Selected profiles of high-pressure methanol–air flames in supercritical water

Abstract

A semi-batch bench-scale visual flame cell system was designed to spontaneously ignite high-pressure flames in supercritical water as a step in evaluating the effect of presence of these flames on supercritical water oxidation of organics. Methanol proportions between 15 and 40 (v/v%) were used as fuel. Oxidation and flame ignition were achieved by injecting a preheated high-pressure air stream into the supercritical water–methanol mixture. Air was preferred to pure oxygen to maintain the practicality and possible full-scale feasibility of the supercritical water flame system. Flames were ignited successfully at methanol fractions between 21 and 35 (v/v%). Ignition zone temperatures up to 1010 °C were measured. High carbon monoxide production rates were observed in both flame and flameless oxidation in the reaction cell. Noticeable concentrations of nitrogen oxides were also present even in the absence of flames. Highest oxidation levels and strongest flame luminosities were observed at 23 (v/v%) methanol. The optimal methanol range for NO X minimization was found to be 25–30 (v/v%). A near-infrared thermal imaging system was used to obtain accurate visual and thermal gradient images of flame behavior in supercritical water and to propose a mixing-limited ignition scenario in the visual flame cell.