Note: Descriptions are shown in the official language in which they were submitted.
CA 02530974 2005-12-20
1
METHODS AND APPARATUS FOR CONDITIONING AND DEGASSING LIQUIDS
AND GASES IN SUSPENSION
This invention relates to methods and apparatus for conditioning mixtures of
gas
and liquids by agglomerating gas bubbles existing with or in a liquid or for
coalescing droplets of liquid dispersed in another liquid.
Liquids produced in oilfield applications comprise a hydrocarbon component,
(which
may be a low density oil, termed condensate, or a medium density oil, termed
medium oil, or a high density oil, termed heavy oil) and some accompanying
water
which may be naturally occurring with the oil or may have been pumped into the
reservoir to help drive out the oil. In order to process the oil successfully,
the water
must be separated out allowing relatively dry oil to be exported. In turn the
water
itself must be treated to an acceptable content of oil suitable for disposal.
Separation of water from a predominantly oil stream or treatment of a water
stream
to remove oil is generally more difficult and expensive as the droplet size of
the
dispersed, minority phase decreases. In many cases, there is a need to
increase
droplet size to improve separation or reduce costs of separation.
In most oilfield applications there is a need to remove gas from the liquid
phase.
This may be in the form of foam which needs to be broken down, discrete gas
bubbles in a liquid which are required to be removed as part of a separation
process, or dissolved gas which needs to be evolved from solution as discrete
bubbles and removed as part of the separation process. Foaming is deleterious
to
the separation function since it may, for example, fill process equipment. It
is
commonly suppressed by the continuous use of additive chemicals. Furthermore,
foaming can lead to false readings on apparatus such as level detectors in
vessels.
Therefore it is desirable to break down foam as quickly and cheaply as
possible
without the use of chemicals.
US Statutory Invention Registration No. H1668 discloses a coalescer which
proposes the application of a standing wave ultrasonic field with a frequency
range
between 20kHz and 1MHz, with 680kHz disclosed as an optimum frequency, for
wastewater. The standing wave is created using at least two radially opposed
pairs
of transducers to cause coalescence of oil droplets in a flowing wastewater
stream,
CA 02530974 2005-12-20
2
with subsequent separation in conventional separators. The wastewater flows
through a circular section vessel and the preferred embodiment includes seven
pairs
of transducers in groups at particular positions axially along and external to
the
treatment vessel. Intensity of application of acoustic energy is below
cavitation
levels.
However, the applicant's research has shown that the configuration disclosed
in this
document is unlikely to succeed as the fluid velocities typically encountered
in pipe-
flow are too high and the flow is too turbulent for the ultrasonic forces to
be effective.
Also the residence in the field of the transducers is too short.
US Patent No. 5,527,460 described a multi-layered composite resonator system
using a plane transducer and an opposing and parallel plane mirror for
separating
particles suspended in a fluid on a small scale. The technique uses an
ultrasonic
resonant wave.
Other prior art solutions include the use of electrostatic treatments which
aim to use
forces created by the interaction of electrically charged bodies to cause
coalescence. For oil-from-water separation, filter-coalescers are commonly
used to
grow drop size by means of interference coalescence such as meshes or packing.
Such techniques, in the case of electrostatic coalescers are not effective on
water
continuous-mixtures, or in the case of filter coalescers have limitations due
to the
likelihood of blockage.
US Patent No. 6,210,470 describes apparatus for degassing a moving liquid. The
apparatus uses a transducer and reflector arrangement to produce ultrasonic
standing waves which are inclined at an acute angle to a horizontal axis of
liquid
flow.
The techniques described below act to coalesce the dispersed droplets into
larger
droplets thereby improving the downstream separation efficiency and/or
reducing
the cost of downstream separation. In another embodiment the techniques
described below are used to breakdown foam or promote the separation of
suspended or dissolved gas, which also improves separation and/or reduces the
costs of downstream separation.
CA 02530974 2005-12-20
3
The present invention generally relates to a method and apparatus for the
controlled
application of ultrasonic energy for conditioning of mixtures of gas and
liquids by
In a first aspect of the invention, there is provided coalescing apparatus for
increasing the droplet size of a mixture formed as a liquid dispersed in
another liquid
This provides the controlled application of ultrasonic energy in the form
preferably of
Thus the ultrasonic energy is used for coalescing droplets of one liquid
dispersed in
In a second aspect of the invention there is provided de-gassing apparatus
arranged
to evolve and/or agglomerate gaseous bubbles in a gas/liquid mixture
comprising a
CA 02530974 2012-05-14
4
= vibrational energy in the frequency range 200kHz to 3MHz and more
particularly in
the range 20kHz to 800kHz. In this case, the ultrasonic energy is used for
evolving
and/or agglomerating gas bubbles (foam) developed in or with liquids. More
particularly, when the gas is hydrocarbon gas and the liquids are hydrocarbon
liquids and or water. Most particularly when the gas and liquids result from
the
activities of production, transport and storage of natural gas and crude oil.
In a further aspect, the invention provides a cell comprising a transducer
couplable
to drive electronics, a reflector and at least one baffle extending between
the
transducer and the reflector and dividing the space between the transducer and
reflector into separate volumes, the baffles being arranged in use to be
sufficiently
rigid to generally prevent vibration passing between the volumes.
Preferably a plurality of such cells may be arranged to be generally co-planar
in a
matrix or honeycomb configuration in order to condition a larger volume of
material
over time than a single cell.
Optionally, a plurality of such cells may be arranged in series along a pipe,
the pipe
being arranged to carry a flow of material to be conditioned.
In a method aspect, the invention provides a method of increasing droplet size
of a
liquid dispersed in another liquid comprising passing vibrational energy
through the
liquid in a plurality of volumes defined by at least one baffle extending
between a
transducer and a reflector.
In a further method aspect, the invention provides evolving and/or
agglomeration of
bubbles of gaseous material dispersed in liquid by passing vibrational energy
through the liquid in a plurality of volumes defined by at least one baffle
extending
between a transducer and a reflector.
According to an embodiment of the present invention, there is provided a
coalescing
apparatus for increasing the droplet size of a flowing mixture formed as a
liquid
dispersed in another liquid comprising an ultrasonic transducer arranged to
impart
vibrational energy to the mixture and a reflector located generally opposite
the
transducer, wherein the apparatus is further arranged to flow the mixture
perpendicular to a notional line between the transducer and reflector and
includes at
CA 02530974 2012-05-14
4a
=
least one baffle extending in a direction generally between the transducer and
the
reflector and which divides the space between the transducer and reflector
into
separate volumes, wherein the baffles are arranged in use to be sufficiently
rigid to
generally prevent transmission of vibration between the volumes and the
distance
between the transducer and the reflector is in the range 10 to 250mm.
According to another embodiment of the present invention, there is provided a
de-
foaming or degassing apparatus arranged to evolve and agglomerate gaseous
bubbles in a gas/liquid mixture comprising a transducer arranged to impart
vibrational energy to the mixture and a reflector located generally opposite
the
transducer, wherein the apparatus is arranged to flow the mixture
perpendicular to a
notional line between the transducer and reflector and includes at least one
baffle
extending in a direction generally between the transducer and the reflector
and
which divides the space between the transducer and reflector into separate
volumes, and the baffles are arranged in use to be sufficiently rigid to
generally
prevent vibration passing between the volumes, wherein the distance between
the
transducer and the reflector is in the range 10 to 250mm.
According to a further embodiment of the present invention, there is provided
a cell
comprising an ultrasonic transducer couplable to drive electronics, and a
reflector,
wherein the cell is arranged to flow a fluid mixture perpendicular to a
notional line
between the transducer and reflector, said cell further comprising at least
one baffle
extending between the transducer and the reflector and dividing the space
between
the transducer and the reflector into separate volumes, and the baffles are
arranged
in use to be sufficiently rigid to generally prevent vibration passing between
the
volumes, wherein the distance between the transducer and the reflector is in
the
range 10 to 250mm.
According to a further embodiment of the present invention, there is provided
a
method of increasing droplet size of a flowing liquid dispersed in another
liquid
comprising passing vibrational energy through the liquid in a plurality of
volumes
defined by at least one baffle extending between a transducer and a reflector,
wherein the liquid flow is perpendicular to a notional line between the
transducer
and reflector, the baffles are arranged in use to be sufficiently rigid to
generally
prevent transmission of vibration between the volumes and the distance between
the transducer and the reflector is in the range 10 to 250mm.
CA 02530974 2012-05-14
4b
According to a further embodiment of the present invention, there is provided
a
method of evolving and agglomerating bubbles of gaseous material dispersed in
liquid comprising passing vibrational energy through the liquid in a plurality
of
volumes defined by at least one baffle extending between a transducer and a
reflector, wherein the liquid flows perpendicular to a notional line between
the
transducer and reflector and the at least one baffle is arranged generally to
prevent
vibration passing between the volumes, wherein the distance between the
transducer and the reflector is in the range 10 to 250mm.
Although techniques are described below in connection with separation of a
dispersed oil phase in a continuous water phase, it will be understood that
they have
general application in the treatment of any liquid dispersed in another
liquid, and/or
any liquid containing dissolved or dispersed gas.
CA 02530974 2005-12-20
Preferred embodiments of the invention will now be described with reference to
the
drawings.
Figure 1 is a schematic cross-section of a generally square section vessel
with
5 apparatus in accordance with the invention applied to the external
surface thereof;
Figure 2 is a schematic cross-section of a generally square section vessel
with
apparatus generally in accordance with the invention contained internally;
Figure 3 is a schematic cross-section of a generally circular section vessel
with
apparatus in accordance with the invention contained therein;
Figure 4 is a schematic cross-section of a generally circular section vessel
with
apparatus in accordance with the invention applied to the external surface;
Figure 5 is a schematic cross-section of a generally circular section vessel
showing
apparatus in accordance with the invention contained therein; and
Figure 6 is a schematic cross-section of a generally circular vessel with a
matrix of
cells in accordance with the invention contained therein.
With reference to Figure 1, a generally square section vessel 2 has a
transducer 4
mounted along one side and a reflector 6 mounted on the opposite side of the
vessel 2. The transducer 4 is typically formed as a piezoelectric layer 5
which
converts an oscillating electrical voltage applied across the layer into a
corresponding mechanical vibration, with an optional carrier 8.. Typically,
the layer
6 is made from a piezoceramic material.
The transducer 4 is optionally coupled to the vessel 2 by a carrier 8 which
effectively
provides impedance matching between the transducer and the vessel wall. The
carrier 8 represents an electrically insulative layer which isolates the
piezoceramic
layer 5 from the liquid. Its thickness and acoustic impedance are important
for
achieving efficient transmission of acoustic energy into the vessel 2_
However, in
some applications and including the other embodiments described below, the
transducer 4 may be mounted directly to the wall of the vessel 2 and the
carrier 8
may be omitted. Similarly, the reflector 6 may also be omitted in some
applications.
CA 02530974 2005-12-20
6
In use, the transducer 4 is electrically coupled to a drive circuit (not
shown) which is
operable to cause the transducer to vibrate at ultrasonic frequencies
(typically in the
range 200kHz to 1.5MHz and optionally in the range 400kHz to 1.5MHz for
coalescing operation or 20kHz to 800kHz for defoaming/degassing operation. The
transducer 4 may, for example, be made from a piezoceramic material which
changes dimension with the application of voltage across the material.
In the space generally marked 10, fluid is contained. In a preferred
embodiment, the
fluid flows between the transducer 4 and the reflector 6 in a plane into or
out of the
drawing sheet. Also, the transducer and reflector are generally co-extensive
into
and/or out of the plane of the sheet. Thus fluid flowing through the apparatus
spends a period of time flowing between the reflector and transducer (the
period
depending on the flow rate of the liquid and the length of extension of the
transducer
and reflector).
In coalescer operation, as ultrasonic energy is passed through the liquid, if
standing
waves are set up within the vessel 2, material of different densities within
the liquid
tend to separate and material gathers at the nodes or antinodes of the
standing
wave which is created. In the case of oil dispersed in water, typically oil
droplets
begin to coalesce at the pressure antinodes of the standing waves. These
coalesced droplets may then more readily be separated using conventional
apparatus downstream of the ultrasonic coalescing portion of the vessel.
Thus the vessel may, for example, be a pipe and advantageously may be retro-
fitted
with the transducer 4, carrier 8 and reflector 6. Alternatively, a single
transducer
may be used in which case the pipe wall may act as both carrier and reflector.
Also,
a transducer may act as a reflector. Thus any combination of these components
(carrier, transducer and reflector) may be used in appropriate circumstances;
the
minimum configuration being an unmounted transducer 5. The components may be
duplicated , for example, by placing a plurality of transducers, carrier and
reflectors
in a direction extending into the plane of the figure. This allows the units
to have a
cumulative effect as fluid flows along the pipe. Different units may also be
tuned
differently (by adjusting power, transducer/reflector characteristics and/or
frequency)
to take account of differing average droplet sizes along the length of the
pipe_
CA 02530974 2005-12-20
7
Typically the distance between the transducer and reflector is of the order of
10 to
100 mm for droplet coalescence, and may be up to 250mm or more for
defoaming/degassing applications. This has been found to give good results in
the
frequency range mentioned above, with fine dispersions of water in oil or oil
in water
having dispersion droplets of the order of 1 to 100 1.,,m and at flow rates of
tens of
m3/hr at velocities in the range 0.01 to 0.2m/s.
Preferably, the frequency of the transducer operation is automatically
controlled to
keep the whole system at resonance (which will generally provide standing
waves).
Input power levels are preferably kept as high as possible; the limiting
factor being
cavitation within the liquid and/or acoustic streaming which causes turbulence
and
results in turbulent mixing of the fluid.
Typically, following coalescence or
defoaming, the fluid is passed through a separator. The output quality of the
oil or
water stream may be monitored downstream of the separator and the results may
be used to produce a feedback signal to adjust the operating parameters of the
transducer.
Generally, increased power levels are desirable since this produces a stronger
coalescing or de-foaming/degassing effect. By providing baffles 12 which
divide the
area of the vessel 2 into a matrix of smaller channels, the point at which
acoustic
streaming occurs with increasing ultrasonic power put into the fluid, may be
deferred. Thus higher power intensities may be applied to the fluid using
baffles of
the type shown in Figure 1.
Streaming typically is a function of non-linearities in power emission over
the surface
of the transducer. Without constraint this can lead to acoustically driven
turbulence
which may disrupt the coalescing effect. The constraint offered by baffles
tends to
delay the onset of streaming and ensures that if it occurs it does so only in
localised
areas.
The dimensions of the channels formed by the baffles has been found to be most
effective when the distance L between the carrier 8 and reflector 6 is greater
than
the width W of the channel defined between the baffles 12.
With reference to Figure 2, an alternative approach is to insert a cell 20
having
baffles 12', a transducer 41',and reflector 6' contained within a vessel 22.
Preferably,
CA 02530974 2005-12-20
8
the area between the cell 20 and the inner surface of the vessel 22 is made
substantially fluid tight (although some leaks may be permitted) to force
flowing fluid
through the cell 20. An alternative is to carry out conditioning in a batch
process
whereby a body of liquid is let into the vessel, the vessel is closed, the
apparatus is
activated and subsequently the vessel is opened to release liquid having
larger
droplet sizes for the dispersed phase.
Figure 3 shows an alternative embodiment in which a cell 20 is contained
within a
generally circular section vessel 24. In other respects, the cell 20 may be
similar to
that of Figure 2.
Figure 4 shows the application of the technique to a circular section vessel
30. in
this case, the vessel 30 is surrounded by carrier material 32 which acts both
as
carrier and reflector (as in the case of the earlier embodiments in which the
same
material may be used).
A curved or flat transducer 34 is mounted to the outside of the carrier 32.
Baffles 36
preferably form smaller channels as discussed above and extend generally away
from the transducer 34 towards the opposite side of the vessel 30. This
embodiment may readily be retro-fitted to an existing pipe arrangement_
Figure 5 shows an alternative embodiment for dealing with circular section
vessels.
In this case, a vessel 40 has a generally axial transducer 42 mounted
centrally
therein. An optional carrier 44 surrounds the transducer 42 and a reflector 46
surrounds the outer surface of the vessel 40. Radial baffles 48 improve the
power
absorption characteristics of the fluid in the way described above.
Figure 6 shows a technique for dealing with large section vessels or pipes.
The
drawing shows a circular section vessel 50 although it will be appreciated
that the
vessel may be any section. Presently, the size of the cell 20 (Figure 2) has
been
found to have a limited maximum size. This is due, for example, to losses in
the
liquid (and the above mentioned limitation on the amount of power which may be
put
into the liquid before cavitation/streaming occurs) and non-linearities in the
transducers particularly at high driving levels. Nevertheless, for situations
in which
the vessel cross-section is very much larger than a maximum desired size of
cell 20,
the cells may simply be placed into a generally co-planer matrix or honeycomb
form
CA 02530974 2005-12-20
9
as shown in Figure 6. In this way, no liquid bottleneck is caused and yet the
performance of the individual cells is unaffected. It will be appreciated that
the
matrix may be formed in any shape and need not be a 9 x 9 matrix as shown
here.
Similarly, it will be appreciated that several cells could be placed in
series.
Alternative embodiments may include apparatus mounted at the oil interfaces in
an
existing separator in order to increase the rate of resolution of and to
promote
separation at the interface and provide a more sharply defined interface
between
liquids such as oil and water or at a gas/liquid interface. Thus it will be
appreciated
that the use of the apparatus may conveniently be targeted at problem areas in
existing process equipment.
Other adjustments include operating the apparatus for longer periods of time
at
lower powers (which achieves the same result although slower) and using
alternative materials for the transducer such as magneto-restrictive materials
(which
typically have lower operating frequencies of the order of 100 KHz or less).
In the
case of the embodiments of Figures 2 and 3, it will be noted that the space
between
the outside of the cell 20 and the internal surface of the vessels (22 and 24
respectively) typically would be pressurised to the same pressure as the
liquid
flowing through the cell 20. In oil processes, the pressure within the cell
may be of
the order of 10bar(a)?) or higher. Using a fluid connection from the internal
area of
the cell via a suitable isolating diaphragm, clean generally non-compressible,
material such as transformer oil, may be used to pressurize the reverse side
of the
cell 20 (i.e. the area between the cell outer surface and the cell inner
surface).
Alternatively, process liquid may be allowed into the area behind the cell.
This not
only helps to prevent damage to the cell from loads caused by excessive
pressure
differentials but may also provide an insulating medium to facilitate
electrical
connection to the transducer(s) and to ensure that all process liquid is
treated.
