Investigation of combustion emissions in industrial burner-boiler system

In this thesis, experimental tests were carried out at various burner thermal loads, excess air coefficients and boiler lengths in an industrial burner-boiler to investigate the combustion emissions. Subsequently, with the data that was obtained from the burner-boiler experimental tests, a Computational Fluid Dynamics (CFD) model of the combustion system was established. Numerical simulations were performed with different combustion and turbulence models in ANSYS FLUENT 16 software to determine the optimal combustion and turbulence models in accordance with the experimental results. After validation of the CFD model, the experimental test parameters were also examined by the CFD method. On the other hand, combustion emissions of natural gas, methane, natural gas-hydrogen fuel mixtures (consisted of 25%, 50% and 75% hydrogen addition) and pure hydrogen (100%) were also investigated. Finally, a new swirl generator was designed and replaced with the original swirl generator on the burner to reduce the combustion emissions. Blade number (7, 9, 11, 13, 15, 17) and blade angle (15 °, 20 °, 25 °, 30 °) of the new swirl generator were examined parametrically. Thus, the effects of blade number and blade angle on the combustion emissions were determined. The experimental study that was carried out with different thermal loads and boiler lengths resulted with limited variations in combustion emissions such as NOx, CO and CO2. However, when different excess air coefficients (λ=1.05, λ=1.38) were used, the variation in emissions were more pronounced. For instance, the differences in NOx, CO and CO2 emissions were 32 ppm, 46 ppm and 24%, respectively. According to the CFD results, it can be seen that natural gas can be modeled also with methane gas. Furthermore, as the hydrogen ratio of the natural gas-hydrogen fuel mixture was increased, the flame length and flame diameter were increased but the CO and CO2 emission levels were decreased simultaneously. When 100% H2 was used as fuel, CO and CO2 emissions were zero but NOx emission was significantly increased. Finally, implementing the new swirl generator with 11 blades resulted with the lowest NOx emission. It was also found that increasing blade angle led to decreased NOx emission in the flue gas.