No abstract

Supercritical water oxidation (SCWO) development is limited by corrosion and salt precipitation. Transpiring wall reactors are emerging to cope with these problems. A reactor has been developed in which the inner porous shell is composed of pure α-alumina, to handle organic effluents generated by nuclear activities. The reactor was not proven to be efficient enough to oxidize salty effluents. However, experimental results concerning the oxidation of a mixture of dodecane and tributyl phosphate, which is used as a model effluent, confirmed the ability of the reactor to treat corrosive wastes. High destruction rates were actually achieved (>98%). Phosphorus was totally recovered in the aqueous effluent as phosphoric acid. No corrosion was noticed in the reactor, except upstream from the waste injector. As expected, the inner alumina tube shielded the pressure vessel from corrosion. The assumed sensibility of alumina to thermal gradients was not a limiting factor of the reactor operation.

No abstract

Supercritical water oxidation (SCWO) performances are limited by salt precipitation and corrosion when it comes to treating real wastes. A porous reactor has been developed to overcome these problems. It consists of a concentric double-wall reactor in which the corrosive reactants are maintained inside an alumina porous tube, whereas pressure resistance is ensured by a stainless steel external vessel. Hydrodynamics in the reactor is thought to be rather complex. Thus, a residence time distribution study was performed to investigate the flow pattern. The experiments were carried out in supercritical carbon dioxide for experimental consideration. According to the experimental results, the axially dispersed-plug-flow model as well as the tanks in the series model can be used to describe the tubular reacting zone when there is no radial flow through the porous barrier. The whole reactor can then be considered as a cascade of equal ideally mixed tanks with a stage radial feed. This proposed hydrodynamic model was validated by the experiments of ethanol oxidation in supercritical water. Our model enables us to estimate and optimize the conversion of a waste if its oxidation kinetics is known.