NOx emissions and the component changes of ternary molten nitrate salts in thermal energy storage process

The objective of this work is to investigate the NOx emissions from HITEC (ternary molten nitrates of 7 wt.%NaNO3-53 wt.%KNO3-40 wt.%NaNO2) in thermal energy storage (TES) process and the effects of 45# carbon steel (1045, ASTM) on NOx emission as well as the component changes in HITEC. Referring to the national environmental protection standard (HJ479-2009) in China, NOx emissions in tail gases were measured in one hour for heating the molten salts in a quartz glass boat during TES process. Furthermore, the concentrations of nitrate and nitrite ion in molten salts samples were determined, and chemical thermodynamic calculations of related reactions were carried out to explain the mechanism of NOx emissions. The results show that HITEC contained in a quartz glass or carbon steel container in air atmosphere can release NOx in the operating temperature range, which were caused by several reactions between nitrate and SiO2 or Fe. The concentrations of NOx emissions increase with the rise of temperature. In the practical application, NOx emission is acceptable since the amount of NO2 or NO will dramatically decreased in the liquid salts by reacting with NaNO2.