Note: Descriptions are shown in the official language in which they were submitted.
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MAGNETIZATION DEVICE FOR A NUCLEAR MAGNETIC FLOW METER
Background of the Invention
Field of the Invention
[0001] The invention relates to a magnetization device for permeation of a
multiphase
fluid flowing through a measurement tube of a nuclear magnetic flow meter with
a magnetic
field which is homogenous at least in one plane, with a plurality of permanent
magnets for
generation of a magnetic field and with a carrier, the carrier having at least
one magnet receiver,
each of the magnet receivers accommodating at least one of the permanent
magnets, the shape of
the magnet receivers and of the permanent magnets allowing movement of the
permanent
magnets only in one direction in the magnet receivers and the permanent
magnets held by the
magnet receivers being arranged by the magnet receivers with reference to the
magnetic field.
Description of Related Art
[0002] A nuclear magnetic flow meter determines the flow of the individual
phases of a
multiphase fluid, the flow velocities of the individual phases and the
relative proportions of the
individual phases in the multiphase fluid in the measurement tube by measuring
and evaluating
the voltage induced by the nuclear magnetic resonance of the multiphase fluid
into a suitable
sensor. The measurement principle of the nuclear magnetic resonance is based
on the property of
atomic nuclei with a free magnetic moment to precess to the nuclear spin in
the presence of a
magnetic field. The precession of the vector representing the magnetic moment
of the atomic
nucleus takes place around the vector representing the magnetic field in place
of the of atomic
nucleus, the precession inducing a voltage into the sensor. The frequency of
precession is called
the Larmor frequency col, and is computed according to oh, = y B, y being the
gyromagnetic
ratio and B being the amount of the magnetic field strength. The gyromagnetic
ratio y is
maximum for hydrogen -nuclei, for which reason especially fluids with hydrogen
nuclei are
suited for nuclear magnetic flow meters.
[0003] A multiphase fluid composed essentially of crude oil, natural gas and
salt water
is delivered from an oil source. So-called test separators branch off a small
part of the delivered
fluid, separate the individual phases of the fluid from one another and
determine the proportions
of the individual phases in the fluid. Test separators are expensive, cannot
be installed under the
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sea and do not allow real-time measurements. In particular, test separators
are, however, unable
to reliably measure crude oil proportions smaller than 5%. Since the crude oil
proportion of each
source drops continuously and the crude oil proportion of a plurality of
sources is already less
than 5%, it is currently impossible to exploit these sources.
[0004] Both crude oil and also natural gas and salt water contain
hydrogen nuclei, for
which, as already mentioned, the gyrornagnetic ratio y is maximum. Nuclear
magnetic flow
meters are therefore suited especially for use on oil sources, also undersea
directly on the source
on the sea bed, but are not limited to this application. Other applications
arise, for example, in
the petrochemical or chemical industry. Branching off of the fluid is not
necessary, and the
entire fluid is measured in real time. Compared to test separators, nuclear
magnetic flow meters
are more economical and require less maintenance and can also especially
reliably measure
crude oil proportions less than 5% in the fluid, as a result of which the
further exploitation of a
host of oil sources becomes possible for the first time.
[0005] It is immediately apparent from the equation for computing
the Larmor
frequency oh, that the Larmor frequency coL is proportional to the magnetic
field strength B, and
thus, the magnetic field strength B also acts directly on the voltage induced
into the sensor.
Heterogeneities in the magnetic field therefore reduce the measurement quality
of nuclear
magnetic flow meters, for which reason the task of the magnetization device is
the permeation of
the fluid with a magnetic field which is ordinarily homogeneous within the
measurement tube.
The required measurement accuracy determines the necessary homogeneity of the
magnetic
field. Often measurement methods are used which use a known gradient in the
magnetic field so
that the magnetic field is constant only in one plane.
[0006] U.S. Patent 7,872,474 82 discloses a magnetic resonance based
apparatus and
method to analyze and measure bi-directional flow that utilizes a stack of
disks, formed of a
plurality of bar magnets, which forms a hollow cylindrical permanent magnet,
the magnetic field
being homogeneous in the cylindrical interior of the magnet. The magnets of
each disk are held
between rings of non-magnetic material and fixed by the screws that are also
made of non-
magnetic material the discs of magnets piled up and held by non-magnetic
screws.
[0007] In each individual disk of magnets forms a Halbach array. The
important feature
of a Halbach array is that the magnetic field forms largely on one side of the
Halbach array,
here, in the interior of the cylindrical magnet, and on the other side, only a
very weak magnetic
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field forms, here, in the external space of the cylindrical magnet Since a
strong magnetic field is
required for high voltages induced into the sensor by the precession of the
hydrogen atoms
contained in the fluid, correspondingly strong bar magnets are used. Due to
the plurality of bar
magnets which are arranged tightly in each of the magnet disks, the
introduction of the bar
magnets into the magnet receivers is associated with a high expenditure of
force. Moreover, the
resulting magnetic field is initially not homogenous enough, for which reason
the magnetic field
must be made homogeneous by manipulation on each of the bar magnets. This
process is called
shimming. The introduction and shimming of the numerous bar magnets mean a
considerable
production and time expenditure, which is accompanied by the corresponding
costs.
Summary of the Invention
[0008] The primary object of the present invention is to devise a
magnetization device
with reduced production and time expenditure which will achieve sufficient
homogeneity of the
magnetic field that permeates the fluid.
[0009] The magnetization device in accordance with the invention in
which the
aforementioned object is achieved is, first of all, essentially characterized
in that the magnet
receivers are made as hollow profiles.
[0010] A hollow profile can be economically produced with various
inner cross
sectional contours which are perpendicular to the longitudinal axis of the
hollow profile. For
example, the inner cross sectional contour of a channel-shaped hollow profile
is rectangular and
one of the outer cross sectional contours of the permanent magnets is likewise
rectangular and is
dimensioned such that the permanent magnets can be moved in the hollow profile
along only the
longitudinal axis of the hollow profile, therefore are form-fit except for the
longitudinal axis.
The length of the hollow profile in this example is dimensioned such that a
plurality of
permanent magnets can be introduced. It is immediately apparent that the
fixing of the
permanent magnets by pushing the permanent magnets into these hollow profiles
means a much
lower production and time expenditure than the fixing of the permanent magnets
with screws
between a pair of rings as in the above described prior art. The complex
stacking of the disks of
individual magnets is replaced by a simple carrier for accommodating the
hollow profiles, the
carrier aligning the hollow profiles such that the fluid is permeated by a
sufficiently homogenous
magnetic field.
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[0011] In one preferred embodiment of the magnetization device in
accordance with the
invention, the friction in the movement of the permanent magnets in the hollow
profiles is
reduced by lining of the hollow profiles, for example, with a
polytetrafluoroethylene (PTFE)
coating on the inner surfaces of the hollow profiles. The reduced friction
distinctly reduces the
expenditure of force for introducing the permanent magnets into the hollow
profiles. After
introducing the permanent magnets into the hollow profiles, the permanent
magnets can be fixed
in the hollow profiles by a first liquid adhesive and then a hardening
substance. Sealing
compounds, for example, are possible for this purpose.
[0012] In another preferred embodiment of the magnetization
device in accordance with
the invention, the carrier has plurality of receiving tubes. In each of the
receiving tubes, a hollow
profile is formed for accommodating at least one of the permanent magnets. The
material for the
receiving tubes can be a glass fiber composite material since it is easily
possible in this material
to form, for example, rectangular hollow profiles in the production process.
Then, permanent
magnets with a conventional rectangular cross section can be introduced into
the rectangular
hollow profiles so that the permanent magnets in the hollow profile move only
along the
longitudinal axis of the hollow profile, but cannot turn around the
longitudinal axis of the hollow
profile.
[0013] As the holder of the receiving tubes, the carrier can have
at least one disk with
receivers for the receiving tubes in which there is, preferably, a penetration
for the measurement
tube. Usually the receiving tubes of a magnetization device are of the same
length so that the
holder of the receiving tubes can be a disk on each end of the receiving
tubes. The carrier then is
comprised essentially of the receiving tubes and the two disks. If there is to
be a homogenous
magnetic field in the measurement tube along the longitudinal axis of the
measurement tube, the
alignment of the longitudinal axes of the receiving tube parallel to the
longitudinal axis of the
measurement tube is possible. Often, the permanent magnets are located in the
receiving tubes
as a Halbach array.
[0014] In another preferred exemplary embodiment of the
magnetization device in
accordance with the invention which is a development of the preceding
exemplary embodiment,
at least one of the receiving tubes is produced partially from a material
which influences the
magnetic field. For example, if a material having good magnetic conductivity
is used in the
receiving tubes on the poles of the permanent magnets, the resulting magnetic
field can thus be
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advantageously influenced with respect to a homogenous magnetic field in the
measurement
tube. In addition or alternatively, the receiving tubes can be arranged in the
carrier to be able to
rotate around their longitudinal axis for advantageously influencing the
homogeneity of the
magnetic field in the measurement tube and then fixed against rotation. The
rotation of the
receiving tube is a first shimming of the magnetic field.
100151 In another quite especially preferred configuration of the
invention, the carrier
encompasses at least one profile body, the profile bodies preferably being
extrusion profile
bodies. The cross-sectional profile of each of the profile bodies is constant
along the respective
longitudinal axis of the profile body, and in at least one of the profile
bodies, at least one hollow
profile is made to accommodate at least one of the permanent magnets.
Preferably, here the
hollow profiles are also made for accommodating rectangular permanent magnets
such that the
permanent magnets introduced into one of the hollow profiles can move along
the longitudinal
axis of the hollow profile, but cannot turn around the longitudinal axis of
the hollow profile.
Material for the profile bodies can be, for example, aluminum alloys or
ceramics. For
permeation of the measurement tube with a homogeneous magnetic field along the
longitudinal
axis of the measurement tube, again, an alignment of the longitudinal axes of
the profile bodies
parallel to the longitudinal axis of the measurement tube is recommended.
[0016] In another preferred embodiment of the magnetization device in
accordance with
the invention, at least one of the hollow profiles in at least one of the
profile bodies of the carrier
is made such that there is an adapter tube in this hollow profile that is able
to rotate and the
adapter tube can be fixed against rotation. In each of the adapter tubes, a
hollow profile for
accommodating at least one of the permanent magnets is made. The rotation of
the adapter tube
is a first shimming to improve the homogeneity of the magnetic field in the
measurement tube.
[0017] In another quite especially preferred embodiment of the
magnetization device of
the invention in accordance with the invention, the carrier comprises at least
two profile bodies
and two profile bodies at a time are detachably connected by at least one
positively shaped
connecting profile on the first profile body and at least one negatively
shaped connecting profile
on the second profile body. The positive and the negative connecting profile
are shaped such that
two connected profile bodies can execute translational movement against one
another only along
one axis. By this type of connection, the profile bodies can be easily
arranged, for example,
around the measurement tube, and thus, the magnetization device can be easily
installed.
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100181 In another special embodiment of the magnetization device in accordance
with
the invention, the carrier which contains at least one profile body is made as
a yoke for guiding
the magnetic backflow generated by the permanent magnets. The cross sectional
profiles of each
of the profile bodies are constant along the respective longitudinal axis of
the profile body and in
at least one of the profile bodies there is at least one hollow profile for
accommodating at least
one of the permanent magnets. The guidance of the magnetic backflow is an
alternative to the
arrangement of the permanent magnets as a Halbach array. Material at least for
the yoke can be
one with high magnetic conductivity.
[0019] In particular there are a plurality of possibilities for configuring
and developing
the magnetization device claimed in the invention. In this respect reference
is made to the claims
subordinate to Claim 1 and to the description of preferred exemplary
embodiments in
conjunction with the drawings.
Brief Description of the Drawings
[0020] Figure 1 is an exploded perspective view of a first exemplary
embodiment of the
magnetization device in accordance with the invention,
[00211 Figure 2 is a perspective view of second exemplary embodiment of the
magnetization device in accordance with the invention with several rotatable
receiving tubes,
[0022] Figure 3 is an exploded perspective view third exemplary embodiment of
the
magnetization device in accordance with the invention with a carrier for
several extrusion profile
bodies, and
[0023] Figure 4 shows a fourth embodiment with a carrier of several extrusion
profile
bodies, in an exploded diagram.
Detailed Description of the Invention
[0024] Figure 1 shows the essential components of a magnetization device 1 in
accordance with the invention; there are a plurality of permanent magnets 2
and a carrier 3 made
of nonmagnetic material. The primary components of the carrier 3 are a
plurality of receiving
tubes 5 in the form of hollow profiles 4, two disk rings 6 with a central
opening 7 for a
measurement tube and with receivers 8 for the receiving tubes 5 and two end
disk rings 9 which
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also have a central opening 7 for the measurement tube. In Figure 1, not all
receiving tubes 5 are
visible in order to be able to show the permanent magnets 2 as well.
[00251 In each of the receiving tubes 5, eight permanent magnets 2 of the
same length
are introduced, the cross-sectional contour of these permanent magnets 2 being
rectangular and
form-fit with the hollow profiles 4 so that the permanent magnets 2 can be
moved in one of the
hollow profiles 4 only along the longitudinal axis of the hollow profile 4,
but cannot turn around
the longitudinal axis of the hollow profile 4. The permanent magnets 2 can be
divided into
groups with cross-sectional areas of different size, as a result of which the
permanent magnets 2
have different magnetic field strengths.
[00261 The receivers 8, which are provided in the disk rings 6 which have
been screwed
to the end disk rings 9, arrange the receiving tubes 5 equipped with the
permanent magnets 2
around the measurement tube such that the permanent magnets 2 form a Halbach
array. The
receiving tubes 5 are arranged essentially in two rings around the measurement
tube and are
fixed by long screws which are not shown here and which connect the two end
disk rings 9 to
one another and draw the two end disk rings 9 toward one another. A carrier
known from the
prior art for the same arrangement of the permanent magnets 2 requires sixteen
disk rings 6, two
disk rings 6 for each of the eight rings of the permanent magnets 2 so that
the reduced cost
associated with the present invention is quite apparent.
100271 The exemplary embodiment of the magnetization device I in
accordance with
the invention which is shown in Figure 2 differs from the exemplary embodiment
which is
shown in Figure I essentially by the ability of several receiving tubes 5 to
be turned around their
longitudinal axis. Since the magnetic field strengths and directions of the
individual permanent
magnets 2 are subject to inevitable fluctuations by the production process of
the permanent
magnets 2, even in an optimum arrangement of the permanent magnets 2 by the
carrier 3,
heterogeneities of the resulting magnetic field in the measurement tube arise.
The
heterogeneities can be reduced by rotating individual receiving tubes 5.
[0028] The outer cross sectional contour of the rotatable receiving tubes
5 perpendicular
to their longitudinal axis is circular and the pertinent receivers 8 in the
disk rings 6 are
accordingly circular and form-fit to the receiving tubes 5. Fach of the
rotatable receiving tubes 5
is provided with a rotation device 10 for rotation and fixing thereof. F.ach
of the rotation
devices 10 includes two opposite pins for turning and two opposing screws for
fixing of the
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respective receiving tube 5. Accordingly, there are sets of four longitudinal
holes in the end disk
ring 9 that are arranged concentrically around the longitudinal axis of each
of the rotatable
receiving tubes 5.
[0029] Figure 3 shows a magnetization device 1 in accordance with the
invention with
the carrier 3 assembled essentially from several extrusion profile bodies 11
produced from an
aluminum alloy. All extrusion profile bodies 11 have the same length and each
of the extrusion
profile bodies 11 has a plurality of hollow profiles 4. The inner cross
sectional contour of each
of the hollow profiles 4 perpendicular to the longitudinal axis of the
corresponding hollow
profile 4 is made rectangular, not all cross-sectional contours of the
extrusion profile bodies 11
being closed, i.e., some have channel-shaped open contours. The open contours,
in the
assembled state, are closed by the other extrusion profile bodies 11.
[0030] The permanent magnets 2 all have the same length so that the
same number of
permanent magnets 2 is introduced into each of the hollow profiles 4, and they
can be divided
into groups with rectangular cross-sectional areas of different sizes
perpendicular to their
longitudinal axis, as a result of which the permanent magnets 2 have different
magnetic field
strengths. The permanent magnets 2 which have been introduced into one of the
hollow
profiles 4 cannot turn around the longitudinal axis of the corresponding
hollow profile 4, the
inner cross sectional contour of the hollow profile 4 perpendicular to the
longitudinal axis of the
hollow profile 4 not being equal to the outer cross sectional contour of the
permanent magnets 2
which have been introduced into the hollow profile 4.
[0031] In the cylindrical extrusion profile body 11, concentrically
along the longitudinal
axis of the cylindrical extrusion profile body II there is an opening 7 for
the measurement tube
and the other four extrusion profile bodies 11 are arranged around the
cylindrical extrusion
profile body 11 so that the longitudinal axes of the hollow profiles 4 are
aligned parallel to one
another and parallel to the longitudinal axis of the cylindrical extrusion
profile body 11. The
permanent magnets 2 arearranged in the carrier 3 such that they form a Halbach
array.
[0032] Each pair of the extrusion profile bodies 11 have a first
extrusion profile body 11
with a positive connecting profile 12a and a second extrusion profile body 11
with a negative
connecting profile 12b. The outer cross-sectional contour perpendicular to the
longitudinal axis
of the positive connecting profile 12a and the inner cross-sectional contour
perpendicular to the
longitudinal axis of the negative connecting profile 12b are shaped to form-
fit with each other
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and are made such that, in the connected state, only mutual movement of the
two extrusion
profile bodies 11 along the longitudinal axis of the positive connecting
profile 12a is possible.
[0033] A movement of the permanent magnets 2 in the hollow profiles 4
along the
longitudinal axis of the cylindrical extrusion profile body 11 and a movement
of the extrusion
profile bodies 11 relative to one another along the longitudinal axis of the
cylindrical extrusion
profile body 11 are inhibited by two end disk rings 9, which are not shown
here. In each of the
two end disk rings 9, there is a central opening for the measurement tube and
there are bores for
the penetration of screws as shown in Fig. 1. Accordingly, in the end faces of
the extrusion
profile bodies II there are threads for screw connection to the end disk rings
9.
[00341 Figure 4 shows another magnetization device 1 in accordance
with the invention
with the carrier 3 assembled essentially from several extrusion profile bodies
11 which have
been produced from a plastic in an injection molding process. The
magnetization device 1
differs from the magnetization device 1 shown in Figure 3 essentially by the
replacement of the
one-piece cylindrical extrusion profile body 11 by a multi-part extrusion
profile body 11.
[0035] Compared to the magnetization devices 1 in accordance with the
invention which
are shown in Figures 1 and 2, the production effort and thus also the costs
are again reduced in
the magnetization devices 1 shown in Figures 3 and 4.
[0036] In part plastic, in part ceramic have been addressed above as
the material to be
used. Instead, ceramic or aluminum can also be used.
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