GB2540888A

GB2540888A - Waste processing

Info

Publication number: GB2540888A
Application number: GB1617312.2A
Authority: GB
Inventors: Christensen Mark; Manser Anthony
Original assignee: Biocentre Tech Ltd
Current assignee: Biocentre Tech Ltd
Priority date: 2010-05-14
Filing date: 2010-05-14
Publication date: 2017-02-01
Anticipated expiration: 2030-05-14
Also published as: GB201617312D0; GB2540888B; GB2480318A; GB201008058D0; GB2480318B

Abstract

A method of processing waste material to produce a fuel pellet product having a chlorine content less than 0.3%w/w and a biomass content greater than 90%, the method comprises the steps of: receiving waste material 20; manually selecting specific items for removal from the waste 30; mechanically reducing the size of some of the waste 40 preferably where certain items are automatically rejected and preferably using a trommel; mechanically separating the waste into at least two size fractions preferably using a trommel 50; mechanically reducing the size of some of the waste in one of said at least two size fractions to form floc preferably using a vertical shaft shredder 70; mechanically separating the floc into two density fractions preferably using an air classifier 90; flash drying the lighter of the two said density fractions 100 preferably for approximately 1 second at approximately 400°C; mechanically removing dust 110 and/or any residual organic consent form the flash dried lighter of the two said density fractions to form a fuel product 120; removing plastics form the waste 60 before forming floc and/or after separating the floc. Preferably the method further comprises a step of removing textiles 160.

Description

Waste Processing

The present invention relates generally to a method of processing waste, a fuel product, a waste processing plant, a refined secondary biomass fuel product, and a computer program.

With regard to the term “waste” this may be understood as relating to mixed, substantially solid and substantially non-hazardous waste from domestic, commercial and/or industrial sources.

It is known to process waste in order to extract useful materials for further uses (i.e. the materials are recycled possibly for onward further processing/manufacturing into different products) and also sometimes for the purpose of producing a fuel product. Such fuel products may be burnt in conventional or purpose built power generation facilities and may be a fuel substitute for, or used in addition to, existing fuels such as coal, biomass etc. It is desirable for the fuel product to have relatively consistent characteristics. The fuel product may be considered to be a refined fuel product.

Due to regulations relating to emissions from such processes, and from the resultant products themselves, being regularly changed and generally tightened in relation to the limits on certain elements and/or compounds being released into the environment it is desirable to have a process which meets and possibly exceeds the requirements of these regulations. The present invention provides not only a process which meets this target but also allows for further adjustment and modification to keep pace with regulatory and commercial pressures.

In a first aspect, the invention provides a method of processing waste to produce a fuel product comprising the steps of: (a) receiving waste material; (b) selecting specific items for removal from the waste; (c) mechanically reducing the size of some of the waste; (d) mechanically separating the waste into at least two size fractions; (e) mechanically reducing the size of some of the waste in one of the said at least two size fractions to form floe; (f) mechanically separating the floe into two density fractions; (g) flash drying the lighter of the two said density fractions; (h) mechanically removing dust and,/or any residual organic content from the flash dried lighter of the two said density fractions to form a fuel product.

The received waste may be solid. In this context the term “solid” refers to the waste being substantially dry, however, it is understood that the waste may have a moisture content up to 70%, but more commonly between 35 and 50%. Furthermore, the term “mechanically” used herein refers to the use of plant/equipment/machines whether automatically and/or manually operated.

The term “floe” is a term well understood by those skilled in the art and refers to relatively small, loose particles of matter.

The size fraction in step (e) may be the larger of the two.

This method contains the steps necessary for making a fuel product. However it does not describe other processes for dealing with all of the other waste streams derived during the process. Accordingly, the method may include other steps as discussed below and as claimed herein. For instance, the method may further comprise the step of mechanically separating the waste in the other of the said at least two size fractions derived in step (d) into inorganic and organic waste components. In this regard, the terms “organic” and “inorganic” are biological references and not chemistry references. The size fraction in question may be the smaller of the two. This separation may be effected by using a density separator. The separator may be a wet density separator and rely on a water-based density media, although other types of media are contemplated as required. The processing of the waste in this manner may reduce one or more of the chlorine, ash, silica, nitrogen and sulphur content by a washing effect.

The method may further comprise the step of at least partially biologically digesting the derived organic waste components. This may be by aerobic and/or anaerobic digestion in one or more digesters in parallel and/or in series. Prior to this step, the derived organic waste components may be de-watered by using one or more of a wedge wire screen and a screw-press. The removed water may pass through a centrifuge to remove any residual solids and then be treated aerobically to reduce biochemical oxygen demand.

The method may further comprise the step of processing the derived organic waste component into a biomass fuel. This processing may be relatively simple such as one or more of moving, drying and pelletising the organic waste. This step may occur before or after the biological digestion of the organic waste component.

The method may further comprise the step of magnetically and/or electro-magnetically separating metals from the denser of the two said density fractions derived in step (f) and from the derived inorganic waste component. These metals may be recycled and/or reprocessed.

The method may further comprise the step of removing textile components from the denser of the two said density fractions derived in step (f) and from the derived inorganic waste component. This may be effected by a ragger.

The method of producing the fuel product in step (h) may further comprise including (possibly by mixing) at least some of the derived organic waste components into the fuel product. This may be organic waste which has been at least partially, or completely, digested and/or treated in another way, such as by drying, bio-stabilising, and/or autothermic pasteurisation/digestion. This organic matter may be further screened before being added to the fuel product to remove any trace physical and/or chemical contaminants.

The method may further comprise the step of pelletising the produced fuel product. The apparatus provided for pelletisation may be controllable to vary the bulk density of the product.

The method may further comprise the step of mechanically reducing the size of the waste, remaining after the removal of the metals and/or textiles, to produce an aggregate. This may be effected by use of a ball mill. This waste may comprise glass and/or inerts. The term “aggregate” may be understood to mean “aggregate replacement” as understood in the aggregate industry. It may be shard-free

The aggregate may contain substantially only one or more of glass, stone, concrete and soil.

Certain waste items may be automatically rejected from step (e). This may be by ballistically ejecting the item from the size reduction device.

Either or both of steps (c) and (d) may be effected by using a trommel. The trommel may include bag splitters. Other types of mechanical size reduction means may be employed as well as, or instead of, a trommel. For instance a shredder may be employed to reduce the size of at least some of the waste prior to separation in step (d) and after receipt of the waste in step (a). This may be a coarse shredder. It may be a relatively low speed shredder.

The mechanical reduction of the size of some of the waste in step (e) may be effected by using a vertical shaft shredder. It may be a relatively high speed shredder.

The mechanical separation of the floe in step (f) may be effected by using an air classifier. More than one air classifier may be employed. The operating characteristics of the one or more air classifiers may be adjustable, for instance, the air speed may be varied.

The residence time of the waste in the flash drier in step (g) may be approximately one second, although other times are contemplated.

The temperature at which the waste is flash dried in step (g) may be approximately 400 degrees centigrade, although other temperatures are contemplated.

The method may further comprise the step of removing plastics from the waste before step (e) and/or after step (f). This plastics removal may be effected by use of near infrared spectroscopy equipment.

It is to be understood that the steps of the method do not necessarily have to be performed in the sequence disclosed and that at least some of the steps may be repeated and/or performed at other stages within the process. For instance, it is conceivable that it would be desirable to reduce the size, or separate, at least some of the waste at other stages throughout the process. Alternatively, or additionally, the removal of plastics may take place before step (e).

In a second aspect, the invention provides a refined secondary biomass fuel product, manufactured using the method of the first aspect and/or as described and/or as claimed herein.

The fuel product may comprise one or more of the following characteristics: greater than approximately 80% biomass content; average calorific value of approximately 10-17MJ/kg; average moisture of approximately 6-8%; average ash content after burning approximately 6-8%; sulphur content less than approximately 0.3% w/w; chlorine content less than approximately 0.3% w/w; and a bulk density of approximately 350-650kg/m3.

The fuel product may also comprise any one or more of the following characteristics: total Group II metal content less than approximately 20 mg/kg; mercury content less than approximately 10 mg/kg; cadmium content less than approximately 6 mg/kg; thallium content less than approximately 20 mg/kg; total Group III metal content less than approximately 750 mg/kg; antimony content less than approximately 150 mg/kg; arsenic content less than approximately 100 mg/kg; chromium content less than approximately 120 mg/kg; cobalt content less than approximately 60 mg/kg; copper content less than approximately 150 mg/kg; lead content less than approximately 120 mg/kg; nickel content less than approximately 80 mg/kg; tin content less than approximately 40 mg/kg; vanadium content less than approximately 100 mg/kg.

The biomass content may be greater than approximately 90%. This may be because there are substantially no plastics included in the fuel product.

The calorific value may be as high as 22 MJ/kg due to the inclusion of certain materials such as plastics. It may lie in the range 17-20 MJ/kg. It may be approximately 17 MJ/kg substantially without plastic content. The fuel product may be in the form of a pellet. It may contain less than 5% plastics. The fuel product may be called a refuse derived fuel.

In a third aspect, the invention provides a waste processing plant operable according to the method of the first aspect and/or as described and/or as claimed herein. The plant may be considered to be a mechanical waste separation and processing plant.

In a fourth aspect, the invention provides a refined secondary biomass fuel product comprising one or more of the following characteristics: greater than approximately 80% biomass content; average calorific value of approximately 10-17MJ/kg; average moisture of approximately 6-8%; average ash content after burning approximately 6-8%; sulphur content less than approximately 0.3% w/w; chlorine content less than approximately 0.3% w/w; and a bulk density of approximately 350-650kg/m3.

The processes described herein have been designed in order to ensure that the fuel products described herein as Refuse Derived Fuel and Secondary Biomass Fuel, will be of such specification and commercial fuel quality as to be capable of satisfying the relevant legal criteria laid down by the European Court of Justice and the Court of Appeal in England for a “completely recovered” or “end of waste” fuel product. Those criteria are that: (a) the fuel is a distinct and marketable product, (b) the fuel can be used in exactly the same way as an ordinary fuel, and (c) the use of the processed fuel in the particular intended applications must not require any greater environmental protection precautions nor result in any greater impact on the environment or human health than those applying to the use of the relevant virgin fossil fuel in the same application.

In a fifth aspect, the invention provides a computer program comprising computer program code means adapted to operate and/or control plant required to perform the method of the first aspect and/or as described and/or as claimed herein when said program is run on a computer.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing, which illustrates, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawing.

Figure 1 is a flowchart of one way in which the invention may be put into effect.

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawing described is only schematic and is non-limiting.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Similarly, it is to be noticed that the term “connected”, used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression “a device A connected to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Connected” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some, but not other, features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

The overall process of waste processing is shown in Figure 1. As explained already, not all of the elements are crucial to its effectiveness and other arrangements and features may be included as required.

The waste is received 20 in a reception hall where removal of specific items 30 may be effected by manually selection. For instance, oversize articles, hazardous waste etc. may be removed. Some of it may be shredded to a size less than 300mm and returned to the waste stream along with the remainder of the waste from the reception stage. The waste is then passed to a primary separation stage 50 which in the present example is a trommel. This may be up to 10m in length, up to 2.5m in diameter, have apertures of approximately 45-50mm, and an open surface area of approximately 48%. It may be rotated at a speed of approximately 17rpm and be inclined to the horizontal to aid throughflow.

The trommel may include internal bag splitters and lifting bars to help agitate and reduce the waste in size.

The oversize typically comprises larger metals, plastics, paper and card, whereas the undersize typically comprises organic material, smaller metals, some heavy plastics, glass, textiles and stone/concrete etc.

The oversize material is passed to a shredder 70. This may be a high speed vertical shaft flail shredder which reduces the material to a floe. The size of the floe, may be substantially less than 20mm. Any objects which are rejected 80 as being large or resistant to the shredder tend to be ejected ballistically from the top. These may be further processed and reintroduced to the waste stream at any appropriate point. The resultant shredded material is then passed to the base of an air column classifier 90. In this column, the lighter material tends to be directed out of the top while the heavier material tends to drop to the base. The classifier may remove any remaining metals and inerts.

The lighter, less dense, material is then directed to a flash drier 100. This may operate at 400 degrees centigrade and the residence time may be only approximately one second. This is enough to dry the material without combustion occurring. This drying may destroy any bacteria or pathogens and therefore may be described as a pasteurising and/or sterilising step.

This dried material is then directed to a stage 110 where dust and/or residual organic material may be removed. This is effected by a rotating drum screen with a 5mm mesh. This step may reduce or eliminate chlorine and sulphur content.

The resultant fuel 120 is then directed to a pelletiser 130 where it may be made into suitably sized pellets for storage and/or transportation. The shape of the pellets may be substantially cylindrical with an approximate length of 30mm long and approximate diameter of 18mm. The pelletisation step may induce a rise in temperature in the resultant fuel/material due to compression/friction thereof.

The undersize from the primary separation stage 50 is directed to a density separation unit 140 which relies on agitation of the material in a fluid together with removal of the upper and lower levels of the fluid in which are carried the two respective density fractions. These tend to be predominantly organic and inorganic in character.

The organic component is sent to one or more digesters 150 where it can reside for up to 10 days or more, as required. The digesters are typically enclosed and may reach temperatures of more than 70 degrees centigrade.

Some of this digested organic matter may be added to the fuel product 120 as it may be very similar to peat, which is itself a form of combustible fuel.

The inorganic component from the density separator 140 together with the more dense fraction from the air classifier 90 is then subjected to magnetic fields 160 to remove ferrous metals and to eddy currents to remove non-ferrous metals. Before or after this stage 160 textiles may also be removed by means of raggers. The recovered metals and textiles 170 may be recyclable (in that they may be used again in further manufacturing processes), however, some of the textiles may be included in the fuel product 120. The proportion of included textiles may be controlled to ensure the biomass content of the final fuel product has the desired characteristics, such as a relatively high biomass content by the inclusion of only natural (i.e. non-man-made) textiles.

These steps enable the removal of organic, metallic and inert materials.

The waste remaining after the metals and textiles have been removed at stage 160 is then directed to a ball mill 180 for further size reduction to any desired size or granulometry. For instance, the size of the particles in this resulting aggregate may be substantially equivalent to that of typical sand. This aggregate 190 may be further screened to provide an oversize waste which may be reintroduced into the waste stream at an appropriate point. The aggregate may be used as an aggregate replacement.

It is possible for some or all of the organic waste component derived from the density separator 140, either before or after at least partial digestion in the one or more digesters 150, is treated as a biomass fuel 200. It may be further processed such as by pelletisation.

The process may be fully automated and operated by one or more computer-based systems. The equipment may be compact and/or linear.

Claims

1. A method of processing waste material to produce a fuel product having a chlorine content less than 0.3% w/w and a biomass content greater than 90%, the method comprising the steps of: (a) receiving waste material; (b) manually selecting specific items for removal from the waste; (c) mechanically reducing the size of some of the waste; (d) mechanically separating the waste into at least two size fractions; (e) mechanically reducing the size of some of the waste in one of the said at least two size fractions to form floe; (f) mechanically separating the floe into two density fractions; (g) flash drying the lighter of the two said density fractions; (h) mechanically removing dust and/or any residual organic content from the flash dried lighter of the two said density fractions to form a fuel product; (i) removing plastics from the waste before step (e) and/or after step (f).

2. The method of claim 1, further comprising the step of removing textile components in step (i).

3. The method of any preceding claim, further comprising the step of pelletising the produced fuel product.

4. The method of any preceding claim, wherein certain waste items are automatically rejected from step (e).

5. The method of any preceding claim, wherein either or both of steps (c) and (d) are effected by using a trommel.

6. The method of any preceding claim, wherein the mechanical reduction of the size of some of the waste in step (e) is effected by using a vertical shaft shredder.

7. The method of any preceding claim, wherein the mechanical separation of the floe in step (f) is effected by using an air classifier.

8. The method of any preceding claim, wherein the residence time of the waste in the flash drier in step (g) is approximately one second.

9. The method of any preceding claim, wherein the temperature at which the waste is flash dried in step (g) is approximately 400 degrees centigrade.

10. The method of any preceding claim, wherein the plastics are removed using near infrared spectroscopy equipment.