(163c) Simplified Modelling of Crude Oil Distillation Columns Meeting Refining Product Specifications

The design and optimisation of crude oil distillation columns is of great importance in the refining industry. The process consumes considerable amount of energy and the refining product properties are mainly determined by the performance of the separation.

Simplified models offer a number of benefits for the design and analysis of crude oil distillation columns, compared with rigorous simulation, in terms of their flexibility and robustness. Simplified models have been developed to facilitate grassroots and retrofit design and analysis of crude oil distillation columns (Suphanit, 1999; Gadalla, 2003; Rastogi, 2006). These models require the specification of key components and their recoveries to define the separation. These models perform well, compared to rigorous simulations. However, due to the large number of components in crude oil, even with application of pseudo-components to dramatically reduce the number of components, making an appropriate choice of key components and their associated recoveries becomes a problem when applying the simplified models for the design and analysis of crude oil distillation columns. Previous approaches have required preliminary rigorous simulation results, and have used trial and error to determine the most appropriate key components and recoveries to give a good match between rigorous and simplified models.

Conventionally, refining products are specified in terms of true boiling properties, bulk properties, such as Specific Gravities, Sulphur Content, Refractive Index, Watson K, Research Octane Number, Viscosity, Reid Vapour Pressure, Flash Point, Cetane Index, etc.. and flow rates. In this paper, a novel methodology is proposed to automatically identify appropriate key components and recoveries given conventional product specifications. This new approach enables the use of simplified models to solve industrial relevant design problems.

Case studies illustrate the approach, and compare the results of simplified models with those of more rigorous models. These simplified models can then be coupled with heat exchanger network models to allow the simultaneous optimisation of the column and heat recovery system.

Reference

M. Gadalla, M. Jobson, and R. Smith, Shortcut models for retrofit design of distillation columns, Trans IChemE, September, 81(A), 971-986 (2003)

Rastogi, V., Heat Integrated Crude Oil Distillation System Design, PhD Thesis, The University of Manchester, Manchester, UK (2006)

Suphanit, B., Design of Complex Distillation System, PhD Thesis, UMIST, Manchester, UK (1999)