Problems with the setup of the Pro2 distillation tower
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1 In pro2, a distillation column is used to separate a certain mixture. In the performance specifications of the column, the reboiler load and the temperature of the top condenser are specified; the variables that can be adjusted are the condenser load and the reboiler load. Eventually, a solution is still found – why is that? Since the load of the reboiler has been specified, why is it still necessary to adjust its load? 2 Still in the distillation column, for the feed and products, it is required to specify the flow rate of certain products. After that, if the flow rate of a particular product is not specified in the performance specifications, then the value specified in feed and products at the beginning serves only as an initial value for calculations, rather than being considered a target value, right? 3 In the distillation column, aside from the number of trays, feed position, pressure, and pressure drop, are the values on the other setup pages (including product flow rate, reflux ratio, and the load on the condenser and reboiler) treated as initial values if they are not specified in the performance specifications? This post was last edited by huanglei on 2009-3-8 16:26.]
The original poster is absolutely correct; the points you mentioned are all preset initial values. Generally, systems don’t have strict requirements regarding these initial values, so they can be set rather arbitrarily. However, in some cases higher standards are required, such as when there is a circulating flow in a tower.
So what about point 1? How should this be understood?
The poster can understand this in terms of degrees of freedom. Temperature, pressure, and composition are set as fixed values (the number of trays, feed position, pressure, and pressure drop are also fixed), while all other variables can vary. The PRO-II calculation method first calculates the variables related to performance specifications; if these requirements are not met, then factors such as product flow rate and reflux ratio are adjusted
I learned a lot by watching the duel between those two top experts!
It’s also an estimation, a calculation of an initial value.
It is divided into set values, calculated values, and initial estimates. In my opinion, Pro2 doesn’t handle this aspect well; actually, distillation column simulations can converge without relying on any initial values
In Aspen, the set values such as the reflux ratio and the top product flow rate are calculated as target values. It seems that in this regard, pro differs from Aspen, with Aspen’s approach appearing to be better.
I think what is specified in the performance specifications are set values (target values), and they have nothing to do with the initial values. The initial value can be set or left unspecified; it is not a process that converges particularly difficultly, so the impact of the initial value is minimal. In performance specifications, it is crucial that each target value corresponds to a variable.
Could everyone discuss how to set variables after determining target values? For example, I can say that if a demister is used at the top of the tower with gas-phase extraction, it is relatively easy for the heat load using the condenser as a variable to converge; whereas it is less easy if the reboiler heat load is used as the variable. I hope everyone can share their experiences in this area.
The solution process of simulation software relies on numerical methods, which involve numerous iterations; this necessitates the use of initial values
As a supplement to some of the questions regarding my answer, in the case of side-stream extraction, requiring the specification of the flow rate of the side-stream products within the feed and products parameters affects the final results, which is different from other initial values. Regarding the selection and setting of variables, there is indeed a lot of flexibility, which requires experience and reflection in practice. This post was last edited by LTY on 2009-3-9 16:53.]
Is this value considered the target value?