A Decoking Computational Model for Steam-Cracking Furnace Coils

Sedimentation is one of the most popular water treatment processes and is used to separate solid particles from carrier fluid in settling tanks known as clarifiers. The clarifier as the last major facility in waste water treatment plant (WWTP) can affect and sometimes even limit the overall performance of the WWTP. An industrial-scale clarifier investigated in this work experienced lower than designed performance, which limited its wastewater handling capacity. The interested clarifier has a non-conventional feedwell design. The objective of this study was to analyze the ramifications of the current clarifier design and to come up with design modifications to improve the performance. A novel 3-dimensional unsteady CFD (computational fluid dynamics) model, where an effective and simplified approach was employed to address solids removal and slow-rotating rake (at about 1 rotation per hour), was developed to analyze the clarifier performance. The root causes for the unsatisfactory performance of the current clarifier design were identified. Subsequently, various design modifications were developed using the model to significantly improve the clarifier performance. This work shows that the present numerical model can become a computationally effective tool that will help researchers to design and optimize complex industrial clarifier geometries with rotating rakes in order to reduce the effluent TSS (total suspended solids) and optimize the clarifier performance.