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In the present research, numerical simulations and combustion experiments were carried out using a 35 kW biomass low nitrogen combustion furnace. For this purpose, the boiler structure and fluid area in the furnace were modeled. Subsequently, the grid was divided and the parameters such as speed and pressure were set using Gambit. Then, the model was introduced into Fluent in order to simulate the combustion process and for flow field output and analysis. By analyzing the distribution and changes in temperature field, velocity field, and NOx concentration field under different air supply schemes, and performing low nitrogen combustion experiments, the influence of different air supply schemes on fuel combustion and NOx emission was determined. Through the mutual verification of simulation and experimental research, the optimal air distribution scheme was obtained. The results showed that: without the air staged combustion, combustible gas and air were not properly mixed. As a result, the loss of mechanical incomplete combustion occurred. Under air-staged combustion, the addition of the secondary air reduced the “chimney flow” phenomenon in the furnace to a certain extent. The combustible gas and air were mixed more adequately and the reaction rate and efficiency significantly increased. In addition, with the introduction of the secondary air, the air and the flue gas in the furnace were more efficiently mixed. Moreover, the temperature in the upper combustion area of the furnace decreased by 300–500 K, which slowed down the rate of nitrogen oxides production. This effect was intensified when the proportion of the secondary air increased. The status of the combustion process and changes in the concentration of NOx in the flue gas were compared and analyzed under various working conditions. Data indicated that the optimal air distribution scheme was that with 70% of the primary air and 30% of the secondary air. In this case, the NOx emissions were 27% lower than those without the air staged combustion. |
