Plant Operability Optimization through Dynamic Simulation, a Case Study Focused on Phosphoric Acid Concentration Unit

Abstract

All phosphoric acid concentration units suffer from fouling requiring frequent shutdowns, cleaning and start-up cycles. These cycles are time consuming. Any process and control improvement facilitating the operations can lead to significant increase on strong acid production. This study shows how dynamic simulation can be used to conduct engineering studies, operational studies and training simulators to optimize the operability of a greenfield phosphoric acid concentration unit. In order to perform this optimization, a first principle model predicting how process and associated control will respond as a function of time was created based on all plant's engineering information. The model can be further combined to DCS graphics and field operated devices schematics to facilitate procedure testing. Constant pressure and constant temperature start-up procedures were tested in order to estimate which procedure minimizes time to concentrate acid from 25% to 50% P2O5. It was found that both procedures were equivalent in terms of time and energy consumption, but constant pressure strategy is simpler and safer, potentially leading to less human related losses. These procedures were performed executing step-by-step actions, allowing determining most frequent mistakes, any missing actions and improving the existing written procedure. Furthermore, the simulator allowed verifying equipment design, interlocks, control logic and identifying new control enhancement opportunity. In addition, many tools available with the dynamic simulator can be used for operator training purposes leading to potential operability gains.