Ammonia sorption thermal battery with water-loaded sorbent driven by low-temperature heat source

Sorption thermal batteries are systems that can store heat for a long period without heat loss through the reaction of the gas and adsorbent. However, a sorption thermal battery driven by a heat source of less than 100 ℃ is required because solar and waste heat are low-temperature heat sources. Given that the sorption process in solid sorbents typically requires high charging temperatures, this study investigates the loading of water into the sorbent in combination with ammonia to lower the charging temperature. Zeolite 13X, HZSM-5 and HKUST-1 are evaluated as the potential sorbents based on their material properties, water loading capacity, and ammonia sorption performance. Among them, zeolite 13X loaded with water is selected as the working pair and applied to a laboratory-scale sorption thermal battery to evaluate its energy storage performance. When the charging pressure of ammonia was 5 bar under normal coolant conditions, the energy storage density was 204.2 kWh m⁻³ and the coefficient of performance was 0.53. It can be operated with a low-temperature heat source of 80 ℃; therefore, renewable heat sources such as solar energy or industrial waste heat, can be used. Then the coefficient of performance increases 6.2 times from 0.53 to 3.31 (with the coolant). The ammonia- sorption thermal battery based on zeolite 13X loaded with water is expected to play an important role in thermal energy storage to solve the imbalance problem between demand and supply of renewable energy.