Enhancing energy efficiency in crude distillation units via process simulation and SQP-based optimization

Abstract

The paper introduces a unique approach combining Aspen HYSYS simulation, actual refinery operating data (Basrah refinery), ASTM D86-based validation, and sequential quadratic programming (SQP) optimization into one practical framework in the context of energy optimization in a Crude Distillation Unit (CDU). To model the separation performance of the main side products, a strict steady-state model was created to depict the refinery operating conditions and assess the performance of the separation process. The validation of the model with reference reports of ASTM D86 distillation indicated a good fit between the simulated and reference outcomes with a correlation coefficient ( R ²  ≈ 0.9858) and validates the credibility of the developed model. The objective of the optimization was to minimize the total energy used by the overall operation, through varying operating variables, that is, the pump-around circulation rates, stripper steam flow rates, and column pressures, without compromising the quality of products. The optimized case achieved a reduction of 1.61 % in furnace duty and 4.93 % of stripping steam duty, resulting in a total energy saving of about 2 % over the base case. Simultaneously, the values of kerosene, LGO, and HGO according to ASTM D86 T95 were kept within the necessary specifications. It has been proven in the study that with well-coordinated control of the pump-around circuit, stripper steam rate, and column pressure, energy consumption of crude distillation units can be reduced under actual operating conditions without violating product quality requirements.