Differential And/or Discontinuous Heating Along Pipelines By Heat-generating Pipes Utilizing Skin-effect Current

Abstract

Heating a pipeline by means of at least one ferromagnetic heat-generating pipe wherein an electric conductor is disposed along the interior length of said ferromagnetic pipe but is insulated from the inner wall thereof so that upon passage of alternating voltage through said electric conductor there is a concentrated flow of current along the inner skin of the ferromagnetic pipe to thereby generate heat in said ferromagnetic pipe, said heat being transferred to said pipeline by conduction, and controlling the amount of heat conducted to various sections of said pipeline by varying the placement density of said ferromagnetic pipe along various sections of said pipeline.

Description

CROSS-REFERENCES

Japanese Pat. application No. 43-41785.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a method for adjusting heat quantities to be supplied to pipeline, when a pipeline is to be electrically heated by one or more heat-generating pipes utilizing skin-effect current. More particularly it relates to a method for efficiently transporting a fluid through pipelines while maintaining it at an adequate temperature without overheating and overcooling. The variation in fluid temperature is minimized by means of adjustment of heat quantities in accordance with variations of heat losses due to variations of pipe diameter and/or of circumstance in the location of pipeline.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING

FIG. 1 shows a schematic longitudinal, cross-sectional view of a known heat-generating pipe utilizing skin-effect current.

FIG. 2 shows a schematic longitudinal cross-sectional view of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The above heat-generating pipe utilizing skin-effect current to be applied to this invention corresponds to the heat-generating pipe as specified in Japanese Pat. application No. 40-12128 (Japanese Pat. No. 460,224) invented by the present inventor and filed by the present applicant. Referring now to FIG. 1, the principle and nature of the above-mentioned heat-generating pipe is illustrated. A pipe 1 is made of ferromagnetic material such as steel, in which a conductor line 2 is laid and electrically insulated from the pipe wall. A circuit is made by connecting one end of this conductor with one end 3 of the pipe 1 and connecting the other ends of both the conductor 2 and a conductor 5 (connected with the other end 4 of pipe), respectively with terminals of a power source. When an alternating current of a suitable frequency is applied to this circuit consisting of the conductor 2-- the ferromagnetic pipe 1-- the conductor 5, the current forms a concentrated flow along the inner skin portion of the pipe wall because of skin effect, generating Joule's heat at the skin parts. Now, the skin thickness for such cases is given by: ##SPC1##

Employing an ordinary steel pipe and using an alternating power of a commercial frequency (50 Hz. or 60 Hz.), we have about 0.1 (cm.) for d. When a thickness of the pipe 1 is more than this value, no voltage appears practically on the outer surface of pipe; therefore, there is no leaking to other substances, nor shock to animals, even if they are placed in contact with the pipe surface or they touch it.

It is possible, therefore, to facilitate the thermal conduction between the heat-generating pipe and the pipeline by placing both in close contact or by welding, because no electrical insulation is required between them in applying the above heat-generating pipe to the heating of a pipeline. Further, needless to say, there is no need of electrically insulating pipe supports from the ground when laying a pipeline equipped with such a heating system.

The foregoing pipeline heating system (Skin Electric Current Tracing) is referred to as "SECT System" hereinafter.

In the case of a pipeline of a constant pipe diameter through which fluid flows without any other inflow and outflow, and where there is substantially no difference in circumstances of pipeline locations and therefore heat loss is substantially constant along the pipeline, temperature may be controlled one-dimensionally over its entire length according to flow quantities. However, when a pipeline has any other inflow or outflow along its length or has different quantities of fluid along its lengths because of partial variations in pipe diameter, and further when heat loss varies according to the variation of circumstance for the pipeline installation, heat output to be supplied to the pipeline must be varied according to the heat loss of each part of the pipeline in order to transport fluid at a temperature as constant as possible.

In the prior SECT System, it is possible to change heat output to some extent by changing partially the size of the ferromagnetic pipe 1 and/or the conductor line 2 however, the possible variations of heat output are in the order of .+-.50 percent at most. Therefore, if it is desired to vary the heat output more than the above-mentioned extent, it is necessary to divide a pipeline into sections according to the heat losses in each section and to provide an amount of electric power that is suitable for every section. For this purpose, every section needs separate power source equipment including a transformer etc., which not only results in a large installation cost, but also a large maintenance cost because of the large number of these power sources.

An object of the present invention is to provide a method for heating a pipeline having many sections with different heat losses, by the use of a single power source and with simple equipment that has a great deal of economical advantage.

This object can be attained by the method of the present invention. This method comprises adjusting the placements density of the heat-generating pipe by length adjustment of the heat-generating pipe or by the spacing of successive heat generating pipes in accordance with heat losses of the pipeline in any given section.

The invention will be better understood from the following description taken in connection with the accompanying drawing, FIG. 2, in which number 6 is a pipeline through which fluid flows from one end 7 to the other end 10. Since there is another inflow of fluid from a branch pipe 8 and a partial outflow of fluid from a branch pipe 9, flow quantities through sections A, B and C are not constant. Obviously fluid flowing through the section B has the largest quantity. If the flow quantity flowing through the section A is greater than that through the section C, the relation among the flow quantities flowing through the respective section is B>A>C. Accordingly, when each pipe diameter for every section as above-mentioned is to be varied in accordance with the respective flow quantity, the relation among the heat losses as well as the relation among the pipe surface area per unit length should also be B>A>C. If a heat-generating pipe with the same heat output per unit length is applied to these sections so as to heat the pipelines over its entire length, and at the same time, is the setting-up of temperature to be generated by the heat-generating pipe is made on the basis of section B, where the heat loss is maximum, so as to maintain fluid flowing through this section at an adequate temperature, the fluid temperature will rise up unreasonably higher than required in those sections (A and C) which are less than the section B in flow quantity. It is likewise improper to base the temperatures to be generated by the heat-generating pipe on the section C where the heat loss is minimum, it is because the fluid in the other sections could not then maintain the desired temperature.

In view of the foregoing, it is a general object of this invention to provide a method which remedies the above problem by varying the placement density of the heat-generating pipes in various sections of the pipeline in accordance with the amount of heat required. More specifically, by adjusting the length of heat-generating pipe or the distance between successive heat generating pipes it is possible to effect heating of the pipeline over its entire length in a satisfactory way while supplying power from one source.

Further, by way of example reference is made to FIG. 2, wherein number 11 is a ferromagnetic pipe laid onto the section B (which has the maximum flow quantity, i.e., the largest pipe diameter.) (This Figure is shows only one heat-generating pipe, but it is to be understood that a plurality of pipes may be used instead of one.) Numbers 12 and 12' are ferromagnetic pipes laid onto the section A which has a flow quantity smaller than the section B, that is, a smaller pipe diameter. Accordingly installation density can be made smaller in section A than the section B. Numbers 13 and 13' denote ferromagnetic pipes laid onto the section C which are to be installed with less installation density than either section A or section B. Number 14 is an electric conductor, which is inserted in each ferromagnetic pipe with electrical insulation interposed between the conductor and each of the inner walls of pipe starting from the left end of a ferromagnetic pipe 12 to the end of a ferromagnetic pipe 13. One end of the conductor 14 is connected electrically to the right end 16 of 13 and the other end thereof is connected to one terminal of an alternating power source. Further, the left end 15 of a ferromagnetic pipe 12 is connected to another terminal of the alternating power source through a conductor 17. When an alternating voltage is applied to this circuit, the current which flows through each ferromagnetic pipe is concentrated limitedly only through the thin inner wall portion of each ferromagnetic pipe, and in each generates a relatively a large amount of heat; on the other hand, at the locations where the heat-generating pipes are omitted, heat generation is so small as to be negligible, because the current diffuses to the pipeline at those locations.

Therefore, it is thus seen that the heat output can be changed to the desired amount for any section of the pipeline with the arrangement as illustrated in FIG. 2; by varying placement density of the heat-generating pipes for each of the sections A, B and C of pipeline, and yet the maintenance is easy because the control of the system can be done one-dimensionally from one power source.

In FIG. 2, based upon the assumption that the section B has the maximum flow quantity, the heating of this section is carried out in conformity with the aforesaid SECT System. However, one heat-generating pipe is not necessarily laid onto this entire section as shown in Figure, but it is economical and desirable to design the SECT System on the basis of the section requiring a maximum heat output.

In the foregoing description, explanation of the invention has been related to variations of flow quantities in a pipeline. However, it goes without saying that the present invention is applicable to the adjustment of heat output in accordance with possible variations of heat losses due to the variations of circumstances in pipeline locations (underground, in water, in the open air, outdoors, indoors etc.), regardless of whether flow quantity is subjected to variations or not.

In practicing this invention, care must be given to groundings and pipe supports of pipelines to be installed.

As set forth above, in the SECT System where the current flows concentratedly through the inner wall portion of ferromagnetic pipe constituting the heat-generating pipe without any significant potential appearing on the outer surface thereof and pipeline, there is no current flowing to the ground even if grounding is made at any point. For example, groundings at two points 18 and 19 in section B of FIG. 2 make no trouble. However, at a span devoid of the heat-generating pipe as in the section C, when groundings are made at two points such as 20 and 21 within this span, there appear ground currents. Therefore, it is preferred and recommended to avoid such groundings. In general, the values of these ground currents are less than one-several hundredth, triflingly small as compared with the current applied to the heat-generating pipe, so that decrease of power efficiency for heating is out of the question. It is evident, however, that every safety measure should be taken against dangers when transporting a fluid having a low flash point in a pipeline.

The present invention is applicable to the transportation by pipeline of such substances as heavy fuel oil; certain kinds of crude oil etc. which is too viscous at normal temperature to be sent by pipelines; for substances which solidify at low temperatures such as benzene, cyclohexane, acetic acid, asphalt and certain kinds of fats; for substances which are solids at normal temperature, such as fatty acids, sulphur, phthalic anhydride etc. to be liquidized for transportation; and for mixed gases having a dew point higher than normal temperature.

Claims

1. A method for electrically heating a fluid-transporting pipeline that is composed of a plurality of sequentially disposed pipeline sections, each pipeline section having different heat requirements depending upon the amount of fluid flowing therethrough and the heat loss therefrom, said method comprising:

a. sequentially disposing a plurality of ferromagnetic pipes in a heat transmitting relationship with said sequentially disposed pipeline sections,

b. selecting the length of each ferromagnetic pipe that is associated with each pipeline section so that its length is directly proportional to the heat requirements of that pipeline section to thus produce a fluid-transporting pipeline having an unbroken sequence of pipeline sections and a discontinuous sequence of ferromagnetic pipes associated therewith,

c. electrically connecting said discontinuous sequence of ferromagnetic pipes in series,

d. passing an electrical conductor through the interior of said discontinuous sequence of ferromagnetic pipes but electrically insulating said electrical conductor from the interior of said discontinuous sequence of ferromagnetic pipes,

e. connecting one end of said electrical conductor to the outer extremity of the last in a discontinuous sequence of ferromagnetic pipes,

f. connecting the other end of said electrical conductor to an AC power source,

g. also connecting said AC power source to the first of the ferromagnetic pipes in said discontinuous sequence of ferromagnetic pipes,

h. arranging the AC source frequency and the thickness of the ferromagnetic pipe so that the AC source current flowing in the pipe wall will be concentrated by the AC skin effect into the interior surface regions of the walls of the discontinuous sequence of ferromagnetic pipes to thereby generate Joulean heat in each sequentially disposed pipeline section in

2. A fluid-transporting pipeline provided with electrical heating means which is characterized by:

a. a plurality of sequentially disposed pipeline sections, each pipeline section having different heat requirements depending upon the amounts of fluid flowing therethrough and the heat loss therefrom,

b. a plurality of sequentially disposed ferromagnetic pipes associated with said sequentially disposed pipeline sections and in heat-transmitting relation therewith,

c. said plurality of sequentially disposed ferromagnetic pipes being connected together electrically in series,

d. the total length of a ferromagnetic pipe that is associated with each pipeline section being directly proportional to the heat requirements of that pipeline section which results in a fluid-transporting pipeline having an unbroken sequence of ferromagnetic pipes associated therewith,

e. an electrical conductor extending through said discontinuous sequence of said ferromagnetic pipes,

f. said electrical conductor passing through the interior of a discontinuous sequence of ferromagnetic pipes but being electrically insulated from the interior of said discontinuous sequence of ferromagnetic pipes,

g. said electrical conductor having one end thereof electrically connected to the outer extremity of the last in a discontinuous sequence of ferromagnetic pipes and the other end thereof connected to an AC power source,

h. said AC power source also being electrically connected to the first ferromagnetic pipe in said discontinuous sequence of ferromagnetic pipes,

i. the AC source frequency and the wall thickness of the ferromagnetic pipe being such that the AC source current flowing in the pipe wall will be concentrated by the AC skin effect into the interior surface regions of the walls of the discontinuous sequence of ferromagnetic pipes to thereby generate Joulean heat in each sequentially disposed pipeline section in accordance with its heat requirements.