Controlling the emissions of nitrogen oxides (NO_x) from the flue gas has been developed and innovated over the world to meet the needs of the stringent regulations. The post-combustion techniques include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and the hybridization of SNCR-SCR. The hybrid SNCR-SCR technology, as applied for NO_x control from the stationary combustion systems, combines SNCR and SCR with the intention of optimizing the NO_x reduction performance, minimizing the operating cost, and reducing the ammonia slip from the process.

In this study, the urea-based hybrid SNCR-SCR process in a pilot-scale flow reactor is investigated through the experimentation and computational fluid dynamics (CFD) simulation. The pilot system is installed with a 150kW LPG burner. The V₂O₅-WO₃/TiO₂ monolith honeycomb is used as a catalyst in the SCR zone.

A reduced chemical kinetics for the SNCR process using urea-water solution is cooperated with a two phase CFD model to account for the coupling between gas phase and droplet phase. The turbulent reacting flow CFD model is used to predict the turbulent chemistry of NO reduction, ammonia slip and N₂O evolution. A Arrhenius-type reduced model is applied to predict the surface chemistry at the SCR reactor.

The full scale two-dimensional turbulent volumetric and surface reacting CFD model is validated with the experiments in the pilot scale hybrid SNCR-SCR. The CFD simulation results agree well with the experimental data.

Keywords: NO_x reduction, Selective non-catalytic reduction (SNCR), Selective catalytic reduction (SCR), Hybrid SNCR-SCR, Urea solution, Computational fluid dynamics (CFD), Pilot-scale flow reactor.