Case Studies in Chemical and Environmental Engineering (Dec 2023)
Graphical analysis and revamping of crude distillation units under variable operational scenarios
Abstract
Energy cost represents a significant part of the total operating costs of many processing units. Crude distillation is an energy intensive process. Energy integration is a typical solution to reduce heating and cooling utilities through maximizing the target temperature of crude oil streams before entering the furnace. Over the past few decades, significant progress has been made in energy integration methods including pinch technology and mathematical programming approaches. Very recently, graphical techniques have been developed for revamping studies and energy analysis. Such diagrams are valuable in energy targeting to identity energy inefficiencies and are key to potential modifications for maximum energy integration. The current research applies the recent graphical revamping methodology on an existing crude atmospheric distillation unit. The unit is located in north of Egypt (Suez region) and is operated under two different operational modes; (1) without naphtha stabilizer; the process reformer is in operation to reform all naphtha streams without stabilization and (2) with naphtha stabilizer; LPG is separated from naphtha stream. A graphical-based revamping methodology is applied to retrofit the existing preheat train. The revamping procedure starts by simulating the existing HEN data, followed by validation against the real data. The current performance of the HEN is analyzed using the graphical axes of Thot-Tcold diagrams. The graphical method is then used to identify exchangers across the pinch and recognize the potential modifications to improve the energy performance and reduce fuel consumption. Implementing the graphical identified modifications on the plant resulted in the following benefits: (1) when stabilizer is in operation, energy savings are achieved by 21.1% with additional capital investment of 0.81 MM$ and annual energy savings of 0.82 MM$, with a payback period of one year. (2) when reformer is in operation, the energy savings are 0.42 MM$ with capital investment of 0.33 MM$. The methodology results provide a flexibility in refineries operations.
