Effect of auxiliary fuel on degradation of ammonia in supercritical water: Kinetics analysis. (15th May 2021) - Zhang, Jie
Highlights: Satisfactory removal of ammonia was achieved at 540 °C with 800 mmol/L methanol. A kinetics model was developed to explore kinetic and thermal actions of methanol. Synergy between the two effects was achieved for ~100 mmol/L methanol. Abstract: Methanol was introduced as an auxiliary fuel during supercritical water oxidation of typical nitrogen-containing compound of ammonia. A mechanism-based kinetics model for oxidation of methanol/ammonia in supercritical water was developed, which involved Real-Gas model for reaction species. The combination of experimental data analysis and reaction kinetics simulation was executed to examine the release of radicals and heat with reaction time for methanol with different concentration ranges. Furthermore, the synergy mechanism between kinetic and thermal effects of auxiliary fuel was clarified, in order to achieve enhanced degradation of refractory pollutants under appropriate reaction temperature. It was observed that the effective time ranges for radical production and reaction temperature rise for methanol at the concentration order of magnitude of ~100 mmol/L overlapped. And the kinetic action could promote the chain reactions of ammonia, which initiated from elementary steps with low activation energy, while the thermal action further improved reaction rate constants of these initiation steps, achieving synergy between the two effects and leading to the promising removal of ammonia (99.24%) at moderate temperature of 540 °C. Furthermore, in the binary reaction system, ammonia could enhance combustion of hydrothermal flame under adequate supply of radicals from methanol, otherwise it would have played a negative effect.