CONTROL-SYSTEM DESIGN AND ANALYSIS FOR REFINERY STABILIZER

A refinery stabilizer is a unique type of a fractionator with a multic omponent feed of naphtha, total vapor overhead product and air-cooled condenser. The traditionally reduced 2 x 2 quality control problem is shown to be inadequate. The inherent interaction present within the co ntrol loops are accounted for by adding a third variable viz, reflux d rum accumulation rate. Light key recovery in the bottom product and he avy key recovery in the top product are chosen as the quality variable s. The manipulated variables are the reflux rate, reboiler and condens er duties. The steady state analysis tools reveals inconsistencies bet ween the RGA and SVD pairings. MIC are found to favor RGA pairing and thus the energy balance control scheme are selected. Further interacti on compensators are used to reduce the interaction by almost 10 folds (in terms of the condition no.) It is also shown that dynamic elements can be accounted for in the compensation matrixes by calculating the effective dead time in the stripping and rectifying sections. These de ad times are readily obtained from the columns hydraulic data.