Kinetic Study on Ammonia Oxidation Acceleration by Multi-Injection of Methanol in Supercritical Water

Abstract

The effectiveness of multistage methanol injection in supercritical water oxidation (SCWO) of an ammonia/methanol mixture as a method for utilizing the alcohol co-oxidation effect was studied at 530 °C and 25 MPa. A simple global reaction rate model was developed based on the results of kinetic experiments performed at various ammonia, methanol, and oxygen concentrations, yielding excellent agreement with experimental values. Ammonia conversion was predicted when the same molar flow rate of methanol was split between two points: a first injection at the entrance of a reactor and a second injection midway in the reaction stream. Two-stage methanol injection resulted in higher ammonia conversion than in the model calculation when methanol was injected once at the reactor entrance. Model calculations under the same experimental conditions showed that two-stage injection improves ammonia conversion, which aligns closely with predicted values. Moreover, our calculations suggest that ammonia conversion depends on injection timing and on methanol concentration of the flow after injection as well.

Effect Mechanism of Auxiliary Fuel in Supercritical Water: A Review

“…Correspondingly, the investigation with two-stage injection of methanol was executed by Shimoda et al to determine the effect of continuous radical supply on ammonia conversion. 28 A more evident acceleration action was observed as compared to that with methanol injected once at the entrance. And the conversion rate of ammonia was reversely related to the injection time of reactive component which could affect the accumulation of OH• radicals (see Figure 1).…”

“…Besides, previous research has reported that the co-oxidative promotion with the multistage injection of methanol was superior to that with only injecting methanol at the reactor entrance. 28 Therefore, we added two inlets for the auxiliary fuel methanol in the front part of the tubular reactor 12, as expressed in the dotted lines in Figure 5. But further investigation of the influence mechanism for the distribution ratio, injection position, and nozzle configuration of the auxiliary fuel still need to be executed, which can be conducted through the experimental, reaction kinetics, and CFD simulation approaches.…”

“…Correspondingly, the investigation with two-stage injection of methanol was executed by Shimoda et al to determine the effect of continuous radical supply on ammonia conversion . A more evident acceleration action was observed as compared to that with methanol injected once at the entrance.…”

Experimental and kinetics study on oxidation of three‐component in supercritical water

“…The research on the reaction kinetics of ammonia/methanol mixture SCWO at 803 K was conducted by Shimoda et al The mutual promotion between the methanol and the ammonia was observed due to the sharing of the generated radicals, whereas the radical supply from the methanol oxidation stopped after the methanol reaction was complete, and the methanol‐derived enhancement in the SCWO of the ammonia vanished. Therefore, they considered the multi‐injection of methanol, revealing an improvement from when the methanol was only injected once . Isopropyl alcohol was introduced by Al‐Duri et al as the co‐fuel to discuss the SCWO mixture effect on a nitrogen‐containing heterocyclic hydrocarbon.…”

“…Therefore, they considered the multi-injection of methanol, revealing an improvement from when the methanol was only injected once. [24] Isopropyl alcohol was introduced by Al-Duri et al [25] as the co-fuel to discuss the SCWO mixture effect on a nitrogen-containing heterocyclic hydrocarbon. It was suggested that the addition of isopropyl alcohol accelerated the recalcitrant aqueous NH 4 þ oxidation to gaseous nitrogen (N 2 and N 2 O) with respect to the extra free radicals OHÁ.…”