Numerical Simulation Of Low Nitrogen Combustion In 1 T/h Biomass Chain Boiler Based On Staged Combustion And Swirl Control

At present,bulk coal is mainly used for heating in rural areas,which has the problems of low energy utilization and high pollutant emission.Based on the actual situation of rural areas and current environmental protection policies,biomass clean heating has become a research hotspot,and the development of small-scale biomass boilers suitable for rural central heating with low pollutant emission has become the key.In view of the fact that the NO_x emission of small-scale biomass boilers exceeds the standard and it is difficult to bear the high cost of denitration before and after combustion,a method of strengthening flue gas swirl on the basis of air staging in the combustion process is proposed to reduce NO_x emission.In this paper,through the numerical simulation of a small-scale biomass chain furnace,the better combustion scheme is found in the furnace,which provides guidance for boiler debugging and boiler parameter setting.By changing the furnace structure and reasonably organizing the air flow in the furnace,it provides the basis for the transformation of small-scale biomass boilers.Further optimize the low-nitrogen combustion mode,reduce NO_x emissions and improve air quality.FLUENT software was used to carry out numerical simulation research on the DZL 1-1.25-M boiler with wide application range and strong fuel applicability independently developed by a boiler plant.The temperature distribution in the furnace and the concentration distribution of each component including NO_x were analyzed under different air distribution ratios of primary air,different secondary air inlet modes,different secondary air inclination angles of rear arch and different baffle angles,and the influence mechanism of combustion conditions and NO_x concentration in the furnace was explored.By analyzing the simulation results,the following conclusions are drawn:In terms of operating strategy,when the air distribution ratio of four primary air inlets is 20%,45%,30%and 5%,the combustion condition in the furnace is good,and the NO_x concentration at the outlet of the furnace is 262 mg/m³.Under the condition of hedging secondary air,the air flow in the furnace is better,and the distribution of NO_x is more reasonable.The concentration of NO_x at the outlet of the furnace is 16mg/m³ lower than that of the primary air,which is reduced by 6.1%.In terms of structure optimization,with the decrease of the secondary air angle of the rear arch,the range of the swirl area gradually expands,the residence time of the flue gas in the furnace increases,the burn-off rate of the fuel increases,the airflow disturbance increases,and the turbulence intensity increases.When the secondary air angle of the rear arch is 20°,the combustion condition in the furnace is better,and the NO_x concentration at the outlet of the furnace is 27 mg/m³ lower than that of the primary air,which is 10.3%lower.The baffle is arranged under the front arch,on the one hand,it can block the rapidly rising high-temperature flue gas,so that it forms a swirl under the front arch,prolongs the flue gas residence time,and promotes the burn-off of combustibles.On the other hand,the generated NO can fully react with reducing gases such as NH₃,H₂,and CO to reduce NO_x emissions.When the angle between the baffle and the horizontal direction is 20°,the temperature in the furnace is low,and the NO_x concentration at the outlet of the furnace can be reduced to 150 mg/m³,which meets the national boiler pollutant emission standard.It is 112 mg/m³ less than that when only primary air is set,which is 42.7%lower.The low-nitrogen combustion scheme proposed in this paper has been applied in several demonstration sites of the national key R&D project,and achieved good effects.At the same time,the research in this paper is of great significance for accelerating rural heating reform,alleviating rural heating pressure and reducing environmental pollution.