Note: Descriptions are shown in the official language in which they were submitted.
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Detailed Description of the Invention
This invention relates to an apparatus for economically
varying heat quantities when different heat quantities are
required along the longitudinal direction of a lengthy to-be-
heated material such as a pipeline which is to-be-heated for ¦~
maintaining a temperature or a material surrounding a lengthy
pipeline. -
~` This invention can be applied to generally a lengthy
to-be-heated material, but as examples in order to give
; 10 better understanding of the nature of the present invention
to persons skilled in the art, description will be made
hereinafter with regard to two cases: i.e. a pipeline for
transporting benzene and the other pipeline which passes
through the area of ground wherein freezing and melting of
the ground are repeated all the year round.
Since the freezing point of benzene is about 5C, it is
; necessary not only to insulate a pipeline carrying benzene 7
but also to heat it to prevent benzene from freezing in
a cold area where atmospheric temperature becomes lower than
5C. I ,
For example, if a pipeline is to be buried under the
ground in the southern districts of Japan, to an extent of
; about 1.2 ~1.8 m deep from the surface which is a usual
depth in case of a buried pipeline, then the ground temper-
ature does not drop far below 5C even in the winter season.
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Accordingly only a few heating makes it possible to prevent
a liquid in the pipeline from freezing even if the pipeline
is not covered with any other insulating layer than the
surrounding ground, because the ground performs the role
of an insulating layer. It is, however, difficult to bury
such a pipeline all through its entire length. It is often
unavoidable that some parts of the pipeline are laid above
the ground. In such a case, since such parts above the ground
may sometimes be exposed to atmospheric temperature of about
-10C, it is impossible to prevent the liquid from freezing
only by the heat quantities applied to the buried parts of
the pipeline without the insulating layer. Therefore, the
parts of the pipeline above the ground require any insulation
means and a larger amount of heating than that in the buried
- parts.
An object of this invention is to provide a heating
element which produces different heat quantities in the 3
longitudinal direction in response to the requirement of
a to-be-heated material requiring different heat quantities
in the longitudinal direction.
According to the present invention, a heat-generating
' pipe of induction type skin effect current is installed for- the parts where the to-be-heated material requires a heat
~ quantity larger than for the other parts, and it is so
-i~ arranged for the other parts requiring a smaller heat
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quantity or no heat that at least one extension part of at
least two rows of the wire passin~ through said heat-
generating pipe, is passed through the inside of another
ferromagnetic pipe whereby heat generation is suppressed
due to cancellation of induction effect. Alternatively,
said extension part is passed through a non-ferromagnetic
pipe or a plastics pipe to avoid induction heating for the
latter parts, where heat is generated only by the electric
resistance of the wire.
The heat-generating pipe of induction type skin effect
current herein referred to is the one the principle of which
; is described in U.S. Pat., 3,515,837 or Canada Pat. 844,088
~; and which consists of one or a plurarity of ferromagnetic
pipes and an insulated electric wire passed through these
pipes and connected with an alternating current source to
form a primary circuit wherein both the ends of said ferro-
magnetic pipe are connected with each other so that a secondary
current, induced in said pipes by the alternating current
flowing in the insulated electric wire forming a primary
circuit, concentrates on and flows only through the inner
skin portion of said pipes, and the thickness of said pipe
walls is several times larger than the skin depth of said
secondary current so that the induced voltage formed by said
secondary current does not appear on the outer surface of
said pipe.
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The connections of both the ends of said ferromagnetic
pipe will be concretely illustrated hereinafter. It is
assumed that there are two ferromagne-tic pipes desiynated
as A and B which are disposed mutually in the outside of
the other, i.e. one is not disposed in the inside of the
other. An insulated wire extending from one of the two ter-
minals of a single phase current source, passes through
the inside of A from the first end to the second end thereof,
and after leaving the second end~further passes through the
s from the second end of B to the first end thereof, and
after leaving the first end of B, it is connected with the
other end of said single phase current source. Both the
first ends of A and B and both the second ends of A and B
are connected with each other so as to give impedance as
!small as possible. In order to make the impedance as small ~-
as possible, both the ends of A and B to be connected with
each other are disposed as close as possible.
According to another embodiment of the heat-generating i
pipe of induction type, the second ends of said pipes A and
B are connected with the ends of a pipe bent to form a half
circle, through which said insulated wire is laid. There
is a case where both the pipes A and B form one piece U-form
pipe. In either case, the remaining ends of pipes A and B
are connected with each other.
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If another example is to be illustrated, there is
a case where three ferromagnetic pipes C, D and E are in
the relationship mutually disposed outside the others,
three insulating wires extending from the three terminals
of a three phase electric source, pass from the respective
first ends of the pipes C, D and E through the inside of
the respective same pipes,and after leaving the respective
second ends, they are connected with each other, the first
ends of C, D and Eare connected with each other so as to
give impedance as small as possible and the second ends
~; thereof are also connected with each other so as to give
impedance as small as possible.
In the above-mentioned heat-generating pipe of
induction type skin effect current, commonly and practically
~ steel pipes are used as ferromagnetic pipe and electric
'J wires of copper or aluminum are used as insulating electric
wires. In such a case, a greater part of generated heat
-, (normally 80 ~90% of the total generated heat) is produced
in the steel pipe but there is also heat generation (remain-
ing 10 ~20%) in the electric wire. Accordingly, in the
above-mentioned examples, it is possible to utilize the
insulating wires extending from the first ends of the pipes
A and B or the pipes C, D and E to the electric source as
well as the insulating wires extending outward from the
second ends of these pipes, for the heating of the parts
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108029~ .
requiring a smaller hea-t quantity of a to-be-heated material.
Thus, in the apparatus of the present invention, for
the parts re~uiring a larger heat quantity, heating is
effected by the heat-generating pipe of induction type
skin effect current that comprises the ferromagnetic pipe
and the insulated wire disposed within said pipe, and for
the parts requiring a smaller heat quantity, heating is
effected by the electric wires extending outside said
ferromagnetic pipe (including the part of the wire extending
from said ferromagnetic pipe in the directions to an electric
source and opposite to the electric source.
In the above-mentioned concrete examples, there may
be a case where the extension parts of the two electric
wires from inside the pipes A and B pass through another
set of pipes A' and B'. This arrangement becomes necessary
in the case where a part of a to-be-heated material requiring
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a small heat quantity is interposed between the parts 31
requiring a larger heat quantity in the to-be-heated material.
It goes without saying that this may be applied to the third,
the fourth, and the subsequent sets of A", B"; A"', B"';
..., etc.
Furthermore, there may be also cases where the diameter,
length, etc. of pipes are different from each other in the
combinations of A, B; A', B'; ..., etc. It is also naturally
possible, as the cases dictate, to vary the kind of the material of
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the insulating layer of the electric wire to be passed
through these pipes, particularly the material thereof
in terms of its heat-resisting property, and the kind of the
material and the size in the cross-sectional area, of the
conductor of the electric wire, depending upon the requirements
of the to-be-heated material. Particularly between the
part of the above-mentioned insulating electric wire lying
within the above-mentioned ferromagnetic pipe and the part
extending outside the pipe, the above-mentioned variations
may be often preferable.
The apparatus of the present invention will be described
` more concretely by referring to the drawings. Figure l is
a schematic plane view of one example of the heating element
of the present invention stretched linearly in the direction }
of length. Figure 2 1S a schematic side view of a pipeline
` equipped with the heating element of Figure l. Figure 3 is
an enlarged view of the cross-section taken along the line
III-III of Figure 2. Figure 4 is an enlarged view of the
cross-section taken along the line IV-IV of Figure 2.
Figure 5 is a schematic cross-sectional view of a pipeline
~t and two heat-generating pipes of the present invention laid
-~ along said pipeline so as to warm the ground close to said
pipeline.
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In Figures 1 and 2, a pipe 6 corresponds to the part
buried in an underground 10, a heat-generating pipe 3
corresponds to an overground part 11. Similarly, there are
correspondences between 7 to 12; 4 to 13; 8 to 14; and 5 to
15, respectively.
In Figure 1, feeders 2 and 2' from a single phase
electric source 1 pass through the inside of the pipe 6
as a go-and-return circuit, and the heat in this part is
generated by the feeders without any induction current on
10the pipe. This holds true even when the pipe 6 is of
ferromagnetic steel pipe because the induction electro-
magnetic fluxes are cancelled within the pipe 6 by the
go-and-return currents which flow in the electric wires
2 and 2'. Thus there will be only the heat generation due
to the electric resistance of the wires 2 and 2'. On the
other hand, 3 forms a heat-generating pipe of induction t
type skin effect current. Namely, the feeders 2 and 2'
pass through the respective insides of two ferromagnetic
steel pipes 31 and 32 which form secondary circuits consist-
20ing of these pipes and the connection parts 3' and 3"
relative to the primary circuits 2 and 2', and if only
necessary conditions are satisfied, the secondary current
concentrates on and flows through only the inner skin
portions of the two steel pipes. Accordingly, even when
any other metal is placed in contact with the outer surface
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of these two st~el pipes, no current appears on this metal
and thus these two steel pipes can be used as a safe heat-
generating pipe.
In Figure 2, the aboveground part 11 of a pipeline
represents the part where there is a larger heat loss and
lower ambient temperature. It is further assumed that only
the insulating layer 20 shown in Figure 3 is insufficient
for temperature maintenance and the heat generation in the
; inside of the steel pipes 31 and 32 must be added to the
heat generation due to the electric resistance of wires 2
and 2'.
In Figure 3, if a transportation pipe 11 is of a metal,
it is a common practice to wela two heat-generating pipes 31
and 32 to the transportation pipe 11. In such a case, the
role of the connection parts 3' and 3" on both the ends in
Figure 1 is taken by a part of the transportation pipe 11.
It goes without saying that if said transportation pipe 11
is a plastics pipe, a special connection material is
necessary.
The above-mentioned fact will be explained again by
referring to Figure 1. The electric wires 2 and 2' carrying
the electric current from the single phase source 1 do not
cause the heat generation due to the induction current of
pipes in the parts of pipes 6, 7 and 8, and the heat
generation due to skin effect current is added to the heat
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1080Z9l
generation due to the resistance of wires in the parts of
the heat-generating pipe of skin effect current. The
primary circuit of these heat-generating pipe of skin
effect current is constructed usually by connecting the
electric wires 2 and 2' on the side 9 remote from the electric
source 1.
In Figure 2, there is shown a case where a liquid
from a tank 17 is sent through transportation pipes 10, 11,
12, 13, 14 and 15 to a tank 18 by a pump 16. Since 19 shows
the surface of the ground, 10, 12 and 14 are the buried
underground parts and 11, 13 and 15 are overground parts.
In Figure 4, there are shown two pipes indicated as 8
and 8' in which electric wires 2 or 2' are passed. Pipe 8
is situated in the inside of the transportation pipe 14, and
' pipe 8' is installed on the outside of the transportation
pipe 14. Since it is a customary practice to apply an anti-
corrosion coating around the outer surface of a transportation
pipe when it has no thermal insulation layer, inner tracing
as shown in 8 is common.
The foregoing description is directed to the examples
of application for preventing the transporting liquid
flowing through a pipeline from freezing but the heating
apparatus is also useful for the prevention of freezing
of the soil surrounding buried pipelines.
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Near the north pole, there is an area where the ground
is frozen all the year round. There is also an area where
the ground repeats freezing and melting all the year round
in the southern part of these areas and there is also
an area where the ground is not frozen all the year round
in the southern part of the last mentioned areas. Let us
assume a case of transportation of, for example, natural
gas through a pipeline spanning all the above-mentioned
areas. Even in a permafrost area, the temperature of gas
can rise above 0C due to the friction loss of flowing gas
relative to the wall of pipe and melt the frozen soil
surrounding a pipeline. The melting of the frozen soil
often makesthe fixing of the pipeline difficult, and, in
the worst case, it would work havoc with the pipeline. It 1S
is possible to prevent the melting of the frozen soil by
precooling the gas to keep its temperature lower than 0C
throughout such an area and to make the fixing of the pipe-
line stable.
However, it is often insufficient for preventing the
melting only by precooling the gas in such an area where
melting of soil and freezing thereof occur all the year
; round. In such an area, if the soil surrounding the pipeline
is electrically heated and prevention of freezing is possible
all the year round,the fixing of pipeline becomes rather
easier. However, the boundary line between the zone where
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such melting and freezing are repeated and the zone of
permafrost soil is not always drawn clearly, and it is
rather common that area of permafrost soil and areas of
repeated melting and freezing are existing in non-orderly
state.
According to the apparatus of the present invention,
the above-mentioned problem can be solved economically.
Namely, in the area requiring heating i.e. the area which
repeats the freezing and melting as mentioned above~a heat-
generating pipe of induction type skin effect current isinstalled in the lower part ground surrounding a pipeline,
and in the area of permafrost land, heat generation is
restricted only to the heat generation caused by the electric
resistance of wire, in order to minimize heat generation.
Figure 5 shows the cross-section of a pipeline laid in
the region requiring heating. In Figure 5, 11 is a pipeline
for transporting natural gas; 20 is its insulation layer;
31' and 32' are heat-generating pipes of induction type
skin effect current containing insulated wires 2 and 2'
therein (not shown in the drawing); 19 is a ground surface
and 21 is a sand layer.
With the above-mentioned arrangement, the soil surround-
ing the pipeline 11 will not be froæen all the year round by
the heat generation of the heat-generating pipe of skin effect
current, and the unstability in the fixing of a pipeline,
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which results from frost heave of the surrounding soil can
be avoided. Moreover, wasteful heat generation of permafrost
land can be minimized.
Further when even a small quantity of heat generation
is detrimental to the permafrost landj it is possible to
prevent heating by keeping the parts of the wire extending
to the outside of the ferromagnetic pipe of a heat-generating ,
pipe of skin effect current (the parts 6, 7 and 8 of Figure 1)
slightly away from the pipeline (it will be sufficient to keep
about a distance (center to center) of 5 m away therefrom).
The electric power necessary for the prevention of freezing
is unexpectedly small. It is usually about 10 to several
tens watts per meter though it varies depending upon the
diameter of pipe, the flow quantity of a gas, change of 1,
atmospheric temperature, etc. Accordingly,it hardly affects
the cost of transportation cost of the gas.
In Figure 1, it is preferable that the heat-generating
pipes of skin effect current 3, 4, 5, etc. are electrically
connected with each other. The reason for the necessity of
such connections is due to the fact that if the insulation
of wires 2 and 2' laid through the heat-generating pipes
3, 4, 5, etc. should be broken, such a failure would be
detected easily by a leakage current detector as provided
on a switch panel, with the mutual connection of the heat- .
generating pipes, tho~gh such a connection is not shown in
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the drawinc~s. Such a connec~ion can utilize the transportation
pipe itself when the pipe is made of a metal but if the trans- ¦
portation pipe ll in Figure 3 is made of a plastics, the
purpose can be attained by using metal pipes for the pipes
of 6, 7 and 8 of Figure l and connecting them together with
the heat-generating pipes 3, 4 and 5.
As above-mentioned, according to the apparatus of the
present invention, the heating or temperature maintenance
of a pipeline requiring a wide range of variation of heat
generation in the direction of the lengthy pipeline or
prevention of local freezing of the soil surrounding
a pipeline becomes feasible with a single electric source
apparatus without requiring any special feeder lines and
thus without loss occurring in these lines.
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