The processing and disposal of municipal and other waste is an environmentally sensitive issue. It is also expensive. Large volumes of waste material are produced. This waste will include a wide range of different materials, including plant matter, paper, cardboard, plastics, glass, metal and the like. One option is to deposit all waste material in landfill sites. However, this is expensive since the landfill sites must be purchased, excavated to allow the depositing of the waste and, when full, it is usually necessary to landscape the site to return it to its original, or an alternative acceptable, state.

Another alternative is to incinerate the waste. There are a number of disadvantages with this method of disposal. The waste may include potentially hazardous material. Therefore, when the waste is incinerated, potentially harmful gases may be given off. Even if the gases produced by the combustion are not harmful, there may be a perceived risk that the gases are harmful, either to individuals or to the environment at large. The incineration of waste material will result in some solid matter remaining, for example some material that cannot be burnt, as well as ash left from the combustion. This material must be disposed of, for example in landfill sites.

This has associated the problems outlined above.

In the UK alone, around 30 million tonnes of municipal waste is collected annually. Around 80% of this waste is disposed of in landfill sites, each of which take between 50 and 100 years to digest the material. The effects of depositing waste in landfill sites will therefore last for many generations.

Commercial waste, including that from supermarkets, offices, catering

establishments and the like typically produce about two to three times as much waste annually as municipal waste amounting to an additional 70 million tonnes.

With the disposal of municipal waste either by incineration or in a landfill site, it is not generally possible to make use of any of the waste material.

However, some of the waste material may be re-usable or re-cycleable.

Therefore, it is known to separate or sort the waste material to remove material that may be re-used or re-cycled. This sorting may either be carried out after the waste material has been collected, in which case this may be done manually or with some automation, or may be done prior to collection, for example by providing different bins or collections for different types of waste material. It is known to provide central sites where waste material of different types can be collected, and also to provide different kerb-side collections for re-cycleable products such as glass, cans and paper. However, such separations systems have disadvantages. For example, it is possible for the collection of separate materials to become contaminated with materials of an inappropriate type. Also, where producers of the waste material are asked to separate the material, and especially where they are required to travel to a collection point to dispose of certain types of material, there is likely to be some apathy to sorting and re-cycling the material, and therefore much of the material is merely collected with other waste material and cannot be re-cycled or re-used. Where systems are provided for separating material of particular types from general waste material, whether this is manual or automatic, there will be some inefficiencies in the separation, and therefore not all of the material that could be re-used or re-cycled will be so re-used or re-cycled.

This is especially the case where the waste is dirty, wet, or may be contaminated with unsafe, dangerous material.

A system has been proposed by Alma International, Inc of Columbus, Ohio, USA which seeks to treat municipal waste using an autoclave system.

In an autoclave, material is subjected to saturated steam at a high pressure and temperature, typically at a pressure in excess of about 2x105 Pa (about 2 atmospheres) and at a temperature in excess of 120°C. This"cooking"of the waste material over a prolonged period acts to sterilise the material, making it safe to handle. It also acts to clean much of the waste, for example removing the labels and printing on cans and bottles. Material such as plastics tends to become malleable and reduce in size to form small globules of material.

Other material, such as fibres, plant matter, paper and the like tends to form a fibre mass having small, elongate particles, with a typical length in the order of 0 to 6 mm, generally no greater than 15mm, and a width of up to around 2 mm, typically between 1 and 2 mm.

In the autoclave system, high pressure, saturated steam contacts the material. Rotation of the autoclave vessel brings the material into contact with other material in the autoclave, thereby compacting and breaking down the structure of the material.

The result is that the volume of the waste after the treatment is greatly reduced, typically by around 60 to 70%, compared to the volume of the material provided to the system. Nevertheless, the overall mass of the processed material is generally the same as that of the unprocessed material.

This significant reduction in the volume of the material by the exposure to saturated steam is of particular advantage as this processed waste material takes up less volume in a landfill site, and is sterilised, and therefore is less expensive and more environmentally acceptable than where larger volumes of unprocessed waste are disposed of in a similar manner.

According to a first aspect of the present invention, a system for the treatment of waste material includes providing an hermetically salable vessel for the waste to be treated and a source of steam for charging the vessel to a temperature in excess of about 120°C and a pressure in excess of about

2x1 05Pa, maintaining the waste material in the high temperature, high pressure environment for at least 20 minutes, and passing the treated waste material though a separation unit to separate out small particles of processed waste material.

The advantage of separating out the small particles of the waste material is that these particles have been found to have a number of applications. For example, the separated particles have been found to be useful as a composting agent or growth promoter on reclaimed land sites. It has also been found that the particles contain many of the base elements which are used in fertilisers. It has also been found that the particles can be combined with plastics materials for moulding or otherwise forming articles. It has also been found that the particles can be used as a fuel source. The particles may be combusted to produce energy, or may be gasified or pyrolyse to produce gas known as"syngas"that can be used to generate electricity. Each of these uses, and potentially other uses, have the advantage that waste material is re-used, rather than being deposited or treated in an expensive, un-ecological manner.

The waste material, which may be municipal or other waste, is preferably processed by being subjected to a temperature in the range of 150 to 190°C, preferably at a temperature of below 180°C. Advantageously, the temperature does not exceed 192°C, since above this temperature chlorine-containing plastics may melt. The pressure within the vessel is advantageously in the range of 2x105Pa to 6x105Pa (2 to 6 atmospheres), and more preferably in the range of 4x105Pa to 6x105Pa (4 to 6 atmospheres). The high pressure and temperature are preferably maintained for a period of between 35 and 50 minutes. Maintaining the waste material at such temperatures and pressures over such a period of time ensures the material is fully treated to obtain the advantages of the present invention, without incurring unnecessary costs and energy.

The small particles, being predominantly the organic fraction, separated by the separation unit preferably have a maximum dimension of less than 15mm and more preferably have a maximum dimension of less than 6mm.

The particles may be separated from the remaining waste material using a number of different systems. It is preferred that a rotating trommel is used to separate out the small particles. This has been found to be efficient. The rotation of the trommel helps ensure that all of the waste material has an opportunity to be sorted, and, as described below, assists in moisture reduction of the material.

Preferably, the trommel is of a twin or dual type having two or more screens sequentially separating particles of increasingly smaller size from larger particles. The material is sorted by a first screen that separates particles of up to a first size. The remaining, larger, particles are then discharged. The first screen may separate out particles having a size of up to 15 mm. The separated material comprising only material having a size up to the first size is then sorted by a further screen that separates particles of up to a second size, smaller than the first size. For example, the second size may be about 6 mm.

In this way, the material is first sorted to collect particles of a small size, and then this material is further sorted to select particles of an even smaller size.

This series arrangement of screening is more efficient than a single screening procedure, as this helps avoid blockage or"blinding"of the screens. The screens may be arranged with the second screen spaced from and surrounding the first screen, or may be provided separately.

Alternative sorting systems include vibrating screens, that may be flat or inclined, finger screens, flip flop or air knife separation units as described below.

To avoid the means for separating the small particles from becoming blocked or blinded by large matter, especially textiles, it is preferred that a system is

provided for removal of such matter. This may include a textile remover located at a suitable transfer point, for example on the infeed conveyor to the trommel. The textile remover may include a hydraulically activated inclined hinged grid with adjustable vibrating bars over which the processed material passes. The textiles will be allowed to build up on the grid until such time as a sensor is activated in response to which the grid may lift, for example through about 180°, depositing the textiles for example in a receiving hopper and/or conveyor for re-use or disposal. Alternatively, a textile picker may be provided having a series of grippers or hooks for removal of such matter.

Such a removal system is preferably provided upstream of the separation unit.

The small particles fraction separated from the processed waste are advantageously treated to reduce the moisture content.

Typically, the material leaving the waste treatment vessel will have a moisture content of between about 38 and 48%. The treated material will tend to dry out naturally as this is conveyed to the trommel or other sorting system.

Especially where a trommel is used, this further dries out the material by the action of moving the material and thereby allowing this to be air dried. The material from the trommel or other separation system may typically have a moisture content of around 28 to 38%. However, further reduction of the moisture content is preferred.

It is beneficial to remove glass shards and other deleterious material from the separated particles. Preferably, a means is provided to remove this materiai.

It is preferred that an air knives separation unit is provided to treat the separated material. Such a unit can remove deleterious material. An air knives separation unit is also advantageous in reducing the moisture content in the material.

An air knives unit, such as available from General Kinematics, may comprise a chamber through which the material passes, the chamber having openings in the bottom. The unit may also include a receiving screen. Air or other gas is jetted into the chamber. In this way, the material in the unit is aerated. This acts to dry the material, reducing the moisture content typically to between 22 and 28%. Also, heavier particles will drop out of the chamber through the openings in the bottom of the chamber.

The material is preferable further dried to have a water content of between about 8 and 12%. The material is preferably also formed into logs or other suitable blocks of product. Both of these requirements may be achieved by the use of a compaction unit that compacts the material. This compaction acts both to squeeze moisture from the material, and forms the product into blocks or logs. A suitable compaction unit for this purpose is a screw compactor, for example available from Optima International or ET Revolution Systems.

Typically, the log will have a length of around 1m and a diameter of around 300mm. Of course, other sizes are possible depending upon the apparatus used. The log will typically have a moisture content of between 8 and 12%.

The moisture content may vary dependent on the nature of the raw waste material, the conditions under which this was processed, and the drying units provided.

The moisture content of the product can be reduced by other drying systems, for example using vacuum servo units or the like. The product may also be formed into blocks or logs using other apparatus, for example using an extruder.

The formed blocks or logs are advantageously further dried so that the final moisture content is between about 4 and 6%. This may be achieved by storing the blocks of material in a hot room, typically for about 24 hours. By

reducing the moisture content of the material, and especially where the moisture content is reduced to below about 10%, the material becomes inactive, and therefore is completely safe.

Although the treated material may be used in many applications, a preferred example is to use the fuel for the generation of the steam used for the treatment of waste according to the present invention. In this way, the processed material itself is able to produce the fuel required to treat further raw waste, and therefore the system can be self-sustaining, or at least reduce the additional energy that must be provided to treat the waste material. The fuel produced may be used alone, however it is preferred that this is combined with other fuel, such as coal. Generally the fuel at 6% moisture has a calorific value of 4500 to 5200 Kcal/kg (20x106 to 22x106 joules/kg), approximately 56% calorific value of power station coal.

A particular preferred use of the material is for the generation of gas using a gasification or pyrolysing system. In this, the material is heated in a reduced pressure environment to generate gas having a high methane content. This gas may be used to generate various gaseous elements which may be used to generate electricity using a gas engine or gas turbine.

The other treated material not removed by the small particle separation system may be further processed. For example, the other material may include plastics, metals, glass etc. These materials may be sorted and re- cycled. It is preferred that, automatic separation systems such as eddy current separators, magnetic separators and the like are provided to remove materials of a particular type from the waste stream for separate handling.

Alternatively, the material may be sorted manually. With the system according to the present invention, the materials processed by the system are clean, having had the labels and printing removed from their surfaces and converted into small particles, and therefore require minimum further

processing before they are re-cycled. Further, due to the treatment, the waste material will generally be compacted, and therefore is easy and economical to handle. For example, plastics materials will tend to ball up, and therefore may be separated and handled more easily than if they retained their original structure.

Due to the heat treatment of the waste material with steam, the volume of processed waste material will be greatly reduced compared to the untreated material. Further, since the material is subjected to high temperature, high pressure steam for a prolonged period, the material will be sterilised.

Therefore, for any material that is not re-used or re-cycled-such as ceramics, bricks, tree roots, concrete and rubber-may safely be disposed of in a landfill site without risk of contamination. Further, as the volume of material is reduced, even without the removal for re-use or re-cycling of some of the material, any material that is deposited in a landfill site or the like will occupy less volume, and therefore makes such disposal more economical and more environmentally acceptable, than conventional landfill disposal systems.

An apparatus for use with the first aspect of the present invention includes a pressure vessel for the processing of the waste material that may have a number of advantageous features.

The pressure vessel may be formed of carbon steel, stainless steel or other material that is able to withstand the high temperatures and pressures required in accordance with the present invention. The size of the pressure vessel will be dependent upon the volume of waste that is to be processed, and on the number of vessels that are provided. In preferred examples, the vessel has a diameter of 2m to 2.5m. The vessel may have a length of around 9m to prove a capacity of between 5 and 8 tonnes or 12m to provide a

capacity of 10 and 15 tonnes. Another example is a vessel having a diameter of 3m and a length of 18m to provide a capacity of between 20 and 30 tonnes.

The weight in any vessel will be determined by the density of the waste material to be processed, which generally will be between 200 and 250 kg/m3.

It is advantageous to provide a plurality of pressure vessels, such that one may be discharged and refilled whilst another is processing waste material.

This allows for generally continuous treatment of waste material.

The vessel is preferable mounted on a support that allows the vessel to be moved between a first position, in which the axis of the vessel is generally horizontal, and a second position in which the axis of the vessel is inclined to the horizontal. It is preferred that in the second, inclined position, the axis of the vessel is inclined at an angle of around 6 to 45°. It is preferred that the angle of inclination is not greater than 45° since this would make it difficult to lift the end of the vessel to the required height. In this case, it is preferred that the vessel has a generally central pivot point. Especially where the pivot point is not central along the length of the vessel, it is preferred that the vessel is inclined in the second position at an angle of no more than 12°. Typically, the vessel will be lifted using a hydraulic arrangement. If the amount of lift required is too great, this may require the use of a multiple stage hydraulic lift, increasing the cost and complexity of the hydraulic lift arrangement compared to a single stage lift. Further, if the lift height is large, this will require a high building. The inclination of the vessel is advantageous during charging the vessel with waste material to be processed, as gravity can then be used to assist in filling the vessel. The vessel may then be brought to a generally horizontal orientation for processing, helping distribute the material and steam throughout the vessel during processing. The generally horizontal position is typically within 1° of horizontal. It is preferred that the vessel is at a small

angle to the horizontal to ensure that any liquid within the vessel drains to the back of the vessel from where it can be removed.

The pressure vessel preferably includes a means for assisting with the loading, unloading and/or distribution of material within the vessel. To assist with the loading and unloading of the vessel, the vessel is provided with one or more internal helixes. In this case, the rotation of the autoclave in one direction will tend to move material towards one end of the vessel, and rotation of the autoclave in the opposite direction will tend to move material towards the other end of the vessel. When loading the vessel, the waste material is introduced into the upper opening of the vessel. The provision of a helix prevents the material from sliding down the side of the vessel to the bottom. However, as the vessel is rotated, causing rotation of the or each helix fixed within the vessel, the material is moved gradually towards the end of the vessel opposite the end through which the material enters the vessel.

When unloading the vessel, the vessel, and therefore the or each helix fixed within the vessel, is rotated in the opposite direction to move material towards the open end of the vessel.

Where provided, it is preferred that the internal helixes include a series of holes drilled into them to allow maximum exposure of the waste to the steam, and to stop build up of material.

Preferably lifters in the form of projections from the inside surface of the vessel are provided. The lifters extend along substantially the entire length of the vessel. During processing of the material, the lifters within the vessel act to lift the material, and tumble the material through the centre of the autoclave vessel. This operation is similar to the effect achieved on clothes in an automatic washing machine. By tumbling the material through the centre of the autoclave, the material is treated efficiently with the available steam. This

may not be the case if the material remains in contact with the sides of the vessel.

The opening to the vessel through which the waste material is added to and removed from the vessel will be hermetically sealed with a door or other closure. It is preferred that the door or other closure is automatically controlled, for example using a hydraulic closure system, for example fitted with a"bayonet type"locking ring. Advantageously, sensors are provided to ensure that the door is closed, and/or that the vessel is sealed, before the vessel is charged with steam. Additionally there is a solenoid locking bolt which cannot be withdrawn until the pressure inside the vessel is equal to or less than atmospheric pressure is preferably provided. It is preferred that the door or closure may be removed completely to facilitate loading and unloading.

The vessel preferably includes a filter, for example in the form of a mesh, or a wedge wire screen that prevents material clogging the steam inlet and/or outlet. The filter or screen acts to deflect material from the end of the vessel.

This is advantageous as it ensures material does not collect at the end of the vessel from where it is difficult to remove the material. Further, the steam inlet and outlet are typically provided at one end of the vessel, opposite the end through which the waste material is provided into the vessel. In this case, the filter may be in the form of a mesh that extends across the vessel.

Preferably such a mesh extends across a rotary steam inlet, usually located at the opposite end to the door.

It is preferred that the charging of the vessel with steam and/or the removal of condensate, is automatically controlled. In this case, the pressure and/or temperature in the pressure vessel may be monitored, and the flow of steam into, and/or the venting of steam or removal of condensate may be varied accordingly.

The vessel advantageously stops at the same point every time after processing. This ensures that the vessel is correctly aligned to allow automatic control of the venting and door opening procedures. It is preferred that, before the door is opened, the pressure within the vessel is reduced to a pressure below the atmospheric pressure surrounding the vessel. In this way, a rush of steam is prevented from escaping from the vessel when the door is opened.

Advantageously, some or all of the components of the system are insulated to help reduce heat loss and optimise efficiency. In particular, the processing vessel can be insulated. Also, where provided, a steam accumulator for accumulating steam to charge the vessel is insulated. Insulation with around 30cm of insulation can reduce energy loss dramatically, for example reducing overnight temperature loss to a few degrees.

An example of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a schematic view of the waste treatment method and apparatus of the present invention; Figure 2 shows a cross-sectional view through an autoclave ; and, Figure 3 shows a schematic view of a steam generation system.

Figure 1 shows a schematic view of a waste processing system according to the present invention. The system includes a rotating autoclave 1, shown in greater detail in Figure 2. The autoclave 1 may be formed from a carbon steel or stainless steel material with suitable insulation. The autoclave 1 includes an open end through which waste material to be treated is provided to and removed from the autoclave 1. The open end is hermetically salable with a closure 7, such that the pressure within the autoclave 1 can be increased.

The closure 7 is hydraulically controlled and includes an interlock mechanism

with a sensor to ensure that the autoclave is hermetically and safely sealed.

In this way, an operator need not come into contact with the vessel during operation. The closure is able to open quickly and give a large clearance.

The door may have a diameter of about 1.5m, allowing most waste materials to be provided directly to the vessel through the opening without requiring compaction or size reduction. To ensure correct sealing of the door over the opening, a system is provided to remove any material that may have been deposited on the rim of the opening, for example using a jet of compressed air to blow any such material away. The door is locked into place by a solenoid actuated bolt that is not released until the pressure within the vessel is within a small predetermined range of the ambient pressure.

The autoclave 1 includes two helixes 21 and four lifters 23, as shown in Figure 2. The helixes 21 are fixed relative to the vessel which is rotated such that waste introduced into the autoclave 1 is mixed and moved towards the rear of the autoclave 1. During this filling, the autoclave 1 is inclined to assist filling, the axis of the vessel being inclined to between 6 and 12° from the horizontal.

During processing of the waste, the autoclave 1 is moved to a generally horizontal orientation, for example at an inclination of 1°. The inclination of the vessel is achieved using hydraulic rams that pivot the vessel about a rear pivot point. During processing, super heated steam is supplied to the vessel for a prolonged period of time, during which the temperature and pressure within the vessel is increased. The vessel is continuously rotated during this time. Material within the vessel will be lifted by the lifters 23 as the vessel rotates. As the rotation continues, the lifted material will drop from the lifters, tumbling through the central, axial, region of the vessel. In this way, the steam within the vessel can have optimal contact, and therefore action, on the material.

When the waste material has been processed within the autoclave 1, the direction of rotation of the vessel is reversed to cause the processed waste material to be discharged from the autoclave. During emptying, the autoclave 1 may be returned to its inclined orientation.

Towards the end of the autoclave opposite the opening, there is provided a wedge wire screen 22 that prevents large particles of waste material from reaching and clogging the bottom of the autoclave 1 through which the steam is provided, and from which condensate is removed from the autoclave 1 through a drip. The provision of the wedge wire screen causes particles coming into contact with the screen to be deflected away from the end of the vessel. As well as preventing the particles from blocking the steam inlets and outlets to the vessel, this ensures the particles remain in the region of the helixes and lifters, and thereby continue to be processed correctly and can be removed at the end of processing. The removal of condensate from the autoclave 1 allows the duration of the steaming and venting cycle to be minimized. The removal of condensate increases the volume available within the autoclave for the steam, and ensures that the steam is as dry as possible, minimising the moisture content of the processed waste. The condensate may be removed through a condensate outlet 12 that has a flexible rotating coupling at the rear of the autoclave 1 through which the condensate removal drip pipe is provided.

In use, waste material to be processed is introduced into the open end of the autoclave 1, for example using a conveyor feed system. The amount of waste material that may be introduced will depend on the size of the autoclave 1, and the nature of the waste. The waste can typically have a density of between about 200 and 750 kg/m3, more usually between 200 and 250 kg/m3.

For general municipal waste, with an autoclave 1 having a 2m to 2.5m diameter, the capacity will typically be between 5 and 8 tonnes for a 9m long autoclave and, between 10 and 15 tonnes for a 12m long autoclave. For a

capacity of between 20 and 30 tonnes, an autoclave of 3m diameter and 18m length is suitable. The amount of waste material added to the autoclave 1 is controlled, for example using a computerised system. This control can be based on the measured weight of material being added to the autoclave 1, and/or analysis of the composition of the waste material, and/or on previous loads.

The material will generally be deposited from the refuse delivery vehicle onto a totaliser system. The moisture and density of the material is determined.

Based on the density of the material, a determination can be made of the weight of material that can be treated by the vessel. For example, if the material is of high density, a greater weight of material can be processed in the vessel than for material of a lower density. Based on this determination, the appropriate weight of material is batched off and supplied to the vessel.

After introduction of the waste, the pressure door 7 is closed automatically over the open end of the autoclave 1, hermetically sealing the autoclave 1.

Steam is then introduced into the autoclave 1 to increase the pressure within the autoclave 1. Steam is introduced into the autoclave 1 though the inlet 9.

This could be a 4 or 6 inch (10 or 15cm) rotating steam joint axially located on the autoclave. The steam is superheated, and is supplied to the autoclave 1 to increase the pressure. Typically the temperature within the autoclave will be increased to between 150 and 180°C. The temperature should be increased to at least 150°C to ensure proper sterilisation of the waste material being processed. However, the temperature should not be too high as it should not exceed the melting point of some of the plastic materials that may be treated. For example, chlorine-containing plastics have a melting point of 192°C, and it is therefore preferred that the temperature should not increase this level. The pressure in the autoclave 1 should be increased, typically to between 4x105 and 6x105Pa (4 and 6 atmospheres).

The charging of the autoclave 1 with steam is controlled by a valve or other control means. The control may be based on the determination of temperature and/or pressure within the autoclave 1, and may be dependent on the determined load of waste materials.

The increased pressure and temperature within the autoclave 1 are maintained for a period in excess of 20 minutes to ensure that the waste material is sterilised. Ideally, the material is processed from between 35 and 50 minutes to ensure that the material is treated optimally.

In one example, two 10 tonne capacity vessels are provided, each weighing about 18 tonnes. The peak demand for steam to charge this vessel will be around 3000 kg/h (about 7000 Ibs/hr) over a 15 minute period. The average steam demand over a 90 to 120 minute cycle time will be around 1600 kg/h (about 3500 Ibs/hr). For two 20 tonne capacity vessels, weighing approximately 52 tonnes each, a peak demand for steam would be about 16000 kg/h (about 35000 Ibs/hr) over 15 minutes, with an average demand of about 4000 kg/hr (about 9000 Ibs/hr) over a 115 minute cycle time.

During the heat treatment, the twin autoclaves with fixed helixes and lifters rotate. This ensures that the material being processed is agitated so that all of the material comes into contact with the saturated steam, and the material is broken down by contact with other material in the autoclave 1. Additionally, the autoclave 1 itself is rotated to further agitate the material being treated. <BR> <BR> <P>Typical rotation speeds are of the order of 0 to 10 r. p. m. , depending on the material being processed. The rotation is achieved using a hydraulic drive, for example using a chain drive with a sprocket wheel on the vessel. The autoclave vessel may be supported on suitable rollers, such as two tyre paths.

The processing of the material in the rotating autoclave 1 sterilises the material, and breaks down much of the material. Typically, the volume of the processed material is reduced by as much as 70%.

During the processing, there may be some condensation of liquid within the vessel. Due to the 1° inclination of the vessel, the condensate will run down the vessel to the back of the vessel. This condensate can then drip from the vessel into the condensate pumping vessel for re-use as described below.

At the conclusion of the steam treatment of the waste, the vessel is depressurised. Steam from within the vessel is vented to a steam vent condensate vessel 34. Within the steam vent condensate vessel 34 works in connection with a chiller 34a and an air-blast cooler 34b to reduce the pressure and temperature so that the steam condenses. There will be only small amounts of steam vented to atmosphere, thereby maintaining an essentially safe and closed system. The energy released by the steam condensing can be used to pre-heat water in the steam generation system described below. The treated waste is discharged and will cool at a rate of about 4°C per minute, allowing the vessel to cool from 160°C to 100°C in 15 minutes.

After treatment, the waste is removed from the autoclave 1 by removing the closure 7, and reversing the rotation of the autoclave 1 and the helixes 21, thereby lifting the material out of the autoclave 1. The processed material is discharged onto a conveyor 8.

A textile remover is provided to remove large pieces of textile before the material is sorted. If this material was not removed, the material may block the sorting system. The textile remover should remove at least 80% of the textile material prior to post separation.

The remaining treated material is transported to a rotary trommel 2. A large proportion of the processed waste will have a particle size of less than 15mm.

These particles are largely formed from organic waste, paper and lightweight packaging fraction that produces stranded cellulose fibre during the processing of the waste material in the autoclave. As the processed material

is passed through the rotary trommel screen, the"fibre"or small particle size material is separated from the processed waste. The remaining waste, which includes larger size particles and the non-organic fraction may be passed for further sorting and processing. For example, the remaining material may pass through an over-band magnetic separator 4 that removes ferrous material, an eddy current separator 5 that removes non-ferrous metal together with other sorting means, shown schematically as 6, which may to other automated or manual sorting systems, for example to remove glass, plastics and other separable materials. All of the separated materials will be clean and sterilised, for example cans and bottles will be stripped of their labels and lacquers, as well as any paints or grease. Glass bottles will be clean and, in many cases, crushed. Plastics materials will have reduced their volume considerably, and will be moulable. Therefore, the materials are in an ideal condition to be further processed, for example re-cycled and re-used.

The trommel is a twin screen trommel, comprising an inner screen which allows particles of a size up to 15mm to pass through, and an outer trommel screen which allows particles of a size up to 6mm to pass through. With this arrangement, all particles having a size of greater than 15 mm are removed by the inner trommel screen, and this material is removed for downstream processing as described above. The remaining material, including all particles having a size of less than 15mm, is then sorted by the second screen which separates particles having a size of less than 6mm from those having a size of 6 to 15 mm. The larger particles are removed for downstream processing, whilst the particles having a size of less than 6mm are treated as usable fibre. The two stage separation helps ensure efficiency of the separation system, and in particular avoids blocking of the filter screens.

The small particles, or fibre, removed by the rotary trommel will have a high moisture content, having absorbed steam in the autoclave 1. Typically, the

fibre may have a moisture content of 28 to 38%. Further, the material may include shards of glass and other small pieces of material that are disadvantageous.

Alternative separation units may be used, for example including finger screen vibrating classifiers, such as that available from General Kinematics Ltd.

An air knife unit, such as a GK Single Knife De-Stoner (Trade Mark) available from General Kinematics Ltd, is provided to reduce the moisture content of the material, and to remove glass shards and similar material. An air knife unit comprises a trough or chamber through which the material passes. The chamber is typically vibrated to move the material, and to cause the high density material to settle to the bottom. Air may pass through the material to fluidise this. This also acts to dry the material, reducing the moisture content typically to between 22 and 28%. Heavier particles will drop out of the chamber through openings in the bottom of the chamber. Air is jetted through the material at high velocity but at low pressure. The heavy particles fall through the air stream and are thereby separated from the remaining fraction of the material.

The moisture content is further reduced to have a moisture content of between about 8 and 12%, and is formed into logs or other suitable blocks of product. Both of these requirements are achieved by the use of a compaction unit that compacts the material. This compaction acts both to squeeze moisture from the material, and forms the product into blocks or logs. A suitable compaction unit for this purpose is a screw compactor, for example one of the Series CP300 Compactors available from Optima International.

The formed blocks or logs are further dried so that the final moisture content is between about 4 and 6% by storing the blocks of material in a hot room, typically for about 24 hours.

Whilst it is expected that the calorific content of the resulting logs will vary with different waste materials, and compositions of waste material, a calorific value in the range of 6 to 9,000 Btu/lb (about 5000 kcal/kg) may be achieved. In this case, it is possible to use 4 to 6 tonnes per hour of the"fibre fuel"to generate about 13 to 17 tonnes per hour of superheated steam at between 265 psig at 265°C for low pressure turbine systems. This may be passed though a standard low-pressure steam turbine to generate around 3MW of electricity and a further 3MW of steam energy from the passout steam via a heat exchanger. This may be re-used in the autoclave. Alternatively, for high pressure turbines, steam at 600psig at 265°C can be produced, or at different pressures and temperatures as required.

One important use of the fibre product is in the production of gas fuel using a gasification or pyrolysis technique. In such a technique, the fibre material is provided to a sealed, typically spherical, chamber. The pressure inside the chamber is reduced, and the product heated. The heating of the material generates gas that is drawn off as the heating continues. After treatment, the material remaining in the chamber is under 20% of the original weight of product, and is typically between 8 and 15%. Of this, about 30% is pure carbon, which is itself a useful product. Of the gas generated, over 90%, and typically at least 94%, is usable. Of this around 64% is methane. This is compared to standard"landfill"gas from landfill sites, of which between 45 and 55% is usable. For every 1.5 tonnes of fibre with an energy content of about 5000kcal/kg, about 1 tonne of gas can be generated per hour. 1 tonne of gas can be used with a gas engine or gas turbine to generate between 1 and 1.4MW/hr of electricity. This energy generation can be further increased by the addition of up to about 15% by weight of plastics material with the fibre, and in this case can increase the energy output by a further 20%. The waste heat from a gas turbine or gas engine can be used to pre-heat water for steam generation.

The fibre material has also been found to be useful for composting, as a growth promoter for reclaimed land sites, and for mixing with plastics materials to form plastics articles. The fibre also contains many of the basic elements used in fertilisers.

It will be understood that the fibre may be removed by systems other than a rotary trommel. Other systems may be used for separating the remainder of the processed waste, and this may include entirely manual systems for sorting the waste, as well as automated systems or a combination of manual and automated systems.

In a preferred embodiment, two autoclaves 1 are provided, and are arranged such that one is able to be sealed and pressurised to process waste material contained within it, whilst the other is being emptied of processed waste material and being filled with more, raw, material. In this way, it is possible to continually process material, rather than needing to wait until material in a single autoclave is processed and removed from the autoclave before the next load of material can be added. It will be appreciated that additional autoclaves may be provided, and these can each run independently or in sequence to achieve the optimum processing.

Steam Generation The autoclave 1 requires a large volume of saturated steam for the processing of the waste material. Whilst this may be provided using a standard tube/shell steam generator, according to a preferred embodiment of the present invention, an efficient steam generation system is used.

As shown in Figure 3, the steam is generated in a boiler 31. In the example shown in Figure 3, the boiler 31 is powered using either gas oil (diesel) from a gas oil tank 32, or using natural gas from a gas or LPG source 41, for example from the mains supply. Alternatively or additionally, a waste fired

boiler 31 may be fired using the processed fibre fuel as described above, or using biogas. Where a gas oil tank 32 is provided, the tank may be filled with gas oil, for example from a tanker. The gas oil tank 32 should have an air vent. Suitable isolation and control valves are provided to control the flow of fuel to the boiler 31. The use of isolation valves allows the supply to be shut off, for example to allow maintenance of the boiler 31. Where necessary, a booster may be provided to the burner mechanism of the boiler 31 to permit the use of gas having a low pressure.

The preferred boiler 31 is a three-pass, economic, wetback firetube type boiler. A suitable boiler is a Beevor boiler with a capacity of 3175 kg/hr F & A 100°C, designed to operate to a pressure of 250 psig, or a Minister M boiler with a capacity of 7759 kg/h F&A 100°C, both available from Beel Industrial Boilers pic. To improve efficiency, the burner should be a high efficiency boiler with suitable controls, for example with direct digital combustion controls.

In use, there will be a collection of solids in the boiler 31, known as TDS (Total Dissolved Solids). These solids must be removed to ensure the continued, efficient operation of the boiler 31. As described below, the removal of these solids is achieved by a blow down operation, and this is automatically controlled to reduce manual intervention in the operation of the boiler 31.

To ensure optimum efficiency of the boiler 31, the rate at which water is introduced to the boiler 31 to be heated, and the amount of air introduced to the boiler 31 for efficient burning of the fuel is carefully controlled. This is achieved by providing a variable speed controller to drive the pumps that supply water to the boiler 31 at variable speeds, and by providing a variable speed controller to the variable drive of a forced air fan 38 that forces air into the boiler 31. The provision of the variable speed drives also reduces the amount of energy required to drive the pumps, since these are not over driven.

The water supplied to the boiler 31 should be clean to avoid contamination of the system, and damage to the components. The raw water is therefore treated, for example by pH balancing. The treated water is then provided to a raw water break tank 36 to treat water before this is supplied to the boiler 31.

Water may be taken from any available source 39, for example from a bore hole, reservoir or from the mains supply. The provision of water from the water supply 39 to the raw water break tank 36 may be controlled automatically to ensure the optimum rate of supply. The raw water break tank 36 may merely be a simple tank. The raw water break tank 36 may have a capacity in the order of 1350 gallons, although this will depend on the capacity of the boiler 31, the accumulator 33 and the autoclave 1. The supply rate from the tank may be 300 gallons/hour or 600 gallons/hour. The provision of raw water break tank 36 may be required to meet statutory obligations in some countries. The broken water is pumped from the bottom of the raw water break tank 36, into a water softening unit 42. The water softening unit may include a softening resin that may be regenerated by backflushing with brine. This regeneration should be carried out periodically to ensure the correct operation of the unit. The water softening unit 42 may include a pair of water softening units that are arranged in a duty/standby mode, in which one of the pair of units is treating the water at any one time. During operation of one of the units, the other unit may be regenerated. Ideally, the control of the water softening units is automated.

From the water softening unit, the treated water is supplied to the boiler feed tank via a waste heat recovery system 44. This may use waste heat from any suitable part of the system, for example from the condensing of steam from the autoclave 1. The waste heat recovery system 44 pre-heats the water before this is supplied to a boiler feed tank 37, from which the water is supplied to the boiler 31 as required. The water is typically pre-heated to around 45°C.

The boiler feed tank 37 is provided at a level higher than the boiler 31, such that the water from the feed tank 37 can be fed to the boiler 31 by a gravity system, through a boiler feed pump. The supply of water to the boiler 31 may be controlled automatically by suitable control valves. The level of water in the tank 37 is monitored to control the water volume.

Within the boiler feed tank 37, the water is further treated and pre-heated. As shown in Figure 3, some of the steam from the boiler 31 is injected, at reduced pressure compared to the pressure of the steam supplied to the accumulator 33, from the boiler 31 into the water tank 37. To maintain the desired temperature of the water in the feed tank 37, a temperature sensor is provided to determine the temperature of the water, and this is used to control the rate at which steam is injected from the boiler 31 into the feed tank 37.

The water in the feed tank is typically maintained at a temperature of at least 45°C.

The water in the feed tank 37 is treated to minimise the oxygen content in the water. This assists in the efficiency of the system, helps inhibit corrosion, prevents the formation of scale and controls the pH levels of the water. This also removes oxygen and gas bubbles from the water that would otherwise effect the efficiency of the boiler system. This treatment may include the addition of chemicals, which are added to the water in the feed tank 37 in a controlled, preferably automated manner. Further, the amount of chemical required can be reduced by designing the feed tank 37 as a partial deaereator. The water may also pass through a filter to remove any solids.

To further assist the pre-heating of the water supplied to the boiler 31, part of the water passing from the feed tank 37 to the boiler 31 may pass through a flue gas economiser system 46 such as those available from Beel Industrial Boilers pic. This comprises a heat exchanger 46 through which the flue gas from the boiler 31 passes. This heats the water passing through the heat

exchanger 46 to the boiler 31. The heat exchanger 46 may include a run- around coil, and suitable safety features, for example including a safety valve.

The use of the flue gases to pre-heat the water allows some of the energy of the boiler fuel lost due to the inefficiencies of the system to be recovered.

This has been found to give a saving of between 3 and 5% of the fuel. This also increases the evaporative capacity of the boiler which increases the efficiency of the boiler.

As noted above, the boiler 31 is provided with a blow down system 45 for example a BIB Type 6 blow down system from Beel Industrial Boilers pic.

The blow down system 45 includes a pressure vessel that is able to accept blow down from a number of points on the boiler 31.

Water within the boiler 31 may include some suspended solids that are present within the incoming water. These suspended solids will tend to collect towards the bottom of the boiler shell 31. There is provided a lower exit from the boiler shell 31 to the pressure vessel 45 through which high pressure, high temperature water containing the contaminants is transmitted to the pressure vessel 45. As the steam enters the pressure vessel 45, it falls to atmospheric pressure and vents the latent heat in the form of flash steam, which is vented to the atmosphere. The remaining water, which will be at around 100°C can then be discharged. Due to the minimal blow down when removing the suspended particles in this way, it is neither considered practical or efficient to seek to recover the energy. In cases there the boiler 31 is not under pressure, an outlet from the boiler 31 may be provided for directly draining the contaminated water from the boiler 31.

Another form of contamination in the water in the boiler 31 are dissolved solids. A second exit is provided close to the lowest gravitation point of the boiler 31. This exit is also connected to the pressure vessel 45 of the blow down system. The boiler system includes a sensor to monitor the level of

total dissolved solids within the boiler 31. When the sensor determines that the level exceeds a pre-determined level, a small volume of boiler water is bled off, through the exit until the correct concentration of total dissolved solids is reached. It is preferred that a heat recovery system is employed to make use of the steam bled from the boiler 31 during this time, for example being used in the waste heat recovery system 44 to pre-heat the water introduced tot he boiler feed tank 37.

By automatically monitoring and controlling the level of total dissolved solids within the boiler 31, it is possible to ensure that the water being heated remains of an acceptable quality. This in turn eliminates the effects of contamination that may occur, including foaming of the water within the boiler that would result in the actual amount of water within the boiler differing from the measured volume of water. This may lead to errors in the calculation of parameters and control of the steam generation system. Further, any foaming may be carried into the other components of the steam generation system, resulting in corrosion of the pipework and fittings and poor performance of the vessels. By automatically controlling the blow down, it is ensured that only the minimum amount of steam must be removed from the boiler 31 to correct the levels of total dissolved solids, and therefore ensures minimum waste of steam.

A third outlet is provided from the bottom of a water level gauge on the side of the boiler 31 to meet health and safety requirements.

The majority of the steam generated in the boiler 31 is provided to the autoclave 1 (or autoclaves where a number of these are provided). To obtain a sufficient volume of steam for charging the autoclave 1 to a sufficiently high temperature, the steam is collected in a thermostore or accumulator 33. This allows the provision of a large quantity of steam in a short period that is greater than the quantity of steam that can be provided directly from the boiler

31. This in turn ensures that the autoclave 1 can quickly be brought to the required temperature and pressure with dry steam at the saturation temperature.

To remove condensate from the steam line from the boiler 31 to the accumulator 33, steam traps are provided, for example on each vertical rise and vertical fall of the steam line, and every 30 m of the pipe run. As shown in Figure 3, this condensate is recovered and passed to a reclaimed water tank 35 for feeding to the boiler feed tank 37. This minimises loss of water in the system, and also avoids loss of heat.

Typically, the accumulator 33 will be formed of carbon steel or other material able to withstand the high temperatures and pressures that are present within the boiler 31. To conserve energy, the accumulator 33 should be suitably insulated. The accumulator 33 is initially charged with water, typically to about 90% of its volume, and the steam from the boiler 31 is injected into the water in such a way that the steam condenses in the water without breaking the surface of the water. This may be achieved by providing a series of steam injectors that inject the steam into the water in a suitable pattern. This also ensures non-stratification within the vessel. By accumulating the steam in this way, and especially where the supply of steam to the accumulator is automatically controlled, it is possible to charge the accumulator at a steady rate, allowing the boiler 31 to operate in a steady condition without requiring the burners in the boiler to be repeatedly turned on and off. This steady state operation is a more efficient way of operating the boiler 31 than repeatedly turning the burners on and off, thereby giving greater fuel efficiency and avoiding damage to the boiler 31 due to excessive cycle demands. Further, there will be less boiler water carry over and faster autoclave cycle time.

Boiler water carry over occurs where a boiler is directly supplying steam, without the use of an accumulator. In this case, since the boiler will need to

work at full capacity, the steam may become overstated, with a liquid content.

This water may carry over to the device to which the steam is supplied.

A pressure control valve is provided to ensure that the steam pressure is correct before this is supplied to the autoclave. The steam is provided to the autoclave 1 through a control valve. To ensure that the steam supplied is dry and of high quality, steam traps may be provided in the vertical rises and falls of the supply line.

Whilst the vessel is in the generally horizontal position, typically at an angle of around 1° to the horizontal, moisture is recovered from the vessel. This moisture is recycled to the boiler feed tank. The steam within the vessel is condensed in a steam vent condense vessel 34. From the steam vent condense vessel 34, the water may pass to the reclaimed cooling water tank 35 or directly to a mixer for return to the boiler feed tank 37. The water collected in the reclaimed cooling water tank 35 is also passed, through the mixer, to the boiler feed tank 37.

Dual filters may be provided to filter the water being supplied to the boiler water feed tank. By providing dual filters, one may be on-line whilst the other is cleaned, thereby allowing for continuous filtering of the water.

Alternatively, some of the condensate may be drained from the autoclave 1 into a condensate pumping vessel 40. This water may contain contaminants, and it is therefore desirable to remove these rather than to re-introduce these into the system. It is preferred that a proportion of the water collected in the condensate pumping vessel 40 is drained away and disposed of, and the remaining water is provided to the steam vent/condensate vessel 34.

When the material within the autoclave 1 has been processed, the steam within the autoclave is exhausted into the steam vent/condensate vessel 34.

The venting of the steam to the steam vent/condensate vessel 34 can be

automatically controlled by the system. The presence of the vented steam in the vessel is detected, for example using a temperature probe. In response to this, water is sprayed into the vessel, condensing the steam. The condensed steam and water are collected in the bottom of the steam vent/condensate vessel 34, and are pumped to the reclaimed cooling water tank 35 where the water is cooled using a chiller unit 34a and air-blast cooler 34b before being fed to the boiler feed tank 37. Waste heat can be used in the waste heat recovery system 44 to preheat the water from the raw water break tank 36.

Some of the water from the reclaimed cooling water tank 35 may be used as the spray to condense the vented steam in the steam vent/condense vessel 34.

It will be appreciated from the above description that the system of the present invention provides control of the steam generation system, by monitoring temperatures and pressures within the system, and ensuring these are optimised, for example by the use of waste heat to pre-heat fluid at different parts of the system, to control the amount and rate of fuel and combustion air provided to the burners of the boiler, and to control the rate at which water is provided to the boiler. The control system may also control the rate at which waste is introduced to the autoclave, and the timing of filling and emptying the autoclave.

Depending on the operational location of any plant, the control system may be monitored by a computer or conventional manual push button controls using gauges and meters for information and operation using a mimic board.

Where a computer system is used, computer hardware or software is provided to calculate fuel usage, water usage and period audits, as well as providing management reports. The computer may be connected, for example via a modem, to allow the information obtained by the control system to be sent to a remote location, for example to allow remote fault and error resolution. The system may also be networked to on-site monitoring.

Without limitation, the control system may control one or more of the following.

The pressure within the boiler is controlled by modulating the control valve provided between the boiler and the charging system on the steam accumulator. This can be monitored using a closed loop with feedback from a pressure transmitter.

The pressure within the steam accumulator may also be monitored, and if this is too high, appropriate action may be taken. For example, a pressure reducing valve may be provided between the steam accumulator and the autoclave that is controlled from a pressure transducer via a closed loop feedback system. If it is determined that the pressure is too low to charge the autoclave, charging of the autoclave can be delayed until the pressure is sufficient.

) Sensors may be associated with the door of the autoclave, for example confirming when the door is closed, and in particular that safety devices associated with the door are operating correctly.

The increase in pressure and temperature within the autoclave may be monitored via suitable pressure and temperature detectors. The rate of increase in the temperate and pressure may be compared with pre- determined acceptable values or gradients. In the event that the increase in the pressure or temperature does not compare correctly with the predetermined values or gradients, for example due to a leak in the autoclave or the incorrect closure of the door, an alarm may be triggered. Similarly, the fall in temperature and pressure can be monitored and compared with predetermined values or gradients during the depressurisation of the autoclave after treatment of the waste.

The rotation of the autoclave may be monitored, for example to ensure that the rotation is in the correct direction and does not exceed a pre-determined "safe"speed. The monitoring of the speed of rotation of the autoclave with the helix within the autoclave can be used to control the motors that drive the autoclave, for example to ensure that there is the optimum speed of rotation, irrespective of the load. Alternatively, the speed of rotation may be dependent upon the load.

The control system may monitor the level of fluid in the steam vent condensate vessel 34 to ensure that this does not overfill. Appropriate control over the drain from the vessel may be provided to ensure the correct level of fluid is maintained.

To maintain the boiler feed water at the required temperature, the temperature may be monitored and the results of this monitoring may be used to control the heat exchanger, and the flow of heated steam to the heat exchanger, to ensure the correct temperature is maintained.

The temperature and level of water in the reclaimed water tank 35 may be monitored by the control system, and water removed or added as necessary to maintain the correct levels.

The contamination level in the boiler water is monitored. If the contamination level is determined to be too great, a suitable blowdown operation, as described above, is implemented.

All boiler controls may be achieved using the overall control system. This can include the measurement and blowdown of total dissolved solids, the frequency of the bottom blow down, status of the Direct Digital Combustion Controller, measurement and control of the temperature of the flue gases into and out of the economiser, level of water, control of the boiler feed water

pump, forced draught fan, gas flow and pressure, the flow of fuel and steam to the accumulator.

Based on the monitoring and control of the system, alarms may be provided to indicate and levels that are outside a predetermined acceptable range. For some measurements, a override facility may be provided, however for others the determination of an unacceptable limit may result in the system automatically being shut down.

Monitoring and control of the plant can be achieved remotely, for example through the use of remote plant monitoring software, such as e-plint (Trade Mark) available from Adaptive Control Systems. This allows monitoring and control over the Internet.