US2453776A - Electrical conductance heater - Google Patents

Description

NOV. 16, 1948. BEATH AL 2,453,776

ELECTRICAL CONDUGTANCE HEATER Filed May 14, 1947 2 Sheets-Sheet l Fzauaz 2 122109314302 5.- Mm 6 476 Hum/1 8. 6 7/ flCxU RE 1 Nov. 16, 1948. L. R. BEATH ET AL ELECTRICAL CONDUCTANCE HEATER 2 Sheets-Sheet 2 Filed May 14, 194'? FIGUFSE3 FIGURE Patented Nov. 16, 1948 ELECTRICAL CONDUCTANCE HEATER Laurence R. Beath and Harold S. Hill, Kenogami, Quebec, Canada, assignors to Price Brothers & Company, Limited, Quebec, Quebec, Canada, a corporation of Quebec, Quebec, Canada Application May 14, 1947, Serial No. 747,920

6 Claims.

Our invention relates to that type of apparatus for electrically heating liquids in which the passage of an electrical current through the liquid develops the desired heating action.

It is a primary object of our invention to provide an apparatus suitable for electrically heating large volumes of waste sulphite liquor as required for the recovery of the solids content of said liquid according to the process described in our pending applications Nos. 588,756 and 657,220, the latter now abandoned.

Other objects of our invention are to provide an electrical conductance heater of a form which is suitable for operation at high perssures, which is simple and economical in construction, and which may be readily adapted for operation with liquids having a wide range of electrical conductivities.

In the apparatus of our invention a tube or shell made of an electrical insulating material is mounted within a metallic pipe or pressure vessel and means are provided to keep the pressures on the inside and outside surfaces of the insulating shell substantially in balance. Adjacent each end of the insulating shell we place an electrode kept at substantially earth potential by means of metallic connections to the outer metallic vessel which is grounded. Within the insulating shell, intermediate the grounded electrodes, 2. high tension electrode is supported on an insulation covered metallic rod which passes through a central opening in one of the grounded electrodes and continues through the head of the metallic vessel to provide a connection for a high voltage wire from a power source.

In general, materials which are good electrical insulators are relatively weak mechanically while those possessing good mechanical strength are very poor electrical insulators. Our construction of apparatus is specifically designed so that the electrical insulating shell serves to confine and define the path of the electrical current through the liquid to be heated without being called upon to sustain any material proportion of the hydraulic or vapor pressures which may exist in the heater. At the same time the metallic vessel which carries the pressure is shielded from any stray electric currents of such magnitude as might damage it. The novelty and value of our invention resides in the construction provided to assure the above efficient separation of functions and to attain the other attributes required for heaters of large capacity which may be operated at high pressures to heat liquids having medium to high electrical conductivities.

The nature of our invention will be more fully described with reference to the drawings in which:

Figure 1 is a sectioned elevational View of a preferred embodiment of our apparatus;

Figure 2 is a sectioned elevational view of another embodiment of our invention;

Figure 3 indicates in elevation the combination of three units of the type shown in Figures 1 or 2 to operate with a three phase, three wire power source; and.

Figure 4 is a plan view of the same grouping of units shown in Figure 3.

In Figure 1 we show at I a tube or shell of insulating material which may suitably be made of heat-resistant glass (Pyrex type), porcelain, stoneware, enamelled metal, or other insulating material resistant to the operating conditions of the heater. The shell I may be a single length as shown, or it may be built up of shorter sections suitably gasketed and clamped together. Within the shell I is supported a high tension electrode 2 by'means of the metallic rod 3 which is surrounded by an insulating structure l which may suitably be made of glazed porcelain. A grounded electrode 5 is supported near the bottom of shell I by supports 6 which carry current from the electrode 5 to the metallic fitting! which is grounded as indicated at 8. Another grounded electrode 9 is mounted near the upper end of the shell I and is electrically connected by its supports II! with the metallic head I I of the metallic vessel I2. Both head II and vessel I2 are also connected electrically to the ground 8. The insulating shell I is supported in the Vessel I2 by brackets I3 extending inwardly from the inner wall of the vessel I2 in such a way as to leave an open passage by which the interior and exterior of the shell I are in communication. Supports I4 spaced around the inside of vessel I2 near the top of shell I serve to stabilize and center shell I. The supports I4 are spaced to leave passageways giving access between the inside and outside of the shell I. This construction provides an open space or passage along the full length of both the inside and outside walls of the shell I, and as these passages are in communication with each other at both ends of the shell I, a means is thus provided by which the hydraulic or vapor pressures inside and outside the shell I are necessarily balanced. The shell I acts in its function of an insulator without being subjected to hydraulic or vapor pressure stresses. This construction also permits of independent axial motion of the shell I and the vessel I2, hence their differential thermal expansion or contraction can impose no stress upon shell 5. The grounded electrodes and i are best made to almost fill the free cross sectional area of the shell l and may be perforated to permit the liquid to flow through them. Alternatively, the electrodes 5 and s could be placed just beyond the ends of the shell i and they might then be somewhat larger in diameter than the inside of shell ,I. in either case, the size and location of the electrodes should be such as to minimize the amount of current which will flow to the vessel I2 by way of the liquid, thus protecting the vessel from electrolytic attack.

The apparatus shown in Figure .1 maybe operated on single phase current but is best used, in the larger capacities particularly, with two added identical units connected to a three wire, three phase power source. For operation, one wire of the three phase power line is connected to the protruding upper end of the rod Ill-of each of the three heaters. The liquid to be heated is pumped into the apparatus through the tting l, rises to fill both the shell i and the space between shell I and vessellz, and leaves through the metallicheadi 5. With the liquid closin the circuit between the electrode 2. and the grounded electrodes 5 and 9, application of voltage to the heaters causes current to flow through thefluid between these electrodes and effects the desired heating of the fluid.

The proper'dimensions and proportions of the apparatus to obtain any desiredheating rate may be calculated by known methods giving consideration to the electrical conductivity of the fluid, voltagaspacing of the electrodes, inside .diameter of the shell 5 and size of the portion of the insulator i withinthe shell l. By appropriate combinations cf'these factors, heaters having capacities from 5% to 15,080 kilowatts per phase may be made.

In Figure 2 we show a modified construction of our apparatus in which the pressure balance between the inside-and-cutside of the shell 3 is obtained in a diifercnt manner. Here we pro-- vide the-same general disposition of the electrodes 2, s and 9,'sh'ell i and insulated rod'fi asshown in Figure i. In our modified apparatus though we support'the shell l on a shell or ledge l5 projecting inwardly from the upper rim of the fitting l of which it may be an integral part. The ledge l5 also serves here to support the electrode A gasket it provides a sealing cushion between the shell I! and the ledge 55. At the upper end of the shell 8 a'second seal'is provided by the joint action of the gasket H, the sealing ring IB, and the diaphragm 59 which is welded or otherwise sealed to the projection 26 on the lower interioredge of the head H and to-the-outer rim of the ring it. The springs 2i and their tensioning screws '22 provide pressure tomaintain a seal across the face of gasket El while still permitting differential longitudinal thermal expansion of the shell 9 and the-vessel 12. It will be seen thatithis construction provides a closed space 23 between the shell 5 and the vessell'i which is completely sealed off fromthe material to'be heated for a purpose which will become apparent. An auxiliary chamber 24 containingabellows 25 isconnectedby the conduit 26 to thediquid in the fitting? Another conduit 12"! connects the inside of the bellows :25 to the :space 23 enclosed between the shell l and the vessel 12. The bellowsilfi, conduit Eland the space :23 are filled with a suitable fiuidsuchas the type of oil used in transformers. It will be seen that any hydrostatic or vapor pressure inside fitting and the shell i will act through the conduit 26 upon the outside of the bellows 25 and that this pressure will be transmitted by the oil without essential diminution to the outside of shell 5, thus achieving balanced pressure across that member. We may place a weight 28 on top of the bellows 25 in order that the oil in space 23 may have a slight excess of pressure over the liquid inside-the shell 5 thus assuring, should the shell l or its end seals leak, that non--conducting oil rather than the conducting liquid within shell 'i should pass through the leak. An indicator rod '29 and scale (it may be provided to advise of oil volume changes due to leakage. Signal lights or protective relays'could also be actuated by rod if desired. The bellows 25 also serves to accommodate the increased oil volume resulting from thermal expansion of the oil in space it when the apparatus is heated. In this modified construction, the vessel l2 does not come into contactwith the liquid being heated, thus avoiding, where corrosive media are to be heated, the necessity for making the vessel 22 from expensive corrosion resisting materials.

'It will'be understood that while in describing this modification of our invention. we have done so in terms of only one specific embodiment, other arrangements maybe used to achieve the principal structural features of our invention. Thus fluids other than oil may be used in the space 23, or a gas may be used; the sealing assembly at the top of shell I may be of quite a different construction than that shown; and other means of approximately balancing the pressures inside and outside shell i may be used, all without departing from the scope of our in vention.

It will be apparent that, in the improbable event of a gross failure of the shell l, a severe short circuit would arise between the high tension electrode '2 and the adjacent wall of the vessel i2. In applications where protection against'such a contingency seems desirable, we say interpose a second insulating shell between the first insulating shell i and the vessel [2 to prevent such a short circuit. In the embodiment described withreference to Figure 1, this secondary insulating shell would be of such size and so located as to leave clear annular spaces between its interior surface and the shell l and between its exterior surface and the vessel l2. These spaces may be open at both ends to maintain pressure balance between the interior and exterior surfaces of both shells. A secondary in suiating shell may also be used in an embodiment such as'is shown in Figure 2. In this case both the space between the insulating shells and the space between the outer shell and the vessel i2 may be independently sealed off and each space provided with a separate pressure balancing means such, for example, as that shown Fig ure 2. Alternatively, one such space may be open as in the embodiment of Figure l, and. the second scaled up and provided with external meansfor balancing pressure as in Fig. 2.

111 a compound. embodiment of our invention. permitting theme of three phase power in a unit apparatus, we provide three adjoining insulating shells withina single pressure vessel. Each insulating shell is provided with grounded electrodes adjacent its ends and a high tension electrode within-theshell. lEach high tension electrode is separately supported .in :some manner, such ,as is shown in Figure 1, and together they furnish three connections external of the pressure vessel to which connections may be fastened the three wires of a three phase power source, thus providing a unit apparatus for use with three phase power. In this construction, we space the three insulating shells slightly apart from one another and from the interior wall of the pressure vessel to create, as before, a space around the shells in which to maintain a pressure balancing the fluid pressure within the shells. The balancing pressure may in this instance also be had either by providing for free access of the liquid flowing through the shells to the space between them, or by sealing off the ends of the space around the shells and providing to the space so isolated balancing pressure from an external source.

The apparatus of our invention when used to provide heat for the evaporation of waste sulphite liquor may suitably be set up as shown in Figures 3 and 4. In Figure 3 we show in elevation and in Figure 4 in plan view, three heating units 31, 3| and 3|" such as are described in the foregoing, together with the associated equipment required to efiect the desired evaporation. The dilute liquor to be evaporated enters the system by the pipe 32, passing through the feed control valve 33 and joining a circulating stream of concentrated liquor in the pipe 34 leading to the pump 35. From the pump 35 the liquor is forced through the control valve 36 into the distributor fitting 31 where the stream is split into three equal equal parts, one part flowing to each of the heaters 3!, 3i and 3!" by the heater inlet pipes 38, 3B and 38". In its flow through the heaters the liquor is heated by passage of current through it between the electrodes, current being supplied to the centre electrode of each heater from a source of three phase power, as indicated at 45. The heated liquor leaves the heaters by way of the pressure reducing valves 39, 39' and 39" and enters the steam separating chamber 40 by the tangential entry pipes 4|, 4| and 4!". The centrifugal, swirling action set up by the tangential entry of the liquor into the chamber 40 effects eflicient separation of steam which is removed through the pipe 42. The residual liquor returns to the lower part of the chamber 46 for further recycling. The pipe 43 and valve 44 permit and control removal of the concentrated liquor product from the circulating stream. The pressure reducing valves 39, 39 and 39" maintain a pressure in the heaters 3|, 3| and 3! in excess of the pressure in the chamber 40, permitting the liquor to absorb the electrically generated heat as sensible heat from which steam will be evolved in consequence of the pressure drop on passing through the pressure reducing valves 39, 39 and 39".

The electrical heating apparatus of our invention is not restricted to applications where evaporation is an object but may as readily be used Where heating alone is desired. Such heating may be obtained in any desired degree by a single pass through the heater of the fluid to be heated or in multiple passes as may be most convenient.

We claim:

1. In an electrical conductance heater the combination comprising an elongated cylindrical pressure vessel mounted vertically having an inlet near the bottom and an exit near the top, a ceramic electrical insulating shell with open ends mounted coaxially within said pressure vessel so as to provide a space between the walls of said pressure vessel and said shell and so as to provide open communicating channels between said space and the open ends of said shell so that liquid entering said pressure vessel and flowing through said shell is free to enter and circulate through said space, grounded electrodes positioned adjacent to both of the open ends of said shell, a high tension electrode positioned within said shell and between said grounded electrodes, and an insulated electric conductor attached to said high tension electrode and extending through the upper end of said shell and thence through the casing of said pressure vessel to a terminal connection for high tension electric current.

2. In an electrical conductance heater or" the character described the combination comprising an electrical insulating shell having openings for inflow and outflow of the liquid to be heated, grounded electrodes adjacent said openings, a high tension electrode between said grounded electrodes and within said shell, a pressure vessel enclosing said shell in such relationship thereto as to provide between the inner surface of said pressure vessel and the outer surface of said shell a space in which a fluid pressure may be maintained to substantially balance the fluid pressure within said shell, and means to provide a balancing fluid pressure within said space.

3. In an electrical conductance heater of the character described the combination comprising an electrical insulating shell having openings for inflow and outflow of the liquid to be heated, grounded electrodes adjacent said openings, a high tension electrode between said grounded electrodes and within said shell, a pressure vessel enclosing said shell in such relationship thereto as to provide a space between the inner surface of said pressure vessel and the outer surface of said shell, and a channel providing access to said space for liquid flowing through said shell whereby the pressures inside and outside said shell are maintained substantially in balance.

4. In an electrical conductance heater of the character described the combination comprising an electrical insulating shell having openings for inflow and outflow of the liquid to be heated, grounded electrodes adjacent said openings, a high tension electrode between said grounded electrodes and within said shell, a pressure vessel enclosing said shell in such relationship thereto as to provide a space between the inner surface of said pressure vessel and the outer surface of said shell, sealing means to substantially isolate said space from the interior of said shell, and means for furnishing to said space fluid under a pressure substantially balancing the pressure within the shell.

5. In an electrical conductance heater of the character described the combination comprising an electrical insulating shell having openings for inflow and outflow of the liquid to be heated, grounded electrodes adjacent said openings, a high tension electrode between said grounded electrodes and within said shell, 2. pressure vessel enclosing said shell in such relationship there to as to provide a space between the inner surface of said vessel and the outer surface of said shell, sealing means to substantially isolate said space from the interior of said shell, a bellows and a conduit connecting said space and said bellows, a pressure chamber enclosing said bellows and a conduit through which the fluid pressures Within said chamber and within said shell may freely balance.

6. In an electrical conductance heater or the character described the combination comprising a cylindrical pressure vessel, an imperiorate annular ledge within said vessel, a cylindrical electrical insulating shell having an outside diameter substantially less than the inside diameter of said vessel, said shell being coaxial with said vessel and having its lower rim supported on said ledge in such a way as to substantially seal off across its lower rim the inside from the outside of said shell, sealing means adjacent the upper rim of said shell to isolate the space between said vessel and said shell from the [interior of said shell, said sealing means being i adapted to permit differential axial thermal expansion of said vessel and said shell, a grounded electrode adjacent each end rim of said shell, a

high tension electrode between said grounded 8 electrodes and within said shell and means for furnishing to the space confined between said vessel and said shell fluid pressure substantially balancing the pressure within said shell.

LAURENCE R. BEATI-I. HAROLD S. HILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,977,232 Ginder Oct. 16, 1934 1,993,843 Kaelin Mar. 12, 1935 2,404,336 Wicks July 16, 1946

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