Production of hydrogen from ammonia cracking using a rotating gliding arc plasma*

Ammonia(NH₃) is getting attention as an effective H₂ carrier whose volumetric energy density is 1.5 times higher than liquid H₂. NH₃ has a high hydrogen content ~18 wt%(75 mol%) and can readily be liquefied at a reasonable temperature(-33°C) at atmospheric pressure. The recent attention to ammonia decomposition stems from its capability to produce hydrogen without emitting carbon dioxide and its ease of storage. This work investigated ammonia decomposition back to H₂ using a rotating gliding arc plasma (RGAP) with a focus on optimizing operating paramaters such as applied voltage, NH₃ flow rate (3.5~5L/min) and inlet NH₃ concentration (10%). The RGAP reactor consisted of conical Cu high voltage electrode coaxially placed in a stainless steel tube. The RGAP was generated using a 400 Hz alternating current (AC) power supply. The feed gas was composed of NH₃ and H₂ of which flow rates were controlled using mass flow controllers (MFC). The inlet and outlet gas compositions were analyzed by a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD). Increasing the electrical power (0~200 W) by raising the applied voltage tended to increase the NH₃ decomposition efficiency and the concentration of H₂. Around 2.5% H₂ was obtained at an energy density of 2.4 KJ/L ; the energy density stands for the power divided by gas flow rate.