Numerical modelling of a supercritical water oxidation reactor containing a hydrothermal flame

Supercritical water oxidation (SCWO) is a high-pressure process for the disposal of toxic and hazardous aqueous wastes. A novel reactor that achieves SCWO using a hydrothermal flame as an internal heat source, has been recently constructed to examine the ignition and extinction process, flame properties, temperature, and influence of salts over a broad range of operating conditions. In addition, a computational fluid dynamics (CFD) tool has been developed with the goal of gaining an understanding of the interdependency of various phenomena. Simulation of supercritical single-phase combustion has been performed for two methanol inlet mass fractions, and the results compared to experimental data. The position of the flame is well reproduced. The reaction is controlled by the rate of mixing between the fuel and oxygen streams. Simulations were also performed to analyse the effect of intrusive temperature measurement by including the thermo-couple probe in the simulation. The presence of the probe was seen to move the flame significantly closer to the inlet. The simulations over-predicted the rise in temperature at the axis of the reactor by 15–18%, although, significant variations also exist in the experimental data. It has been demonstrated that a simple mathematical model can capture many of the features of a SCWO reactor. Possibilities to improve the predictions are discussed.