Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Treatment of hydrocarbon containing materials
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.
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.
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
W02008/059240. 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.
The present applicant has identified a number aspects of the arrangement
disclosed in
W02008/059240 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.
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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,
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.
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.
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.
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.
As described hereinbefore, rapid heating leads to thermal desorption of the
oil from the
solid matrix.
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.
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The material feeder may be oriented vertically, horizontally or inclined.
The material matrix may be pushed through the treatment chamber by the
material
matrix leaving the material feeder.
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.
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.
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.
The microwave power output of the microwave emitter may be arranged to be
controlled in response to a measurement of the reflected microwave power.
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.
The window may comprise a flexible film or belt.
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.
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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.
The treatment chamber may be substantially concentric with the microwave
cavity.
The microwave cavity may comprise a moveable microwave reflector operable to
adjust the modes of the microwave cavity.
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.
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.
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
hereinbef ore.
The present invention will now be described, by way of example, with reference
to the
following drawings in which:
Figure 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.
Figure 2 is a schematic diagram of an alternative arrangement wherein a
cylindrical
treatment chamber is disposed within a substantially cylindrical microwave
cavity.
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Figure 3 is a schematic diagram of an embodiment of the invention wherein the
window
of the treatment chamber comprises a film.
5 Figure 4 is a schematic diagram of an embodiment of the invention wherein
the window
is larger than the aperture of the treatment chamber.
Figure 5 is a schematic diagram of an embodiment of the invention wherein the
material feeder is oriented horizontally.
Figure 6 is a schematic diagram of an embodiment of the invention wherein the
material feeder is inclined at an oblique angle.
The apparatus shown in Figure 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.
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
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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 W02008/059240.
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.
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 W02008/059240, 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 W02008/059240. 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.
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.
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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.
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.
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.
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.
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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.
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.
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.
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
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field within the chamber 8 thereby providing substantially uniform average
heating
therein. However, a non-uniform heat distribution may be acceptable in some
applications.
A cooling arrangement may be provided to extract heat from the treated
materials.
Figure 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.
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.
Figure 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.
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Figure 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
5 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.
10 Although as illustrated the window moves vertically, an arrangement in
which the
window moves horizontally or in other orientations is also envisaged.
Where the window 13 is of substantially circular cross section, as for example
in the
embodiment of Figure 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.
Figure 5 shows an alternative embodiment of the invention in which the screw
conveyor 5 is oriented horizontally. Figure 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.
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.
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.
