US1942382A - Electrically heated apparatus - Google Patents

Description

Jan. 2, 1934. E. c. BRITTON 1,942,382

ELECTRICALLY HEATED APPARATUS Filed Oct. 25, 1929 Fig.4

a a O INVENTOR ATTORNEY Patented Jan. 2, 1934 ELECTRICALLY HEATED APPARATUS Edgar C. Britton, Midland, Mich., assignor to The Dow Chemical Company, Midland, Micl1., a corporation of Michigan Application October 23, 1929. Serial No. 401,744

4 Claims. (01. 21938) The heating of various types of apparatus, such for instance, as stills, evaporators, reactors, tubes and the like has been commonly accomplished by the use of a jacket or bank of tubes through 5 which steam or other heating fluid could be passed. In some cases where conditions required it or electric current was sufficiently cheap, are, grid or space heaters of. the conventional type have been used. The use of electric heaters of these types for many purposes has been found cumbersome and often relatively inefficient. I have discovered, however, that for many purposes electric heating may be accomplished in convenient and efiicient manner by embedding the resistor of electricity in a suitable material applied directly to the apparatus to be heated. Such material when used in this manner has preferably the property of hardening or drying after application in the plastic condition and at the same time has satisfactory. dielectric and heat conducting properties.

Among the objects of the present invention is accordingly the provision of a relatively simple and economical method of electrically heating various types of apparatus characterized by having the heating element embedded in a suitable dielectric and heat conducting material. Other objects and advantages of the invention will appear as the description proceeds.

3 i To the accomplishment of the foregoing and related ends, the invention, then, consists of the steps and means hereinafter fully described and particularly pointed out in the claims, the annexed drawing and the following description setting forth in detail certain means and modes of carrying out the invention, such disclosed means and modes illustrating, however, but several of the various ways in which the principle of the invention may be used.

In said annexed drawing:

Fig. 1 shows in partial section one typeof apparatus utilizing the invention; Figs. 2 and 3 illustrate two forms of spacers for the resistor; Fig. 4 shows a portion of Fig. l on enlarged scale.

The present invention is in general concerned with a method of heating various types of apparatus, such as stills, evaporators, reactors, tubes and the like, such heating being accomplished by embedding a suitable resistance material, for instance nichrome wire, in a material such as alundum cement that can be applied in plastic form to the apparatus and subsequently hardened or dried so as to retain its shape and hold the resistance element in proper position. The entire '55 apparatus following such assembly will be preferably insulated against heat loss in manner well known to the art.

Referring more particularly to the drawing, 1 is a cone bottom type still, shown in conventional manner and partially cross sectioned. Welded my to the outer surface of said still is a series of angles 2 placed in circumferential manner, so as to divide its surface into convenient belt-like areas for the application to each of a heating unit. Each such heating unit is composed of a 5, resistor 3 having leads from its free ends 9 and. middle point 10, such resistor being in the form of a wire or band wound spirally in the belt area it serves, and being embedded in a material 4 that may be applied in plastic'form and have satisfactory hardening, dielectric, and heat conducting properties. To assemble the heating unit a thin coat of material 4, for instance alundum cement, is applied directly to the still and dried either by heating the inner surface of the still 7 or by external heating. When this-layer is dry, a second layer may be placed thereon, and dried in like manner; such application being repeated until the coating has a sufficient thickness, a half inch or more having been found satisfactory. The resistor 3, which as stated may be made in wire form and preferably made'from a material such as nichrome, or other suitable metal or alloy, may then be wound around the still over the layer of dried alundum cement. To prevent adjacent turns of the resistor from coming in contact with each other, the windingmay be accomplished by winding therewith and in parallel thereto a spacer cable or cord which may be unwound after the heating element has been completely Wound and fastened in place by anchoring ends 9. A thin coat of alundum cement is then plastered over the so-assembled resistance heating element and dried. The drying of this layer and subsequent layers, may, if desired, be 5 accomplished by heating with the embedded resistor 3. One or more layers of alundum cement may then be added and dried so as to cover resistor 3 to a depth of approximately a half inch or more. This will bring the assembly of cement and resistor to a thickness approximately the height of the circumferentially placed angles which I normally prefer to use in one inch size. In order to prevent the alundum cement from flaking or chipping off from heat while in use, I prefer to cover it with a sheet metal jacket 5, whichmay be wrapped thereabout in circumferential manner and drawn up along a line which preferably includes the resistor leads which may be insulated. Such leads may be anchored 1'10 to insulators attached to the still or anchored in the cement. The exact manner of attaching or anchoring the resistor during the application of the cement or other coating and the manner of insulating the leads are immaterial to the invention, since such details of connection are variable with the type, shape or other characteristics of the apparatus. The three point connection described above is well known to the art and can be utilized to provide low, intermediate and high heat for each section. Having brought out all the leads with insulators thereon in a relatively straight line, a piece of insulating material, such as transite board may be placed on either side thereof to form an outlet block which by means of suitable bolts may be drawn tightly into place. The sheet metal jacket, in like manner, may be tightened in place by bolts passing through this outlet block. However, prior to fastening the jacket in place, I prefer to make a thin paste of alundum cement and apply the same to the outer coat of the previously dried assembly. This permits the so applied cement to flow when the jacket is tightened and thus eliminate high and low spots on the so assembled heating unit. Where the bottom of the still or apparatus to be heated is rounded or of cone shape as shown in Fig. l, I prefer to use in spaced manner several notched pieces 6 of insulation material (Fig. 3), for holding resistor 3 in place during and after winding. In some cases instead of using notched piece 6, a similar piece 7 may be used, such piece having drilled or punched holes 8 through which the heating element or resistor wire 3 may be threaded, such drilled piece 7 being used in equivalent manner to notched piece 6 described above. The use of notched or drilled pieces 6 or 7 is not limited to being used on the bottom of a still or the like but is applicable to use on the sides thereof for spacing the heating element or resistor wire, for instance, in similar manner to a spacer cable or cord. After completing the assembly or embedding of the resistor 3 in alundum cement covering 4, all of which is held in place by means of sheet metal jacket 5, the whole may be covered with a substantial layer of heat insulation. As such insulating material I prefer one of the magnesia type, which may be conveniently obtained in a block form. Part of the apparatus, however, may be preferably insulated by applying the magnesia in plastic form, such being particualrly desirable where the portions of the apparatus are so curved or are of a form hard to fit with standard block type insulation. However, other type of heat insulation, such as fire-brick and the like may be used, depending, of course, upon the conditions to be met with. It is to be noted, however, that regardless of the type insulation used, it is preferably placed on the still or o her apparatus in belts or other areas corresponding to the heating unit covered. Such arrangement of the insulation will permit the replacement of burned out heating units without disturbing the insulation placed over adjacent heating units. To facilitate the placing of the insulation in sectional or group manner on the still it may be preferable in some cases to use angles 2 having the projecting edge thereof extending to or near the outer surface of the heat insulating layer.

Among the numerous advantages of placing the heating elements on the still or other apparatus in sectional form is that any number of the units may be turned on to meet the conditions at hand. Where liquid containing materials are being subjected to evaporation or distillation, it is ordinarily preferable for economical operation to apply the heat to the liquid below its upper surface. The use of sectional heaters of the type described permits such heating to be readily accomplished. In case the so evolved vapors were to be decomposed or cracked, still further heating units could be utilized to accomplish such end.

The term heat conducting dielectric material as described above and used in the appended claims is intended to cover all those materials which have a heat conductivity and dielectric strength suflicient to enable their economic use for the purpose described.

While I have described my invention in terms of coating the apparatus with alundum cement I do not wish to be limited to that particular material, as I have found that among other materials magnesium oxide mixed with a water solution of sodium silicate may be satisfactorily used in like manner. I further do not wish to be limited to the placing of more than one layer of plastic material on the apparatus, or the manner of its application as long as the heating element is embedded therein. The heating element further need not be wound about the still or other apparatus but may be placed thereon in sectional units or in any other manner suitable for the purpose at hand.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the means and steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:---

1. In an apparatus capable of being electrically heated, comprising a container for a material to be heated, a plurality of layers of suitable heat conducting dielectric material placed edge to edge thereon and each layer having embedded therein but out of contact with said container a resistor element.

2. In an apparatus capable of being electrically heated, comprising a container for a material to be heated, a plurality of layers of suitable heat conducting dielectric material placed edge to edge thereon and each layer having embedded therein but out of contact with said container a resistor element, a heat insulating jacket covering said layers, and means to connect said heating elements to a source of power.

3. In an apparatus capable of being electrically heated, comprising a container for a material to be heated, a plurality of layers 01. alundum cement placed edge to edge thereon and each layer having embedded therein but out of contact with said container a nichrome wire heating element.

4. In an apparatus capable of being electrically heated, comprising a container for a material to be heated, a plurality of layers of alundum cement placed edge to edge thereon and each layer having embedded therein but out of contact with said container a nichrome wire heating element, a heat insulating jacket covering said layers, and means to connect said heating elements to a source of power.

EDGAR C. BRI'I'ION.

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