CFD Modelling – Development of computational tools for modeling the behavior of supercritical water oxidation reactions working under hydrothermal flame regime

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Supercritical water oxidation (SCWO) is an useful technology for the destruction of waste. In presence of hydrothermal flames (yes, a flame in aqueous media!) complete oxidation of organics is achieved in less than 1 s. The properties of water above its critical point (374◦4 C, 22.1 MPa) make possible the destruction of organic waste in homogeneous phase due to the total miscibility of gases (O2, N2, CO2) and organics with supercritical water. Due to these advantages SCWO has been also proposed as a technology for replacing combustion in power generation. CFD is an essential tool for understanding the behavior of actual SCWO reactors and predicting the efficiency of new designs.

Joao Queiroz

The modeling of the SCWO process starts with a description of physical properties of the system. Methods of estimation for thermal and transport properties of supercritical water and its mixtures are studied.

Kinetics – the velocity of the reaction process

The next step is understanding the kinetics of oxidation in supercritical water. A new global reaction rate for the oxidation of isopropyl alcohol in hydrothermal regime is adjusted from experimental temperature profiles. This kinetic model is applied in a parametric analysis of flame formation, and it is used to analyze the behavior of a supercritical water oxidation in vessel reactors. The model predicts both flameless and hydrothermal flame regimes. Turbulence-chemistry interaction is also studied.

Geometry – it makes the difference

The influence of the internal configuration of vessel reactors for the process is evaluated by simulation and compared to experimental data. The CFD-model developed provides a good prediction of the experimental results and can be used for designing reactors working under hydrothermal flame looking at performance and flame stabilization.

Energy – the key for creating a sustainable process

The energetic possibilities of the process are analyzed through theoretical calculations. Heat integration, generation of high pressure steam and generation of electricity by products expansion, are feasible in SCWO.

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