Selective non-Catalytic Reduction of NOx in a cyclone reactor

This project is focused mainly on providing background knowledge of the cyclonereactors and mapping the effect of fluid dynamics involving flow pattern and transport phenomena on a chemical reaction. Targeting this main purpose,SNCR for NOx reduction with the injection of ammonia as a reductant has been chosen as the reaction to be studied.

To follow the effect of fluid dynamics on reaction parameters, including temperature profile, residence time and mixing, this thesis presents a detailed study, both with experiments and CFD modeling. Due to environmental demands and legislation, NOx emission control is becomingstricter worldwide. In some industries, NOx pass by cyclones before emission; therefore, it is essential to investigate the potential of applying cycloneas an SNCR reactor.

This is a more available and cost-effective way to control the NOx emission as a process in the cyclones with some modifications before emission. Considering all the practical and theoretical demands, a pilot set-up is designedand assembled for this study, providing broad measurement access. An extensive experimental design is developed with a focus on fluid dynamics and considering effective reaction parameters, including temperature profile, concentration distribution, injection zone, ammonia inlet velocity, molar ratio, and initial NOx.

Finally, the effect of particle loading on cyclone is studied. In the next step,a CFD model is developed to map the flow pattern further and provide a supportive base to discuss mixing and residence time inside the cyclone. The modelis applied to predict temperature profile and residence time distribution inside cyclone targeting SNCR reduction.

In the final step of CFD modeling, the system worked well, including SNCR reaction, and was validated with pilot scale experiments.This CFD model is highly predictive for effective parameters such as RTD, temperature profile, flow pattern, mixing conditions and reaction zone. The model has been validated with experiments and shows good agreement with experimental results of a detailed study.The results show that cyclone is non-isothermal and the reactants need to bein a proper temperature zone of the cyclone to react.

The cyclone swirl flow provides proper time for the reactants with a good chance of meeting the high temperature zone in both downward and upward flow. Rapid mixing of injected ammonia into the flue gas is also necessary and is provided by turbulence.The results also prove that cyclones ensure excellent heat transfer and provide proper mixing in a short time for SNCR reduction.

Adding ammonia from different positions makes a tiny difference in reduction efficiency. The reaction mainly takes place in the upper part of the cyclone, called reaction zone, in this thesis and is the upper zone of the cyclone with proper temperature.The results presented here provide the background knowledge about the cyclonereactor for SNCR and could be applied to scale-up, design and optimization studies.