Internal Versus External Heat Integration: Operational and Economic Analysis

In this paper we compare internally heat integrated (HIDiC) with state of the art vapour recompression (VR) distillation column on the basis of two criteria: economics and oper-ability for a propylene-propane splitter. A two-step (model-based) procedure was followed consisting of a steady-state optimization followed by a dynamic optimization. First the design of HIDiC was optimized with respect to annualized cost (steady-state optimization). Next the control of both VR and HIDiC were optimized with respect to operability for a given disturbance scenario (dynamic optimization). The results showed that HIDiC can save 14% in annualized cost compared to VR (safe estimate), but at the cost of operability. Adding only a small percentage of the nominal duty of VR results in much better operability of HIDiC. It is to be expected that model predictive control will improve operability to a degree possibly beyond VR.