Research On The Technology Of Improving Combustion Stability Under Deep Peak Shaving Of Ultra-supercritical Boilers

The foundation of power development is energy,and thermal power generation has long occupied a dominant position in the industry.In recent years,the country has vigorously developed new renewable energy.However,due to some weaknesses of new energy sources such as photovoltaics,poor stability and intermittence,thermal power units need to participate in deep peak shaving.In the process,due to the low load of units,accidents such as unstable combustion and even shutdown are prone to occur.Therefore,a new type of primary separation device for pulverized coal concentration and dilution was designed and developed in this paper,which carries out primary concentration and dilution separation before the pulverized coal enters the burner.Numerical study on the flow separation process of pulverized coal in the separator was carried out,and the best structural parameters was obtained from the study.Accord to that technical scheme of low-load stable combustion,group optimization design of burners was carried out,and concentrated arrangement of dense phase and light phase was carried out respectively.The influence of grouping optimization of burners on combustion in furnace under different loads was numerically studied,and the combustion characteristics in furnace under low load operation of units were deeply studied,so as to achieve the purpose of stable combustion under low load.Study on separation characteristics of a new type of primary separation device for pulverized coal concentration.According to the structural parameters of the separator,the geometric model and grid model were established.The influence of baffle position,baffle angle,primary air volume and pulverized coal particle size on velocity field,particle trajectory and pulverized coal separation performance in the separator were numerically studied.The results show that the farther the baffle is from the entrance,the smaller the influence on the aerodynamic field will be in the separator.And the best baffle position is 650 mm away from the inlet.Increasing the baffle angle properly can improve the separation performance.But when the baffle angle is too large,the speed deviation between the two sides of the shade will increase greatly.And the best baffle angle is 45°.Properly increasing the particle size of pulverized coal can improve the separation performance,but excessively large particle size of pulverized coal will reduce the following performance of air flow and lead to the degradation of separation performance.The change of air volume has little influence on the separation performance,and the better separation effect can be achieved by properly increasing the air volume.Study on combustion characteristics of boiler under original working conditions.According to the actual parameters of the boiler,the geometric model and grid model are established.The combustion characteristics in the boiler under100%load condition are numerically studied.The results show that the aerodynamic field in the furnace is good,the temperature distribution is uniform,the flue gas fullness is high,and the temperature reaches the peak in the main combustion area.The burnt-out air arranged in stages effectively controlled the generation of NO_xin the combustion process in the furnace,and the simulation results were consistent with the actual situation.Study on influence of burner grouping optimization on combustion in furnace.The combustion characteristics of boilers under different loads,different dilution ratios and different primary air temperatures are numerically studied.The results show that the combustion conditions of boilers under low load are greatly improved after the burner grouping optimization,the overall temperature of the furnace rises,the rigidity of air flow becomes stronger,and the flame sticking phenomenon disappears.The change of concentration ratio has a significant influence on the combustion.Increasing the concentration ratio properly can improve the combustion situation in the furnace,but the excessive concentration ratio leads to delayed ignition of pulverized coal,which is not conducive to stable combustion at low load.The best concentration ratio is 8:2.The higher the primary air temperature is,the better the combustion condition in the furnace will be.Within the unit tolerance range,the primary air temperature can be appropriately increased to achieve better combustion stability.