Note: Descriptions are shown in the official language in which they were submitted.
1078906
001 BACKGROUND OF THE INVENTION
002 Field of the Invention
003 This invention relates to a system for reducing heat
004 output in a specific segment of an internal wire impedance
005 system for heating a pipeline.
006 DESCRIPTION OF THE PRIOR ART
007 Pipelines often require the fluid flowing in them to
008 have lower viscosities than they would have at the ambient
009 temperature of the pipe. In order to reduce the viscosity of
010 the fluid, heat is generally transferred into the fluid. A way
011 to achieve this is through steam tracing, that is, a system
012 which uses steam flowing in a separate conduit adjacent to the
013 one transporting the fluid. Another system is one using
014 alternating electrical current and the effects of a magnetic
015 field produced by the current to increase the temperature of
016 the fluid in the flow pipe. This second method has in the past
017 been called "skin effect heating", or more correctly, "internal
018 wire impedance heating".
019 Industry has used the skin effect or internal wire
020 impedance heating which, under current practice, uses a ferro-
021 magnetic pipe attached substantially parallel and either
022 interior of or exterior to a fluid-flow pipe. The
023 ferromagnetic pipe has longitudinally extending through it an
024 electrically insulated metallic wire that is electrically
025 connected to the ferromagnetic pipe at a point remote from the
026 point of entry of the insulated wire so that both the wire and
027 pipe may be connected in series with each other and an
028 alternating current (AC) source of power. Thus, the electric
029 current flows through the insulated wire and returns through
030 the wall of the ferromagnetic pipe. Due to the skin effect,
031 most of the current flows near the inside wall of the pipe,
032 with essentially no current flowing at the outside wall.
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001 ~eat is generated in the wall of the ferromagnetic
002 pipe by: magnetic hysteresis resulting from a type of internal
003 friction as the magnetic domains within the pipe wall are
004 reversed; eddy currents in the pipe wall due to the presence of
005 the pipe wall in a changing magnetic field which induces
006 currents to circulate throughout the pipe wall yielding and I2R
007 heating effect; and the I2R effect of the current returning
008 through the pipe wall. Additional heat is also generated in
009 the insulated wire according to Joule's Law, i.e., the I2R
010 effect of the current flowing in it.
011 A point worth mentioning here is the reason for using
012 a pipe having the property called "ferromagnetismn. It simply
013 is that this property greatly increases the magnetic field in
014 the pipe wall due to the alternating current through the
OlS conductor which results in significant heating by hysteresis
016 and eddy currents. Examples of ferromagnetic elements are
017 iron, nickel and cobalt. Additionally, some alloys may have
018 components which by themselves are not ferromagnetic, but when
019 combined together as an alloy show this property, e.g., MnBi.
020 In prior installations of internal wire impedance
021 heating systems of which I am aware, there is no known way to
022 decrease the heat output of a given segment of the pipe for any
023 length of time while the rest of the pipe is at higher heat
024 output. The present invention, however, includes several
025 embodiments which do reduce the heat output for a given segment
026 without affecting the heat output of the adjacent pipe. The
027 utilization of the present invention results in both an
028 economical and efficient use of electrical power, such as where
029 a heat reduction segment connects two or more noncontiguous
030 fluid-flow pipes that are heated by a single heat-generating
031 pipe. For example, a heated pipeline in a refinery may have a
032 termination point a short distance away from a second heated
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pipeline which continues on to another place in the refinery.
When a common internal wire impedance system is used for heat-
ing each of them, a heat-reduction section is desirable in the
space between the two lines since there is no need to heat that
space. It is also usable whenever less heat is required in a
segment of a continuous fluid-flow pipe, such as a segment
where the heat loss is less due to reduced size in a segment of
the pipe, better thermal insulation, or a supplementary source
of heat.
SUMMARY OF THE INVENTION
In accordance with one aspect of this invention there
is provided a method for reducing the heat output of a segment
of heat generating pipe, comprising the steps of: electrically
connecting one end of a first electrical conductor means to a
first terminal of an alternating current power source; extend-
~- ing the opposite end of said first conductor means into a
, .
ferromagnetic pipe up to an extreme point of said ferromagnetic
pipe where heat is desired and electrically connecting said
opposite end to said ferromagnetic pipe at said extreme point; ;~
electrically connecting a second terminal of said power source
to said ferromagnetic pipe at a preselected point on said
ferromagnetic pipe spaced apart from said extreme point; -
connecting in place of a segment of ferromagnetic pipe located ~`
between said extreme point and said preselected point an
electrically non-conductive non-ferromagnetic section of pipe
to reduce the magnetic field and heat output produced within
said segment of pipe; and providing a second electrical con-
ductor means extending through said non-conductive non-ferro-
magnetic section of pipe and connected at each end of said
non-conductive non-ferromagnetic section of pipe to said
ferromagnetic pipe in order to establish a current path across
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said non-conductive non-ferromagnetic section of pipe.
In accordance with another aspect of this invention
there is provided in a system for reducing the heat output of
a segment of heat-generating pipe, said heat-generating pipe
including a ferromagnetic pipe having a first electrical con-
ductor means extending through said ferromagnetic pipe up to
an extreme point of said ferromagnetic pipe where heat is
desired, one end of said first conductor means connected to
said ferromagnetic pipe at said extreme point, the opposite
end of said first conductor means connected to a first
- terminal of an alternating current power source, a second
terminal of said power source connected to a preselected point
on said ferromagnetic pipe spaced apart from said extreme
point, the improvement comprising: an electrically non-
conductive non-ferromagnetic section of pipe connected in
place of a segment of ferromagnetic pipe located between
said extreme point and said preselected point to reduce the
magnetic field and heat output produced within said segment
of pipe; and a second electrical conductor means extending
through said non-conductive non-ferromagnetic section of pipe
and connected at each end of said non-conductive non-ferro-
magnetic section of pipe to said ferromagnetic pipe in order
to establish a current path across said non-conductive non-
ferromagnetic section of pipe.
By way of added explantion, in one aspect the
present invention provides a novel system that reduces the
heat output of a segment of an internal wire impedance system.
In an internal wire impedance system, a continuous insulated
electrical conductor means extends longitudinally through a
ferromagnetic pipe and is connected at one end to a source of
alternating current and at the other end to a return path means.
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The return path may be the ferromagnetic pipe or an electrical
conductor; in either case, they must be respectively connected
to the source of alternating current.
An electromagnetic field-decreasing means is pro-
vided in the series circuit to reduce the alternating magnetic
field produced by the current flowing through the electrical
conductor. The means may be located inside a segment of the
pipe and parallel to the electrical conductor extending
longitudinally throughout the pipe to diminish the alternating
magnetic field induced in the wall of the ferromagnetic pipe.
This arrangement results in a corresponding reduced heat
output,
Similarly, another embodiment of the present in-
vention requires replacing a segment of the ferromagnetic pipe
with a non-ferromagnetic but electrically conductive segment.
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001 When this replaced segment is in series with the ferromagnetic
002 pipe, it is the segment of reduced heat output because no heat
003 is generated in the nonferromagnetic pipe by hysteresis and the
004 heat generated by eddy currents is significantly reduced. The
005 foregoing may be accomplished with an electrically noncon-
006 ductive means, provided an electrically conductive means is
007 introduced into the series circuit to complete a return path
008 for the current to the source of alternating current.
009 An alternate embodiment further described below uses
010 a ferromagnetic pipe with a first and a second means for ;=
011 passing the insulated conductor through the wall of the pipe at
012 each end of the segment where the reduced heat output is
013 desired. The insulated conductor means, which extends longi-
014 tudinally in the pipe, is positioned through the first means
015 extended adjacent to the exterior of the pipe wall, and back
016 through the second means from where it continues inside the
017 pipe. A ferromagnetic field is not created within the pipe
018 segment between the two means when the insulated conductor is
019 located in the foregoing manner, since there is no current flow
020 in that segment.
021 This invention also includes a step-by-step procedure
022 for reducing the heat output of a segment of a heat-generating
023 pipe that is located internally or externally to a pipeline.
024 In brief, the steps include electrically connecting an insu-
025 lated conductor means to a first terminal of an alternating
026 current power source; extending the insulated conductor means
027 through the ferromagnetic pipe and directly connecting it up to
028 an end point in the pipe where heat is desired. The second
029 terminal of the power source is then connected to the pipe to
030 make a complete electrical series circuit. Next~ an
031 electromagnetic field-decreasing means for reducing the
032 alternating magnetic field described above is electrically
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~01 connected into the series circuit. The steps may include
002 connecting the electromagnetic field-decreasing means in the
003 form of a second electrical conductor internal and parallel to
004 the segment of reduced heat output and in series with the pipe
005 to produce an alternating magnetic field which is equal and
006 opposite to a similar field produced in the insulated conductor
007 means. Alternatively, when the electromagnetic field-
008 decreasing means is a nonferromagnetic pipe, the above step
009 becomes connecting this pipe in series with the ferromagnetic
010 pipe which may have an additional step of connecting an
011 electric-wire bypass to make a complete series circuit. As a
012 result, a changing magnetic field and the corresponding heating
013 effects do not occur in the newly connected section.
014 Moreover, the method may take the steps of passing
015 the insulated electrical conductor means through the wall of
016 the ferromagnetic pipe and extending it along the exterior of
017 the pipe to the end point of the segment where a reduced heat
018 output is desired, and then passing it through the wall of the
019 pipe. When the preceding steps are carried out, alternating
020 current does not flow in a conductor within the pipe in this
021 segment, and consequently the alternating magnetic field within
022 the pipe wall is reduced a predetermined amount.
023 BRIEF DESCRIPTION OF THE DRAWINGS
024 The above-described embodiments and advantages will
025 be further illustrated and described in the drawings and the
026 following description of the preferred embodiment.
027 FIG. 1 illustrates schematically a first embodiment
028 of the present invention having an electrical conductor
029 parallel to the reduced heat output segment.
030 FIG. 2 is a schematic illustration of another embodi-
031 ment of the present invention having a nonferromagnetic but
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001 electrically conductive section throughout the length of the
002 segment where a reduced heat output is desired.
003 FIG. 3 schematically depicts an alternate embodiment
004 of the present invention wherein a segment having both elec-
005 trically nonconductive and nonferromagnetic properties is
006 connected to the ferromagnetic pipe to form the segment with a
007 reduced heat output.
008 FIG. 4 is a schematic diagram of an embodiment of the
009 present invention where the electrically conductive means which
010 extends longitudinally through the ferromagnetic pipe passes
011 outside the pipe along the segment wherein a reduced heat
012 output is sought.
013 DESCRIPTION OF THE PREFERRED EMBODIMENT
014 Referring to FIG. 1, ferromagnetic pipe 100 has a
015 segment where a reduced heat output is sought, designated by
016 point A and point B. Throughout the following discussion,
017 point A is considered the beginning of the segment of reduced
018 heat output and point B is the end of this segment within pipe
019 100. A power source of alternatingcu~rent 101 is directly
020 connected to a point D that is adjacent to the entering point
021 of an insulated conductor means 102 which terminates at a
022 remote point C. At point C conductor 102 is directly connected
023 to pipe 100 so that the flow path for the current is through
024 the ferromagnetic pipe. Internal to pipe 100 is an
025 electromagnetic field-decreasing means for reducing the heat
026 output, such as means 103, characteri~ed by being electrically
027 conductive, which is electrically connected to pipe 100
028 respectively at points A and B. The means 103 is a path for
029 the alternating electrical current to flow past the reduced
030 heat segment on its return path to the source of alternating
031 current. Most of the current will flow through this means
032 since it is the path of least impedance. The current in the
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001 electromagnetic field-decreasing means 103 sets up an opposite
002 and approximately equal magnetic field to that created in
003 conductor means 102. In effect, the two magnetic fields cancel
004 each other.
005 Particularly referring to FIG. 2, the electromagnetic
006 field-decreasing means in this embodiment is a nonferromagnetic
007 electrically conductive means 104 which is electrically
008 connected in series with pipe 100. This means 104 may be an
009 aluminum pipe that allows the alternating current generated
010 from power source 101 to return through it; but, because of the
011 aluminum's nonferromagnetic characteristics, the heat generated
012 in the pipe by the alternating magnetic field produced by
013 current flowing through the insulated conductor means 102 is
014 substantially reduced.
015 The embodiment illustrated in FIG. 2 may give rise to
016 galvanic corrosion when dissimilar metals are used for the
017 electromagnetic-field-reducing means 104 and the ferromagnetic
018 pipe 100. To avoid galvanic couples that lead to corrosion, a
019 pipe fitting such as a dielectric union between means 104 and
020 the pipe 100 is suggested. When a dielectric union of the type
021 which electrically insulates one pipe segment from another is
022 used with means 104, the wall of means 104 cannot be used as
023 the return path for the alternating current. In this case, an
024 electrical bypass of segment 104 is necessary.
025 Another embodiment of the electromagnetic field-
026 decreasing means is shown in FIG. 3, where an electrically
027 nonconductive segment 105 is physically connected in series
028 with pipe 100. Also included is a second electrically
029 conductive means 106, electrically connected in series with
030 pipe 100, either external (not illustrated) or internal to pipe
031 100, thus bypassing the segment 105. This arrangement prevents
032 the creation of a magnetic field, yet allows the alternating
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001 current to bypass this nonconductive segment through conductor
002 105.
003 An alternative embodiment of the electromagnetic
004 field-decreasing means is diagrammatically illustrated in FIG.
005 4, which is advantageous in the case where the ferromagnetic
006 pipe 100 is desired to be continuous, e.g., where pipe 100 is
007 used as the fluid flow pipe. In this embodiment, insulated
008 conductor means 107 is electrically connected to power source
009 101. The conductor means 107 passes through pipe 100 at point
010 A and is continuous with a second insulated conductor means
011 108, which is the electromagnetic field-decreasing means. The
012 conductor means 108 passes through the wall of pipe 100 at
013 point B and is continuous with a third wire means 109.
014 In situations where the pipe 100 is also the conduit
015 for fluid flow, the passage of the conductor means through the
016 pipe wall may be made fluid-impermeable by using appropriate
017 fittings 110 so that the contents of the pipe 100 will not leak
018 at these places. Thus, the means for passing the conductor
019 through the pipe may be a grommetted penetration, a screwable
020 or weldable fitting or other leak-proof means. Additionally,
021 this particular embodiment may have instead of the three
022 separate insulated conductors one continuous wire means which
023 passes through the wall of pipe 100 to become the
024 electromagnetic field-decreasing means and returns through the
025 wall at the end of the segment of reduced heat output. The
026 conductor is then connected in series with the power source.
027 In general, instead of pipe 100 being the return path
028 for the current, it may be an electrical conductor, preferably
029 insulated, which is in series with the insulated conductor
030 means extending longitudinally through the ferromagnetic pipe
031 and the power source. Alternatively, a combination of the pipe
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001 100 and an electrical conductor may form the return path for
002 the current.
003 Although only selected embodiments of the present
004 invention have been described in detail, the invention is not
005 to be limited to any specific embodiments, but rather only by
006 the scope of the appended claims.
061
