Use of methanol as a promoter for ammonia combustion
Adrián Ruiz-Gutiérrez, I. De Diego, María U. Alzueta
Abstract
This work aims to study the oxidation of ammonia and methanol mixtures (NH 3 /CH 3 OH). For this purpose, laboratory experiments were conducted using a quartz flow reactor at atmospheric pressure, in a temperature range of 875–1425 K. The oxygen excess ratio (λ) and the NH 3 /CH 3 OH ratio were modified during the experiments. The experimental results have been simulated with a literature-based kinetic mechanism. The results show that the presence of CH 3 OH and the oxygen excess ratio affect the conversion of NH 3 , shifting its oxidation to lower temperatures as these variables increase. The oxidation of both fuels was slightly boosted with increasing CH 3 OH concentration. The λ study showed that the fuel-lean conditions accelerate NH 3 oxidation at lower temperatures whereas do not have the same effect on CH 3 OH oxidation. The H radical concentration significantly influences fuel consumption, especially in reactions involving CH 3 OH and NH 2 , and it is also key for inhibition processes. CH 3 OH was found to initiate NH 3 reactions, with strong competition for OH radicals between the two fuels. Nevertheless, methanol helps reduce ammonia's oxidation temperature. CH 2 OH was identified as the predominant species following H-abstraction from CH 3 OH. In the NH 3 /CH 3 OH ratio studies, increasing methanol concentration lowered the oxidation temperature of both fuels, with a temperature difference of up to 150 K observed for NH 3 /CH 3 OH ratios from 0.6 to 10. Increasing methanol concentration for a given NH 3 value also shifted the prominence of secondary reaction pathways, further influencing the overall oxidation process. • CH 3 OH presence shifts NH 3 oxidation to low temperatures. • Fuel-lean conditions accelerate NH 3 /CH 3 OH oxidation at low temperatures. • CH 3 OH competes for OH radicals, initially delaying NH 3 oxidation. • Higher CH 3 OH concentration lowers the oxidation temperature of both fuels. • Up to 150 K temperature difference was observed during NH 3 oxidation when varying NH 3 /CH 3 OH ratio from 0.6 to 10.