How are variables in process simulators related to variables in the refinery planning LP models?
Catalytic reformers are typically used for transforming naphtha which is a low Octane stream into a high octane, high aromatics stream. The C5+ yield of the reformate, which is the main product of reformers, is typically correlated to the N+2A rating of the reformer feed in refinery planning models. There is no provision in process simulator such as HYSYS to change the N+2A values as an independent variable. This is infact true of the actual process as well, where the N+2A in the reformer feed changes as a function of some other change upstream of the reformer in the process plant. One common way of varying the N+2A values in the process simulator is by increasing or decreasing the composition of naphthenes and aromatics in the feed. The amount of aromatics and naphthene components can be varied simultaneously or one at a time, depending on the requirements. This in turn has an effect on C5+ yield.
One such example for the variation of C5+ yield for different N+2A values when the C5 + RON of reformate is 102 is shown below:
Tools such as Excel or other regression tools can then be used to correlate between N+2A of the reformer feed and C5+ yield of reformate. It must be noted that such regressions have to be done simultaneously for all products from the reformer to maintain an overall material balance.