Optimisation of Column Pressure

While these decisions are outside the scope of the control engineer, there still remains an opportunity to adjust pressure within the constraints of the installed equipment. Again it is 

In the same way that pressure can be manipulated to exploit the difference in product prices, so can target compositions. We saw in the first section of this chapter how cut and separation can be adjusted to maximise revenue. The feasible operating region developed for these variables can be converted to one based on the actual MVs. For our case study LPG splitter. 

If however propane is more valuable than butane we still want to produce propane exactly on specification (to maximise the C4 sold at propane prices) but may wish to operate with giveaway against the butane specification. If the additional C3 recovered from bottoms is more valuable than the additional energy cost we want to move away for the intersection of the constraints along the line of constant The decision we have to make is how far we move along this line. 

Ryskamp, C. J. (1980) New strategy improves dual composition control. Hydrocarbon Processing, 59(6) 51-59. 

Prediction of vapour pressure of pure hydrocarbons and narrow-boiling petroleum fractions, in API Technical Data Book, procedure 5A1.19. 

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