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Title:
PYROLYSIS FEEDSTOCK CONDITIONING COMPRISING DRYER AND SEPARATOR
Document Type and Number:
WIPO Patent Application WO/2017/221006
Kind Code:
A1
Abstract:
An apparatus for conditioning organic feedstock prior to combustion in a pyrolysis kiln is disclosed. In one arrangement a container is provided having an inlet and an outlet for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the heater comprises a liquid to air heat exchanger that comprises a network of conduits through which a heated liquid is flowed. Multiple arrangements can be provided where the fluid to the heaters can be supplied through a manifold room multiple heaters of a multiple lane pyrolysis system to allow continued operation with one or more of the heaters taken off line. Also disclosed is a conditioner that uses a rotating drum and an air knife to help separate material.

Inventors:
HARRADINE, Mark (17 Milestone Road, OakdalePoole, Dorset BH15 3DR, BH15 3DR, GB)
Application Number:
GB2017/051813
Publication Date:
December 28, 2017
Filing Date:
June 20, 2017
Export Citation:
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Assignee:
SYNGAS PRODUCTS LIMITED (Energy Site Control Centre, Arena WayMagma Road,Wimbourne, Dorset BH21 3BW, BH21 3BW, GB)
International Classes:
C10B57/08; B07B4/06; C10B53/00; F26B3/20; F26B17/04; F26B23/10
Domestic Patent References:
WO2005043057A12005-05-12
Foreign References:
US20110097680A12011-04-28
GB2503065A2013-12-18
GB207809A1925-04-23
Other References:
SOL ENVIRONMENT ET AL: "EPR SWIP PERMIT APPLICATION SUPPORT DOCUMENT Syngas Products Ltd Canford Low Carbon Energy Facility", 1 October 2015 (2015-10-01), pages 9372811, XP055398145, Retrieved from the Internet [retrieved on 20170810]
Attorney, Agent or Firm:
BARKER BRETTELL LLP (100 Hagley Road, EdgbastonBirmingham, West Midlands B16 8QQ, B16 8QQ, GB)
Download PDF:
Claims:
CLAIMS

1. A feedstock conditioner stage for conditioning organic feedstock prior to combustion in a pyrolysis kiln, the conditioner stage comprising a container having an inlet and an outlet for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the heater comprises a liquid to air heat exchanger that comprises a network of conduits through which a heated liquid is flowed.

2. A feedstock conditioner stage according to claim 1 in which the heat exchanger comprises a fin type heat exchanger in which air passes over and around a set of fins similar to a normal vehicle radiator, the air obtaining heat from the hot water passing through the heat exchanger.

3. A feedstock conditioner stage according to claim 1 or claim 2 in which the dryer includes a fan which blows air through, or sucks air through, the heat exchanger and across the material in the container. 4. A feedstock conditioner stage according to claim 3 in which the heat exchanger and the fan is located outside of the container, air entering the container through openings in at least one of the top, bottom and sides of the container.

5. A feedstock conditioner stage according to any preceding claim in which the conduits of the heat exchanger are connected in a closed loop of pipes that connects the flow to an output of a secondary heat exchanger, an input of the secondary heat exchanger being connected to a source of heat from a heat engine.

6. A feedstock conditioner stage according to claim 5 in which the source of heat from the heat engine comprises a closed loop of pipe through which a liquid flows that extracts heat from the heat engine, the two closed loops being isolated so that fluid in one loop does not flow into the other loop.

7. A feedstock conditioner stage according to claim 5 or claim 6 in which the secondary heat exchanger comprises a first part heated by cooling fluid circulating in the loop to the engine and a second part that transfers the heat to the loop to the dryer. 8. A feedstock conditioner stage according to claim 7 in which the secondary heat exchanger extracts heat from a plurality of heat engines, and where a single closed loop may be provided for each heat engine, each closed loop being isolated from the others so that fluid can flow in one loop when the other loop is opened or blocked. 9. A feedstock conditioner stage according to any preceding claim in which the heater in use heats the air that flows to the container to no more than 70 degrees C.

10. A feedstock conditioner stage according to any preceding claim in which the container includes a conveyor which moves feedstock material slowly from the inlet to the outlet as it is dried.

1 1. A feedstock conditioner stage according to any preceding claim which includes a bale shredder that in use shreds bales of feedstock and passes the shredded bales to the inlet of the dryer.

12. A feedstock conditioner stage for conditioning feedstock prior to combustion in a pyrolysis system, the conditioner stage comprising a separating means for separating heavy material from lighter material, the separating means comprising a first rotating drum onto which material drops from a feeder located upstream of the first rotation drum, the drum in use rotating in a direction that causes the material to be flicked away from the drum towards a second rotating drum, the second rotating drum in use rotating in the same direction as the first drum, and a stream of air that flows forcefully upwards between the two rotating drums, in which the stream of air is sufficient to blow lighter material flicked from the first drum to clear the second drum or to land on the second drum which in turn helps the material clear the second drum, and insufficient to blow heavier items onto the second drum or far enough onto the second drum for them to be carried over.

13. A feedstock conditioner stage according to claim 12 which further includes a motor that causes the first drum to rotate and a motor controller.

14. A feedstock conditioner stage according to claim 12 or claim 13 which further includes a motor that rotates the second drum and a motor controller.

15. A feedstock conditioner stage according to any one of claims 12 to 14 which includes one motor that rotates both the drums through a system of gears.

16. A feedstock conditioner stage according to any one of claims 12 to 15 which further comprises a collection bin located below the gap between the two drums to collect the heavy items.

17. A feedstock conditioner stage according to any one of claims 12 to 16 which includes a fan located below the two drums that generates the air stream.

18. A feedstock conditioner stage according to any one of claims 12 to 17 which further includes an extractor for extracting the air in the stream and filtering the air to remove any light material that has become entrained.

19. A feedstock conditioner stage according to any one of claims 12 to 18 which includes an output bin into which the light material that has cleared the second drum is collected, the output bin being connected to an input of a pyrolysis kiln for pyrolysing the light material.

20. A feedstock conditioner stage according to any preceding claim which includes a means for weighing the dried and sorted material.

21. A pyrolysis system comprising in parallel at least two process lines, each process line comprising the following:

A pyrolysis kiln having an inlet for the dried material output from the dryer and an outlet for pyrolysis gas produced in the kiln, and

A heat engine that burns the pyrolysis gas, the heat engine being cooled by a fluid cooling system,

And further in which each line is associated with a dryer having an inlet and an outlet and a container therebetween for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the dryer comprises a network of conduits through which heated liquid is flowed.

22. A pyrolysis system according to claim 21 comprising one dryer for each line.

23. A pyrolysis system according to claim 21 or claim 22 in which at least one of the dryers is arranged so as to be able to extract heat from more than one heat engine.

Description:
PYROLYSIS FEEDSTOCK CONDITIONING COMPRISING DRYER AND SEPARATOR

The present invention relates to a feedstock conditioner stage for conditioning feedstock prior to combustion in a pyrolysis process.

In a known pyrolysis process, a feedstock of combustible organic material is fed into a heated pyrolysis kiln. Suitable feedstocks include municipal sourced waste (MSW) and refuse derived fuel (RDF) and also include wood and pellets, crops and other agricultural waste . Heat from a furnace that surrounds the kiln heats the feedstock material to a temperature at which pyrolysis of the material occurs. During this heating it is important that the flow of air into the kiln is prevented, as otherwise the heated pyrolysis gases and char would combust and prevent the production of syngas, and in extreme circumstances may cause an explosion. The pyrolysis process converts the organic material into char by releasing volatile pyrolysis gases and tars and an amount of fine carbon particulates.

The pyrolysis kiln may be a rotary kiln type kiln as described in GB2441721 B which is incorporated herein by reference . This document describes a rotary kiln having a stationary inlet, a stationary outlet, and a rotary kiln, the inlet being upstream of the kiln which is in turn upstream of the outlet. A rotary seal connects the kiln to the inlet and a further rotary seal connects the kiln to the outlet, the seals preventing air entering the kiln. The kiln typically slopes down from the inlet to the outlet to encourage the feedstock that enters through the inlet to move towards the outlet. The dust laden pyrolysis gases, which may also contain evaporated oils and water vapour, is removed from the outlet stage of the kiln and passed through a filter. The filter must be able to cope with high temperatures and may be a ceramic filter of the kind described in GB2409655B which is also incorporated herein by reference . The ceramic filter is located within a vessel and is scrubbed by a set of rings that can be moved up and down the outer wall of the cylindrical filter element. This removes the solids such as char and entrained dust from the gas.

The filtered gas is then passed through a quencher to cool the gas and remove entrained contaminants such as tars and water to leave a relatively pure synthesized gas known as syngas. This gas can then be burnt to drive a heat engine, such as a spark ignition gas engine or gas turbine, in order to generate electricity, or may be partially used as fuel for the furnace, or simply stored for later use or sale.

The solids that are separated from the gas by the filter, in the form of char, may also be used to extract further energy. They may typically be fed to a gasifier which again heats the solids but in the presence of both oxygen (as pure oxygen or in air) and steam, and this gasification extracts any remaining gases and turns the char into ash. These extracted gases, also a form of syngas, may be used as fuel to heat the pyrolyser kiln.

A range of different gasifiers may be used. In the example taught in GB2409655B the gasification takes place towards the top end of the gasifier, and the ash that is left over from the process falls down to the bottom where it can be removed, cooled and bagged.

The use of the pyrolysis process enables the energy contained in the feedstock to be extracted and put to use rather than the traditional process of sending the waste to a landfill site . Because the gases and other waste products can be carefully contained and not emitted into the atmosphere, the process is far cleaner than other combustion processes such as a incineration of organic feedstocks.

The present invention aims to ameliorate at least one limitation on the efficiency of operation of prior pyrolysis systems, in particular relating to the effect of processing low quality mostly solid feedstocks.

According to a first aspect the invention provides a feedstock conditioner stage for conditioning organic feedstock prior to combustion in a pyrolysis kiln, the conditioner stage comprising a container having an inlet and an outlet for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the heater comprises a liquid to air heat exchanger that comprises a network of conduits through which a heated liquid is flowed.

The heat exchanger may comprise a plate type heat exchanger in which the fluid conduits are connected to, or located within, a plurality of thermally conductive plates, air being passed across the plates where it is heated. The heat exchanger may comprise a shell type heat exchanger in which the conduits extend within an insulating shell, air being passed through the shell over the conduits where it is heated.

The heat exchanger may comprise a fin type heat exchanger in which air passes over and around a set of fins defined by the plates similar to a normal vehicle radiator, the air obtaining heat from the hot water passing through the heat exchanger. The dryer may include a fan which blows air through, or sucks air through, the heat exchanger and across the material in the container. There may be more than one fan.

The heat exchanger and the fan or fans may be located outside of the container, air entering the container through openings in at least one of the top, bottom and sides of the container.

The conduits of the heat exchanger may be connected in a closed loop of pipes that connects the flow to an output of a secondary heat exchanger, an input of the secondary heat exchanger being connected to a source of heat from a heat engine.

The source of heat from the heat engine may comprise a closed loop of pipe through which a liquid flows that extracts heat from the heat engine, the two closed loops being isolated so that fluid in one loop does not flow into the other loop. The heat engine may comprise a gas turbine .

The secondary heat exchanger may comprise a first part heated by cooling fluid circulating in the loop to the engine and a second part that transfers the heat to the loop to the dryer. The first and second parts may comprise a plurality of interleaved thermally conductive plates.

The secondary heat exchanger may extract heat from a plurality of heat engines, for example by taking heat from liquids that flow in a respective closed loop associated with each heat engine. A single closed loop may be provided for each heat engine. These loops may be isolated from each other so that fluid can flow in one loop when the other loop is opened or blocked.

An advantage of providing a separate flow loop of fluid between the heater and the secondary heat exchanger and a separate flow loop of fluid to cool the engine(s) is that there is no risk of contamination of the fluid in the heater. A further advantage is that the engine can be shut down without the flow of heated fluid through the heater having to be shut down.

A pump may be provided for moving the heated fluid through the loop of the heater. A pump may also be provided for moving fluid around the loop to the heat engine .

The container may comprise a metal walled container having openings in at least one of the sides, top and bottom that allow the heated air to enter the container from the heater. The heater may therefore be located outside of the container.

The heater may in use heat the air that flows to the container to no more than 70 degrees C, with the air typically exiting the container at around 30 degrees C. Using a low heat ensures there is no risk of fire of the feedstock, and also that volatile organic compounds are not boiled off as the feedstock is heated.

The liquid that flows through the heater may comprise water. The container may include a conveyor which moves feedstock material slowly from the inlet to the outlet as it is dried. The conveyor may comprise a belt type conveyor, and may rise from the inlet end to the outlet end.

A feeder may be provided for adding material at the inlet of the container that is picked up by the conveyor and moved through the dryer to the outlet.

The feedstock conditioner stage may include a bale shredder that in use shreds bales of feedstock and passes the shredded bales to the inlet of the dryer. Use of the shredder allows for feedstock to be received and handled in a more convenient baled form, rather than as loose feedstock. This can be thrown into the shredded without the need to manually open the bale, reducing the amount of manual labour required to condition the material.

The shredder may be sized to receive one bale at a time. It may be sized to receive standard bales that measure between 0.8m and 1.2m in both length and diameter.

According to a second aspect the invention comprises a feedstock conditioner stage for conditioning feedstock prior to combustion in a pyrolysis system, the conditioner stage comprising a separating means for separating heavy material from lighter material, the separating means comprising a first rotating drum onto which material drops from a feeder located upstream of the first rotation drum, the drum in use rotating in a direction that causes the material to be flicked away from the drum towards a second rotating drum, the second rotating drum in use rotating in the same direction as the first drum, and a stream of air that flows forcefully upwards between the two rotating drums, in which the stream of air is sufficient to blow lighter material flicked from the first drum to clear the second drum or to land on the second drum which in turn helps the material clear the second drum, and insufficient to blow heavier items onto the second drum or far enough onto the second drum for them to be carried over.

The feedstock conditioning stage may include a motor that causes the first drum to rotate and a motor controller. A separate motor may be provided that rotates the second drum, which may also be associated with a motor controller. In a modification, a single motor may rotate both the drums through a system of gears.

The stage may include a collection bin located below the gap between the two drums to collect the heavy items. The conditioner stage may be located adjacent a conveyor which drops feedstock onto the first rotating drum as it falls off the end of the conveyor.

The stage may include a fan located below the two drums that generates the air stream. The air stream may be considered to be an air knife, cutting through the supply of material that is flicked from the first drum. The stage may include an extractor for extracting the air in the stream and filtering the air to remove any light material that has become entrained. The stage may include an output bin into which the light material that has cleared the second drum is collected.

The output bin may be connected to an input of a pyrolysis kiln for pyrolysing the light material.

The features of the first two aspects may be combined to provide an overall material processing system that first dries and then separates the material before passing it to a pyrolysing kiln. Thus, the conditioner of the second aspect may be located downstream from a heater for drying material as described in relation to the first aspect of the invention. The conveyor of the heater may drop material directly onto the first rotating drum of the conditioner.

The material processing system may include a means for weighing the dried and sorted material. This may comprise an electronic scales onto which the dried and sorted material is placed.

The kiln may comprise a rotary kiln and there may be provided between the inlet stage and the rotary kin and/or between the rotary kiln and the outlet stage a rotary joint mechanism.

The system may comprise a face seal between a rotating surface of a first seal member fixed to the kiln and a stationary surface of a second seal member fixed to the respective stage. In a preferred embodiment the sealing surfaces of the first and second seal members are annular.

The seal members are preferably attached to respective inlet and outlet pipes of the rotary joint mechanism. It will be noted that the inlet stage is upstream of the kiln and that the kiln is upstream of the outlet stage. It will be also noted that the outlet stage is downstream of the kiln and that the kiln is downstream of the inlet stage. In preferred arrangements the upstream device comprises an outlet pipe which extends through an inlet pipe of larger diameter of the downstream device . Most preferably, said outlet pipe extends into the downstream device itself, which has the advantage of directing the conveyed material away from the respective rotary joint mechanism.

The rotary joint mechanism may incorporate a passageway for the introduction of an inert purging gas to prevent entry of air into the system and/or to prevent gases from leaving the system. The passageway preferably extends to the sealing surface of the stationary seal member from another surface of the stationary seal member, preferably from an outer cylindrical surface thereof.

To cater for solid materials to be pyrolysed which are not substantially plastic, the inlet stage may be provided with a valve mechanism to constitute an inlet seal. The valve may be a rotary valve or a double flap valve or other mechanical sealing device.

Alternatively, to cater for liquids or slurry materials to be pyrolysed, the inlet seal is achieved by means of a pump connected to a feed pipe. The outlet side of the system preferably comprises a filter for dust-laden gases leaving the kiln, the filtered gases passing to a gas outlet. Solids emerging from the kiln pass from an outlet receptacle or drop out box to a conveying device.

A valve, such as a rotary valve or a double flap valve, may be provided between the container and the conveying device to serve as an outlet seal. Alternatively, the seal can be made by maintaining a column of material between the container (e.g. a drop out box) and the conveying device.

The applicant has appreciated that the dryer and separator are especially suitable for use in a modular pyrolysing system.

Therefore, according to a further aspect the invention provides a pyrolysis system comprising in parallel at least two process lines, each process line comprising the following: A pyrolysis kiln having an inlet for the dried material output from the dryer and an outlet for pyrolysis gas produced in the kiln, and

A heat engine that burns the pyrolysis gas, the heat engine being cooled by a fluid cooling system,

And further in which each line is associated with a dryer having an inlet and an outlet and a container therebetween for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the dryer comprises a network of conduits through which heated liquid is flowed. The may be one dryer provided for each line, or two or more lines may share one dryer.

The dryer, or multiple dryers, may each be able to extract heat from more than one heat engine .

The system may comprise more than two parallel lines. In that case, the heater of each line may be able to source heat from the engine of any of the other lines.

Each of the lines may be configured for operation independent of the other lines.

Each of the heaters may be connected to a common secondary heat exchanger that transfers heat from each heat engine to the dryers.

The system may include flow valves that enable the flow of heat energy, via the transfer liquids, from the secondary heat exchangers to the dryers to be independently controlled.

There will now be described, by way of example only, one embodiment of the present invention with reference to and as illustrated in the accompanying drawings of which:

Figure 1 is a schematic of a pyrolysis system that incorporates various embodiments of features that fall within the scope of the present invention;

Figure 2 is a more detailed block diagram showing the parts of the drying/shredding stage shown in Figure 1 ; Figure 3 is a view of an exemplary bale shredder;

Figure 4 is a view of an embodiment of a dryer that forms a part of the drying/shredding stage; and

Figure 5 is a view of an air knife and separator that follows the dryer.

Figure 6 is an overview of an alternative embodiment of a pyrolysis system including multiple lines that can be operated in parallel.

Figure 1 is an overview of the different stages of a complete pyrolysis system that embodies several features that are in accordance with aspects of the present invention. The reader will appreciate that various modifications to the system can be made within the scope of the present invention, and that the modified system would also fall within the scope of the present invention.

The system starts with feedstock material 1 on the left side of Figure 1 , which may be municipal source waste or refuse derived waste although other solid wastes can be used. The feedstock moves through the process from the left to the right hand side of the flow diagram, being transformed into char and gas and other materials during the process to the final output gas and energy 2 on the right hand side. The feedstock material is fed into a feedstock conditioner 3 which shreds, dries and sorts the waste before it is weighed and then compacted 4 and fed into a pyrolysis kiln 4. The compaction ensures an air tight seal is achieved at the input to the pyrolysis kiln 5. The kiln may be of the rotating drum type described in GB2441721.

The kiln is heated by combustion 5 to cause the material in the kiln to be pyrolysed, and the pyrolysed gas and carbon particulate is removed from the kiln at high temperature and fed into a filtering stage 6 which removes solids and the gas is then quenched 7 to cool the gas and remove effluents 8, heavy oils 9 and light oils 10. The cleaned gas is the fed via a diverter valve 1 1 to a heat engine 12, such as a gas turbine, which generates heat or electricity as the energy output 2. In the event that the rate of production of gas is too high for the engine 12 to consume- say if the engine is off line- the diverter valve 1 1 can send the gas to a flare 13 where it is burnt off.

The filter 6, as well as passing the solid free gas, also extracts char 14 which is collected and further gasified 15. The gas produced, together with any light oil 10 removed during quenching 7, is used as fuel to heat the combustion furnace 5 that heats the pyrolysis kiln. The hot air and exhaust from the heating of the pyrolysis chamber is recirculated to extract the heat energy in a process of regeneration 16, and the extract heat is used in turn to heat the air being fed to the furnace . This ensures that no energy is wasted. The ash produced from gasification is cooled and bagged for removal.

In order to maximize the cost benefit of the system it is desirable to reduce the amount of manual input that is needed, automating as much as possible . It is also desirable to maximize the amount of gas produced for a given weight of feedstock. The reason for this is that in most countries the process can only be operated under licence and the licence will determine how much feedstock a site can process in a given period. The process is closely regulated because of the potential for waste gas to be emitted into the environment in the event of a fault, and because the delivery of large volumes of feedstock- typically municipal waste- can cause an environmental hazard if unlimited.

In order to maximize the efficiency of the process, the feedstock material is conditioned before it is compacted and fed to the pyrolysis kiln. The conditioning stage, which shreds and dries and sorts the material, is shown in more detail in the block diagram of Figure 2 of the drawings. As can be seen this comprises a bale shredder 17, a dryer 18, and an air knife/separator 19 and finally an output hopper. The material in the output hopper is picked up and fed to the kiln and will be of a higher quality than the feedstock entering the conditioning stage 2. The bale shredder 17 is shown in Figure 3 of the drawings and comprises a hopper 17a into which bales of feedstock, typically compacted and partially shredded municipal waste, can be dropped

The hopper has a die 17c partway down its length and a set of powered blades 17d that slide through the bale and force the sliced bales down through the die . The material dropping out of the bottom of the die is therefore shredded and removed from the bales.

The reader will appreciate that other forms of bale shredder may be used, and indeed the shredder could even be omitted if a form of non-compacted feedstock was provided which did not need to be shredded.

The material drops into the dryer 18, which is shown in Figure 4. The dryer 18 comprises a low speed conveyor belt 180 located inside a relatively large metal walled container 181. The container has a set of holes (not shown) in its sides and top and is surrounded by a water heated radiator 182. The radiator 182 is in turn surrounded by an insulating jacket 183. The radiator comprises a set of conductive fins that surround conduits through which heated water is passed. As the water passes through the conduits heat energy passes into the fins, which in turn heats the surrounding air. This air passes through the openings in the sides and top of the metal container to heat and dry the shredded material.

The water that passes through the radiator flows around a closed loop circuit 184. As shown the circuit has an inlet pipe for carrying water to the radiator and an outlet pipe for carrying the relatively cooler water away from the radiator. A pump 185 moves the water around the loop. The loop passes through a heat exchanger 186 which transfers heat from a secondary water loop 187 that passes through the heat engine 2. The water in the secondary loop is heated by waste heat from the heat engine, in the process helping to cool the heat engine 2. This heat is transferred by the heat exchanger into the first loop which then transfers the heat to the radiator 182

The heat dries the material as it is moved slowly through the container by the conveyor. The now drier material exits the dryer 18 by falling from the conveyor onto the air knife/separator 19. This is shown in Figure 5.

The separator 19 sorts light material, which is predominantly organic and suitable for pyrolysis, from heavier materials such as metal which are not suitable . The separator 19 comprises a first rotating drum 191 onto which material drops as it falls off the end of the conveyor, the drum rotating in a direction that causes the material to be flicked away from the drum 191 towards a second rotating drum 192. The second rotating drum rotates in the same direction as the first drum. A high velocity focused stream of air from an air knife flows forcefully upwards between the two rotating drums. The flicked material is thrown through the stream of air. The stream of air is sufficiently powerful to blow lighter material flicked from the first drum clear over the second drum or to land on the second drum which in turn helps the material clear the second drum, and insufficient to blow heavier items onto the second drum or far enough onto the second drum for them to be carried over. The heavy items therefore fall down between the two drums 191 and 192.

By conditioning the material with a shredder and dryer and a separator which fluffs up the material and dries it, unwanted water and inorganic material such as metal components are removed. The dryer and sorted material is then weighed, and this weight is used as the starting measure for the material that is processed. As this sorted and dried material will have a higher percentage of organics for a given weight, the amount that can be processed under licence is maximized.

Although Figure 1 shows the layout of a single stage pyrolysis system, the present invention is especially advantageous when implemented as a set of parallel stages or pyrolysis lines. Figure 6 shows the connection of the various parts of the system where two pyrolysis kilns and two heat engines are operated in parallel. The first line comprises one dryer 60, one kiln 61 and one heat engine 62, the second line also comprising one dryer 63, one kiln 64 and one heat engine 65. Each of these lines can be run independently of the other, meaning that one line can be shut down for servicing without the need to shut the other.

To maximize profitability and throughput for the system, it is important to minimize the time that a line has to be shut for maintenance of repair work. The applicant has appreciated that one of the key areas of maintenance is the heat engines 62, 65, and in the event that an engine is shut down the whole line may need to be closed as the engine supplies heat for the dryers.

To reduce downtime, each of the two dryers 60, 63 can be supplied with heat from any one of the two engines 62, 65. This is possible by connecting each of the heaters of the dryers through a suitable manifold 66 and pipes to each of the two engines. Each heater has its own closed loop water circuit 60a, 63a that connects the heater to the single manifold 66, and the manifold 66 is then connected through a series of water loops to both of the engines. The heat from both of the engines therefore heats the water in the loops to all of the heaters. Hence as long as one engine is running all of the heaters can be supplied with heat.

The provision of the separate loops from heater to manifold, and manifold to engine, also allow the water in the engine cooling to be drained down without the need to drain down the heater and take it off line.