Supercritical water oxidation of recalcitrant compounds under a hydrothermal flame

Supercritical water oxidation (SCWO) is able to completely mineralize every kind of waste in residence times lower than one minute. Supercritical water oxidation in presence of hydrothermal flames can reduce residence times to the order of milliseconds. The most recalcitrant compounds in terms of difficulty to oxidation for the supercritical water oxidation are acetic acid and ammonia. The object of this work is to study the destruction of high concentrations of the recalcitrant compounds ammonia and an industrial waste containing acetic acid by supercritical water oxidation in presence of a hydrothermal flame using isopropanol (IPA) as a co-fuel. The experiments were performed in the demonstration SCWO plant of the High Pressure Process Group of University of Valladolid sited in the premises of the company CETRANSA. A tubular reactor of 1.5 m length and 1⁄4” diameter made of C-276 Ni-Alloy with residence times between 1 – 1.6 seconds was used. Oxygen was used as the oxidant. Experiments were monitored through temperature profiles in the reactor and TOC concentrations in the effluent. In general, the increase of IPA concentrations in the feeds resulted in higher reaction temperatures and better reaction conversion. For mixtures with 1% acid acetic total elimination of TOC was been achieved at temperatures higher than 740oC. In the case of mixtures with ammonia TOC removal were over 99.9% while maximum removals of NNH4 + was never higher than 94%, even for reaction temperatures higher than 750oC. No improvements in the N and TOC removal were found for temperatures higher than 710oC.