Compartmental Modelling of Shell Side Fouling in a Shell and Tube Heat Exchanger

Abstract

Abstract Accurate and fast models are required to optimise the design, control and operations of shell and tube heat exchangers (STHE) subject to fouling. To date, research effort has mainly focused on tube side fouling. Techniques proposed for the shell side fouling are limited to i) mechanistic thermo-hydraulic models with simple Flow Stream Analysis (FSA) and ii) Computational Fluid Dynamics (CFD) models. The former ignore flow dynamics on the shell side. The latter cannot quantitatively predict fouling, are computationally very heavy and cannot be utilised for optimisation and control. In the paper, we combine the benefits of FSA and CFD methods by creating a hybrid Compartmental Model (CM). For an actual exchanger subject to crude oil fouling we analyse its outcomes and compare them to CFD and FSA methods. A preliminary CFD study yields detailed shell side velocity field information, based on which an appropriate compartments network is created. A simulation is performed using a two dimension (2D) distributed dynamic STHE model which utilises a FSA for the shell side. A dynamic model for the compartments with a shell side threshold fouling model is developed, utilising selected results from the CFD (velocity data) and 2D-FSA (heat duty) studies. Results from the CM model and comparison with the CFD and 2D-FSA models, for the same operation, provide valuable insights regarding the role of shell side velocities in predicting overall exchanger performance. Computationally, for this case study, the CM model is solved 5.5 times faster than the distributed dynamic model and 36 times faster than the CFD model, indicating the approach has good potential for use in design and operations optimisation.