Optimization Model of Crude Oil Distillation Units for Optimal Crude Oil Blending and Operating Conditions

Abstract

This work presents the mathematical formulation of a nonlinear programming (NLP) model which optimizes simultaneously crude oil blending and operating conditions for a system of several crude oil distillation units (CDUs) at a Colombian refinery. The CDU system consists of three industrial units processing a blending of five extra-heavy crude oils and producing two commercial fuels, Jet-1A and Diesel. The NLP model involves typical restrictions (e.g., flow rate according to capacity of pumps, distillation columns, etc.) and the heat integration of streams from atmospheric distillation towers (ADTs) and vacuum distillation towers (VDTs) with the heat exchanger networks for crude oil preheating. A metamodeling approach is used so as to represent the ADTs. Preheating networks are modeled with mass, energy balances, and design equations of each heat exchanger. The NLP model has been implemented in GAMS using CONOPT as solver. Different cases are solved by the NLP model such that the optimal case with less profit increment had an economical benefit of 13% with respect to its case without optimization. In each optimal case the extra-heavy crude oils in the feed blending of each CDU required more severe operating conditions such as higher temperature of the crude oil at the entrance to the towers, greater flow rate of stripping steam at the bottom, and minor pressure of the tower tops

Optimization of Heat-Integrated Crude Oil Distillation Systems. Part III: Optimization Framework

“…Loṕez C. et al 8 present a methodology to perform operational optimization of crude oil distillation systems using nonlinear programming (NLP). The distillation model employs second-order polynomial functions, while mass and energy balances are developed for each heat exchanger in the HEN.…”

“…The distillation model employs second-order polynomial functions, while mass and energy balances are developed for each heat exchanger in the HEN. The approach of Loṕez C. et al 8 optimizes the crude oil blending fractions and operating conditions (e.g., product yields, pump-around flow rates and return temperatures, stripping steam flow rates, etc.) for a system with several distillation units.…”

“…A detailed HEN simulation model is used to calculate and constrain furnace inlet temperatures and pumparound return temperatures. Loṕez C. et al 8 reports that including a detailed HEN model in the optimization approach produces results that are more practicable and more credible to operations engineers than results from optimizing the distillation units alone.…”

“…Furthermore, optimizing the distillation process without considering the HEN details may produce impractical solutions; that is, operating conditions may not be accommodated in the distillation system. 8 This paper explores a third scenario, in which the distillation process and HEN are considered together in the optimization framework. The proposed framework optimizes the operating conditions of the distillation unit and proposes a retrofitted HEN that is able to accommodate the changes made to the distillation process.…”

A rigorous simulation-based procedure for retrofitting an existing Egyptian refinery distillation unit

“…Those models were used to optimise existing CDUs for energy saving and CO 2 emission reduction. Also, other models for the CDUs were developed for various design and optimisation purposes [21,22]. Thus, there is a regular concern to find out solutions to enhance the energy efficiency and the overall performance of existing CDUs in refineries [23].…”