U.S. patent application number 14/374755 was filed with the patent office on 2014-11-13 for treatment of hydrocarbon containing materials.
This patent application is currently assigned to NOV Downhole Eurasia Limited. The applicant listed for this patent is NOV Downhole Eurasia Limited, University of Nottingham. Invention is credited to George Burnett, Chris Dodds, Sam Kingman, John Robinson.
Application Number | 20140332366 14/374755 |
Document ID | / |
Family ID | 45840916 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332366 |
Kind Code |
A1 |
Robinson; John ; et
al. |
November 13, 2014 |
Treatment of Hydrocarbon Containing Materials
Abstract
An apparatus for separating a hydrocarbon content from a
material matrix composes the hydrocarbon content and a water
content, the apparatus comprising: a material feeder arranged to
feed material through a treatment chamber, the treatment chamber
comprising a window which is substantially transparent to
microwaves; a microwave emitter arranged in use to expose feed
material in the treatment chamber to microwaves via the window in
order to cause rapid heating of at least part of the water content
of the matrix to form steam, so as to remove at least part of the
hydrocarbon content from the matrix; wherein the material feeder
and treatment chamber are arranged so that in use, the treatment
chamber is substantially tilted with material/matrix.
Inventors: |
Robinson; John; (Nottingham,
GB) ; Kingman; Sam; (Nottingham, GB) ; Dodds;
Chris; (Nottingham, GB) ; Burnett; George;
(Aberdeenshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NOV Downhole Eurasia Limited
University of Nottingham |
Gloucestershire
Nottingham |
|
GB
GB |
|
|
Assignee: |
NOV Downhole Eurasia
Limited
Gloucestershire
GB
University of Nottingham
Nottingham
GB
|
Family ID: |
45840916 |
Appl. No.: |
14/374755 |
Filed: |
January 25, 2013 |
PCT Filed: |
January 25, 2013 |
PCT NO: |
PCT/GB2013/050160 |
371 Date: |
July 25, 2014 |
Current U.S.
Class: |
203/14 ;
202/234 |
Current CPC
Class: |
C10G 32/02 20130101;
C10B 19/00 20130101; C10G 1/00 20130101; C10G 1/02 20130101; C10B
53/06 20130101 |
Class at
Publication: |
203/14 ;
202/234 |
International
Class: |
C10B 19/00 20060101
C10B019/00; C10G 1/02 20060101 C10G001/02; C10B 53/06 20060101
C10B053/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2012 |
GB |
1201226.6 |
Claims
1. An apparatus for separating a hydrocarbon content from a
material matrix comprising the hydrocarbon content and a water
content, the apparatus comprising: a material feeder arranged to
feed material through a treatment chamber, the treatment chamber
comprising a window which is at least partially transparent to
microwaves; a microwave emitter arranged in use to expose feed
material in the treatment chamber to microwaves via the window in
order to cause heating of at least part of the water content of the
matrix to form steam, so as to remove at least part of the
hydrocarbon content from the matrix: wherein the material feeder
and treatment chamber are arranged so that in use, the treatment
chamber is filled with material matrix.
2. The apparatus of claim 1, wherein the material feeder stops
short of, and does not extend into, the treatment chamber.
3. The apparatus of claim 1 wherein the material feeder is arranged
to allow at least some of the water content to drain from the
material matrix before it passes through the treatment chamber.
4. The apparatus of claim 1, wherein the material feeder is
vertical,
5. The apparatus of claim 1, wherein the material feeder is
inclined.
6. The apparatus of claim 1, wherein the material feeder is
horizontal.
7. The apparatus of claim 1 wherein the material matrix is pushed
through the treatment chamber by the material matrix leaving the
material feeder.
8. The apparatus of claim 1 wherein the material feeder comprises
at least one of a screw conveyor, a peristaltic pump, a positive
displacement pump and a piston feed mechanism.
9. The apparatus of claim 8, wherein the material feeder comprises
a twin screw conveyor.
10. The apparatus of claim 1 wherein the material feeder is
arranged to control a rate at which material is fed through the
treatment chamber in response to a signal indicative of the
cleanliness or dryness of the material.
11. The apparatus of claim 1 wherein the microwave power output of
the microwave emitter is arranged to be controlled in response to a
measurement of the reflected microwave power.
12. The apparatus of claim 1 wherein: a window is arranged to cover
an aperture in the treatment chamber with a first area of the
window, the window extends beyond the extent of the aperture, and
the window is arranged to be repositioned during operation of the
apparatus to present a second area to the aperture.
13. The apparatus of claim 12 wherein the window comprises a
flexible film or belt.
14. The apparatus of claim 1, wherein the treatment chamber is of
substantially circular cross section.
15. The apparatus of claim 1 wherein the treatment chamber is
substantially disposed within a microwave cavity arranged to direct
microwave radiation from the microwave emitter to the treatment
chamber.
16. The apparatus of claim 15 wherein the treatment chamber is
substantially concentric with the microwave cavity.
17. The apparatus of claim 15 wherein the microwave cavity
comprises a moveable microwave reflector operable to adjust the
modes of the microwave cavity.
18. The apparatus of claim 1 wherein material matrix leaving the
treatment chamber is deposited within an output container which
substantially confines microwave radiation escaping from the
treatment chamber.
19. The apparatus of claim 1 further comprising a discharge
mechanism extracting and controlling the level of materials within
the output container.
20. The apparatus of claim 1 further comprising a valve located
between the container and the treatment chamber to control free
flowing liquid levels.
21. A method for separating a hydrocarbon content from a material
matrix comprising the hydrocarbon content and a water content,
comprising the steps of: continuously feeding the material matrix
through a treatment chamber; exposing the material matrix within
the treatment chamber to microwave radiation arranged to cause
rapid heating of at least some of the water content to form steam,
wherein the rapid steam formation results in thermal desorption of
at least some of the hydrocarbon content from the matrix; wherein
the treatment chamber is substantially filled with the material
matrix to be treated.
22. A method for separating a hydrocarbon content from a material
matrix comprising the hydrocarbon content and a water content, the
method comprising using an apparatus comprising a material feeder
arranged to feed material through a treatment chamber, the
treatment chamber comprising a window which is at least partially
transparent to microwaves, a microwave emitter arranged in use to
expose feed material in the treatment chamber to microwaves via the
window in order to cause heating of at least part of the water
content of the matrix to form steam, so as to remove at least part
of the hydrocarbon content from the matrix, wherein the material
feeder and treatment chamber are arranged so that in use, the
treatment chamber is filled with material matrix.
Description
[0001] The present invention relates to a method and apparatus for
treating hydrocarbon containing materials using electromagnetic
radiation. The invention particularly relates to continuous
microwave treatment to separate hydrocarbons from a matrix of solid
materials, although it is not limited in this regard.
[0002] Hydrocarbons are often mixed within a matrix of other solid
materials such as sand, soil or rock, and it is frequently
desirable to separate or remove the hydrocarbons from such a
matrix. For example, a substantial fraction of the world's
hydrocarbon reserves are to be found in oil sands and in order to
extract the oil, it must first be separated from the sand with
which it is mixed. A further example is oil contaminated drill
cuttings, which are a mixture of rock fragments, oil and water, and
which are produced in significant quantities during exploration for
and production of hydrocarbons. Removing sufficient oil from such
drill cuttings allows them to be disposed of in a more cost
effective manner for instance by direct discharge into the sea.
Whilst potentially the arrangements described herein could be used
in the removal of oil from sands, the invention is directed
primarily towards the removal of oil from drill cuttings.
[0003] It is known to use microwave energy to reduce oil levels in
mixtures of oil and solid materials, and an example of such a
method and apparatus is disclosed in WO2008/059240. This document
describes an arrangement whereby a matrix of oil or hydrocarbon
contaminated material is continuously treated by exposing it to
microwave radiation, thereby causing rapid heating of the water
content of the matrix leading to thermal desorption of the oil from
the solid matrix. The oil carrying matrix is continuously fed
through a microwave cavity on a trough conveyor belt. Microwave
chokes are used to limit the levels of electromagnetic radiation
escaping from the open input and output ends of the conveyor
belt.
[0004] The present applicant has identified a number aspects of the
arrangement disclosed in WO2008/059240 that could be improved. The
conveyor belt and the microwave chokes are relatively large and
comprise a significant fraction of the footprint of the apparatus
described. A more compact system with a smaller footprint would be
advantageous, particularly given the very limited space available
on offshore platforms.
[0005] Due to the desirability of controlling the liquid, for
example water, content in the matrix to be treated, it would be
advantageous if some liquid was allowed to drain from it prior to
exposure to microwaves.
[0006] The profile of the material on the conveyor belt is subject
to variation, resulting in non-uniform interaction with the
microwave radiation. It would be advantageous if the feed system
provided a flow of material through the microwave cavity with a
substantially uniform profile to allow the interaction to be more
consistent and better optimised.
[0007] Arcing may take place within the microwave cavity. Such
arcing is preferably avoided, since it may result in combustion of
the hydrocarbon vapours, or other undesirable chemical reactions
such as the formation of nitric oxides or ozone.
[0008] The conveyor belt system of the prior art must be fed
material from bulk storage by a further material handling system.
Handling of the oil contaminated materials can be difficult. It
would be desirable if the handling system that feeds the material
through the microwave cavity was capable of feeding itself from
bulk storage of the said material.
[0009] According to a first aspect of the present invention there
is provided an apparatus for separating a hydrocarbon content from
a material matrix comprising the hydrocarbon content and a water
content, the apparatus comprising: a material feeder arranged to
feed material through a treatment chamber or applicator, the
treatment chamber comprising a window which is substantially
transparent to microwaves; a microwave emitter arranged in use to
expose feed material in the treatment chamber to microwaves via the
window in order to cause heating, conveniently rapid heating, of at
least part of the water content of the matrix to form steam, so as
to remove at least part of the hydrocarbon content from the matrix;
wherein the material feeder and treatment chamber are arranged so
that in use, the treatment chamber is substantially filled with
material matrix.
[0010] As described hereinbefore, rapid heating leads to thermal
desorption of the oil from the solid matrix.
[0011] The material feeder may be arranged to allow at least some
of the liquid content to drain from the material matrix before it
passes through the treatment chamber.
[0012] The material feeder may be oriented vertically, horizontally
or inclined.
[0013] The material matrix may be pushed through the treatment
chamber by the material matrix leaving the material feeder.
[0014] The material feeder may comprise a screw conveyor.
Conveniently, a twin screw conveyor is used. Such an arrangement is
advantageous in that the interaction between the two screws of the
conveyor serves, at least to some extent, to clean the conveyor
and/or reduce clogging thereof.
[0015] Alternatively, the material feeder could comprise, for
example, a piston device, or a pump such as a peristaltic pump,
positive displacement pump, or the like.
[0016] The material feeder may be arranged to control a rate at
which material is fed through the treatment chamber in response to,
for example, a measurement of the reflected microwave power.
Ideally, the feeder speed is dependent upon the cleanliness or oil
content, or the dryness, of the material. By measuring moisture
content, a value indicative of the oil content, and hence
cleanliness, can be derived for used in controlling the feed
rate.
[0017] The microwave power output of the microwave emitter may be
arranged to be controlled in response to a measurement of the
reflected microwave power.
[0018] The window may be arranged to cover an aperture in the
treatment chamber with a first area of the window, the window
extending beyond the extent of the aperture, and for the window to
be repositioned during operation of the apparatus to present a
second area to the aperture.
[0019] The window may comprise a flexible film or belt.
[0020] The treatment chamber may be of substantially circular cross
section. However, where the material feeder comprises a twin screw
conveyor, the treatment chamber may match the profile of the
conveyor and so have generally planar sides, and part cylindrical
ends. The window, in such an arrangement, may be formed on the side
and so be of generally planar form, easing manufacture.
[0021] The treatment chamber is may be substantially disposed
within a microwave cavity arranged to direct microwave radiation
from the microwave emitter to the treatment chamber.
[0022] The treatment chamber may be substantially concentric with
the microwave cavity.
[0023] The microwave cavity may comprise a moveable microwave
reflector operable to adjust the modes of the microwave cavity.
[0024] The material matrix leaving the treatment chamber may be
deposited within an output container which substantially confines
microwave radiation escaping from the treatment chamber. A
discharge feeder, for example in the form of a screw or rotary
valve, may be used to extract and control the level of materials
within the output container.
[0025] According to a second aspect of the present invention there
is provided a method for separating a hydrocarbon content from a
material matrix comprising the hydrocarbon content and a water
content, comprising the steps of: continuously feeding the material
matrix through a treatment chamber; exposing the material matrix
within the treatment chamber to microwave radiation arranged to
cause rapid heating of at least some of the water content to form
steam, wherein the rapid steam formation results in thermal
desorption of at least some of the hydrocarbon content from the
matrix; wherein the treatment chamber is substantially filled with
the material matrix to be treated.
[0026] The method for separating a hydrocarbon content from a
material matrix comprising the hydrocarbon content and a water
content may use an apparatus as described hereinbefore.
[0027] The present invention will now be described, by way of
example, with reference to the following drawings in which:
[0028] FIG. 1 is a schematic diagram of an embodiment of the
invention wherein the material is fed vertically through a
treatment chamber of a first type.
[0029] FIG. 2 is a schematic diagram of an alternative arrangement
wherein a cylindrical treatment chamber is disposed within a
substantially cylindrical microwave cavity.
[0030] FIG. 3 is a schematic diagram of an embodiment of the
invention wherein the window of the treatment chamber comprises a
film.
[0031] FIG. 4 is a schematic diagram of an embodiment of the
invention wherein the window is larger than the aperture of the
treatment chamber.
[0032] FIG. 5 is a schematic diagram of an embodiment of the
invention wherein the material feeder is oriented horizontally.
[0033] FIG. 6 is a schematic diagram of an embodiment of the
invention wherein the material feeder is inclined at an oblique
angle.
[0034] The apparatus shown in FIG. 1 takes a material matrix 1
comprising hydrocarbons and water and for example rock fragments or
sand, and separates at least some of the hydrocarbons from the
material matrix 1 to leave a treated material matrix 2. The
apparatus comprises an input container 3, a material feeder 5, a
treatment chamber or applicator 8, microwave emitter 6 and output
container 4. The treatment chamber 8 comprises a window 13 which is
substantially transparent to microwave radiation. The microwave
emitter 6 is provided with a waveguide 7. The input container 3 and
output container 4 are provided with doors 12 and 11 respectively.
A fluid inlet 9 and a fluid outlet 10 are provided within the
output container 4 and/or treatment chamber 8.
[0035] In use, material matrix 1, which may comprise rock
chippings, hydrocarbons, sludge, filter cake, sand, etc, is
introduced to the input container 3 via the door 12. The door 12
may be closed when material is not being introduced to the chamber.
The material feeder 5 is a vertical screw conveyor which takes
material matrix 1 from the input container 3 and feeds it through
the treatment chamber 8. Conveniently, the screw conveyor is a twin
screw arrangement, the interaction between the screws or augers of
which serves, at least in part, to clean the conveyor and to reduce
the risk of clogging thereof. The screw conveyer 5 ends before the
treatment chamber 8, and the material within the treatment chamber
8 is pushed through the chamber by the material leaving the screw
conveyor 5. Within the treatment chamber 8 the material matrix 1 is
exposed to microwave radiation, which causes rapid and preferential
heating of the water in the material matrix 1, producing steam.
This in turn causes thermal desorption of the hydrocarbon
component, leaving substantially hydrocarbon free treated material
matrix 2. The general principles of hydrocarbon removal by
continuous microwave treatment are described in more detail in
WO2008/059240.
[0036] The fluid inlet 9 may be provided in the wails of the
treatment chamber 8 and/or the output container 3 to allow inert
gas to be swept through or over the material, matrix after or while
it is exposed to radiation. The inert sweep gas will entrain the
steam and thermally desorbed hydrocarbons from the material matrix
and may be removed via the fluid outlet 10. The sweep gas may
subsequently be directed to a condenser (not shown) where the
hydrocarbons and/or water may be recovered from the sweep gas. The
sweep gas may comprise steam or nitrogen.
[0037] The microwave emitter 6 is connected to a waveguide 7 which
is arranged to direct microwave radiation from the emitter 6 to the
treatment chamber 8. The treatment chamber 8 comprises a window 13
made from a material which is substantially transparent to the
microwave radiation from the emitter 6 to allow the microwave
radiation to enter the treatment chamber 8. The microwave emitter
6, waveguide 7, output chamber 4 and treatment chamber 8 are
arranged to provide an electric field with appropriate uniformity
within the treatment chamber 8. One approach for achieving this is
described in more detail in WO2008/059240, and the output container
4 and treatment chamber 8 of the present invention may be arranged
to provide an analogous configuration wherein the microwave cavity
is provided by the output container 4 and the treatment chamber 8
confines the material matrix 1 in a position corresponding to that
of the material on the conveyor of WO2008/059240. The walls of the
treatment chamber 8 may substantially comprise microwave
transparent windows 13, or chamber walls which are not microwave
transparent may be provided with an aperture which is covered by a
microwave transparent window 13.
[0038] Where a twin screw conveyor is used, it will be appreciated
that the shape thereof may include part cylindrical end walls and
generally planar side walls. Conveniently the chamber 8 is similar
shaped, and the window 13 is conveniently formed in or on one of
the side walls, and thus can also be of generally planar form. The
window is conveniently of a suitable ceramic glass material.
[0039] The treatment chamber 8 conveniently includes a dead-zone or
section which extends into the output container and is after the
point at which treatment takes place. In use, the section, like the
remainder of the treatment chamber, is full of material and so
serves to contain the applied electrical field. Its length is
chosen to achieve a sufficient level of containment whilst being
sufficiently short that reabsorption of oil into the treated
material is avoided or limited to an acceptable level.
[0040] In use the microwaves may be confined within the closed
output container 4 which may comprise materials which are not
microwave transparent such as metal, thereby preventing unwanted
emissions of microwave radiation from the apparatus. The door 11 of
the output container 4 may be opened to discharge treated material
2, and the door 11 may be provided with a safety interlock to cut
power to the microwave emitter 6 in the event that the door 11 is
open. Microwave radiation entering the screw conveyor 5 will be
rapidly attenuated by the material matrix 1, but the input
container 3 may similarly comprise a material which is
non-transparent to microwaves and the door 12 may be kept closed in
use. The use of microwave chokes is thereby rendered unnecessary,
considerably reducing the size and footprint of the apparatus over
prior art systems.
[0041] The arrangement of the chamber 8 and screw conveyor 5 is
such that the treatment chamber 8 is substantially full of material
matrix 1 during operation of the apparatus. This results in a
consistent profile of material and allows the characteristics of
the apparatus to be optimised to provide appropriate levels of
microwave heating throughout the material as it passes through the
treatment chamber 8. This is in contrast to prior art systems
employing an open treatment area through which material was
conveyed using a belt system, and where control over the
distribution of material on the belt was a significant
challenge.
[0042] The use of a screw conveyor 5 to move material through the
treatment chamber 8 means that a single material feeding system can
be used to take up material from the input container 3 and feed it
through the apparatus to the output container 4. The need for a
separate material handling system to introduce material from a
container to a conveyor as required in prior art systems is thereby
avoided.
[0043] The vertical orientation of the screw conveyor 5 allows
unbound water to drain from the material matrix 1 before it is
introduced to the treatment chamber 8, controlling the water
content of the material matrix 1. Such control over water content
is known to be advantageous, since an excess of water content has a
negative impact on the efficiency of the process. The vertical
orientation has further advantages in reducing the footprint of the
equipment. Equipment with a small footprint is highly advantageous
in offshore applications, where platform area is typically in short
supply.
[0044] In prior art systems, arcing may occur within the microwave
cavity as a result of electric field interactions with the
distribution of material matrix within the treatment area, leading
to the potential for combustion of the hydrocarbon vapours that are
formed during operation of the apparatus. Substantially filling the
treatment chamber 8 with material matrix 1, and minimising air
spaces in the chamber 8, limits the potential for electrical arcs
to occur, since microwave absorbing material 1 will prevent arcs in
the chamber 8, and a properly designed waveguide 7, output
container 4 and chamber 8 will not be subject to arcing. It may be
desired to provide a nitrogen purging arrangement to further reduce
the risk of arcing.
[0045] It is known from the prior art that monitoring the reflected
microwave power can provide an indication of the appropriate feed
rate or microwave power radiated from the emitter 6. Where the
microwave power output substantially exceeds the power required to
remove the water in the inflowing material 1, the material matrix 1
will become less microwave absorbent, resulting in an increase in
reflected power. The feed rate of the material 1 or the output
microwave power from the emitter 6 may therefore be adjusted in
response to the measured reflected power. For instance, the feed
rate may be increased when a predetermined threshold reflected
power is measured, or the microwave power output may be reduced. In
addition, an automatic control system may be provided in which the
feed rate or microwave power or both are adjusted while the
reflected power is monitored to characterise the optimum feed rate
and/or microwave power for a given material matrix 1.
[0046] A moveable microwave reflector (not shown) may be provided
within the waveguide 6 or the output container 4 and its position
used to tune the microwave cavity, for example to compensate for
variations in effective dielectric properties of the material
matrix 1, or to provide a mode stirrer to continuously vary the
distribution of the electric field within the chamber 8 thereby
providing substantially uniform average heating therein. However, a
non-uniform heat distribution may be acceptable in some
applications.
[0047] A cooling arrangement may be provided to extract heat from
the treated materials.
[0048] FIG. 2 shows an alternative arrangement in which the
treatment chamber 8 comprises a microwave transparent tube 13 which
is arranged within a microwave cavity 18. The tube provides a
continuous window 13 through which the material 1 within the
chamber 8 may be exposed to microwave radiation. The microwave
cavity 18 is substantially cylindrical and may comprise a single
mode microwave cavity. This arrangement of chamber 8 and cavity 18
may be advantageous since it may provide a substantially
axisymmetric or radially symmetric electric field leading to
relatively uniform heating of the material matrix. The microwave
cavity 18 may be fed microwave radiation from the microwave emitter
6 via a waveguide 7, and the modes of the microwave cavity 18 may
be adjusted or stirred by varying the position of a microwave
reflector 16 arranged within the cavity.
[0049] During use hydrocarbons, or other components of the material
matrix which are not microwave transparent, may be deposited on the
window 13 of the treatment chamber 8. Such deposits may interfere
with the functioning of the equipment by preventing microwaves
passing through the window 13 properly. Where the deposits are
microwave absorbing, they may lead to heating of the window 13
resulting in damage. It is therefore advantageous for the window 13
of the treatment chamber 8 to be kept clean and free from such
deposits.
[0050] FIG. 3 shows an arrangement whereby the window 13 is formed
from a film or belt of flexible microwave transparent material
which may be continuously fed from a reel 14, and stored on a
further reel 14. Such a film may be used only for a single pass and
subsequently discarded, thereby ensuring that the window 13 is kept
clean. Alternatively the film may be used for multiple passes. The
film may be cleaned by fixed wipers 15, or by a further cleaning
means (not shown). Although as illustrated the film moves
vertically, an arrangement in which the film moves horizontally or
in other orientations is also envisaged.
[0051] FIG. 4 shows an arrangement whereby the window 13 comprises
a rigid material which is larger than is required to cover the
aperture in the treatment chamber 8, so that the window may be
moved between a first position in which a first area of the window
covers the aperture of the treatment chamber 8 and a second area is
exposed for cleaning, and a second position in which a second area
of the window covers the aperture of the treatment chamber 8 and a
first area is exposed for cleaning. Fixed wipers 15 may be provided
which clean the window 13 when it is moved between positions. The
window may be periodically or continually moved in order to keep it
clean, and such movements may take place while the apparatus is in
operation. Although as illustrated the window moves vertically, an
arrangement in which the window moves horizontally or in other
orientations is also envisaged.
[0052] Where the window 13 is of substantially circular cross
section, as for example in the embodiment of FIG. 2, the window may
be continuously or periodically rotated past a fixed wiper (not
shown) arranged within the treatment chamber 8 so that the internal
surface of the window 13 is kept clean.
[0053] FIG. 5 shows an alternative embodiment of the invention in
which the screw conveyor 5 is oriented horizontally. FIG. 6 shows a
further alternative embodiment in which the screw conveyor is
inclined at an oblique angle. Such arrangements may be advantageous
in adapting the apparatus to the requirements of a particular
installation, or in ensuring the proper feeding of material, and
may permit the installation of a valve between the container 3 and
the treatment chamber 8 to control free flowing liquid levels.
[0054] Whilst the use of screw conveyors, and in particular twin
screw arrangements, is outlined hereinbefore, it will be
appreciated that other forms of material feeder could be used. For
example, peristaltic pumps, or piston based pumping arrangements
could be used to move the material within the device.
[0055] Whilst several specific embodiments are described herein, it
will be appreciated that a number of modifications may be made
without departing from the scope of the invention.
* * * * *