The role and significance of free water in aspen

I’m trying on my own and hope to get some guidance; I’ve just started learning *aspen!

I’ll contribute too; looking forward to answers from experts. . .

Regarding free water, it is only known to be used in hydrocarbon-water systems, especially in petroleum process simulation. The specific details are not quite clear; where are the experts?

http://bbs.hcbbs.com/viewthread.php?tid=509742&page=1#pid2830967

This post was last edited by lsrwan on 2009-7-18 21:05. For liquid-liquid phase equilibrium simulations, the available types of phase equilibrium calculations are L-L, L-FreeWater, or L-DirtyWater. If the gas phase is also to be taken into account, an additional gas phase option is added, resulting in V-L-L, V-L-FreeWater, or V-L-DirtyWater. The differences among these three calculation types lie in the liquid phase: 1) L-L represents a strict gamma-gamma based liquid-liquid calculation. 2: The calculation process for L-FreeWater is also rigorous. The difference from L-L lies in the assumption that the aqueous phase consists of pure water; this is where the term \"FreeWater\" comes from. In the organic phase, the solubility of water is calculated using polynomials related to various organic compounds, along with certain rules for combining these values. Thus, the result obtained for the pure aqueous phase is correct, as the FreeWater calculation is indeed based on this assumption. Such calculations are feasible if the organic compounds present in the aqueous phase can be ignored; however, if those organic compounds are important, then this calculation method cannot be used. 3: The calculation process for L-DirtyWater is also rigorous. The calculation of the organic phase differs from that of L-FreeWater in that the solubility of various organic compounds in the aqueous phase must be taken into account; this is done using polynomial equations representing the solubility of simple organic compounds in water. Since the aqueous phase is no longer pure, it is referred to as DirtyWater. You need to decide which type to choose based on your own requirements. Then, for the thermodynamic model, you should choose an activity coefficient model; you cannot use the Wilson model here as it cannot be applied to two-phase calculations. I think NRTL is the preferred choice. If the parameters are not available, you can then switch to UNIFAC – there is a high likelihood that parameters will be available for your system. Let me remind you again: as the previous user mentioned, if gas phase is taken into consideration, choose the FLASH3 module; if only liquid phase is considered, use the decanter module. Be sure to modify the valid phase setting for the module. Finally, good luck to you.