RU2462497C2 - Heat-retaining composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: heat-retaining composition contains 16-18 wt % lithium fluoride and 82-84 wt % potassium molybdate. The disclosed composition ensures operating capacity in a heat accumulator in the temperature range 674-700°C with specific enthalpy of fusion of 302-310 kJ/kg, which is 64-72 kJ/kg higher than the closest counterpart.

EFFECT: high operating capacity.

1 tbl, 3 ex

Description

The invention relates to the field of power engineering, in particular to the development of heat storage compositions, including halides and molybdates of alkaline elements.

Heat storage compositions are known: the first includes an individual substance - potassium molybdate, however, the working temperature of the composition is 926 ° C and the relatively low specific melting enthalpy is 163 kJ / kg (Thermal constants of substances. Edited by Glushko V.P. Issue X, part 2 M.: VINITI, 1981. - 441 p.); the second includes an individual substance - lithium fluoride, however, this substance with a relatively high enthalpy of melting of 1043 kJ / kg (Thermal constants of substances. Edited by Glushko V.P. Issue X, part 1. M .: VINITI, 1981. - 300 C.) provides a working temperature at 849 ° C.

Also known is a composition containing potassium bromide and molybdate (Verdiev N.N. et al. Bulletin of Moscow University. Series 2. Chemistry. - 2009, vol. 50, issue 2, pp. 138-144). However, this composition ensures the operation of the heat accumulator at 625 ° C and has a specific melting enthalpy of 90.5 kJ / kg.

Closest to the claimed composition in temperature and components is the low-melting composition of the LiF-Li ₂ MoO _{4 system} (Handbook on the fusibility of salt systems. - Ed. By Voskresenskaya N.K. M.-L .: Publishing House of the USSR Academy of Sciences, 1961, t .1, p. 707). The enthalpy of melting at an operating temperature of 617 ° C is 238 kJ / kg.

The technical result of the present invention is to ensure the health of the composition in the temperature range 674-700 ° C and increase the specific enthalpy of melting.

The novelty of the claimed composition compared to the known one lies in the fact that the heat storage composition containing lithium fluoride and alkali element molybdate contains potassium salt as molybdate in the following ratio, wt.%:

lithium fluoride 16 ... 18

potassium molybdate 82 ... 84

Examples of specific performance

Example 1

In a shaft-type electric furnace, anhydrous salts of the qualification “hch” (LiF) and “chda” (K ₂ MoO ₄ ) are melted 0.16 g (16.0 wt.%) Lithium fluoride +0.84 g (84.0 wt.%) Potassium molybdate.

The melting point of the mixture is 695 ° C.

The specific melting enthalpy was calculated by the formula:

, кДж/кг,

kJ / kg

where Δ _t H _et 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 differential curves corresponding to 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. Na ₂ MoO ₄ (melting point 645 ° C, specific enthalpy of melting 95.5 kJ / kg) was taken as a reference substance.

The specific enthalpy of the composition is 310 kJ / kg.

Example 2

In the conditions of example 1, the anhydrous salts of the qualification “hch” (LiF) and “chda” (K ₂ MoO ₄ ) are melted - 0.171 g (17.1 wt.%) Lithium fluoride +0.829 g (82.9 wt.%) Potassium molybdate.

The melting point of the mixture is 674 ° C. The specific enthalpy of melting is 307 kJ / kg.

Example 3

Under the conditions of Example 1, anhydrous salts of the qualification “hch” (LiF) and “chda” (K ₂ MoO ₄ ) are smelted - 0.18 g (18.0 wt.%) Lithium fluoride +0.82 g (82.0 wt.%) Potassium molybdate.

The melting point of the mixture is 700 ° C. The specific enthalpy of melting is 302 kJ / kg.

Compositions 1 ... 3 with inseparable thermal effects on the cooling curves were obtained by studying the fusibility diagram of the system using differential thermal analysis (Fig. 1).

Beyond the claimed limits, the single-phase composition is violated, which leads to uneven heat generation.

The table shows the comparative characteristics of the properties of the claimed composition and composition, selected as a prototype.

Compositions The composition of the mixture, wt.% Specific enthalpy of melting, kJ / kg Melting point, ° С LiF Li ₂ MoO ₄ K ₂ MoO ₄ Prototype 8.4 91.6 - 238 609 Proposed one 16.0 - 84.0 310 695 2 17.1 - 82.9 307 674 3 18.0 - 82.0 302 700

As can be seen from the table, the proposed composition ensures operability in a heat accumulator in the temperature range of 674-700 ° C with a specific melting enthalpy of 302-310 kJ / kg, which is 64-72 kJ / kg higher compared to the prototype.

Claims (1)

A heat storage composition comprising lithium fluoride and an alkali element molybdate, characterized in that it contains potassium molybdate as the alkali element molybdate in the following ratio, wt.%:
lithium fluoride 16-18 potassium molybdate 82-84

Images