This operation attempts to achieve a user-defined requirement expressed as a desired value for the total concentration or mass fraction of a selected group of components contained in an intermediate or output stream. Normally, such compositions are assumed to be the outputs of the simulation and cannot be set by the user. By using an intermediate or output stream as input to the operation’s procedure icon, this model can be used to adjust the flow of a chosen input stream to the process in order to achieve a desired composition for the procedure’s input stream.
● Design Spec (Composition) Procedure
The iterations for converging the design specification(s) are done after the M&E balances are completed. In other words, the entire solution proceeds as follows:
1. Guess a value for the manipulated stream’s flow
2. Solve M&E Balances
3. Observe the value of the target stream composition
4. If target composition matches the user’s specification (within a reasonable tolerance) then end, otherwise make another guess for the manipulated flow and go back to Step #2.
Since such iterations can significantly slow down the calculations, it is strongly recommended to place such design specifications when nearing the end of the design and after all other errors have been resolved (therefore the M&E balances complete without problems). If you wish, you may include design specs from the beginning, but keep them de-activated (simply have the active box un-selected, see Design Spec (Composition): Oper. Conds Tab) till the last phase of the simulation.
Finally care must be taken to choose the manipulated input stream wisely. At minimum, you must make sure that the flow of the chosen manipulated stream has some effect on the target stream. Otherwise, no convergence will be achieved.
The interface of this operation has the following tabs:
● Design Spec., see Design Spec (Composition): Oper. Conds Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab