Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

Experimental data from a bench-scale reactor was used to validate the computation fluid dynamics (CFD) methodology for modeling the supercritical water oxidation (SCWO) process. The reactor was operated on ethanol as pilot fuel and H2O2 as an oxidizer. Fluid properties were modeled using polynomial fit approximations validated against NIST data over a range of subcritical and supercritical temperatures at 25 MPa. The model predicts the fluid temperature in the reactor within 30 degrees C of measured values over a range of inlet fuel concentrations. The ethanol decomposition of similar to 99% occurs within 20% of the reactor length at T similar to 600 degrees C. The nondimensional analysis shows that the reactor operates in a distributed reaction regime due to the enhanced stability of the inverted gravity reactor configuration. The modeling approach can inform the designs of practical SCWO reactors, increase operational safety related to material limits, and optimize operating conditions required to destroy toxic wastes.