(261a) Exergy Combined Economic Analysis As a Novel and Simple Energy Optimization Methodology: Application to Regeneration Process of Spent Rds Catalyst

We propose a novel method to easily identify specific unit processes with low efficiency and high energy cost in the overall process using a specially devised exergy combined economic analysis. Once the inefficient unit processes are identified, then we can focus our efforts on them to improve the overall process performance and achieve a better energy-saving process. In the method, the exergy analysis is performed to investigate the exergy values of all process streams in the first step. Next, the capital and operating costs of each unit process are estimated to combine the exergy values obtained in the previous step. Finally, the production cost of each unit process is calculated by adding its input stream cost based on the exergy value to the capital and operating costs, and dividing it by the mass flowrate. By cost balance between input and output streams, high production cost is caused when exergy destruction is large or capital and operating costs are high. We applied the proposed method to a regeneration process of the spent RDS catalyst to verify its effectiveness. As a result, three roasters showed relatively high production costs despite their moderate exergy efficiency. The result means that it is difficult to identify the cost-intensive unit processes by exergy analysis alone. By rearranging the whole heat exchanger network through pinch analysis and optimally splitting oxalic acid solution feed stream to vanadium extractor into two separate streams, we could significantly reduce the production costs of the three roasters and achieved remarkable improvement in total energy consumption. Thus, the application result shows that the proposed method enables us to detect unit processes with low efficiency in terms of both exergy and cost and provides us with a new opportunity for process improvement and rationalization.