Field of the Invention

The present invention relates to compressors, more

specifically to dewatering compressors, and processes and methods using such compressors to process slurries, which may be animal waste derived slurries, mineral oil-based slurries, or other waste materials which it may be desirable to reduce their liquid content prior to further processing.

Background to the Invention

Processing of waste materials may involve various stages.

For example, the waste material may be in the form of an animal slurry, comprising a liquid or semi-liquid material. Absorbents may be added and it may be treated with heat in order to convert it into a more useful product, for example fertiliser or growth media.

It may be desirable to reduce the amount of liquid within the waste material as its processed into a drier and more solid form of material. This liquid may typically be water, although other liquids may be present which it is

advantageous to remove.

Summary of the Invention

According to a first aspect of the present invention there is provided a compressor for dewatering, comprising an outer body, a fluid inlet, a fluid outlet, and a fluid cavity defined within the outer body, a screw shaft located within the fluid cavity, the screw shaft comprising a central shaft and a helical screw surrounding said central shaft, and a filter surrounding the screw shaft, the compressor further including a micro-solids capture assembly.

The fluid inlet and fluid outlet may comprise pipe or tubing external connections.

The fluid inlet and fluid outlet may comprise flanged

external connections .

The micro-solids capture assembly may comprise a capture screen, one or more water jets directed towards and across the capture screen, and a micro-solids entry port.

There may be provided one or more capture screens.

The one or more capture screens may be provided in layers.

The capture screen (s) will be substantially planar, and thereby define a capture screen plane.

The one or more water jets may be suspended above the capture screen (s) at a first end.

The micro-solids entry port may be provided adjacent a second end of the capture screen (s) .

The first and second ends may be on distal edges of the capture screen (s) .

The one or more capture screens may be wire mesh screen.

The one or more capture screens may be a wire wedge screen.

Different types of capture screen may be employed e.g. there may be provided a wire wedge screen and a wire mesh screen, two wire wedge screens sandwiching a wire mesh screen, two wire mesh screens sandwiching a wire edge screen, four mesh screens arranged mesh-wedge-mesh-wedge or mesh-mesh-wedge- wedge, etc.

The one or more capture screens may have a non-stick coating such as TEFLON® coating, Polytetrafluoroethylene (PTFE) coating or other suitable non-stick coating.

The capture screen (s) may have a filter size of between 100 and 900 pm.

The capture screen may have a filter size of 500 pm.

Successive capture screens may be arranged such that they employ successively narrower filter sizes, such that

different sizes of material are filtered at each screen.

The micro-solids capture assembly may include spray bar and one or more spray jets. There may be two such jets.

The spray jets may be spade / flat fan jets.

The spray bar may be provided across the capture screen with one or both of the jets extending from the spray bar and being angled toward the capture screen plane.

The jets may be provided at an angle of between 10 and 45° to the capture screen plane.

The jets may be orientated generally towards the second end of the capture screen. Thus, water may be sprayed across the capture screen, urging micro-solids towards the micro-solids port.

The micro-solids port may be connected to a micro-solids collection assembly.

The micro-solids collection assembly may include a screw conveyor or slurry pump or slurry conveyance device.

The compressor may further include a non-return valve at the fluid outlet.

The non-return valve mechanism may be constructed such that it is housed internally inside the fluid outlet.

The non-return valve mechanism may be hermetically sealed against the inner bore of the fluid outlet.

There may be provided a filter around at least part of the fluid cavity.

The filter may be cylindrical.

The filter may be contra-rotatable with respect to the screw shaft .

The filter may comprise one or more screen sections.

There may be three screen sections.

One or more of the screens may be wire screens.

One or more of the screens may be wedge wire screens. The screens may comprise an initial screen, an intermediate screen and a terminal screen.

One or more of the screens may be contra-rotatable with respect to the screw shaft.

The one or more screens may have a non-stick coating such as TEFLON® coating, Polytetrafluoroethylene (PTFE) coating or other suitable non-stick coating.

The screens may have a filter size of between 50 and 500 pm.

The initial screen may have the largest filter size.

The initial screen may have a filter size of between 200 and

300 pm.

The initial screen may have a filter size of 250 pm.

The intermediate screen may have a filter size of between 100 and 200 pm.

The intermediate screen may have a filter size of 175 pm.

The terminal screen may have a filter size of between 50 and 150 pm.

The terminal screen may have a filter size of 100 pm.

The screw conveyor may be an offset screw conveyor.

The screw conveyor may redirect micro-solids into or adjacent the fluid inlet of the compressor. The central shaft may include a non-uniform section, the non- uniform section having a first outer diameter at a first end and a second outer diameter at a second end, wherein the second diameter is greater than the first diameter.

The central shaft may include a uniform section and a non- uniform section.

The screw shaft may be of any suitable type, including auger- type, but may also be any other suitable type.

The non-uniform section may increase in diameter from the first outer diameter to the second outer diameter in a linear fashion .

The second section may increase in diameter from the first outer diameter to the second outer diameter in a non-linear fashion, such as a step change, a multi-step change, a parabolic change, etc.

The second section may therefore have a generally frusto- conical shape.

The helical screw may have an outer diameter.

The outer diameter of the helical screw over the non-uniform section may remain constant.

This constant outer diameter may be achieved by a decrease in the extent by which the helical screw projects from the non- uniform section of the screw shaft.

The decrease may be complementary to the increase in diameter of the shaft. The helical screw may have a variable pitch.

The helical screw may have different pitches on the non- uniform and uniform sections.

The helical screw may have a discontinuous section where one or more slots are provided through the helical screw. These slots may allow material to flow more easily along the screw shaft .

The discontinuous section may commence at a first end of the screw shaft (the end adjacent the fluid inlet to the

compressor) and may terminate before a second end of the screw shaft.

The discontinuous section may be less than 50% of the total length of the screw shaft.

The discontinuous section may be around 30-40% of the length of the screw shaft.

The discontinuous section may comprise at least 720° along the helical screw i.e. two full revolutions around the screw shaft .

According to a second aspect of the present invention there is provided a compressor for dewatering, comprising an outer body, a fluid inlet, a fluid outlet, and a fluid cavity defined within the outer body, a screw shaft located within the fluid cavity, the screw shaft comprising a central shaft and a helical screw surrounding said central shaft, and a filter surrounding the screw shaft, wherein the central shaft includes a non-uniform section, the non-uniform section having a first outer diameter at a first end and a second outer diameter at a second end, wherein the second diameter is greater than the first diameter.

The compressor of the second aspect may comprise a micro solids capture assembly. Further optional features of the second aspect may be inferred from optional features listed with respect to the first aspect.

According to a third aspect of the present invention there is provided a material treatment process including at least one compressor according to the first and/or second aspect of the present invention.

According to a fourth aspect of the present invention there is provided a method of treating a material including a stage whereby a material being treated is at least partially dewatered by being fed through a compressor according to the first and/or second aspect of the present invention.

Brief Description of the Drawings

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

Fig. 1 is a perspective view from a first end of a compressor according to the present invention;

Fig. 2 is a perspective view from a second end of the compressor of Fig. 1;

Fig. 3 is a part-sectional perspective view of the dewatering compressor of Fig. 1; Fig. 4 is a part-sectional side elevation of the

compressor of Fig. 1;

Fig. 5 is a part-sectional perspective detail view of the micro-solids capture assembly of the compressor of Fig. 1;

Fig. 6 is a further part-sectional perspective detail view of the micro-solids capture assembly of the

compressor of Fig. 1;

Fig. 7 is a further part-sectional perspective detail view of the micro-solids capture assembly of the

compressor of Fig. 1;

Fig. 8 is a part-sectional side elevation detail view of the micro-solids capture assembly of the compressor of Fig. 1;

Fig. 9 is a further perspective view of the compressor of Fig. 1;

Fig. 10 is a detail perspective view of a capture tray of the compressor of Fig. 1;

Fig. 11 is part-sectional side elevation detail view of the outlet valve in a closed position of the compressor of Fig. 1;

Fig. 12 is part-sectional side elevation detail view of the outlet valve in an open position of the compressor of Fig. 1; Fig. 13 is a part-sectional perspective view of the dewatering compressor of Fig. 1;

Fig. 14 is a part-sectional side elevation of the intake assembly of the compressor of Fig. 1;

Fig. 15 is a perspective view of a material treatment process train including the compressor of Fig. 1;

Fig. 16 is side elevation an alternative screw

compressor profile usable with the compressor of Fig. 1;

Fig. 17 is a side elevation of a further alternative screw compressor profile usable with the compressor of Fig. 1; and

Fig. 18 is a perspective view of the screw compressor of Fig. 17.

Referring to the drawings and initially to Fig. 1, there is depicted a compressor for dewatering generally referred to as 10, comprising an outer body 12, a fluid inlet 14, a fluid outlet 16, and a fluid cavity 18 defined within the outer body 12, a screw shaft 20 located within the fluid cavity 18, the screw shaft 20 comprising a central shaft 22 and a helical screw 24 surrounding the central shaft 22, and a cylindrical filter 26 surrounding the screw shaft 20, the compressor 10 further including a micro-solids capture assembly 28.

It will be noted that the compressor 10 is generally

orientated at an angle to the horizontal, with the fluid inlet 14 being lower than the fluid outlet 16. The micro-solids capture assembly 28 comprises a capture screen 30, and two water jets 32 directed towards and across the capture screen 30, and a micro-solids entry port 34.

The capture screen 30 is substantially planar, and thereby defines a capture screen plane 36.

There may be provided one or more capture screens. These one or more capture screens may be provided in layers.

Different types of capture screen may be employed e.g. there may be provided a wire wedge screen and a wire mesh screen, two wire wedge screens sandwiching a wire mesh screen, two wire mesh screens sandwiching a wire edge screen, four mesh screens arranged mesh-wedge-mesh-wedge or mesh-mesh-wedge- wedge, etc.

The one or more capture screens may have a non-stick coating such as TEFLON® coating, Polytetrafluoroethylene (PTFE) coating or other suitable non-stick coating.

Successive capture screens may be arranged such that they employ successively narrower filter sizes, such that

different sizes of material are filtered at each screen.

A capture tray 38 is provided at the lowermost portion of the body 12 and generally beneath the fluid cavity 18 and screw shaft 20. The capture tray 38 is a generally shallow

rectangular frustum shape comprising two greater length angled side walls 40 running generally parallel to an axis X- X of the compressor 10, and a shorter length angled side wall 42 located adjacent the fluid outlet 16. The micro-solids capture 28 assembly is located distally from the shorter side wall 42 and adjacent the fluid inlet 14. A lower outer wall 44 is positioned at the base of the capture tray 38.

As can be seen from the Figs, the section of the capture tray 38 connected to and adjacent the micro-solids capture

assembly 28 is located lower than side wall 42, resulting in the lower outer wall 44 being provided at an angle to the horizontal .

The two water jets 32 are suspended above the capture screen 30 at a first end 46. A spray bar 48 both supplies and provides a mounting point for the two water jets 32. It will be appreciated by the skilled addressee that the location and number of spray jets 32 may be varied. The spray jets 32 are spade or flat fan jets.

The spray bar 48 is provided across the capture screen with both of the jets 32 extending from the spray bar 48 and being angled toward the capture screen plane 36.

The jets 32 are provided at an angle of between 10° and 45° to the capture screen plane 36. In the present embodiment, this is set at 30 ° .

A micro-solids capture assembly body 50 is used to mount the various components of the micro-solids capture assembly 28. The assembly body 50 also defines the micro-solids entry port 34. The micro-solids entry port 34 is provided adjacent a second end 52 of the capture screen 30. The first 46 and second ends 52 are on distal edges of the capture screen 30.

A simple spray bar valve 49 is located on the spray bar 48 outside the assembly body 50 to enable fluid control.

The capture screen 30 is a generally wire mesh screen type; more specifically the capture screen 30 is a wire wedge screen type. However, the skilled addressee will appreciate that alternative forms of filter media may be employed.

The capture screen 30 may for certain applications have a filter size of generally between 100 and 900 pm, although in the present embodiment the capture screen 30 has a filter size of 500 pm.

As can be seen from the various Figs, the jets 32 are

orientated generally towards the second end 52 of the capture screen 30 and the micro-solids entry port 34.

The micro-solids port 34 feeds into and is connected to a micro-solids collection assembly 54.

The micro-solids collection assembly 54 comprises a

collection chute 56 which attaches directly to the micro solids collection port 34 and a micro-solids feed tube 58, the latter being joined to the former, and there being defined therein a flow path between the too. A screw

conveyor (not shown) is located within the feed tube 58.

A micro-solids flanged water outlet pipe 60 extends from the micro-solids assembly body 50, generally perpendicular to the main axis X-X of the compressor 10.

The compressor 10 includes a non-return valve 62 at the fluid outlet 16. The fluid outlet 16 comprises a flanged outlet pipe 64 within which sits the non-return valve 62.

The non-return valve 62 includes a valve shuttle 66. The valve shuttle 66 is generally cylindrical in form, and may slide to a limited extent within the flanged outlet pipe 64. The valve shuttle 68 comprises an initial plug section 68a, generally in the form of a flattened ellipsoid or disc portion 68a, from which extends a frusto-conical connecting section 68b, which joins at its apex to a larger frusto- conical inlet portion 68c, and onto the main cylindrical section 68d. Seal indentations 68e, 68f are located adjacent the junction between the frusto-conical connecting section 68b and the main cylindrical section 68d, and at the distal extent of the main cylindrical section 68b. Suitable o-ring seals (not shown) are placed within these seal indentation 68e, 68f .

The frusto-conical connecting section 68b and the main cylindrical section 68d are hollow and allow material to pass through them when the valve is in the open position (see Fig. 12) . Four or more apertures 68g are provided on the frusto- conical connecting section 68b to enable a fluid pathway to form into the interior of the main cylindrical section 68f.

A valve seat 70 is provided within the flanged outlet pipe 64, which at its narrowest point is narrower than the

greatest diameter of the disc portion 68a. The valve seat 70 prevents the valve shuttle 66 from moving too far towards the screw shaft 20.

A valve control yoke 72 is provided round the approximate mid-portion of the valve shuttle 68 via a collar attachment groove 74 provided around the valve shuttle 68 on the main cylindrical section 68d. Pneumatic actuators 76 are

connected to the control yoke 72 to enable control over the amount of travel and the resistance to travel of the valve shuttle 68, thereby enabling control over back-pressure within the compressor 10. The central shaft 22 of the screw shaft 20 has a non-uniform diameter along its length, and is split into two discrete sections: an initial uniform section 22a and a second, non- uniform section 22b. The non-uniform section 22b has a first outer diameter at a first end (which is equal in diameter to the initial uniform section 22a) and a second outer diameter at a second end, wherein the second diameter is greater than the first diameter.

The screw shaft 20 is an auger-type screw.

The non-uniform section 22b increases in diameter from the first outer diameter to the second outer diameter in a linear fashion, albeit it will be appreciated by the skilled

addressee that the non-uniform section 22b may increase in diameter from the first outer diameter to the second outer diameter in a non-linear fashion, such as a step change, a multi-step change, a parabolic change, etc. Furthermore, the diameter may be non-uniform along the entire length i.e. the non-uniform section accounts for up to 100% of the length of the shaft. In the present embodiment, the uniform section 22a accounts for approximately 33% of the total length, although this may be varied in alternative embodiments.

The second section 22b therefore has a generally frusto- conical shape.

The flights 24a of the helical screw 24 has an outer diameter that remains constant over the entire length of the screw shaft 20 i.e. it forms a generally uniform cylindrical outer shape along its entire length.

This constant outer diameter is achieved by a decrease in the extent by which the helical screw 24 projects from the non- uniform section of the screw shaft 20.

The helical screw 24 has a constant pitch in the present embodiment, although that may be different in alternative embodiments without departing from the scope of the present invention .

The helical screw 24 may have different pitches on the non- uniform and uniform sections.

A constant torque Variable Frequency Drive (VFD) motor 75 and gearbox 77 is provided to rotate the screw shaft 20. A screw shaft geared slew ring 79 is driven by the VFD motor 75. The slew ring 79 to drive gear ratio is in the region of 6:1 to 5:1 in the present embodiment, which reduces the required torque from the motor 75.

In the present embodiment the auger screw shaft 20 is a right hand helix, meaning that it is driven clockwise (from the vantagepoint of the fluid inlet 14) in use.

The rotational speed of the screw shaft 20 is fully variable such that the volumetric flow rate may be varied and

optimised. The highest rotational speed will be typically around 20 RPM for most applications, but will preferably be around 5 RPM. Rotational speed may be varied beyond this level .

An alternative embodiment screw shaft is shown in Fig. 16, generally referred to as 320 . Analogous technical features are numbered similarly, save for a prefix 3 .

The screw shaft 320 is also an auger type, but this has variable pitch helical screw section 324a, wherein the distance between subsequent flights narrow progressively over the length of the non-uniform section 322b. There may be some direct proportional relationship between the distance between subsequent flights 324a and the increase in diameter of the second section 322b.

The rotational direction of the screw shaft is reversable. This may help with the clearance of blockages.

An alternative embodiment screw shaft is shown in Figs. 17 and 18, generally referred to as 420 . Analogous technical features are numbered similarly, save for a prefix 4 .

The screw shaft 420 is also an auger type, but is provided with an initial discontinuous section 422a which has a central shaft section with a uniform diameter and a non- uniform section where the central shaft has a taper.

The discontinuous section 422a commences at the first end of the screw shaft and terminates at the non-uniform section.

The discontinuous section 422a in the present embodiment is therefore less than 50% of the total length of the screw shaft 420, and is more specifically around 30-40% of the length of the screw shaft 420.

The discontinuous section may comprise at least 720° along the helical screw i.e. two full revolutions around the screw shaft 424. It will be understood that the discontinuous section may be more or less than this.

Slots 424s are provided around the screw shaft 424 which means there is no material in those slots between the central shaft and around the outer circumference. The slots 424s are provided with chamfered edges 424t, with the chamfered edges 424t being formed to be complementary to the direction of rotation of the screw shaft.

These slots 424s partially remove impedance to material flowing along the compressor and may be beneficial when such material has particular physical or flow characteristics for example if the material entering the compressor is

particularly viscous, dry, etc.

A filter 26 is provided around the fluid cavity 18 and screw shaft 20. The filter 26 is cylindrical and forms a close fit around the flights of the screw shaft 20. The outermost edges of the flights may be provided with a coating or may be treated to minimise friction or minimise the gap between the outermost edge of the helical screw 24 and the filter 26.

The filter 26 in the present embodiment is rotatable, and contra-rotates with respect to the screw shaft 20.

The change in diameter across the non-uniform section 22b of the central shaft 22 results in the flow area (i.e. the annular area between the outer diameter of the central shaft 22 and the inner diameter of the filter 26) being reduced by between 80 and 90%. In the present embodiment, this is achieved by use of a central shaft 22 having a uniform section diameter of 100mm (also being the initial diameter of the non-uniform section 22b) increasing to a maximum diameter of around 450mm.

The filter 26 comprises three individual screen sections 26a, 26b, 26c in the present embodiment, although this may be replaced with more or fewer individual sections, and may comprise simply a uniform screen section across the entire length .

The screen sections 26a, 26b, 26c in the present embodiment are wire screens, more specifically wedge wire screens.

The screens comprise a lower screen 26a, an upper screen 26c and a centre screen 26b.

The screens 26a, 26b, 26c may have a filter size of between 50 and 500 pm in typical applications, with the lower screen 26a typically having the largest filter size. The lower screen 26a may have a filter size of between 200 and 300 pm, but in the present embodiment has a specific filter size of 250 pm.

The centre screen 26b may have a filter size of between 100 and 200 pm, but in the present embodiment the centre screen has a filter size of 175 pm.

The upper screen 26c may have a filter size of between 50 and 150 pm, but in the present embodiment the upper screen 26c has a filter size of 100 pm.

The filter 26 is rotatably mounted at either end of the fluid cavity 18, on an inlet-side hub 78 adjacent the fluid inlet 14 and on an outlet-side hub 80 adjacent the fluid outlet 18.

The inlet-side hub 78 has rotational motion imparted through it whereas the outlet-side hub 80 is free-rotating or slave hub. The inlet-side hub 78 is a generally disc-shaped hub mounted on a suitable bearing 82. A geared slew ring 83 attaches to the inlet-side hub 78.

The outlet-side hub 80 has a more complex shape than its distal counterpart. The outlet-side hub 80 comprises an attachment flange 84 which mechanically attaches to the filter 26, a frusto-conical hub section 86 attaching to the flange 84, from which extends a cylindrical boss section 88, the latter surrounding the initial inboard portion of the outlet pipe 64. Rotational rod seals are provided between the boss section 88 and the outlet pipe 64. A gasket 92 is provided between the filter 26 and the attachment flange 84.

A constant torque Variable Frequency Drive (VFD) motor 94 and gearbox 96 is provided to rotate the filter 26 which drives the filter slew ring 83. The slew ring 83 to drive gear ratio is in the region of 6:1 to 5:1 in the present

embodiment, which reduces the required torque from the motor 94.

A support frame 100 mounts the compressor body 12. The support frame 100 comprises an upper support frame 116 which is directly connected to and supports the compressor body 12, a lower stand 118 which contacts the surface upon which the compressor body 10 is to be mounted, first and second support stanchions 120,122 which are provided with pivot pins 124, the stanchions connecting the lower stand 118 to the upper support frame 114 adjacent the inlet pipe 14, and an

adjustable support frame 126, which connects the lower stand 118 to the upper support frame 114 adjacent the outlet pipe 16.

The adjustable support frame 126 is connected to the upper support frame 114 via pin and lug arrangements 128 at their uppermost portions.

A variable sliding support mechanism 130 mounts the

adjustable support frame 126 to the lower support frame 118. The variable sliding support mechanism 130 enables the relative position of the join between the adjustable support frame 126 to the lower support frame 118 to be varied such that the angle of adjustable support frame 126 to the lower support frame 118 may be varied, thereby varying the angle of the upper support frame 116 to the horizontal and increasing the relative angle of the compressor body 12.

As can be seen from the Figs, the frame 100 allows the compressor body 12 to be maintained at an angle of around 15 degrees in the present embodiment. Moreover, this angle may be varied using the variable sliding support mechanism 130.

Referring to Fig. 15, there is shown a water compressor 10 being used in a material treatment process.

In the present embodiment the treatment apparatus, generally referred to as 200, includes a macerator/hopper unit 202 which may be fed with an animal slurry. Absorbents or other materials may be added to aid in the treatment of the said animal slurry and, in the present embodiment, the apparatus 200 and method may be being employed to create growth media.

The macerated slurry is pumped along macerator feed line 204 by a positive displacement pump 206 towards a flocculator unit 208 which flocculates the slurry.

Slurry is then pumped towards compressor 10 whilst still retaining a significant portion of water.

The compressor 10 having both the inlet flanged pipe and outlet flanged pipe is colloquially hard-piped into the apparatus i.e. it can sustain an internal pressure without risk of the contents leaking or being exposed to the

atmosphere, all of which is beneficial in such processes for obvious reasons .

Animal slurry enters the fluid chamber 18 and is drawn along it under the action of the screw shaft. This forces the animal slurry against the filter 26 compressing it and allowing the liquid fraction of the slurry to pass through the filter 26 and falls into the capture tray 38. Such water may include micro-solids and the capture tray water jet flushes the water and entrapped micro-solids towards micro solids capture assembly 28.

As the water/micro-solids land on the screen 30, part of the water is further filtered by the screen 30 and falls into and may be pumped away via the water outlet pipe 64. This may then be further filtered as required.

Micro-solids in a slightly drier form fall into the micro solids port 34, through the chute portion 54 and are then transported through the pipe 58 via the screw compressor.

Whilst these may be transported anywhere, in the present embodiment these are fed back into the top of the

macerator/hopper unit 202 to be fed back through the process.

The animal slurry as it travels up the screw shaft is

progressively compressed as the diameter of the non-uniform portion 22b begins to increase. As the slurry is generally confined between successive augur flights, this increase in diameter causes a proportional reduction in volume for the slurry, and a greater outward pressure is exerted on the slurry, causing further dewatering in combination with the reduction in filter media size as it travels along the three screens 26a, 26b and 26c. The slurry is then driven by the screw shaft 20 towards the non-return valve 62. The force of the slurry acting on the initial plug section 68a causes the valve shuttle to travel away from the centre of the compressor 10 thereby opening the valve and allowing the now drier slurry to move through the valve and onto the next process stage. As the valve shuttle is biased into a closed position, this creates an additional back pressure on the slurry which may aid in further

dewatering the animal slurry.

The animal slurry may then travel on to further process steps, such as a thermal dewatering stage and so forth to finally result in a usable product, such as growth media.

Certain relative terms such as upper , lower , lowermost , uppermost , etc are used within the specification and are primarily for clearer understanding and from the perspective of the Figs. The skilled addressee that the absolute

position of such elements may be varied depending on the specific application of the invention and are not to be taken as limiting.

The invention is not limited to the embodiments hereinbefore described and may be varied in construction and detail.