2 and the post-evaporator 3.

The plastic waste 4 is fed into the melting reactor 1 via the plastic feed unit 10. The melting reactor 1 is heated by the melting reactor heater 17 to melt the plastic waste 4. The resulting plastic melt 5 is circulated by the melting agitator 13. The melting agitator 13 is driven by the melting agitator drive 12, which is an electric motor.

The sedimentation chamber 11 is located in the bottom section of the melting reactor 1, where the non-melting or difficult-to-melt residues 6 can settle. The residues 6 are removed from the melting reactor 1 via the residue discharge channel 18, through which the sedimentation chamber 11 can be emptied when the residue discharge valve 19 is open. The residue discharge valve 19 is symbolically represented as a valve, but could also be designed, for example, as a flap.

The pre-evaporator liquid 7, which forms in the melting reactor 1 in the polymer melt 5 and accumulates in the area of the liquid level of the polymer melt 5 due to its density, enters the pre-evaporator 2 via the pre-evaporator supply line 20. In addition to the pre-evaporator liquid 7, the gases and vapors 9 already generated in the melting reactor 1 also enter the pre-evaporator 2 via the pre-evaporator supply line 20.

After transferring from the melting reactor 1, the pre-evaporator liquid 7 fills the pre-evaporator 2, where it is heated and evaporated by the pre-evaporator heater 26. The resulting gases and vapors 9 are discharged via the pre-evaporator exhaust 28 – for example, to a fractionation unit (not shown) of the plastics thermolysis plant.

The pre-evaporator agitator 24, driven by the pre-evaporator agitator drive 22, circulates the pre-evaporator liquid 7 within the pre-evaporator 2. The bottom of the pre-evaporator 2, or the pre-evaporator liquid 7 contained within the pre-evaporator 2, forms the pre-evaporator sump 30. The pre-evaporator discharge channel 32 is connected to or extends into the pre-evaporator sump 30. The pre-evaporator 2 can be emptied as needed via the pre-evaporator discharge channel 32 by opening the pre-evaporator drain valve 34.

The post-evaporator liquid 8, which forms in the pre-evaporator 2 in the pre-evaporator liquid 7 and accumulates in the area of the liquid level of the pre-evaporator liquid 7 due to density, enters the post-evaporator 3 via the post-evaporator supply line 21.

After passing from the pre-evaporator 2, the post-evaporator liquid 8 fills the post-evaporator 3, where it is heated and evaporated by the post-evaporator heater 27. The resulting gases and vapors 9 are discharged via the post-evaporator exhaust 29, which merges with the pre-evaporator exhaust 28.

The secondary evaporator agitator 25, driven by the secondary evaporator agitator drive 23, circulates the secondary evaporator liquid 8 within the secondary evaporator 3. The bottom of the secondary evaporator 3, or the secondary evaporator liquid 8 contained within the secondary evaporator 3, forms the secondary evaporator sump 31. The secondary evaporator discharge channel 33 is connected to the secondary evaporator 3 in the area of the secondary evaporator sump 31 or extends into the secondary evaporator sump 31. The secondary evaporator 3 can be emptied as needed via the secondary evaporator discharge channel 33 by opening the secondary evaporator drain valve 35.

The return line 38 leading to the return feed pump 15 is connected on one side via the pre-evaporator return valve 36 to a branch of the pre-evaporator discharge channel 32 and on the other side via the post-evaporator return valve 37 to a branch of the post-evaporator discharge channel 33. The flow rate of the pre-evaporator liquid 7 from the pre-evaporator discharge channel 32 into the return line 38 is controlled by means of the pre-evaporator return valve 36. Similarly, the post-evaporator return valve 37 serves to control the flow rate of the post-evaporator liquid 8 from the post-evaporator discharge channel 33 into the return line 38. By adjusting or controlling the pre-evaporator return valve 36 and the post-evaporator return valve 37, it is determined whether only the pre-evaporator liquid 7, only the post-evaporator liquid 8, or a specific mixture of both is directed to the return feed pump 15.

The pre-evaporator liquid 7 and/or the post-evaporator liquid 8 is fed into the polymer melt 5 in the melting reactor 1 via the return feed pump 15 in a predetermined quantity or dosage. The added quantity of pre-evaporator liquid 7 and/or post-evaporator liquid 8 is rapidly distributed in the polymer melt 5, which is circulated by the stirring motion, thus reducing the viscosity of the polymer melt 5.

To determine the viscosity, the torque and rotational speed of the melt stirrer drive 12 are recorded and transmitted to the controller 14 via the signal line 16. The melt stirrer The drive unit 12 thus functions simultaneously as the drive unit for the melt stirrer 13 and as a viscometer. The return pump 15 is controlled by means of the controller 14, which in turn is connected to the return pump 15 via the signal lines 16.

The above descriptions apply to the two exemplary embodiments according to the 1 and the 2 identical. The two embodiments differ only in the design of the return feed line 39.

In the exemplary embodiment according to 1 The return feed line 39 is designed in the form of a guide cone or cone located above the sedimentation compartment 11. The outlet opening of the return feed line 39 is oriented counterclockwise, towards the melt agitator 13, and is located centrally in the area of the cone tip. The pre-evaporator liquid 7 and/or post-evaporator liquid 8 exiting the return feed line 39 into the polymer melt 5 is rapidly distributed in the polymer melt 5 by the proximity of the agitator.

In the exemplary embodiment according to 2 The pre-evaporation liquid 7 and/or the post-evaporation liquid 8 are introduced into the polymer melt 5 at a similar position – and thus with a comparable effect – above the (unlabeled) guide cone. In contrast to the embodiment according to the 1 The melt agitator 13 exhibits according to the 2 A melt agitator hollow shaft 40 is used, the inner channel of which forms part of the return feed line 39, namely the part ending in the polymer melt 5. The pre-evaporation liquid 7 and/or the post-evaporation liquid 8 are thus introduced directly from the interior of the melt agitator hollow shaft 40 into the polymer melt 5.

Reference symbol list

1

melting reactor

2

Pre-evaporator or pre-evaporation reactor

3

Post-evaporator or post-evaporation reactor

4

Plastic waste

5

Plastic melt

6

Residues

7

Pre-evaporator fluid

8

Post-evaporation fluid

9

Gases and vapors

10

Plastic entry unit

11

Sedimentation department

12

Melt agitator drive

13

Melt agitator

14

regulator

15

Return feed pump

16

Signal line

17

Melting reactor heating

18

Residue discharge channel

19

Residue discharge valve

20

Pre-evaporator supply line

21

Post-evaporator supply line

22

Pre-evaporator agitator drive

23

Post-evaporator agitator drive

24

Pre-evaporator agitator

25

Post-evaporator agitator

26

Pre-evaporator heater

27

Post-evaporator heater

28

Pre-evaporator extraction

29

post-evaporator extraction

30

Pre-evaporator sump

31

Post-evaporator sump

32

Pre-evaporator discharge channel

33

Post-evaporator discharge channel

34

Pre-evaporator drain valve

35

Post-evaporator drain valve

36

Pre-evaporator return valve

37

Post-evaporator return valve

38

Return line

39

Return feed line

40

Melt agitator hollow shaft

Claims (10)

Reactor unit for plastic thermolysis, comprising: - a melting reactor (1) for melting plastic waste (4) introduced into the melting reactor (1) and for receiving the plastic melt (5) formed from the plastic waste (4), - a pre-evaporator (2) for receiving and partially evaporating a pre-evaporator liquid (7), and - a post-evaporator (3) for receiving and partially evaporating a post-evaporator liquid (8), wherein - the melting reactor (1) is equipped by means of a melting a melt stirrer (13) driven by a stirrer drive (12) for circulating and mixing the polymer melt (5), - the melting reactor (1) is connected to the pre-evaporator (2) via a pre-evaporator inlet (20) through which the pre-evaporator liquid (7) forming in the melting reactor (1) at the liquid level of the polymer melt (5) passes into the pre-evaporator (2), - the pre-evaporator (2) is connected to the post-evaporator (3) via a post-evaporator inlet (21) through which the post-evaporator liquid (7) forming in the pre-evaporator (2) at the liquid level of the pre-evaporator liquid (7) passes into the post-evaporator (2), and - the pre-evaporator (2) has a pre-evaporator outlet (28) and the post-evaporator (3) has a post-evaporator outlet (29), The reactor unit is characterized in that the gases and/or vapors (9) generated in the melting reactor (1), the pre-evaporator (2), or the post-evaporator (3) can be removed from the reactor unit as valuable materials, and further comprises: - a viscometer for determining the viscosity of the polymer melt (5) in the melting reactor (1), a controllable recirculation pump (15), and a controller (14) coupled to the viscometer and the recirculation pump (15) via signal lines (16), wherein the controller (14) is configured to control the delivery rate of the recirculation pump (15) as a function of the viscosity of the polymer melt (5), and by means of the recirculation pump (15) controlled by the controller (14), a predetermined quantity of the pre-evaporator liquid (7) from the pre-evaporator sump (30) of the pre-evaporator (2) and/or the post-evaporator liquid (8) from the post-evaporator sump (31) of the post-evaporator. (3) to discharge and introduce into the polymer melt (5) in the melting reactor (1) as soon as the measured viscosity of the polymer melt (5) exceeds a predetermined maximum viscosity; - a reflux line (38) connected to the return feed pump (15), wherein the reflux line (38) is connected to the pre-evaporator (2) for discharge of pre-evaporator liquid (7) from the pre-evaporator sump (30) of the pre-evaporator (2) and/or to the post-evaporator (3) for discharge of post-evaporator liquid (8) from the post-evaporator sump (31) of the post-evaporator (3); - a return feed line (39) connected to the return feed pump (15) and extending into the melting reactor (1) for the quantity-controlled introduction of the pre-evaporator liquid (7) and/or post-evaporator liquid (8) conveyed via the return line (38) to the return feed pump (15) from an outlet opening of the return feed line (39) into the plastic melt (5). reactor unit after Claim 1 , characterized in that the viscometer is the melt stirrer (13) driven by means of the melt stirrer drive (12), wherein the torque and/or the rotational speed of the melt stirrer drive (12) are the measured quantities for determining the viscosity of the polymer melt (5). reactor unit after Claim 1 or 2 , characterized in that the melting reactor (1) has a sedimentation compartment (11) in the area near the bottom for settling non-melting or difficult-to-melt residues (6), wherein the sedimentation compartment (11) can be emptied via a closable residue discharge channel (18). reactor unit after Claim 3 , characterized in that the melt agitator (13) is arranged vertically in the melt reactor (1) and above the sedimentation section (11), wherein the outlet opening of the return feed line (39) projecting into the melt reactor (1) is arranged between the sedimentation section (11) and the melt agitator (13) facing the melt agitator (13) and the outlet-side end region of the return feed line (39) is aligned axially to the melt agitator (13). Reactor unit according to one of the Claims 1 until 3 , characterized in that the melt agitator (13) has a vertically aligned melt agitator hollow shaft (40), wherein the inner channel of the melt agitator hollow shaft (40) forms part of the return feed line (39), and wherein the outlet opening of the return feed line (39) is arranged at the bottom end of the melt agitator hollow shaft (40). Plastic thermolysis plant, comprising a reactor unit according to one of the Claims 1 until 5 , characterized in that the plastic thermolysis plant further comprises a plastic feed unit (10) connected to the melting reactor (1) for feeding the plastic residues (4) and a fractionation unit with quench connected to the pre-evaporator exhaust (28) and the post-evaporator exhaust (29) for liquefaction and fractionation of the gases and vapors (9) discharged from the reactor unit. Plastic thermolysis plant according to Claim 6 , characterized in that the plastic input unit (10) has a conveying and sluice system for pre-compacting the plastic residues (4) and for introducing gas-free or low-gas plastic residues (4) into the melting reactor (1). Plastic thermolysis plant according to Claim 6 or 7 , characterized in that the plastic thermolysis plant further comprises a separation stage connected to the melting reactor (1) for separating thermolysis-interfering substances from the reactor unit. Method for operating a reactor unit according to one of the Claims 1 until 5 or a plastic thermolysis plant according to one of the Claims 6 until 8 , characterized in that the viscosity of the polymer melt (5) is continuously measured during operation by means of the viscometer and transmitted to the controller (14) by means of a signal, wherein a predetermined quantity of the pre-evaporator liquid (7) from the pre-evaporator sump (30) of the pre-evaporator (2) and/or the post-evaporator liquid (8) from the post-evaporator sump (31) of the post-evaporator (3) is discharged and introduced into the polymer melt (5) in the melting reactor (1) by means of the return feed pump (15) controlled by the controller (14) depending on the transmitted viscosity. Procedure according to Claim 9 , characterized in that additional plastic residues (4) are introduced into the plastic melt (5) as soon as the measured viscosity of the plastic melt (5) falls below a predetermined minimum viscosity.