Simulation-optimisation-based Design of Crude Oil Distillation Systems with Preflash Units

Crude oil distillation systems are energy intensive processes. A crude oil distillation system typically comprises a preheat train, a preflash unit and an atmospheric distillation unit. Preflash units in a crude oil distillation system create opportunities to reduce demand for fired heating. This work aims to develop a new design approach to enhance production and to reduce energy consumption and operating cost. Existing design methodologies do not allow systematic design optimisation of crude oil distillation systems with preflash units. Thus, a systematic approach is proposed that exploits interactions between the separation units and the heat recovery system, while meeting product quality specifications. The optimisation framework applies a stochastic optimisation algorithm (simulated annealing) to minimise utility consumption by selecting optimal values for operational variables: stripping steam, pump-around duties, pump-around temperature drops, column feed inlet temperature and preflash temperature. An interface between Aspen HYSYS v8.6 and MatLab R2016a facilitates integration of modelling and optimisation. Heat recovery is systematically evaluated using pinch analysis (grand composite curve) to account for the impact of operational variables on energy demand. A case study demonstrates the capabilities of the approach and illustrates that implementing preflash units can reduce hot utility demand.