Modeling and simulation of hydrothermal oxidation of cutting oil in supercritical water

Abstract

AbstractSupercritical water oxidation may be used as waste treatment technique that consists of oxidizing organic and inorganic matter using water at supercritical conditions. It was developed as an alternative technique in order to limit the risks of secondary pollution. The purpose of this study is the development of simulation tools in stationary state in supercritical water oxidation (SCWO) tubular reactor which has been numerically investigated basing on using a two-dimensional modeling approach applying the k-ε turbulence model, and on the international association for the properties of water and steam formulation (IAPWS-IF97). A Multiphysics simulation using Comsol Multiphysics 5.2 software for the supercritical water oxidation of “cutting oil Biocut 35” as a pollutant is reported. First, the heat transfer coefficient was estimated and the obtained temperature and species concentration profiles were compared to experimental data where a quite good agreement was obtained as confirmed by the acceptable coefficient of determination value. Finally, once the used model was validated, numerical simulations were performed to describe the behavior of the reactor investigating the effects of operating conditions such as temperature, pollutant feed concentration and reactor inlet flow rate, on dependent variables like outlet temperature, chemical oxygen demand removal (COD) and the highest temperature reached inside the reactor. This last parameter was considered in the study to take into account the operation safety. The significance of the studied factors and their interactions were quantified and analyzed by means of the full factorial design of experiment (DOE). The results showed that the effect of initial temperature was the most important for the three responses, followed by the feed concentration then to a lesser extent the flow rate. The effect of initial temperature was positive for outlet temperature, maximal temperature and cutting oil removal. The interaction temperature-feed concentration was the only significant one for the COD removal and the maximal temperature. The results defined an operation safety zone of the SCWO reactor based on the superposition of the three studied dependent variables and imposed constraints on the inside reactor temperature and the pollutant outlet concentration.