Post-Ignition Natural-Gas Pyrolysis After Interruption of the Recorded Auxiliary Argon Flow in a Three-Anode Transferred-Arc Reactor

Thermal-plasma methane pyrolysis often uses auxiliary argon during ignition and stabilization. We examined an archived high-throughput run in a three-anode DC transferred-arc reactor, focusing on the response after interruption of the recorded auxiliary-Ar command. The command reached zero at 130.0 min and remained there for 11.67 min while the arc was energized; natural-gas throughput remained near 200 L min−1 for approximately 8 min. A three-minute interval selected by a reproducible stationarity criterion (131–134 min) had a mean natural-gas flow of 197.8 L min−1 and mean arc power of 45.79 kW. The H2 and CH4 analyzer readings gave a 90.31% ratio-derived process indicator. Its mean over the entire eight-minute high-throughput period was 86.1%, declining to approximately 78% by 137.5 min. Under an assumed direct-pyrolysis pathway and the 298.15 K volumetric-flow reference reported by the operator, the reconstructed H2 rate was approximately 1.68 kg h−1, and the arc-power-based specific energy consumption was approximately 27.2 kWh kg−1 H2 (1.84 kg h−1 and 25.0 kWh kg−1 H2 if 273.15 K were used). A calibrated one-step surrogate provided complementary sensitivity analysis. The observations demonstrate sustained high-flow arc operation after the recorded Ar-command interruption. Gas-phase Ar and absolute performance remain conditional on the unmeasured outlet-Ar fraction, the possible protection-gas branch and instrument calibration; the ratio-derived indicator is not an independently closed methane conversion.