The Simulation And Optimize Of The Low NOx Natural Gas Burner

Natural gas is one of the main energies in China. Except for its high combustion efficiency, and low SO2 emission characteristic, the higher temperature generated from burning is suited for NOx formation. Therefore, optimal design of natural gas burners has important effect on the cleaning and efficient use of natural gas.This study presents a new low-NOx emission burner, and air staged combustion, fuel staged combustion and swirling jetting technologies are combined. Meanwhile, experiment study, theoretical analysis, and numerical simulation were studied systematically. The main contents of this study including these four parts: experimental study of flow characteristic under cold state, computational fluid dynamics(CFD) simulation of the cold flow and nature gas combustion using low-NOx emission burner, investigation of effect of multiple factors on the NOx emissions, and the key factors study based on response surface methodology(RSM) method.This study designed and built a gas burner experiment facility to conduct the cold flow field test of the gas burner. The velocity of the cold flow field in the combustion chamber was measured with the hot wire anemometer. Results showed that a central recirculation region is formed in the combustion chamber; the length of the recirculation region is about 0.75 m. The axial velocity distribution along the width direction of combustion chamber shows a central concave and both sides convex trend which like a saddle shape. The cold flow field was simulated by the FLUENT software, and the axial velocity in the flow field was extracted to compare with that of the cold test. Results showed that the simulation results are basically consistent with that of the cold experiment, indicating that the simulation model is reliable.The effects of the structural parameter(burner-swirl angle) and the operating parameters(excess air ratio, and air preheat temperature) on the combustion performance were simulated in this study. Results showed that the NOx emission decreased first and then increased with the increases of swirl angle, the recirculation region in combustion chamber is largest when the swirl angle is 40°. And in this condition, the uniformity of temperature distribution is the best and the NOx emissions have the minimum value. NOx increased first and then decreased with the increases of excess air coefficient, while it increases with the increases of air preheating temperature. The average temperature in the combustion increased, and the NOx emissions also increased at higher air preheating temperature.An optimize analysis of these parameters was investigated using RSM method to obtain a second prediction model. Results showed that all the three factors have significant effect on the NOx emissions, and it follows the order as air preheating temperature>excess air coefficient>swirl angle. The NOx emissions have the minimum value when the swirl angle is 40°, the excess coefficient is 1.05, and the air preheating temperature is 293 K.