Integrated Design of a Conventional Crude Oil Distillation Tower Using Pinch Analysis

Abstract

The substantial energy requirement of crude oil distillation columns is met partly by costly utilities, such as steam and fuel for fired heaters, and partly by heat recovered from the process, using process-to-process heat exchange. Energy savings, therefore, demand not only a distillation column that is energy-efficient, but also a heat exchanger network (HEN) which minimizes utility costs by maximizing heat recovery. A new crude oil distillation design procedure is presented which considers the column, the HEN and their interactions simultaneously, to minimize utility costs. Pinch analysis is used to determine minimum utility costs prior to the design of the HEN. In this method, the column is decomposed into a sequence of simple columns, which enables appropriate distribution of stages and simplifies analysis. Modifications, which further increase the efficiency of the process, are proposed: these are the installation of reboilers, rather than stripping steam, and the thermal coupling of column sections. The detrimental effects of these modifications on the heat recovery opportunities of the process are analysed for a distillation tower with side-strippers. A new step-by-step design procedure is derived from this analysis, and is applied to a case study. In the case study, the resulting design offers nearly 20% savings in utility costs over the base case design. The vapour flow in the column is reduced by a similar amount, offering capital savings, additional flexibility or the opportunity to increase throughput. The new integrated design procedure considers the column and its associated HEN simultaneously, aiming to minimize operating costs by obtaining the best fit between the process and the available utilities.