How to calculate the gas phase composition of ammonia in a storage tank using Aspen
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It is now necessary to calculate the gas phase composition in the ammonia water storage tank. The tank pressure is 102.325 kPa, the temperature of the ammonia water is 20°C, and the mass concentration is 20%. The Flash2 flash calculation module is used, with the ELECNRTL property method selected. As a result of the calculations, only a liquid phase exists; there is no gas phase composition. In reality, the gas phase must contain water vapor and vaporized ammonia. I would like to ask the experts: how should such calculations be carried out?
You are not in the two-phase region; what Aspen provides is only the value for the liquid phase, which is fine. As for the concentration in the gas phase of the closed system you mentioned, you can use Raoult’s law to approximately calculate the partial pressure of NH3