GB2475951A

GB2475951A - Method and apparatus for processing waste

Info

Publication number: GB2475951A
Application number: GB1019261A
Authority: GB
Inventors: Paul Anthony Burrows; Adrian Martin Burt
Original assignee: Babcock Environmental Engineering Ltd
Current assignee: Shanks Environmental Engineering Ltd
Priority date: 2009-11-13
Filing date: 2010-11-15
Publication date: 2011-06-08
Also published as: GB201019261D0; GB0919933D0

Abstract

A waste treatment method comprises feeding waste 1 to a first waste processing unit 5, applying heat and/or pressure and/or moisture to the waste in the first waste processing unit; feeding the waste from the first waste processing unit to a second waste processing unit 13, passing a gas flow over the waste in the second waste processing unit and/or heating the waste in the second waste processing unit by heat generated from a property of and/or process occurring within the waste. The second waste processing unit may include pyrolysis and/or gasification. The second unit may be a dryer and the first unit may be an autoclave. The waste stream which leaves the second unit may be a fibre waste stream with a moisture content of less than 25% by weight. There may be a third unit 7 after the second unit which includes a pyrolysis and/or gasification step. The third unit may produce a product stream including hydrogen and carbon monoxide. An apparatus for carrying out the method is also provided.

Description

IMPROVEMENTS IN AND RELATING TO PROCESSING

The present invention concerns improvements in and relating to processing, particularly, but not exclusively in relating to the processing of waste, such as household waste, commercial waste and the like.

Various solutions have been proposed to try and increase the amount of waste which is recycled and/or to reduce the amount of waste which is disposed of in landfill sites.

In some approaches, the waste is processed to enable it to be subjected to a pyrolysis/gasification step so as to generate useful fuel. The cost of the processing stages required can limit the commercial suitability of such approaches. The form of the waste fed to the pyrolysis/gasification step can impact upon the performance of that step.

The present invention has amongst its possible aims to reduce the cost of operating a waste processing system. The present invention has amongst its possible aims to improve the form of feed to subsequent steps within a waste processing system. The present invention has amongst its possible aims to improve the performance of the waste processing system.

According to a first aspect, the invention provides a system for processing waste, the system including: a first waste processing unit, the first waste processing unit being connected to a heat source and/or being connected to a pressure source and/or a moisture source; and/or a second waste processing unit, the second waste processing unit being connected to a gas flow source.

According to a second aspect, the invention provides a method of processing waste, the method including: providing waste; feeding waste to a first waste processing unit, applying heat and/or pressure and/or moisture to the waste in the first waste processing unit; feeding the waste from the first waste processing unit to a second waste processing unit, passing a gas flow over the waste in the second waste processing unit and/or heating the waste in the second waste processing unit by heat generated from a property of and/or process occurring within the waste.

The waste may be or include domestic or household waste. The waste may be or include commercial waste. The waste may be a mixture of two or more components. A component may be one or more of: ferrous metals, non-ferrous metals, plastics, wood, textiles, organics, inorganics.

The waste may be conveyed to a first location at the site of the system. The first location may be within an enclosure. The enclosure may have one or more doors for waste and/or waste delivery vehicles. The enclosure may be at a negative pressure compared with the enclosures environment. The enclosure may have an inward airflow at an open door into the enclosure. The enclosure may be provided with a gas and/or an odour treatment system.

The waste may be emptied from delivery vehicles within the enclosure. One or more initial storage locations may be provided for the waste within the enclosure.

The first waste processing unit may be connected to a heat source and a pressure source and a moisture source. The moisture source may also provide some or all of the heat source. The moisture source may be a steam source.

The first waste processing unit may be an autoclave. One or more autoclaves may be provided, preferably operating in parallel.

The waste may be conveyed from the first location to the first waste processing unit.

The means of conveying may include one or more conveyors, for instance hi-directional conveyors. The waste may be loaded into one or more storage locations, for instance one or more hoppers. The one or more storage locations may provide a waste flow rate buffering.

The waste may be loaded from one or more of the storage locations and/or hoppers into the first waste processing unit.

The loading of the first waste processing unit may include one or more of: opening a door on the first waste processing unit; moving one or more of the storage locations and/or hoppers towards the first waste processing unit; discharging waste from the one or more storage locations and/or hoppers into the first waste processing unit, for instance by using a hydraulic ram; closing the door on the first waste processing unit.

The first waste processing unit may be at least 1 Om in length. The first waste processing unit maybe less than 30m in length. The first waste processing unit may have a diameter of at least 2m. The first waste processing unit may have a diameter of less than 5m.

The first waste processing unit may have a capacity of at least 5 tonnes of waste.

The first waste processing unit may include a plurality of autoclaves.

The first waste processing unit may include one or more of the steps: introducing an above atmospheric pressure gas and/or vapour into the first waste processing unit, for instance steam; applying the pressure for at least 5 minutes and/or less than 45 minutes and/or for a period of 15 to 20 minutes +1-2 minutes; rotating the first waste processing unit; venting air from the first waste processing unit; increasing the temperature within the first waste processing unit, for instance to at least 150°C; increasing the pressure within the first waste processing unit to at least 5 bar.

The first waste processing unit may have its axis of rotation inclined. The first waste processing unit may be provided with one or more elements which lift the waste during rotation and/or which drop the waste from an elevated position during rotation.

The first waste processing unit may include one or more of the steps: reducing the pressure within the first waste processing unit, preferably to atmospheric, over a period of at least 10 minutes and/or less than 20 minutes; venting gas and/or vapour, for instance steam, from the first waste processing unit; rotating the first waste processing unit during the venting and/or pressure reduction; opening a door in the first waste processing unit; rotating the first waste processing unit to discharge the waste, for instance onto a discharge conveyor.

The first waste processing unit may provide one or more of: converting the organic elements of the waste into fibre form and/or a biomass form; providing the inorganic elements in a clean form; removing labels and/or lacquer paints, for instance from cans and bottles; deforming plastics, particularly heavy plastics, and metals; converting plastics, particularly light plastics, to lump form.

The steam for the first waste processing unit may be generated using a composite boiler. The steam may be generated using hot exhaust gas from a combined heat and power engine and/or a gas burner, for instance to raise steam to the temperature and pressure required for the first waste processing unit.

The steam vented from the first waste processing unit may be processed, for instance using a condenser and/or then a heat exchanger. The water obtained may be passed through a water treatment unit, for instance to allow its reuse in the process system.

Any gas and/or vapour arising from the first waste processing unit may be treated, for instance by being passed through a scrubber, for instance a bioscrubber with carbon polisher.

The scrubber may also be fed gas and/or vapour from extractor hoods provided over the door(s) for the first waste processing unit.

The first waste processing unit may generate a waste stream, particularly a solid and/or liquid waste stream which is fed, directly or indirectly, to the second waste processing unit.

The second waste processing unit may be connected to a gas source, for instance an air source. The second waste processing unit may be connected to an off gas and/or off vapour treatment unit.

The second waste processing unit may be a dryer, particularly a bio-dryer.

The second waste processing unit may be continuously process waste.

The solid waste stream leaving the second waste processing unit is preferably the fibre waste stream. The fibre waste stream may have a reduced moisture content when leaving the second waste processing unit compared with the moisture content of the waste entering the second waste processing unit. The fibre waste stream leaving the second waste processing unit may have a moisture content of less than 25% by weight, more preferably less than 22% by weight. The moisture content may be 20% +/-2%.

The second waste processing unit may be loaded from one or more storage locations and/or hoppers.

Particularly in one form, the second waste processing unit may include a plurality of process units of the same type, preferably operated in a parallel.

Particularly in one form, the second waste processing unit may be rotated.

Particularly in one form, the second waste processing unit may have a rate of rotation of more than 1 revolution per hour and/or less than 15 revolutions per hour, for instance 3 revolutions per hour +7-1 revolution. Particularly in one form, the second waste processing unit may be in the form of a drum. Particularly in one form, the second waste processing unit may be at least 2m in diameter and preferably at least 3m in diameter. Particularly in one form, the second waste processing unit maybe at least 20m long and preferably more than 30m long.

Particularly in one form, the second waste processing unit may have one or more internal helixes running along at least a part of the length. Particularly in one form, the second waste processing unit may include one or more means to promote movement of the waste from one part of the second waste processing unit to another part, preferably one end to the other end.

Particularly in one form, the second waste processing unit may provide for dispersing microorganisms and/or a microorganism seeded material in the waste.

Particularly in one form, the second waste processing unit may provide for the distribution of oxygen through the waste.

Particularly in one form, the second waste processing unit may provide a residence time of at least 24 hours and/or less than 125 hours, for instance 72 hours +/-10 hours.

Particularly in one form, the second waste processing unit may provide for self heating by the waste. The self heating may be provided by biodegradation of the organic components in the waste. The self heating may promote the transfer of moisture out of the waste, and preferably into a gas flow.

Particularly in one form, the second waste processing unit may provide a flow of gas, for instance warm air, over the waste. The gas may be blown through the second waste processing unit, ideally to remove moisture from the waste.

Particularly in one form, the second waste processing unit may not receive any external thermal energy.

Particularly in one form, the second waste processing unit may receive additional thermal energy, for instance from heat exchangers located at one or more locations in the process system.

Particularly in second form, the second waste processing unit may provide a contained working area, for instance a flat bottomed and/or walled enclosure and/or roofed enclosure. The waste, particularly a given volume of waste, maybe introduced to an area within the enclosure. The waste may be resident in the area for the desired time period. The desired period of time may be a residence time of at least 24 hours and/or less than 125 hours, for instance 72 hours +/-10 hours. Subsequent volumes of waste may each be introduced to other distinct areas with the enclosure.

Particularly in second form, the second waste processing unit may, for instance periodically, provide for agitation of the waste in an area. The agitation may promote moisture transfer to a gas flow, for instance air. The agitation may prevent and/or reduce compaction of the waste, for instance under its own weight. At the end of the desired residence time, the waste in a given area is removed from the enclosure and passes on to the next step.

The system may include a third waste processing unit. The third waste processing unit may be provided after the second processing unit. The third waste processing unit may include a pyrolysis step and/or gasification step. The third waste processing unit may provide both a pyrolysis step and a gasification step. The third waste processing unit may provide a product stream including hydrogen and carbon monoxide. The third waste processing unit may provide a product stream including a solid and/or liquid residue.

The system may include a burner for the hydrogen and carbon monoxide product.

The burner may be provided as a part of a combined heat and power unit. The burner may be provided after the third waste processing unit.

The system may recycle steam and/or hot water to one or more locations within the process system. The system may use electricity generated by the burning at one or more locations within the system. The system may fed electricity generated by the burning into an electricity distribution network.

The system may include processing the emissions from the burner, for instance using an emission control system.

The system may include a further waste processing unit. The further waste processing unit may be provided between the first waste processing unit and the second waste processing unit. The further waste processing unit may be a waste sorting unit. The waste sorting unit may segregate the waste into two or more waste streams. The waste streams may include a fibre waste stream. The fibre waste stream may be conveyed to the second processing unit.

The further waste processing unit may produce a series of waste streams which are not fed to the third waste processing unit. One or more of the waste streams may be fed to containers, for instance for transportation to other sites and/or other processes.

The further waste processing unit maybe a be fed from one or more storage locations and/or hoppers.

The further waste processing unit may include a first sized based separation, preferably a first screen. The first size based separation may remove textiles and/or other oversize items from the remainder of the waste.

The further waste processing unit may include a second size based separation, preferably a second screen. The second screen may be a vibrating screen. The second size based separation may remove used beverage cans, plastics containers, cans, tins, batteries, bottles and parts thereof to the oversize stream. The second size based separation may leave the smaller size waste, potentially including the fibre waste and/or broken glass and/or stones and/or small pieces of plastics/metal/etc.

The further waste processing unit may provide that the first and second size based separation are both provided and ideally that the second sized based separation is made after the first.

The further waste processing unit may include one of more further separation stages for the oversize stream. The one or more further separation stages may include one or more of: one or more ballistic separators; one or more metal from non-metal separator, such as a ferrous metal separator and/or a non-ferrous metal separator; one or more magnetic separators; one or more eddy current separators; one or more selective plastics type separators, such as a near infra-red separator or separators; one or more density based separators and/or mass based separators, such as X-ray separators. The further waste processing unit may include that two or three or four of these types of separator may be provided, ideally, when present, in the order provided in the previous sentence.

The further waste processing unit may one or more ballistic separators. One or more separators may be used to separate a stream containing significantly 3-dimensional and/or rollable components from the other components, preferably by their removal. One or more separators may be used to separate a stream containing predominantly 2-dimensional and/or non-rollable components from the other components, preferably by leaving them in-situ. The 2-dimensional waste may include textiles and plastics film and the like. The 3-dimensional waste may include tins, cans, bottles, batteries and the like. One or both streams may be provided to a further separator, preferably a ferrous and/or non-ferrous metal separator and/or a magnet and/or eddy current separator. One or both streams may be provided to a still further separator, for instance Near Infra-Red (NIR) separator(s), which preferably uses compressed air to positively eject a mixed plastics fraction from the waste. One or more different plastics can be detected and ejected into separate streams using such detectors.

The further waste processing unit may provide that one or more separate waste streams and/or components which are not going to be fed to the pyrolysis/gasification step are fed into containers. The containers maybe conveyed to another site and/or another process.

The smaller sized stream, form the first size based separation and/or second size based separation may be provided to a fibre waste sorting unit. The fibre waste sorting unit may provide one or more further separations, for instance to separate ferrous and/or non-ferrous metals from the fibre waste and/or to separate larger components from the fibre waste and/or heavy components from the fibre waste. The fine fraction from the fibre waste sorting unit may pass through a de-stoner. The resulting fibre waste may be provided to the second waste processing unit. The fibre waste may have a moisture content in excess of 35% moisture, or even 45% moisture by weight.

The system may include a preliminary processing unit. The preliminary processing unit may be provided before the first processing unit. The preliminary processing unit may be a waste sorting unit. The preliminary processing unit may include a size based separation.

The preliminary processing unit may include a weight based separation. Waste which is below a size and/or below a weight may be fed to the first waste processing unit. Waste which is not below or is above a size and/or is not below or is above a weight may be subjected to a further process. The further process maybe a manual sort.

The preliminary processing unit may generate a waste stream which is fed to the first processing unit. The preliminary processing unit may generate a waste stream which is collected and conveyed to a landfill site. The preliminary processing unit may generate a waste stream which is collected and conveyed to one or more on site or off site processing steps.

The preliminary processing unit may or a part thereof may separate out recyclable components and/or components which can by-pass the second waste processing unit and/or which can be fed to the third waste processing unit.

The preliminary processing unit may include a crusher. The preliminary processing unit may include a size based separation, for instance a screen. The larger components from the size based separation may be manually sorted or processed further.

The system may include a preliminary processing unit and/or first waste processing unit and/or further waste processing unit and/or second waste processing unit and/or third waste processing unit and/or heat and/or steam and/or electricity generating unit. The system may include a preliminary processing unit followed by one or more of, and preferably in this order: a first waste processing unit and/or further waste processing unit and/or second waste processing unit and/or third waste processing unit and/or heat and/or steam and/or electricity generating unit. The system may include a first waste processing unit followed by one or more of, and preferably in this order: a further waste processing unit and/or second waste processing unit and/or third waste processing unit and/or heat and/or steam and/or electricity generating unit. The system may include a further waste processing unit followed by one or more of, and preferably in this order: a second waste processing unit and/or third waste processing unit and/or heat and/or steam and/or electricity generating unit. The system may include a second waste processing unit followed by one or more of, and preferably in this order: a third waste processing unit and/or heat and/or steam and/or electricity generating unit.

The system may include a third waste processing unit followed by a heat and/or steam and/or electricity generating unit.

The aspects of the invention may include any of the features, options or possibilities set out elsewhere within this document, including in the other aspects.

Various embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a flow diagram of a waste treatment process according to an embodiment of the invention.

Process Overview The basic process steps provided are: 1) an autoclave step for treatment of the waste; 2) a waste sorting step for segregation of waste types into various streams, including a fibre waste stream; 3) a bio-dryer step for reducing the moisture content in the fibre waste stream; and 4) a polysis and gasification step to generate sthesis gas, "sgas" from the fibre waste stream.

The process steps are more fully presented in the overview of the process steps shown in Figure 1.

The input waste 1 is in the form of a wide variety of waste components which are collected and transported to the process site. Waste which is below a set size limit and/or weight limit is then fed to the pre-autoclave sort step 3.

In the pre-autoclave sort step 3, a screen is used to separate components by size, with the larger components then being hand sorted. The smaller components then pass to the autoclave step 5. Certain waste components bypass the autoclave step 5 and go to the pyrolysis/gasiflcation step 7. Certain components are stored before being sent as a residue to a landfill. Certain components are extracted and form products streams for recycling. The majority of the components form the autoclave feed waste.

The autoclave step 5 uses a pair of autoclaves operating in parallel to apply steam, heat and pressure to the waste. This encourages cleaning of the inorganic components, the breakdown of certain plastics to small easily separated forms and a significant organic fibre form component. After autoclaving, the waste passes to a post-autoclave sort step 9.

The post-autoclave sort step 9 uses various sorts to generate a series of waste components which are not going to be fed to the pyrolysis/gasification step 7 and which are fed into containers ready for transportation to materials merchants or recyclate reprocessing facilities. The fibre forms the waste component going towards the pyrolysis/gasification step 7.

The post-autoclave residue sort step 11 handles the residue from the post-autoclave sorting step 9 and renders it suitable for being passed to the autoclave step 3 once more.

The fibre is first fed to a bio-drying step 13. The bio-dryer step 13 uses six bio-dryers operating in parallel to reduce the moisture level down to around 20%.

After buffering storage, the fibre waste is fed to the pyrolysis/gasification step 7 to produce syngas and a residue.

The syngas is fed to a combined heat and power step 15 where it is burnt. The steam, hot water and electricity products can be used within the process itself and/or used elsewhere.

The emissions from the CHP step are processed using an emission control system, not shown.

Detailed Description

The input waste is collected and transported to the process site and enters a reception hall. The reception hail is a large flat floored area, capable of storing approximately four days of input waste. Access is via two fast-acting doors. Delivery vehicles drive into the hail and the fast-acting doors close behind them. To minimise the escape of odour, an odour treatment system is fitted in the building and the building is kept at a slight negative pressure to ensure air is drawn into the building, including through the doors when they are open, and so odours do not leak from the building.

The waste is emptied from the delivery vehicles within the reception hall.

As required, waste is taking from one of the storage locations and the waste is loaded onto a loading conveyor by a front-end loader vehicle. The waste is buffered through a regulating device to ensure appropriate waste flow to the next process. In the next process, the waste is passed through over-size and over-weight sensors.

Any object which exceeds the limits, size and/or weight, is ejected into a reject skip via a reversible conveyor. Such waste may be broken down into sizes and/or weights suitable for return to the process before the over-size and over-weight sensors or may pass to the residue product. The residue product may be sent to a landfill site.

The waste which passes the over-size and over-weight sensors passes to the pre-autoclave sort step.

Pre-Autoclave Sort Step The waste may be received from civil amenity sites, be commercial skip waste or contain other elements of municipal solid waste, MSW, such as bulky waste, fly-tipped waste and constructionldemolition. As such, it is sorted before autoclaving.

The pre-autoclave sort seeks to remove waste components that can obviously be recycled or that can be fed directly to the pyrolysis/gasification process step.

The pre-autoclave sort is carried out in an annex to the reception hail. Delivered waste is tipped onto the floor and stored against push walls. A grab operator removes large items from the waste. These may be broken up and then fed to the next step for crushing.

This ensures that bulky components, such as items like furniture, are broken up.

The remainder of the waste is loaded into a crusher using a front end loader.

After crushing, the waste is then passed over a screen. The screen separates the larger components from the smaller components. The screen thus separates larger components such as wood, plastics and textiles from smaller ones, such as aggregate and smaller wastes.

The larger components are then hand segregated into: 1) Components for feeding to the pyrolysis system, by-passing the autoclave step. Such components include wood and textiles; 2) Components that can be sent directly to an end market or re-processor. Such components include plastics, metals, waste electrical and electronic equipment, WEEE, waste and hazardous waste; 3) Components that can join the smaller components and go to the autoclave step.

Autoclave Step The waste is loaded onto a bi-directional conveyor to fill one of two autoclave loading hoppers. The loading hopper accommodates and bulks up a single charge of waste for loading into an autoclave.

When the autoclave is ready for loading the door mechanism automatically moves the door to the loading position. The loading hopper then moves forwards on runners towards the mouth of the autoclave. A hydraulic ram at the base of the loader pushes the waste into the autoclave.

The auto claves themselves are 1 8m in length and 3.5m in diameter, with a capacity of 14 tonnes. The process can use an expanded number of autoclaves to achieve the required throughput per annum.

Once an autoclave has been fully loaded, the upper door mechanism moves the door back to the autoclave mouth and secures it in place. High pressure saturated steam is injected over a period of 15 to 20 minutes through a set of internal sparge pipes to ensure steam is injected evenly along the length of the vessel. The autoclave is rotated. This may serve to break down the waste into its organic and inorganic components. Air is vented from the vessel during the initial steam injection to maximise the useful energy absorption to the waste from the steam.

The autoclave reaches a maximum pressure of 7 bar, at around 165 C. At this temperature plastics bottles in the waste will soften and deform, but will not begin to melt or release chemicals into the waste.

The autoclave is inclined at an angle of 6 which aids the loading and unloading process. An internal helix inside the vessel lifts and tumbles the waste and also mixes it; lifting the waste up' the autoclave to then tumble down under gravity.

After this cook' period, the autoclave is depressurised over a period of 15 minutes.

During this period the vessel is vented to remove the steam whilst the waste tumbles in the autoclave. The aim of this is to reduce the moisture content in the fibre product reducing the amount of drying required later in the process.

Once the vessel has been depressurised, the lower door will open and the vessel is slowly rotated to discharge the waste. The internal helix will screw' the waste out of the autoclave onto the discharge conveyor. The organic elements of the discharged waste form a compost-like fibre which has a high biomass content. The inorganic elements are thoroughly cleaned by the process. For instance, all labels and lacquer paints are removed from cans and bottles and dense plastics and metals are deformed. Light plastics such as polythene bags often cause problems in sorting systems, getting wrapped around conveyors and blocking screens.

The autoclave process reduces these plastics down to small, hard pebbles that drop easily out of the fibre.

An overhead manually operated grab crane is located at the exit of the autoclave. In the event that a large item such as a textile bundle which may block the sorting system emerges, the crane will be operated to lift the item off the output conveyor and into a skip.

Steam for the autoclave process is generated using a composite boiler. This will use hot exhaust gas from the combined heat and power (CHP) engine operating at around 400°C in tandem with a gas burner to raise steam to the temperature and pressure required for the autoclave.

Steam vented from the autoclave is passed through a condenser and then a heat exchanger to cool it. This water contains impurities from the waste stream and therefore is passed through a water treatment unit to clean it before being reused in the system. Effluent from the water treatment unit is discharged to tanks for further treatment off site.

The autoclave process produces an odour, particularly from the steam condenser system. The output from the condenser is passed through a bioscrubber with carbon polisher.

The scrubber is also fed from the extractor hoods that are installed above the autoclave doors.

The autoclave unit operates with full compliance to Environment Agency and Health & Safety requirements.

Post-A utociave Sorting Step The output waste from the autoclave passes via conveyor to a mechanical sorting system in order to separate fibre for the pyrolysis/gasification step from the other recyclates and residues.

A storage buffer receives the waste discharged from the autoclave. The purpose of this storage is to buffer the batch output from the autoclaves to create a continuous flow of waste to the sorting system and pyrolyser/gasification step as these steps work better with a steady feed flow. Due to the temperatures involved, the pyrolysers work more efficiently as a continuous process,. If the system is continually stopped and allowed to cool more energy is required to start it up again.

The storage buffer comprises a walking floor' fed by a shuttling conveyor that spreads waste evenly along its length.

After the storage buffer, material is metered onto a primary screen. This screen separates textiles and other bulky items from the remainder of the waste. These are beneficially removed first as they are large enough to disrupt other separations if still present, for instance by becoming caught up and/or masking other components.

The remaining waste, including the vast majority of the fibre waste, that passes through the primary screen is conveyed to the secondary screen. This provides a vibrating size sort, designed to separate smaller sized waste. This smaller size fraction will mainly consist of fibre component along with broken glass, stones and small pieces of plastics. The smaller sized fraction enters a fibre sorting process. The remaining larger fraction from the secondary screen is conveyed to the ballistic separator. This larger fraction includes a wide variety of recyclable components. These are more easily processed once separated from the bulk of the smaller components, and particularly the fibre waste. If still combined, the bulk will potentially cover or otherwise restrict the access needed to achieve the separation.

The larger components are next passed to a ballistic separator to separate relatively flat two dimensional (2D) waste, such as textiles and plastics film, from rolling three dimensional (3D) waste, such as tins, cans, bottles and batteries.

The flat and rolling waste is conveyed separately to a metal and plastics sorting step for further separation.

Any remaining small sized waste is collected and fed back into the fibre sorting step.

The metal and plastics segregation step receives the 3D and 2D waste in separate streams. The majority of 2D flat waste from the ballistic separator is textiles and plastics film.

Most of the 3D rolling items from the ballistic separator are plastics bottles, tins, cans and batteries, along with shoes and other contamination. Ferrous and non-ferrous metals are removed using a magnet and eddy current separator respectively.

The removal of the ferrous components and non-ferrous components at this stage generates useful recycle streams and also enhances the ability of the subsequent step to identify and separate the components. Importantly, the removal of the metal waste, and waste such as batteries and other chemical containing wastes, prevents those reaching the pyrolysis/gasification step and so contributing problematic off gases.

The remaining components are conveyed to a Near Infra-Red (NIR) separator, which uses compressed air to positively eject a mixed plastics fraction from the waste.

Different plastics can be detected and ejected into separate streams.

For both streams, there is an option on the control system to selectively eject specific plastic polymers to suit changing market demand and prices.

The various waste components which are not going to be fed to the pyrolysis/gasification step are fed into containers ready for transportation to materials merchants or recyclate reprocessing facilities.

Around 20% of the waste passing through the post-autoclave sort is not sorted into one of the output streams. These may be waste components which cannot be recycled, reused, or converted in the pyrolyser or waste mis-sorted by the sorting system. These components could be disposed of to landfill, but in a preferred form these components will go to residue bin where they are be subjected to a second sort to ensure the minimum amount of waste is sent to landfill. This second sort will consist of a simple screen to separate soil and aggregate from larger components. The larger components will then be hand-sorted and transferred to separate bins if they are suitable for further processing or recycling.

Before being used, the fibre waste is further processed to separate out any ferrous or non-ferrous metals present. This is achieved by recovering such small components using a magnet and eddy current separator.

The fibre waste then passes to a further separation which uses a flexible screen to remove any relatively large components. These larger components are conveyed to an X-Ray separator to recover heavy components, such as glass, stones and ceramics as an aggregate output stream.

The fine fraction from the flexible screen, containing the fibre waste, is passed through a de-stoner which removes any fine, but heavy components, such as glass, stones and ceramics. These join the aggregate output stream.

The remaining waste is a fibre fraction, which is conveyed to the energy recovery facility. The process recovers fibre at a proportion of approximately 50 to 60% by weight of the input waste. At this point, the fibre waste is approximately 50% moisture by weight.

The fibre produced by the autoclave and refined in the post autoclave sort is very consistent in shape and calorific value and virtually free of impurities, such as plastics and metals. Due to the high biomass content the plant is likely to qualify for a higher level of Renewable Obligation Certificates, ROC s.

Rio-dryer step The organic fraction, the fibre, is then conveyed to the bio-dryer step. This starts with a feed hopper to receive the waste ready for drying. This hopper will take up any volume variation in fibre production from the sorting system and ensure that a consistent feed is offered up for drying.

The biodryer is a continuous process and consists of six rotating drums operating in parallel. The number of drums can be varied depending upon the capacity which requires handling. Each drum is 4m in diameter and 35m long and has an internal helix running along its length to move the waste through it. Lifters help to turn over the waste throughout the process to ensure an even drying process. The lifters also promote movement of the waste through the drum to the discharge end. The rate of rotation is fairly low, for instance 3 revolutions per hour.

The rotation is also important in spreading the microorganisms which cause the biodegradation and hence self-heating, throughout the waste. This can be particularly important where the microorganisms are introduced using seeded material and the seeded material needs to be mixed throughout the waste. Rotation also assists with distributing oxygen through the waste to feed the aerobic digestion processes.

The dryer has a residence time of three days, during which time the fibre will self heat. The self heating is caused by biodegradation of the organic components in the waste, the fibre. The self heating promotes the transfer of moisture out of the waste. Whilst generating significant, the biodegradation does not have any significant impact upon the amount of syngas which can subsequently be generated from the waste fibre.

Warm air is blown through the drum to remove moisture from the fibre too. The airflow is carefully balanced so as to remove moisture, but not cause cooling to an undesirable extent of the waste. As the fibre reaches the end of the dryer its moisture content is around 20% by weight, having reduced in weight by 15%. As the biodryer uses heat generated naturally in the fibre product itself it requires very little external thermal energy. Additional thermal energy can be generated from heat exchangers located in other elements of plant and equipment, if necessary.

In an alternative design, the bio-dryer step can be provided using a large contained working area, for instance a flat bottomed, walled enclosure. The waste is introduced to an area within the enclosure and is resident there for the desired time period. Subsequent volumes of waste are introduced to other areas, with the enclosure having sufficient areas to handle the volume and residence time required. Periodically, the waste in an area is agitated so as to promote moisture transfer to the air and to avoid compaction of the waste under its own weight. Once again, warm air flows through the enclosure and hence over the waste.

At the end of the desired residence time, the waste in a given area is removed from the enclosure and passes on to the next step.

The next step in the process is the conversion of the fibre waste to syngas. The pyrolysis/gasification step provides this conversion and generates syngas and a residue.

The syngas may subsequently be burnt in a combined heat and power plant. The electricity, heat and/or hot water arising may be used in steps within the process to reduce energy consumption.

Claims

CLAIMS1. A method of processing waste, the method including: providing waste; feeding waste to a first waste processing unit, applying heat and/or pressure and/or moisture to the waste in the first waste processing unit; feeding the waste from the first waste processing unit to a second waste processing unit, passing a gas flow over the waste in the second waste processing unit and/or heating the waste in the second waste processing unit by heat generated from a property of and/or process occurring within the waste.
2. A method according to claim 1 in which the second waste processing unit is a diyer.
3. A method according to claim 1 or claim 2 in which a solid waste stream leaves the second waste processing unit, the solid waste stream is a fibre waste stream and the fibre waste stream has a reduced moisture content when leaving the second waste processing unit compared with the moisture content of the waste entering the second waste processing unit.
4. A method according to any preceding claim in which the solid or fibre waste stream leaving the second waste processing unit has a moisture content of less than 25% by weight.
5. A method according to any preceding claim in which the second waste processing unit is loaded from one or more storage locations and/or hoppers.
6. A method according to any preceding claim in which the second waste processing unit include a plurality of process units of the same type.
7. A method according to any preceding claim in which the second waste processing unit is rotated.
8. A method according to any preceding claim in which the second waste processing unit includes one or more means to promote movement of the waste from one part of the second waste processing unit to another part.
9. A method according to any preceding claim in which the second waste processing unit provides for dispersing microorganisms and/or a microorganism seeded material in the waste.
10. A method according to any preceding claim in which the second waste processing unit provides for the distribution of oxygen through the waste.
11. A method according to any preceding claim in which the second waste processing unit provides a residence time of at least 24 hours and/or less than 125 hours for a unit of waste in the second waste processing unit.
12. A method according to any preceding claim in which the second waste processing unit provides for self heating by the waste.
13. A method according to any preceding claim in which the second waste processing unit provides a flow of gas over the waste
14. A method according to any preceding claim in which the second waste processing unit is provided in a contained working area.
15. A method according to claim 14 in which the contained working area includes a flat bottomed and/or walled enclosure and/or roofed enclosure.
16. A method according to any preceding claim in which a given volume of waste is introduced to an area within an enclosure and the waste is resident in the area for a desired time period.
17. A method according to claim 16 in which the desired period of time is a residence time of at least 24 hours and/or less than 125 hours
18. A method according to any preceding claim in which the second waste processing unit provides for agitation of the waste in an area.
19. A method according to claim 16 or any claim depending thereon in which at the end of the desired residence time, the waste in a given area is removed from the enclosure and passes on to the next step in the method.
20. A method according to any preceding claim in which the waste is or includes domestic or household waste.
21. A method according to any preceding claim in which the first waste processing unit is connected to a heat source and a pressure source and a moisture source.
22. A method according to any preceding claim in which the first waste processing unit includes one or more autoclaves.
23. A method according to any preceding claim in which the method includes a third waste processing unit which is provided after the second processing unit and the third waste processing unit includes a pyrolysis step and/or gasification step.
24. A method according to claim 23 in which the third waste processing unit provides a product stream including hydrogen and carbon monoxide and a burner is provided for the hydrogen and carbon monoxide product.
25. A method according to any preceding claim in which the method provides a further waste processing unit, the further waste processing unit being provided between the first waste processing unit and the second waste processing unit and the further waste processing unit is a waste sorting unit.
26. A method according to claim 25 in which the waste sorting unit segregates the waste into two or more waste streams, the waste streams including a fibre waste stream, with the fibre waste stream being conveyed to the second processing unit.
27. A method according to claim 25 or claim 26 in which the further waste processing unit includes a first sized based separation and a second size based separation.
28. A method according to any of claims 25 to 27 in which the further waste processing unit includes one of more further separation stages for the oversize stream from the first sized based separation and/or the second sized based separation.
29. A method according to claim 28 in which the one or more further separation stages include one or more of: one or more ballistic separators; one or more metal from non-metal separator; one or more magnetic separators; one or more eddy current separators; one or more selective plastics type separators; one or more density based separators and/or mass based separators.
30. A system for processing waste, the system including: a first location at which the waste is provided; a first waste processing unit to which the waste is fed, sources being connected to the first waste processing unit to apply heat and/or pressure and/or moisture to the waste in the first waste processing unit; a second waste processing unit to which the waste is fed from the first waste processing unit, a source being connected to the second waste processing unit for passing a gas flow over the waste in the second waste processing unit and/or in use, the waste in the second waste processing unit heating the waste by heat generated from a property of and/or process occurring within the waste.
31. A system according to claim 30 method according to claim 1 in which the second waste processing unit is a dryer.
32. A system according to claim 30 or claim 31 in which the second waste processing unit isrotatable.
33. A method according to claim 32 in which the second waste processing unit includes one or more means to promote movement of the waste from one part of the second waste processing unit to another part.
34. A system according to any of claims 30 to 33 in which the second waste processing unit is provided in a contained working area.
35. A system according to claim 34 in which the contained working area includes a flat bottomed enclosure and/or walled enclosure and/or roofed enclosure.
36. A system according to any of claims 30 to 35 in which the first waste processing unit includes one or more autoclaves.
37. A system according to any of claims 30 to 36 in which the system includes a third waste processing unit which is provided after the second processing unit and the third waste processing unit includes a pyrolysis unit and/or a gasification unit.
38. A system according to any of claims 30 to 37 in which the system provides a further waste processing unit, the further waste processing unit being provided between the first waste processing unit and the second waste processing unit and the further waste processing unit is a waste sorting unit.
39. A system according to claim 38 in which the further waste processing unit includes a first sized based separation unit and a second size based separation unit.
40. A system according to claim 39 in which the further waste processing unit includes one of more further separation units for the oversize stream from the first sized based separation unit and/or the second sized based separation unit.
41. A system according to claim 40 in which the one or more further separation stages include one or more of: one or more ballistic separators; one or more metal from non-metal separator; one or more magnetic separators; one or more eddy current separators; one or more selective plastics type separators; one or more density based separators and/or mass based separators.
42. A method of processing waste, the method including: providing waste; feeding the waste to a first waste processing unit, applying heat and/or pressure and/or moisture to the waste in the first waste processing unit; feeding the waste from the first waste processing unit to a second a second waste processing unit, passing a gas flow over the waste in the second waste processing unit, the second waste processing unit including pyrolysis and/or gasification.
43. A method according to claim 42 in which a waste processing unit to provided between the first waste processing unit and the second waste processing unit, that waste processing unit being a dryer.
44. A method according to claim 44 or claim 43 in which the second waste processing unit provides a product stream including hydrogen and carbon monoxide and a burner is provided for the hydrogen and carbon monoxide product.
45. A system for processing waste, the system including: a first waste processing unit, the first waste processing unit being connected to a heat source and/or being connected to a pressure source and/or a moisture source; and/or a second waste processing unit, the second waste processing unit being connected to a gas flow source, the second waste processing unit includes a pyrolysis step and/or gasification step.
46. A method according to claim 45 in which a waste processing unit to provided between the first waste processing unit and the second waste processing unit, that waste processing unit being a dryer.
47. A system according to claim 45 or claim 46 in which the second waste processing unit provides a product stream including hydrogen and carbon monoxide and a burner is provided for the hydrogen and carbon monoxide product.