Supercritical water oxidation for the destruction of hazardous waste: better than incineration

Abstract

Supercritical water oxidation (SCWO) is an advanced process mainly employed for the treatment of hazardous stable wastes, otherwise treatable by incineration. It is based on the unique properties of water above its critical point (T(c)=675 K, P(c)=22.2 MPa), making it a superior reaction medium for the destruction of all organics in the presence of oxygen. This work presents preliminary laboratory scale studies on SCWO of nitrogen (N)-containing hazardous hydrocarbons, with a view to enhancing the process performance, using available reagents and non-complex reactor design. This article investigates the destruction of dimethylformamide (DMF), carried out in a continuous (plug flow) reactor system. SCWO of DMF was enhanced by (i) a split-oxidant system, where stoichiometric oxidant was divided between two inlet ports at various ratios and (ii) the addition of isopropyl alcohol (IPA) as a co-fuel, premixed with the feedstock. Testing a range of temperatures, initial DMF concentrations, oxidant ratios, IPA ratios and oxidant split ratios, selected results were presented in terms of % total organic carbon and % N removal. Reaction kinetics were studied and showed a dramatic decrease in the activation energy upon adding IPA. Split-oxidant-feeding enhancement depended on the split ratio and secondary feed position.

Supercritical water oxidation (SCWO) for the removal of nitrogen containing heterocyclic waste hydrocarbons. Part II: System kinetics

“…On the other hand, IPA addition enhanced TN% removal by a significant 66% raising it to over 85% N removal at 450C. The effect has been observed in literature [20,14]…”

Supercritical water oxidation (SCWO) for the removal of N-containing heterocyclic hydrocarbon wastes. Part I: Process enhancement by addition of isopropyl alcohol

“…Enhancement of SCWO of DMF was also investigated using multi-port oxidant injection [13,14], which showed improved TOC % conversion and N speciation upon gradual oxidant feed. Other studies confirmed the positive influence of IPA addition to SCWO of DMF, in view of process enhancement [15,16]. (at 20°C).…”

Functional Materials for Waste-to-Energy Processes in Supercritical Water

“…For this, the SCWO systems differ from SCWGs in the feeding section, as proper mixing and preheating of the feed, water, and oxidant streams should be achieved before the reaction. In this view, feeding systems based on oxidant multiinjection at different reactor points has been proposed to avoid the corrosion and salt deposition problems [93][94][95]. It was found that oxidant dosage in a SCWO reactor is also an aspect in energy management [93].…”