| |
Abstract |
We developed a fully coupled 2D axisymmetric model for NH3 cracking in a warm low-current arc pin-to-pin plasma reactor, by solving the equations of gas flow dynamics, heat transfer, electric currents, and chemistry. The full chemistry is first reduced to a set of 12 species and 23 reactions, feasible to solve in a 2D model. Our model was validated by experiments over a wide range of electric currents (2–180 mA), flow rates (5–20 NLM), and different interelectrode gap distances (3–5 cm). This ensures we explore a significant range of specific energy input (SEI = 7–55 kJ/mol). As our model yields excellent agreement with experimental results, we can use it to understand the underlying physics and chemistry. The conversion happens predominantly in a narrow chemically active region with gas temperatures between 2400 and 3000 K. Importantly, the conversion is determined by the transport of NH3 and H atoms to this region. Furthermore, our model reveals that thermal chemistry is dominant for NH3 cracking in warm plasmas. The calculated energy cost is around 200 kJ/mol, and remarkably constant over a wide range of SEI. Finally, we identified that 60–64 % of the deposited energy is lost as residual heat, limiting the achievable energy efficiency. Overall, our study helps to better understand the mechanisms of NH3 cracking in warm plasma, and what is needed to improve the performance, and can thus be used as a steppingstone for improved reactor design. |
|
