Numerical Study On The High Temperature Air Combustion Of A Swirling Burner

High Temperature Air Combustion (HTAC) is an advanced combustion technology developed for the industrial furnaces since 80s, 20^th century and has been applied successfully to the field of steel, glass, ceramic heating furnace. By recovering maximally the waste heat of the flue gas for the heating of the combustion air to approach or exceed the ignition point of the fuel, the fuel can be burnt at a super low oxygen level with a stable flame. HTAC conserves 30% to70% of the energy for gas combustion and emits very low nitrogen oxide pollutant, 40～70mg/m³.It's shown that the burner design plays important role in keeping the steady combustion and low NOx generation if the jets of the fuel and air could produce a reasonable recirculation in the furnace. The interaction of the jets determines the distribution of the local oxygen, temperature, the mixing of the fuel and air, which determines the local production of the thermal NOx. Therefore, it's very important to achieve low NOx emission by keeping the combustion of the fuel in a low oxygen atmosphere through a reasonable arrangement of the burner parameters and operation parameters.The objective of the thesis is to carry out a numerical simualton of the high temperation air combustion of natural gas in an industrial furnace with a swirling burner. A Homocentric Axial Swirling (HCAS) Burner was designed and the burner geometric parameters and operation parameters were intensively studied on how these parameters influenced the combustion process and the final NO eimission. The Reynolds Stress Model was used to calculate the flow field and PDF (Probability Density Function) combustion model based on aβfunction was selected to simulate the gas combustion. The radiation was simulated by a Discrete Ordinates method. The NOx was simulated by thermal NOx model based on the modified Zeldovich reaction model. The software FLUENT was used to carry out the simulation. The following conclusions can be drawn from the simulation results. First, the results show that the swirling injection of preheated air reduces NOx emission obviously when compared to direct injection of preheated air. For HCAS burner, the central jet of gas has rigidity characteristics, while the external swirling jets of the preheated air enhances the mixing of the gases and induces a good recirculation flow field in the furnace and leads to a better low oxygen distribution and low temperature field, resulting a low NO generation. The final NO mole fraction decreases from 35.2ppm to 12.3 ppm when a swirling burner was used.Second, the effect of the burener configuration was studied. The maximum temperature region will move toward the burner inlet, flame length will decrease and flame width will increase with the increase of the spiral angle of the swirling fin.The NOx emission will first decrease, then increase with the increase of the spiral angle of the swirling fin. Therefore by regulating the spiral angle of the swirling fin, NOx emission can be reduced. The simulated results showed that when the spiral angle of the swirling fin is 180°, the dimentionless stretch factor of fin length is 2, the better combustion characteristics as well as lower NOx emissions were achieved.Finally, when the burner structure parameters were fixed, the effect of the operation parameters was studied. Results were discussed and analyzed for the combustion character and NOx emission at different inlet preheated air temperature, excess air coefficient and oxygen concentration.The results and conclusion drawn from this thesis can provide useful references for engineering application of HTAC burner design.