(A) study on the optimal crude selection and process optimization for refinery with lube hydro-processing

Abstract

Petroleum refining industry is very complex in decision levels and value chains. In addition the environment regulation and product specification are tighter than before and the crude price & product demand are also fluctuating continuously. Thus the importance of the optimization in refining industry is increasing more and more. Refining company is focusing on two directions in optimization in order to maximize the refining margin and minimize the fluctuation of the profit. The first is optimal crude selection and the second is product value maximization. Lube base oil is one of the high value added products and produced from the low value VGO (Vacuum Gas Oil) and DAO (De-Asphaltene Oil) through lube hydro-processing. And viscosity index (VI) is one of the most important properties that determine the quality grade of lube base oil but strongly depends on the molecular structure unlike typical fuel products. Thus it is absolutely required to select optimal crude and optimize operating condition for satisfying the target VI of lube oil and maximizing the overall refining margin at the same time. But the VI prediction from crude to final lube product is very challenging due to the diversity of crude oils and the heavy boiling & complex composition of lube range. And it is also challenging to optimize the overall refinery combining the lube hydro-processing model. Thus most of the refinery mainly focused on the fuel products and it is common that refinery with lube plant depends on the experience and empirical information to select crude oil. In this study, the compositional change of hydrocarbon component and the VI in lube hydro-processing was investigated using the representative crude types. And the lube hydro-processing model for predicting VI and yield was developed according to the crude type and conversion. And then optimization model was formulated combining the lube hydro-processing model into the overall refinery model for the maximization of margin satisfying all the specifications of lube and fuel products simultaneously. Through the practical case study by scenarios and sensitivity analysis, optimal decision strategy was suggested for the crude purchase, production grade of lube base oil and the conversion rate in lube hydro-cracking. Finally, multi-stage (period) optimization for lube refinery was implemented through the integration of the model based crude selection and the scheduling including crude procurement and inventory dynamics for real execution.