GB2499826A

GB2499826A - Processing of waste material

Info

Publication number: GB2499826A
Application number: GB1203605.9A
Authority: GB
Inventors: Robert Grierson
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-03-01
Filing date: 2012-03-01
Publication date: 2013-09-04
Also published as: GB201203605D0

Abstract

A method for treatment of waste material comprises passing the waste material through a rotating drum 11 at atmospheric pressure and at the temperature in the range 60 to 100Â°C. The method may employ apparatus 10 comprising a drum 11 rotatable about the longitudinal axis of the drum under the action of drive means 16, said axis being substantially horizontal, the drum having an inlet 21 for introducing waste material into the drum and an outlet 22 for discharge of waste material processed within the drum, the interior of the drum being at atmospheric pressure, a moisturising unit (28, Fig 3) whereby waste material having an initial moisture content less than 50% can be moistened to a moisture content in the range 45-60% and a heating unit (25) to heat the waste material to a temperature in the range 60 to 100Â°C.

Description

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PROCESSING OF WASTE MATERIAL

This invention relates to a method of and an apparatus for processing of waste material.

The invention relates in particular, though not exclusively, to a method and apparatus suitable for processing of so-called solid waste such as commercial or domestic waste (known also as municipal solid waste) which typically may comprise a mixture of paper, food, glass, metals and plastics. It has the aim of enabling at least some of said material to be made suitable for recycling and/or for use in providing useable energy.

The invention accordingly is directed to a more environmentally favourable alternative to the historic procedures of landfill and incineration.

Many different systems have been proposed for treating waste material in a manner which results in at least some of the material being broken down and separated into forms suitable for use in creating recycled products and/ for use in providing a source of useable energy. Some of the known systems comprise a processing plant intended to be operated on a continuous basis, with refuse material being fed through a processing zone in which it is subject to the combined effects of heat and pressure. Other known systems operate on a batch type basis and again typically require the use of an autoclave in which the waste material is subject to heat and pressure. Disadvantages of many of these known systems is that, in the case of a continuous system, the required apparatus and means for subjecting waste material to a pressurised environment whilst passing through that environment on a continuous basis is relatively expensive. In the case of batch type systems relatively high levels of energy are required for their operation due to the inherent inefficiency of such systems.

The aforementioned costs and inefficiencies of many known systems renders them unsuitable for use by small and relatively remote communities. To

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address the requirements of small or remote communities it is common practice to transport waste material some distance to a remote processing station where it can be processed along with waste material from other sources. However that need for transportation necessarily involves further costs.

The present invention seeks to provide a method and apparatus for processing of waste material which is of a type suitable for the processing of relatively small quantities of waste material, for example from in the order of 100K tons per annum down to in the order of 25K tons per annum, and which facilitates a reduction in the capital and/or operating costs of hitherto known processing systems.

In accordance with one aspect of the present invention apparatus for the treatment of waste material comprises a drum mounted for rotation about the longitudinal axis of the drum, said axis being substantially horizontal in use of the apparatus, drive means for effecting rotation of the drum, the drum having at one end an inlet for introducing waste material into the drum and an outlet at the other end of the drum for discharge of waste material processed within the drum for providing communication between the interior of the drum and the surrounding environment whereby the interior of the drum is at atmospheric pressure, and said apparatus comprising a moisturising unit whereby waste material having an initial moisture content less than 50% can be moistened to a moisture content in the range 45-60% and a heating unit whereby the waste material in the drum has a temperature in the range 60 to 100°C.

Preferably the moisturising unit is operable to provide the waste material with a moisture content of 50-55%. The moisturising unit may comprise a spray device, and a spray device may be of a type which sprays the waste material with steam or with heated water to at least assist in raising the temperature of the waste material to a temperature in the range 60-100°C.

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Preferably the heater unit is operable to raise the temperature of the waste material to a temperature in the range 65-80°C, more preferably in the order of approximately 70°C. The heating unit may comprise means for heating water which is then sprayed on to the waste material and/or it may comprise radiant or convection heaters. It may comprise a hot air blower for directing hot air onto the waste material within the drum and/or prior to the waste material entering the drum. The drum may be provided with a heating unit.

The apparatus may comprise a heated surface over which the waste material passes. That surface may for example be a surface of a heating jacket, such as one through which heated oil, hot air or other fluid is circulated, or which contains a heating coil through which heated fluid is circulated to heat a heat transfer fluid contained within the jacket.

In contrast to conventional pressurised systems in which material is heated to a higher temperature to result in sterilisation, the present invention merely requires heating sufficient to effect pasteurisation, though temperatures higher than necessary for pasteurisation but less than that for sterilisation are not excluded by the present invention. The risk of disadvantageously breaking down the non-organic material is thereby substantially eliminated.

The drum may comprise in known manner lifters, risers, baffles and pulping helices for the purpose of mixing, wetting, kneading, pulverising and pulping the organic fraction into a fibre fraction, it thus acting as a defibrillator and organic separator. The pulping action washes and scrubs the non-organic fraction, the process thereby producing clean recyclates that are raised to or maintained at a pasteurising temperature together with the pulp fibre to create a sanitised discharged product prior to screening and final separation. The resulting fibre fraction may be employed in a further process to produce a fuel such as ethanol.

In accordance with another aspect of the present invention a method for treatment of waste material comprises passing the waste material through a rotating drum at atmospheric pressure and at a temperature in a range 60-

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100°C, more preferably 65-80°C, said rotating drum being provided with internal components to result in kneading, pulverising and pulping of the waste material. More preferably the waste material passes through the drum at a temperature of approximately 70°C.

Operation of the apparatus preferably is controlled such that the drum performs the steps of conglomeration, digestation and homogenisation. It is envisaged that the drum shall be rotated at a speed of between 5 and 30 rpm, more preferably between 10 and 15 rpm.

It is further preferred that in the method and use of the apparatus of the present invention the waste material is subjected to pre-treatment prior to entering the drum, said pre-treatment comprising raising the moisture content of the waste material to in the range 45-60% more preferably 50-55%, and to increasing the temperature to in the range 60-100°C, more preferably 65-80°C and even more preferably approximately 70°C. Preferably said pre-treatment is effected in an auger through which the waste material passes to enter the drum. Moisturising and/or heating may be effected in an auger unit prior to material entering into the auger screw region and/or whilst passing through the auger screw. Thus the auger unit may operate as a pre-conditioning auger unit.

The auger unit may comprise a heated surface such as that aforedescribed and which may be the surface of a heating jacket. The heating jacket may be of a tubular shape to provide a surface which surrounds the auger screw.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which:-

Figure 1 is a schematic view of an apparatus for the use in the method of the present invention;

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Figure 2 is a perspective view, part cut away, of the drum section of the apparatus of Figure 1;

Figure 3 is a cross-sectional view of the feed unit and part of the drum of the apparatus of Figure 1, and

Figure 4 is an end view of part of the feed unit of Figure 3.

Apparatus 10 for treatment of domestic waste material comprises a rotatable processing drum 11, a feed unit 12 for introducing waste material 18 into the drum, and a separation unit 13 (not shown in Figures 2 and 3) at the outlet end of the drum for separating pulped fibre material from the remainder of the drum output.

The rotatable drum may be of a type which incorporates constructional features already well known and proven for use in the processing of waste material. Accordingly it may incorporate many of the features of the rotatable drum described in US 3405873 and as reflected in the perspective view of our accompanying Figure 2.

Thus, the drum is mounted on rollers 15 for rotation about the longitudinal axis of the drum under the action of electric motor 16 and a ring gear 17 on the outer surface of the drum.

Internally the drum is provided with a series of axially spaced vanes 18. Each vane is formed from a flat metal sheet and is secured to the internal surface of the drum to lie in a plane inclined to the longitudinal axis of rotation of the drum and to a plane perpendicular to said longitudinal axis.

Accordingly the outer edges 19 of the vanes are of an elliptical shape for making line contact with the inner wall of the drum. Each vane in this example has a straight edge 20 which extends between two positions on the inner wall of the drum, that edge lying between the axis of rotation of the drum

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and the part of the drum to which the elliptical edge is secured to the inner wall of the drum.

The respective vanes are positioned and oriented such that during rotation of the drum they tend to direct in-coming material in a direction back towards that end 21 of the drum at which the material has been introduced. In consequence the material is subject to a tumbling action to result in agglomeration and pulverising, with pulverised material being urged towards the outlet end 22 of the drum by the force exerted thereon by in-coming material acting in a direction opposite the direction in which the vanes act on the material.

In contrast to the drum described in US 3405873, in this embodiment of the invention the drum is maintained at an internal pressure that is atmospheric and there is no requirement for the drum to be internally pressurised. Furthermore there is no requirement for a downstream section of the drum to incorporate a perforated internal cylinder as hitherto often provided for separation of processed material. Additionally, in contrast to many prior known processing drums, there is no requirement for the drum to incorporate means for heating the drum contents, though the provision of such heaters is not excluded by the present invention.

Following treatment in the drum the material discharges from the outlet end 22 of the drum and is directed onto a trommel 13 which, in known manner, is operable to separate the pulped fibre material from the residue and provide two outlet steams 23, 24. The residue may then be fed through a ballistic separator, a magnetic separator to separate ferrous material and an eddy current separator to remove non-ferrous metallic material. The ballistic separator of this embodiment of the invention is provided for the purpose of providing a clean feed of processed material to a dry anaerobic digester for provision of quality methane gas.

A particular feature of this embodiment of the present invention is that the waste material is conditioned to be at a required pasteurising temperature and

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at a required moisture content percentage by passing through the feed unit 12. For that purpose the feed unit 12 comprises an auger screw 27 which is rotatable within a heated casing 25 under the action of a shaft 34 driven by an electric motor 35. At the inlet zone 26 of the auger a series of jets 28 are provided for directing a spray of heated water onto the waste material 18 just prior to it entering the auger screw 27. However, alternatively the sprayer may be operable to spray heated water onto the waste material when passing through the auger screw and in that case the auger casing need not be of a type which is able to heat the waste material.

In this embodiment of the invention the heated casing 25 is in the form of a jacket of circular cross-section and through which heated air is circulated. The inner surface of the jacket defines the passage within which the auger screw 27 rotates and thus is effective to heat the waste material as it passes through the auger.

The end face 30 of the jacket is provided with a series of orifices 31 such that a portion of the heated air flowing through the jacket 25 issues from the jacket and enters the inlet end opening 21 of the drum as a de-pressurised heat source.

Moisture and temperature sensors are provided in know manner at the auger outlet region and also at the drum outlet to facilitate control of the rate at which moisture and heat are added to the waste material and thereby assist in ensuring that the waste material is preferentially pre-conditioned for subsequent pulverisation within the rotatable drum.

From the foregoing it will be understood that the present invention advantageously provides a method and an apparatus which is operable to permit relatively modest quantities of waste material to be processed at relatively low cost, and in particular without the need for the significantly more expensive provision of an autoclavic or other such type of pressure vessel. Furthermore the size of the apparatus for processing of relatively small quantities of material avoids the need necessarily to provide bespoke

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foundations, and the apparatus may be mounted on means such as rollers, wheels or skids that enable it, or sections of the apparatus, readily to be relocated. Control of the processing temperature to be less than that required for sterilisation results in the method and apparatus being able to provide an output of good quality organic fibre fraction as well as clean non-organic recyclates.

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Claims

1. Method for treatment of waste material comprising passing the waste material through a rotating drum at atmospheric pressure and at the temperature in the range 60 to 100°C.

2. Method according to any one of the preceding claims wherein the temperature is in the range 65 to 80°C.

3. Method according to claim 2 wherein the temperature is 70°C.

4. Method according to any one of the preceding claims wherein the rotating drum comprises internal components for subjecting the waste material to one or more of a kneading, pulverising or pulping action.

5. Method according to any one of the preceding claims wherein the drum performs one or more of the steps of conglomeration, digestation and homogenisation.

6. Method according to any one of the preceding claims wherein the waste material is subjected to pre-treatment prior to entering the drum, said pre-treatment comprising raising the moisture content of the waste material to in the range 45 to 60%.

7. Method according to claim 6 wherein the moisture content is raised to in the range 50 to 55%.

8. Method according to any one of the preceding claims wherein the waste material is heated to a temperature in the range 60 to 100°C prior to entering the drum.

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9. Method according to claim 8 wherein the temperature of the waste material is increased to within the range 65 to 80°C.

10. Method according to claim 9 wherein the temperature of the waste material is increased to 70°C.

11. Method according to any one of the preceding claims wherein the waste material is subjected to pre-treatment by passing through an auger unit prior to entering the drum.

12. Method according to claim 11 wherein the waste material is subject to a pre-treatment of moisturising and or heating by passage through an auger unit prior to entering the drum.

13. Method according to claim 12 wherein at least a part of said moisturising and/or heating in the auger unit is effected in the auger unit prior to the waste material entering a screw region of the auger unit.

14. Method according to any one of claim 11 to13 wherein the waste material is subject to moisturising and/or heating during passage through a screw region of the auger unit.

15. Method according to any one of the preceding claims wherein prior to entering the drum the waste material is subject to heating by means of a heated fluid at least some of which is directed to enter the drum concurrent with entry of the waste material into the drum.

16. Method according to claim 1 and substantially as hereinbefore described.

17. Apparatus for the treatment of waste material comprising a drum mounted for rotation about the longitudinal axis of the drum, said axis being substantially horizontal in use of the apparatus, drive means for effecting rotation of the drum, the drum having at one end an inlet for introducing waste

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material into the drum and an outlet at the other end of the drum for discharge of waste material processed within the drum for providing communication between the interior of the drum and the surrounding environment whereby the interior of the drum is at atmospheric pressure, and said apparatus comprising a moisturising unit whereby waste material having an initial moisture content less than 50% can be moistened to a moisture content in the range 45-60% and a heating unit whereby the waste material in the drum has a temperature in the range 60 to 100°C.

18. Apparatus according to claim 17 wherein the moisturising unit comprises a spray device to spray heated water or steam onto the waste material.

19. Apparatus according to claim 18 wherein the moisturising unit is operable to spray heated water or steam onto the waste material prior to the waste material entering the drum.

20. Apparatus according to any one of claims 17 to 19 wherein the heater unit is operable to heat the waste material prior to entry of the material into the drum.

21. Apparatus according to claim 20 wherein the heating unit for heating waste material prior to entry into the drum comprises means for permitting heating fluid to enter the drum concurrent with waste material.

22. Apparatus according to any one of claims 17 to 21 wherein the heating unit comprises a substantially tubular heating jacket through which waste material passes prior to entry into the drum.

23. Apparatus according to claim 22 wherein means is provided for circulating heated air through said jacket and an end region of the jacket closest to the drum is provided with apertures for allowing heated air to pass from within the jacket to within the drum.

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24. Apparatus according to claim 22 or claim 23 wherein an auger screw extends through said jacket for directing waste material into the drum.

25. Apparatus according to claim 17 and substantially as hereinbefore described.