Field of the Invention

The invention relates to a feeding system for supplying solid feed material to a reactor, to a system for pyrolysis comprising such feeding system and to a process for pyrolysis using such system for pyrolysis, in particular a process for pyrolysis of a polyolefin-comprising solid material.

Background of the Invention

Packages for in particular liquid food products that are composed of a sheet of aluminium covered on both sides by a film of polyolefm, usually polyethylene, and having an outer layer of paper are widely used. Such packages are produced and sold under different names such as for example TetraBrik. For the recovery of aluminium from used packages of the "tetrabrik" type, several solutions have been proposed. Such solutions typically comprise a pretreatment step for the recovery of paper that yields an aluminium-polyolefm laminate. The aluminium-polyolefm laminate is then subjected to a pyrolysis step at a temperature below the melting temperature of aluminium such that the polyolefm is pyrolysed and solid aluminium can be recovered. Pyrolysis is a known process wherein organic material is thermally decomposed without the participation of oxygen. Upon pyrolysis of organic materials, a gaseous phase and a solid carbonaceous phase are formed. Upon condensing the condensable part of the gaseous phase, a liquid phase, usually referred to as pyrolysis oil or bio-oil is obtained. In order to provide an atmosphere in the pyrolysis reactor that is substantially free of oxygen, it is important to effectively seal the reactor from the environment, in particular to supply feed material to the reactor without at the same time supplying air to the reactor.

In US 6,193,780 is disclosed a process for the recovery of aluminium and energy from used packages wherein paper is first removed from the used packages leaving an aluminium sheet between first and second polyethylene film layers and wherein the aluminium sheet is then passed to a pyrolysis reactor for pyrolysis of the polyethylene film layers. A heavy and a light fraction from the polyethylene pyrolysis are collected and the light fraction is used as fuel for the pyrolysis process. The reactor is vertically extending. The aluminium sheets are supplied to the reactor by supply means having an endless screw with a final section of locally reduced helix pitch effective to produce a seal.

In WO 94/17919 is disclosed a process for recovery of aluminium from a composite material comprising at least one aluminium layer and one polyolefm layer. The material is carbonised in a rotary drum type furnace that is heated by carbonation gas that is combusted in a combustion chamber that is surrounding the rotary drum wherein carbonisation takes place. The composite material is fed to the rotary drum by means of a screw that is not completely filling the screw house in order to transport the feed material loosely and without compression. A disadvantage of the process of WO 94/17919 is that air will be supplied to the rotary drum with the feed material.

In WO 98/30818 is described a sealing arrangement between a rotary drum kiln and the stationary feed end thereof that serves to prevent process gas and solid matter dust to leak from the connection point of the rotary drum and the feed chamber. In the arrangement of WO 98/30818, pressurised gas such as air is fed into the rotary drum near its vertical end surface at a certain angle in order to prevent such leakage. The system of WO 98/30818 prevents leakage of gas from the reactor, but does not prevent the supply of air to the reactor with the solid feed material.

There is a need for improved feeding systems that are able to provide solid feed material, including solid feed material with a low density such as polyolefm- comprising material, to a pyrolysis reactor without supplying air to such reactor, without the need to use large amounts of nitrogen gas or other inert gases.

Summary of the Invention

It has now been found that solid feed material, including solid feed material with a low density such as for example polyolefin-comprising feed material, can be supplied to a reactor, in particular a pyrolysis reactor, with no or negligible amounts of air entering the reactor, by using a novel feeding system. The novel feeding system comprises an annular sealing space wherein, during normal operation of the system, the material to be fed to the reactor is compressed and forms an annular seal and thus prevents air from the environment to be fed into the reactor. Moreover, the annular sealing space may be provided with means for withdrawing gas, in particular air, from the annular sealing space and/or for supplying an inert non-oxidant gas, e.g. nitrogen, to the annular sealing space. Accordingly, the invention provides a feeding system for supplying a solid feed material comprising organic material to a reactor, the feeding system comprising a cylindrical housing containing a feed screw having an upstream end and a downstream end, the feed screw comprising a helical screw blade and a screw axis, wherein the screw axis is extending beyond the screw blade at the downstream end of the feed screw such that an annular sealing space is defined between the cylindrical housing and the extending part of the screw axis and wherein the cylindrical housing is extending beyond the extending screw axis, wherein the helical screw blade has a helix pitch that is increasing in downstream direction.

The feeding system according to the invention is capable of compressing solid feed material with a relatively low density to provide a seal that effectively seals the feed inlet of the reactor from the environment. Moreover, in case the compression would not provide sufficient seal, the system may be equipped with additional means to withdraw air from the seal formed by the compressed feed material and/or to supply an inert, non-oxidant gas to the seal formed by the compressed feed material. The feeding system can be advantageously used to supply solid feed material to a reactor wherein a conversion reaction under oxygen- free or oxygen-restricted conditions is to be carried out, such as for example a pyrolysis reactor.

The invention further provides a system for pyrolysis comprising the feeding system as hereinabove defined. Accordingly, the invention provides a system for pyrolysis of a solid feed material comprising organic material, the system for pyrolysis comprising:

a) a pyrolysis reactor;

b) a feeding system as hereinbefore defined for supplying the solid feed material to the pyrolysis reactor; and

c) a condensation system for condensing pyrolysis gas produced during pyrolysis of the solid feed material in the pyrolysis reactor.

The feeding system according to the invention is particularly suitable to be used in combination with a horizontal rotary pyrolysis reactor, since such reactor can suitably be equipped with means that loosen the material that has been compressed in the annular sealing spaces.

In a further aspect, the invention provides a process for pyrolysis of a solid feed material comprising organic material using the system for pyrolysis as hereinbefore defined, the process comprising supplying the solid feed material to the pyrolysis reactor by means of the feeding system and pyrolysing the organic material comprised in the solid feed material in the pyrolysis reactor at pyrolysis conditions to obtain pyrolysis gas, and condensing at least part of the pyrolysis gas in the condensing system to obtain pyrolysis oil.

In the process according to the invention, polyolefms, lignocellulosic material or other organic compounds comprised in the solid feed material are converted into pyrolysis gas that is at least partly condensed into pyrolysis oil. The pyrolysis oil may be advantageously used to provide heat for the pyrolysis process in the pyrolysis reactor or for other process steps. The process is particularly suitable for a solid feed material that comprises pyrolysable, organic material in combination with non- pyrolysable, inorganic material such as for example metals or minerals. The organic material comprised in the solid material is then pyrolysed in the pyrolysis reactor to obtain pyrolysis gas that yields, after condensation, pyrolysis oil. The metals or minerals can be recovered as a solid material from the pyrolysis reactor. The process is particularly suitable for recovery of aluminium from solid feed material comprising both polyolefm and aluminium, such as for example polyolefin-aluminium laminates that are obtained after removal of the outer paper layer from used beverage packages of the tetrabrik type. The process may also suitably be used for recovery of minerals from paper sludge.

Summary of the Drawings

In Figure 1 is schematically shown a longitudinal section of a feeding system according to the invention and the upstream end of a pyrolysis reactor.

In Figure 2 is schematically shown a cross-section through the plane II-II of the feeding system of Figure 1, showing the annular sealing space and the means for supplying and withdrawing gas to the annular sealing space.

Detailed Description of the Invention

The feeding system according to the invention is a feeding system for supplying a solid feed material that comprises an organic, pyrolysable compound to a pyrolysis reactor.

The feeding system comprises a cylindrical housing containing a feed screw. The feed screw has an upstream end and a downstream end and comprises a helical screw blade mounted on a screw axis. The screw axis is extending beyond the screw blade at the downstream end of the feed screw. Thus, an annular sealing space is provided defined by the inner surface of the cylindrical housing and the part of the screw axis extending beyond the screw helix. During normal operation of the system according to the invention, solid feed material is fed to the upstream end of the feed screw by means known in the art, for example by means of a hopper. The feed material is then transported by the feed screw towards the downstream end of the screw and compressed in the annular sealing space to form an annular seal. The cylindrical housing is extending beyond the downstream end of the feed screw, i.e. beyond the screw axis.

The helical screw blade has a helix pitch that is increasing in downstream direction.

In the feeding system according to the invention, compression of the feed material will occur as a result of the cylindrical housing extending beyond the screw blade. In order to achieve sufficient compression for preventing air to enter the pyro lysis reactor with the feed material, the ratio of the length over which the cylindrical housing is extending beyond the end of the screw blade and the inner diameter of the cylindrical housing is preferably at least 2.5, more preferably at least 3.0, even more preferably at least 4.0. In order to avoid too much compression and therewith undesired compression in the screw blade of the feed screw, the ratio of the length over which the cylindrical housing is extending beyond the end of the screw blade and the inner diameter of the cylindrical housing is preferably at most 8.0, more preferably at most 7.0, even more preferably at most 6.0. The ratio is preferably in the range of from 3.0 to 7.0, more preferably of from 4.0 to 6.0.

In order to prevent or minimize undesired compression in the screw blade of the feed screw, the screw blade has a helix pitch that is increasing in downstream direction. The helix pitch may for example gradually increase in downstream direction.

Alternatively, the helix pitch is stepwise increasing. The screw blade has then a first helix pitch in an upstream section and a second, larger helix pitch in a downstream section. Preferably, the helix pitch gradually increases in downstream direction. It will be within the skills of the skilled person to choose a helix pitch that will, for given dimensions of the feed screw, prevent undesired compression in the screw blade.

Preferably, the helix pitch at the downstream end of the screw blade is in the range of from 1.5 to 4 times larger than the helix pitch at the upstream end of the screw blade, more preferably in the range of from 2 to 3 times larger.

Reference herein to downstream or upstream is with regard to the direction of flow of the feed material.

In order to form a seal of compressed solid feed material in the sealing space, i.e. between the inner surface of the cylindrical housing and the extending screw axis, that prevents air from entering the reactor, the cylindrical housing is preferably a straight cylindrical housing with a constant diameter. The distance between the inner surface of the cylindrical housing and the screw axis is thus constant over the length of the feed screw. An inclined cylindrical housing would either (in case of a cylindrical housing that is diverging in downstream direction) not result in sufficient compression of the feed material to form a seal or would (in case of a cylindrical housing that is converging in downstream direction) result in undesired compression of feed material in the screw blade of the feed screw.

It will be appreciated that the absolute dimensions of the feed screw will strongly depend on the size of the pyrolysis reactor to be supplied with feed material and on the desired feed supply rate. It is within the skills of the skilled person to choose the proper dimensions given the size of the pyrolysis reactor and the desired feed rate.

Preferably, the screw axis is extending from the screw blade at the downstream end of the feed screw over a length in the range of 2 to 50 cm, thus providing an annular sealing space with a length in the range of from 2 to 50 cm. More preferably, the screw axis is extending from the screw blade at the downstream end of the feed screw over a length in the range of 10 to 30 cm.

The cylindrical housing is preferably extending beyond the end of the screw blade over a length in the range of from 50 to 300 cm, more preferably of from 100 to 250 cm.

Preferably, the system is further equipped with additional means to withdraw air from the seal formed by the compressed feed material in the annular sealing space and/or to supply an inert non-oxidant gas to the seal formed by the compressed feed material in the annular sealing space. Therefore, the cylindrical housing defining the annular sealing space has preferably openings for withdrawal of gas from and/or supply of gas to the annular sealing space. The openings are in fluid communication with one or more gas flow channels for withdrawal from and/or supply of gas to the annular sealing space. Such openings are preferably provided with filters in order to prevent feed material from being withdrawn from the process via the openings and the gas flow channel(s). Any suitable filters may be used. Preferably, the filters are made of a porous, fraction-resistant material. Ceramic filters are particularly suitable.

The system may comprise separate gas flow channels for withdrawal of gas, e.g. air, from the annular sealing space and for supply of an non-oxidant inert gas, e.g. nitrogen, to the annular sealing space. Alternatively, the same gas flow channel may be used both for withdrawal from and for supply of gas to the annular sealing space.

The cylindrical housing defining the annular sealing space may have any suitable number of openings, preferably in the range of from 1 to 10 openings, more preferably of from 3 to 6 openings. Suitably, several openings are connected to the same gas flow channel via a so-called collector.

The system for pyrolysis of a solid feed material comprising organic material according to the invention, comprises:

a) a pyrolysis reactor;

b) the feeding system according to the invention for supplying the solid feed

material to the pyrolysis reactor; and

c) a condensation system for condensing pyrolysis gas produced during pyrolysis of the solid feed material in the pyrolysis reactor.

The pyrolysis reactor may be any pyrolysis reactor known in the art. The reactor may be a vertically- or a horizontally-extending reactor, a stationary or a rotary reactor. It may be a reactor for flash pyrolysis or for conventional pyrolysis. Preferably, the pyrolysis reactor is a horizontally-extending, rotary pyrolysis reactor. Horizontally- extending rotary pyrolysis reactors are well-known in the art and are often referred to as rotary drum kilns. Any suitable horizontally-extending rotary pyrolysis reactor known in the art may be used.

During normal operation of the pyrolysis system, the feeding system is supplying the solid feed material to the pyrolysis reactor. Preferably therefore, the cylindrical housing of the feed screw is partly extending into the pyrolysis reactor via an inlet opening at the upstream end of the pyrolysis reactor, such that the compressed solid material will be passed into the pyrolysis reactor. Alternatively, the cylindrical housing may end in an inlet conduit of the reactor. In order to prevent air from the environment to enter the pyrolysis reactor, suitable seals are provided between the outer surface of the stationary cylindrical housing and the inlet opening or inlet conduit of the pyrolysis reactor. Suitable seals are known in the art. In case the reactor is a rotary reactor, a seal capable of sealing the stationary feeding system to the rotary reactor is needed. Such seals are known in the in art.

In case the cylindrical housing is partly extending into the pyrolysis reactor, the distance between the annular sealing space and the inlet of the pyrolysis reactor, i.e. between the end of the extending screw axis and the inlet opening at the upstream end of the rotary pyrolysis reactor through which the cylindrical housing is entering the reactor, needs to be sufficient to avoid solid feed material, such as polyolefm- comprising feed material, to melt in the feed screw or in the annular sealing space.

Preferably, such distance is at least 1 metre, more preferably in the range of from 1.5 to 3 metres.

In case of a horizontally-extending rotary pyrolysis reactor, the reactor has an upstream end with an inlet opening through which the downstream end of the cylindrical housing of the feed supply means is entering the reactor as hereinbefore described. The reactor has a downstream end with an outlet for pyrolysis gas formed during normal operation of the system and optionally an outlet for any inorganic material such as metals or minerals that remains after pyrolysis of the organic material. The outlet for pyrolysis gas is in fluid communication with the condensation system wherein the pyrolysis gas is condensed.

The horizontally- extending rotary pyrolysis reactor may be exactly horizontally extending in the sense that the angle of its central longitudinal axis with the horizontal is 0°. Preferably, however, in order to facilitate transportation of feed material and remaining inorganic material towards the downstream end of the reactor, the reactor is extending such that its central longitudinal axis has a angle of above zero with the horizontal, preferably an angle in the range of from 0.1° to 5°, more preferably of from 0.5° to 3°.

Preferably, the pyrolysis reactor comprises means for conveying solid feed material and any non-pyrolysed inorganic solid material from the upstream end to the downstream end of the reactor and to loosen any solid material that may stick together or to the reactor walls. Any suitable means may be used. Such means are well-known in the art and include but are not limited to baffles, cables, screw blades and lifters or combinations of two or more thereof. The pyrolysis system according to the invention further comprises a

condensation system. The condensation system may be any suitable condensation system for condensing pyrolysis oil. Such systems are well-known in the art. A suitable condensation system may for example comprise in sequence a venturi scrubber using a spray of pyrolysis oil for removing dust from the pyrolysis gas, a primary condenser using thermal oil as coolant and a secondary condenser using water as coolant. For controlling the preferred underpressure in the pyrolysis reactor, the system may further comprise a venturi ejector using steam as motive fluid and using any non-condensable pyrolysis gas withdrawn from the condensation system as inlet gas stream.

In the process according to the invention, the pyrolysis system according to the invention as defined hereinbefore is used for pyrolysis of a solid material that comprises organic material. The process comprises supplying the solid feed material to the pyrolysis reactor by means of the feeding system and pyrolysing the organic material comprised in the solid fed material in the pyrolysis reactor at pyrolysis conditions to obtain pyrolysis gas and condensing at least part of the pyrolysis gas in the condensing system to obtain pyrolysis oil. The pyrolysis oil may be advantageously used to provide heat to the pyrolysis reactor to attain and maintain the desired pyrolysis temperature.

The solid feed material may be any material comprising pyrolysable organic material. Preferably, the solid material comprises lignocellulose or polyolefin as organic material, more preferably polyolefin. The solid feed material may further comprise inorganic material such as metal or minerals that is not pyrolysable.

In case the feed material is a polyolefin-comprising material, it may be any solid material comprising polyolefms, optionally in combination with other pyrolysable organic material. Examples of suitable polyolefin-comprising solid feed material are mixed plastic material such as waste plastics, aluminium-polyolefms laminates, for example aluminium-polyethylene laminates obtained after removal of paper from used "tertrabrik" type beverage packages.

The pyrolysis conditions may be any pyrolysis conditions known to be suitable for the pyrolysis of the organic material comprised in the solid feed material.

Preferably, the pyrolysis conditions comprise a pyrolysis temperature in the range of from 200 to 1000 °C, more preferably of from 300 to 800, even more preferably of from 350 to 660 °C. The pyrolysis conditions may comprise any suitable pressure. Preferably the pyrolysis conditions comprise a pressure in the range of from ambient pressure to a slight under-pressure, for example up to 20 mbar under-pressure. More preferably, the pyrolysis conditions comprise an under-pressure in the range of from 3 to 10 mbar, i.e. a pressure that is 3 to 10 mbar below ambient pressure. Reference herein to ambient pressure is to the pressure prevailing in the environment of the system, i.e. the space in which the system is placed.

Preferably, the solid material comprises polyolefm, more preferably

polyethylene, and aluminium. In case of an aluminium- and polyolefin-comprising solid material, the pyrolysis temperature is below the melting temperature of aluminium, i.e. below 660 °C. In case of an aluminium- comprising feed material, pyrolysis gas and solid aluminum are obtained in the pyrolysis reactor. The system then preferably comprises means for withdrawing solid aluminium from the pyrolysis reactor. In the process according to the invention, solid aluminium withdrawn from the pyrolysis reactor may be further processed by means known in the art in order to recover the solid aluminium, for example as flakes or briquettes.

The process preferably is a process for recovery of aluminium from solid material comprising polyolefms and aluminium, which process further comprises a pretreatment step wherein paper is separated from used laminated beverage packages comprising paper, aluminium and polyolefms to obtain the solid material comprising polyolefms and aluminium. Such pretreatment step is well-known in the art and typically includes soaking used laminated beverage packages comprising paper, aluminium and polyolefms in water to separate the paper from the aluminium and polyolefms layers. The paper thus removed is preferably used to manufacture new paper products in a paper mill, such as for example toilet paper, paper of newspapers, or tissues. In a preferred embodiment of the process according to the invention, pyrolysis gas condensed in the condensing system is used to generate steam for use in the paper mill that manufactures paper from the paper separated from the used laminated beverage packages.

Detailed Description of the Drawings

In Figure 1 is shown a longitudinal section of feeding system 1 and part of pyrolysis reactor 2. Feeding system 1 comprises cylindrical housing 4 wherein feed screw 5 is contained. Feed screw 5 comprises helical screw blade 6 and screw axis 7. Screw axis 7 is connected to motor 8 to drive the feed screw. Feed screw 5 has an upstream end 9 and a downstream end 10. Hopper 11 is placed above upstream end 9 of feed screw 5 for supplying solid feed material to feed screw 5. At its downstream end 10, screw axis 7 is extending beyond helical screw blade 6 such that annular sealing space 12 is defined between the inner surface of cylindrical housing 4 and the extending screw axis. Helical screw blade 6 has a helix pitch that is gradually increasing in downstream direction.

Feeding system 1 is provided with means 15 for withdrawing and/or supplying gas from and/or to annular sealing space 12. Means 15 comprises gas flow path 16 that is in fluid communication with annular sealing space 12 via openings 17 in cylindrical housing 4.

Cylindrical housing 4 is extending into pyro lysis reactor 2. Pyro lysis reactor 2 comprises a horizontally extending rotary pyrolysis chamber 20 defined by cylindrical wall 21 and surrounded by furnace 22. A seal 23 is provided between the outer surface of cylindrical housing 4 and the inner surface of cylindrical wall 21 to prevent air from entering pyrolysis chamber 20.

In Figure 2 is schematically shown a cross-section of means 15, i.e. a cross- section through the plane II-II of the feeding system of Figure 1. Corresponding reference numbers have the same meaning as in Figure 1. Means 15 comprises four openings 17 in cylindrical housing 4 that are all provided with a filter 25. All four openings 17 are in fluid communication with gas flow path 16 that has an inlet 26 for supplying gas to annular sealing space 12 and an outlet 27 or withdrawing gas from annular sealing space 12.