US1984369A - Heat carrier for high temperatures - Google Patents

Description

Patented Dec. 18, 1934 HEAT CARRIER FOR HIGH TEMPERATURES Karl Gensch, Berlin, Germany, assignor to Gesellschaft fiir Drucktranslormatoren (Koenemann-Transformatoren) G. m. b. 11., Berlin, Germany, a corporation of Germany No Drawing. Application May 24, 1933, Serial No.

672,734. In Austria May 30, 1932 m.

8 Claims.

The invention relates to a heat carrier for high temperatures for indirectly heated plants. While I prefer the illustrative salt melt embodiments disclosed herein, which are particularly desirable because of their cheapness and efiectiveness, my invention contemplates, and my preferred embodiments are illustrative of, such like substances as will be suggested to the skilled chemist by my present specification. A salt melt consisting of zinc chloride and several other metal chlorides which form double salts with zinc chloride, was found to suit very well the aforesaid purpose.

Chiefiy a melt is used which contains approximately zinc chloride, 10% sodium chloride, and 15% potassium chloride. This melt has all properties which are required from such a heat carrier, e. g. low melting point, high boiling point, good heat transfer, low viscosity, high specific heat, low specific weight; and last but not least it is very cheap. Besides it does not attack iron, is not combustible, not explosive, and does not form any explosive mixtures with other substances. The composition being as stated above, the melting point ranges approximately at 180 centigrade. If the melting point is desired to be lower, it can be reduced to approximately 140 centigrade by adding other salts such as lithium chloride and ferric chloride. Compared to other heat carriers known so far, the above heat carrier offers the following advantages.

It is much cheaper than any metal melt. Metals with low melting point, such as mercury or bismuth alloys, cost approximately from ten to twenty Reichsmarks per kilogram. Their specific weight amounts approximately from 10 to 13. The chloride melt can be supplied at a price of one half Reichsmark per kilogram and has a specific weight of approximately 2. The metallic filling of an apparatus would cost approximately -260 times as much. Even if comparatively cheap metals, such as lead and zinc, are used, the filling'still would cost approximatly fouftimes as much. Now, the melting point of these metals ranges above 300 centigrade, and this 'fact renders operation conditions so difiicult that these metals can not be used. Also the high coefficient of expansion and the good conduction of heat of the metals in the solid state are of disadvantage. When the solid metals are heated they expand very much before getting liquid; consequently, the apparatuses are stressed to such an extent that they are liable to burst. Furthermore, the high specific weight of the metals has the disadvantage that if a high apparatus is used the lower parts of it are subjected to a considerably high hydrostatic pressure. Finally, several metal melts, e. g. molten zinc, attack iron very much.

Oils having high boiling points, and other organic liquids, e. g. diphenyl oxide, can not be 5 used at temperatures over 400 centigrade. Up to the present no organic liquids are known which are stable above this temperature. They decompose, incrust the heating surface, especially in the highly loaded tubes, and then these tubes 10 burn through.

Compared to other salt melts, the above heat carrier has the special advantage that it is very cheap. Zinc chloride, sodium chloride, and potassium chloride are by-products of very low price. Further the above heat carrier has such a low melting point that it can be melted by heating it by steam of customary pressure, e. g. 15 atmospheres. Besides it contains neither water nor oxygen; therefore it does not attack iron 20 even at high temperatures and cannot form any explosive mixtures with other substances, e. g. with coal, as is the case with nitrate melts.

The above heat carrier can be used especially in the chemical industry and in the oil industry, 25 in other words everywhere where heating at high temperatures is involved, and where the products,

e. g. oil or other substances very sensitive to high temperatures, have to be treated as gently as possible. 30

In the field of generation of high pressure steam, indirect heating by means of the above heat carrier offers great advantages. Under" these conditions, the feed water treatment is not such an important factor because scale incrustations can only result in reducing the heat transfer, in other words in a decrease of efliciency; but never can they result in boiler explosions.

I claim:

1. An indirect heating system employing as the heat carrying medium a molten mixture of metal chlorides, predominantly consisting of chloride of zinc, and including substantial quantities of metal chlorides of the class consisting of alkali metal chlorides and chlorides having sim- "ilar effect in the molten mixture, the medium thus constituted having a melting point substantially below that of chloride of zinc.

2. An indirect heating system employing as the heat carrying medium a molten mixture of chloa ride of zinc and other metal chlorides forming with chloride of zinc double salts existing in the molten mixture, the medium thus constituted having a melting point substantially below that of chloride of zinc. 55

3. An indirect heating system employing as the heat carrying medium a molten mixture approximately '75% chloride of zinc, 15% chloride of potassium and 10% chloride of sodium.

5 4. An indirect heating system employing as the heat carrying medium a molten mixture of approximately '75% chloride of zinc, 12% chloride of potassium, 8% chloride of sodium, 5% chloride of lithium and 5% chloride of iron,

5. An indirect heating system employing as the heat carrying medium a molten mixture preponderantly chloride of zinc, and containing sufficient alkali metal chloride to impart to the mixture a melting point materi allynbglc w that of chloride of zinc. F m

\- 6:"An'indirectheating system employing as the heat carrying medium a molten mixture comprising preponderantly chloride of zinc, and containing sufficient metal halide of the class consisting of potassium-, sodium-, lithium-, and

iron-chloride to impart to the mixture a melting point materially below that of the preponderant metal halide.

'7. An indirect heating system employing as the heat carrying medium a molten mixture comprising preponderantly chloride of zinc, which is a halide of a weak negative, acid forming metal, and sufiicient halides of the class consisting of NaCl, KCl and LiCl, which are halides of strong positive, base forming metals, to impart to the mixture a melting point materially below that of the preponderant metal halide.

8. An indirect heating system employing as the heat carrying medium a molten mixture comprising preponderantly chloride of zinc, which is a halide of a weak negative, acid forming metal, having incorporated therewith at least one of the halides of the class consisting of NaCl, KCl or LiCl, which are halides of strong positive base forming metals, characterized in that one or more of the incorporated latter halides forms with the preponderant halide a double salt existing in the molten state, and further characterized in that the quantity of these latter halides present is sufiicient to impart to the mixture a melting point materially below that of the preponderant metal halide.

KARL GEN'SCH.