Pellet Processing Drum

Abstract

The present invention relates to a desiccation apparatus, the apparatus comprising: a hollow drum mounted for revolution about a substantially longitudinal axis, the drum comprising a shell having an interior surface and an exterior surface; and a means to generate airflow through the hollow drum.

Claims

1. A desiccation apparatus, the apparatus comprising: a hollow drum mounted for revolution about a substantially horizontal axis, the drum being defined by a shell having an interior surface and an exterior surface; and a fan, air blower, vacuum or suction device to generate airflow through the hollow drum.

2. A desiccation apparatus according to claim 1, wherein the desiccation apparatus is adapted to remove water and other liquids from a wet feedstock, thereby reducing the liquid content of the feedstock.

3. A desiccation apparatus according to claim 1, wherein the apparatus further comprises a liner provided on at least a portion of the interior surface.

4. A desiccation apparatus according to claim 3, wherein the liner is a porous liner.

5. A desiccation apparatus according to claim 4, wherein the porous liner is constructed from a material selected from the group comprising porous textiles, porous fabrics, porous rubbers, porous plastics, porous ceramics, porous wood, porous cement, porous concrete or porous brick.

6. A desiccation apparatus according to claim 3, wherein the liner is a woven or non-woven textile.

7. A desiccation apparatus according to claim 3 wherein the liner covers at least 50% of the interior surface

8. A desiccation apparatus according to claim 3, wherein the shell is provided with a number of perforations.

9. A desiccation apparatus according to claim 3, wherein the ratio of the diameter of the drum to the length of the drum is between 1:2.5 and 1:10.

10. A desiccation apparatus according to claim 3, wherein the desiccation apparatus further comprises a feed inlet.

11. A desiccation apparatus according to claim 3, wherein the desiccation apparatus further comprises an outlet.

12. A desiccation apparatus according to claim 3, wherein the desiccation apparatus further comprises a rotating means for controllably rotating the hollow drum.

13. A desiccation apparatus according to claim 3, wherein the means for generating airflow through the hollow drum is a fan or air blower.

14. A method for the removal of water from a feedstock comprising water, the method comprising: introducing the feedstock into a hollow drum mounted for revolution about a substantially horizontal axis, the drum being defined by a shell having an interior surface and an exterior surface; generating an airflow through the hollow drum; and at least periodically rotating the hollow drum.

15. A method according to claim 14, wherein the volume of feedstock is controlled to between 5% and 40% of the internal volume of the drum.

16. A method according to claim 14, wherein the airflow has speed of at least 2 km/hr.

17. A method according to claim 14, wherein the airflow is passed through the drum at a rate of at least 2.5 m.sup.3/s.

18. A method according to claim 14, wherein the feedstock comprises pellets, powders, seeds, biomass matter, muds, sludges, lumps, slurry, suspensions, ores, concentrates or agglomerates.

19. A method according to 14 claim, wherein the drum is continuously operated or batch operated.

20. A method according to claim 14, the method comprising rotating the drum at a rate of between 1 and 25 revolutions per minute.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0076] FIG. 1 is an upper perspective view of a desiccation apparatus in accordance with a first embodiment of the present invention; and

[0077] FIG. 2 is an upper perspective view of a desiccation apparatus in accordance with a second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0078] In FIG. 1 there is shown a desiccation apparatus 10 in accordance with a first embodiment of the present invention. The desiccation apparatus 10 of the present invention comprises a hollow drum 12. The hollow drum is defined by an elongate shell 14 having a substantially horizontal axis. The shell 14 has an interior surface 16 which faces the inside of the hollow drum 12 and an exterior surface 18 which faces the outside of the hollow drum 12.

[0079] The hollow drum 12 is supported for rotation about a substantially horizontal axis 20. In the embodiment shown in FIG. 1, the cylindrical shell 14 is supported for rotation on a number of rollers 22. The rollers 22 are spread out along the length of the cylindrical shell 14. Is envisaged that as the length of the hollow drum 12 increases, additional rollers 22 may be required. In the embodiment shown in FIG. 1, the rollers 22 are mounted on a base structure 24.

[0080] Rotation of the hollow drum 12 is driven by a drive means, for example an electric motor 26. Suitable drive means include combustion motors, electric motors, hydraulic motors and prime mover direct drives. In the embodiment shown in the figures, a teeth track 28 is provided around the circumference of the hollow drum 12 to engage with the electric motor. To facilitate the engagement of the electric motor to the teeth track 28, the electric motor is coupled to a gear 30. In the embodiment shown in FIG. 1, the gear 30 directly engages with the teeth track 28 to rotate the hollow drum 12. Alternatively, it is envisaged that the gear 30 and the teeth track 28 may be engaged by way of chain (not shown) that surrounds both the gear 30 and the teeth track 28. Other conventional means of rotating the drum may be implemented without departing from the scope of the present invention. Rotation of the hollow drum 12 may be operated at steady speed, variable speed or in intermittent motion.

[0081] The interior surface of the shell 14 is lined with a liner 32. In a preferred embodiment, the liner 32 is constructed from a porous material. By lining the interior surface of the shell 14 with a porous liner 32, the feedstock will come into intimate contact with the porous liner 32 during operation of the desiccation apparatus 10. During this contact, the porous liner 32 will absorb liquid from the feedstock whilst rejecting solids. The inventors have found that a porous layer that is constructed from a porous material is particularly useful in the removal of liquid from the feedstock. As would be appreciated by a person skilled in the art, porous materials absorb liquid through a mechanism known as capillary action, also known as wicking. In this mechanism, the intermolecular forces between the liquid and surrounding solid surfaces cause liquid to be drawn into the pores of the porous material. It is envisaged that the porous liner 32 can be constructed from any material that can be adapted to absorb liquids. Examples include a wide range of woven and non-woven fabrics, rubber, plastic, ceramic, wood, cement, concrete or brick liners. A particularly useful material used to construct the porous liner 32 is a geosynthetic textile. Such materials comprise a woven or non-woven textile constructed from synthetic fibres. Materials that have been found to be particularly useful by the inventors include Texcel™, Bidim™, Mirafi™ and Megaflow™GT500 and GT 750 supplied by Tecate™ and GEOFABRICS AUSTRALASIA PTY LTD.

[0082] In order to ensure efficient removal of the liquid from the feedstock, it is recommended to maximise throughput that at least 50% of the interior of the shell 14 should be lined with a porous liner 32.

[0083] The pore size of the porous liner 32 is between 2 microns and 100 microns. As would be appreciated by a person skilled in the art, the size of the pores needs to be sized to provide the required capillarity or surface tension to retain liquids in the pores of the porous layer.

[0084] The thickness of the porous liner 32 is usually 1 mm to 10 mm thick but preferably 3 mm to 6 mm in thickness depending upon the type of material is used to construct the porous liner 32. Generally, a thicker porous liner 32 is required when the porous liner 32 is constructed from a material that is susceptible to being damaged by the solids in the feedstock.

[0085] The apparatus further comprises a means to generate an airflow through the hollow drum 12. The preferred airflow direction is parallel to the horizontal axis of the drum over the wet feedstock. It is envisaged that the airflow can be generated by a fan, blower, vacuum or by differential pressure. The inventors have found that the airflow generated through the drum will enhance the rate of evaporation of volatile liquids, such as water, from the feedstock. Without wishing to be bound by theory, the inventors believe that as water evaporates into the atmosphere of the desiccation apparatus as water vapour, the airflow will continually direct the water vapour out of the desiccation apparatus. This is understood to increase the rate of evaporation of water from the feedstock whilst also preventing the recondensation of water vapour.

[0086] The hollow drum 12 may be mounted on a slightly decline position to allow for gravity to move the feedstock along the length of the hollow drum 12 during rotation. It is envisaged that the movement of the feedstock along the length of the drum will increase the contact of the feedstock with the airflow and the porous liner 32, thereby increasing the rate in which liquids are removed from the feedstock by evaporation or wicking.

[0087] The desiccation apparatus further comprises a feed inlet (not shown). The feed inlet provides a point at which the feedstock may be introduced into the interior of the hollow drum 12. It is envisaged that the feed inlet may be in communication with a hopper or other storage vessel to introduce the feedstock into the hollow drum 12 at a controlled rate. The desiccating further comprises an outlet adapted to discharge the dried material from the interior of the hollow drum 12. The feed inlet and the outlet are provided at opposing end of the hollow drum 12, thereby allowing the feedstock to travel the length of the hollow drum 12. This maximises the contact time between the feedstock and the porous liner 32. Where the hollow drum 12 is positioned on an inclined position, the feed inlet is provided at the inclined end of the hollow drum 12, with the outlet positioned at the declined end. In this arrangement, gravity will slowly move the feedstock between the feed inlet and the outlet by cascade and finally discharged by overflow.

[0088] The interior of the hollow drum 12 may be provided with plurality of lifting means that are mounted on the interior surface of the shell 14, extending inwardly therefrom. As would be appreciated by a person skilled in the art, the lifting means are adapted to continuously pick up and drop the feedstock in response to rotation of the hollow drum 12. This in turn increases the mixing of the feedstock and exposing the feedstock to the airflow and the porous liner 32, thereby increasing the rate in which liquids are removed from the feedstock by evaporation or wicking. The use of lifting and turning the feedstock by the means of “lifters” is more applicable to discrete solid particles where the interior of the feedstock would normally not be exposed to the porous liner 32.

[0089] The desiccation apparatus further comprise a drainage means (not shown) provided underneath the hollow drum 12. The drainage means is shaped so as to catch any liquids expelled by the hollow drum 12 and direct them to an appropriate recycle, storage or disposal means. One or more filter may be associated with the drainage means.

[0090] During operation of the desiccation apparatus, the feedstock is gently tumbled in the hollow drum 12 as it rotates. During the rotation, the feedstock comes into intimate contact with the porous liner 32. When the feedstock comes into contact with the porous liner 32, water is absorbed by the porous liner 32. The airflow travels through the hollow drum 12, to evaporate water from the feedstock and some air also contacts the fabric not covered by feedstock.

[0091] It is envisaged that the desiccation apparatus may be adapted to operate in either a batch configuration or a continuous configuration. In a batch operation, a finite amount of feedstock is loaded into the hollow drum 12 through the feedstock inlet and the desiccation apparatus is operated. Once the feedstock has been sufficiently dried, the operation of the desiccation apparatus is ceased and the dried material is removed from the outlet.

[0092] In continuous configuration, the feedstock is continuously fed into the feedstock inlet during operation of the desiccation apparatus and the dried material is withdrawn through the outlet. In operation, it is envisaged that the feedstock will need to be fed into the feedstock inlet at a controlled rate to allow sufficient time for the feedstock to lose excess surface water to the airflow and the porous medium Furthermore, it is envisaged that by providing the hollow drum 12 in an inclined position, the feedstock may move along the hollow drum 12 from the feedstock inlet to the outlet under influence of gravity by cascading down the drum as the drum is rotated. The extent of water removal can likewise be controlled by controlling the contact time between the feedstock and the porous liner 32.

[0093] It is envisaged that two or more hollow drums 12 may be used in parallel or series. It is envisaged that series operation may operate in a multiple pass type arrangement with different process conditions for subsequent hollow drum 12s. Furthermore, a hollow drum 12 can consist of cylinders of different diameters joined together or running adjacent to each other feeding product from one cylinder to the next. It is envisaged that parallel operation will allows a higher throughput of feedstock processing.

[0094] The inventors envisage that the desiccation apparatus is suitable to treat feedstocks selected from pellets, powders, seeds, muds, sludges, lumps, mashes, aggregates, slurry, suspensions or agglomerates.

[0095] The desiccation apparatus is adapted to treat feedstocks with a solids content of at least 1% but preferably a minimum of 12% solids.

[0096] It is envisaged that additional products can be added separately into the hollow drum 12 to aid with the overall process such as dry solids, powders, liquids, chemicals or adsorbents.

[0097] In FIG. 2 there is shown a desiccation apparatus 100 in accordance with a further aspect of the present invention. Desiccation apparatus 100 shares many features with desiccation apparatus 10 and like numerals denote like parts.

[0098] In the embodiment shown in FIG. 2, the shell 14 is provided with a number of perforations 102. The perforations are provided at regular intervals around the circumference of the hollow drum 12 and at regular intervals along the length of the hollow drum 12. The perforations permit communication between the interior of the hollow drum 12 and the exterior. Whilst not shown in FIG. 2, the use of a porous liner 32 is particularly useful when the drum 12 is provided with perforations. In this embodiment, the perforations provide an additional means by which absorbed liquids may be removed from the porous liner 32. Furthermore, the airflow generated through the interior of the drum 12 may pass through the pores of the porous liner 32 and out the perforations. As it passes through the porous liner 32, the airflow carries with it the removed water, thereby evaporating it from the porous material. The action of the rotating drum 12 generates airflow on the outside of the drum 12 which has also been found to assist in the evaporation of water from the wet or damp porous liner 32. During operation, the porous liner 32 will contact the feedstock and wick water away from the feedstock. As the drum 12 is rotated, the wet or damp porous liner 32 will cease contact with the feedstock thereby by allowing the water held within the porous liner 32 to evaporate. As the drum 12 completes a full revolution and the porous liner 32 is again in contact with the feedstock, further water is wicked into the porous liner 32.

[0099] The inventors have found that the efficiency of the desiccation apparatus 100 is increased when the volume of feedstock within the drum 12 is maintained to between 10% and 50% of the internal volume of the drum 12. This has been found to permit a sufficient volume of air to flow over the feedstock permit evaporation of the water. To maintain a suitable volume of feedstock, the outlet of the drum 12 may be partially capped. In the embodiment shown in FIG. 2, the end is partially capped by a funnel piece 104. The funnel piece 104 provides an outlet with a reduced size. This arrangement has been found to permit the dried feedstock to slowly exit the drum 12 in an overflow manor.

Example 1

[0100] A desiccation apparatus in accordance with an embodiment of the present invention was tested to determine the rate of evaporation of water from a sewage sludge feedstock.

[0101] The desiccation apparatus used had an internal diameter of 1 m and a length of 4 m. The interior surface of the drum was lined with a porous liner constructed from polyethylene fibres. The pore size of the liner was less than 75 μm (AS 3706.7). The thickness of the liner was 6 mm.

[0102] Ambient temperature air was passed through the drum was 8-10 m.sup.3/sec. The drum was rotated as a rate of 2 revolutions per minute and was periodically stopped every 30 seconds to 1 minute for 5 to 10 minutes.

[0103] The water content was periodically measured and the results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Water Content Measurements Ambient Discharge Product Time Air Temp Ambient Air Air Speed Air Temp Discharge Air Water (days) (° C.) Humidity (km/hr) (° C.) Humidity Content 0 85% 1 20 46 10 11 56 75% 2 20 43 11 12 59 62% 3 22 34 11 12 58 50% 4 21 32 11 13 57 38% 5 23 33 11 14 54 22% 6 22 32 11 17 45 16% 7 21 40 11 17 45 13% 8 22 38 11 19 42 12%

[0104] The results show that the apparatus successfully reduced the liquids content from 85% to 12% over a period of 8 days. As can be noted from the above, this test was undertaken with an ambient temperature of 20-23° C. It should be noted that the apparatus achieved a significant reduction of the water content in relatively mild ambient conditions and without the need for any heating of the air or the interior of the drum.

Example 2

[0105] A series of tests were undertaken to determine the effect that different liner materials had on the rates of evaporation.

[0106] Four different lining materials were lined on the interior surface of the desiccation apparatus in accordance with one embodiment of the present invention. The desiccation apparatus used had an internal diameter of 1 m and a length of 4 m. The volume of air passed through the drum was 8 to 10 m.sup.3/sec. The drum was rotated as a rate of 2 revolutions per minute and was periodically stopped every 30 seconds to 1 minute for 5 to 10 minutes.

[0107] Details of the four liners tested are provided in Table 2.

TABLE-US-00002 TABLE 2 Test Criteria Trial Test 1 Test 2 Test 3 Test 4 Liner Material HDPE Conveyor Polyethylene Polypropylene Plastic belt fabric fabric Liner Thickness 2 mm 8 mm 4 mm 6 mm Pore size 0 0 <75 μm <75 μm (AS 3706.7) Pore size 0 0 182 μm 124 μm (ASTM 6767) Coefficient of 0 0 48 m/s 10.sup.−4 34 m/s 10.sup.−4 permeability (AS 3706.9)

[0108] The feed materials had a starting water concentration of 85%. The apparatus was operated and the water content was measured daily to track the water loss. The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Water content measurements Test 1 Test 2 Test 3 Test 3 Days Water (%) Water (%) Water (%) Water (%) 0 85 83 85 84 1 75 73 75 77 2 68 65 62 60 3 62 58 50 53 4 56 51 38 40 5 50 44 22 27 6 44 36 16 20 7 38 29 13 16 8 32 22 12 13 9 26 15 12 10 20 12 11 14 11 12 12 12

[0109] As can be seen from the results, whilst non-porous liners still permitted the evaporation of water from the feedstock, the porous fabric liners demonstrated increased evaporation rates over the non-porous materials.

[0110] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.