Numerical Simulation Of Preheated Decomposed Combustion Mode And Its Impact On Boiler Performance

In China,coal-fired power generation will still occupy an energy-dominated position in the future.In order to reduce the emission of pollution gas from coal-fired power plants,a new type of highly efficient NOx removal technology is proposed.It uses hightemperature preheat pyrolysis device to pyrolyze pulverized coal,and the pyrolyzed products are sent into the furnace to reduce NOx and achieveultra-low NOx emission.In this paper,660MW ultrasupercritical tangentialfired boiler in a power plant is used as the simulation object.Threedimensional numerical simulation was performed on the boiler's pure coal combustion conditions and pyrolysis gas coupled pulverized coal combustion conditions,and the influence of the transformation on combustion performance and component concentration is studied.By optimizing the proportion of the pyrolysis gas,the height of the pyrolysis gas nozzle and the vertical swing angle of the nozzle,the better NOx removal effect can be achieved while the combustion efficiency of the boiler can be ensured at the same time.The results show that the high-efficiency NOx removal technology has hardly no influence on the flow field stability and boiler efficiency in the furnace,and the over temperature phenomenon in the burnout area is alleviated.At the same time,the NOx removal efficiency is increased by 46%compared to pure coal combustion.According to the comparison of different simulation conditions,it is considered that the conditions of 15%of the pyrolysis gas,41.3m of the height of the pyrolysis gas nozzle and 0° of the upper and lower swing angle of the nozzle are the most favorable conditions for the overall combustion of the furnace and efficient NOx removal.The mass concentration of NOx at the outlet of the furnace is 47mg/Nm3.If the proportion of pyrolysis gas is higher than 15%or the nozzle is located at a higher position in the furnace,the flue gas temperature at the furnace outlet will rise,which will affect the boiler efficiency.The pyrolysis gas ratio below 15%or the downward displacement of the pyrolysis gas nozzle will cause the reduction of NOx removal efficiency.In addition,adjusting the angle of pyrolysis gas nozzle will also have a negative impact on the safety of water wall and boiler performance.The thermal calculation method was used to complete the thermal calculation of pure coal combustion and transformation under different loads,and the outcome was compared with the numerical simulation results.Based on the traditional thermal calculation method,consideringthat the use of air staged combustion technology and highly efficient NOx removal technology can make the relative position of the highest temperature of the flame move up,the M value in the traditional thermal calculation method should be modified.The modified formula is used to calculate the temperature and heat load parameters of the high temperature pre-pyrolysis NOx removal project transformation,and it is confirmed that after the transformation,the furnace exit smoke temperature will increase,but it will not affect the heating safety of the water wall and the platen superheater.The results of the thermal calculation related to the change of the swing angle of the heat removal gas nozzle are also consistent with the performance of the numerical simulation.It can ensure the correctness of this research,so as to fully grasp the combustion performance of the boiler after the transformation.