Numerical Investigation of a Regenerative Thermal Oxidizer for the Abatement of VOCs

Volatile Organic Compounds (VOCs) are dangerous for human health and the environment; hence their emission in the atmosphere is strictly regulated. To treat exhaust gases containing VOCs, thermal oxidizers are commonly used, especially in industrial processes with large volumetric flow rates. In this framework, Regenerative Thermal Oxidizers (RTOs) represent an effective solution, combining high removal efficiency with high energy saving. RTOs employ multiple beds of ceramic media in a cyclic operation mode, to recover the combustion heat from VOC oxidation, thus reducing the consumption of the auxiliary fuel. The objective of the present work is to apply Computational Fluid Dynamics (CFD) techniques to investigate and optimize an industrial 3-canister RTO. The use of CFD for modeling the RTO behavior is partially hindered by the large computational cost, related to the numerous equations needed to describe turbulence, transport/reaction of chemical species as well as heat transfer in a complex 3-dimensional domain. In this framework, transient simulations required by the periodic RTO behavior could be unaffordable. Regenerative Thermal Oxidizers (RTOs) represent a widely accepted technology for the abatement of VOCs, combining high removal efficiency with low operating costs. This work describes a numerical approach for the effective design of an industrial-scale 3-canisters RTOs, coupling a 1-dimensional dynamic model with 3-dimensional CFD simulations. Such a model is validated by using data on pressure drops available from the plant. The model provides a detailed analysis of the thermo-fluid dynamics field at distinct instants within the RTO operation, allowing to explain how different inlet-outlet-purge configurations affect the efficiency of VOCs oxidation.