Supercritical water oxidation of feeds with high ammonia concentrations: Pilot plant experimental results and modeling

Supercritical water oxidation (SCWO) is an effective method for the treatment of industrial wastes. SCWO of organic compounds containing nitrogen, found frequently in industrial wastes, results in the rapid conversion into molecular nitrogen without generation of NOx. The stable intermediate in the SCWO of nitrogenous compounds is ammonia. Thus, SCWO of feeds with high ammonia concentrations is studied, in order to make the process more efficient and energetically profitable.All the experiments presented have been performed using the cooling wall reactor at pilot plant scale. Several feeds with concentrations of ammonia up to 7 wt.% have been oxidized using isopropyl alcohol (IPA) as a fuel. Results show that total ammonia removal is possible, even at high concentrations, with stoichiometric air quantity and residence times of 40 s.In our reactor, keeping the feed flow constant, that is keeping the residence time approximately constant between 35 and 45 s, the reaction temperature necessary for reaching the complete TOC and NH3 removal is higher when the ammonia concentration is increased: 710 °C for 1 wt.% of NH3, and 780 °C for 7 wt.% of NH3.A theoretical study of the experimental results has been performed using a simple flow patterns model specifically developed for this reactor, based on an extensive literature search of ammonia destruction kinetics.