Rotary KILN reactor and method of operating a rotary KILN reactor

Abstract

According to an example aspect of the present invention, there is provided a rotary kiln reactor (1) comprising a rotatable hollow chamber (2) having a front end (3) and a back end (4), a feeding system (5) configured to feed material into the hollow chamber (2) via at least one feed outlet (6), a gas outlet (7) for collecting a product comprising a gas (8) from at least partially pyrolyzed material, a residue outlet (9), wherein at least one movable object (10) is arranged within the rotatable hollow chamber (2), and an internal structure (17) is fixedly attached to an inner surface (15) of the rotatable hollow chamber (2) between the at least one movable object (10 and the back end (4), wherein an inner diameter of the structure (17) is smaller than an inner diameter of the rotatable hollow chamber (2).

Description

ROTARY KILN REACTOR AND METHOD OF OPERATING A ROTARY KILNREACTORFIELD

[0001] The present invention relates to a rotary kiln reactor.

[0002] Further, the present invention relates to a method of operating a rotatable kiln reactor.BACKGROUND

[0003] Rotary kiln reactors are known for a variety of applications, for example for treating polymer waste material. Polymers are used in a wide variety of products. The polymers are typically acquired through petroleum resources, which are considered nonrenewable. While a need for a more sustainable supply of raw material has arisen, the accumulation of polymer waste has also been recognized as an environmental problem. As a consequence, polymer waste is often collected and sorted for recycling or thermal decomposition purposes. Environmental problems can be reduced by subsequent polymer waste material treatment and re-use of at least a part of the material as raw material for new polymers and other materials.

[0004] For example, polymer waste material can be treated by pyrolysis, i.e. by thermal decomposition of the polymer waste material at elevated temperatures in an inert atmosphere, in order to obtain a product comprising a gas from at least partially pyrolyzed polymer waste. Such treatment may, for example, take place in a reactor, such as a rotary kiln reactor, into which the polymer waste is fed.

[0005] Properties and quality of kiln solids are crucial for successful and reliable operation of a rotary kiln waste plastic pyrolysis reactor. If the kiln solid stream is not a dry and free-flowing material it can cause severe fouling issues in the kiln solids disposal system. These issues are typically related to remaining non-pyrolysed hydrocarbon content in the kiln solids stream, and the waxy properties of said residual hydrocarbons. Thereasons for why non-pyrolysed carbonaceous content may reach the kiln solids disposal system are related to insufficient heating of the said material stream to drive off remaining volatile hydrocarbon content. Heating of the kiln solids can be insufficient if the residence time and / or mixing of the material in the section of a rotary kiln dedicated for solids drying is less than what is necessary to ensure favorable kiln solids quality / properties. Sufficient heating is challenging to ensure if the kiln solids stream is inconsistent (heterogenous) by its consistency.

[0006] Heating of solid pyrolysis residue inside a rotary kiln can be controlled primarily by adjusting the wall temperature of the kiln drum in the section where drying of the solids is considered to take place. Residence time of these solids inside the reactor is predominantly determined by the incline and the rotational speed of the reactor drum.

[0007] The kiln incline is typically fixed and cannot be manipulated with reasonable effort. The rotational speed of a reactor can be an important parameter also for other phenomena taking place inside a rotary kiln reactor. Trade-offs might be necessary when optimizing the rotational speed of the kiln drum, however non-pyrolyzed hydrocarboneus content in the kiln char stream can cause severe operability issues in the kiln solids disposal system leading to shutdown of the entire reactor unit. Therefore even parameters having high importance for the overall commercial performance of the plant, such as feed rate or liquid product yield, might be necessary to compromise to ensure reliable operation of a reactor unit (ensuring dry char).

[0008] In view of the foregoing, it would be beneficial to provide a rotary kiln reactor capable of obtaining a product comprising a gas from at least partially pyrolyzed material, wherein control over a solid residue residence time can be improved, and wherein it can be ensured that the pyrolysis solid residue is a homogeneous, dry of hydrocarbons, and free-flowing material stream.SUMMARY OF THE INVENTION

[0009] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a rotary kiln reactor comprising a rotatable hollow chamber having a front end and a back end, a feeding system configured to feed material into the hollow chamber via at least one feed outlet, a heating system for heating a wall of the rotatable hollow chamber, a gas outlet for collecting a product comprising a gas from at least partially pyrolyzed material, a residue outlet for collecting a residue, wherein at least one movable object is arranged within the rotatable hollow chamber, and an internal structure is fixedly attached to an inner surface of the rotatable hollow chamber between the at least one movable object and the back end, wherein an inner diameter of the structure is smaller than an inner diameter of the rotatable hollow chamber.

[0011] Various embodiments of the first aspect may comprise at least one feature from the following bulleted list:• the at least one movable object is a rotatable cylindrical object having a plurality of elongated openings• the rotatable cylindrical object comprises a plurality of flat steel bars or rods• the elongated openings are arranged parallel to each other• the at least one movable object is arranged in the proximity of the back end• the internal structure is in the form of a dam arranged between the at least one movable object and the residue outlet• the internal structure has a plurality of steps, each step having a different inner diameter• a plurality of movable objects is arranged within the rotatable hollow chamber• a further fixed internal structure is arranged in the rotatable hollow chamber between two adjacent movable objects• the movable object is a cage-like object, wherein the plurality of flat bars is located between two ring-shaped elements, discs or plate-like substrates, wherein each flat bar is arranged such that one comer of the flat bar is located more distal from an axis of rotation of the movable object than other parts of the flat bar

[0012] According to a second aspect of the present invention, there is provided a method of operating a rotary kiln reactor, the method comprising rotating a rotatable hollow chamber having a front end and a back end, heating a wall of the rotatable chamber,feeding material into the rotatable hollow chamber via at least one feed outlet of a feeding system, collecting a product comprising a gas from at least partially pyrolyzed material via a gas outlet, collecting a residue via a residue outlet, moving at least one movable object arranged within the rotatable hollow chamber by rotating the rotatable hollow chamber, and providing an internal structure fixedly attached to an inner surface of the rotatable hollow chamber between the at least one movable object and the back end, wherein an inner diameter of the structure is smaller than an inner diameter of the rotatable hollow chamber.

[0013] Various embodiments of the second aspect may comprise at least one feature from the following bulleted list:• the method comprises rotating the at least one movable object, wherein the at least one movable objectis a rotatable cylindrical object having a plurality of elongated openings• the method comprises providing the internal structure in the form of a dam between the at least one movable object and the residue outlet• the method comprises providing the internal structure with a plurality of steps, each step having a different inner diameter• the method comprises moving a plurality of movable objects within the rotating hollow chamber• the method comprising arranging a further fixed internal structure in the rotatable hollow chamber between two adjacent movable objects

[0014] Considerable advantages are obtained by certain embodiments of the invention. In particular, a rotary kiln reactor capable of obtaining a product comprising a gas from at least partially pyrolyzed material is provided, wherein control over a solid residue residence time can be improved, and wherein it can be ensured that the pyrolysis solid residue is a homogeneous, substantially dry of hydrocarbons, and free-flowing material stream.

[0015] A combination of a fixed internal structure and a moving object as described below can easily be added into an existing rotary kiln reactor if it turns out ensuring dry and free flowing kilns solids is challenging by other means. Also the size / height and location of the fixed internal structure can be modified and adjusted with reasonable effort.

[0016] A moving mixing object provides more efficient mixing and homogenization of the kiln char over fixed alternatives such as lifters as cutting, crushing and scraping functionalities are involved.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIGURE 1 illustrates a schematic view of an example of a rotary kiln reactor,

[0018] FIGURE 2 illustrates a schematic view of a rotary kiln reactor in accordance with at least some embodiments of the present invention, and

[0019] FIGURE 3 illustrates a schematic view of a fixed internal structure of a rotary kiln reactor in accordance with at least some embodiments of the present invention.EMBODIMENTS

[0020] In FIGURE 1 a schematic view of an example of a rotary kiln reactor 1 is illustrated. The reactor 1 comprises a hollow chamber 2 into which material 14, for example polymer waste, can be fed by a stationary feeding system 5 via a feed outlet 6. The material 14 fed into the hollow chamber 2 via the at least one feed outlet 6 falls on a heated inner surface 15 of the rotatable hollow chamber 2 due to gravity. The rotation of the hollow chamber 2 around an axis of rotation A causes the material 14 to distribute over at least a part of the inner surface 15 of the hollow chamber 2. The high temperature wall 13 of the hollow chamber 2 heated by a heating system 12 causes thermal decomposition of the material 14 within the hollow chamber 2, thus converting the material 14 into a gas 8 from at least partially pyro lyzed material and a residue. The reactor further comprises a gas outlet 9 for collecting a product comprising a gas 8 from at least partially pyrolyzed material. The reactor 1 is configured to allow flowing of the gas 8 from at least partially pyrolyzed material within the rotatable hollow chamber 2 substantially in a direction from the front end 3 to the back end 4 - as indicated by arrows 16 - of the hollow chamber 2 prior to guiding the gas 8 via the gas outlet 9 out of the reactor 1.

[0021] FIGURE 2 a schematic view of a rotary kiln reactor 1 in accordance with at least some embodiments of the present invention is illustrated. The rotary kiln reactor 1comprises a rotatable hollow chamber 2 having a front end 3 and a back end 4. The rotatable hollow chamber 2 is typically in the form of an elongated hollow cylinder. The term ’’elongated” means in this connection that a length of the hollow cylinder is substantially greater than a diameter of the hollow cylinder. For example, the length of the hollow cylinder may be 18 m and the diameter of the hollow cylinder may be 2 m. The hollow chamber 2 is typically made of a metal or metal alloy. The entire hollow chamber 2 is configured to be rotated around an axis of rotation A. The axis of rotation A is typically orientated horizontally or substantially horizontally. The term ’’axis orientated horizontally” means an axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. Similarly, the term ’’axis orientated substantially horizontally” means an axis that is tilted a few degrees, for example less than 10 degrees, from the axis that is orientated perpendicular to a gravity vector or perpendicular to the normal on the surface of the Earth. The rotational speed of the entire hollow chamber 2 may be, for example, in the range between 0.1 and 5 revolutions per minute (rpm), for example in the range between 1 and 2 rpm.

[0022] The rotary kiln reactor 1 further comprises a feeding system 5 configured to feed material 14 into the hollow chamber 2 via at least one feed outlet 6. The feeding system 5 may, for example, comprise a lance having a single feed outlet 6 as shown in FIGURE 1. The lance is typically stationary, i.e. the lance is not configured to rotate and the rotatable hollow chamber 2 is configured to rotate around the lance. The lance may be, for example, in the form of a hollow cylinder. A center axis of the lance is typically arranged or orientated coaxially with the axis of rotation A. The lance is typically made of metal or a metal alloy. The lance may, for example, extend into the hollow chamber 2. The system 1 may be, for example, configured to feed polymer waste into the hollow chamber 2 via the feed outlet 6. The feeding system is typically an extrusion-type feeding system. The material 14 is (predominantly) pre-molten so that the feed is converted into a flowable form allowing travelling through the lance.

[0023] The material 14 fed into the hollow chamber 2 via the at least one feed outlet 7 falls on a heated inner surface 15 of the rotatable hollow chamber 2 due to gravity as shown in FIGURE 1. The rotation of the hollow chamber 2 causes the material 14 to distribute over at least a part of the inner surface 15 of the hollow chamber 2. Distribution of the material 14 over at least a part of the inner surface 15 of the hollow chamber 2 may be improved by tilting the rotatable hollow chamber 2 a few degrees, for example 1 degreeto 5 degrees from the horizontal axis. In such a configuration, the rotatable hollow chamber 2 is arranged substantially horizontally.

[0024] The high temperature wall of the hollow chamber 2 causes thermal decomposition of the material 14 within the hollow chamber 2, thus converting the material 14 into a gas 9 from at least partially pyro lyzed material and a residue. The residue may comprise inorganics or inorganic contaminants, for instance. The rotatable hollow chamber 2 typically comprises a residue outlet 9 in the proximity of the back end 4 of the hollow chamber 2.

[0025] The rotary kiln reactor 1 yet further comprises a gas outlet 7 for collecting a product comprising a gas 8 from at least partially pyrolyzed material. The reactor 1 is typically configured to allow flowing of the gas 8 from at least partially pyrolyzed material within the rotatable hollow chamber 2 substantially in a direction from the front end 3 to the back end 4 of the hollow chamber 2 as indicated by arrow 16.

[0026] Additionally, the rotary kiln reactor 1 comprises a stationary heating system 12 capable of heating a wall 13 of the rotatable hollow chamber 2. For example, hot flue gas may be introduced at various points into the heating system 13 in order to heat different sections of the rotatable hollow chamber 2. The temperature of the hot flue gas may be, for example, 550 °C or 600 °C. Of course, also any other suitable heating system 12 may be utilized.

[0027] According to the present invention, a residence time of solids in the rotatable hollow chamber 2 can be controlled by adding one or more fixed internal structures 17 having a smaller inner diameter than the rotatable hollow chamber 2 inside the rotatable hollow chamber 2 in order to slow down the forward movement of the solids. Such fixed internal structures 17 can include e.g. different baffle dam structures so that the solid material needs to go over the structures in order to move forward inside the rotatable hollow chamber 2. A similar effect can be achieved by changing the inner diameter of the rotatable hollow chamber 2 in a stepwise manner. In conjunction with certain types of fixed internal structures 17 for controlling the kiln solids flow utilization of at least one moving mixing object 10 is possible. Freely moving mixing objects 10, which are not attached to the rotatable hollow chamber 2, require some sort of a barrier to be placed inside the rotatable hollow chamber 2 to prevent the mixing objects 10 from exiting the rotatable hollow chamber 2 altogether with the forward moving kiln solids.

[0028] The at least one movable object 10 arranged within the rotatable hollow chamber 2 may be, for example, a rotatable cylindrical object having a plurality of elongated openings 11. The rotatable cylindrical object may be, for example, a cage-like object, wherein a plurality of flat bars 19 or rods are located between two ring-shaped elements 18, discs or plate-like substrates. Each of the flat bars 19 is typically arranged parallel to an axis of rotation B of the rotatable cylindrical object. As a consequence, elongated openings 11 are provided between the ring-shaped elements 18. The length of each elongated opening 11 may be identical with the length of each flat bar 19. The length of each elongated opening 11 may be 0.5 m to 1.5 m, for instance. The cylindrical shape of the rotatable cylindrical object 10 allows a free rolling movement around axis of rotation B within the rotatable hollow chamber 2 and ensures that the object 10 stays at the bottom of the rotatable hollow chamber 2. The cage-like structure of the rotatable cylindrical object 10 enables functionalities including mixing of the kiln solids, cutting and breaking of larger agglomerates or lumps, and scraping clean the inner surface 15 of the rotatable hollow chamber 2 and of the fixed internal structure 17 holding the moving object 10 lengthwise stationary. Each flat bar 19 is typically arranged such that one comer or edge of the respective flat bar 19 is located more distal from the axis of rotation B than other parts of the flat bar 19 in order to improve scraping, mixing, grinding and / or cutting of solids present in the rotatable hollow chamber 2. Each flat bar 19 can be further perforated. The described structure, in addition to its significant weight, also prevents the object 10 from floating on top of a kiln solids layer, possibly leading the moving mixing object 10 to go over the dam-like structure 17 that is supposed to be limiting the forward movement of the moving mixing object 10. A cylindrical cage mixer can be manufactured of e.g. flat bar 19 of suitable steel grade. The steel grade is typically softer than the material of the rotatable hollow chamber 2 in order to avoid or at least reduce abrasive wear of the rotatable hollow chamber 2.

[0029] Extended length of such a freely moving object 10, in addition to the rotation of the rotatable hollow chamber 2, will ensure the object 10 stays parallel to rotatable hollow chamber 2 in all possible situations as there is no space to misalign significantly. The length of the object 10 also allows the dam-like fixed internal structure 17 to be placed in the proximity of the back end 4 of the rotatable hollow chamber 2 where the risk of fouling is minimized. In certain embodiments, the fixed internal structure 17 may belocated outside of the actively heated section of the rotatable hollow chamber 2 to reduce the risk of fouling.

[0030] There can be one or more freely moving objects 10 in one rotatable hollow chamber 2. For example, two rotatable cylindrical objects may be provided. In the case of several such freely moving objects 10, a further fixed internal structure 17 is necessary between two adjacent objects 10 to avoid interfering with each other.

[0031] In FIGURE 3 a schematic view of a fixed internal structure 17 of a rotary kiln reactor 1 in accordance with at least some embodiments of the present invention is illustrated. Only a part of the rotary kiln reactor is shown. As can be seen, the internal structure 17 has a plurality of steps 20, each step having a different inner diameter. Providing a plurality of steps 20 is beneficial for controlling a residence time of solids in the rotatable hollow chamber 2. The inner diameter of each step typically decreases from the front end 3 towards the back end 4 in order to slow down the forward movement of solids present in the rotatable hollow chamber 2 towards the residue outlet 9. As shown in FIGURE 3, the fixed internal structure 17 may be located outside of the section of the rotatable hollow chamber 2 actively heated by the heating system 12 to reduce the risk of fouling.

[0032] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0033] Reference throughout this specification to one embodiment or an embodiment m8eans that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0034] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identifiedas a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, b8ut are to be considered as separate and autonomous representations of the present invention.

[0035] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0036] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0037] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0038] At least some embodiments of the present invention find industrial application in operating rotary kiln reactors.REFERENCE SIGNS LIST1 rotary kiln reactor rotatable hollow chamber3 front end4 back end5 feeding system6 feed outlet7 gas outlet8 gas from at least partially pyrolyzed material9 residue outlet10 movable object11 elongated opening12 8heating system13 wall14 material15 inner surface16 direction of flow of gas from at least partially pyrolyzed material17 internal structure18 ring-like structure19 flat bar20 stepA axis of rotation of rotatable hollow chamberB axis of rotation of cylindrical object

Claims

CLAIMS:

1. A rotary kiln reactor (1) comprising:- a rotatable hollow chamber (2) having a front end (3) and a back end (4),- a feeding system (5) configured to feed material into the hollow chamber (2) via at least one feed outlet (6),- a heating system (12) for heating a wall (13) of the rotatable hollow chamber (2),- a gas outlet (7) for collecting a product comprising a gas (8) from at least partially pyrolyzed material,- a residue outlet (9) for collecting a residue,- at least one movable object (10) is arranged within the rotatable hollow chamber (2), and8- an internal structure (17) is fixedly attached to an inner surface (15) of the rotatable hollow chamber (2) between the at least one movable object (10) and the back end (4), wherein an inner diameter of the structure (17) is smaller than an inner diameter of the rotatable hollow chamber (2), characterized in that,- wherein the at least one movable object (10) is a rotatable cylindrical object having a plurality of elongated openings (11), and- wherein the rotatable cylindrical object comprises a plurality of flat steel bars (19) or rods.

2. The rotary kiln reactor (1) according to claim 1, wherein the elongated openings (11) are arranged parallel to each other.

3. The rotary kiln reactor (1) according to claim 1 or 2, wherein the at least one movable object (10) is arranged in the proximity of the back end (4).

4. The rotary kiln reactor (1) according to any one of claims 1 - 3, wherein the internal structure (17) is in the form of a dam arranged between the at least one movable object (10) and the residue outlet (9).

5. The rotary kiln reactor (1) according to any one of claims 1 - 4, wherein the internal structure (17) has a plurality of steps (20), each step having a different inner diameter.

6. The rotary kiln reactor (1) according to any one of claims 1 - 5, wherein a plurality of movable objects (10) is arranged within the rotatable hollow chamber (2).

7. The rotary kiln reactor (1) according to claim 6, wherein a further fixed internal structure (17) is arranged in the rotatable hollow chamber (2) between two adjacent movable objects (10).

8. The rotary kiln reactor (1) according to any one of claims 1 - 7, wherein the movable object (8) is a cage-like object, wherein the plurality of flat bars (19) is located between two ring-shaped elements, discs or plate-like substrates, wherein each flat bar (19) is arranged such that one comer of the flat bar (19) is located more distal from an axis of rotation (B) of the movable object (10) than other parts of the flat bar (19).

9. A method of operating a rotary kiln reactor, the method comprising:- rotating a rotatable hollow chamber (2) having a front end (3) and a back end (4),- heating a wall (13) of the rotatable chamber (2),- feeding material into the rotatable hollow chamber (2) via at least one feed outlet (6) of a feeding system (5),- collecting a product comprising a gas (8) from at least partially pyrolyzed material via a gas outlet,- collecting a residue via a residue outlet (9),- movi8ng at least one movable object (10) arranged within the rotatable hollow chamber (2) by rotating the rotatable hollow chamber (2), wherein the at least one movable object (10) is a rotatable cylindrical object having a plurality of elongated openings (11), and the rotatable cylindrical object comprises a plurality of flat steel bars (19) or rods, and- providing an internal structure (17) fixedly attached to an inner surface (15) of the rotatable hollow chamber (2) between the at least one movable object (10) and the back end (4), wherein an inner diameter of the structure (17) is smaller than an inner diameter of the rotatable hollow chamber (2).

10. The method according to claim 9, wherein the method comprises rotating the at least one movable object (10), wherein the at least one movable object (10) is a rotatable cylindrical object having a plurality of elongated openings (11).

11. The method according to claim 9 or 10, wherein the method comprises providing the internal structure (17) in the form of a dam between the at least one movable object (10) and the residue outlet (9).

12. The method according to claim 9 or 10, wherein the method comprises providing the internal structure (17) with a plurality of steps (20), each step having a different inner diameter.

13. The method according to any one of claims 9 - 12, wherein the method comprises moving a plurality of movable objects (10) within the rotating hollow chamber (2).

14. The method according to claim 13, the method comprising arranging a further fixed internal structure (17) in the rotatable hollow chamber (2) between two adjacent movable objects (10).

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