Study On The Performance Of CFB Coal-PC Coal Dynamic Compound Combustion Based On Deep Peak Load Regulation Of A CFB Unit

With the development of economy and society,people's awareness of environmental protection and energy crisis gradually increases,which promotes the progress of green,environment-friendly and sustainable energy utilization technology,and the new energy power generation technologies represented by solar power generation and wind power generation have been developed rapidly.In Shanxi Province and the Inner Mongolia Autonomous Region,where coal resources are abundant but water resources are relatively poor,a large number of wind and solar power generating units and circulating fluidized bed?CFB?boiler units mainly burning low-grade coal have been built.Therefore,the problems of peak load regulation of the power grids and utilizing the new energy power generation in these regions are prominent and need to be solved urgently.It is necessary to improve the peak load regulation ability of thermal power units in the grid,especially CFB units,to improve the grid's capacity to absorb new energy generation.However,due to the great thermal inertia and hysteresis inherent in CFB boiler,the load response rate is very slow.A large number of CFB units are still difficult to meet the requirements of power grid automatic generation control?AGC?,and no effective solution has been found yet.In order to improve the load change rate of a CFB boiler,this paper compared the difference between CFB boiler combustion and pulverized coal boiler combustion,and proposed a CFB coal-pulverized coal?PC?dynamic compound combustion technology to improve the load change rate of a CFB boiler.A CFB coal-PC coal dynamic compound combustion boiler was built based on a 240 t/h CFB boiler.The load change rate,the variation of temperature and oxygen content in the furnace,the heat transfer characteristics and pollutant discharge characteristics of the CFB boiler during CFB coal-PC coal dynamic compound combustion were studied.The main conclusions are as follows:?1?The study on load change rate of CFB coal-PC coal dynamic compound combustion showed that no matter the PC coal was fed through secondary air pipes or was fed through coal pipes,the dynamic compound combustion can improve the CFB boiler load change rate.Compound combustion through secondary air pipes can gain a higher boiler load change rate than compound combustion through secondary air pipes.?2?In CFB coal-PC coal dynamic compound combustion,burning high calorific value and high volatile pulverized coal can obtain a much higher boiler load change rate.The compound combustion through coal pipes was more sensitive to the quality of the pulverized coal and had higher requirements for the pulverized coal,while the compound combustion through secondary air pipes had stronger adaptability and lower requirements for the pulverized coal.Increasing the proportion of pulverized coal can further increase the boiler load change rate.?3?During CFB coal-PC coal dynamic compound combustion,as the pulverized coal fed,the combustion enhanced rapidly,and the furnace temperature and heat transfer coefficient increased,and the temperature difference of the heat transfer became larger,so that the boiler output increased and the load change rate accelerated.?4?Compared with the boiler combustion efficiency in stable operation condition before the test,the combustion efficiency decreased during compound combustion through coal pipes,while the boiler combustion efficiency increased during compound combustion through secondary air pipes.Increasing the calorific value and volatile of pulverized coal can improve the combustion efficiency of the boiler.The boiler CO emission increased during compound combustion through coal pipes,while decreased during compound combustion through secondary air pipes.?5?As to the emission of flue gas pollutants,in the process of only CFB coal heat step and compound combustion,the NO_X emission of the boiler increased compared with those in stable operation condition.Under the same operate condition,the increase of NO_X in compound combustion was higher than that in only CFB coal heat step,and the increase of NO_X during compound combustion through secondary air pipes was slightly higher than that of compound combustion through coal pipes.NO_X emission increased with the increase of the ratio of pulverized coal and its volatile.The same limestone added into the furnace,the SO₂ emissions during dynamic compound combustion was larger than that in only CFB coal heat step.However,the operating temperature was still in the best desulfurization temperature range,so the SO₂ emissions can be reduced by desulfurization in the furnace.A fluidized bed compound combustion test bench boiler was also set up to analyze the stable combustion performance and banking fire performance of the boiler during CFB coal-PC coal dynamic compound combustion.The results showed that:?1?The compound combustion through lower secondary air pipes with high calorific value and high volatile pulverized coal can significantly improve the stable combustion performance of the boiler under low load.?2?The compound combustion through lower secondary air pipes with high calorific value and high volatile pulverized coal can make the boiler start-up without oil injection at lower bed temperature after banking fire,thus it extends the boiler banking fire time and provides a technical guarantee for the CFB unit to realize the deep peak load regulation by banking fire.The research shows that the method for increase the CFB load change rate by CFB coal-PC coal dynamic compound combustion in a CFB boiler can reduce the impact of large thermal inertia properties of the CFB boiler,and increase the load change rate of the unit significantly,and enhance the stable combustion performance of boiler under low load,and extend the boiler banking fire time.It is a feasible deep peak-regulation method of power grid.