Flow Reactor Studies of the Thermal De-NOx Process

The Thermal De-NOx process was investigated experimentally, using a high temperature flow reactor. In order to simulate conditions prevalent in post-flame gases, hydrogen and oxygen were allowed to react in the upstream part of the reactor. NH3 was injected into a mixture consisting of the reaction products, NO and a noble gas diluent. Measurements were made of the resulting reductions in NO-concentration. Considerable reduction was observed at temperatures as low as 850 K, indicating an influence of heterogeneous reactions. This influence w as investigated experimentally by using both argon and helium as the diluent. The results were analyzed using a simplified model based on fully developed laminar flow with first order chemical Kinetics of the trace reactant. The data obtained are compatible with a wall reaction rate constant on the order of 0.12 cm/s. Maximum reductions occurred at temperatures near 1100 K, and were on the order of 70% and 85% with argon and helium as the diluent, respectively. The difference is ascribed to different diffusion coefficients of the reacting species in argon and helium. At the higher temperatures, most of the reduction is due to gas phase reactions. The results can be fitted quite well by curves generated with either of two simple analytical models described by de Boer.