Initializing Equation Oriented (EO) models in Aspen HYSYS / RefSYS
Equation Oriented simulations are very powerful, as they can solve a very large set of linear or non-linear equations simultaneously. For business problems where we need to specify the output or portion of the output and calculate some of the “input” values such as a temperature that meets a certain quality of an output product, conventional simulation techniques require iterative solutions. However, with EO-based simulation techniques, we can solve all the equations related to simulations simultaneously and therefore the continuous iteration of entire flowsheets can be avoided.
These solution techniques require robust initialization of variables, which can sometimes be challenging.
In this post we look at one way in which HYSYS and Refsys for refinery reactor models provide ways so that we can use a similar, but not exactly the same converged simulation for solving complex refinery reactor problems.
As shown in the image below, HYSYS provides the option to manage and save data sets.
Manage data sets→ OOMF files→ Save
In the converged case, save the name and the values.
In order to retrieve these values on the target case, restore these values by:
Manage data sets→ OOMF files→ Restore
In either case, make sure to tick the name and value boxes to ensure that the converged values are copied from the parent case and get reflected in the target case. After restoring these values, the calibration is run. On doing so, HYSYS is directed to start iterating from the converged values of the parent case and subsequently process the target case values. This can be done only when the parent case and target case are similar in structure and approach.
This can save valuable time in some situations where convergence is not successful with other techniques.