A Nonpremixed Annular Jet Vortex Chamber Reactor for Methane Pyrolysis under Oxygen-Enriched Conditions

A novel high-swirl reactor ANJEVOC-CP (annular jet vortex chamber for combustion pyrolysis) was designed for producing high-value chemicals such as alkynes and olefins from natural gas. In such a single-stage nonpremixed combustion pyrolysis process, methane and oxygen streams are spirally conveyed into the ANJEVOC-CP burner creating high-swirl annular jets around an internal recirculation zone, leading to a compact nonpremixed fuel-rich flame for methane pyrolysis. Computational fluid dynamics (CFD) simulations of this reactor concept indicate the potential for high alkyne yield due to the rapid mixing of combustion products with CH4 under a broad range of operating conditions; and this was experimentally verified in a lab-scale reactor under a subset of conditions (enriched oxygen concentration from 21% to 60% by volume and equivalence ratio from 1.28 to 2.4). The experimental studies showed 10.4 mol % carbon-based overall acetylene yield with up to 60% enriched oxygen molar concentration in the oxidizer stream in the lab-scale experiment. The CFD simulation predictions of the fluid flow and reactor performance are in reasonable agreement with the experimental observations and provided complementary insights into the respective roles of high swirl, species and thermal transport, and reaction kinetics that contribute to the high performance. Using a reduced GRI-Mech 3.0 and a modified GRI mechanism, the model predicted 20-25% overall acetylene yield at the same scale with higher enriched oxygen concentration. Considering the fact that excessive heat loss due to the high surface-area-to-volume ratio in the small lab-scale prototype with inert gas dilution could degrade performance, ANJEVOC-CP is a promising methane conversion technology for acetylene production and deserves further investigation at larger scales.