US2571462A - Electric steam generator - Google Patents

Description

Oct. 16, 1951 w LOHMAN 2,571,462

ELECTRIC STEAM GENERATOR Filed Jan. 10, 1949 2 Sheets-Sheet l INVENTOR. RALPH W LOHMAN ATTOR N EY R. W. LOHMAN ELECTRIC STEAM GENERATOR Oct. 16, 195] 2 Sheets-Sheet 2 Filed Jan. 10, 1949 RALPH W LOHMAN l I I ATTORNEY IN VEN TOR.

Patented Oct. 16, 1951 UNITED STATES PATENT OFFICE 2 Claims.

Thepresent invention relates to electric liquid heaters or steam generators, and, more specifically, to liquid heaters r steam boilers of the resistance-heating type in which the heating element includes a conductor of suitable resistance located within the heater or boiler, in distinction to the electrode type of heater in which the heating is done by a plurality of electrodes immersed in the liquid.

'In the conventional resistance-heating type of electric heater or boiler, electrical energy is caused to pass through an electrical conductor, 'or"a plurality of conductors within the heating unit, and the heating unit has an outer shell or sheath within which the conductors are contained, the conductors being electrically, and therefore thermally, insulated from the sheath and consequently insulated from the liquid surrounding the sheath.

Conventional resistance-heating units have certain objectionable features. Among these may be mentioned their high first cost, th relatively high space required by such units for a given output, the high temperature of the source of the heat therein, and the extremely high temperature gradient between such source and the sheath about the unit which is caused by the electrical, and therefore thermal, insulation necessarily interposed between such source of heat and the sheath.

A general object of the present invention is to provide an improved resistance-heating unit in which the above objectionable features will be avoided, and which will be of relatively low cost, due to the use of a non-insulated resistanceheating element of new and novel form which is placed in direct contact with the liquid to be heated or vaporized, regardless of whether the liquid is'electrically conducting or is non-conduct- .ing.

A specific object of this invention is to provide an improved steam generator in which the resistance-heatin elements are in direct contact with the liquid and not electrically or thermally insulated therefrom.

Another specific object of this invention is to provide an improved closed pressure vessel in which either electrically conducting or electrically non-conducting liquid may be used.

A further object of this invention is to provide a steam generator with resistance-heating elements of such design that the maximum possible effective heating surface thereof will be presented to the ambient fluid.

Another object of this invention is to provide a steam generator with resistance-heating elements in which the temperature gradient, from the resistance element itself to the ambient liquid, will be very low compared to that of the conventional thermally and electrically insulated resistance-heating unit.

A still further object of this invention is to provide an electric steam generator in which the interior surface of the desired sections of the boiler will be electrically insulated from the boiler liquid, if the liquid is electrically conducting, so that the current will not pass from any part of the un-insulated resistance-heating element radially across the liquid to the boiler shell, thence along the shell, and finally back across the liquid to some other part of the element, but will, for all practical purposes, be confined to the heatin element itself.

These objects and other advantages I attain by including in my electric steam generator, uninsulated, non-sheathed, resistance-heating elements of open-ended tubular form, directly immersed in the boiler liquid, and so constructed and arranged that not only will the boiler liquid have complete contact with both inner and outer surfaces of such heating elements but also that the walls of these elements may be very thin, thus affording the high electrical resistance required and the desired rapidity of thermal response to the amount of electrical energy applied; this being possible because the Walls of such heating ele ments will not be subjected to the external collapsing pressure of the ambient liquid, as is the case with the conventional thick-walled, closed sheath heating units, which contain interiorly located electrically and thermally insulated, heatproducing members. Also, when electricallyconducting boiler liquid is to be used, I apply electrical insulation to the interior surfaces of certain sections of the boiler; as hereinafter described with reference to the accompanying drawmgs.

In the drawings, in which, by way of illustration, a preferred embodiment of my invention is disclosed:

Fig. 1 is a top plan view of a three-phase boiler embodying my invention;

Fig. 2 is an end elevation, taken on line 22 of Fig. l but partly in section;

Fig. 3 is a vertical section through one of the pairs of the flanged fittings illustrating the manner in which various parts of the boiler are connected.

Referring to Figs. 1 and 2, the three-phase boiler illustrated comprises three separate but identical heating sections, one of which is shown in Fig. 2. In the particular boiler which I have illustrated the three heating sections are arranged to extend substantially vertically, although they could also extend obliquely upwardly in the manner of water tubes in other well known types of fuel burning boilers. Each heating section is connected by a tubular, substantially horizontal, steam-separating section 2 to the steam or vapor drum 6. A separate return section 3 connects the lower portion of each heating section with the drum 6.

Since the three heating sections in the boiler illustrated are identical, and since the related steam separating sections and liquid-return sections are identical respectively, it will suifice to describe one heating section with its steam separating section and liquid-return section, illustrated in Fig. 2.

Referring to Fig. 2, the heating section for the boiler comprises a main central tubular metal portion I terminating at each end in an integral flanged fitting 5. A connecting T-shaped upper portion 3| and a similarly shaped lower portion 32 are also formed with corresponding similar flanges 33 at their three terminals.

The central portion l and upper and lower portions 3| and 32 are lined throughout their extent with an insulating lining made of suitable material, for example, a plastic, or ceramic, indicated in general by the reference character it.

While this insulating lining may be formed and mounted in various ways, I consider it preferable to have such lining molded in place within the separate portions of the heating sections and to have this lining extend out over the faces of the flanges 5 and 33, the lining thus forming insulating washers or gaskets between the abutting flanges of the adjacent portions. However, separate insulating gaskets can be substituted for the lining at the flange faces where the flanges come together.

The insulated portions of the steam generator are secured together by means of bolts [8 passing through insulating sleeves I? in the abutting flanges, said bolts 18 being provided with insulating washers [9 under their heads and under their nuts 2! (see Fig. 3).

Thus with each portion of the heating section completely insulated from the adjacent portion, even failure in some part of the insulating lining within one portion of a heating section would nevertheless not result in any electrical current passing from one portion of the heating section to another.

The heating section I is joined to the steamseparating section 2 and to the liquid-return section 3 similarly by means of insulated bolts securing the abutting flanges of the upper portion of the heating sections and steam-separating section together and securing the flanges of the lower portion of the heating section and flanges of the liquid-return section. The steam-separating sections and liquid-return sections for the three heating sections are welded, or otherwise rigidly secured, to the steam drum 6.

A heating element l I is located in each heating section. The heating element extends for the greater part of the length of the heating section and is positioned concentrically with respect to the tubular wall of the heating section. This heating element is an important and novel feature of the heating section of my improved steam generator.

As apparent from Fig. 2, the heating element II is tubular and is open at top and bottom. Not only is the heating element in direct contact with the liquid to be heated, but the element is so mounted that the liquid may circulate freely inside the element as well as outside the element.

Consequently, since the liquid pressures on the inside and on the outside of the element will be equal, no external hydrostatic collapsing pressure can be exerted on such an element and it can, therefore, be made thin enough to afford the high electrical resistance required, and the desired rapidity of thermal response to the amount of electrical energy applied.

The tubular resistance-heating element H is mounted between a pair of perforated terminals l6, located at top and bottom respectively, which permit the ambient liquid in the heating section to,.have free access to and through the interior of the heating element. Each of these perforated terminals [6 is secured to a conductor element 12 which is mounted in and extends through an insulating sleeve or support [3.

Blind flanges 22 and 23 having insulating lining extending over their inner faces, are secured to the-flanged ends at the top of the upper portion of the heating section and at the bottom of the lower portion of the heating section, respectively. The insulating supports [3, carrying the conductors I2, pass through the blind flanges 22 and 23 and are rigidly secured therein by means of clamping nuts l4. Wires from the current supply system are connected to the outer ends of the conductors !2 in any suitable manner, for example, through the intermediary of a termina lug under each of the nuts [5.

The water or other liquid used in my steam generator is maintained at a desired predetermined level by a boiler-water-level controller (not shown) connected with the drum 6. For this purpose any of the commercial boiler-water-level controllers may be used. These are well known in the art and therefore need not be described. The

level of the water or liquid in my steam genera-- tor is thereby maintained at a desired level such as that indicated by the broken line 24 in Fig. 2. The drum 6 also has the usual water-level gauge 34.

From Fig. 2 it will now be apparent that as heat is imparted to the boiler liquid in each heating section, the heated liquid will rise and will flow through a steam-separating section 2 at the level indicated by the broken line 24. Here partial separation of the vapor and liquid will take place, further separation being accomplished by impingement on the baflle plate 35 in the steam drum 6, and by the disengagement therein of the steam from the surface 24 of the liquid. The curved bafiie plate 35, preferably extends throughout the greater portion of the length of the drum 6 but is open at the ends to permit the steam to escape freely around the ends. The steam collected in the drum may be taken therefrom in any convenient outlet pipe such as the outlet pipe 36.

When my invention is embodied in a threephase electric steam generator or boiler, as illustrated in the drawings, the current supply wires A, B, and C of the three-phase system are connected respectively to the three heating elements, for example, at the top terminals. The opposite terminals of the three heating elements will then be connected to a common neutral point.

Assuming that water or other electricallyconducting liquid is used in my steam generator, it will be evident, since there will be a difference of potential between the two terminals of each heating element, that if there were no insulating lining in the heating sections, an undesirable current flow would take place from the liquid near one end of each heating element to the surrounding metal wall, thence longitudinally along the wall to the liquid near the other end of the same heating element and thence radially inward to such element end. However, the insulation which I provide in my heating sections prevents such current flow, and the only remaining leakage path will be that longitudinally alon the water column in the heating section from the vicinity of one end of the heating element to the vicinity of the opposite end of the heating element in each heating section.

However, one of the novel features of the present invention is that the resistance of the above leakage path, axially along the water column can be made such that the resulting current therethrough will be negligible, compared to the current through the heating element. This may be accomplished in the following manner.

Assuming for example a 440 volt, 80 ampere, 3 phase 60 kw. boiler, the required resistance per leg of a heater element would be about 3.2 ohms. Now, as before stated, available boiler waters will be found to have resistivities, at 100 C. varying from that of certain waters in the Northwest of 4000 ohms per inch cube, to 500 ohms per inch cube in certain parts of the East. Assuming the latter as the more favorable for high leakage, a length of heating element of 36 inches, and consequently a water-leakage path of about the same length, and restricting the diameter of the leakage path to that of the inside diameter of a 1% inch pipe, the resistance of such leakage path (inside and outside of the hollow heating element) would be where whence =9000 ohms compared to 3.2 ohms of the heatin element, or 9000/32, or 2800 times that of the latter, with the correspondingly negligible current through the water column of about 0.028 ampere, compared to the 80 amperes through the heating element.

The above illustrates the operation of the boiler with an electrically-conducting boiler liquid. If an electrically-non-conducting boiler liquid is employed, of which there are a number on the market, one, for example, known as orthodichlorobenzene, having a boiling point of 355 F. at atmospheric pressure, or 450 F. at 35 lbs. gage pressure, the insulating lining and insulating flanges could be omitted, and the boiler could be operated with the above described heating elements as a source of high temperature vapor or liquid, either or both of which could be taken from the steam drum 6 at appropriate points and returned to the boiler after passage through tire molds,-

plastics presses, process kettles or other apparatus which it is desired to heat.

A pressure switch (not shown) is connected to drum 6 and operates through a relay and circuit breaker, in the well known manner, to open the power supply circuit to the boiler when the pressure therein exceeds a predetermined value, and to close said circuit when the pressure falls below said value.

Although I have described and illustrated my invention as employed or embodied in a particular steam generator, namely three-phase water tube pressure vessel, many modifications might be made in the device which I have illustrated and described within the scope of my invention.

I claim:

1. In an electric boiler, a plurality of tubular upwardly-extending heating sections, an insulating lining covering the entire interior surface of each heating section, a single, integral, tubular, open-ended, resistance-heating element positioned in axial alignment within each heating section, means for mounting the ends of said element within and near the ends of the heating section respectively, said mounting means providing ports within the heating section for the free passage of liquid from the heating section into each end of said element, whereby liquid in the heating section will have unrestricted contact with the inner and outer surfaces of said element, an electrical conductor at each end of the heating section connected with the respective mounting means and respective end of said element and having a terminal on the outside of the heating section, a vapor drum, a connection, insulated on its interior surface, leading from the upper end of each of said heating sections to said drum, and similar insulated connections leading from said drum to the lower ends of said heating sections respectively.

2. A three-phase electric steam generator of the character described including three tubular upwardly-extending heating sections, an insulating lining covering the entire interior surface of each heating section, a single, integral, tubular, open-ended, resistance-heating element positioned in axial alignment within each heating section, means for mounting the ends of said element within and near the ends of the heating section respectively, said mounting means providing ports within the heating section for the free passage of liquid from the heating section into each end of said element, whereby liquid in the heating section will have unrestricted contact with the inner and outer surfaces of said element, an electrical conductor at each end of the heating section connected with the respective mounting means and respective end of said element and having a terminal on the outside of the heating section, the current supply wires of a three-phase system connected to the outside terminals of said conductor at an end of each of said heating sections respectively, the opposite terminals of said heating sections connected to a common neutral point, a steam drum, a connection, insulatedon its interior surface, leading from the upper end of each of said three heating sections to said drum, and similar insulated connections leading from said drum to the lower ends of said heating sections respectively.

RALPH W. LOHMAN.

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

UNITED STATES PATENTS Number Name Date 1,072,748 McElroy Sept. 9, 1913 1,197,552 Shoenberg Sept. 5, 1916 1,599,544 Reed Sept. 14, 1926 1,727,585 Carleton Sept. 10, 1929 1,983,649 Welter Dec. 11, 1934

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