NOx emissions and NO2- formation in thermal energy storage process of binary molten nitrate salts

• NOx emissions in TES process of binary molten nitrate salts are discussed.
• The effect of 45# carbon steel on NOx emissions was also studied.
• The concentrations of NOx emissions increase with the rise of the temperature.
• The concentrations of nitrite ion creep with increasing temperature.
• Fe element in the carbon steel may result in the increment of NO emissions.

Referring to the national environmental protection standard of PR China, HJ479-2009, NOx emissions and the effect of 45# carbon steel (1045, ASTM) on it in thermal energy storage (TES) process of binary molten nitrate (BMN) salts (a eutectic salt mixture named as solar salt with the component of 60% NaNO3 and 40% KNO3) are discussed in this paper. The accumulative absorption concentrations of NOx emissions in tail gases of molten salts heated at different temperatures were measured to study the thermal decomposition situation of molten salts in TES process. Furthermore, the concentrations of nitrite ion in molten salts samples were determined and chemical thermodynamic calculations of related reactions were done to explain the results. The research shows that BMN salts contained in silica or carbon steel container in the air under certain conditions can release NOx in its use of temperature range. The concentrations of NOx emissions and nitrite ion in molten salts both increase with the rise of the temperature. After contacting with 45# carbon steel, the total concentrations of NOx emissions and nitrite ion in molten salts increased, which may be caused by Fe component in the carbon steel.