Background

The invention relates to a method for thermolysing organic material.

The invention further relates to a thermolysing apparatus.

It is known to use extruders in heating/melting material to be pro- cessed. The main challenge in the existing methods and apparatuses is a rela- tively small feeding zone opening area compared to volume flow and the chal- lenges in effective heating of thermolysing material in conventional one screw extruders. Relatively small feeding zone opening area restricts the use of big- ger dimension and fluffy feeding material in conventional extruders.

The challenges of effective heating of materials in thermolysis tem- peratures with conventional extruders are due to physical phenomena where the major of heating energy input is gained through the inner friction/viscosity of the processed material. However, as the temperature rises the inner fric tion/viscosity lowers and high temperatures needed in thermolysis cannot be reached in a techno-economically feasible way.

In this description, thermolysis means a chemical decomposition caused by heat.

In this description, pyrolysis means converting fuel in inert condi- tions and in high temperature into gaseous state, which forms oil-like, different organic compounds comprising liquid as it condensed. Inert conditions mean oxygen-free conditions where no combustion of the fuel occurs. In the pyrolysis process fuel is pyrolyzed, formed gaseous compounds, i.e. pyrolysis gases are separated from the char residue and the pyrolysis gases are condensed into pyrolysis oil. Pyrolysis oil may be used as fuel or refined into different chemi- cals.

In this description, organic material means any material comprising carbon-based natural or engineered compounds. Thus the organic material may comprise biomasses, for example wood, wood chips, peat, saw dust, fire- wood, forest residue, products and waste of the papermaking industry, lumber waste, urban wood waste, or other biomass; sludges, recycled fuels, and waste coals; agro fuels, such as straw, straw pellets, palm oil waste and any other waste produced in agricultural production. The organic material may comprise plastic material, such as thermoplastics or thermosets. The plastic material may be e.g. waste material and derived from side-streams of industry, trade or transportation. The organic material may also be composite material, e.g. wood-polymer composites or cardboards laminated or cast coated with plastic films.

Brief description

Viewed from a first aspect, there can be provided a method for thermolysing organic material, the method comprising steps of:

A) feeding the material in a single-screw extruder, the extruder comprising

-- a cylindrical rotor member having diameter and length and corn- prising a feeding zone,

- the rotor member arranged in a barrel,

- the cylindrical surface of the rotor member carrying cavity/cavities and/or projection(s) arranged in helically extending rows,

- the helically extending row(s) of the rotor member having a pitch and depth in the feeding zone of the rotor member, wherein

- the relation of the depth to the diameter of the rotor member, i.e. d:D, is not more than 1 :20, and

- the relation of the pitch of the rotor member to the diameter of the rotor member, i.e. P:D, is not more than 1 :4,

B) heating the material in the single-screw extruder to a flowable state, and

C) thermolysing the material.

Thereby a method capable to process low bulk weight feed materi- als and continuously convey it through heating section may be achieved. Mix- ing capability and large area for heat transfer may enable thermolysis of more challenging feeding materials. Low bulk weight recycled conventional plastics, composites or biobased materials are possible to feed even without any pre- ceding compacting steps.

Viewed from a further aspect, there can be provided a thermolysing apparatus, comprising a single-screw extruder, the single-screw extruder corn- prising

- a cylindrical rotor member having diameter and length and corn- prising a feeding zone,

- the rotor member arranged in a barrel,

- the cylindrical surface of the rotor member carrying cavity/cavities and/or projection(s) arranged in helically extending rows, - the helically extending row(s) of the rotor member having a pitch and depth in the feeding zone of the rotor member, and the extruder further comprising

- a drive system for the rotation of the rotor member in the barrel, wherein

the relation of the depth to the diameter of the rotor member, i.e. d:D, is not more than 1 :20, and

the relation of the pitch of the rotor member to the diameter of the rotor member, i.e. P:D, is not more than 1 :4.

Thereby an apparatus capable to process low bulk weight feed ma- terials and having large area for heat transfer that enables thermolysis of more challenging feeding materials may be achieved.

Furthermore, the heating of thermolysing material in the extruder is techno-economically notably more effective than with conventional extruders. This is caused by the fact that heat transfer can be effectively implemented from the barrel and from the rotor member side due to the large thermally con- ductive area thereof. Larger thermally conductive area enables also more con- trolled temperature even in fast thermolysis, thereby decreasing the possibility of local over heating and charring on rotor and stator surfaces.

Furthermore, because of the large diameter of the barrel, the inner surface of the barrel may be machined into favourable geometry with low cost contrary to conventional extruders. The favourable barrel surface geometry further enables more efficient and precise mixing of material and thereby faster and more precise tempering. Also due to the large diameter of the barrel, it is possible to utilize 3-D geometry in the barrel (additional to rotor). This may en- able a more precise control of pressure gradient between zones of the extrud- er, which in turn may promote reject gas removal in desired temperature and/or zone. This enables the removal of halogen containing compounds al- ready in extruder phase thus enabling the use of halogenated plastics as feed- ing material to thermolysis.

Finally, the possibility to use paper, cardboard and cellulose fiber containing polymer composites as extruder feeding materials multiplies the feed material flow from recycling compared to restriction to plastics.

The method and the apparatus are characterized by what is stated in the independent claims. Some other embodiments are characterized by what is stated in the other claims. Inventive embodiments are also disclosed in the specification and drawings of this patent application. The inventive content of the patent application may also be defined in other ways than defined in the following claims. The inventive content may also be formed of several separate inventions, especially if the invention is examined in the light of expressed or implicit sub-tasks or in view of obtained benefits or benefit groups. Some of the definitions contained in the following claims may then be unnecessary in view of the separate inventive ideas. Features of the different embodiments of the invention may, within the scope of the basic inventive idea, be applied to other embodiments.

Brief description of figures

Some embodiments illustrating the present disclosure are described in more detail in the attached drawings, in which

Figure 1 a is a schematic side view of an apparatus in partial cross- section,

Figure 1 b is a schematic view of a detail of the apparatus shown in Figure 1 a in partial cross-section,

Figure 2 is a schematic view of a piece of an extruder barrel,

Figure 3 is side view of another apparatus in partial cross-section, Figure 4 a schematic illustration of a method for thermolysis, and Figure 5 a schematic illustration of another method for thermolysis.

In the figures, some embodiments are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

Detailed description

Figure 1 a is a schematic side view of an apparatus in partial cross- section, and Figure 1 b is a schematic view of a detail of the apparatus shown in Figure 1a in partial cross-section.

The apparatus is a single-screw extruder 100. The extruder 100 is preferably capable to process any kind of organic material (material hereafter) to be thermolysed, and it may also be used as pre-thermolyser. The form of the material does change when passing through the extruder, i.e. material or mixture of materials may, for instance, compress, compact, consolidate, grind, break apart, melt, react, decompose, and/or degrade. The extruder 100 is a single-screw extruder comprising a cylindrical rotor member 1 , a barrel 2, a feed opening 3, and a drive system 4 for the rota- tion of the rotor member 1 in the barrel 2.

The rotor member 1 has diameter D and length L. In an embodi- ment, the relation of the length to the diameter, i.e. L:D, is in range of 2:1 to 4:1.

The cylindrical outer surface of the rotor member 1 comprises pro- jections 5 that realizes a screw thread comprising at least one screw flight 6 and at least one screw channel 7 between the at least one screw flight 6.

The screw thread constitutes a structure that transfers the material to be thermolysed in the barrel from the feed opening 3 towards the outlet 9 while the rotor member 1 is rotating in the barrel 2. In an embodiment, the pro- file of the screw thread is invariable. In another embodiment, the profile of the screw thread is variable such that the volume of the screw channel decreases towards the outlet 16 of the extruder. In an embodiment, the depth d of the cavity/cavities and/or projection(s) 5 arranged on the surface of rotor is ar- ranged to decrease after feed zone (10).

The decreasing of the screw channel volume causes a compression ratio which is typically 1 :2 to 1 :4. The profile may change step by step, or it may comprise at least one section where the profile changes rapidly from one profile to another profile.

The screw flight 6 has pitch P and the screw channel 7 has depth d in the feeding zone 14 of the rotor member 1. The“feeding zone” means that part of the rotor member 1 that is directly under the feed opening 3 and one to five lap(s) of the flight 6 following the feed opening.

According to an aspect, the relation of the depth d to the diameter D, i.e. d:D, is not more than 1 :20, and the relation of the pitch P to the diameter D, i.e. P:D, is not more than 1 :4.

An advantage is that the volume of the screw channel 7 is very low compared to the screw diameter D. Thus it is possible to provide the extruder 100 with a very large feed opening 3 compared to the volume of the screw channel 7. Following this, light density and/or heterogeneous materials, such as materials comprising fibres, waste/recycled plastic, can be fed in the ex- truder 100 in amounts sufficient to fill optimally the screw channel 7. Thus there is no need, necessarily, for any preceding compacting steps. Another advantage is that the low volume compared to the screw diameter D decreases power requirement of the extruder.

In an embodiment, d:D is in range of 1 :300 to 1 :20 (in the feeding zone 14 of the rotor member 1 ).

An advantage is that the temperature of the material to be pro- cessed in the screw channel 7 may be controlled very precisely due to large surface area of the screw channel compared to volume of the material, and thus e.g. materials or processes highly sensitive to temperature may be pro- cessed by the extruder. Further, the large surface area enables an efficient energy transfer from the rotor member and/or the barrel to the material.

In an embodiment, P:D is in range of 1 :60 to 1 :4.

An advantage is that the material to be processed may be trans- ferred towards the outlet 7 by low power usage.

In an embodiment, the rotor member 1 realizes equation

CL d < RD 0.01 , wherein

CL = CL = channel length measured in direction of length (L) of the rotor member 1 ,

d = channel depth measured in radial direction of the rotor member

1 , and

RD = cross-sectional area of the rotor member, including also the cross-sectional area of the channel 8.

An advantage is that the volume of the screw channel 7 is very low compared to the screw diameter D, and thus easily filled with the material to be processed due to a large feed opening 3.

For instance, the diameter of the rotor member 1 may be 350 mm whereas the length following the feed opening is 400 mm.

In an embodiment, the feed opening 3 or the feeding zone 14 corn- prises shearing or cutting means for reducing the particle size of the material being fed in the extruder 100. This means may comprise e.g. cutting teeth ar- ranged on the rotor member 1 and counterpart(s) arranged in the barrel 2.

According to an aspect, the rotor member 1 is hollow. In an embod- iment, the rotor member comprises a cylindrical channel 8, such as circular cylinder, the diameter of which is at least 75%, preferably 80 to 85 %, of the diameter D of the rotor member. This means that the diameter D of the rotor member may be increased compared to the known rotor members without in- creasing the weight and expenses thereof. In an embodiment, the rotor member comprises one screw flight. In another embodiment, the rotor member comprises two, or even more, screw flights.

Thanks to the large diameter of the rotor member 1 , the drive sys- tem 4 may be construed to transmit high torques in the rotor member 1. Also the structure of the rotor member 1 may stand high torques without risk for damages.

The extruder 100 may be realized many alternative ways. For in- stance, in an embodiment the rotor member 1 comprises helically extending rows of plurality of separate cavities, instead of the screw thread. Said cavities constitute a structure that transfers the material to be processed in the barrel from the feed opening 3 towards the outlet 9.

The shape of the cavities may be e.g. dome, hemispheric, a section or calotte of tear-drop, oval or combinations thereof.

According to an aspect, the relation of the depth d to the diameter D in the feeding zone 14 of the rotor member 1 , i.e. d:D, is not more than 1 :20, and the relation of the pitch P to the diameter D, i.e. P:D, is not more than 1 :4.

An advantage is that the volume of the cavities is very low corn- pared to the screw diameter D, and thus light density and/or heterogeneous materials, such as materials comprising fibres, waste/recycled plastic, can be fed in the extruder 100 in amounts sufficient to fill optimally the volume be- tween the rotor member 1 and the barrel 2.

In an embodiment, d:D is in range of 1 :300 to 1 :20.

In an embodiment, P:D is in range of 1 :60 to 1 :4.

In another embodiment, the rotor member 1 comprises projections that realize helically extending rows of plurality of discrete projections, the row comprising pitch P.

According to an aspect, the relation of the depth d, or height of the projections, to the diameter D, i.e. d:D, is not more than 1 :20, and the relation of the pitch P to the diameter D, i.e. P:D, is not more than 1 :4.

In an embodiment, d:D is in range of 1 :300 to 1 :20.

In an embodiment, P:D is in range of 1 :60 to 1 :4.

According to an aspect, the cylindrical inner surface of the barrel 2 may comprise barrel cavity/cavities and/or projection(s). In an embodiment, said barrel cavity/cavities and/or projection(s) are arranged in helically extend- ing rows. In another embodiment, the barrel cavity/cavities and/or projection(s) are arranged parallel with longitudinal axis of the rotor member 1. In still an- other embodiment, the barrel cavity/cavities and/or projection(s) are arranged perpendicular with the longitudinal axis of the rotor member 1.

In an embodiment, the barrel 2 comprises a barrel screw thread comprising at least one barrel flight 10 and at least one barrel channel 11 be- tween the at least one flight, the barrel flight having a barrel pitch (BP) and the barrel channel having a barrel depth (BD).

An advantage is that transfer of the material to be processed to- wards the outlet 9 may be enhanced.

In another embodiment, the cavities arranged in the barrel 2 realize helically extending rows of plurality of separate cavities.

An advantage is that the mixing and blending properties of the ex- truder may be enhanced.

The cavities arranged in the barrel 2 may be invariable in their shape and size in all the length of the barrel they exist. In another embodiment, the barrel 2 may comprise variable sized and/or shaped cavities.

In an embodiment, the barrel cavity/cavities and/or projection(s) (5) are not continuous, such that there are several cavities or grooves side by side.

Figure 2 is a schematic view of a piece of an extruder barrel. Ac- cording to an aspect, the barrel 2 is construed from two or more barrel mod- ules 12 that are separately manufactured and then connected consecutively.

An advantage is that the barrel cavity/cavities and/or projection(s), such as barrel screw thread comprising at least one barrel flight 10 and at least one barrel channel 11 , may be manufactured in short pieces of the barrel more easily into short and large in diameter barrel module 12 than they would be manufactured in one monolithic barrel having equal length. It is to be noted, however, that the barrel 2 may also be manufactured in one piece. In the latter case, the barrel cavity/cavities and/or projection(s) can still be manufactured extremely easily due to high D:L relationship of the extruder.

Figure 3 is side view of another apparatus in partial cross-section. The feed opening 3 is substantially big comparing to the motor power and ca- pacity of the extruder and the depth of the rotor cavities. The projected area of the feed opening could be 20 to 200 times the size of a feed opening of a con- ventional plastic single screw extruder with the same rotor motor power. According to an aspect, the projected area of the feed opening is about 15 cm ² - 150 cm ² per kilowatt (kW) of rotor motor power, preferably about 30 cm ² - 100 cm ² . In an embodiment, the projected area of the feed opening is about 50 cm ² /kW. In an embodiment, the feed opening 3 is cut to the halfway of the diameter of the barrel 2, i.e. approximately D/2. Thus the feed opening 3 potentially weakens the structure of the barrel 2 such an ex- tent, that the barrel 2 is not able to carry the load caused during an extrusion process. Especially when the diameter of the barrel is large and the barrel is short, the axial forces tend to bend the barrel at the feeding zone 14.

In an embodiment, the barrel 2 is supported by a support structure 15 that lies outside of the barrel 2. The support structure 15 comprises a first support part 17 that is attached to a section of the barrel 2 between the feed opening 3 and the discharge end 16 of the barrel, a second support part 18 attached to the drive system side 19 of the extruder, and a load transmit struc- ture 20 connecting the first support part 17 to the second support part 18. In the embodiment shown in Figure 4, the second support part 18 has been fixed to a bearing housing 22 that covers the drive system 4. The load transmit structure 20 may be composed of one or more beam(s), plate structre or trussed construction, for instance.

The support structure 15 bears a part of the loads and stresses caused in an extrusion process and prevents the structure of the extruder from bending.

In an embodiment, there is an axial slot 21 arranged between the feeding zone 14 of the barrel and the bearing housing 22 of the extruder for receiving material (if any) flowing from the feeding zone backwards. Thus the axial slot 21 is to prevent the material to enter in the bearing housing 22. In- stead, the material will drop through the slot in a room where it does not cause any problems to the extruder or the extrusion process.

In an embodiment, the barrel 2 is totally separated from the bearing housing 22, i.e. the axial slot 21 extends 360 ° around longitudinal axle of the extruder.

In another embodiment, there are plurality of axial slots 21 that are separated by short sections of material .The invention is not limited solely to the embodiments described above, but instead many variations are possible within the scope of the inventive concept defined by the claims below. Within the scope of the inventive concept the attributes of different embodiments and ap- plications can be used in conjunction with or replace the attributes of another embodiment or application.

In an embodiment, the extruder 100 may comprise at least one gas- removing channel 24 for removing gas in the extruder 100. The gas removing channel 24 is arranged in the barrel 2 and connected to a gas-removing zone 23 arranged in the extruder 100.

In the gas-removing zone 23 there is such a geometry in the barrel and/or the rotor member that lowers the pressure of the material entering in the gas-removing zone 23. Due to this geometry, harmful gaseous components and/or remaining humidity of the material, if any, may be removed or at least reduced prior to thermolysis process. The large diameter of the barrel 2 makes it easier to manufacture the geometry needed in the gas-removing zone 23 than in known single-screw extruders.

This way halogenated, e.g. chlorine-containing gas(es) and/or bro- mine-containing gas(es), may be removed from the extruder 100. In an embod- iment, one or more additive(s), such as calcium compound for chlorine- containing gas(es), are added in the material for promoting removal of the harmful components.

In an embodiment, the gas-removing zone 23 comprises barrel cavi- ty/cavities 11 that have larger volume that the zones of the extruder before and after said gas-removing zone. According to another embodiment, the cavi- ty/cavities having larger volume are arranged in the rotor member, or both in the barrel and the rotor member.

In an embodiment, the gas removing channel 24 may comprise a vacuum pump and a counter-extruder (not shown) being arranged to suck gaseous components out of the extruder 100 but, at the same time, prevent the mass outflow.

The extruder 100 can be heated through the rotor member 1 and/or barrel 2 in order to heat the material. The heating may be realised e.g. by elec- trical heating means or by using heat transfer medium, such as liquid or gas. The extruder shown in figure 3 is heated by heat transfer medium, and it corn- prises a barrel heating connection 25, a barrel heating discharge 26 and a ro- tor heating connection 27.

Figure 4 a schematic illustration of a method for thermolysis. The method is a continuous process and comprises: A) feeding the material in a single-screw extruder 100,

B) heating the material in the single-screw extruder 100 to a flowa- ble state, and

C) thermolysing the material.

The features of the extruder 100 have been described above.

According to an aspect, the extruder 100 is used as a thermolysis reactor. In an embodiment, the extruder 100 constitutes a pyrolysis reactor for a pyrolysis process. The extruder 100 may be divided into a drying zone 300 and a pyrolysis zone 400 arranged successively.

The moisture and harmful gaseous matter, if any, separated from the material in the drying zone 300 will be removed from the extruder 100, and the dried material is further passed to the pyrolysis zone 400 for pyrolysis.

According to an aspect, the pyrolysis takes place in temperature be- tween 200 °C to 700 °C. The temperature depends on e.g. the material char- acteristics of the organic material.

The method and apparatus further uses a control system for control- ling the process. The control system comprises a control unit 28 and sensors or analyzers (not shown). The control unit 28 comprises receiving means for receiving the measurement signals from the sensors and analyzers, calculating means for forming control signals and transmitting means for transmitting the formed control signals to the process. The calculating means comprise algo- rithms for conditioning the measurement signals and forming the control sig nals for controlling the process.

The pyrolysis creates pyrolysis gases G and solid residue S. These are removed continuous way from the extruder 100. The term“pyrolysis gases” refers to gases that are formed in pyrolysis and that will be condensated in a later process to form pyrolysis oil.

Figure 5 a schematic illustration of another method for thermolysis. In an embodiment of the invention, the method comprises feeding the material in flowable state from the single-screw extruder 100 in a thermolysis reactor 200 separate from but connected to the extruder 100, and the thermolysis - such as pyrolysis - takes place in the thermolysis reactor 200. The extruder 100 may be used in drying the material and for removing harmful compounds from the material. Still further, the extruder 100 may heat, compress, compact, consolidate, grind, break apart, melt, react, decompose, and/or degrade the material into physical and chemical state that is advantageous for the thermol- ysis taking place in the thermolysis reactor 200.

The thermolysis reactor 200 may comprise e.g. a rotary kiln, a fluid ized bed boiler or a screw thermolyser. These reactors are known as such, and therefore they are not described more detailed in this description.

In an embodiment, secondary gas G2 generated in the thermolysis process is used for heating the single-screw extruder 100 s shown in Figure 5. An advantage is that the energy consumption of the method and apparatus may be lowered.

The drawings and the related description are only intended to illus- trate the idea of the invention. The invention may vary in detail within the scope of the inventive idea defined in the following claims.

Reference symbols

1 rotor member

2 barrel

3 feed opening

4 drive system

5 projection or cavity

6 screw flight

7 screw channel

8 channel

9 outlet

10 barrel flight

1 1 barrel channel

12 barrel module

13 hollow bar

14 feeding zone

15 barrel support structure

16 extruder outlet end

17 first support part

18 second support part

19 drive system side

20 load transmit structure 21 axial slot

22 bearing housing

23 gas-removing zone

24 gas-removing channel

25 barrel heating connection

26 barrel heating discharge

27 rotor heating connection

28 control unit

100 extruder

200 thermolysis reactor

300 drying zone

400 pyrolysis zone BD barrel depth

BP barrel pitch

CL channel length

D diameter of the rotor member

d depth

G produced gas

G2 secondary gas

L length of the rotor member

M material

P pitch

RD cross-sectional area of the rotor member S produced solid