doi: 10.3850/978-981-08-7614-2_IMPRES032

ABSTRACT

Heat pumps type II can be used for upgrading industrial waste heat to above pinch temperatures with a typical lift from 130°C to 180°C. At ECN such a heat pump is developed based on the reaction of ammonia with lithium chloride and magnesium chloride as respectively the low and high temperature salt. The thermodynamic properties of these salts are required to determine temperature lift and coefficient of performance. This paper presents the behavior of the low temperature salt, lithium chloride, under typical working conditions with temperatures ranging from ambient to 150°C and ammonia pressures ranging from 0.3 to 30 bars. Measurements using a HPDSC, an autoclave and a custom-made ammonia pressure cell have been conducted to determine the pressure-temperature lines and their corresponding enthalpy and entropy values for lithium chloride ammonia complexes. The results show a direct transformation of lithium chloride mono-ammonia to lithium chloride tri-ammonia complex for ammonia pressures up to 4 bars and temperatures up to 90°C. At higher temperatures and pressures a stable, intermediate ammonia complex, lithium chloride di-ammonia complex, is formed. Under these conditions also a liquid phase has been observed. The latter can greatly affect the heat pump performance, both positive (no lattice degradation) as negative (escape from matrix, form impenetrable film).

Keywords: Adsorption, Ammonia, Thermodynamic analysis, Lithium chloride

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