Study of the Thermochemistry for Oxygen Production for a Solar Sulfur-ammonia
- ISBN-10
- 1267478721
- ISBN-13
- 9781267478726
- Pages
- 70
- Language
- English
- Published
- 2012
- Author
- Mimi Kai Wai Wang
Description
The purpose of this study was to investigate the oxygen sub-cycle of a solar- thermochemical water-splitting cycle for hydrogen production. The study focuses on the thermal decomposition of molten salts in a sulfur-ammonia cycle, which evolves ammonia and SO3 in two reactors. The molten salts proposed are a mixture of (NH4)2SO4, K2SO4, K2S2O7, Na2SO4, and Na2S2O7. For this cycle to work, the salts must remain liquid with low viscosity for pumping, and ammonia and SO3 must be released separately. Therefore, melting temperatures and the viscosity of various salt mixtures were measured. Thermogravimetric, differential thermal (TG/DTA), residual gas (RGA), and chemical analyses were employed to study the salt decomposition. The mixtures of K2SO4+4K2S2O7+Na2SO4+ 4Na2S2O7 and K2SO4+9K2S2O7+Na2SO4+ 9Na2S2O7 with melting temperatures 343±11°C and 332±7.8°C, respectively, would be appropriate for the streams between the reactors. The TG/DTA showed that (NH4)2SO4+2K2SO4+8K2S2O7 decomposition resulted in separate ammonia (269°C) and SO3 release (373°C). The RGA data for (NH4)2SO4+K2SO4+4K2S2O7+Na2SO4+4Na2S2O7 decomposition suggested that 25°C separated the end of ammonia (475°C) and the start of SO3 release (500°C). This was confirmed by monitoring the pH of a solution through which the evolved gas was bubbled. The mass balance experiment showed that, when held at 475°C for 60 minutes, 21% of the ammonia expected to be evolved was released. The addition of 10g of water to 2g of salt mixtures resulted in 58% of the ammonia expected being released. The viscosity of K2SO4+4K2S2O7+Na2SO4+4Na2S2O7 and K2SO4+9K2S2O7+Na2SO4+9Na2S2O7 ranged from 2.6cP to 9.3cP between 393°C and 510°C, which means that they could be pumped.
