RU2478115C1 - Heat-retaining composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: described is a heat-retaining composition which contains a fluoride, a bromide or a salt of lithium, the lithium salt used being lithium chromate, with the following ratio of components, wt %: lithium fluoride 1.0…1.4 lithium bromide 42.7…44.7 lithium chromate 54.3…56.3.

EFFECT: enabling use of the composition in a heat accumulator and high specific enthalpy.

1 tbl, 4 ex

Description

The invention relates to the development of compositions comprising fluorides, bromides and chromates of alkaline elements, which are used as heat storage substances.

Known heat storage composition containing bromide, chloride and lithium molybdate with a melting point of a mixture of 444 ° C (Frolov E.I., Gubanova T.V., Garkushin I.K. Model for choosing the composition of three-component systems from lithium salts and their research for further use eutectic compositions of these systems as electrolytes of chemical current sources and heat storage materials. In the book: Dokl. X Int. Conf. "Physicochemical Processes in Inorganic Materials" KemSU. October 10-12 in 2 volumes. Kemerovo: Kuzbasvuzizdat , 2007.v.2, p.188-192). The disadvantage of this composition is to ensure operability at a temperature of 444 ° C and the inability to operate at lower temperatures.

Closest to the claimed composition in temperature and components is the low-melting composition of the LiF-LiBr-Li ₂ MoO _{4 system} (I.K. Garkushin, T.V. Gubanova, E.I. Frolov. Phase equilibria in systems with lithium salts. Yekaterinburg : Ural Branch of the Russian Academy of Sciences, 2010.121 p. ISBN 978-5-7691-2059-6). The melting point of the mixture is 444 ° C and the specific enthalpy of melting is 206 kJ / kg. The disadvantage of this composition is also the provision of operability at a temperature of 444 ° C and the inability to operate at lower temperatures and a low value of specific enthalpy of melting.

The present invention provides the composition as a heat storage material in the temperature range 342 ... 352 ° C.

The novelty of the claimed composition compared to the known ones lies in the fact that the heat storage composition contains fluoride, bromide and another lithium salt, where lithium chromate in the following ratio of components, wt.%: Was taken as a lithium compound to achieve an increase in specific melting enthalpy

Lithium fluoride 1.0 ... 1.4 Lithium bromide 42.7 ... 44.7 Lithium chromate 54.3 ... 56.3

Examples of specific performance.

Example 1

In a shaft-type electric furnace, anhydrous salts of the “hch” qualification (LiBr, Li ₂ CrO ₄ ), “chda” (LiF), 0.010 g (1.0 wt.%) Lithium fluoride + 0.447 g (44.7 wt.%) Lithium bromide + 0.543 are melted g (54.3 wt.%) lithium chromate. The melting point of the mixture is 352 ° C.

The specific melting enthalpy was calculated by the formula:

where Δ _t H _E is the specific enthalpy of the phase transition of a substance close in phase transition temperature to the composition under study, kJ / kg; S _E , S _et - peak areas of the differential curves corresponding to the melting of the eutectic composition and phase transition of the reference substance, respectively; T _E , T _et are the melting points of the eutectic composition and phase transition of the reference substance, respectively, K. The final enthalpy was found as the average of three measurements. Sodium nitrate was taken as a reference substance (melting point 306 ° C, specific melting enthalpy of 150 kJ / kg).

The specific melting enthalpy of the composition is 326 kJ / kg.

Example 2

In the conditions of example 1, anhydrous salts of the qualification “hch” (LiBr, Li ₂ CrO ₄ ), “chda” (LiF), 0.010 g (1.0 wt.%) Lithium fluoride + 0.553 g (55.3 wt.%) Lithium bromide are remelted + 0.437 g (43.7 wt.%) lithium chromate. The melting point of the mixture is 342 ° C. The specific enthalpy of melting is 310 kJ / kg.

Example 3

In the conditions of example 1, anhydrous salts of the qualification “hch” (LiBr, Li ₂ CrO ₄ ), “chda” (LiF), 0.014 g (1.4 wt.%) Lithium fluoride + 0.430 g (43.0 wt.%) Lithium bromide are re-melted + 0.556 g (55.6 wt.%) lithium chromate. The melting point of the mixture is 349 ° C. Specific melting enthalpy of 308 kJ / kg.

Example 4

In the conditions of example 1, the anhydrous salts of the qualification “hch” (LiBr, Li ₂ CrO ₄ ), “chda” (LiF), 0.010 g (1.0 wt.%) Lithium fluoride + 0.427 g (42.7 wt.%) Lithium bromide are smelted + 0.563 g (56.3 wt.%) lithium chromate. The melting point of the mixture is 346 ° C. The specific enthalpy of melting is 313 kJ / kg.

Beyond the indicated concentration limits, the compositions are non-phase, as a result of which the heat release becomes non-uniform.

The table shows the comparative characteristics of the physico-chemical properties of the proposed composition and the composition selected as a prototype.

Compositions The composition of the mixture, wt.% Melting point, ° C Specific enthalpy of melting, J / g LiF LiBr Li ₂ CrO ₄ Li ₂ MoO ₄ Prototype 5.5 73 - 21.5 444 206 Proposed one one 44.7 54.3 - 352 326 2 one 55.3 43.7 - 342 310 3 1.4 43 55.6 - 349 308 four one 42.7 56.3 - 346 313

From the results of the table it can be seen that the proposed composition ensures operability in a heat accumulator in the temperature range 342-352 ° C with a specific melting enthalpy of 308 ... 326 J / g, which is 136 ... 146 kJ / kg higher compared to the prototype.

Claims (1)

The heat storage composition, including fluoride, bromide and lithium salt, characterized in that its chromate is introduced as a lithium salt in the following ratio of components, wt.%:
Lithium fluoride 1,0 ... 1,4 Lithium bromide 42.7 ... 44.7 Lithium chromate 54.3 ... 56.3