Characteristic study of nitrogen microwave plasma decomposition of ammonia at atmospheric pressure for hydrogen production

Ammonia (NH3) is decomposed in afterglow of an atmospheric-pressure nitrogen microwave plasma torch for hydrogen production. Its physiochemical processes are diagnosed by optical emission spectroscopy in terms of the characteristic molecular bands and rotational temperature determined with Boltzmann plot method. The mechanism of NH3 decomposition in plasma afterglow caused by chemical and joule heating is discussed by investigating variations of rotational temperature and concentration of excited species as a function of microwave power and NH3 flow rate, respectively. Additionally, the gas flow field distributed in reaction chamber is numerically calculated using computational fluid dynamics. It is found that enhancing the effective collisions between NH3 molecules and the active species in N2 plasma afterglow aids in achieving a high hydrogen production rate, which is materialized by modifying gas flow field by means of optimizing the gas inlet position and NH3 flow rate and introducing a metal rod in reaction chamber. The experimentally achieved results are as follows: hydrogen production rate of 544 l h-1, energy yield of 274 l kWh-1, and ammonia conversion rate of 86%, respectively.