Reasons for the deviation between simulated and actual values in liquefied ammonia flashing
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There is currently a stream at 18 bar and 25°C, with a composition of 13% acetylene, 63% ammonia, 6% water, and the remainder being high-boiling-point organic compounds; this stream is evaporated in a flash evaporator to 1.2 bar and -7°C. The evaporation rate simulated by Aspen is 2050 kg/h, while in actual production it is 1560 kg/h; almost all of the acetylene evaporates, whereas there is a significant variation in the amount of ammonia that evaporates. According to theoretical analysis, when the temperature is constant, the amount of evaporation depends only on pressure. Moreover, the evaporation process is a type of low-temperature flash evaporation, with no heat loss occurring; only heat is supplied from the outside. I’m a bit confused as to why
My personal guess is that it has something to do with ammonia dissolving in water.
Check two aspects: first, whether there are any errors in the simulation, and second, whether the temperature detection is accurate
The temperature is the one used in actual production; there are no issues. An electrolyte model is used for simulation, and the interaction parameters related to ammonia water are taken from the available data – no ammonia packets are used