A screw conveyor arrangement with a device for cleaning a screw conveyor

Abstract

The present invention concerns a screw conveyor arrangement for a process equipment, such as a reactor (103) in a pyrolysis plant, wherein said screw conveyor arrangement comprises at least one main screw conveyor (112) moving material along a first transport direction towards an outlet at the downstream end of said main screw conveyor, and where a second screw conveyor (150) is provided receiving material from the main screw conveyor and forwarding the material in a second transport direction different than said first transport direction, wherein the arrangement comprises an impeller wheel (10), which is provided at the downstream end of the main screw conveyor, said impeller wheel having a plurality of blades (12) that are adapted to swiping the upper side of the second screw conveyor, and wherein the blades are formed with a concave curvature at the peripheral edges (13) of the blades, where said curvature matches the diameter of the second screw conveyor.

Description

[0001] A SCREW CONVEYOR ARRANGEMENT WITH A DEVICE FOR CLEANING A SCREW CONVEYOR

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a screw conveyor arrangement with a device for cleaning a screw conveyor and a method of cleaning same.

[0004] BACKGROUND OF THE INVENTION

[0005] In many process plants materials products are being transported by screw conveyor arrangement and in several places in the process equipment there is a risk of build up of material on all internal parts interferring or even clogging the material transport as the granular material build.

[0006] In a pyrolysis plant for recycling plastic by converting the waste plastic to oil, a biproduct is black carbon, i.e. the dirt in the wast plastic products. The material is transported and heated through the processing equipment, such as the pyrolysis reactor, and the black carbon is removed at the end of the screw conveyors in the process equipment. At the end of the screw conveyors where the blakc carbon or fine particle ash is transferred to a removal conveyor there is a risk of the ash building up and thereby clogging the screw conveyors.

[0007] Hence, it is an object of the present invention to provide a device for cleaning a screw conveyor to prevent the build-up of material.

[0008] SUMMARY OF THE INVENTION

[0009] This object is achieved in a first aspect of the invention by providing a screw conveyor arrangement for a process equipment, such as a reactor in a pyrolysis plant, wherein said screw conveyor arrangement comprises at least one main screw conveyor moving material along a first transport direction towards an outlet at the downstream end of said main screw conveyor, and where a second screw conveyor is provided receiving material from the main screw conveyor and forwarding the material in a second transport direction different than said first transport direction, wherein the arrangement comprises an impeller wheel, which is provided at the downstream end of the main screw conveyor, said impeller wheel having a plurality of blades that are adapted to swiping the upper side of the second screw conveyor, and wherein the blades are formed with a concave curvature at the peripheral edges of the blades, where said curvature matches the diameter of the second screw conveyor.

[0010] According to a second aspect of the invention, there is provided a method for cleaning a screw conveyor in a screw conveyor arrangement in a process equipment, such as a reactor in a pyrolysis plant, wherein the arrangement comprises

[0011] - a main screw conveyor moving material along a first transport direction towards an outlet at the downstream end of said main screw conveyor, and

[0012] - a second screw conveyor which is provided receiving material from the main screw conveyor and forwarding the material in a second transport direction different than said first transport direction, said method comprising that the second screw conveyor is being swiped by rotating blades of an impeller wheel, which is provided at the downstream end on the axis of the main screw conveyor, and wherein the rotating swiping blades of the at least one impeller wheel are swiping the upper receiving section of the second screw conveyor as the blades are formed with a concave curvature at the peripheral edges of the blades, where said curvature matches the diameter of the second screw conveyor.

[0013] By the screw conveyor arrangement and the method according to the invention, the above-mentioned object is achieved by installing cleaning impellers where screw conveyors are located. The impeller is installed on and preferably driven together with the main screw conveyor. The impeller has the ability to scrape of excess settled material from the transverse screw conveyor.

[0014] The material being transported comprises a particulate material, such as black carbon dust or the like granular material. When using the invention in a plastic-to- oil pyrolysis plant, the impellers are located both in the degasser and in the Pyrolysis reactor.

[0015] In an embodiment of the invention, the second transport direction is preferably perpendicular to said first transport direction. However, it is realised that other angular displacements may also be implemented.

[0016] In a preferred embodiment, the impeller wheel is driven by the main screw conveyor for rotating the impeller wheel in either the same direction as the main screw conveyor or in the opposite direction. Accordingly, the impeller may be connected directly on the shaft of the screw conveyor or mounted via a gear. Consequently, the rotation speed of the impeller can be the same as the screw conveyor or the impeller rotational speed may be different either more or less than the rotational speed of the screw conveyor. Thus, the impeller wheel is rotating about the main screw conveyor axis preferably above the second screw conveyor, so that the particulate material falls by gravity into the second conveyor and the impeller sweeps over the top of the second conveyor.

[0017] In order to ensure a "tight sweep" of the impellers over the second conveyor, wherein the blades are formed with a concave curvature at the peripheral edges of the blades, where said curvature matches the diameter of the second screw conveyor. Hereby an effective cleaning is achieved and a good distribution of the powdered material, such as the black carbon, is ensured.

[0018] Preferably, the concave curvature at the peripheral edges of the blades is concentric with the diameter of the second screw conveyor.

[0019] In one preferred embodiment, the screw conveyor arrangement comprises two parallel main screw conveyors, which are both moving material along a first transport direction towards their outlets at the downstream ends of said main screw conveyors, where one common second screw conveyor is provided transversely oriented in the second transport direction for receiving material from the main screw conveyors. The two parallel main screw conveyors may be rotated in opposite directions, and preferably two impeller wheels are provided on each of the downstream end of the main screw conveyors. Furthermore, the two impeller wheels are preferably provided on each of the main screw conveyors rotating in opposite directions. This arrangement ensures an effective sweeping with high conveyor capacity.

[0020] DETAILED DESCRIPTION

[0021] In the following, the invention is described in more detail with reference to the embodiments shown in the accompanying drawings, in which:

[0022] Fig. 1 is a schematic view of an embodiment of a pyrolysis plant for recycling of plastics making use of the present invention;

[0023] Fig. 2 is a perspective view of a first embodiment of the invention; and Fig. 3 is a perspective view of a second embodiment of the invention.

[0024] In fig. 1, a schematic diagram of a pyrolysis plant for recycling of plastics making use of the present invention is shown.

[0025] In this pyrolysis plant, a residual polymer product (also referred to as waste plastic) is fed to a densifier 101 wherein the product is compressed, preferably at a ratio of 2-3.5, by screw conveyors 111. A vapour outlet 121 is provided to release water vapour released from the residual polymer products being compressed. By removing the water vapour, vapour explosions in the system may be avoided as well as it is avoided that the pyrolysis oil produced is being oxidized. The compressed residual polymer product is forwarded through a degas feeder 101a, where a pH regulating additive, preferably Calcium Oxide (CaO), is added through an inlet 132 at the entry region in the degas feeder 101a. The Calcium Oxide is then mixed with the residual polymer product quickly in the degas feeder 101a. During the travel through the degas feeder the residual polymer product is heated in a heatable pipe 131. In a first section 102a the product is heated to 180-220°C and in a second section 102b, 102c further heated to approx. 200-280°C. The residual polymer product is then fed into the degasser 102. In the degasser 102 the residual polymer product is moved substantially horizontally by a screw conveyor 112 through three heating zones 102a, 102b and 102c. In the degasser 102, the zones heat the media, i.e. the residual polymer product, up to max. 240°C in the first zone 102a and heat the media up to max. 260°C in the second zone 102b and up to max. 280°C in the third zone 102c. A gas outlet 122b is provided above at least the zones 102b and 102c as shown in the fig. 1. Inside the degasser 102 the pressure is within the range of 0.1 to 1 bar, such as 0.2-0.45 bar.

[0026] The residual polymer product, also referred to as the media or plastic pulp is then transferred to the pyrolysis reactor 103 through a pipe conveyor 150 containing a transport screw conveyor. The degasser, which is horizontally oriented, and the pyrolysis reactor, which is tilted upwards, are connected so there is a fluid communication between the outlet 122a at the bottom of the degasser 102 and the inlet 123a at the lowermost region of the tilted pyrolysis reactor 103. As indicated in fig. 1 the liquid level 191 is about the same as in the degasser 102.

[0027] The pyrolysis reactor 103 preferably comprises two screw conveyors 113, preferably arranged in parallel hence only one is shown in fig. 1. The screw conveyors 113 are conveying the residual polymer product and mixing the product whilst lifting upwards and out of the liquid level towards a black carbon outlet 123b at the top of the reactor 103. The pyrolysis liquid in the reactor 103 is heated by a heater, such as an electrical heater, for heating the residual polymer product to a temperature of up to max. 500 °C to generate pyrolysis vapour. The heating can be arranged in heating zones. The pressure inside the pyrolysis reactor 103 is similar to the pressure of the degasser, i.e. 0.1 to 1 bar, such as 0.2-0.45 bar.

[0028] The pyrolysis vapour is released from the reactor 103 via a reactor vapour outlet 123c. The reactor vapour outlet 123c is away from the dry portion of the reactor to avoid dripping of any condensed vapour onto the dried black carbon. Towards the end of the reactor screw conveyors 113 substantially all of the residual polymer product will have been decomposed and a solid fraction comprising black carbon residue will leave the process in the end of the reactor 103. The black carbon is transported out of the reactor 103 via the black carbon outlet 123b placed in the reactor to receive the black carbon. At the outlet 123b a black carbon screw conveyor 133 may be arranged in extension of the black carbon outlet 123b for transferring the black carbon to a container. Advantageously, also a gas lock valve (not shown) may be provided to ensure that no gases escape through the black carbon outlet 123b. The pyrolysis vapour released from the reactor 103 via a reactor vapour outlet 123c is fed into the oil reactor 104. The oil reactor 104 functions as a vapourliquid separator. The reactor vapour outlet pipe 123c is positioned in the oil reactor 104 such that the pipe exit 123d is below the liquid level 104d in the oil reactor 104. The oil reactor 104 may be heated in three zones 104a, 104b and 104c as indicated in fig. 1. In each zone the pyrolysis vapour product is heated to max. 450 °C. The pyrolysis vapour is released into the oil reactor 104 below the liquid level as shown in the fig. 1. If the product liquefies in the oil reactor 104 and fall to the bottom thereon, this heavy oil and any solid particles is returned to the pyrolysis reactor 103 via the pipe 124c for further decomposition in the pyrolysis reactor 103.

[0029] In the top of the oil reactor 104 two outlets 124a, 124b are provided for transferring vapour components to the two reflux condensers 105a, 105b. All the pyrolysis vapour enters at the bottom of each of the reflux condensers 105 and exits at the top of the reflux condensers 105a, 105b with a temperature of max. 260°C. From the top of the reflux condensers 105a, 105b, the pyrolysis vapour is led to the raw pyrolysis oil (RPO) condensers 106a and 106b, where the vapour is condensed to heavy products (Raw Pyrolysis Oil or RPO) with an outlet temperature of approx. 150-180°C. Furthermore, pyrolysis vapours are transferred to the Nafta Pyrolysis Oil condenser 107, in which the vapours are condensed and chilled and exits as a light product at a temperature of 10-35°C.

[0030] The transfer of the product from the degasser 102 through the pipe conveyor 150 and the transfer of the black carbon in carbon screw conveyor 133 from the reactor 103 are both shown schematically to be in line with the degasser 102 and the reactor 103, respectively. However, it is found of preference to provide the pipe conveyor 150 at an angle to the degasser and also to provide the carbon screw conveyor 133 at an angle to the reactor 103. As shown in figures 2 and 3, these angled configurations could be perpendicular angles to the main transport directions in the degasser 102 and the pyrolysis reactor 103, respectively.

[0031] With reference to fig. 2, a first embodiment of the screw conveyor arrangement according to the invention is shown implemented in a degasser 102 of a pyrolysis plant of the kind shown in fig. 1. The screw conveyor arrangement in this embodiment comprises a main screw conveyor 112 moving material along a first transport direction towards an outlet at the downstream end of the degasser 102 in which the main screw conveyor 112 is accommodated. The second screw conveyor 150 is provided so that it is receiving material from the end of the main screw conveyor 112 and further conveying the material in a second transport direction, which is substantially perpendicular to the first transport direction.

[0032] Above the second screw conveyor there is provided an impeller wheel 10, which is provided at the downstream end of the shaft of the main screw conveyor 112. The impeller wheel 10 has a plurality of blades 12 that are adapted to swiping the upper side of the second screw conveyor 150 to remove any build-up of material which has not proceeded into the helical fin or fins 151 of the second screw conveyor 150.

[0033] The blades 12 are formed with a concave curvature at the peripheral edges 13 of the blades 12, where this curvature is concentric with the outer diameter of the helical fins 151 of the second screw conveyor 150. This ensures the impeller swipes the outer region of the second screw conveyor 150 and distributes any surplus build-up of material between the openings of the helical fins 151 and thereby also ensures a quick transfer of the material as well as prevents any clogging of the material transfer between the main screw conveyor 112 and the second screw conveyor 150.

[0034] In a second embodiment as shown in fig. 3, the screw conveyor arrangement comprises two parallel main screw conveyors 113, whereby a larger transport and processing capacity can be achieved. This screw conveyor arrangement according to the invention is shown implemented in a pyrolysis reactor 103 of a pyrolysis plant of the kind shown in fig. 1. As shown in fig. 1, the reactor 103 is inclined upwards, so that the liquid level 191 (see fig. 1) does not reach all the way to the downstream end (with regard to the first transport direction of the screw conveyors 113) of the reactor 103. The liquid is heated and vapourised so that only residue solid materials remain in the material flow towards the end of the reactor. Thus, the two screw conveyors 113 are both moving material along a first transport direction towards the outlets at the downstream end of the reactor 103. As shown in fig. 3, at the end of the reactor 103, one common second screw conveyor 113 constitutes the black carbon conveyor 133 is provided transversely oriented in the second transport direction and adapted for receiving material from the two main screw conveyors 113.

[0035] Each of the main screw conveyors 113 are provided with an impeller wheel 10 at the outlet end as shown in fig. 3. The impellers 10 are provided with a plurality of blades 12 that are adapted to swiping the upper side of the second screw conveyor 133 to remove any build-up of material which has not proceeded into the helical fin or fins 134 of the second screw conveyor 133.

[0036] The two parallel main screw conveyors 113 are rotated in opposite directions and accordingly, the impeller wheels 10 that are preferably directly connected to each of the screw conveyors 113 are also driven with rotation in opposite directions. However, if appropriate in a specific implementation the impellers 10 may be driven in the same direction and connected to the screw conveyors 113 via a set of gears whereby both the rotational speed and the direction of rotation may be altered or adjusted.

[0037] As it is also described in the previous embodiment, the blades 12 of the impellers 10 are formed with a concave curvature at the peripheral edges 13 of the blades 12, where this curvature matches the outer diameter of the helical fins 134 of the second screw conveyor 133.

[0038] Above, the invention is described with reference to some currently preferred embodiments. However, by the invention it is realised that other embodiments and variants may be provided without departing from the scope of the invention as defined in the accompanying claims. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. A screw conveyor arrangement for a process equipment, such as a reactor in a pyrolysis plant, wherein said screw conveyor arrangement comprises at least one main screw conveyor moving material along a first transport direction towards an outlet at the downstream end of said main screw conveyor, and where a second screw conveyor is provided receiving material from the main screw conveyor and forwarding the material in a second transport direction different than said first transport direction, wherein the arrangement comprises an impeller wheel, which is provided at the downstream end of the main screw conveyor, said impeller wheel having a plurality of blades that are adapted to swiping the upper side of the second screw conveyor, and wherein the blades are formed with a concave curvature at the peripheral edges of the blades, where said curvature matches the diameter of the second screw conveyor.

2. A screw conveyor arrangement according to claim 1, wherein the second transport direction is perpendicular to said first transport direction.

3. A screw conveyor arrangement according to claim 1 or 2, wherein the impeller wheel is driven by the main screw conveyor for rotating the impeller wheel in either the same direction as the main screw conveyor or in the opposite direction.

4. A screw conveyor arrangement according to any one of the preceding claims, wherein the impeller wheel is rotating about the main screw conveyor axis above the second screw conveyor.

5. A screw conveyor arrangement according to any one of the preceding claims, wherein the concave curvature at the peripheral edges of the blades is concentric with the diameter of the second screw conveyor.

6. A screw conveyor arrangement according to any one of the preceding claims, wherein the screw conveyor arrangement comprises two parallel main screw conveyors, which are both moving material along a first transport directiontowards their outlets at the downstream ends of said main screw conveyors, where one common second screw conveyor is provided transversely oriented in the second transport direction for receiving material from the main screw conveyors.

7. A screw conveyor arrangement according to claim 6, wherein the two parallel main screw conveyors are rotated in opposite directions.

8. A screw conveyor arrangement according to claim 6 or 7, wherein two impeller wheels are provided on each of the downstream end of the main screw conveyors.

9. A screw conveyor arrangement according to claim 8, wherein the two impeller wheels are provided on each of the main screw conveyors rotating in opposite directions.

10. A method for cleaning a screw conveyor in a screw conveyor arrangement in a process equipment, such as a reactor in a pyrolysis plant, wherein the arrangement comprises- a main screw conveyor moving material along a first transport direction towards an outlet at the downstream end of said main screw conveyor, and- a second screw conveyor which is provided receiving material from the main screw conveyor and forwarding the material in a second transport direction different than said first transport direction, said method comprising that the second screw conveyor is being swiped by rotating blades of an impeller wheel, which is provided at the downstream end on the axis of the main screw conveyor, and wherein the rotating swiping blades of the at least one impeller wheel are swiping the upper receiving section of the second screw conveyor as the blades are formed with a concave curvature at the peripheral edges of the blades, where said curvature matches the diameter of the second screw conveyor.

11. A method according to claim 10, where the second transport direction is perpendicular to said first transport direction.

12. A method according to claim 10 or 11, where the impeller wheel is rotating about the main screw conveyor axis above the second screw conveyor and said impeller may be driven by the main screw conveyor.

13. A method according to any one of claims 10 to 12, where the concave curvature at the peripheral edges of the blades is concentric with the diameter of the second screw conveyor.

14. A method according to any one of claims 10 to 13, where the blades of the at least one impeller wheel are swiping the second screw conveyor rotating in a swiping direction opposite the second transport direction.

15. A method according to any one of claims 10 to 14, where the material being transported comprises a particulate material, such as black carbon dust or the like granular material.

16. A method according to any one of claims 10 to 15, wherein the screw conveyor arrangement comprises two parallel main screw conveyors, which are both moving material along a first transport direction towards their outlets at the downstream ends of said main screw conveyors, where one common second screw conveyor is provided transversely oriented in the second transport direction for receiving material from the main screw conveyors.

17. A method according to claim 16, wherein two impeller wheels on each of the downstream end of the main screw conveyors and preferably also wherein said two impeller wheels on each of the main screw conveyors rotate in opposite directions.

18. A method according to any one of claims 10 to 17 being performed by a screw conveyor arrangement according to any one of claims 1 to 9.

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